Nitroglycerin enhances cGMP expression in specific neuronal and cerebrovascular structures of the rat brain

Emodin Interferes With Nitroglycerin-Induced Migraine in Rats Through CGMP-PKG Pathway

The purpose of this research was to explore the effect and mechanism of emodin in interfering with nitroglycerin-induced migraine rats. We carried out behavioral research within 2 h post-nitroglycerin (NTG) injection, and blood samples were collected through the abdominal aorta for measurements of nitric oxide (NO), calcitonin gene-related peptide (CGRP), substance P (SP), tumor necrosis factor (TNF-α) and cyclic guanosine monophosphate (cGMP) levels. Immunohistochemistry was adopted to detect the activation of c-Fos immunoreactive neurons in brain tissues. The number and integrated optical density (IOD) of c-Fos positive cells were measured using Image-Pro Plus. Western blotting was applied to detect the levels of PKG protein in rat brain tissues. The results showed that emodin can alleviate the pain response of migraine rats and significantly reduce the levels of NO, CGRP, SP, TNF-α and cGMP in migraine rats. In addition, emodin can significantly reduce the number of c-Fos positive cells and the IOD value. Moreover, the expression of PKG protein was significantly inhibited by emodin. Therefore, it is inferred that emodin can relieve migraine induced by NTG through the cGMP-PKG pathway, and can be used as a potential botanical medicine for the treatment of migraine.

Insulin-like growth factor-1 inhibits nitroglycerin-induced trigeminal activation of oxidative stress, calcitonin gene-related peptide and c-Fos expression

Migraineurs experience increased oxidative stress which drives the initiation and maintenance of migraine-related pain in animal models and, by extension, migraine in humans. Oxidative stress augments calcitonin gene-related peptide (CGRP) levels, a mediator of migraine pain. Insulin-like growth factor-1 (IGF-1), a neuroprotective growth factor, reduces susceptibility to spreading depression, a preclinical model of migraine, in cultured brain slices by blocking oxidative stress and neuroinflammation from microglia. Similarly, nasal delivery of IGF-1 inhibits spreading depression in vivo. After recurrent cortical spreading depression, nasal administration of IGF-1 also significantly reduces trigeminal ganglion oxidative stress and CGRP levels as well as trigeminocervical c-Fos activation. Here, we probed for the impact of nasal IGF-1 pretreatment on trigeminal system activation using a second well-established preclinical model of migraine, systemic nitroglycerin injection. Adult male rats were treated with one of three doses of IGF-1 (37.5, 75 or 150 μg) and the optimal dose found in males was subsequently used for treatment of female rats. One day later, animals received an intraperitoneal injection of nitroglycerin. Measurements taken two hours later after nitroglycerin alone showed increased surrogate markers of trigeminal activation - oxidative stress and CGRP in the trigeminal ganglion and c-Fos in the trigeminocervical complex compared to vehicle control. These effects were significantly reduced at all doses of IGF-1 for trigeminal ganglion metrics of oxidative stress and CGRP and only at the lowest dose in both males and females for c-Fos. The latter inverted U-shaped or hormetic response is seen in enzyme-targeting drugs. While the specific mechanisms remain to be explored, our data here supports the ability of IGF-1 to preserve mitochondrial and antioxidant pathway homeostasis as means to prevent nociceptive activation in the trigeminal system produced by an experimental migraine model.

Dynamic sodium imaging at ultra-high field reveals progression in a preclinical migraine model

Under the hypothesis that increased extracellular sodium induces sustained neuronal excitability with the onset and progression of migraine, this study evaluates dynamic in vivo Na fluxes in the brain of a preclinical rodent analogue of migraine. Ultra-high field Na magnetic resonance imaging (MRI) at 21.1 T has demonstrated potential to quantify sodium concentrations with good spatial and temporal resolution after the onset of central sensitization. Sprague-Dawley male rats with implanted intraperitoneal lines were studied by MRI before and after an in situ injection of 10 mg/kg of nitroglycerin (NTG) vs vehicle and saline controls. Slice-selective Na images were acquired using a multislice free induction decay-based chemical shift imaging sequence with resolution of 1.1 × 1.1 × 3 mm for a 9-minute acquisition. A total of 27 repeated scans were acquired over 1 hour of baseline scanning and longitudinally up to 3 hours after injection. Increases of Na MRI signal in the brainstem, extracerebral cerebrospinal fluid, and cisterna magna were evident almost immediately after NTG injection, gaining significance from controls in 36 minutes. The cerebellum and third ventricle also showed sustained trends of increased Na, with the former gaining significance at over 2 hours after NTG injection. The data provide evidence of an early change in sodium concentration, markedly in posterior fossa cerebrospinal fluid and brainstem regions. Further study of fluctuations of sodium concentration and their modulation with treatments could help understand the dynamic features of migraine, locate a putative migraine generator, and guide development of therapeutic measures to correct the disturbance of sodium homeostasis.

