Excitatory action of TRH on spinal motoneurones

Abstract

THE recent isolation and characterisation of a number of peptide hypothalamic-releasing (and release-inhibiting) hormones led to an unexpected bonus. Many of these peptides have been found to be widely distributed in brain in areas remote from established hypothalamic neuro-endrocrine systems. For instance, two thirds of the brain thyrotropin-releasing hormone (TRH) is located outside the hypothalamus^1,2. This finding suggests that TRH might have some neuroregulatory role in the brain besides its role as a releasing hormone. The marked behavioural effects of central origin produced by TRH support this notion^3–7. In particular, the finding that TRH can be localised by immunohistochemical techniques to nerve fibres in a variety of brain regions⁸, that it depresses neuronal activity when applied by microiontophoresis^9–11 and that it has stereoselective, high-affinity binding sites in brain¹² suggests that TRH may be a neurotransmitter. There is little evidence, however, on the transmembrane effects and mechanism of action of TRH or other peptides on central neurones.