Chaube R, Joy K P
Department of Zoology, Banaras Hindu University, Varanasi-221005, India.
J Exp Zool. 2002 Nov 1;293(6):585-93. doi: 10.1002/jez.10185.
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.
将雌性胡子鲶（Heteropneustes fossilis）暴露于为期30天的长光照周期（16小时光照）、高温（28±2摄氏度）或两者结合的环境中，与处于性腺静止期（10.5小时光照：13.5小时黑暗，10±2摄氏度）和准备期（12.5小时光照：11.5小时黑暗，18±2摄氏度）自然条件下的对照鱼相比，显著刺激了其脑酪氨酸羟化酶（TH）的活性。在两个阶段中，联合组的反应都很高。前脑区域（端脑和下丘脑）TH活性的增加高于延髓。无论温度如何，将鱼暴露于短光照周期（8小时光照：16小时黑暗）和完全黑暗环境中，在静止期和准备期均显著降低了酶活性。在完全黑暗环境中的鱼抑制作用很强。性腺体指数（GSI）在长光照周期和高温组单独或联合作用下显著升高，而在短光照周期（仅在准备期）和完全黑暗组中显著降低。给予血清素前体5-羟色氨酸（5-HTP；5毫克/100克体重[BW]，在处死前每日腹腔内[i.p.]注射三次）刺激了处于长光照周期和正常光照周期两个阶段的鱼的TH活性。在处死前每日注射三次血清素阻断剂对氯苯丙氨酸（p-CPA；10毫克/100克BW）和褪黑素（75微克/100克BW）在两个阶段均显著抑制了脑TH活性。GSI受到5-HTP的显著刺激，并受到p-CPA和褪黑素注射的抑制。TH活性和GSI的变化可以根据先前关于调节鲶鱼促性腺激素分泌的儿茶酚胺活性变化的报道进行关联和解释。此外，光照周期和温度诱导的TH活性变化可能受到血清素能活性改变的调节。
