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

Effect of systemic nitroglycerin on CGRP and 5-HT afferents to rat caudal spinal trigeminal nucleus and its modulation by estrogen

Systemic administration of nitroglycerin, a nitric oxide donor, triggers in migraine patients a delayed attack of unknown mechanism. After puberty migraine is more prevalent in women. Attacks can be triggered by abrupt falls in plasma estrogen levels, which accounts in part for sexual dimorphism, but lacks an established neurobiological explanation. We studied the effect of nitroglycerin on the innervated area of calcitonin gene-related peptide (CGRP) and serotonin-immunoreactive afferents to the superficial laminae of the spinal portion of trigeminal nucleus caudalis, and its modulation by estrogen. In male rats, nitroglycerin produced after 4 h a significant decrease of the area innervated by CGRP-immunoreactive afferents and an increase of that covered by serotonin-immunoreactive fibres. These effects were not observed in the superficial laminae of thoracic dorsal horns. The effect of nitroglycerin was similar in ovariectomized females. In estradiol-treated ovariectomized females the area in the spinal portion of trigeminal nucleus caudalis laminae I-II covered by CGRP-immunoreactive fibres was lower and that of serotonin-immunoreactive fibres was higher than in males and for both transmitters not significantly changed after nitroglycerin. The bouton size of CGRP profiles was smaller in estradiol-treated ovariectomized females, whereas after nitroglycerin it decreased significantly but only in males and ovariectomized females. Nitroglycerin, i.e. nitric oxide, is thus able to differentially influence afferent fibres in the superficial laminae of rat spinal trigeminal nucleus caudalis. Estradiol modulates the basal expression of these transmitters and blocks the nitroglycerin effect. These data may contribute to understanding the mechanisms by which estrogens influence migraine severity and the triggering of attacks by nitric oxide.

Nitroglycerin-induced activation of monoaminergic transmission in the rat

When administered to migraine patients, nitroglycerin induces a spontaneous-like migraine attack, with a latency of several hours. Nitroglycerin acts directly and/or indirectly on the central nervous system, through the release of nitric oxide (NO). Systemic administration of the drug to the rat causes neuronal activation in selected subcortical areas, particularly in monoaminergic nuclei of the brainstem. In this study, we sought to investigate whether this activation correlates with changes in monoaminergic neurotransmission. For this purpose, we evaluated the tissue levels of catecholamines and serotonin in the hypothalamus, mesencephalon, pons and medulla of rats treated with systemic nitroglycerin or vehicle, at different time points (1, 2 and 4 h). We also evaluated the peripheral sympathetic response to the drug by measuring the concentrations of plasma catecholamines. Nitroglycerin caused an early (1 h) increase in cerebral (pons) and plasma levels of norepinephrine, followed by a delayed (4 h) decrease in medullary and pontine levels of serotonin. The initial noradrenergic activation may reflect the autonomic response to the rapid cardiovascular effects of the drug, while the delayed response may result from the interaction of nitroglycerin-released NO and 5-HT in central areas devoted to the modulation of nociception. These data might therefore help to clarify the mechanisms underlying the delayed migraine attack observed in migraine sufferers after systemic administration of nitroglycerin.

Nuclear factor-kappaB as a molecular target for migraine therapy

Nitric oxide (NO) generated from inducible NO synthase (iNOS) participates in immune and inflammatory responses in many tissues. The NO donor glyceryl trinitrate (GTN) provokes delayed migraine attacks when infused into migraineurs and also causes iNOS expression and delayed inflammation within rodent dura mater. Sodium nitroprusside, an NO donor as well, also increases iNOS expression. Because inflammation and iNOS are potential therapeutic targets, we examined transcriptional regulation of iNOS following GTN infusion and the consequences of its inhibition within dura mater. We show that intravenous GTN increases NO production within macrophages. L-N(6)-(1-iminoethyl)lysine, a selective iNOS inhibitor, attenuates the NO signal, emphasizing the importance of enzymatic activity to delayed NO production. iNOS expression is preceded by significant nuclear factor kappa B (NF-kappaB) activity, as reflected by a reduction in the inhibitory protein-kappa-Balpha (IkappaBalpha) and activation of NF-kappaB after GTN infusion. IkappaBalpha degradation, NF-kappaB activation, and iNOS expression were attenuated by parthenolide (3mg/kg), the active constituent of feverfew, an anti-inflammatory drug used for migraine treatment. These findings suggest that GTN promotes NF-kappaB activity and inflammation with a time course consistent with migraine attacks in susceptible individuals. We conclude, based on results with this animal model, that blockade of NF-kappaB activity provides a novel transcriptional target for the development of anti-migraine drugs.

Fos and nitric oxide synthase in rat brain with chronic mesostriatal dopamine deficiency: effects of nitroglycerin and hypoxia

We found sustained proto-oncogene c-fos expression in neurons of the lateral and medial neostriatum and suppression of this expression in nitric oxide synthase (NOS)-containing cells within the islands of Calleja after lesions of the dopaminergic mesostriatal system induced by 6-hydroxydopamine. Systemic administration of nitroglycerin (NTG) or mild hypoxia resulted in a decreased of c-fos expression in the dorsolateral part of the denervated neostriatum. However, in other brain structures NTG or mild hypoxia evoked sustained c-fos expression in NOS-containing neurons and in the sources catecholaminergic projections involved in the control of cardiovascular function. We propose that the administration of NTG, an NO donor, or hypoxia partially attenuate the consequences of an excessively increased glutamate level in the denervated neostriatum which are manifest in high level of c-fos expression.

Glyceryl trinitrate treatment up-regulates soluble guanylyl cyclase in rat dura mater

Nitric oxide (NO) is a key molecule in vascular headaches and the dura mater has been implicated as a tissue where vascular headache develops. Here we demonstrate expression, enzyme activity and cellular distribution of the intracellular receptor for NO, soluble guanylyl cyclase (sGC), in rat dura mater. Subcutaneous treatment of rats with the NO-donor glyceryl trinitrate (GTN) induced an increase of sGC expression and activity in dural blood vessels after 20-30 min. It has previously been shown that GTN induces headache in normal subjects after 20-30 min. Our findings suggest that an up-regulation of the NO target enzyme contributes to the pathogenesis of GTN-induced headache explaining the subacute rather than acute onset of symptoms.

Parallel circuits mediating distinct emotional coping reactions to different types of stress

All animals, including humans, react with distinct emotional coping strategies to different types of stress. Active coping strategies (e.g. confrontation, fight, escape) are evoked if the stressor is controllable or escapable. Passive coping strategies (e.g. quiescence, immobility, decreased responsiveness to the environment) are usually elicited if the stressor is inescapable and help to facilitate recovery and healing. Neural substrates mediating active versus passive emotional coping have been identified within distinct, longitudinal neuronal columns of the midbrain periaqueductal gray (PAG) region. Active coping is evoked by activation of either the dorsolateral or lateral columns of the PAG; whereas passive coping is triggered by activation of the ventrolateral PAG. Recent anatomical studies indicate that each PAG column receives a distinctive set of ascending (spinal and medullary) and descending (prefrontal cortical and hypothalamic) afferents. Consistent with the anatomy, functional studies using immediate early gene expression (c-fos) as a marker of neuronal activation have revealed that the preferential activation of a specific PAG column reflects (i) the type of emotional coping reaction triggered, and (ii) whether a physical or psychological stressor was used.

