Medullary monoamines and NMDA-receptor regulation of cardiovascular responses during peripheral nociceptive stimuli

Interactions among Endothelial Nitric Oxide Synthase, Cardiovascular System, and Nociception during Physiological and Pathophysiological States

Nitric oxide synthase (NOS) plays important roles within the cardiovascular system in physiological states as well as in pathophysiologic and specific cardiovascular (CV) disease states, such as hypertension (HTN), arteriosclerosis, and cerebrovascular accidents. This review discusses the roles of the endothelial NOS (eNOS) and its effect on cardiovascular responses that are induced by nociceptive stimuli. The roles of eNOS enzyme in modulating CV functions while experiencing pain will be discussed. Nociception, otherwise known as the subjective experience of pain through sensory receptors, termed "nociceptors", can be stimulated by various external or internal stimuli. In turn, events of various cascade pathways implicating eNOS contribute to a plethora of pathophysiological responses to the noxious pain stimuli. Nociception pathways involve various regions of the brain and spinal cord, including the dorsolateral periaqueductal gray matter (PAG), rostral ventrolateral medulla (RVLM), caudal ventrolateral medulla, and intermediolateral column of the spinal cord. These pathways can interrelate in nociceptive responses to pain stimuli. The alterations in CV responses that affect GABAergic and glutamatergic pathways will be discussed in relation to mechanical and thermal (heat and cold) stimuli. Overall, this paper will discuss the aggregate recent and past data regarding pain pathways and the CV system.

Excessive exercise induces cardiac arrhythmia in a young fibromyalgia mouse model

Background

Fibromyalgia patients experience cardiovascular complications in addition to musculoskeletal pain. This study aimed to investigate the cardiac effects of a prolonged shallow water gait in a fibromyalgia-induced young mouse model.

Methods

To produce a fibromyalgia mouse model, wild-type mice were administered an intraperitoneal injection of reserpine once a day for three days, and two primary experiments were performed. First, three types of gait tests were performed before and after the reserpine injections as follows: (i) 5 minutes of free gait outside the water, (ii) 1 minute of free gait in shallow warm water, and (iii) 5 minutes of free gait in shallow warm water. Second, electrocardiogram recordings were taken before and after the three gait tests. The average heart rate and heart rate irregularity scores were analyzed.

Results

Exercise-induced cardiac arrhythmia was observed at 1-minute gait in shallow water during the acute stage of induced FM in young mice. Further, both cardiac arrhythmia and a decrease in HR have occurred at 5-minute gait in shallow water at the same mice. However, this phenomenon was not observed in the wild-type mice under any test conditions.

Conclusion

Although a short-term free gait in shallow warm water may be advantageous for increasing the motor activity of FM-model mice, we should be aware of the risk of prolonged and excessive exercise-induced cardiac arrhythmia. For gait exercises in shallow water as a treatment in FM patients. We suggest a gradual increase in exercise duration may be warranted.

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.

Cannabinoid receptor 1 signaling in cardiovascular regulating nuclei in the brainstem: A review

Cannabinoids elicit complex hemodynamic responses in experimental animals that involve both peripheral and central sites. Centrally administered cannabinoids have been shown to predominantly cause pressor response. However, very little is known about the mechanism of the cannabinoid receptor 1 (CB₁R)-centrally evoked pressor response. In this review, we provided an overview of the contemporary knowledge regarding the cannabinoids centrally elicited cardiovascular responses and the possible underlying signaling mechanisms. The current review focuses on the rostral ventrolateral medulla (RVLM) as the primary brainstem nucleus implicated in CB₁R-evoked pressor response.

Glutamate injection into the cuneiform nucleus in rat, produces correlated single unit activities in the Kolliker-Fuse nucleus and cardiovascular responses

The cuneiform (CnF) and Kolliker-Fuse (KF) nuclei are implicated in several functions including regulation of cardiovascular system and pain modulation. The KF also is a potential candidate for relaying the CnF cardiovascular responses to the rostral ventrolateral medulla (RVLM). In a previous study we showed that blockade of the KF strongly attenuated the short responses and moderately attenuated the long responses to glutamate microinjection into the CnF, suggesting that the cardiovascular effects of the CnF, especially the short responses, were mediated by the KF. In the present study the cellular basis of the cardiovascular responses of the CnF and possible role of the KF in relaying them to the RVLM were explored. In one group, l-glutamate was microinjected in the CnF and the cardiovascular responses were recorded. In another group the single unit responses of the KF to l-glutamate injection into the CnF were recorded. Our results showed that chemical stimulation of the CnF with glutamate produced mainly excitatory cardiovascular and single unit responses and a minority of mixed (excitatory and inhibitory) responses. In about one fourth of the cases there were no responses to stimulation. Various patterns of each group were presented and compared between cardiovascular and single unit responses. Similarities were found between cardiovascular and single unit response patterns, suggesting a significant role of KF neurons in mediating the CnF cardiovascular responses to the RVLM.

