The benzodiazepine receptor ligand CL218,872 has both anxiolytic and sedative properties in rodents

The triazolopyridazine, CL218,872, inhibited the binding of [3H]flunitrazepam in the cerebellum more potently than in cortex, both in vitro and in vivo. The relationship between this phenomenon and the selectivity of benzodiazepine receptor subtypes is considered. In a range of behavioural tests the overall profile of CL218,872 was similar to that of diazepam in the rat and mouse, although CL218,872 was half as potent as diazepam in the rat and some 20-fold weaker in the mouse. In particular contrast to published observations, CL218,872 reduced locomotor activity in rats and mice at doses only slightly larger than those required to inhibit conflict in rats and footshock-induced fighting in mice. The only qualitative difference between the compounds that could be detected was in the mouse where large doses of CL218,872 did not produce the marked degree of motor incoordination seen after diazepam. However, no such difference was observed in the rat. The presently held view that CL 218,872 is a non-sedative anxiolytic agent needs to be revised in the light of these observations.