Influence of reticular mechanisms upon hypoglossal, trigeminal and phrenic activities

Studies were undertaken to evaluate the hypothesis that mechanisms within the reticular formation influence activities of nerves to muscles of the upper airways more than the bulbospinal-phrenic system. In decerebrate, vagotomized, paralyzed and ventilated cats, activities of the phrenic, trigeminal, and the hypoglossal nerves were monitored. Activity of the pontile and medullary reticular formation was increased directly by electrical stimulation within the brainstem and indirectly by stimulating the sciatic nerve. Trigeminal and hypoglossal discharges increased more than phrenic during stimulations at many brainstem loci. Changes were typically maintained for one or more respiratory cycles following termination of stimulation. At some loci, activation of neurons by microinjections of glutamate increased trigeminal and hypoglossal activities more than phrenic. Although responses were extremely variable, activities of the trigeminal and/or hypoglossal nerves usually increased more than phrenic during stimulations of the sciatic nerve or upon termination of stimulation. The results support the conclusion that respiratory-modulated trigeminal and hypoglossal discharges are dependent upon reticular mechanisms for their expression.