FOOTSHOCK STRESS BUT NOT CONTEXTUAL FEAR CONDITIONING INDUCES LONG-TERM ENHANCEMENT OF AUDITORY-EVOKED POTENTIALS IN THE BASOLATERAL AMYGDALA OF THE FREELY BEHAVING RAT

In this study, rats were bilaterally implanted with electrodes in the amygdala for chronic recording. Auditory click stimulation evoked in t he basolateral nucleus a field potential characterized by three positi ve components: P1, P2 and P3 (peak latencies around: 10, 20 and 30 ms, respectively) which were each followed by three negative components: N1, N2 and N3 (peak latencies around: 13, 30 and 50 ms, respectively). Animals were divided into three groups (context-same, context-differe nt and control). Following footshock administration, animals were eith er re-exposed to the same conditioning chamber (context-same group) or placed in a different context (context-different group) for electroph ysiological and behavioural (evaluation of freezing response) recordin gs. The two early positive-negative complexes (P1-N1 and P2-N2) increa sed in amplitude from 2 min to 24 h following footshock in both contex t-same and context-different groups. No significant difference was obs erved between these two groups. The demonstration of significantly lar ger freezing responses in context-same subjects on exposure to the ave rsive conditioned environment indicated that this similarity of effect s was not due to lack of conditioning of context under the experimenta l conditions chosen. We conclude that footshock stress produces genera l long-lasting changes in amygdala auditory field potentials that are not significantly affected by contextual fear conditioning.