Some determinants of the time course of saccharin ingestion in hungry rats

Abstract In rats that are food- but not water-deprived, a saccharin “meal” is characterized by a progressive decrease in lap rate as the bout progresses. However, saccharin does not trigger a fixed rate of lapping at any point in the sequence. When rats have only intermittent access to saccharin early in the session, they increase their rates of lapping so that, within each few minutes, the amount of lapping (or some correlate such as volume drunk) is held constant. This happens over a wide range of restriction conditions. And if compensation cannot occur during a period of constraint, then it occurs ofterward, promptly and precisely. When constraint is withdrawn, rats drink amounts such that the total amount of drinking (or its correlate), through that point in the ingestive bout, is defended. These findings imply that the controlling system includes (1) an integrator that keeps track of the amount of drinking that has occurred, even across interruptions; and (2) a short-term feedback loop that operates minute by minute within the bout. This loop regulates, not the rate of lapping to be emitted, but the amount of lapping to be done (or its correlate); Thus the decline in responsiveness to saccharin as drinking progresses reflects a depression of this regulated value, not of lap rate per se .