Decrease in hippocampal [3H]vinylidene kainic acid binding in genetically epilepsy-prone rats

Specific [3H]vinylidene kainic acid binding to the kainate-sensitive subtype of glutamate receptor was studied in brain of 31-day-old non-epileptic Sprague-Dawley control and two colonies of genetically epilepsy-prone rats using in vitro autoradiographic techniques. At 37.5 nM [3H]vinylidene kainic acid, specific [3H]vinylidene kainic acid binding was reduced significantly by 18 and 22% in dorsal and ventral hippocampal formation stratum lucidum of 31-day-old genetically epilepsy-prone-9 rats compared with non-epileptic controls. Hippocampal [3H]vinylidene kainic acid binding was reduced in genetically epilepsy-prone-3 rats by 15 and 18%, but these reductions were not statistically significant. Saturation of [3H]vinylidene kainic acid binding studies indicated that the total number of ventral hippocampal [3H]vinylidene kainic acid binding sites was decreased by 21% in genetically epilepsy-prone-3 rats and 28% in genetically epilepsy-prone-9 rats. The reduction in ventral hippocampal [3H]vinylidene kainic acid binding in genetically epilepsy-prone rats resembles the reduction in ventral hippocampal [3H]vinylidene kainic acid binding sites observed in perinatal hypothyroid rats. As genetically epilepsy-prone rats are hypothyroid during the neonatal period, the reduction in hippocampal [3H]vinylidene kainic acid binding in the genetically epilepsy-prone rats may be a consequence of a hypothyroid-induced defect in the development or maturation of the hippocampal mossy fiber projection in genetically epilepsy-prone rats. An alternative hypothesis is that the putative occurrence of spontaneous limbic seizures in genetically epilepsy-prone rats may lead secondarily to a reduction in hippocampal [3H]vinylidene kainic acid binding sites.