Effects of Decreases in Dopamine (D1 and D2) Receptor Expression in the Basolateral Amygdala of Rats on Conditioned Defensive Reflexes

Abstract

RNA interference studies using lentivirus transduction were performed to investigate the effects of decreased expression of dopamine receptors (D1R and D2R) in the basolateral nucleus of the amygdala on the acquisition and extinction of conditioned defensive reflexes in rats. Immunohistochemical staining showed that transduction affected both neurons (mean 19%) and astrocytes (73%). As compared with controls, rats with decreased D1R expression showed degraded acquisition and facilitated extinction of a conditioned defensive reflex to sound, with acceleration of extinction of a passive avoidance reflex, and slowing of learning to seek a hidden platform in the Morris water maze by 1–2 days. In conditioned reflex fear, the behavior of rats with prolonged freezing changed more than that of rats with short periods of freezing when D1R expression in the amygdala was decreased. In rats with decreased D2R expression, extinction of the classical defensive reflex and the passive avoidance reflex was quicker. These results provide evidence of differences in the roles of D1R and D2R in the amygdala – functioning of D1R, in contrast to D2R, is important for acquisition of defensive refl exes and the manifestation of conditioned refl ex fear in the form of prolonged freezing. The activity of both D2R and D1R is significant for the resistance of reflexes to extinction.