Skip to main content
PMC home page
Age logoLink to Age
. 2010 Apr 13;32(3):283–296. doi: 10.1007/s11357-010-9137-9

Age-related decreases in SYN levels associated with increases in MAP-2, apoE, and GFAP levels in the rhesus macaque prefrontal cortex and hippocampus

Gwendolen E Haley 1,2, Steven G Kohama 2, Henryk F Urbanski 1,2,3, Jacob Raber 1,2,4,5,✉
PMCID: PMC2926858  PMID: 20640549

Abstract

Loss of synaptic integrity in the hippocampus and prefrontal cortex (PFC) may play an integral role in age-related cognitive decline. Previously, we showed age-related increases in the dendritic marker microtubule associated protein 2 (MAP-2) and the synaptic marker synaptophysin (SYN) in mice. Similarly, apolipoprotein E (apoE), involved in lipid transport and metabolism, and glial fibrillary acidic protein (GFAP), a glia specific marker, increase with age in rodents. In this study, we assessed whether these four proteins show similar age-related changes in a nonhuman primate, the rhesus macaque. Free-floating sections from the PFC and hippocampus from adult, middle-aged, and aged rhesus macaques were immunohistochemically labeled for MAP-2, SYN, apoE, and GFAP. Protein levels were measured as area occupied by fluorescence using confocal microscopy as well as by Western blot. In the PFC and hippocampus of adult and middle-aged animals, the levels of SYN, apoE, and GFAP immunoreactivity were comparable but there was a trend towards higher MAP-2 levels in middle-aged than adult animals. There was significantly less SYN and more MAP-2, apoE, and GFAP immunoreactivity in the PFC and hippocampus of aged animals compared to adult or middle-aged animals. Thus, the age-related changes in MAP-2, apoE, and GFAP levels were similar to those previously observed in rodents. On the other hand, the age-related changes in SYN levels were not, but were similar to those previously observed in the aging human brain. Taken together, these data emphasize the value of the rhesus macaque as a pragmatic translational model for human brain aging.

Keywords: Aging, Nonhuman primate, MAP-2, Synaptophysin, apoE

Introduction

Decline in cognitive function with age has been reported in humans, nonhuman primates, and rodents (Zyzak et al.1995; Albert and Moss 1999; Moss et al.1999; Benice et al.2006), yet the biological cause of age-related cognitive decline is not fully understood. The areas of interest for age-related cognitive decline in humans and nonhuman primates are the prefrontal cortex (PFC) and hippocampus, brain regions highly associated with learning and memory (Paulesu et al.1993; Levy and Goldman-Rakic 1999). During normal aging, the hippocampus is one of the first structures to decline (Geinisman et al.1995; Winocur and Gagnon 1998), observed behaviorally as a change in performance in hippocampal dependent cognitive tasks in rodents, nonhuman primates, and humans (Rapp et al.1997; Maguire and Cipolotti 1998; Rosenbaum et al.2001). It has been commonly hypothesized that cognitive decline results from a loss of neurons within the brain. However, there is convincing evidence that the number of neurons does not significantly change during normal aging (Rapp and Gallagher 1996; Merrill et al.2000; Keuker et al.2003). Consequently, a more plausible alternative hypothesis is that a change of the integrity of the synapses mediating learning and memory contributes to the decline in cognitive function.

Microtubule associated protein 2 (MAP-2) and synaptophysin (SYN) are synaptic proteins associated with learning and memory. MAP-2 is a dendritic protein responsible for the assembly of the microtubules in the dendrites and aids in dendritic plasticity (Harada et al.2002). SYN is a presynaptic vesicle protein located in axons associated with synaptic vesicles and is responsible for formation of synapses (Tarsa and Goda 2002). SYN levels also positively correlate with cognitive function in rodents (Dawson et al.1999; Mulder et al.2004). Reports from rodent studies indicate that the levels of MAP-2 and SYN immunoreactivity are dependent on age, area of the brain, and amount of cognitive testing (Chauhan and Siegel 1997; Calhoun et al.1998; Di Stefano et al.2001; Shapiro and Whitaker-Azmitia 2004; Himeda et al.2005; Benice et al.2006; Adams et al.2008; Minkeviciene et al.2008; Prieto-Gomez et al.2008).

Apolipoprotein E (apoE), a protein with an integral role in lipid transport and metabolism, can also alter synaptic activity. Age-related increases of apoE in the rat hippocampus positively correlates with cognitive impairment (Kadish et al.2009). In addition, the human apoE ε4 allele is linked to an increased risk of developing Alzheimer’s disease (AD), a disease known to decrease the function of the hippocampus in humans (Gosche et al.2002). ApoE appears to play a mechanistic role as plaques associated with AD are constructed of β-amyloid (Aβ) and apoE proteins (Nakamura et al.1996; Burns et al.2003). Similarly, interactions of increased apoE levels with alpha synuclein in the brain can lead to neuronal degeneration (Gallardo et al.2008).

Glial fibrillary acidic protein (GFAP), an astrocyte specific marker, increases with age in mice (Kohama et al.1995), rats, and humans (Nichols et al.1993). An increase of GFAP has also been reported in the subcortical white matter of elderly rhesus macaques, compared to younger animals (Sloane et al.2000). Furthermore, in aged cynomolgus macaques, GFAP immunoreactive processes are present around Aβ and apoE plaques (Nakamura et al.1996). Interestingly, high expression levels of GFAP have also been associated with AD (Nichols et al.1993; Hol et al.2003; Si et al.2004), with higher GFAP expression found in subjects with apoE ε4 allele (Overmyer et al.1999).

Although an age-related change in immunoreactivity of MAP-2, SYN, apoE, and GFAP has been reported in rodents and humans, these proteins have not been extensively studied in the nonhuman primate. One report indicated that no difference in MAP-2 and SYN was observed between young adult (5-year) and old (18-year) nonhuman primates; however, there were only two old animals in the study and the analysis was performed in the pallido-nigral region (Fukuda et al.2005). However, since rhesus macaques in captivity can live longer than 30 years (Uno et al.1996), the current study includes much older animals and examined cortical regions linked to cognitive function. Additionally, studying older animals could provide more translational insight into the elderly human brain and bridge the translational efforts of rodent and human research (Chauhan and Siegel 1997; Calhoun et al.1998; Benice et al.2006; Kadish et al.2009).

In the present study, immunohistochemistry and Western blot were used to assess age-related changes in MAP-2, SYN, apoE, and GFAP in the PFC and hippocampus from a heterogenous population of adult, middle-aged, and elderly rhesus macaques. In addition, some of the brain sections were double-labeled immunohistochemically for apoE and GFAP or apoE and Aβ, to assess potential colocalization of these proteins.

