The parafascicular nucleus relays spinal inputs to the striatum: an electron microscope study in the rat.

A disynaptic projection from the spinal cord to the striatum was observed in the rat light and electron microscopically. An anterograde tracer, wheat germ agglutinin conjugated to horseradish peroxidase was injected into the ventral gray matter of the upper cervical spinal cord, and a retrograde tracer, biotinylated dextran amine was injected into the striatum of a rat. Then the parafascicular nucleus was examined. Some anterogradely labeled axon terminals originating in the spinal cord were observed to synapse with retrogradely labeled dendrites of parafascicular nucleus neurons which sent axons to the striatum. We concluded that information from the spinal cord was transmitted to the striatum, being relayed by parafascicular nucleus neurons.