Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2016 Jan 31.
Published in final edited form as: Neurobiol Learn Mem. 2014 Dec 24;0:162–166. doi: 10.1016/j.nlm.2014.12.008

Stronger Learning Recruits Additional Cell-Signaling Cascades: c-Jun-N-Terminal Kinase 1 (JNK1) is Necessary for Expression of Stronger Contextual Fear Conditioning

Prescott T Leach 1,1, Justin W Kenney 1,2, Thomas J Gould 1,*
PMCID: PMC4331248  NIHMSID: NIHMS655489  PMID: 25543025

Abstract

Increased training often results in stronger memories but the neural changes responsible for these stronger memories are poorly understood. It is proposed here that higher levels of training that result in stronger memories recruit additional cell signaling cascades. This study specifically examined if c-Jun n-terminal kinase 1 (JNK1) is involved in the formation of stronger fear conditioning memories. Wildtype (WT), JNK1 heterozygous (Het), and JNK1 knockout (KO) mice were fear conditioned with 1 trial, 2 trials, or 4 trials. All mice learned both contextual (hippocampus-dependent) and cued (hippocampus-independent) fear conditioning but for contextual fear conditioning only, the JNK1 KO mice did not show higher levels of learning with increased trials. That is, WT mice showed a significant linear increase in contextual fear conditioning as training trials increased from 1 to 2 to 4 trials whereas KO mice showed the same level of contextual fear conditioning as WT mice for 1 trial training but did not have increased levels of contextual fear conditioning with additional trials. These data suggest that JNK1 may not be critical for learning but when higher levels of hippocampus-dependent learning occur, JNK1 signaling is recruited and is necessary for stronger hippocampus-dependent memory formation.

1. Introduction

Long-term memory formation involves the recruitment of intracellular signaling cascades that regulate mRNA expression and de novo protein synthesis (Abel, Nguyen, Barad, Deuel, Kandel, and Bourtchouladze, 1997; Bourtchouladze, Abel, Berman, Gordon, Lapidus, and Kandel, 1998; Bourtchuladze, Frenguelli, Blendy, Cioffi, Schutz, and Silva, 1994; Schafe, Nadel, Sullivan, Harris, and LeDoux, 1999). It is clear that with increased training, stronger learning can occur (Bourtchouladze et al., 1998; Carew, Walters, and Kandel, 1981). However, it is unclear whether the cellular processes involved in learning change as learning becomes stronger. One possibility is that with increased training, the same cellular substrates are activated but perhaps in greater amount and/or with a different timing. Another possibility is that with increased training, additional cell-signaling cascades are recruited and the activation of these cascades contributes to the formation of stronger memories.

There are multiple ways to strengthen learning that include increased training and pharmacological manipulation. For instance, acute nicotine enhances learning and prior work suggests that hippocampus-dependent learning is particularly sensitive to the effects of acute nicotine (Davis, James, Siegel, and Gould, 2005; Gould and Lommock, 2003; Gould and Wehner, 1999; Gulick and Gould, 2008; Portugal, Wilkinson, Kenney, Sullivan, and Gould, 2012; Portugal, Wilkinson, Turner, Blendy, and Gould, 2012). This enhancement was associated with an increase in c-Jun n-terminal kinase 1 (JNK1) expression and JNK (46 kD) activation, and inhibition of JNK (non-selective) blocked the enhancement of learning by nicotine and yet the same dose did not block learning in nicotine-naïve mice (Kenney, Florian, Portugal, Abel, and Gould, 2010). JNK1 has been associated with apoptosis (Ham, Eilers, Whitfield, Neame, and Shah, 2000) and development of the brain (Gelderblom, Eminel, Herdegen, and Waetzig, 2004) but the results from the studies with nicotine also suggest that activation of JNK1 may modulate learning. JNK has cytoplasmic and nuclear effectors (Barr and Bogoyevitch, 2001; Chang, Jones, Ellisman, Goldstein, and Karin, 2003; Eminel, Roemer, Waetzig, and Herdegen, 2008; Kim, Futai, Jo, Hayashi, Cho, and Sheng, 2007; Thomas, Lin, Nuriya, and Huganir, 2008; Weston and Davis, 2002), making it a versatile signaling molecule. Furthermore, JNK1 interacts with many cytoplasmic proteins that are critical to learning and memory processes. For instance, JNK1 is important for AMPA receptor trafficking to the membrane (Thomas et al., 2008), PSD-95 phosphorylation (Kim et al., 2007), neurite outgrowth (Eminel et al., 2008), and microtubule associated protein activation and polymerization (Chang et al., 2003). Thus, it is possible that stronger learning recruits JNK1 signaling.

