Expression of c-fos-like immunoreactivity in brainstem after meningeal irritation by blood in the subarachnoid space

Discrepancy between Jun/Fos Proto-Oncogene mRNA and Protein Expression in the Rheumatoid Arthritis Synovial Membrane

Rheumatoid arthritis (RA) is a chronic inflammatory and destructive joint disease characterized by overexpression of pro-inflammatory/pro-destructive mediators, whose regulation has been the focus of our previous studies. Since the expression of these proteins commonly depends on AP-1, the expression of the AP-1-forming subunits cJun, JunB, JunD, and cFos was assessed in synovial membrane (SM) samples of RA, osteoarthritis (OA), joint trauma (JT), and normal controls (NC) using ELISA and qRT-PCR. With respect to an observed discrepancy between mRNA and protein levels, the expression of the mRNA stability-modifying factors AU-rich element RNA-binding protein (AUF)-1, tristetraprolin (TTP), and human antigen R (HuR) was measured. JunB and JunD protein expression was significantly higher in RA-SM compared to OA and/or NC. By contrast, jun/fos mRNA expression was significantly (cjun) or numerically decreased (junB, junD, cfos) in RA and OA compared to JT and/or NC. Remarkably, TTP and HuR were also affected by discrepancies between their mRNA and protein levels, since they were significantly decreased at the mRNA level in RA versus NC, but significantly or numerically increased at the protein level when compared to JT and NC. Discrepancies between the mRNA and protein expression for Jun/Fos and TTP/HuR suggest broad alterations of post-transcriptional processes in the RA-SM. In this context, increased levels of mRNA-destabilizing TTP may contribute to the low levels of jun/fos and ttp/hur mRNA, whereas abundant mRNA-stabilizing HuR may augment translation of the remaining mRNA into protein with potential consequences for the composition of the resulting AP-1 complexes and the expression of AP-1-dependent genes in RA.

Current understanding of meningeal and cerebral vascular function underlying migraine headache

BACKGROUND

The exact mechanisms underlying the onset of a migraine attack are not completely understood. It is, however, now well accepted that the onset of the excruciating throbbing headache of migraine is mediated by the activation and increased mechanosensitivity (i.e. sensitization) of trigeminal nociceptive afferents that innervate the cranial meninges and their related large blood vessels.

OBJECTIVES

To provide a critical summary of current understanding of the role that the cranial meninges, their associated vasculature, and immune cells play in meningeal nociception and the ensuing migraine headache.

METHODS

We discuss the anatomy of the cranial meninges, their associated vasculature, innervation and immune cell population. We then debate the meningeal neurogenic inflammation hypothesis of migraine and its putative contribution to migraine pain. Finally, we provide insights into potential sources of meningeal inflammation and nociception beyond neurogenic inflammation, and their potential contribution to migraine headache.

Cerebrospinal fluid-stem cell interactions may pave the path for cell-based therapy in neurological diseases

Recent studies have suggested that the regulation of endogenous neural stem cells (NSCs) or transplanting of exogenous nerve cells are the newest and most promising methods for the treatment of dementia and other neurological diseases. The special location and limited number of endogenous NSCs, however, restrict their clinical application. The success in directional differentiation of exogenous stem cells from other tissue sources into neural cells has provided a novel source for NSCs. Study on the relative mechanisms is still at the preliminary stage. Currently the induction methods include: 1) cell growth factor induction; 2) chemical induction; 3) combined growth factor-chemical induction; or 4) other induction methods such as traumatic brain tissue homogenate, gene transfection, traditional Chinese medicine, and coculture induction. Cerebrospinal fluid (CSF), as a natural medium under physiological conditions, contains a variety of progrowth peptide factors that can promote the proliferation and differentiation of mesenchymal stromal cells (MSCs) into neural cells through the corresponding receptors on the cell surface. This suggests that CSF can not only nourish the nerve cells, but also become an effective and suitable inducer to increase the yield of NSCs. However, some other studies believed that CSF contained certain inhibitory components against the differentiation of primary stem cells into mature neural cells. Based on the above background, here we review the relative literature on the influence of the CSF on stem cells in order to provide a more comprehensive reference for the wide clinical application of NSCs in the future.

Migraine Enters the Molecular Era

Migraine headache is the first neurological condition treatable by a drug targeted to a specific receptor binding site. Originally viewed as a disorder of brain blood vessels, migraine may have as its biological basis a disturbance in brain function. Regarding therapy, recent molecular data document that 5-HT1D receptors on primary afferent fibers are coupled to inhibition of neuropeptide release, blockade of neurogenic inflammation, and c-fos expression within the trigeminal nucleus caudalis after noxious meningeal stimulation in experimental animals. The 5-HT1Dα receptor subtype (as opposed to the 5-HT 1Dβ receptor) has emerged as an important therapeutic target aimed at blocking trigeminal nerve fibers without constricting vascular smooth muscle. NEUROSCIENTIST 2:191-200, 1996

Corneal pain activates a trigemino-parabrachial pathway in rats

Corneal pain is mediated by primary afferent fibers projecting to the dorsal horn of the medulla, specifically the trigeminal nucleus caudalis. In contrast to reflex responses, the conscious perception of pain requires transmission of neural activity to higher brain centers. Ascending pain transmission is mediated primarily by pathways to either the thalamus or parabrachial nuclei. We previously showed that some corneal afferent fibers preferentially contact parabrachial-projecting neurons in the rostral pole of the trigeminal nucleus caudalis, but the role of these projection neurons in transmitting noxious information from the cornea has not been established. In the present study, we show that noxious stimulation of the corneal surface activates neurons in the rostral pole of the nucleus caudalis, including parabrachially projecting neurons that receive direct input from corneal afferent fibers. We used immunocytochemical detection of c-Fos protein as an index of neuronal activation after noxious ocular stimulation. Animals had previously received injections of a retrograde tracer into either thalamic or parabrachial nuclei to identify projection neurons in the trigeminal dorsal horn. Noxious stimulation of the cornea induced c-Fos in neurons sending projections to parabrachial nuclei, but not thalamic nuclei. We also confirmed that corneal afferent fibers identified with cholera toxin B preferentially target trigeminal dorsal horn neurons projecting to the parabrachial nucleus. The parabrachial region sends ascending projections to brain regions involved in emotional and homeostatic responses. Activation of the ascending parabrachial system may explain the extraordinary salience of stimulation of corneal nociceptors.

