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

Terfenadine induces toxicity in cultured cerebellar neurons: a role for glutamate receptors

Exposure of cultured cerebellar neurons to the histamine H1 receptor antagonist terfenadine resulted in neuronal degeneration and death. Terfenadine neurotoxicity was dependent upon concentration and time of exposure. After 2 h exposure, 20 microM terfenadine reduced the number of surviving neurons by 75%, and as low as 10 nM terfenadine induced significant neurotoxicity after 5 days of exposure. Neuronal sensitivity to terfenadine changed with age in culture, and at 25 days in culture neurons appeared to be much less sensitive than at 5 or 9-17 days in culture. Neurotoxicity by terfenadine could not be prevented by high concentrations of histamine (5 mM), but it was significantly delayed by blocking NMDA or non-NMDA glutamate receptors with MK-801 or CNQX respectively, suggesting the involvement of excitatory transmission mediated by glutamate in the neurotoxicity induced by terfenadine in these neurons. We also found that the presence of terfenadine (5 microM) unveiled the potential excitotoxity of the non-NMDA receptor agonist AMPA (100 microM), and reduced the concentration of glutamate necessary to induce excitotoxicity, compared to untreated cultures. These results suggest a role for terfenadine in the modulation of the excitotoxic response mediated in cerebellar neurons through ionotropic glutamate receptors.

Stress-induced increase in blood-brain barrier permeability in control and monosodium glutamate-treated rats

Glutamate administration in neonatal rats causes reversible changes in blood-brain barrier (BBB) permeability and known neurotoxic lesions. This study was aimed to evaluate whether glutamate administered to neonatal rats influences properties of the developing BBB with consequences on adult BBB function. The vulnerability of the BBB was examined after short-lasting stress exposure by measurement of plasma albumin extravasation using immunoelectrophoresis. In control rats, 30 min of immobilization stress resulted in increased endogenous albumin extravasation in the hypothalamus, hippocampus, brain stem and cerebellum, but not in the cortex and striatum. Basal levels of albumin in adult glutamate-treated rats (4 mg monosodium glutamate/g BW, IP, five times during neonatal period) were significantly lower in the hypothalamus compared to that in controls. Stress-induced increase in albumin levels was lower in the brain stem, higher in the hypothalamus, and similar in other brain regions studied in glutamate-treated rats in comparison with controls. It is concluded that short-lasting immobilization stress increased BBB permeability in some but not all brain regions studied. Glutamate treatment of neonatal rats resulted in low basal albumin levels in the hypothalamus but did not exert a pronounced influence on adult BBB function. BBB vulnerability in glutamate-treated rats during stress exposure was increased in the hypothalamus and decreased in the brain stem.

Involvement of nitric oxide in the pathophysiology of acute heat stress in the rat. Influence of a new antioxidant compound H-290/51

The possibility that nitric oxide (NO) is involved in the pathophysiology of brain injury caused by heat stress (HS) was examined using immunohistochemistry of a constitutive isoform of neuronal nitric oxide synthase (c-NOS) in a rat model. In addition, to discover the role of oxidative stress in inducing c-NOS activity in HS, the effect of a new antioxidant H-290/51 on HS-induced expression of c-NOS immunoreactivity was examined. Subjection of conscious young animals to a 4-h HS in a biological oxygen demand (BOD) incubator at 38 degrees C resulted in marked upregulation of c-NOS in the cerebral cortex and hippocampus of stressed rats compared to normal rats kept at room temperature (21 +/- 1 degrees C). The c-NOS immunoreactivity was found in distorted neurons located in the edematous regions not normally showing c-NOS activity. Pretreatment with H-290/51 significantly attenuated the upregulation of c-NOS in animals subjected to HS, and the signs of neuronal distortion and edema were less pronounced. These results suggest that HS has the capacity to induce upregulation of c-NOS, and these effects can be reduced by prior treatment with H-290/51, indicating a possible neuroprotective effect of antioxidants in thermal brain injury.

Brain mast cell degranulation regulates blood-brain barrier

Mast cells synthesize vasoactive agents and a number of neurotransmitters. They are particularly numerous in the medial habenular region of the epithalamus, the attachment site of the choroid plexus. The present study examined whether degranulation of brain mast cells alters the permeability of the blood-brain barrier (BBB). To this end, doves were injected intramuscularly with the mast cell degranulator, compound 48/80 (C40/80), followed by i.v. injection of Evans blue. The distribution of the dye in the parenchyma was examined using digital imaging. Three brain areas were analyzed: the medial habenula (which also contains mast cells), the paraventricular nucleus (PVN, which abuts the third ventricle, but has no mast cells), and the lateral septal organ (LSO, a circumventricular organ with fenestrated capillaries). Significantly more Evans blue tracer and fewer toluidine blue-positive mast cells were detected in the medial habenula of subjects treated with C48/80 compared to saline controls. Evans blue did not enter the PVN in either the experimental or control group, while it entered the LSO equally in both. Degranulation of mast cells after C48/80 treatment was confirmed histochemically and ultrastructurally. The results support the hypothesis that brain mast cell degranulation locally alters BBB permeability. Activation of brain mast cells may provide a mechanism for regulated opening of the BBB.

