Connections Between NO Synthase-Containing Neurons of the Pedunculopontine Tegmental Nucleus and the Substantia Nigra in Rats

Experiments on rats with detection of the NADP-d-activity in neurons of the pedunculopontine tegmental nucleus (PPTg) and their processes demonstrated that between the substantia nigra (SN) and PPTg there are connections established by the neurons containing nitric oxide synthase (NOS). Two types of connections were observed. Axon-like collaterals of the neuronal pathways sent by PPTg neurons toward the forelimb penetrate the SN from its dorsal side. In addition, dendrites of the NOS-containing neurons localized within the rostral PPTg part penetrate the caudoventral region of the reticular SN (SNr). It is supposed that NO produced by these processes within the SN can exert modulating influences on synaptic transmission in this structure; when produced in excessive amounts under some pathological conditions, NO can be a factor evoking neurodegeneration in the midbrain.