The role of vagal neurocircuits in the regulation of nausea and vomiting

Nausea and vomiting are among the most frequently occurring symptoms observed by clinicians. While advances have been made in understanding both the physiological as well as the neurophysiological pathways involved in nausea and vomiting, the final common pathway(s) for emesis have yet to be defined. Regardless of the difficulties in elucidating the precise neurocircuitry involved in nausea and vomiting, it has been accepted for over a century that the locus for these neurocircuits encompasses several structures within the medullary reticular formation of the hindbrain and that the role of vagal neurocircuits in particular are of critical importance. The afferent vagus nerve is responsible for relaying a vast amount of sensory information from thoracic and abdominal organs to the central nervous system. Neurons within the nucleus of the tractus solitarius not only receive these peripheral sensory inputs but have direct or indirect connections with several other hindbrain, midbrain and forebrain structures responsible for the co-ordination of the multiple organ systems. The efferent vagus nerve relays the integrated and co-ordinated output response to several peripheral organs responsible for emesis. The important role of both sensory and motor vagus nerves, and the available nature of peripheral vagal afferent and efferent nerve terminals, provides extensive and readily accessible targets for the development of drugs to combat nausea and vomiting.

Obesity increases nociceptive activation of the trigeminal system

BACKGROUND

Obesity is a risk factor associated with several pain syndromes. However, the mechanisms underlying the association between obesity and pain are not known. The aim of this study was to test the hypothesis that obesity enhances neuronal responses to nociceptive stimulation within the trigeminal nucleus caudalis (TNC).

METHODS

Male and female C57BL/6J mice were fed a high-fat or regular diet from the time of weaning until 20 weeks of age. We then quantified neuronal activation by measuring Fos immunoreactivity within the TNC in response to a facial injection of a low dose of capsaicin (1 μg/10 μL).

RESULTS

We found that 0.01% capsaicin did not significantly increase Fos immunoreactivity in control mice fed a regular diet. In contrast, this low dose of capsaicin caused a 3.3-fold increase in Fos in the TNC in obese mice (p < 0.001).

CONCLUSIONS

These results support the hypothesis that diet-induced obesity in mice enhances nociceptive processing within the TNC. Diet-induced obesity may be a useful model for mechanistic studies. Future studies will improve our understanding of how obesity may contribute to trigeminal pain by sensitizing the trigeminal nociceptive system.

Increase of capsaicin-induced trigeminal Fos-like immunoreactivity by 5-HT(7) receptors

OBJECTIVE

To explore whether pharmacological stimulation of the 5-hydroxytryptamine(7) (5-HT(7) ) receptor modulates Fos-like immunoreactivity in the trigeminal nucleus caudalis of rats.

BACKGROUND

The serotonin 5-HT(7) receptor was proposed to be involved in migraine pathogenesis and evidence suggests it plays a role in peripheral nociception and hyperalgesia through an action on sensory afferent neurons.

METHODS

The potential activating or sensitizing role of 5-HT(7) receptors on trigeminal sensory neurons, as visualized by Fos-like immunoreactivity in the superficial layers of the trigeminal nucleus caudalis in rats, was investigated using the 5-HT(7) receptor agonist, LP-211, in the absence and the presence of intracisternal capsaicin, respectively. The agonist effect was characterized with the 5-HT(7) receptor antagonist, SB-656104. Male Wistar rats received a subcutaneous injection of LP-211, SB-656104, and SB-656104 + LP-211. They were then anesthetized and prepared to receive an intracisternal injection of capsaicin or its vehicle. Animals were perfused and brains removed; sections of the brain stem from the area postrema to the CI level were obtained and processed for Fos immunohistochemistry.

RESULTS

Capsaicin but not its vehicle induced Fos-like immunoreactivity within laminae I and II of trigeminal nucleus caudalis. Pretreatment with LP-211 had no effect on Fos-like immunoreactivity but strongly increased the response produced by capsaicin; this effect was abolished by SB-656104. Interestingly, capsaicin-induced Fos-like immunoreactivity was abolished by SB-656104 pretreatment thus suggesting involvement of endogenous 5-HT.

CONCLUSIONS

Data suggest that 5-HT(7) receptors increase activation of meningeal trigeminovascular afferents and/or transmission of nociceptive information in the brain stem. This mechanism could be relevant in migraine and its prophylactic treatment.

Different trigemino-vascular responsiveness between adolescent and adult rats in a migraine model

BACKGROUND

Pediatric migraine displays different clinical features from adult migraine. Because the trigemino-vascular system (TGVS) plays a pivotal role in migraine pathophysiology, this study compared TGVS responses in a migraine model induced by intracisternal (i.c.) instillation of capsaicin in adolescent and adult rats.

METHODS

TGVS responses measured included c-Fos-protein-expressing neurons in the trigeminal cervical complex (TCC), calcitonin gene-related peptide (CGRP) expression in the trigeminal ganglia (TG) and dura mater, and dural protein extravasation. The formulas for estimating total numbers of activated TCC neurons were established based on the c-Fos-positive neuronal numbers in three sample sections, +0.6, -1.2 and -9 mm and +0.6, -0.6 and -6 mm, from the obex in adult and adolescent rats, respectively.

RESULTS

After capsaicin instillation, adolescent rats had comparable TCC neurons activated as adult rats, but less TGVS peripheral responsiveness than adults, including CGRP immunoreactivity in the TG, and protein extravasation and CGRP depletion (inversely reflected by CGRP immunoreactivity) in the dura mater.

CONCLUSIONS

Age-dependent differences in TGVS responsiveness in the i.c. capsaicin-induced migraine model of rats are reminiscent of less severe migraine in pediatric patients. This finding may provide new insight into the pathophysiology of migraine and guide the development of new anti-migraine drugs for children.

