A comparison of the effects of atropine on real-feeding and sham-feeding of sucrose in rats.

In Experiment 1 the influence of atropine methyl nitrate on the sham-feeding response of adult female rats to a sucrose solution was determined. Atropine (1 or 5 mg/kg) reliably suppressed the sham-intake of sucrose when the drug was administered 30 or 0 min prior to, or 17 min after the start of the feeding session. The suppressive effect was less, however, when the drug was administered 30 min before testing compared to the other two injection-test conditions. In Experiment 2 atropine failed to reliably decrease the real-feeding of a sucrose solution whether it was injected 30, 15, or 0 min prior to testing. These results were replicated in Experiment 3; atropine (0 min injection-test interval) reduced the sham-intake but not the real-intake of a sucrose solution. However, atropine decreased the rate of feeding under both real- and sham-feeding conditions. The fact that atropine reduced feeding rate but not meal size in the real-feeding condition was attributed to the drug's lack of effect on postingestive satiety. The present findings along with other recent results indicate that (1) the injection-test interval is a potentially important variable in studies involving atropine; (2) results obtained with sham-feeding animals do not always generalize to real-feeding animals; and (3) cholinergically-mediated cephalic responses are of questionable importance in the control of meal size.