Neuropeptide Y-like substances are released from the rostral brainstem of cats during the muscle pressor response.

1. In this study, the release of immunoreactive neuropeptide Y (NPY)-like substances (irNPYs) was measured from the rostral brainstem in response to fatiguing isometric contractions of the hindlimb muscle of cats anaesthetized with alpha-chloralose. 2. The irNPYs were measured using a solid phase autoradiographic immunoassay. NPY antibody-coated glass microelectrodes were inserted stereotaxically into the rostral brainstem during rest and contractions. Control procedures such as passive leg flexing, stimulation of the central end of the cut tibial nerve, brief repeated carotid occlusions and carotid sinus nerve stimulations were performed to determine whether patterns of release of irNPYs were specific to the pathways activated during the muscle pressor response. 3. During isometric contractions, the mean arterial blood pressure (MABP) and heart rate (HR) increased by 60-70 mmHg and 15-20 beats min-1, respectively. Only the brief carotid occlusions caused a similar increase in MABP and HR. 4. During isometric contractions, less irNPYs were released from sites in the lateral reticular nucleus, lateral tegmental field and vestibular nuclei at a level in the brainstem 4.0-4.4 mm rostral to the obex. In contrast, irNPYs were released from sites near the lateral tegmental field and nucleus ambiguus at a more caudal level tested (1.3 mm anterior to the obex) in response to contractions. Brief carotid occlusions caused a release of irNPYs from the lateral reticular nucleus on the contralateral side of the brainstem (at 3.5 mm anterior to the obex). None of the other procedures resulted in a release of irNPYs from these sites in the brainstem. 5. These data indicate there are differences in the patterns of release of irNPYs in response to activation of reflex pathways which increase arterial pressure. Given the sites in the rostral brainstem where irNPYs were released, irNPYs may be involved with the central regulation of arterial pressure during the muscle pressor response.