京都大学 / 新制・課程博士 / 博士(医学) / 甲第24088号 / 医博第4864号 / 新制||医||1059(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 林 康紀, 教授 渡邉 大, 教授 髙橋 良輔 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

<p>Conversational code-switching is common among bilingual speakers, in fact, we consider this routine; however, the reasons for switching and the location of this mechanism in the brain remain largely unknown. There is much to be discovered about bilingual code-switching especially in relation to autobiographical memories shared between immigrants. This study investigates the two phenomena: code-switching and autobiographical memories. The research is based on the following major theories: 1) Schrauf (2009) who said that one’s “…particular personal memories are associated with one or the other of the bilingual’s languages” (p. 26), which he called the language-specificity effect; 2) Marian & Neisser (2000) who proposed that “…memories become more accessible when language at retrieval matches language at encoding…any increase in the similarity between the linguistic environments at encoding and at retrieval should facilitate recall” (p. 361); 3) Marian & Kaushanskaya (2005), who found that “…bilinguals are more likely to code-switch to the other language when the language of encoding does not match the language of retrieval” (p. 1483). The results of this study both supported and disproved the above mentioned research, which indicate that language alone may not be the only influence on autobiographical memory recall or code-switching in elderly bilinguals. It is my belief that both phenomena stem from a higher process that is involved with cognitive control and located in the cingulate gyrus, one part of the limbic system.</p> / Master of Science (MSc)

Pain is the primary reason why patients seek medical care and there is a great unmet need for the development of pain relieving medications. The treatments that are currently available either have limited efficacy or are accompanied by a multitude of unwanted side effects. However, discovering novel therapeutics for the treatment of pain has been challenging. Part of the reason for this may be that that the ways in which pain is assessed in the preclinical setting are different from the way that it is evaluated clinically in human trials. The most common method for evaluating pain in preclinical models is to measure responses to evoked stimuli. However, a change in the threshold of response to evoked pain likely does not measure whether the unpleasant component of pain has actually been reduced. The most clinically relevant question for pain is whether the treatment actually makes the patients "feel better". Here, we demonstrate that the aversiveness of pain can be captured using motivated behavior to seek pain relief. We used conditioned place preference (CPP) to establish that animals with ongoing pain will seek a context that has been paired with effective pain relief, likely as a result of negative reinforcement. These studies allowed for mechanistic investigation. Our results show that: 1) effective pain relief can be achieved by either blocking noxious peripheral input or by directly attenuating pain related unpleasantness in the brain, and 2) pain relief is rewarding and activates the reward circuitry. These studies provide a basis for development of a future platform for drug discovery for pain.

The studies in this thesis explored how pain and its relief are represented in the human brain. Pain and relief are important survival signals that motivate escape from danger and search for safety, however, they are often evaluated by subjective descriptions only. Studying how humans learn and adapt to pain and relief allows objective investigation of the information processing and neural circuitry underlying these internal experiences. My research set out to use computational learning models to provide mechanistic explanations for the behavioural and functional neuroimaging data collected in pain/relief learning experiments with independent groups of healthy human participants. With a Pavlovian acute pain conditioning task in Experiment 1, I found that 'associability' (a form of uncertainty signal) had a crucial role in controlling the learning rates of different conditioned responses, and can be used to anatomically dissociate underlying neural systems. Experiment 2 focused on relief learning of terminating a tonic pain stimulus, in which the priority for relief-seeking is in conflict with the general suppression of cognition and attention. I showed that associability during active learning not only controls the relief learning rate, but also correlates with endogenously modulated (reduced) ongoing pain. This finding was confirmed in Experiment 3 using an independent active relief learning paradigm in a complex dynamic environment. Critically, both experiments showed that associability was correlated with responses in the pregenual anterior cingulate cortex (pgACC), a brain region previously implicated in aspects of endogenous pain control related to attention and controllability. This provided a potential computational account of an information-sensitive endogenous analgesic mechanism. In Experiment 4, I explored the implications of endogenous controllability for technology-based pain therapeutics. I designed an adaptive closed-loop system that learned to control pain stimulation using decoded real-time pain representations from the brain. Subjects were shown to actively enhance the discriminability of pain only in the pgACC, and uncertainty during learning again correlated with endogenously modulated pain and were associated with pgACC responses. Together, these studies (i) show the importance of uncertainty in controlling learning during both acute and tonic pain, (ii) describe how uncertainty also flexibly modulates pain to maximise the impact of learning, (iii) illustrate a central role for the pgACC in this process, and (iv) reveal the implications for future technology-based therapeutic systems.

