MK801 increases feeding and decreases drinking in nondeprived, freely feeding rats

The noncompetitive NMDA receptor antagonist MK801 has been reported to incr ease food intake in rats during scheduled test meals of palatable foods or after food deprivation, but not in nondeprived rats given rodent chow. To d etermine if MK801 has an effect on spontaneous meals, MK801 (100 mug/kg) wa s administered 15 min prior to dark onset to nondeprived rats maintained on powdered rodent chow, and spontaneous food and water access was measured. MK801 increased the length of the first meal and the amount of time spent f eeding within the meal. Conversely, MK801 decreased the length and size of the first drinking bout. MK801 did not alter the latency to the first meal or drinking bout, nor the intervals between successive meals or bouts. The effects of MK801 on feeding and drinking bouts were partially confirmed by measuring total chow and water intake over the first 2 h of the dark period . Thus, acute MK801 can significantly alter spontaneous chow feeding and dr inking in nondeprived rats when administered prior to dark onset. (C) 2001 Elsevier Science Inc. All rights reserved.