Anatomy and physiology of goldfish oculomotor system. II. Firing patterns of neurons in abducens nucleus and surrounding medulla and their relation to eye movements

Abstract

Simultaneous recordings were made of eye movements and the activity of cells in and around the abducens nucleus of the goldfish, Carassius auratus. Of the 4 major cell types found, 2 were almost certainly motoneurons and lie in anatomically separate parts of the nucleus. The phasic-tonic cells, concentrated in the caudal cell group, fired phasically before posterior saccades and tonically at a rate that varied with eye position and velocity. The tonic cells, concentrated in the rostral group, fired only tonically at a much lower rate than the phasic-tonic cells. The phasic-tonic cells probably innervate the fast fibers of the posterior rectus, and the pure tonic cells probably innervate its slow fibers. Comparisons of various measures of a phasic-tonic cells''s excitability indicated that excitability is not a unitary property of the cell, determined by a single factor such as its size.