Ultrastructural localization of TRH-like immunoreactivity.

With the peroxidase-antiperoxidase (PAP) method TRH-like immunoreactivity (TRH-LI) was observed in certain neurons of the central nervous system. Their distribution agreed well with findings previously obtained with the indirect immunofluorescence technique. At the ultrastructural level electron-dense precipitates representing TRH-LI were observed in so-called large dense core vesicles, which were localized both in the cytoplasm of some hypothalamic neuronal cell bodies, as well as in boutons in the hypothalamus and spinal cord. The boutons often seemed to form axo-somatic or axodendritic synapses.