Skip to main content
PMC home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2016 Jan 1.
Published in final edited form as: Neuroepigenetics. 2015 Jan 1;1:34–40. doi: 10.1016/j.nepig.2014.10.005

HDAC2 expression in parvalbumin interneurons regulates synaptic plasticity in the mouse visual cortex

Alexi Nott 1,*, Sukhee Cho 1,2,*, Jinsoo Seo 1, Li-Huei Tsai 1
PMCID: PMC4331030  NIHMSID: NIHMS639780  PMID: 25705589

Abstract

An experience-dependent postnatal increase in GABAergic inhibition in the visual cortex is important for the closure of a critical period of enhanced synaptic plasticity. Although maturation of the subclass of Parvalbumin (Pv)-expressing GABAergic interneurons is known to contribute to critical period closure, the role of epigenetics on cortical inhibition and synaptic plasticity has not been explored. The transcription regulator, histone deacetylase 2 (HDAC2), has been shown to modulate synaptic plasticity and learning processes in hippocampal excitatory neurons. We found that genetic deletion of HDAC2 specifically from Pv-interneurons reduces inhibitory input in the visual cortex of adult mice, and coincides with enhanced long-term depression (LTD) that is more typical of young mice. These findings show that HDAC2 loss in Pv-interneurons leads to a delayed closure of the critical period in the visual cortex and supports the hypothesis that HDAC2 is a key negative regulator of synaptic plasticity in the adult brain.

Introduction

The normal maturation of the visual cortex is dependent on environmental visual stimulus during a period of postnatal development of enhanced plasticity, termed the ‘critical period’. In rodents, the onset of the critical period in the visual cortex coincides with eye-opening at 2-weeks of age, and the subsequent closure of the critical period occurs around the onset of puberty, at 5-weeks. During this period, cortical responses within the primary visual cortex (V1) can be altered by simple manipulation of sensory experience. Mechanisms by which this experience-dependent cortical plasticity can be altered require changes in N-methyl-D-aspartate receptor (NMDAR)-mediated synaptic responses, such as long-term potentiation (LTP) and depression (LTD) [1]. The subsequent decrease in cortical plasticity that occurs during the closure of the critical period has been shown to be modulated by gamma-aminobutyric acid (GABA)-ergic inhibitory interneurons.

The maturation of inhibitory interneurons in the cortex of rodents mirrors the timing of the critical period, slowly maturing during postnatal development until around 5-weeks of age. Reduced or ablated expression of the GABA synthesizing enzymes delays the closure of the critical period [2–5], while conversely, an early onset in critical period plasticity can be induced by accelerating GABA circuit function [6–9]. The largest class of interneurons is the parvalbumin (Pv)-expressing neurons, comprising up to 50% of the inhibitory cells in the mouse cortex [2, 10]. In rodents the parvalbumin-expressing cells also emerge and mature with a postnatal time course that follows the critical period in the visual cortex [11–14]. Maturation of Pv-expressing cells is triggered by non-cell autonomous factors, such as BDNF and Otx2, and artificial elevation of these factors accelerates Pv cell maturation and prematurely closes the critical period [9, 11, 13, 14].

Molecular mechanisms of cortical plasticity require changes in gene expression. Indeed, the alteration of visual experience during the critical period in rodents has been shown to modify the expression of many genes [11, 13, 15]. Activity-dependent changes in neuronal gene expression are mediated in part by posttranslational modification of histones. The exposure of dark-reared mice to light triggers the phosphorylation and acetylation of histones, and is more pronounced in mice during the critical period than in adulthood [6, 8, 16]. Manipulation of histone acetylation by treatment of adult mice with histone deacetylase (HDAC) inhibitors promotes increased plasticity of the visual cortex and is able to rescue visual acuity deficits elicited during early life that are normally irreversible [16–19]. The positive effects of HDAC inhibition on the critical period is not confined to the visual system, and can also increase auditory perception in both adult mice and humans [18, 19].

Histone deacetylation therefore plays an important role in mediating enhanced cortical plasticity of the visual system, however, the importance of cell-type specific histone deacetylation and its regulation by individual HDACs on cortical plasticity has not been explored. Previous studies show that HDAC2 acts as an epigenetic blockade for learning and memory processes through its interaction at the promoters of synaptic plasticity genes causing a reduction in the expression of these genes [20–22]. The aim of this study was to investigate the role of HDAC2-mediated gene regulation of Pv-expressing cells on synaptic plasticity of the visual cortex. We report that the loss of HDAC2 expression specifically in Pv-positive interneurons leads to a reduction in inhibitory synaptic strength and an increase in NMDAR-mediated long-term plasticity in adult mice, and more closely reflects that of responses normally observed in young mice associated with enhanced cortical plasticity.

