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

Cerebrospinal inflammatory response following scorpion envenomation: role of histamine H1 and H3 receptors

BACKGROUND

The mechanism of the inflammatory process induced by scorpion venom in the cerebrospinal tissues has not yet been completely elucidated. Therefore, we aimed to investigate the role of histamine through its H1 and H3 receptors in this process.

METHODS

Histamine H1 and H3 receptor antagonists, Hydroxyzine (10 mg/kg) and Betaserc (20 mg/kg), respectively, were administered by intraperitoneal route to mice 1 h before subcutaneous envenomation with a subletal dose (0.5 mg/kg) of Androctonus australis hector venom. Cerebrospinal inflammation response was assessed 24 h after envenomation by evaluating the vascular permeability changes, inflammatory cell infiltration, oxidative/nitrosative stress marker levels (hydrogen peroxide, nitric oxide, malondialdehyde, glutathione and catalase) and by histological examination of cerebrospinal tissue.

RESULTS

Envenomed mice displayed an installation of an inflammatory response marked by increased vascular permeability (76% and 68% in brain and spinal cord, respectively, in comparison to controls), inflammatory cell infiltration, increased pro-oxidant levels and decreased anti-oxidant markers (p  < 0.05 to p  < 0.001). Scorpion venom also induced structural changes in brain and spinal cord tissues. Hydroxyzine seemed to be more efficient than Betaserc in the prevention of the induced cerebrospinal inflammation response, as evidenced by the decreased vascular permeability, inflammatory cell infiltration, pro-oxidant levels, increased anti-oxidant defense (p  < 0.05 to p  < 0.001) and a reduction of the anatomo-pathological alterations.

CONCLUSION

The results showed that the histamine H1 receptor is more involved in the induced central nervous system inflammatory response during scorpion envenomation.

The effects of cimetidine chronic treatment on conventional antiepileptic drugs in mice

PURPOSE

The aim of this study was to evaluate the effects of 1-day, 7-day and 14-day administrations of cimetidine on the anticonvulsant activity of conventional antiepileptic drugs (AEDs; valproate, carbamazepine, phenytoin and phenobarbital) against maximal electroshock (MES)-induced convulsions in mice.

METHODS

Electroconvulsions were evoked in Albino Swiss mice by a current delivered via ear-clip electrodes. In addition, the effects of cimetidine, AEDs alone and their combinations were studied on performance and long-term memory tests. Pharmacokinetic changes in plasma and brain concentrations of AEDs after cimetidine administration were evaluated with immunofluorescence.

RESULTS

Cimetidine (up to 100mg/kg) after 1-day administration did not affect the electroconvulsive threshold in animals. Moreover, in the 14-day treatment, cimetidine administered at a dose of 40mg/kg did not significantly change the electroconvulsive threshold in the MES-test, cimetidine administered 14-day (at 20mg/kg) significantly increased the anticonvulsant activity of carbamazepine, staying without effects after a 1-day and 7-day studies. In contrast, both the 7-day and 14-day administrations of cimetidine resulted in significant reductions of protective efficacy of the phenobarbital. Only valproate and phenytoin were not affected by cimetidine (20mg/kg) in all experimental period. Cimetidine administered 1-day, did not alter total brain concentrations and free plasma levels of all AEDs tested, whilst the 14-day study elevated carbamazepine plasma and brain concentration and reduced phenobarbital brain concentration. Cimetidine co-applied with AEDs did not impair performance of mice evaluated in the chimney test however, it worsened long-term memory in animals.

CONCLUSIONS

Based on this preclinical study, a special caution is advised when treating epileptic patients with combinations of phenobarbital or carbamazepine with cimetidine.

Acute administration of 3,4-methylenedioxymethamphetamine induces profound hyperthermia, blood-brain barrier disruption, brain edema formation, and cell injury

