The Distribution and Concentration of Thyrotropin-Releasimg Hormone in Discrete Human Hypothalamic Nuclei*

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Abstract
TRH has been measured by RIA in 8 discrete human hypothalamic nuclei, the mammillary complex, the median eminence, and infundibular stalk. Tissues were derived from 13 subjects during autopsy after sudden death. Serial micropunch brain samples were secured from 300-μm frozen sections with stainless steel cannulae 1000 or 2000 μm in diameter. Pooled samples were extracted with 0.1 N HC1, lyophilized, and resuspended in phosphate-saline buffer for TRH determinations. Stability of TRH in postmortem tissues was assessed in rats sacrificed at varying time intervals before tissue extraction. TRH was detected in all structures examined. Highest concentrations of TRH were found in the median eminence area (3.139 ng/mg protein) and arcuate nucleus (2.034 ng/mg protein). Intermediate TRH concentrations, representing 5–10% of total TRH activity, were localized to the paraventricular and periventricular nuclei. Lowest TRH concentrations were found in the mamillary complex and the posterior, supraoptic, and anterior hypothalamic nuclei. TRH activity in two rat central nervous system structures, the hypothalamus and cerebral cortex, appeared to be completely stable up to 16 h postmortem at 4 C. It is concluded that TRH is localized in part in those human hypothalamic nuclei corresponding precisely to areas implicated in TSH regulation in experimental animals. The presence of TRH in additional human hypothalamic sites also, however, suggests that TRH may be subserving other functions as well in the role of neurotransmitter or neuromodulator.

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