The current study tested the hypothesis that JNK1 is necessary when stronger learning occurs. Wildtype (WT), JNK1 heterozygous (Het), and JNK1 knockout (KO) mice were tested in contextual fear conditioning and cued fear conditioning. In addition to varying genotype, the level of training was varied. Each genotype was trained with either 1 trial, 2 trials, or 4 trials. If JNK1 is involved with higher levels of learning, it was predicted that learning would remain asymptotic across number of conditioning trials in the JNK1 KO mice but would increase with increased trials in the wildtype mice.

2. Methods

2.1. Subjects

Male and female JNK1 mutant mice (8-12 weeks of age originally created by Dong and colleagues (1998)) were obtained from Jackson Laboratory (Bar Harbor, ME) and bred at Temple University. All breeding was carried out using heterozygous by heterozygous matings. Mice were weaned at 3-4 weeks of age into group housing conditions (2-4 per cage) with same sex littermates. Mice were maintained in a temperature and humidity controlled vivarium and allowed ad libitum access to food and water.

2.2. Fear Conditioning Procedures

Male and female mice were trained in modular fear conditioning chambers (18 × 19 ×38 cm) contained in sound attenuating cubicles (Med Associates, St Albans, VT). Subjects were placed into the fear conditioning chamber and allowed to explore for 120 seconds. After the 120 second baseline period, a white noise conditioned stimulus (CS) played for 30 seconds and co-terminated with a 2 second shock (0.57 mA) delivered through the grid floor which acted as an unconditioned stimulus (US). Separate groups of mice either received 1 training session that consisted of either 1 trial (WT n=9; Het n=14; KO n=12), 2 trials (WT n=9; Het n=14; KO n=10), or 4 trials (WT n=7; Het n=11; KO n=9). The intertrial interval for multiple trial sessions was 120 seconds. After the last trial, the mice remained in the chamber with the chamber lights on for 30 seconds. Twenty-four hours later, mice were assessed for freezing behavior in the training context for five minutes. One hour after contextual fear conditioning testing, mice were placed into an altered context and assessed for freezing in the novel environment for 3 minutes before the CS was introduced for an additional 3 minutes. The altered context chambers (20.30 × 22.90 × 17.80 cm) were located in a different room and had different visual, tactical, and olfactory cues than the conditioning chambers.

2.3. Western Blotting Procedures

To confirm the absence of JNK1 protein in the JNK1 KO mice, hippocampal homogenates from JNK1 WT and KO mice were subjected to standard SDS-PAGE and western blotting to verify the presence and absence of JNK1 protein levels, respectively. Briefly, whole hippocampi from JNK1 WT and KO mice were sonicated in homogenization buffer A (Sambrook, Fritsch, and Maniatis, 1989) and total protein level was verified using DC Protein Assay (Bio-Rad, Hercules, CA). 10 μg protein was added to each well of a polyacrylamide gel (12%) and samples were subjected to electrophoresis to separate the protein bands. After transferring to a nitrocellulose membrane using a standard wet transfer, immunoblotting was conducted using a mouse monoclonal antibody specific for JNK1 (BD Pharmingen, San Jose, CA) diluted 1:1000 in Tris-buffered saline with Tween (T-TBS) containing 5% non-fat dry milk, and incubated at 4 degrees C overnight. After primary antibody incubation, blots were washed in T-TBS prior to incubation with horseradish peroxidase-conjugated secondary antibody (goat anti-mouse) diluted 1:10000 in T-TBS. Blots were developed with ECL (Pierce, Thermo Scientific, Rockford, IL) and imaged using a Gel Logic 1500 imager (Kodak, Rochester, NY).

