Cerebral histamine: indications for neuronal and vascular regulation

A double-blind controlled trial of a single dose naproxen and an amino acid medical food theramine for the treatment of low back pain

To study the safety and efficacy of a new medical food (Theramine) in the treatment of low back pain, we performed a 28-day double-blind randomized controlled trial in 129 patients. Back pain was present for at least 6 weeks and was not mild. Patients were randomly assigned to receive medical food alone (n = 43), naproxen alone (250 mg/d, n = 42), or both medical food and naproxen (n = 44). All patients were assessed by using Roland-Morris Disability Questionnaire, Oswestry Low Back Pain Scale, Visual Analog Scale Evaluation and laboratory analysis performed at baseline and at 28 days for assessing the safety and impact on inflammatory markers, which included complete blood counts, C-Reactive protein (CRP), and liver function (alkaline phosphatase, aspartate transaminase, and alanine transaminase). At baseline, there were no statistically significant differences in low back pain when assessed by Roland-Morris function or Oswestry assessments nor were there differences in the blood indices of inflammation. At day 28, both the medical food group and combined therapy group (medical food with naproxen) were statistically significantly superior to the naproxen-alone group (P < 0.05). The medical food and naproxen group showed functional improvement when compared to the naproxen-alone group. The naproxen-alone group showed significant elevations in CRP, alanine transaminase, and aspartate transaminase when compared with the other groups. Medical food alone or with naproxen showed no significant change in liver function tests or CRP, with medical food potentially mitigating the effects seen with naproxen alone. The medical food (Theramine) appeared to be effective in relieving back pain without causing any significant side effects and may provide a safe alternative to presently available therapies.

Histamine-induced depolarization: ionic mechanisms and role in sustained contraction of rabbit cerebral arteries

The role of membrane depolarization in the histamine-induced contraction of the rabbit middle cerebral artery was examined by simultaneous measurements of membrane potential and isometric force. Histamine (1-100 microM) induced a concentration-dependent sustained contraction associated with sustained depolarization. Action potentials were observed during depolarization caused by histamine but not by high-K(+) solution. K(+)-induced contraction was much smaller than sustained contraction associated with the same depolarization caused by histamine. Nifedipine attenuates histamine-induced sustained contraction by 80%, with no effect on depolarization. Inhibition of nonselective cation channels with Co(2+) (100-200 microM) reversed the histamine-induced depolarization and relaxed the arteries but induced only a minor change in K(+)-induced contraction. In the presence of Co(2+) and in low-Na(+) solution, histamine-evoked depolarization and contraction were transient. We conclude that nonselective cation channels contribute to histamine-induced sustained depolarization, which stimulates Ca(2+) influx through voltage-dependent Ca(2+) channels participating in contraction. The histamine-induced depolarization, although an important and necessary mechanism, cannot fully account for sustained contraction, which may be due in part to augmentation of currents through voltage-dependent Ca(2+) channels and Ca(2+) sensitization of the contractile process.

Prediction of stroke outcome with echoplanar perfusion- and diffusion-weighted MRI

OBJECTIVES

We examined the utility of echoplanar magnetic resonance perfusion imaging and diffusion-weighted imaging (DWI) in predicting stroke evolution and outcome in 18 patients with acute hemispheric infarction.

METHODS

Patients were studied within 24 hours (mean, 12.2 hours), subacutely (mean, 4.7 days), and at outcome (mean, 84 days). Comparisons were made between infarction volumes as measured on perfusion imaging (PI) and isotropic DWI maps, clinical assessment scales (Canadian Neurological Scale, Barthel Index, and Rankin Scale), and final infarct volume (T2-weighted MRI).

RESULTS

Acute PI lesion volumes correlated with acute neurologic state, clinical outcome, and final infarct volume. Acute DWI lesions correlated less robustly with acute neurologic state, but correlated well with clinical outcome and final infarct volume. Three of six possible patterns of abnormalities were seen: PI lesion larger than DWI lesion (65%), PI lesion smaller than DWI lesion (12%), and DWI lesion but no PI lesion (23%). A pattern of a PI lesion larger than the DWI lesion predicted DWI expansion into surrounding hypoperfused tissue (p < 0.05). In the other two patterns, DWI lesions did not enlarge, suggesting that no significant increase in ischemic lesion size occurs in the absence of a larger perfusion deficit.

CONCLUSIONS

Combined early PI and DWI can define different acute infarct patterns, which may allow the selection of rational therapeutic strategies based on the presence or absence of potentially salvageable ischemic tissue.

In vitro relaxation of dog cerebral veins in response to histamine is mediated by histamine H2 receptors

There is little information on the histamine receptor mechanisms involved in cerebral venodilation, thus the role of histamine present in human cerebrospinal fluid is difficult to assess. In isolated canine pial veins, concentration-response curves to histamine (10[-7]-10[-3] M), the histamine H1 receptor agonist, 2-pyridylethylamine (10[-6]-10[-2] M), the histamine H2 receptor agonist, dimaprit (S-(3-dimethylaminopropyl) isothiourea dihydrochloride, 10[-6]-10[-2] M), and the histamine H3 receptor agonist, imetit (S-[2-(1 midazol-4-yl)ethyl]isothiourea dihydrobromide, 10[-7]-10[-3] M) were isometrically determined. In resting veins, histamine, 2-pyridylethylamine and dimaprit had no significant effect, whereas in endothelin-1-precontracted veins, these drugs produced concentration-dependent relaxation (Emax in % of active tone and pD2 were: for histamine, 72 +/- 6 and 5.36 +/- 0.09; for 2-pyridylethylamine, 59 +/- 5 and 3.28 +/- 0.05; for dimaprit, 65 +/- 7 and 4.81 +/- 0.10, respectively). The relaxations in response to histamine and dimaprit were competitively antagonized by the histamine H2 receptor antagonist, cimetidine (3 x 10[-6]-10[-4] M) (pA2 = 6.07 +/- 0.03 for histamine, and 6.09 +/- 0.07 for dimaprit), but were not affected by the histamine H1 receptor antagonist, chlorpheniramine (10[-6] M) or the histamine H3 receptor antagonist, thioperamide (N-cyclohexyl-4-(1-H-imidazol-4-yl)-1-piperidine-carbothioamide maleate, 10[-6] M). The relaxation in response to 2-pyridylethylamine was inhibited by cimetidine (10[-5] M), but not by chlorpheniramine (10[-6] M). Imetit produced a small contraction in resting veins (14 +/- 4 mg) and precontracted veins (20 +/- 3 mg), which was not modified by thioperamide (10[-6] M). The relaxation of veins in response to histamine was not modified by endothelium removal, nor by the inhibitor of nitric oxide synthase, N(G)-nitro-L-arginine methyl ester (10[-4] M), or the cyclooxygenase inhibitor, meclofenamate (10[-5] M). Therefore, in pial veins: (1) histamine produces relaxation by activation of histamine H2 receptors, probably located in the smooth musculature, with no participation of histamine H1 and H3 receptors, and (2) endothelium, nitric oxide and prostanoids are probably not involved in the relaxation in response to histamine.