Neuronal Nitric Oxide Synthase (nNOS, NOS1) rs693534 and rs7977109 Variants and Risk for Migraine

BACKGROUND/OBJECTIVES

Many biochemical, pharmacological, neuropathological, and experimental data suggest a possible role of nitric oxide in the pathogenesis of migraine. We investigated the possible association between functional single nucleotide polymorphisms (SNPs) in the neuronal nitric oxide synthase gene (NOS1 or nNOS; chromosome 12q24.22) and the risk for migraine.

METHODS

We studied the frequency of the of rs7977109 and rs693534 genotypes and allelic variants in 197 patients with migraine and 308 healthy controls using a TaqMan-based qPCR assay. As a secondary analysis, we studied the possible influence of gender, age at onset of migraine, positive family history of migraine, and presence or absence of aura on the genotypes frequency.

RESULTS

The frequencies of rs7977109 and rs693534 genotypes and allelic variants were not associated with the risk for migraine with OR for minor alleles = 0.94 (95% CI 0.72-1.23) and = 0.88 (0.68-1.15), respectively, and the lack of association was not influenced by gender, age at onset of migraine, positive family history of migraine, and presence or absence of aura.

CONCLUSION

NOS1 rs7977109 and rs693534 genotypes and allelic variants are not associated with the risk for migraine in Caucasian Spanish people.

Vinpocetine reduces lipopolysaccharide-induced inflammatory pain and neutrophil recruitment in mice by targeting oxidative stress, cytokines and NF-κB

In response to lipopolysaccharide (LPS), tissue resident macrophages and recruited neutrophils produce inflammatory mediators through activation of Toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) signaling pathway. These mediators include inflammatory cytokines and reactive oxygen species that, in turn, sensitize nociceptors and lead to inflammatory pain. Vinpocetine is a nootropic drug widely used to treat cognitive and neurovascular disorders, and more recently its anti-inflammatory properties through inhibition of NF-κB activation have been described. In the present study, we used the intraplantar and intraperitoneal LPS stimulus in mice to investigate the effects of vinpocetine pre-treatment (3, 10, or 30mg/kg by gavage) in hyperalgesia, leukocyte recruitment, oxidative stress, and pro-inflammatory cytokine production (TNF-α, IL-1β, and IL-33). LPS-induced NF-κB activation and cytokine production were investigated using RAW 264.7 macrophage cell in vitro. Vinpocetine (30mg/kg) significantly reduces hyperalgesia to mechanical and thermal stimuli, and myeloperoxidase (MPO) activity (a neutrophil marker) in the plantar paw skin, and also inhibits neutrophil and mononuclear cell recruitment, superoxide anion and nitric oxide production, oxidative stress, and cytokine production (TNF-α, IL-1β and IL-33) in the peritoneal cavity. At least in part, these effects seem to be mediated by direct effects of vinpocetine on macrophages, since it inhibited the production of the same cytokines (TNF-α, IL-1β and IL-33) and the NF-κB activation in LPS-stimulated RAW 264.7 macrophages. Our results suggest that vinpocetine represents an important therapeutic approach to treat inflammation and pain induced by a gram-negative bacterial component by targeting NF-κB activation and NF-κB-related cytokine production in macrophages.

