Site-Specific and Temporal Effects of Apraglutide, a Novel Long-Acting Glucagon-Like Peptide-2 Receptor Agonist, on Intestinal Growth in Mice

Long-acting glucagon-like peptide-2 receptor (GLP-2R) agonists are well-established to increase intestinal growth in rodents and, most notably, humans with short bowel syndrome. Most of the trophic effects of GLP-2R agonists are reported to be mediated through increased growth of the crypt-villus axis, resulting in enhanced mucosal mass and improved intestinal function. The present study examined the effects of apraglutide, a novel GLP-2R agonist, on the growth of the small intestine and colon after 3, 7, and 10 weeks of treatment in male and female mice. Apraglutide (3 mg/kg; three times per week) significantly increased small intestinal weight (P < 0.001) and length (P < 0.001) after 3 weeks of administration, with a further increase in effectiveness after 10 weeks (P < 0.01). Crypt depth and villus height were both markedly increased after 3 weeks of apraglutide administration (P < 0.001) but did not show any further increase with duration of treatment, whereas crypt number and intestinal circumference were increased after 7 and 10 weeks (P < 0.01) but not after 3 weeks of apraglutide treatment. Both the weight and the length of the colon were also enhanced by apraglutide treatment for 3 weeks (P < 0.001), and these effects were maintained but did not improve further with continued apraglutide administration. The results of this study demonstrate that the novel, long-acting GLP-2R agonist, apraglutide, demonstrates an unexpected marked ability to increase intestinal length as well as exert time- and location-dependent specificity in its intestinotrophic actions. SIGNIFICANCE STATEMENT: The novel long-acting glucagon-like peptide 2 receptor agonist, apraglutide, enhances intestinal weight as well as intestinal length in a time- and site-dependent fashion.

Modulation of the Contact Hypersensitivity Response by Æ-941 (Neovastat), a Novel Antiangiogenic Agent

Background:

Æ-941 (Neovastat) is an angiogenesis inhibitor noted to have antiinflammatory properties.

Objective:

We tested Neovastat in a contact hypersensitivity (CHS) model to determine the mechanism of action of its antiinflammatory effects.

Methods:

Neovastat was orally administered (200 mg/kg/day) during the sensitization and challenge phases of a murine CHS assay and inflammatory responses were measured. Subsequent assays were performed on mice treated with Neovastat or Cortisone (120 mg/kg/day, IP) and differential mRNA expression of several pro- and antiinflammatory cytokines was quantified using RT-PCR.

Results:

Neovastat decreased inflammation by 39% when administered during sensitization but did not alter the CHS response when given during the challenge phase. Neovastat significantly induced IL-10 expression in skin and skin-draining lymph nodes (49% and 45%, respectively) and decreased IFNγ expression in the lymph nodes (35%).

Conclusion:

Antiinflammatory effects of Neovastat observed in CHS could be linked to modulation of cytokines early in the sensitization phase.

Ultrastructural evidence of brain mast cell activation without degranulation in monkey experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is an animal model for the human demyelinating disease multiple sclerosis (MS). Increased permeability of the blood-brain barrier (BBB) precedes the development of clinical or pathologic findings in MS and may be induced by perivascular brain mast cells secreting vasoactive and proinflammatory molecules. Brain mast cells were investigated ultrastructurally in acute EAE of the non-human primate common marmoset Callithrix jacchus, which develops a mild neurologic relapsing-remitting course. Control diencephalic samples contained perivascular mast cells with mostly intact electron dense granules. In contrast, EAE samples had marked demyelination and mast cells with numerous altered secretory granules; their electron dense content varied in amount and texture with a "honeycomb" or "target" appearance, but without degranulation. These changes were evident even before the development of any clinical symptoms and suggest that brain mast cells may be involved in EAE, and possibly MS, through a unique process that may involve selective secretion of molecules able to disrupt the BBB.

Modulation of the contact hypersensitivity response by AE-941 (Neovastat), a novel antiangiogenic agent

BACKGROUND

AE-941 (Neovastat) is an angiogenesis inhibitor noted to have antiinflammatory properties.

OBJECTIVE

We tested Neovastat in a contact hypersensitivity (CHS) model to determine the mechanism of action of its antiinflammatory effects.

METHODS

Neovastat was orally administered (200 mg/kg/day) during the sensitization and challenge phases of a murine CHS assay and inflammatory responses were measured. Subsequent assays were performed on mice treated with Neovastat or Cortisone (120 mg/kg/day, IP) and differential mRNA expression of several pro- and antiinflammatory cytokines was quantified using RT-PCR.

RESULTS

Neovastat decreased inflammation by 39% when administered during sensitization but did not alter the CHS response when given during the challenge phase. Neovastat significantly induced IL-10 expression in skin and skin-draining lymph nodes (49% and 45%, respectively) and decreased IFNgamma expression in the lymph nodes (35%).

CONCLUSION

Antiinflammatory effects of Neovastat observed in CHS could be linked to modulation of cytokines early in the sensitization phase.

Hydroxyzine inhibits experimental allergic encephalomyelitis (EAE) and associated brain mast cell activation

Experimental allergic encephalomyelitis (EAE) has been used as an animal model for the human demyelinating disease multiple sclerosis (MS). In acute MS or EAE, early disruption in the integrity of the blood-brain-barrier (BBB) precedes brain infiltration by inflammatory cells or any clinical evidence of disease. BBB permeability could be affected by vasoactive mediators and cytokines released from perivascular brain mast cells. We investigated the number and degree of activation of brain mast cells in EAE and the effect of the heterocyclic histamine-1 receptor antagonist hydroxyzine, a piperazine compound known to also block mast cells. Acute EAE was induced in Lewis rats by immunization with whole guinea pig spinal cord homogenate and complete Freund's adjuvant (CFA). A second group of animals were treated orally with hydroxyzine for one day before immunization and then continuously for 14 days. Control rats were treated with CFA or hydroxyzine alone. The clinical progression of EAE was assessed on days 10, 12 and 14 after immunization. The number of metachromatic mast cells and the degree of degranulation was assessed in the thalamus with light microscopy. At day 14, there was a three-fold increase in the number of brain mast cells with EAE, as compared to controls. These cells were positive for the immunoglobulin E binding protein (FcepsilonRI), while those from control rats were not. Over 40% of all thalamic mast cells studied in EAE showed partial staining or extruded secretory granule indicative of secretion. Hydroxyzine treatment inhibited (p<0.05) the progression and severity of EAE by 50% and the extent of mast cell degranulation by 70% (p<0.05). These findings indicate that brain mast cells are associated with EAE development and that inhibition of their activation correlates positively with the clinical outcome.