Role of nitric oxide in histamine-induced increases in permeability of the blood-brain barrier

While previous studies have examined the effects of histamine on the permeability of the blood-brain barrier and reactivity of cerebral blood vessels, cellular mechanisms which account for histamine-induced affects on the cerebral microcirculation are not clear. The goals of this study were to determine the role of nitric oxide in histamine-induced increases in permeability of the blood-brain barrier and dilatation of pial arterioles. We examined the pial microcirculation in rats using intravital fluorescence microscopy. Permeability of the blood-brain barrier (clearance of fluorescent-labeled dextran; molecular weight 10,000 daltons; FITC-dextran-10K) and diameter of pial arterioles were measured in the absence and presence of histamine (10 and 100 microM). During superfusion with vehicle (saline), clearance of FITC-dextran-10K from pial vessels was minimal and diameter of pial arterioles remained constant. Topical application of histamine (10 and 100 microM) produced an increase in clearance of FITC-dextran-10K and diameter of pial arterioles. To determine a potential role for nitric oxide in histamine-induced increases in permeability of the blood-brain barrier and dilatation of pial arterioles, we examined the effects of NG-monomethyl-L-arginine (L-NMMA; 10 microM). L-NMMA inhibited histamine-induced increases in permeability of the blood-brain barrier and attenuated histamine-induced dilatation of cerebral arterioles. The findings of the present study suggest that histamine increases permeability of the blood-brain barrier and diameter of pial arterioles via the synthesis/release of nitric oxide or a nitric oxide containing compound.

Carrier-mediated uptake and release of histamine by cultured rat cerebral endothelial cells

The present study demonstrates that histamine could be taken up by and released from endothelial cells of brain capillaries. Incubation of cultured endothelial cells, with low (0.01-0.50 microM) concentrations of [3H]histamine, resulted in a rapid uptake of the amine. The uptake was saturable, Na(+)-dependent and yielded an apparent Km 0.3 +/- 0.02 microM and a Vmax 4.6 +/- 0.04 pmol/mg protein per min. After a 10-min incubation in a histamine-free medium, about 65% of [3H]histamine was released from the cells. Na(+)-deprivation and high K+, as well as the treatment of the cells with ouabain affected the release, resulting in significantly higher rates of the efflux. The ability of cerebral endothelial cells to take up histamine from both luminal and abluminal sides but to release it mainly luminally, may function as an important mechanism to protect the neural tissue from the harmful effects of this endogenous mediator of inflammation.

Histaminergic and non-histamine-immunoreactive mast cells within the cat lateral geniculate complex examined with light and electron microscopy

Mast cells and their location in the cat lateral geniculate complex of the thalamus were examined by means of histamine immunohistochemistry and the mast cell stain pinacyanol erythrosinate. Brain sections from seven normal adult pigmented cats were processed for light or electron microscopy. Histamine-containing and pinacyanol erythrosinate-stained mast cells were widespread throughout the dorsal and ventral lateral geniculate nuclei and the surrounding regions. Mast cells were especially numerous rostrally in the complex and in the geniculate C laminae. The cells were found consistently in association with blood vessels, ranging from capillary size to vessels c. 150 microns diameter, and twice as often with arterioles as with venules. Large clusters of many mast cells associated with single blood vessels were seen. Individual mast cells were typically 8 microns in diameter and somewhat oval, although multipolar and crescent-shaped cells were also seen, up to twice as long. The amount of histamine labeling varied across cells. When histamine-labeled material was secondarily stained with pinacyanol erythrosinate, many mast cells were double labeled. In addition, there was a small population of mast cells that stained only with pinacyanol erythrosinate, but was otherwise identical to the histamine-immunoreactive mast cells. Electron microscopic examination showed that the mast cells lie on the brain side of the blood-brain barrier. Mast cells were found in close proximity to the thalamic neuropil, primarily apposed to the processes of astrocytes, but also apposed to neural elements. The distinctive electron-dense cytoplasmic granules in the fully granulated, mature state were largely amorphous in appearance and as large as 700 nm in diameter. Histamine was dispersed throughout some granules and contained within restricted areas of other granules. In degranulated mast cells, large, irregularly shaped, electron-lucent granules were seen fused with the cell membrane on the neuropil side, as well as the lumen side of the mast cell. More mast cells were observed at the electron microscopic level than were expected from the light level observations, which suggests that, despite the numbers of mast cells labeled, these results may still underestimate the total mast cell population present in this region of the thalamus. Mast cells, by their numbers, their distribution and the potent chemical substances they contain, may significantly influence vascular and neural function, directly and indirectly, in the cat lateral geniculate complex.

Hypothalamo-preoptic histaminergic projections in sleep-wake control in the cat

Cats were chronically implanted with electrodes for polygraphic recordings and cannulae for intracerebral microinjections in order to study the functional role of histaminergic innervation of the preoptic-anterior hypothalamus in sleep-wake control. alpha-Fluoromethylhistidine (alpha FMH, 50 micrograms in 1 microliter), a specific inhibitor of the histamine-synthesizing enzyme, when injected bilaterally into the preoptic area, where numerous histaminergic fibres and terminal-like structures are present, caused a significant increase in deep slow wave sleep (S2) and paradoxical sleep (PS) and a decrease in wakefulness. In contrast, microinjections of histamine (5 or 30 micrograms in 1 microliter) in the same area dose-relatedly increased wakefulness and decreased both slow wave sleep and paradoxical sleep. The effects of histamine were reduced by pretreatment with mepyramine (1 mg/kg i.p.), a well known histamine H1 receptor antagonist, and were mimicked by a local injection of impromidine (1 microgram in 1 microliter), a potent histamine H2 receptor agonist. Microinjections of mepyramine alone (120 micrograms in 1 microliter) caused an increase in slow wave sleep. These results suggest that preoptic histaminergic innervation is involved in sleep-wake control and that the action might be mediated via both H1 and H2 receptors.

