Analysis of classical neurotransmitter markers in tapeworms: Evidence for extensive loss of neurotransmitter pathways

Parasitic flatworms have complex neuromuscular systems that serve important functions in their life cycles. However, our understanding of neurotransmission in parasitic flatworms is limited. Pioneering studies have suggested the presence of several classical neurotransmitter systems, but their molecular components have not been characterized in most cases. Because these components are conserved in bilaterian animals, we searched the genomes of parasitic flatworms for orthologs of genes required for neurotransmitter synthesis, vesicular transport, reuptake, and reception. Our results indicate that tapeworms have lost the genes that are specifically required in other animals for synaptic signaling using the classical neurotransmitters dopamine, tyramine, octopamine, histamine and gamma-aminobutyric acid (GABA). These results imply that these signaling pathways are either absent in these parasites, or that they require completely different molecular components in comparison with other animals. The orthologs of genes related to histaminergic and GABA signaling are also missing in trematodes (although Schistosoma-specific histaminergic receptors have been previously described). In contrast, conserved genes required for glutamatergic, serotonergic and cholinergic signaling could be found in all analyzed flatworms. We analyzed the expression of selected markers of each pathway in the tapeworm Hymenolepis microstoma by whole-mount in situ hybridization. Each marker was specifically expressed in the nervous system, although with different patterns. In addition, we analyzed the expression of proprotein convertase 2 as a marker of peptidergic cells. This gene showed the widest expression in the nervous system, but was also expressed in other tissues, suggesting additional roles of peptidergic signaling in tapeworm development and reproduction.     

Regulation of histamine release in rat hypothalamus and hippocampus by presynaptic galanin receptors.

The effect of galanin, a peptide present in a subpopulation of histaminergic neurons emanating from the rat posterior hypothalamus, was investigated on K(+)-evoked [3H]histamine release in slices and synaptosomes from rat cerebral cortex, striatum, hippocampus and hypothalamus. Porcine galanin (0.3 microM) significantly inhibited histamine release induced by 25 mM K+ in slices from hypothalamus and hippocampus, but not from cerebral cortex and striatum, i.e., only in regions in which a colocalization of histamine and galanin has been described. The inhibitory effect of galanin was concentration dependent, with an EC50 value of 5.8 +/- 1.9 nM. The maximal inhibition was of 30-40% in hypothalamic and hippocampal slices depolarized with 25 mM K+. The galanin-induced inhibition observed in hypothalamic slices was not prevented in the presence of 0.6 microM tetrodotoxin and also occurred in hippocampal and hypothalamic synaptosomes, strongly suggesting the activation by galanin of presynaptic receptors located upon histaminergic nerve endings. The maximal inhibitory effect of galanin in slices or synaptosomes was lower than that previously reported for histamine acting at H3-autoreceptors, possibly suggesting that not all histaminergic axon terminals, even in the hypothalamus and hippocampus, are endowed with galanin receptors. It increased progressively in hypothalamic and hippocampal synaptosomes as the strength of the depolarizing stimulus was reduced. It is concluded that galanin modulates histamine release via presynaptic receptors, presumably autoreceptors located upon nerve terminals of a subpopulation of cerebral histaminergic neurons.     

Effect of manganese and verapamil on electrical and contractile responses of pulmonary artery smooth muscle induced by noradrenaline and histamine

Action of noradrenaline and histamine on the resting potential, membrane resistance and contractility of rabbit pulmonary artery muscle cells was investigated in normal and Ca-blockers (manganese and verapamil)-containing Ringer-Lock solutions. It was shown that catecholamine and histamine induced depolarization by different mechanisms. Thus, noradrenaline action is accounted for by the decreased membrane permeability to potassium ions, while the histamine-induced depolarization is a consequence of sodium and, probably, chlorine permeability. The contraction induced by the transmitters is activated primarily by the extracellular calcium ions entering the cells by two ways: via chemosensitive Ca-channels activated by adrenergic and histaminergic receptors or via potential-dependent slow Ca-channels activated by the transmitter-induced membrane depolarization. It is not excluded that during activation of muscle cells by the transmitters part of calcium is release from both intramembrane and intracellular stores.     