The psychostimulant 3,4-,ethylenedioxymethamphetamine (MDMA, "ecstasy") is known to induce hyperthermia and alterations in neurochemical metabolism in the CNS. However, the detailed cellular or molecular mechanisms behind MDMA-induced neurotoxicity are still not well known. Since MDMA induces profound hyperthermia that could lead to intense cellular stress and cause disruption of the blood-brain barrier (BBB), this investigation examined the effects of acute MDMA on BBB dysfunction, brain edema, and cell injury in rats and mice. When MDMA (40 mg/kg, i.p.) was administered to rats or mice, these animals exhibited profound behavioral disturbances (hyperactivity and hyperlocomotion) and hyperthermia (>40 to 41 degrees C) at 4 h. At this time, the leakage of Evans blue dye was evident, particularly in the cerebellum, hippocampus, cortex, thalamus, and hypothalamus. This effect was most pronounced in mice compared to rats. Marked increase in brain water along with Na(+), K(+), and Cl(-) content was also seen in the aforementioned brain regions. Presence of distorted neuronal and glial cells in brain regions associated with leakage of Evans blue is quite common in MDMA-treated animals. Increased albumin immunoreactivity, indicating breakdown of the BBB, and upregulation of glial fibrillary acidic protein (GFAP), suggesting activation of astrocytes, were seen in most brain regions showing edematous changes. Upregulation of heat-shock protein (HSP72) immunoreactivity in the nuclei and cell cytoplasm of the neurons located in the edematous brain regions are quite common. Taken together, these observations are the first to show that MDMA has the capacity to disrupt BBB permeability to proteins and to induce the formation of edema, probably by inducing hyperthermia and cellular stress, as evident with HSP overexpression leading to cell injury.

Brain edema and breakdown of the blood-brain barrier during methamphetamine intoxication: critical role of brain hyperthermia

To clarify the role of brain temperature in permeability of the blood-brain barrier (BBB), rats were injected with methamphetamine (METH 9 mg/kg) at normal (23 degrees C) and warm (29 degrees C) environmental conditions and internal temperatures were monitored both centrally (nucleus accumbens, NAcc) and peripherally (skin and nonlocomotor muscle). Once NAcc temperatures peaked or reached 41.5 degrees C (a level suggesting possible lethality), animals were administered Evans blue dye (protein tracer that does not normally cross the BBB), rapidly anaesthetized, perfused and had their brains removed. All METH-treated animals showed brain and body hyperthermia associated with relative skin hypothermia, suggesting metabolic activation coupled with peripheral vasoconstriction. While METH-induced NAcc temperature elevation varied from 37.60 to 42.46 degrees C (or 1.2-5.1 degrees C above baseline), it was stronger at 29 degrees C (+4.13 degrees C) than 23 degrees C (+2.31 degrees C). Relative to control, METH-treated animals had significantly higher brain levels of water, Na(+), K(+) and Cl(-), suggesting brain edema, and intense immunostaining for albumin, indicating breakdown of the BBB. METH-treated animals also showed strong immunoreactivity for glial fibrillary acidic protein (GFAP), possibly suggesting acute abnormality or damage of astrocytes. METH-induced changes in brain water, albumin and GFAP correlated linearly with NAcc temperature (r = 0.93, 0.98 and 0.98, respectively), suggesting a key role of brain hyperthermia in BBB permeability, development of brain edema and subsequent functional and structural neural abnormalities. Therefore, along with a direct destructive action on neural cells and functions, brain hyperthermia, via breakdown of the BBB, may be crucial for both decompensation of brain functions and cell injury following acute METH intoxication, possibly contributing to neurodegeneration resulting from chronic drug use.

Histamine receptors influence blood-spinal cord barrier permeability, edema formation, and spinal cord blood flow following trauma to the rat spinal cord

The role of histamine in edema formation, blood-spinal cord barrier (BSCB) permeability, and spinal cord blood flow (SCBF) following spinal cord injury (SCI) was examined using modulation of histamine H1, H2, and H3 receptors in the rat. Focal trauma to the spinal cord at the T10-11 level significantly increased spinal cord edema formation, BSCB permeability to protein tracers and SCBF reduction in the T9 and T12 segments. Pretreatment with histamine H1 receptor antagonist mepyramine (1 mg, 5 mg, and 10 mg/kg, i.p.) did not attenuate spinal pathophysiology following SCI. Blockade of histamine H2 receptors with cimetidine or ranitidine (1 mg, 5 mg, or 10 mg/kg 30 minutes before injury) significantly reduced early pathophysiological events in a dose dependent manner. The effects of ranitidine were far superior to cimetidine in identical doses. Pretreatment with a histamine H3 receptor agonist alpha-methylhistamine (1 mg and 2 mg/kg/i.p.), that inhibits histamine synthesis and release in the CNS, thwarted edema formation, BSCB breakdown, and SCBF disturbances after SCI. The lowest dose of histamine H3 agonist was most effective. Blockade of histamine H3 receptors with thioperamide (1 mg, 5 mg/kg, i.p.) exacerbated spinal cord pathology. These observations suggest that stimulation of histamine H3 receptors and blockade of histamine H2 receptors is neuroprotective in SCI.

