?-Carbolines can enhance or antagonize the effects of punishment in mice

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Abstract
Six β-carboline ligands at central benzodiazepine (BZ) receptors were tested for their anxiolytic or anxiogenic properties in mice in the four-plate test. ZK 93 423 and ZK 91 296 increased activity which had been suppressed by punishment (1 mA, 60 ms footshock) at doses which exerted no effect on unpunished locomotion. ZK 93 426, ZK 90 886, FG 7142, and DMCM exerted no antipunishment activity themselves, and antagonized the ability of diazepam to increase both punished and unpunished locomotor activity. DMCM, FG 7142, and ZK 90 886, but not ZK 93 426, also enhanced the ability of a reduced level of footshock (0.3 mA) to suppress activity. This propunishment activity of DMCM and ZK 90 886 took place at doses which had no effect on unpunished locomotion. The nature of the effect of the individual β-carbolines on punishment was related to the nature of their interaction with the BZ/GABA receptor/chloride channel complex (GBC complex). Thus the antipunishment properties of ZK 93 423 and ZK 91 296 were associated with their ability to increase binding of 35S-t-butylbicyclophosphorothionate (TBPS) to its binding site associated with the chloride channel, whereas DMCM, FG 7142 and ZK 90 886, which exerted propunishment effects, reduced TBPS binding. ZK 93 426, which was neutral with respect to punished activity, had the weakest effect on TBPS binding. These results are discussed in the context of a possible role of the GBC complex in anxiety.