Background: Functional imaging studies have examined the neural circuitry of subjects with obsessive compulsive disorder (OCD), and the changes associated with oral treatment. However, the effect of intravenous (IV) serotonin reuptake inhibitors (SRIs) on neuronal activation has not been investigated in OCD subjects, even though IV SRIs have been shown to be more effective than oral pharmacotherapy. Methods: Six OCD and 6 control subjects underwent functional magnetic resonance imaging while receiving infusions of citalopram and placebo, in a randomized, crossover design. Results: Compared to controls, OCD subjects exhibited hyperactivation of the orbitofrontal cortex and anterior cingulate cortex while looking at symptom provoking pictures at baseline. However, after the citalopram infusion, patients displayed attenuations of these regions, which correlated with reductions in subjective anxiety ratings. Conclusion: The effects observed after the IV citalopram infusion are similar to modulations observed after prolonged oral pharmacotherapy trials, illustrating the benefits of IV SRIs.

Background: Functional imaging studies have examined the neural circuitry of subjects with obsessive compulsive disorder (OCD), and the changes associated with oral treatment. However, the effect of intravenous (IV) serotonin reuptake inhibitors (SRIs) on neuronal activation has not been investigated in OCD subjects, even though IV SRIs have been shown to be more effective than oral pharmacotherapy. Methods: Six OCD and 6 control subjects underwent functional magnetic resonance imaging while receiving infusions of citalopram and placebo, in a randomized, crossover design. Results: Compared to controls, OCD subjects exhibited hyperactivation of the orbitofrontal cortex and anterior cingulate cortex while looking at symptom provoking pictures at baseline. However, after the citalopram infusion, patients displayed attenuations of these regions, which correlated with reductions in subjective anxiety ratings. Conclusion: The effects observed after the IV citalopram infusion are similar to modulations observed after prolonged oral pharmacotherapy trials, illustrating the benefits of IV SRIs.

Conflict resolution is essential for human cognitive system which renders adaptability to the environment, providing humans to fulfill daily activities. The main aim of this thesis is to create a task where the conflict activates emotional networks exclusively, while investigating how the cognitive and emotional conflicts are monitored and then resolved in the brain. After creating the appropriate material composed of controlled words in terms of emotional dimensions and concreteness values, a new Word-face Stroop Task is designed using Turkish words. Firstly subjects participated in a classical Stroop task to measure cognitive conflict and then in the Word-face Stroop task, the conflict between emotional words and emotional faces is investigated. The same Stroop tasks are then administered to depression patients. The results of the classical Stroop replicated the previous findings: (1) Healthy population was slower in responding to incongruent cases than congruent cases (2) Depressed patients were significantly slower than healthy population. The Word-face Stroop, conducted on healthy population also replicated the earlier findings: (1) People were slower in reacting to incongruent stimuli than congruent stimuli (2) People reacted faster to positive words than negative ones. Same Stroop tasks conducted on depressed patients however revealed interesting results, novel to the literature: (1) Congruency scores were significantly different when healthy population and Depressive Disorder patients with Hamilton scores higher than 20 were compared (2) Patients with Hamilton scores higher than 20 and lower than 20 significantly differed in congruency scores (3) Patients showed a tendency to react faster to incongruent stimuli rather than congruent stimuli, contrary to normal population (4) Normal population showed greater congruency effect in positively valenced abstract words, whereas depression patients showed greater congruency effect in negatively valenced concrete words.

