In order to continue the decline of smoking prevalence, it is imperative to understand the factors that contribute to the development of nicotine and tobacco addiction, such as adolescent initiation of nicotine use, stress, and the interaction of adolescent stress and adolescent nicotine. Both clinical and preclinical literature indicates that adolescent, but not adult, nicotine administration leads to long-lasting impairments in learning and memory and affect. Specifically, chronic nicotine treatment beginning in early adolescence or late adolescence resulted in adult deficits in contextual fear learning. However, the current study demonstrated that these adult learning deficits did not occur solely from nicotine administration. Rather, an interaction between adolescent nicotine and adolescent stress resulted in adult learning deficits in contextual fear. Additionally, it was found that dietary choline supplementation that began immediately following cessation of adolescent nicotine treatment and continued through a protracted abstinence period lasting thirty days reversed adult deficits in contextual fear. Finally, the current study found that adolescent nicotine exposure beginning at either early adolescence or late adolescence increased depressive-like behaviors, but not anxiety-like behaviors, following a protracted abstinence period. In contrast, chronic nicotine treatment in adult increased anxiety-like behaviors measured by the elevated plus-maze following a protracted abstinence period. The work encompassed in this dissertation suggests that the interactions between adolescent stress and adolescent nicotine increases the risk for developing cognitive and affective impairments, which may promote continued use of nicotine in adulthood. / Psychology

The mechanisms underlying cannabinoid impairment of fear memory is not clear. This study investigated the effects of the synthetic cannabinoid HU210 and the endocannabinoid hydrolysis inhibitor JZL 195 on fear memory following contextual fear conditioning (CFC; an animal model of fear). The long-term depression (LTD)-blocking peptide Tat-GluR2 was utilized to investigate whether the expression of cannabinoid-induced LTD (CB-LTD) is required for the cannabinoid impairment of acquisition and consolidation of contextual fear memory. HU210 reduced freezing throughout the test phase of the acquisition protocol, which was not affected by pre-administration of Tat-GluR2. High and moderate doses of HU210 reduced freezing during the first and last half, respectively, of the test phase of the consolidation protocol, which was prevented by pre-treatment with Tat-GluR2. HU210 did not affect freezing during the test phase of the retrieval protocol. Thus, these results suggest that HU210 impairs acquisition and consolidation, but not retrieval of contextual fear memory, and that in vivo CB-LTD expression is required for HU210 impairment of the consolidation, but not acquisition, of contextual fear memory. We also observed that HU210 and JZL 195 do not facilitate the acquisition of contextual fear memory extinction.

A amígdala participa dos processos de aprendizagem e memória de natureza emocional, incluindo os comportamentos aversivos. Essa estrutura compreende vários núcleos que estabelecem diferentes conexões com outras estruturas do sistema nervoso. Seu núcleo basal (BA) é um dos principais alvos amigdalares de informações processadas pelo hipocampo. Evidências apontam que o hipocampo seria responsável pela aprendizagem contextual, construindo uma representação integrada dos diferentes estímulos do ambiente numa representação única, denominada representação configuracional do contexto, que inclui também representações do espaço. Congruente com essa hodologia, lesões seletivas do BA resultam em prejuízos comportamentais similares aos encontrados após lesão hipocampal. Por exemplo, ratos com lesão no BA exibem deficiências na tarefa de medo condicionado ao contexto, mas não ao som, indicando que essa região está envolvida no processo de condicionamento aversivo contextual. Porém, não está claro se esse prejuízo decorre da participação do BA na aquisição e/ou evocação e expressão do medo contextual. Os objetivos do presente estudo incluíram avaliar, por meio da inativação reversível do BA, (1) se ele é necessário na aquisição do condicionamento aversivo ao som e/ou ao contexto e (2) qual a natureza da sua participação no condicionamento aversivo ao contexto, isto é, se é necessário para a construção do contexto, para