Vol. 280, Issue 1, 316-325, 1997

Effects of Negative Allosteric Modulators of -Aminobutyric Acid_A Receptors on Complex Behavioral Processes in Monkeys¹

J. Auta, P. J. Winsauer, W. B. Faust, P. Lambert and J. M. Moerschbaecher

Department of Pharmacology and Experimental Therapeutics, Louisiana State University, Medical Center, New Orleans, Louisiana

A multiple schedule of repeated acquisition and performance of conditional discriminations was used to characterize the effects of two negative allosteric modulators of the -aminobutyric acid (GABA_A) receptor (ethyl -carboline-3-carboxylate [-CCE] and N-methyl--carboline-3-carboxamide [FG-7142]), a hallucinogenic -carboline derivative (harmine), a benzodiazepine receptor antagonist (flumazenil) and a positive allosteric modulator (alprazolam). In the acquisition component, subjects acquired a different discrimination each session. Acquisition of a discrimination was defined by a decrease in errors as the session progressed. In the performance component, the discrimination was the same each session. Responding in both components was maintained by food presentation under a variable-ratio schedule. Incorrect responses in both components produced a 5-sec timeout. Alprazolam (0.1-18 mg/kg), -CCE (0.01-0.32 mg/kg), FG-7142 (0.1-18 mg/kg) and harmine (0.1-1.8 mg/kg) all dose-dependently decreased response rate in both components. However, accuracy of responding was differentially affected by the drugs. Alprazolam selectively and dose-dependently increased percent errors in acquisition, whereas -CCE increased acquisition errors only at the highest doses tested in each subject. In contrast, FG-7142 and harmine had no effects on percent errors at doses that virtually eliminated responding. In all cases, performance accuracy was generally not affected. Flumazenil, at doses that had little or no effect (0.1 and 0.32 mg/kg) or occasionally decreased response rates (1 mg/kg) when administered alone, dose-dependently antagonized the rate-decreasing and error-increasing effects of -CCE, FG-7142 and alprazolam. In contrast, flumazenil failed to antagonize the effects of harmine. Thus, the negative allosteric modulators only moderately disrupted acquisition in comparison with the positive allosteric modulator, but the effects of both types of modulator were antagonized by the benzodiazepine antagonist flumazenil.