Methods

Animals

HDAC2 conditional knockout mice (HDAC2f/f;Pv-cre) were generated by crossing HDAC2 floxed mice (HDAC2f/f) [20] with the transgenic Parvalbumin promoter-driven Cre line[23]. All experiments were performed using male mice at either 3-weeks or 8-weeks old in a FVB×C57/BL6 background; and each experiment was performed using littermate age-matched controls. The age and number of mice used for each experiment has been indicated in the appropriate figure legends. All animal work was approved by the Committee for Animal Care of the Division of Comparative Medicine at the Massachusetts Institute of Technology.

Immunohistochemistry

8-week old male mice were perfused with 10% formaldehyde under deep anesthesia and brains were post-fixed overnight in 10% formaldehyde. Brains were sectioned at 40 µm using a vibratome (Leica). Sections were permeabilized and blocked in PBS containing 0.3 % Triton X-100 and 10 % normal donkey serum at room temperature for 1 hr. Sections were incubated overnight at 4 °C in primary antibody diluted 1:200 in PBS with 0.3 % Triton X-100 and 10 % normal donkey serum. Primary antibodies used were anti-HDAC2 (Abcam; #12169) and anti-Parvalbumin (Swant, 235). Primary antibodies were visualized with Alexa Fluor 488, and Alexa Fluor 647 antibodies (Jackson ImmunoResearch Laboratories) and Hoechst 33342, all diluted 1:500 in PBS and incubated at room temperature for 90 min. Sections were mounted on slides with Fluoromount G (Electron Microscopy Sciences) overnight at room temperature and stored at 4 °C. Images were acquired using an LSM 710 Zeiss confocal microscope and analyzed using ImageJ 1.46a software.

Western Blot

Whole cell lysates of the V1 visual cortex were prepared using tissue from 8-week old male mice. Tissue was homogenized in 1 ml RIPA buffer (50mM Tris HCl pH 8.0, 150mM NaCl, 1% NP-40, 0.5% sodium deoxycholate, 0.1% SDS) with a hand homogenizer (Sigma), incubated on ice for 15 min, and rotated at 4 °C for 30 min. Cell debris were isolated and discarded by centrifugation at 14,000 rpm for 10 minutes. Lysates were loaded on 10 % acrylamide gels and protein transferred from acrylamide gels to PVDF membranes (Invitrogen) at 100 V for 90 min. Membranes were blocked using bovine serum albumin (5 % w/v) diluted in TBS:Tween. Membranes were incubated in primary antibodies overnight at 4 °C and secondary antibodies at room temperature for 90 minutes. Western blots were imaged using the Odyssey Imaging System (LI-COR Biosciences) and analyzed with ImageJ 1.46a software.

Field potential recording

Coronal slices (400 µm thick) of mice visual cortical slices were prepared in ice-cold dissection buffer (in mM: 211 sucrose, 3.3 KCl, 1.3 NaH2PO4, 0.5 CaCl2, 10 MgCl2, 26 NaHCO3 and 11 glucose) that is oxygenated with 95% O2, 5% CO2 [11]. After dissection using a Leica VT1000S vibratome (Leica, Nussloch, Germany), slices were moved into recovery chamber with 95 % O2, 5 % CO2-saturated artificial cerebrospinal fluid (ACSF) consisting of (mM) 124 NaCl, 3.3 KCl, 1.3 NaH2PO4, 2.5 CaCl2, 1.5 MgCl2, 26 NaHCO3 and 11 glucose for 1 hr at 28–30 °C. To stimulate layer IV pyramidal neurons, tungsten bipolar electrode (200 µm diameter; FHC, Bowdoinham, ME) was used and glass microelectrode filled with ACSF was placed in layer II/III to record extracellular field potential. White matter to layer IV recording was made with the same paradigm. Long-term depression (LTD) was induced by single-pulse low frequency stimulation (900 pulses at 1 Hz).

Whole-cell patch-clamp recording

Coronal brain slices (250 µm thick) were used for whole-cell patch-clamp recordings. Miniature inhibitory postsynaptic potential (mIPSC) was measured from layer II/III pyramidal neurons using recording pipettes (3–5 MΩ) filled with internal solution containing (mM) 145 CsCl, 5 NaCl, 10 HEPESCsOH, 10 EGTA, 4 MgATP and 0.3 Na2GTP in the presence of tetrodotoxin (1 µM), 2-amino-5-phosphonovaleric acid (APV) (100 µM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (200 µM). For compound IPSCs and EPSCs, synaptic responses were evoked with a bipolar stimulating electrode with 0.2 msec of current pulse delivery at layer IV of the visual cortical slices. Layer II/III cells were held at 0 mV for IPSCs and −60 mV for EPSCs with recording pipettes filled with internal solution containing (mM) 130 Cs-gluconate, 2 MgCl2, 2 CaCl2, 10 EGTA, 10 Hepes, 2 Na-ATP, 10 QX-314 [2, 35]. A MultiClamp 700B amplifier and a Digidata 1440A A-D converter (Axon Instruments, Union City, CA) were used for data acquisition and data were analyzed with pClamp10 (Axon Instruments).

