A class of pyrazolo¢4,3-c!pyridazin-3-one analogues of formula (I), substituted at the 2-position by an optionally substituted aryl or heteroaryl moiety, and wherein the pyridazine ring of the pyrazolo-pyridazinone ring system is fused to an alkylene chain, are selective ligands for GABAA receptors, in particular having affinity for the .alpha.2 and/or .alpha.3 subunit thereof, and are accordingly of benefit in the treatment and/or prevention of disorders of the central nervous system, including anxiety and convulsions.
TRICYCLIC PYRAZOLO-PYRIDAZINONE ANALOGUES AS GABA-A RECEPTORLIGANDS