Morphological and functional demonstration of rat dura mater mast cell-neuron interactions in vitro and in vivo

Mast cells derive from a distinct bone marrow precursor and mature in tissues under the influence of stem cell factor, nerve growth factor (NGF) and certain interleukins. Intracranial mast cells first appear in the meninges and are located perivascularly close to neurons. They can be activated by antidromic stimulation of the trigeminal nerve, as well as by acute immobilization stress. Substance P (SP) and corticotropin-releasing hormone (CRH) are particularly potent in stimulating mast cell release of vasoactive, inflammatory and nociceptive molecules. These findings have suggested that mast cells may be involved in neuroinflammatory conditions, such as migraines. In this study, dura mast cells were shown to have characteristics of connective tissue mast cells (CTMC) as they contained histamine, heparin and rat mast cell protease I (RMCP-I). Mast cells were localized close to SP-positive neurons immunocytochemically and mast cell-neuron contacts were also documented using scanning electron microscopy. Dura stimulated by SP and carbachol in situ released histamine. Preincubation of dura with estradiol slightly augmented histamine release by SP, an effect possibly mediated through estrogen receptors identified on dura mast cells. Acute stress by immobilization led to dura mast cell degranulation which was prevented by pretreatment with a neutralizing antibody to CRH or a CRH receptor antagonist. The present results further clarify the biology of intracranial mast cells and support their involvement in the pathophysiology of migraines which are precipitated or worsened by stress.

Expression of functional major histocompatibility complex class II molecules on HMC-1 human mast cells

Mast cells hold a key position in the defensive mechanisms against exogenous intruders. In this study, we investigated whether human mast cells express functional major histocompatibility complex (MHC) class II molecules that can transduce endogenous signals and present staphylococcal enterotoxin A (SEA) to T cells. Similar to HMC-1 human mast cell line, umbilical cord blood-derived mast cells express HLA-DR, -DP and -DQ molecules on their surface. MHC class II molecules expressed on HMC-1 cells bind significantly the SEA (a natural MHC class II ligand), and their ligation with specific mAbs or with SEA, leads ultrastructural changes, suggesting their degranulation. Recognition of SEA-bound MHC class II molecules on HMC-1 mast cells by the T cell receptor of K25 cells, an SEA-specific murine T cell hybridoma, triggers significant IL-2 secretion by these T cell hybridomas. Hence, our data point out the expression of functional MHC class II molecules on human mast cells, reinforcing the implication of these cells in the defense mechanisms of acquired immunity.

Mast cell specific proteases in rat brain: changes in rats with experimental allergic encephalomyelitis

Mast cell populations were identified within brain parenchyma by their specific proteases, using antibodies for immunohistochemistry and ELISAs, and riboprobes were developed for in situ hybridisation. Connective tissue mast cells expressing rat mast cell protease I (RMCPI) mRNA and immunoreactivity were observed in thalamus and showed no degranulation at 3, 8 and 13 days after induction of experimental allergic encephalomyelitis (EAE). Mucosal-like mast cells were clearly demonstrated in control rats by measuring RMCPII and by visualising cells expressing RMCPII mRNA and immunoreactivity. At day 13, but not 3 and 8 post immunisation, the number of RMCPII-expressing cells markedly increased in the EAE-induced group, mainly within brainstem and spinal cord close to inflammed blood vessels. The markers of histaminergic neurons were marginally affected 13 days after immunisation and the increase of [3H] histamine synthesis elicited by the H3-receptor antagonist, thioperamide, was not modified in any region of the brain. It is concluded that the cerebral RMCPII-expressing mast cells could play a role during EAE.

Neuromuscular development in the avian paralytic mutant crooked neck dwarf (cn/cn): further evidence for the role of neuromuscular activity in motoneuron survival

Neuromuscular transmission and muscle activity during early stages of embryonic development are known to influence the differentiation and survival of motoneurons and to affect interactions with their muscle targets. We have examined neuromuscular development in an avian genetic mutant, crooked neck dwarf (cn/cn), in which a major phenotype is the chronic absence of the spontaneous, neurally mediated movements (motility) that are characteristic of avian and other vertebrate embryos and fetuses. The primary genetic defect in cn/cn embryos responsible for the absence of motility appears to be the lack of excitation-contraction coupling. Although motility in mutant embryos is absent from the onset of activity on embryonic days (E) 3-4, muscle differentiation appears histologically normal up to about E8. After E8, however, previously separate muscles fuse or coalesce secondarily, and myotubes exhibit a progressive series of histological and ultrastructural degenerative changes, including disarrayed myofibrils, dilated sarcoplasmic vesicles, nuclear membrane blebbing, mitochondrial swelling, nuclear inclusions, and absence of junctional end feet. Mutant muscle cells do not develop beyond the myotube stage, and by E18-E20 most muscles have almost completely degenerated. Prior to their breakdown and degeneration, mutant muscles are innervated and synaptic contacts are established. In fact, quantitative analysis indicates that, prior to the onset of muscle degeneration, mutant muscles are hyperinnervated. There is increased branching of motoneuron axons and an increased number of synaptic contacts in the mutant muscle on E8. Naturally occurring cell death of limb-innervating motoneurons is also significantly reduced in cn/cn embryos. Mutant embryos have 30-40% more motoneurons in the brachial and lumbar spinal cord by the end of the normal period of cell death. Electrophysiological recordings (electromyographic and direct records form muscle nerves) failed to detect any differences in the activity of control vs. mutant embryos despite the absence of muscular contractile activity in the mutant embryos. The alpha-ryanodine receptor that is genetically abnormal in homozygote cn/cn embryos is not normally expressed in the spinal cord. Taken together, these data argue against the possibility that the mutant phenotype described here is caused by the perturbation of a central nervous system (CNS)-expressed alpha-ryanodine receptor. The hyperinnervation of skeletal muscle and the reduction of motoneuron death that are observed in cn/cn embryos also occur in genetically paralyzed mouse embryos and in pharmacologically paralyzed avian and rat embryos. Because a primary common feature in all three of these models is the absence of muscle activity, it seems likely that the peripheral excitation of muscle by motoneurons during normal development is a major factor in regulating retrograde muscle-derived (or muscle-associated) signals that control motoneuron differentiation and survival.

