PARALLEL CHANGES IN DOPAMINE-D-2 RECEPTOR-BINDING IN LIMBIC FOREBRAIN ASSOCIATED WITH CHRONIC MILD STRESS-INDUCED ANHEDONIA AND ITS REVERSAL BY IMIPRAMINE

Chronic sequential exposure to a variety of mild stressors has previously been found to cause an antidepressant-reversible decrease in the consumption of palatable sweet solutions, associated with abnormalities of dopaminergic neurotransmission in the nucleus accumbens. In the present study, 5 weeks of treatment with imipramine (10 mg/kg b.i.d.) reversed the decreased sucrose intake of rats exposed to chronic mild stress. Stress also caused a decrease in D-2-receptor binding in the limbic forebrain (but not the striatum), which was completely reversed by imipramine. In nonstressed animals, imipramine decreased D-1-receptor binding in both regions. However, in stressed animals, imipramine did not significantly alter D-1-receptor binding in either area. Stress alone slightly increased D-1-receptor binding, in striatum only. Scatchard analysis showed that all changes in receptor binding resulted from changes in receptor number (B-max) rather than receptor affinity (K-D). The results support the hypothesis that changes in D-2-receptor function in the nucleus accumbens are responsible for chronic mild stress-induced anhedonia and its reversal by antidepressant drugs. They do not support the hypothesis that the sensitization of D-2-receptors seen following chronic antidepressant treatment is caused by a down-regulation of D-1-receptors.