Zinc is present in presynaptic nerve terminals throughout the mammalian central nervous system and likely serves as an endogenous signaling substance. However, excessive exposure to extracellular zinc can damage central neurons. After transient forebrain ischemia in rats, chelatable zinc accumulated specifically in degenerating neurons in the hippocampal hilus and CA1, as well as in the cerebral cortex, thalamus, striatum, and amygdala. This accumulation preceded neurodegeneration, which could be prevented by the intraventricular injection of a zinc chelating agent. The toxic influx of zinc may be a key mechanism underlying selective neuronal death after transient global ischemic insults.

Cell death was examined by studying the spinal cords of rats subjected to traumatic insults of mild to moderate severity. Within minutes after mild weight drop impact (a 10 gm weight falling 6.25 mm), neurons in the immediate impact area showed a loss of cytoplasmic Nissl substances. Over the next 7 d, this lesion area expanded and cavitated. Terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL)-positive neurons were noted primarily restricted to the gross lesion area 4-24 hr after injury, with a maximum presence at 8 hr after injury. TUNEL-positive glia were present at all stages studied between 4 hr and 14 d, with a maximum presence within the lesion area 24 hr after injury. However 7 d after injury, a second wave of TUNEL-positive glial cells was noted in the white matter peripheral to the lesion and extending at least several millimeters away from the lesion center. The suggestion of apoptosis was supported by electron microscopy, as well as by nuclear staining with Hoechst 33342 dye, and by examination of DNA prepared from the lesion site. Furthermore, repeated intraperitoneal injections of cycloheximide, beginning immediately after a 12.5 mm weight drop insult, produced a substantial reduction in histological evidence of cord damage and in motor dysfunction assessed 4 weeks later. Present data support the hypothesis that apoptosis dependent on active protein synthesis contributes to the neuronal and glial cell death, as well as to the neurological dysfunction, induced by mild-to-moderate severity traumatic insults to the rat spinal cord.

Background and Purpose: Infarct volume is one of the common indexes for assessing the extent of ischemic brain injury following focal cerebral ischemia. Accuracy in the measurement of infarct volume is compounded by postischemic brain edema that may increase brain volume in the infarcted region. We evaluated the effect of brain edema on infarct volume determined by triphenyltetrazolium chloride and hematoxylin and eosin stains in a focal cerebral ischemia model in rats.Methods: In a middle cerebral artery occlusion model in rats, infarction is confined to the cerebral cortex. The infarct was delineated by triphenyltetrazolium chloride stain and, in selected samples, by hematoxylin and eosin stain. We determined infarct size at different times after the ischemic insult (6 hours to 7 days) in relation to the evolution of brain edema by the direct measurement of infarct volume. Indirect measurement to reduce the effect of edema on infarct volume was also conducted in the same brain samples.Results: Direct measurement showed that infarct volume fluctuated with the evolution of brain edema (one-way analysis of variance, p

THE ADVANTAGES of using the rat for stroke study include the similarity of its intracranial circulation to that of man, 1 the abundant neurochemical data derived from rat brain, 2 and the relatively low animal cost which is important for large scale studies for statistical analysis. The several models of cerebral ischemia developed in the rat*" 13 can be classed by topography as global or focal and by chronology into reversible and irreversible. These methods entail intravascular embolization or exfravascular ligation. "16 For studies of the molecular events in cerebral ischemia, an animal model of focal and irreversible ischemia allowing only partial reperfusion to create a reproducible infarction of predictable size and location would be of considerable value. Intravascular embolization can cause focal irreversible ischemia without need for craniectomy but precise control of the ultimate site of the emboli is impossible and the infarction produced is usually multifocal and variable in size and location. 14 " 16 The extensive intracranial collateral circulation in the rat provided by the Circle of Willis, leptomeningeal anastomoses and dorsal collateral junctions 17 constrains the use of either unilateral or bilateral common carotid artery (CCA) ligation to produce consistent ischemic lesions unless a systemic insult such as hypoxia hypotension 6 is added. The additional systemic variable may cause generalized metabolic derangement and/or compromise cardiopulmonary function.The procedure of Tamura et al 9 of ligation of the proximal middle cerebral artery (MCA) through a subtemporal approach has been reported to result in consistent ischemic changes, but the procedure is technically difficult and sufficiently invasive that the survival of hours limits it to acute experiments.10 Coyle used a less invasive surgical approach with MCA ligation above the rhinal fissure but did not produce cerebral infarction in young Wistar rats. 11 We have undertaken to develop a reliable infarction model reasoning that the collateral circulation to the MCA territory is decisive in infarct occurrence after MCA ligation and that graded interruption of this collateral circulation would determine the lesion size in the bed of the occluded MCA. A systematic approach employing a relatively non-invasive surgical procedure has resulted in the development of a predictable large cortical infarct. Materials and Methods Laser Doppler FlowmetryTo determine that the blood flow in the right MCA territory after right MCA ligation was further reduced by occlusion of CCAs, we first measured the cerebral blood flow in the cortex supplied by the right MCA with a laser Doppler flowmeter

The temporal evolution of cerebral infarction was examined in rats subjected to transient occlusion of both common carotid arteries and the right middle cerebral artery. After severe (90-min) ischemia, substantial right-sided cortical infarction was evident within 6 h and fully developed after 1 day. After mild (30-min) ischemia, no cortical infarction was present after 1 day. However, infarction developed after 3 days; by 2 weeks, infarction volume was as large as that induced by 90-min ischemia. These data suggest that infarction after mild focal ischemia can develop in a surprisingly delayed fashion. Some evidence of neuronal apoptosis was present after severe ischemia, but only to a limited degree. However, 3 days after mild ischemia, neurons bordering the maturing infarction exhibited prominent TUNEL staining, and DNA prepared from the periinfarct area of ischemic cortex showed internucleosomal fragmentation. Furthermore, pretreatment with 1 mg/kg cycloheximide markedly reduced infarction volume 2 weeks after mild ischemia. These data raise the possibility that apoptosis, dependent on active protein synthesis, contributes to the delayed infarction observed in rats subjected to mild transient focal cerebral ischemia.