Responses to hemithyroidectomy and thyroxine treatment were examined in normal cats and in animals in which the basal hypo thalamus had been deafferented. Deafferented cats exhibit a compensatory response to hemithyroidectomy similar to that of normal animals. Treatment with thyroxine (2.5 µ g/kg/day) for 14 days caused inhibition of thyroid function in normal cats but not in deafferented ones. Pellets composed of cholesterol and thyroxine in different proportions were implanted subcutaneously and in the preoptic area of the hypothalamus of hemithyroidectomized cats. A pellet composition was found that was ineffective subcutaneously but effective intracerebrally in preventing the compensatory response to hemithyroidectomy. This pellet, which was effective intracerebrally in hemithyroidectomized cats with intact basal hypothalami, was ineffective in deafferent, hemithyroidectomized animals. It is concluded that an inhibitory neural pathway from the preoptic area to some region closer to the median eminence is involved in the negative feedback action of thyroxine.

Keywords:
Hypothalamus, Preoptic area, TSH secretion, Thyroxine feedback, Deafferentation
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© 1971 S. Karger AG, Basel
1971
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