Nigral inputs to the pedunculopontine region: intracellular analysis.

Intracellular recordings were made from neurons of the pedunculo-pontine region (PPR), the midbrain-pontine tegmentum around the brachium conjunctivum, in pentobarbital-anesthetized cats. Stimulation of the substantia nigra (SN) induced inhibitory postsynaptic potentials (IPSPs) in PPR neurons at a short latency (mean 2.17 ms, S.D. 0.66, n = 34) with a considerably long duration (mean 65.3 ms, S.D. 22.6). These neurons were distributed not only in the pedunculopontine tegmental nucleus (27 cells), but also in the cuneiform nucleus (5 cells) and the parabrachial nucleus (2 cells). Out of 34 cells, only two cells showed convergent synaptic inputs from SN and the cerebellar nuclei. Thus, it is concluded that PPR neurons receive mainly the inhibitory inputs from SN, one of the outputs of basal ganglia, and are infrequently influenced by the cerebellar outflow.