Two experiments investigated variables influencing the acquisition of a conditioned aversion in juvenile and adult rats. In the first experiment, juvenile and adult subjects received six scopolamine-illness pairings utilizing a forced single-bottle measurement technique. Whereas adult rats learned an aversion to sucrose more rapidly when sucrose was novel rather than familiar, neither familiarized nor novel juvenile animals exhibited any aversion to sucrose. The second experiment compared acquisition of a taste aversion in juvenile and adult animals with either a one-bottle forced technique or a two-bottle choice procedure. Adult rats acquired an aversion to sucrose associated with LiCI illness more rapidly with a two-bottle than with a one-bottle measurement technique, although a strong sucrose aversion was seen in adult rats after four sucrose-illness pairings with the one-bottle technique. Young juvenile rats avoided sucrose when a two-bottle free-choice procedure was employed, while showing only a weak aversion to sucrose with the forced technique after four pairings. These results show that young animals can learn to avoid a taste associated with illness if the appropriate conditions are employed.Animals readily avoid a taste stimulus paired with illness (e.g . • Garcia & Koelling, 1966). Conditioned aversion refers to the phenomenon where an organism associates a taste with subsequent illness, even though the gustatory stimulus may precede illness by several hours.Since, in a conditioned aversion situation, the rat is required to inhibit consumption of a previously ingested taste, one might expect developmental processes to influence the occurrence oftaste aversion. Young animals appear to have more difficulty than adults in passively avoiding an aversive event, where shock is the aversive stimulus (e.g., Riccio, Rohrbaugh, & Hodges, 1968;Riccio & Schulenberg, 1969). One purpose of the first experiment was to determine if young juvenile rats would avoid a taste whose consumption preceded illness.Novelty of the taste solution appears to be an important determinant influencing acquisition of a conditioned aversion (e.g., Garcia & Koelling, 1%7;Revusky & Bedarf, 1967). Animals develop aversions to novel tastes more rapidly than they do to familiar tastes (e.g., Fenwick, Mikulka, & Klein, 1975). Kalat and Rozin (1973) have suggested that when illness does not occur after consumption of a particular taste the rat learns that the taste is safe and can be ingested again. Thus, learned safety interferes with the development of aversions to previously experienced tastes. Young animals also appear to have more difficulty inhibiting previously appropriate responses than do adults. Egger (1974) found that 24-day-old rats extinguished an acquired escape response more slowly than either 50-or 100-day-old animals. Since, as a consequence offamiliarization, the subject learns that a particular taste is safe, young rats may exhibit more interference with taste aversion acquisition when previously experiencing that taste wi...

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Weanling rats, 20 days old, received 0, 1, 2, 4, or 8 pre-exposures to 12% sucrose prior to a single pairing of sucrose with an intraperitoneal injection of lithium chloride (LiCl; 3.0 mEq of a .15Msolution) or distilled water (20 mg/kg). Testing for sucrose taste aversion with a 2-bottle-choice procedure on 9 test trials reliably showed that increasing numbers of pre-exposures to sucrose directly attenuated taste aversion effects in the LiCl-injected groups but did not appreciably affect intake performance in the distilled water-injected groups. Comparisons between the injection conditions yielded reliable evidence for sucrose taste aversion at each pre-exposure level. These results show that flavor stimulus pre-exposures reliably attenuate subsequent taste aversion in weanling rats as had previously been reported for adult rats.

Sixty rat pups, 21 days old, drank 9% sucrose and then received a single injection of distilled water or .3, .6, 1.8, or 3.0 mEq of lithium chloride (LiCI). Testing with a two-bottle choice procedure showed that sucrose taste aversion occurred reliably following injections of 1.8 and 3.0 mEq of LiCI, but not following .3-or .6·mEq injections. In Experiment 2, 80 rat pups, 21 days old, drank 9% sucrose and received an injection of LiCI (3.0 mEq) or distilled water and then were tested for taste aversion 24, 48, 72, or 168 h later. Aversion effects were reliable at each retention interval; the magnitude of aversion was invariant across intervals.Recent studies of taste aversion learning have shown that when the conditions of training and testing are appropriate, young rats 22 to 29 days old learn to inhibit consummatory responding toward a taste stimulus that previously accompanied toxicosis (e.g., Ader & Peck, 1977;Baker, Baker, & Kesner, 1977; Grote & Brown, 1971 b; Klein, Domato, Hallstead, Stephens, & Mikulka, 1975). However, Baker et aL (1977) and Klein et al. (1975) have indicated that although taste aversion effects were demonstrable with young rats, these effects seemed more labile than they appeared to be for older rats, 80 days of age. That is, 'conditions that yielded reliable taste aversion effects in adult rats yielded only marginal effects in younger rats. Unfortunately, the relatively sparse amount of information about the parameters of taste aversion for weanling rats makes it difficult to ascertain the basis for the weanlings' performance in aversion learning. One apparently potent taste aversion variable whose effects have been reported for adult rats (Nachman & Ashe, 1973) but not for weanlings is the intensity (concentra· tion) of the toxicosiS-inducing agent. Nachman and Ashe (1973) showed that for adult rats, 60 days old, taste aversion increased reliably with increasing milleeqUivalents (mEq) of lithium chloride (LiCl) up to 3.0 mEq. Since there are no dose·response data available for infant rats, Experiment 1 investigated the effects of injecting .3-, .6-, 1.8-, or 3.O-mEq liCI on taste aversion in rats, 21 days old at injection. On Days 2, 3, 4, and 5, each pup received l·h daily access to tap water; the wet mash was made progressively drier over days until on Day 5 only dry ground chow served as food. On Day 6 the rat pups, 21 days old, were randomly assigned to injection conditions (n = 12). Each pup received 1-h access to 9% sucrose (weight/volume), and within 15 min after the end of the drinking period, each received an intraperitoneal injection of .3, .6, or 1.8 mEq of .15·molar Lic!, or 3.0 mEq of .30-molar LiCl, or 12 ml/kg of distilled water. Beginning 24 h after injection, each rat was tested for sucrose taste aversion with a two-bottle choice procedure: One bottle contained 9% sucrose, the other, tap water. Each pup received nine 1-h test periods, one period every 24 h. The measure of performance was the amount drunk (in milliliters) from each bottle, as calculated by the diff...