Role of serotonergic input in the down-regulation of beta-adrenoceptors following long-term clorgyline treatment.

Administration of the selective monoamine oxidase (MAO) type A-inhibiting antidepressant clorgyline (1 mg/kg per day) to rats for 21 days caused a significant decrease in cortical [3H]dihydroalprenolol binding. Selective lesioning of central serotonergic axons by 5,7-dihydroxytryptamine (5,7-DHT; confirmed by the presence of the serotonin syndrome in response to a 40 mg/kg dose of 5-hydroxytryptophan (5-HTP) or inhibition of 5-HT synthesis by parachlorophenylalanine (PCPA) caused significant 5-HT and 5-HIAA depletions in the cortex without much effect on NE and DA concentrations, but did not have any significant effect on beta-adrenoceptor density, and furthermore failed to attenuate clorgyline-induced decreases in beta-adrenoceptor density. Clorgyline treatment partially antagonized 5-HT depletion by the 5,7-DHT lesion or PCPA treatment. These findings suggest that due to their ability to raise 5-HT concentrations, MAO-inhibiting antidepressants may be a better alternative than the tricyclics in treating depressed patients with reduced 5-HT if down-regulation of beta-adrenoceptors is critical for antidepressant efficacy.