Abstracts

Some of the more catastrophic epilepsies are associated with childhood and arise through abnormal development. One example is the genetically based disorder Angelman[apos]s Syndrome, which is associated with abnormal craniofacial development, severe mental retardation, atypical absence and myoclonic epilepsy, sleep deficits, and hyperactivity. One mouse model for Angelman[apos]s Syndrome is the knockout (KO) mouse for the GABA-A receptor beta3 ([beta]3) subunit, based on close phenotypic similarities of high neonatal mortality due primarily to cleft palate, deficiencies in learning and memory, hyperactivity and circling, and myoclonic and aptypical absence epilepsy. Diazepam (Valium) is a benzodiazepine with anxiolytic and sedative properties which acts on the GABA-A receptor to enhance channel activity, and is used to treat seizure disorders. We are using the [beta]3 KO mouse to study the effects of early intervention with diazepam.
[beta]3(-/-) mice are recognizeable at birth by their pink eyes, although only 10% survive the first 24h. [beta]3(-/-) and littermates(C) were injected SC with either physiological saline (SAL) or diazepam 1.5mg/kg (DIAZ) on a daily basis for either the first (PN WK1) or second (PN WK2) postnatal week. At 11 weeks, injected mice were implanted with two bipolar cortical electrodes, and EEGs recorded periodically. Behavior was examined using open field, rotarod, and elevated plus maze assays.
[beta]3(-/-) DIAZ WK1: overall EEG baseline calmer and less disorganized than [beta]3(-/-) SAL but exhibit severe ongoing myoclonic twitches, rare ictal spikes and electrographic seizures, and convulsions with facial distortions, protruding tongue, and forelimb clonus; show no tendency to circling behavior and are much calmer than [beta]3(-/-) SAL, resembling C mice in the open field test and rotarod; show slightly decreased anxiety on elevated plus maze. [beta]3(-/-) DIAZ WK2: overall calming effect on EEG, with no seizures and much suppression of baseline irregularities; only moderate tendency towards the frantic circular running of [beta]3(-/-) SAL, and locomoter activity intermediate between [beta]3(-/-) SAL and C; on the elevated plus maze, coordination and anxiety comparable to C but increased novelty-seeking (jumping off the platform). Both DIAZ WK1 and DIAZ WK2 have irregular edges of the iris, indicating abnormal eye development.
Early intervention with diazepam in this epileptic mouse model has some therapeutic advantages, but may produce severe side effects in PN WK1. This is likely due to the developmental change of GABA from excitatory to inhibitory at the end of PN WK1; enhanced excitatory action of GABA induced by diazepam in PN WK1 would produce an increase in intracellular calcium through activation of the NMDA receptor, resulting in downstream modifications. These results indicate narrow stage-specific effects of diazepam on fetal brain and eye development and suggest increased caution on the part of expectant mothers taking Valium.
[Supported by: NIH Grant NS35985]