Neuroanatomical Specificity of Conditioned Responses to Rewarding Versus Aversive Stimuli in Mice
Rationale: Drug addiction is a powerful, complex disease that has a strong biological component. However, brain regions involved in compulsive motivation for drug use, have not been clearly differentiated from those involved in natural forms of motivation. Methods: Male B6D2F1/J mice were conditioned to associate morphine or lithium chloride with a grid or hole floor texture, then tested for their preference to either floor type using a Conditioned Place Preference/Aversion paradigm (CPP). Results: Morphine did not affect locomotor activity at 10 mg/kg but significantly increased activity after 20 mg/kg. Lithium chloride (130 mg/kg) did not affect locomotor activity. Aversion for lithium chloride was very strong in the first CPP test. Morphine at a dose of 10 mg/kg did not produce strong CPP. Preference for morphine remained weak for 20 mg/kg while aversion for lithium chloride was still strong in the second preference/aversion test. Conclusions: Locomotor activity was not a good indicator of preference or aversion for the doses of morphine and lithium chloride used here. A higher dosage of morphine may be required to induce associative learning between the drug and the context in this strain.