Co-existence of TRH with mesotocin in the same axon terminals of the bullfrog pars nervosa as revealed by double labeling immunocytochemistry.

The co-existence of thyrotropin-releasing hormone (TRH)- and mesotocin (MT)-like immunoreactivities in single axon terminals in the frog pars nervosa was observed using a method combining pre-embedding peroxidase-antiperoxidase for TRH with post-embedding immunocolloidal gold staining for MT. Both TRH- and MT-like immunoreactivities were localized in the same large dense elementary granules 130-220 nm in diameter (170 nm mean diameter). A few axons contained only TRH-like immunoreactive small granular vesicles 80-120 nm in diameter (92 nm mean diameter). Axon terminals containing both TRH- and MT-like immunoreactive granules were in direct contact with the perivascular basal lamina of blood capillaries.

Innervation of thyrotropin-releasing hormone-containing neurons in the bullfrog pars intermedia.

We studied immunocytochemical localization of thyrotropin-releasing (TRH) in the bullfrog pats intermedia. Many TRH-like immunoreactive terminals containing immunoreactive granular vesicles 80-150 nm in diameter (116 nm mean diameter) were found in the pars intermedia. Some TRH-like immunoreactive terminals were in synaptic contact with the intermedia cells. These findings support the hypothesis that TRH directly activates the intermedia cells via synapses to secrete alpha-melanocyte-stimulating hormone.

Immunocytochemical observations of corticotropin-releasing-factor-containing neurons in the rat hypothalamus with special reference to neuronal communication.

Synapses between neurons with corticotropin-releasing-factor-(CRF)-like immunoreactivities and other immunonegative neurons in the hypothalamus of colchicine-treated rats, especially in the paraventricular nucleus (PVN) and the supraoptic nucleus (SON) were observed by immunocytochemistry using CRF antiserum. The immunoreactive nerve cell bodies and fibers were numerous in both the PVN and the SON. The CRF-containing neurons had synaptic contacts with immunonegative axon terminals containing a large number of clear synaptic vesicles alone or combined with a few dense-cored vesicles. We also found CRF-like immunoreactive axon terminals making synaptic contacts with other immunonegative neuronal cell bodies and fibers. And since some postsynaptic immunonegative neurons contained many large neurosecretory granules, they are considered to be magnocellular neurosecretory cells. These findings suggest that CRF functions as a neurotransmitter and/or modulator in addition to its function as a hormone.