The role of genotype as a determinant of biologically based inter-individual differences in vulnerability to
substance abuse has received little systematic investigation except in the case of alcohol. This report describes the use of an animal model, the inbred mouse, to identify and to characterize variants with inherently altered susceptibilities to the rewarding and other behavioral actions of
cocaine. Among a battery of nine inbred strains chosen solely for their genetic diversity, genetic polymorphisms commonly occurred which altered the potency and/or efficacy of
cocaine to induce conditioned place preference, oral
self-administration, motor activity activation,
seizures and lethality. These changes in
cocaine sensitivity generally were of a behavior-specific and pharmacodynamic nature. One strain, DBA/2J, found to be markedly hyporesponsive to the rewarding action of
cocaine, also was hyporesponsive to the rewarding effects of
amphetamine,
etonitazene,
phencyclidine,
caffeine and
procaine. We speculate that this strain has an inherent generalized appetitive defect. The frequent occurrence and large magnitude of inherent phenotypic changes in
cocaine responsiveness which we have identified among inbred mouse strains now permits an analytical genetic study of processes underlying
cocaine-mediated reinforcement.