Behavioral regulation of the blood glucose level in rats

Rats bearing one or two intravenous (IV) or one intravenous and one intragastric (IG) chronic catheters, were allowed to press one or two levers controlling the IV injection of either insulin or glucagon alone, or insulin paired with glucagon or with a glucose solution IV or IG. It was shown that rats readily learned to press for the various solutions and exhibited a sustained pattern of self-injection specific to these solutions and to their combinations. The rats self-injected insulin, glucagon and glucose preferentially during the 20 min preceding and following meals. Alone, or in combination with other solutions, glucose and glucagon were self-injected preferentially before meals and insulin after meals. Consequently, glucose or glucagon to insulin self-injection ratios were inversed from the pre-meal to the post-meal periods. In addition, rapid alternations from one lever to the other were observed in the coupled self-injections of insulin and glucose or insulin and glucagon. No effects of the self-injections on the free feeding pattern were observed. The results are interpreted as evidence for the reinforcing effects of a correction of both hypoglycemia and hyperglycemia and for a role of these systemic primary reinforcements in the normal post-ingestive modulation of oral feeding responses.