The differential role of alpha1- and alpha5-containing GABA(A) receptors in mediating diazepam effects on spontaneous locomotor activity and water-maze learning and memory in rats

Abstract

The clinical use of benzodiazepines (BZs) is hampered by sedation and cognitive deterioration. Although genetic and pharmacological studies suggest that alpha1- and alpha5-containing GABA(A) receptors mediate and/or modulate these effects, their molecular substrate is not fully elucidated. By the use of two selective ligands: the alpha1-subunit affinity-selective antagonist beta-CCt, and the alpha5-subunit affinity- and efficacy-selective antagonist XLi093, we examined the mechanisms of behavioural effects of diazepam in the tests of spontaneous locomotor activity and water-maze acquisition and recall, the two paradigms indicative of sedative- and cognition-impairing effects of BZs, respectively. The locomotor-activity decreasing propensity of diazepam (significant at 1.5 and 5 mg/kg) was antagonized by beta-CCt (5 and 15 mg/kg), while it tended to be potentiated by XLi093 in doses of 10 mg/kg, and especially 20 mg/kg. Diazepam decreased acquisition and recall in the water maze, with a minimum effective dose of 1.5 mg/kg. Both antagonists reversed the thigmotaxis induced by 2 mg/kg diazepam throughout the test, suggesting that both GABA(A) receptor subtypes participate in BZ effects on the procedural component of the task. Diazepam-induced impairment in the declarative component of the task, as assessed by path efficiency, the latency and distance before finding the platform across acquisition trials, and also by the spatial parameters in the probe trial, was partially prevented by both, 15 mg/kg beta-CCt and 10 mg/kg XLi093. Combining a BZ with beta-CCt results in the near to control level of performance of a cognitive task, without sedation, and may be worth testing on human subjects.

Fig. 1

The scheme representing the virtual division of the water maze used in the analysis of rats’ performance.

Fig. 2

The effects of diazepam (Sol+DZP 0.5, 1.5 and 5.0 mg/ kg) on total distance (a) and distance travelled in 5-min intervals (b). * p<0.05 compared to solvent (Sol+Sol) group; ** p<0.01 compared to solvent. Animals per treatment (n=8).

Fig. 3

The effects of combinations of diazepam (DZP), at doses of 0, 0.5, 1.5 and 5.0 mg/kg, and the antagonists β-CCt (0, 5, 15 mg/kg) and XLi093 (0, 10, 20 mg/kg), on total distance travelled in the spontaneous locomotor activity test. * p<0.05, compared to solvent (Sol+Sol) group; ⁺ p<0.05 compared to DZP 0.5+Sol group; ^## p<0.01 compared to XLi093 10+Sol group; ^# p<0.05, ^### p<0.001 compared to XLi093 20+Sol group. Animals per treatment (n=6).

Fig. 4

Mean distance travelled in successive 5-min blocks for groups designated as in Fig. 3.

Fig. 5

The effects of diazepam 1.0, 1.5, 2.0 and 5.0 mg/kg (DZP 1.0+Sol to DZP 5.0+Sol) on (a) latency to platform, (b) total distance, (c) average swim speed and (d) path efficiency of rats during 5 d acquisition trials in the water maze. * p<0.05, ** p<0.01, p<0.001 compared to solvent (Sol+Sol) group; ⁺p<0.05, ⁺⁺ p<0.01, ⁺⁺⁺ p<0.001 compared to DZP 1.0+Sol group; ^# p<0.05, ^## p<0.01, ^### p<0.001 compared to DZP 1.5+Sol group; ^# p<0.05, ^## p<0.01 compared to DZP 2.0+Sol group. Animals per treatment (n=7).

Fig. 6

The effects of diazepam (DZP 1.5+Sol), diazepam and β-CCt (DZP 1.5+β-CCt 5 and DZP 1.5+β-CCt 15) and diazepam and XLi093 (DZP 1.5+XLi093 10 and DZP 1.5+XLi093 20) (all doses in mg/kg) on (a) latency to platform, (b) total distance, (c) average swim speed and (d) path efficiency of rats during 5 d acquisition trials in the water maze. * p<0.05, ** p<0.01 compared to solvent (Sol+Sol) group; ⁺ p<0.05 compared to DZP 1.0+Sol group; ^# p<0.05, ^## p<0.01 compared to DZP 1.5+β-CCt 5 group; ^# p<0.05, ^## p<0.01 compared to DZP 1.5+β-CCt 15 group. Animals per treatment (n=6).

Fig. 7

The effects of diazepam (DZP 2+Sol), diazepam and β-CCt (DZP 2+β-CCt 15) and diazepam and XLi093 (DZP 2+XLi093 10) (all doses in mg/kg) on (a) latency to platform, (b) average total distance, (c) average swim speed and (d) path efficiency of rats during 5 d acquisition trials in the water maze. * p<0.05 compared to solvent (Sol+Sol) group; ⁺ p<0.05 compared to DZP 2+Sol group; ^† p<0.05 compared to DZP 2+β-CCt 15 group. Animals per treatment, for Sol+Sol to DZP 2+XLi093 10 (n=6, 6, 7, 7, respectively).

Fig. 8

The effects of (a) solvent (Sol+Sol) ; (b) diazepam (DZP 2+Sol), (c) diazepam and β-CCt (DZP 2+β-CCt 15) and (d) diazepam and XLi093 (DZP 2+XLi093 10) (all doses in mg/kg) on the distance rats travelled in the SE quadrant and target region during 5 d acquisition trials in the water maze. The numbers inside the columns are the percent of the distance swam inside the target (NE) quadrant which was travelled in the target region.