Histamine as a neuroregulator

Electrophysiological correlates for antinociceptive effects of histamine after intracerebral administration to the rat

Data have been collected indicating possible functions for histamine in brain but there are only a very few data, collected exclusively with behavioural tests, about the effects of histamine on the perception of the pain, an important aspect in the homeostasis of the human body. The purpose of the present study was to investigate the effects of histamine, injected directly into the lateral cerebral ventriculi on the firing of nociceptive thalamic neurones, detected by electrophysiological techniques in rats rendered arthritic by injection of Freund's adjuvant into the left hindfoot. The noxious test stimuli used were either extension or flexion of the ankle or mild lateral pressure on the heel. With increasing doses of histamine (5, 10, 20, 40 micrograms) it was possible to observe an increasing inhibitory and long-lasting effects of the evoked activity, with a significant dose-effect linear regression. The inhibitory responses, induced by histamine, probably by a hyperpolarization phenomenon that decreased excitatory postsynaptic potentials, were clues for the presence of a histaminergic pathway in parallel with and/or in connection with other adrenergic, gabaergic, serotoninergic and opioidoergic pathways that regulate the transmission and the modulation of algogenic electrophysiological messages.

Interactions of mast cells with the nervous system ?Recent advances

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

Histamine modulates heat stress-induced changes in blood-brain barrier permeability, cerebral blood flow, brain oedema and serotonin levels: an experimental study in conscious young rats

The possibility that endogenous histamine plays an important role in modulating the pathophysiology of heat stress was examined in young rats using a pharmacological approach. Subjection of young animals (six to seven weeks old) to heat stress at 38 degrees C for 4 h in a biological oxygen demand incubator (relative humidity 47-50%, wind velocity 20-25 cm/s) resulted in a profound increase in blood-brain barrier permeability to Evans Blue albumin (whole brain 375%) and [131I]sodium (whole brain 478%) along with a significant reduction in the cerebral blood flow (mean 34%). The water content of the whole brain was elevated by 4.5% (about 19% volume swelling) from the control. At this time-period, the plasma and whole brain 5-hydroxytryptamine levels were elevated by 656% and 328%, respectively, from the control group. Pretreatment with cimetidine (a histamine H2 receptor antagonist) significantly thwarted the increases in the brain water content and the blood-brain barrier permeability. In cimetidine-pretreated animals, the cerebral blood flow was significantly elevated and the plasma and brain 5-hydroxytryptamine (serotonin) levels were slightly but significantly reduced as compared with the untreated stressed group. However, prior treatment with mepyramine (a histamine H1 receptor antagonist) neither attenuated the changes in water content and the blood-brain barrier permeability nor altered the cerebral blood flow and 5-hydroxytryptamine levels. In fact, there was a significantly higher permeation of the tracers across the cerebral vessels in these drug-treated animals along with a greater accumulation of the brain water content as compared with the untreated stressed group. The cerebral blood flow and 5-hydroxytryptamine levels showed only minor changes from the untreated stressed group. These results show, probably for the first time, that (i) the endogenous histamine plays an important role in the pathophysiology of heat stress, and (ii) this effect appears to be mediated via specific histamine H2 receptors.

Histamine H1 receptors in human brain visualized in vivo by [11C]doxepin and positron emission tomography

Histamine H1 receptors in the living human brain were visualized by positron emission tomography (PET) using [N-11C-methyl]-(E)-doxepin ([11C]doxepin). The regional distribution of the carbon-11-labeled compound in the brain corresponded well with that of the histamine H1 receptors measured in vitro using [3H]pyrilamine. The radioactivity in the brain was significantly reduced by intravenous pretreatment with d-chlorpheniramine (5 mg), a histamine H1 antagonist. The regional distribution of [11C]doxepin in the brain 45-90 min after its injection was almost the same as that of [11C]pyrilamine in the brain. These results indicate that [11C]doxepin is useful for measuring histamine H1 receptors in human brain by PET.

Immunocytochemical and biochemical studies of histamine in the retina of the turtle Pseudemys scripta

A combination of immunocytochemical and biochemical methods was used to study histamine in the turtle retina. Histamine-like immunoreactivity was localized within paraboloids of certain cone photoreceptors by use of two different antisera directed against histamine. Preincubation of eyecups in Ringer's containing 10 microM histamine selectively increased the immunoreactivity of these photoreceptor paraboloids. The present localization of histamine in paraboloids indicated that, although histamine is in photoreceptors of the turtle retina, it may play some metabolic or neuromodulatory role, and not function as a neurotransmitter.

Dimaprit--induced neurotoxicity

The neurotoxicity of the histamine H2 agonist dimaprit was characterized. Dimaprit (100 micrograms administered into the lateral cerebral ventricle) induced a large area of brain necrosis 1-3 days later which was uniformly lethal. Lower doses caused dose - related effects on survival, gross brain pathology and body weight. Experiments with other H2 agonists and H2 antagonists, together with studies by others demonstrating a similar toxicity of the congener homodimaprit suggest that the neurotoxicity of dimaprit is independent of brain H2 receptors. Although dimaprit is a useful tool for the characterization of H2 receptor responses, the present results show that this agent must be used with caution, if at all, in classifying brain H2-receptor mediated events.

