Cerebellar stimulation modulates the intensity of a visceral nociceptive reflex in the rat

The cerebellum modulates different nociceptive phenomena and influences visceral functions. This study shows cerebellar modulation of an abdominal reflex elicited by a visceral noxious stimulus (colorectal distension, CRD). The intensity of the reflex was measured by electromyographic (EMG) recording from the rectus abdominus muscle, and the cerebellar cortex (vermis, lobule VIII), the fastigial nucleus, or the dentate nucleus was stimulated using D,L-homocysteic acid (0.1 M, 1 mul). To release the fastigial nucleus from inhibition by the Purkinje cells, bicuculline (GABA(A) receptor antagonist, 100 muM, 1 mul) was used. Stimulation of the cerebellar cortex enhanced, whereas stimulation or disinhibition of the fastigial nucleus decreased, the responses to CRD measured by EMG. Stimulation of the dentate nucleus did not have an obvious effect on the intensity of the reflex. These results are in agreement with the hypothesis that the cerebellum modulates visceral nociceptive functions, whereby the cerebellar cortex and the fastigial nucleus, respectively, play a pro-nociceptive and an anti-nociceptive role.