DECREASED RAPHE UNIT-ACTIVITY IN A RAT MODEL OF ENDOGENOUS-DEPRESSION

One theory about the pathogenesis of endogenous depression is that dec reased serotonergic (5-HT) neurotransmission is involved in producing the disorder. A key component of brain 5-HT neurotransmission is the d ischarge rate of 5-HT neurons in the dorsal raphe nucleus (DRN), a maj or aggregation of 5-HT neurons. We tested the hypothesis that the disc harge rate of 5-HT neurons in the DRN was decreased in a new animal (r at) model of human endogenous depression. In this model, rats are trea ted neonatally with the antidepressant chlorimipramine. When adult, th ese animals exhibit several behavioral, REM sleep, and treatment respo nse features of the human disorder. We found in single unit measuremen ts in adult, pentobarbital-anesthetized rats that, compared with 'non- depressed' control rats, the 'depressed' rats had a lower discharge ra te of 5-HT neurons in the DRN. This correlation is consistent with the theory that 5-HT neurotransmission is diminished in endogenous depres sion.