Effects of melatonin on testicular function in adult male mice under different photoperiods

Abstract

Photoperiod is an important environmental factor affecting animal physiological function. Melatonin is an endogenous hormone that plays an important role in circadian and seasonal (or cyclical) rhythms and seasonal reproduction in mammals. To investigate the effects of melatonin on the reproductive performance of adult male mice under different photoperiods, sixty mice were randomly allotted to six groups: control (Light Dark, 12 L:12 D), control plus melatonin (MLD, 12 L:12 D), 24-hour continuous light (LL, 24 L:0 D), 24-hour continuous light plus melatonin (MLL 24 L:0 D), constant darkness (DD, 0 L:24 D), and constant darkness plus melatonin (MDD, 0 L:24 D). Normal saline (100 μL) was injected into the LD, LL, and DD groups at noon each day; the MLD, MLL, and MDD groups were injected with melatonin (1 mg/mL; 2 mg/kg·body weigh). After 24 hours of prolonged light exposure, testis morphology decreased, convoluted seminiferous tubules became sparse, the diameter of convoluted seminiferous tubules decreased, and the level of sex hormones decreased. After the administration of exogenous melatonin, testicular morphology and sex hormone levels decreased in the MLD group under normal light conditions. In the MLL group, the testicular tissue morphology returned to normal, the diameter of convoluted tubules increased, the hormone levels of LH (Luteinizing hormone) and MTL (melatonin) significantly increased (P<0.05), and th0e gene expressions of LHβ and Mtnr1A (Melatonin receptors 1A) increased. There was almost no difference in the MDD group under continuous darkness. In conclusion, melatonin can damage the reproductive performance of male mice under normal light conditions, while exogenous melatonin can alleviate and protect the testicular injury of male mice under continuous light conditions.

Keywords: melatonin; photoperiod; reproductive function; testicular function.

Figure 1. Experimental treatment of the mice.

Figure 2. Effect of photoperiod on the development of testis (A,B:×200;C,D:×400). LD: control group; MLD: control plus melatonin group; LL: 24 h light group; MLL: 24h light plus melatonin group; DD: complete darkness group; MDD: complete darkness plus melatonin group.

Figure 3. Effect of photoperiod on convoluted tubule histological index. (A) Effects of exogenous melatonin and different photoperiods on the diameter of convoluted seminiferous tubules; (B) effects of exogenous melatonin and different photoperiods on Leydig cell density of convoluted tubules; (C) effects of exogenous melatonin and different photoperiods on the number of convoluted germ cells. Data are expressed as the mean ± SEM, n = 4. *P < 0.05; **P < 0.01.

Figure 4. Hormone levels in male mice. (A) Serum luteinizing hormone (LH) levels; (B) serum melatonin (MT) levels; (C) serum testosterone (T) levels. Data are expressed as the mean ± SEM, n = 10. *P < 0.05; **P < 0.01.

Figure 5. Effects of different photoperiods on the expression of reproduction-related genes. (A) Relative mRNA expression of GnRH in the hypothalamus; (B) relative mRNA expression of RFRP-3 in the hypothalamus; (C) relative mRNA expression of LH in the pituitary; (D) relative mRNA expression of Mtnr1A in the pituitary. Data are expressed as the mean±SEM, n=6. * P<0.05; **P <0.01.