Vinpocetine reduces carrageenan-induced inflammatory hyperalgesia in mice by inhibiting oxidative stress, cytokine production and NF-κB activation in the paw and spinal cord

Vinpocetine is a safe nootropic agent used for neurological and cerebrovascular diseases. The anti-inflammatory activity of vinpocetine has been shown in cell based assays and animal models, leading to suggestions as to its utility in analgesia. However, the mechanisms regarding its efficacy in inflammatory pain treatment are still not completely understood. Herein, the analgesic effect of vinpocetine and its anti-inflammatory and antioxidant mechanisms were addressed in murine inflammatory pain models. Firstly, we investigated the protective effects of vinpocetine in overt pain-like behavior induced by acetic acid, phenyl-p-benzoquinone (PBQ) and formalin. The intraplantar injection of carrageenan was then used to induce inflammatory hyperalgesia. Mechanical and thermal hyperalgesia were evaluated using the electronic von Frey and the hot plate tests, respectively, with neutrophil recruitment to the paw assessed by a myeloperoxidase activity assay. A number of factors were assessed, both peripherally and in the spinal cord, including: antioxidant capacity, reduced glutathione (GSH) levels, superoxide anion, tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β) levels, as well as nuclear factor kappa B (NF-κB) activation. Vinpocetine inhibited the overt pain-like behavior induced by acetic acid, PBQ and formalin (at both phases), as well as the carrageenan-induced mechanical and thermal hyperalgesia and associated neutrophil recruitment. Both peripherally and in the spinal cord, vinpocetine also inhibited: antioxidant capacity and GSH depletion; increased superoxide anion; IL-1β and TNF-α levels; and NF-κB activation. As such, vinpocetine significantly reduces inflammatory pain by targeting oxidative stress, cytokine production and NF-κB activation at both peripheral and spinal cord levels.

Animal migraine models for drug development: status and future perspectives

Migraine is number seven in WHO's list of all diseases causing disability and the third most costly neurological disorder in Europe. Acute attacks are treatable by highly selective drugs such as the triptans but there is still a huge unmet therapeutic need. Unfortunately, drug development for headache has almost come to a standstill partly because of a lack of valid animal models. Here we review previous models with emphasis on optimal characteristics of a future model. In addition to selection of animal species, the method of induction of migraine-like changes and the method of recording responses elicited by such measures are crucial. The most naturalistic way of inducing attacks is by infusion of endogenous signaling molecules that are known to cause migraine in patients. The most valid response is recording of neural activity in the trigeminal system. The most useful headache related responses are likely to be behavioral, allowing multiple experiments in each individual animal. Distinction is made between acute and prophylactic models and how to validate each of them. Modern insight into neurobiological mechanisms of migraine is so good that it is only a question of resources and efforts that determine when valid models with ability to predict efficacy in migraine will be available.

Botulinum toxin type a therapy in migraine: preclinical and clinical trials

BACKGROUND

Botulinum toxin type A (BTX-A) has been reported to be effective for the therapy for migraine. The purpose of this study was to investigate the effect of BTX-A on the immunoreactive levels of calcitonin gene-related peptide (CGRP) and substance P (SP) in the jugular plasma and medulla oblongata of migraine in rats induced by nitroglycerin (NTG), and then to evaluate and compare the effectiveness of fixed (muscle)-sites and acupoint-sites injection of BTX-A for migraine therapy of patients in a randomly controlled trial extending over four months.

MATERIALS AND METHODS

Rats with NTG-induced migraine were subcutaneously injected with vehicle or BTX-A (5 U/kg or 10 U/kg bodyweight). CGRP- and SP-like immunoreactivity (CGRP-LI and SP-LI) were determined by radioimmunoassay. In clinical trials, sixty patients respectively received BTX-A (2.5 U each site, 25 U per patient) at fixed-sites (group F, n = 30) including occipitofrontalis, corrugator supercili, temporalis and trapezius or at acupoint-sites (group A, n = 30) including EX-HN3, EX-HN5, GV20, GB8, GB20 and BL10.

RESULTS

Local BTX-A injection suppressed NTG-induced CGRP-LI and SP-LI levels in jugular plasma and oblongata. BTX-A injection for both groups with migraine significantly reduced the attack frequency, intensity, duration and associated symptoms. The efficacy of BTX-A for migraine in group A (93% improvement) was more significant than that in group F (83% improvement) (P < 0.01).

CONCLUSIONS

The evidence that BTX-A decreases NTG-induced CGRP-LI and SP-LI levels in trigeminovascular system suggests that BTX-A attenuates migraine by suppression of neuropeptide release. BTX-A injections for migraine at acupoint-sites and fixed-sites are effective. Acupoint-sites BTX-A administration shows more efficacy for migraine than fixed-sites application.