Evidence that histamine-stimulated prolactin secretion is not mediated by an inhibition of tuberoinfundibular dopaminergic neurons

The effects of histamine on prolactin secretion and the activity of tuberoinfundibular dopaminergic (DA) neurons were examined in male rats. Tuberoinfundibular DA neuronal activity was estimated in situ by measuring the metabolism [concentration of 3,4-dihydroxyphenylacetic acid (DOPAC)] and synthesis [accumulation of 3,4-dihydroxyphenylalanine (DOPA) after administration of a decarboxylase inhibitor] of dopamine in the median eminence. Intracerebroventricular (icv) injection of histamine produced a dose- and time-dependent increase in plasma prolactin levels but had no effect on DOPA accumulation or DOPAC concentrations in the median eminence. These results indicate that the stimulation of prolactin secretion following icv histamine is not mediated by an inhibition of tuberoinfundibular DA neurons.

Aminergic neurons in the brain of blowflies and Drosophila: dopamine- and tyrosine hydroxylase-immunoreactive neurons and their relationship with putative histaminergic neurons

The distribution and morphology of neurons reacting with antisera against dopamine (DA), tyrosine hydroxylase (TH) and histamine (HA) were analyzed in the blowflies Calliphora erythrocephala and Phormia terraenovae. TH-immunoreactive (THIR) and HA-immunoreactive (HAIR) neurons were also mapped in the fruitfly Drosophila melanogaster. The antisera against DA and TH specifically labeled the same neurons in the blowflies. About 300 neurons displayed DA immunoreactivity (DAIR) and THIR in the brain and subesophageal ganglion of the blowflies. Most of these neurons were located in bilateral clusters; some were distributed as bilateral pairs, and two ventral unpaired median (VUM) neurons were seen in the subesophageal ganglion. Immunoreactive processes were found in all compartments of the mushroom bodies except the calyces, in all divisions of the central body complex, in the medulla, lobula and lobula plate of the optic lobe, and in non-glomerular neuropil of protocerebrum, tritocerebrum and the subesophageal ganglion. No DA or TH immunoreactivity was seen in the antennal lobes. In Drosophila, neurons homologous to the blowfly neurons were detected with the TH antiserum. In Phormia and Drosophila, 18 HA-immunoreactive neurons were located in the protocerebrum and 2 in the subesophageal ganglion. The HAIR neurons arborized extensively, but except for processes in the lobula, all HAIR processes were seen in non-glomerular neuropil. The deuto- and tritocerebrum was devoid of HAIR processes. Double labeling experiments demonstrated that TH and HA immunoreactivity was not colocalized in any neuron. In some regions there was, however, substantial superposition between the two systems. The morphology of the extensively arborizing aminergic neurons described suggests that they have modulatory functions in the brain and subesophageal ganglion.

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.

Histamine-induced cyclic AMP accumulation in type-1 and type-2 astrocytes in primary culture

Histamine-induced cyclic AMP (cAMP) accumulation was studied in purified primary cultures of type-1 and type-2 astrocytes from neonatal rat brain. Histamine induced remarkable cAMP accumulation in type-1 astrocytes in a dose-dependent manner (EC50 = 1.2 x 10(-5) M, Emax = 1100% of control). In contrast, histamine had no significant effect on cAMP accumulation in type-2 astrocytes. Famotidine, an H2-antagonist, dose-dependently inhibited histamine-induced cAMP accumulation in type-1 astrocytes (Ki = 3 x 10(-8) M), but mepyramine (10(-6) M), an H1-antagonist, had no effect. Dimaprit and impromidine, H2-agonists, stimulated cAMP accumulation, but 2-pyridylethylamine, an H1-agonist, did not stimulate it nor augment the H2-agonist-induced cAMP accumulation. These results indicate that (1) histamine induces cAMP accumulation in type-1 astrocytes but not in type-2 astrocytes, and that (2) histamine-induced cAMP accumulation in type-1 astrocytes is mediated by H2-receptors without significant augmentation via H1-receptors.

Is the histaminergic neuron system a regulatory center for whole-brain activity?

Recent immunocytochemical studies have demonstrated the existence of histaminergic neurons in the brain, which are concentrated in the tuberomammillary nucleus of the posterior hypothalamus, and which project efferent fibers to almost all parts of the brain. Three subtypes of histamine receptors are widely distributed in the brain, not only on neurons but also on astrocytes and blood vessels. Consistent with its wide-ranging output, the histaminergic neuron system regulates various activities of the brain, such as the arousal state, brain energy metabolism, locomotor activity, neuroendocrine, autonomic and vestibular functions, feeding, drinking, sexual behavior, and analgesia--this regulation is possibly achieved by the histaminergic system as a whole.

Histaminergic neuron system in the brain: distribution and possible functions

Recent immunocytochemical studies have identified the histaminergic neuron system in the brain. In the rat brain, histaminergic neuronal cell bodies are located in the tuberomammillary nucleus in the posterior hypothalamus, while histaminergic fibers are distributed in almost all regions of the brain. Similar distributions of histaminergic neuronal cell bodies and fibers have been reported in the brains of other mammals and nonmammalian vertebrates. As expected from the widespread distributions of the efferent fibers, the central histaminergic neuron system seems to be involved in multiple functions in the brain. The results of intracerebral injection of histamine and administration of alpha-fluoromethylhistidine (FMH), which depletes brain histamine level, suggest that the central histaminergic system may modulate feeding, drinking and sexual behaviors, sleep-wakefulness and circadian rhythm, neuroendocrine and cardiovascular controls and thermoregulation.

