Immunohistochemical characterization of thyrotropin-releasing hormone-containing neurons in rat septum.

A sensitive and specific immunohistochemical technique has been used to reveal the distribution of thyrotropin-releasing hormone (TRH) in extrahypothalamic regions. Numerous cell bodies of the lateral septum were surrounded by profiles of dense, spotted TRH-containing axon terminals, suggesting the presence of synaptic contacts. The immunoreactive TRH was found to decrease markedly after electrolytic lesion of the medial preoptic area. The same lesions also lowered the septal content of TRH to 65%, as estimated by radioimmunoassay.