Histamine H1 receptors in UC-11MG astrocytes and their regulation of cytoplasmic Ca2+

Experiments were carried out on UC-11MG human astrocytoma cells, a continuous cell line that expresses a broad range of the biochemical and electrophysiological properties found in well-differentiated astrocytes. Because of a number of recent reports that astrocytes may express receptors for a variety of neuro-active substances, we measured the effects of 12 different neurotransmitters on intracellular free Ca2+ (Ca2+i) in UC-11MG cells. Of these neurotransmitters only histamine was found to have a significant effect. Further characterization of the nature of the histamine response showed that UC-11MG cells express mepyramine-sensitive H1 receptors the activation of which causes both mobilization of Ca2+ from intracellular stores and entry of Ca2+ from the extracellular solution. No evidence was found for the presence of H2 receptors. The Ca2+i response was maximal at 300 microM histamine and was attenuated by increasing cell density. We suggest that this neurotransmitter may play a role in astrocytic function in the human CNS.

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.

Effects of histamine on spontaneous electrical activity of neurons in rat suprachiasmatic nucleus

The hypothalamic suprachiasmatic nucleus (SCN) is thought to be a light-entrained pacemaker in mammals, inducing a wide range of endogenous circadian events. In rat brain, histaminergic (HAergic) fibres are particularly rich in the hypothalamus. This prompted an investigation of the influence of bath-applied HAergic compounds on the spontaneous electrical activity of SCN neurons, recorded extracellularly in the hypothalamic slice preparation. Cells activated by bath application of HA (n = 28) outnumbered those inhibited by HA (n = 6). 48% of cells tested (n = 28) were unresponsive to HA application. HA-induced activation of SCN neurons' discharge rate could be suppressed by the H1-antagonist mepyramine, but not by the H2-antagonist cimetidine. HAergic effects were still present when synaptic transmission was blocked, indicating a postsynaptic site of action for HA within SCN. Due to the anatomical distribution of HA-responsive SCN neurons and the independence of HA-effects with respect to circadian time, HA seems not to endow a pivotal role within generation and maintenance of circadian rhythm. Although data were obtained from SCN deprived of neural input, results show clear evidence for a modulatory impact of HA on the spontaneous electrical activity of part of SCN neurons.

[3H]mepyramine binding sites, histamine H1-receptors, in bovine retinal blood vessels

The presence of histamine H1-receptors in the bovine retinal blood vessels was studied with a [3H]mepyramine binding assay. The membranes of purified vessels obtained from bovine retinas showed specific [3H]mepyramine binding sites with a dissociation constant (KD) of 2.78 +/- 0.32 nM. This was similar to values obtained from the retinal neuronal fractions. The binding capacity (Bmax) was 53.8 +/- 1.7 fmol/mg protein, which was about a half that of the retinal neuronal fractions (108.9 +/- 3.1 fmol/mg protein). Some H1-antagonists proved to be potent competitors for [3H]mepyramine binding sites in bovine retinal blood vessels. These results indicate that histamine H1-receptors exist in the retinal blood vessels which may be involved in the physiological and the pathological responses of blood circulation in retinas.

Effects of aminoguanidine on pre- and post-irradiation regional cerebral blood flow, systemic blood pressure and plasma histamine levels in the primate

Exposure to ionizing radiation causes hypotension, cerebral ischemia and release of histamine (HA). To investigate the relationship among these three responses, rhesus monkeys (Macaca mulatta) received aminoguanidine (AG) (1 mg/kg), then were given either 50 Gy whole-body irradiation or sham-irradiation. Monkeys receiving AG had lower mean arterial blood pressure (MABP) than saline-treated controls. Compared to controls, rCBF was lower in irradiated monkeys but pre-treatment with AG did not influence this effect. Among untreated, irradiated monkeys, HA levels were increased only at two minutes post-irradiation, but among AG-treated, irradiated monkeys, HA levels were higher at all times postirradiation. Radiation-induced release of HA may be associated with radiation-induced hypotension and reduced rCBF, but failure of AG to alter rCBF suggests that released HA may not be the sole mediator of these effects. Because elevations in plasma HA are probably due to HA derived from degranulation of mast cells, release of other bioactive substances from mast cells may also influence these cardiovascular effects. Surprisingly, in sham-irradiated monkeys, AG alone had a slight but significant hypotensive effect.

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.

Role of histamine in pathophysiology of heat stress in rats

Role of histamine in pathophysiology of heat stress (HS) was examined using a pharmacological approach. Subjection of young animals (6-7 wks old) to HS at 38 degrees C for 4 in a B.O.D. incubator resulted in a profound increase in blood-brain barrier (BBB) permeability to Evans blue albumin (EBA) and 131I-sodium by 375% and 478% from the control values respectively. At this time period, the brain water content showed a 3.6% increase from the control. Pretreatment with histamine H2 receptor antagonist cimetidine significantly reduced the extravasation of both the tracers and thwarted the increase of brain water content as compared to the untreated group. On the other hand, pretreatment with histamine H1 antagonist mepyramine failed to reduce these parameters. On the contrary, there was a significantly higher permeation of the tracers in brain along with a greater accumulation of brain water content as compared to the untreated group. These results point out a beneficial effect of histamine H2 receptor antagonists in the pathophysiology of HS.

