Gonadal steroids regulate the number and activational state of mast cells in the medial habenula

D2 dopamine receptor-mediated mechanisms of dopaminergic system modulation in in vivo and in vitro experimental models of migraine

The dopaminergic system is implicated in the pathophysiology of migraine. However, the underlying mechanisms remain unclear. We explored the effects and mechanisms of dopaminergic system modulation in the in vivo and in vitro rat models of migraine. Dopaminergic agonist apomorphine, D2 receptor antagonists metoclopramide and haloperidol and 5-HT3 receptor antagonist ondansetron alone and together were tested in nitroglycerin-induced migraine model, in vivo. Likewise, the combinations of drugs were also tested on basal calcitonin gene-related peptide (CGRP) release in vitro hemiskull preparations. Mechanical allodynia was tested by von Frey filaments. CGRP concentrations in trigeminovascular structures and in vitro superfusates and c-Fos levels in the brainstem were determined by enzyme-linked immunosorbent assay. Meningeal mast cells were evaluated with toluidine blue staining. Apomorphine further enhanced nitroglycerin-induced mechanical allodynia, brainstem c-fos expression, trigeminal ganglion and brainstem CGRP concentrations and meningeal mast cell degranulation, in vivo. Haloperidol completely antagonised all apomorphine-induced effects and also alleviated changes induced by nitroglycerin without apomorphine. Metoclopramide and ondansetron partially attenuated apomorphine- or nitroglycerin-induced effects. A combination of haloperidol and ondansetron decreased basal CGRP release, in vitro, whereas the other administrations were ineffective. Apomorphine-mediated dopaminergic activation exacerbated nitroglycerin-stimulated nociceptive reactions by further enhancing c-fos expression, CGRP release and mast cell degranulation in strategical structures associated with migraine pain. Metoclopramide partially attenuated the effects of apomorphine, most likely because it is also a 5-HT3 receptor antagonist. Haloperidol with pure D2 receptor antagonism feature appears to be more effective than metoclopramide in reducing migraine-related parameters in dopaminergic activation- and/or NTG-induced migraine-like conditions.

Mast Cell Population and Histamine Content in Hypothyroid Rat Tissues

Simple Summary

In this study, we investigated the putative regulatory role of the pituitary–thyroid axis on mast cells (MCs). We found that hypothyroidism resulted in a significant increase in number of MCs and the histamine content in the skin and exorbital lacrimal gland of Wistar rats, Rattus norvegicus. Furthermore, an increase in the percentage of degranulating MCs suggests that the thyroid status also influences the activation state of these cells.

Abstract

The morphological features and relative number of mast cells (MCs) were studied in the skin and exorbital lacrimal glands of hypothyroid Wistar rats, Rattus norvegicus. Hypothyroidism significantly increased the number of MCs (up to 4.5-fold) and histamine content (up to 50%) in the examined tissues. The magnitude of the increase in the number of MCs was greater in the cheek skin and exorbital lacrimal glands than in the back skin. In the skin, the MCs were mainly located within the hypodermis and closely associated with the blood vessels, nerve fascicles, and adipocytes. In the exorbital lacrimal gland, which is a seromucous gland located lateral to the cheek below the ear, the MCs were distributed in the connective tissue surrounding the acini. The secretory granules of MCs showed histochemical characteristics of connective tissue MCs. They were metachromatic with Toluidine blue and safranin positive with the Alcian blue/safranin reactions. Finally, a significant increase in degranulating MCs was observed in hypothyroid tissues, relative to euthyroid tissues. At the ultrastructural level, the MCs of euthyroid rats were predominantly non-degranulating (Stage I). In hypothyroid animals, numerous MCs showed partial degranulation (Stage II–III) or were in a stage of complete degranulation. Our results concerning the skin and exorbital lacrimal gland suggested that the thyroid status might be involved in regulating the frequency and activation state of MCs.