Growth factors mediate glucocorticoid receptor function and dexamethasone-induced regression of osteoblastic lesions in hormone refractory prostate cancer

We investigated the ability of important regulators of osteoblast function, such as insulin-like growth factor I (IGF-I), transforming growth factor beta 1 (TGF beta 1), and urokinase-type plasminogen activator (uPA) to act as mediators in cell-cell interactions between osteoblast-like cells and metastatic prostate cancer cells, in vitro. In addition, we assessed whether these growth substances can (a) mediate glucocorticoid receptor (GR) function and (b) be implicated in dexamethasone-induced regression of osteoblastic tumors. Exogenous IGF-I, rat/human uPA, and PA-III (rat)/PC-3 (human) prostate cancer cells conditioned media (CM) stimulated the proliferation of rat (UMR 106 cells) and human (MG-63 cells) osteosarcoma cells. This mitogenic activity was completely neutralized by anti-IGF-I specific antibody. In addition, dexamethasone decreased cell growth, up regulated TGF beta 1 mRNA, and down regulated uPA mRNA expression in prostate cancer cells. Furthermore, it inhibited cell growth by activating latent-TGF beta 1 in osteoblast-like cells. In addition, dexamethasone down regulated the expression of IGF-I mRNA in osteoblast-like cells. Therefore, it is conceivable that uPA, TGF beta 1 and IGF-I mediate at least in part cell-cell interactions and GR function in osteoblastic metastases. Conceivably, regression of the osteoblastic tumors produced by high-dose dexamethasone treatment in hormone-refractory prostate cancer patients is been mediated by differential regulation of growth factors, locally.

Mast cell-tumor cell interactions: for or against tumour growth and metastasis?

This review comes up with the possible association between mast cells and tumour progression and summarizes some of the most recent data on the subject. The accumulation of mast cells around tumour areas is a very old observation. However, the functional significance of such phenomenon is a subject of controversy because of contradictory experimental data. In this review, two hypotheses are suggested. The first, refers on the possibility that the accumulation of mast cells is part of a general immunological host-defense reaction since, mast cells have been shown to be cytotoxic for some tumours (especially those sensitive to tumor necrosis factor-alpha). However, if such hypothesis is correct, one should explain why in most clinical and experimental cases, tumours continue to progress although the high incidence of such immune's system cells. We are therefore brought to consider a second possibility, in which, mast cells products could promote tumoural growth and metastasis. In fact, it is well documented that heparin, combined to a range of heparin-binding factors such as bFGF or TGF beta is able to promote neovascularisation, and that mast cell proteases cause cell structural alterations and loss of the extracellular matrix integrity. The role of histamine secreted by mast cells is less clear. There is indeed controversial experimental data referring to histamine's content within tumoural tissues and to histamine's proper effect on tumour expansion. Finally, this review discuss the mechanisms resulting to mast cell accumulation around tumours and more particularly the contribution of tumoural cells.

Functional relationships between sensory nerve fibers and mast cells of dura mater in normal and inflammatory conditions

In this study, we have characterized the phenotype of mast cells in rat dura mater and their topological and functional relationships with C-fibers in normal and inflammatory conditions. Three mast cell populations with different size, morphology and localization were characterized by their content of specific neutral serine proteases. They showed immunoreactivity corresponding to rat mast cell protease I, rat mast cell protease II, or both proteases. Using confocal microscopy, all three mast cell types were observed in close apposition (distance less than 100 nm) to calcitonin gene-related peptide- and substance P-immunoreactive nerve fibers in both controls and rats infected with the nematode Nippostrongylus brasiliensis. After nematode infection or neonatal treatment with capsaicin, a large increase in the number of rat mast cell protease II-immunoreactive mast cells was found within dura mater segments (+1478% and +596%, respectively), without concomitant changes of rat mast cell protease I- or rat mast cell protease I/II-immunoreactive mast cells. Under both these conditions, the increase in mast cell number was accompanied by a significant increase in rat mast cell protease II level within tissue extracts (+281% after nematode infection and +36% after capsaicin treatment). The functional interaction of mast cells with sensory nerve fibers in the dura mater was assessed by evaluating [3H]histamine synthesis after administration of L-[3H]histidine, an index of mast cell activity. The H3 receptor agonist (R)-alpha-methylhistamine (15 mg/kg, i.p.) had no effect, but administration of the H3 receptor antagonist, thioperamide (10 mg/kg, i.p.), resulted in a significant increase of [3H]histamine synthesis (+62%). This effect was reduced in neonatal capsaicin-treated rats, but not completely suppressed (+35%), very likely because of partial denervation, as assessed by monitoring calcitonin gene-related peptide immunoreactivity. It is concluded that, in the dura mater, as in peripheral tissues, sensory nerve fibers and mast cells actively synthesizing and releasing histamine form a short inhibitory feedback loop involving prejunctional H3 receptors that could regulate the release of pro-inflammatory mediators, thus limiting the extent of inflammatory reactions.