Maintenance of local cerebral blood flow after acute neuronal death: possible role of non-neuronal cells

In brain, a major factor regulating local perfusion is local neuronal activity. However, we have recently discovered that, in rat, five days after selective neuronal destruction in the parietal cortex by local microinjections of the excitotoxin ibotenic acid, local cerebral blood flow, within the lesion, remains in the normal range. We studied whether proliferating non-neuronal cells and/or local changes in microvascular density participate to maintain local cerebral blood flow. Rats were anesthetized (halothane 1-3%), ibotenic acid (10 micrograms in 1 microliter) was locally microinjected in a restricted region of the parietal cortex, and animals were allowed to recover. Three, five, seven, 11, 30 days later local cerebral blood flow was measured autoradiographically under chloralose anesthesia (40 mg/kg, s.c.) by the [14C]iodoantipyrine technique. Cellular density or microvascular area were determined on sections stained with Thionine or processed for the endothelial marker alkaline phosphatase, respectively. Local neurons were destroyed by 24 h after microinjections of ibotenic acid. However, from three to 11 days after lesion local cerebral blood flow was unchanged (P greater than 0.05; n = 5), thereafter declining so that by 30 days blood flow was 48 +/- 6% of control (P less than 0.05; n = 5). Cellular density increased within the lesion by 17.5-fold at seven to 11 days (P less than 0.01) and declined to a 11.7-fold elevation above control at day 30 (P less than 0.01). New cells consisted of macrophages, endothelium and glial fibrillary acidic protein-positive astrocytes. The microvascular area increased 4.2-fold from three to 11 days (P less than 0.01). The patency of the presumably newly formed vessels was determined by the presence of intravascular red blood cells, which were revealed histochemically. The area occupied by red blood cells within cerebral microvessels, in contrast to microvascular area, did not increase until seven days after lesion, reaching a 3.2-fold increase at 11 days. Thus within the lesion, local cerebral blood flow remains constant during the phase in which cellular and microvascular density increases. The presumably newly formed vessels cannot contribute to maintain local cerebral blood flow since during this phase they are not patent; rather patency develops coincident with the decline in local cerebral blood flow. We conclude that non-neuronal cells, most likely activated macrophages, may be an important factor regulating local cerebral perfusion, after acute neuronal death.

Pharmacological studies on relaxation of spastic primate cerebral arteries in subarachnoid hemorrhage

Chronic cerebral vasospasm was induced in 16 monkeys by direct placement of a clot of autologous blood over the arteries of the circle of Willis on the right side. The middle cerebral arteries (MCA's) on the clot side all showed angiographic vasospasm, which was maximal 7 days after subarachnoid hemorrhage. Animals were sacrificed at this time and vascular responses to acetylcholine (ACh), histamine, and the calcium ionophore A23187 were studied in MCA rings from the clot (spastic) side and the non-clot (control) side. In control preparations with an intact endothelium, which had been precontracted by prostaglandin F2 alpha (PGF2 alpha), histamine and A23187 produced significant relaxation. The same concentrations of histamine and A23187 did not relax vascular tissues in which the endothelium had been mechanically removed. Acetylcholine did not produce a significant endothelium-dependent relaxation of primate MCA rings, but did relax rings of primate common carotid artery. Pretreatment with chlorpheniramine (an H1-receptor antagonist) prevented histamine-induced relaxation; however, cimetidine (an H2-receptor antagonist) had no inhibitory action. It thus seems that histamine mediates relaxation of intact MCA's mostly by an H1-receptor-mediated release of endothelium-derived relaxing factor (EDRF). Relaxations induced by histamine and A23187 in MCA's from the clot side were substantially reduced. Moreover, the small component of ACh-induced relaxation was also abolished. Endothelium-independent relaxation induced by glyceryl trinitrate (GTN) occurred in arteries from both the control and the clot sides. Constrictions induced by KC1 and PGF2 alpha were reduced on the clot side of the MCA's. These results suggest that subarachnoid hemorrhage influences both the generation of EDRF and the constriction of affected arteries. The small contraction which was elicited in spastic arteries was fully relaxed by GTN.

Inhibitory effect of GABA on cerebrovascular sympathetic neurotransmission

The possibility that gamma-aminobutyric acid (GABA) could modulate sympathetic neurotransmission in the cerebrovascular bed of the goat has been investigated by means of 3 experimental approaches: measurement of cerebral blood flow in the anesthetized animal, recording of isometric tension in isolated cerebral arteries, and measurement of tritium efflux from cerebral arteries preloaded with [3H]noradrenaline. Electrical stimulation of cervical sympathetic nerve produced reductions in cerebral blood flow which were significantly diminished during continuous infusion of GABA (20-40 micrograms/min) into the internal maxillary artery. Picrotoxin (3 mg) did not change the inhibitory effect of GABA. Exogenously administered noradrenaline (1-9 micrograms) and tyramine (50-500 micrograms) reduced cerebral blood flow as well, but this effect was unchanged by GABA infusion. Transmural electrical stimulation elicited frequency-dependent contractile responses in isolated cerebral arteries which were significantly blocked when GABA was present, at a dose (10(-4) M) which did not modify the contractile response to exogenous noradrenaline (10(-8)-10(-4) M). Moreover, GABA (10(-5)-10(-4) M) inhibited transmural electrical stimulation-evoked tritium efflux from arteries preloaded with [3H]noradrenaline. These results show that GABA inhibits adrenergic neurotransmission in cerebral arteries by a mechanism involving inhibition of transmitter release. Probably, specific presynaptic GABA-B receptors mediate this inhibitory effect.

Brain and spinal cord levels of histamine in Lewis rats with acute experimental autoimmune encephalomyelitis

Acute experimental autoimmune encephalomyelitis (EAE) was induced in Lewis rats by inoculation with guinea pig spinal cord homogenate emulsified with Mycobacterium tuberculosis-enriched complete Freund's adjuvant (CFA). Control rats were inoculated with CFA alone. Control and EAE rats were killed on days 7, 9, 11, and 13 postinoculation, and regional brain and spinal cord levels of histamine were determined. No regional differences in histamine content between control and EAE rats were seen on day 7 or 9 postinoculation. However, depending on the region, EAE rats exhibited significantly higher levels of histamine in their CNS on day 11 or 13 postinoculation or on both. Thus, regionally and temporally specific increases in brain and spinal cord levels of histamine develop concomitant with or just after the appearance (on day 10 postinoculation) of clinical signs of acute EAE, a finding suggesting that histamine may be involved in the development or expression of acute EAE in Lewis rats.

