Annual and diurnal variations in, and effects of altered photoperiod and temperature, ovariectomy, and estradiol-17 beta replacement on catechol-O-methyltransferase level in brain regions of the catfish, Heteropneustes fossilis.

The annual data show that catechol-O-methyltransferase (COMT) content increases with the progress of ovarian recrudescence in all the brain regions (telencephalon, hypothalamus, thalamus + tegmentum, and medulla oblongata) and declines after spawning to low values in quiescent phase. Diurnal variation in enzyme concentration with peak values at 24 hr was noticed in the hypothalamus throughout the reproductive cycle; in other brain regions, it was observed only in February and March. The stimulatory response of the enzyme to photoperiod and temperature alterations was differential and region-specific; an effect of photoperiod change was noticed only in the hypothalamus and was less in magnitude compared to the temperature effect. The response of the enzyme to ovariectomy (OVX) and E2 supplementation was region-specific (hypothalamus only), season-specific (prespawning phase), and varied:inhibitory at 3 and 4 weeks, stimulatory at 6-week of OVX and after 0.05, 0.1, 5, and 10 micrograms/g doses of E2, and none at week 2 and 5 of OVX and after 0.5 and 1 microgram/g doses of E2. The season-specific changes in hypothalamic COMT may be indicative of its involvement in catecholamine (and possibly catecholestrogen)-mediated neuroendocrine control of gonadotropin.