VARIATIONS IN THE BEHAVIORAL-RESPONSES TO APOMORPHINE IN DIFFERENT STRAINS OF RATS

The present experiments compared patterns of locomotor activity during repeated acclimation sessions and determinations of locomotion and st ereotypy elicited by administration of the direct dopamine receptor ag onist apomorphine in five inbred strains of rats: the results suggest that each strain can be differentiated phenotypically according to the se behavioral responses. Brown Norway rats demonstrated the greatest l ocomotion during acclimation sessions. Low doses of apomorphine (0.1 a nd 0.32 mg/kg) produced a flat body posture in Lewis animals. A higher dose of apomorphine (1.0 mg/kg) markedly increased locomotion in Fish er rats. Buffalo animals showed licking during control sessions and th e greatest increase in gnawing at higher doses of apomorphine. DA rats were less responsive than the other strains of apomorphine. Between-s trains autoradiographic determination of dopamine receptor densities r evealed several differences in D1 receptors labeled by H-3-SCH 23390 a nd D2/D3 receptors labeled by I-125-NCQ 298 in the caudate-putamen and nucleus accumbens. However, the heterogeneity of dopamine receptor de nsities was not sufficient to explain the strain-specific behavioral r esponses. These experiments demonstrate variations in behavioral and n eurochemical characteristics of inbred strains of rats which could be used to model genetically determined differences in dopamine-mediated behavioral responses.