Type I glutaric aciduria, part 2: a model of acute striatal necrosis

Type I glutaric aciduria (GA1) is an inborn error of organic acid metabolism that is associated with acute neurological crises, typically precipitated by an infectious illness. The neurological crisis coincides with swelling, metabolic depression, and necrosis of basal ganglia gray matter, especially the putamina and can be visualized as focal, stroke-like, signal hyperintensity on MRI. Here we focus on the stroke-like nature of striatal necrosis and its similarity to brain injury that occurs in infants after hypoxia-ischemia or systemic intoxication with 3-nitropropionic acid (NPA). These conditions share several features including abrupt onset, preferential effect in the striatum and age-specific susceptibility. The pathophysiology of the conditions is reviewed and a model proposed herein. We encourage investigators to test this model in an appropriate experimental system.

Circadian rhythms of body temperature and activity levels during 63 h of hypoxia in the rat

The hypothermic response of rats to only brief ( approximately 2 h) hypoxia has been described previously. The present study analyzes the hypothermic response in rats, as well as level of activity (L(a)), to prolonged (63 h) hypoxia at rat thermoneutral temperature (29 degrees C). Mini Mitter transmitters were implanted in the abdomens of 10 adult Sprague-Dawley rats to continuously record body temperature (T(b)) and L(a). After habituation for 7 days to 29 degrees C and 12:12-h dark-light cycles, 48 h of baseline data were acquired from six control and four experimental rats. The mean T(b) for the group oscillated from a nocturnal peak of 38.4 +/- 0.18 degrees C (SD) to a diurnal nadir of 36.7 +/- 0.15 degrees C. Then the experimental group was switched to 10% O(2) in N(2). The immediate T(b) response, phase I, was a disappearance of circadian rhythm and a fall in T(b) to 36.3 +/- 0.52 degrees C. In phase II, T(b) increased to a peak of 38.7 +/- 0.64 degrees C. In phase III, T(b) gradually decreased. At reoxygenation at the end of the hypoxic period, phase IV, T(b) increased 1.1 +/- 0.25 degrees C. Before hypoxia, L(a) decreased 70% from its nocturnal peak to its diurnal nadir and was entrained with T(b). With hypoxia L(a) decreased in phase I to essential quiescence by phase II. L(a) had returned, but only to a low level in phase III, and was devoid of any circadian rhythm. L(a) resumed its circadian rhythm on reoxygenation. We conclude that 63 h of sustained hypoxia 1) completely disrupts the circadian rhythms of both T(b) and L(a) throughout the hypoxic exposure, 2) the hypoxia-induced changes in T(b) and L(a) are independent of each other and of the circadian clock, and 3) the T(b) response to hypoxia at thermoneutrality has several phases and includes both hypothermic and hyperthermic components.

Endothelin inhibits histamine-induced cyclic AMP accumulation in bovine brain vessels

We have studied whether endothelin isopeptides have any effects on histamine-induced cyclic AMP in [(3)H]adenine-prelabeled brain vessels isolated from bovine brain. Basal levels of [(3)H]cyclic AMP were enhanced by histamine in a concentration-dependent manner (EC(50) = 1.1 +/- 0.3 microM). Endothelin-1 inhibited histamine-elicited [(3)H]cyclic AMP generation with an IC(50) value of 3 +/- 2.5 nM. Sarafotoxin 6c, an ET-B receptor agonist, had no effect. ET-1 inhibition of histamine-induced [(3)H]cyclic AMP was reversed by the ET-A receptor antagonist BQ-123 while the ET-B receptor antagonist BQ-788 had no effect. The levels of [(3)H]cyclic AMP induced by isoprenaline were not altered by endothelin-1. Taken together, these results show that endothelins modulate the actions of histamine on the blood-brain barrier, probably by type A endothelin receptors.