Functions of habenula in reproduction and socio-reproductive behaviours

Habenula is an evolutionarily conserved structure in the brain of vertebrates. Recent reports have drawn attention to the habenula as a processing centre for emotional decision-making and its role in psychiatric disorders. Emotional decision-making process is also known to be closely associated with reproductive conditions. The habenula receives innervations from reproductive centres within the brain and signals from key reproductive neuroendocrine regulators such as gonadal sex steroids, gonadotropin-releasing hormone (GnRH), and kisspeptin. In this review, based on morphological, biochemical, physiological, and pharmacological evidence we discuss an emerging role of the habenula in reproduction. Further, we discuss the modulatory role of reproductive endocrine factors in the habenula and their association with socio-reproductive behaviours such as mating, anxiety and aggression.

Decoding Mast Cell-Microglia Communication in Neurodegenerative Diseases

Microglia, resident immune cells of the central nervous system (CNS), play a pivotal role in immune surveillance and maintenance of neuronal health. Mast cells are also important resident immune cells of the CNS but they are underappreciated and understudied. Both microglia and mast cells are endowed with an array of signaling receptors that recognize microbes and cellular damage. As cellular sensors and effectors in the CNS, they respond to many CNS perturbations and have been implicated in neuroinflammation and neurodegeneration. Mast cells contain numerous secretory granules packaged with a plethora of readily available and newly synthesized compounds known as 'mast cell mediators'. Mast cells act as 'first responders' to a pathogenic stimuli and respond by degranulation and releasing these mediators into the extracellular milieu. They alert other glial cells, including microglia to initiate neuroinflammatory processes that culminate in the resolution of injury. However, failure to resolve the pathogenic process can lead to persistent activation, release of pro-inflammatory mediators and amplification of neuroinflammatory responses, in turn, resulting in neuronal dysfunction and demise. This review discusses the current understanding of the molecular conversation between mast cells and microglia in orchestrating immune responses during two of the most prevalent neurodegenerative diseases, namely Alzheimer's disease and Parkinson's disease. Here we also survey the potential emerging therapeutic approaches targeting common pathways in mast cells and microglia to extinguish the fire of inflammation.

Enduring neuroimmunological consequences of developmental experiences: From vulnerability to resilience

The immune system is crucial for normal neuronal development and function (neuroimmune system). Both immune and neuronal systems undergo significant postnatal development and are sensitive to developmental programming by environmental experiences. Negative experiences from infection to psychological stress at a range of different time points (in utero to adolescence) can permanently alter the function of the neuroimmune system: given its prominent role in normal brain development and function this dysregulation may increase vulnerability to psychiatric illness. In contrast, positive experiences such as exercise and environmental enrichment are protective and can promote resilience, even restoring the detrimental effects of negative experiences on the neuroimmune system. This suggests the neuroimmune system is a viable therapeutic target for treatment and prevention of psychiatric illnesses, especially those related to stress. In this review we will summarise the main cells, molecules and functions of the immune system in general and with specific reference to central nervous system development and function. We will then discuss the effects of negative and positive environmental experiences, especially during development, in programming the long-term functioning of the neuroimmune system. Finally, we will review the sparse but growing literature on sex differences in neuroimmune development and response to environmental experiences.

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The immune system is essential for development and function of the central nervous system (neuroimmune system)

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Environmental experiences can permanently alter neuroimmune function and associated brain development

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Altered neuroimmune function following negative developmental experiences may play a role in psychiatric illnesses

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Positive experiences can promote resilience and rescue the effects of negative experiences on the neuroimmune system

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The neuroimmune system is therefore a viable therapeutic target for preventing and treating psychiatric illnesses

Sex differences in the effects of early life stress exposure on mast cells in the developing rat brain

