Lithium chloride and inescapable, unsignaled tail shock differentially affect meal patterns of rats

Several motivational states, such as malaise, fear, and satiety, reduce spontaneous food ingestion by rats, and differentiation of these states is often desirable. The present study used the spontaneous meal pattern to this end. The illness-inducing toxin lithium chloride delayed initiation of the first postinjection meal, and that meal was smaller and eaten more slowly (Experiments 1A and 1B). Rats exposed to tail shock also subsequently took longer to initiate meals, but meals were eaten faster and were slightly larger relative to control conditions (Experiment 2). These changes in meal patterns are different from those produced by satiety-related hormones, such as CCK or insulin, which solely reduce meal size in paradigms designed to assess physiological regulation of food intake. Taken together, these findings attest to the ability of meal patterns to distinguish malaise, fear, and satiety from one another.