It has been shown that lesions in the anterior hypothalamus will interfere with secretion of thyrotropin by the pituitary ( 1-4).Since it has not yet been ascertained whether the hypothalamus exerts a primary role in controlling thyrotropin secretion or merely transmits influences from higher centers, the present investigation was undertaken. Originally, it was planned to study thalamic preparations, but it was not possible to keep such animals alive more than one week in spite of forced-feeding and daily antibiotics. Therefore the operation was limited to removal of the neocortex. Such animals had a reasonable survival and permitted evaluation of the goitrogenic response to propylthiouracil administration. The size of the goiter produced was considered an index of the ability of such animals to secrete thyrotropin in response to maximal stimulus.Materids and methods. Female Holtzman rats of the same age, weighing approximately 180-200 g were used as both control and experimental subjects. Removal of the neocortex was accomplished by exposing dorsum of skull through a longitudinal incision, scraping away the galea, and coagulating the underlying vascular tissue by application of electrocautery to the skull. A dental drill was then used to perforate the skull in several places along the border of muscle insertions and the piece of bone was removed with the aid of small bone cutters. This exposed most of the dorsum of the brain with very little bleeding. The neocortex was then removed by suction through a fine glass pipette under direct vision. The ablated cortical tissue was replaced by small pieces of oxycellulose and the skin sutured over the operative site without replacement of the dorsum of the skull.Postoperative care included intramuscular penicillin for the first few days and intraperitoneal isotonic saline until the animals began drinking spontaneously. Pelleted and powdered purina checkers were supplied ad lib.In 2 groups, one week of postoperative recovery was allowed and in one group 5 weeks. One ml of propylthiouracil suspension in 10% acacia containing 30 mg/ml was then injected subcutaneously once daily a t rotated sites. Control animals received only the propylthiouracil injections. All animals were killed 11 days after beginning propylthiouracil treatment and thyroids, adrenals, uteri and ovaries weighed on a 200 mg torsion balance. The skin and mandible were removed from the skulls of the decorticate animals. After a few days fixation in formalin, the brains were then examined to determine the extent of cortical ablation.Results. The autopsy data are summarized in Table I. No great difference was found between the goitrogenic response of the control and operated animals nor did the other endocrine organs examined show striking deviation of the operated from control animals. Although gross inspection of the brains of the operated animals revealed that ablation of the neocortex was not always quite complete, no correlation existed between deficiency of cortical tissue and size of the thyroid or oth...

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