Abstract: Compounds of formula (I) in which: each A is independently hydrogen, C1-6alkyl optionally substituted by hydroxyl, C1-6alkoxy, C1-6alkenyl or C1-6acyl group or a halogen atom or hydroxyl, CN or CF3 group; R3 is hydrogen, methyl or ethyl; R4 is an optionally substituted aromatic carbocyclic or heterocyclic ring; Z is an O or S atom, or an NH or CH2 group, or a single bond, at the 3 or 4 position of R4 relative to the carbonyl group; R5 is an optionally substituted aromatic carbocyclic or heterocyclic ring, or an optionally substituted, saturated or unsaturated, carbocyclic or heterocyclic ring; and Q is (a) Where X, Y, R1 and R2 are as defined in claim 1; are antagonists of a human 11CBy receptor.