Role of histaminergic mechanisms in the regulation of some stress responses in rats

The involvement of histaminergic mechanisms in the regulation of some stress responses was studied in rats. The brain neuronal histamine (HA) depletor, alpha-fluoromethyl histidine (alpha-FMH), at doses (50 or 100 mg/kg) which markedly lower brain HA, significantly attenuated the gastric ulcer formation and the elevation in plasma corticosterone in response to cold restraint stress (CRS). alpha-FMH also appreciably reduced gastric mucosal HA content. The H1-antagonist, pheniramine (25 mg/kg), attenuated both the gastric mucosal and endocrine response to CRS, while the effects of the H2-antagonist, cimetidine (200 mg/kg), were on the plasma corticosterone levels. These results are discussed in light of complex HA-ergic mechanisms in the maintenance of physiological homeostasis during stress.

Organization of the histaminergic system in the brain of the teleost, Trachurus trachurus

To accumulate phylogenetic information on the central histaminergic system, we investigated the histaminergic system in the brain of a teleost, the jack mackerel (Trachurus trachurus), using the indirect immunofluorescent method with antiserum against histamine. A small number of histamine-immunoreactive cell bodies were observed in the posterior hypothalamus around the posterior recess. Histamine-immunoreactive fibers innervated the telencephalon, diencephalon, tegmentum, and rostral part of the medulla oblongata. The immunoreactive fibers were very sparse or absent in the olfactory bulb, optic tectum, cerebellum, caudal part of the medulla oblongata, spinal cord, and hypophysis. Ascending fiber bundles were seen in the basal hypothalamus, supplying fiber collaterals to the telencephalon and diencephalon, whereas descending fibers were observed in the midline of the lower brainstem. These findings suggest that the central histaminergic system of the jack mackerel is homologous to those of mammals, reptiles, and amphibians, although poorly developed compared with them. The histamine-immunoreactive neuronal cell bodies found in the border area between the mesencephalon and rhombencephalon of the river lamprey were not detected in the brain of the jack mackerel.

Immunohistochemical evidence for the presence of type B monoamine oxidase in histamine-containing neurons in the posterior hypothalamus of cats

Using a double immunostaining method, we demonstrated that type B monoamine oxidase (MAO-B) immunoreactivity was present in virtually all histamine (HA)-immunoreactive neurons in the posterior hypothalamus of the cat. Not all MAO-B-positive neurons, however, displayed HA immunoreactivity: a minor group of neurons immunoreactive for MAO-B alone was observed in the area dorsolateral to the caudal arcuate nucleus. The results suggest that the degradation of tele-methylhistamine might occur within the intraneuronal structures of histaminergic neurons.

Histidine decarboxylase measurement in brain by 14CO2 trapping

A method for measuring histidine decarboxylase (HDC) in crude rat brain homogenates was developed by modification of existing 14CO2-trapping methods. The addition of EDTA to tissue homogenates and assay buffer reduced non-enzymatic decarboxylation, and improved assay sensitivity and reliability. Addition of polyethylene glycol (molecular weight 300, PEG300) to the homogenizing buffer increased enzyme stability, permitting storage of crude homogenates. Studies of time course, tissue dilution and blanks showed that up to 8 mg of tissue could be assayed successfully with a 3.5-hr incubation. S-alpha-Fluoromethylhistidine (FMH) and alpha-hydrazinohistidine, specific inhibitors of HDC, induced concentration-dependent reductions of enzyme activity by up to 90%, whereas inhibitors of other decarboxylases had little or no effect. Kinetic studies of the enzyme in crude homogenates yielded Km and Vmax values similar to those found previously with other HDC methods, although a poor fit was found to a single enzyme model. When determined by the new method, the distribution of HDC in seven regions of the rat brain agreed well with previous results. The method is rapid, simple to perform, and requires no specialized equipment other than a scintillation counter.

Biochemical characterization of histamine H1 receptors in bovine adrenal medulla

Bovine adrenal medullary membranes display high affinity and saturable binding to [3H]mepyramine, a selective H1 antagonist, with Kd of 1.5 +/- 0.1 nM and Bmax of 694 +/- 12 fmol/mg protein. [3H]Azidobenzpyramine, an azidobenzamide derivative of mepyramine, was synthesized and used to photolabel the high affinity mepyramine binding sites. Following photolysis, a protein component with an approximate molecular weight of 53-58 kDa was shown to be covalently labeled, as judged by gel filtration and SDS/PAGE; labeling being greatly reduced in the presence of excess unlabeled mepyramine. These results indicate that bovine adrenal medulla expresses a large number of H1 receptors, which are pharmacologically and biochemically indistinguishable from the H1 receptor of many other tissues of various species.

Histamine-immunoreactive neurons in the midbrain and suboesophageal ganglion of sphinx moth Manduca sexta

This paper describes the distribution of histamine-like immunoreactivity in the midbrain and suboesophageal ganglion of the sphinx moth Manduca sexta. Intense immunocytochemical staining was detected in ten bilateral pairs of neurons in the median protocerebrum and in one pair of neurons in the suboesophageal ganglion. Whereas most areas of the brain and suboesophageal ganglion are innervated by one or more of these neurons, typically no immunoreactive fibers were found in the mushroom bodies, the protocerebral bridge, and the lateral horn of the protocerebrum. The 11 histamine-immunoreactive neurons were reconstructed from serial sections. Ten neurons have bilateral arborizations, often with axonal projections in symmetric areas of both hemispheres. One neuron, whose soma resides in the lateral protocerebrum, has only unilateral projections. Of the 11 neurons, 6 occur in pairs with similar morphological features. In addition to these neurons, weak histamine-like immunoreactivity was detected in 7-13 interneurons that were not reconstructed individually. The central projections of the ocellar nerves from the intracranial ocelli also exhibit histamine-like immunoreactivity. The single-cell reconstructions reveal similarities between the organization of histamine- and serotonin-immunoreactive neurons in the brain and suboesophageal ganglion of this insect.

