The viscacha (Lagostomus maximus maximus) is a seasonal South American wild rodent. The adult males exhibit an annual reproductive cycle with periods of maximum and minimum gonadal activity. Four segments have been identified in the epididymis of this species: initial, caput, corpus, and cauda. The main objective of this work was to relate the seasonal morphological changes observed in the epididymal duct with the data from epididymal sperm during periods of activity and gonadal regression using light and scanning electron microscopy (SEM). Under light and electron microscopy, epididymal corpus and cauda showed marked seasonal variations in structural parameters and in the distribution of different cellular populations of epithelium. Initial and caput segments showed mild morphological variations between the two periods. Changes in epididymal sperm morphology were observed in the periods analyzed and an increased number of abnormal gametes were found during the regression period. During this period, anomalies were found mainly in the head, midpiece, and neck, while in the activity period, defects were found only in the head. Our results confirm that the morphological characteristics of the epididymal segments, as well as sperm morphology, undergo significant changes during the reproductive cycle of Lagostomus. 1. Introduction Animal species that develop their life cycle in contact with nature must adapt physiologically to the annual changes conditioned by the environment. The role of environment signals in synchronization has been described in previous reports, especially the circannual regulation of pituitary and gonadal function by photoperiod [1, 2]. Depending on the season, adult males have reproductive cycles that are expressed by morphological and biochemical changes in their reproductive organs [3]. Also, some species show testes devoid of all signs of spermatogenic activity during the winter months [4]. Moreover, mammalian spermatozoa produced in the testis must mature in the epididymis to acquire their fertilizing capability [5, 6]. Specific proteins secreted by epithelial cells of the epididymis and factors generated by accessory glands modulate the structure and function of the sperm plasma membrane. The size and secretory activity of epithelia in the epididymis as well as in the accessory glands are influenced by testosterone [7]. In this study, the model animal used is the viscacha (Lagostomus maximus maximus), a South American rodent which lives in burrows built deep in the ground and only leaves its cave at dawn to look for food [8, 9].
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