Dopaminergic mechanisms underlying involvement of the prefrontal cortex and amygdala in acoustique startle modificftion during the action of stimulus associated with positive reinforcement

Abstract

We studied the neurochemical mechanisms underlying the action of the conditioned stimulus associated with positive reinforcement on the amplitude of the acoustic startle response (ASR). To this aim, we injected a blocker of dopamine D2 receptors, sulpiride, into the rat medial prefrontal cortex or basolateral amygdala during the repeated procedure of ASR habituation. We have shown that, after the injection of saline to control rats into both the prefrontal cortex and amygdala, the change in ASR amplitude after an increase in illumination depends on the preliminary learning of a behavioral skill associated with a conditioned light signal. We found that if an acoustic signal appeared immediately after the change in the illumination the blockage of D2 dopamine receptors in the medial prefrontal cortex induced an increase in ASR amplitude. This disturbed the habituation of animals that were preliminarily subjected to associative training before this procedure. The injection of sulpiride into the basolateral amygdala during the increase in illumination did not affect the dynamics of ASR amplitude. This effect of the drug did not depend on the preliminary acquirement of positive conditioning to light. Our data suggest that D2 dopamine receptors of the medial prefrontal cortex, but not the basolateral amygdala, are involved in the reproduction of previously acquired skills associated with positive reinforcement under conditions of current defensive behavior.