2.4. Statistics

Results were analyzed using GraphPad Prism 5 statistical software. Fear conditioning results were analyzed using 3 × 3 factorial ANOVAs with genotype (WT, Het, and KO) and training paradigm (1, 2, and 4 CS-US pairings) as between subject factors. Separate ANOVA analyses were conducted for contextual and cued fear conditioning. Bonferroni corrected planned comparisons were used to determine genotype differences at each level of fear conditioning training. Since it would be expected that increased strength of training would increase freezing levels in both contextual and cued conditioning, each genotype was also evaluated for linear trend contrast analysis with Bonferroni correction.

3. Results

3.1. Fear Conditioning

JNK1 KO mice expressed similar levels of contextual fear conditioning as WT mice when trained with 1 CS/US pairing but not with 2 and 4 CS/US pairings (Figure 1). A two-way ANOVA of contextual fear conditioning with genotype (WT, Het, and KO) and trial number (one, two, and four) as between-subjects factors revealed significant main effects of genotype [F(2, 86) = 10.53, p<0.05] and trial number [F(2,86) = 3.979, p<0.05]; but no interaction [F(4,86) = 1.037, p>0.05]. Bonferroni corrected a priori analyses revealed that KO mice exhibited significantly less contextual fear conditioning than WT when trained with 2 CS/US pairings or 4 CS/US pairings, but not when trained with 1 CS/US pairing: ps<0.05. KO mice froze significantly less than Het mice at 2 CS/US pairings only: p<0.05.

Fig 1.

Fig 1

Open in a new tab

The effect of training strength on contextual and delay-cued fear conditioning in JNK1 WT, Het, and KO mice. JNK1 KO mice exhibit selective deficits at moderate (2 CS-US Pairings) and strong (4 CS-US Pairings) training paradigms, but are normal under weak (1 CS-US Pairing) training conditions. * indicates significantly different than WT control (p<0.05).

There were no overall effects of JNK1 gene dosage on freezing to the auditory cue. A two-way ANOVA of cued freezing (with the same factors as above) revealed no effect of genotype [F(2,86) = 0.0780, p>0.05] but a significant main effect of trial number [F(2,86) = 9.467, p<0.05]. No significant interaction was found [F(4,86) = 1.527, p>0.05]. Bonferroni corrected a priori analyses revealed no significant differences between WT and KO or WT and Het mice. There were no observed effects of genotype, trial number, or interactions during altered context (pre-CS) freezing.

Studies have shown that strength of training increases fear conditioning responses (Bourtchouladze et al., 1998; Maren, 1999; Wiltgen, Sanders, Anagnostaras, Sage, and Fanselow, 2006). WT mice showed significant linear trends, revealing strength of training-dependent increases in both contextual and cued fear conditioning (Slope=13.02 and r2=0.2901, p<0.05; slope=15.96 and r2=0.3777, p<0.05 respectively, Figure 2). Het mice did not have a significant linear trend for contextual conditioning but did show a linear trend for cued fear conditioning (Slope=3.571 and r2=0.02597, p>0.05; slope=9.145 and r2=0.1276, p<0.05, respectively, Figure 2). KO mice did not have a linear trend for either contextual or cued fear conditioning (Slope=2.963 and r2=0.01763, p>0.05; slope=6.25 and r2=0.07162, p>0.05 respectively, Figure 2). The lack of a linear trend for cued fear conditioning in the KO mice was due to a higher level of cued fear conditioning with 1 trial training, which is why the KO mice did not have a deficit in cued fear conditioning at any level of conditioning. Specifically, regardless of the number of conditioning trials, KO mice exhibited similar levels of cued fear conditioning (60% ± 7, 63% ± 4, and 72% ± 5; 1, 2, or 4 trials respectively) in contrast to WT and Het mice (WT: 45% ± 5, 73% ± 6, 77% ± 5; Het: 56% ± 5, 60% ± 6, 74% ± 4; 1, 2, or 4 trials respectively). For contextual fear conditioning, KO and Het mice exhibited similar levels of freezing within genotype regardless of the strength of training protocol (KO: 41% ± 6, 41% ± 5, 47% ± 7; Het: 56% ± 4, 63% ± 6, 63% ± 5; 1, 2, or 4 trials respectively), whereas WT mice showed a clear increase in contextual fear conditioning as the number of shocks increased (48% ± 6, 65% ± 5, 74% ± 8; 1, 2, or 4 trials respectively).

