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

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.

Effects of 12-O-tetradecanoyl-phorbol-13-acetate [corrected] and sodium lauryl sulfate on the production and expression of cytokines and proto-oncogenes in photoaged and intrinsically aged human keratinocytes

Skin aging may be divided into photoaging and intrinsic aging. The purpose of this study was to investigate the effects of 12-O-tetradecanoyl-phorbol-13-acetate and sodium lauryl sulfate on the production and expression of cytokines and proto-oncogenes in photoaged and intrinsically aged skin, compared with young skin. Keratinocytes were taken from newborns, young adults in their twenties, and from the forearm and thigh of volunteers in their fifties and seventies. Interleukin-1alpha and -6, and interleukin-1 receptor antagonist, c-fos and c-myc were measured after cultured keratinocytes had been treated with 12-O-tetradecanoyl-phorbol-13-acetate and sodium lauryl sulfate. There has been no report concerning the dependence of cytokine production by sodium lauryl sulfate upon photoaging and intrinsic aging. This study also involves the first investigation of the effects of aging on c-myc expression by 12-O-tetradecanoyl-phorbol-13-acetate treatment. Cytokine production decreased markedly with age. These results suggest the progressive decline of cellular function with age. The ratio of cytokine production in the irritant-treated group compared with that in the control group showed a different pattern in photoaging and intrinsic aging. With the significant difference between photoaging and intrinsic aging, T/C ratio decreased in interleukin-1alpha and interleukin-1 receptor antagonist upon aging, whereas it increased in interleukin-6. S/C ratio was uniquely elevated on photoaged skin in the 50 y age group. It is suggested that photoaged skin shows an exaggerated reaction to surfactant. Compared with the control, c-fos expression in 12-O-tetradecanoyl-phorbol-13-acetate-treated keratinocytes decreased with age in the thigh, but increased in the photoaged skin of forearm. The increased c-fos expression in 12-O-tetradecanoyl-phorbol-13-acetate-treated keratinocytes could be relevant for the predisposition of photoaged keratinocytes to malignant transformation.

The role of the dura in conditioned taste avoidance induced by cooling the area postrema of male rats

Experiments were designed to assess the contribution of the dura mater to the formation of conditioned taste avoidance induced by cooling the area postrema. The results of the first experiment verified that the temperature of the dura showed a temperature gradient at various distances from the tip of the cold probe. In the second and third experiments, a circle of dura was cut away so that different amounts of the area postrema could be cooled without cooling the overlying dura. Cooling the dura plus the area postrema did not produce a stronger avoidance than just cooling the area postrema. In the fourth experiment, the cerebellar cortex was cooled with and without cooling the dura. Cooling the cerebellar cortex produced conditioned taste avoidance, and cooling the dura plus the cerebellar cortex did not produce a stronger avoidance. Taken together, these results suggest that cooling the dura mater does not contribute to the conditioned taste avoidance induced by cooling the area postrema. The results of the fifth experiment showed that cooling the area postrema produced a stronger conditioned taste avoidance than cooling the cerebellar cortex. It is suggested that the avoidance induced by cooling both of these structures is the result of physiological changes occurring when neurons in these structures are inactivated and when the subdural meninges are cooled. Furthermore, these changes are more severe when the area postrema is cooled.

Nitric oxide potentiates response of trigeminal neurones to dural or facial stimulation in the rat

Infusing glyceryl trinitrate as a donor molecule, we have used electrophysiological and c-fos immunostaining techniques to study the effects of nitric oxide on neurones in the nucleus trigeminalis caudalis. Following infusion of glyceryl trinitrate, responses of neurones to electrical stimulation of periorbital cutaneous afferents were potentiated and threshold for activation of neurones by stimulation of dural afferents was reduced. Expression of c-fos was unchanged by glyceryl trinitrate compared to saline controls. Intradermal injection of capsaicin in the periorbital area increased c-fos expression in nucleus trigeminalis caudalis; this was significantly potentiated by glyceryl trinitrate. These results suggest that, in the anaesthetized rat, glyceryl trinitrate alone may not acutely activate the trigeminovascular system to a significant degree at doses that cause headache and later trigger migraine headache in migraineurs. Nevertheless, it is susceptible to exogenous nitric oxide in that activation of trigeminal neurones through cutaneous or dural pathways is potentiated. This may in some measure underlie the pathogenesis of migraine headache.

Nerve fibers innervating the cranial and spinal meninges: morphology of nerve fiber terminals and their structural integration

Pachymeninx and leptomeninx of cranial cavity and spine are considerably different in their collagenous fiber texture, cellular composition, vascularization, and innervation. The majority of meningeal nerve fibers terminate as free nerve endings whereas encapsulated and lamellated nerve terminals additionally occur in higher vertebrates including man. With respect to nerve fiber classification, arborization pattern, topography, and organization of the microenvironment at the termination site afferent and efferent nerve terminals are differentiated. Only the dura mater and the pial subcompartment of the leptomeninx possess the morphological prerequisites for neurogenic inflammation. In the current review, the results of morphological studies regarding the meningeal innervation including the sites of CSF (cerebrospinal fluid) production and absorption are discussed with emphasis on their structure-function relationships.

Spinal sources of noxious visceral and noxious deep somatic afferent drive onto the ventrolateral periaqueductal gray of the rat

Studies utilizing the expression of Fos protein as a marker of neuronal activation have revealed that pain of deep somatic or visceral origin selectively activates the ventrolateral periaqueductal gray (vlPAG). Previous anatomical tracing studies revealed that spinal afferents to the vlPAG arose from the superficial and deep dorsal horn and nucleus of the dorsolateral funiculus at all spinal segmental levels, with approximately 50% of vlPAG-projecting spinal neurons found within the upper cervical spinal cord. This study utilized detection of Fos protein to determine the specific populations of vlPAG-projecting spinal neurons activated by noxious deep somatic or noxious visceral stimulation. Pain of cardiac or peritoneal (i.e., visceral) origin activated neurons in the superficial and deep dorsal horn and nucleus of the dorsolateral funiculus of the thoracic cord, whereas pain of hindlimb (i.e., deep somatic) origin activated neurons in the same laminar regions but in the lumbosacral cord. Each of these deep noxious manipulations also activated neurons in the superficial and deep dorsal horn and nucleus of the dorsolateral funiculus of the upper cervical spinal cord. In a second set of experiments, the combination of retrograde tracing and Fos immunohistochemistry revealed that vlPAG-projecting spinal neurons activated by deep somatic pain were located in both the upper cervical and lumbosacral cord, whereas those activated by visceral pain were restricted to the thoracic spinal cord. Thus pain arising from visceral versus deep somatic body regions influences neural activity within the vlPAG via distinct spinal pathways. The findings also highlight the potential significance of the upper cervical cord in integrating pain arising from deep structures throughout the body.

Simultaneous depletion of neurokinin A, substance P and calcitonin gene-related peptide from the caudal trigeminal nucleus of the rat during electrical stimulation of the trigeminal ganglion

The central terminals of the primary sensory trigeminal ganglion (TG) neurons projecting into the caudal trigeminal nucleus (CTN) of the rat exhibit neurokinin A (NKA)-, substance P (SP)-, and calcitonin gene-related peptide (CGRP)-immunoreactivities (IRs). We stimulated the TG in the rat to induce some of the alterations which might occur during migraine (neurogenic inflammation). Under a stereotaxic apparatus and by means of a bipolar electrode, one-side TG of the animals were electrically stimulated (7.5 Hz, 5 ms, 0.8-1. 4 mA) with square pulses for 5 min. Then, using immunohistochemical methods, the lower medulla of each rat was studied for NKA-, SP- and CGRP-IRs. Light microscopic examination of brain-stem sequencial sections revealed a simultaneous decrease in the immunoreactivities of all neuropeptides (NKA, SP and CGRP) in the CTN ipsilateral to TG stimulation in comparison with the other (not stimulated) side CTN. It is suggested that this decrease in immunoreactivity would be due to the co-release of neuropeptides following noxious stimuli and that NKA, SP and CGRP might therefore act as co-transmitters or co-modulators at the first central synapses of the trigeminal sensory pathway.

