γ-Aminobutyric acid type A receptors (GABA A -Rs) mediate the bulk of rapid inhibitory synaptic transmission in the central nervous system. The β3 subunit is an essential component of the GABA A -R in many brain regions, especially during development, and is implicated in several pathophysiologic processes. We examined mice harboring a β3 gene inactivated by gene targeting. GABA A -R density is approximately halved in brain of β3-deficient mice, and GABA A -R function is severely impaired. Most β3-deficient mice die as neonates; some neonatal mortality, but not all, is accompanied by cleft palate. β3-deficient mice that survive are runted until weaning but achieve normal body size by adulthood, although with reduced life span. These mice are fertile but mothers fail to nurture offspring. Brain morphology is grossly normal, but a number of behaviors are abnormal, consistent with the widespread location of the β3 subunit. The mice are very hyperactive and hyperresponsive to human contact and other sensory stimuli, and often run continuously in tight circles. When held by the tail, they hold all paws in like a ball, which is frequently a sign of neurological impairment. They have difficulty swimming, walking on grids, and fall off platforms and rotarods, although they do not have a jerky gait. β3-deficient mice display frequent myoclonus and occasional epileptic seizures, documented by electroencephalographic recording. Hyperactivity, lack of coordination, and seizures are consistent with reduced presynaptic inhibition in spinal cord and impaired inhibition in higher cortical centers and/or pleiotropic developmental defects.