The effect of sodium nitroprusside on cerebral hemodynamics and headache in healthy subjects

Investigation

Sodium nitroprusside (SNP) is a powerful vasodilatory agent that, similarly to glyceryl trinitrate (GTN), releases nitric oxide (NO) but in contrast does not pass the blood-brain barrier. Nevertheless, it has already been used in animal models without any knowledge of its headache-inducing potential. We hypothesized that SNP would induce headache and vasodilation of cephalic and radial but not cerebral arteries.

Methods

Five healthy volunteers received intravenous infusions of SNP in a non-randomized dose-titration (1–5 µg/kg/min) study. We recorded headache intensity (verbal rating scale from 0 to 10), velocity in the middle cerebral artery (VMCA), and diameters of the superficial temporal artery (STA) and radial artery (RA).

Results

All participants reported a dose-related headache (median peak = 2.5, range 0–3). SNP dilated the STA and RA, caused a marked increase of heart rate and a decrease of mean arterial pressure (MAP) and partial pressure of end-tidal carbon dioxide (PetCO2). We found that SNP decreased the velocity of the VMCA, but this was canceled by a decrease of cerebral blood flow (CBF) due to hypocapnia.

Conclusion

The present study shows that SNP is a headache-inducing agent with close similarities to headaches induced by GTN and probably without effect on intracerebral arteries.

Sodium MRI in a rat migraine model and a NEURON simulation study support a role for sodium in migraine

INTRODUCTION

Increased lumbar cerebrospinal fluid (CSF) sodium has been reported during migraine. We used ultra-high field MRI to investigate cranial sodium in a rat migraine model, and simulated the effects of extracellular sodium on neuronal excitability.

METHODS

Behavioral changes in the nitroglycerin (NTG) rat migraine model were determined from von Frey hair withdrawal response and photography. Central sensitization was measured by counting cFos-immunoreactive cells in the trigeminal nucleus caudalis (TNC). Sodium was quantified in vivo by ultra-high field sodium MRI at 21 Tesla. Effects of extracellular sodium on neuronal excitability were modeled using NEURON software.

RESULTS

NTG decreased von Frey withdrawal threshold (p=0.0003), decreased eyelid vertical height:width ratio (p<0.0001), increased TNC cFos stain (p<0.0001), and increased sodium between 7.5 and 17% in brain, intracranial CSF, and vitreous humor (p<0.05). Simulated neurons exposed to higher sodium have more frequent and earlier spontaneous action potentials, and corresponding earlier sodium and potassium currents.

CONCLUSIONS

In the rat migraine model, sodium rises to levels that increase neuronal excitability. We propose that rising sodium in CSF surrounding trigeminal nociceptors increases their excitability and causes pain and that rising sodium in vitreous humor increases retinal neuronal excitability and causes photosensitivity.

Sumatriptan alleviates nitroglycerin-induced mechanical and thermal allodynia in mice

The association between the clinical use of nitroglycerin (NTG) and headache has led to the examination of NTG as a model trigger for migraine and related headache disorders, both in humans and laboratory animals. In this study in mice, we hypothesized that NTG could trigger behavioural and physiological responses that resemble a common manifestation of migraine in humans. We report that animals exhibit a dose-dependent and prolonged NTG-induced thermal and mechanical allodynia, starting 30-60 min after intraperitoneal injection of NTG at 5-10 mg/kg. NTG administration also induced Fos expression, an anatomical marker of neuronal activity in neurons of the trigeminal nucleus caudalis and cervical spinal cord dorsal horn, suggesting that enhanced nociceptive processing within the spinal cord contributes to the increased nociceptive behaviour. Moreover, sumatriptan, a drug with relative specificity for migraine, alleviated the NTG-induced allodynia. We also tested whether NTG reduces the threshold for cortical spreading depression (CSD), an event considered to be the physiological substrate of the migraine aura. We found that the threshold of CSD was unaffected by NTG, suggesting that NTG stimulates migraine mechanisms that are independent of the regulation of cortical excitability.

Temporal profile of vascular changes induced by systemic nitroglycerin in the meningeal and cortical districts

BACKGROUND

Clinical studies indicated that nitric oxide (NO) donors cause regional changes in cerebral blood flow (CBF), similar to those reported in spontaneous migraine. Systemic nitroglycerin (NTG), a NO donor, is a well-accepted experimental model of migraine. In this study we have examined the effects of NTG on the meningeal and cortical blood flow in rats.

