Focal cerebral ischaemia and post-ischaemic reperfusion cause cerebral capillary dysfunction, resulting in oedema formation and haemorrhagic conversion. There are substantial gaps in understanding the pathophysiology, especially regarding early molecular participants. Here, we review physiological and molecular mechanisms involved. We reaffirm the central role of Starling's principle, which states that oedema formation is determined by the driving force and the capillary "permeability pore". We emphasise that the movement of fluids is largely driven without new expenditure of energy by the ischaemic brain. We organise the progressive changes in osmotic and hydrostatic conductivity of abnormal capillaries into three phases: formation of ionic oedema, formation of vasogenic oedema, and catastrophic failure with haemorrhagic conversion. We suggest a new theory suggesting that ischaemia-induced capillary dysfunction can be attributed to de novo synthesis of a specific ensemble of proteins that determine osmotic and hydraulic conductivity in Starling's equation, and whose expression is driven by a distinct transcriptional program.Correspondence to: Dr J Marc Simard, Department of Neurosurgery, 22 S. Greene St., Suite 12SD, Baltimore, MD 21201−1595, USA msimard@smail.umaryland.edu. Contributors JMS originated the overall concept for this review and wrote the first and second drafts. TAK contributed to and helped edit the first and second drafts, and supplied important citations. MC participated in the original work on the sections on the NC Ca-ATP channel and contributed to the first draft. KVT did the computer analysis of the gene promoter regions. VG engaged in numerous intellectual exchanges with JMS during formulation of concepts for this review.Conflict of interest JMS and MC have applied for a US patent, "A novel non-selective cation channel in neural cells and methods for treating brain swelling" (application number 10/391,561). NIH Public Access

Pathological conditions in the central nervous system, including stroke and trauma, are often exacerbated by cerebral edema. We recently identified a nonselective cation channel, the NC Ca-ATP channel, in ischemic astrocytes that is regulated by sulfonylurea receptor 1 (SUR1), is opened by depletion of ATP and, when opened, causes cytotoxic edema. Here, we evaluated involvement of this channel in rodent models of stroke. SUR1 protein and mRNA were newly expressed in ischemic neurons, astrocytes and capillaries. Upregulation of SUR1 was linked to activation of the transcription factor Sp1 and was associated with expression of functional NC Ca-ATP but not K ATP channels. Block of SUR1 with low-dose glibenclamide reduced cerebral edema, infarct volume and mortality by 50%, with the reduction in infarct volume being associated with cortical sparing. Our findings indicate that the NC Ca-ATP channel is crucially involved in development of cerebral edema, and that targeting SUR1 may provide a new therapeutic approach to stroke.Edema complicates many conditions that affect the central nervous system (CNS), including stroke and trauma. Edema worsens neurological function and can threaten life. Swelling resulting from malignant cerebral edema after a large middle cerebral artery (MCA) stroke is responsible for the high mortality of 60−80% of the patients 1 . Molecular mechanisms of cerebral edema are poorly understood, and available treatments are nonspecific and only moderately effective 1 .SUR1 is a regulatory subunit that associates with Kir6.x pore-forming subunits to form heterooctameric K ATP channels 2 . SUR1 confers sensitivity to sulfonylurea inhibitors such as glibenclamide and to channel activators such as diazoxide. Apart from involvement with

Advancements in molecular biology have led to a greater understanding of the individual proteins responsible for generating cerebral edema. In large part, the study of cerebral edema is the study of maladaptive ion transport. Following acute CNS injury, cells of the neurovascular unit, particularly brain endothelial cells and astrocytes, undergo a program of pre- and post-transcriptional changes in the activity of ion channels and transporters. These changes can result in maladaptive ion transport and the generation of abnormal osmotic forces that, ultimately, manifest as cerebral edema. This review discusses past models and current knowledge regarding the molecular and cellular pathophysiology of cerebral edema.

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Nicotinic acetylcholine receptors formed from combinations of ␣3, ␤2, ␤4, and ␣5 subunits are found in chicken ciliary ganglion neurons and some human neuroblastoma cell lines. We studied the co-expression of various combinations of cloned human ␣3, ␤2, ␤4, and ␣5 subunits in Xenopus oocytes. Expression on the surface membrane was found only for combinations of ␣3␤2, ␣3␤4, ␣3␤2␣5, and ␣3␤4␣5 subunits but not for other combinations of one, two, or three of these subunits. ␣5 subunits assembled inside the oocyte with ␤2 but not with ␣3 subunits or other ␣5 subunits. ␣5 subunits coassembled very efficiently with ␣3␤2 or ␣3␤4 combinations. The presence of ␣5 subunits had very little effect on the binding affinities for epibatidine of receptors containing also ␣3 and ␤2 or ␣3 and ␤4 subunits. The presence of ␣5 subunits increased the rate of desensitization of both receptors containing also ␣3 and ␤2 or ␣3 and ␤4 subunits. In the case of receptors containing ␣3 and ␤4 subunits, the addition of ␣5 subunits had little effect on the responses to acetylcholine or nicotine. However, in the case of receptors containing ␣3 and ␤2 subunits, the addition of ␣5 subunits reduced the EC 50 for acetylcholine from 28 to 0.5 M and the EC 50 for nicotine from 6.8 to 1.9 M, while increasing the efficacy of nicotine from 50% on ␣3␤2 receptors to 100% on ␣3␤2␣5 receptors. Both ␣3␤2 and ␣3␤2␣5 receptors expressed in oocytes sedimented at the same 11 S value as native ␣3-containing receptors from the human neuroblastoma cell line SH-SY5Y. In the receptors from the neuroblastoma ␣3, ␤2, and ␣5 subunits were co-assembled, and 56% of the receptor subtypes containing ␣3 subunits also contained ␤2 subunits. The ␤2 subunitcontaining receptors from SH-SY5Y cells exhibited the high affinity for epibatidine characteristic of receptors formed from ␣3 and ␤2 or ␣3, ␤2, and ␣5 subunits rather than the low affinity exhibited by receptors formed from ␣3 and ␤4 or ␣3, ␤4, and ␣5 subunits. Nicotine, like the structurally similar toxin epibatidine, also distinguishes by binding affinity two subtypes of receptors containing ␣3 subunits in SH-SY5Y cells. The affinities of ␣3␤2 receptors expressed in oocytes were similar to the affinities of native ␣3 containing receptors from SH-SY5Y cells for acetylcholine, cytisine, and 1,1-dimethyl-4-phenylpiperazinium. Nicotinic acetylcholine receptors (AChRs)1 are members of a gene superfamily of homologous ligand-gated ion channels which include receptors for glycine, ␥-aminobutyric acid, and serotonin (1). There are three branches of the AChR gene family (2-5). The best characterized are muscle and electric organ AChRs which consist of a pentameric array of homologous subunits oriented around a central ion channel like barrel staves. The order of these subunits around the channel is ␣1␥␣1␦␤1 in the fetal form and ␣1⑀␣1␦␤1 in the adult form (6). The two ligand binding sites in each AChR are thought to be formed at the interfaces between ␣1 and ␥, ␦, or ⑀ subunits (6). One group of neuronal AChRs which is capable of f...

