A possible role for mast cells in controlling the diameter of arterioles on the surface of the brain

Primary headache syndromes in systemic mastocytosis

Aim: To investigate the relationship between clinical mast cell activity and primary headache syndromes.

Methods: We surveyed individuals with systemic mastocytosis, an uncommon disorder associated with increased mast cell activity. Diagnoses of primary headache syndromes in addition to the relationship of headache and symptoms of mastocytosis were ascertained.

Results: A response rate of 64/148 (43.2%) was achieved. Headache diagnoses in our respondents (n = 64) were largely migraine (37.5%) and tension-type headaches (17.2%). Typical aura with and without migraine headache was highly represented in our patient population (n = 25, 39%). Three individuals met criteria for primary cough headache (4.7%). Symptoms reflective of mast cell activity were significantly greater in individuals reporting headaches. Patients experiencing headache concurrently with mastocytosis flairs were more likely to be male (p = 0.002), have histaminergic symptoms, such as itching (p = 0.02) and runny nose (p = 0.03), and have unilateral cranial autonomic features (p = 0.04). However, using standardized International Headache Society criteria, we did not identify individuals with cluster headache or other trigeminal autonomic cephalalgias in this population.

Conclusions: Our observational survey-based data supports a clinical relationship between mast cell activity and primary headache syndromes. Generalizability of our results is limited by the low response rate and possible tertiary referral bias.

Developmental changes of mast cell populations in the cerebral meninges of the rat

It is known that both the dura and the pia mater attract and support the differentiation of mast cells. The present study shows that unevenly distributed mast cells in the cerebral meninges of the rat can be found in perivascular sites and vessel ramification points, but can also be unrelated to the meningeal vasculature. It also documents changes in the number, localization and staining preferences of the mast cells in the two meninges of the developing and mature rat brain. Quantitative examination of all types of histochemically differentiated meningeal mast cells reveals no major (although some exist) differences between right and left side subpopulations, but strongly suggests a different origin and fate of the dural and the pial mast cells. The number of dural mast cells, already high from postnatal day 0, although declining from postnatal day 21 onwards, remains conspicuous up to postnatal day 180. In contrast, pial mast cells are comparatively very few in the first day of the postnatal life, and despite a transient significant increase in the following two weeks, they reach almost zero levels from postnatal day 21.

Abolition of arteriolar dilation but not constriction to histamine in cremaster muscle of eNOS-/- mice

Histamine increases the permeability of capillaries and venules but little is known of its precapillary actions on the control of tissue perfusion. Using gene ablation and pharmacological interventions, we tested whether histamine could increase muscle blood flow through stimulating nitric oxide (NO) release from microvascular endothelium. Vasomotor responses to topical histamine were investigated in second-order arterioles in the superfused cremaster muscle of anesthetized C57BL6 mice and null platelet endothelial cell adhesion molecule-1 (PECAM-1-/-) and null endothelial NO synthase (eNOS-/-) mice aged 8-12 wk. Neither resting (17 +/- 1 microm) nor maximum diameters (36 +/- 2 microm) were different between groups, nor was the constrictor response (approximately 5 +/- 1 microm) to elevating superfusate oxygen from 0 to 21%. For arterioles of C57BL6 and PECAM-1-/- mice, cumulative addition of histamine to the superfusate produced vasodilation (1 nM-1 microM; peak response, 9 +/- 1 microm) and then vasoconstriction (10-100 microM; peak response, 12 +/- 2 microm). In eNOS-/- mice, histamine produced only vasoconstriction. In C57BL6 and PECAM-1-/- mice, vasodilation was abolished with Nomega-nitro-l-arginine (30 microM); in all mice, vasoconstriction was abolished with nifedipine (1 microM). Vasomotor responses were eliminated with pyrilamine (1 microM; H1 receptor antagonist) yet remained intact with cimetidine (1 microM; H2 receptor antagonist). These findings illustrate that the biphasic vasomotor response of mouse cremaster arterioles to histamine is mediated through H1 receptors on endothelium (NO-dependent vasodilation) as well as smooth muscle (Ca2+ entry and constriction). Thus histamine can increase as well as decrease muscle blood flow, according to local concentration. However, when NO production is compromised, only vasoconstriction and flow reduction occur.

