Disclosed are compounds of Formula (a) or the pharmaceutically acceptable non-toxic salts thereof wherein: the C ring is a(n) (un)substituted carbocycle; X is hydrogen, hydroxyl or lower alkyl; and W is (un)substituted alkyl, aryl, arylalkyl, or heteroaryl, which compounds are highly selective agonists, antagonists or inverse agonists for GABAa brain receptors or prodrugs of agonists, antagonists or inverse agonists for GABAa brain receptors. These compounds are useful in the diagnosis and treatment of anxiety, sleep and seizure disorders, overdose with benzodiazepine drugs and for enhancement of memory.