could be due to the absence of the cell-type-specific repressor element mentioned earlier. Interestingly, while β4 mRNA and protein expression is high in the interpeduncular nucleus (Dineley-Miller and Patrick, 1992; Gahring et al., 2004; Winzer-Serhan and Leslie, 1997), we detected no β4 promoter activity in this region (not shown). However, Deneris and colleagues reported that CNR4 drives high transgene expression in the interpeduncular nucleus (Xu et al., 2006). The absence of CNR4 in the β4/β-gal transgene used in the current study may explain why no β4 promoter activity was seen in this nucleus.
