Comparative, topographically-based evaluation of behavioural phenotype and specification of D₁-like: D₂ Interactions in a line of incipient congenic mice with D₂ dopamine receptor 'knockout'

Phenotypes were assessed topographically in mice lacking functional D₂ dopamine receptors ['knockouts'], using an ethologically based approach to assess all behaviours in the natural repertoire. D₂-null mice evidenced an ethogram 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 D₂-like agonist RU 24213, both inhibition of rearing at a lower dose and induction of stereotyped sniffing and ponderous locomotion at higher doses were essentially absent in D₂-null mice. Following challenge with the D₁-like agonist A 68930, vacuous chewing was released in D₂-null mice. This topographical approach to phenotypic characterisation implicates: (i) the D₂ receptor in these D₂-like agonist effects and in oppositional D₁-like: D₂-like interactions; and (ii) the operation of material compensatory processes consequent to the developmental absence of D₂ receptors which are able to maintain ethological function under tonic, 'naturalistic' conditions but not under 'phasic' challenge.