A naturalistic glyceryl trinitrate infusion migraine model in the rat

BACKGROUND AND AIM

Glyceryl trinitrate (GTN) infusion is a reliable method to provoke migraine-like headaches in humans. Previous studies have simulated this human model in anaesthetized or in awake rodents using GTN doses 10,000 times higher than used in humans. The relevance of such toxicological doses to migraine is not certain. Anaesthesia and low blood pressure caused by high GTN doses both can affect the expression of nociceptive marker c-fos. Therefore, our aim was to simulate the human GTN migraine model in awake rats using a clinically relevant dose.

METHODS

Awake rats were infused with GTN (4 µg/kg/min, for 20 min, i.v.), a dose just 8 times higher than in humans. mRNA and protein expression for c-fos were analysed in the trigeminal vascular system at various time points using RT-PCR and immunohistochemistry, respectively.

RESULTS

A significant upregulation of c-fos mRNA was observed in the trigeminal nucleus caudalis at 30 min and 2 h that was followed by an upregulation of Fos protein in the trigeminal nucleus caudalis at 2 h and 4 h after GTN infusion. Pre-treatment with sumatriptan attenuated the activation of Fos at 4 h, demonstrating the specificity of this model for migraine.

CONCLUSION

We present a validated naturalistic rat model suitable for screening of acute anti-migraine drugs.

A trigeminoreticular pathway: implications in pain

Neurons in the caudalmost ventrolateral medulla (cmVLM) respond to noxious stimulation. We previously have shown most efferent projections from this locus project to areas implicated either in the processing or modulation of pain. Here we show the cmVLM of the rat receives projections from superficial laminae of the medullary dorsal horn (MDH) and has neurons activated with capsaicin injections into the temporalis muscle. Injections of either biotinylated dextran amine (BDA) into the MDH or fluorogold (FG)/fluorescent microbeads into the cmVLM showed projections from lamina I and II of the MDH to the cmVLM. Morphometric analysis showed the retrogradely-labeled neurons were small (area 88.7 µm(2)±3.4) and mostly fusiform in shape. Injections (20-50 µl) of 0.5% capsaicin into the temporalis muscle and subsequent immunohistochemistry for c-Fos showed nuclei labeled in the dorsomedial trigeminocervical complex (TCC), the cmVLM, the lateral medulla, and the internal lateral subnucleus of the parabrachial complex (PBil). Additional labeling with c-Fos was seen in the subnucleus interpolaris of the spinal trigeminal nucleus, the rostral ventrolateral medulla, the superior salivatory nucleus, the rostral ventromedial medulla, and the A1, A5, A7 and subcoeruleus catecholamine areas. Injections of FG into the PBil produced robust label in the lateral medulla and cmVLM while injections of BDA into the lateral medulla showed projections to the PBil. Immunohistochemical experiments to antibodies against substance P, the substance P receptor (NK1), calcitonin gene regulating peptide, leucine enkephalin, VRL1 (TPRV2) receptors and neuropeptide Y showed that these peptides/receptors densely stained the cmVLM. We suggest the MDH- cmVLM projection is important for pain from head and neck areas. We offer a potential new pathway for regulating deep pain via the neurons of the TCC, the cmVLM, the lateral medulla, and the PBil and propose these areas compose a trigeminoreticular pathway, possibly the trigeminal homologue of the spinoreticulothalamic pathway.

Pharmacology

Headache treatment has been based primarily on experiences with non-specific drugs such as analgesics, non-steroidal anti-inflammatory drugs, or drugs that were originally developed to treat other diseases, such as beta-blockers and anticonvulsant medications. A better understanding of the basic pathophysiological mechanisms of migraine and other types of headache has led to the development over the past two decades of more target-specific drugs. Since activation of the trigeminovascular system and neurogenic inflammation are thought to play important roles in migraine pathophysiology, experimental studies modeling those events successfully predicted targets for selective development of pharmacological agents to treat migraine. Basically, there are two fundamental strategies for the treatment of migraine, abortive or preventive, based to a large degree on the frequency of attacks. The triptans, which exhibit potency towards selective serotonin (5-hydroxytryptamine, 5-HT) receptors expressed on trigeminal nerves, remain the most effective drugs for the abortive treatment of migraine. However, numerous preventive medications are currently available that modulate the excitability of the nervous system, particularly the cerebral cortex. In this chapter, the pharmacology of commercially available medications as well as drugs in development that prevent or abort headache attacks will be discussed.

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.

Cerebral activity during the anesthesia-like state induced by mesopontine microinjection of pentobarbital

Microinjection of pentobarbital into a restricted region of rat brainstem, the mesopontine tegmental anesthesia area (MPTA), induces a reversible anesthesia-like state characterized by loss of the righting reflex, atonia, antinociception, and loss of consciousness as assessed by electroencephalogram synchronization. We examined cerebral activity during this state using FOS expression as a marker. Animals were anesthetized for 50 min with a series of intracerebral microinjections of pentobarbital or with systemic pentobarbital and intracerebral microinjections of vehicle. FOS expression was compared with that in awake animals microinjected with vehicle. Neural activity was suppressed throughout the cortex whether anesthesia was induced by systemic or MPTA routes. Changes were less consistent subcortically. In the zona incerta and the nucleus raphe pallidus, expression was strongly suppressed during systemic anesthesia, but only mildly during MPTA-induced anesthesia. Dissociation was seen in the tuberomammillary nucleus where suppression occurred during systemic-induced anesthesia only, and in the lateral habenular nucleus where activity was markedly increased during systemic-induced anesthesia but not following intracerebral microinjection. Several subcortical nuclei previously associated with cerebral arousal were not affected. In the MPTA itself FOS expression was suppressed during systemic anesthesia. Differences in the pattern of brain activity in the two modes of anesthesia are consistent with the possibility that anesthetic endpoints might be achieved by alternative mechanisms: direct drug action for systemic anesthesia or via ascending pathways for MPTA-induced anesthesia. However, it is also possible that systemically administered agents induce anesthesia, at least in part, by a primary action in the MPTA with cortical inhibition occurring secondarily.

