Monosynaptic and disynaptic projections from the substantia nigra pars reticulata to the parafascicular thalamic nucleus in the rat

We examined a direct pathway and an indirect pathway via the reticular thal amic nucleus (RT) from the substantia nigra pars reticulata (SNr) to the pa rafascicular thalamic nucleus (PF) by using anterograde and retrograde trac t tracing methods. After biotinylated dextranamine (BDA) injection into the dorsolateral part of the SNr, many labeled fibers and axon terminals were distributed in the ventral part of the RT, as well as in the ventrolateral part of the PF, bilaterally with an ipsilateral dominance. After BDA inject ion into the ventral part of the RT, a plexus of labeled axons was found bi laterally with an ipsilateral dominance in the ventrolateral part of the PF . After combined injections of BDA into the dorsolateral part of the SNr an d cholera toxin B subunit (CTD) into the ventrolateral part of the PF on th e same side, overlapping distribution of BDA-labeled fibers and CTb-labeled neurons was observed in the ventral part of the RT ipsilateral to the inje ction sites, where the BDA-labeled axon terminals made symmetrical synaptic contacts with soma and dendrites of the CTb-labeled neurons. (C) 2000 Else vier Science B.V. All rights reserved.