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A gain‐of‐function mutation in the GABAA receptor produces synaptic and behavioral abnormalities in the mouse

In mammalian species, inhibition in the brain is mediated predominantly by the activation of GABAA receptors. We report here changes in inhibitory synaptic function and behavior in a mouse line harboring a gain‐of‐function mutation at Serine 270 (S270) in the GABAA receptor α1 subunit. In recombinant α1β2γ2 receptors, replacement of S270 by Histidine (H) results in an increase in sensitivity to γ‐aminobutyric acid (GABA), and slowing of deactivation following transient activation by saturating concentrations of GABA. Heterozygous mice expressing the S270H mutation are hyper‐responsive to human contact, exhibit intention tremor, smaller body size and reduced viability. These mice also displayed reduced motor coordination, were hypoactive in the home cage, but paradoxically were hyperactive in a novel open field environment. Heterozygous knockin mice of both sexes were fertile but females failed to care for offspring. This deficit in maternal behavior prevented production of homozygous animals. Recordings from brain slices prepared from these animals revealed a substantial prolongation of miniature inhibitory postsynaptic currents (IPSCs) and a loss of sensitivity to the anesthetic isoflurane, in neurons that express a substantial amount of the α1 subunit. The results suggest that the biophysical properties of GABAA receptors are important in determining the time‐course of inhibition in vivo, and suggest that the duration of synaptic inhibition is a critical determinant that influences a variety of behaviors in the mouse.