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

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Selective discrete intraaxoplasmic deposits of hydroxyapatite crystallites were observed in adult male rats subjected to experimental trauma to the lumbosacral spinal cord. Although previously unreported in spinal cord trauma, the presence of these deposits in minimally altered axons and during the early posttrauma period suggests that such selective calcification may be of more than secondary significance. In view of the current emphasis on cytotoxicity of calcium, especially in relation to axonal degeneration, an evaluation of the role of calcium in augmenting traumatic spinal cord necrosis is warranted.

The association of intracranial dermoids and epidermoids and recurrent meningitis is usually related to the presence of dermal sinuses that allow bacterial entry. Epidermoid cysts rarely discharge their contents into subarachnoid space to cause meningitis, except after surgical removal. We describe a child who had 10 separate episodes of chemical meningitis between age 13 months and her death at age 2 years 9 months. Death was caused by an intra-axial epidermoid in the ventral pons which had ruptured into the subarachnoid space, as shown at autopsy. There was no evidence of sinus tracts, and radiographic studies revealed no mass.