Potentiation by a taste of toxicosis-based context conditioning: effects of varying the test fluid.

Rats that drank water in a distinctive environment and were then injected with lithium chloride (water-lithium condition) were compared with those given an added taste on those conditioning sessions (sucrose-lithium condition). In three experiments this taste potentiated a conditioned aversion to the context, as measured by suppression of intake of another solution: either a novel sour taste (Experiments 1 and 2) or a familiar saline solution (Experiment 3). In contrast, this potentiation effect was not detected when subjects were tested with water, whether a high or low dose of lithium was used (Experiment 2). Instead, in Experiments 1 and 2 water-lithium subjects drank less water than did the sucrose-lithium subjects on such tests i.e. an apparent overshadowing effect, which was the opposite outcome to that found previously using almost identical procedures. Intake on recovery sessions in another context suggested that, when water is used as the test fluid, potentiation can be masked by two factors: a context-dependent aversion to water in water-lithium subjects, and a conditioned inhibition effect of water in sucrose-lithium subjects. These may account for previous failures to detect potentiation of context conditioning.