A formação de memórias de medo contextuais, como as estudadas no presente trabalho, requer a indução da plasticidade sináptica iniciada pela ativação de receptores transmembrana localizados nos neurônios de estruturas encefálicas como o hipocampo. O fluxo iônico mediado pelos receptores N-metil-D-aspartato (NMDARs) é essencial para ativar vias de sinalização intracelular que darão suporte à formação da memória. No entanto, esses receptores parecem não ser necessários em situações onde os animais passaram por uma experiência prévia similar a que está sendo aprendida. Dessa forma, um aprendizado anterior pode modificar os mecanismos de plasticidade que serão utilizados para codificar uma nova informação, caracterizando um fenômeno de metaplasticidade. Esse fenômeno ocorre quando os animais são pré-expostos ao local onde posteriormente serão submetidos a um aprendizado associativo ou quando são re-submetidos a mesma tarefa comportamental com dicas contextuais/espaciais diferentes. No presente trabalho, investigamos (i) os mecanismos de plasticidade sináptica (receptores) e de plasticidade não-sináptica (excitabilidade neuronal) recrutados para a formação do segundo aprendizado e (ii) se a independência dos NMDARs é mantida quando a memória anterior foi adquirida remotamente. Os animais utilizados nesse trabalho (camundongos ou ratos) foram expostos a dois aprendizados sequenciais realizados na tarefa de condicionamento aversivo ao contexto (CAC). O intervalo entre os condicionamentos foi de dois dias nos experimentos do Capítulo I e de três ou quarenta dias nos experimentos do Capítulo II. Cada aprendizado ocorreu em uma caixa de condicionamento com características próprias de formato, odor e iluminação (contexto A ou contexto B), sendo que o primeiro aprendizado ocorreu no contexto A e o segundo no contexto B. Nos experimentos do Capítulo I foram avaliadas no hipocampo dorsal as modificações na excitabilidade neuronal hipocampal induzidas pelo primeiro condicionamento, bem como os receptores envolvidos com a aquisição da memória subsequente e a sobreposição neuronal entre os dois aprendizados. Com a utilização do camundongo transgênico Teg-Tag foi possível identificar os neurônios recrutados para o primeiro aprendizado. Esse animal tem a expressão da proteína fluorescente verde (GFP, do inglês, green fluorescent protein) controlada pela ativação do gene c-fos, que é fisiologicamente transcrito após a atividade neuronal. Dessa forma, os neurônios ativados pelo aprendizado são marcados com GFP. Através da técnica de patch clamp foi observado que os neurônios GFP+ mantiveram a excitabilidade elevada por até dois dias após o treinamento no CAC. Além disso, a identificação dos neurônios recrutados 8 para o aprendizado subsequente foi realizada através da marcação imunofluorescente da proteína Fos, no seu pico de expressão endógena, noventa minutos após o re-treino. Foi observada uma maior sobreposição neuronal (GFP+, Fos+) quando os animais foram retreinados no mesmo contexto dois dias após o primeiro treino. Uma sobreposição intermediária (GFP+, Fos+) foi vista quando os animais tiveram o segundo condicionamento no contexto B, sendo ela significativamente maior do que a sobreposição nos animais não re-treinados. Adicionalmente, foi demonstrado que a aquisição do aprendizado subsequente é mediada por receptores metabotrópicos glutamatérgicos (mGluRs) ao invés de NMDARs. No Capítulo II foi investigado se uma memória remota, adquirida há quarenta dias, ainda seria capaz de influenciar nos mecanismos de plasticidade recrutados para aquisição do aprendizado subsequente. A dinâmica da consolidação sistêmica foi considerada nesses experimentos já que a evocação da memória remota passa a depender de estruturas encefálicas neocorticais, sem recrutar a atividade hipocampal. Apesar da evocação da memória remota não requerer a atividade hipocampal, foi observado que a aquisição do aprendizado subsequente a uma memória remota necessita a atividade de pelo menos uma sub-região do hipocampo (dorsal ou ventral). Complementarmente, os resultados indicaram que, quando o intervalo entre os aprendizados é aumentado (de três para quarenta dias), a formação do aprendizado subsequente, que era independente de NMDARs, volta a depender da plasticidade sináptica mediada por esses receptores no hipocampo (dorsal e ventral). Juntos, nossos resultados sugerem que o primeiro aprendizado causa um aumento da excitabilidade neuronal e modifica a plasticidade sináptica recrutada para o aprendizado subsequente, sendo este último mediado por mGluRs ao invés de NMDARs. Além disso, a metaplasticidade induzida pelo primeiro condicionamento é transiente; quando o intervalo entre as exposições é aumentado, o segundo aprendizado passa a depender novamente da ativação dos NMDARs. / Contextual fear memory formation, like the ones explored in the current work, requires the induction of the synaptic plasticity mediated by the activation of transmembrane receptors that are present in the brain structures as the hippocampus. The ionic flux through the N-methylaspartate- D-aspartate is crucial for activation of the intracellular signaling pathways that will support memory formation. However, these receptors are not necessary when