When feeding was restricted to a single meal scheduled at a fixed time (1300-1700 h) in the day, rats exhibited increased prefeeding locomotor activity 1-3 h before the feeding time, which increased over 6 days. The activity increase was seen for about 5 h (1100-1600 h) on the seventh day when no food was provided (fasting day), as the rat anticipated mealtime. Thus, mealtime-associated activity rhythm on the fasting day was considered to be another good index of food-anticipatory activity. In this study, we investigated the effects of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801, which has been reported to cause impairment of spatial learning, on food-anticipatory activity in rats. Daily injection of MK-801 (0.2 mg/kg) at 1700 h for 6 successive days impaired the development of increased prefeeding activity. The appearance of mealtime-associated activity was impaired by daily injection of MK-801 (0.2 mg/kg) at 1700 h (immediately after food restriction, FR) or at 1900 h (2 h after FR) but not at 0900 (16 h after FR). In addition, mealtime-associated activity was impaired by MK-801 injected at 1700 h in a dose-dependent manner (0.1-1 mg/kg). The present results demonstrate that NMDA receptor mechanisms were involved in learning processes of food anticipation and suggest that an impairment of food-anticipatory activity may be considered an animal model of a deficit of "temporal learning".

Animals↗

PubMedDate not supplied

Attenuating effect of serotonin receptor antagonists on impairment of mealtime-associated activity rhythm in old rats.

In the present study, we examined attenuating effect of serotonin (5-HT) receptor antagonists on the impairment of the time perception presented by daily scheduled feeding in old rats. When feeding was restricted to a single meal at a fixed time of day (1300-1700 h) for six consecutive days, young rats exhibited intense locomotor activity from 1-3 h before feeding time. Intense locomotor activity was observed between 1200 adn 1700 h in young animals even on the fasting day (day 7) (mealtime-associated activity). However, this mealtime-associated activity was impaired in 24-mo-old rats. Daily injections of 5-HT2 receptor antagonists, mianserin or ritanserin, or a 5-HT3 receptor antagonist, Y25130, at 1700 h for 6 consecutive days significantly and dose-dependently attenuated the impairment of mealtime-associated activity on the fasting day in old rats without affecting the food intake. Our results suggest that the blockade of 5-HT2 and/or 5-HT3 receptors attenuates impairment of the manifestation of mealtime-associated anticipatory activity related to temporal learning in old rats.

Aging↗

PubMedDate not supplied

Temporary treatment with sirolimus and low-trough cyclosporine prevents acute islet allograft rejection, and combination with starch-conjugated deferoxamine promotes islet engraftment in the preclinical pig model.

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Acute Disease↗