Spinal cholinergic modulation of cardiovascular tone and a somatosympathetic reflex response.

The purpose of this study was to examine the relationship between spinal cholinergic pressor neurons and a somatosympathetic reflex response in rats. Intrathecal (IT) injection of the cholinesterase inhibitor, neostigmine (NEO), produced marked pressor and tachycardic responses without any changes in respiratory parameters. On the other hand, stimulation of the sciatic nerve produced increases in both cardiovascular and respiratory (tidal volume, minute volume, respiratory rate) responses. These cardiorespiratory responses to nerve stimulation were inhibited by IT NEO. A pressor response could also be induced by topical application of NEO to the surface of lower spinal cord, which was not altered by prior dorsal rhizotomy. These results indicate that two independent cholinergic systems exist in the spinal cord, one of which participates in the inhibitory modulation of the somatosympathetic reflex, and the other which mediates a sympathoexcitatory response. It is unlikely that the pressor response to spinal administration of NEO is mediated through this somatosympathetic response.