Neuronal regulation of astrocyte morphology in vitro is mediated by GABAergic signaling

The addition of isolated neurons to monolayers of cultured astrocytes induced a morphological change in the astrocytes that came into contact with the added neuronal cell bodies or neurites. The change, which included an increase in the complexity of cell shape, took at least 3 days to become detectable and was enhanced in proportion to the number of attached neurons. Astrocytes that did not make contact with any neurons had a less complex contour, comparable to those in control cultures with no neurons added. Treatment of neuron-astrocyte cocultures with a sodium channel blocker, tetrodotoxin, suppressed the neuron-induced morphological changes in astrocytes. A GABAA-receptor antagonist, bicuculline, mimicked the inhibitory effect of tetrodotoxin. In cultures without added neurons, morphological alteration of astrocytes was also observed when cultures were incubated for 1 or more days with exogenous GABA together with a GABA-uptake inhibitor, 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol. The effect of exogenous GABA was mimicked by treatment with a GABAA-receptor agonist, muscimol, and blocked by bicuculline treatment. These results suggest that GABA released from neurons with their activity serves as a signal from neurons to astrocytes that triggers the morphological change in astrocytes through the activation of GABAA receptors.