Topographical evaluation of the phenotype of spontaneous behaviour in micewith targeted gene deletion of the D-1A dopamine receptor: paradoxical elevation of grooming syntax

The phenotype of spontaneous behaviour in mice with targeted gene deletion of the D-1A dopamine receptor was investigated topographically. Via direct visual observation, individual elements of behaviour were resolved and quan tified using an ethologically-based, rapid time-sampling behavioural check- list procedure. Relative to wildtypes (D-1A(+/+)), D-1A-null ((-/-)) mice e videnced over initial exploration significant reductions in rearing free, s ifting and chewing, but significant increases in locomotion, grooming and i ntense grooming. Sniffing and rearing to a wall habituated less readily in D-1A-null mice uch that these behaviours occurred subsequently to significa nt excess: increases in locomotion were persistent. The ethogram of spontan eous behaviour in D-1A-null mice was characterised by neither 'hypoactivity ' or 'hyperactivity' but. rather, by prominent topographical shifts between individual elements of behaviour that could not be encapsulated by either term. Given the substantial body of evidence that grooming and particularly intense grooming constitute the most widely accepted behavioural index of D-1-like receptor function, the elevation of such behaviour in D-1A-null mi ce was paradoxical: it may reflect (over)compensatory processes subsequent to developmental absence of D-1A receptors and/or the involvement of a D-1- like receptor other than/additional to the D-1A subtype. (C) 1998 Elsevier Science Ltd. All rights reserved.