Effects of Administration of an Agonist and an Antagonist of GABAA Receptors into the Basolateral Nucleus of the Amygdala on the Expression and Extinction of Fear in Rats with Different Freezing Durations

Abstract

Rats were divided into groups expressing small and large amounts of freezing on the basis of differences in freezing duration after acquisition of conditioned reflex fear. The effects of local bilateral administration into the basolateral nucleus of the amygdala of a GABAA receptor agonist (muscimol, 0.1 μg/0.5 μl), antagonist (bicuculline, 0.07 μg/0.5 μl), and physiological saline (0.5 μl, controls) on the expression and extinction of conditioned reflex fear in these two groups of rats were studied. Administration of muscimol before testing for conditioned reflex fear led to a decrease in freezing duration, with a greater effect on the expression of fear in rats with a low freezing level. Administration of bicuculline increased aggressivity in the rats, decreased freezing duration, and led to the expression of elements of panic behavior, with greater effects in animals with high levels of freezing. Administration of both muscimol and bicuculline into the amygdala before extinction sessions led to acceleration of the extinction of fear in rats with high levels of freezing but had no effect in animals with a low level of freezing. These result provide evidence that the GABAA receptor agonist and antagonist have different effects in animals with different levels of fear, suggesting differences in the receptor apparatus in relation to GABAergic transmission in the amygdala.