Mast cells are essential for early onset and severe disease in a murine model of multiple sclerosis

In addition to their well characterized role in allergic inflammation, recent data confirm that mast cells play a more extensive role in a variety of immune responses. However, their contribution to autoimmune and neurologic disease processes has not been investigated. Experimental allergic encephalomyelitis (EAE) and its human disease counterpart, multiple sclerosis, are considered to be CD4(+) T cell-mediated autoimmune diseases affecting the central nervous system. Several lines of indirect evidence suggest that mast cells could also play a role in the pathogenesis of both the human and murine disease. Using a myelin oligodendrocyte glycoprotein (MOG)-induced model of acute EAE, we show that mast cell-deficient W/W(v) mice exhibit significantly reduced disease incidence, delayed disease onset, and decreased mean clinical scores when compared with their wild-type congenic littermates. No differences were observed in MOG-specific T and B cell responses between the two groups, indicating that a global T or B cell defect is not present in W/W(v) animals. Reconstitution of the mast cell population in W/W(v) mice restores induction of early and severe disease to wild-type levels, suggesting that mast cells are critical for the full manifestation of disease. These data provide a new mechanism for immune destruction in EAE and indicate that mast cells play a broader role in neurologic inflammation.

Mast cells in the sheep, hedgehog and rat forebrain

The study was designed to reveal the distribution of various mast cell types in the forebrain of the adult sheep, hedgehog and rat. Based on their histochemical and immunocytochemical characteristics, mast cells were categorised as (1) connective tissue-type mast cells, staining metachromatically purple with the toluidine blue method, or pale red with the Alcian blue/safranin method, (2) mucosal-type or immature mast cells staining blue with the Alcian blue/safranin method and (3) serotonin immunopositive mast cells. All 3 types of brain mast cells in all species studied were located in both white and grey matter, often associated with intraparenchymal blood vessels. Their distribution pattern exhibited interspecies differences, while their number varied considerably not only between species but also between individuals of each species. A distributional left-right asymmetry, with more cells present on the left side, was observed in all species studied but it was most prominent in the sheep brain. In the sheep, mast cells were abundantly distributed in forebrain areas, while in the hedgehog and the rat forebrain, mast cells were less widely distributed and were relatively or substantially fewer in number respectively. A limited number of brain mast cells, in all 3 species, but primarily in the rat, were found to react both immunocytochemically to 5-HT antibody and histochemically with Alcian blue/safranin staining.

Definitive characterization of rat hypothalamic mast cells

Mast cells have previously been identified in mammalian brain by histochemistry and histamine fluorescence, particularly in the rat thalamus and hypothalamus. However, the nature of brain mast cells has continued to be questioned, especially because the electron microscopic appearance often shows secretory granule morphology distinct from that of typical connective tissue mast cells. Here we report that mast cells in the rat hypothalamus, identified based on metachromatic staining with Toluidine Blue, fluoresced after staining with berberine sulfate, indicating the presence of heparin. These cells were also positive immunohistochemically for histamine, as well as for rat mast cell protease I, an enzyme characteristically present in rat connective tissue mast cells. In addition, these same cells showed a very strong signal with in situ hybridization for immunoglobulin E binding protein messenger RNA. However, use of antibodies directed towards immunoglobulin E or its binding protein did not label any cells, which may mean either the binding protein is below the level of detection of the techniques used or that it is not expressed except in pathological conditions when the blood-brain barrier becomes permeable. At the ultrastructural level, perivascular mast cells contained numerous, intact, electron-dense granules which were labeled by gold-labeled anti-rat mast cell protease I. These results clearly demonstrate the presence of perivascular mast cells in the rat hypothalamus, where they may participate in homeostatic processes.

Interactions of mast cells with the nervous system ?Recent advances

This article reviews recent advances in the understanding of mast cell-nervous system interactions. It is drawn largely from work published within the last ten years, and discusses the anatomical and biochemical evidence of a functional connection between mast cells and the nervous system, and the implications that such a relationship may have for normal and abnormal physiological functioning. Mast cells are found at varying levels of association with the nervous system; in CNS parenchyma (mainly thalamus), in connective tissue coverings (e.g. meninges, endoneurium), and in close apposition to peripheral nerve endings in a variety of tissues. There is, as yet, no clearly defined role for mast cells in nervous system function, or vice-versa, and it seems most likely that their interactions fulfil mutually modulatory roles. By extension, pathological situations where one of the partners in this relationship is overly stimulated may lead to a dysregulation of the other, and contribute to disease symptomatology.

