In rats, the ejaculatory response and other behaviors linked to serotonin (5-HT) were tested after giving a serotonin-releasing drug (5-MeODMT) following treatment with various serotonin reuptake inhibitors (fluoxetine, zimeldine, alaproclate, citalopram). Acute doses of fluoxetine and zimeldine reduced the ejaculatory response when given 48 hours before 5-MeODMT, an effect blocked by a serotonin receptor antagonist. After 7 or 14 days, a single dose of fluoxetine enhanced the response, which returned to normal by day 24. Repeated fluoxetine treatment extended the blockade and delayed sensitization. Alaproclate and citalopram only blocked the response 1 hour after acute dosing. The findings indicate that different serotonin reuptake inhibitors do not uniformly alter serotonin receptor functions.
Repeated but not single treatment with the 5-HT agonist 5-MeODMT strongly but reversibly reduced the ejaculatory response and other behavioral responses in rats. Repeated treatment with nonselective, irreversible MAO inhibitors nialamide and pargyline markedly reduced the ejaculatory response but only slightly affected behavioral responses. Repeated treatment with MAO-B inhibitor (-)-deprenyl, MAO-A inhibitor clorgyline, reversible MAO-A inhibitor moclobemide, and low doses of PCA did not affect either response. Combined repeated treatment with clorgyline plus PCA caused an almost complete blockade of all responses. Selective, reversible MAO-A inhibitors amiflamine, alpha-ethyltryptamine, and alpha-methyltryptamine reduced the ejaculatory response after both single and repeated treatments, with behavioral responses blocked only after repeated treatment. The authors conclude that single and repeated treatments with different MAO inhibitors do not produce a common alteration in 5-HT2 receptor functions.