Selective effect of cinnarizine on the vestibular nucleus neurons

Effects of cinnarizine were studied on the lateral vestibular nucleus (LVN) and spinal trigeminal nucleus (STN) of cats anesthetized with alpha-chloralose. Cinnarizine did not produce any obvious alterations of the field potential and spike generation of type B interneurons in STN elicited by trigeminal nerve stimulation as well as the field potential in LVN by vestibular nerve stimulation. Spike generation of monosynaptic LVN neurons elicited by the suprathreshold stimulus to the vestibular nerve was unaffected by cinnarizine up to 4 mg/kg. When the subthreshold stimulus was applied to the vestibular nerve, however, the spike number of LVN monosynaptic neurons was significantly increased after cinnarizine treatment. The enhancement of spike firing by cinnarizine upon both supra- and subthreshold stimuli to the vestibular nerve was found to be more pronounced in LVN polysynaptic neurons than monosynaptic ones. Since the effect of cinnarizine on LVN neurons was not dose-dependent, it is suggested that the enhanced responsiveness of the neurons by the drug might be due to an increase of blood flow, but not to a direct excitation of the neurons themselves.