METHODS

Regional blood flow was monitored in male Sprague-Dawley rats using laser Doppler flowmetry before and after NTG/saline injection over 150 minutes. The effect of pre-treatment with Nω-nitro-L-arginine ester (L-NAME) or 7-nitroindazole (7-NI) on NTG-induced changes on blood flow was also investigated.

RESULTS

In the dura NTG caused a biphasic response represented by an initial decrease in blood flow followed by a significant increase. At variance, in the cortex NTG caused only an increase in blood flow. Pre-treatment with either L-NAME or 7-NI prevented NTG-induced increase in blood flow in both districts, while only L-NAME also prevented NTG-induced decrease in dural blood flow.

CONCLUSION

The present findings provide additional information on the timing of effects of NTG on blood flow at both the meningeal and cortical levels. These effects seem to be related to vasoregulatory mechanisms and/or metabolic activity in response to the synthesis of endogenous NO.

Cerebral blood flow regulation by nitric oxide in neurological disorders

There has been a rapid increase in the amount of information on the physiological and pathophysiological roles of nitric oxide (NO) in the brain. This molecule, which is formed by the constitutive isoforms of NO synthase, endothelial (eNOS) and neuronal (nNOS), plays an obligatory role in the regulation of cerebral blood flow and cell viability and in the protection of nerve cells or fibres against pathogenic factors associated with Alzheimer's disease, Huntington's disease, seizures, and migraine. Cerebral blood flow is impaired by decreased formation of NO from endothelial cells, autonomic nitrergic nerves, or brain neurons and also by increased production of reactive oxygen species (ROS). The NO-ROS interaction is an important topic in discussing blood flow and cell viability in the brain. Excessive production of NO by inducible NOS (iNOS) and nNOS in the brain participates in neurotoxicity. Recent studies on brain circulation have provided useful information about the involvement of impaired NO availability or uncontrolled NO production in cerebral pathogenesis, including Alzheimer's disease, seizures, vascular headaches, and inflammatory disorders. Insight into the role of NO in the brain will contribute to our better understanding of cerebral hemodynamic dysfunction and will aid in developing novel therapeutic measures in diseases of the central nervous system.

Experimental models of migraine

In vitro studies on animal and human cephalic vessels allow the measurement of second messengers or intracellular calcium concentrations and the evaluation of the role of endogenous neuropeptides in perivascular nerve endings involved in migraine pathophysiology. In addition, in vitro human models allow the assessment of receptorial cranial selectivity and the collection of reliable information regarding the behavior of these vessels in migraine headache. The availability of animal models of migraine has favoured impressive advances in understanding the mechanisms and mediators underlying migraine attacks, as well as the development of new and more specific therapeutic agents. The trigeminovascular system (TVS) has emerged as a critical efferent component, and the mediators of its activity have been identified and characterized, as have some of the receptors involved. The similarity of the trigeminal innervation across species has made it possible to draw conclusions on the neurophysiological responses to electrical or chemical stimulation of the trigeminal fibers. Studies involving substances known to induce migraine-like attacks, i.e., nitric oxide (NO) donors, have provided interesting insights into the central nuclei probably involved in the initiation and repetition of migraine attacks. The neuronal and vascular effects of such substances might yield an increasing body of evidence for a better understanding of the pathophysiology of migraine attacks.

Increase in NADPH-Diaphorase-Positive and Neuronal NO Synthase Immunoreactive Neurons in the Rat Spinal Trigeminal Nucleus Following Infusion of a NO Donor—Evidence for a Feed-Forward Process in NO Production Involved in Trigeminal Nociception

