Reflex carotid body chemoreceptor control of phrenic sympathetic neurons

The reflexes reaction of phrenic sympathetic neurons to stimulation of carotid body chemoreceptors we tested in chloralos-anaesthetized and paralyzed cats with both vago-aotic nerves cut. During systemic hypoxia (animals ventilated with 10%₂ in O_₂ in N₂) the sympathsti phrenic nerve activity increased from 100% in the control to 269%. The increase was markedly attentuad after cutting both nerves, Reflex exciatotry response in phrenic sympathetic neurons with the latency of 150 msec was evoked by electrical stimulation of the right carotid sinus nerve (3 pulses of 0.2 msec, 333 Hz). The central transmission time of the reflex was about 90 msec. Injecting 0.1 ml of 1 M NaHCO₃ saturated with CO₂ (in order to activate carotid body chemoreceptors) into the right or left carotid sinus, evoked excitatory responses in sympathetic neuronsp regardless of the side. The stimulation of carotid body chemoreceptors also increased somatic phrenic nerve activity. The three methods applied to the stimulation of carotid body chemoreceptors produced increase of phrenic nerve sympathetic activity.