Neurochemical pathology最新文献

It is now widely accepted that acidosis is an important component of the pathogenetic events that lead to ischemic brain damage. The objective with this article is to recall the evolution of the concept, to describe the conditions under which tissue acidosis arises and causes enhanced brain damage, and to probe into the cellular and molecular mechanisms involved.

Ca2+ is now recognized to play a central role in the cellular signal transduction system. The hydrolysis of inositol phospholipids is an initial and essential event in Ca2+-mobilizing receptor activation. Phospholipase C cleaves phosphatidylinositol 4,5-bisphosphate to yield two intracellular messengers: inositol 1,4,5-trisphosphate that mobilizes Ca2+ from intracellular storage sites, and 1,2-diacylglycerol that activates protein kinase C. In this chapter, I will describe the functional role of phosphoinositide breakdown during receptor activation and the regulatory mechanism of phospholipase C.

Following prolonged cerebral ischemia, primary electrophysiological recovery may be followed by secondary deterioration of the recovery process. It has been suggested that the secondary deterioration is caused by "late" cytotoxic brain edema. To test this hypothesis, adult normothermic cats were submitted to 1 h complete cerebral ischemia followed by 3 and 6 h recirculation, respectively. Postischemic recovery of energy metabolism was imaged by ATP-induced bioluminescence, and regional tissue pH and electrolyte content was measured in regions with and without metabolic recovery. In areas with postischemic restitution of metabolic activity, sodium gradually rose from 338 +/- 17 to 488 +/- 28 mumol/g protein and calcium from 8.81 +/- 0.35 to 18.24 +/- 0.97 mumol/g protein. Tissue potassium content decreased from 761 +/- 12 to 676 +/- 19 mumol/g protein and magnesium from 46.8 +/- 0.8 to 36.3 +/- 1.1 mumol/g protein. Tissue pH rose from 7.09 +/- 0.04 to 7.31 +/- 0.13 and 7.26 +/- 0.17 after 3 and 6 h recirculation, respectively. In areas without metabolic recovery, electrolyte disturbances were even more pronounced and pH--after transient alkalization--fell to 6.82 +/- 0.12. These data demonstrate that during the later phase of postischemic recirculation, progressive disturbances of electrolyte homeostasis create a preedematous situation that has to be considered for preventing delayed postischemic complications.

Because of the complexity and cost of clinical investigations and the virtual lack of pharmacological leads, drugs for the treatment of strokes have to be tested extensively in animal models closely mimicking the human disorder. With the recent introduction of in vivo NMR imaging (MRI) and spectroscopy (MRS), it is now possible to evaluate the consequences of strokes and to monitor the effects of therapeutic interventions in animals with the same methodology as in humans. The appearance and evolution of brain infarcts in spontaneously hypertensive rats (SHR), after occlusion of the middle cerebral artery (MCA), were detected with MRI. In coronal sections through the rat brain, regions with increased MRI signal started to become discernible after 6 h and turned out to be largely necrotic already after 24 h, as revealed by histology. The location (fronto-parietal cortex, caudate-putamen) and total infarct size, as determined from MR images or histology, were highly reproducible. Posttreatment with the dihydropyridine calcium antagonist isradipine (PN 200-110), at a daily dose of 3 X 0.3 mg/kg sc, reduced the total infarct size by 30-40%, determined by quantitative MRI and confirmed by histology. Biochemical markers of necrosis, such as the increased brain wet wt, the levels of sodium, potassium, dopamine, and noradrenaline, were changed toward normal values. The functional consequences of these morphological effects of isradipine were reflected by the parallel improvement of a neurological score. Follow-up observations made by MRI and histology indicated that the morphological differences between treated and control animals were still present to the same extent after 2 wk and, therefore, seem to be permanent. In order to elucidate the putative mechanisms involved, the influence of calcium antagonists on cerebral blood flow (CBF) and high energy phosphates (HEPs) was investigated. CBF was measured quantitatively with [14C] iodoantipyrine in MCA-occluded SHRs. Although isradipine had no effect on CBF in the contralateral hemisphere, at a dose reducing infarct size, it increased the reduced blood flow in the lesioned hemisphere toward normal values. HEPs (PCr and ATP) as well as inorganic phosphate (Pi) and intracellular pH were measured noninvasively in the rat brain by 31P MRS using a surface coil. Under normal conditions, calcium antagonists had no effect on these parameters.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain function is severely disturbed in ischemia. Within seconds, consciousness and spontaneous activity is lost, whereas interstitial concentrations of major ions are kept near normal levels. After a few minutes, there is a dramatic increase of potassium and a lowering of sodium, chloride, and calcium concentrations. Similar ionic changes are observed during spreading depression, however, that is spontaneously reversible and may be elicited in the otherwise normally perfused brain. In focal ischemia, the two events occur simultaneously. The central core of very low flow displays the ischemic increase of interstitial potassium concentration, whereas the surrounding tissue exhibits repeated episodes of spreading depression. This may induce energy failure by stimulating metabolism in areas with depressed flow thereby causing cell damage outside the ischemic core.

