Distribution and local differentiation of mast cells in the parenchyma of the forebrain

The pathogenic role of c-Kit+ mast cells in the spinal motor neuron-vascular niche in ALS

Degeneration of motor neurons, glial cell reactivity, and vascular alterations in the CNS are important neuropathological features of amyotrophic lateral sclerosis (ALS). Immune cells trafficking from the blood also infiltrate the affected CNS parenchyma and contribute to neuroinflammation. Mast cells (MCs) are hematopoietic-derived immune cells whose precursors differentiate upon migration into tissues. Upon activation, MCs undergo degranulation with the ability to increase vascular permeability, orchestrate neuroinflammation and modulate the neuroimmune response. However, the prevalence, pathological significance, and pharmacology of MCs in the CNS of ALS patients remain largely unknown. In autopsy ALS spinal cords, we identified for the first time that MCs express c-Kit together with chymase, tryptase, and Cox-2 and display granular or degranulating morphology, as compared with scarce MCs in control cords. In ALS, MCs were mainly found in the niche between spinal motor neuron somas and nearby microvascular elements, and they displayed remarkable pathological abnormalities. Similarly, MCs accumulated in the motor neuron-vascular niche of ALS murine models, in the vicinity of astrocytes and motor neurons expressing the c-Kit ligand stem cell factor (SCF), suggesting an SCF/c-Kit-dependent mechanism of MC differentiation from precursors. Mechanistically, we provide evidence that fully differentiated MCs in cell cultures can be generated from the murine ALS spinal cord tissue, further supporting the presence of c-Kit+ MC precursors. Moreover, intravenous administration of bone marrow-derived c-Kit+ MC precursors infiltrated the spinal cord in ALS mice but not in controls, consistent with aberrant trafficking through a defective microvasculature. Pharmacological inhibition of c-Kit with masitinib in ALS mice reduced the MC number and the influx of MC precursors from the periphery. Our results suggest a previously unknown pathogenic mechanism triggered by MCs in the ALS motor neuron-vascular niche that might be targeted pharmacologically.

Brain histamine modulates recognition memory: possible implications in major cognitive disorders

Several behavioural tests have been developed to study and measure emotionally charged or emotionally neutral memories and how these may be affected by pharmacological, dietary or environmental manipulations. In this review, we describe the experimental paradigms used in preclinical studies to unravel the brain circuits involved in the recognition and memorization of environmentally salient stimuli devoid of strong emotional value. In particular, we focus on the modulatory role of the brain histaminergic system in the elaboration of recognition memory that is based on the judgement of the prior occurrence of an event, and it is believed to be a critical component of human declarative memory. The review also addresses questions that may help improve the treatment of impaired declarative memory described in several affective and neuropsychiatric disorders such as ADHD, Alzheimer's disease and major neurocognitive disorder. LINKED ARTICLES: This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc.

Evidence for the modulation of nociception in mice by central mast cells

BACKGROUND

Hyperalgesia that develops following nerve ligation corresponds temporally and in magnitude with the number of thalamic mast cells located contralateral to the ligature. We tested the possibility that mast cells modulate nociception centrally, similar to their role in the periphery.

METHODS

We examined the central effect of two hyperalgesic compounds that induce mast cell degranulation and of stabilized mast cells using cromolyn.

RESULTS

Thermal hyperalgesia (tail flick) induced by nerve growth factor (NGF, a neurotrophic compound) and mechanical hyperalgesia (von Frey) induced by dynorphin A (1-17) (opioid compound) each correlated with the per cent of thalamic mast cells that were degranulated. Degranulation of these mast cells by the central injection of compound 48/80, devoid of neurotrophic or opioid activity, was sufficient to recapitulate thermal hyperalgesia. Stabilization of mast cells by central injections of cromolyn produced no analgesic effect on baseline tail flick or von Frey fibre sensitivity, but inhibited thermal hyperalgesia produced by compound 48/80 and tactile hyperalgesia induced by dynorphin and by Freund's complete adjuvant. Finally, chemical nociception produced by the direct activation of nociceptors by formalin (phase I) was not inhibited by centrally injected cromolyn whereas chemical nociception dependent on central sensitization (formalin-phase II and acetic acid-induced abdominal stretches) was.

CONCLUSIONS

These convergent lines of evidence suggest that degranulation of centrally located mast cells sensitizes central nociceptive pathways leading to hyperalgesia and tonic chemical sensitivity.

SIGNIFICANCE

Hyperalgesia induced by spinal nerve ligation corresponds temporally and in magnitude with degranulation of thalamic mast cells. Here, we provide evidence that hyperalgesia induced by NGF, formalin and dynorphin also may depend on mast cell degranulation in the CNS whereas cromolyn, a mast cell stabilizer, blocks these effects in mice.