sua associação com o estímulo aversivo e/ou para a evocação da memória e expressão das respostas condicionadas. Num primeiro experimento, muscimol foi infundido no BA antes do treinamento na tarefa de condicionamento aversivo concorrente ao som e ao contexto, e os testes de medo condicionado ao som e ao contexto foram realizados separadamente, na ausência de muscimol. Como esperado, os resultados revelaram prejuízo de desempenho na tarefa de medo condicionado ao contexto, mas não na tarefa de medo condicionado ao som. Num segundo experimento, muscimol foi infundido, em grupos independentes de animais, antes de cada fase da variante do condicionamento aversivo ao contexto que envolve facilitação pela pré-exposição ao contexto, a qual permite distinguir entre a construção configuracional do contexto (fase 1), sua associação com o estímulo aversivo (fase 2) e posterior evocação e expressão do medo condicionado (fase 3). Resultados mostraram que somente os ratos que receberam muscimol antes da fase 2, mas não os que receberam muscimol antes das fases 1 e 3, apresentaram prejuízo de desempenho na tarefa de medo condicionado ao contexto. No conjunto, esses resultados indicam que o BA participa do condicionamento aversivo ao contexto sendo imprescindível no processo de associação da representação configuracional do contexto com o estímulo aversivo, mas não nos processos de construção da representação sobre o contexto e nem de evocação da memória e expressão das respostas condicionadas de medo / The amygdala is involved in emotional learning and memory, including fear conditioning. This brain structure includes several nuclei with distinct hodology. The basal nucleus (BA) receives processed information from the hippocampal formation. Evidence indicates that the hippocampus integrates environmental stimuli in a single representation thus rendering it involved in contextual (including spatial) learning and memory. Congruent with this hodological evidence, selective damage to the BA results in behavioral impairments similar to those found after hippocampal damage. For instance, rats with BA damage exhibit performance impairments in contextual, but not auditory, fear conditioning tasks. However, it is not clear to which extent this disruption is related to the BA involvement in either acquisition of contextual fear or retrieval of memory and fear expression, or both. This study aimed at investigating, by way of reversible inactivation of the BA, (1) its involvement in acquisition of auditory and contextual fear conditioning, and (2) the nature of its participation in contextual fear conditioning, that is, if it is necessary for building a representation about the context, for associating the context with the aversive stimulus and/or for memory retrieval and expression of contextual fear conditioning. In the first experiment, muscimol was infused into the BA before training in a concurrent auditory and contextual fear conditioning task, and testing for auditory and contextual fear conditioning was run separately in the absence of muscimol. As expected, results revealed disruption of performance in the contextual, but not in the auditory, conditioning task. In the second experiment, muscimol was infused into the BA, in independent groups of animals, before each of the three phases of a contextual fear conditioning variant that involves context pre-exposure facilitation, thus allowing to evaluate if functional reversible inactivation of the BA interfered with (1) building an integrated representation of the environment (the context), (2) its association with the aversive stimulus, and/or (3) memory retrieval and expression of fear conditioning. Results showed that muscimol infusion into BA before phase 2, but not phases 1 and 3, impaired performance in the contextual fear conditioning task. Together, these results indicate that a functional BA is required for acquisition of contextual fear conditioning in order to establish an association between the context and the aversive stimulus, but not for building a context neither for memory retrieval and expression of fear conditioned responses