Evidence that hemorrhagic hypotension is mediated by the ventrolateral periaqueductal gray region

Severe hemorrhage lowers arterial pressure by suppressing sympathetic activity. This study tested the hypothesis that the decompensatory phase of hemorrhage is mediated by the ventrolateral periaqueductal gray (vlPAG), a region importantly involved in the autonomic and behavioral responses to stress and trauma. Neuronal activity in the vlPAG was inhibited with either lidocaine or cobalt chloride 5 min before hemorrhage (2.5 ml/100 g body wt) was initiated in conscious, unrestrained rats. Bilateral injection of lidocaine (0.5 microl of a 2% or 1 microl of a 5% solution) into the caudal vlPAG delayed the onset and reduced the magnitude of the hypotension produced by hemorrhage significantly. In contrast, inactivation of the dorsolateral PAG with lidocaine was ineffective. Cobalt chloride (5 mM; 0.5 microl), which inhibits synaptic transmission but not axonal conductance, also attenuated hemorrhagic hypotension significantly. Microinjection of lidocaine or cobalt chloride into the vlPAG of normotensive, nonhemorrhaged rats did not influence cardiovascular function. These data indicate that the vlPAG plays an important role in the response to hemorrhage.

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.

The chemical architecture of the rat's periaqueductal gray based on acetylcholinesterase histochemistry: a quantitative and qualitative study

The chemoarchitecture of the periaqueductal gray has been extensively studied, based on acetylcholinesterase reaction and comparing it to other chemical markers. We have divided the periaqueductal gray into four main longitudinal columns, namely dorsomedial, dorsolateral, lateral and ventrolateral. We also identified the dorsal midline column, the supraoculomotor cap and the juxta-aqueductal ring. The acetylcholinesterase gave rise to a strong reaction in the outer half of the lateral column, the outer half of the dorsomedial column, the supraoculomotor cap and the ventral half of the juxta-aqueductal ring. This labeling was in part complementary to that of the NADPH diaphorase and allowed the lateral column to be differentiated from the ventrolateral column. However, the inner half of both lateral and ventrolateral columns displayed the same chemical properties including acetylcholinesterase, tyrosine hydroxilase and serotonin. Thus, from the chemical view, these inner halves should be considered as one different region. Finally, the juxta-aqueductal ring was composed of two clearly different halves, i.e. dorsal and ventral. The dorsal half did not show any clear differences from the above columns and was negative for acetylcholinesterase, NADPH diaphorase and tyrosine hydroxilase, while the ventral half was clearly different from the lateral and ventrolateral columns and displayed a positive reaction to all those chemical markers. From these results, we strongly suggest the use of acetylcholinesterase histochemistry as a tool for accurate parcellation of the periaqueductal gray.

Effect of serotonin depletion on nitric oxide induced cerebrovascular nociceptive response

The study was conducted to investigate the effect of serotonin depletion on nitric oxide-induced meningeal vascular response and cerebrovascular nociception. Nitroglycerin was infused i.v. to control and serotonin-depleted rats. Pial circulation was monitored by intravital fluorescent videomicroscopy and Fos immunoreactivity trigeminal nucleus caudalis neurons was used as an indicator for the cerebrovascular nociception. The results showed that the degree of nitric oxide-induced pial microvascular dilatation was significantly greater in the serotonin-depleted group than the control. The number of nitric oxide-evoked Fos-immunoreactive cells between the two groups remained comparable. The results suggest that though depletion of serotonin can facilitate the vascular response to nitric oxide it does not alter the nitric oxide-induced craniovascular nociceptive response.

Activation of trigeminovascular neurons by glyceryl trinitrate

The effect of intra-carotid arterial infusions of glyceryl trinitrate (GTN), a substance known to precipitate headache, including migraine, upon the spontaneous activity of trigeminal neurons with craniovascular input was studied in cats. Second-order craniovascular neurons which received sensory input from the superior sagittal sinus were recorded in the trigeminal nucleus caudalis. Infusions of GTN were administered via a catheter inserted retrogradely into the common carotid artery through the lingual artery. Infusions of GTN (100 microg kg(-1) min(-1) in a volume of 2 ml min(-1)) increased the mean basal discharge rate of all second-order neurons to 239+/-47% of control. GTN produced a fall in mean blood pressure, but there was no correlation between this fall and the changes in discharge rate. GTN infusions sensitised neurons to the effects of electrical stimulation of the superior sagittal sinus, but not to subsequent GTN infusions. Infusions of similar volumes of vehicle did not alter the discharge rate of neurons. We conclude that GTN activates craniovascular sensory pathways at a site at, or peripheral to, the second-order neuron and that such an action may account for at least the acute-onset headache induced by GTN.

The awareness of thirst: proposed neural correlates

The neural and endocrine bases of the generation of thirst are reviewed. Based on this review, a hierarchical system of neural structures that regulate water conservation and acquisition is proposed. The system includes primary sensory-receptive areas; secondary sensory structures (circumventricular organs), which detect levels of hormones, including angiotensin II and vasopressin, which are involved in generating thirst; preoptic and hypothalamic structures; and an area within the ventrolateral quadrant of the periaqueductal gray matter. Hodological and other data are used to determine the hierarchical organization of the system. Based on studies of the effects of lesions to various structures within the hierarchy of the system, it is proposed that the awareness of thirst in rodents is either entirely or predominantly due to neuronal activities in a subsection of the ventrolateral periaqueductal gray matter. It is also hypothesized that the awareness of thirst in primates is due to neuronal activities in both the ventrolateral periaqueductal gray and in a region within the medial prefrontal and anterior cingulate cortex.

Systemic nitroglycerin increases nNOS levels in rat trigeminal nucleus caudalis

Systemic administration of nitroglycerin, a nitric oxide donor, triggers in migraineurs a delayed attack of unknown mechanisms. Subcutaneous nitroglycerin (10 mg/kg) produced a significant increase of nitric oxide synthase (NOS)- and c-fos-immunoreactive neurons in the cervical part of trigeminal nucleus caudalis in rats after 4 h. This effect was not observed in the thoracic dorsal horn. Similar increase of NOS and c-fos was obtained in the brain stem after a somatic nociceptive stimulus, i.e. on the side of the formalin injection in the lip. Nitric oxide is thus able to increase NOS availability in second order nociceptive trigeminal neurons, which may be relevant for central sensitization and the understanding of its effect in migraine.

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.