Methods

Animals

Post-mortem brains were obtained from adult (5–7 years; n = 5; 2 male, 3 female), middle-aged (10–15 years; n = 5; 2 male, 3 female), and aged (23–31 years; n = 5; 2 male, 3 female) rhesus macaques (Macaca mulatta), through the Tissue Distribution Program at ONPRC/OHSU. At death, the average weight was 6.0 ± 0.7 kg for adult, 6.5 ± 0.8 kg for middle-aged, and 8.5 ± 0.7 kg for aged animals. In general, all animals were in overall good health during their lifetime. One female in the adult group and one female in the middle-aged group had been ovariectomized. None of the animals used in this study were behaviorally tested. All of the brains were perfused with saline at room temperature followed by ice-cold 4% paraformaldehyde. After perfusion, the brains were cut into blocks, briefly post-fixed in paraformaldehyde solution, cryoprotected, then frozen and stored in −80°C.

Histology

Frozen brains were sectioned at 25 µm (PFC coronal sections) or 40 µm (hippocampal coronal sections) using a Microm HM 400 microtome (GMI, Ramsey, MN, USA). For PFC assessment of MAP-2, SYN, apoE, and GFAP, six sections (2.0 mm between each section) were selected from each brain for each protein. Likewise, for hippocampus assessment of MAP-2, SYN, apoE, and GFAP, 10 sections (1.2 mm between sections) were selected from each brain for each protein. Free-floating sections were washed with fresh PBS followed by a 10% Normal Goat Serum (NGS; MAP-2/SYN) or Normal Sheep Serum (NSS; apoE/GFAP/apoE + GFAP/apoE + β-amyloid) in PBS + 0.3% Triton for 1 h. Next, sections were incubated in 0.3% Triton + 1% NGS/NSS in PBS with the primary antibody (anti-MAP-2 raised in mouse, Sigma-Aldrich, 0.5 µg/ml; anti-SYN raised in mouse, Sigma-Aldrich, 0.5 µg/ml; anti-apoE raised in goat, Calibiochem, La Jolla, CA, USA, 1:4,000; anti-GFAP raised in rabbit, Sigma-Aldrich, 1.0 µg/ml; anti-β-amyloid [Aβ 1–42] raised in mouse, Sigma-Aldrich, 1.0 µg/ml) overnight at room temperature. Two sets of tissue sections were double-labeled for apoE and GFAP or apoE and β-amyloid. For double-labeled sections, primary antibodies were added at the same time for a single primary antibody incubation. Sections were washed three times in fresh PBS, for 10 min each wash. They were then incubated in 0.3% Triton + 1% NGS/NSS in PBS with a secondary antibody (MAP-2: anti-mouse FITC raised in donkey, Jackson, 15 µg/ml; SYN: anti-mouse Texas Red raised in donkey, Jackson, 15 µg/ml; apoE: anti-goat FITC raised in donkey, Jackson, 15 µg/ml; GFAP: anti-rabbit Texas Red raised in donkey, Jackson, 15 µg/ml; β-amyloid: anti-mouse Texas Red raised in donkey, Jackson, 15 µg/ml) for 2 h at room temperature. Control sections were processed as described above, but without the primary antibody. Sections were mounted on slides (Fisher plus, Fisher Scientific, Pittsburg, PA, USA), dehydrated, and coverslipped with DPX Mountant (Sigma-Aldrich) and imaged with a Confocal Microscope (Olympus Spinning Disk Confocal, Center Valley, PA, USA).

Imaging and quantification

Images of the brain sections were acquired with Slidebook (Olympus) from layers 2–4 in the dorsal, lateral, medial, orbitofrontal, dorsal area 46, and ventral area 46 of the PFC, as well as the CA1, CA3, dentate gyrus (DG) of the hippocampus and layers 2–4 of the entorhinal cortex (EhC). Immunofluorescence was analyzed from six images per section for each section in the PFC set and four images per section for each of the sections in the hippocampus set. Images were taken of the same areas of the PFC or hippocampus from each brain section, using identical confocal parameters, including exposure time. To further address intensity issues, background intensity was determined using representative images for each brain section. Furthermore, all images were taken in a z-plane of 3 µm. A maximum intensity collapsed image was used for quantification. Area occupied by fluorescence immunoreactivity was calculated for each image. Subsequently, for each tissue set, the area occupied by fluorescence immunoreactivity in all images was averaged for the PFC and hippocampus. Quantification of the number of cells expressing GFAP was also performed.

Western blot analysis

A second set of post-mortem brain tissue, different from the brains used for were for immunohistochemistry but similar in age, were obtained from the PFC and hippocampus of adult (5–9 years; n = 4; 2 males, 2 females), middle-aged (11–18 years; n = 4; 2 males, 2 females), and aged (23–31 years; n = 4; 2 males, 2 females) male and female rhesus macaques, through the Tissue Distribution Program at ONPRC/OHSU. At death, the average weight was 7.9 ± 1.2 kg for adult, 7.2 ± 0.5 kg for middle-aged, and 7.6 ± 0.7 kg for aged animals. All animals were in overall good health during their lifetime. One female in the adult group was ovariectomized. None of the animals used in this study were behaviorally tested. All of the brains were flushed with 1 L of saline solution kept at room temperature. After perfusion, the brains were dissected, frozen, and stored at −80°C.

The tissues were homogenized using 1 ml of RIPA buffer (Pierce Pharmaceuticals, Rockford, IL, USA) and Halt protease inhibitor (Pierce Pharmaceuticals). Homogenized tissues were spun at 12,000×g for 15 min, and the supernatants were transferred to new tubes and kept for analysis. Protein concentrations were determined using a Nanodrop Spectrometer (NanoDrop ND-1000).

For each sample and lane, 40 µg of protein was used for Western blot analysis. Proteins were first denatured for 15 min by boiling them in a solution of Laemmli’s buffer containing 2-mercaptoethanol (Sigma-Aldrich) and samples were loaded onto pre-prepared gels (Criterion Bio-Rad Ready Gels, 4–15% Tris–HCl, 18-well). In addition to the tissue samples, one lane was used for the Precision Plus Protein Western Standard (Bio-Rad). Gels were run using a Bio-Rad Power Pac for 60 min at 175 V. Subsequently, proteins were transferred to PVDF membranes for 90 min at 30 V.

