Response of astrocytes to gamma-aminobutyric acid in the neonatal rat optic nerve.
The electrophysiological response to gamma-aminobutyric acid (GABA) was determined in astrocytes of the isolated intact optic nerves of rats aged 8 to 12 days old, identified morphologically following intracellular injection of horseradish peroxidase. At this age, astrocytes had a mean (+/- S.E.M.) resting membrane potential of -62.25 +/- 1.9 mV (n = 32), and responded to GABA by a depolarization characterized by an initial peak of mean 9.1 +/- 0.6 mV, which was not sustained and fell to a plateau level. The effect of GABA was mimicked by the GABAA-receptor agonist muscimol, but not by the GABAB-receptor agonist baclofen, and was reduced in the presence of the GABAA-receptor antagonist bicuculline. Astrocytes responded to 10 mM [K+]o by a single phase depolarization of 16 +/- 2 mV (n = 5). It is concluded that GABA acts directly on astrocytes and its effect is not mediated by K+ released by axons. This study indicates the presence of functional GABAA receptors in neonatal rat optic nerve astrocytes in situ. The results suggest immature astrocytes may be the source of the GABA response described in two recent studies on the rat whole optic nerve preparation. The astrocyte response to GABA may be important in axon-glial signalling during development.
Butt
A M
AM
Sherrington School of Physiology, U.M.D.S., St. Thomas's Hospital, London, UK.
Jennings
J
J
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D001418:Baclofen / Q000494:pharmacology; D001640:Bicuculline / Q000494:pharmacology; D004594:Electrophysiology / Q000379:methods; D005071:Evoked Potentials / Q000187:drug effects; D058787:GABA-A Receptor Antagonists; D006735:Horseradish Peroxidase; D066298:In Vitro Techniques; D008564:Membrane Potentials; D008839:Microelectrodes; D009118:Muscimol / Q000494:pharmacology; D009900:Optic Nerve / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
D058787:GABA-A Receptor Antagonists; D011963:Receptors, GABA-A; D009118:Muscimol; D006735:Horseradish Peroxidase; D001418:Baclofen; D001640:Bicuculline