Reciprocal synaptic relations between CRF-immunoreactive- and TRH-immunoreactive neurons in the paraventricular nucleus of the rat hypothalamus.

By double immunoelectron microscopy, we studied synaptic relations between corticotropin-releasing factor (CRF)-immunoreactive (ir) and thyrotropin-releasing hormone (TRH)-ir neurons in the paraventricular nucleus (PVN) of the rat hypothalamus. CRF-ir and TRH-ir neurons made reciprocal synaptic connections in the medial and periventricular parvocellular regions. These results may suggest that both the parvocellular neurons interplay on their hypophysiotropic functions within the PVN.