Effect of superficial radial nerve stimulation on the activity of nigro-striatal dopaminergic neurons in the cat: role of cutaneous sensory input.

The release of 3H-dopamine (DA) continuously synthesized from 3H-tyrosine was measured in the caudate nucleus (CN) and in the substantia nigra (SN) in both sides of the brain during electrical stimulation of the superficial radial nerve in cats lightly anaesthetized with halothane. Use of appropriate electrophysiologically controlled stimulation led to selective activation of low threshold afferent fibers whereas high stimulation activated all cutaneous afferents. Results showed that low threshold fiber activation induced a decreased dopaminergic activity in CN contralateral to nerve stimulation and a concomitant increase in dopaminergic activity on the ipsilateral side. Stimulation of group I and threshold stimulation of group II afferent fibers induced changes in the release of 3H-DA mainly on the contralateral CN and SN and in the ipsilateral CH. High stimulation was followed by a general increase of the neurotransmitter release in the four structures. This shows that the nigro-striatal dopaminergic neurons are mainly--if not exclusively--controlled by cutaneous sensory inputs. This control, primarily inhibitory in the side contralateral to the stimulation, seems rather non-specific when high threshold cutaneous fibers are also activated. Such activations could contribute to reestablish sufficient release of DA when the dopaminergic function is impaired as in Parkinson's disease.