Linear arrays of homogeneous mast cells in the dura mater of the rat

Using fluorescence histochemistry, 5-HT, histamine and heparin were colocalized in a large population of cells in the dura mater thereby identifying them as mast cells. In addition, because these cells were highly sensitive to compound 48/80 and were densely packed with granules of a consistent density, they were identified specifically as 'connective tissue' mast cells. Other types of mast cells, i.e. 'mucosal' or 'neurolipomastocytes', were not present in the rat dura mater. 5-HT immunohistochemistry was the best technique for demonstrating that there were populations of mast cells, one associated with each of the two layers of dura. Although shaped differently the type of mast cell in each layer was the same. It was observed that mast cell shape is dependent on the contiguity, density and orientation of its surrounding elements, not its type. In general, mast cells in the outer layer were aligned parallel to the middle meningeal artery and those in the inner layer were parallel to trigeminal nerve branches that coursed obliquely across the middle meningeal artery. Examination of cross-sections of dura revealed that most mast cells also were aligned at the interface between the two dural layers. The linear orientation of mast cells in two planes of each layer suggests a programmed lamellar seeding of these cells during development of the dura. This study also demonstrated that the majority of dural mast cells were more closely related to other connective tissue elements than to blood vessels and nerves. These results (1) are compatible with the suggestion that dural mast cells play a non-obligatory role in the neuroinflammatory response, (2) leave open to question the role of the dural mast cell in headache or the regulation of blood flow, and (3) support evidence that dural mast cells play an important role in connective tissue related functions, e.g. development, inflammatory response to injury and wound repair.

Structure and sympathetic innervation of the intracranial arteries in the giraffe (Giraffa camelopardalis)

Fluorescence histochemistry discloses that the carotid rete mirabile in the giraffe has a poor sympathetic innervation. In contrast, the efferent artery of the rete (internal carotid artery) and the cerebral arteries show moderate sympathetic innervation. A certain degree of regional variability was noted in which the rostral arteries (anterior and middle cerebral) receive more sympathetic nerves than the caudal (posterior communicating and basilar) arteries. The sympathetic nerves on the giraffe cerebral vessels may constitute part of a host of mechanisms by which regional blood flow to the brain is regulated. Conversely, the paucity of sympathetic innervation of the carotid rete mirabile may indicate that this structure does not play an active role in vasoconstrictor responses during postural changes of the head.

Release of histamine in rat hypothalamus and corpus striatum in vivo

Histamine has remained a putative neurotransmitter for many years, partially because some of the criteria necessary to define it as a central nervous system neurotransmitter have not been established. The demonstration of in vitro release and the quantification of turnover as an indirect measure of release have been complicated by the histological evidence for multiple histamine pools in the central nervous system. In brain, there are multiple cell types which probably contain histamine. These cells include mast cells, neurolipomastocytoid cells, microvascular endothelial cells, and a histaminergic neuronal system which has been visualized using immunocytochemical methods. Using in situ brain microdialysis and a sensitive and specific radioenzymatic assay for histamine, we have identified histamine in the extracellular space of the rat hypothalamus and corpus striatum in vivo. Following neuronal selective stimuli, significant increases in extracellular histamine levels only were observed in the posterior hypothalamus, where dense histaminergic neuronal terminals have been described. However, after manipulations targeted towards histamine-containing mast cells, such increases were seen in both the posterior hypothalamus and corpus striatum. In summary, this study demonstrates that endogenous histamine can be released from the posterior hypothalamus by stimuli targeted towards histamine neurons and that histamine may also be released by non-neuronal mast cell elements.

Histamine elicits competing endothelium-dependent constriction and endothelium-independent dilation in vivo in mouse cerebral arterioles

We used television microscopy and an image-splitting technique to monitor the changes in diameter produced by histamine applied locally to mouse pial arterioles in vivo. A high dose (50 micrograms/ml, 3 X 10(-4) M) of histamine constricted the arterioles, whereas lower doses (20 and 10 micrograms/ml) relaxed them. Constriction was blocked and dilation occurred when selective injury of the endothelium was produced by light from a helium-neon laser in the presence of intravascular Evans blue. From this we conclude that the constriction was endothelium-dependent and was caused by the release of an endothelium-derived constricting factor. Constriction was also blocked by each of two antagonists of the H1 histamine receptor and by pretreatment of the arterioles with indomethacin. H1 blockade unmasked a dilating action of 1 micrograms/ml histamine, a dose too low to affect the diameter of arterioles not treated with the H1 blocker. An H2 blocker interfered with the relaxation by low-dose (10 micrograms/ml, 6 X 10(-5) M) histamine. These data indicate that for mouse pial arterioles, histamine can interact with H1 receptors on the endothelium to release an endothelium-derived constricting factor that causes constriction of the underlying muscle while simultaneously interacting with H2 receptors in the muscle that mediate relaxation of the vessel.

