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SUMMARY
Under stereotaxic guidance, the connexions between the hypothalamus and the rest of the brain were severed surgically in mature female guinea-pigs, and reproductive function was assessed by following the vaginal cycle and by histological study of the ovaries. Animals in which the hypothalamic island incorporated the suprachiasmatic nuclei, or in which the anterior connexions to the hypothalamus were severed by a cut placed just anterior to the suprachiasmatic nuclei, developed persistent vaginal oestrus. Such an anterior cut in the hypothalamus did not influence luteal function in hysterectomized animals. When the anterior border of a hypothalamic island, or an anterior cut through the hypothalamus, was caudal to the suprachiasmatic nuclei, oestrous cycles continued although they were slightly irregular. The ovaries contained corpora lutea. Severance of the posterior connexions to the hypothalamus did not alter the oestrous cycle. The role of the suprachiasmatic area in the generation of persistent vaginal oestrus is discussed.
Search for other papers by JEAN E. M. BUTLER in
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PubMed
Search for other papers by B. T. DONOVAN in
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PubMed
SUMMARY
Surgical isolation of the hypothalamus from the rest of the brain was used in a study of the hypothalamic control of gonadotrophin secretion. Rats with hypothalamic islands of differing sizes and animals in which the hypothalamus was partially deafferentated were prepared. Oestrous cycles were followed by taking daily vaginal smears and the reproductive state assessed from histological examination of the genital tract collected at autopsy 28 days postoperatively. In rats with 'large' and 'long' hypothalamic islands persistent vaginal oestrus ensued and the ovaries were follicular. Rats in which smaller islands disconnected the suprachiasmatic nuclei from the median eminence displayed persistent vaginal dioestrus and the ovaries contained corpora lutea. Rats with frontal cuts placed anterior to the suprachiasmatic nuclei behaved similarly to rats with 'large' and 'long' islands in developing persistent vaginal oestrus, but when the anterior connexions to the hypothalamus were severed caudal to the suprachiasmatic nuclei the animals had oestrous cycles which were sometimes interrupted by periods of dioestrus of pseudopregnancy length. Posterior and transverse cuts in the hypothalamus did not alter the oestrous cycle although there was some indication that luteal function was favoured.