Nitric oxide (NO) donors, which cause delayed headaches in migraineurs, have been shown to activate central trigeminal neurons with meningeal afferent input in animal experiments. Previous reports indicate that this response may be due to up-regulation of NO-producing cells in the trigeminal brainstem. To investigate this phenomenon further, we determined nitric oxide synthase (NOS)-containing neurons in the rat spinal trigeminal nucleus (STN), the projection site of nociceptive trigeminal afferents, following infusion of the NO donor sodium nitroprusside (SNP). Barbiturate anaesthetized rats were infused intravenously with SNP (50 μg/kg) or vehicle for 20 min or 2 h, and after periods of 3–8 h fixed by perfusion. Cryostat sections of the medulla oblongata containing the caudal STN were histochemically processed for detection of nicotineamide adenine dinucleotide phosphate (NADPH)-diaphorase or immunohistochemically stained for NOS isoforms and examined by light and fluorescence microscopy. The number of neurons positive for these markers was determined. Various forms of neurons positive for NADPH-diaphorase or immunoreactive to neuronal NOS (nNOS) were found in superficial and deep laminae of the STN caudalis and around the central canal. Neurons were not immunopositive for endothelial (eNOS) or inducible (iNOS) NOS isoforms. The number of NADPH-diaphorase-positive neurons increased time dependently after SNP infusion by a factor of more than two. Likewise, the number of nNOS-immunopositive neurons was increased after SNP compared with vehicle infusion. Around the central canal the number of NADPH-diaphorase-positive neurons was slightly increased and the number of nNOS+ neurons not changed after SNP treatment. NO donors increase the number of neurons that produce NO in the STN, possibly by induction of nNOS expression. Increased NO production may facilitate neurotransmitter release and promote nociceptive transmission in the STN. This mechanism may explain the delayed increase in neuronal activity and headache after infusion of NO donors.

The cholinomimetic agent carbachol induces headache in healthy subjects

The parasympathetic nervous system is likely to be involved in migraine pathogenesis. We hypothesized that the cholinomimetic agonist carbachol would induce headache and vasodilation of cephalic and radial arteries. Carbachol (3 microg/kg) or placebo was randomly infused into 12 healthy subjects in a double-blind crossover study. Headache was scored on a verbal rating scale from 0-10. Velocity in the middle cerebral artery (V(MCA)) and diameter of the superficial temporal artery (STA) and radial artery (RA) were recorded. Nine participants developed headache after carbachol compared with three after placebo. The area under the curve for headache was increased after carbachol compared with placebo both during infusion (0-30 min) (P = 0.042) and in the postinfusion period (30-90 min) (P = 0.027). Carbachol infusion caused a drop in V(MCA) (P = 0.003) and an increase in STA diameter (P = 0.006), but no increase in the RA diameter (P = 0.200). In conclusion, the study demonstrated that carbachol caused headache and dilation of cephalic arteries in healthy subjects.

Role of central dopaminergic circuitry in pain processing and nitroglycerin-induced hyperalgesia

Experimental evidence shows that dopaminergic transmission within the basal ganglia is involved in the modulation of nociceptive information. Epidemiological studies show that in some disease states inherent pathophysiological mechanisms that involve degenerative changes (Parkinson's disease; PD) can also impact negatively on other unrelated functional systems (i.e. nociception). Delayed Fos expression in response to nitroglycerin (NTG) administration is a procedure used to identify the neuroanatomical substrates of the migraine condition. In this study, we investigated the influence of dopaminergic nigrostriatal denervation, obtained by intrastriatal injection of 6-hydroxydopamine (6-OHDA), on this response in Sprague-Dawley rats. We also explored the effects on the NTG-induced hyperalgesic response to painful stimuli (formalin and tail-flick tests). Nigrostriatal lesion prevented the neuronal activation typically induced by NTG in sub-cortical areas involved in pain perception, autonomic control and neuroendocrine functions, such as hypothalamic nuclei, periaqueductal grey, parabrachial nucleus and the medullary nuclei. In addition, 6-OHDA-induced lesion inhibited NTG-induced hyperalgesia. Our data show that integrity of central dopaminergic neurotransmission is required for the NTG-induced activation of sub-cortical areas involved in the expression of migraine symptoms, as well as for the hyperalgesic response to painful stimuli elicited by the drug.

Immunohistochemical assessment of cyclic guanosine monophosphate (cGMP) and soluble guanylate cyclase (sGC) within the rostral ventrolateral medulla

