Were then cryoprotected in increasing concentrations of sucrose in PBS (10, 20, and 30 ) over 3 d at 4 C. They were then snap frozen in liquid nitrogen, cryosectioned at 12 m, and mounted on slides. For labeling, sections from approximately bregma 0 (the level at which the septum and striatum are visible) or bregma 2.0 (hippocampus and thalamus are visible) were used; they were rehydrated in PBS,