RB AND CDC2 EXPRESSION IN BRAIN - CORRELATIONS WITH H-3 THYMIDINE INCORPORATION AND NEUROGENESIS

Expression of the cell cycle regulatory proteins RB and p34cdc2 was ex amined in the adult rat brain, with special emphasis on proliferation and neuronal differentiation in the hippocampal formation and olfactor y bulb. RB-like immunoreactivity (RB-IR) was detected throughout the b rain, with particularly intense staining observed in hippocampal pyram idal cells, pyriform cortex, and cerebellar Purkinje cells. Intense RB -IR and cdc2-IR were also detected in proliferating neuronal precursor cells in the subgranular region of the dentate gyrus and in the subep endymal region extending from the anterior lateral ventricle into the olfactory bulb. Many of these cells developed into neurons as- assesse d by the expression of neuron-specific enolase (NSE) and, in the hippp ocampal formation, the expression of Fos-IR following pentylenetetrazo l-induced seizure activity. A good correlation was observed between th e number of proliferating cells expressing intense nuclear RB-IR stain ing and the number of thymidine-labeled cells that had differentiated into functional hippocampal neurons. A substantial decrease in RB-IR d uring differentiation was also observed and occurred prior to the expr ession of NSE. The possibility that the loss of RB may be necessary fo r neuronal differentiation to proceed is discussed.