Early life stress leads to long lasting effects on behavior. Neuroimmune cells have been implicated as key mediators of experience-induced changes in brain and behavioral development, in that they are highly responsive to stress. Mast cells are one such type of neuroimmune cell, but little is known about their role in brain development or following early life stress. Here, we assessed the impact of three different early life stress exposure paradigms on mast cell dynamics in the developing brain of male and female rats, focusing on the hippocampus and hypothalamus, where most mast cells reside. We found that exposure to two weeks of chronic variable stress during gestation led to increased mast cell number and activation in the female offspring hypothalamus on the day of birth. Acute exposure to maternal separation stress on postnatal day (PN) 2 led to significant decreases in mast cells within the hypothalamus and hippocampus of females, but not males. In contrast, one week of exposure to brief daily maternal separation stress (e.g., handling), increased mast cell numbers in the female, but not male, hippocampus. We found significant sex differences in mast cell number and activation, including males having more mast cells than females in the hippocampus on the day of birth and males having significantly more degranulated mast cells on PN11. Thus, mast cells may be an unappreciated mediator of sex-specific brain development in response to early life perturbations.

Obesity-induced immune dysfunction and immunosuppression: TEM observation of visceral and subcutaneous lymph node microarchitecture and immune cell interactions

Background Inflammation, induced by excessive adiposity, links obesity to disease risk yet little attention has been devoted to the lymphoid tissues embedded within adipose tissue depots. Lymph nodes are the primary site for the development of protective immunity, hence any disease process that affects these tissues will also directly impact immunity. Here we examined how obesity alters secondary lymphatic tissue structure and encapsulated immune cells. Materials and methods Four-month-old C57BL/6 male mice were fed standard rodent chow or a Western high fat diet (HFD) for 6 months. Center regions of visceral and subcutaneous lymph nodes (SQLNS) were observed via transmission electron microscopy (TEM). Results Compared with chow, HFD-induced obesity deleteriously modified the structural microarchitecture and immune cell morphology of visceral and SQLNs. In HFD mice, fibroblastic reticular cells (FRCs) were dysregulated while laying among excessive amounts of disorganized collagen (C). In addition HFD lymph nodes contained a disproportionate amount of cellular debris from damaged or dead cells, increased sinus spacing and decreased immune cell interactions. Specifically, dendritic cells (DCs) that are necessary for adaptive immune response where embedded among extracellular debris with decreased pseudopodia. Similarly, the extraneous fibrous extracellular matrix (ECM) in HFD mice limited contact between lymphocytes (LCs) causing their microvilli extensions to decrease. Discussion Overall, excessive C production within lymph nodes, driven by diet-induced obesity, creates a physical barrier that impedes proper lymph flow and cellular communication. Obesity-induced disorganization of the immune cell guidance network interrupts immune cell adhesion and consequently inhibits travel within cortex regions needed for cell interactions, survival and proliferation.

Characterization of mast cell populations using different methods for their identification

Mast cells are ubiquitous throughout the human tissues and play an essential role in physiology and pathology. For evaluation of patients with pathological conditions, mast cells were primarily detected using metachromatic staining with toluidine blue. In the last decades, the staining arsenal of pathologists was enriched with enzyme histochemical and immunohistochemical methods, and it was established that depending on species and tissue localization mast cells are not similar both in appearance and function. The aim of this study was to characterize different mast cell populations using the up-to-date methods of their identification. We compared standard metachromatic method for mast cells with enzyme histochemical detection of chloroacetyl esterase and with immunohistochemical detection of tryptase and chymase in human and rodent tissues. Combination of these methods allowed us to assay quantitatively mast cell populations in different organs of humans and rodents. Furthermore, we assessed the appropriate implementation of each of these methods for mast cell identification in diagnostic labs.

