Fig. 2.

Immunocytochemistry reveals the expression of various cell cycle proteins in pyramidal neurons of the hippocampus. In both MCI (A) and AD (B), immunostaining for cyclin D reveals that a fraction of the hippocampal pyramidal cells express proteins that are normally found only in actively dividing cells. In contrast, age-matched controls (C) show little if any evidence for cyclin D expression. A second mitotic marker, the DNA polymerase subunit PCNA, is also found in neurons of the hippocampus in MCI cases (D) as well as in material from subjects who died with mild to moderate AD (E). Little evidence for reexpression of PCNA is detected in control material (F). Arrows indicate neurons stained positive for the two cell cycle markers. Scale bars, 25 μm.