Fig 2.

Fig 2

Open in a new tab

Linear trend analyses across the different JNK1 genotypes. WT mice exhibited a significant linear trend of training strength in contextual and cued fear conditioning. Het mice exhibited a significant linear trend of training strength in cued fear conditioning, but not in contextual fear conditioning. KO mice exhibited no linear trend of training strength in either fear conditioning paradigm. → and * indicates significant linear trends (p<0.05).

3.2. Western Blotting

Hippocampi from JNK1 WT mice had detectable levels of JNK1 protein, whereas KO mice did not (Figure 3). Samples from 3 WT and 3 KO revealed consistent and reproducible effects.

Fig 3.

Fig 3

Open in a new tab

Genotype confirmation by western blot analysis. Blots were probed with JNK1 specific antibody. Wells contain lysate from JNK1 WT and KO (3 per genotype).

4. Discussion

The present study found that while JNK1 may not be necessary for fear conditioning, JNK1 is necessary for stronger contextual fear conditioning but not for stronger cued fear conditioning. JNK1 KO and WT mice showed similar levels of contextual fear learning after 1 trial. However, JNK1 KO mice showed significantly less contextual fear conditioning than WT mice when training consisted of 2 or 4 trials. This was due to the JNK1 KO mice showing asymptotic levels of contextual fear conditioning across 1, 2 and 4 trial training while WT mice showed a significant linear increase in contextual fear conditioning with increasing numbers of trials. Wildtype and JNK1 KO mice also showed similar levels of cued fear conditioning when trained with 1, 2 or 4 trials. Because contextual fear conditioning is hippocampus-dependent while cued fear conditioning is not (Kim and Fanselow, 1992; Logue, Paylor, and Wehner, 1997; Phillips and LeDoux, 1992), the current results suggest that stronger levels of hippocampus-dependent learning may require activation of JNK1. In addition, these results further demonstrate that the cell signaling molecules involved in hippocampus-dependent learning are not necessarily involved in hippocampus-independent learning as no significant effects were seen on cued fear conditioning; however, it remains untested if an effect on cued fear conditioning would be seen if a weaker CS was used or if cued freezing was assessed without contextual freezing assessed beforehand.

It appears that stronger learning is not mediated by identical cellular processes that support lower levels of learning. This is supported by prior work and the current results. It was previously found that fear conditioning with 1 CS-US pairing recruited two periods of PKA-dependent protein synthesis during consolidation whereas a stronger training paradigm with 3 CS-US pairings recruited only one period of PKA-dependent protein synthesis during consolidation (Bourtchouladze et al., 1998). While those results do not demonstrate that stronger learning recruits different cell signaling cascades, they do show that the underlying cellular and molecular substrates of learning change with higher levels of learning. The present results suggest that different signaling pathways, such as the JNK1 pathway, may be recruited to form stronger memories but that these signaling pathways may not be necessary in situations where a more modest level of learning occurs.