PSA-NCAM in the posterodorsal medial amygdala is necessary for the pubertal emergence of attraction to female odors in male hamsters

During puberty, attention turns away from same-sex socialization to focus on the opposite sex. How the brain mediates this change in perception and motivation is unknown. Polysialylated neural cell adhesion molecule (PSA-NCAM) virtually disappears from most of the central nervous system after embryogenesis, but it remains elevated in discrete regions of the adult brain. One such brain area is the posterodorsal subnucleus of the medial amygdala (MePD). The MePD has been implicated in male sexual attraction, measured here as the preference to investigate female odors. We hypothesize that PSA-NCAM gates hormone-dependent plasticity necessary for the emergence of males' attraction to females. To evaluate this idea, we first measured PSA-NCAM levels across puberty in several brain regions, and identified when female odor preference normally emerges in male Syrian hamsters. We found that MePD PSA-NCAM staining peaks shortly before the surge of pubertal androgen and the emergence of preference. To test the necessity of PSA-NCAM for female odor preference, we infused endo-neuraminidase-N into the MePD to deplete it of PSAs before female odor preference normally appears. This blocked female odor preference, which suggests that PSA-NCAM facilitates behaviorally relevant, hormone-driven plasticity.

The production of alpha/beta and gamma/delta double negative (DN) T-cells and their role in the maintenance of pregnancy

The ability of the thymus gland to convert bone marrow-derived progenitor cells into single positive (SP) T-cells is well known. In this review we present evidence that the thymus, in addition to producing SP T-cells, also has a pathway for the production of double negative (DN) T-cells. The existence of this pathway was noted during our examination of relevant literature to determine the cause of sex steroid-induced thymocyte loss. In conducting this search our objective was to answer the question of whether thymocyte loss is the end product of a typical interaction between the reproductive and immune systems, or evidence that the two systems are incompatible. We can now report that "thymocyte loss" is a normal process that occurs during the production of DN T-cells. The DN T-cell pathway is unique in that it is mediated by thymic mast cells, and becomes functional following puberty. Sex steroids initiate the development of the pathway by binding to an estrogen receptor alpha located in the outer membrane of the mast cells, causing their activation. This results in their uptake of extracellular calcium, and the production and subsequent release of histamine and serotonin. Lymphatic vessels, located in the subcapsular region of the thymus, respond to the two vasodilators by undergoing a substantial and preferential uptake of gamma/delta and alpha/beta DN T- cells. These T- cells exit the thymus via efferent lymphatic vessels and enter the lymphatic system.The DN pathway is responsible for the production of three subsets of gamma/delta DN T-cells and one subset of alpha/beta DN T-cells. In postpubertal animals approximately 35 % of total thymocytes exit the thymus as DN T-cells, regardless of sex. In pregnant females, their levels undergo a dramatic increase. Gamma/delta DN T-cells produce cytokines that are essential for the maintenance of pregnancy.

Activation of protease-activated receptor 2 reduces glioblastoma cell apoptosis

Background

The pathogenesis of glioma is unclear. The disturbance of the apoptosis process plays a critical role in glioma growth. Factors regulating the apoptosis process are to be further understood. This study aims to investigate the role of protease activated receptor-2 (PAR2) in regulation the apoptosis process in glioma cells.

Results

The results showed that U87 cells and human glioma tissue expressed PAR2. Exposure to tryptase, or the PAR2 active peptide, increased STAT3 phosphorylation in the radiated U87 cells, reduced U87 cell apoptosis, suppressed the expression of p53 in U87 cells.

Conclusions

Activation of PAR2 can reduce the radiated U87 cell apoptosis via modulating the expression of p53. The results implicate that PAR2 may be a novel therapeutic target in the treatment of glioma.

The crustacean central nervous system in focus: subacute neurodegeneration induces a specific innate immune response

