Abstract:

Seasonal reproduction is a strategy for mammals to adapt to environmental changes. Daurian ground squirrel (Spermophilus dauricus) is a hibernating species and a typical seasonal breeder that mates and reproduces only once a year after emerging from hibernation in the wild. Under laboratory conditions, the artificial mating and breeding technology after hibernation is still immature, and this species has not yet been domesticated as a laboratory animal. Vitamin A (VA) can be metabolized into retinoic acid (RA) within mammalian organisms. Recent research has revealed that RA promotes the differentiation of spermatogonia, the meiotic division of spermatocytes, and the transformation of round spermatids into mature spermatozoa. To explore whether VA from food, after digestion and absorption, can be metabolized into RA in the body of Daurian ground squirrel and affect the gonads, this study divided male Daurian ground squirrels into three groups, which were fed with food containing different levels of VA throughout the year. Group 1VA was fed with food containing the standard amount of vitamin A (17 500 IU/kg), Group 2VA was fed with food containing twice the amount of vitamin A (35 000 IU/kg), and Group 0VA was fed with food without added vitamin A. At the end of hibernation, samples were taken to determine the morphological and histological indicators of the testis and epididymis, and to detect the differentiation of spermatogonia in the testes, as well as the levels of VA, RA, gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (T) in the serum. The results showed that the levels of VA, RA, GnRH, LH, FSH, T in the serum, as well as the expression levels of retinoic acid gene 8 (Stra8) and meioticrecombination protein 8 (Rec8) in the testes of Spermophilus dauricus in Group 2VA and Group 1VA, were significantly higher than those in Group 0VA. However, there were no significant differences in the aforementioned indicators between Group 2VA and Group 1VA. This indicates that vitamin A can be metabolized into retinoic acid in the body of Daurian ground squirrel, promoting the development of gonads and spermatogenesis in male Daurian ground squirrels during seasonal reproduction. Adding an excessive amount of VA in the food has no significant effect on the gonads of male Daurian ground squirrels, but removing VA from the food does inhibit the differentiation of spermatogonia and the occurrence of sperm. This suggests that vitamin A in food is very important for the successful reproduction of Daurian ground squirrels under artificial breeding conditions.

Key words: Vitamin A, Retinoic acid, Daurian ground squirrel (Spermophilus dauricus), Testis

摘要：

季节性繁殖是哺乳动物适应环境变化的一种策略，冬眠动物达乌尔黄鼠（Spermophilus dauricus）是典型的季节性繁殖动物，野外条件下每年只在春季出眠后交配繁殖一次。实验室条件下冬眠后人工配对繁殖技术还不成熟，该物种至今尚未实验动物化。维生素A（vitamin，VA）可以在哺乳动物体内代谢成维甲酸（retinoic acid，RA），近年来的研究发现RA可以促进精原细胞分化，精母细胞减数分裂以及圆形精子细胞变形为成熟精子。为了探究食物中的VA经消化吸收后是否可以在达乌尔黄鼠体内代谢成RA并对性腺产生影响，本研究将雄性达乌尔黄鼠分为三组，全年分别喂养不同VA含量的饲料：1VA组饲喂标准含量维生素A（17 500 IU/kg）的饲料；2VA组饲喂2倍含量维生素A（35 000 IU/kg）的饲料；0VA组饲喂0添加维生素A的饲料。在冬眠末期取材测定睾丸和附睾的表型特征与组织结构，检测睾丸中精原细胞分化的情况以及血清中的VA、RA、促性腺激素释放激素（gonadotropin-releasing hormone，GnRH）、黄体生成素（luteinizing hormone，LH）、卵泡刺激素（follicle-stimulating hormone，FSH）和睾酮（testosterone，T）水平。结果显示2VA组和1VA组达乌尔黄鼠血清的VA、RA、GnRH、LH、FSH、T以及睾丸内生殖细胞视黄酸响应基因8（Stra8）和减数分裂重组基因8（Rec8）表达量均显著高于0VA组，但2VA组与1VA组达乌尔黄鼠体内的上述指标无显著差异。表明VA可以在达乌尔黄鼠体内代谢成RA，促进季节性繁殖雄性达乌尔黄鼠的性腺发育和精子发生。在饲料中添加过量VA对雄性达乌尔黄鼠的性腺无显著影响，但是饲料中去除VA会抑制精原细胞分化和精子发生。提示在人工饲养条件下食物中维生素A对达乌尔黄鼠的成功繁殖非常重要。

关键词: 维生素A, 维甲酸, 达乌尔黄鼠, 睾丸