Studies in General Activity

Abstract

The purpose of the present experiment was to study the acute and chronic effects of methamphetamine hydrochloride on the spontaneous activity in rats.The Ss were ten male albino rats, aged about three months at the beginning of the experiment. The battery of ten activity wheels and the open field apparatus were used. Each wheel with a small living cage located in a sound-proof box, was always illuminated by a 10 watt lamp throughout the experiment. The temperature in the box averaged 20°C with a range of 19° to 23°C. The activity wheel have been described in detail previously (Annual of Animal Psychol., 11, 1962). The open field apparatus consisted of a circular floor 100 cm in diameter having a enclosing wall 40 cm in height. The grey circular floor was divided into 32 sections equal in area by drawing three concentric circles and four diameter lines with black color paint. Each S was put at the center of the floor just 30 min later since the administration of drug, and permitted to explore the open field for 3 min per day.The procedures and the main results of wheel-activity were as follows. The Ss were first given a 15-day habituation period in the activity wheel. Food and water were always available, replenished at 2 : 00 P. M. There followed a 5-day period during which a 3mg/kg dose of methamphetamine was subcutaneously injected every day at 2 : 00 P. M. This administration of drug produced a marked increase in activity which lasted for about four hours after injection. After the next non-injection period (5 days), there followed a 35-day period during which the Ss were given a daily injection of 6mg/kg of methamphetamine. The injection of a 6mg/kg dose first produced a striking decrease in activity for about one hour, but thereafter, showing the gradual increase in activity, it instigated the activity to the level which was higher than that of a 3mg/kg dose. And then, the rats were returned to the non-injection condition for next 55 days. It was surprising that under such a condition the marked decrease in activity was observed. The long-lasting inactivity thus obtained might be regarded as due to the chronic effect of repeated doses. The next 25 days constituted a 23-hr food deprivation period, i. e. during these days the food dishes were removed each day at 2 : 00 P. M. and returned on the following day at 1 : 00 P. M. It was shown that the level of activity gradually increased and the most clear-cut increase was in the activity during the two hours just preceding the daily feeding. Finally, the feeding condition was shifted from the 23-hr food deprivation to the ad libitum feeding. The level of activity under the condition of ad libitum feeding (for 10 days) declined again to the level shown during the habituation period. From these results it could not be concluded that the introduction of hunger drive produced by a 23-hr food deprivation had the permanent disinhibiting effect on the depressive state resulted from the chronic methamphetamine intoxication. Further studies will be required to reveal whether the disinhibiting effect is temporal or permanent.The results of the open field test were parallel to that of the activity wheel mentioned above except that the locomotive activity in intoxicated rats increased to the normal level immediately after the cessetion of long lasting administration of methamphetamine (6mg/kg). It would seem that this increase is not due to the recovery from the drug intoxication, but due in part to the increment of reactivity in animals to the change of external stimulus situation.