Single type-2 astrocytes show multiple independent sites of Ca2+ signaling in response to histamine

Intracellular Ca2+ plays an important role in signal transduction as a second messenger. In various types of cells, inositol 1,4,5-trisphosphate-induced elevations of intracellular free Ca2+ concentration ([Ca2+]i) have been reported to be uniform in single cells or originate at discrete sites from which they then propagate throughout the cells. These observations so far imply that a single cell functions as a minimal unit for inositol 1,4,5-trisphosphate-induced Ca2+ signaling. In this study, we examined the effects of histamine on [Ca2+]i of type-2 astrocytes using fura-2-based digital imaging fluorescence microscopy and found an unusual type of Ca2+ signaling in these cells. Histamine induced [Ca2+]i elevation in type-2 astrocytes by means of histamine H1 receptors. Submaximal concentrations of histamine (10(-7)-10(-6) M) evoked multiple sites of oscillatory [Ca2+]i elevation in single type-2 astrocytes. These Ca2+ "hot spots" were localized in the processes of the astrocytes but not in the cell bodies. The time courses of [Ca2+]i oscillations in different hot spots were not synchronized, indicating that each of them formed an independent compartment of Ca2+ signaling. When higher concentrations (10(-5)-10(-4) M) of histamine were added, [Ca2+]i in the processes remained elevated at high levels and [Ca2+]i elevations propagated from the processes to the cell bodies. These results suggest that individual processes of type-2 astrocytes can form minimal units for Ca2+ signaling in response to submaximal concentrations of histamine and that single type-2 astrocytes may function as multiple units for Ca2+ signaling.

Effects of thioperamide, a histamine H3 receptor antagonist, on locomotor activity and brain histamine content in mast cell-deficient W/Wv mice

The purpose of this study was to examine the effects of thioperamide, a histamine H3 antagonist, on the locomotor activity and the brain histamine content in mast-cell-deficient W/Wv mice. Thioperamide (12.5 and 25 mg/kg) showed significant increase in the locomotor activity of W/Wv mice, measured by a photo-beam system, 1 hr after the intraperitoneal injection. However, more than 75 mg/kg of thioperamide showed not only the reduction of the locomotor activity but also the inhibition of motor coordination measured by the rotarod performance. The increase in the locomotor activity by thioperamide was blocked by i. p. pretreatment with (R)-alpha-methyl-histamine, an H3 agonist, or pyrilamine, an H1 antagonist, or zolantidine, an H2 antagonist. The brain histamine content was decreased by thioperamide (12.5-75.0 mg/kg), 1 hr after administration. Thus, the blockade of histamine H3 receptor by thioperamide showed the activation of locomotor activity of mice, which may be mediated by H1 and/or H2 receptors. The present data support the hypothesis that central histaminergic neurons may be involved in the control of state of wakefulness.

Histaminergic neuron system: morphological features and possible functions

The histaminergic neuron systems in rat brain have been identified by immunocytochemical techniques using antibodies against histidine decarboxylase or histamine itself. Here, the details of the distribution of the histaminergic neuron networks are presented. Judging from the widespread distribution of the nervous system, it is postulated that the histaminergic neuron system is involved in various brain functions. Some functions, including the circadian rhythms, sleep-arousal cycles, drinking, feeding, thermoregulation, and neuroendocrine controls which were elucidated by administration of alpha-fluoromethylhistidine, a suicide substrate for histidine decarboxylase, are discussed here, although the true functions are still under investigations.

Histamine in the treatment of vertigo

The vasodilating properties of histamine were the basis for histamine treatment of episodic vertigo and other inner ear dysfunctions. The successes obtained led to the development of betahistine: an orally active histamine analogue; its general pharmacology resembles that of histamine. Animal pharmacology experiments proved that betahistine increases cerebral blood flow and probably also affects vestibular neurons. From clinical studies, it appears that betahistine is an effective agent for the symptomatic treatment of Meniere's syndrome. Efficacy has also been shown in the treatment of patients suffering from paroxysmal vertigo.

Influence of age and gender on the levels of histamine metabolites and pros-methylimidazoleacetic acid in human cerebrospinal fluid

The metabolites of histamine, tele-methylhistamine (t-MH) and tele-methylimidazoleacetic acid (t-MIAA), were measured in cerebrospinal fluid (CSF) from 47 subjects with neurological disorders and healthy controls. In lumbar CSF, concentrations of these metabolites were significantly correlated. Levels of t-MH, t-MIAA and their sum (which represents virtually all histamine metabolized in brain) were significantly higher in CSF from older subjects and were positively correlated with age. Females had higher levels of histamine metabolites than males. Males had higher levels of pros-methylimidazoleacetic acid (p-MIAA), an isomer of t-MIAA that is not a metabolite of histamine. Levels of p-MIAA increased with age among men. Analysis of covariance indicated that the subjects' health status had little or no effect on age- or sex-related differences in levels of analytes in CSF; sex-related differences were independent of changes attributed to age. These results are in contrast to those of age-related effects on levels of other aminergic transmitter metabolites in CSF and suggest that metabolic activity of histamine in brain may increase with age.