Mast Cells Participate in Corneal Development in Mice

The development of the cornea, a highly specialized transparent tissue located at the anterior of the eye, is coordinated by a variety of molecules and cells. Here, we report that mast cells (MCs), recently found to be involved in morphogenesis, played a potentially important role in corneal development in mice. We show that two different waves of MC migration occurred during corneal development. In the first wave, MCs migrated to the corneal stroma and became distributed throughout the cornea. This wave occurred by embryonic day 12.5, with MCs disappearing from the cornea at the time of eyelid opening. In the second wave, MCs migrated to the corneal limbus and became distributed around limbal blood vessels. The number of MCs in this region gradually increased after birth and peaked at the time of eyelid opening in mice, remaining stable after postnatal day 21. We also show that integrin α4β7 and CXCR2 were important for the migration of MC precursors to the corneal limbus and that c-Kit-dependent MCs appeared to be involved in the formation of limbal blood vessels and corneal nerve fibers. These data clearly revealed that MCs participate in the development of the murine cornea.

A focus on mast cells and pain

Mast cells (MCs) are immunocytes with secretory functions that act locally in peripheral tissues to modulate local hemodynamics, nociceptor activation and pain. They are also able to infiltrate the central nervous system (CNS), especially the spinal cord and the thalamus, but their cerebral function remains an enigma. A role in regulating the opening of the blood-brain barrier has been proposed. Paracrine-like action of MCs on synaptic transmission might also signal a modulation of the nervous system by the immune system. In this review, we examine the link between MCs and nociceptive process, at the periphery as well as in the CNS.

Mast cells on the mind: new insights and opportunities

Mast cells (MCs) are both sensors and effectors in communication among nervous, vascular, and immune systems. In the brain, they reside on the brain side of the blood-brain barrier (BBB), and interact with neurons, glia, blood vessels, and other hematopoietic cells via their neuroactive prestored and newly synthesized chemicals. They are first responders, acting as catalysts and recruiters to initiate, amplify, and prolong other immune and nervous responses upon activation. MCs both promote deleterious outcomes in brain function and contribute to normative behavioral functioning, particularly cognition and emotionality. New experimental tools enabling isolation of brain MCs, manipulation of MCs or their products, and measurement of MC products in very small brain volumes present unprecedented opportunities for examining these enigmatic cells.

Serotonin of mast cell origin contributes to hippocampal function

In the central nervous system, serotonin, an important neurotransmitter and trophic factor, is synthesized by both mast cells and neurons. Mast cells, like other immune cells, are born in the bone marrow and migrate to many tissues. We show that they are resident in the mouse brain throughout development and adulthood. Measurements based on capillary electrophoresis with native fluorescence detection indicate that a significant contribution of serotonin to the hippocampal milieu is associated with mast cell activation. Compared with their littermates, mast cell-deficient C57BL/6 Kit(W-sh/W-sh) mice have profound deficits in hippocampus-dependent spatial learning and memory and in hippocampal neurogenesis. These deficits are associated with a reduction in cell proliferation and in immature neurons in the dentate gyrus, but not in the subventricular zone - a neurogenic niche lacking mast cells. Chronic treatment with fluoxetine, a selective serotonin reuptake inhibitor, reverses the deficit in hippocampal neurogenesis in mast cell-deficient mice. In summary, the present study demonstrates that mast cells are a source of serotonin, that mast cell-deficient C57BL/6 Kit(W-sh/W-sh) mice have disrupted hippocampus-dependent behavior and neurogenesis, and that elevating serotonin in these mice, by treatment with fluoxetine, reverses these deficits. We conclude that mast cells contribute to behavioral and physiological functions of the hippocampus and note that they play a physiological role in neuroimmune interactions, even in the absence of inflammatory responses.

Mast cell population in the frog brain: distribution and influence of thyroid status

In the developing frog brain, the majority of mast cells (MC) are distributed in the pia mater, and some immature MC are located adjacent to the blood capillaries in and around the neuropil. In the adult brain, MC are more numerous than in pre- and pro-metamorphic tadpoles; they are mainly located within the pia mater and are particularly numerous in the choroid plexuses. Many MC are found within the brain ventricles juxtaposed to the ependymal lining. MC are rarely observed in the brain parenchyma. In the adult brain, MC number is much higher than in the brain of post-metamorphic froglets. In the latter, MC number is nearly 2-fold over that found in the pre-metamorphic brain. Treatment of pre- and pro-metamorphic tadpoles with 3,5,3'-triiodothyronine (T(3)) and thyroxine (T(4)) stimulates overall larval development but does not induce a significant change in MC population within the brain. By contrast, treatment with 6-n-propyl-2-thiouracil (PTU) delays larval development and leads to a significant numerical increase of brain MC. In the adult, PTU treatment also has a similar effect whereas hypophysectomy causes a drastic decrease of MC population. The negative effects of hypophysectomy are successfully counteracted by a two-week replacement therapy with homologous pars distalis homogenate. In the adult frog, MC population seems to be refractory to thyroid hormone treatment. The present study on frog brain suggests that pituitary-thyroid axis may be involved in the regulation of MC frequency.