To date nothing is known about the subacute phase of neurodegeneration following injury in invertebrates. Among few clues available are the results published by our group reporting hemocytes and activated glial cells at chronic and acute phases of the lesion. In vertebrates, glial activation and recruitment of immunological cells are crucial events during neurodegeneration. Here, we aimed to study the subacute stage of neurodegeneration in the crab Ucides cordatus, investigating the cellular/molecular strategy employed 48 hours following ablation of the protocerebral tract (PCT). We also explored the expression of nitric oxide (NO) and histamine in the PCT during this phase of neurodegeneration. Three immune cellular features which seem to characterize the subacute phase of neurodegeneration were revealed by: 1) the recruitment of granulocytes and secondarily of hyalinocytes to the lesion site (inducible NO synthase- and histamine-positive cells); 2) the attraction of a larger number of cells than observed in the acute phase; 3) the presence of activated glial cells as shown by the round shaped nuclei and increased expression of glial fibrillary acidic protein. We suggest that molecules released from granulocytes in the acute phase attract the hyalinocytes thus moving the degeneration process to the subacute phase. The importance of our study resides in the characterization of cellular and biochemical strategies peculiar to the subacute stage of the neurodegeneration in invertebrates. Such events are worth studying in crustaceans because in invertebrates this issue may be addressed with less interference from complex strategies resulting from the acquired immune system.

Histamine from brain resident MAST cells promotes wakefulness and modulates behavioral states

Mast cell activation and degranulation can result in the release of various chemical mediators, such as histamine and cytokines, which significantly affect sleep. Mast cells also exist in the central nervous system (CNS). Since up to 50% of histamine contents in the brain are from brain mast cells, mediators from brain mast cells may significantly influence sleep and other behaviors. In this study, we examined potential involvement of brain mast cells in sleep/wake regulations, focusing especially on the histaminergic system, using mast cell deficient (W/W^v) mice. No significant difference was found in the basal amount of sleep/wake between W/W^v mice and their wild-type littermates (WT), although W/W^v mice showed increased EEG delta power and attenuated rebound response after sleep deprivation. Intracerebroventricular injection of compound 48/80, a histamine releaser from mast cells, significantly increased histamine levels in the ventricular region and enhanced wakefulness in WT mice, while it had no effect in W/W^v mice. Injection of H1 antagonists (triprolidine and mepyramine) significantly increased the amounts of slow-wave sleep in WT mice, but not in W/W^v mice. Most strikingly, the food-seeking behavior observed in WT mice during food deprivation was completely abolished in W/W^v mice. W/W^v mice also exhibited higher anxiety and depression levels compared to WT mice. Our findings suggest that histamine released from brain mast cells is wake-promoting, and emphasizes the physiological and pharmacological importance of brain mast cells in the regulation of sleep and fundamental neurobehavior.

Mast cell degranulation promotes ischemia-reperfusion injury in rat liver

BACKGROUND

Mast cells (MCs) play a role in ischemia-reperfusion (I/R) injury in many organs. However, a recent study found that MCs are not involved in I/R injury in isolated rat livers that were perfused only for 1 h. The purpose of this study is to reevaluate the role of MCs in hepatic I/R injury in rat.

MATERIALS AND METHODS

A warm hepatic I/R injury model of 1 h ischemia followed by 24 h of reperfusion was used. MC modulation was induced via cromolyn injection or a method called MC depletion using compound 48/80. The effects of MC modulation were evaluated by toluidine blue staining and assessment of mast cell tryptase in sera. The role of MCs in I/R injury was evaluated by hematoxylin and eosin staining graded by Suzuki criteria, alanine aminotransferase and aspartate aminotransferase levels in sera, and malondialdehyde levels in liver homogenates.

RESULTS

First, MC degranulation peaked after 2 h of reperfusion and liver damage peaked after approximately 6 h of reperfusion. Second, a method called MC depletion previously used in the skin with repeated injections of compound 48/80 worked similarly in the hepatic setting. Third, stabilization of MCs with cromolyn or depletion of MCs with compound 48/80 each decreased hepatic I/R injury. The most noticeable effects of cromolyn and compound 48/80 treatment were observed after approximately 6 h of reperfusion.

CONCLUSIONS

MC degranulation promotes hepatic I/R injury in rats.