Results

Conditional deletion of HDAC2 in Parvalbumin-expressing interneurons

To address the effects of the loss of HDAC2 on Parvalbumin inhibitory neurons, HDAC2 conditional knockout mice (HDAC2f/f;Pv-cre) were generated by crossing HDAC2 floxed mice (HDAC2f/f) [20], with the transgenic Parvalbumin promoter-driven Cre line [23]. HDAC2 was first verified as being strongly expressed in Pv-positive interneurons by co-immunostaining brain slices for HDAC2 and Parvalbumin from HDAC2f/f wildtype mice (Fig. 1A). The loss of HDAC2 in Parvalbumin inhibitory neurons of the V1 region of the visual cortex was confirmed by co-immunostaining of brain slices from HDAC2f/f;Pv-cre mice (Fig. 1A). Loss of HDAC2 expression leads to a decrease in expression of Parvalbumin, as quantified by immunostaining and western blot analysis of tissue from the V1 region of the visual cortex, with no loss in the total number of Pv-expressing cells (Fig. 1A, 1B). The loss of HDAC2 expression in Pv neurons had no effect on the expression of glutamate decarboxylase 1 (GAD1/GAD67) or GAD2 (GAD65) in the visual cortex as determined by western blot analysis (Fig. 1B).

Figure 1.

Figure 1

Open in a new tab

HDAC2 conditional knockout from Pv-expressing interneurons. A, Coronal brain slices of HDAC2f/f and HDAC2f/f;Pv-cre male mice at 8-weeks old were stained using Hoescht (blue), anti-Parvalbumin (green) and anti-HDAC2 (red), and images captured of the V1 visual cortex using a confocal microscope. Scale bar, 20 µm. Mean grey value quantification of HDAC2 and Parvalbumin immunofluorescence was compared between HDAC2f/f and HDAC2f/f;Pv-cre mice in the visual cortex. Two-tailed t test; p < 0.0001, HDAC2; p < 0.05, Parvalbumin; n = 5 mice (HDAC2f/f), 5 mice (HDAC2f/f;Pv-cre). Cell number quantification of Parvalbumin expressing cells in the V1 visual cortex. Two-tailed t test; p > 0.05; n = 5 mice (HDAC2f/f ), 7 mice (HDAC2f/f;Pv-cre). B, Western blot analysis of GABAA Receptor Gamma 2 Subunit, GAD65, GAD67 and Parvalbumin protein levels using whole cell lysates of the V1 visual cortex from HDAC2f/f and HDAC2f/f;Pv-cre mice. Mean grey value quantification of Parvalbumin protein levels. Two-tailed t test; p < 0.0001; n = 4 mice (HDAC2f/f), 3 mice (HDAC2f/f;Pv-cre).

Inhibitory synaptic plasticity is reduced in the visual cortex of HDAC2f/f;Pv-cre mice

To examine whether loss of HDAC2 in Pv-expressing interneurons affected the strength of inhibitory synapses, we measured the evoked postsynaptic responses of pyramidal neurons in the visual cortex from brain slices of wildtype HDAC2f/f and mutant HDAC2f/f;Pv-cre mice. We determined the maximal inhibitory postsynaptic currents (IPSCs) and excitatory postsynaptic currents (EPSCs) in layer II/III pyramidal neurons evoked by layer IV stimulation. To isolate maximal IPSCs, the membrane potential was held at 0 mV (I0), which is the reversal potential for AMPA and NMDA receptors. Maximal EPSCs were measured by holding the same pyramidal cells at −60 mV (I−60), which is the approximate reversal membrane potential for IPSCs. The amplitude of maximal IPSC (Fig. 2A) was significantly reduced in HDAC2f/f;Pv-cre mice (635.4 pA ± 87 pA; n = 16) compared to wildtype HDAC2f/f mice (933.5 pA ± 100.4 pA; n = 16). Whereas, no significant difference was observed for maximal EPSC between wildtype HDAC2f/f mice (1175 pA ± 170.4 pA; n = 16) and HDAC2f/f;Pv-cre mice (1093 pA ± 179.4 pA; n = 16). These results are indicative of a reduction in the evoked GABAergic inhibition of pyramidal cells in the visual cortex in adult mice that lack HDAC2 in Pv-expressing interneurons. This finding mirrors that of rats reared in the dark for 5-weeks, which have profoundly reduced maximal IPSCs compared to normally reared animals [2].

Figure 2.