组胺对大鼠小脑皮层浦肯野细胞的兴奋作用

在离体大鼠小脑脑片上观察了组胺对小脑皮层第Ⅹ小叶浦肯野细胞的作用。组胺（３～１００μｍｏｌ／Ｌ）主要引起浦肯野细胞的兴奋反应（９４４％,５１／５４）,在少数细胞上也观察到组胺所引起的放电抑制现象（５６％,３／５４）。用低Ｃａ２＋／高Ｍｇ２＋人工脑脊液灌流脑片,不能取消浦肯野细胞对组胺的兴奋反应（ｎ＝４）。Ｈ２受体对抗剂ｒａｎｉｔｉｄｉｎｅ（０１～５μｍｏｌ／Ｌ）能够阻断浦肯野细胞对组胺的兴奋反应（ｎ＝２０）,而Ｈ１受体对抗剂ｔｒｉｐｒｏｌｉｄｉｎｅ（０５～５μｍｏｌ／Ｌ）不能够（ｎ＝９）或仅轻微地（ｎ＝４）阻断浦肯野细胞对组胺的兴奋反应。这些结果提示,组胺可能主要通过Ｈ２受体的介导对浦肯野细胞起兴奋性调节作用,下丘脑小脑组胺能神经通路可能参与了小脑的某些躯体的和非躯体的功能调节。     

Histamine in brain development

J. Neurochem. (2012) 122, 872-882. ABSTRACT: The function of histamine in the adult central nervous system has been extensively studied, but data on its actions upon the developing nervous system are still scarce. Herein, we review the available information regarding the possible role for histamine in brain development. Some relevant findings are the existence of a transient histaminergic neuronal system during brain development, which includes serotonergic neurons in the midbrain and the rhombencephalon that coexpress histamine; the high levels of histamine found in several areas of the embryo nervous system at the neurogenic stage; the presence of histaminergic fibers and the expression of histamine receptors in various areas of the developing brain; and the neurogenic and proliferative effects on neural stem cells following histamine H(1) - and H(2) -receptor activation, respectively. Altogether, the reviewed information supports a significant role for histamine in brain development and the need for further research in this field.     

Identification of a histamine H4 receptor on human eosinophils--role in eosinophil chemotaxis

Eosinophils are recruited to sites of inflammation via the action of a number of chemical mediators, including PAF, leukotrienes, eotaxins, ECF-A and histamine. Although many of the cell-surface receptors for these mediators have been identified, histamine-driven chemotaxis has not been conclusively attributed to any of the three known histamine receptor subtypes, suggesting the possibility of a 4th histamine-responsive receptor on eosinophils. We have identified and cloned a novel G protein-coupled receptor (GPCR), termed Pfi-013, from an IL-5 stimulated eosinophil cDNA library which is homologous to the human histamine H3 receptor, both at the sequence and gene structure level. Expression data indicates that Pfi-013 is predominantly expressed in peripheral blood leukocytes, with lower expression levels in spleen, testis and colon. Ligand-binding studies using Pfi-013 expressed in HEK-293Galpha15 cells, demonstrates specific binding to histamine with a Kd of 3.28 +/- 0.76 nM and possesses a unique rank order of potency against known histaminergic compounds in a competitive ligand-binding assay (histamine > clobenpropit > iodophenpropit > thioperamide > R-alpha-methylhistamine > cimetidine > pyrilamine). We have therefore termed this receptor human histamine H4. Chemotaxis studies on isolated human eosinophils have confirmed that histamine is chemotactic and that agonists of the known histamine receptors (H1, H2, and H3) do not induce such a response. Furthermore, studies employing histamine-receptor antagonists have shown an inhibition of chemotaxis only by the H3 antagonists clobenpropit and thioperamide. Since these compounds are also antagonists of hH4 we postulate that the receptor mediating histaminergic chemotaxis is this novel histamine H4 receptor.     

