Tetsu Hayashi

Automatic measurement of drinking in rats: effects of hypophysectomy.

A new apparatus for the continuous measurement of drinking in the rats was assembled. The principle of the device is as follows: a cartridge which makes water drops (0.05 ml) is inserted between a water tank and a drinking spout. When a rat drinks, water falls into the cartridge drop by drop and the number of drops is electrically counted. The total count of drops per day, as well as counts at definite intervals, can be atuomatically printed out. To test apparatus reliability and applicability, drinking behavior in hypophysectomized rats was investigated in the light and dark phases, alternating every 12 hr. Activity and feeding in these phases were also observed. In the sham-operated rats, the total daily water intake was 30-40 ml, which corresponded to 10-15% of the body weight, and 85-95% of the total daily drinking counts were recorded in the dark phase. In the hypophysectomized rats, a large amount of water was drunk immediately after the operation. However, the high rate of drinking rapidly returned to near the normal level within a few days. Drinking in the dark phase decreased to about 75% of the total daily, but synchronization with the light-dark cycle was still maintained. The daily patterns of activity and eating ran nearly parallel with the drinking behavior. These results indicate that our drinkometer could have extensive applications within many fields of research.

Enhancement of avoidance-suppressing effect after repeated administration of haloperidol and serum haloperidol in rats

Adult male rats of the Wistar strain, which were trained under a discriminated lever-press avoidance schedule (intertrial interval; 25 sec. presentation of conditioned stimuli; 5 sec), were given SC 0.025-0.05 mg/kg of haloperidol at fixed intervals of 1, 3-4 and 7 days. The avoidance-suppressing effect of haloperidol was enhanced in parallel to the number of drug administrations until it attained a maximum level. The intensity of the maximum effect tended to be stronger, and the number of administrations necessary to attain it was smaller, when a higher dose was given. When the administration interval exceeded one day, the enhanced effect remained irreversible one month after withdrawal of drug administration. The enhancement of the effect was produced after repeated administrations in an experimental chamber, but not in a home cage. Temporal changes in serum haloperidol concentration were determined 30-90 min after 0.035 mg/kg given SC to the haloperidol-pretreated and saline-pretreated groups. No significant difference in the pharmacokinetic change was detected between the two groups. These results suggest that learning during the drug effect under repeated exposure to a fixed experimental situation influences the enhancing effect.