Figure 2

Open in a new tab

Effects of HDAC2 conditional knockout in Pv-positive interneurons on IPSCs recorded in Layer II/III Pyramidal neurons of the visual cortex at 8-weeks old. A, Average magnitude of maximal IPSCs and maximal EPSCs of pyramidal cells from the visual cortex of 8-week old HDAC2f/f and HDAC2f/f;Pv-cre mice. Two-tailed t test; IPSC, p < 0.05; EPSC, p > 0.05; n = 16 cells, 4 mice (HDAC2f/f), 16 cells, 4 mice (HDAC2f/f;Pv-cre). B, I-V plot of the IPSC recorded at different membrane potentials in the visual cortex of brain slices from 8-week old HDAC2f/f and HDAC2f/f;Pv-cre mice. Inset, Typical traces of IPSCs recorded at different membrane potentials from HDAC2f/f and HDAC2f/f;Pv-cre mice (scale bars, 200 pA and 20 mSec). Analysis of covariance; p < 0.0001; n = 24 cells from 5 mice (HDAC2f/f), 25 cells, 5 mice (HDAC2f/f;Pv-cre). C, Cumulative probability distribution of mIPSC amplitude of layer II/III pyramidal cells in the visual cortex of 8-week old HDAC2f/f and HDAC2f/f;Pv-cre mice. Inset, Column bar graph represents the average mIPSC amplitude from all cells recorded. Two-tailed t test; p < 0.05; n = 15 cells, 2 mice (HDAC2f/f), 13 cells, 2 mice (HDAC2f/f;Pv-cre). D, Cumulative probability distribution of mIPSC inter-event interval as in C. Inset, Column bar graph represents the average mIPSC frequency from all cells recorded. Two-tailed t test; p > 0.05; n = 15 cells, 2 mice (HDAC2f/f), 13 cells, 2 mice (HDAC2f/f;Pv-cre). E. Traces represent mIPSCs recorded from HDAC2f/f (blue) and HDAC2f/f;Pv-cre mice from C and D.

The peak conductance underlying the maximal IPSC was estimated from the slope of the linear fit using the I-V plot in Fig. 2B. The peak conductance was significantly reduced in the visual cortex of HDAC2f/f;Pv-cre mice (6.145 nS ± 0.2014 nS; n = 25) compared to wildtype HDAC2f/f mice (9.817 nS ± 0.4442 nS; n = 24). This is in accordance with rodents that have been dark-reared for 5-weeks and have a reduced peak conductance compared to 5-week normally reared animals [2]. The data obtained from 5-week dark reared animals closely reflects that of 3-week old normally reared animals, an age within the critical period of the rodent visual cortex [2]. The reduced peak conductance observed in adult HDAC2f/f;Pv-cre mice is in agreement with Fig. 2A and collectively shows that the inhibitory postsynaptic response of pyramidal neurons is reduced in the visual cortex of adult HDAC2f/f;Pv-cre mice.

To examine whether the observed decrease of maximal IPSCs in visual cortex of HDAC2f/f;Pv-cre mice is due to an alteration in the number of GABAergic inputs and/or an alteration in the number of synaptic contacts, miniature IPSCs (mIPSCs) were measured. Recordings were performed using conditions that block Na+ channels, AMPA and NMDA receptors to inhibit the generation of action potentials and to eliminate the contribution of excitatory inputs; this allows quantification of spontaneous inhibitory responses. An effect was observed with mIPSC amplitude, which was significantly higher in the visual cortex of HDAC2f/f;Pv-cre mice (19.5 pA ± 1.062 pA; Fig. 2C, 2E) compared to wildtype HDAC2f/f mice (16.04 pA ± 1.064 pA; Fig. 2C, 2E). There was no significant change in the mIPSC frequency of recordings from the visual cortex of brain slices from HDAC2f/f;Pv-cre mice (7.273 Hz ± 0.0.9934 Hz; Fig. 2D, 2E) compared to wildtype HDAC2f/f mice (6.378 Hz ± 0.5579 Hz; Fig. 2D, 2E). These results indicate that loss of HDAC2 leads to an increase in the amplitude of unitary inhibitory responses. This data is in keeping with observations of 5-week old rodents that have been reared in the dark, which exhibit higher mIPSC amplitudes compared to 5-week old normally reared animals, and are similar to recordings of 3-week old animals. Thus, similar to observations during sensory deprivation, loss of HDAC2 appears to reduce the total potency of evoked GABAergic inputs as measured by maximal IPSC and peak conductance, whereas the amplitude of spontaneous GABAergic responses appears to be upregulated. In the case of dark-rearing, this is suggested to occur through a compensatory mechanism similar to that described for excitatory synapses (Turrigiano 1998, Murthy 2001).

Delayed developmental decline of visual cortical LTD of HDAC2f/f;Pv-cre mice

A period of enhanced long-term plasticity in the visual cortex requires visual stimulation [6, 8], and coincides with a three-fold increase in the number of GABAergic inputs that converge onto pyramidal cells [2]. To examine whether HDAC2 expression in Pv-expressing interneurons affects previously observed postnatal reductions in NMDAR-mediated synaptic plasticity in the visual cortex we utilized a long-term depression (LTD) paradigm. A single-pulse low frequency stimulation (SP-LFS) procedure of delivering 900 stimuli at 1 Hz has been shown to induce homosynaptic depression in the visual cortex of young mice that is subsequently absent in the visual cortex of adult mice [11, 13].

