cycle and ad lib access to food and water. Genotype of all animals was confirmed after completing experiments. For genotyping, tail samples were used to extract genomic DNA. A quantitative polymerase chain reaction protocol developed by the Jackson Laboratory, Bar Harbor, ME (http://www.jax.org/cyto/quanpcr.html) was used to measure expression of the Mx1 gene, which is present in three copies in Ts65Dn. To determine number of gene copies of Kcnj6, PCR reaction for this gene was performed using primers RK2-1: 5′- TAT GGC TAC CGG GTC ATC AC −3′; RK2-3: 5′- GAT CAA CTT GGC TCT GAT GG −3′, and G2KO-A: 5′- GAG TAG AAG TGG CGC GAA GG −3′, as described (Signorini et al., 1997). In addition, all mice were prescreened for Pde6brd1 homozygosity, a recessive retinal degeneration mutation that results in blindness (Bowes et al., 1993), and only animals free of retinal degeneration were used.