Mast cells as early responders in the regulation of acute blood-brain barrier changes after cerebral ischemia and hemorrhage

The inflammatory response triggered by stroke has been viewed as harmful, focusing on the influx and migration of blood-borne leukocytes, neutrophils, and macrophages. This review hypothesizes that the brain and meninges have their own resident cells that are capable of fast host response, which are well known to mediate immediate reactions such as anaphylaxis, known as mast cells (MCs). We discuss novel research suggesting that by acting rapidly on the cerebral vessels, this cell type has a potentially deleterious role in the very early phase of acute cerebral ischemia and hemorrhage. Mast cells should be recognized as a potent inflammatory cell that, already at the outset of ischemia, is resident within the cerebral microvasculature. By releasing their cytoplasmic granules, which contain a host of vasoactive mediators such as tumor necrosis factor-alpha, histamine, heparin, and proteases, MCs act on the basal membrane, thus promoting blood-brain barrier (BBB) damage, brain edema, prolonged extravasation, and hemorrhage. This makes them a candidate for a new pharmacological target in attempts to even out the inflammatory responses of the neurovascular unit, and to stabilize the BBB after acute stroke.

Mast cells in the amphibian brain during development

This is the first descriptive study of ontogenesis and anatomical distribution of mast cells in the developing brain of three different amphibian species. In the toad and the green frog, mast cells are preferentially located in: (i) the meningeal lining (pia mater), (ii) the choroid plexuses, both anterior and posterior, and (iii) the neuropil, in close association with the epithelial cell lining of blood vessels. It is only in the perennially aquatic African clawed frog that mast cells never appear inside brain ventricles and within the neuropil. Mast cells first become identifiable in brain of different species in different stages of development. While there are differences in the number of mast cells in different species at different stages of development, the number nearly doubles in all three species during the transition from pro-metamorphic stage of larval development to the peak of metamorphic climax. Furthermore, the number of mast cells is comparatively higher in the toad and remarkably lower in the fully aquatic Xenopus laevis, in which species the first appearance of identifiable mast cells during larval development occurs much later than in equivalent stages of development of the toad and the green frog. The secretory nature of mast cells can be assumed by the presence of cytoplasmic granules, which may show species-specific texture. Further experimental analyses are required to unveil the usefulness of mast cells in the amphibian brain.

Mast cell adhesion induces cytoskeletal modifications and programmed cell death in oligodendrocytes

In this paper we show that rat peritoneal mast cells (RPMC) adhere to rat oligodendrocytes (ODC) in culture and switch on a bi-directional signal affecting both adhering cell and its target. Following heterotypic interaction, RPMC release granule content and ODC show morphological changes and enter the apoptotic programme. Altogether, these findings indicate that the interaction of MC with ODC could play a role in the mechanism of CNS damage induced by the inflammatory reaction.

Mast cells populations fluctuate along the spinal dura mater of the developing rat

The present study reveals developmental changes in the number, the phenotype and the distribution pattern of mast cells (MCs) along the cervical, the thoracic and the lumbar parts of the spinal dura mater. Postnatal infiltration of spinal dura by MCs does not appear to follow a sequential developmental pattern and meningeal MCs are unevenly distributed along the various parts of the examined dura. At each spinal level, areas most densely populated by MCs are the dorsal dura and the dural sleeves of the dorsal (sensory) spinal roots The developmental time course of the total MCs number is characterized by significant fluctuations in all three parts examined, with notable increases at P1, P4, P21 and P60 (peak value) for the cervical part, at P1 (peak value), P7 and P21 for the thoracic part and at P1, P7 (peak value) and P30 for the lumbar part. At P180, MCs number declines to 56%, 33% and 13% of the peak values for the cervical, the thoracic and the lumbar part, respectively. However, a different developmental pattern is followed by each subpopulation of MCs identified on the basis of their staining characteristics, namely connective tissue type mast cells (CTMCs), mucosal type or cells with characteristics of immature mast cells (MTMCs) and mixed type MCs, in each part examined. The findings may be of importance in elucidating physiological and pathological processes in the dura mater and the vertebral column.