Endogenous GABA Modulates Histamine Release from the Anterior Hypothalamus of the Rat

Abstract: Using a microdialysis method, we investigated the effects of the nipecotic acid-induced increase in content of endogenous GABA on in vivo release of histamine from the anterior hypothalamus (AHy) of urethane-anesthetized rats. Nipecotic acid (0.5 m M ), an inhibitor of GABA uptake, decreased histamine release to ∼60% of the basal level. This effect was partially antagonized by picrotoxin (0.1 m M ), an antagonist of GABA_A receptors, or phaclofen (0.1 m M ), an antagonist of GABA_B receptors. These results suggest that histamine release is modulated by endogenous GABA through both GABA_A and GABA_B receptors. When the tuberomammillary nucleus, where the cell bodies of the histaminergic neurons are localized, was stimulated electrically, the evoked release of histamine from the nerve terminals in the AHy was significantly enhanced by phaclofen, suggesting that GABA_B receptors may be located on the histaminergic nerve terminals and modulate histamine release presynaptically. On the other hand, picrotoxin caused an increase in histamine release to ∼170% of the basal level, and this increase was diminished by coinfusion with d (−)-2-amino-5-phosphonopentanoic acid (0.1 m M ), an antagonist of NMDA receptors. Previously, we demonstrated tonic control of histamine release by glutamate mediated through NMDA receptors located on the histaminergic terminals in the AHy. These results suggest the possible localization of GABA_A receptors on glutamatergic nerve terminals and that the receptors may regulate the basal release of histamine indirectly.     

The contribution of mast cells to the histamine content of the central nervous system: A regional analysis

W/W^V mice are severely deficient in mast cells. The absence of mast cells in skin and salivary glands was found to be paralleled by a drastic decrease of the histamine levels in these tissues when compared to non-anemic +/+ control mice. Brains of W/W^V mice are also devoid of mast cells. A comparison of the histamine concentrations in several brain regions of W/W^V mice and controls revealed a moderate decrease in cerebral cortex, thalamus, hypothalamus and midbrain but no change in pons, medulla and cerebellum. These findings provide strong evidence that mast cells contribute to the histamine content in forebrain regions but not in hindbrain regions. It is speculated that there may exist histaminergic neurons intrinsic to the medulla and pons.     

Neuronal storage of histamine in the brain and tele-methylimidazoleacetic acid excretion in portocaval shunted rats

Rats with portocaval anastomosis (PCA), an animal model of hepatic encephalopathy (HE), have very high brain histamine concentrations. Our previous studies based on a biochemical approach indicated histamine accumulation in the neuronal compartment. In this study, immunohistochemical evidence is presented which further supports the amine localization in histaminergic neurons. These neurons become pathological in appearance with cisternae frequently seen along histaminergic fibres in many brain areas, including the hypothalamus, amygdala, substantia nigra and cerebral cortex. Such formations were not observed in sham-operated animals. The neuronal deposition is predominant, and unique for histamine. It serves as a mechanism to counterbalance excessive brain neurotransmitter formation evoked by PCA. However, there are other mechanisms. The data provided here show that there is also a significant increase in histamine catabolism in the shunted rats, as reflected by both the higher brain N-tele-methylhistamine (t-MeHA) concentration and urinary excretion of N-tele-methylimidazoleacetic acid (t-MelmAA), a major brain histamine end product. The stomach, in addition to the brain, is a site of enhanced histamine synthesis in portocavally shunted subjects. After gastrectomy or food deprivation to eliminate the contribution of the stomach, shunted rats excrete significantly more t-MelmAA, implying the role of the CNS. This last finding suggests that under strictly defined conditions, namely in parenterally fed HE patients with abnormal plasma L-histidine, the measurement of urinary t-MelmAA might provide valuable information concerning putative brain histaminergic activity.     