Neuroendocrine functions of histamine

The neurotransmitter histamine (HA) participates in the neuroendocrine regulation of pituitary hormone secretion and in the regulation of some peripheral hormones. In general, HA has a stimulatory but indirect effect on the release of these hormones by activation of postsynaptic receptors in the hypothalamic region. The release of the pro-opiomelanocortin-derived peptides ACTH, beta-endorphin (beta-END), and alpha-melanocyte-stimulating hormone (alpha-MSH) occurs by stimulation of H1- and H2-receptors and seems to be mediated via release of corticotropin-releasing hormone and vasopressin from the hypothalamus. The HA-induced release of prolactin (PRL) involves H2-receptors in some hypothalamic areas and H1-receptors in other areas. The release of PRL occurs by histaminergic inhibition of tuberoinfundibular dopaminergic neurons and by stimulation of serotoninergic and vasopressinergic neurons. Histaminergic neurons seem to participate in the mediation of the stress-induced release of ACTH, beta-END, alpha-MSH, and PRL. The neurohypophysial hormones vasopressin and oxytocin are stimulated by HA, and a physiological role of HA in the control of vasopressin secretion is likely. HA stimulates the release of peripheral catecholamines and renin. The stress-induced increase in plasma catecholamines and plasma renin activity (PRA) seems also to involve central histaminergic neurons. The effect of HA and stress on peripheral catecholamines is mediated via H1- and H2-receptors, while that on PRA is mediated via H2-receptors.

L-histidine attenuates the effects of pentazocine on rewarding brain-stimulation

Previous research has indicated that the antihistamine tripelennamine potentiates the threshold lowering effects of pentazocine on brain stimulation reward, a model of drug-induced euphoria. To determine the importance of histamine in this interaction, we studied the effects of co-administration of L-histidine and pentazocine on the threshold for brain stimulation reward. Pentazocine (2.5-10.0 mg/kg) lowered the threshold for rewarding stimulation to the medial forebrain bundle-lateral hypothalamus in male F344 rats. L-histidine (500 and 750 mg/kg) by itself had no significant effects, yet antagonized the threshold lowering effects of pentazocine. These doses of L-histidine are known to significantly raise brain histamine concentrations. Our results suggest that histamine may play a tonic inhibitory role, at least in part, on the neural systems responsible for the reinforcing properties of pentazocine.

Histamine metabolites and pros-methylimidazoleacetic acid in human cerebrospinal fluid

In cerebrospinal fluid, levels of the histamine metabolites, tele-methylhistamine and tele-methylimidazole-acetic acid, were higher in elderly than in young people, and women had higher levels than men. Therefore, age and gender should be considered in studies of histamine metabolites as exemplified by their measurements in cerebrospinal fluid of patients with Huntington's disease. Levels of pros-methylimidazoleacetic acid, an isomer of tele-methylimidazoleacetic acid and not a metabolite of histamine, were higher in cerebrospinal fluid of men than of women. Levels of pros-methylimidazoleacetic acid in cerebrospinal fluid were highly positively correlated with the severity of Parkinson's disease in a group of non-medicated, mildly to moderately affected patients.

Visualization of histamine H1 receptors in dog brain by positron emission tomography

Histamine H1 receptors were visualized in the living dog brain using [11C]pyrilamine or [11C]doxepin by positron emission tomography (PET). The regional distribution of these carbon-11 labeled compounds in the brain corresponded well with that of the histamine H1 receptors separately determined by in vitro binding assay. The radioactivity in the brain was reduced by treatment with triprolidine (1 mg/kg), a histamine H1 antagonist. The results of our study indicate that it is feasible to visualize histamine H1 receptors in human brain using these 11C-labeled compounds and PET.

Three histamine receptors (H1, H2 and H3) visualized in the brain of human and non-human primates

The distribution of histamine H1, H2 and H3 receptors in postmortem human and rhesus monkey brain was examined using receptor autoradiography. [125I]Iodobolpyramine, [125I]iodoaminopotentine and [3H](R) alpha-methylhistamine were used as ligands to label H1, H2 and H3 receptors respectively. The 3 receptor subtypes were identified in the human and monkey brains. Each receptor presented comparable distribution in the two primate brains. H1 and H2 receptors were particularly enriched in the caudate and putamen and observed in other brain areas such as the neocortex and hippocampus. H3-receptors were found to predominate in the basal ganglia where the highest densities were localized in the two segments of the globus pallidus. They were also observed in the hippocampus and cortical areas. The distribution of these 3 histamine receptors in the primate brain suggests the involvement of histaminergic mechanism in the functions of many brain areas. In particular, H2 and H3 receptors could play a role in the regulation of the basal ganglia functions in primates.

Histamine H1-receptor-like binding sites in the locust nervous tissue

The histamine H1-receptor-like binding sites in the nervous tissue of the locust Locusta migratoria were investigated with a conventional radio-receptor assay using [3H]mianserin as the radio ligand. Binding of [3H]mianserin to the binding site is sensitive to proteases and heat treatment. It shows the characteristics of ligand-receptor interactions. The single binding site has high affinity for mianserin (KD = 7.05 nM) and is present in high concentrations (Bmax = 1.53 pmol/mg) in the whole nervous tissue. All tested antihistamines have a high affinity for the binding site, which suggests that it represents an insect histamine receptor. Nevertheless, it shows its peculiarities distinguishing it from vertebrate histamine H1-receptors.

