DevelopmentalBrain Research, 17 (1985) 95-104 95 Elsevier BRD 50130 Motoneurone Survival is Induced by Immature Astrocytes from Developing Avian Spinal Cord K. L. EAGLESON, T. R. RAJU and M. R. BENNETT The Neurobiology Research Centre, University of Sydney, N.S. W. 2006 (Australia) (Accepted July 5th, 1984) Key words: motoneurone - - astrocytes - - muscle - - development Dissociated spinal cords of 6-day chick embryos were grown on monolayers consisting primarily of either flat (relatively immature) or process-bearing (relatively mature) astrocytes. Cultures rich in fiat astrocytes maintained about 80% of the motoneurones original- ly plated for 48 h in vitro. However, process-bearing astrocytes were unable to support motoneurone survival. Medium conditioned by contact with the monolayers of fiat astrocytes also promoted motoneurone survival for 48 h. Maximal activity occurred over the con- centration range 55-110/~g/ml protein. After 48 h, the number of motoneurones dropped to control levels both in the conditioned medium and on the monolayers. This effect could not be reversed by the introduction of fresh conditioned media at 48 h. This indicated a decrease in the requirements of more matt~re motoneurones for this media as muscle-conditioned medium could support 80% of the motoneurones initiallyplated for 96 h. Thus, relativelyimmature astrocytes were capable of supporting the survival of 6-day motoneu- rones in vitro for up to 48 h and this effect is mediated through the release of a soluble substance. INTRODUCTION During development, motoneurones in the spinal cord are dependent on their target tissue for surviv- a114,29, 42. Culture studies show that embryonic moto- neurones may be kept viable through the cell death period by muscle or media conditioned over mus- cle8,41,51. The greatest survival activity in the muscle is obtained from myotubes rather than from myo- blasts or fibroblasts53. These observations suggest that the eventual survival of the motoneurone may be de- pendent on its maintaining contact with myotubes6. The question arises, however, as to whether the mo- toneurone requires trophic support during that peri- od in which it is projecting its axon from the spinal cord to muscle7, 47. Whilst the motor growth cone is in contact with unidentified mesenchymal cells 31,4°, both motoneurone and glial cells are in the anterior horn. In the present study we have sought to test the possibility that astroglial cells can support the surviv- al of motoneurones. Several culture studies have demonstrated the im- portance of glial-neuronal interactions in the devel- opment of neurones in vitro. Media conditioned over primary cultures enriched in astroglial cells derived from the cerebral hemisphere have been shown to support the survival of, as well as morphological dif- ferentiation of, central neurones2, 50. Soluble sub- stances released by C6 glioma cells are also impor- tant in maintaining peripheral neurones 3 and it has been shown that this effect is not mediated by nerve growth factor (NGF) 3,33. McCaffery et al. 36 have shown that cultures of astrocytes which predominant- ly have a flat morphology (relatively immature) pro- moted both the survival of and neurite expression from rat neonatal retinal ganglion cells; cultures rich in process-bearing (more mature) astrocytes had no effect. These trophic effects were mediated by mem- brane contact between the flat astrocytes and gangli- on cells rather than by soluble substances. Lindsay et al. 34 have also demonstrated that flat astrocytes de- rived from the adult corpus callosum are capable of supporting the survival of neurones from sensory and sympathetic ganglia; although they also generated cultures rich in process-bearing cells, the effect of these on neurone survival was not examined. Partic- Correspondence: M. R. Bennett, The Neurobiology Research Centre, University of Sydney, N.S.W. 2006, Australia. 0165-3806/85/$03.30 © 1985 Elsevier Science Publishers B.V.