DIRECT PROJECTIONS FROM CATECHOLAMINERGIC NEURONS IN THE CAUDAL VENTROLATERAL MEDULLA TO VASOPRESSIN-CONTAINING NEURONS IN THE SUPRAOPTIC NUCLEUS - A TRIPLE-LABELING ELECTRON-MICROSCOPE STUDY IN THE RAT

Direct projections from the A1 catecholaminergic cell group in the cau dal ventrolateral medulla (CVLM) to arginine-vasopressin-containing (A VP-containing) neurosecretory neurons in the hypothalamic supraoptic n ucleus (SON) were examined electron microscopically in the rat by a tr iple-labeling technique in which an anterograde tract-tracing method o f wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) wa s combined with immunocytochemistry for tyrosine hydroxylase (TH) and that for AVP. In the SON, TH-like immunoreactive axon terminals which were labeled with WGA-HRP injected in the CVLM were in synaptic contac t with neuronal profiles with AVP-like immunoreactivity. The results i ndicate that AVP-containing neurons in the SON receive monosynaptic ca techolaminergic synaptic input from the CVLM. (C) 1996 Elsevier Scienc e Ireland Ltd.