Early exposure to sugars influences the sugar preference of the adult rat.

Female rats were maintained on either a High Sucrose or High Glucose diet during gestation and lactation. Their pups were continued on the same diet as their dam until they were 42 days of age; thereafter all animals were maintained on laboratory chow. From 21-84 days of age, each rat was given a weekly two-choice preference test between the High Sucrose and High Glucose diets. Rats that were fed the High Sucrose diet throughout their early development had heavier body weights and a greater preference for the High Sucrose diet beginning on Day 63 than did the rats that were fed the High Glucose diet. Rats fed the High Glucose diet demonstrated a greater preference for the High Glucose diet during adulthood. These data indicate that early dietary experience can modify the rat's subsequent preference for sugars.

Signaled tailshock is perceived as similar to a stronger unsignaled tailshock: implications for a functional analysis of classical conditioning.

Water-deprived rats given fixed-electrode, variable-intensity tailshock at random times rated each trial by pressing either a "high-aversiveness" or "low-aversiveness" lever in order to obtain water. Trials on which a warning signal preceded tailshock resulted in more "high-aversiveness" leverpressing than did otherwise equivalent unsignaled trials. The magnitude of this effect increased and decreased as a function of several parameters including signal-shock interval, signal duration, and range and absolute value of shock intensities but was never reversed despite efforts to achieve such a reversal. Variation in the size of the effect as a function of signal parameters as well as lick suppression scores indicated that the signal had acquired aversive characteristics, which suggests that the effect of the signal on lever choice was due largely to the aversiveness of the signal summating with the aversiveness of the tailshock. Several hypotheses concerning factors that might have either masked or prevented classically conditioned preparatory responses elicited by the signal from reducing tailshock aversiveness were tested and rejected. Despite the greater aversiveness of the signaled condition, when given the choice of receiving or not receiving the signal, the animals displayed a preference for signaled tailshock. Implications for the role of preparatory responding both in the preference-for-signaled-shock phenomenon and in classical conditioning are discussed.

Associations to contextual stimuli as a determinant of long-term habituation.

A series of experiments was performed to determine whether long-term habituation of the acoustic startle response in rats is mediated by conditioned associations between contextual cues and the test stimulus. Experiment 1 established parameters yielding demonstrable long-term habituation of the startle response. Experiment 2 attempted to overshadow the hypothesized associations to contextual cues by providing a more reliable predictor of the acoustic stimulus. Experiment 3 investigated the effect of changes in contextual cues on long-term habituation. Experiment 4 provided treatments designed to extinguish the hypothesized associations between the context and the habituated stimulus. Experiment 5 sought latent inhibition of the hypothesized association between the contextual cues and the acoustic stimulus. The results of these experiments uniformly failed to support an associative model of long-term habituation of the startle response, but they are consistent with a nonassociative model emphasizing habituation to the entire experimental situation rather than exclusively to the iterated stimulus.