Effect of hypothalamic deafferentation on thyrotropin-releasing hormone levels in rat brain.

The medial basal hypothalamus was isolated from the remainder of the brain of the rat using a Halász knife. Ten to 14 days after the surgical procedure the concentration of thyrotropin-releasing hormone within the island of hypothalamic tissue was 76% lower than in tissue from sham-operated control rats. Thus, much of the thyrotropin-releasing hormone that is normally present in the medial basal hypothalamus may be synthesized by cells outside of this region. There were no reductions in hormone levels in regions outside of the hypothalamic island after the surgical procedure. Extrahypothalamic thyrotropin-releasing hormone does not appear to be produced by hypothalamic neurosecretory cells.