Inflammatory mediators and modulation of blood-brain barrier permeability

1. Unlike some interfaces between the blood and the nervous system (e.g., nerve perineurium), the brain endothelium forming the blood-brain barrier can be modulated by a range of inflammatory mediators. The mechanisms underlying this modulation are reviewed, and the implications for therapy of the brain discussed. 2. Methods for measuring blood-brain barrier permeability in situ include the use of radiolabeled tracers in parenchymal vessels and measurements of transendothelial resistance and rate of loss of fluorescent dye in single pial microvessels. In vitro studies on culture models provide details of the signal transduction mechanisms involved. 3. Routes for penetration of polar solutes across the brain endothelium include the paracellular tight junctional pathway (usually very tight) and vesicular mechanisms. Inflammatory mediators have been reported to influence both pathways, but the clearest evidence is for modulation of tight junctions. 4. In addition to the brain endothelium, cell types involved in inflammatory reactions include several closely associated cells including pericytes, astrocytes, smooth muscle, microglia, mast cells, and neurons. In situ it is often difficult to identify the site of action of a vasoactive agent. In vitro models of brain endothelium are experimentally simpler but may also lack important features generated in situ by cell:cell interaction (e.g. induction, signaling). 5. Many inflammatory agents increase both endothelial permeability and vessel diameter, together contributing to significant leak across the blood-brain barrier and cerebral edema. This review concentrates on changes in endothelial permeability by focusing on studies in which changes in vessel diameter are minimized. 6. Bradykinin (Bk) increases blood-brain barrier permeability by acting on B2 receptors. The downstream events reported include elevation of [Ca2+]i, activation of phospholipase A2, release of arachidonic acid, and production of free radicals, with evidence that IL-1 beta potentiates the actions of Bk in ischemia. 7. Serotonin (5HT) has been reported to increase blood-brain barrier permeability in some but not all studies. Where barrier opening was seen, there was evidence for activation of 5-HT2 receptors and a calcium-dependent permeability increase. 8. Histamine is one of the few central nervous system neurotransmitters found to cause consistent blood-brain barrier opening. The earlier literature was unclear, but studies of pial vessels and cultured endothelium reveal increased permeability mediated by H2 receptors and elevation of [Ca2+]i and an H1 receptor-mediated reduction in permeability coupled to an elevation of cAMP. 9. Brain endothelial cells express nucleotide receptors for ATP, UTP, and ADP, with activation causing increased blood-brain barrier permeability. The effects are mediated predominantly via a P2U (P2Y2) G-protein-coupled receptor causing an elevation of [Ca2+]i; a P2Y1 receptor acting via inhibition of adenyl cyclase has been reported in some in vitro preparations. 10. Arachidonic acid is elevated in some neural pathologies and causes gross opening of the blood-brain barrier to large molecules including proteins. There is evidence that arachidonic acid acts via generation of free radicals in the course of its metabolism by cyclooxygenase and lipoxygenase pathways. 11. The mechanisms described reveal a range of interrelated pathways by which influences from the brain side or the blood side can modulate blood-brain barrier permeability. Knowledge of the mechanisms is already being exploited for deliberate opening of the blood-brain barrier for drug delivery to the brain, and the pathways capable of reducing permeability hold promise for therapeutic treatment of inflammation and cerebral edema.

The histaminergic system in the brain: structural characteristics and changes in hibernation

Histaminergic neurons in adult vertebrate brain are confined to the posterior hypothalamic area, where they are comprised of scattered groups of neurons referred to as the tuberomammillary nucleus. Histamine regulates hormonal functions, sleep, food intake, thermoregulation and locomotor activity, for example. In the zebrafish, Danio rerio, histamine was detected only in the brain, where also the histamine synthesizing enzyme L-histidine decarboxylase (HDC) was expressed. It is possible that histamine has first evolved as a neurotransmitter in the central nervous system. We established sensitive quantitative in situ hybridization methods for histamine H(1) and H(2) receptors and HDC, to study the modulation of brain histaminergic system under pathophysiological conditions. A transient increase in H(1) receptor expression was seen in the dentate gyrus and striatum after a single injection of kainic acid, a glutamate analog. H(1) antagonists are known to increase duration of convulsions, and increased brain histamine is associated with reduced convulsions in animal models of epilepsy. No HDC mRNA was detected in brain vessels by in situ hybridization, which suggests lack of histamine synthesis by brain endothelial cells. This was verified by lack of HDC mRNA in a rat brain endothelial cell line, RBE4 cells. Both H(1) and H(2) receptor mRNA was found in this cell line, and the expression of both receptors was downregulated by dexamethasone. The findings are in agreement with the concept that histamine regulates blood-brain barrier permeability through H(1) and H(2) receptor mediated mechanisms. Hibernation is characterized by a drastic reduction of central functions. The activity of most transmitter systems is maintained at a very low level. Surprisingly, histamine levels and turnover were clearly elevated in hibernating ground squirrels, and the density of histamine-containing fibers was higher than in euthermic animals. It is possible that histamine actively maintains the low activity of other transmitters during the hibernation state.