Previous research investigating the neural circuitry underlying memory consolidation has primarily focused on single “nodes” in the circuit rather than the neural connections between brain regions, despite the likely importance of these connections in mediating different aspects or forms of memory. This focus has, in part, been due to technical limitations; however the advent of optogenetics has altered our capabilities in this regard, enabling optical control over neural pathways with temporal and spatial precision. The current set of experiments took advantage of optogenetics to control activity in specific pathways connecting brain regions in rats immediately after different kinds of learning. Chapter 2 first established the use of optogenetics to manipulate activity in the basolateral amygdala (BLA), which has been shown to modulate memory consolidation for a variety of types of learning likely through its connections to various downstream regions. Using a one-trial inhibitory avoidance task, a simple and robust fear learning paradigm, we found that both post-training stimulation and inhibition of BLA activity could enhance or impair later retention of the task, respectively. Enhancement was specific to stimulation using trains of 40, but not 20, Hz light pulses. Chapters 3 and 4 examined the projections from the BLA to the ventral hippocampus (VH) and medial entorhinal cortex (mEC) as the BLA’s ability to influence the consolidation for many types of memory is believed to be mediated through discrete projections to distinct brain regions. Indeed, the BLA innervates both structures, and prior studies suggest that the mEC and VH have distinct roles in memory processing related to contextual and nociceptive (footshock) learning, such as those involved in contextual fear conditioning (CFC). Optogenetic stimulation or inhibition of the BLA-VH or BLA-mEC pathway after training on a modified CFC task, in which the nociceptive or emotional stimulus (the footshock) and the context are separated, enabled experimental manipulations to selectively affect the consolidation for learning about one component and not the other. Optogenetic stimulation/inhibition was given to each candidate pathway immediately after the relevant training to determine its role in influencing consolidation for that component of the CFC learning. Chapter 3 results showed that stimulation of the BLA-VH pathway following footshock, but not context, training enhanced retention, an effect that was specific to trains of 40 Hz stimulation. Post-footshock photoinhibition of the same pathway impaired retention for the task. Similar investigations of the BLA-mEC pathway in Chapter 4 produced complementary findings. Post-context, but not footshock, stimulation of the pathway enhanced retention. In this particular case, only trains of 8 Hz stimulation were effective at enhancing retention. These results are the first, to our knowledge, to find that BLA inputs to different structures selectively modulate consolidation for different aspects of learning, thus enhancing our understanding of the neural connections underlying the consolidation of contextual fear conditioning and providing a critical foundation for future research.

The mechanisms underlying cannabinoid impairment of fear memory is not clear. This study investigated the effects of the synthetic cannabinoid HU210 and the endocannabinoid hydrolysis inhibitor JZL 195 on fear memory following contextual fear conditioning (CFC; an animal model of fear). The long-term depression (LTD)-blocking peptide Tat-GluR2 was utilized to investigate whether the expression of cannabinoid-induced LTD (CB-LTD) is required for the cannabinoid impairment of acquisition and consolidation of contextual fear memory. HU210 reduced freezing throughout the test phase of the acquisition protocol, which was not affected by pre-administration of Tat-GluR2. High and moderate doses of HU210 reduced freezing during the first and last half, respectively, of the test phase of the consolidation protocol, which was prevented by pre-treatment with Tat-GluR2. HU210 did not affect freezing during the test phase of the retrieval protocol. Thus, these results suggest that HU210 impairs acquisition and consolidation, but not retrieval of contextual fear memory, and that in vivo CB-LTD expression is required for HU210 impairment of the consolidation, but not acquisition, of contextual fear memory. We also observed that HU210 and JZL 195 do not facilitate the acquisition of contextual fear memory extinction.

