Connections of hypothalamic paraventricular neurons with the dorsal medial thalamus and neurohypophysis: an electrophysiological study in the rat.

Connections between the hypothalamic paraventricular nucleus (PVN) and thalmic paraventricular nucleus ( PVT ) were examined using electrophysiological methods. Efferent projections of adjacent PVN cells were defined on the basis of antidromic activation from either PVT (n = 12) or neurohypophyseal (n = 38) stimulation; antidromic activation from both sites (n = 3) suggested that some PVN cells project both to the PVT and to the neurohypophysis. PVT stimulation evoked only weak orthodromic responses from 21% of PVN neurohypophyseal neurons, whereas short latency, high probability orthodromic responses were observed from 43% of PVN non-neurosecretory neurons. These data indicate reciprocal PVN- PVT connections and suggest that PVT afferents preferentially innervate non-neurosecretory PVN cells.