NK3 receptors in the feline nucleus tractus solitarius are not involved with the muscle pressor Response

Isometric muscle contractions cause an increase in mean arterial pressure a nd heart rate. Previously, we showed that substance P (SP) is released from sites in the feline medial nucleus tractus solitarius (mNTS) in response t o isometric muscle contractions, and that it most likely interacted with NK , tachykinin receptors at these sites. This study was undertaken to determi ne whether other tachykinin receptors in this area of the brainstem are inv olved with the muscle pressor response. Receptor autoradiography, using [I- 125]Bolton-Hunter SP and [I-125][MePhe(7)] neurokinin B to label NK1 and NK 3 receptors, respectively, indicated that NK3 tachykinin receptors are as a bundant as NK, receptors in this region of the feline brainstem Injections of the specific NK3 receptor antagonist, SR 142801 (0.1 to 10 muM) into the mNTS did not modify the pressor response or the heart rate response to iso metric muscle contractions. Injection of SR142801 into the NTS prior to the injection of the NK, antagonist, GR82334 did not affect the action of GR82 334 to attenuate the muscle pressor reflex. We conclude that NK3 receptors in the NTS are not involved with the regulation of cardiovascular function during activation of the muscle pressor response. (C) 2001 Harcourt Publish ers Ltd.