There has been some discrepancy regarding the effect of JNK inhibition on learning, but those differences may be due to differences in the level of training used in the conflicting studies. In a prior study, we found that that infusion of the pan JNK (i.e., JNK1, JNK2, JNK3) inhibitor SP600125 (20 μM) directly into the dorsal hippocampus during consolidation (i.e., after training) produced a deficit in contextual fear conditioning (Kenney et al., 2010). Another study, however, reported that infusion JNK SP600125 (30 μM) into the dorsal hippocampus during consolidation did not disrupt contextual fear conditioning and instead increased freezing (Sherrin, Blank, Hippel, Rayner, Davis, and Todorovic, 2010). Differences in training procedures may explain the discrepant results as the Sherrin study used one trial contextual fear conditioning and the Kenney study used 2 trial contextual fear conditioning. Given the current data that suggest that the involvement of JNK1 in contextual fear conditioning changes with the level of training, the different results from the two studies might be because Sherrin and colleagues used a training paradigm that does not require JNK1 but Kenny and colleagues' study used a training paradigm that did. If JNK1 is recruited with stronger learning, this may also explain why JNK1 is involved in the nicotine enhancement of learning (Gould and Higgins, 2003; Gould and Wehner, 1999). Nicotine produces stronger hippocampus-dependent learning (Gould and Leach, 2014; Kenney and Gould, 2008), similar to what is seen with more learning trials, and thus JNK1 may be activated by nicotine during learning for the formation of stronger memories.

An important direction for future studies is to identify the mechanisms through which JNK1 activation could contribute to stronger memory formation. JNK1 activates many transcription factors including JUN family, ATF-2, and Elk-1 (Bogoyevitch and Kobe, 2006; Gupta, Barrett, Whitmarsh, Cavanagh, Sluss, Derijard, and Davis, 1996) that are associated with learning and plasticity. Specifically, hippocampal long-term depression (LTD) was disrupted in JNK1 KO mice and this disruption was associated with decreased activation of c-Jun and ATF-2 (Li, Li, Yu, Chen, Sabapathy, and Ruan, 2007). Other studies, while not examining JNK1, have shown a critical role of Elk-1 and JunB in learning. For example, contextual fear conditioning was associated with an increase in Elk-1 activation in the CA3 region of the hippocampus (Sananbenesi, Fischer, Schrick, Spiess, and Radulovic, 2002). This increase in Elk-1 was associated with an increase in ERK1/2 activation, which was proposed to be a critical component of contextual fear memory consolidation. In addition, increased JunB was seen in the dorsal hippocampus after contextual fear conditioning (Strekalova, Zorner, Zacher, Sadovska, Herdegen, and Gass, 2003). Thus, one possible mechanism through which JNK1 could strengthen memory is through increasing activation of transcription factors such as JUN family, ATF-2, and Elk-1.

In addition to activating transcription factors associated with learning and plasticity, JNK1 interacts with many cytoplasmic proteins that are critical to learning and memory processes. For instance, JNK1 is important for AMPA receptor trafficking to the membrane (Thomas et al., 2008), PSD-95 phosphorylation (Kim et al., 2007), neurite outgrowth (Eminel et al., 2008), and microtubule associated protein activation and polymerization (Chang et al., 2003); all of which can contribute to memory formation. AMPA receptor trafficking has been proposed as a fundamental mechanism of learning and plasticity (for review see Malinow and Malenka, 2002; Stern and Alberini, 2013). PSD-95 is a scaffolding protein that strengthens synapses in part through increasing surface levels of AMPA receptors and JNK1 signaling was associated with increased synaptic accumulation of PSD-95 (Kim et al., 2007). Neurite outgrowth has been proposed to be critically involved in synaptogenesis (for review see Pfenninger, de la Houssaye, Helmke, and Quiroga, 1991) and changes in microtubule associated proteins in the hippocampus have been proposed to be an important part learning-related plasticity (Fanara P1, Husted KH, Selle K, Wong PY, Banerjee J, Brandt R, Hellerstein, 2010). Thus, there are several pathways through which JNK1 could contribute to memory formation. If it is a goal of science to not only understand the neurobiology of learning but to also facilitate the development of treatments for cognitive disorders, then it will be important to also identify the neural substrates that enable the formation of stronger memories.

Highlights.

  • Stronger learning recruits additional cell signaling cascades.

  • JNK1 is differentially involved in weak versus strong learning.

  • WT, but not JNK1 KO, mice show increased contextual memory with stronger training.

