The antinociceptive effects of stimulating the pretectal nucleus of the rat

Changes in the tail-flick latency to noxious heat were studied following electrical stimulation of the dorso-medial thalamus of the rat. Brief (15 sec), low intensity (35 microA) stimulation of the anterior pretectal nucleus caused no escape behavior or motor deficits but increased tail-flick latency for more than 45 min. Responses to non-noxious stimuli were enhanced but the animals were not hyperactive. The anterior pretectal nucleus does not receive retinal or accessory visual inputs like other parts of the pretectal complex but is known to receive axons from somatosensory cortex and project to the perirubral mesencephalic reticular formation and the periaqueductal gray (PAG). The antinociceptive effects of anterior pretectal stimulation were much longer lasting than those of PAG, less disrupting to motor performance and the stimulation was not aversive.