Environmental influences on viscero(noci)ceptive brain activities: the effects of sheltering

Visceral disorders are always accompanied by pain and/or a sense of ill-being that entails people to isolate themselves both physically and socially. By analogy with what happens in human beings, we have transferred to the rat the question of whether a protective, dark and quiet environment would influence the brain activities induced by visceral chemically-induced (cyclophosphamide [CP], 100 mg/kg/ip) adverse conditions of life. CP is an antitumoral drug that induces severe side effects (cystitis, headache, nausea, photophobia, phonophobia) and produces a strong state of ill-being in human beings. Brain activities were quantified using the expression of the Fos protein, a molecular marker of neuronal activity. The results compare data from groups of paired animals having been offered a shelter or not. Data were collected 4 h after the injection of CP, i. e., when cystitis was fully developed. Sheltered and unsheltered groups did not differ in bladder pathology. Intentional sheltering was shown to attenuate the expression of the CP-related Fos-Li activity within the locus coeruleus (LC) without affecting that of the structures known preferentially to process nociceptive inputs of bladder origin (dorsal vagal complex, ventrocaudal bulbar reticular formation, nucleus centralis of amygdala, dorsolateral portion of bed nucleus of stria terminalis). The LC levels of tyrosine hydroxylase and galanin neuronal contents were not affected. The LC belongs to the emotional activation system and can respond to a wide range of somatosensory and viscerosensory stimuli. Our hypothesis is that the LC would be processing the nervous activities that accompany the sense of ill-being coming from adverse conditions of life, including visceral disorders, and that voluntary isolation, by reducing its activity, would enable animals to minimize their level of distress.

Central circuits mediating patterned autonomic activity during active vs. passive emotional coping

Animals, including humans, react with distinct emotional coping strategies to different sets of environmental demands. These strategies include the capacity to affect appropriate responses to "escapable" or "inescapable" stressors. Active emotional coping strategies--fight or flight--are particularly adaptive if the stress is escapable. On the other hand, passive emotional coping strategies-quiescence, immobility, decreased responsiveness to the environment-are useful when the stress is inescapable. Passive strategies contribute also to facilitating recovery and healing once the stressful event is over. Active vs. passive emotional coping strategies are characterised further by distinct patterns of autonomic change. Active strategies are associated with sympathoexcitation (hypertension, tachycardia), whereas passive strategies are associated with sympathoinhibitory patterns (hypotension, bradycardia). Distinct neural substrates mediating active vs. passive emotional coping have been identified within the longitudinal neuronal columns of the midbrain periaqueductal gray region (PAG). The PAG offers then a potentially useful point of entry for delineating neural circuits mediating the different forms of emotional coping and their associated patterns of autonomic activity. As one example, recent studies of the connections of orbital and medial prefrontal cortical (PFC) fields with specific PAG longitudinal neuronal columns are reviewed. Findings of discrete orbital and medial PFC projections to different PAG columns, and related PFC and PAG columnar connections with specific subregions of the hypothalamus, suggest that distinct but parallel circuits mediate the behavioural strategies and patterns of autonomic activity characteristic of emotional "engagement with" or "disengagement from" the external environment.

Pressor response to pulsatile compression of the rostral ventrolateral medulla mediated by nitric oxide and c-fos expression

It has been reported that neurovascular compression of the rostral ventrolateral medulla might be causally related to essential hypertension. Recently, we found that pulsatile compression of the rostral ventrolateral medulla increases sympathetic nerve activity and elevates arterial pressure via activation of glutamate receptors in rats. We also found that increases in sympathetic and cardiovascular activities by microinjection of L-glutamate into the rostral ventrolateral medulla are mediated by c-fos expression-related substance(s) following activation of the nitric oxide-cyclic GMP pathway. Herein, we investigated whether responses to pulsatile compression are mediated by local activation of the nitric oxide-cyclic GMP pathway and/or c-fos expression-related substance(s) in rats. Increases in arterial pressure (15+/-1 mmHg), heart rate (9+/-1 b.p.m.), and sympathetic nerve activity (% change: 8.5+/-1.1%) induced by pulsatile compression were partially but significantly inhibited after local microinjection of a nitric oxide synthase inhibitor, L-N(G)-nitroarginine methyl ester (8+/-2 mmHg, 1+/-1 b.p.m., 4.0+/-1.3%; P<0.05 vs compression without pretreatment) or 7-nitroindazole (7+/-2 mmHg, 2+/-1 b.p.m., 4.0+/-1. 5%; P<0.05), or a soluble guanylate cyclase inhibitor, methylene blue (9+/-1 mmHg, 4+/-1 b.p.m., 4.1+/-1.4%; P<0.05). In addition, increases in arterial pressure, heart rate, and sympathetic nerve activity by pulsatile compression were significantly reduced 6 h after microinjection of antisense oligodeoxynucleotide to c-fos mRNA (2+/-2 mmHg, 2+/-1 b.p.m., 1.0+/-1.0%; P<0.05 vs sense oligodeoxynucleotide). These results suggest that increases in sympathetic and cardiovascular activities induced by pulsatile compression of the rostral ventrolateral medulla are mediated, at least in part, by local activation of the nitric oxide-cyclic GMP pathway and c-fos expression-related substance(s) in rats.

Effects of sumatriptan on nitric oxide and superoxide balance during glyceryl trinitrate infusion in the rat. Implications for antimigraine mechanisms

Infusion of glyceryl trinitrate (GTN) into patients with migraine precipitates the onset of a migraine attack several hours after completion of the infusion. Using an infusion of GTN into anaesthetised rats, this study investigates the relationship of regional cerebral blood flux rCBF(ldf), cortical nitric oxide (NO) and cortical superoxide concentrations and the effect of sumatriptan on each variable. In saline treated animals, a 30 min infusion of GTN (2 microgram kg(-1) min(-1), i.v.) was found to markedly increase cortical rCBF(ldf) (133+/-3% of baseline) and NO concentrations (141+/-13% of baseline). Superoxide levels exhibited an inverse relationship to NO levels, decreasing below basal to 48+/-14% of baseline. It is hypothesised that high NO levels during GTN infusion may decrease the detectable superoxide due to "leeching" of the superoxide into low level peroxynitrite formation. In the presence of sumatriptan, a decrease below baseline in cortical rCBF(ldf) (82+/-5% of baseline) and NO concentration (64+/-13% of baseline) was observed throughout GTN infusion, although superoxide levels significantly increased above baseline by 105+/-14 nM (p<0.05, ANOVA post hoc LSD test). The mechanism for this action of sumatriptan is unknown but may include; modulation of cell redox state, NO scavenging or direct manipulation of superoxide release.

