NONNEURONAL CELLS INHIBIT CATECHOLAMINERGIC DIFFERENTIATION OF PRIMARY SENSORY NEURONS - ROLE OF LEUKEMIA INHIBITORY FACTOR

Although some sensory ganglion cells in mature animals are catecholami nergic, most mammalian sensory neurons that express the catecholamine- synthesizing enzyme tyrosine hydroxylase (TH) do so only transiently d uring early gangliogenesis in vivo. The lack of TH expression at later stages appears to be due to modulation of this catecholaminergic pote ntial. A previous study showed that the phenotype reappears, for examp le, when E16.5 and older sensory ganglia are dissociated in culture in to single cells, suggesting that extracellular influences can modulate TH expression. Moreover, TH expression in dissociate cultures is cell -density dependent, as a four-fold increase in plating density led to a 30% decrease in the percentage of TH neurons. The present study demo nstrates that inhibition of TH expression in high density cultures is mediated by ganglionic non-neuronal cells (NNC), as removal of NNC abo lished density-dependent inhibition. Moreover, plating E16.5 trigemina l neurons at low density on top of NNC monolayers resulted in an 85% d ecrease in the percentage of TH neurons. Treatment of cultures with no n-neuronal cell conditioned medium (NNC-CM) reproduced the effect of c oculture with NNC, suggesting that diffusible factors from NNC were in volved in the inhibition of TH. The inhibitory effect of NNC-CM was mi micked by treatment of dissociate cultures with ciliary neurotrophic f actor (CNTF) and leukemia inhibitory factor (LIF). However, immunoprec ipitation of NNC-CM with antibodies against LIF or CNTF showed that on ly anti-LIF antibodies were able partially to remove the TH inhibitory activity of NNC-CM. Therefore, LIF is one, but not the only, factor m ediating NNC inhibition of TH expression in cultured sensory neurons. In summary, these data indicate that ganglionic NNC can regulate senso ry transmitter phenotype in culture by inhibiting expression of specif ic molecular traits. The finding that LIF can partially account for th e inhibitory effect of ganglionic NNC on TH expression suggests a nove l role for this cytokine in regulating differentiation of catecholamin ergic properties in sensory neurons.