  • JNK1 WT and Het mice show increased cued memory in response to stronger training.

Acknowledgments

This work was funded with grant support from the National Institute on Drug Abuse (T.J.G., DA017949). PTL and JWK were supported by NIH-NIDA Training Grant (DA007237). The authors would like to thank Sheree Logue, Ph.D. and Munir Gunes Kutlu, Ph.D. for critical reading and feedback on earlier drafts of this manuscript.

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.

Contributor Information

Prescott T. Leach, Email: prescott.leach@temple.edu.

Justin W. Kenney, Email: justin.kenney@sickkids.ca.

Thomas J. Gould, Email: tgould@temple.edu.

References

  1. Abel T, Nguyen PV, Barad M, Deuel TA, Kandel ER, Bourtchouladze R. Genetic demonstration of a role for PKA in the late phase of LTP and in hippocampus-based long-term memory. Cell. 1997;88:615–626. doi: 10.1016/s0092-8674(00)81904-2. [DOI] [PubMed] [Google Scholar]
  2. Barr RK, Bogoyevitch MA. The c-Jun N-terminal protein kinase family of mitogen-activated protein kinases (JNK MAPKs) The International Journal of Biochemistry & Cell Biology. 2001;33:1047–1063. doi: 10.1016/s1357-2725(01)00093-0. [DOI] [PubMed] [Google Scholar]
  3. Bogoyevitch MA, Kobe B. Uses for JNK: the many and varied substrates of the c-Jun N-terminal kinases. Microbiol Mol Biol Rev. 2006;70:1061–1095. doi: 10.1128/MMBR.00025-06. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Bourtchouladze R, Abel T, Berman N, Gordon R, Lapidus K, Kandel ER. Different training procedures recruit either one or two critical periods for contextual memory consolidation, each of which requires protein synthesis and PKA. Learn Mem. 1998;5:365–374. [PMC free article] [PubMed] [Google Scholar]
  5. Bourtchuladze R, Frenguelli B, Blendy J, Cioffi D, Schutz G, Silva AJ. Deficient long-term memory in mice with a targeted mutation of the cAMP-responsive element-binding protein. Cell. 1994;79:59–68. doi: 10.1016/0092-8674(94)90400-6. [DOI] [PubMed] [Google Scholar]
  6. Carew TJ, Walters ET, Kandel ER. Classical conditioning in a simple withdrawal reflex in Aplysia californica. J Neurosci. 1981;1:1426–1437. doi: 10.1523/JNEUROSCI.01-12-01426.1981. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Chang L, Jones Y, Ellisman MH, Goldstein LS, Karin M. JNK1 is required for maintenance of neuronal microtubules and controls phosphorylation of microtubule-associated proteins. Dev Cell. 2003;4:521–533. doi: 10.1016/s1534-5807(03)00094-7. [DOI] [PubMed] [Google Scholar]
  8. Davis JA, James JR, Siegel SJ, Gould TJ. Withdrawal from chronic nicotine administration impairs contextual fear conditioning in C57BL/6 mice. J Neurosci. 2005;25:8708–8713. doi: 10.1523/JNEUROSCI.2853-05.2005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Dong C, Yang DD, Wysk M, Whitmarsh AJ, Davis RJ, Flavell RA. Defective T cell differentiation in the absence of Jnk1. Science. 1998;282:2092–2095. doi: 10.1126/science.282.5396.2092. [DOI] [PubMed] [Google Scholar]
  10. Eminel S, Roemer L, Waetzig V, Herdegen T. c-Jun N-terminal kinases trigger both degeneration and neurite outgrowth in primary hippocampal and cortical neurons. J Neurochem. 2008;104:957–969. doi: 10.1111/j.1471-4159.2007.05101.x. [DOI] [PubMed] [Google Scholar]
  11. Gelderblom M, Eminel S, Herdegen T, Waetzig V. c-Jun N-terminal kinases (JNKs) and the cytoskeleton--functions beyond neurodegeneration. Int J Dev Neurosci. 2004;22:559–564. doi: 10.1016/j.ijdevneu.2004.07.014. [DOI] [PubMed] [Google Scholar]