Effect of cortical spreading depression on activity of trigeminovascular sensory neurons

The effect of cortical spreading depression, a proposed initiating event for migraine pain, on cortical blood flow (laser Doppler method) and on the spontaneous firing rate and stimulus-evoked responses of trigemino-cervical neurons with craniovascular input was studied in 17 neurons in 8 cats anesthetized with chloralose. Cortical spreading depression, induced via cortical pinprick injury, produced an initial wave of cortical hyperemia (243+/-57% of control) and a later and smaller phase of oligemia (96+/-4% of control). Neither the basal discharge rate (6.7+/-1.7 sec(-1)) nor the evoked responses to electrical stimulation of the superior sagittal sinus (4.1+/-0.8 discharges per stimulus) of upper cervical spinal cord neurons was altered over periods of up to 2 h following one, two, or three waves of spreading cortical depression. We conclude that a small number of episodes of cortical spreading depression is not capable of activating C2 cervical spinal cord craniovascular sensory neurons in the cat.

Effects of PNU-109,291, a selective 5-HT1D receptor agonist, on electrically induced dural plasma extravasation and capsaicin-evoked c-fos immunoreactivity within trigeminal nucleus caudalis

We studied the effects of PNU-109291 [(S)-(-)-1-[2-[4-(4-methoxyphenyl)-1-piperazinyl]ethyl]-N-methyl-isoc hroman-6-carboxamide], a receptor agonist showing 5000-fold selectivity for primate 5-HT1D versus 5-HT1B receptors (Ennis et al., J. Med. Chem. 41, 2180-2183), on dural neurogenic inflammation and on c-fos like immunoreactivity within trigeminal nucleus caudalis evoked by electrical and chemical activation of trigeminal afferents, respectively. Subcutaneous injection of PNU-109291 in male guinea pigs dose-dependently reduced dural extravasation of [125I]-labeled bovine serum albumin evoked by trigeminal ganglion stimulation with an IC50 of 4.2 nmol kg(-1). A dose of 73.3 nmol kg(-1) blocked the response completely. The selective 5-HT1B/1D receptor antagonist GR-127935 (> or = 2 micromol kg(-1) i.v.) prevented this effect. In addition, the number of c-fos immunoreactive cells within guinea pig trigeminal nucleus caudalis induced by chemical meningeal stimulation (intracisternally administered capsaicin) was reduced by more than 50% with PNU-109291 (> or = 122.2 nmol kg(-1) administered s.c. 45 min before and 15 min after capsaicin). These data indicate that the 5-HT1D receptor subtype plays a significant role in suppressing meningeal neurogenic inflammation and attenuating trigeminal nociception in these guinea pig models. Since 5-HT1D receptor mRNA and protein are expressed in trigeminal ganglia but not vascular smooth muscle, the 5-HT1D receptor subtype may become a useful therapeutic target for migraine and related headaches.

Non-NMDA glutamate receptors modulate capsaicin induced c-fos expression within trigeminal nucleus caudalis

1. We examined the effects of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzol[f]quinoxaline-7-sulpho namide (NBQX), the kainate receptor antagonists gamma-(R-)-glutamylaminomethanesulphonic acid (GAMS) and 6,7,8,9-tetrahydro-5-nitro-1H-benz[g]indole-2,3-dione-3-oxime (NS-102), and the group III metabotropic glutamate receptor (mGluR) agonist 2-amino-4-phosphono-S-butanoic acid (L-AP4) on c-fos-like immunoreactivity (c-fos LI) in trigeminal caudalis (Sp5C), lateral reticular (LRt), medullary reticular (Md) and solitary tract (Sol) nuclei, after intracisternal injection of capsaicin in urethane anaesthetized Sprague-Dawley rats. 2. Few c-fos labelled cells were observed within Sp5C in capsaicin-vehicle treated animals. The number of positive c-fos cells increased by 17 fold after intracisternal capsaicin (5 nmol) administration. 3. Pretreatment with CNQX (0.02, 0.1, 0.6, 3 and 15 mg kg-1) or NBQX (0.01, 0.1 and 1 mg kg-1), administered intraperitoneally 15 min before capsaicin, significantly reduced labelled cells within Sp5C by a maximum of 45 and 34%, respectively. The number of c-fox LI cells within LRt, Md and Sol was not affected. Pretreatment with L-AP4 (1, 3 and 10 mg kg-1) decreased the number of Sp5C c-fos LI cells by a maximum of 30%, whereas GAMS (1 and 10 mg kg-1) and NS-102 (1 and 5 mg kg-1) did not show any significant effect. 4. These results suggest that blockade of AMPA receptors, but not kainate receptors, or the activation of group III mGluRs, decrease the response of Sp5C neurons to trigeminovascular activation. Thus, in addition to NMDA receptors, mGluRs and AMPA receptors may modulate cephalic pain and may provide a potential therapeutic target for antimigraine drugs.

Immediate early gene expression in vascular smooth-muscle cells synergistically induced by hemolysate components

OBJECT

Vasospasm after subarachnoid hemorrhage is associated with changes in modulators of vascular tone in the arterial wall and is related to the presence of erythrocyte hemolysate in the subarachnoid space. The purpose of this study was to determine the compounds in erythrocyte hemolysate that are responsible for changing smooth-muscle cell gene expression.

METHODS

Rat aorta smooth-muscle cells were exposed to erythrocyte hemolysate in vitro and the effects on immediate early gene messenger (m)RNA levels were determined by competitive reverse transcriptase-polymerase chain reaction. Message levels for c-fos, jun B, and c-jun were increased in the presence of hemolysate, reaching maximum expression between 30 and 60 minutes, whereas the level of jun D mRNA was unaffected. Increasing doses of hemolysate caused greater expression of c-fos and jun B, but not c-jun. Adenosine triphosphate and hemoglobin, possible spasmogens present in hemolysate, caused much smaller and more rapid increases in c-fos expression than whole hemolysate. Size fractionation showed that all of the c-fos mRNA-inducing activity of hemolysate was recovered with molecules greater than 6 kD. Following separation of hemolysate proteins by hydrophobic interaction chromatography, only one of the three fractions had partial activity. Recombining the three fractions, however, yielded greater c-fos activation than any combination of two.

CONCLUSIONS

Multiple high-molecular-weight components present in erythrocytes have synergistic effects on gene expression in smooth-muscle cells. The differences in patterns of gene induction suggest that multiple signaling pathways are activated.