animals had a prior similar learning. In this way, a previous learning can modify the plasticity mechanism that will be recruited to encode a new information, featuring a metaplasticity phenomenon. This phenomenon occurs when animals are pre-exposed to an environment where they will learn an associative learning later or when animals are re-exposed to the same behavioral task with distinct contextual/spatial cues. In the present study, we investigated (i) the synaptic plasticity mechanisms (receptors) and the non-synaptic plasticity mechanisms (neuronal excitability) required for the acquisition of the second learning and (ii) whether a subsequent learning that occurs in a remote time-point is still NMDAR-independent. The animals used in this study (mice or rats) were exposed to two sequential learnings that were performed in the contextual fear conditioning (CFC). The interval between conditionings were two days in the experiments of Chapter I and three or forty days in the experiments of the Chapter II. Each learning was performed in a box with differences on shape, odor and illumination (context A or context B). The first learning occurred in the context A followed by learning on context B. In the experiments of Chapter I it was evaluated the changes in the hippocampal neuronal excitability induced by the first conditioning, the receptors involved with the acquisition of the subsequent memory and the neuronal overlapping between the two sequential learnings. The Teg-Tag transgenic mouse allowed to identify the neurons activated for the first learning experience. This animal has the GFP expression under control of c-fos promoter that is activated by neuronal activity. It was shown by patch clamp that GFP+ neurons are still more excitable two days after learning. Also, the identification of neurons recruited for the subsequent learning was made through immunofluorescent staining of the Fos protein in its peak of endogenous expression, ninety minutes after learning. A greater overlapping (GFP+, Fos+) was observed when animals were retrained in the same context two days after first training. An intermediate overlapping was observed when animals were conditioned in the context B and this expression was significantly higher when compared to animals that were not 10 retrained in either context. Additionally, it was shown that acquisition of the subsequent learning is mediated by metabotropic glutamate receptors (mGluRs) instead of NMDARs In the Chapter II it was investigated whether a remote memory, acquired forty days earlier, is still able to influence in the synaptic plasticity mechanisms recruited for the acquisition of the subsequent learning. Systems consolidation dynamics was considered in these experiments because memory retrieval of a remote memory depends on neocortical brain regions, it not requires hippocampal activity. It was confirmed that hippocampus is not necessary for remote memory retrieval, however at least one longitudinal division of the hippocampus (dorsal or ventral) is essential for learning following a prior remote memory. Moreover, the results indicate that acquisition of the second learning is once again mediated by NMDARs in the hippocampus when the interval between learnings is extended from three to forty days. Altogether, our results suggest that the first learning lead to an increase in the neuronal excitability and modify the synaptic plasticity mechanism recruited for following learning, mGluR are required instead of NMDAR. Furthermore, the metaplasticity induced by first conditioning is transient; the second learning once again requires NMDARs activation when the interval between learnings is longer.

Made available in DSpace on 2016-06-02T19:23:02Z (GMT). No. of bitstreams: 1 6369.pdf: 1124310 bytes, checksum: 0ca17967bc2f98ad5efcffdb78af91d5 (MD5) Previous issue date: 2014-05-09 / Universidade Federal de Minas Gerais / Empathy can be defined as the capacity for perceive emotional signals from others. Among these signals, the ability to perceive pain has clear adaptive and evolutionary value. Pain can be defined as a subjective experience that includes sensorial, emotional and cognitive components. Evidence has emphasized the role of amygdala, anterior cingulate cortex (ACC) and insula in modulation of pain and empathy. Research indicates the capacity of rodents to express empathy to a conspecific in pain or suffering. Works from literature and finds from our laboratory demonstrated that living together with a cagemate is able to alter the nociceptive behavior in mice. However, there are no works evidencing if occur alterations in nociception by living together with a cagemate with chronic pain and which encephalic structures would be involved in this modulation. To overcome this, male Swiss-albino mice were housed in groups or in pairs. The role of amygdala, ACC and insula are accessed by non-selective inactivation with cobalt chloride (CoCl2). Mice housed in groups (Experiment 1), aging 6-8 weeks, underwent a stereotaxic surgery. 