The advantages of the alumina gel model of cortical focal epilepsy are several. First, it is a model that is focal in its initiation and then proceeds with time to produce spontaneous focal seizures that often become generalized. Focal motor seizures in the human are well characterized, and this model produces seizures that are extremely similar to those in regard to their behavior, electrophysiology, biochemistry, neuropathological, and pharmacologic responses (Lockard, 1980). The second advantage of this model is the time course of the development of seizures: They usually begin 4 to 8 weeks following the application of the alumina gel, allowing time to analyze electroencephalographic (EEG) and neuropathological changes that may underlie the cause of the seizures. This delay in seizure development, as opposed to the use of fast-acting convulsants like bicu-
culline, provides ample time to study these morphologic and electrophysiologic changes. Third, the initial injury caused by the injection of alumina gel into the sensorimotor cortex is well localized and provides the topographic focus for seizure initiation. Such localized foci are essential for analyzing different stages along the time line of seizure development using anatomic methods. Several studies have taken advantage of these features and are reviewed subsequently herein.
The central sulcus of either adult or adolescent monkeys is exposed through a frontal craniotomy under general anesthetic, taking great care not to damage the cortex. After opening the dura, the hand-face region of the sensorimotor cortex is identified with cortical stimulation and injected with alumina gel. Although different injection patterns have been used, one of the most successful is the Ward modification of the Kopeloff technique (Bakay and Harms, 1981). In this method, two injections are made 4mm apart in the precentral gyrus and two injections in the postcentral gyrus, paralleling each other. A 27-gauge needle is used for the injection, which is placed into the cortex to a depth of approximately 4 mm. A volume of 0.1ml of aluminum hydroxide (fully saturated solution) in the form of alumina gel is injected at each site. Each injection is made quite slowly to allow time for volume equilibrium to be reached before removing the needle. In general an injection under the pia is avoided because greater scarring will occur in this situation. The epidural space is covered with Gelfoam, and perioperative steroids are used to avoid brain swelling because a watertight dura closure is extremely difficult to
Models of Seizures and Epilepsy
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