Acute spinal cord injury (SCI) causes progressive hemorrhagic necrosis (PHN), a poorly understood pathological process characterized by hemorrhage and necrosis that leads to devastating loss of spinal cord tissue, cystic cavitation of the cord, and debilitating neurological dysfunction. Using a rodent model of severe cervical SCI, we tested the hypothesis that sulfonylurea receptor 1-regulated (SUR1-regulated) Ca 2+ -activated, [ATP] i -sensitive nonspecific cation (NC Ca-ATP ) channels are involved in PHN. In control rats, SCI caused a progressively expansive lesion with fragmentation of capillaries, hemorrhage that doubled in volume over 12 hours, tissue necrosis, and severe neurological dysfunction. SUR1 expression was upregulated in capillaries and neurons surrounding necrotic lesions. Patch clamp of cultured endothelial cells exposed to hypoxia showed that upregulation of SUR1 was associated with expression of functional SUR1-regulated NC Ca-ATP channels. Following SCI, block of SUR1 by glibenclamide or repaglinide or suppression of Abcc8, which encodes for SUR1 by phosphorothioated antisense oligodeoxynucleotide essentially eliminated capillary fragmentation and progressive accumulation of blood, was associated with significant sparing of white matter tracts and a 3-fold reduction in lesion volume, and resulted in marked neurobehavioral functional improvement compared with controls. We conclude that SUR1-regulated NC Ca-ATP channels in capillary endothelium are critical to development of PHN and constitute a major target for therapy in SCI.

Background: Sur1-NCCa-ATP channels implicated in acute CNS injury are hypothesized to be formed by co-association of Sur1 and a nonselective cation channel.Results: Sur1 and Trpm4 form heteromers that exhibit pharmacological properties of Sur1 and biophysical properties of Trpm4.Conclusion: Sur1 and Trpm4 co-assemble to form the unique Sur1-Trpm4 channel.Significance: Identification of Sur1-Trpm4 channels has broad implications in acute CNS injuries.

Chronic exposure to nicotine has been reported to increase the number of nicotinic acetylcholine receptors (AChRs) in brain. The mechanism of up-regulation for the alpha4beta2 AChR subtype, which accounts for the majority of high affinity nicotine binding in mammalian brain, has previously been shown to involve a decrease in the rate of alpha4beta2 AChR turnover. Here, we report an investigation of the extent and mechanism of nicotine-induced up-regulation of alpha3 AChRs and alpha7 AChR subtypes expressed in the human neuroblastoma cell line SH-SY5Y. Up-regulation of human alpha3 AChRs and alpha7 AChRs, unlike alpha4beta2 AChRs, requires much higher nicotine concentrations than are encountered in smokers; the extent of increase of surface AChRs is much less; and the mechanisms of up-regulation are different than with alpha4beta2 AChRs. The mechanisms of up-regulation may be different for alpha3 AChRs or alpha7 AChRs. Chronic treatment with nicotine or carbamylcholine, but not d-tubocurarine, mecamylamine, or dihydro-beta-erythroidine, induced a 500-600% increase in the number of alpha3 AChRs but only a 30% increase in alpha7 AChRs. Chronic nicotine treatment did not increase affinity for nicotine or increase the amount of RNA for alpha3 or alpha7 subunits. The effect of nicotine on up-regulation of alpha7 AChRs was partially blocked by either d-tubocurarine or mecamylamine. The effect of nicotine treatment on the number of alpha3 AChRs was only slightly blocked by the antagonists d-tubocurarine, mecamylamine, or dihydro-beta-erythroidine at concentrations that efficiently block alpha3 AChR function. Most of the nicotine-induced increase in alpha3 AChRs was found to be intracellular. The alpha3 AChRs, which accumulate intracellularly, were shown to have been previously exposed on the cell surface by their susceptibility to antigenic modulation. The data suggest that chronic exposure to nicotine may induce a conformation of cell surface alpha3 AChRs that at least in this cell line are consequently internalized but not immediately destroyed.