Comparative, topographically-based evaluation of behavioural phenotype andspecification of D-1-like: D-2 interactions in a line of incipient congenic mice with D-2 dopamine receptor "knockout"

Phenotypes were assessed topographically in mice lacking functional D-2 dop amine receptors [knockouts], using an ethologically based approach to asses s all behaviours in the natural repertoire, D-2-null mice evidenced an etho gram characterised initially by modest reductions in locomotion and shifts in rearing topographies. Subsequently, topographies of behaviour habituated similarly for wildtypes and 'knockouts'. Following challenge with the D-2- like agonist RU 24213, both inhibition of rearing at a lower dose and induc tion of stereotyped sniffing and ponderous locomotion at higher doses were essentially absent in D-2-null mice. Following challenge with the D-1-like agonist A 68930, vacuous chewing was released in D-2-null mice. This topogr aphical approach to phenotypic characterisation implicates: (i) the D-2 rec eptor in these D-2-like agonist effects and in oppositional D-1-like: D-2-l ike interactions; and (ii) the operation of material compensatory processes consequent to the developmental absence of D-2 receptors which are able to maintain ethological function under tonic, 'naturalistic' conditions but n ot under 'phasic' challenge.