Differential effects of psychotropic drugs on feeding in rats: is histamine blockade involved?

The present animal studies tested the hypothesis that drug-induced blockade of histamine-1 receptors leads to appetite stimulation. Test agents included the antipsychotic promazine which has very potent antihistaminic effects, as well as the antipsychotic haloperidol and the antidepressant desipramine which both have negligible antihistaminic effects. In support of the hypothesis, significant appetite stimulation occurred only with promazine, while the other two test agents did not increase feeding, and even produced some suppression in food intake.

Histaminelike immunoreactive neurons innervating putative neurohaemal areas and central neuropil in the thoraco-abdominal ganglia of the flies Drosophila and Calliphora

The fused thoraco-abdominal ganglia of the flies Calliphora vomitoria and Drosophila melanogaster were investigated immunocytochemically with antisera against histamine. In both insect species, 18 histaminelike immunoreactive (HA-IR) neurons were resolved in these ganglia. Six of these neurons have cell bodies in the thoracic neuromeres and 12 in the fused abdominal neuromeres. All cell bodies are situated ventrally. In Calliphora all cell bodies are arranged in a segmental pattern. In Drosophila only the thoracic cell bodies have a segmental arrangement, whereas the abdominal ones are clustered anteriorly close to the last thoracic neuromere. In both species the six thoracic neurons supply processes to the synaptic neuropil in the thoracic neuromeres and to the dorsal neural sheath. The processes in the neural sheath run anteriorly in the lateral portions of the ganglion into the cervical connective. In a few regions laterally arborizing terminals are found in putative neurohaemal areas. These areas were investigated by electron microscopic immunocytochemistry in Calliphora. The HA-IR terminals (containing small granular vesicles) were found outside the "blood-brain barrier" below the acellular basal lamina of the neural sheath. Release of histamine into the circulation is therefore theoretically possible. The central processes of the six thoracic HA-IR neurons may interact synaptically with large numbers of other neurons in the neuropil, and the peripheral varicose fibers from the same HA-IR neurons possibly are neurohaemal release sites. The abdominal HA-IR neurons, in contrast, form extensive arborizations within the synaptic neuropil only. Both thoracic and abdominal neurons have ipsilateral and contralateral branches as well as processes that invade more than one neuromere. A single HA-IR neuron thus invades large volumes of synaptic neuropil. Histamine may be used by neurons of the ventral ganglia both as neurotransmitter (or neuromodulator) and as a circulating neurohormone released from the neural sheath.

Organization of the histaminergic system in the brain of the turtle Chinemys reevesii

To accumulate phylogenetic information on the central histaminergic system, we investigated the histaminergic system in the brain of the Reeves turtle, Chinemys reevesii, using the indirect immunofluorescent method with antiserum against histamine. Histaminergic neuronal cell bodies were found exclusively in the posterior part of the ventral hypothalamus. Histaminergic varicose fibers innervated almost all parts of the turtle brain, but tended to be concentrated in several areas. Very dense innervation was observed in the medial part of the telencephalon, ventrolateral part of the hypothalamus, nucleus habenularis lateralis, and ventromedial part of the tegmentum. Medium density of innervation was seen in the olfactory bulb, nucleus medialis amygdalae, and tectum. Only a few fibers were detected in the lateral part of the telencephalon, dorsal part of the hypothalamus, thalamus, rhombencephalon, and spinal cord. The main ascending fibers were observed in the lateral part of the hypothalamus, sending dense fiber bundles to the cortices dorsomedialis and medialis and nucleus habenularis lateralis. Descending fibers appeared to run in the ventral tegmental area, passing through the dorsal and ventral parts of the midline of the brain stem to the spinal cord. These findings indicate that the general morphological features of the histaminergic system in the turtle brain are similar to those in the mammalian and frog brains.

Influence of age and gender on the levels of histamine metabolites and pros-methylimidazoleacetic acid in human cerebrospinal fluid

The metabolites of histamine, tele-methylhistamine (t-MH) and tele-methylimidazoleacetic acid (t-MIAA), were measured in cerebrospinal fluid (CSF) from 47 subjects with neurological disorders and healthy controls. In lumbar CSF, concentrations of these metabolites were significantly correlated. Levels of t-MH, t-MIAA and their sum (which represents virtually all histamine metabolized in brain) were significantly higher in CSF from older subjects and were positively correlated with age. Females had higher levels of histamine metabolites than males. Males had higher levels of pros-methylimidazoleacetic acid (p-MIAA), an isomer of t-MIAA that is not a metabolite of histamine. Levels of p-MIAA increased with age among men. These results are in contrast to those of age-related effects on levels of other aminergic transmitter metabolites in CSF and suggest that metabolic activity of histamine in brain may increase with age.

