A model system has been used to provide a sinusoidal angular or linear acceleration to a stereotaxically fixed cat. Individual second order vestibular neurons may be studied by intracellular or extracellular recording methods while the animal is in continuous motion. The response of these motion-modulated vestibular neurons has been studied following systemic administration of pharmacological agents. The present proposal provides for an extension of the above studies into the following two areas of research: (1) intracellular recording and current injection in vestibular neurons, and (2) iontophoretic application of drugs onto motion-modulated vestibular neurons. The purpose of this investigation was to consider the characteristics of repetitive impulse firing elicited in vestibular neurons by steady one sec current pulses. Resting potentials ranged from 40-65 mV and action potentials (AP) attained 40-50 mV. Frequency vs injected current (f-I) curves were determined and were linear with a slope of 4.5 plus or minus 0.88 imp/sec/nA (n equals 10). Adaptation to injected current was noted in only one neuron which responded to contralateral angular acceleration. Nine neurons which responded to ipsilateral angular acceleration showed no adaptation. The data indicated that the transduction characteristics of the vestibular membrane are linear and for the low currents used, exhibit only a single slope. Initial studies with iontophoresis will be directed towards determining the responses of vestibular neurons to norepinephrine, d- amphetamine and acetylcholine. Further studies will consider the antagonists to these agents as a means of further defining the exact role played by norepinephrine and acetylcholine in neurotransmission. Bibliographic references: Kirsten, E.B. Responses of Vestibular Neurons to Intracellular Current Injection. Sixth Int. Congress of Pharmacol. 1975.