Rat cerebral mast cells undergo phenotypic changes during development

The evolution of rat cerebral mast cell phenotype during development was studied using antibodies against the granule chymases, rat mast cell protease I (RMCP-I) and rat mast cell protease II (RMCP-II) and their gene transcripts, as markers for serosal and mucosal mast cells, respectively. In situ hybridization using specific oligoprobes for RMCP-II permitted visualization of RMCP-II mRNA-containing cells as early as day 15 of embryonic development (E15). From E19 to day 4 postpartum (D4) their number increased whilst they migrated from the pia mater to the choroid fissure; at D8 cells expressing RMCP-II gene transcripts were no longer observed. The 3'-end untranslated nucleotide sequence of the RMCP-I cDNA was established in order to design selective cDNA probes for Northern blot analysis of both enzymes. Northern blot analysis revealed a strong expression of RMCP-I and RMCP-II mRNAs at D2. At D4, RMCP-I mRNA expression was still high, whereas that of RMCP-II was decreased. In adult brain, mRNA expression for both proteases was low, but detectable. Quantification of both proteases by ELISA showed that, from E19 to D4, levels of RMCP-II were maximal at E19 and remained constant until D4, whereas RMCP-I increased as a function of age. Thereafter, levels of both proteases decreased progressively, but were still present in the adult brain, with RMCP-II being uniformly distributed and RMCP-I concentrated in the thalamus. Immunohistochemical staining showed RMCP-II-immunoreactive cells within the pia mater at E19; on D2 and D4, cells with both RMCP-I and RMCP-II immunoreactivities were found within the choroid fissure and from D8, only RMCP-I-immunoreactive mast cells were observed. In the thalamus of adult rats, the latter had a perivascular localization. This study shows that in the adult, both types of mast cells are present, although in small numbers, except for RMCP-I-immunoreactive mast cells which are abundant in the thalamus. The changes in the number and phenotype of cerebral mast cells may result from the influence of a number of growth factors during development.

Phenotypic and quantitative changes in mast cells after syngeneic unilateral lung transplantation in the rat

1. Lung transplantation causes a total interruption of the inneration and vascularization within the transplanted organ, followed by repair processes. This is frequently associated with bronchial hyper-responsiveness. A common feature of tissue repair is an increase in the number of mast cells. Three phenotypically distinct mast cell subsets, with respect to their protease content, have been identified in rat lung, and it is probable that mast cells of differing protease phenotype fulfil different functions. 2. We have compared the number, protease phenotype and distribution of mast cells in left lung from transplanted and control Lewis rats 1 month after syngeneic unilateral left lung transplantation, without interference of inflammation, graft rejection or of any treatment. Connective and mucosal-type mast cell phenotypes were characterized using antibodies directed against their specific rat mast cell proteases, RMCPI and RMCPII, respectively. 3. After transplantation, RMCPI and RMCPII tissue concentrations increased by 172% and 239%, respectively, compared with controls (13.1 +/- 1.2 and 5.6 +/- 1.0 micrograms/g). 4. Localization of mast cell phenotypes was studied by immunohistochemistry after double immunostaining. The number of mast cells increased after transplantation: the increase in the number of RMCPI-immunoreactive mast cells (RMCPI+) was significant around bronchioles and arterioles, around large vessels and in the pleura. The number of RMCPII+ mast cells also significantly increased around bronchioles and arterioles, as well as in the smooth muscle layer of large airways. Some mast cells stained for the presence of both RMCPI and RMCPII, supporting the existence of co-expressing phenotype in rat lung. The number of mast cells of the RMCPI+/II+ phenotype significantly increased around bronchioles and arterioles and in the pleura. Moreover, the distribution of the mast cell phenotypes was modified in the different areas after transplantation. 5. This indicates a local differentiation/maturation of mast cells after transplantation.

Prodynorphin mRNA expression in the rat dentate gyrus after cerebral ischemia

The beneficial effects of exogenous kappa receptor agonists in preventing neuronal damage elicited by brain ischemia suggest a role for endogenous dynorphins. In agreement prodynorphin (PDYN) gene expression in granule cells of the dentate gyrus detected by in situ hybridization was drastically but transiently decreased 18-32 h after four-vessel cerebral ischemia for 20 min in rats. We propose that decreased dynorphin synthesis and release could contribute to the delayed neuronal death of hippocampal pyramidal cells in this model.

Endogenous histamine induces c-fos expression within paraventricular and supraoptic nuclei

Thioperamide, an H3-receptor antagonist that enhances endogenous histamine release, induced c-fos mRNA expression and Fos-like immunoreactivity in magnocellular neurones of rat supraoptic and paraventricular nuclei. This response was prevented as a result of blockade of the H1 receptor, indicating that endogenous histamine is able to activate these magnocellular neurones via stimulation of this receptor.

Substance P, calcitonin gene-related peptide, and capsaicin release serotonin from cerebrovascular mast cells

Rabbit leptomeningeal arteries contain granular cells resembling mast cells that frequently contact autonomic and sensory nerve profiles. In the present in vitro study, we determined whether these cells could be stimulated by substance P (SP) and calcitonin gene-related peptide (CGRP), which are stored and released by sensory C fibers. Immunohistochemistry of the middle cerebral artery showed that 5-HT was stored only in mast cell-like granules. This pool of 5-HT decreased in a dose-dependent manner when exogenous SP and CGRP were added to the incubation solution or when endogenous neuropeptides were released from nerve terminals by capsaicin. The simultaneous administration of CGRP and SP induced a dramatic exocytosis and a 5-HT release significantly greater than the sum of the individual effects of the two neuropeptides. We conclude that, as in classical connective tissue mast cells, the amine content of these granular cells can be released by a degranulation process induced by neuropeptides. The effects of capsaicin suggest that this phenomenon can be triggered by axon reflex of C fibers. The data also provide the first evidence of a synergistic action of SP and CGRP on mast cell degranulation.

