Inhibitory response of pallidal neurons to cortical stimulation and the influence of conditioning stimulation of substantia nigra.

Single pulse stimulation of the sensory motor cortex of rats anesthetized with urethane was observed to inhibit the activity of neurons in the globus pallidus. When a train of 10 pulses delivered to the substantia nigra, preceded the cortical stimulation, the inhibitory response was significantly reduced in 46 of 66 globus pallidus neurons tested. A single pulse stimulus to the substantia nigra had no effect on the inhibitory response of globus pallidus neurons to cortical stimulation. Similar interaction experiments were performed in rats treated with haloperidol (HPL), a dopamine antagonist, or with 6-hydroxydopamine. In such experiments a train of stimulus pulses delivered to the substantia nigra did not attenuate the inhibitory response of globus pallidus neurons to cortical stimulation, suggesting that the observed interactions are dopamine-mediated.