Post-traumatic headache: facts and doubts

The International Classification of Headache Disorders does not separate the moderate from severe/very severe traumatic brain injury (TBI), since they are all defined by Glasgow coma scale (GCS) < 13. The distinction between the severe and very severe TBI (GCS < 8) should be made upon coma duration that in the latter may be longer than 15 days up to months in the case of vegetative state. Post-traumatic amnesia duration may double the coma duration itself. Therefore, the 3-month parameter proposed to define the occurrence or resolution of post-traumatic headache (PTH) appears inadequate. Following TBI, neuropathic pain, central pain, thalamic pain, combined pain are all possible and they call for proper pharmacological approaches. One more reason for having difficulties in obtaining information about headache in the early phase after regaining consciousness is the presence of concomitant medications that may affect pain perception. Post-traumatic stress disorder (PTSD) develops days or weeks after stress and tends to improve or disappear within 3 months after exposure; interestingly, this spontaneous timing resembles that of PTH. In our experience the number of TBI patients with PTH at 1-year follow-up is lower in those with longer coma duration and more severe TBI. Cognitive functioning evaluated after at least 12 months from TBI, showed mild or no impairment in these patients with severe TBI and PTH, whereas they have psychopathological changes, namely anxiety and depression. The majority of patients with PTH after severe/very severe TBI had skull fractures or dural lacerations and paroxystic EEG abnormalities. The combination of psychological changes (depression and anxiety) and organic features (skull fractures, dural lacerations, epileptic EEG abnormalities) in PTH may be inversely correlated with the severity of TBI, with prevalence of psychological disturbances in mild TBI and of organic lesions in severe TBI. On the other hand, only in severe TBI patients with good cognitive recovery the influence of the psychopathological disorders may play a role. In fact, the affective pain perception is probably related to the integrity of cognitive functions as in mild TBI and in severe TBI with good cognitive outcome.

Melatonin treatment decreases c-fos expression in a headache model induced by capsaicin

The aim of the present work was to analyze c-fos response within the trigeminal nucleus caudalis (TNC) of pinealectomized rats and animals that received intraperitoneal melatonin, after intracisternal infusion of capsaicin, used to induce intracranial trigeminovascular stimulation. Experimental groups consisted of animals that received vehicle solution (saline-ethanol-Tween 80, 8:1:1, diluted 1:50) only (VEI, n=5); animals that received capsaicin solution (200 nM) only (CAP, n=6); animals submitted to pinealectomy (PX, n=5); sham-operated animals (SH, n=5); animals submitted to pinealectomy followed by capsaicin stimulation (200 nM) after 15 days (PX + CAP, n=7); and animals that received capsaicin solution (200 nM) and intraperitoneal melatonin (10 mg/kg) (CAP + MEL, n=5). Control rats, receiving vehicle in the cisterna magna, showed a small number of c-fos-positive cells in the TNC (layer I/II) as well as the sham-operated and pinealectomized rats, when compared to animals stimulated by capsaicin. On the other hand, pinealectomized rats, which received capsaicin, presented the highest number of c-fos-positive cells. Animals receiving capsaicin and melatonin treatment had similar expression of the vehicle group. Our data provide experimental evidence to support the role of melatonin and pineal gland in the pathophysiology of neurovascular headaches.

Sumatriptan inhibits synaptic transmission in the rat midbrain periaqueductal grey

Background

There is evidence to suggest that the midbrain periaqueductal grey (PAG) has a role in migraine and the actions of the anti-migraine drug sumatriptan. In the present study we examined the serotonergic modulation of GABAergic and glutamatergic synaptic transmission in rat midbrain PAG slices in vitro.

Results

Serotonin (5-hydroxytriptamine, 5-HT, IC₅₀ = 142 nM) and the selective serotonin reuptake inhibitor fluoxetine (30 μM) produced a reduction in the amplitude of GABA_A-mediated evoked inhibitory postsynaptic currents (IPSCs) in all PAG neurons which was associated with an increase in the paired-pulse ratio of evoked IPSCs. Real time PCR revealed that 5-HT1A, 5-HT1B, 5-HT1D and 5-HT1F receptor mRNA was present in the PAG. The 5-HT1A, 5-HT1B and 5-HT1D receptor agonists 8-OH-DPAT (3 μM), CP93129 (3 μM) and L694247 (3 μM), but not the 5-HT1F receptor agonist LY344864 (1 – 3 μM) inhibited evoked IPSCs. The 5-HT (1 μM) induced inhibition of evoked IPSCs was abolished by the 5-HT1B antagonist NAS181 (10 μM), but not by the 5-HT1A and 5-HT1D antagonists WAY100135 (3 μM) and BRL15572 (10 μM). Sumatriptan also inhibited evoked IPSCs with an IC₅₀ of 261 nM, and reduced the rate, but not the amplitude of spontaneous miniature IPSCs. The sumatriptan (1 μM) induced inhibition of evoked IPSCs was abolished by NAS181 (10 μM) and BRL15572 (10 μM), together, but not separately. 5-HT (10 μM) and sumatriptan (3 μM) also reduced the amplitude of non-NMDA mediated evoked excitatory postsynaptic currents (EPSCs) in all PAG neurons tested.

Conclusion

These results indicate that sumatriptan inhibits GABAergic and glutamatergic synaptic transmission within the PAG via a 5-HT1B/D receptor mediated reduction in the probability of neurotransmitter release from nerve terminals. These actions overlap those of other analgesics, such as opioids, and provide a mechanism by which centrally acting 5-HT1B and 5-HT1D ligands might lead to novel anti-migraine pharmacotherapies.

