Extracellular protons inhibit N-methyl-D-aspartate (NMDA) receptors with an IC 50 value in the physiological pH range. To identify the molecular determinants of proton sensitivity, we used scanning mutagenesis of the NR1 subunit to search for residues that control proton inhibition of NMDA receptors. Homology modeling of the extracellular domains suggested that residues at which mutations perturbed pH sensitivity were localized in discrete regions. The majority of mutations that strongly affected proton sensitivity were clustered in the extracellular end of the second transmembrane domain (M3) and adjacent linker leading to the S2 portion of the glycine-binding domain of NR1. Mutations in NR2A confirmed that the analogous region controls the pH sensitivity of this subunit and also identified the linker region between the third transmembrane domain (M4) and the S2 portion of the NR2 glutamate binding domain as an additional determinant of proton sensitivity. One mutant receptor, NR1(A649C)/NR2A(A651T), showed a 145-fold reduction in the IC 50 for protons (IC 50 , 17.3 M corresponding to pH 4.9). The M3-S2 linker region has been suggested to control NMDA receptor gating, leading to the hypothesis that the proton sensor and receptor gate may be structurally and functionally integrated.

Background: Chiari I malformation (CMI) is diagnosed by rigid radiographic criteria along with appropriate clinical symptomatology. The aim of this study was to investigate the dimensions of the posterior cranial fossa in patients without significant tonsillar descent but with symptoms comparable to CMI.

Microvascular decompression is an effective treatment for elderly patients with TN. The authors' experience suggests that the rate of complications and death after MVD for TN in elderly patients is no different from the rate in younger patients.

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✓Spinal glioblastomas multiforme (GBMs) are rare lesions of the central nervous system with a prognosis as poor as that of their intracranial counterpart. The authors present a case of a 50-year-old man with a GBM of the spinal cord treated with surgical removal of the mass and cordectomy after the onset of paraplegia. Six years later, the patient developed hepatitis C and received interferon therapy. Six months after the start of interferon therapy, magnetic resonance imaging revealed a right cerebellar mass pathologically consistent with a GBM. Despite aggressive treatment, the patient died 1 month later. Although intracranial dissemination of spinal GBMs has been reported, this case illustrates the longest reported interval between the occurrence of a spinal GBM and its intracranial dissemination. Thus, cordectomy should be considered as a reasonable alternative in patients with complete loss of neurological function at and below the level where they harbor a malignant spinal cord astrocytoma.

Acute disseminated encephalomyelitis (ADEM), also known as postinfectious encephalomyelitis, is an immunologically mediated demyelinating disorder affecting the central nervous system that typically occurs after infection or vaccination. The prognosis of ADEM is generally favorable. In a small subset of patients with ADEM, however, fulminant cerebral edema requiring neurosurgical intervention will develop. Few recommendations are available to help the neurosurgeon in dealing with such cases. In this report, the authors present the case of a patient with ADEM in whom central brain herniation developed secondary to medically intractable cerebral edema. The authors review the salient features of the disease and suggest a role for neurosurgeons in cases of fulminant ADEM.

Over the past 50 years, various shunting procedures involving the peritoneum have been performed for the treatment of hydrocephalus. During placement of the peritoneal portion of the catheter, complications may arise secondary to a lack of direct visualization. We describe a reduced complication rate with laparoscopically-assisted placement of the peritoneal portion of the catheter. A retrospective chart review was performed of seventy-six (76) laparoscopically-assisted cases performed without consideration of prior abdominal surgery or obesity. Subjects ranged in age from 19 to 80 years. Mean operative time was 55.3 minutes. No visceral injuries occurred. To date, no infectious complications have occurred. In 3% of subjects, conversion to an open procedure was necessary after failure to establish pneumoperitoneum. Laparoscopic placement of peritoneal shunts is safe and efficacious. It provides visualization of the distal catheter target. Moreover, it reduces the risk of visceral complications, CSF pseudocysts, or extraperitoneal placement of the catheter. In the future, laparoscopic placement of the peritoneal portion of the catheter may become a standard treatment in those patients requiring placement of a peritoneal catheter.

A 14% incidence (95% confidence interval 3.9-31.7%) of hydrocephalus in patients with unruptured aneurysm undergoing embolization with hydrogel coils was discovered. This incidence is much higher than previously reported. The mechanism by which hydrogel coils may induce hydrocephalus remains poorly understood.