[Right/left discrimination learning in rat pups neonatally treated with 6-hydroxydopamine].

At 2 and 4 days of age, rat pups were treated with 6-hydroxydopamine (6-OHDA; 70 micrograms, ivt) following desmethylimipramine (20 mg/kg, sc) pretreatment. Spontaneous activity test in a novel cage at 16 and 17 days of age revealed a sustained higher level of locomotor activity in 6-OHDA-treated rats, which was characterized by a deficit of habituation. For right/left discrimination learning trained from 18 days of age, "homing" was used as an reinforcer, i.e., pups could enter the goal area adjacent to home cage if they chose a predetermined correct arm of T-maze. Rats were trained 10 trials a day until they attained the learning criterion (at least 17 correct choices in 2 days). Thereafter, they were re-trained for the reversal learning to the criterion (at least 8 correct choices in a day). 6-OHDA-treated rats were required significantly more trials to attain the learning criterion both in the original and the reversal learnings. Biochemical assay confirmed a marked depletion of brain dopamine contents in striatum, cortex and midbrain with thalamus in 6-OHDA-treated rats. Therefore, the neonatal depletion of brain dopamine produced hyperactivity (habituation deficit) and a discrimination deficit during the developmental period.