Investigation of the immunoreactivities of NOS enzymes and the effect of sumatriptan in adolescent rats using an experimental model of migraine

The aim was to investigate the immunoreactivities for NOS enzymes in frontal cortex and meningeal vessels after chemical stimulation of the subarachnoid space of adolescent rats and the effect of sumatriptan pre-treatment on the immunoreactivities of the NOS enzymes. Male adolescent Wistar rats were used. Rats in group 1 did not taken intracisternal injection. Rats in group 2 were taken intracisternal autologous blood injection, but no sumatriptan pre-treatment. Rats in group 3 were taken intracisternal autologous blood injection, but they were taken sumatriptan pre-treatment. Tissue samples were investigated for the presence of NOS immunoreactivity. The mean values of immunolabeling intensities for NOS enzymes in frontal cortex and meningeal vessels were significantly increased in group 2 compared to group 1. The mean values of immunolabeling intensities for NOS enzymes in frontal cortex and meningeal vessels were significantly reduced in group 3 compared to group 2. These results suggest that, chemical stimulation of the subarachnoid space increased the immunoreactivities of NOS enzymes in the brain of adolescent rats. The increased NOS immunoreactivities could be antagonized by pre-treatment with sumatriptan.

Animal models of migraine headache and aura

PURPOSE OF REVIEW

Over the past 30 years, animal models of migraine have led to the identification of novel drug targets and drug treatments as well as helped to clarify a mechanism for abortive and prophylactic drugs. Animal models have also provided translational knowledge and a framework to think about the impact of hormones, genes, and environmental factors on migraine pathophysiology. Although most acknowledge that these animal models have significant shortcomings, promising new drugs are now being developed and brought to the clinic using these preclinical models. Hence, it is timely to provide a short overview examining the ways in which animal models inform us about underlying migraine mechanisms.

RECENT FINDINGS

First generation migraine models mainly focused on events within pain-generating intracranial tissues, for example, the dura mater and large vessels, as well as their downstream consequences within brain. Upstream events such as cortical spreading depression have also been modeled recently and provide insight into mechanisms of migraine prophylaxis. Mouse mutants expressing human migraine mutations have been genetically engineered to provide an understanding of familial hemiplegic migraine and possibly, by extrapolation, may reflect on the pathophysiology of more common migraine subtypes.

SUMMARY

Animal models of migraine reflect distinct facets of this clinically heterogeneous disorder and contribute to a better understanding of its pathophysiology and pharmacology.

Review of frovatriptan in the treatment of migraine

Triptans are recommended for the acute treatment of moderate to severe migraine or failure to respond to other acute migraine treatments. Seven triptans are available providing a wide range of choices. These triptans are more similar than dissimilar but patients do note differences in effectiveness and in tolerance. Also migraine situations may differ from attack to attack, providing the opportunity to exploit the uniqueness of a particular triptan. Frovatriptan has a uniquely long-half life, five times that of other triptans. This provides the opportunity to use frovatriptan in mini-prophylaxis such as in menstrual-related migraine and other situations, as well as use in long-lasting or recurrent migraine.

Activation of c-jun in the rat basilar artery after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) initiates a series of cellular and molecular events, some of which involve a mitogen activated protein kinase, c-jun N-terminal kinase (JNK). However, precise details regarding activation of c-jun in the vessel wall after SAH largely remain to be elucidated. In this study, we therefore investigated the localization and time-dependent expression of c-jun in the rat basilar artery after SAH in a rat single-hemorrhage model featuring infusion of autologous arterial blood. Basilar arteries were obtained at 2, 6 and 12h and 1, 2, 4 and 7 days after SAH, as well as from controls. Western blot analysis with c-jun, phosphorylated c-jun at Ser(63), and actin antibodies revealed that c-jun was immediately phosphorylated at Ser(63) within 2h, thereafter gradually becoming dephosphorylated, while total c-jun and actin levels remained almost unchanged. Immunohistochemistry demonstrated phosphorylation of c-jun at Ser(63) to occur in smooth muscle cells of the basilar artery 2h after SAH. These results indicate that c-jun is activated in the basilar artery immediately after the onset of SAH, presumably resulting in transcription of immediate early genes and smooth muscle cell proliferation.

Serotonin receptor ligands: treatments of acute migraine and cluster headache

Fuelled by the development of the serotonin 5-HT(1B/1D) receptor agonists, the triptans, the last 15 years has seen an explosion of interest in the treatment of acute migraine and cluster headache. Sumatriptan was the first of these agonists, and it launched a wave of therapeutic advances. These medicines are effective and safe. Triptans were developed as cranial vasoconstrictors to mimic the desirable effects of serotonin, while avoiding its side-effects. It has subsequently been shown that the triptans' major action is neuronal, with both peripheral and central trigeminal inhibitory effects, as well as actions in the thalamus and at central modulatory sites, such as the periaqueductal grey matter. Further refinements may be possible as the 5-HT(1D) and 5-HT(1F) receptor agonists are explored. Serotonin receptor pharmacology has contributed much to the better management of patients with primary headache disorders.

Modulation of nociceptive dural input to the trigeminal nucleus caudalis via activation of the orexin 1 receptor in the rat

Migraine pathophysiology is thought to involve the trigeminal innervation of the dura mater and intracranial blood vessels. Electrical stimulation of dural blood vessels is painful in humans and causes activation of neurons in the caudal-most portion of the trigeminal nucleus in experimental animals. The hypothalamic neuropeptides orexin A and B are selectively synthesized in the lateral and posterior hypothalamus, and recent findings have implicated their involvement in nociceptive processing. To evaluate the potential for orexin receptor modulation of trigeminovascular nociceptive afferents, we examined the effects of intravenous orexin A and B on responses of neurons in the trigeminal nucleus caudalis. To dissect the receptor pharmacology of responses to stimulation we utilized the novel orexin 1 receptor (OX(1)R) antagonist N-(2-methyl-6-benzoxazolyl)-N''-1,5-naphthyridin-4-yl urea (SB-334867). Orexin A 30 microg/kg (F(1.9,9.8) = 21.93, P < 0.001) and 50 microg/kg (F(3.2,16.4) = 3.28, P < 0.045) inhibited the A-fibre responses to dural electrical stimulation over 60 min. Maximum inhibition was achieved at 25 min for both 30 microg/kg (t(5) = 19.83, n = 6, P < 0.001) and 50 microg/kg (t(5) = 7.74, n = 6, P < 0.001). The response with orexin A 30 microg/kg was reversed by pretreatment with the OX(1)R antagonist SB-334867 (F(3.5,17.5) = 0.49, P = 0.73), which had no effect when given alone. Orexin B and control vehicle administration had no significant effect on trigeminal neuronal firing. The current study demonstrates that orexin A is able to inhibit A-fibre responses to dural electrical stimulation via activation of the OX(1)R.

