The reciprocal electrophysiological influence between the nucleus tegmenti pedunculopontinus and the substantia nigra in normal and decorticated rats

The electrophysiological characteristics of neurons of the nucleus tegmenti pedunculopontinus (PPN), in particular of those projecting to the substantia nigra (SN), and the reciprocal influence between the PPN and SN were investigated in normal and decorticated rats. In intact animals 65 of the 363 PPN recorded neurons (17.9%) were activated antidromically by SN stimulation, 96 (26.3%) were inhibited after stimulation while 43 (11.8%) were activated. In decorticated rats excitatory responses were decreased (4.8%) while antidromic and inhibitory responses did not change substantially. Electrical stimulation of the PPN induced a brief short-latency excitation of SN neurons (26/77, 33.7%) which was not modified by removing the cortex bilaterally 7-10 days prior to the recording session. This excluded the possibility that corticofugal fibers could be involved in the excitatory responses evoked by PPN stimulation in SN neurons. The latency of the antidromic response evoked in PPN cells by SN stimulation ranged from 0.5 to 12.0 ms and the estimated conduction velocity of these PPN output neurons ranged from 1.1 to less than 0.5 m/s. The electrophysiological heterogeneity of PPN cells was supported also by the fact that two types of neurons, both projecting to the SN, could be distinguished on the basis of their spontaneous firing rate and impulse waveform. The first had a low spontaneous activity (0.5-8 spikes/s) with a triphasic impulse which lasted 3-4 ms. The second had a high firing rate (15-20 spikes/s) and its impulse was usually biphasic and not longer than 3 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

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