DETECTION OF IMMUNOREACTIVE SUBSTANCE P-LIKE SUBSTANCES FROM CAT BRAIN-STEM SITES DURING FATIGUING ISOMETRIC CONTRACTIONS

Isometric contractions were generated on the left hindlimb muscles fro m adult cats (n=11) anesthetized with alpha-chloralose (75 mg/kg) to d etermine whether immunoreactive substance P (irSP) was released from e ither the right periaqueductal grey (FAG) or ventrolateral medulla (VL M), sites shown to be involved with the integration of the muscle pres ser response. The release of immunoreactive SP was measured using SP a ntibody-coated microelectrodes that were inserted into the FAG or the VLM during periods of rest, fatiguing isometric contractions and post- contraction. Mean arterial pressure increased by 78 +/- 11 mmHg during the contractions. There was a release of irSP from sites in the medul la during the contractions compared to the non-contraction periods but none was detected from the FAG in response to muscle stimulation. The se results provide further evidence that SP-like substances may be inv olved with the central integration of the muscle presser response.