Learning and retention of sucrose taste aversion in weanling rats

Abstract

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...

Fornix transections disrupt the ontogeny of latent inhibition in the rat

“…However, it would be amistake to emphasize a particular age range as critical, in an absolute sense, for the development of latent inhibition, because parametric and other methodological factors are likely to have a large effect on the point in ontogeny when this phenomenon can first be demonstrated. For example, more stimu-lus preexposure might cause latent inhibition to appear earlier in development, and indeed one study that employed eight preexposures to the CS (twice the number in the present one) showed significant latent inhibition of taste-aversion learning in rats at 20-25 days of age (Franchina et al, 1980). More recently, interference with conditioning by taste preexposure has been provisionally reported in 12-day-old rats by Kraemer, Hoffman, and Spear (1988).…”

“…Previous developmental studies of latent inhibition in taste-aversion learning have tended to focus on the weanling period or to compare weanling rats and adults (Franchina et al, 1980;Klein et al, 1977;Misanin et al, 1983). In the first experiment, we sought to test several age groups over a narrower age range under the same experimental conditions.…”

“…Previous developmental studies of latent inhibition of taste-aversion conditioning have yielded conflicting results and little detailed information regarding the age at which this phenomenon first emerges (Franchina, Domato, Patsiokas, & Griesemer, 1980;Klein, Mikulka, Domato, & Hallstead, 1977;Misanin, Guanowsky, & Riccio, 1983). And, although some writers have attributed the development oflatent inhibition to hippocampal maturation (Nadel & Zola-Morgan, 1984), there have been, to our knowledge, no studies of the effects of early hippocampal damage on the subsequent ontogeny of this phenomenon.…”

Latent inhibition in preweanling rats

“…It may indeed be that hippocampal functioning is involved in the age-related expression of LI, but it is also clear that the behavioral evidence is equivocal. Studies of aversive conditioning have shown that conditioned reactions to odors and tastes can be reduced by nonreinforced preexposure to these stimuli (Franchina, Domato, Patsiokas, & Griesemer, 1980;Hoffmann & Spear, 1989;Rudy & Cheatle, 1979). Perhaps LI with olfactory and gustatory stimuli involves a different mechanism from that involved in other forms oflearning, in which U has failed to appear in preweanlings, or perhaps differences in experimental parameters are crucial in determining whether or not LI will appear in immature rats.…”

“…This conclusion does not imply that the neurological substrate for LI functions as well in preweanlings as it does in adults, nor that LI will be evident in immature rats with all kinds of learning procedures (seeKraemer et al, 1988; Nicolleet al, 1989). Rather, we suggest that we have discovered additional empirical evidence of a CSpreexposure effect in the immature rat, and that this and other evidence of LI in preweanling rats (e.g.,Franchina et al, 1980;Hoffmann & Spear, 1989;Kraemer et al, 1988;Rudy & Cheatle, 1979) is important both for the analysis of behavioral development and for understanding the biological basis oflearning and memory (see, e.g.,Nadel & Zola-Morgan, 1984;Nicolle et al, 1989;Sutherland & Rudy, 1989).…”