First, we determined whether LTD in the visual cortex of layer II/III induced with SP-LFS stimulation in layer IV (IV→II/III LTD) of young mice is altered by deletion of HDAC2 in Pv-expressing cells. Brain slices from 3 week of age wildtype HDAC2f/f and age-matched littermate HDAC2f/f;Pv-cre mice were subjected to the layer IV→II/III LTD protocol. SP-LFS of layer IV induced an LTD in brain slices of wildtype mice (Fig. 3A; 81.01 % ± 8.56 % of baseline during final 10 min after SP-LFS), as has been previously reported for mice at 3-weeks of age [11, 13]. A similar magnitude of LTD were induced in the brain slices of HDAC2f/f;Pv-cre mice (Fig. 3A; 84.12 % ± 8.23 % of baseline during final 10 min after SP-LFS) as observed in the wildtype mice. This indicates that loss of HDAC2 from Pv-expressing cells has no effect on layer IV→II/III LTD during the critical period in the mouse visual cortex. To determine whether HDAC2 expression in Pv-positive interneurons is important for NMDAR-mediated synaptic plasticity in adult mice, layer IV→II/III LTD was measured in 8 week of age mice. Previous studies have shown that after 5 weeks of age, there is a closure of the critical period in the visual cortex, and this correlates with a large reduction in the magnitude of LTD recorded compared to 3 week of age mice [11, 13]. In agreement with this observation, in 8 weeks old wildtype HDAC2f/f mice the induction of layer IV→II/III LTD was of very small magnitude (Fig. 3B; 99.14 % ± 4.92 % of baseline during final 10 min after SP-LFS). However, application of SP-LFS in layer IV in littermate HDAC2f/f;Pv-cre mice elicited induction of layer IV→II/III LTD with a magnitude comparable to that observed in mice that are 3 weeks of age (Fig. 3B; 75.24 % ± 6.05 % of baseline during final 10 min after SP-LFS). This is reminiscent of enhanced long term plasticity measured in the visual cortex of dark-reared adult mice, but is almost absent in normally reared adult mice [6, 8]. This would suggest that HDAC2 expression in Pv-expressing interneurons is important for the developmental reduction in plasticity of the visual cortex.

Figure 3.

Figure 3

Open in a new tab

Effects of HDAC2 deletion from Pv-interneurons on LTD recorded in the visual cortex. A, LTD in layer II/III induced by 1 Hz stimulation (900 pulses) in layer IV in the visual cortex of brain slices from 3-week old HDAC2f/f and HDAC2f/f;Pv-cre mice (HDAC2f/f: 81.01 % ± 8.56 % of baseline during final 10 min after SP-LFS, n = 5 slices, 3 mice; HDAC2f/f;Pv-cre: 84.12 % ± 8.23 % of baseline during final 10 min after SP-LFS, n = 5 slices, 3 mice. Two-tailed t test; p > 0.05). Right, Sample traces of fEPSP before and 1 hr after SP-LFS are superimposed. B, LTD in layer II/III induced by 1 Hz stimulation (900 pulses) in layer IV in the visual cortex of brain slices from 8-week old HDAC2f/f and HDAC2f/f;Pv-cre mice (HDAC2f/f: 99.14 % ± 4.92 % of baseline during final 10 min after SP-LFS, n = 10 slices, 4 mice; HDAC2f/f;Pv-cre: 75.24 % ± 6.05 % of baseline during final 10 min after SP-LFS, n = 9 slices, 5 mice. Two-tailed t test; p < 0.01). Right, Sample traces of fEPSP before and 1 hr after SP-LFS are superimposed. C, LTD in layer IV induced by 1 Hz stimulation (900 pulses) of the white matter-layer VI border in the visual cortex of brain slices from 8-week old HDAC2f/f and HDAC2f/f;Pv-cre mice (HDAC2f/f: 98.84 % ± 12.71 % of baseline during final 10 min after SP-LFS, n = 4 slices, 3 mice; HDAC2f/f;Pv-cre: 81.30 % ± 2.717 % of baseline during final 10 min after SP-LFS, n = 4 slices, 2 mice. Two-tailed t test; p > 0.05). Right, Sample traces of fEPSP before and 1 hr after SPLFS are superimposed.

