The effects of monoamine oxidase inhibitors on the ejaculatory response induced by 5-methoxy-N,N-dimethyltryptamine in the rat.

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.

Study at a glance

Abstract

The ejaculatory response and other components of the 5-hydroxytryptamine (5-HT) behavioural syndrome induced by 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) (3 mg kg-1, i.p.) were studied following single and repeated treatment of rats with eight different monoamine oxidase (MAO) inhibitors. Single and repeated treatment with the 5-HT agonist 5-MeODMT, and with low doses of the potent releaser of 5-HT, p-chloroamphetamine (PCA) were also included in the study. Repeated but not single treatment with 5-MeODMT reduced strongly but reversibly the ejaculatory response and the behavioural responses. Repeated but not single treatment with the nonselective and irreversible MAO inhibitors nialamide and pargyline reduced markedly the ejaculatory response but only slightly the 5-HT behavioural responses. Repeated treatment with the irreversible MAO-B inhibitor (-)-deprenyl, with the irreversible MAO-A inhibitor, clorgyline, with the reversible MAO-A inhibitor moclobemide, and with low doses of PCA did not affect either of the responses. Repeated but not single combined treatment with clorgyline plus PCA caused an almost complete blockade of all the four responses. The selective and reversible MAO-A inhibitors (as well as 5-HT releasers) amiflamine, alpha-ethyltryptamine, and alpha-methyltryptamine reduced markedly the ejaculatory response after both single and repeated treatments. The behavioural responses were blocked only after repeated treatment. It is concluded that single and repeated treatments of rats with different MAO inhibitors do not produce a common alteration in 5-HT2 receptor functions. Repeated treatment with 5-MeODMT caused a blockade of 75-95% of the ejaculatory response and 5-HT behavioural responses. A similar strong blockade was only produced by the combined effect of MAO-A inhibition and 5-HT release.