Role of female sex hormones, estradiol and progesterone, in mast cell behavior

Female sex hormones have long been suspected to have an effect on mast cell (MC) behavior. This assumption is based on the expression of hormone receptors in MCs as well as on the fact that many MC-related pathophysiological alterations have a different prevalence in females than in males. Further, serum IgE levels are much higher in allergic female mice compared to male mice. Ovariectomized rats developed less airway inflammation compared to sham controls. Following estrogen replacement ovariectomized rats re-established airway inflammation levels’ found in intact females. In humans, a much higher asthma prevalence was found in women at reproductive age as compared to men. Serum levels of estradiol and progesterone have been directly correlated with the clinical and functional features of asthma. Around 30–40% of women who have asthma experienced worsening of their symptoms during the perimenstrual phase, the so-called perimenstrual asthma. Postmenopausal women receiving hormone replacement therapy have an increased risk of new onset of asthma. Beside, estrus cycle dependent changes on female sex hormones are related to changes on MC number in mouse uterine tissue and estradiol and progesterone were shown to induce uterine MC maturation and degranulation. We will discuss here the currently available information concerning the role of these female sex hormones on MC behavior.

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.

Spontaneous locomotor activity correlates with the degranulation of mast cells in the meninges rather than in the thalamus: disruptive effect of cocaine

Mast cells are located in the central nervous system (CNS) of many mammals and stress induces their degranulation. We postulated that mast cells are associated with wakefulness and stimulatory tone in the CNS, as reflected by spontaneous motor activity. Because stress also precipitates drug-seeking behavior in cocaine addicts, we also postulated that cocaine manifests its effects through this relationship. We investigated the influence of single and repeated injections of cocaine on circulating corticosterone, motor activity and degranulation of mast cells in both the thalamus and meninges of mice. Mice were subjected to 5 consecutive days of cocaine or saline followed by a single injection of cocaine or saline 11 days later. Spontaneous locomotor activity was measure for 1h after the final injection before death. Neither a single injection nor prior treatment with cocaine increased motor activity compared to saline-injected controls, however, repeated administration of cocaine induced a significant sensitization to its behavioral effect when delivered 11 days later. In mice that received only saline, motor activity correlated positively with mast cell degranulation in the meninges but not in the thalamus. Cocaine, regardless of the treatment schedule, disrupted this correlation. The concentration of corticosterone did not differ amongst groups and did not correlate with either behavior or mast cell parameters in any group. The correlation between behavioral activity and the mast cell degranulation in the meninges suggests that these parameters are linked. The disruptive effect of cocaine on this relationship indicates a role downstream from mast cells in the regulation of motor activity.

Cell secretion mediated by granule-associated vesicle transport: a glimpse at evolution

Regulated secretion allows extrusion of cell products stored in specialized membrane-bound organelles called secretory granules or secretory vesicles. Regulated secretion provides basic functions in living organisms, and in a phylogenetic perspective, it is recognizable in the most primitive eukaryotic forms. This article is an attempt to trace the evolutionary history of a special type of secretory pattern, which has been referred to as vesicle-mediated degranulation or piecemeal degranulation (PMD). First described in the early 70s of the last century in inflammatory cells, such as the basophils, mast cells, and eosinophils, this regulated secretory route has subsequently been recognized in endocrine cells, in particular in the chromaffin cells of the adrenal medulla. This vesicle-mediated degranulation is held to mobilize small and specific aliquots of granule-associated material for selective paracrine or endocrine transport to the cell exterior. PMD has been identified in many vertebrate classes. By contrast, no data are available for invertebrates. We speculate that this pattern of cell secretion emerged early in phylogenesis, when the first metazoans appeared. In this review article, we will first revise the concept of vesicle-mediated degranulation in the light of the most recent experimental discoveries and theoretical implications. Then, the distribution of this secretory mode among vertebrates and its molecular basis will be highlighted. Finally, the potential occurrence of PMD in invertebrates, its biological significance from an evolutionary perspective and the future direction of investigations will be briefly sketched.

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.

