Prolonged changes in dopaminergic terminal excitability and short changes in dopaminergic neuron discharge rate after short peripheral stimulation in monkey.

Time-courses of responses to peripheral somatosensory stimulation were studied in the nigrostriatal dopamine (DA) system by comparing rates of neuronal discharges with changes in nerve terminal excitability, an indicator of DA release. The excitability of DA nerve terminals in the putamen was assessed as probability for evoking an antidromic response in substantia nigra DA cells with electrical stimulation in an anesthetized monkey. At about 30-60% decrease of excitability was seen during and about 15 min beyond pain pinch stimulation (PPS) in 12 of 17 tested DA neurons, while 4 neurons showed a 40% increase. Discharge rates were decreased in 7 and increased in 5 of the 17 DA neurons during, but not after PPS. It is concluded that the release of DA in the striatum may be controlled in two ways: rapid reactions would be mediated by changes in discharge rate, while slower, prolonged responses could be due to presynaptic interactions with other striatal afferents.