Effects of melatonin implants on winter fur growth and testicular recrudescence in adult male raccoon dogs (Nyctereutes procyonoides)

Abstract

The effects of melatonin implants were investigated on winter fur growth, monitored by counting growing and mature hairs per bundle and testicular recrudescence, judged by testis width, score count of spermatogenesis, and serum testosterone in the adult male raccoon dogs. Melatonin administration in July highly elevated melatonin concentrations in serum and urine and induced an earlier decrease in prolactin secretion (August in the treated group vs September in the control group), winter fur growth (July-beginning of November in the treated group vs. August-end of November in the control group) and testicular recrudescence (October in the treated group vs. November in the control group). In the control animals, urinary excretion of melatonin between 1500-0900 hr increased during autumn followed by a rapid fall in winter. The increase from July (1.8 +/- 0.4 ng) to August (3.9 +/- 0.5 ng) and the subsequent unchanged levels until October coincided with the period of winter fur growth. The further increase in November (6.5 +/- 1.2 ng) coincided with the significant elevation in both testis width and score count of spermatogenesis. These results suggest a role of the increase in endogenous melatonin secretion during autumn in the growth of winter fur and testicular recrudescence in this species under natural conditions. Relatively high serum concentrations of prolactin were shown in two animals, one in the control group and another in the treated group. However, the parameters for testis and winter fur growth in the two cases were similar to those in the remainder of the animals. Thereby, the role of prolactin in the winter fur growth and the initiation of testicular recrudescence, if it is truly involved, is manifested through its decreasing secretion rather than the actual blood concentrations.

Seasonal Changes in Spermatogenesis and Testicular Steroidogenesis in Wild Male Raccoon Dogs (Nyctereutes procynoides)

“…The cyclical alternation in the growth and involution of testes is a well-known phenomenon [5], and the seasonality of testicular mass and spermatogenesis shown in this study is in general agreement with some reports on this species [36][37][38]. We observed testicular recrudescence and regression in the adult male raccoon dog as judged by testis weight, size and score count of spermatogenesis with highest values of weight and size in the mating season.…”

“…The raccoon dog (Nyctereutes procyonoides) is a typical seasonal breeder with a short sexually active period lasting about 6 weeks in February and March, followed by a long period of sexual dormancy from April to January [38]. During the mating period, male raccoon dogs are willing to mate and produce mature spermatozoa.…”

“…Although much information on reproduction in the raccoon dog has been reported recently [10,16,[36][37][38][39], many gaps in our understanding of the mechanisms of their reproduction remain. The aim of the present study was to investigate the mechanisms that regulate spermatogenesis and testicular steroidogenesis by immunocytochemical and histological observations in wild male raccoon dogs.…”

Seasonal Changes in Immunolocalization of Inhibin/Activin Subunits and Testicular Activity in Wild Male Raccoon Dogs (Nyctereutes procyonoides)

“…C y c l i c a l t e r n a t i o n b e t w e e n g r o w t h a n d i n v o l u t i o n o f t h e t e s t e s i s a w e l l -k n o w n phenomenon [29]. The seasonality of testes mass shown in the present study is in agreement with extensive reports on this species [15][16][17][18][19] [16]. In the present study, we observed testicular recrudescence and regression in the male raccoon dog as judged by testis weight and size and seminiferous tubule diameter, with the highest values seen during the breeding season.…”

“…In China, there are marked seasonal changes in the serum testosterone concentrations of farmed raccoon dogs, with a significant rise in October, a peak in the early breeding season, and a rapid drop at the end of the breeding season [17]. Although several observations about reproduction in the raccoon dog have been reported recently [18][19][20][21][22][23], there are still many gaps in the understanding of the mechanisms of reproduction, especially concerning secretion of inhibin in the development process of the testes. The aim of the present study was to investigate the localization of inhibin subunits in the testes during the non-breeding and breeding seasons and to elucidate the relationship between inhibin and reproductive function in wild male raccoon dogs.…”