Modification of the Macaque's Vestibulo-ocular Reflex by Picrotoxin

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Abstract
• The vestibulo-ocular reflex (VOR) in the macaque was tested by a modified Bárány spinning test before and after subcutaneous administration of 1 mg/kg of picrotoxin. The drug caused a decrease in the nystagmus time constant to a value near that of the cupula and a decrease in nystagmus asymmetry. Picrotoxin prevented diazepam from increasing the time constant of vestibular nystagmus. Furthermore, picrotoxin reduced the nystagmus time constant after vermisectomy, a lesion that increases the nystagmus time constant and prevents some VOR modifications. Because picrotoxin and diazepam interact antagonistically in the γ-aminobutyric acid (GABA) neurotransmitter system, these results show a role of GABA in the neural network that transforms a short cupula time constant into a longer nystagmus time constant. (Arch Otolaryngol 1981;107:372-376)