Changes in hypothalamic monoamine oxidase activity in relation to 17 beta-estradiol and clomiphene citrate treatments in the teleost Channa punctatus during three seasons.

Hypothalamic monoamine oxidase (MAO) activity displayed biphasic responses to administration of estradiol-17 beta (E2) depending on season. Lower doses of 0.05 and 0.10 microgram/g BW of E2 had enhanced enzyme activity and higher doses (0.5 and 1.0 microgram/g BW) depressed it significantly in preparatory season. In prespawning phase, the lowest dose of 0.05 microgram/g BW of E2 was stimulatory and the higher doses were inhibitory to MAO activity. In postspawning season, lower doses (0.05 and 0.10 microgram/g BW) of E2 failed to elicit any significant change in enzyme activity whereas the higher doses (0.5 and 1.0 microgram/g BW) elevated it significantly. Administration of clomid (5, 10, and 20 micrograms/g BW) inhibited MAO activity in a dose-dependent manner during all the three seasons. The results show that E2 may participate in feedback control of gonadotropin secretion by modifying monoaminergic activity at the level of oxidative deamination by MAO.