Modulation of γ-aminobutyric acid responses in the rat optic nerve

Depolarising GABA(A) receptor-mediated responses recorded from the optic nerve using a grease gap technique were modulated by classical potentiators of GABA(A) receptors. The benzodiazepine, chlordiazepoxide, the barbiturate, pentobarbitone and the widely used anaesthetic, propofol, all potentiated gamma-aminobutyric acid (GABA) responses. They did so with different maximal efficacies, propofol > pentobarbitone > chlordiazepoxide, and potencies on the basis of EC50 estimates, chlordiazepoxide. propofol > pentobarbitone. The greater than expected GABA potentiating properties of propofol were explained by a direct hyperpolarising action that occurred in the same concentration range as its action at the GABA(A) receptor but that was unlikely to be mediated by GABA(A) receptors. (C) 2000 Elsevier Science B.V. All rights reserved.