A extinção é uma forma de aprendizado inibitório que se origina na omissão do reforço ou estímulo incondicionado, inibindo a evocação de uma resposta ou comportamento aprendido anteriormente. Muitas formas de aprendizado são moduladas por receptores β- noradrenérgicos, D1-dopaminérgicos e H2-histaminérgicos no córtex pré-frontal ventromedial (vmPFC), no complexo basolateral da amígdala (BLA) e no hipocampo dorsal (DH). Assim, o objetivo do presente trabalho foi investigar a modulação da extinção de memória aversiva nestas três regiões cerebrais. Para isso, utilizamos ratos machos Wistar, que foram submetidos ao paradigma de esquiva inibitória (EI) ou condicionamento contextual ao medo (CCM). As diferentes drogas utilizadas foram infundidas através das cânulas guias implantadas estereotaxicamente no DH, BLA ou vmPFC imediatamente após a sessão de extinção e seus efeitos sobre a extinção foram avaliados em uma sessão de teste realizada 24 h depois. A DSerina (50 μg/lado), modulador positivo do receptor NMDA, e o SKF9188 (12.5 μg/lado), inibidor da enzima histamina metil-transferase, melhoraram a consolidação da memória de extinção nas tarefas de EI e CCM. Entretanto, o AP5 (5 μg/lado), antagonista do receptor glutamatérgico NMDA, e a ranitidina (17.5 μg/lado), antagonista do receptor histaminérgico H2, prejudicaram a extinção em ambos os paradigmas, indicando que os receptores glutamatérgicos do tipo NMDA estão envolvidos na consolidação dos dois paradigmas utilizados, e que os receptores histaminérgicos H2 modulam a extinção nas três estruturas estudadas. A noradrenalina (1 μg/lado), o antagonista β-adrenoreceptor, timolol (1 μg/lado), o agonista dos receptores D1, SKF38393 (12.5 μg/lado) e o antagonista dos receptores D1, SCH23390 (1.5 μg/lado) também afetam a extinção nas duas tarefas, porém, seus efeitos são variados dependendo da tarefa e do local da infusão, sugerindo que a modulação da extinção pelos receptores β- e D1 é mais complexa. Nossos resultados mostram que as três estruturas são ativadas durante o processo de extinção da memória e que os sistemas neuromodulatórios atuam de formas distintas nessas tarefas. / Extinction consists of the learned inhibition of retrieval of previously acquired memory. Many forms of learning are modulated by β-noradrenergic, D1-dopaminergic and H2-histaminergic receptors on ventromedial prefrontal cortex (vmPFC), basolateral amygdala (BLA) and dorsal hippocampus. Therefore, the aim of this work was investigated the modulation of aversive memory extinction in these brain structures. Male Wistar rats were submitted to inhibitory avoidance paradigm (EI) or contextual fear conditioning (CCM). The drugs were infused through cannulae implanted into the DH, BLA or vmPFC immediately after the extinction session and their effects were evaluated 24 h later. D-serine (50 μg/side), a NMDA receptor stimulant, and SKF9188 (12.5 μg/side), a histamine methyl-transferase inhibitor, enhanced the consolidation of the extinction memory in EI and CCM tasks. However, AP5 (5 μg/side), a NMDA-antagonist, and ranitidine (17.5 μg/side), a H2- histaminergic antagonist, impaired the extinction of both tasks, indicated that NMDA receptors are involved in the consolidation of extinction of both tasks, and histamine H2 receptors modulate that process in all areas studied. Noradrenaline (1 μg/side), timolol 1 μg/side), a β-adrenergic antagonist, SKF38393 (12.5 μg/side) and SCH23390 (1.5 μg/side), D1 agonist and antagonist receptor, respectively, also affected the extinction, but their effects varied with the task and with the site of infusion, suggesting that extinction modulation by β- and D1 is more complex. In conclusion, the three structures investigated are activated in the aversive memory extinction and the neuromodulatory systems act of different forms in these structures.

A extinção é uma forma de aprendizado inibitório que se origina na omissão do reforço ou estímulo incondicionado, inibindo a evocação de uma resposta ou comportamento aprendido anteriormente. Muitas formas de aprendizado são moduladas por receptores β- noradrenérgicos, D1-dopaminérgicos e H2-histaminérgicos no córtex pré-frontal ventromedial (vmPFC), no complexo basolateral da amígdala (BLA) e no hipocampo dorsal (DH). Assim, o objetivo do presente trabalho foi investigar a modulação da extinção de memória aversiva nestas três regiões cerebrais. Para isso, utilizamos ratos machos Wistar, que foram submetidos ao paradigma de esquiva inibitória (EI) ou condicionamento contextual ao medo (CCM). As diferentes drogas utilizadas foram infundidas através das cânulas guias implantadas estereotaxicamente no DH, BLA ou vmPFC imediatamente após a sessão de extinção e seus efeitos sobre a extinção foram avaliados em uma sessão de teste realizada 24 h depois. A DSerina (50 μg/lado), modulador positivo do receptor NMDA, e