Ultrastructure of intracellularly labeled trigeminal vascular convergence neurons.

Brainstem trigeminal vascular convergence (TVC) neurons receive an excitatory, nociceptive input from cranial blood vessels as well as the facial skin or cornea. In the present study, a population of cat TVC neurons was electrophysiologically identified and then intracellularly labelled with horseradish peroxidase. One TVC neuron from lamin IV and one from lamina V were processed for electron microscopy. Both cells have extensive axon terminal fields within trigeminal nucleus interpolaris as well as lamina IV and V of trigeminal nucleus caudalis. Analysis of thin sections showed that the soma and dendrites of the TVC neurons are contacted by synaptic terminals of various types. Both cells have myelinated axons and collaterals that give rise to unmyelinated preterminal processes. Within nucleus caudalis, terminals of the TVC cells contain round synaptic vesicles that synapse primarily with dendrites and spines.