Submitted on September 5, 2008
Revised on March 10, 2009
Accepted on March 18, 2009
GABAC receptor-mediated inhibition is altered, but not eliminated in the superior colliculus of GABAC 
1 knockout mice
Katja Schlicker1, Maureen A McCall2, and Matthias Schmidt1*
1 Ruhr-University
2 University of Louisville
* To whom correspondence should be addressed. E-mail: matthias.schmidt{at}rub.de.
GABAC receptors (GABACRs) are widely expressed in the mammalian subcortical visual system, particularly in the retina and superior colliculus (SC). GABACRs are composed of specific 
1-3 subunits whose expression varies among visual structures. Thus, 1 subunits are most abundant in retina and their loss eliminates GABACR expression and function (McCall et al. J Neurosci 22:4163-4174). In the SC, 2 subunit expression may be equal to or stronger than 1 subunit expression, however, results across studies vary considerably. To more directly assess the expression of GABACR subunits, we characterized inhibition in the SC of wild type (WT) and GABAC 1 Null mice that lack expression of GABAC 1 subunits. We used whole-cell patch clamp recordings and evaluated GABACR-mediated modulation of electrically-evoked post synaptic currents using either agonists or antagonists in WT mice. In GABAC 1 Null SGS cells, IPSCs were shorter in duration and their EPSCs were longer, indicating that a slow GABACR-mediated inhibitory component in each was reduced. In contrast to retina, GABACR-mediated currents in the SC were altered, but not eliminated in GABAC 1 Null mice. In the majority of SC cells in GABAC 1 Null mice, GABACR activation could still be induced to alter EPSC peak amplitudes in putative interneurons and in many projection neurons. These results, compared to previously published data, indicate a fundamental difference between retina and SC in the control of GABACR expression and subunit composition.