Role of cuneiform nucleus in regulation of sympathetic vasomotor tone in rats

The cuneiform nucleus (CnF) is a sympathoexcitatory area involved in the central cardiovascular regulation. Its role in the maintaining vasomotor tone has, however, not yet been clarified. In the present study the effects of cobalt chloride (CoCl(2)) a nonselective synapse blocker and NMDA and non-NMDA glutamate receptors on resting mean arterial blood pressure and heart rate of CnF have been evaluated. CoCl(2), AP5 (an NMDA receptor antagonist) and CNQX (an AMPA/kinase receptor antagonist) (100nl) were microinjected into the CnF of anesthetized rats. The blood pressure and heart rate were recorded throughout the experiment. The responses of blood pressure and heart rate were compared with the pre-injection (paired t-test) and control (independent t-test) values. Microinjection of CoCl(2), AP5 and CNQX did not change the basal blood pressure and heart rate. In conclusion, our present study indicates that the CnF is not important in the regulation of cardiovascular tone.

Effect of glutamate stimulation of the cuneiform nucleus on cardiovascular regulation in anesthetized rats: role of the pontine Kolliker-Fuse nucleus

Cuneiform nucleus (CnF) is a reticular nucleus of the midbrain involved in cardiovascular function and stress. There is no report on the cardiovascular effects of the glutamatergic system in the CnF. In the present study, we investigated the cardiovascular effects of glutamate and its NMDA and AMPA/kainate receptors in the CnF. In addition, the possible mediation of Kolliker-Fuse (KF) nucleus in the cardiovascular effects of the CnF was explored. l-glutamate, AP5 (an NMDA receptor antagonist), and CNQX (an AMPA/kainate receptor antagonist) (50-100 nl) were microinjected into the CnF of anesthetized rats. Also, the KF was blocked by cobalt chloride (CoCl(2)) then l-glutamate was microinjected into the CnF. The maximum changes of blood pressure and heart rate were compared with the pre-injection (paired t-test) and control (independent t-test) values. Microinjection of glutamate (25 nmol/100 nl) into the CnF produced either a short pressor and bradycardic or a long pressor and tachycardic responses. Microinjection of AP5 or CNQX alone did not affect the basal arterial pressure and heart rate. However, co-injection of glutamate with AP5 strongly attenuated the short and moderately attenuated the long cardiovascular responses elicited by glutamate. Co-injection of glutamate with CNQX did not attenuate the short and weakly attenuated the long cardiovascular responses elicited by glutamate. These data suggest that the responses are mediated mainly through NMDA receptors. Blockade of the KF nucleus strongly attenuated the short response and weakly attenuated the long response to glutamate microinjection, suggesting that the cardiovascular effects of glutamate in the CnF, especially the short responses, were mediated by the KF nucleus.

Chronic stress during paradoxical sleep deprivation increases paradoxical sleep rebound: association with prolactin plasma levels and brain serotonin content

Previous studies suggest that stress associated to sleep deprivation methods can affect the expression of sleep rebound. In order to examine this association and possible mechanisms, rats were exposed to footshock stress during or immediately after a 96-h period of paradoxical sleep deprivation (PSD) and their sleep and heart rate were recorded. Control rats (maintained in individual home cages) and paradoxical sleep-deprived (PS-deprived) rats were distributed in three conditions (1) no footshock--NF; (2) single footshock--SFS: one single footshock session at the end of the PSD period (6-8 shocks per minute; 100 ms; 2 mA; for 40 min); and (3) multiple footshock--MFS: footshock sessions with the same characteristics as described above, twice a day throughout PSD (at 7:00 h and 19:00 h) and one extra session before the recovery period. After PSD, animals were allowed to sleep freely for 72 h. Additional groups were sacrificed at the end of the sleep deprivation period for blood sampling (ACTH, corticosterone, prolactin and catecholamine levels) and brain harvesting (monoamines and metabolites). Neither SFS nor MFS produced significant alterations in the sleep patterns of control rats. All PS-deprived groups exhibited increased heart rate which could be explained by increased dopaminergic activity in the medulla. As expected, PS deprivation induced rebound of paradoxical sleep in the first day of recovery; however, PSD+MFS group showed the highest rebound (327.3% above the baseline). This group also showed intermediate levels of corticosterone and the highest levels of prolactin, which were positively correlated with the length of PS episodes. Moreover, paradoxical sleep deprivation resulted in elevation of the serotonergic turnover in the hypothalamus, which partly explained the hormonal results, and in the hippocampus, which appears to be related to adaptive responses to stress. The data are discussed in the realm of a prospective importance of paradoxical sleep for processing of traumatic events.

