ANTERIOR BRAINSTEM AND SCIATIC NERVE CONNECTIONS TO VESTIBULAR NUCLEI IN CAT

Abstract

The relationship between the anterior brainstem and vestibular nuclei in the cat were investigated with electrophysiologic techniques. Electric stimulation of a locus either in the midbrain reticular formation just ventral to the central gray, or the adjacent median longitudinal fasciculus and other midline structures, such as the third nerve nucleus, resulted in maximal action potentials in the vestibular nuclei. Unilateral midbrain stimulation evoked bilateral vestibular responses. Stimulation of midline thalamic nuclei or the hypothalamic region evoked no potentials in the vestibular nuclei. The recorded action potentials usually consisted of one or two short latency, short duration waves followed immediately by a third wave which was of considerably longer duration. The first spike was quite resistant to anesthesia and anoxia, while the second wave was less resistant. The slowest, or third wave, quickly diminished in amplitude, even with relatively low frequency of stimulation. It was quite sensitive to anesthesia. The characteristics of these potentials suggest that both direct axonal and polysynaptic pathways exist between the midbrain and the vestibular nuclei. Unilateral stimulation of the sciatic nerve evoked a bilateral response in the vestibular nuclei. The usual response was a negative wave. Its properties were somewhat similar to the response recorded in the reticular formation upon sciatic nerve stimulation. The vestibular potentials interacted with those produced upon midbrain stimulation suggesting a common neuronal pool.