Distribution and heterogeneity of mast cells in female reproductive tract and ovary on different days of the oestrus cycle in Angora goats

The physiological distribution of mast cells (MCs) in the reproductive tract and ovary of 12 Angora goats was determined using light microscopic histochemical techniques. Uterus (corpus uteri and cornu uteri), uterine cervix, uterine tubes (isthmus and ampulla) and ovary samples were obtained by laparatomy from groups of animals during metoestrus, dioestrus and proestrus (days 5, 10 and 16 of the oestrous cycle). Tissues were fixed in Mota's fixative (basic lead acetate) for 48 h and embedded in paraffin. Six-micrometre-thick sections were stained with toluidine blue in 1% aqueous solution at pH 1.0 for 5 min and alcian blue-Safranin at pH 1.0 for 30 min. MCs were generally associated with blood vessels in all reproductive organs. In the uterus, they were concentrated mainly in the close of the uterine gland and deep stroma in the endometrium. Higher MC numbers were observed by toluidine blue staining in the uterus, uterine cervix and uterine tubes on days 10 (corpus uterine: 4.7 +/- 3.8 and cornu uterine: 4.9 +/- 3.5) and 16 (corpus uterine: 5.9 +/- 4.5 and cornu uterine: 5.4 +/- 2.4) of the oestrous cycle compared with day 5 (p < 0.05). Mast cells were not observed in the follicles, the corpus luteum and the underside of the surface epithelium of the ovarian cortex, but were observed in the interstitial cortical stroma and the ovarian medulla. In the ovary, MC numbers were significantly higher on day 16 of the oestrous cycle (cortex: 3.4 +/- 2.4 and medulla: 5.7 +/- 4.5, p < 0.05). Safranin-positive connective tissue MCs were not observed in the uterine tube on any occasion. These results indicate oestrous cycle-related changes in the number and location of MCs in goat reproductive organs.

Stroke induces histamine accumulation and mast cell degranulation in the neonatal rat brain

Inflammatory processes are a major cause of hypoxic-ischemic brain damage. The present study focuses on both the cerebral histamine system and mast cells in a model of transient focal ischemia induced by permanent left middle cerebral artery, and homolateral transient common carotid artery occlusion (50 minutes) in the P7 newborn rat. Immunohistochemical analysis revealed that ischemia induces histamine (HA) accumulation in the core of the infarct 6-12 h post-ischemia, and in the penumbra at 24-48 h, although in situ hybridization failed to detect any histidine decarboxylase gene transcripts in these regions. Immunohistochemical co-localization of HA with the MAP2 marker revealed that HA accumulates in neuronal cells before they degenerate, and is accompanied by a very significant increase in the number of mast cells at 12 h and 48 h of reperfusion. In mast cells, histamine immunoreactivity is detected at 2, 6 and 12 h after ischemia, whereas it disappears at 24 h, when a concomitant degranulation of mast cells is observed. Taken together, these data suggest that the recruitment of cerebral mast cells releasing histamine may contribute to ischemia-induced neuronal death in the immature brain.

The effects of viscero-somatic interactions on thalamic mast cell recruitment in cystitic rats

Mast cells accessing the brain parenchyma through the blood-brain barrier in healthy animals are limited to pre-cortical sensory relays - the olfactory bulb and the thalamus. We have demonstrated that unilateral repetitive stimulation of the abdominal wall generates asymmetry in midline thalamic mast cell (TMC) distribution in cyclophosphamide-injected rats, consisting of contralateral side-prevalence with respect to the abdominal wall stimulation. TMC asymmetry 1) was generated in strict relation with cystitis, and was absent in disease-free and mesna-treated animals, 2) was restricted to the anterior portion of the paraventricular pars anterior and reuniens nuclei subregion, i.e., the rostralmost part of the paraventricular thalamic nucleus, the only thalamic area associated with viscero-vagal and somatic inputs, via the nucleus of the solitary tract, and via the medial contingent of the spinothalamic tract, respectively, and 3) originated from somatic tissues, i.e., the abdominal wall where bladder inflammation generates secondary somatic hyperesthesia leading to referred pain in humans. Present data suggest that TMCs may be involved in thalamic sensory processes, including some aspects of visceral pain and abnormal visceral/somatic interactions.

Brain mast cell relationship to neurovasculature during development

Mast cells, derived from the hematopoietic stem cell, are present in the brain from birth. During development, mast cells occur in two locations, namely the pia and the brain parenchyma. The current hypothesis regarding their origin states that brain mast cells (or their precursors) enter the pia and access the thalamus by traveling along the abluminal wall of penetrating blood vessels. The population in the pia reaches a maximum at postnatal (PN) day 11, and declines rapidly thereafter. Chromatin fragmentation suggests that this cell loss is due to apoptosis. In contrast, the thalamic population expands from PN8 to reach adult levels at PN30. Stereological analysis demonstrates that mast cells home to blood vessels. More than 96% of mast cells are inside the blood-brain barrier, with ~90% contacting the blood vessel wall or its extracellular matrix. Mast cells express alpha4 integrins -- a potential mechanism for adhesion to the vascular wall. Despite the steady increase in the volume of microvasculature, at all ages studied, mast cells are preferentially located on large diameter vessels (>16 microm; possibly arteries), and contact only those maturing blood vessels that are ensheathed by astroglial processes. Mast cells not only home to large vessels but also maintain a preferential position at branch points, sites of vessel growth. This observation presents the possibility that mast cells participate in and/or regulate vasculature growth or differentiation. The biochemical and molecular signals that induce mast cell homing in the CNS is an area of active investigation.

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.