Mediators of cerebral edema

The blood-brain barrier (BBB) which is located in the continuous endothelial lining of cerebral blood vessels rigidly controls exchange of water soluble compounds under physiological conditions. Under pathological conditions such as trauma or ischemia, BBB permeability may increase thus allowing plasma constituents to escape into brain tissue. This "opening" of the BBB may, at least in part, be mediated by massive release of autacoids resulting in vasogenic brain edema. Five criteria have to be fulfilled by an individual autacoid to be considered a mediator candidate of cerebral edema: i) a permeability-enhancing action under physiological conditions, ii) a vasodilatory action, iii) the ability to induce vasogenic brain edema, iv) an increase of concentration in the tissue or interstitial fluid under pathological conditions, and v) a decrease of brain edema by specific interference with the release or action of a given autacoid. Among the mediator candidates considered, bradykinin is the only one to meet all criteria. Histamine, arachidonic acid and free radicals including nitric oxide may also be considered mediators of brain edema, but for each of these compounds evidence is less clear than for bradykinin. Although the concept of mediators inducing brain edema is well established by experimental studies, only a bradykinin receptor antagonist has so far gained entrance into clinical evaluation.

Effects of N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine on the blood-brain barrier permeability in the rat

Histamine plays a role in the regulation of the blood-brain barrier function. In this study, effects of N, N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine (DPPE), an intracellular histamine binding site antagonist on the cerebrovascular permeability were investigated in control and post-ischemic male Wistar rats. Intravenous administration of DPPE, in a dose of 1 and 5 mg/kg, was not followed by any major clinical change, but 20 mg/kg proved to be toxic. A significantly (P<0.05) increased permeability for sodium fluorescein (MW=376) was seen in hippocampus, striatum, and cerebellum, but not in parietal cortex, of rats 2 h after the injection of 5 mg/kg DPPE, whereas no increase was measured later. There was a more intense (5- to 12-fold) and prolonged elevation in Evan's blue-labeled albumin (MW=67,000) extravasation 2, 4, and 8 h after 5 mg/kg DPPE administration in each brain region. In parietal cortex, a dose-dependent increase in albumin extravasation developed 4 h after intravenous injection of 1, 5, and 20 mg/kg DPPE, but doses applied resulted in no significant change in sodium fluorescein permeability. Cerebral ischemia-reperfusion evoked by four-vessel occlusion caused a significant (P<0.05) increase in the permeability for albumin in each region, but few changes in that of sodium fluorescein. DPPE treatment failed to prevent the ischemia-reperfusion-induced changes in the blood-brain barrier permeability. In conclusion, DPPE induced an increased permeability in the rat, which supports a role for histamine, as an intracellular messenger, in the regulation of the blood-brain barrier characteristics.

Lack of histamine synthesis and down-regulation of H1 and H2 receptor mRNA levels by dexamethasone in cerebral endothelial cells

The purpose of this work was to determine whether cerebral endothelial cells have the capacity to synthesize histamine or to express mRNA of receptors that specifically respond to available free histamine. The histamine concentrations and the expression of L-histidine decarboxylase (HDC) and histamine H1 and H2 receptor mRNA, both in adult rat brain and in cultured immortalized RBE4 cerebral endothelial cells, were investigated. In this study endothelial cells were devoid of any kind of detectable histamine production, both in vivo and in the immortalized RBE4 cells in culture. Both the immunostainings for histamine and the in situ hybridizations for HDC were negative, as well as histamine determinations by HPLC, indicating that endothelial cells do not possess the capacity to produce histamine. Also, glucocorticoid (dexamethasone) treatment failed to induce histamine production in the cultured cells. Although the cerebral endothelial cells lack histamine production, a nonsaturable uptake in RBE4 cells is demonstrated. The internalized histamine is detected both in the cytoplasm and in the nucleus, which could indicate a role for histamine as an intracellular messenger. Histamine H1 and H2 receptor mRNA was expressed in RBE4 cells, and glucocorticoid treatment down-regulated the mRNA levels of both H1 and H2 receptors. This mechanism may be involved in glucocorticoid-mediated effects on cerebrovascular permeability and brain edema.