Role of histamine in traumatic brain edema. An experimental study in the rat

The possibility that histamine plays a role in the formation of traumatic brain edema was investigated in the rat. A 3 mm deep and 3 mm long stab injury was performed in the right parietal cortex under urethane anaesthesia. The brain water content and histamine levels in plasma and brain were measured at the end of 1, 2 and 5 h periods after trauma. There was a 3.46% increase in brain water content in the traumatized hemisphere from the value in the control group at 5 h. The histamine content was increased by 107% in plasma and 51% in the traumatized brain hemisphere from the control value at this time period. The increased brain water content as well as the elevated plasma and brain histamine levels were prevented by prior treatment with the histamine H2-receptor antagonist cimetidine. Mepyramine (a histamine H1-receptor antagonist) failed to reduce the increased brain water content and the histamine levels in plasma and brain remained high. The results strongly indicate that histamine has a role in the formation of early traumatic brain edema and that this reaction can be influenced by pharmacological procedures.

Pharmacological characterization of histamine receptors in the human temporal artery

1. The subtypes of histamine-receptors which mediate dilatation of small human temporal arteries have been characterized in vitro using 'selective' agonists and antagonists. 2. Dilatory responses were studied after preconstriction with prostaglandin F2 alpha since contraction was not seen at histamine concentrations up to 10(-4) M. Histamine caused a concentration-related relaxation of cerebral vessels with an IC50 value of 2.8 +/- 0.6 X 10(-7) M. 3. Cimetidine caused a parallel shift to the right of the histamine concentration-response curve whereas mepyramine was without observable effect. This suggests the presence of histamine H2-receptors only. However, combined treatment with mepyramine and cimetidine caused a more marked displacement of the concentration-response curve to the right. Schild analysis indicated that in situations of near complete blockade of the histamine H1-receptor subtypes, simple competitive antagonism at H2-receptors can be revealed with a pA2 value of 6.58 for cimetidine. The apparent pA2 value for mepyramine was 8.58. 4. The 'selective' H1-receptor agonists pyridylethylamine, 2-methylhistamine and thiazolylethylamine, and the H2-receptor agonists dimaprit, impromidine and 4-methylhistamine all mimicked the histamine response, but all except impromidine were less potent than histamine. The order of potency was impromidine greater than thiazolylamine greater than 4-Me-histamine greater than 2-Me-histamine greater than dimaprit greater than pyridylethylamine greater than tele-Me-histamine. 5. These results indicate that the histamine-induced dilatation in small human temporal arteries is mediated by both H1- and H2-receptors and that the latter subtype of histamine receptors predominates.

Characterization of histamine receptors in isolated human cerebral arteries

1. The subtypes of histamine-receptors which mediate dilatation of small human cerebral arteries have been characterized in vitro using 'selective' agonists and antagonists. 2. Dilator responses were studied after preconstriction with prostaglandin F2 alpha, since contraction was not seen with histamine concentrations up to 10(-4) M. Histamine caused a concentration-related relaxation of cerebral vessels with an IC50 value of 5.2 +/- 1.6 x 10(-8) M. 3. Mepyramine caused a parallel shift to the right of the histamine concentration-response curve whereas cimetidine was without observable effect. This suggests the presence of histamine H1-receptors only. However, combined treatment with mepyramine and cimetidine caused a more marked displacement of the concentration-response curve to the right. Schild analysis indicated that in situations of near complete blockade of either of the histamine receptor subtypes, simple competitive antagonism both at H1- and H2-receptors can be revealed with a pA2 value of 8.64 for mepyramine and a pA2 value of 6.52 for cimetidine. 4. The 'selective' H1-receptor agonists pyridylethylamine, 2-methylhistamine (2-Me-histamine) and thiazolylethylamine, and the H2-receptor agonists dimaprit, impromidine and 4-methylhistamine (4-Me-histamine) all mimicked the histamine response, but were less potent than histamine. The order of potency was thiazolylethylamine greater than dimaprit greater than impromidine greater than 2-Me-histamine greater than pyridylethylamine greater than 4-Me-histamine. 5. These results indicate that the histamine-induced dilatation in small human cerebral arteries is mediated by both H1- and H2-receptors and that the former subtype of histamine receptor predominates.

Evidence for histaminergic arousal mechanisms in the hypothalamus of cat

Polygraphic 23-hr recordings were carried out in 25 adult cats in order to examine the effects of both systemic and local injections of various histaminergic and antihistaminergic drugs on sleep-waking cycles. alpha-Fluoromethylhistidine (alpha-FMH), a specific inhibitor of histidine decarboxylase, when injected intraperitoneally at a dose of 20 mg/kg, induced a significant increase in deep slow wave sleep (S2) and a decrease in wakefulness (W), without modifying light slow wave sleep (S1) and paradoxical sleep (PS). Intraperitoneal injections of mepyramine (1 mg and 5 mg/kg), a well-known histamine H1-receptor antagonist, increased deep slow wave sleep and decreased wakefulness, as well as paradoxical sleep. Bilateral injections of alpha-FMH (50 micrograms/1 microliter) into the ventrolateral posterior hypothalamus, where histamine immunoreactive neurones have been recently identified, resulted in a significant decrease in wakefulness and increase in deep slow wave sleep. Similarly, injections of mepyramine (120 micrograms/1 microliter) in the same structures caused a significant decrease in wakefulness and an increase in deep slow wave and paradoxical sleep as well. In contrast, local injections of SKF-91488 (50 micrograms/1 microliter), a specific inhibitor of histamine-N-methyltransferase, led to a significant increase in wakefulness and decrease in both slow wave sleep (SWS) and paradoxical sleep. Injections of histamine, at doses of 5, 30 and 60 micrograms/1 microliter, also increased wakefulness and decreased slow wave sleep dose dependently, while these effects were completely blocked by pretreatment with mepyramine. The results suggest that histaminergic systems in the hypothalamus play an important role in arousal mechanisms and their actions are mediated through H1-receptors.

Involvement of histamine H1 and H2 receptors in hypothermia induced by ionizing radiation in guinea pigs

Radiation-induced hypothermia was examined in guinea pigs. Exposure to the head alone or whole-body irradiation induced hypothermia, whereas exposure of the body alone produced a small insignificant response. Systemic injection of disodium cromoglycate (a mast cell stabilizer) and cimetidine (H2-receptor antagonist) had no effect on radiation-induced hypothermia, whereas systemic and central administration of mepyramine (H1-receptor antagonist) or central administration of disodium cromoglycate or cimetidine attenuated it, indicating the involvement of central histamine through both H1 and H2 receptors in this response. Serotonin is not involved, since the serotonin antagonist methysergide had no effect on radiation-induced hypothermia. These results indicate that central histaminergic systems may be involved in radiation-induced hypothermia.