Knockout of the mu opioid receptor enhances the survival of adult-generated hippocampal granule cell neurons

Recent evidence suggests that mu opioid receptors (MOR) are key regulators of hippocampal structure and function. For example, exogenous MOR agonists morphine and heroin negatively impact hippocampal function and decrease adult hippocampal neurogenesis. Here we explored the role of MOR in the birth and survival of hippocampal progenitor cells by examining adult neurogenesis in mice that lack MOR. Adult male mice lacking exon 1 of MOR were injected with the S phase marker bromodeoxyuridine (BrdU) and killed either 2 hours or 4 weeks later to evaluate proliferating and surviving BrdU-immunoreactive (IR) cells, respectively, in the adult hippocampal granule cell layer. Wild-type (WT), heterozygote, and homozygote mice did not differ in the number of BrdU-IR cells at a proliferation time point. However, 4 weeks after BrdU injection, heterozygote and homozygote mice had 57% and 54% more surviving BrdU-IR cells in the hippocampal granule cell layer as compared with WT mice. A decrease in apoptosis in the heterozygote and homozygote mice did not account for the difference in number of surviving BrdU-IR cells since there were no alterations in number of pyknotic, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive, or activated caspase 3-IR cells compared with WT. In concordance with the increased numbers of granule cells maturing into neurons, heterozygote and homozygote mice had larger hippocampal granule cell layers and increased numbers of granule cells. These findings indicate that MOR may play a role in regulating progenitor cell survival and more generally encourage further exploration of how MOR activation can influence hippocampal structure and function.

Mast cells accumulate in the anogenital region of somatosensory thalamic nuclei during estrus in female mice

Mast cells are located in the mammalian thalamus where their numbers are sensitive to reproductive hormones. To evaluate whether differences between sexes and over the estrus cycle influence the nuclear distribution of mast cells in mice, we mounted a comprehensive analysis of their distribution in males compared to females and in females over the estrus cycle. Compared to males, mast cells were more numerous in the lateral intralaminar and posterior nuclei of females during estrus and in the ventral posterolateral (VPL) and medial geniculate nuclei during proestrus. During estrus, mast cells were especially concentrated in those regions within the VPL and posterior thalamic nuclei that receive somatosensory information from the anogenital region. Treatment of ovariectomized mice with estrogen increased the number and the percent of mast cells that were degranulated compared to that after ovariectomy alone, an effect that was most apparent in the lateral intralaminar, VPL and posterior nuclei. In estrogen-primed, ovariectomized females, progesterone delivered 5 h before tissue collection counteracted the effects of estrogen. Cromolyn, a mast cell stabilizer, injected centrally 1 h prior to and 24 h after estrogen in ovariectomized mice, prevented the increase in number of mast cells in the whole thalamus and in the intralaminar, VPL and posterior nuclei. This suggests that estrogen induces hyperplasia by a mechanism that involves mast cell degranulation. Based on the discrete anatomical location of mast cells in areas of somatosensory nuclei that receive anogenital input together with the temporal correspondence of these cells with estrus, mast cells are well situated to influence sensory input in females during mating.

Mast cells modulate maintained neuronal activity in the thalamus in vivo

Single cell unit activity of 187 neurons of 24 rats were analysed to study the possible involvement of intracranial mast cells on modifying thalamic neuronal activity. Mast cells were activated with microiontophoretical application of compound 48/80. This substance did not modify the firing rate of cortical or hippocampal neurons (no mast cells are found here), however it caused excitation (70% in females, 11% in males), or inhibition (7% in females, 33% in males) on thalamic neurons, possibly due to mast cell activation. In consecutive anatomical evaluation many partially or fully degranulated mast cells were found in the recorded thalamic areas.

Central nervous system neurons acquire mast cell products via transgranulation

Resting and actively degranulating mast cells are found on the brain side of the blood-brain barrier. In the periphery, exocytosis of mast cell granules results in the release of soluble mediators and insoluble granule remnants. These mast cell constituents are found in a variety of nearby cell types, acquired by fusion of granule and cellular membranes or by cellular capture of mast cell granule remnants. These phenomena have not been studied in the brain. In the current work, light and electron microscopic studies of the medial habenula of the dove brain revealed that mast cell-derived material can enter neurons in three ways: by direct fusion of the granule and plasma membranes (mast cell and neuron); by capture of insoluble granule remnants and, potentially, via receptor-mediated endocytosis of gonadotropin-releasing hormone, a soluble mediator derived from the mast cell. These processes result in differential subcellular localization of mast cell material in neurons, including free in the neuronal cytoplasm, membrane-bound in granule-like compartments or in association with small vesicles and the trans-Golgi network. Capture of granule remnants is the most frequently observed form of neuronal acquisition of mast cell products and correlates quantitatively with mast cells undergoing piecemeal degranulation. The present study indicates that mast cell-derived products can enter neurons, a process termed transgranulation, indicating a novel form of brain-immune system communication.