Functional evidence suggests that nitric oxide (NO) signalling in the rostral ventrolateral medulla (RVLM) is cGMP-dependent and that this pathway is impaired in hypertension. We examined cGMP expression as a marker of active NO signalling in the C1 region of the RVLM, comparing adult (>18 weeks) Wistar-Kyoto (WKY, n = 4) and spontaneously hypertensive rats (SHR, n = 4). Double label immunohistochemistry for cGMP-immunoreactivity (IR) and C1 neurons [as identified by phenylethanolamine N-methyltransferase (PNMT-IR) or tyrosine hydroxylase TH-IR)], or neuronal NO synthase (nNOS) neurones, failed to reveal cGMP-IR neurons in the RVLM of either strain, despite consistent detection of cGMP-IR in the nucleus ambiguus (NA). This was unchanged in the presence of isobutylmethylxanthine (IBMX; 0.5 mM, WKY, n = 4, SHR n = 2) and in young animals (WKY, 10-weeks, n = 3). Incubation of RVLM-slices (WKY, 10-weeks, n = 9) in DETA-NO (100 mum; 10 min) or NMDA (10 muM; 2 min) did not uncover cGMP-IR. In all studies, cGMP was prominent within the vasculature. Soluble guanylate cyclase (sGC)-IR was found throughout neurones of the RVLM, but did not co-localise with PNMT, TH or nNOS-IR neurons (WKY, 10-weeks, n = 6). Results indicate that within the RVLM, cGMP is not detectable using immunohistochemistry in the basal state and cannot be elicited by phosphodiesterase inhibition, NMDA receptor stimulation or NO donor application.

Neuroprotective effect of nitroglycerin in a rodent model of ischemic stroke: evaluation of Bcl-2 expression

Transient focal ischemia caused by middle cerebral artery occlusion (MCAo) produces apoptotic cell death in the penumbra area. Bcl-2 is a protooncogene that plays a major antiapoptotic role, at the cellular level, by counteracting the activation of apoptosis effectors, that is, caspases. It has been suggested that nitroglycerin (NTG), a nitric oxide donor, reduces ischemia/reperfusion-induced brain damage via the inhibition of caspase activity and NMDA receptor. In this chapter, we evaluated the protective effects of NTG against cerebral damage caused by transient (2h) MCAo (tMCAo) focusing our interest on the potential effects on Bcl-2 expression. Male Wistar rats were administered intraperitoneally (i.p.) with NTG (10mg/kg) or vehicle (PEG, 1ml/kg) 20min before the induction of MCAo by intraluminal silicon-coated filament (0.37-mm diameter). Cerebral infarct volume was measured 22h after reperfusion, while cortical Bcl-2 expression was evaluated at the end of 2-h MCAo (without reperfusion) and at 5h of reperfusion. The results show significant reduction of the infarct volume in rats preinjected with NTG, as compared to the vehicle group. After 2h of occlusion, no significant difference was seen in Bcl-2 expression in the ipsilateral and contralateral cortex of either experimental groups (NTG and vehicle). However, 5h after reperfusion, a significant increase of Bcl-2 expression was detected in the damaged cortex of control rats, probably reflecting a compensatory response aiming at counteracting the cell death process; this increase was absent in the NTG-treated rats. These data, while confirming the neuroprotective effect of NTG in an in vivo ischemia/reperfusion model, seem to suggest that the drug may act by downsizing the complex chain of events underlying apoptosis activation and consequent activation of antiapoptotic responses.

Animal models of migraine: looking at the component parts of a complex disorder

Animal models of human disease have been extremely helpful both in advancing the understanding of brain disorders and in developing new therapeutic approaches. Models for studying headache mechanisms, particularly those directed at migraine, have been developed and exploited efficiently in the last decade, leading to better understanding of the potential mechanisms of the disorder and of the action for antimigraine treatments. Model systems employed have focused on the pain-producing cranial structures, the large vessels and dura mater, in order to provide reproducible physiological measures that could be subject to pharmacological exploration. A wide range of methods using both in vivo and in vitro approaches are now employed; these range from manipulation of the mouse genome in order to produce animals with human disease-producing mutations, through sensitive immunohistochemical methods to vascular, neurovascular and electrophysiological studies. No one model system in experimental animals can explain all the features of migraine; however, the systems available have begun to offer ways to dissect migraine's component parts to allow a better understanding of the problem and the development of new treatment strategies.

