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Pilot experiment: Effect of meal timing on VS-reinforced responding
Objective:
The aim of this experiment is to examine whether the timing of daily meal affects the vigor of VS-reinforced responding.
Methods:
In this experiment, animal housing, chronic food restriction, drug administration, and testing for VS seeking behavior were all conducted in accordance with the methods described for the three experiments described in the main paper, except the timing of daily meals. The present rats were used to receiving their daily meal about the time of day, which was about 3 hours before test sessions.
The meal-timing experiment
Five rats were exposed to three different meal-timing conditions over three VS seeking sessions, separated by 48 hours. Each trial began immediately after an IP injection of 2.5 mg/kg methylphenidate, and each rat. The rats received their daily meals 3 and 1 hours before and after VS-reinforced responding tests: Two rats received meals in this order, while three rats received in a reversed order.
Experimental history of rats
The five rats used in this experiment had the following experimental history prior to the present experiment. Rats were chronically food-restricted as described in the method section throughout experiments. Three weeks after commencing CFR, this group of five rats received the VS-reinforced responding test. The present rats received their daily meal 3 hours before the following sessions. After two habituation sessions, the rats received four doses of methylphenidate (0, 2.5, 5, and 10 mg/kg, IP) over four sessions, separated by 48 hours. Then, the rats received doses of a 5-mg/kg dose of methylphenidate and a 1-mg/kg dose of d-amphetamine over two sessions, separated by 48 hours.
Results:
The time of daily meals in relation to behavioral testing had no significant effect on active lever-presses (Figure 4; F2,8 = 2.58, P > 0.05) or crosses (F2,8 = 0.11, P > 0.05), with a trend that meal one-hour behavior tended to increase active lever-presses.
Conclusions:
The timing of daily meal does not appear to play a significant role in increasing active lever-pressing, reinforced by VS.
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