Histological Changes in the Male Reproductive System During the Annual Reproductive Cycle

Abundant evidence obtained during more than four decades of research has demonstrated that adult male plains vizcacha who inhabit west-central Argentina exhibit a seasonal reproductive cycle synchronized by environmental signals, mainly the natural photoperiod. The cycle has three well characterized gonadal stages: activity (early summer-fall), regression (late fall-winter), and recovery (spring). During regression, the testis has a significant reduction in the number of seminiferous tubules sections as well as in their diameter, until their transformation into cords. Sperm was not observed within the tubular lumen. Sertoli and Leydig cells showed marked signs of involution: declined in organelles content such as mitochondria, smooth endoplasmic reticulum, and Golgi complex and increased content of dense bodies. In the epididymis, corpus and cauda segments showed greater sensitivity to seasonal variations: a decrease in luminal diameter and an increase in both the epithelium height and the thickness of the lamina propria, especially in cauda, during the regression period. In both epididymal segments, principal and clear cells showed signs of involution with respect to the activity period: irregular nuclei, small cytoplasms, large vacuoles, altered mitochondria, and glycogen deposits. All cellular populations of the epididymal epithelium in regression exhibited abundant lysosome-like dense bodies. Finally, in seminal vesicles and prostate, the epithelial height and the luminal diameter decrease. The muscle tunic increased in the seminal vesicles and decreased in the prostate. In both glands, the main epithelial cell populations exhibit morphological characteristics consistent with a reduced functional activity. The seasonal morphological changes observed in the male reproductive system of vizcacha show a high degree of synchrony between the different organs along the seasonal reproductive cycle. These morphological variations are regulated by pineal melatonin, whose serum concentrations are high during winter while the pituitary gland activity decreases in this season.