Limb vasodilation provoked by stimulation of the carotid sinus. Importance of histaminergy in the dog

The vasodilator reflex induced by baroreceptor stimulation was studied on the hindlimbs of the dog. The reflex was induced by norepinephrine (1 microgram/kg) either by intravenous injection or by direct injection into the carotid sinus. In other experiences, the baroreceptor stimulation was obtained by distension of the sinus by rapid injection of 100 ml of physiological serum. The vascular response was studied by recording the hindlimbs blood flow. One of the limbs was previously pretreated by mepyramine and cimetidine (blockage of histaminergic H1 and H2 receptors). During the first minute after the baroreceptor stimulation, blood samples were collected from the venous blood of hindlimbs for histamine assay (fluorometric assay). Our results show: a much lower vasodilation on the limb pretreated by histamine antagonist, a significant increase during the reflex vasodilation of histamine blood levels measured in the efferent blood of hindlimbs. These results, obtained in experimental conditions as physiological as possible (blood perfusion of the limbs with "natural" hemodynamic parameters) permit to conclude that the vasodilation induced by baroreceptor reflex is at least partially histaminergic in the dog.     

Studies on the specificity of uptake and release of radiolabelled histamine in rat brain slices

Previously it has been shown that radiolabelled histamine is taken up by brain slices and may subsequently be released by depolarizing stimuli in a calcium-dependent manner, indicating the involvement of neurons in uptake and release of histamine.The present study demonstrates that after incubation of brain slices with low (nM) concentrations of [³H]histamine the amine may be taken up by (and released from) dopaminergic and serotonergic neurons (nerve terminals). Thus 6-hydroxydopamine- and 5,7-dihydroxytryptamine-induced lesions not only reduced the uptake of [³H]dopamine (in striatal slices) and [³H]serotonin (in hippocampal slices), but also, though to a lesser extent, that of [³H]histamine. Immunocytochemical findings revealed that the neurotoxins did not visibly affect histaminergic neurons. Lesioning of noradrenergic neurons appeared not to alter significantly the uptake of [³H]histamine. Further, various drugs acting on either catecholamine-, serotonin- or opioid-receptors and known to cause presynaptic inhibition of the release of [³H]dopamine or [³H]wrotonin from striatal or hippocampal slices also inhibited [³H]histamine release.It is concluded that incubation of brain slices with low concentrations of [³H]histamine does not result in a selective labelling of histaminergic neurons. The possibility that, unlike other monoamines, histamine is not subject to high-affinity uptake by the nerve terminals from which it was released, is discussed.     

The role of histaminergic system of the brain in the regulation of sleep-wakefulness cycle

The structure and the morphological and neurochemical connections of the histaminergic system of the brain, which plays one of the most important roles in maintaining wakefulness, are considered. The biochemistry of histamine metabolism and histamine receptors is briefly described. The special role of the relation between the histamine system and orexin/hypocretin system is noted. Some examples of the effects of experimental manipulations with the histaminergic system on the wakefulness-sleep cycle are given.     

Changes in the immunoreactivity of substance P and calcitonin gene-related peptide in the laryngeal taste buds of chronically hypoxic rats

The distribution of substance P (SP)- and calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers in the taste buds of the epiglottis and aryepiglottic folds was compared between normoxic control and chronically isocapnic hypoxic rats (10% O2 and 3-4% CO2 for 3 months). In the normoxic laryngeal taste buds, SP- and CGRP-immunoreactive fibers were detected within the taste buds, where they appeared as thin processes with many varicosities. Most CGRP fibers showed coexistence with SP, but a few fibers showed the immunoreactivity of CGRP only. The density of intra- and subgemmal SP and CGRP fibers penetrating into the laryngeal taste buds was significantly higher in chronically hypoxic rats than in normoxic control rats. Water intake in the hypoxic rats was significantly lower than in the normoxic rats. These results indicate that the increased density of SP- and CGRP-containing nerve fibers within the laryngeal taste buds is a predominant feature of hypoxic adaptation. The altered peptidergic innervation and reduced water intake support the hypothesis that the laryngeal taste buds are involved in water reception, and that the water reception may be under the control of peptidergic innervation.     

