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 stereotypy elicited by administration of the direct dopamine receptor agonist apomorphine in five inbred strains of rats: the results suggest that each strain can be differentiated phenotypically according to these behavioral responses. Brown Norway rats demonstrated the greatest locomotion during acclimation sessions. Low doses of apomorphine (0.1 and 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 Fisher rats. Buffalo animals showed licking during control sessions and the greatest increase in gnawing at higher doses of apomorphine. DA rats were less responsive than the other strains of apomorphine. Between-strains autoradiographic determination of dopamine receptor densities revealed several differences in D1 receptors labeled by ³H-SCH23390 and D2/D3 receptors labeled by ¹²⁵I-NCQ 298 in the caudate-putamen and nucleus accumbens. However, the heterogeneity of dopamine receptor densities was not sufficient to explain the strain-specific behavioral responses. These experiments demonstrate variations in behavioral and neurochemical characteristics of inbred strains of rats which could be used to model genetically determined differences in dopamine-mediated behavioral responses.