Vestibular and optokinetic nystagmus in the ketamine-anesthetized rabbit.
Abstract
Ketamine, or ketamine hydrochloride, is a non-barbiturate, rapid-acting disassociative anesthetic: the primary central nervous system action of ketamine appears to be a non-competitive block of NMDA (named after the selective agonist N-methyl-D-aspartate).
In the current study, we examined the effect of ketamine on cortical and subcortical function by exploiting evoked eye movements: we analyzed the modification of vestibular ocular reflex (VOR), optokinetic nystagmus (OKN) and visual-vestibular-optokinetic reflex (VVOR) in the rabbit after administration of therapeutic doses of ketamine.
All the animals underwent to electronystagmography examination: the animals were placed on a “Tonnies rotatory chair Pro model” which was placed in the middle of a rotatory cylindrical chamber (2 metres in diameter and 1.9 metres in height), the animal’s head affixed rigidly to a superstructure of the chair in a way that semicircular horizontal canals were on the horizontal plane.
Ketamine produces a “dissociative anaesthesia” which implies that the patients are detached from their surroundings. Unlike other forms of general anaesthesia the patient’s eyes often remain open and present a nystagmus.
Our results, taken together, demonstrate that after ketamine administration cortical circuits continue to processes visual patterns in a dose-dependent manner despite the animal’s behavioral dissociation.
