Failure of kynurenic acid to inhibit amino acid release from the ischemic rat cerebral cortex

Systematic Review on the Involvement of the Kynurenine Pathway in Stroke: Pre-clinical and Clinical Evidence

Background: Stroke is the second leading cause of death after ischemic heart disease and the third leading cause of disability-adjusted life-years lost worldwide. There is a great need for developing more effective strategies to treat stroke and its resulting impairments. Among several neuroprotective strategies tested so far, the kynurenine pathway (KP) seems to be promising, but the evidence is still sparse.

Methods: Here, we performed a systematic review of preclinical and clinical studies evaluating the involvement of KP in stroke. We searched for the keywords: (“kynurenine” or “kynurenic acid” or “quinolinic acid”) AND (“ischemia” or “stroke” or “occlusion) in the electronic databases PubMed, Scopus, and Embase. A total of 1,130 papers was initially retrieved.

Results: After careful screening, forty-five studies were included in this systematic review, being 39 pre-clinical and six clinical studies. Despite different experimental models of cerebral ischemia, the results are concordant in implicating the KP in the pathophysiology of stroke. Preclinical evidence also suggests that treatment with kynurenine and KMO inhibitors decrease infarct size and improve behavioral and cognitive outcomes. Few studies have investigated the KP in human stroke, and results are consistent with the experimental findings that the KP is activated after stroke.

Conclusion: Well-designed preclinical studies addressing the expression of KP enzymes and metabolites in specific cell types and their potential effects at cellular levels alongside more clinical studies are warranted to confirm the translational potential of this pathway as a pharmacological target for stroke and related complications.

An in vitro spinal cord slice preparation for recording from lumbar motoneurons of the adult mouse

The development of central nervous system slice preparations for electrophysiological studies has led to an explosion of knowledge of neuronal properties in health and disease. Studies of spinal motoneurons in these preparations, however, have been largely limited to the early postnatal period, as adult motoneurons are vulnerable to the insults sustained by the preparation. We therefore sought to develop an adult spinal cord slice preparation that permits recording from lumbar motoneurons. To accomplish this, we empirically optimized the composition of solutions used during preparation in order to limit energy failure, reduce harmful ionic fluxes, mitigate oxidative stress, and prevent excitotoxic cell death. In addition to other additives, this involved the use of ethyl pyruvate, which serves as an effective nutrient and antioxidant. We also optimized and incorporated a host of previously published modifications used for other in vitro preparations, such as the use of polyethylene glycol. We provide an in-depth description of the preparation protocol and discuss the rationale underlying each modification. By using this protocol, we obtained stable whole cell patch-clamp recordings from identified fluorescent protein-labeled motoneurons in adult slices; here, we describe the firing properties of these adult motoneurons. We propose that this preparation will allow further studies of how motoneurons integrate activity to produce adult motor behaviors and how pathological processes such as amyotrophic lateral sclerosis affect these neurons.

Inhibition of Na(+)/H(+) exchange by 5-(N-ethyl-N-isopropyl)-amiloride reduces free fatty acid efflux from the ischemic reperfused rat cerebral cortex

Brain tissue acidosis is considered to be a contributor to ischemic brain injury. The deleterious effects of marked acidosis may be associated with reperfusion and an excessive entry of Na(+) into cerebral neurons and glia as intracellular pH is restored by Na(+)/H(+) exchange. Normalization of pH, with activation of many calcium-dependent and other phospholipases and proteases with pH optima in the neutral or alkaline range, could account for the pronounced elevation in extracellular levels of free fatty acids which occurs during reperfusion following cerebral ischemia. In the present investigation we evaluated the effects of inhibition of Na(+)/H(+) exchange with N-(N-ethyl-N-isopropyl)-amiloride (EIPA; 25 microM) applied topically onto the rat cerebral cortex prior to and during ischemia. Free fatty acid levels in cortical superfusates, withdrawn at 10-min intervals from bilateral cortical windows, were analyzed by high pressure liquid chromatography. EIPA application effectively inhibited the increases in arachidonic and linoleic acid release observed in the control rats during reperfusion, and non-significantly depressed that of palmitic and oleic acids. Superfusate levels of glucose, which decline to near zero levels during ischemia and then rebound during reperfusion, were not affected by EIPA administration. Lactate levels in cortical superfusates from EIPA-treated animals rose more rapidly during reperfusion than did those in the control rats and then significantly declined towards basal levels. The data indicate that inhibition of Na(+)/H(+) exchange prevented the activation of phospholipases that usually occurs during reperfusion following a cerebral ischemic episode. These results are the first demonstration of such an effect and may provide an explanation for the cerebroprotective effects that have been observed in stroked animals following administration of Na(+)/H(+) exchange inhibitors.