Neural Control of Thyrotropin Secretion: Effect of Forebrain Removal on Thyroid Function

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Abstract
The entire brain rostral to the superior colliculus was removed, leaving either a “hypothalamic island” or a “median eminence island” attached to the pituitary. Operated and control animals were force-fed for 10 days postoperatively; approximately half of each group additionally received 30 mg propylthiouracil (PTU) daily. Thyroid weights and radioiodine uptake were compared in various experimental and control groups. Thyrotropin secretion appeared approximately equal in similarly treated intact and hypothalamic island groups. No thyroid hypertrophy developed in the PTU-treated median eminence island rats, but only 3 of these survived the full 10 days. No pituitary infarction was found in any operated animal. It thus appears that the forebrain outside the limits of the hypothalamus is not essential for normal functioning of the servomechanism which results in increased TSH release in response to thyroxine deficiency.