Peripheral Chemoreflex Control of Sympathetic Nerve Activity

Abstract

The rhythmicity of sympathetic neurons and nerves has been studied extensively since 1930’s (Adrian et al., 1932; Koizumi et al., 1971; Gootman and Cohen, 1974; Trzebski et al., 1975; Preiss et al., 1975; Barman and Gebber, 1976; Bachoo and Polosa, 1987). Parallel activities of phrenic nerve (PN) and cervical preganglionic sympathetic nerve (PSN) led to the belief that central respiratory drive generates both the rhythms and that PSN chemoreflex is dependent on the respiratory neuronal network (Bachoo and Polosa, 1987). Accordingly, PSN activity would not be elicited or augmented by carotid chemoreflex in the absence of PN activity (between PN bursts and during hypocapnic apnea). It is possible that the PSN activity during expiratory phase is due to expiratory neuron activity (Bachoo and Polosa, 1986) and that PSN response during apnea depends on expiratory activity, since expiratory neurons often fire continuously during hypocapnic apnea in the cat (Nesland and Plum, 1965; Batsel, 1967; Cohen, 1968; Sears et al., 1982). The possibility was strengthened by the observation that the PSN rhythmic activity correlated with the expiratory activity in the rat (Czyzyk et al., 1987). Also, other respiration-related brain-stem neurons could mediate the PSN chemoreflex response. Hypoglossal nerve (HGN) activity was reported to be preferentially responsive to hypoxia than PN (Bruce et al., 1982). Accordingly, the possibility that PSN activity is dependent on HGN activity needs to be tested.