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.

Cortical cooling induces conditioned consumption reduction in male rats

Previous studies have shown that male rats acquire a conditioned reduction in consumption of a sucrose solution when consumption of that taste solution is followed by cooling the caudate putamen. Because the shaft of the cold probe was not insulated, this cooling also included the cortex and meninges overlying the caudate putamen. When cooling the meninges was eliminated as a factor, the conditioned consumption reduction was weaker but it was not abolished. This suggests that meninges cooling contribute to the conditioned consumption reduction induced when all three structures are cooled, but it is not sufficient. Five experiments were designed to determine whether cooling the cortex also contributes. In the first experiment, the temperature of the cortex and meninges overlying the caudate putamen was measured during cooling. In the following three experiments the ability of male rats to acquire a conditioned consumption reduction was determined after pairing a sucrose solution with cooling the cortex and meninges overlying the caudate putamen, cooling the cortex with and without cooling the dura meninges membrane, and cooling the cortex with and without cooling the entire meninges. When the cortex was cooled without cooling the caudate putamen, dura, or entire meninges, a conditioned consumption reduction was acquired. The last experiment demonstrated that contingent pairing of sucrose and cortical cooling was required to obtain consumption reduction. These results clearly indicate that cortical cooling contributes to the acquisition of conditioned consumption reduction induced when the caudate putamen and overlying cortex and meninges are cooled. Two hypotheses are suggested to account for the ability of neural cooling to act as an unconditioned stimulus in the conditioned consumption reduction paradigm: (1) neuronal inactivation produces physiological changes that can serve as unconditioned stimuli and (2) cooling itself produces physiological changes that can serve as unconditioned stimuli.

Occipital afferent activation of second order neurons in the trigeminocervical complex in rat

Stimulation of the greater occipital nerve produces excitation of second order neurons in the trigeminocervical complex. Given that neck pain is very common in primary headache disorders, this convergent excitation may play a role in pain referral from cervical structures. While previous studies have demonstrated a physiological model for this convergence, this study sought an anatomical approach to examine the distribution of second order neurons in the trigeminocervical complex receiving greater occipital nerve input. In addition, the role of glutamatergic NMDA receptor activation within the trigeminocervical complex in response to cervical afferents was studied. Noxious stimulation of the occipital muscle in rat using mustard oil and mineral oil produced significantly altered Fos expression in the trigeminocervical complex compared with the surgical control (H(4)=31.3, P<0.001, Kruskal-Wallis). Baseline expression was 11 (median, range 4, 17) fos positive cells in the trigeminocervical complex, occipital muscle treated with mustard oil produced 23 (17, 33) and mineral oil a smaller effect of 19 (15, 25) fos positive cells, respectively (P=0.046). The effects of both mustard and mineral oil were reversed by the NMDA-receptor antagonist MK801. This study introduces a model for examining trigeminocervical complex activity after occipital afferent stimulation in the rat that has good anatomical resolution and demonstrates involvement of glutamatergic NMDA receptors at this important synapse.

Gastric stasis in migraine: more than just a paroxysmal abnormality during a migraine attack

OBJECTIVE

The aim of this article is to evaluate gastric motility and emptying in the ictal and interictal period in migraine.

BACKGROUND

Nausea is a predominant symptom of migraine and the basis of it is thought to be gastric stasis. Objective methods to establish this are however lacking. We utilized gastric scintigraphy studies to determine gastric motility in the ictal and interictal period of migraine.

METHODS

Ten migraine subjects were compared to equal number of age and sex matched controls. Gastric scintigraphy using a standard meal was performed in all control subjects once and in all 10 migraine subjects in the interictal period and nine studies were performed in the ictal period migraine.

RESULTS

The time to half emptying was delayed in migraine ictally (78%) and interictal period (80%) using normative data at this institution. Gastric stasis was less pronounced ictally (149.9 minutes) compared to interictal period (188.8 minutes). There was a significant delay compared to nonmigrainous controls (migraine 188.8 minutes vs normal controls 111.8 minutes; P < .05). These data were replicated in percentage of radioactive material remaining in the stomach at 2 hours.

CONCLUSIONS

Contrary to previous belief, this study has demonstrated that migraineurs suffer from gastric stasis both during and outside an acute migraine attack. This may suggest that migraineurs may have an abnormal autonomic function compared to nonmigrainous controls. The potential role of this in pathophysiology of migraine is discussed and avenues for further investigations are explored.

Migraine Pathophysiology

A combination of basic science and human physiology, particularly functional neuroimaging, has radically altered our understanding of migraine with a focus on brain mechanisms for this common and disabling disorder. Genetic studies have begun to provide plausible targets for the basic molecular defect in terms of ion channels, albeit thus far in the rare condition of familial hemiplegic migraine (FHM). Migraine pathophysiology involves the trigeminovascular system and central nervous system modulation of the pain-producing structures of the cranium. The degree to which head pain results from the activation of the nociceptors of pain-producing intracranial structures, or to the facilitation or lack of inhibition of afferent signals, is not clear at this time. An understanding of the pain mechanism is likely to provide insights into the mechanisms underlying the more generalized sensory dysfunction that is so typical of migraine.