Stimulation of the middle meningeal artery leads to Fos expression in the trigeminocervical nucleus: a comparative study of monkey and cat

The pain of a migraine attack is often described as unilateral, with a throbbing or pulsating quality. The middle meningeal artery (MMA) is the largest artery supplying the dura mater, is paired, and pain-producing in humans. This artery, or its branches, and other large intracranial extracerebral vessels have been implicated in the pathophysiology of migraine by theories suggesting neurogenic inflammation or cranial vasodilatation, or both, as explanations for the pain of migraine. Having previously studied in detail the distribution of the second order neurons that are involved in the transmission of nociceptive signals from intracranial venous sinuses, we sought to compare the distribution of second order neurons from a pain-producing intracranial artery in both monkey and cat. By electrically stimulating the middle meningeal artery in these species and using immunohistochemical detection of the proto-oncogene Fos as a marker of neuronal activation, we have mapped the sites of the central trigeminal neurons which may be involved in transmission of nociception from intracranial extracerebral arteries. Ten cats and 3 monkeys were anaesthetised with alpha-chloralose and the middle meningeal artery was isolated following a temporal craniotomy. The animals were maintained under stable anaesthesia for 24 h to allow Fos expression due to the initial surgery to dissipate. Following the rest period, the vessel was carefully lifted onto hook electrodes, and then left alone in control animals (cat n = 3), or stimulated (cat n = 6, monkey n = 3). Stimulation of the left middle meningeal artery evoked Fos expression in the trigeminocervical nucleus, consisting of the dorsal horn of the caudal medulla and upper 2 divisions of the cervical spinal cord, on both the ipsilateral and contralateral sides. Cats had larger amounts of Fos expressed on the ipsilateral than on the contralateral side. Fos expression in the caudal nucleus tractus solitarius and its caudal extension in lamina X of the spinal cord was seen bilaterally in response to middle meningeal artery stimulation. This study demonstrates a comparable anatomical distribution of Fos activation between cat and monkey and, when compared with previous studies, between this arterial structure and the superior sagittal sinus. These data add to the overall picture of the trigeminovascular innervation of the intracranial pain-producing vessels showing marked anatomical overlap which is consistent with the often poorly localised pain of migraine.

The effects on the central nervous system of nitroglycerin--putative mechanisms and mediators

Nitroglycerin is an organic nitrate that has been used as a vasodilator in the treatment of cardiac diseases for over a century. Only recently it has been demonstrated that the vasodilator effect of this drug depends upon the formation of nitric oxide in the blood vessel wall. However, clinical and research data gathered during the last decades have suggested that nitroglycerin possesses, besides its peripheral vasodilator effect, additional, puzzling biological activities. This organic nitrate compound provokes reflex cardiovascular activities via its interaction with the central sympathetic system. Its cerebrovascular effect, on the other hand, is probably mediated by the local release of neuropeptides. The direct application of nitroglycerin onto brain nuclei causes a prompt increase in the neuronal discharge rate. From a neurological point of view, nitroglycerin consistently induces a specific headache attack in patients suffering from migraine. Because of its temporal pattern and clinical characteristics, nitroglycerin-induced headache cannot be solely ascribed to the a drug-induced vasorelaxation. The demonstration that systemic nitroglycerin administration activates a widespread set of vegetative, nociceptive and neuroendocrine structures in the central nervous system seems to further support the occurrence of central mechanisms in the biological activity of nitroglycerin. Double labeling immunocytochemical and neuropharmacological studies have provided information on the putative neurotransmitters and neurochemical mechanisms involved in nitroglycerin-induced neuronal activation.

Both 5-HT1B and 5-HT1F receptors modulate c-fos expression within rat trigeminal nucleus caudalis

A possible mechanism of action of antimigraine drugs such as sumatriptan is inhibition of the trigeminovascular pathway. Sumatriptan's effects might be mediated by 5-HT1B, 5-HT1D or 5-HT1F receptors. To establish the relative importance of these subtypes, we compared the effects of sumatriptan with those of a selective 5-HT1F receptor agonist (LY 344864) on c-fos protein expression in the trigeminal nucleus caudalis. c-fos expression was induced in urethane-anaesthetized rats by intracisternal capsaicin administration. Sumatriptan and LY 344864 decreased the number of capsaicin-induced c-fos-like immunoreactive cells within trigeminal nucleus caudalis (ID50 = 0.04 and 0.6 mg kg(-1)). The effect of sumatriptan, but not of LY 344864, was prevented by pretreatment with the antagonist SDZ 21-009, which displays high affinity for rat 5-HT1B receptors. LY 344864 appears to attenuate c-fos-like immunoreactivity via 5-HT1F receptors, while sumatriptan acts via 5-HT1B receptors. The fact that activation of 5-HT1F receptors is sufficient to modulate the activity of the trigeminal system suggests that this receptor may be a target for antimigraine drugs with improved safety profile.

Serotonin in migraine: theories, animal models and emerging therapies

A role for serotonin in migraine has been supported by changes in circulating levels of serotonin and its metabolites during the phases of a migraine attack, along with the ability of serotonin-releasing agents to induce migraine-like symptoms. The development of serotonin receptor agonists with efficacy in the clinic for the alleviation of migraine pain further implicates serotonin as a key molecule in migraine. Several theories regarding the etiology of migraine have been proposed. The vasodilatory theory of migraine suggested that extracranial arterial dilation during an attack was related to migraine pain; a theory supported when vasoconstrictors such as sumatriptan alleviated migraine pain. The neurological theory of migraine proposed that migraine resulted from abnormal firing in brain neurons. Cortical spreading depression, one facet of the neurological theory, could explain the prodrome of migraine. The neurogenic dural inflammation theory of migraine supposed that the dural membrane surrounding the brain became inflamed and hypersensitive due to release of neuropeptides from primary sensory nerve terminals. Substance P, calcitonin gene related peptide and nitric oxide are all though to play a role in the dural inflammatory cascade. Animal models of migraine have been utilized to study the physiology of migraine and develop new pharmaceutical therapies. One model measures the shunting of blood to arteriovenous anastomoses based on a proposal that migraine primarily involves cranial arteriovenous vasodilation. Another model utilizes electrical stimulation of the trigeminal ganglion to induce neurogenic dural inflammation quantified by the resulting extravasation of proteins. Pharmacological agents such as meta-chlorophenylpiperazine (mCPP) and nitroglycerin have also been used to induce dural extravasation in animals. Both compounds also induce migraine attacks in individuals with a history of migraine. In addition, Fos, a protein produced by activation of the c-fos gene, has been measured as an index of migraine-like pain transmission to the CNS following chemical or electrical stimulation of the trigeminal nerve. A role for serotonin in migraine is further supported by the efficacy of serotonin receptor ligands. Sumatriptan is an agonist at 5-HT1D and 5-HT1B receptor subtypes, and effective in treating migraine pain and associated symptoms. Recently, selective 5-HT1F agonists have been proposed for the treatment of migraine, without the side effects associated with the present 5-HT1D and 5-HT1B receptor agonists. A role for 5-HT2B receptors has also been suggested the initiation of migraine, supporting use of selective 5-HT2B receptor antagonists in migraine. Thus, agents that modulate 5-HT1B, 5-HT1D, 5-HT1F and 5-HT2B receptors either have or may have clinical utility in the therapy of migraine headache.

Arachidonylethanolamide (AEA) activation of FOS proto-oncogene protein immunoreactivity in the rat brain

It is thought that the physiological actions of endogenous cannabinoid arachidonylethanolamide (AEA), as well as exogenous cannabinoids such as Delta9-tetrahydrocannabinol (THC), are mediated by two subtypes of cannabinoid receptors, CB1 and CB2, which have recently been characterized. Injection of AEA leads to alterations in motor behavior and endocrine function. While these phenomena have been well characterized, the neuronal substrate of AEA's actions remains undetermined. In this study, FOS immunoreactivity (FOSir) was used to map rat brain nuclei that are responsive to a single intracerebroventricular injection of AEA. The results showed that FOSir was induced in several nuclei including the bed nucleus of the stria terminalis (BNST), paraventricular nucleus of the hypothalamus (PVN), central nucleus of the amygdala (Ce), periaqueductal gray area (PAG), dentate gyrus in the hippocampus (Dg), paraventricular nucleus of the thalamus (PVA), median preoptic nucleus (MnPO), periventricular nucleus (Pe), caudate putamen (CPU) and the ependymal lining of the ventricles. The pattern of activation identified correlates, in part, with the distribution of CB receptors. At the same time, a new subset of nuclei, without demonstrable CB receptors, have been shown to respond to an AEA challenge. Activation of these nuclei is consistent with the physiological effects of AEA. These findings provide valuable information on the response to AEA at the level of neuronal activation and provide the basis for a broader understanding of the possible role of CB receptors in the modulation of motor and endocrine function associated with the use of exogenous cannabinoids, such as marijuana.