Phosphodiesterase 3 and 5 and cyclic nucleotide-gated ion channel expression in rat trigeminovascular system

Activation of the trigeminovascular pain signalling system appears involved in migraine pathophysiology. However, the molecular mechanisms are only partially known. Stimulation of cAMP and cGMP production as well as inhibition of their breakdown induce migraine-like headache. Additionally, migraine may be associated with mutations in ion channels. The aim of the present study was to describe the expression of phosphodiesterase 3 (PDE3) and 5 (PDE5) and cyclic nucleotide-gated ion channels (CNG) in cerebral arteries, meninges, and the trigeminal ganglion. mRNA for PDE and CNG was determined in the rat middle cerebral artery, basilar artery, trigeminal ganglion, and dura mater using real-time PCR. PDE and CNG proteins were identified using Western blot. For comparison, rat aorta and mesenteric artery were analysed. PDE3A, PDE3B, and PDE5A mRNA were detected in all tissues examined except for PDE3A mRNA in dura mater and the trigeminal ganglion. PDE5A and PDE3A protein expression was present in both cerebral and peripheral arteries, whereas PDE3B protein was present only in the cerebral arteries. The CNGA4 and B1 subunit mRNAs were detected in cerebral arteries and CNGA2 also in the mesenteric artery. CNGA2 and A3 proteins were found in cerebral arteries and dura and CNGA1, CNGA2 and CNGA3 in the trigeminal ganglion. In conclusion, PDE3A, PDE3B, PDE5A, and five CNG subunits were expressed in several components of the trigeminovascular system of the rat. This suggests that modulation of cAMP and cGMP levels by PDE and activation of CNG may play a role in trigeminovascular pain signalling leading to migraine headache.

Activation of the Transcription Factor NF-κB in the Nucleus Trigeminalis Caudalis in an Animal Model of Migraine

The infusion of nitroglycerin (NTG) induces an inflammatory state in perivascular meningeal tissues of rat via the activation, inter alia, of nuclear factor kappa B (NF-kappaB). This phenomenon has been related to the mechanisms involved in the pathophysiology of migraine, a common neurovascular disorder. In the present study, we sought to elucidate whether NF-kappaB activation might have a role in the determinism of migraine attacks also at the neuronal level. Therefore, we investigated the transcriptional activity of NF-kappaB in the brainstem of rats systemically injected with NTG and killed 4h later. Activation of NF-kappaB in brain areas was detected by means of both the immunohistochemical technique and the Western blot analysis. A significant increase of nuclear immunostaining of p65, an indicator of NF-kappaB activation, was detected in lamina I and II of nucleus trigeminalis caudalis in rats injected with NTG when compared with the control group. Western blot analysis confirmed the activation of the NF-kappaB pathway showing an increase in the optical density of p65 in nuclear extracts of lower brainstem of rats injected with the nitric oxide (NO) donor. The present study contributes to expand on our understanding of the complex mechanisms by which NTG may trigger migraine-like headaches in migraineurs. Furthermore, these findings pave the way to new bio-molecular and pharmacological avenues for the development of innovative migraine therapies.

Effects of acute and chronic restraint stress on nitroglycerin-induced hyperalgesia in rats

Nitric oxide (NO) plays an important role in initiation and maintenance of pain, and NO precursor nitroglycerin is able to activate spinal and brain structures involved in nociception. It is also known that acute and chronic stress induce biochemical changes affecting both pain threshold and behaviour, and that the biological pattern of depression can be mimicked in the laboratory using chronic unavoidable stress paradigms (learned helplessness). We, therefore, evaluated the effects of acute and chronic immobilization stress on pain response to nitroglycerin administration in the rat. Pain perception was expressed as the latency of response to a tail-flick test (hot stimulus). Measures were made 1, 2 and 4 h following nitroglycerin (10 mg/kg i.p.) or vehicle. Nitroglycerin caused hyperalgesia after 2 and 4 h (p < 0.05 versus baseline). Acute stress (90 min) induced a clear analgesic state (p < 0.01 versus non-stressed control animals), and nitroglycerin injection was unable to reverse stress-induced analgesia in this setting. By contrast, exposition to chronic immobilization stress (7 days) caused a significant increase in pain response (p < 0.05); in this case, hyperalgesia was shown to be further enhanced by nitroglycerin administration (p < 0.05 versus vehicle). These findings support the view that a condition of chronic stress used in the laboratory to reproduce the biological features of depression can enhance hyperalgesia induced by nitroglycerin administration. These observations may be relevant to pain disorders, and particularly to migraine, since nitroglycerin is able to induce spontaneous-like pain attacks in humans, and an unfavourable migraine outcome (transformation into a chronic daily headache) is associated with chronic stress and comorbid depression.