Preclinical neuropharmacology of naratriptan

The basic CNS neuropharmacology of naratriptan is reviewed here. Naratriptan is a second-generation triptan antimigraine drug, developed at a time when CNS activity was thought not to be relevant to its therapeutic effect in migraine. It was, however, developed to be a more lipid-soluble, more readily absorbed and less readily metabolized variant on preexisting triptans and these variations conferred on it a higher CNS profile. Naratriptan is a 5-HT(1B/1D) receptor agonist with a highly selective action on migraine pain and nausea, without significant effect on other pain or even other trigeminal pain. Probable sites of therapeutic action of naratriptan include any or all of: the cranial vasculature; the peripheral terminations of trigeminovascular sensory nerves; the first-order synapses of the trigeminovascular sensory system; the descending pain control system; and the nuclei of the thalamus. Naratriptan may prevent painful dilatation of intracranial vessels or reverse such painful dilatation. Naratriptan can prevent the release of sensory peptides and inhibit painful neurogenic vasodilatation of intracranial blood vessels. At the first order synapse of the trigeminal sensory system, naratriptan can selectively suppress neurotransmission from sensory fibers from dural and vascular tissue, while sparing transmission from other trigeminal fibers, probably through inhibition of neuropeptide transmitter release. In the periaqueductal gray matter and in the nucleus raphe magnus, naratriptan selectively activates inhibitory neurons which project to the trigeminal nucleus and spinal cord and which exert inhibitory influences on trigeminovascular sensory input. Naratriptan has also a therapeutic effect on the nausea of migraine, possibly exerting its action at the level of the nucleus tractus solitarius via the same mechanisms by which it inhibits trigeminovascular nociceptive input. The incidence of naratriptan-induced adverse effects in the CNS is low and it is not an analgesic for pain other than that of vascular headache. In patients receiving selective serotonin uptake inhibitors (SSRIs) naratriptan may cause serotonin syndrome-like behavioral side effects. The mechanism of action involved in the production of behavioral and other CNS side effects of naratriptan is unknown.

The 5-hydroxytryptamine1B/1D/1F receptor agonists eletriptan and naratriptan inhibit trigeminovascular input to the nucleus tractus solitarius in the cat

Migraine pain arises in the trigeminovascular system and is often associated with nausea and sometimes with vomiting. In this study, an in vivo cat model of trigeminovascular stimulation was used to determine first whether there is a functional connection between the trigeminovascular system and the nucleus tractus solitarius (NTS), which is involved in regulating vomiting, and second whether anti-migraine drugs have any effect on such a connection. Chloralose-anaesthetised cats (n=16) were prepared for single neuron recording. The superior sagittal sinus (SSS) was isolated and stimulated electrically. The brainstem near the obex was exposed and a metal microelectrode equipped with six glass barrels for microiontophoresis was placed in the NTS. Recordings were made from 44 NTS neurons which responded to SSS stimulation with A-delta latencies. Iontophoretic ejection (50 nA) of eletriptan or naratriptan suppressed the response in 75% (15/20) and 78% (11/14) of cells and caused an average suppression of cell firing of 42+/-5% (n=20) and 54+/-8% (n=14), respectively. This suppression could be antagonized by the concurrent ejection (20-50 nA) of the 5-HT(1B/1D) receptor antagonist GR127935. We conclude that activation of the trigeminovascular system excites cells in the NTS that can be inhibited by eletriptan and naratriptan through activation of 5-HT(1B/1D) receptors. It is possible that in patients having a migraine attack trigeminovascular activation triggers nausea and vomiting, and that the alleviation of these symptoms by anti-migraine compounds may be via an action at 5-HT(1B/1D) receptors in the NTS.

Migraine

Migraine is a very common neurobiological headache disorder that is caused by increased excitability of the CNS. It ranks among the world's most disabling medical illnesses. Diagnosis is based on the headache's characteristics and associated symptoms. The economic and societal effect of migraine is substantial: it affects patients' quality of life and impairs work, social activities, and family life. There are many acute and preventive migraine treatments. Acute treatment is either specific (triptans and ergots) or non-specific (analgesics). Disabling migraine should be treated with triptans. Increased headache frequency is an indication for preventive treatment. Preventive treatment decreases migraine frequency and improves quality of life. More treatments are being developed, which provides hope to the many patients whose migraines remain uncontrolled.

Convergence of cervical and trigeminal sensory afferents

Cranial nociceptive perception shows a distinct topographic distribution, with the trigeminal nerve receiving sensory information from the anterior portions of the head, the greater occipital nerve, and branches of the upper cervical roots in the posterior regions. However, this distribution is not respected during headache attacks, even if the etiology of the headache is specific for only one nerve. Nociceptive information from the trigeminal and cervical territories activates the neurons in the trigeminal nucleus caudalis that extend to the C2 spinal segment and lateral cervical nucleus in the dorsolateral cervical area. These neurons are classified as multimodal because they receive sensory information from more than one afferent type. Clinically, trigeminal activation produces symptoms in the trigeminal and cervical territory and cervical activation produces symptoms in the cervical and trigeminal territory. The overlap between the trigeminal nerve and cervical is known as a convergence mechanism. For some time, convergence mechanisms were thought to be secondary to clinical observations. However, animal studies and clinical evidence have expanded our knowledge of convergence mechanisms. In this paper, the role of convergence mechanisms in nociceptive physiology, physiopathology of the headaches, clinical diagnosis, and therapeutic conduct are reviewed.

Innocuous jaw movements increase c-fos expression in trigeminal sensory nuclei produced by masseter muscle inflammation

Muscle tenderness and pain during movements are prominent symptoms associated with persistent jaw muscle pain. However, there is virtually no information on how trigeminal neurons respond to jaw movements (JM) or muscle palpation in the presence of muscle tissue injury or myositis. In this study, we investigated the effects of innocuous JM in the presence of acute masseteric inflammation on postsynaptic responses in the trigeminal brainstem nuclei by examining the expression of c-fos. In one group of rats, unilateral injections of an inflammatory substance, mustard oil (MO: 20%, 25 microl) were made into a masseter muscle. In another group, controlled and systematic JM were provided following MO injection. Three additional groups of rats were used to control for anesthetic, JM, and injection procedure. MO injected in the masseter muscle induced a high level of Fos protein expression in four principal trigeminal regions: the subnucleus caudalis (Vc), the ventral and dorsal regions of the Vc/Vi (subnucleus interpolaris) transition zone, and the paratrigeminal nucleus (PTN). Movements following MO injection consistently produced a significantly greater level of Fos expression in all these areas, especially in the Vc/Vi transition region and caudal Vc on the ipsilateral side. Importantly, movements also induced a significantly greater level of Fos expression in the caudal Vc on the contralateral side. The present results provide the first documentation that innocuous JM in the presence of muscle inflammation significantly increase the MO-induced c-fos expression in the trigeminal brainstem nuclei, which may explain the greater pain experienced during movement of inflamed or injured muscles.