To test whether increased plasticity in the HDAC2f/f;Pv-cre mice at 8-weeks of age was specific to layer IV→II/III LTD, long-term depression of layer IV synaptic responses was induced by application of SP-LFS to the white matter–layer VI border of the visual cortex (WM→IV LTD). As expected, 8 weeks of age wildtype HDAC2f/f mice did not exhibited substantial WM→IV LTD (Fig. 3C; 98.84 % ± 12.71 % of baseline during final 10 min after SP-LFS). However, littermate age-matched HDAC2f/f;Pv-cre mice elicited WM→IV LTD (Fig. 3C; 81.30 % ± 2.717 % of baseline during final 10 min after SP-LFS), which is comparable to that observed in 3 weeks of age mice for IV→II/III LTD (Fig. 3A). Together, this data indicates that HDAC2-mediated epigenetic control of Pv-expressing cells is important for regulating inhibitory inputs that contribute to defining the temporal closure of the critical period in the mouse visual cortex.

Discussion

An experience-dependent maturation in GABAergic inhibition during postnatal development contributes to the closure of a critical period of enhanced synaptic plasticity in the mouse visual cortex. Little is known regarding the transcriptional regulation of this process, however, studies have indicated that increases in histone acetylation play an important role in mediating increased cortical plasticity in adult mice and humans [16–19]. Here we have shown that loss of HDAC2 from Parvalbumin-expressing inhibitory cells leads to a reduction in the potency of inhibitory inputs in the visual cortex in adult mice, whereas the potency of excitatory inputs appears to be unaffected. This data is reminiscent of previous studies showing that visual deprivation by dark-rearing prevents the normal developmental increase in GABAergic inputs in the visual cortex, and is thought to delay the maturation of intracortical inhibitory circuits [2]. Likewise, an accelerated maturation of Parvalbumin inhibitory cells, leads to a premature increase in inhibitory synaptic strength, with little effect on excitatory inputs [9, 14].

A growing consensus is that the closure of the critical period in the mouse visual cortex, as measured by reduced NMDA receptor-mediated synaptic plasticity, is modulated by the maturation of GABAergic cells. The critical period timing can be manipulated by genetic manipulations that enhance or reduce GABAergic inhibition, which respectively leads to a premature or delayed closure of the critical period [3, 7, 9]. This affect of inhibitory maturation on the critical period has been demonstrated specifically for accelerated maturation of Pv-expressing cells [9, 14]. However, little is known regarding the transcriptional control mediating this developmental increase in cortical inhibition. Along with a delayed developmental increase in inhibitory inputs in the HDAC2f/f;Pv-cre adult mice; we observe a robust LTD in the visual cortex of adult mice lacking HDAC2 in Pv-expressing cells. As previously demonstrated by others, we find that LTD appears to be absent in HDAC2f/f littermate control adult mice [11, 13]. Collectively, these findings suggest that HDAC2-mediated transcriptional control of Pv-expressing neurons is important for the developmental increase in cortical inhibition, and the temporal closure of the critical period in the visual cortex.

HDAC2 has been shown to be an important factor that mediates an epigenetic blockade of synaptic plasticity mechanisms required for learning and memory [20, 21]. The chromatin function of HDAC2 can be negatively regulated following a posttranslational modification by nitric oxide, called S-nitrosylation [24]. HDAC2 nitrosylation has been shown to have a role in regulating both cortical development and memory formation [22, 24, 25]. Interestingly, neuronal nitric oxide synthase (nNOS), an enzyme which provides a major source of nitric oxide in neurons, is highly expressed specifically in interneuron cell populations in the adult mouse cortex [26, 27]. Furthermore, nitric oxide has been demonstrated to have positive effects on neuronal plasticity [28, 29], and learning and memory [22, 30–34]. An appealing hypothesis that waits to be tested is that negative regulation of HDAC2 by nitric oxide and its effect on transcription may modulate the activity of inhibitory circuits in a manner that is permissive for enhanced synaptic plasticity.

Acknowledgements

We thank members of the Tsai lab for helpful advice and discussion, and we thank Mali Taylor for assistance with animal maintenance. We also thank Dr. Mark Bear, Dr. Arnold Heynen, and members of the Bear lab for helpful discussions during the progression of this project. This work is supported by an NIH NINDS/NIA (NS078839) to L-H T and the Picower Innovation Investigator Fund (PIIF) to L-H T.

