title: Abnormal activity of neurons in abducens nucleus of strabismic monkeys.
abstract: OBJECTIVE
  Infantile strabismus is characterized by persistent misalignment of the eyes. Mounting evidence suggests that the disorder is associated with abnormalities at the neural level, but few details are known. This study investigated the signals carried by abducens neurons in monkeys with experimentally induced strabismus. We wanted to know whether the firing rates of individual neurons are exclusively related to the position and velocity of one eye and whether the overall level of activity of the abducens nucleus was in the normal range.
  
  
  METHODS
  We recorded 58 neurons in right and left abducens nuclei while strabismic monkeys (one esotrope and one exotrope) performed a saccade task. We analyzed the firing rates associated with static horizontal eye position and saccades by fitting the data with a dynamic equation that included position and velocity terms for each eye. Results were compared to previously published data in normal monkeys.
  
  
  RESULTS
  For both strabismic monkeys the overall tonic activity was 50 to 100 spikes/s lower, for every suprathreshold eye position, than what has previously been reported for normal monkeys. This was mostly the result of lower baseline activity; the slopes of rate-position curves were similar to those in previous reports in normal monkeys. The saccade velocity sensitivities were similar to those of normal monkeys, 0.35 for the esotrope and 0.40 for the exotrope. For most neurons the firing rate was more closely related to the position and velocity of the ipsilateral eye.
  
  
  CONCLUSIONS
  These data suggest that strabismus can be associated with reduced neural activity in the abducens nucleus.
authors.affiliation: Washington National Primate Research Center, University of Washington, Seattle, Washington, United States.
authors.forename: Mark M G
authors.initials: MM
authors.lastname: Walton
authors.affiliation: Washington National Primate Research Center, University of Washington, Seattle, Washington, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Mustari
authors.affiliation: Department of Ophthalmology and Visual Neurosciences, University of Minnesota, Minneapolis, Minnesota, United States Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota, United States.
authors.forename: Christy L
authors.initials: CL
authors.lastname: Willoughby
authors.affiliation: Department of Ophthalmology and Visual Neurosciences, University of Minnesota, Minneapolis, Minnesota, United States Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota, United States.
authors.forename: Linda K
authors.initials: LK
authors.lastname: McLoon
mesh_terms: D065827:Abducens Nucleus / Q000503:physiopathology*; D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D008253:Macaca mulatta; D009046:Motor Neurons / Q000502:physiology*; D012438:Saccades / Q000502:physiology*; D013285:Strabismus / Q000503:physiopathology*
keywords: abducens nucleus; esotropia; exotropia; neurophysiology; strabismus