Somatosensory input to dopamine neurones of the monkey midbrain: responses to pain pinch under anaesthesia and to active touch in behavioural context.
The somatosensory responses of single dopamine (DA) neurones were recorded in the pars compacta of substantia nigra and in neighbouring DA cell groups of four Macaca fascicularis monkeys. These neurones were electrophysiologically discriminated against other cells by their polyphasic, relatively long impulses (2.0-5.0 ms) occurring at low rates (mostly 1.0-5.0/s), by antidromic activation from caudate or putamen, and by reduction of impulse rate following subcutaneous injection of apomorphine (0.05-0.15 mg/kg). Of 140 DA neurones recorded in two monkeys under barbiturate anaesthesia, 51% showed reductions and 17% increases in impulse rate during intense noxious pinch stimulation. Neurones responded non-somatotopically to stimulation of the hand, foot, face, dorsum and tail on both sides of the body. Innocuous, even intense, surface or deep somatosensory stimuli were ineffective. Systemic injection of the DA receptor antagonist haloperidol (0.33-0.5 mg/kg) strongly reduced the pinch responses. Of 154 DA neurones recorded in two monkeys during self-initiated arm movements, 84% showed phasic activations with latencies of 65 ms when the monkey's hand touched a food morsel inside the target box. Responses were absent when touching other objects. Touch responses to food did not occur when the reaching movement into the same food box was performed in reaction to an external trigger stimulus. In conclusion, DA neurones were activated in specific behavioural contexts by somatosensory stimuli of low intensities while responding unconditionally to noxious input.
Romo
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Schultz
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D000200:Action Potentials / Q000187:drug effects; D000758:Anesthesia; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D004298:Dopamine / Q000502:physiology*; D004558:Electric Stimulation; D006220:Haloperidol / Q000494:pharmacology; D008251:Macaca / Q000502:physiology*; D008252:Macaca fascicularis / Q000502:physiology*; D009068:Movement / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D013378:Substantia Nigra / Q000378:metabolism / Q000502:physiology* / Q000503:physiopathology; D014110:Touch / Q000502:physiology*
D006220:Haloperidol; D004298:Dopamine