Histamine Receptor and its Regulation of Energy Metabolism

In a series of studies on brain functions of histamine, probes to manipulate activities of histaminergic neuronal systems were applied to assess histaminergic function in non-obese normal, and lean and obese Zucker rats. Food intake was suppressed by both activation of H₁-receptors and inhibition of H₃-receptors in the ventromedial hypothalamic nucleus (VMH) and the paraventricular nucleus, each of which is a satiety center. Feeding circadian rhythm was decreased in its amplitude through histaminergic modulation in the hypothalamus. Histamine neurons in the mesencephalic trigeminal nucleus (Me5) were involved in regulation of masticatory functions, particularly eating speed, while histamine-containing neurons in the VMH controlled intake volume of meals. Energy deficiency in the brain enhanced satiation through histaminergic activation of VMH neurons, which in turn produced glycogenolysis in the hypothalamus to maintain homeostatic control of glucose supply. A very-low-calorie conventional Japanese diet, which is a fiber rich and low energy food source, enhanced satiation by increased mastication and because of the low energy supply of the diet. Hypothalamic histamine neurons were activated by high ambient temperature and also by interleukin-1β, an endogenous pyrogen, to maintain homeostatic thermoregulation. Behavioral and metabolic abnormalities of Zucker obese rats were mediated by a deficit in hypothalamic neuronal histamine, and the Zucker rat was evaluated as an animal model of histamine deficiency. Transplantation of the lean fetal hypothalamus into the third cerebroventricle of host obese Zuckers attenuated the abnormalities.     

Ontogeny of Histaminergic Neurotransmission in the Rat Brain: Concomitant Development of Neuronal Histamine, H-1 Receptors, and H-1 Receptor-Mediated Stimulation of Phospholipid Turnover

The ontogeny of histaminergic neurotransmission in the rat brain was studied by assessing development of histamine levels in brain regions, along with H-1 receptor binding of [3H]mepyramine and H-1 receptor-mediated cellular events. In the hypothalamus, which is rich in histaminergic innervation, levels of the amine were low at birth, increased sharply at 8 days of age, and reached adult concentrations shortly thereafter; this pattern is typical of most neurotransmitters. In contrast, regions poor in neuronal histamine showed an initially high histamine level and a subsequent decline with development, as is known to occur during general growth of tissues. The developmental profile of H-1 receptor binding sites resembled that of the neuronal histamine pool, and the increases with age resulted from changes in the number of binding sites without alterations in Kd. Cellular responses to H-1 receptor activation were assessed by determining the stimulation of phospholipid turnover evoked by intracisternally administered histamine, a process that has been shown to involve only the neuronal compartment. Again, the developmental profile was superimposable upon that of H-1 receptor binding and that of hypothalamic histamine levels. These studies indicate that ontogeny of histaminergic neurotransmission is a coordinated process, with simultaneous development of neuronal histamine, its key biosynthetic enzyme, and H-1 receptors coupled directly to cellular events.     

Effects of (S)-alpha -fluoromethylhistidine and metoprine on locomotor activity and brain histamine content in mice.

We examined the effects of (S)-alpha -fluoromethylhistidine (FMH), an inhibitor of histidine decarboxylase, and metoprine, an inhibitor of histamine N-methyltransferase, on the locomotor activity and the brain histamine content of ICR mice. The brain histamine content was decreased by FMH (12.5 or 50 mg/kg, i.p.) and increased by metoprine (4 mg/kg, i.p.). Under these conditions, the locomotor activity and the number of rearing were significantly decreased and increased by FMH and metoprine, respectively. The higher the brain histamine content, the greater the locomotor activity and vice versa. In a previous paper [Sakai et al., Life Sciences, 48, 2397-2404 (1991)], we showed that thioperamide, a histamine H3 antagonist, which enhances the release of histamine from histaminergic neurons, in doses of 12.5 and 25 mg/kg, i.p. increases the locomotor activity, whereas it decreases the brain histamine content. Taken together, these results support the hypothesis that central histaminergic neurons may be involved in the control of state of locomotion and rearing.     