o SKF9188 (12.5 μg/lado), inibidor da enzima histamina metil-transferase, melhoraram a consolidação da memória de extinção nas tarefas de EI e CCM. Entretanto, o AP5 (5 μg/lado), antagonista do receptor glutamatérgico NMDA, e a ranitidina (17.5 μg/lado), antagonista do receptor histaminérgico H2, prejudicaram a extinção em ambos os paradigmas, indicando que os receptores glutamatérgicos do tipo NMDA estão envolvidos na consolidação dos dois paradigmas utilizados, e que os receptores histaminérgicos H2 modulam a extinção nas três estruturas estudadas. A noradrenalina (1 μg/lado), o antagonista β-adrenoreceptor, timolol (1 μg/lado), o agonista dos receptores D1, SKF38393 (12.5 μg/lado) e o antagonista dos receptores D1, SCH23390 (1.5 μg/lado) também afetam a extinção nas duas tarefas, porém, seus efeitos são variados dependendo da tarefa e do local da infusão, sugerindo que a modulação da extinção pelos receptores β- e D1 é mais complexa. Nossos resultados mostram que as três estruturas são ativadas durante o processo de extinção da memória e que os sistemas neuromodulatórios atuam de formas distintas nessas tarefas. / Extinction consists of the learned inhibition of retrieval of previously acquired memory. Many forms of learning are modulated by β-noradrenergic, D1-dopaminergic and H2-histaminergic receptors on ventromedial prefrontal cortex (vmPFC), basolateral amygdala (BLA) and dorsal hippocampus. Therefore, the aim of this work was investigated the modulation of aversive memory extinction in these brain structures. Male Wistar rats were submitted to inhibitory avoidance paradigm (EI) or contextual fear conditioning (CCM). The drugs were infused through cannulae implanted into the DH, BLA or vmPFC immediately after the extinction session and their effects were evaluated 24 h later. D-serine (50 μg/side), a NMDA receptor stimulant, and SKF9188 (12.5 μg/side), a histamine methyl-transferase inhibitor, enhanced the consolidation of the extinction memory in EI and CCM tasks. However, AP5 (5 μg/side), a NMDA-antagonist, and ranitidine (17.5 μg/side), a H2- histaminergic antagonist, impaired the extinction of both tasks, indicated that NMDA receptors are involved in the consolidation of extinction of both tasks, and histamine H2 receptors modulate that process in all areas studied. Noradrenaline (1 μg/side), timolol 1 μg/side), a β-adrenergic antagonist, SKF38393 (12.5 μg/side) and SCH23390 (1.5 μg/side), D1 agonist and antagonist receptor, respectively, also affected the extinction, but their effects varied with the task and with the site of infusion, suggesting that extinction modulation by β- and D1 is more complex. In conclusion, the three structures investigated are activated in the aversive memory extinction and the neuromodulatory systems act of different forms in these structures.

A extinção é uma forma de aprendizado inibitório que se origina na omissão do reforço ou estímulo incondicionado, inibindo a evocação de uma resposta ou comportamento aprendido anteriormente. Muitas formas de aprendizado são moduladas por receptores β- noradrenérgicos, D1-dopaminérgicos e H2-histaminérgicos no córtex pré-frontal ventromedial (vmPFC), no complexo basolateral da amígdala (BLA) e no hipocampo dorsal (DH). Assim, o objetivo do presente trabalho foi investigar a modulação da extinção de memória aversiva nestas três regiões cerebrais. Para isso, utilizamos ratos machos Wistar, que foram submetidos ao paradigma de esquiva inibitória (EI) ou condicionamento contextual ao medo (CCM). As diferentes drogas utilizadas foram infundidas através das cânulas guias implantadas estereotaxicamente no DH, BLA ou vmPFC imediatamente após a sessão de extinção e seus efeitos sobre a extinção foram avaliados em uma sessão de teste realizada 24 h depois. A DSerina (50 μg/lado), modulador positivo do receptor NMDA, e o SKF9188 (12.5 μg/lado), inibidor da enzima histamina metil-transferase, melhoraram a consolidação da memória de extinção nas tarefas de EI e CCM. Entretanto, o AP5 (5 μg/lado), antagonista do receptor glutamatérgico NMDA, e a ranitidina (17.5 μg/lado), antagonista do receptor histaminérgico H2, prejudicaram a extinção em ambos os paradigmas, indicando que os receptores glutamatérgicos do tipo NMDA estão envolvidos na consolidação dos dois paradigmas utilizados, e que os receptores histaminérgicos H2 modulam a extinção nas três estruturas estudadas. A noradrenalina (1 μg/lado), o antagonista β-adrenoreceptor, timolol (1 μg/lado), o agonista dos receptores