Effects of SR140333, a selective non-peptide NK1 receptor antagonist, on trigemino-thalamic nociceptive pathways in the rat

Trigeminal stimulation of C-fibers increased c-fos expression within the trigeminal nucleus caudalis (NtV) and thalamic neuronal activity which both reflect the transmission of a nociceptive message. We examined the effects on both these phenomena of the selective NK1 and NK2 receptor antagonists, SR140333 and SR48968. SR140333 (0.3, 1 and 3 micrograms/kg intravenously [i.v.]) dose-dependently, reversibly and stereoselectively antagonized the increase of contralateral thalamic activity. This compound, when given i.v. (30 micrograms/kg) or orally (10 mg/kg), also reduced the number of Fos-like immunoreactive cells particularly at the medial and caudal level of the NtV. In contrast, SR48968 did not exert any antagonistic effect either on thalamic activity or on Fos-like immunoreactivity. The data strongly suggest a preferential involvement of NK1 vs NK2 receptors in nociceptive transmission following trigeminal ganglion stimulation. Taken together, our results indicate that SR140333 could provide a potent drug for the relief of pain occurring under excessive activity of sensory trigeminal fibers.

Attenuation of Fos-like immunoreactivity in the trigeminal nucleus caudalis following trigeminovascular activation in the anaesthetised guinea-pig

The present study has examined the involvement of sensory neurotransmitters in activating neurones in the trigeminal nucleus caudalis following stimulation of the trigeminovascular system in anaesthetised guinea-pigs. Electrical stimulation of the right trigeminal ganglion produced a unilateral expression of Fos-like immunoreactivity (Fos-LI) in the trigeminal nucleus caudalis. The tachykinin NK1 receptor antagonist, GR205171 (100 micrograms/kg i.v.) and the N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 (1 mg/kg i.v.) each inhibited expression of Fos-LI following electrical stimulation. The calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP8-37 (1.3 mg/kg i.v.), administered following rostral intracarotid infusion of mannitol to disrupt the blood-brain barrier, tended to reduce Fos-LI evoked by electrical stimulation, although this failed to reach statistical significance. Capsaicin (10 nmol in 0.1 ml), administered intracisternally, produced a bilateral expression of Fos-LI in the trigeminal nucleus caudalis. This expression was unaffected by the peripherally acting NK1 receptor antagonist, GR82334 (0.2 mg/kg i.v.) or CGRP8-37 (1.3 mg/kg i.v.). The centrally penetrant NK1 receptor antagonist, GR205171 (100 micrograms/kg i.v.), inhibited significantly Fos-LI evoked by intracisternal capsaicin administration. It is concluded that the sensory neurotransmitters, substance P and glutamate are released centrally following activation of the trigeminovascular system and that each may be involved in activation of cells in the trigeminal nucleus caudalis.

Ineffectiveness of neurokinin-1 antagonist in acute migraine: a crossover study

Lanepitant is a high-affinity, selective neurokinin-1 receptor (NK-1) and is effective in the dural inflammation model of acute migraine. Lanepitant 30, 80, and 240 mg given orally was evaluated in a double-blind, placebo-controlled crossover study to determine its effect in reducing migraine pain and severity of associated symptoms. Outpatients treated four migraine headaches of moderate or severe pain intensity with study drug according to a randomization schedule. They recorded their pain intensity and severity of migraine-associated symptoms at 30, 60, 90, and 120 min. Although 53 patients were randomly allocated to a treatment sequence, only 40 patients completed all treatments. There was no statistically significant difference in improvement in migraine pain at any time for any of the treatments. Additionally, there was no change in severity of migraine-associated symptoms associated with lanepitant therapy. No adverse events could be attributed to lanepitant. Lanepitant was ineffective orally in treating acute migraine in this trial. This may be due to poor bioavailability during a migraine attack. Alternatively, the neurogenic inflammation hypothesis may not apply to migraine.

Recordings from brain stem neurons responding to chemical stimulation of the subarachnoid space

The subarachnoid space at the base of the skull was perfused continuously with artificial cerebrospinal fluid in anesthetized rats. A combination of inflammatory mediators consisting of histamine, bradykinin, serotonin, and prostaglandin E2 (10(-5) M) at pH of 6.1 was introduced into the flow for defined periods to stimulate meningeal primary afferents. Secondary neurons in the caudal nucleus of the trigeminal brain stem were searched by electrical stimulation of the cornea. Of the units receiving oligosynaptic input from the cornea, 44% were excited by stimulation of the meninges with inflammatory mediators. Most of these units had small receptive fields including cornea and the periorbital region, and their responsiveness was restricted to stimuli of noxious intensity. Three types of responses to stimulation of the meninges with algogenic agents were encountered: responses that did not outlast the stimulus period, responses outlasting the stimulus period for several minutes, and oscillating response patterns containing periods of enhanced and suppressed activity. The response pattern of a unit was reproducible, however, upon repetitive stimulation at 20-min intervals; the response magnitude showed tachyphylaxis upon stimulus repetition. The preparation presented mimics pathophysiolocial states normally accompanied by headache, e.g., subarachnoidal bleeding. Responsiveness of neurons in the caudal nucleus of the trigeminal brain stem to inflammatory mediators may play a role in the generation and maintenance of headache, e.g., migraine.

Possible mechanisms of valproate in migraine prophylaxis

Valproate has been shown to be an effective prophylactic treatment in migraine. Investigation of the mechanism of its antimigraine action is difficult due to the broad range of its biochemical effects and the complex nature of migraine pathophysiology. Valproate increases brain GABA levels and, in doing so, may suppress migraine-related events in the cortex, perivascular parasympathetics or trigeminal nucleus caudalis. There is experimental evidence that it suppresses neurogenic inflammation and directly attenuates nociceptive neurotransmission. In addition, valproate reportedly alters levels of excitatory and inhibitory neurotransmitters and exerts direct effects on neuronal membranes in vitro. Valproate's observed effect may ultimately result from a combination of actions at different loci.

Trigeminovascular stimulation in conscious rats

Intracisternal infusion of capsaicin was used to induce intracranial trigeminovascular stimulation in conscious rats. Both behaviour and trigeminal nucleus caudalis c-fos expression were examined. Exploratory behaviour was dose-dependently reduced and different types of behaviours were induced with various doses of capsaicin. Head grooming and scratching show that intracranial activation of trigeminal afferents can be referred as extracranial trigeminal stimulation. Analysis of behaviour exhibited during trigeminovascular stimulation may provide a powerful tool to study effects of central acting anti-migraine drugs.

