The habenula is the region of highest nACh receptor β4 subunit expression in the brain (Dineley-Miller and Patrick, 1992; Duvoisin et al., 1989; Gahring et al., 2004; Winzer-Serhan and Leslie, 1997). As expected, β4 promoter activity was quite strong in the medial habenula, but was lower in the lateral habenula (Fig. 6C). Interestingly, β4 promoter activity was much higher in PD30 animals versus ED18.5 animals. This is in contrast to β4 mRNA levels - which are high throughout development (Winzer-Serhan and Leslie, 1997; Zoli et al., 1995) - and may reflect the absence of other regulatory elements in the β4/β-gal transgene, for example, CNR4, that may be active early in development (Xu et al., 2006).
