POSTNATAL-DEVELOPMENT OF SURVIVAL RESPONSIVENESS IN RAT SYMPATHETIC NEURONS TO LEUKEMIA INHIBITORY FACTOR AND CILIARY NEUROTROPHIC FACTOR

Embryonic rat sympathetic neurons undergo programmed cell death upon N GF deprivation. We show that during postnatal development, these neuro ns acquire the ability to be supported in vitro by LIF and CNTF as wel l as NGF. LIF and CNTF do not promote the long-term survival of embryo nic day 21 sympathetic neurons in vitro. However, after 5 days of cult ure in the presence of NGF, the majority of embryonic day 21 sympathet ic neurons can be supported by either of these factors. Furthermore, p ostnatal day 6 sympathetic neurons can be immediately supported by LIF and CNTF, indicating that acquisition of survival responsiveness occu rs in vivo as well as in vitro. During this period, neuronal expressio n of LIF and CNTF receptor mRNAs remains constant, suggesting that sym pathetic neurons alter their responsiveness to LIF and CNTF by allowin g additional intracellular signaling pathways to promote survival.