| Although neuroanatomical abnormalities have been noted in human epileptics, studies in patients cannot directly address the causal relationships between these changes, and the epileptic seizures. An animal model, the seizuring Mongolian gerbil (Meriones unguiculatus), has been utilized in these studies to better understand anatomical substrates of ictal activity. Our principal dependent variables were the pyramidal cell dendritic spine, and the mossy tuft of the dentate granule cell, both located in area CA(,3) of hippocampus. We studied spines in two gerbil strains which had been bred selectively over many years to display either the seizure phenotype (the "SS" strain), or no seizures (the "SR" strain).; Using light and transmission electron microscopy, we found that adult SS gerbils have fewer spines than their SR counterparts, while younger (30- or 50-day old) SS animals have more. It should be noted that gerbils at 30 days of age do not have seizures, while 50-day old animals have them only about half the time. In addition, the SS gerbil has a greater proportion of mossy tuft area devoted to vesicles, and a smaller proportion to spines. Considering the localization of these differences within hippocampus, we suggested that seizures in the gerbil, unlike some other models, could result from activation of an excitatory system. The spine density decrease in adulthood could then be a consequence, rather than a cause, of the seizures. Different trends with age were also noted for the two strains.; We also found that, while the frequency of testing did not have an effect on spine density, it did alter the parameters of the seizures themselves. Animals which had been tested more often had less intense seizures of shorter duration; latency from time to placement into the testing situation was not affected by test history.; In addition to these quantitative studies, we examined the hippocampus of gerbil and other mammals with the scanning electron microscope. This instrument permits three-dimensional analysis of a large area of brain tissue without tedious reconstruction procedures, and is part of a continuing series of studies of different regions. |