Current concepts of the pathophysiology of migraine

An understanding of the basic anatomy and physiology of the cranial circulation facilitates the assessment and management of patients with headache, particularly vascular-type headaches, such as migraine. At the very least, all pain is perceived and processed in the brain. With migraine it is likely that the fundamental problem and its clinical expression are driven by the CNS; thus study of the brain regarding headache is warranted. As therapy evolves during the 1900s, such an understanding will be necessary, as new and highly specific receptor-targeted compounds allow treatment and improvement of headache in many patients. Since writing this article, the nomenclature for serotonin (5HT) receptors has changed so that any reference herein to 5HTID alpha is now 5HTID and 5HTID beta is now 5HTI beta. This change in nomenclature is discussed in Martig PR, Hoyer D, Humphrey PPA, et al: Alignment of receptor nomenclature with the human genome: Classification of 5HT-1 beta and 5HT-1D receptor subtypes. Trends in the Pharmacological Sciences 17:103, 1996.

Release of immunoreactive substance P in the trigeminal brain stem nuclear complex evoked by chemical stimulation of the nasal mucosa and the dura mater encephali--a study with antibody microprobes

In order to study a possible involvement of substance P in the processing of chemonociceptive input from the nasal mucosa and the dura mater encephali in the spinal trigeminal, the release of immunoreactive substance P was measured in the trigeminal brain stem nuclear complex in anaesthetized rats. Microprobes coated with antibody to substance P were inserted into the lateral area of the brain stem up to 1 mm posterior to the obex corresponding to the trigeminal subnucleus caudalis. When the nasal mucosa was stimulated by topical administration of mustard oil (1% and 5%) into the nostrils, immunoreactive substance P was mainly detected in the dorsal region of the trigeminal brain stem nuclear complex with a maximum in the superficial gray matter. When the dura mater encephali was stimulated by topical administration of Tyrode's solution (pH 6.2), immunoreactive substance P was mainly released in the ventral region of the trigeminal brain stem nuclear complex; with pH 5.5 the release was more diffuse extending from the ventral to the dorsal part of the spinal trigeminal nucleus. Release was maximal rather after than during the administration of the stimuli, and it considerably outlasted the stimulation periods. These data suggest that substance P plays an important role in the processing of chemonociceptive inputs from the nasal mucosa and the dura mater encephali in the trigeminal brain stem nuclear complex. Substance P may be important, therefore, in the generation of those headaches that are caused by affections of the nasal mucosa and the dura mater encephali. Since enhanced levels of immunoreactive substance P were present for considerable time periods beyond the administration of the stimuli, substance P and neurokinin-1 receptors may be involved in long-lasting neuronal events following noxious stimulation.

[Animal models and their results in relation to the therapy of migraine]

Until now, our understanding of migraine pathophysiology has been fairly incomplete. So far no animal model has allowed an explanation of all facets of the clinically heterogeneous condition migraine. However, it is now generally accepted that the migraine headache is due to activation of the trigeminal system. The model of neurogenic inflammation after stimulation of the trigeminal ganglion or systemic administration of capsaicin allows study of the inhibitory interactions between antimigraine compounds and peripheral trigeminal fibre terminals that sustain a sterile meningeal inflammation through release of allogenic and vasoactive neuropeptides, such as substance P and calcitonin gene-related peptide. Studies with the model of superior sagittal sinus stimulation have revealed central actions of antimigraine agents such as ergotamine and sumatriptan, but also acetylsalicylic acid on neurotransmission of trigeminal nociceptive input in the brainstem. A likely explanation for the slowly progressing neurological deficits is cortical spreading depression (CSD), which can easily be elicited in many species. However, CSD has not been observed in vivo in humans. The described models strongly influenced the development of new medications for migraine treatment and have improved our understanding of migraine pathophysiology.

Differential distribution of Fos-like immunoreactivity in the spinal trigeminal nucleus after noxious and innocuous thermal and chemical stimulation of rat cornea

Corneal afferent nerves project to two spatially distinct sites within the spinal trigeminal nucleus: the subnucleus interpolaris/caudalis transition and the subnucleus caudalis/upper cervical spinal cord transition. The role of these two regions in processing corneal input is uncertain. To determine if neurons in these regions encode different features of an applied corneal stimulus, immunoreactivity for the immediate early gene protein product, Fos, was quantified in barbiturate-anesthetized rats. Intensity was varied across thermal (thermal probe 5, 35, 42, 52 degrees C; radiant heat of approximately 45 degrees C) stimuli and compared with that seen after mustard oil (5 microliters, 20%) or mineral oil application. All stimuli increased the number of Fos-positive neurons located at the ventrolateral pole of the subnucleus interpolaris/caudalis transition compared with unstimulated controls. By contrast, only 52 degrees C thermal probe and mustard oil produced an additional peak of Fos-positive neurons within the superficial laminae at the subnucleus caudalis/cervical cord transition. Further, the magnitudes of the bimodal peaks of Fos produced by 52 degrees C thermal probe and mustard oil stimuli were different quantitatively. Mustard oil caused a greater Fos response at the subnucleus interpolaris/caudalis transition than 52 degrees C thermal probe stimulation, whereas the opposite was true at the subnucleus caudalis/cervical cord transition. Double-labeling revealed that Fos immunoreactive neurons within the spinal trigeminal nucleus were restricted to regions densely labeled for calcitonin gene-related peptide. These results indicate that select features of corneal stimuli such as modality are encoded differently by neurons in the trigeminal subnucleus interpolaris/caudalis transition compared with those located in the subnucleus caudalis/cervical cord transition. It is likely that neurons in these two brainstem regions subserve different aspects of corneal sensation.

Altered c-fos expression in the parabrachial nucleus in a rodent model of CFA-induced peripheral inflammation

Increases in the expression of immediate early genes have been shown to occur in the lumbar spinal cord dorsal horn after peripheral inflammation. Given that the pontine parabrachial nucleus has been implicated in nociceptive as well as antinociceptive processes and is reciprocally connected with the spinal cord dorsal horn, it seems likely that peripheral inflammation will cause alterations in immediate early gene expression in this nucleus. To test this hypothesis we examined cFos-like immunoreactivity in a rodent complete Freund's adjuvant-induced peripheral inflammatory model of persistent nociception. Unilateral hind paw injections of complete Freund's adjuvant produced inflammation, hyperalgesia of the affected limb, and alterations in open field behaviors. Immunocytochemical analysis demonstrated a bilateral increase in cFos-like immunoreactivity in the lateral and Kolliker-Fuse subdivisions of the parabrachial nucleus at 6 and 24 hours postinjection and an ipsilateral decrease below basal levels in the Kolliker-Fuse subdivision at 96 hours postinjection when compared to saline controls. Taken together, these results suggest that select parabrachial neurons are activated by noxious somatic inflammation. These active parabrachial neurons are likely to participate in ascending nociceptive and/or descending antinociceptive pathways.

