Antiepileptic treatment and oculomotor neurons

Abstract

This report describes the changes of the spontaneous firing rate due to an acute non-toxic dose of phenytoin (PHT), a drug commonly used in antiepileptic therapy, in the pre-motor neurons involved in saccadic movement. The drug (500 mg/kg of a 10% PHT suspension in arabic gum) was orally administered, and plasma and brain levels were regularly evaluated (EMIT assay). Results show that PHT significantly modifies the spontaneous electrical activity of the pre-motor neurons localized in the paramedian pontine reticular formation by inducing excitation, inhibition, or a biphasic effect. PHT action was observed 10-15 min after drug administration, when plasma and brain concentrations were still very low. The oculomotor system neurons appear to be a more specific target to this drug in comparison to the cerebellum and the vestibular system. Since the PHT action was observed 1 hour after drug administration in the vestibular nuclei and the cerebellum, which are extensively connected with the oculomotor neurons, it is possible to hypothesize that PHT can affect the oculomotor neurons directly and, with longer latency, indirectly through the vestibular nuclei and the cerebellum.