DevelopmentalBrain Research, 27 (1986) 31-41 31 Elsevier BRD 50388 Effects of Neuron-Conditioned Medium and Fetal Calf Serum Content on Glial Growth in Dissociated Cultures N. SAKELLARIDIS, D. MANGOURA and A. VERNADAKIS Departments of Pharmacology and Psychiatry, Universityof Colorado School of Medicine, Denver, CO 80262 (U.S.A.) (Accepted November 12th, 1985) Key words: dissociated culture - - conditioned medium - - glial growth The influence of the microenvironment as assessed by medium conditioned by 6-day-old chick embryo neurons in culture and of the nutrients derived from fetal bovine serum was evaluated in cultures of primary chick embryo glial cells. Glia-enriched cultures from 15-day-old chick embryo were incubated from culture days 3-9 with various concentrations of neuron-conditioned medium, with or without 10% fetal bovine serum in the final culture medium. Also, glial growth was studied in cultures with 5%, 10% or 20% fetal bo- vine serum in the medium. Glutamine synthetase and 2',3',-cyclic nucleotide 3'-phosphohydrolase were used as astrocytic and otigo- dendrocytic markers, respectively. Cultures were harvested at day 9. The presence of neuron-conditioned medium in the cultures was associated with persistence of immature glioblast-likecells. This persistence of glial immature cells was also reflected by the lower glu- tamine synthetase activity in the cultures with neuron-conditioned medium as compared to cultures with neuron-conditioned medium and fetal calf serum. In cultures with 5% neuron-conditioned medium without fetal bovine serum, cyclic nucleotide phosphohydrolase activity was increased. We are assuming that the input of neurons to the microenvironment is partially mediated through the neuron- conditioned medium. Thus, the present findings show that neurons influence the growth and differentiation of glial cells in culture. INTRODUCTION Epigenetic factors involved in the regulation of neuronal plasticity may also be closely associated with the expression of glial cell function. It has been accepted that glial constituents of the central nervous system are able to proliferate throughout the life span of the individual organism. There is not, howev- er, concrete evidence on which subtypes of glia re- spond to various microenvironmental conditions and which stimuli are able to be mediated through the in- tercellular space and cause glial proliferation and/or differentiation. Evidence accumulated over the years has associated CNS gliosis with neurological disease, trauma and aging and it is possible that the stimuli capable of inducing such effects may be origi- nating in the neurons and could be mediated through either direct cell contact or the microenvironment. Tissue culture techniques are offering an impor- tant number of advantages in studying microenviron- ment-mediated effects on the growth and differentia- tion of the glial cells. These techniques eliminate some of the in vivo complexities and expose the cells to a culture medium which functions as a completely manageable microenvironment: a 'milieu interieur' that can be altered at will by dissecting out individual factors that possibly interfere with processes of cell development. There has been considerable interest in literature on neuron-glia interactions but it is primarily fo- cused on examining the influence of glial cells on the development and survival of neurons35,38, 39,41,42. Re- cently, Estin and Vernadakis 9 found that fibroblast- conditioned medium, killed fibroblast cell substrata or fibroblast extracellular matrix greatly enhanced glial growth and differentiation. We have also exam- ined the growth of glial cells under various coculture conditions36 and found that glial growth as assessed Correspondence: N. Sakellaridis, Department of Pharmacology, University of Colorado School of Medicine, C 263, Denver, CO 80262, U.S.A. 0165-3806/86/$03.50 @ 1986 Elsevier Science Publishers B.V. (Biomedical Division)