Efeitos da desconexão funcional entre o estriado dorsal e a amígdala nas tarefas de condicionamento clássico de medo ao som e ao contexto

• Ano de defesa: 2008
• Autor(a) principal: Ferreira, Tatiana Lima [UNIFESP]
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de São Paulo (UNIFESP)
• Palavras-chave em Português: Condicionamento clássico; Amígdala; Aprendizagem; Gânglios da base; Memória
• Link de acesso: http://repositorio.unifesp.br/handle/11600/9394

The central nucleus of the amygdala (CeA) - a critical structure in emotional memory - projects to the substantia nigra pars compacta and retrorubral nucleus, both of which provide dopaminergic innervation to the dorsal striatum. Dorsal striatum is involved in several learning and memory processes, such as procedural memory, habit learning, reward-association and emotional memory. The purpose of the present study was to verify the effects of lesions in the dorsal striatum and in the indirect pathway between the CeA and dorsal striatum on tone and contextual fear conditioning tasks. In Phase 1, Wistar rats received pre-training bilateral lesions of the CeA and dorsal striatum, and pre-training asymmetrical CeA-dorsal striatum lesions that consist of an electrolytic lesion of the CeA in one cerebral hemisphere combined with a dorsal striatum lesion in the contralateral hemisphere, and were submitted to tone and contextual fear conditioning tasks. Pre-training CeA lesion impaired the performance of animals on both tasks. However, bilateral dorsal striatum lesion and the asymmetrical contralateral CeA-dorsal striatum lesion only disrupted the performance in the tone fear conditioning task. These results suggest that both the dorsal striatum and the indirect CeA-dorsal striatum pathways are important in mediating tone fear conditioning. In Phase 2, bilateral dorsal striatum lesions and asymmetrical CeA-dorsal striatum lesions were performed before the test (after training) of animals in the behavioral tasks. The results showed that animals with bilateral pre-test dorsal striatum lesions showed impairment in tone, but not in contextual fear conditioning tasks. ACTH plasma levels, measured after the behavioral tests, did not differ between lesioned and control animals. Asymmetrical contralateral CeA-dorsal striatum lesion carried out before the test did not impair the performance of animals in the tone fear conditioning task. The results observed in Phase 2 suggest that dorsal striatum is also involved in the expression of the conditioned fear response to tone, and that this involvement is selective to responses that present a somatomotor component, such as freezing response. However, the interaction between CeA and dorsal striatum is not important for the expression of this response. The main findings of the present work were confirmed by pre-training temporal inactivation of the dorsal striatum and the indirect CeA-dorsal striatum pathway in tone fear conditioning (Phase 3). The last experiment of this phase showed that the temporal inactivation of CeA-dorsal striatum, immediately after training, did not impair the behavioral performance of animals in the tone fear xxi conditioning task. These results indicate that the CeA-dorsal striatum pathway is important for the acquisition, but not for the consolidation of this task. On the other hand, the dorsal striatum is involved in the acquisition/consolidation and expression of tone fear conditioning. The present results suggest, for the first time, that an indirect CeA-dorsal striatum pathway is involved in the acquisition of tone fear conditioning, implying that a forebrain structure – the dorsal striatum - mediates a somatomotor conditioned response to an explicit stimulus. Moreover, these results corroborate previous studies showing that tone and contextual fear conditioning are mediated by distinct anatomical pathway.