Schwann cells (nonconfluent) were pulsed with BrdU for 7 hr. Nonconfluent and confluent Schwann cells were cultured with 10% serum and 2 μm forskolin. Schwann cells grown under serum-free conditions were also cultured in the presence or absence of DRG or Schwann cell membranes (see Materials and Methods for details). The percent of cells incorporating BrdU under each condition is listed. SF, Serum-free.