The Cytological and Histological Effects of Photoperiodism and X-irradiation on the Testes of the Syrian Hamster

Summary

The radiosensitivity of meiotic stem cells from photoregressed testes of the Syrian hamster was studied after in vivo irradiation with 2·67 Gy (1·77 Gy/min). The testes of Expt I animals were irradiated at the time of transfer from short days (11 weeks at 6L:18D (6 hours light: 18 hours) darkness) to long days (14L:10D) and sampled at weekly intervals between 5 and 10 weeks and at 15 weeks postirradiation. The Ext II animals received the same X-ray dose, 2, 4, 6, 8 weeks after the transfer to long days and were sampled 10 weeks postirradiation. In Expt I X-irradiation delayed the recovery of testis structure and function by 4 weeks. Animals in Expt II were homogeneous with regard to testicular weight, sperm count, tubule diameter and the level of pachytene, MI and MII damage. The incidence of structural chromosomal changes in primary spermatocytes at pachytene (synaptonemal complexes) and MI and MII was determined. In Exp I and II and data from X-irradiated testes (2·6 Gy) not exposed to short days (Control B, see Cawood and Breckon 1983), these cell types show a difference in sensitivity to the induction of structural damage. The lowest level of pachytene damage was in Expt II, and the ratio of the number of pachytene to MI cells showing structural change was 1·23:1 (P = 0·41), not significantly different from 1:1. In Expt I the pachytene, MI structural change ratio was 1·60:1 (P = 0·010), significantly different from 1:1. The control B ratio was 1·85:1 (P = 0·0037) which was significantly different from 1:1. The preliminary results indicate that testes fully regressed to the ‘stem’ cell level by exposure to short day length have a similar radiosensitivity to normal (non-regressed) testes. However, testes irradiated during the recovery phase from photoperiod-induced regression have increased sensitivity to radiation damage. The relative testis weight was reduced to a mean of 1·25 g by the sequential X-ray treatment—this may indicate that the effects of the X-rays (3 Gy) on a recovering photoregressed testis are independent of the time of the X-ray treatment during the recovery period. Recovery of tubule diameter is not perturbed and may be slightly increased, with an associated elevation of MI—MII activity—but a low spermatogonia count. This phenomenon could be explained by the photo-regression-recovery, causing a change in the cell cycle kinetics of the stem cell spermatogonia, to allow rapid repopulation, a shorter cell cycle resulting in an increased sensitivity to the radiation and selection of spermatogonial cells, and a fractionation effect.