Effects of adenosine triphosphate on neuron activities in the lateral and medial vestibular nuclei

Electrophysiological studies were carried out to elucidate the effects of adenosine triphosphate (ATP) on the vestibular nuclei of cats anesthetized with alpha-chloralose. Intravenous (i.v.) administration of ATP in doses of 0.5-2.0 mg/kg produced an enhancement of spike generation with vestibular nerve stimulation and spontaneous firing in both monosynaptic and polysynaptic neurons in the lateral vestibular nucleus (LVN) as well as in the medial vestibular nucleus (MVN). These effects of ATP, however, were not dose-dependent. In contrast, iontophoretic application of ATP up to 200 nA had only negligible effect on spike generation of mono- and polysynaptic neurons in the LVN and those in the MVN upon vestibular nerve stimulation. The results suggest that the enhancement of neuron activities in the vestibular nuclei following i.v. injection of ATP is due to the indirect effect probably resulting from an increase in blood flow in the brain, but not to a direct, excitatory effect of the drug on the neurons themselves.