In vivo release of substance P in the nucleus tractus solitarii increases during hypoxia.

In vivo release of substance P (SP) was measured by microdialysis in the nucleus tractus solitarii (nTS) in adult cats. Small perfused semipermeable tubules (microdialysis probes) were implanted stereotaxically in the nTS, at the position of respiration-related neurons and perfused with artificial CSF. SP was determined by radioimmunoassay of the perfusate. Increased extracellular concentrations of SP-like immunoreactivity (SP-LI) were measured during hypoxia induced in artificially ventilated cats. In addition, a prolonged increase in the extracellular SP-LI concentration was encountered after cervical vagotomy. The results corroborate the suggestion that SP is a mediator of the central response to hypoxia.