Once proteins were transferred to the membranes, the membranes were placed in blocking buffer [5% dry-milk in PBS containing 0.5% Tween-20 (TBS-Tween)] for 1 h. Membranes were washed with the TBS-Tween buffer (4 × 5 min) and incubated with the dry-milk buffer containing β-actin antibody (Santa Cruz Biotechnology, raised in mouse, 0.5 µg/ml) for 12 h at 4°C. Membranes were washed with TBS-Tween buffer (4 × 5 min) and incubated in the dry-milk buffer containing the secondary antibody for detecting the primary antibody against β-actin, donkey anti-mouse-HRP (Santa Cruz, 1 µg/ml) for 1 h and the secondary antibody for detecting the protein ladder, Precision protein StrepTactin-HRP (Bio-Rad; 5 µl). Subsequently, the membranes were incubated in Immun-Star HRP (Bio-Rad) for 5 min and imaged (FluorChem Q, Alpha Innotech, San Leandro, CA). After imaging, the antibodies were stripped from the membranes using Restore stripping buffer (Pierce Pharmaceuticals) for 5 min at room temperature. Membranes were re-blocked in blocking buffer (5% dry-milk TBS-Tween) for 1 h. Membranes were then washed in TBS-Tween buffer (4 × 5 min) and incubated with one primary antibody (anti-MAP-2 raised in mouse, Sigma-Aldrich, 1 µg/ml; anti-SYN raised in mouse, Sigma-Aldrich, 1 µg/ml; anti-apoE raised in goat, Calibiochem, 1:4,000; anti-GFAP raised in rabbit, Sigma-Aldrich, 1.0 µg/ml) for 12 h at 4°C. Membranes were washed in TBS-Tween buffer (4 × 5 min) and incubated in the corresponding secondary antibody (anti-mouse-HRP, 1 µg/ml for MAP-2 and SYN; anti-goat-HRP raised in donkey, 1 µg/ml for apoE; anti-rabbit-HRP raised in donkey, 1 µg/ml for GFAP; Santa Cruz Biotechnology) for 1 h. Blots were incubated with Immun-star HRP for 5 min and imaged. Blots were probed a maximum of three times, only being stripped twice. β-actin was used as one of the probes for each membrane as the loading control. Pixel densities of the β-actin, MAP-2, SYN, apoE, and GFAP bands were determined using FluorChem Q software. Background levels were automatically determined by the software using upper- and lower-edge interpolation. Semiquantification using densitometry for the β-actin MAP-2, SYN, apoE, and GFAP bands were measured for each sample. The results are presented as a ratio between the antigen of interest (MAP-2/SYN/apoE/GFAP) and β-actin bands.

Statistical analysis

Statistical analyses were performed with SPSS 16.0 (SPSS, Chicago, IL USA). Area occupied by fluorescence of MAP-2, SYN, apoE, and GFAP immunoreactivity, and GFAP cell number was analyzed by one-way ANOVAs with Bonferroni’s post-hoc tests. For the semiquantification of immunoblots, results for each brain area were analyzed using one-way ANOVAs and Bonferroni’s post-hoc tests. Significance was considered at P < 0.05.

Results

Microtubule associated protein 2

In the PFC, there was an interaction between the levels of MAP-2 immunoreactivity and age [F (2, 312) = 9.8, P < 0.001; Figs. 1 and 2a]. Although MAP-2 immunoreactivity was not significantly different between the adult and middle-aged rhesus macaques (P = 1.0), it was significantly greater in the aged macaques compared to the adult and middle-age macaques (P < 0.001). There was no difference in MAP-2 immunoreactivity between the specific regions of the PFC (P = 0.9). As described below in detail, western blot analyses revealed similar patterns for all markers as the fluorescence immunohistochemistry (i.e. See also western results, Fig. 3).

Fig. 1.

Fig. 1

Open in a new tab

Representative photomicrographs of MAP-2, SYN, apoE, and GFAP immunoreactivity from PFC of adult, middle-aged, and aged rhesus macaques. White arrows indicate GFAP cell clusters in the aged animal. Scale bar is 30 µm

Fig. 2.

Fig. 2

Open in a new tab

Age-related change in immunoreactivity in the PFC. a MAP-2 immunoreactivity, b SYN immunoreactivity, c apoE immunoreactivity, and d GFAP immunoreactivity. *P < 0.05 compared to both adult and middle-aged animals

Fig. 3.

Fig. 3

Open in a new tab

Age-related changes in protein expression in the PFC measured by Western blot analysis. Representative images of Western blot and β-actin control for all antigens; Lane 1 is from adult tissue, lane 2 is from middle-aged tissue, and lane 3 is from aged tissue in all images. a MAP-2, b SYN, c apoE, and d GFAP. *P < 0.05 compared to adult and middle-aged animals

Similarly, in the hippocampus, there was an effect of age on MAP-2 immunoreactivity [F (2, 272) = 38.6, P < 0.01; Figs. 4 and 8a]. There was a progressive age-dependent increase in MAP-2 immunoreactivity in hippocampus with all age groups showing significant differences in areas occupied by fluorescence (P < 0.01). There was no difference in MAP-2 immunoreactivity the CA1, CA3, and DG of the hippocampus or the EhC within the age groups (P = 0.2).

Fig. 4.

Fig. 4

Open in a new tab

Representative photomicrographs of MAP-2 immunoreactivity from the hippocampus CA1, CA3, dentate gyrus (DG), and entorhinal cortex (EhC) of adult, middle-aged and aged rhesus macaques. Scale bar is 30 µm

Fig. 8.

Fig. 8

Open in a new tab

Bar graphs representing MAP-2, SYN, apoE, and GFAP immunoreactivity in the CA1, CA3, DG, and EhC. a MAP-2 immunoreactivity. b SYN immunoreactivity. c apoE immunoreactivity. d GFAP immunoreactivity. ***P <0.001, **P <0.01, compared to adult and middle-aged animals and #P <0.01 compared to adult animals

Synaptophysin

There was an effect of age on SYN immunoreactivity in the PFC [F (2, 312) = 5.9, P < 0.01; Figs. 1 and 2b]. While there was no difference in SYN immunoreactivity in the adult and middle-aged rhesus macaque (P = 1.0), SYN immunoreactivity was significantly lower in the aged than the adult and middle-aged macaques. No difference in SYN immunoreactivity was observed between the specific regions of the PFC (P = 0.6).

In the hippocampus, there was an effect of age on SYN immunoreactivity [F (2, 272) = 4.24, P < 0.01; Figs. 5 and 8b]. Although no difference was observed in SYN immunoreactivity between the adult and middle-aged rhesus macaques (P = 1.0), SYN immunoreactivity was significantly lower in the aged macaques (P = 0.01). No difference was observed in SYN immunoreactivity between the CA1, CA3, and DG of the hippocampus or the EhC (P = 0.08).

Fig. 5.

Fig. 5

Open in a new tab

Representative photomicrographs of SYN immunoreactivity from the respective areas of the hippocampus CA1, CA3, DG, and EhC of adult, middle-aged, and aged rhesus macaques. Scale bar is 30 µm

Apolipoprotein E

In the PFC, there was an effect of age on the amount of apoE immunoreactivity [F (2, 312) = 7.3, P < 0.01; Figs. 1 and 2c]. ApoE immunoreactivity was not significantly different between the adult and middle-aged monkeys (P > 0.6), but was significantly greater in the aged macaques (P < 0.001). Interestingly, apoE immunoreactivity in the aged rhesus macaques was concentrated in clusters, whereas the immunoreactivity in the adult and middle-aged rhesus macaques was located in cells and around vessels (Fig. 1). ApoE immunoreactivity was not different between the subregions of the PFC (P = 0.6).

Likewise, in the hippocampus, there was an age-related increase in immunoreactivity [F (2, 272) = 62.7, P < 0.01; Figs. 6 and 8c]. While there was no difference in apoE immunoreactivity between the adult and middle-aged macaques (P = 1.0), apoE immunoreactivity was significantly greater in the aged macaques (P < 0.001). Similar to the PFC, apoE immunoreactivity was concentrated in clusters in the aged macaques, whereas, in the younger animals, apoE was limited to a few cells and around blood vessels (Fig. 6). Area occupied by fluorescence was not significantly different between the subregions of the hippocampus (P = 0.5).