D1, SKF38393 (12.5 μg/lado) e o antagonista dos receptores D1, SCH23390 (1.5 μg/lado) também afetam a extinção nas duas tarefas, porém, seus efeitos são variados dependendo da tarefa e do local da infusão, sugerindo que a modulação da extinção pelos receptores β- e D1 é mais complexa. Nossos resultados mostram que as três estruturas são ativadas durante o processo de extinção da memória e que os sistemas neuromodulatórios atuam de formas distintas nessas tarefas. / Extinction consists of the learned inhibition of retrieval of previously acquired memory. Many forms of learning are modulated by β-noradrenergic, D1-dopaminergic and H2-histaminergic receptors on ventromedial prefrontal cortex (vmPFC), basolateral amygdala (BLA) and dorsal hippocampus. Therefore, the aim of this work was investigated the modulation of aversive memory extinction in these brain structures. Male Wistar rats were submitted to inhibitory avoidance paradigm (EI) or contextual fear conditioning (CCM). The drugs were infused through cannulae implanted into the DH, BLA or vmPFC immediately after the extinction session and their effects were evaluated 24 h later. D-serine (50 μg/side), a NMDA receptor stimulant, and SKF9188 (12.5 μg/side), a histamine methyl-transferase inhibitor, enhanced the consolidation of the extinction memory in EI and CCM tasks. However, AP5 (5 μg/side), a NMDA-antagonist, and ranitidine (17.5 μg/side), a H2- histaminergic antagonist, impaired the extinction of both tasks, indicated that NMDA receptors are involved in the consolidation of extinction of both tasks, and histamine H2 receptors modulate that process in all areas studied. Noradrenaline (1 μg/side), timolol 1 μg/side), a β-adrenergic antagonist, SKF38393 (12.5 μg/side) and SCH23390 (1.5 μg/side), D1 agonist and antagonist receptor, respectively, also affected the extinction, but their effects varied with the task and with the site of infusion, suggesting that extinction modulation by β- and D1 is more complex. In conclusion, the three structures investigated are activated in the aversive memory extinction and the neuromodulatory systems act of different forms in these structures.

A amígdala participa dos processos de aprendizagem e memória de natureza emocional, incluindo os comportamentos aversivos. Essa estrutura compreende vários núcleos que estabelecem diferentes conexões com outras estruturas do sistema nervoso. Seu núcleo basal (BA) é um dos principais alvos amigdalares de informações processadas pelo hipocampo. Evidências apontam que o hipocampo seria responsável pela aprendizagem contextual, construindo uma representação integrada dos diferentes estímulos do ambiente numa representação única, denominada representação configuracional do contexto, que inclui também representações do espaço. Congruente com essa hodologia, lesões seletivas do BA resultam em prejuízos comportamentais similares aos encontrados após lesão hipocampal. Por exemplo, ratos com lesão no BA exibem deficiências na tarefa de medo condicionado ao contexto, mas não ao som, indicando que essa região está envolvida no processo de condicionamento aversivo contextual. Porém, não está claro se esse prejuízo decorre da participação do BA na aquisição e/ou evocação e expressão do medo contextual. Os objetivos do presente estudo incluíram avaliar, por meio da inativação reversível do BA, (1) se ele é necessário na aquisição do condicionamento aversivo ao som e/ou ao contexto e (2) qual a natureza da sua participação no condicionamento aversivo ao contexto, isto é, se é necessário para a construção do contexto, para sua associação com o estímulo aversivo e/ou para a evocação da memória e expressão das respostas condicionadas. Num primeiro experimento, muscimol foi infundido no BA antes do treinamento na tarefa de condicionamento aversivo concorrente ao som e ao contexto, e os testes de medo condicionado ao som e ao contexto foram realizados separadamente, na ausência de muscimol. Como esperado, os resultados revelaram prejuízo de desempenho na tarefa de medo condicionado ao contexto, mas não na tarefa de medo condicionado ao som. Num segundo experimento, muscimol foi infundido, em grupos independentes de animais, antes de cada fase da variante do condicionamento aversivo ao contexto que envolve facilitação pela pré-exposição ao contexto, a qual permite distinguir entre a construção configuracional do contexto (fase 1), sua associação com o estímulo aversivo (fase 2) e posterior evocação e expressão do medo condicionado (fase 3). Resultados