ASTROCYTIC CONTRIBUTION TO FUNCTIONING SYNAPSE FORMATION ESTIMATED BYSPONTANEOUS NEURONAL INTRACELLULAR CA2+ OSCILLATIONS

Glial contribution to in vitro synaptic function was investigated in a neuron-glia co-culture system by monitoring spontaneous oscillations of intracellular Ca2+ in neurons. Rat cortical neurons, grown stably o n a cortical astrocyte monolayer, extended neurites resulting in marke d functional synapse formation. Little synapse formation was observed in neuronal co-culture with meningeal fibroblasts or endothelial cells . Aged astrocytes in vitro (C35) were found to attenuate synaptic deve lopment, while young astrocytes (C5) markedly promoted synaptic functi on. C5 and C35 astrocyte media conditioned yielded no significant syna ptogenic effect, indicating diffusible factor(s) are not responsible f or our observation. Modulation of astrocytic proliferation and differe ntiation by gliostatin, a glial growth inhibitor, or dibutyryl cAMP af fected neuronal synaptic function on the co-cultures. Site-specific an alysis in homologous and heterologous neuron-astrocyte co-cultures amo ng cortex, hippocampus, septum, and striatum revealed that homologous combinations of neurons and astrocytes derived from identical brain re gions elicited the largest number of synchronizing neurons. These resu lts suggest that in vivo neuronal synaptic function essentially requir es the participation of adjacent astrocytes, which is site-specific an d age-dependent.