Quantitative microscopic changes in the mole rat's accessory sex organs during an annual cycle

Abstract

Background: The mole rat, Spalax ehrenbergi, is a solitary, aggressive subterranean rodent. The present study summarizes a year-round investigation of morphological changes in the mole rat's accessory sex organs. Methods: Mole rats maintained in the laboratory were killed after 3 months of acclimation; additional animals trapped in the wild were killed immediately. The accessory sex organs were processed for routine histological examination. Tissues were fixed in Bouin's solution, embedded in paraffin blocks, and stained by hematoxylin-eosin. A systemic sampling approach was used to photomicrograph the tissues for histomorphometric assessment. Results: The volume fraction (Vv, mean ± SEM) of prostate connective tissue from animals kept in captivity increased significantly in January (0.49 ± 0.05 mm3/mm3) and April (0.43 ± 0.04 mm3/mm3) but only 0.26 ± 0.03 mm3/mm3 in November. In the field group, the Vv of prostate connective tissue was significantly higher in January (0.58 ± 0.08 mm3/mm3) and April (0.62 ± 0.08 mm3/mm3) and lower in November (0.44 ± 0.03 mm3/mm3) and February (0.43 ± 0.03 mm3/mm3), with a concomitant decrease in prostate tubuli and lumen. The prostate tubuli star volume (v.) in laboratory animals increased in November (0.009 ± 0.002 mm3) and May (0.09 ± 0.02 mm3). The same pattern was shown in the field group, with a significant increase in December (0.012 ± 0.002 mm3) and March (0. 007 ± 0.001 mm3). The Cowper tubuli Vv in the captive animals increased during February (0.24 ± 0.02 mm3/mm3), with a concomitant reduction in the connective tissue (0.05 ± 0.02 mm3/mm3). The Cowper tubuli v. in same animals increased in December, April, and July (1.37 ± 0.18 x 10-4 mm3, 0.94 ± 0.10 x 10-4 mm3, 1.52 ± 0.20 x 10-4 mm3, respectively). In field group, a slight decrease in star volume took place from November to May (1.25 ± 0.16 mm3 to 0.39 ± 0.05 mm3, respectively). Testosterone levels appeared to be higher in the field group than in the laboratory group. In December the values were 1.62 ± 0.15 ng/ml in the field group and 0.55 ± 0.12 ng/ml in the laboratory group, and in May the laboratory group values were 1.66 ± 0.12 ng/ml. Conclusions: In captivity and in the field, male mole rats probably undergo an annual cycle of accessory gland tissue structural changes that are correlated with testosterone secretion.