For -galactosidase (-gal) staining, free-floating sections were stained for 16 hours with a solution consisting of phosphate buffered saline (PBS) with .1 mol/L potassium ferricyanide, .1 mol/L potassium ferrocyanide, 1 mol/L MgCl2, and 1 mg/mL X-gal in dimethylformamide (all from Sigma, St. Louis, Missouri).