Similarities and differences between "proactive" and "passive" stress-coping rats in responses to sucrose, NaCl, citric acid, and quinine.

A stress-coping style describes a set of behavioral and physiological measures that characterize an individual's response to stressful stimuli. It would follow that different stress-coping styles are associated with differential sensitivity for taste stimuli. Animals with stress-coping characteristics better suited to an environment in which new foods are more frequently encountered may show enhanced orosensitivity to cues that signal toxins and/or nutritional value. Here, rats were categorized as "proactive" or "passive" based on results from a defensive burying test. Next, the brief-access taste procedure was used to compare unconditioned licking responses to a concentration array of compounds that humans describe as "sweet" (sucrose), "salty" (NaCl), "sour" (citric acid), and "bitter" (quinine) across the 2 groups. Both groups displayed concentration-dependent lick responses to sucrose, NaCl, citric acid, and quinine. The passive group initiated significantly fewer trials to sucrose than the proactive rats, but the groups did not significantly differ in trial initiation for the other 3 test compounds. Thus, differences in food intake, body weight, and glucose homeostasis between the stress-coping styles are not likely driven by alterations in orosensory responsivity. However, the current findings lend support to the hypothesis that the 2 groups differ in reward-related signaling mechanisms.