Footnotes

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

References

  • 1.Smith GB, Heynen AJ, Bear MF. Bidirectional synaptic mechanisms of ocular dominance plasticity in visual cortex. Philos Trans R Soc Lond, B, Biol Sci. 2009;364:357–367. doi: 10.1098/rstb.2008.0198. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Morales B, Choi S-Y, Kirkwood A. Dark rearing alters the development of GABAergic transmission in visual cortex. J Neurosci. 2002;22:8084–8090. doi: 10.1523/JNEUROSCI.22-18-08084.2002. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Hensch TK, Fagiolini M, Mataga N, Stryker MP, Baekkeskov S, Kash SF. Local GABA circuit control of experience-dependent plasticity in developing visual cortex. Science. 1998;282:1504–1508. doi: 10.1126/science.282.5393.1504. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Fagiolini M, Hensch TK. Inhibitory threshold for critical-period activation in primary visual cortex. Nature. 2000;404:183–186. doi: 10.1038/35004582. [DOI] [PubMed] [Google Scholar]
  • 5.Chattopadhyaya B, Di Cristo G, Wu CZ, Knott G, Kuhlman S, Fu Y, et al. GAD67-mediated GABA synthesis and signaling regulate inhibitory synaptic innervation in the visual cortex. Neuron. 2007;54:889–903. doi: 10.1016/j.neuron.2007.05.015. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Jiang B, Huang S, de Pasquale R, Millman D, Song L, Lee H-K, et al. The maturation of GABAergic transmission in visual cortex requires endocannabinoid-mediated LTD of inhibitory inputs during a critical period. Neuron. 2010;66:248–259. doi: 10.1016/j.neuron.2010.03.021. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7.Di Cristo G, Chattopadhyaya B, Kuhlman SJ, Fu Y, Bélanger M-C, Wu CZ, et al. Activity-dependent PSA expression regulates inhibitory maturation and onset of critical period plasticity. Nature Publishing Group. 2007;10:1569–1577. doi: 10.1038/nn2008. [DOI] [PubMed] [Google Scholar]
  • 8.Kirkwood A, Lee HK, Bear MF. Co-regulation of long-term potentiation and experience-dependent synaptic plasticity in visual cortex by age and experience. Nature. 1995;375:328–331. doi: 10.1038/375328a0. [DOI] [PubMed] [Google Scholar]
  • 9.Sugiyama S, Di Nardo AA, Aizawa S, Matsuo I, Volovitch M, Prochiantz A, et al. Experience-dependent transfer of Otx2 homeoprotein into the visual cortex activates postnatal plasticity. Cell. 2008;134:508–520. doi: 10.1016/j.cell.2008.05.054. [DOI] [PubMed] [Google Scholar]
  • 10.Gonchar Y, Wang Q, Burkhalter A. Multiple distinct subtypes of GABAergic neurons in mouse visual cortex identified by triple immunostaining. Front Neuroanat. 2007;1:3. doi: 10.3389/neuro.05.003.2007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Kirkwood A, Silva A, Bear MF. Age-dependent decrease of synaptic plasticity in the neocortex of alphaCaMKII mutant mice. Proc Natl Acad Sci USA. 1997;94:3380–3383. doi: 10.1073/pnas.94.7.3380. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 12.del Río JA, de Lecea L, Ferrer I, Soriano E. The development of parvalbumin-immunoreactivity in the neocortex of the mouse. Brain Res Dev Brain Res. 1994;81:247–259. doi: 10.1016/0165-3806(94)90311-5. [DOI] [PubMed] [Google Scholar]
  • 13.Jiang B, Treviño M, Kirkwood A. Sequential development of long-term potentiation and depression in different layers of the mouse visual cortex. J Neurosci. 2007;27:9648–9652. doi: 10.1523/JNEUROSCI.2655-07.2007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 14.Huang ZJ, Kirkwood A, Pizzorusso T, Porciatti V, Morales B, Bear MF, et al. BDNF regulates the maturation of inhibition and the critical period of plasticity in mouse visual cortex. Cell. 1999;98:739–755. doi: 10.1016/s0092-8674(00)81509-3. [DOI] [PubMed] [Google Scholar]
  • 15.Majdan M, Shatz CJ. Effects of visual experience on activity-dependent gene regulation in cortex. Nature Publishing Group. 2006;9:650–659. doi: 10.1038/nn1674. [DOI] [PubMed] [Google Scholar]
  • 16.Putignano E, Lonetti G, Cancedda L, Ratto G, Costa M, Maffei L, et al. Developmental downregulation of histone posttranslational modifications regulates visual cortical plasticity. Neuron. 2007;53:747–759. doi: 10.1016/j.neuron.2007.02.007. [DOI] [PubMed] [Google Scholar]
  • 17.Silingardi D, Scali M, Belluomini G, Pizzorusso T. Epigenetic treatments of adult rats promote recovery from visual acuity deficits induced by long-term monocular deprivation. European Journal of Neuroscience. 2010;31:2185–2192. doi: 10.1111/j.1460-9568.2010.07261.x. [DOI] [PubMed] [Google Scholar]
