Testicular Melatonin and Its Pathway in Roe Deer Bucks (Capreolus capreolus) during Pre- and Post-Rut Periods: Correlation with Testicular Involution

Abstract

Roe deer are seasonal breeders with a complete yearly testicular cycle. The peak in reproductive activity is recorded during summer, the rutting period, with the highest levels of androgens and testicular weight. Melatonin plays a pivotal role in seasonal breeders by stimulating the hypothalamus-pituitary-gonads axis and acting locally; in different species, its synthesis within testes has been reported. The aim of this study was to evaluate the physiological melatonin pattern within roe deer testes by comparing data obtained from animals sampled during pre- and post-rut periods. Melatonin was quantified in testicular parenchyma, along with the genetic expression of enzymes involved in its local synthesis (AANAT and ASMT) and function (UCP1). Melatonin receptors, MT1-2, were quantified both at protein and gene expression levels. Finally, to assess changes in reproductive hormonal profiles, testicular dehydroepiandrosterone (DHEA) was quantified and used for a correlation analysis. Melatonin and AANAT were detected in all samples, without significant differences between pre- and post-rut periods. Despite DHEA levels confirming testicular involution during the post-rut period, no correlations appeared between such involution and melatonin pathways. This study represents the first report regarding melatonin synthesis in roe deer testes, opening the way for future prospective studies in the physiology of this species.

Keywords: ANAAT; ASMT; Capreolus capreolus; melatonin; melatonin receptors; reproductive physiology; roe deer; seasonal breeder; testicular cycle.

Figure 1

Differences between pre-and post-rut groups for the quantification of testicular parenchymal melatonin (A) and DHEA (B). *, p < 0.05. DHEA, dehydroepiandrosterone.

Figure 2

Differences between pre-and post-rut groups for the gene expression of the enzyme AANAT (aralkylamine-N-acetyltransferase).

Figure 3

Western blot analyses and comparisons between pre- and post-rut periods for the melatonin receptors 1 (A) and 2 (B). α tub, alfa-tubulin; MWM, molecular weight markers. (original western blot figures in Figure S1).

Figure 4

Color-coded Spearman’s rank correlation coefficients (ρ) table. Blue background indicates perfect correlations, white shows that the two variables do not vary together; light blue gradients indicate different levels of correlation. DHEA, dehydroepiandrosterone; T°, temperature; AANAT, aralkylamine-N-acetyltransferase; MT1 and MT2, melatonin receptors 1 and 2.