Differential effects of two analgesic drugs, morphine chlorhydrate and acetylsalicylic acid, on thalamic mast cell numbers in rat

Thalamic mast cells (TMCs), the only immunocytes known to infiltrate the brain in physiological conditions, respond to pharmacological agents including sumatriptan - a serotonergic anti-migraine agent - that increases their number. We analysed the effects of two other main analgesics: morphine chlorhydrate, a micro opioid agonist, and acetylsalicylic acid (ASA), a non-steroidal anti-inflammatory drug. All three drugs have specific modes of action, and morphine and ASA, unlike sumatriptan, are also known to interact with peripheral mast cells. Only ASA was effective in promoting TMC number decrease. TMCs, unlike other mast cells, do not express cyclooxygenase (COX) - the key enzyme in the production of prostanoids and the main site of action of ASA - thus dismissing a direct local cellular COX-mediated action. Direct TMC COX-independent mechanisms or effects mediated via distant populations of COX-positive cells such as platelets, leptomeningeal, endothelial and peripheral mast cells are thus probable. ASA, morphine and sumatriptan have distinct TMC effects, suggesting that the TMC number variations they induce are more likely to derive from systemic vasoactive actions than from pharmacological mechanisms devoted to pain relief.

Neuronal TGF-beta1 mediates IL-9/mast cell interaction and exacerbates excitotoxicity in newborn mice

Intraneocortical injection of ibotenate, a glutamate analog, in newborn mice produces damage mimicking lesions observed in human infants with cerebral palsy. Previous research using this model has demonstrated that pretreatment with IL-9, a Th2 cytokine, significantly exacerbated excitotoxic brain lesions. The goal of this study is to identify the underlying pathophysiological mechanism of lesion formation. Pretreatment with TGF-beta1 produced the same effects as IL-9 on ibotenate-induced lesions. IL-9 effects were abolished when a specific TGF-beta1 neutralizing antibody is administered at the same time. Real-time PCR, Western blot, and immunohistochemistry showed that pretreatment with IL-9 increased TGF-beta1 neocortical expression. In vitro studies using real-time PCR and immunocytochemistry demonstrated that neurons were a major contributor in IL-9-induced increase of TGF-beta1. In c-Kit mast cell-deficient mice, TGF-beta1 failed to exacerbate excitotoxic brain lesions, suggesting a key role of mast cells in TGF-beta1 effects. A specific inhibitor of mast cell degranulation and histamine receptor blockers abrogated TGF-beta1 effects on excitotoxic lesions, providing further evidence of mast cell involvement and the role of mast cell-derived histamine. Finally, in vitro studies using a mast cell line showed that TGF-beta1 increased histamine in the supernatant. In aggregate, these data support the notion that neuronal TGF-beta1 plays a key role in the IL-9/mast cell interaction, which leads to an exacerbation of neonatal excitotoxic damage through an increased extracellular histamine concentration. The identification of this pathway, if confirmed in human neonates, might have important implications for understanding and preventing cerebral palsy.

Evidence for serotonin influencing the thalamic infiltration of mast cells in rat

Serotonin (5-HT) is involved in neuroimmunomodulation. We analyzed the effects of sumatriptan, a 5-HT(1B/1D) receptor agonist, and ondansetron, a 5-HT(3) receptor antagonist, on thalamic mast cell (TMC) population, the only immunocytes known to infiltrate the brain in physiological conditions. Only sumatriptan was effective, significantly increasing TMC numbers versus controls, and especially those containing 5-HT. 5-HT(1B) receptors are concentrated in the median eminence on non-serotonergic axonal endings, probably hypothalamic terminal fibers, involved in hypothalamic-pituitary neuroendocrine modulating processes. TMC variations could reflect serotonergic actions on these fibers. TMCs would thus be cellular interfaces mediating immune action in the nervous system in relation with the hormonal status of the organism.

Selective response of various brain cell types during neurodegeneration induced by mild impairment of oxidative metabolism

Age-related neurodegenerative diseases are characterized by selective neuron loss, glial activation, inflammation and abnormalities in oxidative metabolism. Thiamine deficiency (TD) is a model of neurodegeneration induced by impairment of oxidative metabolism. TD produces a time-dependent, selective neuronal death in specific brain regions, while other cell types are either activated or unaffected. TD-induced neurodegeneration occurs first in a small, well-defined brain region, the submedial thalamic nucleus (SmTN). This discrete localization permits careful analysis of the relationship between neuronal loss and the response of other cell types. The temporal analysis of the changes in the region in combination with the use of transgenic mice permits testing of proposed mechanisms of how the interaction of neurons with other cell types produces neurodegeneration. Loss of neurons and elevation in markers of neurodegeneration are accompanied by changes in microglia including increased redox active iron, the induction of nitric oxide synthase (NOS) and hemeoxygenase-1, a marker of oxidative stress. Endothelial cells also show changes in early stages of TD including induction of intracellular adhesion molecule-1 (ICAM-1) and endothelial NOS. The number of degranulating mast cells also increases in early stages of TD. Alterations in astrocytes and neutrophils occur at later stages of TD. Studies with transgenic knockouts indicate that the endothelial cell changes are particularly important. We hypothesize that TD-induced abnormalities in oxidative metabolism promote release of neuronal inflammatory signals that activate microglia, astrocytes and endothelial cells. Although at early stages the responses of non-neuronal cells may be neuroprotective, at late phases they lead to entry of peripheral inflammatory cells into the brain and promote neurodegeneration.