Functional relationship between mast cells and C-sensitive nerve fibres evidenced by histamine H3-receptor modulation in rat lung and spleen

1. Mast cell populations in rat lung and spleen were characterized by the presence of two specific protease markers, rat mast cell protease I and II, using both histochemical and radioimmunoassay techniques. Three mast cell populations with different size, morphology, and localization were found in lung and spleen and were identified according to the expression of rat mast cell protease I (RMCPI+) or rat mast cell protease II (RMCPII+) or of both proteases (RMCPI/II+). 2. All three mast cell types were in the vicinity of calcitonin-gene-related-peptide-immunoreactive (CGRP+) nerve fibres in controls as well as in rats infected by Nippostrongylus brasiliensis in which a large increase in the number of both RMCPII+ and RMCPI/II+ mast cells was found. Ablation of the CGRP+ fibres by neonatal treatment with capsaicin resulted in a marked increase in the number of RMCPII+ and RMCPI/II+ cells in lung and, even more, in spleen of adult rats. 3. The interaction of mast cells with CGRP+ C-fibres was assessed pharmacologically by evaluation of the effects of histamine H3-receptor ligands known to act on various types of nerve endings, including those of C-fibres. The effects of H3-receptor ligands were assessed in controls, nematode-infected rats and neonatally capsaicinized rats. Mast cell activity was evaluated by measurement of [3H]histamine synthesis from [3H]histidine. In control rats, administration of the H3-receptor agonist (R)-alpha-methylhistamine and antagonist thioperamide, decreased and enhanced respectively [3H]histamine synthesis in lung and spleen, indicating a tonic control of mast cell activity by histamine via H3-receptors. Such effects were not found in the jejunum, although RMCPII+ mast cells are in close apposition with neuropeptide-containing fibres. The effects of the H3-receptor agents were maintained in lung and spleen of nematode-infected rats, but were almost suppressed in capsaicinized rats. 4. It is concluded that the control of mast cells by histamine acting at H3-receptors involves neuropeptide-containing nerves and presumably reflects the operation of a local neuron-mast cell feedback loop controlling processes such as 'neurogenic inflammation'. This loop still functions when mast cells proliferate in an inflammatory condition. These observations suggest that the use of histamine H3-receptor agonists may constitute a novel therapeutic approach to limit excessive inflammatory responses resulting from dysregulation of this feedback loop.

Functional coupling of the human dopamine D3 receptor in a transfected NG 108-15 neuroblastoma-glioma hybrid cell line

Transfection of a human dopamine D3 receptor cDNA in a neuroblastoma-glioma hybrid cell line (NG 108-15) provided clonal cell lines stably expressing up to 600 fmol per mg protein of [125I]iodosulpiride binding sites. Dopamine and several agonists distinguished two receptor-affinity states in membranes. In the case of dopamine, the high-affinity state (Ki = 0.9 nM, 30% of total binding) was completely converted into a low-affinity state (Ki = 57 nM) in the presence of 10 microM guanosine-5'-O-(3-thiotriphosphate). In addition to these two sites, a site with a very low affinity for dopamine was evidenced in whole cells. The dopamine D3 receptor mediated two responses: c-fos activation, as measured by the appearance of Fos-like immunoreactivity, and increased mitogenesis, as measured by incorporation of [3H]thymidine. The Fos-like immunoreactivity appeared within 30 min, lasted 2 h and was blocked by the partially selective dopamine D3 receptor compound (+)-UH 232 (cis-(+)-5-methoxy-1-methyl-2-(di-n-propylamino)tetralin). The mitogenic effect, which occurred after a lag time (over 2 h stimulation), was produced with subnanomolar potency and full intrinsic activity by several compounds previously identified as dopamine D2 receptor agonists, e.g. quinpirole, (+)-7-OH-DPAT ((+)-7-hydroxy-2-(di-n-propylamino)tetralin) and RU 24926 (N-n-propyl-di-beta(3-hydroxyphenyl)-ethylamine), and was reversibly blocked by (+)-UH 232 (Ki = 9 nM). Talipexole (B-HT 920, 5-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepin) was identified as a partial agonist at the dopamine D3 receptor. Dopamine D3 receptor-mediated mitogenesis was potentiated by a phorbol ester and was abolished by pretreatment with pertussis toxin. A mitogenic effect of same amplitude was elicited by bradykinin or carbachol, both acting through constitutive receptors. Bradykinin markedly activated inositol phosphate turnover, and had no effect on forskolin-stimulated cyclic AMP accumulation. Carbachol inhibited forskolin-stimulated cyclic AMP accumulation and had no effect on inositol-phosphate turnover. Quinpirole had no effect on any of these second messenger pathways. Thus, in transfected NG 108-15 cells, the dopamine D3 receptor is coupled to a pertussis toxin-sensitive G protein and mediates two possibly unrelated biological effects, through initial biochemical events that remain to be identified.

Synergistic action of estradiol and myelin basic protein on mast cell secretion and brain myelin changes resembling early stages of demyelination

Mast cells are known for their participation in immediate and, more recently, delayed hypersensitivity reactions. They have been found in the meninges and certain brain areas where they are strictly perivascular, in close apposition to neurons, and they are activated by direct nerve stimulation or by neuropeptides. Intracranial mast cells contain many vasoactive substances which can increase the permeability of the blood-brain barrier, proteolytic enzymes which can degrade myelin in vitro, as well as chemotactic molecules which can attract inflammatory molecules in vivo. Connective tissue mast cells, with which intracranial mast cells share many characteristics, contain cytokines which can cause inflammation directly. Multiple sclerosis is a human demyelinating disease of unknown etiology, with a high prevalence in women which results in penetration of blood-borne immune cells within the brain parenchyma and subsequent destruction of myelin. Here, we report that 17 beta-estradiol and myelin basic protein, a major suspected immunogen in multiple sclerosis, had a synergistic action on inducing mast cell secretion. This effect was more pronounced in Lewis rats, which are susceptible to the development of experimental allergic encephalomyelitis, an animal model for multiple sclerosis, than in Sprague-Dawley rats, which are fairly resistant. Moreover, 18 h incubation of purified peritoneal mast cells with homogeneic slices of brain white matter in the presence of 17 beta-estradiol and myelin basic protein resulted in myelin changes resembling early stages of brain demyelination, which were also more evident in Lewis rats than in Sprague-Dawley rats. These results support the notion that mast cells could participate in the pathophysiology of demyelinating diseases.

