REDUCTION OF GABA AND GLUTAMATE TRANSPORTER MESSENGER-RNAS IN THE SEVERE-SEIZURE GENETICALLY EPILEPSY-PRONE RAT

The genetically epilepsy-prone rat is an animal model of inherited gen eralised tonic-clonic epilepsy that shows abnormal susceptibility to a udiogenic seizures and a lowered threshold to a variety of seizure-ind ucing stimuli. Recent studies suggest a crucial role for glutamate and GABA transporters in epileptogenesis and seizure propagation. The pre sent study examines the levels of expression of the messenger RNAs enc oding the glial and neuronal glutamate transporters, GLT-1 and EAAC-1, and the neuronal GABA transporter, GAT-I, in paired male genetically epileptic-prone rats and Sprague-Dawley control rats using the techniq ue of in situ hybridization. In a parallel study, semiquantitative imm unoblotting was used to assess GLT-1 and EAAC-1 protein levels in simi larly paired animals. Animals were assessed for susceptibility to audi ogenic seizures on six occasions, and killed seven days following the last audiogenic stimulus exposure. Rat brains were processed for in si tu hybridization with radioactive S-35-labelled oligonucleotide probes (EAAC-1 and GAT-1), S-35-labelled riboprobes (GLT-1), and Fluorescein -labelled riboprobes (GLT-1 and GAT-1) or processed for immunoblotting using subtype-specific antibodies for GLT-1 and EAAC-1. Semiquantitat ive analyses were carried out on X-ray film autoradiograms in several brain regions for both in situ hybridization and immunoblotting studie s. Reductions in GAT-1 messenger RNA were found in genetically epilept ic-prone rats in ail brain regions examined (-8 to -24% compared to co ntrol). Similar reductions in GLT-1 messenger RNA expression levels we re seen in cortex, striatum, and CAl (-8 to -12%) of genetically epile ptic-prone rats; the largest reduction observed was in the inferior co lliculus (-20%). There was a tendency for a reduced expression of EAAC -1 messenger RNA in most regions of the genetically epileptic-prone ra t brain although this reached statistical significance only in the str iatum (-12%). In contrast, no significant differences in GLT-1 and EAA C-1 protein between genetically epileptic-prone rats and control anima ls were observed in any region examined, although there was a tendency to follow the changes seen with the corresponding messenger RNAs. The se results show differences in the messenger RNA expression levels of three crucial amino acid transporters. For the two glutamate transport ers, GLT-1 and EAAC-1, differences in messenger RNA levels are not ref lected or are only partially reflected in the expression of the corres ponding proteins. (C) 1998 IBRO. Published by Elsevier Science Ltd.