水温对文昌鱼生殖活动的影响及其内分泌机制

采用慢性实验方法,研究在不同水温条件下饲养性腺发生前的文昌鱼(Branchiostoma belcheri)对其性腺分化和发育的影响。另外,在繁殖季节研究在低温16℃、中温22℃和高温28℃下饲养性成熟的文昌鱼对其产卵和排精的影响。同时,采用免疫组织化学方法对几种生殖相关激素在不同发育期文昌鱼的生殖调控轴(脑-哈氏窝-性腺)中的分布进行免疫识别,并用磁酶免定量测定方法检测睾酮和17 β-雌二醇在文昌鱼性腺中的含量,以分析和探讨水温影响文昌鱼生殖活动的内分泌机制。结果表明:低温有利于文昌鱼性腺向雌性分化,雌雄比例为4.2:1,中温和高温组则不受影响,雌雄数量大致相等。高水温则有利于文昌鱼的精巢发育和生精活动。28℃海水适于文昌鱼的产卵和排精。根据免疫组织化学和磁酶免定量测定的结果分析提示,温度影响文昌鱼性别分化和发育以及繁殖活动的内分泌机制是:首先水温经皮肤或哈氏窝化学感受器,刺激神经系统(脑泡)释放GnRH。然后GnRH促进哈氏窝分泌LH,从而可能刺激性腺产生和分泌性类固醇激素,始动文昌鱼性腺的发育至成熟及其生殖活动。此外,脑中芳香化酶可能介导文昌鱼性别分化。

Effects of seawater temperature on the reproductive activity of the amphioxus,Branchiostoma belcheri and its endocrine mechanism

Effects of different seawater temperature(low temperature group 16℃, middle temperature 22℃ and high temperature 28℃) on sex differentiation and gonadal development in the amphioxus Branchiostoma belcheri without gonads and on the spawning and spermiation activity in mature amphioxus Branchiostoma belcheri at the breeding season were studied using the chronic experiment method.The immunological recognition of several reproduction-related hormones in the reproductive endocrine regulation organ(namely, Brain-hatschek’s pit-gonad) of amphioxus at different development stages was studied by immunohistochemistry and the testosterone and 17β-estradiol contents in gonads of amphioxus were detected by magnetic enzyme immunoassay to assay and investigate the endocrine mechanism of the effects of seawater temperature on reproductive activity of amphioxus. The results indicated that low sea water temperature promoted gonadal differentiation and development towards female in amphioxus, and the ratio of female to male was 4.2:1. There were no differences in sex ratio in the middle temperature group and in the high temperature group, but high seawater temperature could promote testis development and spermatogenic activity. The high temperature 28℃ was suitable for the reproductive activity of amphioxus. At the same time, the endocrine mechanism of the influence of temperature on the sex differentiation, gonadal development and reproductive activity in amphioxus was suggested by the results of immunohistochemistry and magnetic enzyme immunoassay as followed: Firstly, the seawater temperature may stimulate GnRH release from nervous system (brain vesicle) via skin receptor or chemical receptor of Hatschek’s pit. Then, GnRH may promote LH secretion from Hatschek’s pit. Finally, LH may stimulate the formation and secretion of sex steroid hormones in the ovary and testis, and thus initiate gonad development and maturation as well as reproductive activity.In addition,aromatase in the brain may be involved in the sex differentiation of amphioxus.