Attenuation by valproate of c-fos immunoreactivity in trigeminal nucleus caudalis induced by intracisternal capsaicin

1. Valproic acid, useful in the treatment of migraine, is an inhibitor of gamma aminobutyric acid (GABA) aminotransferase and activator of glutamic acid decarboxylase. Its mechanism in migraine remains obscure. The effects of valproic acid (2-propylpentanoic acid) were examined on the number of cells expressing c-fos-like immunoreactivity (c-fos-LI), a marker of neuronal activation, within the trigeminal nucleus caudalis (lamina I, IIo, TNC) 2 h after intracisternal injection of the irritant, capsaicin (0.1 ml; 15.25 micrograms ml-1), in urethane-anaesthetized Hartley guinea-pigs. Positive cells were counted in eighteen sections (50 microns) at three representative levels (rostral, middle and caudal) within lamina I, IIo of the TNC in 90 animals. 2. Numerous cells were labelled after capsaicin instillation (244 +/- 25; 1 ml; 15.25 mM) but not after capsaicin vehicle (11 +/- 1). Positive cells were also found within the medial reticular nucleus, the area postrema and the nucleus of the solitary tract. A similar distribution has been demonstrated previously after application of intracisternal irritants such as autologous blood or carrageenin. 3. Valproate (> or = 10 mg kg-1, i.p.) reduced labelled cells by 52% (P < 0.05) in lamina I, IIo but not within the area postrema, the nucleus of the solitary tract or the medial reticular nucleus. A similar finding was obtained previously after administration of sumatriptan, dihydroergotamine or the NK1 receptor antagonist RPR 100,893. 4. Pretreatment with bicuculline (30 micrograms kg-1; i.p.), a GABAA antagonist, but not phaclofen (1 mg kg-1) a GABAB antagonist, reversed the effect of valproate and increased c-fos positive cells within lamina I, IIo. Somewhat paradoxically, bicuculline by itself (30 micrograms kg-1 i.p.) decreased the number of labelled cells suggesting that more than a single GABAergic mechanism can suppress c-fos expression. 5. We conclude that the mechanism of action of valproate is mediated via GABAA receptors. Since valproate decreases both c-fos expression and as previously shown, neurogenic inflammation within the meninges, the GABAA receptor complex might provide an important target for drug development in migraine and related headaches.

Causes and mechanisms of primary headaches: toward a bio-behavioral model

Pathophysiological mechanisms of primary headache remain obscure, despite of numerous hypotheses that have been postulated for either migraine and cluster headache. Human experimental models are not available, however, observation of clinical features of migraine or cluster headache attacks support animal studies documenting the development of neurogenic inflammation in tissues receiving trigeminal innervation. The latter studies provided also the background for better understanding the mechanism of action of aborting drugs such as sumatriptan and dihydroergotamine. The debate is whether the primary cause of migraine and other neurovascular headaches is central or peripheral in origin. Trigger factors (stressful events) and personality traits in migraine patients suggest that activation of neurovascular systems is secondary to more complex events taking place in the central nervous system.

Neurogenic model of migraine

Activation of peripheral trigeminal fibers induces neurogenic inflammation in rat dura mater, as well as vascular and mat cell changes. These changes parallel an increase of vasodilating and permeability promoting peptides in venous effluent of the cephalic circulation. The experimental model of electrical trigeminal ganglion stimulation or systemic capsaicin administration has proven effective in detecting cellular activation in brainstem trigeminal nuclei. Animal experimental models of trigeminovascular activation and the effects of antimigraine drugs on functional and morphological consequences of such activation provide the background for further models and for developing pharmacological strategies in this field.

Systemic nitroglycerin induces Fos immunoreactivity in brainstem and forebrain structures of the rat

Nitroglycerin is a vasodilator which induces vascular relaxation by releasing nitric oxide in the wall of blood vessels. It has been suggested that the cardiovascular inhibitory responses which are induced by this drug are mediated by central structures. In this study, we evaluated the distribution and intensity of Fos immunoreactivity in rat brain nuclei following the systemic administration of nitroglycerin. In the medulla, a significant number of Fos-immunoreactive neurons were observed in the nucleus tractus solitarius, ventrolateral medulla, area postrema and spinal trigeminal nucleus caudalis. A robust staining was seen in the parabrachial nucleus, locus coeruleus and ventrolateral periaqueductal grey. In the hypothalamus, Fos-positive cells were densely packed in the paraventricular and supraoptic nuclei. Other areas where significant staining was observed include the central nucleus of the amygdala and the subfornical organ. These findings demonstrate that the systemic administration of nitroglycerin is capable of activating a spectrum of functionally diverse brain regions. This spectrum includes areas involved in reflex adjustments to nitroglycerin-induced hypotension, areas involved in sensory nociceptive perception and areas associated with integrative regulation of autonomic, behavioral and neuroendocrine functions.

Distribution of Fos-like immunoreactivity in the caudal brainstem of the rat following noxious chemical stimulation of the temporomandibular joint

Central expression of the protooncogene c-fos was used to examine areas receiving noxious sensory input from the rat temporomandibular joint (TMJ). Fos-like immunoreactivity (Fos-LI) in the caudal brainstem was visualized 2 hours after unilateral injection of the small-fiber-specific excitant/inflammatory irritant mustard oil into the TMJ region. Control animals received injection of either mustard oil into the subcutaneous fascia overlying the masseter muscle or mineral oil vehicle into the TMJ region. In all groups, Fos-LI was consistently observed ipsilaterally in the spinal trigeminal nucleus and cervical dorsal horn and, bilaterally, in the nucleus of the solitary tract and the ventrolateral medulla. The expression of Fos-LI ipsilaterally in the paratrigeminal nucleus was variable. Within the trigeminal sensory complex, Fos-LI was restricted to subnucleus caudalis and the caudal portions of subnucleus interpolaris near the level of the obex. Approximately 12% of Fos-LI cells in subnucleus caudalis and in the cervical dorsal horn were found in laminae III-VI. Compared to TMJ mustard oil injection, mineral oil injection produced less Fos-LI at all rostrocaudal levels, whereas subcutaneous mustard oil injection produced less Fos-LI in caudal subnucleus caudalis but similar amounts in the cervical dorsal horn. Neither of these injections yielded significant ipsilateral responses in subnucleus caudalis, indicating that Fos-LI in this region following TMJ mustard oil injection could be ascribed solely to small-fiber stimulation in the deep TMJ region. The wide rostrocaudal distribution of Fos-LI within the caudal brainstem reflects the distribution of TMJ-responsive nociceptive neurons that may underlie the spread and referral of pain from the TMJ region.

Morphine, 5-HT2 and 5-HT3 receptor antagonists reduce c-fos expression in the trigeminal nuclear complex following noxious chemical stimulation of the rat nasal mucosa

Noxious chemical stimulation of the rat nasal mucosa induces the expression of the immediate early gene c-fos in trigeminal brainstem neurons. In the present study, we applied the irritant mustard oil (1%) into the left nostril of urethane anesthetized rats. Immunohistochemical methods were used to evaluate the expression of Fos protein in the trigeminal subnuclei interpolaris and caudalis and to test the effects of putative analgesics that might depress synaptic transmission in neurons related to nociception. For this purpose, morphine (3 mg/kg and 10 mg/kg), the 5-HT2 antagonist ketanserin (0.5 mg/kg and 5 mg/kg) and the 5-HT3 antagonist ICS 205-930 (0.1 mg/kg and 1 mg/kg) were administered intravenously prior to noxious stimulation. Pretreatment with any of the three compounds reduced Fos-like immunoreactivity. The effect of morphine was reversible with naloxone. The reduction of the expression of Fos-like immunoreactivity by exogenous morphine speaks in favour of an opioidergic link in the modulation of orofacial pain in the trigeminal nuclei. The effects of the 5-HT receptor antagonists are most likely mediated via 5-HT2 and 5-HT3 receptors located on primary afferent fibres.

