THE ASTROCYTE RESPONSE TO GAMMA-AMINOBUTYRIC-ACID ATTENUATES WITH AGE IN THE RAT OPTIC-NERVE

There is increasing evidence that glial cells respond to the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), and astrocytes have been shown to possess GABA(A) receptors both in vivo and in vitro. A recent study by Sakatani et al. (Proc. R. Soc. Lond. B 247, 155 (1992)) demonstrated the transient expression of functional GABA(A) receptors in the developing rat optic nerve, but axonal and glial components of the response were not distinguished. To help address this problem, we have determined the electrophysiological response to GABA in astrocytes of the isolated intact optic nerves from neonatal rats, identified morphologically following intracellular injection of horseradish peroxidase. Astrocytes responded to GABA by a GABA(A) receptor-mediated depolarization which attenuated gradually during post-natal development; astrocytes in 21-day-old nerves were not observed to respond to GABA. The results indicate the transient presence of functional GABA(A) receptors in developing rat optic nerve astrocytes in situ, and we speculate upon a role for GABA in glial signalling and the organization of axon-glial interrelations during development.