Choroid plexus histidine transport

System-N transport plays an important role in l-glutamine uptake into isolated rat choroid plexus but its role in the transport of another System-N substrate, l-histidine, has yet to be determined. Similarly, the possible effects on System-N mediated l-histidine transport of changes in pH and extracellular l-glutamine, such as occur in cerebral ischemia and hepatic encephalopathy, have yet to be examined. In the absence of competing amino acids, l-[3H]histidine uptake in isolated rat choroid plexus was mediated by both Na+-independent and Na+-dependent transport. The former was inhibited by 2-amino-2-norbornane carboxlic acid, indicating System-L transport, while the latter appears System-N mediated as it was inhibited by three System-N substrates but not substrates for System-A and -ASC. The Na+-dependent uptake had a Km of 0.2 mM and a Vmax of 1.4 nmol/mg/min. It accounted for 30% of l-histidine uptake in the presence of physiological concentrations of amino acids. Reductions in pH markedly inhibited Na+-dependent but not Na+-independent transport indicating that, as in liver but not neurons, System-N mediated transport at the choroid plexus is pH sensitive. Increases in l-glutamine concentration in the pathophysiological range reduced l-histidine uptake via both System-L and -N.

Effect of inflammatory agents on electrical resistance across the blood-brain barrier in pial microvessels of anaesthetized rats

The effect of histamine, bradykinin and serotonin on blood-brain barrier permeability was investigated using in situ measurement of transendothelial electrical resistance in pial microvessels of anaesthetized rats. Mean resistance of vessels superfused with artificial cerebrospinal fluid was 1800 omega cm2, indicating a tight barrier with extremely low ion permeability. In paired experiments from continuous measurements in single vessels, addition of 10(-3) M serotonin to the solution bathing the brain had no marked effect on resistance; whereas both histamine and bradykinin, applied at a concentration of 10(-4) M, caused a rapid and reversible decrease in resistance. Mean resistance was 408 and 505 omega cm2 in 10(-4) M histamine and bradykinin, respectively, and approximately 50% of vessels had a resistance less than 250 omega cm2, compared to 12% in controls, indicating a leaky blood-brain barrier that is not capable of normal brain ion homeostasis. Histamine and bradykinin had similar dose-response relations, and a maximal effect was observed between 20 and 50 microM. Thus, histamine and bradykinin act at the abluminal (brain-facing) membranes of the cerebral endothelium to mediate blood-brain barrier opening. These results support a role for histamine and bradykinin in brain oedema formation.

The role of cerebral microvessels in the elimination of histamine released during postasphyxial reperfusion in newborn piglets

Histamine, released from intracerebral sources during hypoxic-ischemic conditions, may take part in the pathogenesis of neonatal brain injuries. In order to elucidate the possible role of cerebral microvessels in the elimination of histamine from the extracellular space, we determined the concentration of histamine using a modified radioenzymatic method in plasma taken from the internal jugular vein, in cerebrospinal fluid, and in capillary-rich fraction of cerebral microvessels prepared from cortex in 12 sham-operated piglets. Then, bilateral pneumothorax was induced in 20 piglets, samples were taken from the same compartments as from the controls before and during asphyxia, as well as 15 and 180 min thereafter, respectively. Plasma histamine level was significantly (P < 0.05) elevated in animals during hypoxic cardiovascular and metabolic failure (13.5 +/- 1.9 nM l-1) compared to value measured in the control group (2.2 +/- 0.5 nM l-1), preceding any detectable change of histamine concentration in cerebrospinal fluid (5.2 +/- 1.9 versus 3.8 +/- 1.1 nM l-1, respectively) or in cerebral microvessels (8.4 +/- 0.8 versus 7.1 +/- 0.6 pM (mg protein)-1). After resuscitation, histamine levels in plasma samples remained high during the early (15 min, 16.2 +/- 4.3 nM x l-1) and late (180 min, 15.3 +/- 2.9 nM l-1) reperfusion period. By contrast, histamine concentration was increased considerably (P < 0.05) in cerebrospinal fluid samples obtained 15 min (12.8 +/- 6.5 nM l-1), but not 180 min (5.2 +/- 1.9 nM l-1) after resuscitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment with ranitidine of ischemic brain edema