Comparison of the effects of sumatriptan and the NK1 antagonist CP-99,994 on plasma extravasation in Dura mater and c-fos mRNA expression in trigeminal nucleus caudalis of rats

Dural plasma extravasation produced by electrical stimulation of the trigeminal ganglion was measured in rats and the concomitant expression of c-fos mRNA produced in the trigeminal nucleus caudalis (NtV) was measured using in situ hybridization techniques. The non-peptide NK1 receptor selective antagonist CP-99,994 (1-3000 micrograms kg-1) and the 5HT1D receptor agonist sumatriptan (1-1000 micrograms kg-1) reduced dural plasma extravasation dose-dependently with ID50S of 52 micrograms kg-1 and 30 micrograms kg-1 respectively. CP-99,994 (1000 micrograms kg-1). a compound known to have good brain penetration, decreased c-fos mRNA expression in the NtV by 37 +/- 7% without disruption of the blood brain barrier (BBB). Sumatriptan (1000 micrograms kg-1), known to be poorly brain penetrant, had no significant effect on c-fos mRNA expression in the NtV unless the BBB was disrupted by infusion of a hyperosmolar mannitol solution after which sumatriptan decreased c-fos mRNA expression by 65 +/- 11%. The results suggest that brain penetrant NK1 receptor antagonists may have anti-migraine effects peripherally through blockade of dural extravasation and centrally by inhibition of nociceptive pathways. Furthermore the data indicates that the anti-migraine action of sumatriptan must be predominantly peripherally mediated, be it via inhibition of plasma extravasation or direct vasoconstriction, since it had little effect on the activation of neurones in the NtV unless the BBB was disrupted.

Suppression by the sumatriptan analogue, CP-122,288 of c-fos immunoreactivity in trigeminal nucleus caudalis induced by intracisternal capsaicin

1. The effects of an intravenously administered sumatriptan analogue were examined on c-fos-like immunoreactivity (c-fos-LI), a marker of neuronal activation, evoked within trigeminal nucleus caudalis (TNC) and other brain stem regions 2 h after intracisternal injection of the irritant, capsaicin (0.1 ml, 0.1 mM), in pentobarbitone-anaesthetized Hartley guinea-pigs. 2. C-fos-LI was assessed in eighteen serial sections (50 microns) using a polyclonal antiserum. A weighted average, reflecting total expression within lamina I, IIo of TNC was obtained from three representative levels (i.e., at -0.225 mm, -2.475 mm and -6.975 mm.). 3. Capsaicin caused significant labelling within lamina I, IIo, a region containing axonal terminations of small unmyelinated C-fibres, as well as within the nucleus of the solitary tract, area postrema and medial reticular nucleus. A similar distribution of positive cells was reported previously after intracisternal injection of other chemical irritants such as autologous blood or carrageenin. 4. Pretreatment with a conformationally restricted sumatriptan analogue (with some selectivity for 5-HT1B and 5-HTID receptor subtypes) CP-122,288, reduced the weighted average by approximately 50-60% (P < 0.05) in lamina I, IIo at > or = 100 pmol kg-1, i.v., but did not decrease cell number within area postrema, nucleus of the solitary tract or medial reticular nucleus. A similar pattern was reported previously following sumatriptan, dihydroergotamine or CP-93,129 administration after noxious meningeal stimulation. 5. We conclude that modifications at the amino-ethyl side chain of sumatriptan dramatically enhance the suppression of c-fos expression within TNC, a finding consistent with its remarkable potency against neurogenic plasma protein extravasation within dura mater. CP-122,288 and related analogues may serve as an important prototype for drug development in migraine and related headaches.

The non-peptide neurokinin-1 antagonist, RPR 100893, decreases c-fos expression in trigeminal nucleus caudalis following noxious chemical meningeal stimulation

The effect of RPR 100893, a selective and specific neurokinin-1 antagonist, or its enantiomer RPR 103253 was examined on c-fos antigen expression in brain stem and upper cervical cord 2 h after intracisternal capsaicin injection (30.5 micrograms/ml) in pentobarbital-anesthetized Hartley guinea-pigs. Positive cells were counted at three levels corresponding to obex, -2.25 mm and -6.75 mm in 18 sections (50 microns). Immunoreactivity was strongly expressed within laminae I and IIo of trigeminal nucleus caudalis, area postrema and the leptomeninges. Moderate labeling was present in the nucleus of the solitary tract and the medullary lateral reticular nucleus, whereas few positive cells were found in the ventral portion of the medullary reticular nucleus and Rexed laminae III-V and X. The distribution of labeled cells was consistent with previously reported results following subarachnoid placement of the noxious agents, blood or carrageenin. Pretreatment with RPR 100893 (1, 10 and 100 micrograms/kg, i.v.) but not its enantiomer (100 micrograms/kg, i.v.) 30 min prior to capsaicin injection significantly reduced the number of positive cells in the trigeminal nucleus caudalis (P < 0.01) in a dose-dependent manner, but not within area postrema or nucleus of the solitary tract. These results indicate that (i) the instillation of capsaicin into the subarachnoid space is an effective stimulus for the induction of c-fos antigen within trigeminal nucleus caudalis, presumably through activation of trigeminovascular afferents, and (ii) the neurokinin-1 antagonist RPR 100893 reduces the number of positive cells selectively within this nucleus. The findings are significant because drugs which alleviate vascular headaches decrease the number of c-fos-positive cells within trigeminal nucleus caudalis following noxious meningeal stimulation. Hence, strategies aimed at blocking the neurokinin-1 receptor may be useful for treating migraine and cluster headache.

What brain structures are active during emotions? Effects of brain stimulation elicited aversion on c-fos immunoreactivity and behavior

Aversive behavior is produced by stimulating some brain structures, such as the dorsal periaqueductal gray and the medial hypothalamus. We have used c-fos immunoreactivity to map brain areas which are influenced by stimulation of these two structures. Stimulation was produced in freely moving rats by electrical stimulation or by microinjections of either excitatory amino acids or GABA blocking drugs. Behavior was monitored to detect emotional changes. The effects on labeling induced by the stimulation of either structure were then compared. Structures labeled include the amygdala, the stria terminalis, the supramamillary area, the hypothalamus, the periaqueductal gray, the superior colliculus, the nucleus cuneiformis, and the locus coeruleus. Regardless whether chemical or electrical stimulation was used or the structure stimulated, there was a large overlap among the brain areas labeled. We then compared our results with data from the literature where other methods of inducing aversion have been used, including pain and stress. There was remarkable similarity in the patterning of labeling irrespective of the type of stimulation (central-peripheral, chemical-electrical). There was, however, one interesting difference produced by central vs. peripheral stimulation. Labeling was unilateral in the former case and bilateral in the latter case. Our results suggest that there is a neural substrate that mediates aversive behavior, no matter how it is produced. Nevertheless, that peripheral stimulation produces mainly bilateral activation of this substrate whereas central stimulation produces mainly unilateral activation suggests that natural peripheral stimuli are also integrated at a higher functional level. Future work could be directed toward explicit comparisons of central versus peripheral stimulation to identify the structures involved in higher level integration of aversive behavior.

Expression of c-Fos-like immunoreactivity in the caudal medulla and upper cervical spinal cord following stimulation of the superior sagittal sinus in the cat

Migraine is an episodic vascular headache with a well-recognized clinical picture but a poorly understood pathogenesis. Stimulation of a pain-sensitive trigeminally innervated intracranial structure, the superior sagittal sinus (SSS), was undertaken to map the higher-order neurons potentially involved in the processing of vascular head pain. The animals were prepared for stimulation by exposure of the sinus and then maintained under alpha-chloralose anaesthesia for 24 h before SSS stimulation, perfusion and immunohistochemical processing for the detection of Fos protein. Examination of the medulla and upper cervical cord revealed marked increases in Fos-like immunoreactivity in laminae I and IIo of the trigeminal nucleus caudalis and the dorsal horn of the upper cervical spinal cord. In addition, Fos-like immunoreactivity was observed in lamina X of the upper cervical spinal cord, in the commissural and medial nuclei of the solitary tract and in the nucleus retroambigualis. The use of immunohistochemical detection of Fos has allowed visualization of several populations of neurons likely to be involved in the central neural processing of vascular headache syndromes, particularly migraine.