Fig. 6.

Fig. 6

Open in a new tab

Representative photomicrographs of apoE immunoreactivity from the respective areas of the hippocampus CA1, CA3, DG, and EhC of adult, middle-aged, and aged rhesus macaques. Scale bar is 30 µm

GFAP

The number of cells expressing GFAP was not significantly different between adult, middle-aged, and aged rhesus macaques in either the PFC or hippocampus (P > 0.16). However, there was a significant increase in immunoreactivity of GFAP in both the PFC and hippocampus (P < 0.01).

In the PFC, there was an effect of age on the amount of GFAP immunoreactivity [F (2, 312) = 19.27, P < 0.001; Figs. 1 and 2d]. GFAP immunoreactivity was not different between the adult and middle-aged monkeys (P > 0.4), but it was significantly greater in the aged macaques (P < 0.001). GFAP immunoreactivity in the aged rhesus macaques was concentrated in groups of cells, whereas the immunoreactivity in the adult and middle-aged rhesus macaques was located in individual cells (Fig. 1). GFAP immunoreactivity was not different between the subregions of the PFC (P = 0.2).

Likewise, in the hippocampus, there was an overall interaction between age and GFAP immunoreactivity [F (2, 272) = 6.15, P < 0.01; Figs. 7 and 8d]. Although there was no difference in GFAP immunoreactivity between the adult and middle-aged macaques (P = 1.0), GFAP immunoreactivity was significantly greater in the aged macaques (P < 0.01). Similar to the PFC, GFAP immunoreactivity was concentrated in groups of cells in the aged macaques, whereas, in the younger animals, it was limited to individual cells. GFAP immunoreactivity was not significantly different between the subregions of the hippocampus (P = 0.5).

Fig. 7.

Fig. 7

Open in a new tab

Representative photomicrographs of GFAP immunoreactivity from respective areas of the hippocampus CA1, CA3, DG, and EhC of adult, middle-aged, and aged rhesus macaques. White arrows identify examples of clusters of GFAP positive cells in the aged animals. Scale bar is 30 µm

GFAP and apoE colocalization

At all ages examined, there was little colocalization of GFAP and apoE in both the PFC and hippocampus. In the adult (Fig. 9a), middle-aged (not shown), and aged animals (Fig. 9b, c), there was minimal overlap (yellow) of GFAP (red) and apoE (green), indicating little colocalization of the two proteins. In the aged animals, GFAP immunoreactivity was also frequently found concentrated in groups of cells surrounding apoE clusters (Fig. 9c).

Fig. 9.

Fig. 9

Open in a new tab

Representative photomicrographs of colocalization of apoE and GFAP and apoE and Aβ. a Photomicrograph from adult rhesus macaque demonstrating little overlap of GFAP and apoE from the PFC. b Photomicrograph from an aged rhesus macaque from the PFC. GFAP immunoreactivity (red) and apoE immunoreactivity (green) in the same image. Yellow areas are the overlap of GFAP and apoE immunoreactivity. cWhite boxed area from b enlarged to demonstrate the lack of colocalization of GFAP and apoE. White arrow indicates apoE immunoreactivity in close proximity, but not overlapping with GFAP immunoreactivity. Furthermore, GFAP grouping around apoE positive clusters are observed. d Photomicrograph from an aged rhesus macaque of an Aβ cluster that is not apoE positive from the PFC. e Photomicrograph from an aged rhesus macaque of an Aβ and apoE positive cluster from the PFC. Overlapping of Aβ and apoE immunoreactivity shows yellow. Scale bar is 30 µm

Aβ and apoE colocalization

No Aβ immunoreactivity was observed in the adult and middle-aged rhesus macaques, yet it was observed in clusters in the aged rhesus macaques. All apoE clusters were colocalized with Aβ immunoreactivity (Fig. 9e). However, not all Aβ-positive clusters were also apoE positive (Fig. 9d).

Western blot analysis

In the PFC, MAP-2 [F (2, 11) = 16.8; P = 0.01; Fig. 3a] and apoE [F (2, 11) = 5.2; P = 0.03; Fig. 3c] expression was significantly greater in the aged rhesus macaques compared to the adult and middle-aged animals. A trend of increased GFAP (P = 0.09; Fig. 3d) was also observed. Conversely, SYN expression was significantly less in the aged rhesus macaques compared to the adult and middle-aged animals [F (2, 11) = 4.5; P = 0.04; Fig. 3b]. No significant difference was observed between the adult or middle-aged animals for any of the four antigens.

A similar pattern was observed in the hippocampus, with expression of MAP-2 [F (2, 11) = 6.9; P = 0.01; Fig. 10a], apoE [F (2, 11) = 9.9; P = 0.005; Fig. 10c], and GFAP [F (2, 11) = 4.9; P = 0.04; Fig. 10d] being significantly greater in the aged rhesus macaques compared to the adult and middle-aged animals. SYN expression was significantly less in the aged rhesus macaques compared to the adult and middle-aged animals [F (2, 11) = 8.0; P = 0.01; Fig. 10b]. No significant difference was observed between the adult or middle-aged animals for any of the four antigens.

Fig. 10.

Fig. 10

Open in a new tab

Age-related changes in protein expression in the hippocampus measured by Western blot analysis. a MAP-2, b SYN, c apoE, and d GFAP. **P <0.01, *P <0.05 compared to adult and middle-aged animals

Discussion

A loss of synaptic activity is hypothesized to contribute to age-related decline of cognitive function (Masliah et al.1993; Liu et al.1996). Rodent studies have been equivocal, with reports of an age-related increase of SYN (Himeda et al.2005; Benice et al.2006), no change in SYN with increasing age (Calhoun et al.1998), and an age-related decrease of SYN (Adams et al.2008) in the hippocampus. The differences between these studies could be a result of cognitive testing or experimental manipulation of subjects. On the other hand, human studies indicate that MAP-2, apoE, and GFAP increase in the hippocampus with age while SYN decreases with age (Nichols et al.1993; Hesse et al.1999; Mukaetova-Ladinska et al.2000; Eastwood et al.2006). Similar to human studies, we show an age-related increase of MAP-2, GFAP, and apoE, as well as a decrease of SYN in the rhesus macaque hippocampus. The observed increase in MAP-2 levels might compensate for the age-related decrease in SYN levels. Additionally, the increase in GFAP levels could be a compensatory mechanism for the increase in apoE levels.

MAP-2 has been previously reported to be a sensitive marker for age-related changes in rodents (Benice et al.2006; Peister et al.2006). Here, we demonstrate a significant increase of MAP-2 immunoreactivity with increased age between the adult, middle-aged, and aged animals in the hippocampus of rhesus macaques, but not in the PFC. Conversely, no difference was observed between the adult and middle-aged animals in the SYN, apoE, or GFAP immunoreactivity in either the PFC or hippocampus. Therefore, MAP-2 is a maker for the early age-related changes in the hippocampus than SYN, apoE, or GFAP. Furthermore, the limbic system might be more sensitive to the effect of age than the neocortex.