Absence of serotonergic innervation from raphe nuclei in rat cerebral blood vessels--I. Histological evidence

Anterograde tracing from dorsal raphe neurons by Phaseolus vulgaris leucoagglutinin and serotonin immunocytochemistry revealed no serotonergic projections from raphe nuclei to cerebral pial vessels in the rat. However, cerebrovascular nerve fibres, mainly located in major pial arteries, were immunoreactive to tryptophan-5-hydroxylase antibodies as previously shown by others. It thus seems that the rate-limiting enzyme catalysing the biosynthesis of serotonin, tryptophan-5-hydroxylase, is present in cerebrovascular nerve fibres which do not originate in the dorsal raphe nucleus and which do not contain enough serotonin to be labelled by serotonin immunocytochemistry. We also observed tryptophan hydroxylase-immunoreactive but no serotonin-immunoreactive nerve fibres in the femoral artery and, occasionally, in the dura mater. The femoral artery, like the dura mater, contained numerous mast cells reacting positively to both tryptophan hydroxylase and to serotonin immunocytochemistry. The colocalization of the enzyme and its final product thus appears to be a general feature, since it has already been demonstrated within the central nervous system. The only exception appears to be the tryptophan hydroxylase-immunoreactive nerves present in cerebral and peripheral vessels. These results suggest that there is not a true serotonergic (i.e. serotonin-containing) innervation in cerebral blood vessels. They also strongly suggest that the cerebrovascular nerve fibres which appear to contain tryptophan hydroxylase do not originate in the raphe nuclei.

5-Hydroxytryptamine receptor agonists for the abortive treatment of vascular headaches block mast cell, endothelial and platelet activation within the rat dura mater after trigeminal stimulation

Antidromic stimulation of small caliber trigeminal axons causes neurogenic inflammation in the dura mater and tongue as evidenced by marked increases in mast cell activation, protein extravasation, as well as in the numbers of endothelial cytoplasmic vesicles, endothelial microvilli and platelet aggregates within ipsilateral post-capillary venules. In this report, we examined the effects of pretreatment with serotonin1 receptor agonists, dihydroergotamine (50 micrograms/kg, i.v.) and sumatriptan (100 micrograms/kg, i.v.) on the light and electron microscopic changes which develop after trigeminal ganglion stimulation. Both dihydroergotamine and sumatriptan are useful in the acute treatment of vascular headaches and bind with high affinity to 5-HT1D receptors. Both drugs decreased significantly the number of dural vessels showing endothelial or platelet changes and the numbers of activated mast cells, but did not affect the neurogenic response in the tongue. The drugs also blocked the accumulation of horseradish peroxidase reaction product within the endothelium and perivascular space on the stimulated side. The receptor is not present on trigeminovascular fibers innervating extracranial cephalic tissues. Drug mechanism probably involves inhibition of a proximal step in the pathophysiological cascade (e.g., via activation of a prejunctional receptor) because (a) receptors for sumatriptan have not been identified on mast cells whereas the inflammatory response was attenuated in mast cells as well as within platelets and the endothelium and (b) previous work indicates that sumatriptan and dihydroergotamine block neurotransmitter release. Hence, constriction of vascular smooth muscle mediated by postjunctional 5-hydroxytryptamine receptors is unlikely to explain the anti-inflammatory actions of dihydroergotamine or sumatriptan reported here.

Ultrastructural evidence for neurogenically mediated changes in blood vessels of the rat dura mater and tongue following antidromic trigeminal stimulation

We investigated the effects of unilateral electrical trigeminal ganglion stimulation (0.1 or 1.0 mA, 5 Hz, 5 ms, 5 min) on the morphology of blood vessels within the rat dura mater and tongue using light and transmission electron microscopy. Stimulation at both intensities caused changes which were confined to the ipsilateral post-capillary venules except in the tongue where arterioles were affected as well. Changes were more marked after 1.0 mA. Dramatic increases in the numbers of endothelial pinocytotic vesicles were found along the luminal and abluminal surfaces ipsilateral to the stimulation. Tight junctions remained largely intact, except that injected ferritin particles were occasionally trapped inside these junctions. Cytoplasmic microvilli and endothelial blebs were sometimes present as well. Approximately 80% of the examined dural post-capillary venules showed one or more of these endothelial changes. Horseradish peroxidase injected intravenously 5 min prior to stimulation was detected in the extracellular space surrounding dural blood vessels and within pinocytotic vesicles. Ferritin injected similarly, was also localized in post-capillary venule walls, interstitial spaces, intraendothelial vesicles and in vacuoles. Platelet accumulation and aggregation were present in approximately 10% of post-capillary venules in dura and tongue. These changes were associated with mast cell secretion, but neither vascular nor mast cell activation was observed in adult rats in whom C-fibers were destroyed during the neonatal period with capsaicin. The present observations provide morphological evidence which supports findings from previously reported albumin tracer studies suggesting enhanced transport and endothelial activation following electrical stimulation of small caliber afferent fibers.

Carbachol induces granular cell exocytosis and serotonin release in rabbit cerebral arteries

Previously, we reported that rabbit cerebral arteries contain mast cells that frequently establish close contacts with parasympathetic-like nerve fibers. Here we have examined the possible function of this link by comparing the effects of carbachol and compound 48/80 on mast cell morphology and on the serotonin (5-HT) and histamine content of these arteries. In vivo, 2 micrograms/min of compound 48/80 or 1 micrograms/min of carbachol was infused for 30 min into one internal carotid artery of pentobarbital anesthetized rabbits, the contralateral artery being infused with vehicle. In vitro, the action of 10(-6) M carbachol was tested on isolated middle cerebral artery trees (MCAs) in the presence or absence of 10(-7) M atropine. The effects of carbachol were also tested in vitro on sympathectomized arteries. The 5-HT and histamine contents of all MCAs were measured by radioenzymatic assay, and fragments were prepared for electron microscopy. No histamine was detectable in any artery studied. The 5-HT content of arteries from control animals and those perfused with vehicle (in vivo) or incubated in the physiological solution (in vitro) was 250-300 pmol/mg protein. Both compound 48/80 and carbachol reduced this amount by approximately 50% and induced a marked degranulation of mast cells. Both secretion and degranulation were dramatically blocked in vitro by atropine. No difference in the 5-HT content was observed between intact and sympathectomized arteries under any condition. We conclude that a large proportion of rabbit cerebrovascular 5-HT is stored in mast cells and that cholinergic nerve activation could theoretically release this pool by acting on mast cell muscarinic receptors.

