Role of extracellular calcium in anoxic injury of mammalian central white matter.

Abstract

White matter (WM) of the mammalian brain is susceptible to anoxic injury, but little is known about the pathophysiology of this process. We studied the mechanisms of anoxic injury in WM using the isolated rat optic nerve, a typical central nervous system WM tract. Optic nerve function, measured as the area under the compound action potential, rapidly failed when exposed to anoxia and recovered to 28.5% ofcontrol after a standard 60-min period of anoxia. Irreversible anoxic injury was critically dependent on the molar concentration of extracellular calcium ([Ca2l] Orthodromic stimulation and recording from RONs were accomplished by using suction electrodes. Stimulus strength was set to 25% above the strength that elicited a maximal compound action potential (CAP). Area under the CAP was examined before and after various experimental manipulations by a method that corrected for changes in the recording electrode impedance. Stimuli (50-pus duration) were delivered by an isolation unit at 30-s intervals.Anoxia was achieved by switching to a 95% N2/5% CO2 atmosphere. To ensure that anoxia was complete and rapid, the partial pressure of 02 in the chamber was measured with a Po2 meter (Vascular Technologies; 402 Oxygen Alarm). The sensor was placed at the point in the chamber where the nerve was usually positioned. When the gas was switched from 02 to N2, oxygen tension decreased from 95% to 0% in about 2.5 min; the return to 95% 02 had a similar time course. After reoxygenation, the RONs were allowed a further 60-min recovery period before postanoxic activity was measured, since all nerves attained their maximal recovery by the end of this 60-min interval ( Fig. 1; ref. 15). RESULTSThe effects of anoxia on the CAP (measured as the area under the CAP and normalized to the control CAP area) are illustrated in Fig. 1. The CAP rapidly diminished after the start of anoxia; the CAP decreased to 50% of control by [2][3]

Astrocytic Glycogen Influences Axon Function and Survival during Glucose Deprivation in Central White Matter

“…L ong-Evans rats were anesthetized deeply with C O 2 and then decapitated. The optic nerves were exposed, gently freed from their dural sheaths, and placed in an interface perf usion chamber (Medical Systems, Greenvale, N Y) (see also Stys et al, 1990). Nerves were maintained at 37°C and perf used with artificial C SF (aC SF) that contained (in mM): 153 Na ϩ , 3 K ϩ , 2 Mg 2ϩ , 2 Ca 2ϩ , 143 C l Ϫ , 26 HCO 3 Ϫ , 1.25 HPO 4 2Ϫ , and 10 glucose.…”

Electrophysiological changes in isolated spinal cord white matter in response to oxygen deprivation

“…This is important since both methods are used in different preparations in various labs. 16,18,20,43 Knowing the equivalency of these two methods in some situations will facilitate the comparisons of various findings and avoid duplicated and redundant efforts. Despite the similarity of these two methods in the current study, we suggest that caution be taken in some extreme situations where these two methods may produce significantly different results.…”

“…For example, Waxman and his co-workers have been using the sum of the area under the curve, or CAP area, to quantify the conduction of rat optic nerves. 16,17 On the other hand, Shi, Blight and their co-workers have been using the peak amplitude of the CAP as a means to estimate the impulse conduction in guinea pig spinal cord white matter. 13,[18][19][20] Therefore, the question arises whether the end results are similar when using these two different methods.…”

C-Arm Flat Detector CT Parenchymal Blood Volume Thresholds for Identification of Infarcted Parenchyma in the Neurointerventional Suite

“…However, differences between the gray and white matter exist regarding cellular composition, metabolism, the normal perfusion parameter values, and their neurochemical responses to ischemia. [22][23][24] Tissuespecific infarction thresholds may thus be more informative in predicting the tissue outcomes in the setting of cerebrovascular ischemia. 25 In our cohort, the limited number of patients and DWI lesions precluded such tissue-specific analysis to explore the differential variability of gray and white matter to ischemia.…”