Effect of 5-HT(1A) receptor ligands on Fos-like immunoreactivity in rat brain: evidence for activation of noradrenergic transmission

This study investigated the effects of 8-OH-DPAT and various other 5-HT(1A) receptor agonists on brain noradrenergic transmission using Fos-like immunoreactivity (Fos-LI) as a marker of neural activation. Administration of 8-OH-DPAT (0.1 and 1 mg/kg) induced a marked and dose-related increase in the number of cells positive for Fos-LI in the locus coeruleus (LC), the main source of noradrenergic projections to the forebrain. This effect was also induced by the non-selective, partial 5-HT(1A) receptor agonist buspirone (10 mg/kg). The effect of both 8-OH-DPAT (0.1 mg/kg) and buspirone (10 mg/kg) on Fos-LI in the LC was blocked by pretreatment with the selective 5-HT(1A) receptor antagonist WAY 100635 (1 mg/kg). The active S(-)-enantiomer of the partial 5-HT(1A) receptor agonist (+/-)-MDL 75005EF (1 mg/kg) also induced the expression of Fos-LI in the LC, whereas the inactive R(+)-enantiomer of (+/-)-MDL 73005EF at the same dose did not. In addition to the LC, 8-OH-DPAT (0.1 mg/kg) also induced a marked increase in Fos-LI in various forebrain areas including the medial prefrontal cortex (infralimbic and cingulate cortical areas). More detailed analysis of the Fos response to 8-OH-DPAT in the medial prefrontal cortex revealed that the effect was attenuated by pretreatment with a combination of the beta(1)- and beta(2)-adrenoceptor antagonists ICI 118551 (4 mg/kg) and metoprolol (4 mg/kg), but not the alpha(1)-adrenoceptor antagonist prazosin (5 mg/kg). Taken together, the present findings provide immunocytochemical evidence that 5-HT(1A) receptor agonists activate noradrenergic neurones in the LC and that this leads to increased noradrenergic transmission at postsynaptic sites in the forebrain (specifically medial prefrontal cortex).

Masseteric inflammation-induced Fos protein expression in the trigeminal interpolaris/caudalis transition zone: contribution of somatosensory-vagal-adrenal integration

The effects of vagotomy and adrenalectomy on the expression of Fos protein in brainstem neurons following the inflammation of masseter muscle were examined in order to differentiate the Fos activation related to nociceptive processing in contrast to that due to somatoautonomic processing. The inflammation was induced by a unilateral injection of complete Freund's adjuvant (CFA) into the masseter muscle under methohexital anesthesia after a small skin-cut (S-cut). After the CFA injection, Fos positive neurons were identified in bilateral spinal trigeminal nucleus (VSP), nucleus tractus solitarius (NTS), ventrolateral medulla (VLM) and inferior medial olivary nucleus (IOM). At the level of the trigeminal subnucleus interpolaris/caudalis (Vi/Vc) transition zone, there was a selective induction of Fos-like immunoreactivity (LI) in the VSP and NTS, when compared to control rats (anesthesia with or without S-cut). A major portion of the Fos-LI in the VSP at the level of the caudal Vc was apparently activated by S-cut. Bilateral adrenalectomy or a unilateral vagotomy resulted in a selective reduction of inflammation-induced Fos-LI in the VSP at the Vi/Vc transition zone (P<0.05) and NTS (P<0.05), but had less effect on Fos-LI in the caudal Vc. These results suggest that the inflammation of the masseter muscle, an injury of orofacial deep tissue, results in a widespread change in neuronal activity in the VSP and NTS that depends in part on the integrity of the adrenal cortex and vagus. Thus, in addition to somatotopically organized nociceptive responses, orofacial deep tissue injury also is coupled to somatovisceral and somatoautonomic processing that contribute to central neural activation.

Reciprocal circuits involved in nitroglycerin-induced neuronal activation of autonomic regions and pain pathways: a double immunolabeling and tract-tracing study

This study uses tract-tracing protocols to determine the circuitry of specific nuclei involved in nitroglycerin-induced activation. Combined retrograde and anterograde tracers were injected into nuclei which consistently demonstrate robust Fos expression following our systemic nitroglycerin injection paradigm. The nuclei, which conform to these criteria, that we have evaluated in this study are the locus coeruleus, parabrachial nucleus and paraventricular nucleus of the hypothalamus. Dual Fos/tracer immunocytochemistry in treated animals documented the existence of a subset of autonomic nuclei which are activated by nitroglycerin injection and have reciprocal connections. From the nature of this rich interconnection we suggest that nitroglycerin activates autonomic responses involved in cardiovascular pressor mechanisms. Nuclei which show strong Fos labeling following nitroglycerin administration, but not traced in this study, include the nucleus trigeminalis caudalis and the ventrolateral column of the periaqueductal gray, both of which mediate nociceptive modalities. These data confirm and expand on our previous findings and demonstrate that nitroglycerin activates a complex set of structures that are functionally and structurally interconnected to articulate an integrated response.

Glyceryl trinitrate induces attacks of migraine without aura in sufferers of migraine with aura

Migraine with aura and migraine without aura have the same pain phase, thus indicating that migraine with aura and migraine without aura share a common pathway of nociception. In recent years, increasing evidence has suggested that the messenger molecule nitric oxide (NO) is involved in pain mechanisms of migraine without aura. In order to clarify whether the same is true for migraine with aura, in the present study we examined the headache response to intravenous infusion of glyceryl trinitrate (GTN) (0.5 microg/kg/min for 20 min) in 12 sufferers of migraine with aura. The specific aim was to elucidate whether an aura and/or an attack of migraine without aura could be induced. Fourteen healthy subjects served as controls. Aura symptoms were not elicited in any subject. Headache was more severe in migraineurs than in the controls during and immediately after GTN infusion (p=0.037) as well as during the following 11 h (p = 0.008). In the controls, the GTN-induced headache gradually disappeared, whereas in migraineurs peak headache intensity occurred at a mean time of 240 min post-infusion. At this time the induced headache in 6 of 12 migraineurs fulfilled the diagnostic criteria for migraine without aura of the International Headache Society. The results therefore suggest that NO is involved in the pain mechanisms of migraine with aura. Since cortical spreading depression has been shown to liberate NO in animals, this finding may help our understanding of the coupling between cortical spreading depression and headache in migraine with aura.

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.

Hypotension activates neuropeptide Y-containing neurons in the rat medulla oblongata

The present study was designed to determine whether neurons within cardiovascular control nuclei of the rat brainstem that become activated following a hypotensive insult also possess the capacity to utilize neuropeptide Y. Adult male Wistar-Kyoto rats were injected with glyceryl trinitrate (10 mg/kg, i.p.) or vehicle, and 4 h later anaesthetized (pentobarbitone, 60 mg/kg, i.p.) and transcardially perfused. The brains were removed and processed by standard two-colour peroxidase immunohistochemistry. Activated cells were determined by incubation with a primary antibody to Fos protein, which was followed by a second incubation with a primary antibody to neuropeptide Y for double labelling of Fos-positive cells. Compared to vehicle, glyceryl trinitrate-induced hypotension caused a marked induction of Fos protein in the caudal one-third of the nucleus tractus solitarius (bregma -14 to -13.3 mm), which tailed off rapidly in more rostral sections. Following hypotension, significant populations of activated cells were also observed in the rostral and caudal ventrolateral medulla. In the caudal nucleus tractus solitarius and the posterior part of the medial nucleus tractus solitarius, respectively, 15 of 104 and 40 of 120 Fos-positive cells exhibited cytoplasmic neuropeptide Y immunoreactivity following hypotension, compared to seven of 40 and 15 of 40 in vehicle-treated rats, indicating a significant (two- to three-fold) increase in double-labelled cells following systemic glyceryl trinitrate (P < 0.05, unpaired t-test). In contrast, in the anterior part of the medial nucleus tractus solitarius, the number of double-labelled cells did not change following hypotension. An increase in double-labelled cells was also observed in the rostral ventrolateral medulla (2.5-fold increase compared to vehicle) and caudal ventrolateral medulla (5.8-fold increase compared to vehicle) following hypotension. These data indicate that, in the rat, neuropeptide Y-containing neurons are involved in the central response to a hypotensive challenge. The primary regions where neuropeptide Y-containing neurons appear to be activated are the caudal one-third of the nucleus tractus solitarius and the caudal ventrolateral medulla/rostral ventrolateral medulla, which are key nuclei associated with the integration of the baroreceptor heart rate reflex and sympathetic vasomotor outflow.

