Electrophysiological activity of raphe dorsalis serotoninergic neurones in a possible model of endogenous depression.

It has been proposed that serotoninergic activity is impaired in endogenous depression. We tested this hypothesis in an experimental model, where rats which have been treated with clomipramine during the first month of life exhibit at adult age behavioural and sleep alterations which resemble the human disorder. Recording of serotoninergic neurones in the dorsal raphe nucleus revealed no modification of their spontaneous firing, but a reduced inhibitory response to the 5-HT re-uptake blocker citalopram in clomipramine-treated rats as compared to controls. This suggests that neonatal clomipramine treatment results in a long lasting desensitization of somatodendritic 5-HT1A autoreceptors, leading possibly to a dysregulation of 5-HT neurone activity in this proposed model of depression.