Intrastriatal targets of projection fibers from the central lateral nucleus of the rat thalamus.

We examined light and electron microscopically intrastriatal targets of projection fibers from the central lateral thalamic nucleus (CL), which is a major relay of cerebello-striatal projections. The study was done in the rat by combining the anterograde tract-tracing with immunohistochemistry for parvalbumin (PV); an anterograde tracer (biotin dextran amine: BDA) was injected into the CL. In the striatum, 91% of BDA-labeled axon terminals made asymmetrical synapses on PV immunonegative dendritic spines (assumed to be those of striatal projection neurons); only 0.5% of BDA-labeled axon terminals made synapses on PV immunopositive dendritic shafts. The remaining BDA-labeled axon terminals were in synaptic contact with PV immunonegative dendritic shafts. The results suggest that the cerebello-striatal projections through the CL predominantly access to striatal projection neurons, with only minor access to PV immunopositive (assumed to be GABAergic) interneurons in the striatum.