Methylphenidate effects on avoidance learning at two ages in the rat.

The major purpose of this investigation was to assess the effects of methylphenidate on avoidance learning at two ages. The subjects were 96 naive albino rats, equally divided between the sexes. One-half received daily drug administrations beginning at 47 days of age; one-half began at 87 days of age. Both groups were divided into three drug dosage levels (0.5, 1.5 and 4.5 mg/kg) and a distilled water control group. Methylphenidate was administered s.c. for a total of 18 days. Following 3 days of drug administrations only, 10 daily trials on avoidance conditioning were administered approximately 10 min after drugging to a total of 150 trials. The major findings indicated that: (1) no significant difference in avoidance response acquisition was obtained in the comparison between drug and control groups, (2) a dose effect was obtained in that the M4.5 group made siginificantly more correct responses than the M1.5 group, and (3) animals drugged beginning at 87 days made significantly more correct responses than those drugged beginning at 47 days.