Cerebral ischemia was produced by bilateral common carotid artery occlusion in female Sprague-Dawley rats. Ranitidine, a histamine H2 receptor blocking agent, given intraperitoneally 30 min prior to ischemia, exerted a dose-dependent protective effect on water accumulation and ion shifts in the brain (Na+, K+ and Ca2+). To decide whether ranitidine can prevent ischemia-induced brain edema when given in the postischemic period, ranitidine (10 mg/kg i.p.) was administered 1, 2, and 3 h respectively after the onset of cerebral ischemia. Early (1 h) postocclusion treatment was still able to attenuate the ischemia-induced water accumulation and maldistribution of ions in the brain tissue.

Opening of the blood-brain barrier during cortical superfusion with histamine

Histamine may influence cerebral microcirculation from the intravascular and parenchymal side. The latter route can be simulated by cortical superfusion. The effect of cortical superfusion with histamine (10(-9)-10(-3) M) on blood-brain barrier (BBB) permeability was studied in the cat by measuring extravasation of the tracers Na(+)-fluorescein (MW 376) or fluorescein isothiocyanate (FITC) labelled dextran (MW 62,000 or 145,000) by intravital fluorescence microscopy. Histamine induced an opening of BBB resulting in extravasation of small and large molecular weight tracers with threshold concentrations of 10(-9), 10(-8) and 10(-6) M for Na(+)-fluorescein, FITC-dextran 62,000 and 145,000, respectively. Once tracer extravasation had started the degree of extravasation increased with increasing concentrations of histamine in the superfusion fluid. Similar to histamine the H2 agonist impromidine (3 x 10(-12)-3 x 10(-9) M) induced a concentration dependent extravasation of Na(+)-fluorescein. 2-Pyridylethylamine which is 3-4 times more selective for H1 than for H2 receptors also induced an extravasation of Na(+)-fluorescein. Cortical superfusion with mepyramine (10(-7) M) or cimetidine (10(-4) M), which block the H1 and H2 receptors, respectively, already induced significant extravasation of Na(+)-fluorescein by themselves. These compounds could thus not be used as competitive antagonists to block histamine-induced extravasation. However, our data are in accord with data obtained during intravascular and topical application of histamine and support the hypothesis that H2 receptors at the luminal and abluminal membrane of the endothelium mediate the opening of the BBB.(ABSTRACT TRUNCATED AT 250 WORDS)

Insight into the regulation by second messenger molecules of the permeability of the blood-brain barrier

Recent advances in our knowledge of the blood-brain barrier have in part been made by studying the properties and function of cerebral endothelial cells in vitro. After an era of working with a fraction, enriched in cerebral microvessels by centrifugation, the next generation of in vitro blood-brain barrier model systems was introduced, when the conditions for routinely culturing the endothelial cells were established. This review summarizes the results obtained mainly from this in vitro approach. Different elements of the intracellular signaling messenger systems have been detected in the course of our studies in the cerebral endothelial cells. It has been shown that the synthesizing enzymes of and substrate proteins for the second messenger molecules are present in the cerebral endothelial cells, and their activity and/or amount can change in pathological circumstances, i.e., during the formation of brain oedema. Pharmacological treatments interfering with the second messenger systems proved to be effective in the prevention of brain oedema formation.

The role of histamine in brain oedema formation

The effects of histamine on the cerebral endothelial cells were studied. To determine if the extent of brain oedema formation could be reduced with histamine receptor antagonists, mepyramine (H1-receptor blocker), metiamide, cimetidine and ranitidine (H2-receptor antagonists) were administered at a dose of 5 mg/kg body weight 4, 2 and 0 h before the onset of experimental pneumothorax induced in newborn piglets. Mepyramine and ranitidine given 2 h before the induction of EBP prevented the accumulation of water, sodium and albumin in samples taken from the parietal cortex. In other experiments, carried out on Sprague-Dawley rats of CFY strain after permanent bilateral common carotid ligation (BCCL), the accumulation of water and sodium in the ischemic brain tissue could also be prevented in a dose dependent manner by intraperitoneal injections of ranitidine given 30 min before the surgery. Taken together, these results provide pharmacological evidence for the involvement of histamine receptors in the pathogenesis of brain oedema. Consequently, the use of histamine receptor blockers both in the prevention and in the treatment of brain oedema can be recommended.

