Changes in hypothalamic catecholamine levels in relation to season, ovariectomy, and 17 beta-estradiol replacement in the catfish, Clarias batrachus (L.).

In female Clarias batrachus, hypothalamic levels of noradrenaline (NA) and dopamine (DA) exhibited seasonal changes during different phases of the annual reproductive cycle. The NA level was high during gonadal recrudescence (prespawning and spawning phases) and low during gonadal quiescence (postspawning and resting phases). A reverse trend was noticed in the DA level. After 3 weeks of ovariectomy (Ovx), the catecholamine (CA) levels were elevated significantly in the preparatory, prespawning, and spawning phases and were unaltered in the postspawning season. Administration of 17 beta-estradiol (E2, 1.0 microgram/g BW) to 3-week Ovx fish resulted in both seasonal and differential effects on the CA levels. The NA level was significantly elevated in the preparatory phase, decreased in the prespawning and spawning phases, and remained unaltered in the postspawning season. The DA level was restored by the steroid treatment in the preparatory phase, but registered a significant elevation in the prespawning and spawning phases. In the prespawning phase, Ovx induced a significant elevation of the hypothalamic NA level after 2, 3, and 4 weeks, but was significantly low after 5 weeks. The DA level registered a significant increase after 2, 3, and 5 weeks of Ovx. Administration of E2 to 3-week Ovx fish elicited dose-dependent responses on CA levels. The administration of a low dose of E2 (0.05 microgram) caused a significant elevation of the NA level, while the 0.1 microgram dose did not alter the amine level in comparison to that of the Ovx vehicle group. The higher doses (0.5 and 1.0 microgram) of E2, however, decreased the NA level significantly below that of the sham vehicle and Ovx vehicle groups.(ABSTRACT TRUNCATED AT 250 WORDS)