ABSTRACT
The present study shows the effects of electrical`stimulation of mesencephalic and diencephalic structures on the activity of two types of neuron from the rostral ventromedial medulla,which are related to the nocifensive reflex known as tail flick response (TF). One type of neuron, the off-cell abruptly stops firing immediately before the tail is flicked, while the other type, the on-cell, increases firing just before tyhe flick. When electrical stimulation was applied to mesencephalic and diencephalic structure the TF was inhibited and, simultancously, both kinds of cell showed increment in their activities. On average,this increment was 81ñ22.09%for the off-cell, and 1563ñ257.66%for the on cell. Quantitative analysis showed a directly proportional relationship between the activation of the firing rate of both kinds of cell and the intensy of the simulation currents. Also, when the simulation electrode was positioned more rostrally in the brain, greater currents were needed to reach the threshold of analgesia. The present work contributes to a large body of evidence indicating that off-cell, or both, are involved in the complex mechanism of the control of nociceptive tranmission and nicifensive reflexes