Influence of Photoperiod, Ambient Temperature and Melatonin on Testosterone Synthesis and Release During Reproductive Maturation in Male Deer Mice

Abstract

Four experiments were designed to investigate the influence of photoperiod and other environmental factors on androgen production and reproductive maturation in deer mice. Male prairie deer mice (Peromyscus maniculatus), born in a light/dark cycle of 6L:18D, either remained in this short photoperiod or were switched to a long day regimen of 16L:8D at weaning. In a cross-sectional experiment, the deer mice were killed between 3 and 8 weeks of age for measurement of serum testosterone concentration and reproductive organ weights. In a second experiment, blood was collected from each mouse at weekly intervals between 3 and 9 weeks of age. This repeated measures design was used to reduce the high variability in testosterone values observed in the first experiment. Reproductive organs were weighed at the termination of the experiment. Testosterone concentrations and reproductive organ weights were greater in males reared in the long photoperiod in both experiments. In a third experiment, the animals were housed under five different conditions to test the influence of high ambient temperature and melatonin as well as photoperiod. At 7 weeks of age, they received an injection of hCG or saline. More testosterone was released in deer mice reared in 16L:8D and 27 C than in those reared in short days (6L:18D) or those reared in high ambient temperature (35 C) or those treated with exogenous melatonin. One week later, animals were sacrificed. The single hCG treatment caused significant reversal of the suppression of accessory sex organ weights following melatonin, short days or 35 C temperature. In a fourth experiment, the additive influence of melatonin and 35 C temperature was tested. Animals treated with 35 C or both melatonin and 35 C had lower serum testosterone at 7 weeks of age, released less testosterone after hCG, and had smaller organ weights with or without hCG than long day controls. The influence of melatonin treatment and 35 C temperature appears to be additive for testicular weight and testosterone release after hCG. Thus, the attenuation of reproductive development that accompanied short days, melatonin treatment and high ambient temperature occurred via diminished testosterone secretion, which can be overcome at least in part by gonadotropin treatment.

Effects of continuous light exposure on antioxidant enzymes, porphyric enzymes and cellular damage in the Harderian gland of the Syrian hamster

“…Activities of the three porphyric enzymes studied, ALA‐S, ALA‐D and PBG‐D, did not show differences between subjective day and night under free‐running conditions. The absence of melatonin is known to cause rises in testosterone levels [38]. In the hamster HG, testosterone diminishes ALA‐S mRNA [7].…”

Sex‐specific variation in the onset of reproduction and reproductive trade‐offs in a boreal small mammal

“…For monitoring male maturity and breeding condition (Barkley and Goldman 1977, Fail and Whitsett 1988, Kempenaers et al 2008) blood samples were collected four times during the experiment for testosterone measurements: (1) right after capture (in laboratory conditions), (2) one week after the manipulations started, (3) during the pairing period, and (4) at the end of the chamber phase. To collect blood we used retro-orbital bleeding.…”

The effects of early environmental conditions on the reproductive and somatic development of juvenile guinea pigs (Cavia aperea f. porcellus)

“…In seasonally reproducing species, strong effects of photoperiod on testosterone titers have been reported. Juvenile deer mice, for instance, reared in a long photoperiod had significantly higher testosterone levels than subjects reared in a short photoperiod (Fail and Whitsett, 1988). Similar results were found in Djungarian hamsters (Yellon and Goldman, 1984), and bank voles (Tähkä et al, 1983).…”