  12. Gould TJ, Higgins JS. Nicotine enhances contextual fear conditioning in C57BL/6J mice at 1 and 7 days post-training. Neurobiol Learn Mem. 2003;80:147–157. doi: 10.1016/s1074-7427(03)00057-1. [DOI] [PubMed] [Google Scholar]
  13. Gould TJ, Leach PT. Cellular, molecular, and genetic substrates underlying the impact of nicotine on learning. Neurobiol Learn Mem. 2014;107:108–132. doi: 10.1016/j.nlm.2013.08.004. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Gould TJ, Lommock JA. Nicotine enhances contextual fear conditioning and ameliorates ethanol-induced deficits in contextual fear conditioning. Behav Neurosci. 2003;117:1276–1282. doi: 10.1037/0735-7044.117.6.1276. [DOI] [PubMed] [Google Scholar]
  15. Gould TJ, Wehner JM. Nicotine enhancement of contextual fear conditioning. Behav Brain Res. 1999;102:31–39. doi: 10.1016/s0166-4328(98)00157-0. [DOI] [PubMed] [Google Scholar]
  16. Gulick D, Gould TJ. Interactive effects of ethanol and nicotine on learning in C57BL/6J mice depend on both dose and duration of treatment. Psychopharmacology (Berl) 2008;196:483–495. doi: 10.1007/s00213-007-0982-x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Gupta S, Barrett T, Whitmarsh AJ, Cavanagh J, Sluss HK, Derijard B, Davis RJ. Selective interaction of JNK protein kinase isoforms with transcription factors. Embo J. 1996;15:2760–2770. [PMC free article] [PubMed] [Google Scholar]
  18. Ham J, Eilers A, Whitfield J, Neame SJ, Shah B. c-Jun and the transcriptional control of neuronal apoptosis. Biochem Pharmacol. 2000;60:1015–1021. doi: 10.1016/s0006-2952(00)00372-5. [DOI] [PubMed] [Google Scholar]
  19. Kenney JW, Florian C, Portugal GS, Abel T, Gould TJ. Involvement of Hippocampal Jun-N Terminal Kinase Pathway in the Enhancement of Learning and Memory by Nicotine. Neuropsychopharmacology. 2010 doi: 10.1038/npp.2009.153. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Kenney JW, Gould TJ. Modulation of hippocampus-dependent learning and synaptic plasticity by nicotine. Mol Neurobiol. 2008;38:101–121. doi: 10.1007/s12035-008-8037-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Kim JJ, Fanselow MS. Modality-specific retrograde amnesia of fear. Science. 1992;256:675–677. doi: 10.1126/science.1585183. [DOI] [PubMed] [Google Scholar]
  22. Kim MJ, Futai K, Jo J, Hayashi Y, Cho K, Sheng M. Synaptic accumulation of PSD-95 and synaptic function regulated by phosphorylation of serine-295 of PSD-95. Neuron. 2007;56:488–502. doi: 10.1016/j.neuron.2007.09.007. [DOI] [PubMed] [Google Scholar]
  23. Li XM, Li CC, Yu SS, Chen JT, Sabapathy K, Ruan DY. JNK1 contributes to metabotropic glutamate receptor-dependent long-term depression and short-term synaptic plasticity in the mice area hippocampal CA1. Eur J Neurosci. 2007;25:391–396. doi: 10.1111/j.1460-9568.2006.05300.x. [DOI] [PubMed] [Google Scholar]
  24. Logue SF, Paylor R, Wehner JM. Hippocampal lesions cause learning deficits in inbred mice in the Morris water maze and conditioned-fear task. Behav Neurosci. 1997;111:104–113. doi: 10.1037//0735-7044.111.1.104. [DOI] [PubMed] [Google Scholar]
  25. Malinow R, Malenka RC. AMPA receptor trafficking and synaptic plasticity. Annu Rev Neurosci. 2002;25:103–126. doi: 10.1146/annurev.neuro.25.112701.142758. [DOI] [PubMed] [Google Scholar]
