Limbic, hypothalamic, cortical and spinal regions are enriched in receptors for thyrotropin-releasing hormone: evidence from [3H]ultrofilm autoradiography and correlation with central effects of the tripeptide in rat brain.

Light microscopic autoradiographic localization of specific recognition sites for thyrotropin-releasing hormone (TRH) was determined on thin sections of rat brain using the potent analogue 3H-TRH ([3H]MeTRH). Microdensitometric analysis of the relative optical densities of TRH receptor labelling revealed the following brain regional enrichment: lateral and cortical amygdaloid nuclei greater than ventral dentate gyrus greater than n. accumbens greater than medial septum greater than piriform cortex greater than paraventricular thalamic and hypothalamic nuclei greater than preoptic area greater than diagonal band of Broca greater than lateral septum greater than I-IV layers of frontoparietal cortex greater than dorsal hippocampus greater than olfactory tubercle greater than caudate putamen; globus pallidus. In the spinal cord the apparent relative enrichment of TRH receptors was: substantia gelatinosa = central canal gray greater than ventral gray greater than dorsal gray (layers III-VII) greater than white matter. This heterogeneous distribution of TRH binding sites correlated well with our previous data obtained from membrane binding studies. Furthermore, the specific anatomical localization of receptors for TRH in many nuclei was consistent with those loci involved in the mediation of many physiological and behavioural actions of the peptide in rodent brain.