The extensive extrahypothalamic distribution of TRH, its localisation in nerve endings, and the presence of TRH receptors in brain tissue suggest that this peptide acts as a neurotransmitter or neuromodulator outside the hypothalamus. In particular, its distribution in the spinal cord at nerve endings of the intermediolateral column, which contain the cells of origin of the sympathetic nervous system, may explain the elevation of blood pressure which follows injections of TRH and may be relevant to clinical benefits claimed in treatment of shock and depression.