Involvement of non-muscarinic receptors in phosphoinositide signalling during soman-induced seizures

Previous investigations have indicated that soman-induced convulsions involve the inositol lipid signalling system. We previously reported that 10 min after the onset of seizures, inositol 1,4,5-triphosphate (IP3) build-up was coupled to activation of non-muscarinic receptor subtypes. In the present study, we demonstrate that (1) in addition to muscarinic receptors, histamine H1 subtypes and glutamate metabotropic receptors contribute to the first IP3 increase (first 10 min of seizures) and (2) the histamine H1 subtype and glutamate metabotropic receptors are also involved in the second step of inositol phosphate response (after 10 min of seizures). alpha 1-adrenoceptor and 5-HT2 receptors, known to be coupled to phosphoinositide turnover, did not participate in soman-induced IP3 response. Neurochemical interactions between cholinergic, histamine H1 and glutamate metabotropic systems, responsible of the phosphoinositide hydrolysis under soman are envisaged.

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.

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)

Histamine-induced microvascular leakage in pial venules: differences between the SJL/J and BALB/c inbred strains of mice

The actions of histamine on pial venule leaky site formation were measured intravitally in two inbred strains of mice (BALB/c and SJL/J). Pial venules were visualized using a cranial window microscopy technique, and microvascular leaky site formation was assessed visually using a fluorescein-dextran indicator. SJL/J mice were found to be sensitive to histamine-induced leakage, whereas the BALB/c strain was refractory. Exposure to pertussis toxin enhanced the sensitivity to histamine in the SJL/J strain, but little effect was observed for BALB/c mice. However, the employment of a polymerase chain reaction (PCR) technique for the detection of mRNA for histamine H1 receptor identified receptor-specific message in isolated cerebrovascular endothelium from both strains of mice. The lack of pial responsiveness in the BALB/c mice remains unexplained. Mast cells in the dura mater were found to be more numerous in SJL/J mice than in BALB/c mice. This observation supports previous observations of strain-specific differences in CNS inflammation. The results support the concept that genetically controlled differences in vascular sensitivity and localization of CNS-associated mast cells may play important roles in the generation of vasogenic edema and inflammation in CNS trauma and disease.

Schizophrenia: an extended etiological explanation

Schizophrenia has become an elusive medical conundrum since it was first described at the turn of the 19th century. Over time, a variety of causal hypotheses have been advanced to explain the spectrum of schizophreniform disorders. This etiological explanation outlines the relationship that obtains between smoking, schizophrenia, and impaired glycometabolism which also includes disruption to the dopaminergic and serotinergic pathways. A possible genetic explanation for this disruption will be identified which links mental illness to a locus of genes contained on the short arm of chromosome 11. These genes are all essential to normal glucose transport which positron emission tomography (PET) scans show is seriously abnormal in schizophrenia. Thus, a redefinition of schizophrenia as 'cerebral diabetes' will be proposed since this term implies a diabetic brain state consistent with PET scans of schizophrenic patients.

Prostaglandins modulate alterations of microvascular permeability, blood flow, edema and serotonin levels following spinal cord injury: an experimental study in the rat

The possibility that prostaglandins influence edema formation, microvascular permeability increase and reduction of blood flow following spinal cord trauma was examined in a rat model. In addition, the influence of prostaglandins on serotonin metabolism of the traumatized spinal cord was evaluated. Trauma to spinal cord (2-mm-deep and 5-mm-long incision in the right dorsal horn of T10-11 segments) resulted in a profound increase of the water content 5 h after injury. At this time, the microvascular permeability to Evans Blue and [131I]sodium was increased by 457 and 394%, respectively. The blood flow was reduced by 30%. The serotonin (5-hydroxytryptamine) content of the spinal cord increased by 205%. The plasma serotonin level rose by 152% in the injured group of rats. Pretreatment with indomethacin (10 mg/kg, i.p.) 30 min before trauma significantly reduced the edema and microvascular permeability increase. The local spinal cord blood flow of traumatized animals was partially restored. The increases of serotonin levels of the spinal cord and plasma were significantly attenuated. These beneficial effects of indomethacin were not present in rats given a lower dose (5 mg/kg). Indomethacin in either dose did not influence these parameters of control rats without trauma to the cord. Since indomethacin is a potential inhibitor of prostaglandins synthesis our observations indicate: (i) that prostaglandins participate in many microvascular responses (permeability changes, edema, blood flow) occurring after a trauma to the spinal cord; (ii) that these effects of the drug seem to be dose dependent, and (iii) that the prostaglandins may influence the serotonin metabolism following trauma to the spinal cord.