Hippocampal spreading depression bilaterally activates the caudal trigeminal nucleus in rodents

Spreading depression (SD) and migraine aura involve transiently altered (i.e., increased followed by decreased) electrophysiological activity that propagates at the distinctive rate of millimeters per minute (mm/min), leading to the suggestion that they (and perhaps pain from migraine) are causally related via changes in the same brain structure. Neocortex is considered the anatomical zone associated with migraine aura and is the sole area known to induce caudal trigeminal nucleus (TNC) activation from SD in rodents. However, classical evidence of SD in human neocortex is reported only with severe brain disease, while migraine is a common and comparatively benign disorder. Because SD occurs in human hippocampus, and memory dysfunction referable to hippocampus is seen in migraineurs, we determined whether recurrent SD confined to hippocampus in rat could induce TNC activation. Our work shows that recurrent hippocampal SD evoked a significant (P < 0.05-0.001) increase in bilateral c-fos immunostaining within TNC superficial laminae compared with sham controls. Furthermore, hippocampal SD occurred with a correlated and transient change in spontaneous activity and blood flow in the ipsilateral neocortex without spread of SD to that area. Thus, hippocampal SD may be a previously unrecognized, potential trigger for nociceptive activation of TNC perhaps associated with migraine.

Molecular Mechanisms of Migraine

Migraine is a common complex disorder that affects a large portion of the population and thus incurs a substantial economic burden on society. The disorder is characterized by recurrent headaches that are unilateral and usually accompanied by nausea, vomiting, photophobia, and phonophobia. The range of clinical characteristics is broad and there is evidence of comorbidity with other neurological diseases, complicating both the diagnosis and management of the disorder. Although the class of drugs known as the triptans (serotonin 5-HT(1B/1D) agonists) has been shown to be effective in treating a significant number of patients with migraine, treatment may in the future be further enhanced by identifying drugs that selectively target molecular mechanisms causing susceptibility to the disease.Genetically, migraine is a complex familial disorder in which the severity and susceptibility of individuals is most likely governed by several genes that may be different among families. Identification of the genomic variants involved in genetic predisposition to migraine should facilitate the development of more effective diagnostic and therapeutic applications. Genetic profiling, combined with our knowledge of therapeutic response to drugs, should enable the development of specific, individually-tailored treatment.

The meninges contribute to the conditioned taste avoidance induced by neural cooling in male rats

After consumption of a novel sucrose solution, temporary cooling of neural areas that mediate conditioned taste avoidance can itself induce conditioned avoidance to the sucrose. It has been suggested that this effect is either a result of inactivation of neurons in these areas or of cooling the meninges. In a series of studies, we demonstrated that cooling the outer layer of the meninges, the dura mater, does not contribute to the conditioned taste avoidance induced by cooling any of these areas. The present experiments were designed to determine whether the inner layers of the meninges are involved. If they are involved, then one would expect that cooling locations in the brain that do not mediate conditioned taste avoidance, such as the caudate putamen (CP), would induce conditioned taste avoidance as long as the meninges were cooled as well. One also would expect that cooling neural tissue without cooling the meninges would reduce the strength of the conditioned taste avoidance. Experiment 1 established that the temperature of the neural tissue and meninges around the cold probes implanted in the CP were cooled to temperatures that have been shown to block synaptic transmission. Experiment 2 demonstrated that cooling the caudate putamen and overlying cortex and meninges induced conditioned taste avoidance. In experiment 3, a circle of meninges was cut away so that the caudate putamen and overlying cortex could be cooled without cooling the meninges. The strength of the conditioned taste avoidance was substantially reduced, but it was not entirely eliminated. These data support the hypothesis that cooling the meninges contributes to the conditioned taste avoidance induced by neural cooling. They also allow the possibility that neural inactivation produces physiological changes that can induce conditioned taste avoidance.

5-Hydroxytryptamine(1B/1D) and 5-hydroxytryptamine1F receptors inhibit capsaicin-induced c-fos immunoreactivity within mouse trigeminal nucleus caudalis

In order to investigate the c-fos response within the trigeminal nucleus caudalis (Sp5C) after noxious meningeal stimulation, capsaicin (0.25, 0.5, 1 and 5 nmol) was administered intracisternally in urethane (1 g/kg) and alpha-chloralose (20 mg/kg) anaesthetized male mice. Capsaicin induced a robust and dose-dependent c-fos-like immunoreactivity (c-fos LI) within Sp5C. C-fos LI was observed within laminae I and II of the entire brain stem from the area postrema to C2 level, being maximum at the decussatio pyramidum level. The area postrema, solitary tract, medullary and lateral reticular nuclei were also labelled. The 5-hydroxytryptamine(1B/1D/1F) receptor agonist sumatriptan (0.01, 0.1, 1 and 10 mg/kg), administered intraperitoneally 15 min before capsaicin stimulation (1 nmol), decreased the c-fos response within Sp5C, but not within solitary tract. The novel specific 5-hydroxytryptamine1F agonist LY 344864 (0.1 and 1 mg/kg, i.p.) significantly decreased the c-fos LI within the Sp5C as well. These findings suggest that intracisternally administered capsaicin activates the trigeminovascular system and that the pain neurotransmission can be modulated by 5-hydroxytryptamine(1B/1D/1F) receptors in mice. Thus, the availability of this model in mice, taken together with the possibility of altering the expression of specific genes in this species, may help to investigate further the importance of distinct proteins in the neurotransmission of cephalic pain.