Nitric oxide (NO) expression during annual reproductive activity in buffalo epididymis: a histochemical and immunocytochemical study.

The buffalo is one of the few domestic animals that has a seasonal mating cycle, influenced by the photoperiod. It is known that the photoperiod regulates gonadal function probably via the pineal and/or hypothalamus-pituitary axis. Moreover, the hypothalamus (melatonin) and gonads influence the production of the signaling transmitter nitric oxide (NO), suggesting that the NO may have an important role in the regulation of gonadotropin-releasing hormone secretion. This further suggests the hypothesis that NO in the epididymis has an important role in the maturation of spermatozoa and their motility and posterior fertilization capacity. The aim of the present study is to investigate the seasonal variations in the morphology of the epididymis by means histochemical and immunocytochemical techniques. We used the NADPH-d, nitric oxide synthase (NOS) I and NOS III to clarify the relationship between epididymis function and NO signaling activity. The results of this work show that NO is present in the caput of epididymis during short photoperiods, i.e., periods of maximum gonadal activity (winter) and absent during long photoperiods, i.e., periods of gonadal regression according to the previously described role of NO in spermatozoa capacitation and motility in the caput epididymis.