In the aged animals, immunoreactivity of apoE was concentrated in clusters in both the PFC and the hippocampus. In rodents, elevated apoE levels correlate with impaired cognitive function (Kadish et al.2009). Increased apoE expression resulting from high dietary cholesterol in humans is also associated with an increased incidence of AD (Petanceska et al.2003). Nonhuman primates show an age-related decline in performance on tasks associated with PFC and hippocampal function (Rapp and Amaral 1991; Rapp and Heindel 1994; Rapp et al.1997). Therefore, if higher levels of apoE have a detrimental effect on cognitive function, it is feasible that the clusters of apoE observed here could contribute to the age-related decline in cognition.

As apoE has an integral role in the catabolism of amyloid within the brain, apoE might be increased in the elderly rhesus monkey brain for clearance of the age-related increase in Aβ (Cork et al.1990; Uno et al.1996; Sani et al.2003). Similar to previous studies, we demonstrate that apoE clusters are co-localized with Aβ deposits in aged rhesus macaques (Mufson et al.1994; Hartig et al.1997; Sani et al.2003). Furthermore, all apoE clusters were Aβ-positive, but not all Aβ-clusters were apoE-positive, which has been previously described (Nishiyama et al.1997). Increased Aβ deposits are found in humans who express apoE ε4, a risk factor for developing AD (Poirier 1994; Poirier 2000). Rhesus macaques only have one isoform of apoE, the ε4 allele (Gearing et al.1994; Mufson et al.1994; Poduri et al.1994), but do not develop severe cognitive deficits associated with AD. One potential reason for the lack of behavioral deficits as observed with AD is that the apoE ε4 allele in the rhesus macaque does not have arginine at position 61, which is responsible for the domain interaction observed with human apoE ε4 (Morelli et al.1996; Hatters et al.2006). Thus, the rhesus macaque apoE ε4 allele is more structurally similar to the human apoE ε3 allele.

In rodent studies, GFAP has been reported to increase with age (Lindsey et al.1979; Bjorklund et al.1985; Kohama et al.1995). Similarly, GFAP synthesis, protein, and degraded products increase with age in subcortical white matter of a nonhuman primate (Sloane et al.2000). Here, we report an increase in GFAP immunoreactivity, without an increase in the number of cells expressing GFAP. Thus, the apparent increase in GFAP immunoreactivity observed in this study is most likely due to the increase in cell size and number of processes expressing GFAP, corroborating rodent studies (Landfield et al.1977; Lindsey et al.1979; Garcia-Segura et al., 1994a, b; Garcia-Segura et al. 1994a, b; Berciano et al.1995; Garcia-Segura et al.1996; Struble et al.2006). Moreover, other nonhuman primate studies demonstrate that the cytoarchitecture of glial cells change with age but not the number of glial cells (Peters and Sethares 2002; Sandell and Peters 2002). Therefore, the age-related increase of GFAP suggests an increase in plasticity of GFAP-expressing astrocytes, or an increase in GFAP within astrocytes previously expressing low levels of GFAP (Sloane et al.2000).

Notably, the pattern of GFAP immunoreactivity was different from that of apoE. Although GFAP and apoE immunoreactivity show little colocalization at all ages, apoE clusters found in the elderly animals contain groups of GFAP cells that appear to infiltrate the apoE clusters (Fig. 9c). Due to the location of GFAP cells and the apoE clusters, it is possible GFAP contributes to the formation or function of these clusters. Thus, the increase in GFAP and apoE might be related, and the increase in GFAP could be part of a compensatory mechanism for the age-related increase in apoE.

We report an age-related increase of area occupied by immunofluorescence of MAP-2, apoE, and GFAP, as well as a decrease of SYN. Although we did not count synapses, synaptic vessels, or connections, Western blot analyses support our immunohistochemistry findings. However, the sensitivity of the two techniques is slightly different. For instance, Western blot analysis did not detect the age-related changes in MAP-2 between adult and middle-aged animals that were observed in the immunohistochemical analysis. As expected, these data indicate that immunohistochemistry is more sensitive to detect relatively smaller age-related changes in MAP-2. Similarly, Western blot analysis of GFAP only showed a trend towards a change in the PFC. Thus, the age-related change in GFAP in the PFC was not robust enough to be identified by Western blot analysis. The lack of a robust increase in GFAP levels as measured by Western blot supports the previous discussion of the apparent increase in GFAP processes and the potential of cells expressing low levels of GFAP increasing their GFAP expression over time. Furthermore, it is possible that the number of MAP-2 synapses increase and the number of SYN synapses or synaptic vesicles decrease. Interestingly, a clear difference in structural immunoreactivity in apoE between the adult and middle-aged animals versus the aged was observed.

In summary, age-related changes are observed in MAP-2, SYN, apoE, and GFAP immunoreactivity and protein levels as assessed by Western blot analysis in the rhesus macaque. These observations are more similar to the changes reported in aging human studies than rodent studies. As such, these results further support the rhesus macaque as a valuable translational model of human aging and a useful tool in understanding the biology of the aging brain.

Acknowledgements

The authors would like to thank Dominique Eghlidi and Sharon Kryger for their technical assistance. This work was supported by NIH Grants AG-023477, AG-029612, RR-000163, and an OHSU Tartar Fellowship.