  26. Maren S. Neurotoxic basolateral amygdala lesions impair learning and memory but not the performance of conditional fear in rats. J Neurosci. 1999;19:8696–8703. doi: 10.1523/JNEUROSCI.19-19-08696.1999. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Pfenninger KH, de la Houssaye BA, Helmke SM, Quiroga S. Growth-regulated proteins and neuronal plasticity. A commentary. Mol Neurobiol. 1991;5:143–151. doi: 10.1007/BF02935543. [DOI] [PubMed] [Google Scholar]
  28. Phillips RG, LeDoux JE. Differential contribution of amygdala and hippocampus to cued and contextual fear conditioning. Behav Neurosci. 1992;106:274–285. doi: 10.1037//0735-7044.106.2.274. [DOI] [PubMed] [Google Scholar]
  29. Portugal GS, Wilkinson DS, Kenney JW, Sullivan C, Gould TJ. Strain-dependent effects of acute, chronic, and withdrawal from chronic nicotine on fear conditioning. Behav Genet. 2012;42:133–150. doi: 10.1007/s10519-011-9489-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Portugal GS, Wilkinson DS, Turner JR, Blendy JA, Gould TJ. Developmental effects of acute, chronic, and withdrawal from chronic nicotine on fear conditioning. Neurobiol Learn Mem. 2012;97:482–494. doi: 10.1016/j.nlm.2012.04.003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Sambrook J, Fritsch EF, Maniatis T. Molecular cloning. Cold spring harbor laboratory press; New York: 1989. [Google Scholar]
  32. Sananbenesi F, Fischer A, Schrick C, Spiess J, Radulovic J. Phosphorylation of hippocampal Erk-1/2, Elk-1, and p90-Rsk-1 during contextual fear conditioning: interactions between Erk-1/2 and Elk-1. Mol Cell Neurosci. 2002;21:463–476. doi: 10.1006/mcne.2002.1188. [DOI] [PubMed] [Google Scholar]
  33. Schafe GE, Nadel NV, Sullivan GM, Harris A, LeDoux JE. Memory consolidation for contextual and auditory fear conditioning is dependent on protein synthesis, PKA, and MAP kinase. Learn Mem. 1999;6:97–110. [PMC free article] [PubMed] [Google Scholar]
  34. Sherrin T, Blank T, Hippel C, Rayner M, Davis RJ, Todorovic C. Hippocampal c-Jun-N-terminal kinases serve as negative regulators of associative learning. J Neurosci. 2010;30:13348–13361. doi: 10.1523/JNEUROSCI.3492-10.2010. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Stern SA, Alberini CM. Mechanisms of memory enhancement. Wiley Interdiscip Rev Syst Biol Med. 2013;5:37–53. doi: 10.1002/wsbm.1196. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Strekalova T, Zorner B, Zacher C, Sadovska G, Herdegen T, Gass P. Memory retrieval after contextual fear conditioning induces c-Fos and JunB expression in CA1 hippocampus. Genes Brain Behav. 2003;2:3–10. doi: 10.1034/j.1601-183x.2003.00001.x. [DOI] [PubMed] [Google Scholar]
  37. Thomas GM, Lin DT, Nuriya M, Huganir RL. Rapid and bi-directional regulation of AMPA receptor phosphorylation and trafficking by JNK. Embo J. 2008;27:361–372. doi: 10.1038/sj.emboj.7601969. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Weston CR, Davis RJ. The JNK signal transduction pathway. Current Opinion in Genetics & Development. 2002;12:14–21. doi: 10.1016/s0959-437x(01)00258-1. [DOI] [PubMed] [Google Scholar]
  39. Wiltgen BJ, Sanders MJ, Anagnostaras SG, Sage JR, Fanselow MS. Context Fear Learning in the Absence of the Hippocampus. The Journal of Neuroscience. 2006;26:5484–5491. doi: 10.1523/JNEUROSCI.2685-05.2006. [DOI] [PMC free article] [PubMed] [Google Scholar]

RESOURCES