Descending facilitation from the brainstem determines behavioural and neuronal hypersensitivity following nerve injury and efficacy of pregabalin

Various mechanisms at peripheral, spinal and/or supraspinal levels may underlie neuropathic pain. The nervous system's capacity for long-term reorganisation and chronic pain may result from abnormalities in RVM facilitatory On cells. Hence, via brainstem injections of the toxic conjugate dermorphin-saporin, which specifically lesions facilitatory cells expressing the mu-opioid receptor (MOR), we sought to determine the influence of these cells in normal and spinal nerve-ligated (SNL) rats. We combined behavioural, electrophysiological and pharmacological techniques to show that the supraspinal facilitatory drive is essential for neuronal processing of noxious stimuli in normal and neuropathic states, and that descending facilitatory neurones maintain behavioural hypersensitivities to mechanical stimuli during the late stages of nerve injury. Furthermore, we showed that these neurones are essential for the state-dependent inhibitory actions of pregabalin (PGB), a drug used in the treatment of neuropathic pain. During the early stages of nerve injury, or following medullary MOR cell ablation, PGB is ineffective at inhibiting spinal neuronal responses possibly due to quiescent spinal 5HT(3) receptors. This can however be overcome, and PGB's efficacy restored, by pharmacologically mimicking the descending drive at the spinal level with a 5HT(3) receptor agonist. Since RVM facilitatory neurones are integral to a spino-bulbo-spinal loop that reaches brain areas co-ordinating the sensory and affective components of pain, we propose that activity therein may influence painful outcome following nerve injury, and responsiveness to treatment.

Modulation of cardiovascular responses and neurotransmission during peripheral nociception following nNOS antagonism within the periaqueductal gray

Nitric oxide (NO) within the dorsal periaqueductal gray matter (dPAG) attenuated cardiovascular responses and changes in the concentrations of glutamate during both mechanical and thermal nociceptive stimulation [Ishide, T., Amer, A., Maher, T.J., Ally, A., 2005. Nitric oxide within periaqueductal gray modulates glutamatergic neurotransmission and cardiovascular responses during mechanical and thermal stimuli. Neurosci. Res. 51, 93-103]. Nitric oxide is synthesized from l-arginine via the enzyme, NO synthase (NOS), which exists in 3 isoforms: endothelial (eNOS), neuronal (nNOS), and inducible (iNOS). In this study, we examined the role of nNOS within the dPAG on cardiovascular responses and extracellular glutamate and GABA concentrations during mechanical and thermal nociception in anesthetized rats. The noxious mechanical stimulus was applied by a bilateral hindpaw pinch for 5 s that increased mean arterial pressure (MAP) and heart rate (HR) by 24+/-4 mm Hg and 41+/-7 bpm, respectively (n=10). Extracellular glutamate levels within the dPAG increased by 10.7+/-1.3 ng/mul while GABA concentrations decreased by 1.9+/-0.5 ng/microl. Bilateral microdialysis of a selective nNOS antagonist, 1-(2-trifluoromethylphenyl)-imidazole (TRIM; 10.0 microM), into the dPAG had no effect on MAP, HR, glutamate and GABA values (P>0.05) during a mechanical stimulation. In a separate set of experiments, a noxious thermal stimulus was generated by immersing the metatarsus of a hindpaw in a water-bath at 52 degrees C for 5 s (n=10). Glutamate, MAP, and HR increased by 14.6+/-2 ng/microl, 45+/-6 mm Hg, and 47+/-7 bpm, while GABA decreased by 2.1+/-0.6 ng/microl. Administration of TRIM into the dPAG significantly enhanced the cardiovascular responses and glutamate increases (P<0.05) but further attenuated GABA changes (P<0.05) during subsequent thermal nociception. These results demonstrate that nNOS within the dPAG plays a differential role in modulating cardiovascular responses and glutamatergic/GABAergic neurotransmission during thermal and mechanical nociception.