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.

Effect of a nitric oxide donor on nitroxergic nerve fibers in the rat dura mater

Nitroglycerine, given subcutaneously to rats (10 mg/kg body weight) induces increased beading of nitric oxide synthase immunoreactive (NOS-IR) nerve fibers in the supratentorial cerebral dura mater, and an apparent increase in the number of NOS-IR nerve fibers in the dural areas supplied by the anterior and middle meningeal arteries, and the sinus sagittalis superior. Structural alterations of nitroxergic axons innervating blood vessels of the dura mater support the idea that nitric oxide is involved in the induction of headache also by a primary peripheral action, a well-known side effect of coronary dilator agents.

Brain mechanisms of mammalian fluid homeostasis: insights from use of immediate early gene mapping

A comprehensive review of the literature through mid-1997 is presented on the application of immediate early gene mapping to problems related to brain mechanisms of fluid homeostasis and cardiovascular regulation in mammals. First, the basic mechanisms of fluid intake and the principles and pitfalls of immediate early gene mapping are briefly introduced. Then, data from several principal paradigms are reviewed. These include fluid deprivation and intracellular dehydration, both of which are associated with thirst and water intake. The contributions of peripheral sodium receptors, and of both hindbrain and forebrain integrative mechanisms are evaluated. Extracellular dehydration, and associated aspects of both thirst and sodium appetite are then reviewed. The contributions of both structures along the lamina terminalis and the hypothalamic magnocellular neurosecretory groups figure prominently in most of these paradigms. Effects of hypotension and hypertension are discussed, including data from the endogenous generation and the exogenous application of angiotensin II. Lastly, we summarize the contribution of the early gene mapping technique and consider briefly the prospects for new advances using this method.

Immunohistochemical localization of caffeine-induced c-Fos protein expression in the rat brain

Although caffeine is the most widely used central nervous system stimulant, the neuronal populations and pathways mediating its stimulant effects are not well understood. Using c-Fos protein as a marker for neuronal activation, the present study investigated the pattern of c-Fos induction at 2 hours after low locomotor-stimulant doses (1, 5, 10, and 30 mg/kg, i.p.) of caffeine and compared them with those after a higher dose (75 mg/kg, i.p.) or saline injection in adult male rats. Fos-immunoreactive neurons were counted in selected nuclei across the entire brain. Caffeine induced an increase in locomotor activity in a dose-dependent manner up to doses of 30 mg/kg and a decline at 75 mg/kg. Quantitative analysis of Fos-immunoreactive neurons indicated that no structures showed significant Fos expression at doses below 75 mg/kg or a biphasic pattern of Fos expression, as in locomotion. In contrast, caffeine at 75 mg/kg induced a significant increase compared with the saline condition in the number of Fos-immunoreactive neurons in the majority of structures examined. The structures included the striatum, nucleus accumbens, globus pallidus, and substantia nigra pars reticulata and autonomic and limbic structures including the basolateral and central nuclei of the amygdala, paraventricular and supraoptic hypothalamic nuclei, periventricular hypothalamus, paraventricular thalamic nuclei, parabrachial nuclei, locus coeruleus, and nucleus of the solitary tract. The locomotor-enhancing effects of low doses of caffeine did not appear to be associated with significant Fos expression in the rat brain.

Expression of immediate early gene c-fos in rat brain following increased intracranial pressure

No attention has been given to an influence of the intracranial pressure (ICP) elevation on the brain at the level of the gene. In the present study, we originally attempted to evaluate the molecular biological changes of the brain, especially the expression of c-fos mRNA as a marker of cellular response, caused by increased ICP. Our results confirm that the neurons and non-neuronal cells are well able to tolerate the stress of increased ICP at the level of the gene, under the condition that cerebral blood flow (CBF) is maintained. A severe increase in ICP, which reduces CBF, enhances the c-fos mRNA expression in a similar fashion as in a forebrain ischemia model, except in the choroid plexus.

Medullary catecholaminergic projections to the ventrolateral periaqueductal gray region activated by halothane anaesthesia

Under anaesthesia, blood loss and deep pain can evoke a premature, centrally-mediated sympathoinhibition leading to decompensated shock and sometimes even death. The central circuits evoking premature vasodepressor syncope are unknown, although medullary catecholaminergic pathways have been implicated. The ventrolateral periaqueductal gray region is one of only three brain regions in which catecholamine content is increased during halothane anaesthesia. The ventrolateral periaqueductal gray also contains neurons which are selectively activated by blood loss and deep pain, and recent work from our laboratory has suggested that it is a pivotal structure in central sympathoinhibitory circuits. Using retrograde tracing techniques combined with the immunohistochemical detection of: (i) the catecholamine synthetic enzyme, tyrosine hydroxylase and (ii) the protein product of the immediate-early gene c-fos as a marker of neuronal activation; the results of this study indicate that catecholaminergic projections from the A1, C1 and C2 regions of the medulla to the ventrolateral periaqueductal gray are activated by halothane anaesthesia. These data are consistent with the hypotheses that ascending catecholaminergic projections to the ventrolateral periaqueductal gray: (i) are a component of the central neural circuitry responsible for the sympathoinhibitory effects of halothane anaesthesia, and (ii) may contribute to the premature elicitation of vasodepressor syncope following blood loss and deep pain under conditions of anaesthesia.

Vascular head pain selectively activates ventrolateral periaqueductal gray in the cat

Electrical stimulation of the superior sagittal sinus is an experimental model of migraine which activates neurons within the upper cervical spinal cord. The ventrolateral periaqueductal gray has been proposed as an integrative centre for the autonomic and behavioural responses to deep pain and also receives significant inputs from the upper cervical spinal cord. The noxious-stimulation evoked expression of the immediate-early gene c-fos, was used to determine if sagittal sinus stimulation activates neurons of the ventrolateral periaqueductal gray. The superior sagittal sinus was stimulated in anesthetised cats and Fos-protein was detected in coronal brain sections using standard avidin-biotin immunohistochemistry. A pattern of Fos-positive cells restricted to the caudal ventrolateral periaqueductal gray was revealed suggesting that this region may mediate the pattern of somatic and autonomic responses characteristic of migraine.