Estradiol augments while tamoxifen inhibits rat mast cell secretion

Mast cells have been studied extensively for their involvement in allergic reactions, where they secrete numerous powerful mediators in response to immunoglobulin E and specific antigens. However, they are also triggered by neuropeptides, they have been found in close contact with neurons, and they are activated in diseases such as angioedema, interstitial cystitis and irritable bowel disease, the prevalence of which is much higher in women. When tested on purified rat peritoneal mast cells, 17 beta-estradiol augmented secretion of histamine and serotonin, starting at 1 microM and in a dose-dependent manner, whether stimulated by the mast cell secretagogue compound 48/80 or the neuropeptide substance P. However, 17 beta-estradiol did not augment mast cell secretion stimulated by immunoglobulin E and specific antiserum indicating that immunologic stimulation is under different regulation. Testosterone inhibited secretion induced by compound 48/80. Tamoxifen, an estrogen receptor antagonist used in the treatment of breast cancer, inhibited serotonin and histamine release from purified rat peritoneal mast cells triggered by compound 48/80 or substance P. Tamoxifen also inhibited the increase in intracellular free Ca2+ originating from an influx of extracellular Ca2+ in response to compound 48/80. Moreover, tamoxifen antagonized the synergistic effect of phorbol myristate and the cation ionophore A23187 on mast cell secretion, suggesting that tamoxifen's inhibition may be due to regulation of protein kinase C activity. Tamoxifen may, therefore, have a beneficial effect in other neuroimmunoendocrine disorders both through estrogen receptor blockade and inhibition of mast cell secretion.

Trigeminal sensory fiber stimulation induces morphological changes reflecting secretion in rat dura mater mast cells

Mast cells are involved in allergic reactions, but may also participate in neurogenic inflammation. The morphology of mast cells in rat dura mater and tongue was evaluated by histochemistry, as well as by scanning and transmission electron microscopy following unilateral trigeminal ganglion stimulation (5 min, 5 Hz, 5 ms, and 0.02, 0.1 or 1.0 mA). Mast cells in dura and tongue of normal animals were numerous, perivascular and often in close proximity to nerve fibers. After 5 min of electrical stimulation, mast cells contralateral to the stimulation showed histochemical characteristics of normal peripheral tissue mast cells (Safranin-positive), and by electron microscopy appeared homogeneous with numerous intact electron-dense granules. On the stimulated side, however, the staining characteristics of mast cells showed changes indicating progressive intracellular loss of their granular content. In addition, the total number of stainable mast cells decreased at all three stimulus intensities, but reached significance only at 0.1 and 0.02 mA. Ultrastructural evidence of granule changes consistent with secretion were observed although degranulation was not observed until 20 min after stimulation. There were no mast cell changes after electrical trigeminal stimulation in adult rats treated as neonates with capsaicin to destroy small caliber sensory afferent axons. These results suggest that mast cells may secrete in response to electrical stimulation of trigeminal axons, possibly mediated by antidromic release of neuropeptides, and may participate in the development of neurogenic inflammation.

Migration of mast cells in the developing rat brain

Mast cells are known to derive from the bone marrow and enter the tissues as immature cells which differentiate under local microenvironmental factors. However, it has not been known how and when these cells enter the brain; moreover, the localization of mast cells in the developing rat brain differs from that of the adult animal. Our anatomical and morphological observations showed that during late embryonic stages and the first 11 days after birth, rat brain mast cells were exclusively concentrated within the pia mater surrounding the diencephalon, the choroid fissure and within the choroid plexus. Histochemically these cells contained only a few toluidine blue metachromatic granules, suggesting a 'mucosal' phenotype and the absence of heparin. Later, during a transitional phase from postnatal day 11 to 13, these cells migrated along blood vessels of the fimbria, the hippocampus and the penetrating vessels of the thalamus into the dorsolateral and posterolateral thalamic nuclei. These cells contained more metachromatic granules, and from day 13 on, they assumed their adult perivascular localization within the thalamus with numerous metachromatic granules similar to those described for mature thalamic and serosal mast cells.

Cluster headache: ultrastructural evidence for mast cell degranulation and interaction with nerve fibres in the human temporal artery

It has been suggested that histamine plays an important role in the pathogenesis of cluster headache. In addition, both neurogenic and vascular components have been described during cluster headache attacks without an obvious anatomical link between them. Our ultrastructural observations of human temporal arteries from cluster headache patients and their comparison to those from a control group strongly suggest that mast cells may be this link. Mast cells in both groups show a very close apposition with nerve fibres, suggesting a functional interaction between them. Moreover, in the cluster headache group exclusively, adventitial mast cells show profound morphological modifications suggesting progressive degranulation. These data strongly suggest that mast cells could be directly or indirectly involved in the pathophysiology of cluster headaches.

