As with nACh receptor β4 mRNA (Dineley-Miller and Patrick, 1992; Winzer-Serhan and Leslie, 1997) and protein (Gahring et al., 2004), significant β4 promoter activity was detected in layer 5 of the cortex (Fig. 5A) and the piriform cortex (Fig. 5C). Slightly lower promoter activity was observed in the frontal association cortex and caudate putamen (Fig. 5E and G, respectively) with there being lower levels in the cingulate/retrosplenial cortex (Fig. 5I). There was also substantial β4 promoter activity in other regions of the forebrain/cortex (Table 3) including the olfactory bulb, agranular insular cortex, auditory cortex, cingulated/retrosplenial cortex, piriform cortex and the visual cortex, amongst others. In addition, there were regions where β4 promoter activity was seen for which we know of no reports of β4 mRNA expression, such as the entorhinal, orbital and prelimbic cortices (Table 3). Again, this may be due to the lack of other transcriptional regulatory elements in the β4/β-gal transgene, such as the cell-type-specific repressor element discussed above. Alternatively, it could be due to positional effects on transgene expression.