  • 18.Yang E-J, Lin EW, Hensch TK. Critical period for acoustic preference in mice. Proc Natl Acad Sci USA. 2012;1092(Suppl):17213–17220. doi: 10.1073/pnas.1200705109. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Gervain J, Vines BW, Chen LM, Seo RJ, Hensch TK, Werker JF, et al. Valproate reopens critical-period learning of absolute pitch. Front Syst Neurosci. 2013;7:102. doi: 10.3389/fnsys.2013.00102. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 20.Guan J-S, Haggarty SJ, Giacometti E, Dannenberg J-H, Joseph N, Gao J, et al. HDAC2 negatively regulates memory formation and synaptic plasticity. Nature. 2009;459:55–60. doi: 10.1038/nature07925. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21.Gräff J, Rei D, Guan J-S, Wang W-Y, Seo J, Hennig KM, et al. An epigenetic blockade of cognitive functions in the neurodegenerating brain. Nature. 2012;483:222–226. doi: 10.1038/nature10849. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Gräff J, Joseph NF, Horn ME, Samiei A, Meng J, Seo J, et al. Epigenetic Priming of Memory Updating during Reconsolidation to Attenuate Remote Fear Memories. Cell. 2014;156:261–276. doi: 10.1016/j.cell.2013.12.020. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Hippenmeyer S, Vrieseling E, Sigrist M, Portmann T, Laengle C, Ladle DR, et al. A developmental switch in the response of DRG neurons to ETS transcription factor signaling. PLoS Biol. 2005;3:e159. doi: 10.1371/journal.pbio.0030159. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Nott A, Watson PM, Robinson JD, Crepaldi L, Riccio A. S-Nitrosylation of histone deacetylase 2 induces chromatin remodelling in neurons. Nature. 2008;455:411–415. doi: 10.1038/nature07238. [DOI] [PubMed] [Google Scholar]
  • 25.Nott A, Nitarska J, Veenvliet JV, Schacke S, Derijck AAHA, Sirko P, et al. S-nitrosylation of HDAC2 regulates the expression of the chromatin-remodeling factor Brm during radial neuron migration. Proc Natl Acad Sci USA. 2013;110:3113–3118. doi: 10.1073/pnas.1218126110. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Karagiannis A, Gallopin T, Dávid C, Battaglia D, Geoffroy H, Rossier J, et al. Classification of NPY-expressing neocortical interneurons. J Neurosci. 2009;29:3642–3659. doi: 10.1523/JNEUROSCI.0058-09.2009. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 27.Kubota Y, Shigematsu N, Karube F, Sekigawa A, Kato S, Yamaguchi N, et al. Selective coexpression of multiple chemical markers defines discrete populations of neocortical GABAergic neurons. Cereb Cortex. 2011;21:1803–1817. doi: 10.1093/cercor/bhq252. [DOI] [PubMed] [Google Scholar]
  • 28.Garthwaite J, Boulton CL. Nitric oxide signaling in the central nervous system. Annu. Rev. Physiol. 1995;57:683–706. doi: 10.1146/annurev.ph.57.030195.003343. [DOI] [PubMed] [Google Scholar]
  • 29.Massaad CA, Klann E. Reactive oxygen species in the regulation of synaptic plasticity and memory. Antioxid Redox Signal. 2011;14:2013–2054. doi: 10.1089/ars.2010.3208. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 30.Walton JC, Selvakumar B, Weil ZM, Snyder SH, Nelson RJ. Neuronal nitric oxide synthase and NADPH oxidase interact to affect cognitive, affective, and social behaviors in mice. Behav Brain Res. 2013;256:320–327. doi: 10.1016/j.bbr.2013.08.003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 31.Li C-H, Wang S-Z, Cai Z-L, Liu W-X, Xu S-T, Xiao P. Effects of intrahippocampal L-NAME treatment on the behavioral long-term potentiation in dentate gyrus. Neurosci Lett. 2012;528:201–204. doi: 10.1016/j.neulet.2012.08.056. [DOI] [PubMed] [Google Scholar]
  • 32.Harooni HE, Naghdi N, Sepehri H, Rohani AH. The role of hippocampal nitric oxide (NO) on learning and immediate, short- and long-term memory retrieval in inhibitory avoidance task in male adult rats. Behav Brain Res. 2009;201:166–172. doi: 10.1016/j.bbr.2009.02.011. [DOI] [PubMed] [Google Scholar]
  • 33.Telegdy G, Kokavszky R. The role of nitric oxide in passive avoidance learning. Neuropharmacology. 1997;36:1583–1587. doi: 10.1016/s0028-3908(97)00154-8. [DOI] [PubMed] [Google Scholar]
  • 34.Kendrick KM, Guevara-Guzman R, Zorrilla J, Hinton MR, Broad KD, Mimmack M, et al. Formation of olfactory memories mediated by nitric oxide. Nature. 1997;388:670–674. doi: 10.1038/41765. [DOI] [PubMed] [Google Scholar]
  • 35.Gianfranceschi L, Siciliano R, Walls J, Morales B, Kirkwood A, Huang ZJ, et al. Visual cortex is rescued from the effects of dark rearing by overexpression of BDNF. Proc Natl Acad Sci USA. 2003;100:12486–12491. doi: 10.1073/pnas.1934836100. [DOI] [PMC free article] [PubMed] [Google Scholar]

RESOURCES