Relationships between thalamostriatal neurons and pedunculopontine projections to the thalamus: a neuroanatomical tract-tracing study in the rat

The present study aimed to investigate whether the pedunculopontine project ion to the thalamus overlaps with identified thalamostriatal neurons. These projections were studied using a dual tract-tracing procedure combining an terogradely transported biotinylated dextran amine (pedunculopontine projec tions) and retrogradely transported Fluoro-Gold (thalamostriatal projection s). Overlapping thalamic territories between thalamostriatal neurons and th e axon terminals arising from the pedunculopontine tegmental nucleus were o bserved in the midline (paraventricular) and in the intralaminar (centrolat eral, central medial, paracentral and parafascicular) thalamic nuclei. Othe r thalamic nuclei, such as the ethmoid, intermediodorsal, mediodorsal, para tenial, posteromedian, ventromedian, ventrolateral and rhomboid thalamic nu clei, displayed a lesser degree of overlap. These observations suggest the existence of presumptive contacts between thalamostriatal neurons and axons emerging from the pedunculopontine tegmental nucleus, therefore supporting the possible existence of feedback circuits in the rat basal ganglia in wh ich the tegmento-thalamic projection would play a major role.