References

  1. Adams MM, Shi L, Linville MC, Forbes ME, Long AB, Bennett C, Newton IG, Carter CS, Sonntag WE, Riddle DR, Brunso-Bechtold JK. Caloric restriction and age affect synaptic proteins in hippocampal CA3 and spatial learning ability. Exp Neurol. 2008;211:141–149. doi: 10.1016/j.expneurol.2008.01.016. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Albert MS, Moss MB. Cognitive profiles of normal human aging. In: Peters A, Morrison JH, editors. Cerebral cortexCerebral cortex. New York: Kluwer/Plenum; 1999. pp. 1–20. [Google Scholar]
  3. Benice TS, Rizk A, Kohama S, Pfankuch T, Raber J. Sex-differences in age-related cognitive decline in C57BL/6 J mice associated with increased brain microtubule-associated protein 2 and synaptophysin immunoreactivity. Neuroscience. 2006;137:413–423. doi: 10.1016/j.neuroscience.2005.08.029. [DOI] [PubMed] [Google Scholar]
  4. Berciano MT, Andres MA, Calle E, Lafarga M. Age-induced hypertrophy of astrocytes in rat supraoptic nucleus: a cytological, morphometric, and immunocytochemical study. Anat Rec. 1995;243:129–144. doi: 10.1002/ar.1092430115. [DOI] [PubMed] [Google Scholar]
  5. Bjorklund H, Eriksdotter-Nilsson M, Dahl D, Rose G, Hoffer B, Olson L. Image analysis of GFA-positive astrocytes from adolescence to senescence. Exp Brain Res. 1985;58:163–170. doi: 10.1007/BF00238964. [DOI] [PubMed] [Google Scholar]
  6. Burns MP, Noble WJ, Olm V, Gaynor K, Casey E, LaFrancois J, Wang L, Duff K. Co-localization of cholesterol, apolipoprotein E and fibrillar Abeta in amyloid plaques. Brain Res Mol Brain Res. 2003;110:119–125. doi: 10.1016/S0169-328X(02)00647-2. [DOI] [PubMed] [Google Scholar]
  7. Calhoun ME, Kurth D, Phinney AL, Long JM, Hengemihle J, Mouton PR, Ingram DK, Jucker M. Hippocampal neuron and synaptophysin-positive bouton number in aging C57BL/6 mice. Neurobiol Aging. 1998;19:599–606. doi: 10.1016/S0197-4580(98)00098-0. [DOI] [PubMed] [Google Scholar]
  8. Chauhan N, Siegel G. Age-dependent organotypic expression of microtubule-associated proteins (MAP1, MAP2, and MAP5) in rat brain. Neurochem Res. 1997;22:713–719. doi: 10.1023/A:1027306227402. [DOI] [PubMed] [Google Scholar]
  9. Cork LC, Masters C, Beyreuther K, Price DL. Development of senile plaques. Relationships of neuronal abnormalities and amyloid deposits. Am J Pathol. 1990;137:1383–1392. [PMC free article] [PubMed] [Google Scholar]
  10. Dawson GR, Seabrook GR, Zheng H, Smith DW, Graham S, O'Dowd G, Bowery BJ, Boyce S, Trumbauer ME, Chen HY, Ploeg LH, Sirinathsinghji DJ. Age-related cognitive deficits, impaired long-term potentiation and reduction in synaptic marker density in mice lacking the beta-amyloid precursor protein. Neuroscience. 1999;90:1–13. doi: 10.1016/S0306-4522(98)00410-2. [DOI] [PubMed] [Google Scholar]
  11. Stefano G, Casoli T, Fattoretti P, Gracciotti N, Solazzi M, Bertoni-Freddari C. Distribution of map2 in hippocampus and cerebellum of young and old rats by quantitative immunohistochemistry. J Histochem Cytochem. 2001;49:1065–1066. doi: 10.1177/002215540104900818. [DOI] [PubMed] [Google Scholar]
  12. Eastwood SL, Weickert CS, Webster MJ, Herman MM, Kleinman JE, Harrison PJ. Synaptophysin protein and mRNA expression in the human hippocampal formation from birth to old age. Hippocampus. 2006;16:645–654. doi: 10.1002/hipo.20194. [DOI] [PubMed] [Google Scholar]
  13. Fukuda T, Shimizu J, Furuhata H, Abe T, Shimizu K, Oishi T, Ogihara M, Kubota J, Sasaki A, Sasaki K, Azuma T, Umemura S. Overexpression of heat shock proteins in pallido-nigral axonal spheroids of nonhuman aged primates. Acta Neuropathol. 2005;110:145–150. doi: 10.1007/s00401-005-1030-8. [DOI] [PubMed] [Google Scholar]
  14. Gallardo G, Schluter OM, Sudhof TC. A molecular pathway of neurodegeneration linking alpha-synuclein to ApoE and Abeta peptides. Nat Neurosci. 2008;11:301–308. doi: 10.1038/nn2058. [DOI] [PubMed] [Google Scholar]
  15. Garcia-Segura LM, Chowen JA, Duenas M, Parducz A, Naftolin F. Gonadal steroids and astroglial plasticity. Cell Mol Neurobiol. 1996;16:225–237. doi: 10.1007/BF02088178. [DOI] [PubMed] [Google Scholar]
  16. Garcia-Segura LM, Chowen JA, Duenas M, Torres-Aleman I, Naftolin F. Gonadal steroids as promoters of neuro-glial plasticity. Psychoneuroendocrinology. 1994;19:445–453. doi: 10.1016/0306-4530(94)90031-0. [DOI] [PubMed] [Google Scholar]
  17. Garcia-Segura LM, Luquin S, Parducz A, Naftolin F. Gonadal hormone regulation of glial fibrillary acidic protein immunoreactivity and glial ultrastructure in the rat neuroendocrine hypothalamus. Glia. 1994;10:59–69. doi: 10.1002/glia.440100108. [DOI] [PubMed] [Google Scholar]
  18. Gearing M, Rebeck GW, Hyman BT, Tigges J, Mirra SS. Neuropathology and apolipoprotein E profile of aged chimpanzees: implications for Alzheimer disease. Proc Natl Acad Sci USA. 1994;91:9382–9386. doi: 10.1073/pnas.91.20.9382. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Geinisman Y, Detoledo-Morrell L, Morrell F, Heller RE. Hippocampal markers of age-related memory dysfunction: behavioral, electrophysiological and morphological perspectives. Prog Neurobiol. 1995;45:223–252. doi: 10.1016/0301-0082(94)00047-L. [DOI] [PubMed] [Google Scholar]
  20. Gosche KM, Mortimer JA, Smith CD, Markesbery WR, Snowdon DA. Hippocampal volume as an index of Alzheimer neuropathology: findings from the Nun Study. Neurology. 2002;58:1476–1482. doi: 10.1212/wnl.58.10.1476. [DOI] [PubMed] [Google Scholar]
  21. Harada A, Teng J, Takei Y, Oguchi K, Hirokawa N. MAP2 is required for dendrite elongation, PKA anchoring in dendrites, and proper PKA signal transduction. J Cell Biol. 2002;158:541–549. doi: 10.1083/jcb.200110134. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Hartig W, Bruckner G, Schmidt C, Brauer K, Bodewitz G, Turner JD, Bigl V. Co-localization of beta-amyloid peptides, apolipoprotein E and glial markers in senile plaques in the prefrontal cortex of old rhesus monkeys. Brain Res. 1997;751:315–322. doi: 10.1016/S0006-8993(96)01423-0. [DOI] [PubMed] [Google Scholar]
  23. Hatters DM, Peters-Libeu CA, Weisgraber KH. Apolipoprotein E structure: insights into function. Trends Biochem Sci. 2006;31:445–454. doi: 10.1016/j.tibs.2006.06.008. [DOI] [PubMed] [Google Scholar]
