Effects of Blockade of D1 and D2 Receptors in the Basolateral Amygdala on the Behavior of Rats with High and Low Levels of Anxiety and Fear

Abstract

The effects of local bilateral administration of D1 or D2 receptor antagonists into the basolateral nucleus of the amygdala on anxiety behavior and the acquisition and extinction of conditioned reflex fear were studied in rats. Testing in the elevated plus maze identified groups of rats with high and low anxiety levels and assessment of the freezing duration after acquisition of conditioned reflex fear identified groups with low and high levels of freezing. Administration of a D1 receptor antagonist (SCH 23390, 1 μg/0.5 μl) decreased the signs of conditioned reflex fear in low-freezing rats in response to sound, accelerated its extinction, and degraded repeat learning in all animals. Administration of a D2 receptor antagonist (raclopride, 1 μg/0.5 μl) accelerated extinction of conditioned reflex fear to the experimental context in all rats and had weak anxiolytic actions in high-anxiety rats in the elevated plus maze. These data provide evidence for an important role for D1 receptors in the acquisition, manifestation, and extinction of conditioned reflex fear in response to the stimulus, while D2 receptors have an important role in the occurrence of anxiety states and fear in response to the context. Differences in the sensitivities to administration of dopamine receptor antagonists into the amygdala were seen in animals with different levels of anxiety and fear, which may be linked with differences in dopaminergic transmission.