Activity Studies on Male Castrated Rats with Ovarian Transplants, and Correlation of the Activity with the Histology of the Grafts

As shown independently by Wang (1923) and by Slonaker (1925) caged rats given access to a revolving drum show periodic fluctuations in their daily voluntary activity. Every fourth day there is a sudden burst of activity which is in great excess of the activity recorded on each of the three intervening days. These observers were able to correlate this periodic fluctuation in running activity with the ovulation cycle. They found by means of vaginal smears, first applied to the rat by Long and Evans, that the fourth day peak of spontaneous activity coincided with the time of oestrus, and that the three days of lessened activity were synchronous with the three days of the dioestrus. Wang showed that female rats with both ovaries removed were much less active than normal animals (about 90 to 95 per cent less measured by the number of revolutions per day). This low level of activity is maintained throughout the life of spayed rats. A similar decrease in spontaneous activity occurs during pregnancy, lactation, and pseudo-pregnancy produced by mechanical stimulation of the cervix uteri. The low level of activity is present also before sexual maturity, and recurs in the period of senility. In addition to a very marked decrease in spontaneous activity, the ovariectomiaed, pregnant, pseudo-pregnant, lactating, immature, and senile animals also show a complete disappearance of the characteristic recurrent four-day activity rhythm of normal sexually mature female rats. These several observations led Wang and Slonaker to conclude that the spontaneous activity of the female rat is markedly inf!luenced by the presence of ovaries. The activity of the male rat is greatly affected by the presence of the testes. In contradistinction to the recurring rhythm of the normal female, the male shows no cyclic rhythm of activity; furthermore, the activity of