CONVERGENT PROJECTIONS OF TRIGEMINAL AFFERENTS FROM THE PRINCIPAL NUCLEUS AND SUBNUCLEUS INTERPOLARIS UPON RAT VENTRAL POSTEROMEDIAL THALAMIC NEURONS

Synaptic boutons originating from the trigeminal principal sensory nuc leus (PrV) and the subnucleus interpolaris (Spl) which contact rat ven tral posteromedial (VPM) neurons are similar in appearance. They are l arge boutons and contain a moderate packing density of round synaptic vesicles and establish asymmetric (Gray type I) synaptic contacts prin cipally on dendrites and occasionally on somata. These boutons are sim ilar to RL boutons of dorsal column nuclei and spinothalamic tract ori gin found in the ventral posterolateral thalamic nucleus. The boutons of PrV and SpI origin have an overlapping distribution on proximal den drites of VPM neurons. Double labeling using degeneration and WGA-HRP shows that boutons from PrV and SpI contact the same VPM neuron confir ming there is convergence of trigeminal afferents in VPM.