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The dentate gyrus is one of the few areas of the mammalian brain where new neurons are continuously produced in adulthood. Certain insults such as epileptic seizures and ischemia are known to enhance the rate of neuronal production. We analyzed this phenomenon using the temporary occlusion of the two carotid arteries combined with arterial hypotension as a method to induce ischemia in rats. We measured the rate of cell production and their state of differentiation with a mitotic indicator, bromodeoxyuridine (BrdU), in combination with the immunohistochemical detection of neuronal markers. One week after the ischemic episode, the cell production in dentate gyrus was increased two- to threefold more than the basal level seen in control animals. Two weeks after ischemia, over 60% of these cells became young neurons as determined by colabeling with BrdU and a cytoplasmic protein (CRMP-4) involved in axonal guidance during development. Five weeks after the ischemia, over 60% of new neurons expressed calbindin, a calcium-binding protein normally expressed in mature granule neurons. In addition to more cells being generated, a greater proportion of all new cells remained in the differentiated but not fully mature state during the 2- to 5-week period after ischemia. The maturation rate of neurons as determined by the calbindin labeling and by the rate of migration from a proliferative zone into the granule cell layer was not changed when examined 5 weeks after ischemia. The results support the hypothesis that survival of dentate gyrus after ischemia is linked with enhanced neurogenesis. Additional physiological stimulation after ischemia may be exploited to stimulate maturation of new neurons and to offer new therapeutic strategies for promoting recovery of neuronal circuitry in the injured brain.

Objective: Tracer constants (K i ) for blood-to-brain diffusion of sucrose were measured in the rat to profile the time course of blood-brain barrier injury after temporary focal ischemia, and to determine the influence of post-ischemic hypothermia. Methods: Spontaneously hypertensive rats were subjected to transient (2 hours) clip occlusion of the right middle cerebral artery. Reperfusion times ranged from 1.5 min to 46 hours, and i.v.3 H-sucrose was circulated for 30 min prior to each time point (1h, 4h, 22h, and 46h; n=5-7 per time point). K i was calculated from the ratio of parenchymal tracer uptake and the time-integrated plasma concentration. Additional groups of rats (n=7-8) were maintained either normothermic (37.5 o C) or hypothermic (32.5 o C or 28.5 o C) for the first 6 hours of reperfusion, and K i was measured at 46 hours. Results: Rats injected after 1.5 -2 min exhibited a 10-fold increase in K i for cortical regions supplied by the right middle cerebral artery (p<0.01). This barrier opening had closed within 1 to 4 hours postreperfusion. By 22 hours, the blood-brain barrier had re-opened, with further opening 22 and 46 hours (p<0.01), resulting in edema. Whole body hypothermia (28 o C-29 o C) during the first six hours of reperfusion prevented opening, reducing K i by over 50% (p<0.05). Conclusions: Transient middle cerebral artery occlusion evokes a marked biphasic opening of the cortical blood-brain barrier, the second phase of which causes vasogenic edema. Hypothermic treatment reduced infarct volume and the late opening of the blood-brain barrier. This opening of the blood-brain barrier may enhance delivery of low permeability neuroprotective agents.RÉSUMÉ: Ouverture biphasique de la barrière hémato-encéphalique suite à une ischémie focale transitoire: effets de l'hypothermie. Objectif: Nous avons mesuré les constantes d'un traceur (K i ) de la diffusion de sucrose du sang vers le cerveau chez le rat afin d'observer l'évolution des dommages subis par la barrière hémato-encéphalique après une ischémie focale temporaire et pour déterminer les effets d'une hypothermie postischémique. Méthodes: Des rats spontanément hypertendus ont été soumis à une occlusion de deux heures de l'artère cérébrale moyenne par un clip. Le temps de reperfusion variait de 1.5 minute à 46 heures et une perfusion intraveineuse de 3 H-sucrose a été administrée pendant 30 minutes avant chaque évaluation ponctuelle (1h, 4h, 22h, et 46h; n=5-7 par évaluation ponctuelle). La constante K i a été calculée à partir de l'indice de captation du traceur par le parenchyme et de la concentration plasmatique en fonction du temps. Des groupes additionnels de rats (n=7-8) ont été maintenus soit à la température normale (37.5 o C) ou en hypothermie (32.5 o C ou 28.5 o C) pendant les 6 premières heures de la reperfusion et K i a été mesurée à 46 heures. Results: Les rats qui ont reçu l'injection après 1.5 -2 minutes présentaient une augmentation de K i de dix fois supérieure dans les régions corticales irriguées par l'artère cér...

Minocycline is a potent neuroprotective tetracycline in animal models of cerebral ischemia. We examined the protective properties of chlortetracycline (CTC) and demeclocycline (DMC) and showed that these two tetracyclines were also potent neuroprotective against glutamate-induced neuronal death in vitro and cerebral ischemia in vivo. However, CTC and DMC appeared to confer neuroprotection through a unique mechanism compared with minocycline. Rather than inhibiting microglial activation and caspase, CTC and DMC suppressed calpain activities. In addition, CTC and DMC only weakly antagonized N-methyl-D-aspartate (NMDA) receptor activities causing 16 and 14%, respectively, inhibition of NMDAinduced whole cell currents and partially blocked NMDA-induced Ca 2؉ influx, commonly regarded as the major trigger of neuronal death. In vitro and in vivo experiments demonstrated that the two compounds selectively inhibited the activities of calpain I and II activated following glutamate treatment and cerebral ischemia. In contrast, minocycline did not significantly inhibit calpain activity. Taken together, these results suggested that CTC and DMC provide neuroprotection through suppression of a rise in intracellular Ca 2؉