The blood-brain barrier in vitro: the second decade

Ever since the discovery of Paul Ehrlich (1885 Das Sauerstoff-bedürfnis des Organismus: Hirschwald, Berlin) about the restricted material exchange, existing between the blood and the brain, the ultimate goal of subsequent studies has been mainly directed towards the elucidation of relative importance of different cellular compartments in the peculiar penetration barrier consisting the structural basis of the blood-brain barrier (BBB). It is now generally agreed that, in most vertebrates, the endothelial cells of the central nervous system (CNS) are responsible for the unique penetration barrier, which restricts the free passage of nutrients, hormones, immunologically relevant molecules and drugs to the brain. After an era of studying with endogenous or exogenous tracers the unique permeability properties of cerebral endothelial cells in vivo, the next generation, i.e. the in vitro blood-brain barrier model system was introduced in 1973. Recent advances in our knowledge of the BBB have in part been made by studying the properties and function of cerebral endothelial cells (CEC) with this in vitro approach. This review summarizes the results obtained on isolated brain microvessels in the second decade of its advent.

The role of second messenger molecules in the regulation of permeability in the cerebral endothelial cells

The view that the cerebral endothelial cells represent the cellular analogue of the blood brain barrier has been generally accepted. The regulation of transport processes operating in the cerebral endothelial cells is of great current interest. Different elements of the intracellular signaling messenger systems have been detected in the course of our studies in the cerebral endothelial cells. Our knowledge of these regulatory mechanisms is briefly reviewed here with special emphasis on the importance of second messenger molecules and phosphorylation of certain proteins of microvascular origin.

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.

Effect of histamine and antagonists on electrical resistance across the blood-brain barrier in rat brain-surface microvessels

The effect of histamine on blood-brain barrier permeability was investigated using in situ measurement of transendothelial electrical resistance in brain-surface microvessels of anaesthetized rats. Mean resistance of vessels superfused with artificial cerebrospinal fluid was 1500 omega.cm2, indicating a tight barrier with low ion permeability. The addition of 10(-4) M histamine resulted in a 75% decrease in resistance, in both arterial and venous vessels, indicating a marked increase in barrier permeability. To determine the nature of the response to histamine, rats were given presurgical intraperitoneal injections of promethazine (H1 receptor antagonist), cimetidine (H2 receptor antagonist) or indomethacin (cyclo-oxygenase inhibitor), singularly and in combinations. Cimetidine completely blocked the histamine-mediated increase in barrier permeability whereas promethazine only had a small effect and indomethacin was ineffective. In addition, cimetidine treatment resulted in a 100% increase in basal resistance in both arterial and venous vessels, suggesting endogenous histamine was acting to increase blood-brain barrier permeability. It is concluded that histamine causes an increase in blood-brain barrier permeability which is mediated via endothelial H2 receptors, and that the electrical resistance in cimetidine-treated rats most closely represents the true permeability of the blood-brain barrier.

Chapter 26: Regulation of transendothelial transport in the cerebral microvessels: the role of second messengers-generating systems

Different elements of the intracellular signaling messenger systems have been detected in the course of our studies in the cerebral endothelial cells. It has been shown that the synthesizing enzymes of and substrate proteins for the second messenger molecules are present in the cerebral endothelial cells, and their activity and/or amount can change in pathological circumstances, i.e., during the formation of brain oedema. Pharmacological treatments interfering with the second messenger systems proved to be effective in the prevention of brain oedema formation.

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.

The role of endothelial second messenger's-generating system in the pathogenesis of brain oedema

The role of second messengers in the regulation of protein phosphorylation was studied in microvessels isolated from rat cerebral cortex. Calcium-calmodulin (CAM)-, Ca2+/phospholipid (PK C)-, cyclic GMP (cGMP)-, and cyclic AMP (cAMP)-dependent protein kinases were detected. Autophosphorylation of both the alpha- and beta-subunits of CAM-dependent protein kinase and the proteolytic fragment of the PK C enzyme was also detected. In other experiments, the effect of the protein kinase C enzyme inhibitor H-7 was examined on the brain oedema formation evoked by bilateral occlusion of the common carotid arteries in Sprague-Dawley rats of CFY strain.

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.

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.