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Abstract
In urethane-anesthetized rats discharges of neurons of substantia nigra, pars compacta
(SNC) were recorded extracellularly after natural somatic sensory stimulation and
electrical stimulation of peripheral sensory nerves. (1) Among different modalities
of somatic sensory stimulation tested, noxious stimuli were effective in reducing
spontaneous discharges of SNC neurons. The inhibition appeared with a concomitant
increase of spike amplitude. The same inhibitory effect was obtained by stimulating
the sciatic nerve (SC) repetitively. In response to single shock stimulation of the
SC the inhibition occurred at an average latency of 39.6 msec (S.E. 1.6 msec) and
lasted for 221.6 msec on average (S.E. 10.8 msec). (2) The SC-induced inhibition of
SNC neurons failed to reliably block ortho- and antidromic discharges evoked from
the caudate nucleus (Cd). (3) In rats with the Cd lesioned the SC-induced inhibition
was longer lasting than in controls. When the Cd was stimulated concurrently with
SC stimulation, the inhibition from the SC was weakened. (4) In a majority of SNC
neurons, their inhibition by SC stimulation, their inhibition by SC stimulation was
antagonized by intravenous injection of haloperidol.