Role of the otolith organs in generation of horizontal nystagmus: effects of selective labyrinthine lesions

The direct cellular effects of ethanol on trigeminal motoneurons were studied in chronic cats during sleep and wakefulness. Intracellular and extracellular recordings were obtained while simultaneously injecting ethanol microdroplets onto the surface (juxtacellularly) or within the soma (intracellularly) of these motoneurons. Juxtacellular ethanol injection resulted in a suppression of neuronal excitability as well as a reduction in the amplitude of action potentials and monosynaptically-induced excitatory postsynaptic potentials. Intracellular ethanol injection led to a slight increase in excitability (i.e. membrane depolarization); concurrently, however, there was a reduction in the amplitude of spike and synaptic potentials. We conclude that the predominant response of trigeminal motoneurons to the direct application of ethanol entails a dose-dependent reduction in membrane excitability in addition to a depression of excitatory synaptic transmission. This pattern of ethanol action was observed throughout the states of quiet sleep and active sleep as well as when the animal was awake.