Adrenalectomy enhances Fos-like immunoreactivity within the spinal trigeminal nucleus induced by noxious thermal stimulation of the cornea

Immunocytochemistry was used to assess the distribution of neurons within the spinal trigeminal nucleus that expressed the protein product of the proto-oncogene c-fos after thermal stimulation of the cornea in barbiturate-anesthetized rats. The influence of adrenal steroids on Fos-like immunoreactivity induced by corneal stimulation also was examined by comparison of the results obtained in adrenal intact rats to those in adrenalectomized rats and to those in adrenalectomized rats given corticosterone replacement therapy. Stimuli (42 or 52 degrees C, 20 s per min, 15 min) were applied unilaterally to the cornea by a contact thermode. At 2 h after stimulation animals were perfused with 4% paraformaldehyde and tissue sections were incubated with primary antiserum against the Fos protein and processed with the avidin-biotin method. The pattern of Fos-like immunoreactivity after 52 degrees C stimulation revealed a dominant group of cells ipsilaterally within the superficial laminae of the caudalmost portion of trigeminal subnucleus caudalis that was greatly enhanced in adrenalectomized rats. Low-intensity stimulation did not induce Fos-like immunoreactivity among cells in this caudal region. A second significant group of cells was seen more rostrally at periobex levels within the ventrolateral pole of the nucleus. The number of cells in the periobex grouping was increased after 52 or 42 degrees C corneal stimulation when compared to unstimulated controls and was not affected by levels of corticosterone. The results indicated a discontinuous pattern of Fos-like immunoreactivity within the spinal trigeminal nucleus after thermal stimulation of the cornea and a differential effect of adrenal steroids. The appearance of Fos-like immunoreactivity within caudal portions of the nucleus was increased only by noxious intensities of stimulation and was further enhanced in animals with low levels of corticosterone. In contrast, the Fos-like immunoreactivity at periobex levels was increased after noxious and innocuous thermal stimuli and was independent of the level of corticosterone. The results were consistent with the hypothesis that glucocorticoids modify the expression of immediate early genes among a select group of central trigeminal neurons. Such steroid modulation may contribute to the mechanisms that underlie long-term adaptation to noxious sensory input.

Neocortical spreading depression provokes the expression of c-fos protein-like immunoreactivity within trigeminal nucleus caudalis via trigeminovascular mechanisms

The effects of neocortical spreading depression (SD) on the expression of immunoreactive c-fos protein were examined within the superficial laminae of trigeminal nucleus caudalis (TNC), a brainstem region processing nociceptive information. KCl was microinjected into the left parietal cortex at 9 min intervals over 1 hr, and SD was detected by a shift in interstitial DC potential within adjacent frontal cortex. The stained cells in lower brainstem and upper cervical spinal cord were counted on both sides after tissues were sectioned (50 microns) and processed for c-fos protein-like immunoreactivity (LI) using a rabbit polyclonal antiserum. C-fos protein-LI was visualized in the ventrolateral TNC, chiefly in laminae I and Ilo and predominantly within spinal segment C1-2 (e.g., -1.5 to -4.5 mm from obex) ipsilaterally. SD significantly increased cell staining within ipsilateral TNC. The ratio of cells in laminae I and Ilo on the left: right sides was 1.32 +/- 0.13 after 1 M KCl, as compared to 1.06 +/- 0.05 in control animals receiving 1 M NaCl instead of KCl microinjections (p < 0.01). The ratio was reduced to an insignificant difference after chronic surgical transection of meningeal afferents and recurrent SD (1.09 +/- 0.11). Pretreatment with intravenous sumatriptan, a 5-HT1-like receptor agonist that selectively blocks meningeal C-fibers and attenuates c-fos protein-LI within TNC after noxious meningeal stimulation, also reduced the ratio to an insignificant difference (1.10 +/- 0.09). Sumatriptan or chronic surgical transection of meningeal afferents, however, did not reduce the ability of KCl microinjections to induce SD. On the other hand, combined hyperoxia and hypercapnia not only reduced the number of evoked SDs from 6.3 +/- 1.0 to 2.5 +/- 1.2 after 0.15 M KCl microinjection, but also significantly (p < 0.01) reduced associated c-fos protein-LI in TNC. These data indicate that multiple neocortical SDs activate cells within TNC. The increase in c-fos protein-LI, observed predominantly ipsilaterally, was probably mediated by SD-induced stimulation of ipsilaterally projecting unmyelinated C-fibers innervating the meninges. If true, this is the first report demonstrating that neurophysiological events within cerebral cortex can activate brainstem regions involved in the processing of nociceptive information via trigeminovascular mechanisms.

CP-93,129, sumatriptan, dihydroergotamine block c-fos expression within rat trigeminal nucleus caudalis caused by chemical stimulation of the meninges

1. The effects of intravenously administered 5-HT1B receptor agonists were examined on c-fos like immunoreactivity, an indicator of neuronal activation, within the brain stem. C-fos was induced by injecting an algesic, vasoconstrictor substance (0.3 ml of autologous blood) or a pro-inflammatory molecule, carrageenin (1 mg in 0.1 ml saline) into the cisterna magna of pentobarbitone-anaesthetized Sprague-Dawley rats and was visualized in serial sections (50 micrometers) by use of a polyclonal antiserum. 2. As previously reported, the injection of blood caused significant labelling within laminae I, IIo of the trigeminal nucleus caudalis, a major nociceptive brain stem nucleus, as well as within nucleus of the solitary tract and area postrema. A similar pattern of expression with fewer cells per section was detected after carrageenin instillation. The number of expressing cells was reduced by 54% in trigeminal nucleus caudalis but not within the nucleus of the solitary tract or area postrema when blood was injected in adult rats neonatal capsaicin treatment. 3. Pretreatment with 5-HT1 agonists with some selectivity for the 5-HT1B receptor, CP-93,129 (460 nmol kg-1 x 2, i.v.), sumatriptan (720 nmol kg-1 x 2, i.v.) or dihydroergotamine (86 nmol kg-1 x 2, i.v.) reduced positive cells by 39%, 31%, and 33% respectively in trigeminal nucleus caudalis but not in nucleus of the solitary tract or area postrema after blood instillation. Pretreatment with the analgesic morphine (15 mumol kg-1, s.c.) also decreased the number of positive cells by 63% in trigeminal nucleus caudalis. 4. CP-93,129 (460 nmol kg-1 x 2, i.v.) reduced the number of c-fos labelled cells by 47% within lamina I, IIo after carrageenin instillation. 5. Drug-induced blockade appeared to be tissue-dependent. Pretreatment with sumatriptan (720 nmol kg-1 x 2, i.v.) did not block c-fos expression in trigeminal nucleus caudalis following formalin application to the nasal mucosa.6. Drug-induced blockade may be mediated by an action on primary afferent (trigeminovascular) fibres in as much as CP-93,129 (460 nmol kg-' x 2, i.v.) did not reduce the number of expressing cells within the trigeminal nucleus caudalis following blood instillation in rats treated as neonates with capsaicin.7. We infer from these results that the analgesic actions of agonists at 5-HTB receptors (the receptor subtype analogous to 5-HTID in man) need not depend upon the presence of vasodilatation and, that 5-HTID receptor-mediated blockade of neurotransmission contributes significantly to the analgesic effects of these drugs in headache.8. Based on the demonstrated effects of 5-HTB/D agonists against the actions of two chemicallyunrelated meningeal stimulants, we suggest that treatment with 5-HTID agonists may be useful for the alleviation of pain in other headache conditions associated with meningeal irritation. Bacterial, viral(including AIDS meningovascular inflammation) and other forms of chemical meningitis merit further investigation.