Presence of neuronal cell bodies in the sympathetic pressor areas of dorsal and ventrolateral medulla inhibiting phrenic nerve discharge in cats

To examine whether neuronal cell bodies (perikarya) in the pressor areas of dorsal medulla or ventrolateral medulla also modulate respiratory function, phrenic nerve activity was monitored and correlated with the pressor response in chloralose-urethane anaesthetized cats. The animals were paralyzed and artificially ventilated maintaining the end-tidal fractional concentration of CO₂ at 0.04–0.05. The same pressor point in the dorsal or ventrolateral medulla was stimulated electrically (rectangular pulse of 20–200µA, 80 Hz and 0.5 ms) and then chemically (0.25–0.5 M sodium glutamate, 80–200 n1). Areas producing pressor effects in either the dorsal or ventrolateral medulla produced a current-dependent decrease of phrenic discharge. The decrease in Pna was significant when the electrical current reached 50µA or above. It occurred immediately before the onset of increase in blood pressure. Injection of glutamate to the same pressor point in either the dorsal or ventrolateral medulla produced a similar decrease in phrenic nerve activity. The results suggest that in the pressor areas of dorsal and ventrolateral medulla there are neuronal perikarya that can increase systemic arterial presssure and inhibit phrenic nerve activity. Whether the same or separate neurones are responsible for these responses is to be determined.