Effects of a chronic administration of the new antidepressant pirlindole on biogenic amine receptors in rat prefrontal cortex and hippocampus. Comparison with desipramine, nomifensine and zimelidine.

Chronic effects of the new antidepressant pirlindole on adrenergic and 5-HT2-receptors in rat prefrontal cortex and hippocampus were investigated in comparison to desipramine, nomifensine and zimelidine. The effects of pirlindole could be clearly distinguished from those of the monoamine reuptake blockers: chronic administration (20 days) of pirlindole (10 mg/kg per day, p.o.) increased prefrontal cortical alpha 2-receptor numbers and did not affect alpha 1-, beta-, and 5-HT2-receptor numbers. In hippocampus its action caused significant increases in alpha 1- and alpha 2-adrenoceptor densities. Administration of the monoamine reuptake blockers desipramine, nomifensine and zimelidine (10 mg/kg per day, p.o.) for 20 days mainly induced reductions of central adrenergic and 5-HT2-receptor numbers. Type-specific increases in monoamine receptor affinities were induced by the four antidepressants investigated, an effect not consistently described in other studies. The results on monoamine receptor numbers and the type specific increases in receptor affinities help to understand the contradiction in binding data versus physiological and behavioural findings.