Mast cells: the immune gate to the brain

Mast cells were originally considered wandering histiocytes, but are now known to derive from the bone marrow and enter the tissues as immature or precursor cells which then differentiate under micro-environmental influences such as interleukin-3. At least three types of mature mast cells have been identified as serosal (lung, peritoneal, skin), mucosal (nasal, gastrointestinal) and brain (dural, perivascular, parenchymal) with their own distinct biochemical, morphological and functional characteristics. Mast cells are necessary for immediate hypersensitivity reactions where they release numerous biologically powerful mediators in response to immunoglobulin E (IgE) and antigen (Ag), and appear to be required for delayed reactions. Anaphylatoxins, basic peptides and drugs, as well as certain neuropeptides and hormones, can also trigger mast cell secretion. Recent evidence indicates that mast cells are found in close proximity to neurons, an association which may be regulated by nerve growth factor. Moreover, mast cells may be capable of selective release of mediators which could, in turn, regulate further secretion. This information suggests that mast cells may serve as a link between the immune, endocrine and nervous systems and could have an important role in the access of lymphocytes and pathogens to the brain. The possible role of such interactions in the pathophysiology of specific neuroinflammatory conditions is also discussed.

Serotonin release from rat brain mast cells in vitro

Mast cells are primarily localized in connective tissues, where they secrete numerous mediators. They have also been identified in the mammalian central nervous system on the basis of their histochemical and morphological properties, but their role there remains unknown. A perfusion system was used to investigate in vitro mediator release from rat brain mast cells. Compound 48/80, the classic mast cell secretagogue of connective tissue mast cells, induced dose-dependent and non-cytotoxic release of serotonin, histamine and beta-hexosaminidase from mast cells in the rat thalamus and hypothalamus, but not in the cerebellum which was used as a negative control. Detailed studies were performed on thalamic mast cells, which were identified on the basis of metachromasia with Toluidine Blue and Safranin-positive staining with the Alcian Blue/Safranin technique. Their secretion was characterized by: (a) parallel release of serotonin, histamine and beta-hexosaminidase; (b) lack of dependence on extracellular calcium; (c) susceptibility to inhibition by disodium cromoglycate; and (d) lack of lactate dehydrogenase release. These results indicate that the morphology and secretory characteristics of thalamic mast cells resemble those of connective tissue mast cells. The ability of brain mast cells to secrete their mediators is discussed in the context of their possible involvement in brain pathophysiology.

Ultrastructural evidence for a functional unit between nerve fibers and type II cerebral mast cells in the cerebral vascular wall

By histofluorescence microscopic examinations of pial arteries from rats and rabbits, we have observed that the routes of adrenergic fibers were apparently organized along successive sites of granular autofluorescent cells present in the adventitia. Subsequent electron microscopic studies showed that these cells were often situated in close apposition (80 to 200 nm) to the adventitial nerve bundles. The granular cells and nerve varicosities were frequently enclosed within the same basement membrane, with a membrane-to-membrane distance as small as 20 nm. However, no clear membrane differentiation was seen. These granular cells were identified histochemically by staining with Sudan Black, Oil Red O, Toluidine Blue, Alcian Blue, together with ultrastructural and pharmacological methods (48/80 compound and carbachol intracarotid infusions). The cells, many of which contained large amounts of lipids, showed morphological ultrastructural and pharmacological similarities to peripheral mast cells. Nerve bundles contained two types of varicosities: some of them degenerated after superior cervical ganglionectomy and were thus of sympathetic origin, whereas the others contained small clear vesicles (probably cholinergic) and/or large dense-cored vesicles (probably peptidergic). As we have shown that cholinomimetics induce exocytosis of these granular cells, the close relationship between these cells and the nerve fibers may indicate a neurogenic control of the cerebrovascular mast cell secretion. As these cells contain potent vasoactive substances, this relationship may be of importance in the genesis of physiological or pathological cerebrovascular events which are, as yet, poorly understood.

Indirect adrenergic effect of compound 48/80 in cat cerebral arteries

Compound 48/80 evoked an increase in the spontaneous tritium release from cat cerebral arteries prelabelled with 3H-NA. This increase was abolished after cervical gangliectomy, external calcium removal or in the presence of colchicine. Cocaine brought about an enhancement in the release of radioactivity elicited by compound 48/80 while diphenhydramine did not affect it. These results suggest that compound 48/80 has an indirect adrenergic effect in cat cerebral arteries which is not mediated by the release of histamine from mast cells.

