Effects of axotomy on the activity of the motor neurons of the external ocular motor nucleus during saccadic movements

Abstract

The instantaneous firing frequency of cat abducens nucleus motoneurons (Mns) during spontaneous saccadic eye movements has been analyzed.Recordings were carried out from both control and axotomized Mns.Firing frequency of control Mns increased gradually during the first four to five interspike intervals, at which point maximum firing frequency was reached.Axotomized Mns showed an increase in firing frequency only up to the second or third interval, decreasing rapidly then.Linear relationships, with high correlation coefficients, were established between the first five intervals versus maximum frequency or peak eye velocity during saccades, in both control and axotomized Mns.However, the latter showed a decrease in the linear correlation from the third interval because of the decrease in the slope of the relationship.Functional implications of these results are discussed according to the present hypothesis on the effects of axotomy upon oculomotor neurons.