| Quail is an excellent model for studying the mechanisms of seasonal reproductive regulation in birds,whose reproductive activity is tightly regulated by photoperiod.Photoperiod affects avian reproductive activity by influencing the metabolism of hypothalamic neurotransmitters and serum steroid hormones.There is still unclear explanation for the relationship between steroid hormones and neurotransmitters under different photoperiods.We measured the metabolic changes of 27 neurotransmitters in hypothalamic tissues and 42 steroid hormones in serum of quail under different photoperiodic conditions,in order to reveal the changes of neurotransmitters and steroid hormones and their correlation,and to provide a scientific basis for perfecting the theory of reproductive regulation in birds.In this experiment,quails were divided into two groups.The L-to-S group was kept under a light program of 20L:4D for 4 weeks and then changed to 6L:18D.The Sto-L group was kept under a light program of 6L:18D for 4 weeks and then changed to20L:4D.Hypothalamus,blood and testis samples were collected.Hypothalamus was used for neurotransmitter content determination and expression level of related genes;blood was used for steroid content determination;testis was used for HE sections and expression level of steroid related genes.The results show that photoperiod affects testicular development and spermatogenesis.Long light induced the initiation of reproductive activity and short light induced the degradation of reproductive activity in quail.The results of histomorphological changes in the testes showed that different photoperiods could affect the size and function of the testes,with the L-to-S group showing a significant decrease in testis weight,cross-sectional area and thickness of the seminiferous tubules(P < 0.05)and gradual degeneration of the sertoli cells and leydig cells;S-to-L showed the opposite results,with a significant increase in testis weight,cross-sectional area of the convoluted seminiferous tubules,a significant increase in convoluted seminiferous tubules.S-to-L group showed a significant increase in testicular weight,cross-sectional area of the the convoluted seminiferous tubules,a significant increase in the thickness of the the seminiferous tubules(P < 0.05),progressive development of spermatogonia,the presence of spermatozoa,sertoli cells and spermatogenic cells within the seminiferous tubules,and the presence of interstitial cells around the seminiferous tubules.Furthermore,photoperiod affects the levels of hypothalamic neurotransmitters and serum steroid hormone concentrations.In the L-to-S group,serum levels of testosterone concentrations decreased significantly(P < 0.001)and 11-dehydrocorticosterone increased significantly(P < 0.05);the levels of testosterone decreased continuously and were almost undetectable at SD＿14d.In addition,the concentrations arginine and γ-aminobutyric acid in hypothalamic tissue increased significantly,while 5-hydroxytryptamine and adrenaline levels decreased significantly(P < 0.01 or P < 0.05).In the S-to-L group,serum testosterone and serum androstenedione levels increased,were detectable at LD＿3d and increased significantly at LD＿7d.At the same time,serum androstenedione increased significantly with increasing light duration(P < 0.01);in addition,hypothalamic concentrations of Ltryptophan and phenylalanine increased significantly,as well as L-glutamine and Lglutamic acid levels decreased(P < 0.01 or P < 0.05).The metabolic changes of 5-hydroxytryptamine showed significant differences between the L-to-S group and the Sto-L group.Furthermore,the correlation between serum steroids and neurotransmitters was significantly different under different photoperiods.In the correlation analysis,the results of L-to-S group showed that serum testosterone was positively correlated with5-hydroxyindoleacetic acid,while androstenedione was significantly negatively correlated with L-tryptophan(P < 0.05).However,in the S-to-L group,serum testosterone showed a strong negative correlation with hypothalamic 5-hydroxytryptamine and 5-hydroxyindoleacetic acid(P < 0.05)and a positive correlation with L-tryptophan(P < 0.01),whereas androstenedione showed a significant negative correlation with both 5-hydroxytryptamine(P < 0.05)and L-glutamine(P < 0.01).Photoperiod influenced the expression pattern of genes related to the steroidogenic pathway in the testis and the neurotransmitter metabolic pathway in the hypothalamus.The m RNA levels of MAOB,NR5A1 and 3β-HSD showed opposite expression trends between the two groups.Taken together,the results revealed that quail circulating gonadal steroids and hypothalamic neurotransmitters were significantly impact quail’s seasonal reproduction.Circulating gonadal steroids have different effects on neurotransmitter at different photoperiodism,which may coordinately influence the seasonal reproduction of quail. |
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