Tectal influences on cat ocular motoneurons.

Abstract

Abstract Field and intracellular potentials were recorded in the abducens and trochlear nuclei of the anesthetized cat following electrical stimulation of the superior colliculus. Various lesions were placed to study the course of the tecto-ocular path. Following tectal stimulation ipsilateral abducens motoneurons were inhibited and contralateral ones were excited from the same stimulus site. The thresholds became lower as the stimulating site moved from rostral to caudal, from surface to depth and from medial to midline of the superior colliculus. Combined subthreshold stimulation of different sites revealed spatial facilitation. Our data indicate that for the most part tecto-abducens effects are mediated through polysynaptic paths and that disynaptic tecto-abducens connections, though present, may play a minor role. Lesion studies suggest that the tecto-abducens pathway runs from the tectum to the ipsilateral midbrain reticular formation from where it descends laterally in the brain stem to the motoneurons. Crossing to the contralateral VIth nucleus occurs caudal to the midbrain. Contrary to the abducens results tectal effects on trochlear motoneurons were very weak. The present data are discussed in relation to tectal eye movement studies.