Rostral ventrolateral medulla opioid receptor activation modulates glutamate release and attenuates the exercise pressor reflex

• Published in: Brain research Vol. 865; no. 2; pp. 177 - 185
• Main Authors: Ishide, Takeshi, Mancini, Maria, Maher, Timothy J, Chayaikul, Pasarapa, Ally, Ahmmed
• Format: Journal Article
• Language: English
• Published: London Elsevier B.V 26.05.2000; Amsterdam Elsevier; New York, NY
• Subjects: Animals; Arterial Pressure; Biological and medical sciences; Blood Pressure - drug effects; Blood Pressure - physiology; Enkephalin, Methionine - analogs & derivatives; Enkephalin, Methionine - pharmacology; Female; Fundamental and applied biological sciences. Psychology; Glutamic Acid - drug effects; Glutamic Acid - metabolism; Heart Rate - drug effects; Heart Rate - physiology; Male; Medulla Oblongata - drug effects; Medulla Oblongata - physiology; Microdialysis; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Muscle contraction; Muscle Contraction - drug effects; Muscle Contraction - physiology; Naloxone; Naloxone - pharmacology; Narcotic Antagonists - pharmacology; Rat; Rats; Rats, Sprague-Dawley; Receptors, Opioid - drug effects; Receptors, Opioid - physiology; Vertebrates: nervous system and sense organs; Endocrine and autonomic regulation; Arterial Pressure; Microdialysis; Naloxone; Rat; Muscle contraction; Cardiovascular control; Opioid receptor; Rodentia; Central nervous system; Glutamate; Vertebrata; Mammalia; Excitatory aminoacid; Neurotransmitter; Arterial pressure; Medulla oblongata; Release; Brain (vertebrata)
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/S0006-8993(00)02192-2

We previously reported that the administration of [ d-Ala 2]methionine enkephalinamide (DAME), an opioid receptor agonist, into the rostral (RVLM) but not into the caudal ventrolateral medulla (CVLM), attenuated increases in mean arterial pressure (MAP) and heart rate (HR) during static muscle contraction that had been blocked by prior microdialysis of the opioid receptor antagonist, naloxone [Am. J. Physiol. 274 (1998) H139–H146]. In this study, we determine whether this RVLM-mediated opioidergic-modulation of cardiovascular responses is associated with localized changes in extracellular concentrations of glutamate, an excitatory amino acid, using microdialysis techniques in anesthetized rats. Muscle contraction increased MAP and HR by 37±5 mmHg and 23±3 bpm, respectively. Extracellular glutamate concentrations, determined using HPLC–ECD, increased from 0.8±0.2 to 6.6±1.2 ng/5 μl in the bilateral RVLM areas. Microdialysis of DAME (100 μM) for 30 min attenuated the contraction-evoked increases in MAP, HR, and glutamate levels (20±4 mmHg, 10±2 bpm, and 1.8±0.2 ng/5 μl, respectively). After microdialysis of naloxone (100 μM) for 30 min into the RVLM, muscle contraction blocked the attenuations (35±5 mmHg, 26±4 bpm, and 5.8±1.0 ng/5 μl, respectively). Developed muscle tensions were similar throughout the protocol (676±38, 678±37 and 687±37 g, respectively). These results suggest that an opioidergic receptor-mediated mechanism within the RVLM attenuates cardiovascular responses during static exercise via modulating extracellular concentrations of glutamate in the RVLM.