An adenosine A receptor agonist induces sleep by increasing GABA release in the tuberomammillary nucleus to inhibit histaminergic systems in rats

The adenosine A(2A) receptor (A(2A)R) has been demonstrated to play a crucial role in the regulation of the sleep process. However, the molecular mechanism of the A(2A)R-mediated sleep remains to be elucidated. Here we used electroencephalogram and electromyogram recordings coupled with in vivo microdialysis to investigate the effects of an A(2A)R agonist, CGS21680, on sleep and on the release of histamine and GABA in the brain. In freely moving rats, CGS21680 applied to the subarachnoid space underlying the rostral basal forebrain significantly promoted sleep and inhibited histamine release in the frontal cortex. The histamine release was negatively correlated with the amount of non-rapid eye movement sleep (r = - 0.652). In urethane-anesthetized rats, CGS21680 inhibited histamine release in both the frontal cortex and medial pre-optic area in a dose-dependent manner, and increased GABA release specifically in the histaminergic tuberomammillary nucleus but not in the frontal cortex. Moreover, the CGS21680-induced inhibition of histamine release was antagonized by perfusion of the tuberomammillary nucleus with a GABA(A) antagonist, picrotoxin. These results suggest that the A(2A)R agonist induced sleep by inhibiting the histaminergic system through increasing GABA release in the tuberomammillary nucleus.     

Brain Histaminergic System in Mast Cell-Deficient (Ws/Ws) Rats: Histamine Content, Histidine Decarboxylase Activity, and Effects of (S)α-Fluoromethylhistidine

Abstract: The mast cell-deficient [ Ws/Ws ( W hite spotting in the skin)] rat was investigated with regard to the origin of histamine in the brain. No mast cells were detected in the pia mater and the perivascular region of the thalamus of Ws/Ws rats by Alcian Blue staining. The histamine contents and histidine decarboxylase (HDC) activities of various brain regions of Ws/Ws rats were similar to those of +/+ rats except the histamine contents of the cerebral cortex and cerebellum. As the cerebral cortex and cerebellum have meninges that are difficult to remove completely, the histamine contents of these two regions may be different between Ws/Ws and +/+ rats. We assume that the histamine content of whole brain with meninges in Ws/Ws rats is <60% of that in +/+ rats. So we conclude that approximately half of the histamine content of rat brain is derived from mast cells. Next, the effects of ( S )α-fluoromethylhistidine (FMH), a specific inhibitor of HDC, on the histamine contents and HDC activities of various regions of the brain were examined in Ws/Ws rats. In the whole brain of Ws/Ws rats, 51 and 37% of the histamine content of the control group remained 2 and 6 h, respectively, after FMH administration (100 mg/kg of body weight). Therefore, we suggest that there might be other histamine pools including histaminergic neurons in rat brain.     

Histamine stimulates brain phospholipid turnover through a direct,H-1 receptor-mediated mechanism

Intracisternal administration of histamine produced a dose-dependent increase of incorporation of ³³Pi into brain phospholipids. The effect could not be mimicked by administration of compound 48/80, indicating lack of involvement of non-neuronal histamine. The stimulation was not attenuated by prior depletion of catecholamines with reserpine, indicating that the effect of histamine on phospholipid turnover was mediated by direct histaminergic mechanisms. An H-1 receptor appeared to be involved, as demonstrated by studies with specific histaminergic agonists and antagonists. Incorporation of ³³Pi into phospholipids may be a valuable tool in evaluating cellular effects mediated through H-1 receptors.