Background and Purpose: Nitric oxide has been implicated as a mediator of glutamate excitotoxicity in primary neuronal cultures.Methods: A number of indicators of brain nitric oxide production (nitrite and cyclic guanosine monophosphate [cGMP] concentrations and nitric oxide synthase activity) were examined after bilateral carotid ligation and right middle cerebral artery occlusion in adult rats.Results: Brain nitrite was significantly increased in the right versus left cortex 5, 10, and 20 minutes after middle cerebral artery occlusion (P<.05), with a return to baseline at 60 minutes. There were no significant changes in cerebellar concentrations. Cortical levels of cGMP were increased at 10, 20, and 60 minutes after occlusion, with significant right-to-left differences (P<.05). Cerebellar concentrations of cGMP were also increased but without significant side-to-side differences. Nitric oxide synthase activity increased approximately 10-fold from baseline 10 minutes after occlusion in the right cortex but decreased markedly by 60 minutes from its peak at 10 minutes. The right-to-left difference in nitric oxide synthase activity was significant at 20 minutes (P<.05). Pretreatment of rats with NG-nitro-L-arginine, a nitric oxide synthase inhibitor, abolished the rise in nitrite and cGMP.Conclusions: These results suggest that a sharp transient increase in the activity of nitric oxide synthase occurs during the first hour of cerebral ischemia, which leads to a burst in nitric oxide production and activation of guanylate cyclase. (Stroke. 1993;24:1709-1716 KEY WORDs * cerebral arteries * cerebral ischemia * nitric oxide

The cerebroprotective effects of hypothermia in focal models of ischemia are well established, but little is known about the underlying mechanisms of this form of brain protection. Cortical cooling in global transient ischemic models suggests that hypothermia limits glutamate excitotoxicity by decreasing the release of glutamate during ischemia. Few studies have examined glutamate release in the more physiological model of permanent focal ischemia. In this study, we used a rat model of middle cerebral artery occlusion (MCAO) of permanent focal ischemia. Extracellular glutamate concentration was analyzed bilaterally by microdialysis for 30 minutes before MCAO to 120 minutes after MCAO. Normothermic animals (n = 13) had a baseline glutamate concentration of 9.23 +/- 2.5 mumol/ml (mean +/- standard error of the mean) before MCAO. Extracellular glutamate rose quickly after vessel occlusion and peaked at 33.95 +/- 6.3 mumol/ml 30 minutes after MCAO. By 60 minutes after MCAO, this level had decreased to 25.14 +/- 6.3 mumol/ml; glutamate levels decreased slightly to 21.35 +/- 6.8 mumol/ml by 120 minutes. Hypothermic animals (n = 11) had an initial extracellular glutamate concentration of 5.22 +/- 1.3 mumol/ml before MCAO. This value rose gradually to a maximum of 10.69 +/- 3.3 microns/ml at 50 minutes after MCAO and then returned to a baseline value of 2.58 +/- 1.2 mumol/ml by 120 minutes. Contralateral control glutamate dialysates in the normothermic and hypothermic groups remained near baseline throughout the experimental period. The mean percentages of right hemispheric volumes occupied by infarcts were 11.96 +/- 1.68% in the hypothermic group and 19.77 +/- 2.03% in the normothermic animals.(ABSTRACT TRUNCATED AT 250 WORDS)

In 18 vertebral bodies with titanium fixation screws and in a phantom model, visualization of the vertebral body marrow was improved and susceptibility artifact was reduced on T1-weighted spin-echo magnetic resonance images when the direction of the frequency-encoding gradient was parallel to the long axis of the screw. A perpendicular direction improved image quality only when the region of interest was adjacent to the tip of the screw. In the phantom, the length of the screw was statistically significantly increased and the width and area were reduced (P <.001) when the gradient was parallel to the long axis of the screw.

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Intestinal obstruction due to a phytobezoar within a Meckel diverticulum is exceedingly rare, with only seven reported cases in the surgical literature. The most important precipitating factor is the ingestion of agents high in fiber and cellulose. Small bowel obstruction in all but one case was due to retrograde propagation of the bezoar into the small bowel lumen. We report the clinical and CT findings in such a patient following a vegetarian diet.