Brain mast cells link the immune system to anxiety-like behavior

Mast cells are resident in the brain and contain numerous mediators, including neurotransmitters, cytokines, and chemokines, that are released in response to a variety of natural and pharmacological triggers. The number of mast cells in the brain fluctuates with stress and various behavioral and endocrine states. These properties suggest that mast cells are poised to influence neural systems underlying behavior. Using genetic and pharmacological loss-of-function models we performed a behavioral screen for arousal responses including emotionality, locomotor, and sensory components. We found that mast cell deficient Kit(W-sh/W-sh) (sash(-/-)) mice had a greater anxiety-like phenotype than WT and heterozygote littermate control animals in the open field arena and elevated plus maze. Second, we show that blockade of brain, but not peripheral, mast cell activation increased anxiety-like behavior. Taken together, the data implicate brain mast cells in the modulation of anxiety-like behavior and provide evidence for the behavioral importance of neuroimmune links.

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.

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.

Connections of thalamic modulatory centers to the vocal control system of the zebra finch

The vocal control system of zebra finches shows auditory gating in which neuronal responses to the individual bird's own song vary with behavioral states such as sleep and wakefulness. However, we know neither the source of gating signals nor the anatomical connections that could link the modulatory centers of the brain with the song system. Two of the song-control nuclei in the forebrain, the HVC (used as the proper name) and the interfacial nucleus of the nidopallium, both show auditory gating, and they receive input from the uvaeform nucleus (Uva) in the thalamus. We used a combination of anterograde and retrograde tracing methods to show that the dorsal part of the reticular formation and the medial habenula (MHb) project to the Uva. We also show by choline acetyl transferase immunohistochemistry that the MHb is cholinergic and sends cholinergic fibers to the Uva. Our findings suggest that the Uva might serve as a hub to coordinate neuromodulatory input into the song system.

Unilateral spinal nerve ligation leads to an asymmetrical distribution of mast cells in the thalamus of female but not male mice

Mast cells are restricted to the leptomeninges and thalamus of healthy mice. These populations are increased by stress and highly sensitive to reproductive hormones. To examine the influence of nociception, a form of stress, on thalamic mast cells, we ligated the left fifth lumbar spinal nerve of male and female mice to induce hyperalgesia. Two, 7 and 14 days later, mice were killed and thalami examined histologically using toluidine blue stain. The total number of thalamic mast cells was not influenced by ligation of the spinal nerve compared to sham-operation in either female or male mice. However, in females, the percent of thalamic mast cells located on the side of the thalamus contralateral to the ligation was greater on days 2 and 7, coincident with mechanical hyperalgesia. At these times, areas in which mast cells were most dense contralateral to nerve-injury included the posterior (Po) and lateral geniculate (LG) nuclei compared to their symmetrical distribution in sham-operated mice. These data suggest that local nociceptive signals to each side of the thalamus rather than stress hormones influence the location of mast cells during the development of allodynia and hyperalgesia. In addition, both hyperalgesia and mast cell distribution induced by nerve-ligation differ in females compared to males, reflecting a novel neuroimmune response to pain within the CNS.

Hormone replacement therapy and obstructive airway diseases

Controversy exists as to the role of female reproductive hormones in asthma and COPD and, specifically, the effect of hormone replacement therapy (HRT) on these disorders. The differential incidence of asthma over the menstrual life cycle suggests an effect of female reproductive hormones on asthma; less data are available for COPD. Estrogen and progesterone have protean effects at the cellular level, consistent with potentially harmful and beneficial effects in lung disease. Large epidemiologic studies show an increased risk of development of asthma with the use of HRT but no consistent effects on COPD. Clinical and epidemiologic studies of exacerbations are limited, but suggest either a harmful effect or no effect of HRT on exacerbations of asthma and COPD. HRT appears to increase the risk of development of asthma but is not associated with the loss of lung function characteristic of COPD. Because the development of asthma is rare in postmenopausal women, the absolute increase in risk among women without asthma is modest. Physicians may wish to avoid HRT therapy in patients with difficult to control asthma and COPD. Clinical decisions to start or continue HRT among women without asthma or COPD should be based on the effects of HRT on more common diseases such as cardiovascular disease, breast cancer and osteoporosis, non-vertebral fractures and colon cancer.

