Central injection of physostigmine attenuates exercise-induced pressor response in conscious cats

Role of neuronal nitric oxide synthase on cardiovascular functions in physiological and pathophysiological states

This review describes and summarizes the role of neuronal nitric oxide synthase (nNOS) on the central nervous system, particularly on brain regions such as the ventrolateral medulla (VLM) and the periaqueductal gray matter (PAG), and on blood vessels and the heart that are involved in the regulation and control of the cardiovascular system (CVS). Furthermore, we shall also review the functional aspects of nNOS during several physiological, pathophysiological, and clinical conditions such as exercise, pain, cerebral vascular accidents or stroke and hypertension. For example, during stroke, a cascade of molecular, neurochemical, and cellular changes occur that affect the nervous system as elicited by generation of free radicals and nitric oxide (NO) from vulnerable neurons, peroxide formation, superoxides, apoptosis, and the differential activation of three isoforms of nitric oxide synthases (NOSs), and can exert profound effects on the CVS. Neuronal NOS is one of the three isoforms of NOSs, the others being endothelial (eNOS) and inducible (iNOS) enzymes. Neuronal NOS is a critical homeostatic component of the CVS and plays an important role in regulation of different systems and disease process including nociception. The functional and physiological roles of NO and nNOS are described at the beginning of this review. We also elaborate the structure, gene, domain, and regulation of the nNOS protein. Both inhibitory and excitatory role of nNOS on the sympathetic autonomic nervous system (SANS) and parasympathetic autonomic nervous system (PANS) as mediated via different neurotransmitters/signal transduction processes will be explored, particularly its effects on the CVS. Because the VLM plays a crucial function in cardiovascular homeostatic mechanisms, the neuroanatomy and cardiovascular regulation of the VLM will be discussed in conjunction with the actions of nNOS. Thereafter, we shall discuss the up-to-date developments that are related to the interaction between nNOS and cardiovascular diseases such as hypertension and stroke. Finally, we shall focus on the role of nNOS, particularly within the PAG in cardiovascular regulation and neurotransmission during different types of pain stimulus. Overall, this review focuses on our current understanding of the nNOS protein, and provides further insights on how nNOS modulates, regulates, and controls cardiovascular function during both physiological activity such as exercise, and pathophysiological conditions such as stroke and hypertension.

Modulation of extracellular glutamate and pressor response to muscle contraction during NMDA-receptor blockade in the rostral ventrolateral medulla

Recently our laboratory demonstrated increases in extracellular glutamate concentrations within the rostral ventrolateral medulla (RVLM) during static muscle contraction (Caringi, D.C., Maher, T., Chaiyakul, P., Asmundsson, G., Ishide, T., Ally, A. Pflügers Arch. Eur. J. Physiol., 435:465-471, 1998). In this study, we determined effects of microdialyzing D(-)2-amino-7-phosphonohepatanoic acid (AP-7), an NMDA-receptor antagonist, into the RVLM on changes in mean arterial pressure (MAP), heart rate (HR), and extracellular glutamate levels during muscle contraction in anesthetized rats. Bilateral placements of microdialysis probes into the RVLM were verified by perfusing L-glutamate and obtaining a pressor response. Muscle contraction for 2 min, increased MAP and HR by 22+/-4 mmHg and 28+/-5 bpm, respectively. Extracellular glutamate as determined by microdialysis increased from 0.8+/-0.2 to 6.3+/-1.2 ng/5 microl. Microdialysis of AP-7 (1.0 microM) for 30 min inhibited contraction-evoked MAP and HR responses (10+/-3 mmHg and 13+/-3 bpm) and attenuated increases in glutamate during muscle contraction. Developed tensions did not differ during contractions before and after AP-7. Results demonstrate that NMDA-receptor blockade in the RVLM inhibits cardiovascular responses during static muscle contraction via a reduction in extracellular glutamate levels.

Ventrolateral medullary control of cardiovascular activity during muscle contraction

An overview of the role of ventrolateral medulla (VLM) in regulation of cardiovascular activity is presented. A summary of VLM anatomy and its functional relation to other areas in the central nervous system is described. Over the past few years, various studies have investigated the VLM and its involvement in cardiovascular regulation during static muscle contraction, a type of static exercise as seen, for example, during knee extension or hand-grip exercise. Understanding the neural mechanisms that are responsible for regulation of cardiovascular activity during static muscle contraction is of particular interest since it helps understand circulatory adjustments in response to an increase in physical activity. This review surveys the role of several receptors and neurotransmitters in the VLM that are associated with changes in mean arterial pressure and heart rate during static muscle contraction in anesthetized animals. Possible mechanisms in the VLM that modulate cardiovascular changes during static muscle contraction are summarized and discussed. Localized administration of an excitatory amino-acid antagonist into the rostral portion of the VLM (RVLM) attenuates increases in blood pressure and heart rate during static muscle contraction, whereas its administration into the caudal part of the VLM (CVLM) augments these responses. Opioid or 5-HT1A receptor stimulation in the RVLM, but not in the CVLM, attenuates cardiovascular responses to muscle contraction. Furthermore, intravenous, intracerebroventricular or intracisternal injection of an alpha 2-adrenoceptor agonist or a cholinesterase inhibitor attenuates increases in blood pressure and heart rate during static muscle contraction. Finally, the possible involvement of endogenous neurotransmitters in the RVLM and the CVLM associated with cardiovascular responses during static muscle contraction is discussed. An overview of the role of the VLM in the overall cardiovascular control network in the brain is presented and critically reviewed.