Responses of respiratory neurons of the rabbit to some excitatory and inhibitory stimuli.

The effects of an afferent stimulation of the vagus nerve, hypercapnia and hyperventilation on the discharges of pontine, medullary and phrenic respiratory neurons were studied. The responses were investigated in spontaneously breathing, lightly anaesthetized rabbits with intact vagi, and subsequently during artificial ventilation, after vagotomy and under surgical anaesthesia. We found that the patterns of activity of respiratory neurons depend upon the integrity of vagal conduction, pattern of ventilation and depth of anaesthesia, and that vagotomy and deep anaesthesia markedly modify, and sometimes even reverse, the responses of these neurons to respiratory stimuli. The pre-vagotomy type of response can be restored by stimulating the central end of a cut vagus nerve with standard pulses triggered by action potentials recorded simultaneously from the animal respiratory unit. The significance of these findings is discussed.