The distribution of mast cells in the human area postrema

The topography and phenotype of mast cells in the human area postrema, together with correlation between mast-cell density and microvessel density (MVD), were analysed in 16 brains. Transverse serial sections of formalin-fixed, paraffin-embedded brainstems were stained with toluidine blue and alcian blue/safranin stainings, and with anti-tryptase and anti-CD31 monoclonal antibodies. The mean (+/- SD) numbers of mast cells per section were 1.3 +/- 0.8 and 1.2 +/- 0.7 with toluidine blue and alcian blue/safranin, respectively, whereas anti-tryptase monoclonal antibody showed a mean of 5.1 +/- 2.4 cells. Mast cells were alcian blue- and safranin-positive in 56%, because of the coexistence of low-sulphated (blue-staining) and high-sulphated (red-staining) granules. No significant linear correlation between mast-cell density (4.9 mm(-2)) and MVD (114.5 mm(-2)) was found (r(2) = 0.19, P = 0.09). Mast cells were frequently located close to blood vessels (55%) (33% to venules, 22% to arterioles), indicating that their products play a role in the regulation of blood flow and in vessel permeability in the area postrema. Mast cells were located subependymally in 44% and close to the dorsal aspect of the nucleus of the tractus solitarius in 31%, suggesting a subregional distribution.

Increase of rat medial habenular mast cell numbers by systemic administration of cyclophosphamide

Cyclophosphamide administration generates systemic toxicity having immune and nervous consequences. After focusing on nervous consequences by studying neuronal activity, we now consider cyclophosphamide impact on diencephalic mast cells as part of the brain immune system. Diencephalon, the ultimate sensory relay before neocortical processing, is the only brain structure containing mast cells. Single cyclophosphamide administration (100 mg/(kg 1 ml ip)) was performed in naturally behaving rats and diencephalic mast cell numbers were analyzed once all drug effects had developed (4 h postinjection). Significant increases were observed only in the medial habenular nucleus--bilaterally and especially in its caudal portion. Mast cell increase is temporally related to behavioral impairment and evoked neuronal activity in a restricted number of visceral/limbic extrathalamic structures. The medial habenular nucleus belongs to the limbic system involved in processing emotional reactions and regulation of the autonomic nervous system. Its involvement during toxic challenge is highly compatible with its presumed function in the maintenance of vital functions.

Induced maturation of frog mast cells by nerve growth factor during ontogenesis

The effect of nerve growth factor (NGF) on ontogenesis of frog mast cells was investigated in vivo by histochemical, morphometric, and ultrastructural analysis. Three groups of tadpoles at various stages of development were used. In the first group, the larvae received i.p. injections of 1 ng NGF/g; the second group received 10 ng NGF/g, while the control group received only the vehicle. The first recognizable mast cells arose symmetrically in the tongue at stage 26 of Witschi's standard table. At stages 26 and 29, the mast cell number in the NGF-injected tadpoles was significantly higher than the control group. From stage 29 onward, the mast cell number rapidly increased in all groups. No significant differences in mast cell number were observed between the control group and the NGF-injected groups at stages 31 and 33. Electron microscopy revealed that at metamorphic climax (stage 33), the mast cells in the NGF-treated groups were more mature than those in the control group. Therefore, nerve growth factor at early stages of tadpole development is likely to induce differentiation of mast cell precursors, while at later stages it is likely to induce maturation of immature mast cells. The close anatomical association between mast cells and perineurium, observed during nerve development, is intriguing. Already in the early stages of nerve development, the mast cells form a network around Schwann cell-axon complexes, together with the perineurial cells. At climax, the mast cells are located between the perineurial layers, suggesting that they may play a role in the tissue-nerve barrier of the perineurium. Nerve growth factor also seems to induce perineurial cell maturation.

