Axonal projections and primary afferents of bulbar respiratory modulated and unmodulated neurons travelling with vagal nerve or spinal cord in the rabbit.

Respiratory modulated neurons of the rabbit were examined for efferent projections and afferent connections via the spinal cord or the vagal nerves. Variability of latency of responses proved to be related to latencies. When latency of evoked potentials is plotted versus variability of latency, monosynaptic responses can apparently be discriminated from oligo- or polysynaptic responses. Latency of antidromic responses depends from stimulus frequencies used. Results showed that only 12% of all respiratory modulated neurons have spinal descending axons conducting at 9-45 m per sec and 8% of the inspiratory group of neurons possess axons running along with the vagal nerves conducting at 20-37 m per sec. It is concluded that the respiratory network in the rabbit is essentially different from that in the cat.