4 to 5 days after surgery, these animals received saline or CoCl2 microinjection, and, after 10 minutes, they were submitted to the writhing test during 5 minutes (acetic acid 0.6%, i.p., nociceptive stimulus). On the dyads (Experiment 2), animals lived together for 28 days since weaning. On the 14th day, one animal of each pair were submitted to a sciatic nerve constriction (SNC animal) or not (sham animal). On the 24th day, the cagemate underwent a stereotaxic surgery, and, on the 28th day, they were submitted to the writhing test after microinjection of saline or CoCl2, like the procedure described to Experiment 1. To Experiment 1 were utilized Student s t test to independent samples; to Experiment 2 were utilized two-way analysis of variance (ANOVA; living together x treatment). Duncan s multiple range tests were utilized as post hoc. A p value of 0.05 or less was required for significance in both experiments. In Experiment 1, inactivation of the amygdala increased the number of writhing, while inactivation of ACC and insula did not alter this measure, suggesting a distinct modulatory role of these structures on the sensorial compound of pain. Our results demonstrated that for the mice that lived in groups, while inactivation of the ACC and insula did not change writhing, inactivation of amygdala increased it, suggesting a distinct modulatory role of these structures on sensory component of pain in the writhing test. In Experiment 2, living together with a SNC-cagemate increased writhing on the pair, suggesting that this experience activates the circuitry of neural representation of pain on the observer mouse (state of priming ). Thus, when this animal experienced nociception, its response was exacerbated. In this condition, inactivation of insula and amygdala produces opposite results, i.e., decreased and increased in contortions in those animals that lived together with a SNC animal, respectively. ACC inactivation did not alter writhing behavior. In this sense, our results suggest a different modulatory role of these structures on cognitive, affective-emotional and sensorial components of pain, and on empathy for pain. / Sob uma perspectiva evolucionista, a empatia é expressa pela capacidade de captar sinais emocionais nos outros. Neste sentido, a habilidade em perceber a dor também possui valor claramente adaptativo e evolutivo. A dor pode ser definida como uma experiência subjetiva que inclui componentes sensoriais, afetivo-emocionais e cognitivos. Evidencias apontam para o papel da amídala, córtex cingulado anterior (CCA) e insula na modulação da dor e da empatia. Estudos indicam para a capacidade de roedores em apresentarem empatia frente à dor ou ao sofrimento de seus coespecíficos. Trabalhos da literatura e do nosso grupo demonstram que a convivência em pares é capaz de alterar bidirecionalmente a resposta nociceptiva em camundongos. Entretanto, nenhum estudo havia ainda evidenciado se ocorrem alterações nociceptivas devido à convivência com um coespecífico em quadro de dor crônica, e quais estruturas encefálicas estariam envolvidas nessa modulação. Neste sentido, camundongos machos Suiço-albinos foram alojados em grupos ou em duplas para avaliação do papel da amídala, insula e córtex cingulado anterior por meio de inativação com cloreto de cobalto (CoCl2). Os animais alojados em grupo (Experimento 1), ao atingirem idade entre 6-8 semanas, passaram por cirurgia estereotáxica. De 4 à 5 dias após a cirurgia, esses animais receberam microinjeção de salina ou CoCl2 e, após 10 minutos, foram submetidos ao teste de contorções abdominais (ácido acético 0,6%, i.p., estímulo nociceptivo) durante 5 minutos. Nas duplas (Experimento 2), os animais conviveram por um período de 28 dias após o desmame. No 14º dia, um animal de cada par foi submetido à cirurgia de constrição do nervo ciático (animal CNC) ou não (animal sham). No 24º dia, o camundongo que conviveu com o animal CNC ou animal sham passou por uma cirurgia estereotáxica, e, no 28º dia, foi submetido ao teste de contorções abdominais, após microinjeção de salina ou CoCl2, conforme Experimento 1. Para o Experimento 1 foi utilizado o teste t de Student para amostras independentes; no Experimento 2 foi utilizada a análise de variância (ANOVA) de dois fatores (convívio x tratamento). O post hoc utilizado foi o teste de comparações múltiplas de Duncan. Os valores de p menores ou iguais a 0,05 foram considerados como significativos nos dois experimentos. No Experimento 1, a inativação da amídala aumentou o número de contorções, enquanto a inativação do CCA e da insula não alterou esse parâmetro, sugerindo um papel modulatório distinto dessas estruturas no componente sensorial da dor para o teste de contorções. No experimento 2, o convívio com um animal CNC aumentou o número de contorções no parceiro, sugerindo que essa convivência causou ativação dos circuitos de representatividade neural da dor no camundongo observador (state of priming ). Dessa forma, quando esse animal experiencia nocicepção, sua resposta é exacerbada. Nessa condição, a inativação da insula e amídala produziu resultados opostos, ou seja, diminuição e aumento das contorções naqueles animais que conviveram com o animal CNC, respectivamente. A inativação do CCA não alterou o número de contorções. Nesse sentido, nossos resultados sugerem um papel modulatório distinto dessas estruturas nos componentes cognitivo, afetivo-emocional e sensorial da dor, e na empatia para a dor.

