Ascending spinal tracts of the spino-bulbo-spinal reflex in cats.

Twenty-six chloralosed cats were employed in order to determine spinal ascending pathways of the spino-bulbo-spinal (SBS) reflex evoked by stimulation of the sural nerve. 1. Partial spinal transection of the dorsal part of the lateral funiculus abolished the SBS reflex ipsilateral to sural nerve stimulation. 2. By recording spinal cord potentials in response to sural nerve stimulation two pathways were established in the dorsolateral funiculus as the spinal ascending tracts of the SBS reflex; one is the direct pathway to the bulbar reticular-formation (direct spino-reticular tract) and the other one (indirect spino-reticular tract) is the relayed by the lateral cervical nucleus. Direct stimulation of the dorsolateral funiculus at the lumbar level elicited the SBS reflex. 3. Short-latency unit discharges were recorded from axons of the direct spino-reticular tract by sural nerve stimulation. These axons were discharged antidromically by stimulation of the bulbar reticular formation. 4. Intracellular recordings from the neurons of the lateral cervical nucleus revealed that spike potentials, riding on EPSPs, were induced by sural nerve stimulation and antidromic firings were obtained by stimulation of the bulbar reticular formation. 5. Neurons originating the spino-reticular tract, direct and indirect, were located in the Rexed V-VII laminae in the lower lumbar segments. They were fired monosynaptically by sural nerve stimulation and antidromically by stimulating the dorsolateral funiculus of the lumbar segments. Among them, some were activated antidromically by stimulating the bulbar reticular formation.