Evidence of interaction between fluoxetine and isosorbide dinitrate on neuroleptic-induced catalepsy in mice

Drugs which influence 5-HTergic mechanisms can modify neuroleptic-induced catalepsy (NC) in rodents, a phenomenon produced by striatal dopamine (DA) receptor blockade. Previous research also suggests a role for endogenous nitric oxide (NO) in the modulation of striatal DAergic neurotransmission; in addition, NO seems to play a role in the 5-HT reuptake mechanism. It is known that clomipramine potentiates NC in mice, but the reported effects of selective 5-HT reuptake inhibitors (SSRIs) in this model are rather contradictory. We then decided to re-address this issue, investigating the effect of fluoxetine (FX), an SSRI, on NC. In view of the ubiquitous role of NO as a central neuromodulator, we also studied the effect of isosorbide dinitrate (ID), a centrally active NO donor, and how both drugs interact to affect the phenomenon of NC. Catalepsy was induced in male albino mice with haloperidol (H; 1 mg/kg, i.p.) and measured at 30-min interval by means of a bar test. Drugs (FX, ID and FX + ID) or saline (controls) were injected i.p. 30 min before H, with each animal used only once. FX (5 mg/kg) significantly reduced NC, with maximal attenuation (about 74%) occurring at 150 min after H. ID (5 mg/kg) also inhibited NC (150 min: 62% attenuation). The combined drugs (FX + ID group), however, caused a great potentiation of NC (4.7-fold at its maximum, at 90 min). The effect observed with ID is compatible with the hypothesis that NO increases DA release in the striatum. The attenuation of NC observed with FX may be due to a preferential net effect on the raphe somatodendritic synapse, where inhibitory 5-HT1A autoreceptors are operative. The enhancement of NC caused by combined administration of FX and ID suggests the presence of a pharmacodynamic interaction, whose mechanism, still unclear, may be related to a decrease in striatal DA release.

Substance P receptor (NK1)-immunoreactive neurons projecting to the periaqueductal gray: distribution in the spinal trigeminal nucleus and the spinal cord of the rat

Substance P receptor (SPR)-immunoreactive neurons projecting to the periaqueductal gray (PAG) were examined in the rat spinal trigeminal nucleus and spinal cord by a retrograde tracing method combined with immunofluorescence histochemistry. After injection of Fluoro-gold (FG) into the PAG, SPR-immunoreactive neurons labeled with FG were observed mainly in the lateral spinal nucleus and lamina I of the medullary and spinal dorsal horns and additionally in laminae V and X of the spinal cord.

The ventrolateral periaqueductal gray projects to caudal brainstem depressor regions: a functional-anatomical and physiological study

The reaction of shock, a precipitous, life-threatening fall in arterial pressure and heart rate, is evoked often by the combination of deep pain and blood loss following traumatic injury. A similar "shock-like" pattern of response can be evoked by excitation of the ventrolateral midbrain periaqueductal gray. Further, ventrolateral periaqueductal gray neurons are selectively activated by deep somatic or visceral pain and haemorrhage. The pathways mediating ventrolateral periaqueductal gray evoked hypotension and bradycardia are not known. In this study, the projections from the ventrolateral periaqueductal gray to "cardiovascular" regions in the caudal medulla of the rat were examined. Injections of the anterograde tracer, biotinylated dextran amine at physiologically-defined, ventrolateral periaqueductal gray depressor sites, revealed strong projections to the caudal midline medulla and to the depressor region of the caudal ventrolateral medulla. Injections of excitatory amino acids established that substantial falls in arterial pressure could be evoked from the ventrolateral periaqueductal gray-recipient parts of the caudal midline medulla. Injections of the retrograde tracer, cholera toxin subunit B at physiologically-defined, depressor sites in the caudal midline medulla and the caudal ventrolateral medulla confirmed the existence of substantial projections from the ventrolateral periaqueductal gray. Although previous studies have emphasized the importance of projections from the ventrolateral periaqueductal gray to the pressor region of the rostral ventrolateral medulla, this study has revealed the existence of strong ventrolateral periaqueductal gray projections to depressor regions within the caudal medulla (caudal midline medulla and caudal ventrolateral medulla) which likely contribute to ventrolateral periaqueductal gray-mediated hypotension and bradycardia.

Neurochemical mechanisms of nitroglycerin-induced neuronal activation in rat brain: a pharmacological investigation

Nitroglycerin is a nitric oxide donor which induces sustained expression of Fos protein, a marker of neuronal activation, in specific neuronal groups in the central nervous system. The mechanisms which underlie nitroglycerin-induced neuronal activation are elusive at this time, although a precise role has been suggested for the pool of neurons containing nitric oxide synthase as well as for catecholaminergic and peptidergic pathways. The aim of this study was to provide further details on the central effect of nitroglycerin by means of a pharmacological manipulation of nitroglycerin-induced neuronal activation with inhibitors of the nitric oxide synthase, modulators of the sympathetic drive and mediators of pain perception. Adult male Sprague-Dawley rats received L-NGnitro-arginine methyl ester, 7-nitro-indazole, ephedrine sulfate, indomethacin, capsaicin or vehicle before the subcutaneous injection of nitroglycerin (10 mg/kg b.w.). They were sacrificed 4 hr after nitroglycerin administration and brain sections were processed for immunocytochemical visualization of Fos. All the pharmacological treatments administered before injecting nitroglycerin selectively influenced Fos expression in the different brain nuclei. The data obtained suggest that nitroglycerin-induced neuronal activation is mediated by nociceptive and barosensitive mechanisms. Nitric oxide seems to represent the most important mediator of this phenomenon. The sympathetic system and prostaglandin synthesis are also likely to be involved.

Opposite effects of L-arginine and nitroglycerin on cerebral blood velocity: nitric oxide precursors and cerebral blood velocity

Nitric oxide (NO), a gaseous molecule synthesized in the arteriolar endothelium from the amino acid L-arginine (L-arg), has been identified as the previously described Endothelium-Derived Relaxing Factor (EDRF): nitroderivatives such as nitroglycerin are known to induce vasodilation via NO release. The aim of this study was to evaluate by Transcranial Doppler (TCD) monitoring any changes in cerebral hemodynamics induced by both the infusion of L-arg and the sublingual administration of nitroglycerin in 20 healthy subjects. L-arg infusion induced a significant increase in blood velocity compared to the baseline value (mean +/- S.D. percent change = 18 +/- 8.71; p<0.0001 ) and a slight but significant decrease in Pulsatility Index. By contrast, nitroglycerin was able to cause a significant decrease in blood velocity (mean +/- S.D. percent change = 24.8 +/- 7.68; p<0.0001), while leaving Pulsatility Index unchanged. These data suggest that L-arg and nitroglycerin, both hypothesized to use NO as the final product at the vascular level, result in opposite blood velocity patterns within the cerebral circulation. This may be due to the particular type of artery and/or to the local endothelial environment whereby the released NO may act.

