Distribution of dopamine D2-like receptors in the rat amygdala and their role in the modulation of unconditioned fear and anxiety

Amygdaloid dopamine D2 receptors play an important role in the modulation of fear/anxiety. Their topographical distribution within the amygdala is however unclear, and their role in unconditioned fear/anxiety remains largely unknown. The aim of this paper was to study the intra-amygdaloid distribution of D2 receptors and to ascertain their role in unconditioned anxiety. Chemical anatomical studies in the rat, using D2 and D3in situ hybridization, quantitative receptor autoradiography with either [3H]raclopride or [125I]sulpiride, and D2-like immunocytochemistry showed that the highest density of dopamine D2 receptors is present in the central amygdaloid nucleus, particularly within its latero-capsular division, in which a D2 but not a D3 mRNA signal was observed. However, although at considerably reduced densities dopamine D2 receptors were also found in other locations within the amygdala, including the basolateral nucleus. Behaviorally, the infusion of raclopride (0.75–4 μg/side) in the area of the central amygdaloid nucleus resulted at low doses in the appearance of anxiogenic-like effects in the Shock-Probe Burying test, whereas no effects of raclopride treatment were found at any dose in the Elevated Plus-Maze and the Open-Field test. Our results indicate that amygdaloid dopamine D2-like receptors have a topographically differentiated distribution within the rat amygdala, the major location being in the central amygdaloid nucleus. D2-like receptors play a role in the modulation of anxiety responses involving a potential differential function of D2-like receptors in the central amygdaloid nucleus versus the basolateral amygdaloid nucleus.

▶D2-like receptors within the rat amygdala are mostly restricted to the CeLC. ▶Raclopride infused in the CeA produces anxiogenic effects in defensive burying. ▶A potential differential function of D2-like receptors in the CeA vs. the BLA.