Age dependency in neophobia: Its influence on taste-aversion learning and the flavor-preexposure effect in rats

Abstract

Five experiments were conducted to evaluate various aspects of stimulus preexposure effects on conditioned saccharin aversion in rats of three age groups: weanling (19-25 days), young-adult (92-170 days), and old-age (680-850 days). In Experiment 1, flavor neophobia was examined. Only the young-adult and old-age animals showed evidence of neophobia. Furthermore, habituation of the neophobic reaction differed for these two age groups. Using a brief to moderately long flavorpreexposure period and an intense US (Experiment 2), we demonstrated that the youngest age group was most likely to exhibit retarded conditioning as a result of preexposure to the flavor CS. Using a weaker US and a moderately long saccharin-preexposure period (Experiment 3), age differences in conditioning resulting from preexposure to the flavor CS were reduced. When animals were preexposed to saccharin continuously for 48 h (Experiment 4), age differences in the preexposure effect were not evident. In Experiment 5, the intensity of the US was reduced to determine whether floor effects in the previous experiments had masked age differences in the ability of nonpreexposed rats to acquire an aversion to saccharin. Results indicated that tasteaversion learning was directly related to age. Although open to other interpretations, the results support the notion that the flavor-preexposure effect is influenced by the initial level of flavor neophobia. They also suggest that systematic parametric variation is sometimes necessary to obtain an accurate description of age differences in learning.Nonreinforced preexposure to a stimulus decreases the chances of that stimulus's becoming a conditioned stimulus (CS) when subsequently paired with an unconditioned stimulus (US). This preexposure effect has been demonstrated for a variety of stimuli, for a number of species, and in different learning situations (Lubow, 1973), and has been termed latent inhibition (Lubow & Moore, 1959). Recently, Misanin, Guanowsky, and Riccio (1983) have suggested that when the preexposed stimulus is flavor and the learning situation is taste-aversion conditioning, this effect might vary with age. More specifically, they suggested that the ease with which flavor is established as a latent inhibitor or "safe" stimulus (Kalat & Rozin, 1973) is inversely related to age. They found that three 30-min preexposures to saccharin prevented an aversion from being conditioned to saccharin in weanling rats but only retarded taste-aversion conditioning in young adult rats. They also found that weanling rats did not display neophobia when first exposed to a flavor, whereas young This research was supported by a summer research grant from Susquehanna University to James R. Misanin. Reprint requests should be sent to James R. Misanin, Department of Psychology, Susquehanna University, Selinsgrove, PA 17870. 69 adult rats did. Therefore, they suggested that, just as it is more difficult to convert a conditioned inhibitor than a neutral stimulus into a CS in excitatory learning, it should be mor...

Age differences in the outcome of long-delay taste-aversion conditioning in rats

“…Results of several studies have shown that it is more difficult to condition an aversion to taste in weanling rats than in adults and that conditioned taste aversion fails to occur in young rats with long CS-US intervals (Baker et al, 1977;Gregg , Kittrell , Domjan , & Arnsel, 1978;Martin & Timmins , 1980). Also, a recent study has shown that the ease with which an association is made between taste and an immediate illness is directly related to age in rats whose ages range from weanling to old age (Misanin et al, 1985). In another sense, the present results are surprising since previous work from our laboratory (Hinderliter & Misanin, 1988) suggested that aged rats would be more likely to show poorer long-delay learning than young adults.…”

“…Ingram and Peacock's (1980) failure to find age differences may have been due to their relatively intense US . The results of a recent study (Misanin, Blatt, & Hinderliter, 1985) indicate that age differences in conditioned taste aversion may be obscured by a US of even moderate intensity. Furthermore, Hinderliter and Misanin (1988), using a weaker US (.15 M LiCl) than that used by Ingram and Peacock (.4 M LiCl), found that both weanling and aged rats showed substantially less aversion to a novel flavor than did young adults when the illnessinducing US was delayed 1 h after access to the flavor CS.…”

The effect of taste familiarity on intake and taste reactivity in infant rats

“…While some studies show an increased intake of preexposed tastants in infant rats, that is, a reduction of neophobia (Gemberling, Domjan, & Amsel, 1980;Rudy, Vogt, & Hyson, 1984), in several others this effect is not observed (Chotro & Alonso, 1999;Hoffmann, Molina, Kucharski, & Spear, 1987;Misanin, Blatt, & Hinderliter, 1985;Rudy et al, 1984). In any case, it remains clear that the manifestation of neophobia increases with age (Misanin et al, 1985;Moron & Gallo, 2007;Rudy et al, 1984). The results of those studies in which no clear changes in intake were evidenced after taste exposure could be interpreted as maturational deficits, reflected either as a failure to perceive and discriminate between tastants, a failure to detect novelty/familiarity differences, or, perhaps, an inability to respond to them or to regulate intake.…”

Lack of Age Differences in Context-Illness Associations in the Long-Delay Taste-Aversion Conditioning of Rats

“…It has been suggested that old-adult rats are less lrkely than w e a n h g or young-adult rats to attend to the conditioning context (a suspended galvanized rodent cage) because unWre weanlmgs and young adults they have spent many months in similar home cages (4,9). It has been suggested that old-adult rats are less lrkely than w e a n h g or young-adult rats to attend to the conditioning context (a suspended galvanized rodent cage) because unWre weanlmgs and young adults they have spent many months in similar home cages (4,9).…”