Properties of postganglionic sympathetic neurons with axons in phrenic nerve

The aim of the study was to test the reflex and resting properties of postganglionic sympathetic neurons with axons located in the right phrenic nerve. The experiments have been performed on chloralose-anesthetized cats with both vago-aortic nerves cut. The somata or the postganglionic sympathetic neurons were located in the stellate ganglion. Axons of these neurons passed through the upper and lower phrenic nerve roots and through the phrenic nerve itself. The presence of cardiac and respiratory rhythmicities was detected in the activity of the phrenic postganglionic sympathetic neurons. Hyperventilation, which abolished burst discharges of the phrenic nerve, decreased the sympathetic activity by 14%. Systemic hypoxia (ventilating the animals for 2 min with 8% O2 in N2) increased the sympathetic activity threefold. The results of our experiments suggest that axons of the sympathetic neurons located in the right phrenic nerve could possibly be diaphragmatic muscle vasoconstrictors.