Demonstration of specific neuronal cell groups in rat brain by beta-galactosidase enzyme histochemistry

beta-Galactosidase activity as illuminated by the indigogenic X-gal staining method has been used to demonstrate the presence of genetically modified cells carrying the reporter gene lacZ, coding for the E. coli enzyme. Endogenous activity has been assumed to be minimal since the pH optimum for the mammalian enzyme is 3.5-5.5, while the pH optimum for the E. coli enzyme (and thus of the staining procedure usually employed) is 7.3. Background staining has been reported to be limited to pericytes and a few specific neuronal cell groups. In contrast, our investigations of normal rat brain anatomy demonstrate that many specific neuronal cell groups possess endogenous beta-galactosidase activity when staining is performed at physiological pH. This suggests that background staining of endogenous beta-galactosidase activity in the rat brain has been underestimated. In addition, such specific activity would afford an additional means of identification and illustration of these cells.