Transient increase of contraversive saccade parameters following kainic acid injection in the periparabigeminal area of guinea pig.

Anatomical and electrophysiological data have shown that, in the guinea pig as well as in the cat, the nucleus prepositus hypoglossi gives rise to a disynaptic ascending projection to the superior colliculus via the peri-parabigeminal area in the mesencephalon. The functional role of this indirect pathway in the generation of eye movements has been studied by pharmacologically interfering at the mesencephalic level and by examining the induced effects on two differently elicited saccades in the alert guinea pig. A small iontophoretic injection of kainic acid induces a transient increase of the spontaneous saccadic activity in the contraversive direction leading to a pseudo-nystagmus. Both the amplitude and the mean velocity of the contraversive saccades are greater than before the injection. A similar enhancement also affects the parameters of the contraversive saccades induced by trunk rotations. These results suggest that peri-parabigeminal neurones exert an excitatory influence on their target cells in the ipsilateral superior colliculus which is responsible for contraversive rapid eye movements.