A formação de memórias de medo contextuais, como as estudadas no presente trabalho, requer a indução da plasticidade sináptica iniciada pela ativação de receptores transmembrana localizados nos neurônios de estruturas encefálicas como o hipocampo. O fluxo iônico mediado pelos receptores N-metil-D-aspartato (NMDARs) é essencial para ativar vias de sinalização intracelular que darão suporte à formação da memória. No entanto, esses receptores parecem não ser necessários em situações onde os animais passaram por uma experiência prévia similar a que está sendo aprendida. Dessa forma, um aprendizado anterior pode modificar os mecanismos de plasticidade que serão utilizados para codificar uma nova informação, caracterizando um fenômeno de metaplasticidade. Esse fenômeno ocorre quando os animais são pré-expostos ao local onde posteriormente serão submetidos a um aprendizado associativo ou quando são re-submetidos a mesma tarefa comportamental com dicas contextuais/espaciais diferentes. No presente trabalho, investigamos (i) os mecanismos de plasticidade sináptica (receptores) e de plasticidade não-sináptica (excitabilidade neuronal) recrutados para a formação do segundo aprendizado e (ii) se a independência dos NMDARs é mantida quando a memória anterior foi adquirida remotamente. Os animais utilizados nesse trabalho (camundongos ou ratos) foram expostos a dois aprendizados sequenciais realizados na tarefa de condicionamento aversivo ao contexto (CAC). O intervalo entre os condicionamentos foi de dois dias nos experimentos do Capítulo I e de três ou quarenta dias nos experimentos do Capítulo II. Cada aprendizado ocorreu em uma caixa de condicionamento com características próprias de formato, odor e iluminação (contexto A ou contexto B), sendo que o primeiro aprendizado ocorreu no contexto A e o segundo no contexto B. Nos experimentos do Capítulo I foram avaliadas no hipocampo dorsal as modificações na excitabilidade neuronal hipocampal induzidas pelo primeiro condicionamento, bem como os receptores envolvidos com a aquisição da memória subsequente e a sobreposição neuronal entre os dois aprendizados. Com a utilização do camundongo transgênico Teg-Tag foi possível identificar os neurônios recrutados para o primeiro aprendizado. Esse animal tem a expressão da proteína fluorescente verde (GFP, do inglês, green fluorescent protein) controlada pela ativação do gene c-fos, que é fisiologicamente transcrito após a atividade neuronal. Dessa forma, os neurônios ativados pelo aprendizado são marcados com GFP. Através da técnica de patch clamp foi observado que os neurônios GFP+ mantiveram a excitabilidade elevada por até dois dias após o treinamento no CAC. Além disso, a identificação dos neurônios recrutados 8 para o aprendizado subsequente foi realizada através da marcação imunofluorescente da proteína Fos, no seu pico de expressão endógena, noventa minutos após o re-treino. Foi observada uma maior sobreposição neuronal (GFP+, Fos+) quando os animais foram retreinados no mesmo contexto dois dias após o primeiro treino. Uma sobreposição intermediária (GFP+, Fos+) foi vista quando os animais tiveram o segundo condicionamento no contexto B, sendo ela significativamente maior do que a sobreposição nos animais não re-treinados. Adicionalmente, foi demonstrado que a aquisição do aprendizado subsequente é mediada por receptores metabotrópicos glutamatérgicos (mGluRs) ao invés de NMDARs. No Capítulo II foi investigado se uma memória remota, adquirida há quarenta dias, ainda seria capaz de influenciar nos mecanismos de plasticidade recrutados para aquisição do aprendizado subsequente. A dinâmica da consolidação sistêmica foi considerada nesses experimentos já que a evocação da memória remota passa a depender de estruturas encefálicas neocorticais, sem recrutar a atividade hipocampal. Apesar da evocação da memória remota não requerer a atividade hipocampal, foi observado que a aquisição do aprendizado subsequente a uma memória remota necessita a atividade de pelo menos uma sub-região do hipocampo (dorsal ou ventral). Complementarmente, os resultados indicaram que, quando o intervalo entre os aprendizados é aumentado (de três para quarenta dias), a formação do aprendizado subsequente, que era independente de NMDARs, volta a depender da plasticidade sináptica mediada por esses receptores no hipocampo (dorsal e ventral). Juntos, nossos resultados sugerem que o primeiro aprendizado causa um aumento da excitabilidade neuronal e modifica