Impaired acquisition and operant responding after neonatal dopamine depletion in rats

The effect of neonatal dopamine depletion in rats was examined using operant conditioning. Rat pups were given 6-hydroxydopamine (6-OHDA) or sham lesions at 3 days of age. When tested as adults, 6-OHDA treated subjects were impaired in the acquisition of lever pressing for reward and displayed stereotyped sniffing patterns not observed in the control subjects. In addition, significantly lower rates of responding were measured for the lesion group during continuous reinforcement (CRF), dilution of reinforcer efficacy, and with progressively increasing fixed ratio requirements. Alpha-methyl-p-tyrosine (AMPT), given before one CRF session, attenuated responding in over half the lesion animals and in none of the controls. Dopamine content in caudate nucleus was found to significantly correlate with number of trials to acquisition and rates of responding following AMPT in the lesion group, but not in the control group. Overall, the results of this experiment showed that neonatal dopamine depletion does not lead to severe motor impairment or the inability to learn, but does disrupt the normal patterns of behavior associated with operant conditioning.