Stimuli from conspecifics influence brain mast cell population in male rats

It is well established that mast cells occur within the brain of many species, and that the brain mast cell population is not static, but changes with the behavioral and physiological state of the animal. In this study, we tested whether exposure to conspecifics alters the number of brain mast cells in male rats, and then investigated the nature of stimuli influencing the changes observed in the number and localization of brain mast cells. Five days of cohabitation with an ovariectomized, estrogen-progesterone (OVX + EP)-treated female resulted in the largest number of thalamic mast cells, while pairing with such a female physically separated by a wire mesh or with a novel male produced a smaller, but significant increase over other pairings (OVX females for 5 days, OVX and OVX + EP females for 1 day, familiar or isolated males for 5 days). In all groups, mast cells were localized within specific dorsal thalamic nuclei, including the paraventricular nucleus, anterior nuclear group, or mediodorsal, ventroposterior, or medial geniculate nuclei. The results suggest that the behavioral and/or endocrine factors associated with cohabitation with conspecifics are sufficient to alter the number of brain mast cell-specific nuclei in the thalami of male rats and thus can provide targeted delivery of neuromodulators to specific regions of the brain that process information concerning the normal physiological state of the animal.

Deleterious effects of IL-9-activated mast cells and neuroprotection by antihistamine drugs in the developing mouse brain

Elevated mean IL-9 serum levels have been observed in human neonates who will later develop cerebral palsy. In earlier studies, using a newborn mouse model of excitotoxic lesions mimicking those described in human cerebral palsy, we found that IL-9 pretreatment exacerbated brain damage produced by intracerebral injections of the glutamatergic analog ibotenate. Among its different cell targets, the Th2 cytokine IL-9 is a mast cell growth and differentiation factor that can cause mast cells to release various substances including histamine. In the present study, we sought to determine whether the deleterious effects of IL-9 in our mouse model were mediated by mast cells through histamine release. All mouse pups were pretreated with intraperitoneal injections of IL-9 or saline between postnatal days (P) P1 and P5. Immunohistochemistry for murine mast cell protease-1 performed on P5 showed an increased density of labeled cells in the neopallium of IL-9-treated Swiss pups as compared with controls. Western blot analysis confirmed the increased murine mast cell protease-1 brain content of IL-9-treated Swiss mice. IL-9 pretreatment had no significant effect on ibotenate-induced excitotoxic brain lesions in mast cell-deficient P5 pups (WBB6F1/J kit(W/W-v)), whereas IL-9 exacerbated these lesions in the control littermates with normal mast cell populations. Finally, cromoglycate or antihistamine drugs significantly reduced ibotenate-induced brain lesions in IL-9-treated Swiss pups. Taken together, these data suggest that recruitment of cerebral mast cells with histamine release may contribute to the exacerbation of neonatal excitotoxic brain lesions produced by IL-9. Neuroprotective strategies targeting mast cells may be useful in some neonates at risk for cerebral palsy.

Brain-derived mast cells could mediate histamine-induced inhibition of food intake in neonatal chicks

In the present study, the effect of intracerebroventricular (i.c.v.) administration of histamine on food intake of neonatal chicks was examined over 2 h. Histamine (100, 200 or 400 nmol, respectively) was injected in the lateral ventricle of 2-day-old chicks, and cumulative food intakes were measured. i.c.v. injection of histamine significantly inhibited food intake in a dose-dependent manner. In addition, compound 48/80, which causes degranulation of mast cells and release of histamine, or thioperamide, which is an antagonist of the histamine H3 autoreceptor and increases histamine release from histaminergic nerve terminals, was injected i.c.v. to clarify whether mast cell- or neuron-derived histamine in the central nervous system of chicks is essential to the feeding inhibition. Central administration of compound 48/80 inhibited food intake with a dose-dependent manner, but thioperamide had no effect on feeding. An inhibitor of mast cell degranulation, sodium cromoglycate, somewhat attenuated food intake inhibited by compound 48/80. These results suggest that brain-derived mast cells could be a major source of histamine in the inhibition of food intake of neonatal chicks.

Mast cells migrate from blood to brain

It is well established that mast cells (MCs) occur within the CNS of many species. Furthermore, their numbers can increase rapidly in adults in response to altered physiological conditions. In this study we found that early postpartum rats had significantly more mast cells in the thalamus than virgin controls. Evidence from semithin sections from these females suggested that mast cells were transiting across the medium-sized blood vessels. We hypothesized that the increases in mast cell number were caused by their migration into the neural parenchyma. To this end, we purified rat peritoneal mast cells, labeled them with the vital dyes PKH26 or CellTracker Green, and injected them into host animals. One hour after injection, dye-filled cells, containing either histamine or serotonin (mediators stored in mast cells), were located close to thalamic blood vessels. Injected cells represented approximately 2-20% of the total mast cell population in this brain region. Scanning confocal microscopy confirmed that the biogenic amine and the vital dye occurred in the same cell. To determine whether the donor mast cells were within the blood-brain barrier, we studied the localization of dye-marked donor cells and either Factor VIII, a component of endothelial basal laminae, or glial fibrillary acidic protein, the intermediate filament found in astrocytes. Serial section reconstructions of confocal images demonstrated that the mast cells were deep to the basal lamina, in nests of glial processes. This is the first demonstration that mast cells can rapidly penetrate brain blood vessels, and this may account for the rapid increases in mast cell populations after physiological manipulations.