Cold pressor test in the rat: medullary and spinal pathways and neurotransmitters

Abstract

This study was designed to delineate the medullary and spinal pathways mediating the cardiovascular responses to cold pressor test (CPT) and to identify neurotransmitters in these pathways. Experiments were done in barodenervated, urethane-anesthetized, male Wistar rats. The CPT was performed by immersing the limbs and ventral half of the body of the rat in ice-cold water (0.5 degrees C) for 2 min. CPT elicited an immediate increase in mean arterial pressure (MAP), heart rate (HR), and greater splanchnic nerve activity (GSNA). Bilateral blockade of ionotropic glutamate receptors (iGLURs) in the rostral ventrolateral medullary pressor area (RVLM) significantly attenuated the CPT-induced responses. Bilateral blockade of gamma-aminobutyric acid (GABA) receptors, but not iGLURs, in the nucleus ambiguus (nAmb) significantly reduced the CPT-induced increases in HR, but not MAP. Blockade of spinal iGLURs caused a significant reduction in CPT-induced increases in MAP and GSNA, whereas the increases in HR were reduced to a lesser extent. Combination of the blockade of spinal iGLURs and bilateral vagotomy or intravenous atropine almost completely blocked CPT-induced tachycardia. Midcollicular decerebration significantly reduced CPT-induced increases in MAP and HR. These results indicated that: 1) CPT-induced increases in MAP, HR, and GSNA were mediated by activation of iGLURs in the RVLM and spinal cord, 2) activation of GABA receptors in the nAmb also contributed to the CPT-induced tachycardic responses, and 3) brain areas rostral to the brain stem also participated in the CPT-induced pressor and tachycardic responses.

Local heat application to the leg reduces muscle sympathetic nerve activity in human

“…In particular, the spinoreticular tract projecting to the medullary reticular formation activates the vasomotor center in the medulla oblongata. Activation of the projection from the vasomotor center to the intermediolateral cell column in the thoracolumbar cord results in excitation of the sympathetic preganglionic neurons causing increased MSNA (Nakamura et al 2008). In this regard, Kregel et al (1992) studied the relationship between MSNA and the dynamics of both the stimulus and pain sensation during mild and moderate local skin cooling.…”

Cardiovascular responses to microinjections of urocortin 3 into the nucleus tractus solitarius of the rat

“…The general procedures have been described in detail elsewhere (28). Briefly, the rats were anesthetized with an inhalation of isoflurane (2 to 3% in 100% oxygen), the trachea was cannulated with polyethylene tubing (PE-240), and the rats were artificially ventilated using a rodent ventilator (model 683, Harvard Instruments, Holliston, MA).…”

“…This procedure has been described elsewhere (28). Anesthesia was induced and maintained by tracheal administration of isoflurane as described earlier.…”

“…The details of this technique are described elsewhere (28). Briefly, the rats were placed in a prone position in a stereotaxic instrument with bite bar 18 mm below the interaural line.…”

Blood Pressure Response to Cold Stress in Black Cameroonian Adults

“…The latter reaches the thalamus and also sends collaterals towards the reticulated substance. These collaterals stimulate the vasomotor center at the level of the spinal bulb, which leads to a discharge of the sympathetic nervous system towards the heart and the blood vessels [7]. This results in significant variations in hemodynamic parameters, resulting in an increase in blood pressure due to peripheral vasoconstriction and an increase in cardiac output secondary to an acceleration of the heart rate [8].…”