Melanin: the organizing molecule

The hypothesis is advanced that (neuro)melanin (in conjunction with other pigment molecules such as the isopentenoids) functions as the major organizational molecule in living systems. Melanin is depicted as an organizational "trigger" capable of using established properties such as photon-(electron)-phonon conversions, free radical-redox mechanisms, ion exchange mechanisms, and semiconductive switching capabilities to direct energy to strategic molecular systems and sensitive hierarchies of protein enzyme cascades. Melanin is held capable of regulating a wide range of molecular interactions and metabolic processes primarily through its effective control of diverse covalent modifications. To support the hypothesis, established and proposed properties of melanin are reviewed (including the possibility that (neuro)melanin is capable of self-synthesis). Two "melanocentric systems"--key molecular systems in which melanin plays a central if not controlling role--are examined: 1) the melanin-purine-pteridine (covalent modification) system and 2) the APUD (or diffuse neuroendocrine) system. Melanin's role in embryological organization and tissue repair/regeneration via sustained or direct current is considered in addition to its possible control of the major homeostatic regulatory systems--autonomic, neuroendocrine, and immunological.

Autonomic nerves, mast cells, and amine receptors in human brain vessels. A histochemical and pharmacological study

The studies were performed on operation material from 17- to 63-year-old patients and on fetuses at 19-23 weeks gestational age. Formaldehyde histofluorescence showed the presence of numerous perivascular adrenergic nerves around pial and intracerebral vessels, the carotid system being better supplied than the vertebral system. Cholinergic nerves, visualized by the cholinesterase technique, followed the adrenergic fibers in the plexus formations of the pial arterial system. Histamine-containing mast cells, often with a perivascular distribution, were located with the o-phthaldiadehyde method. Transmural electrical stimulation of the perivascular nerves contracted isolated pieces of pial arteries in a frequency-dependent manner, and the response was inhibited by the adrenergic nerve blocking agent, guanethidine. On the basis of the relative potency of various amines and related compounds in producing a motor response of isolated pial arteries, and the mode of inhibition caused by specific antagonists, various amine receptors could be demonstrated: adrenergic alpha-receptors (mediating contraction) and beta-receptors (dilation), cholinergic muscarinic receptors (dilation) and histamine H2-receptors (mediating dilation). Thus, the amine mechanisms demonstrated in human brain vessels appear to be principally the same of those shown in more extensive studies on laboratory animals.

Pial arteriolar responses in the mouse brain revisited

Arteriolar responses were measured on the cerebral surface of the mouse using an image splitter and TV monitor. The response to locally applied norepinephrine (NOR) was significantly more frequent for vessels greater than 30 mu I.D. than for smaller vessels. However, even the smaller vessels were frequently constricted by NOR in doses of 5 mug per milliliter. Reserpine (5 mg per kilogram) failed to alter the response to NOR at either 24 or 72 hours after reserpinization. At 48 hours the threshold dose of NOR was reduced, but the effect was slight (two-tailed, P = 0.08). Both propranolol (10(-6) M3 and phentolamine (10(-5M) blocked responses to 5 mug per milliliter of NOR, but neither agent altered resting arteriolar diameter. Isoproterenol, tyramine, and histamine had no effect. Serotonin (5HT) constricted the arterioles but did not potentiate the response to NOR. Additive or potentiated effects were not observed with NOR 5HT or histamine in any combination. These data indicate the presence of alpha-adrenergic receptors in murine cerebral surface arterioles, but do not establish a significant tonic effect of norepinephrine. The existence or role of a beta-receptor in these murine cerebral surface arterioles remains an unsettled question.

Constriction of pial arterioles produced by prostaglandin F2alpha

Prostaglandin F2alpha constricted pial arterioles when locally applied to the cerebral surface. Norepinephrine and serotonin each elicted similar contractile effects. The constriction produced by F2alpha in combination with either biogenic amine was greater than the constriction elicited by F2alpha or amine acting alone. The effect of one agent on the other was additive rather than potentiating. Since F2alpha norepinephrine and serotonin are all naturally occurring agents, it is possible that their combined effect is important under pathological circumstances and this combined effect should not be overlooked in the search for single spasmogens of great potency. Before ascribing a pathologically important effect of F2alpha, either alone or in combination, evidence is required showing that doses effective in experiments are similar to the concentrations occurring during disease states and/or that vessels may become hypersensitive to F2alpha during such states.