Spinal afferents to functionally distinct periaqueductal gray columns in the rat: an anterograde and retrograde tracing study

The segmental and laminar organization of spinal projections to the functionally distinct ventrolateral (vlPAG) and lateral periaqueductal gray (lPAG) columns was examined by using retrograde and anterograde tracing techniques. It was found 1) that spinal input to both vlPAG and lPAG columns arose predominantly from neurons in the upper cervical (C1-4) and sacral spinal cord; 2) that there was a topographical separation of vl-PAG projecting and lPAG-projecting neurons within the upper cervical spinal cord; but 3) that below spinal segment C4, vlPAG-projecting and lPAG-projecting spinal neurons were similarly distributed, predominantly within contralateral lamina I, the nucleus of the dorsolateral fasciculus (the lateral spinal nucleus) and the lateral (reticular) part of lamina V. Consistent with the retrograde results, the greatest density of anterograde label, within both the vlPAG and lPAG, was found after tracer injections made either in the superficial or deep dorsal horn of the upper cervical spinal cord. Tracer injections made within the thoraco-lumbar spinal cord revealed that the vlPAG column received a convergent input from both the superficial and deep dorsal horn. However, thoraco-lumbar input to the lPAG was found to arise uniquely from the superficial dorsal horn; whereas the deep dorsal horn was found to innervate the "juxta-aqueductal" PAG region rather than projecting to the lPAG. These findings suggest that similar to spino-parabrachial projections, spinal projections to the lPAG (and juxta-aqueductal PAG) are topographically organised, with distinct subgroups of spinal neurons projecting to specific lPAG or juxta-aqueductal PAG subregions. In contrast, the vlPAG receives a convergent spinal input which arises from the superficial and deep dorsal horn of cervical, thoracic, lumbar, and sacral spinal segments.

Conditioned fear to context is associated with increased Fos expression in the caudal ventrolateral region of the midbrain periaqueductal gray

Immunohistochemical detection of Fos was used to determine which regions of the periaqueductal gray are activated during conditioned fear to a context in the rat. More specifically, the aim of the study was to test the role of its lateral and ventrolateral columns in freezing behaviour during fear. Conditioned fear was evoked by re-exposing rats to the same footshock chamber in which they had received footshocks 4 h earlier. Conditioned Re-exposed rats were compared to Not Conditioned Re-exposed and Conditioned Not Re-exposed rats. Freezing was observed in the Conditioned-Re-exposed group only. It was associated with an overall increase in Fos expression in the entire periaqueductal gray that was significantly greater than in the two other groups. The largest and most significant increase in Fos immunoreactivity was found in the ventrolateral column (especially in its caudal part), whereas only a moderate increase was found in the lateral column. The present results argue in favour of the ventrolateral column as the region of the periaqueductal gray that is preferentially involved in expression of conditioned fear. As previous lesion studies suggested, the ventrolateral periaqueductal gray may play a role in mediating the immobility component of freezing induced by fear. Other lines of evidence suggest that it may also play a role in mediating the quiescence immobility associated with deep pain. We propose that the ventrolateral column of the periaqueductal gray acts as an integrating centre mediating behavioural inhibition.

Haemodynamic correlates of early and delayed responses to sublingual administration of isosorbide dinitrate in migraine patients: a transcranial Doppler study

In normal subjects or migraine patients, nitrates induce a non-specific early headache caused by vasodilation of intracranial arteries. In migraineurs a delayed headache response to nitrates may have a typical clinical profile of a spontaneous migraine attack. The cerebral vasomotor changes of this delayed response require further study. Isosorbide dinitrate (IDN), an exogenous nitric oxide (NO) donor, was given at a dose of 5 mg sublingually and a bilateral transcranial Doppler device was used to monitor bilateral mean velocity (Vm) changes at the middle cerebral artery (MCA) after IDN administration and until delayed headache occurred. Spontaneous migraine-like headache occurred only in migraine patients during the delayed phase after IDN and was accompanied by a prolonged arterial vasodilation compared to normal subjects. This vasomotor response was more evident on the customary side of the head pain of a spontaneous migraine attack. Our findings suggest a particular vasomotor response to nitrates in migraine patients. This response is associated with the nitrate-induced headache and it is not evident in healthy pain-free controls during the delayed phase after administration of an NO donor. Owing to the short half-life of NO, the neurotransmitter released by IDN, and because of the late onset of headache, we believe the mechanism is unlikely to be vascular in origin, but may have a neurogenic component.

Effects of sinoaortic denervation on Fos expression in the brain evoked by hypertension and hypotension in conscious rabbits

We have previously shown [Li and Dampney (1994) Neuroscience 61, 613-634] that periods of sustained hypertension and hypotension each induces a distinctive and reproducible pattern of neuronal expression of Fos (a marker of neuronal activation) in specific regions of the brainstem and forebrain of conscious rabbits. The aim of this study was to determine the contribution of afferent inputs from arterial baroreceptors to the activation of neurons in these various brain regions that is caused by a sustained change in arterial pressure. Experiments were carried out on rabbits in which the carotid sinus and aortic depressor nerves were cut in a preliminary operation. Following a recovery period of seven to 10 days, a moderate hypertension or hypotension (increase or decrease in arterial pressure of 20-30 mmHg) was induced in conscious barodenervated rabbits for 60 min by the continuous infusion of phenylephrine or sodium nitroprusside, respectively. In control experiments, barodenervated rabbits were subjected to the identical procedures except that they were infused with the vehicle solution alone. Compared with the effects seen in barointact rabbits, [Li and Dampney (1994) Neuroscience 61, 613-634] the number of neurons that expressed Fos in response to hypertension was reduced by approximately 90% in the nucleus of the solitary tract and in the caudal and intermediate parts of the ventrolateral medulla. In supramedullary regions, baroreceptor denervation resulted in a reduction of approximately 60% in hypertension-induced Fos expression in the central nucleus of the amygdala and in the bed nucleus of the stria terminalis, but no significant reduction in the parabrachial complex in the pons. Following hypotension, the number of neurons that expressed Fos in barodenervated rabbits, compared with barointact rabbits, [Li and Dampney (1994) Neuroscience 61, 613-634] was reduced by approximately 90% in the nucleus of the solitary tract, area postrema, and caudal, intermediate and rostral parts of the ventrolateral medulla. Baroreceptor denervation also resulted in a similar large reduction in hypotension-induced Fos expression in many supramedullary regions (locus coeruleus, midbrain periaqueductal grey, hypothalamic paraventricular nucleus, and in the central nucleus of the amygdala and the bed nucleus of the stria terminalis in the basal forebrain). In the supraoptic nucleus, hypotension-induced Fos expression in barodenervated rabbits was reduced by 75% compared to barointact animals, but was still significantly greater than in control animals. There was also a high level of Fos expression, much greater than in control animals, in the circumventricular organs surrounding the third ventricle (subfornical organ and organum vasculosum lamina terminalis). The results indicate that in conscious rabbits the activation of neurons that occurs in several discrete regions at all levels of the brain following a sustained change in arterial pressure is largely dependent upon inputs from arterial baroreceptors, with the exception of neurons in the circumventricular organs surrounding the third ventricle that are activated by sustained hypotension. The latter group of neurons are known to project to vasopressin-secreting neurons in the supraoptic nucleus, and may therefore via this pathway trigger the hypotension-induced release of vasopressin that occurs in the absence of baroreceptor inputs.

