The effects of chronic imipramine and electroconvulsive shock alone or combined were assessed on rat brain beta-adrenoceptors and serotonin2 (5-HT2) receptors and on dynorphin and thyrotropin releasing hormone (TRH) levels. These treatments resulted in regionally discrete and treatment-specific patterns of change in beta-adrenoceptor and 5-HT2 receptor density and in TRH and dynorphin levels. Electroconvulsive shock eliminated the serotonergic component of hippocampal DHA binding, suggesting an effect of this treatment on 5-HT1 receptors. The effects of combined electroconvulsive shock and imipramine treatments on cortical 5-HT2 and beta-adrenoceptor density appeared to be the additive sum of the individual treatment effects. No treatment interaction was observed on hippocampal 5-HT2 and beta-adrenoceptors, except after day 2. No treatment interaction on peptide content was observed at any time. These results demonstrate independent anatomical specificity for the effects of electroconvulsive shock and imipramine and provide evidence that the mechanisms responsible for their antidepressant actions differ.