a plasticidade sináptica recrutada para o aprendizado subsequente, sendo este último mediado por mGluRs ao invés de NMDARs. Além disso, a metaplasticidade induzida pelo primeiro condicionamento é transiente; quando o intervalo entre as exposições é aumentado, o segundo aprendizado passa a depender novamente da ativação dos NMDARs. / Contextual fear memory formation, like the ones explored in the current work, requires the induction of the synaptic plasticity mediated by the activation of transmembrane receptors that are present in the brain structures as the hippocampus. The ionic flux through the N-methylaspartate- D-aspartate is crucial for activation of the intracellular signaling pathways that will support memory formation. However, these receptors are not necessary when animals had a prior similar learning. In this way, a previous learning can modify the plasticity mechanism that will be recruited to encode a new information, featuring a metaplasticity phenomenon. This phenomenon occurs when animals are pre-exposed to an environment where they will learn an associative learning later or when animals are re-exposed to the same behavioral task with distinct contextual/spatial cues. In the present study, we investigated (i) the synaptic plasticity mechanisms (receptors) and the non-synaptic plasticity mechanisms (neuronal excitability) required for the acquisition of the second learning and (ii) whether a subsequent learning that occurs in a remote time-point is still NMDAR-independent. The animals used in this study (mice or rats) were exposed to two sequential learnings that were performed in the contextual fear conditioning (CFC). The interval between conditionings were two days in the experiments of Chapter I and three or forty days in the experiments of the Chapter II. Each learning was performed in a box with differences on shape, odor and illumination (context A or context B). The first learning occurred in the context A followed by learning on context B. In the experiments of Chapter I it was evaluated the changes in the hippocampal neuronal excitability induced by the first conditioning, the receptors involved with the acquisition of the subsequent memory and the neuronal overlapping between the two sequential learnings. The Teg-Tag transgenic mouse allowed to identify the neurons activated for the first learning experience. This animal has the GFP expression under control of c-fos promoter that is activated by neuronal activity. It was shown by patch clamp that GFP+ neurons are still more excitable two days after learning. Also, the identification of neurons recruited for the subsequent learning was made through immunofluorescent staining of the Fos protein in its peak of endogenous expression, ninety minutes after learning. A greater overlapping (GFP+, Fos+) was observed when animals were retrained in the same context two days after first training. An intermediate overlapping was observed when animals were conditioned in the context B and this expression was significantly higher when compared to animals that were not 10 retrained in either context. Additionally, it was shown that acquisition of the subsequent learning is mediated by metabotropic glutamate receptors (mGluRs) instead of NMDARs In the Chapter II it was investigated whether a remote memory, acquired forty days earlier, is still able to influence in the synaptic plasticity mechanisms recruited for the acquisition of the subsequent learning. Systems consolidation dynamics was considered in these experiments because memory retrieval of a remote memory depends on neocortical brain regions, it not requires hippocampal activity. It was confirmed that hippocampus is not necessary for remote memory retrieval, however at least one longitudinal division of the hippocampus (dorsal or ventral) is essential for learning following a prior remote memory. Moreover, the results indicate that acquisition of the second learning is once again mediated by NMDARs in the hippocampus when the interval between learnings is extended from three to forty days. Altogether, our results suggest that the first learning lead to an increase in the neuronal excitability and modify the synaptic plasticity mechanism recruited for following learning, mGluR are required instead of NMDAR. Furthermore, the metaplasticity induced by first conditioning is transient; the second learning once again requires NMDARs activation when the interval between learnings is longer.