Two other brain regions of the PD30 mouse where significant β4 promoter activity was detected are the amygdala and the pons. In particular, strong β4 promoter activity was seen in the posteromedial cortical amygdaloid nucleus (Fig. 6G) and the posterolateral cortical amygdaloid nucleus (Table 3). Lower, yet significant, β4 promoter activity was observed in the pons, most notably in the laterodorsal tegmental nucleus, the lateral mammillary nucleus and the lateral parabrachial nucleus (ventral part) as well as in the medial lemniscus (Table 3). To our knowledge, the amygdala and pons have not been reported to express the nACh receptor β4 subunit, once more raising the issue as to why β4 promoter activity is seen in these two brain regions in multiple founder lines. As before, one possibility is the lack of a cell-type-specific repressor element in the β4/β-gal transgene (Fuentes Medel and Gardner, 2007), although it is possible that the endogenous promoter is subject to regulation, negative in this case, to which the transgene promoter is immune.