Reverse pinocytosis induced in cerebral endothelial cells by injection of histamine into the cerebral ventricle

Histamine dihydrochloride (10 micrograms of 500 micrograms/ml) was infused during 1 min into the lateral cerebral ventricle of rats, which resulted in a significant stimulation of pinocytosis in the endothelial cells. Systemic injections of mepyramine or metiamide could not prevent this activation. In contrast, ranitidine, injected with histamine was able to inhibit the stimulation of pinocytosis. Albumin exudation from the blood was not found. There was also no change in water and electrolyte contents of the brain tissue. The results suggest that histamine reaching the abluminal membrane can activate the pinocytosis in the cerebral endothelial cells in the reverse direction, i.e., from brain to blood, without opening the blood-brain barrier.

Zolantidine (SK&F 95282) is a potent selective brain-penetrating histamine H2-receptor antagonist

1. The novel benzthiazole derivative zolantidine (SK&F 95282) is a potent antagonist of histamine at H2-receptors in guinea-pig atrium and rat uterus. Only apparent pA2 values of 7.46 and 7.26 respectively could be calculated since the slopes of the Schild plots were significantly less than unity. 2. Zolantidine is equally potent as an antagonist at histamine H2-receptors in guinea-pig brain. The compound inhibited histamine stimulated adenylate cyclase (pKi 7.3) and dimaprit stimulated adenosine 3':5'-cyclic monophosphate (cyclic AMP) accumulation (approx pA2 7.63), and competed with [3H]-tiotidine binding (pKi 7.17). 3. Zolantidine is at least 30 fold more potent at H2-receptors than at other peripheral and central receptors investigated. 4. Infusion of zolantidine into rats produces a brain concentration greater than the plateau blood concentration (brain/blood ratio 1.45). 5. Zolantidine is thus characterized as a potent selective brain-penetrating H2-receptor antagonist, and will be a valuable pharmacological tool for investigating possible physiological and pathological roles for histamine in the central nervous system.

In vivo studies of pial vascular permeability to sodium fluorescein: absence of alterations by bradykinin, histamine, serotonin, or arachidonic acid

We studied pial vessels in vivo in mice, examining under mercury light the permeability of these vessels to sodium fluorescein. Topical application of hypertonic solutions of NaCl caused leakage of fluorescein. However, putative chemical mediators of leakage, such as histamine, serotonin, arachidonic acid, and bradykinin, all failed to increase permeability to the dye. Apparent increases in permeability only accompanied endothelial damage caused by the dye + light combination, as indicated by production of local platelet aggregates. The technique is useful, provided inadvertent endothelial injury is recognized and avoided. The data in mice suggest that pial vessels may not participate in the permeability changes reportedly produced in parenchymal brain vessels by several of the mediators we tested. Therefore, studies of pial vascular permeability are not expected to provide reliable data concerning the actions of agents that might mediate cerebral edema.

Protective effect of antihistamines on cerebral oedema induced by experimental pneumothorax in newborn piglets

As a consequence of general hypoxaemia evoked experimentally by bilateral pneumothorax, brain oedema of vasogenic type developed in newborn piglets after 4 h survival. Histamine receptor antagonists, mepyramine (H1-receptor blocker), metiamide, cimetidine and ranitidine (H2-receptor antagonists) were administered either intraperitoneally or intrathecally to check to what extent the formation of brain oedema could be reduced. Mepyramine and ranitidine decreased the accumulation of water, sodium and albumin in the parietal cortex. By measuring the concentration of histamine, the presence of a histamine pool was demonstrated in the cerebral microvessels. The results suggest that histamine, if released upon hypoxic injury from the microvascular store, can take an important part in the development of vasogenic brain oedema.

[Demonstration of carcinine synthetase, a new enzyme catalysing the metabolism of histamine in the central nervous system of Carcinus maenas]

Carcinine biosynthesis was induced in vitro from its two components, beta-alanine and histamine. The reaction was catalyzed by muscle, heart, and CNS extracts from Carcinus maenas. The specific activity of the enzyme, carcinine synthetase, was 15 times higher in CNS than in other organs. Only CNS extracts induced biosynthesis of carcinine from histidine, and only in the presence of pyridoxal-5'-phosphate. Hence the seat of carcinine biosynthesis seems to be the CNS. It is highly probable that in the CNS, histidine is transformed into histamine, which is then catabolized into carcinine. The latter would then be transported and accumulated in the cardiac tissue. Thus histamine--the metabolism of which takes place totally within the CNS--would be implicated as a participant in the neuronal activity of Carcinus maenas. Carcinine synthetase is a soluble enzyme that requires the presence of ATP, beta-alanine, and histamine. Mg2+ and dithiothreitol are also essential for activity. Optimum pH is approximately 7.6. Carcinine synthetase differs from carnosine synthetase and gamma-glutamylhistamine synthetase in that it does not catalyze synthesis of beta-alanylhistidine or gamma-glutamylhistamine.

Effect of intravenous heroin and naloxone on regional cerebral blood flow in the conscious rat

Regional cerebral blood flow (RCBF) was measured with the [14C]iodoantipyrine technique and quantitative autoradiography in awake, restrained rats shortly after intravenous injection of heroin, naloxone or naloxone before heroin. The RCBF observed in these animals was compared to those obtained in similarly treated, saline-injected rats. In an identically treated series of animals, no significant change in arterial blood gases, pH or bicarbonate was seen following any of the drug treatments at the equivalent time RCBF was determined. Blood flow increased an average 36% in 37 of the 40 areas measured 1 min after heroin injection. Significant increases were found in 21 areas including visual and piriform cortex, basal ganglia, diencephalon, limbic system, midbrain tegmentum, superior colliculus, periaqueductal gray, internal capsule and fornix. These elevations in blood flow were reversed in rats receiving heroin following naloxone pretreatment. RCBF decreased in 35 areas (mean = -12%) 4 min after naloxone injection; a 40% decrease in blood flow to entorhinal cortex was significant. These results suggest that opiate receptor stimulation by heroin increases functional activity within selected brain areas, and this effect is not limited to regions with dense populations of opiate receptors.