  24. Hesse C, Bogdanovic N, Davidsson P, Blennow K. A quantitative and immunohistochemical study on apolipoprotein E in brain tissue in Alzheimer's disease. Dement Geriatr Cogn Disord. 1999;10:452–459. doi: 10.1159/000017189. [DOI] [PubMed] [Google Scholar]
  25. Himeda T, Mizuno K, Kato H, Araki T. Effects of age on immunohistochemical changes in the mouse hippocampus. Mech Ageing Dev. 2005;126:673–677. doi: 10.1016/j.mad.2004.12.004. [DOI] [PubMed] [Google Scholar]
  26. Hol EM, Roelofs RF, Moraal E, Sonnemans MA, Sluijs JA, Proper EA, Graan PN, Fischer DF, Leeuwen FW. Neuronal expression of GFAP in patients with Alzheimer pathology and identification of novel GFAP splice forms. Mol Psychiatry. 2003;8:786–796. doi: 10.1038/sj.mp.4001379. [DOI] [PubMed] [Google Scholar]
  27. Kadish I, Thibault O, Blalock EM, Chen KC, Gant JC, Porter NM, Landfield PW. Hippocampal and cognitive aging across the lifespan: a bioenergetic shift precedes and increased cholesterol trafficking parallels memory impairment. J Neurosci. 2009;29:1805–1816. doi: 10.1523/JNEUROSCI.4599-08.2009. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Keuker JI, Luiten PG, Fuchs E. Preservation of hippocampal neuron numbers in aged rhesus monkeys. Neurobiol Aging. 2003;24:157–165. doi: 10.1016/S0197-4580(02)00062-3. [DOI] [PubMed] [Google Scholar]
  29. Kohama SG, Goss JR, Finch CE, McNeill TH. Increases of glial fibrillary acidic protein in the aging female mouse brain. Neurobiol Aging. 1995;16:59–67. doi: 10.1016/0197-4580(95)80008-F. [DOI] [PubMed] [Google Scholar]
  30. Landfield PW, Rose G, Sandles L, Wohlstadter TC, Lynch G. Patterns of astroglial hypertrophy and neuronal degeneration in the hippocampus of ages, memory-deficient rats. J Gerontol. 1977;32:3–12. doi: 10.1093/geronj/32.1.3. [DOI] [PubMed] [Google Scholar]
  31. Levy R, Goldman-Rakic P. Association of storage and processing functions in the dorsolateral prefrontal cortex of the non-human primate. J Neurosci. 1999;19:5149–5158. doi: 10.1523/JNEUROSCI.19-12-05149.1999. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Lindsey JD, Landfield PW, Lynch G. Early onset and topographical distribution of hypertrophied astrocytes in hippocampus of aging rats: a quantitative study. J Gerontol. 1979;34:661–671. doi: 10.1093/geronj/34.5.661. [DOI] [PubMed] [Google Scholar]
  33. Liu X, Erikson C, Brun A. Cortical synaptic changes and gliosis in normal aging, Alzheimer's disease and frontal lobe degeneration. Dementia. 1996;7:128–134. doi: 10.1159/000106867. [DOI] [PubMed] [Google Scholar]
  34. Maguire EA, Cipolotti L. Selective sparing of topographical memory. J Neurol Neurosurg Psychiatry. 1998;65:903–909. doi: 10.1136/jnnp.65.6.903. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Masliah E, Mallory M, Hansen L, DeTeresa R, Terry RD. Quantitative synaptic alterations in the human neocortex during normal aging. Neurology. 1993;43:192–197. doi: 10.1212/wnl.43.1_part_1.192. [DOI] [PubMed] [Google Scholar]
  36. Merrill DA, Roberts JA, Tuszynski MH. Conservation of neuron number and size in entorhinal cortex layers II, III, and V/VI of aged primates. J Comp Neurol. 2000;422:396–401. doi: 10.1002/1096-9861(20000703)422:3&#x0003c;396::AID-CNE6&#x0003e;3.0.CO;2-R. [DOI] [PubMed] [Google Scholar]
  37. Minkeviciene R, Ihalainen J, Malm T, Matilainen O, Keksa-Goldsteine V, Goldsteins G, Iivonen H, Leguit N, Glennon J, Koistinaho J, Banerjee P, Tanila H. Age-related decrease in stimulated glutamate release and vesicular glutamate transporters in APP/PS1 transgenic and wild-type mice. J Neurochem. 2008;105:584–594. doi: 10.1111/j.1471-4159.2007.05147.x. [DOI] [PubMed] [Google Scholar]
  38. Morelli L, Wei L, Amorim A, McDermid J, Abee CR, Frangione B, Walker LC, Levy E. Cerebrovascular amyloidosis in squirrel monkeys and rhesus monkeys: apolipoprotein E genotype. FEBS Lett. 1996;379:132–134. doi: 10.1016/0014-5793(95)01491-8. [DOI] [PubMed] [Google Scholar]
  39. Moss MB, Killiany RJ, Herndon JG. Age-related cognitive decline in the rhesus monkey. In: Peters A, Morrison JH, editors. Cerebral cortexCerebral cortex. New York: Kluwer/Plenum; 1999. pp. 21–48. [Google Scholar]
  40. Mufson EJ, Benzing WC, Cole GM, Wang H, Emerich DF, Sladek JR, Jr, Morrison JH, Kordower JH. Apolipoprotein E-immunoreactivity in aged rhesus monkey cortex: colocalization with amyloid plaques. Neurobiol Aging. 1994;15:621–627. doi: 10.1016/0197-4580(94)00064-6. [DOI] [PubMed] [Google Scholar]
  41. Mukaetova-Ladinska EB, Garcia-Siera F, Hurt J, Gertz HJ, Xuereb JH, Hills R, Brayne C, Huppert FA, Paykel ES, McGee M, Jakes R, Honer WG, Harrington CR, Wischik CM. Staging of cytoskeletal and beta-amyloid changes in human isocortex reveals biphasic synaptic protein response during progression of Alzheimer's disease. Am J Pathol. 2000;157:623–636. doi: 10.1016/s0002-9440(10)64573-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Mulder M, Jansen PJ, Janssen BJ, Berg WD, Boom H, Havekes LM, Kloet RE, Ramaekers FC, Blokland A. Low-density lipoprotein receptor-knockout mice display impaired spatial memory associated with a decreased synaptic density in the hippocampus. Neurobiol Dis. 2004;16:212–219. doi: 10.1016/j.nbd.2004.01.015. [DOI] [PubMed] [Google Scholar]
  43. Nakamura S, Kiatipattanasakul W, Nakayama H, Ono F, Sakakibara I, Yoshikawa Y, Goto N, Doi K. Immunohistochemical characteristics of the constituents of senile plaques and amyloid angiopathy in aged cynomolgus monkeys. J Med Primatol. 1996;25:294–300. doi: 10.1111/j.1600-0684.1996.tb00213.x. [DOI] [PubMed] [Google Scholar]
  44. Nichols NR, Day JR, Laping NJ, Johnson SA, Finch CE. GFAP mRNA increases with age in rat and human brain. Neurobiol Aging. 1993;14:421–429. doi: 10.1016/0197-4580(93)90100-P. [DOI] [PubMed] [Google Scholar]
  45. Nishiyama E, Iwamoto N, Ohwada J, Arai H. Distribution of apolipoprotein E in senile plaques in brains with Alzheimer's disease: investigation with the confocal laser scan microscope. Brain Res. 1997;750:20–24. doi: 10.1016/S0006-8993(96)01329-7. [DOI] [PubMed] [Google Scholar]
