As discussed above, significant β4 promoter activity was observed in the medial habenula, a region that expresses high levels of β4 mRNA. In addition, the β4 subunit is also expressed in the paraventricular thalamic nucleus, medial geniculate nucleus, the posterior thalamic nuclear group, the retroparafascicular nucleus, the inferior colliculus and the ventral anterior and ventral posteromedial thalamic nuclei (Gahring et al., 2004). We detected β4 promoter activity in these same regions (Fig. 6C and E and Table 3). With the exception of these structures and the interpeduncular nucleus (see below), nACh receptor β4 expression is either very low or undetectable in the thalamus and hypothalamus (Dineley-Miller and Patrick, 1992; Duvoisin et al., 1989; Gahring et al., 2004; Winzer-Serhan and Leslie, 1997). Thus, it was surprising to observe significant β4 promoter activity in both of these regions (Table 3). Again, this 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