Differential effects of morphine on histamine metabolism in brain and spinal cord of mice

The effects of morphine on the levels of histamine (HA), its metabolite tele-methylhistamine (t-MH) and on t-MH synthesis rates (thought to be indicative of neuronal HA release) were investigated in brain regions and spinal cords of DBA/2J (DBA) and C57/BL6 (C57) mice, two strains known to differ in their sensitivity to morphine. In DBA (a strain highly sensitive to morphine antinociception), morphine (10 mg/kg, s.c.) had no effect on brain regional t-MH or HA levels, but produced a generalized inhibition of regional t-MH synthesis rates ranging from 11 to 53%. The monoamine oxidase (MAO) inhibitor pargyline (used to estimate t-MH synthesis rates) had no effect on HA or t-MH levels in the DBA or C57 spinal cord, indicating the absence of detectable spinal HA turnover. Morphine (10 mg/kg) had no effect on DBA or C57 spinal cord HA or t-MH levels, but significantly increased t-MH synthesis in the DBA but not in the C57 spinal cord. These results suggest that in DBA mice, antinociceptive doses of morphine inhibit HA release in brain, and promote the release of HA from spinal cord. Neither effect was found in C57 mice, which are resistant to morphine antinociception. The relevance of these actions to previous studies showing the blockade of opiate antinociception by H2 antagonists remains to be established.

Intraocular hypothalamic transplants containing histaminergic neurons: innervation of host iris and hippocampal cografts

Hypothalamic tissue containing the tuberomammillary nucleus was dissected from fetuses of Embryonic Day 17 and inserted into the anterior chamber of the eye of young adult recipient rats. The growth of hypothalamic grafts was monitored through the translucent cornea and transplants were found to double in size over the 8 first weeks in oculo. After 4 weeks fetal hippocampal formation (Embryonic Day 18) was inserted into the eye chamber in half of the previously grafted animals and placed in contact with the first grafts. Double grafts were allowed to mature for up to 18 weeks before sacrifice. Recipient rats were anesthetized and superfused with carbodiimide and paraformaldehyde, after which transplants were removed, frozen, sectioned on a cryostat, and incubated with histamine antibodies. Immunohistochemical evaluations revealed a large number of histamine-positive nerve cell bodies with processes innervating the entire hypothalamic graft with a dense plexus of varicose fibers. Such histamine-positive fibers were also seen to invade the surrounding host iris in some cases with thick axon bundles as well as with single fibers. When hypothalamic transplants were combined with hippocampal grafts numerous histamine-immunoreactive fibers invaded the hippocampal tissue to form a plexus of varicose terminals throughout the cografts. After 4 weeks in oculo only a sparse histamine-positive innervation of hippocampal grafts was found, while 18-week-old double grafts contained a considerably larger amount of immunoreactive neurites.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical localization of histamine in flatworms

Specific antibodies against histamine were used to demonstrate the occurrence and cellular distribution of histamine-like immunoreactivity in three species of flatworms (phylum Platyhelminthes). In the parasitic cestode Diphyllobothrium dendriticum, histamine-reactivity was found in neurons of the main nerve cords, and in cells lining the central and peripheral excretory ducts. In the free-living microturbellarian Microstomum lineare and in the planarian Polycelis nigra, histamine-immunoreactivity was restricted to cells and fibres of the nervous system. The occurrence of histamine or a related substance in the nervous system of flatworms, which represent primary bilateria, indicates the importance of this neuroactive substance in the animal kingdom.

Immunohistochemical and biochemical evidence for the putative inhibitory neurotransmitters histamine and GABA in lobster olfactory lobes

As an initial effort to investigate possible inhibitory interactions in the olfactory system of the spiny lobster, studies were conducted to identify and localize the putative inhibitory neurotransmitters histamine and GABA in the olfactory lobe. Biochemical studies demonstrated that olfactory lobe tissue was capable of synthesizing histamine from radioactive histidine and GABA from glutamic acid. Immunohistochemistry was used to localize histamine and GABA in brain sections, by using either avidin-biotin conjugated peroxidase or fluorescein conjugated secondary antibody. Specific histamine-like and GABA-like immunoreactivity was found in soma clusters of olfactory interneurons, adjacent to the olfactory lobe. Small, putative glial cells displaying intense histamine-like immunoreactivity were found interspersed among the glomeruli of the lobe. The accessory lobe exhibited moderate immunostaining for both histamine and GABA. Positive immunostaining for histamine and GABA was also found in the olfactory lobes, with a predominance of staining in the outer caps of the glomeruli, which are thought to be the regions where the primary afferent terminals contact the processes of second-order olfactory neurons. These findings collectively implicate inhibition at the first synaptic level of the olfactory pathway in the spiny lobster.

Histamine in the retina: recent progress and perspectives

This article presents some new findings, and shortly surveys recently published data, on histamine (HA) in the retina of several vertebrates (carp, hen, rabbit, rat, guinea pig, cow, man). Analysis of various parameters (HA level, activity of histidine decarboxylase and HA-methyltransferase, release and uptake of HA, 3H-mepyramine binding, effect of HA on cAMP accumulation, diurnal variations) in vertebrate retina and brain shows that histaminergic systems in these sites are comparable, although some species-dependent differences have been observed. Interestingly, exposure of dark-adapted rabbits to light affects several histaminergic parameters selectively, i.e. in the retina and not in the brain. The reviewed data suggest that in retinas of at least some vertebrates HA may be a physiologically important amine.

