Effects of altered photoperiod and temperature, serotonin‐affecting drugs, and melatonin on brain tyrosine hydroxylase activity in female catfish, Heteropneustes fossilis: A study correlating ovarian activity changes

Abstract

Exposure of female catfish, Heteropneustes fossilis to 30-day regimes of long photoperiod (16L), elevated temperature (28 +/- 2 degrees C), or a combination of both stimulated brain tyrosine hydroxylase (TH) activity significantly over that of control fish held in natural conditions in gonad resting (10.5L:13.5D, 10 +/- 2 degrees C) and preparatory (12.5L:11.5D,18 +/- 2 degrees C) phases. The response was high in the combination group in both phases. The increase in TH activity was higher in forebrain regions (telencephalon and hypothalamus) than medulla oblongata. Exposure of the fish to short photoperiod (8L:16D) and total darkness decreased the enzyme activity significantly in both resting and preparatory phases regardless of the temperature. The inhibition was high in fish held under total darkness. Gonadosomatic index (GSI) was significantly elevated in long photoperiod and high temperature groups, alone or in combination, and decreased significantly in short photoperiod (only in preparatory phase) and total darkness groups. Administration of the serotonin precursor 5-hydroxytryptophan (5-HTP; 5mg/100g body weight [BW], three daily intraperitoneal [i.p.] injections prior to sacrificing) stimulated TH activity in fish held under long and normal photoperiods in both phases. Three daily injections of the serotonin blocker parachlorophenylalanine (p-CPA; 10mg/100g BW) and melatonin (75 microg/100g BW) prior to sacrificing inhibited brain TH activity significantly in both phases. GSI was significantly stimulated by 5-HTP, and inhibited by both p-CPA and melatonin injections. Changes in TH activity and GSI can be correlated and explained on the basis of previous reports on changes in catecholamine activity that modulates gonadotropin secretion in the catfish. Further, the photoperiod and temperature-induced changes in TH activity may be modulated by alterations in serotonergic activity.

Role of photoperiod and melatonin in the regulation of ovarian functions in Indian carp Catla catla: basic information for future application

“…Similar attempts have been made in several fish species in low latitudes but experimental studies are mostly limited to different air-breathing fish such as Heteropneustes fossilis Sundararaj and Vasal 1976;Chaube and Joy 2002), Mystus tengara (Guraya et al 1976), Channa punctatus (Garg and Jain 1985;Joy and Khan 1991;Singh 1992, 1993), and Clarias batrachus (Singh and Joy 1998;Acharia et al 2000), as it is easy to keep them under laboratory conditions for experimentation. However, no data were available for any non-air-breathing subtropical fish to compare the photoperiodic mechanisms with the air-breathing species.…”

Neuroendocrine control by dopamine of teleost reproduction

“…Melatonin effects on the enzymatic activity of TH have been investigated in female H. fossilis in relation to its reproductive cycle. In this species, melatonin inhibited TH enzymatic activity in the telencephalon, hypothalamus and in the medulla oblongata during both resting and preparatory phases (Chaube & Joy, 2002 b ). Because central catecholamine levels fluctuate seasonally in this species, Chaube & Joy (2002 b ) hypothesized that catecholamine modulation resulting from TH changes partly explains the mechanism whereby environmental factors regulated the gonadotrophic axis.…”

Estradiol-17β modulates dose-dependently hypothalamic tyrosine hydroxylase activity inhibited by α-methylparatyrosine in the catfish Heteropneustes fossilis

“…Alpha-MPT competes for the substrate and co-factor [36], and the apparent K m values for the enzyme varied with season and brain regions [27]. During the ovariectomy-induced enzyme inhibition, the kinetics parameters varied significantly; K m values for both the substrate and cofactor, and V max altered differentially [25,27]. These workers have shown further that a-MPT increased the apparent K m value of the substrate several folds, suggesting perhaps a decrease in the binding (affinity) of the enzyme towards the substrate and/or cofactor.…”

“…Tyrosine hydroxylase (TH) which catalyses the hydroxylation of L-tyrosine to L-DOPA is considered the rate-limiting enzyme in CA biosynthesis [24]. It has been shown in the catfish that TH activity varies in relation to season, and is influenced by changes in environmental photoperiod, temperature or circulating titre of E 2 [25][26][27].…”