The pathophysiological chain of events occurring during cerebral ischemia is still poorly understood on a molecular level. Therefore, an in vitro model to study glial swelling mechanisms, using C6 glial cells under controlled extracellular conditions, has been established. Flow cytometry serves to determine even small cell volume changes. In this report, the effects of anoxia and acidosis on glial swelling are summarized. Anoxia alone, or in combination with iodoacetate to inhibit anaerobic glycolysis, did not cause an increase of glial volume for up to 2 h. Acidification of the incubation medium below pH 6.8, on the other hand, was immediately followed by cell swelling to 115% of normal. Amiloride or the absence of bicarbonate and Na+ in the medium significantly reduced glial swelling. The data support the contention that swelling results from an activation of the Na+/H+-antiporter to control intracellular pH. It is suggested that swelling in an ischemic penumbra is promoted by this mechanism. Therapeutic approaches to control cerebral pH might be useful to protect brain tissue in cerebral ischemia.

Temporal ischemia of the brain injures only the selectively vulnerable brain cells. The dying process evolves along with glutamate-mediated intracellular signal-transduction system, together with a loss of Ca2+ homeostasis. Such post-ischemic changes eventually disrupt functional and structural integrity of the cell membrane and kill the neuron. Molecular basis in pharmacoprotective agents is discussed.

The present series of experiments was designed to study regional profiles of polyamines (putrescine, spermidine, and spermine) in reversible cerebral ischemia produced in rats and Mongolian gerbils. Polyamine profiles did not change during ischemia, but did following recirculation. The most prominent changes were a dramatic postischemic increase in putrescine and a marked decrease in spermine in severely damaged regions. Within a given brain structure, the postischemic putrescine levels correlated closely with the density of ischemic cell injury and the time period of cerebral ischemia. Furthermore, putrescine was already considerably increased in the CA1-subfield of the hippocampus of gerbils after 8 h recirculation, i.e., at a time when the cells are still intact. The results indicate that putrescine may be viewed as an excellent biochemical correlate of ischemic cell injury. The postischemic changes in putrescine levels are discussed in relation to the known activities of this compound.

During near complete hyperglycemic brain ischemia, brain lactate levels rise in excess of 16-18 mmol/K and are associated with severe brain infarction. Analyses of pHo, Pt(CO2), and total brain lactate under these circumstances suggest that H+, HCO3, and lactate become unequally distributed between cells and the interstitial space and, perhaps, even between different types of brain cells. In addition, to whatever physiological advantages it may generate, such compartmentalization may be a factor leading to cell death in brain ischemia.

Two post-ischemic circulatory disturbances that play a significant role in pathophysiology of an ischemic lesion are: (1) reactive hyperemia or hyperperfusion and (2) hypoperfusion. The reactive hyperemia promptly follows release of major cerebral artery occlusion, and it is associated with the opening of the blood-brain barrier to serum proteins and ensuing edema. Prevention or reduction of reactive hyperemia results in significant amelioration of edema and the resulting ischemic brain tissue injury. The post-ischemic hypoperfusion, studied in gerbils, develops soon after recirculation and usually lasts up to 6 h. Its relationship to post-ischemic edema is evident in repeated ischemic insults. In these studies, three ischemic insults of 5 min duration when applied at 1 h intervals, i.e., during the period of hypoperfusion, resulted in a cumulative effect, post-ischemic edema and tissue injury becoming considerably more pronounced that those following a single 15 min ischemia. There was no cumulative effect when the ischemic insults were spaced 3 min or longer than 6 h apart. These observations indicate that repeated ischemic insults taking place during the phase of post-ischemic hypoperfusion may significantly increase the development of edema and brain tissue injury.