  46. Overmyer M, Helisalmi S, Soininen H, Laakso M, Riekkinen P, Sr, Alafuzoff I. Astrogliosis and the ApoE genotype. An immunohistochemical study of postmortem human brain tissue. Dement Geriatr Cogn Disord. 1999;10:252–257. doi: 10.1159/000017128. [DOI] [PubMed] [Google Scholar]
  47. Paulesu E, Frith C, Frackowiak R. The neural correlates of the verbal component of working memory. Nature. 1993;362:342–345. doi: 10.1038/362342a0. [DOI] [PubMed] [Google Scholar]
  48. Peister A, Zeitouni S, Pfankuch T, Reger RL, Prockop DJ, Raber J. Novel object recognition in Apoe(-/-) mice improved by neonatal implantation of wild-type multipotential stromal cells. Exp Neurol. 2006;201:266–269. doi: 10.1016/j.expneurol.2006.03.023. [DOI] [PubMed] [Google Scholar]
  49. Petanceska SS, DeRosa S, Sharma A, Diaz N, Duff K, Tint SG, Refolo LM, Pappolla M. Changes in apolipoprotein E expression in response to dietary and pharmacological modulation of cholesterol. J Mol Neurosci. 2003;20:395–406. doi: 10.1385/JMN:20:3:395. [DOI] [PubMed] [Google Scholar]
  50. Peters A, Sethares C. The effects of age on the cells in layer 1 of primate cerebral cortex. Cereb Cortex. 2002;12:27–36. doi: 10.1093/cercor/12.1.27. [DOI] [PubMed] [Google Scholar]
  51. Poduri A, Gearing M, Rebeck GW, Mirra SS, Tigges J, Hyman BT. Apolipoprotein E4 and beta amyloid in senile plaques and cerebral blood vessels of aged rhesus monkeys. Am J Pathol. 1994;144:1183–1187. [PMC free article] [PubMed] [Google Scholar]
  52. Poirier J. Apolipoprotein E in animal models of CNS injury and in Alzheimer's disease. Trends Neurosci. 1994;17:525–530. doi: 10.1016/0166-2236(94)90156-2. [DOI] [PubMed] [Google Scholar]
  53. Poirier J. Apolipoprotein E and Alzheimer's disease. A role in amyloid catabolism. Ann N Y Acad Sci. 2000;924:81–90. doi: 10.1111/j.1749-6632.2000.tb05564.x. [DOI] [PubMed] [Google Scholar]
  54. Prieto-Gomez B, Velazquez-Paniagua M, Cisneros LO, Reyes-Vazquez C, Jimenez-Trejo F, Reyes ME, Mendoza-Torreblanca J, Gutierrez-Ospina G. Melatonin attenuates the decrement of dendritic protein MAP-2 immuno-staining in the hippocampal CA1 and CA3 fields of the aging male rat. Neurosci Lett. 2008;448:56–61. doi: 10.1016/j.neulet.2008.10.041. [DOI] [PubMed] [Google Scholar]
  55. Rapp PR, Amaral DG. Recognition memory deficits in a subpopulation of aged monkeys resemble the effects of medial temporal lobe damage. Neurobiol Aging. 1991;12:481–486. doi: 10.1016/0197-4580(91)90077-W. [DOI] [PubMed] [Google Scholar]
  56. Rapp PR, Gallagher M. Preserved neuron number in the hippocampus of aged rats with spatial learning deficits. PNAS. 1996;93:9926–9930. doi: 10.1073/pnas.93.18.9926. [DOI] [PMC free article] [PubMed] [Google Scholar]
  57. Rapp PR, Heindel WC. Memory systems in normal and patholigical aging. Curr Opin Neurol. 1994;7:294–298. doi: 10.1097/00019052-199408000-00003. [DOI] [PubMed] [Google Scholar]
  58. Rapp PR, Kansky MT, Roberts JA. Impaired spatial information processing in aged monkeys with preserved recognition memory. NeuroReport. 1997;8:1923–1928. doi: 10.1097/00001756-199705260-00026. [DOI] [PubMed] [Google Scholar]
  59. Rosenbaum RS, Winocur G, Moscovitch M. New views on old memories: Re-evaluating the role of the hippocampal complex. Behavioral Brain Research. 2001;127:183–197. doi: 10.1016/S0166-4328(01)00363-1. [DOI] [PubMed] [Google Scholar]
  60. Sandell JH, Peters A. Effects of age on the glial cells in the rhesus monkey optic nerve. J Comp Neurol. 2002;445:13–28. doi: 10.1002/cne.10162. [DOI] [PubMed] [Google Scholar]
  61. Sani S, Traul D, Klink A, Niaraki N, Gonzalo-Ruiz A, Wu CK, Geula C. Distribution, progression and chemical composition of cortical amyloid-beta deposits in aged rhesus monkeys: similarities to the human. Acta Neuropathol. 2003;105:145–156. doi: 10.1007/s00401-002-0626-5. [DOI] [PubMed] [Google Scholar]
  62. Shapiro LA, Whitaker-Azmitia PM. Expression levels of cytoskeletal proteins indicate pathological aging of S100B transgenic mice: an immunohistochemical study of MAP-2, drebrin and GAP-43. Brain Res. 2004;1019:39–46. doi: 10.1016/j.brainres.2004.05.100. [DOI] [PubMed] [Google Scholar]
  63. Si X, Miguel-Hidalgo JJ, O'Dwyer G, Stockmeier CA, Rajkowska G. Age-dependent reductions in the level of glial fibrillary acidic protein in the prefrontal cortex in major depression. Neuropsychopharmacology. 2004;29:2088–2096. doi: 10.1038/sj.npp.1300525. [DOI] [PMC free article] [PubMed] [Google Scholar]
  64. Sloane JA, Hollander W, Rosene DL, Moss MB, Kemper T, Abraham CR. Astrocytic hypertrophy and altered GFAP degradation with age in subcortical white matter of the rhesus monkey. Brain Res. 2000;862:1–10. doi: 10.1016/S0006-8993(00)02059-X. [DOI] [PubMed] [Google Scholar]
  65. Struble RG, Afridi S, Beckman-Randall S, Li M, Cady C, Nathan B, McAsey ME. Neocortical and hippocampal glial fibrillary acidic protein immunoreactivity shows region-specific variation during the mouse estrous cycle. Neuroendocrinology. 2006;83:325–335. doi: 10.1159/000095340. [DOI] [PubMed] [Google Scholar]
  66. Tarsa L, Goda Y. Synaptophysin regulates activity-dependent synapse formation in cultured hippocampal neurons. Proc Natl Acad Sci USA. 2002;99:1012–1016. doi: 10.1073/pnas.022575999. [DOI] [PMC free article] [PubMed] [Google Scholar]
  67. Uno H, Alsum PB, Dong S, Richardson R, Zimbric ML, Thieme CS, Houser WD. Cerebral amyloid angiopathy and plaques, and visceral amyloidosis in aged macaques. Neurobiol Aging. 1996;17:275–281. doi: 10.1016/0197-4580(95)02063-2. [DOI] [PubMed] [Google Scholar]
  68. Winocur G, Gagnon S. Glucose treatment attenuates spatial learning and memory deficits of aged rats on tests of hippocampal function. Neurobiol Aging. 1998;19:233–241. doi: 10.1016/S0197-4580(98)00057-8. [DOI] [PubMed] [Google Scholar]
  69. Zyzak DR, Otto T, Eichenbaum H, Gallagher M. Cognitive decline associated with normal aging in rats: a neuropsychological approach. Learn Mem. 1995;2:1–16. doi: 10.1101/lm.2.1.1. [DOI] [PubMed] [Google Scholar]

Articles from Age are provided here courtesy of American Aging Association

RESOURCES