mostraram que somente os ratos que receberam muscimol antes da fase 2, mas não os que receberam muscimol antes das fases 1 e 3, apresentaram prejuízo de desempenho na tarefa de medo condicionado ao contexto. No conjunto, esses resultados indicam que o BA participa do condicionamento aversivo ao contexto sendo imprescindível no processo de associação da representação configuracional do contexto com o estímulo aversivo, mas não nos processos de construção da representação sobre o contexto e nem de evocação da memória e expressão das respostas condicionadas de medo / The amygdala is involved in emotional learning and memory, including fear conditioning. This brain structure includes several nuclei with distinct hodology. The basal nucleus (BA) receives processed information from the hippocampal formation. Evidence indicates that the hippocampus integrates environmental stimuli in a single representation thus rendering it involved in contextual (including spatial) learning and memory. Congruent with this hodological evidence, selective damage to the BA results in behavioral impairments similar to those found after hippocampal damage. For instance, rats with BA damage exhibit performance impairments in contextual, but not auditory, fear conditioning tasks. However, it is not clear to which extent this disruption is related to the BA involvement in either acquisition of contextual fear or retrieval of memory and fear expression, or both. This study aimed at investigating, by way of reversible inactivation of the BA, (1) its involvement in acquisition of auditory and contextual fear conditioning, and (2) the nature of its participation in contextual fear conditioning, that is, if it is necessary for building a representation about the context, for associating the context with the aversive stimulus and/or for memory retrieval and expression of contextual fear conditioning. In the first experiment, muscimol was infused into the BA before training in a concurrent auditory and contextual fear conditioning task, and testing for auditory and contextual fear conditioning was run separately in the absence of muscimol. As expected, results revealed disruption of performance in the contextual, but not in the auditory, conditioning task. In the second experiment, muscimol was infused into the BA, in independent groups of animals, before each of the three phases of a contextual fear conditioning variant that involves context pre-exposure facilitation, thus allowing to evaluate if functional reversible inactivation of the BA interfered with (1) building an integrated representation of the environment (the context), (2) its association with the aversive stimulus, and/or (3) memory retrieval and expression of fear conditioning. Results showed that muscimol infusion into BA before phase 2, but not phases 1 and 3, impaired performance in the contextual fear conditioning task. Together, these results indicate that a functional BA is required for acquisition of contextual fear conditioning in order to establish an association between the context and the aversive stimulus, but not for building a context neither for memory retrieval and expression of fear conditioned responses

The mechanisms underlying cannabinoid impairment of fear memory is not clear. This study investigated the effects of the synthetic cannabinoid HU210 and the endocannabinoid hydrolysis inhibitor JZL 195 on fear memory following contextual fear conditioning (CFC; an animal model of fear). The long-term depression (LTD)-blocking peptide Tat-GluR2 was utilized to investigate whether the expression of cannabinoid-induced LTD (CB-LTD) is required for the cannabinoid impairment of acquisition and consolidation of contextual fear memory. HU210 reduced freezing throughout the test phase of the acquisition protocol, which was not affected by pre-administration of Tat-GluR2. High and moderate doses of HU210 reduced freezing during the first and last half, respectively, of the test phase of the consolidation protocol, which was prevented by pre-treatment with Tat-GluR2. HU210 did not affect freezing during the test phase of the retrieval protocol. Thus, these results suggest that HU210 impairs acquisition and consolidation, but not retrieval of contextual fear memory, and that in vivo CB-LTD expression is required for HU210 impairment of the consolidation, but not acquisition, of contextual fear memory. We also observed that HU210 and JZL 195 do not facilitate the acquisition of contextual fear memory extinction.