[Biosynthesis and metabolism of histamine in the central nervous system of Carcinus maenas]

The central nervous system of Carcinus maenas synthesizes radioactive histamine when incubated in the presence of [14C] histidine and pyridoxal-5' phosphate. This biosynthesis increases linearly as a function of the amount of enzyme and the incubation time. It is not effected by heart, muscle or hepatopancreas extracts nor by haemolymph. Thus histamine appears to be synthesized mainly in the nervous system. The latter is also the seat of carcinine (beta-alanylhistamine) biosynthesis. Since carcinine seems to be a product of histamine neutralization, histamine metabolism should take place in its entirety in the nervous system. Thus histamine appears to be implicated in the neuronal activity of Carcinus. Different areas of the crustacean central nervous system: brain, eyestalks and thoracic ganglionic mass biosynthesize and metabolize histamine. Thus they all could contain sites of action for histamine. The nervous systems of two other Decapodes, Cancer and Astacus also effect histamine biosynthesis but don't metabolize it into carcinine.

Effects of intraventricular histamine and H2 receptor antagonists on intraocular pressure

Severe ocular hypertension has been reported in a chronic glaucoma patient following use of histamine H2 receptor antagonists for treatment of peptic ulcer. Subsequent studies, however, have failed to demonstrate a significant action of topical or intravenously administered H2 blockers on intraocular pressure (IOP) in humans. In this study, cimetidine and ranitidine were administered into the cerebral ventricles of unanesthetized New Zealand White rabbits. Both drugs caused prolonged increases in IOP at a dose of 1 umol. Maximal elevations of IOP occurred approximately 20 min after drug injections and averaged 5-8 mmHg above pre-drug values. In contrast, histamine (0.3 and 1.0 umol) produced biphasic effects on IOP when given by intracerebroventricular (i.c.v.) injection. These data suggest that central mechanisms may mediate the actions of some histamine receptor agonists and antagonists on IOP.

In vitro inhibition of histamine metabolism in guinea pig lung by S-(-)-nicotine

S-(-)-Nicotine competitively inhibits the metabolism of histamine to its N tau-methylated derivative in guinea pig lung homogenates. S-(-)-Nicotine exhibited a dissociation constant of the enzyme:inhibitor complex, Ki, of 9.4 X 10(-5) M compared with Km's for histamine and co-factor, S-adenosylmethionine, of 4.74 X 10(-5) M and 1.76 X 10(-5) M, respectively. This demonstrates the first reported involvement of nicotine in histaminergic mechanisms.

Adenosine deaminase and histidine decarboxylase coexist in certain neurons of the rat brain

The enzymes adenosine deaminase (ADA) and histidine decarboxylase (HDC) were immunocytochemically detected in rat brain. The gross distributions of ADA- and HDC-immunoreactive neurons in the basal hypothalamus were very similar. The superficial layers of the superior colliculus showed only ADA-containing neurons. Using adjacent thin-sections of basal hypothalamus, stained alternately for ADA and HDC immunoreactivity, it was possible to show the two labels localized within the same neurons. These observations imply a relationship between two neurochemically distinct putative neurotransmitter/modulator systems, that of histamine and adenosine.

Disodium cromoglycate, a mast-cell stabilizer, alters postradiation regional cerebral blood flow in primates

Early transient incapacitation (ETI) is the complete cessation of performance during the first 30 min after radiation exposure, and performance decrement (PD) is a reduction in performance at the same time. Supralethal doses of radiation have been shown to produce a marked decrease in regional cerebral blood flow in primates concurrent with systemic hypotension and a dramatic release of mast-cell histamine. In an attempt to elucidate mechanisms underlying the radiation-induced ETI/PD phenomena and the postradiation decrease in cerebral blood flow, primates were given the mast-cell stabilizers disodium cromoglycate (DSCG) or BRL 22321 (Beecham Pharmaceuticals, Research Division) before exposure to 100 Gy whole-body gamma radiation. Hypothalamic and cortical blood flows were measured by hydrogen clearance, before and after radiation exposure. Systemic blood pressures were determined simultaneously. The data indicated that DSCG was successful in diminishing postradiation decrease in cerebral blood flow. Irradiated animals pretreated with DSCG, showed only a 10% decrease in hypothalamic blood flow 60 min postradiation, while untreated, irradiated animals showed a 57% decrease. The cortical blood flow of DSCG treated, irradiated animals showed a triphasic response, with a decrease of 38% at 10 min postradiation, then a rise to 1% below baseline at 20 min, followed by a fall to 42% below baseline by 50 min postradiation. In contrast, the untreated, irradiated animals showed a steady decrease in cortical blood flow to 79% below baseline by 50 min postradiation. There was no significant difference in blood-pressure response between the treated and untreated, irradiated animals. Systemic blood pressure showed a 60% decrease at 10 min postradiation, falling to a 71% decrease by 60 min. The effects of BRL 22321 in altering postradiation blood flow in the cerebral cortex and hypothalamus were intermediate between the irradiated controls and those pretreated with DSCG, but were not considered to be significant at the concentration employed. The overall results of this study indicate that the postradiation decrease in regional cerebral blood flow may be partially alleviated by treatment with a mast-cell stabilizer.

[Biosynthesis of carcinine (beta-alanyl-histamine) in vivo]

Carcinine was biosynthesized by Carcinus maenas from [14C]beta-alanine, [14C] histidine and [14C] histamine. Since carnosine (beta-alanyl-histidine) could not be detected in crab tissues, biosynthesis of carcinine could only be effected by direct coupling of beta-alanine and histamine resulting from histidine decarboxylation. Biosynthesis of carcinine was weak when [14C]beta-alanine and [14C] histidine were used as precursors. On the contrary when [14C] histamine was used, synthesis was important. Thus carcinine appears to be a product of histamine catabolism. After injecting [14C] histamine, radioactive carcinine was concentrated mainly in the heart and nervous system; nonmetabolized [14C] histamine was recovered mainly in the latter. The nervous system might therefore be the seat of carcinine biosynthesis and thus the site of action of histamine.

