Synaptic contacts between nerve terminals originating from the ventrolateral medullary catecholaminergic area and median preoptic neurons projecting to the paraventricular hypothalamic nucleus

A significant role of catecholaminergic projection to the median preoptic n ucleus (POMe) which activates vasopressin-producing cells of the paraventri cular hypothalamic nucleus (PVN) has been suggested. We investigated the ex istence of the synaptic contacts between catecholaminergic fibers from the ventrolateral medulla and the POMe neurons projecting to the PVN. Rats rece ived a retrograde tracer in the PVN and subsequently an anterograde tracer into the catecholaminergic area of the ventrolateral medulla at the level o f the area postrema. In the POMe, anterogradely labeled nerve terminals wer e found to make axe-somatic and axo-dendritic synaptic contacts onto retrog radely labeled neurons. Additional studies in which a retrograde tracer was injected into the POMe revealed that almost ail retrogradely labeled neuro ns in the ventrolateral medulla at the level of the area postrema were immu noreactive to tyrosine hydroxylase, suggesting that projection to the POMe from the ventrolateral medulla is largely limited to catecholamine neurons. These results provide, for the first time, direct evidence that catecholam inergic inputs from the ventrolateral medulla affect POMe neurons projectin g to the PVN by way of direct synaptic contact. (C) 1999 Elsevier Science B .V. All rights reserved.