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 quantified using an ethologically-based, rapid time-sampling behavioural check-list procedure. Relative to wildtypes (D(1A)(+/+)), D(1A)-null ((-/-)) mice evidenced over initial exploration significant reductions in rearing free, sifting and chewing, but significant increases in locomotion, grooming and intense grooming. Sniffing and rearing to a wall habituated less readily in D(1A)-null mice such that these behaviours occurred subsequently to significant excess: increases in locomotion were persistent. The ethogram of spontaneous 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 D1-like receptor function, the elevation of such behaviour in D(1A)-null mice was paradoxical; it may reflect (over)compensatory processes subsequent to developmental absence of D(1A) receptors and/or the involvement of a D1-like receptor other than/additional to the D(1A) subtype. Copyright (C) 1998 Elsevier Science Ltd.
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