Neurogenic control of cerebral circulation

The cerebral vascular neuromuscular apparatus consists of a varicose perivascular nerve plexus at the adventitial-medial border and smooth muscle cells in the medial coat that are functionally connected. In addition to noradrenaline and acetylcholine, a number of putative non-adrenergic, non-cholinergic neurotransmitters have been identified in cerebral perivascular nerves, including serotonin, substance P, vasoactive intestinal polypeptide, gastrin-releasing peptide, cholecystokinin, somatostatin, neurotensin, calcitonin gene-related peptide and neuropeptide Y. The role of adenosine-5'-triphosphate as a cotransmitter with noradrenaline in some perivascular sympathetic nerves, and of endothelial cells in mediating the vasodilatation produced by some neurohumoral agents is discussed. Speculations are made about the relation between vascular neuroeffector mechanisms and migraine, including the possibility of local vasospasm by serotoninergic nerves, reactive hyperaemia involving purine nucleotides and nucleosides, release of substance P from sensory nerve collaterals during antidromic ('axon reflex') impulses and secondary release of local agents such as prostanoids, histamine and bradykinin.

Further evidence that histamine in hippocampus affects the exploratory behavior in the rat

The effect of histamine (HA) and 3-methyl-histamine (3-MHA) in the hippocampus on hole-board behavior was studied. Male rats were microinjected stereotaxically into the hippocampus with 1 microliter of saline solution containing 9, 45 or 90 nMol of HA or 3-MHA. Five min later, all rats were tested for 5 min in a hole-board and locomotor, rearing, grooming and head-dipping activities were measured by direct observation. HA inhibited rearing and grooming at all the doses used but it affected locomotor activity only at 45 and 90 nMol doses. There was no effect on head-dipping behavior. 3-MHA instead increased locomotor and head-dipping activities at all the doses used and it did not change rearing and grooming. The present results give a further support for a physiological participation of HA in the hippocampus.

Actions of betahistine at histamine receptors in the brain

The actions of betahistine (N alpha-methyl-2-pyridylethylamine) on brain histamine receptors were investigated in a series of biological models. [3H]Mepyramine binding to H1-receptors in membranes from guinea-pig cerebellum was inhibited by betahistine with a Ki value of 31 microM. The binding of [3H]mepyramine in brain of the living mouse was inhibited by betahistine in high dosages (150-300 mg/kg). In slices from mouse cerebral cortex, betahistine induced [3H]glycogen hydrolysis in a concentration-dependent manner with an EC50 value of 9.0 microM with a maximal effect 57% that of histamine. Mepyramine and triprolidine, two H1-receptor antagonists, inhibited the betahistine-induced glycogenolysis with Ki values of 28 nM and 7 nM respectively. In slices from guinea-pig hippocampus, betahistine stimulated the accumulation of cyclic AMP in the presence of 5 microM impromidine, a H2-receptor agonist. The maximal effect represented 22% of that elicited by histamine at the H1-receptor and the EC50 value was 32.4 microM. Mepyramine at 0.1 microM partially blocked the response to betahistine. Together these various observations indicate that betahistine is a partial agonist at cerebral H1-receptors. Finally, betahistine was not an agonist at histamine H3-autoreceptors but was a rather potent antagonist of the inhibitory effect of exogenous histamine on [3H]histamine release elicited by K+ depolarisation in slices from rat cerebral cortex (Ki = 6.9 microM).

Central histaminergic stimulation of hyperlipemic response in rats under stress

In rats subjected to a mild stress of immobilization histamine, the H1-receptor agonist 2-pyridylethylamine (PEA), and the H2-receptor agonists 4-methyl histamine (4-MeHA) and impromidine administered intracerebroventricularly (i.c.v.) 1 h prior to stress, intensified the stress-induced increase in serum free fatty acid (FFA) levels. Impromidine was far more potent than histamine and its agonists in increasing hyperlipemia in stressed rats. The hyperlipemic response to histamine was abolished by i.c.v. pretreatment of rats with mepyramine, a H1-receptor antagonist, but was unchanged in rats pretreated with cimetidine or metiamide, H2-receptor antagonists. The increase in serum FFA levels induced in stressed rats by PEA was abolished by mepyramine but the hyperlipemic responses to 4-MeHA and impromidine were not antagonized by cimetidine. These results suggest that central H1-receptor mediate the histamine-stimulated hyperlipemic response in stressed rats.

Blood-brain barrier: endogenous modulation by adrenal-cortical function

The blood-brain barrier restricts the passage of molecules from the blood to the brain. The permeability of the barrier to iodine-125-labeled bovine serum albumin was examined in rats that had undergone adrenalectomy, adrenal demedullation, and corticosterone replacement. Adrenalectomy, but not adrenal demedullation, increased the permeability of brain tissue to the isotopically labeled macromolecule; corticosterone replacement reversed this effect. These results indicate that the blood-brain barrier may be hormonally regulated; that is, the pituitary-adrenal axis may physiologically modulate the permeability of the brain microvasculature to macromolecules.

Mast cells in rat thalamus: nuclear localization, sex difference and left-right asymmetry

Mast cells were positively identified in rat brain by a combination of staining and histochemical procedures. These cells stained positively with toluidine blue and Astrablau at low pH, indicating the presence of a proteoglycan similar to that found in peripheral mast cells. Brain mast cells also fluoresced after o-phthalaldehyde exposure, indicating that they contain histamine. Mast cells varied greatly in number among brains, but their distribution was almost exclusively thalamic; within thalamus, the ventral complex, medial dorsal, lateral, and paraventricular nuclei contained the most mast cells. Mast cell numbers were greater in brains of females than of males, and greater in left than in right hemispheres. These findings suggest that mast cells have a specialized function in thalamus and/or that the vascular environment of the thalamus is particularly conducive to mast cell accumulation.

Pharmacological modification of blood-brain barrier permeability following a cold lesion

The effect of desipramine, imidazole, thioridazine and trifluoperazine on blood-brain barrier (BBB) permeability after a 24 hour cold lesion was studied in rats. Changes in BBB permeability were determined using a quantitative horseradish peroxidase (HRP) assay. The four drugs tested did not alter the quantity of HRP in the cortex of control animals, or in the contralateral cortex of test animals. However, imidazole, desipramine and trifluoperazine significantly reduced the HRP extravasation in and around the cold lesion. Several mechanisms for this effect are suggested; one possible mechanism common to all these drugs is the reduction of increased vesicular transport in cortical vessels adjacent to the cold lesions.