RESUMO
This study investigated the increase in expression in the amygdala of 2 immediate-early genes, c-fos and NGFI-A, following contextual fear conditioning. The immediate-shock freezing deficit paradigm was used to compare rats that received footshock after exploring a context to rats that received footshock immediately after placement in the chamber. The former procedure produces contextual fear conditioning while the latter does not. Rats were either handled (handled group), placed in a test chamber without receiving footshock (context-no-footshock group), received footshock immediately upon being placed in the chamber (immediate-footshock group), or received footshock after a 1 min delay (delayed-footshock group). Only the delayed-footshock group displayed a fear response (freezing behavior). Rats were sacrificed either 15 min after the experience or after a retention test 24 h later. The c-fos mRNA was increased in the medial nucleus of the amygdala in all of the groups that were placed in the test chamber. However, rats that received footshock (immediate- and delayed-footshock groups) had greater levels of c-fos mRNA expression than rats of the context-no-footshock group. The c-fos mRNA expression in the immediate- and delayed-footshock groups did not differ. However, after the retention test, the expression of c-fos mRNA in the medial nucleus of the amygdala did not differ between groups. In contrast to c-fos, NGFI-A mRNA expression in the lateral nucleus of the amygdala was greater in the delayed-footshock group than the handled and context-no-footshock groups 15 min after the footshock. This elevation in NGFI-A mRNA was not seen in the immediate-footshock group. This suggests that NGFI-A mRNA in the lateral nucleus of the amygdala may play a role in contextual fear conditioning.
Assuntos
Tonsila do Cerebelo/fisiologia , Condicionamento Psicológico/fisiologia , Medo/fisiologia , Expressão Gênica/fisiologia , Genes Precoces/genética , Proteínas Imediatamente Precoces , Estresse Fisiológico/genética , Animais , Comportamento Animal/fisiologia , Proteínas de Ligação a DNA/genética , Proteína 1 de Resposta de Crescimento Precoce , Eletrochoque , Membro Posterior , Masculino , Proteínas Proto-Oncogênicas c-fos/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Endogâmicos , Retenção Psicológica/fisiologia , Fatores de Tempo , Fatores de Transcrição/genéticaRESUMO
The present study asked whether partial amygdala kindling would affect the expression of conditioned fear-potentiated startle. Rats were conditioned to be fearful of a light. They were then stimulated bilaterally in the amygdala or hippocampus on 2 consecutive days (partial kindling). Rats were tested 24 hr later for fear-potentiated startle. Amygdala-kindled rats had exaggerated fear-potentiated startle compared to sham-kindled rats. Hippocampus-kindled rats also displayed fear-potentiated startle, but no greater than that of sham-kindled rats. Partial amygdala kindling induced c-fos messenger RNA (mRNA) expression, a marker for neuronal activation, throughout the limbic and neocortices. In contrast, partial hippocampus kindling induced c-fos mRNA in the hippocampus only. The data suggest that kindled-induced hyperexcitability of the amygdala and limbic cortices produced exaggerated conditioned fear-potentiated startle.