Adrenal gland differences associated with puberty and reproductive inhibition in Peromyscus maniculatus

Laboratory populations of the prairie deermouse (Peromyscus maniculatus) reach a growth asymptote due primarily to the failure of more than 90% of the young born into the population to mature sexually. This inhibition is reversible; when young are removed from the inhibiting influence of the population more than 75% will reproduce within 80 days of pairing. Interestingly, the mechanism of this inhibition does not involve the degree of adrenal hypertrophy as reported in rats and housemice. We report here that the adrenal morphology of reproductively inhibited deermice raised within laboratory populations is different from patterns seen with normal puberty; namely in the area, histology, and apparent activity of the weak androgen-secreting zona reticularis. Our data indicate that the frequency of adrenal cortex cellular apoptosis is not different between the adrenal zones or between reproductively capable versus inhibited animals and therefore does not account for the differences in the numbers of cells with pycnotic nuclei in the zona reticularis of inhibited animals. We also found that the concentration of serum DHEA is significantly reduced in reproductively inhibited animals suggesting that the zona reticularis of inhibited animals may be less active than in controls. We present data to indicate that the adrenal zona reticularis of 30-day-old control animals is likely to be more active than reproductively inhibited animals of the same age. Our data also indicate that older reproductively inhibited animals of both sexes are also likely to have a much less active zona reticularis. These differences may be implicated in the mechanism of reproductive inhibition.