Histochemical and ultrastructural characteristics of rat brain perivascular mast cells stimulated with compound 48/80 and carbachol

Mast cells, known for their involvement in allergic reactions where they secrete numerous chemicals in response to immunoglobulin E and specific antigens, have recently been localized in the central nervous system. The function of these brain mast cells has remained speculative as they have not been the subject of any combined functional or detailed morphological studies. Here it is shown that these cells are primarily perivascular and stain metachromatically with Toluidine Blue, but red with Alcian Blue counterstained with Safranin, indicating that they contain proteoglycans quite similar to those of peritoneal, but not mucosal mast cells. Intracardiac administration of the classic mast cell secretagogue, compound 48/80, or the acetylcholine analog, carbachol, caused ultrastructural changes in brain mast cells consistent with secretion, but without exocytosis. However, it is known that the same concentration of carbachol has no effect on homogeneic peritoneal mast cells. These results indicate that brain mast cells share histochemical characteristics with serosal mast cells, but differ in their reactivity to secretagogues, and apparently in the mechanism of secretion. Their ability to respond to neurotransmitters and their distinct mechanism of secretion, which may be selective, expands their possible role in brain pathophysiology.

Progesterone triggers selective mast cell secretion of 5-hydroxytryptamine

Mast cells are involved in allergic reactions where they secrete numerous mediators in response to immunoglobulin E and antigen. However, they have recently been implicated in neuroinflammatory conditions with a higher prevalence in women, and there have been clinical reports of progesterone anaphylaxis. When tested on purified rat peritoneal mast cells, progesterone alone stimulated release only of 5-hydroxytryptamine (serotonin) in a dose- and time-dependent manner. Serotonin release by progesterone was exceptional because it was not accompanied by histamine release or degranulation and was either augmented or unaffected by drugs which inhibit secretion induced by the classic mast cell secretagogue, compound 48/80. These findings indicate that mast cells are capable of selective serotonin secretion, previously shown only after pretreatment with certain tricyclic drugs, and may be involved in neuroendocrine syndromes.

Ontogenesis and localization of Ca2+ channels in mammalian skeletal muscle in culture and role in excitation-contraction coupling

The mechanism of excitation-contraction (E-C) coupling in skeletal muscle is not yet well established. Cultured mouse skeletal muscle cells have been used to study the relationships between triad formation, Ca2+ channel activities, and contractions. The ontogenesis of voltage-dependent Ca2+ channels and their localization in relation to the ability of muscle to contract and the ultrastructural organization of sarcomeres and triads have been investigated by using an electrophysiological approach together with an electron microscope study. At an early stage of development, both fast (Ifast) and slow (Islow) types of Ca2+ channels are found at the surface membrane. At later stages of development, fast Ca2+ channels remain at the surface membrane, while slow Ca2+ channels migrate to the transverse-tubule membrane. The voltage dependence of fast Ca2+ channels compared to the voltage dependence of contraction clearly shows that these Ca2+ channels have no direct role in E-C coupling. Detubulation at all stages of development has confirmed that T tubules contain essential elements for E-C coupling. However, this work also shows that Ca2+ flowing through slow Ca2+ channels situated in the T-tubular system is not important for contraction. Myotubes lacking slow Ca2+ channels or having no slow Ca2+ channel transport activity (jumps to high membrane potentials, no external Ca2+, block of Islow by Co2+) still retain contraction.

Ultrastructural changes in the cerebral artery wall induced by long-term sympathetic denervation

This study was performed to determine to what extent the morphology of the rabbit middle cerebral artery is affected by the absence of the sympathetic nervous system. Six weeks after unilateral ablation of the superior cervical ganglion, which induced ipsilateral degeneration and disappearance of the perivascular noradrenergic nerve fibers, comparison between the ipsi- and the contralateral middle cerebral arteries revealed that the denervated arterial wall underwent significant thickening. This thickening was principally due to hypertrophy of the smooth muscle cells (SMC), together with an increase in the amount of medial and adventitial collagen. The hypertrophied SMC showed important morphological and ultrastructural modifications--irregular shape, increase in the number of organelles (particularly of Golgi apparatus, free ribosomes, rough endoplasmic reticulum and microtubules), large indented nuclei rich in euchromatin--indicating profound changes in their metabolic and contractile activity which could result in an alteration of their mechanical properties. As these alterations were strictly ipsilateral to the sympathectomy it is likely that they are the direct consequence of the suppression of a regulatory 'trophic' factor linked to the presence of sympathetic nerve fibers. This concept is reinforced by the fact that the first SMC affected are those situated at the media/adventitial border, in the vicinity of adventitial nerve bundles. Thus, the sympathetic nervous system appears to play a key role in the long-term regulation of the cerebral vascular tree structure.

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

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

Histamine-induced constriction and dilatation of rabbit middle cerebral arteries in vitro: role of the endothelium

We studied the effects of histamine on perfused rabbit middle cerebral arteries in vitro. Intact and endothelium-denuded preparations were compared. Histamine caused concentration-dependent constrictions in intact vessels which were competitively inhibited by an H1 receptor antagonist. This constriction was potentiated by either H2-receptor blockade or endothelium denudation. The greatest potentiation was observed with intraluminal as opposed to extraluminal administration. The H1 receptor agonist pyridylethylamine induced similar concentration-dependent constriction in intact and denuded preparations. After preconstriction, histamine, in the presence of an H1 receptor antagonist, dilated intact vessels to a maximum of 45.1%, and endothelium-denuded vessels to a maximum of 22% (p less than 0.02). We conclude that rabbit middle cerebral arteries possess H1 constrictory and H2 dilatory receptors, and that many of the H2 dilatory receptors are situated on the endothelial cells.

Pial artery responses to norepinephrine potentiated by endothelium removal

The effect of endothelium removal on pial artery constriction in response to norepinephrine (NE) was studied in vitro using a perfused vessel setup in which pressure increases indicate vasoconstriction. In deenodothelialized rabbit arteries, the reaction to extraluminal NE was found to be characterized by a much higher Emax (2.0 times) and a slight (but significant) leftward shift of the concentration-response curve (lower EC50) compared with control vessels. In cat arteries subjected to either extra- or intraluminal NE, the Emax was also substantially higher in deendothelialized preparations (4.4 and 5.1 times, respectively), but there was no significant difference in the EC50 values. Anatomical verification and functional tests (acetylcholine-induced dilatation) confirmed the presence and the absence of the endothelium in control and lesioned arteries, respectively. This modulatory influence of the endothelium may be of importance in cerebrovascular pathology.