Release of histamine in rat hypothalamus and corpus striatum in vivo

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

Distribution of histaminergic neurons in the brain of the lamprey Lampetra fluviatilis as revealed by histamine-immunohistochemistry

An antiserum against conjugated histamine was used to study the distribution of histaminergic neurons in the CNS of the lamprey Lampetra fluviatilis. Numerous histamine-immunoreactive cell bodies were detected in the dorsal and ventral hypothalamic nuclei and in the adjacent postinfundibular commissural nucleus. Histamine-immunoreactive fibers of high density were present in the ventral hypothalamus, and fibers could also be traced dorsally from the hypothalamus to the corpus striatum and septal nucleus where they appeared to terminate in dense plexuses. Another, smaller group of histamine-immunoreactive perikarya was observed in the border area between mesencephalon and rhombencephalon, near the caudal pole of the mesencephalic reticular nucleus. Sparsely distributed histamine-immunoreactive fibers were present in the ventral mesencephalon. The distribution of histaminergic neurons in cyclostomes, which diverged very early from the main vertebrate line, shows similarities with the corresponding systems in the CNS of amphibians and mammals, which suggests that histaminergic neuronal systems are phylogenetically old and have been conserved during evolution.

Comparative neuroanatomy of the histaminergic system in the brain of the frog Xenopus laevis

The distribution of the histaminergic neuronal system in the brain of the clawed frog Xenopus laevis was mapped with an antiserum against carbodiimide-fixed histamine and compared to that in mammals. The histamine-immunoreactive cell bodies were located in a small area of the posterolateral hypothalamus, close to the dorsal infundibular nucleus, which contains catecholaminergic and serotonergic neurons. This area may be homologous to the tuberomammillary nucleus in mammals. A thick process extended from each cell between the ependymal cell layer and terminated in the ventricle lumen. The number of histaminergic cell bodies in adult Xenopus brain was relatively low, as compared with the mammalian brain. Preliminary analysis of adjacent sections stained with antisera against GABA or serotonin indicated that the histamine cells were not immunoreactive for these. The pathways and distribution of histaminergic fibers in Xenopus brain showed many similarities to mammals. The densest fiber networks were present in the medial basal forebrain, particularly in the medial amygdala and septum. A distinct cluster of fibers was concentrated around the cell bodies of nucleus accumbens. In most pallial areas, the density was moderate to low. In the primordial piriform cortex and the striatum, very few fibers were seen. In diencephalon, highest fiber densities were found in the anterior and ventral thalamus and posterior and lateral hypothalamus. In hindbrain, the density was highest in the medullary central gray, as in some mammals. The results suggest that the general pattern of the histaminergic system in vertebrate brain is conserved from amphibians to mammals.

Pharmacological receptors: the need for a compendium of classification, nomenclature and structure

In an attempt to contain the chaos of receptor nomenclature, the supplement distributed with this issue of TiPS catalogues cell surface receptors and their subtypes according to the most commonly used nomenclature and describes them in pharmacological, biochemical and molecular terms. This reporting of the status quo will be an invaluable aid to communication, but all scientists (not just pharmacologists) working on receptors would agree that a radical and rational classification of receptors also needs to be initiated. In this article, Jack Peter Green proposes a system of (and mechanism for) classification that should satisfy both the 'taxonomic realists' and the 'taxonomic skeptics'.

Histidine decarboxylase from rat and rabbit brain: partial purification and characterization

Histidine decarboxylase, the synthetic enzyme for histamine, was partially purified from regions of rat or rabbit brain rich in the enzyme. The enzyme was purified using ion exchange and hydrophobic column chromatography and chromatofocusing. Approximately 70-fold and 110-fold enrichments were attained from rat and rabbit brain, respectively. Rat and rabbit brain histidine decarboxylase had isoelectric points of pH 5.4 and 5.6, Km values of 80 microM and 120 microM histidine and Vmax values of 210 and 625 pmol histamine formed/hr-mg protein, respectively. The partially purified histidine decarboxylase from both sources was dependent on pyridoxal phosphate for maximal activity and was inhibited by alpha-fluoromethylhistidine, nickel chloride and cobaltous chloride but was not inhibited by impromidine, alpha-methyldopa, DTNB, zinc chloride or mercuric chloride. The enzyme had a broad pH optimum between pH 7.2 and 8.0. These studies provide further information on the characteristics of mammalian histidine decarboxylase from brain.

Immunopharmacological properties of a protein-bound histamine metabolite

Histamine metabolite was prepared by incubating histamine dihydrochloride and diamino oxidase for 24 h at 37 degrees C. Radioactive histamine was used for monitoring the whole procedure and to select the best experimental protocol. Pharmacological activities of histamine are abolished by this procedure. Histamine metabolite was found to bind to the serum proteins, to inhibit the PHA response of mouse and human mononuclear cells and to accelerate mortality rates in tumor-bearing mice. Thin layer chromatography allowed separation of metabolite from histamine and from known imidazol-derived compounds. This is the first experimental evidence for immunological properties ascribed to a histamine metabolite.

A histamine-containing neuronal system in human brain

A well-organized network of varicose fibers was revealed throughout the frontal and temporal cortex of adult humans with specific antisera against histamine. The densest network of fibers was seen in lamina I, where varicose fibers were seen to run in parallel to the overlying pia mater. Electron microscopic immunohistochemistry revealed histamine-immunostaining in granules in a small number of nerve fibers and varicosities. Hypothalamic samples obtained from autopsy brains of adult humans revealed numerous histamine-immunoreactive nerve cell bodies in the posterior basal hypothalamus in and around the tuberomammillary nucleus. The results suggest that a histaminergic neuronal system reminiscent of that described in rodents is present in human brain.