Thyrotropin releasing hormone (TRH): its widespread distribution in discrete hypothalamic nuclei and areas in rat brain.

The precise distribution of thyrotropin releasing hormone (TRH) in 23 discrete brain nuclei and areas of Wistar strain male rats was determined by specific radioimmunoassay. TRH was detected in most of these areas. The highest concentration was found in the median eminence (27.52 +/- 2.84 ng/mg protein). The arcuate nucleus (4.92 +/- 0.58 ng/mg protein), dorsomedial nucleus (4.77 +/- 0.59 ng/mg protein) and medial preoptic area (3.94 +/- 0.15 ng/mg protein) also contained a considerable concentration of TRH. However, no TRH was detected in cerebral cortex, cerebellar hemisphere, anterior pituitary or pineal body. The data indicated that TRH was widely distributed throughout the hypothalamus; in particular, high concentrations occure in relatively restricted areas: in the median eminence, arcuate nucleus, dorsomedial nucleus and medial preoptic area. These areas coincide well with the so-called "thyrotropic" area of the hypothalamus.