SIMULTANEOUS RECORDING OF SPONTANEOUS ACTIVITIES AND NOCICEPTIVE RESPONSES FROM NEURONS IN THE PARS COMPACTA OF SUBSTANTIA-NIGRA AND IN THELATERAL HABENULA

Using simultaneous extracellular single-unit recording in the pars com pacta of the substantia nigra and in the lateral habenula of rats, 45 pairs of neurons responding to peripheral nociceptive stimulation were recorded. In 41 of these pairs, nigral dopaminergic neurons were inhi bited by peripheral nociceptive stimulation, while lateral habenula ne urons were excited. Moreover, in 14 pairs, when sweeps were triggered randomly by spontaneous spikes from lateral habenula neurons the spont aneous firing rate of the dopaminergic neurons during the first 250 ms after the sweep was much lower than rates after this time period. In this case, the sweep was often triggered by burst-firing of lateral ha benula neurons, Our results indicate a cross-correlation between the s pontaneous activities of these two nuclei, suggesting that the excitat ion of lateral habenula neurons induced by peripheral nociceptive stim ulation might be directly responsible for inhibition of nigral dopamin ergic neurons.