Journal of Neuroscience, Vol 5, 551-561, Copyright © 1985 by Society for Neuroscience
Thyrotropin-releasing hormone (TRH) receptors. Localization by light microscopic autoradiography in rat brain using [3H][3-Me-His2]TRH as the radioligand
PW Mantyh and SP Hunt
Thyrotropin releasing hormone (TRH) is a putative neurotransmitter in both
the central and peripheral nervous system. In the present report, we have
used autoradiography coupled with densitometric analysis of
tritium-sensitive film to investigate the distribution of [3H][3-Me-
His2]TRH [( 3H]MeTRH)-binding sizes in the rat brain. Previous
pharmacological reports have established that many of these [3H]MeTRH-
binding sites have a structure-activity profile consistent with being a
physiological TRH receptor. A high level of TRH receptors were observed in
the accessory olfactory bulb, lateral nucleus of the amygdala, dentate
gyrus, and entorhinal cortex. Moderate levels of TRH receptors were
observed in the rhinal cortex, hypothalamus, superior colliculus, several
brainstem motor nuclei, and lamina I of the spinal trigeminal nucleus pars
candalis, while low concentrations of receptors are present in the cerebral
cortex, striatum and ventral horn of the spinal cord. Very low levels of
receptors were observed in the globus pallidus and in most nuclei of the
dorsal thalamus. Comparisons of the distribution of TRH receptors to
TRH-immunoreactive content indicates that, while in some areas of the brain
there is a rough correlation between levels of TRH peptide and its
receptor, in most brain areas there is little obvious correlation between
the two. While such a discrepancy has been observed for other peptides and
their receptors, the extensive distribution of TRH receptors in the central
nervous system does provide an explanation for the variety of behavioral
effects observed when TRH is infused into the central nervous system.