Western blot analysis revealed an increase in levels of Kal7 in lysates of NAc and in purified striatal PSDs following chronic cocaine treatment (Figure 9). Many factors contribute to steady state protein levels, but the cocaine-stimulated increase in usage of the Kal7-specific 3'-terminal exon, coupled with maintained usage of the full-length Kalrn C promoter could account for the observed change. No cocaine-mediated alteration in Kal9 protein levels was observed (Figure 9B), despite a decrease in usage of the Kal9 specific 3'-terminal exon (Figure 8C). While ΔKal7 is detectable in mouse cortex, it is far less prevalent than predicted by promoter usage. The presence of four start codons followed by in-frame stop codons in the 5'-untranslated region of mouse ΔKal7 may limit successful translation [64], and increased turnover ΔKal7, a soluble, cytosolic protein, may contribute to this discrepancy.
