Study was made of 21 rats which responded by increased bar pressing for a stimulating current to the brain. These were allowed to self-stimulate for 4 or 8 hr. twice a week for 10 wk. At the end of this time the weights of the testes were found to be less than those of control animals and definite histologic changes were found in the adrenal glands. The weights and appearance of the pituitary, thyroid, and thymus glands, the seminal vesicles, and the ventral portions of the prostate glands appeared to be unchanged.
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