Mast cells in the rat brain synthesize gonadotropin-releasing hormone

Mast cells occur in the brain and their number changes with reproductive status. While it has been suggested that brain mast cells contain the mammalian hypothalamic form of gonadotropin-releasing hormone (GnRH-I), it is not known whether mast cells synthesize GnRH-I de novo. In the present study, mast cells in the rat thalamus were immunoreactive to antisera generated against GnRH-I and the GnRH-I associated peptide (GAP); mast cell identity was confirmed by the presence of heparin, a molecule specific to mast cells, or serotonin. To test whether mast cells synthesize GnRH-I mRNA, in situ hybridization was performed using a GnRH-I cRNA probe, and the signal was identified as being within mast cells by the binding of avidin to heparin. GnRH-I mRNA was also found, using RT-PCR, in mast cells isolated from the peritoneal cavity. Given the function of GnRH-I in the regulation of reproduction, changes in the population of brain GnRH-I mast cells were investigated. While housing males with sexually receptive females for 2 h or 5 days resulted in a significant increase in the number of brain mast cells, the proportion of mast cells positive for GnRH-I was similar to that in males housed with a familiar male. These findings represent the first report showing that mast cells synthesize GnRH-I and that the mast cell increase seen in a reproductive context is the result of a parallel increase in GnRH-I positive and non-GnRH-I positive mast cells.

Expression of androgen receptor mRNA in the late embryonic and early posthatch zebra finch brain

Zebra finch males sing and females do not, and the underlying neural circuitry in males is more developed than that in females. Sex steroid hormones influence the development of sex differences in this circuitry, including differences in androgen receptor (AR) expression, although the role of androgens has been controversial. We isolated a cDNA encoding a portion of the zebra finch AR and used in situ hybridization to examine the spatiotemporal pattern of AR mRNA expression in the brain during late embryonic development and at hatching. We detected AR mRNA in all the major subdivisions of the brain as early as embryonic day 10. No qualitative sex differences in AR mRNA expression patterns were observed. Cells lining the ventral arm of the lateral telencephalic ventricles expressed AR mRNA on embryonic day 11 and posthatching day 1, as did cells lining the third ventricle at all three developmental stages examined, suggesting that androgens may play a role in early stages of cellular proliferation, migration, or differentiation. AR mRNA was also detected in the hippocampus, neostriatum, septum, ventromedial archistriatum, hypothalamic regions, dorsal mesencephalon, and in and around the brainstem nucleus tracheosyringealis. Our results suggested that androgens act early in neural development and therefore may contribute to the process of sexual differentiation.

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.

Mast cells in Wallerian degeneration: morphologic and ultrastructural changes

The morphologic and ultrastructural changes of mast cells were followed in degenerating distal and regenerating proximal stumps of frog brachial nerve during Wallerian degeneration. Quantitative analysis included determination of both number and size of mast cells. The mast cell response to injury consisted of an early and a late phase. In the early phase, there was an increase in mast cell numbers in the proximal site of the lesion and a release of Alcian blue material consistent with mediator release. This phase of mast cell activation may be related, through the secretion of biogenic agents such as heparin and histamine, to the increase of endoneurial vessel size and vascular permeability, providing access for macrophages and mast cell precursors. The later phase, which peaked at 40 days after transection in the degenerating distal stump, consisted in the degranulation of the mast cells. These mast cells, closely associated with macrophages and degenerating Schwann cells, released secretory granules into the endoneurial microenvironment. These degranulating mast cells, through the released acid hydrolases, may contribute along with macrophages and Schwann cells, to the degradation of myelin debris. At the same time, mast cells appeared filled with granular content in the regenerating proximal segment. Therefore, we suggest that mast cells in peripheral nerves may play an important role in nerve degenerating and regenerating mechanisms through the secretion of diffusible molecules.