Electrical stimulation of the substantia nigra does not increase tail-flick latency in the rat

The effect of electrical stimulation at multiple sites in the midbrain was investigated in rats lightly anesthetized with barbiturate. The application of monopolar electrical stimulation to the substantia nigra (SN) or the adjacent cerebral peduncle failed to produce an elevation in tail-flick latency (TFL) in response to the application of noxious radiant heat. However, the same intensity of stimulation when applied to an area dorsal to the SN led to an elevation in TFL. This effect was not due to current spread to dopaminergic neurons in the zona compacta compartment of the SN because administration of cis-flupenthixol failed to block the effect. We conclude that, contrary to previous suggestions, discrete electrical stimulation of the SN itself does not give rise to a state of antinociception.