Sensitization of ingestive responding in preweanling rats: time course and specificity

Two experiments measured the response-enhancing effects of oral stimulation in young rats with no feeding experience. In Experiment 1, pups were implanted with oral cannulas and deprived for 0, 6, or 24 hr. In nondeprived rats, sucrose exposure transiently sensitized oral responding to subsequent stimuli for several minutes. Among 24-hr-deprived rats, baseline oral responding had increased to where sucrose exposure was no longer sensitizing. Unlike oral responding, sensitization of activity by sucrose exposure increased with deprivation. Sensitization was also evident in the microstructure of responses to infusions. In Experiment 2, the specificity of sensitization was examined by varying stimulus palatability. Sucrose exposure sensitized oral responding to both sucrose and quinine-adulterated sucrose, but quinine-adulterated sucrose was not sensitizing. The results suggest that in inexperienced rats, oral stimulation initiates changes in responding that may mimic the endogenous sequelae of deprivation, perhaps representing early substrates for learned controls of intake.