Cyclophosphamide cystitis as a model of visceral pain in rats: minor effects at mesodiencephalic levels as revealed by the expression of c-fos, with a note on Krox-24

The evoked expression of the immediate-early gene-encoded proteins c-Fos and Krox-24 was used to study activation of mesodiencephalic structures as a function of the development of cyclophosphamide (CP) cystitis in behaving rats. This article is the third of a series and completes previously published data obtained at both spinal and hindbrain levels. CP-injected animals received a single dose of 100 mg/kg i.p. under transient volatile anesthesia and survived for 1-4 h in order to cover the entire postinjection period during which the disease develops. Survival times longer than 4 h were not used owing to ethical considerations. Results from CP-injected groups are compared with those from either noninjected controls or saline-injected animals having survived for the same times as CP-injected ones. Quantitative results come from c-fos expression. At mesodiencephalic levels a high and widespread basal c-fos expression was observed in control animals; maximum staining was observed at the midthalamic level. Four groups of nuclei were identified with regard to the density of staining. The first group included nuclei showing clustered, intensely labeled cells; these areas were restricted in extent and related to the maintenance of circadian rythms (intergeniculate leaf, suprachiasmatic nucleus, dorsal parts of either paraventricular thalamic nuclei or central gray), sleep-arousal cycle (supramamillary nucleus), or changes in arterial pressure (laterodorsal tegmental nucleus). The second group included nuclei showing scattered, moderately labeled cells; these areas were widespread at all rostrocaudal levels and related to either autonomic/neuroendocrine regulations (central gray, lateral habenula, hypothalamus) or motor behavior, orienting reflex and oculomotor coordination (unspecific subdivisions of both colliculi and their adjoining mesencephalic regions, zona incerta dorsal). The third group included nuclei with evenly distributed, faintly labeled cells; these areas, which, with few exceptions, covered almost the entire diencephalon, mainly concerned nuclei of multisensory convergence having functions in either discriminative tasks (laterodorsal and lateroposterior thalamic nuclei) or emotional responses (intralaminar and midline thalamic nuclei). The fourth group included nuclei free of labeling; these were areas that received the bulk of unimodal sensory/motor inputs (central inferior colliculus, pretectal optic nuclei, ventral medial geniculate nucleus, ventral anterior pretectal nucleus, dorsal lateral geniculate nucleus, ventrobasal complex; zona incerta ventral, parafascicular thalamic nucleus) and are thus the most discriminative regarding specific modalities. Variations in staining were of the same magnitude in both saline- and CP-injected animals. A sequential study spanning every postinjection hour revealed maximum staining at 1 h postinjection, which was followed by a progressive, time-related decrease. Increases in the number of labeled cells 1 h postinjection were significant in only a restricted number of nuclei showing low basal expression (Edinger-Westphal nucleus and paraventricular, supraoptic, and lateral hypothalamic nuclei); time-related reductions in staining that were correlated to sleep or quiescence behaviors finally resulted in staining equal to or below that seen in control animals. No structures showed significantly increased staining in relation to the full development of cystitis, i.e., with the increase of visceronociceptive inputs. Comparing the present results with those previously obtained at more caudal levels, it appears that subtelencephalic levels primarily driven by visceronociceptive inputs, i.e., those that increase and/or maintain their activity in parallel with the degree of nociception, are confined to brainstem-spinal cord junction levels and only comprise certain subdivisions of the nucleus of the solitary tract (nucleus medialis, nucleus commissuralis, and ventralmost part of area po

NF-kappa B transcription factor subunits in rat brain: colocalization of p65 and alpha-MSH

The subunit proteins p50 and p65 of the transcription factor NF-kappa B inhibitory protein were immunocytochemically identified and mapped in rat brain. The p65 subunit was localized to the cytoplasm of neurons in the lateral hypothalamus and colocalized with alpha-MSH in neurons identified as the alpha-2 component of the alpha-MSH system. The p50 subunit protein was distributed throughout the neocortex, basal ganglia, thalamic, and hypothalamic nuclei, and certain nuclei of the pons and medulla. The I-kappa B protein, which is necessary for the cytoplasmic sequestration of the NF-kappa B transcription factor complex, was identified specifically in regions of limbic, hypothalamic, and autonomic nuclei.

Systemic nitroglycerin activates peptidergic and catecholaminergic pathways in rat brain

In this study, we carried out an immunohistochemical evaluation of the neurochemical characteristics of neurons that are activated (i.e., express Fos protein) in response to systemic administration of nitroglycerin. In the brain stem, a significant percentage of activated neurons contained noradrenaline as a neurotransmitter, whereas only a few of them contained serotonin. In the paraventricular and supraoptic nuclei of the hypothalamus, numerous Fos-immunoreactive neurons were also positive for vasopressin, oxytocin, and corticotropin-releasing factor. Codistribution with corticotropin-releasing factor was also observed in the central nucleus of the amygdala. Our findings point out a prominent role for catecholaminergic and peptidergic pathways in the brain in response to systemic nitroglycerin.

NADPH-diaphorase activity and Fos expression in brain nuclei following nitroglycerin administration

Organic nitrates are considered nitric oxide donors in that they have been shown to form nitric oxide in vitro and in vivo. Nitroglycerin is an organic nitrate which possesses peculiar activities mediated, to some extent, by the central nervous system via the noradrenergic system. Previous reports have shown that systemic nitroglycerin is able to induce Fos expression in brain nuclei which are known to contain nitric oxide synthesizing enzyme. Neuronal NADPH-diaphorase has been shown to be a nitric oxide synthase. Thus, in this study we used NADPH-diaphorase histochemistry to evaluate the distribution of Fos-immunoreactive cells within neurons which contain nitric oxide synthase. The data showed co-localization of Fos with NADPH-diaphorase activity in numerous neurons of the paraventricular and supraoptic nuclei of the hypothalamus. In the brainstem, a few neurons were doubly labeled for Fos and NADPH-diaphorase activity, but NADPH-diaphorase positive fibers and Fos-immunoreactive neurons were consistently co-distributed in the locus coeruleus, parabrachial nucleus, nucleus tractus solitarius and spinal trigeminal nucleus caudalis. These findings demonstrate that nitroglycerin administration activates a selective group of neurons which are a source of nitric oxide or which are in close proximity with neuronal processes containing nitric oxide synthase, and suggest that the nitric oxide synthase synthesizing pathway may be involved at various levels in the central effect of nitroglycerin.