Abstracts

RATIONALE: The importance of calcium currents in seizure generation and the establishment of epilepsy has been described in several animal and human studies but the specific roles of the different voltage-gated calcium channel (VGCC) subtypes have not been fully delineated. Specifically, there have been no studies examining hippocampal VGCC structure or function in aged animals immediately following prolonged SE. We sought to determine whether SE resulted in aging-related changes in the expression of hippocampal voltage-gated calcium channel (VGCC) [alpha]1A-D subunits immediately following convulsive SE and after attainment of the epileptic state. At the end of this activity participants should be able to discuss the relationships among status epilepticus, epilepsy, aging, and VGCC [alpha]1A-D subunit expression.
METHODS: Animals at 4-8 months (young adult; n=3), 13-14 months (mid-aged; n=2), and 25-29 months (aged; n=4) underwent kainate-induced SE or were used as controls (2 young adult, 1 mid-aged, 2 aged). Animals were injected with kainate (5 mg/kg in NaCl, i.p.) every hour until they demonstrated 4 hours of stage 4-5 seizure activity after which they were sacrificed. The total dose of kainate was 12.5-20 mg/animal. Animals at 1-2 months (juvenile, n=2) and 5-6 months (young adult, n=2) underwent the same kainate protocol for SE but were not sacrificed until 6 months later when they were demonstrating daily epileptic seizures. The total dose of kainate was 20-50 mg/animal. Following fixative perfusion, brains were cut into 40 [mu]m coronal sections on a sliding microtome. Nissl staining was performed on tissue sections adjacent to or near those immunostained for the [alpha]1subunit of class A-D VGCCs.
RESULTS: Immunoreactivity patterns of animals sacrificed immediately after SE demonstrated marked loss of [alpha]1A staining in CA3 and hilus that was most prominent in aged animals, decreased [alpha]1B staining in SL of CA3, increased [alpha]1C staining of pyramidal and granule neurons of all ages and markedly decreased neuropil staining in SP of CA3 and portions of CA1 that was less pronounced in older animals, and decreased [alpha]1D staining in CA3 and hilus that became more prominent with advancing age. Nissl staining demonstrated mildly dysmorphic neurons in CA3 that was most notable in aged animals. Epileptic animals demonstrated immunoreactivity similar to that of control animals.
CONCLUSIONS: VGCC [alpha]1A-D subunit expression was differentially regulated on both neuronal cell bodies and processes during SE and may have been transient; some changes seen in aged animals were prominent in CA1 and hilus, and marked in CA3. Dysmorphic neurons suggested an aging-related regional hippocampal vulnerability to dysregulation of VGCC subunit expression that may have been associated with the metabolic stress of prolonged convulsive SE.
[Supported by: The Nathan Shock Center of Excellence in the Basic Biology of Aging and the Institute on Aging, Allegheny University of the Health Sciences]