Effects of age and flavor preexposures on taste aversion performance

Age, sex and pre-exposure effects on acquisition and generalization of conditioned taste aversion in rats

The main aim of the present study was to assess the effect of sex and aging in two pre-exposure learning effects, latent inhibition (LI) and perceptual learning (PL), with a conditioned taste aversion paradigm. Young adult (90 days) and aged (more than 18 months) males and females received 8 pre-exposure trials either with stimulus AX (LI conditions) or BX (PL conditions). Then, all animals received a conditioning trial with AX and two test trials, one with AX and other with BX. The level of generalization between AX and BX was assessed by means of the absolute level of consumption of BX and by the difference in consumption between both stimuli. The results showed an attenuation of latent inhibition as well a stronger generalization of conditioned taste aversion in females when generalization is inferred from the BX consumption. A facilitation of conditioning for the aged animals was also found regardless of the pre-exposed stimulus. Pre-exposures to BX resulted in little generalization, but pre-exposures to AX resulted in a very similar consumption of both compounds, indicating a strong generalization between them. Overall, the study provided novel evidence about the effect of sex and aging on taste aversion, raising at the same time some relevant questions about perceptual learning and how such pre-exposure effect has been typically assessed.

Peculiar modulation of taste aversion learning by the time of day in developing rats

The ontogeny of the temporal context modulation of conditioned taste aversion was studied in male Wistar rats using a palatable 1% NaCl solution. A procedure that included two saline preexposures, a single pairing saline-lithium chloride (0.15 M; 1% b.w.) either at the same or a different time of day of preexposures and a one-bottle test at the same time than preexposure was applied. Four age groups (PN32, PN48, PN64, and PN100) covering the complete range from adolescence to the adult period were tested. The results showed no effect of a temporal context shift in PN32. A peculiar enhancement of temporal context-specific saline aversions was exhibited by PN48 and PN64 rats, while the adult typical temporal context specificity of latent inhibition was only evident in PN100 rats. The results are discussed in terms of the peculiar brain functional organization during a protracted adolescence period.

Aging facilitates long-trace taste-aversion conditioning in rats

In order to examine age-related changes in long-trace conditioning, five age groups (0.25, 1, 1.5, 2, and 2.5 years) of Wistar-derived female albino rats were subjected to taste-aversion conditioning at one of five conditioned stimulus-conditioned stimulus (CS-US) intervals (0, 45, 90, 180, and 360 min). Age differences in the strength of the aversion were evident at CS-US intervals greater than 0 min and the strength of the aversion was directly related to age. An aversion was conditioned in only the two oldest age groups when the CS-US interval was 360 min. The age differences in taste-aversion and the superior long-trace conditioning in old-age rats were attributed to factors that accompany aging, for example, the gradual slowing down of a metabolic pacemaker.

Conditioned food aversions: principles and practices, with special reference to social facilitation

Conditioned food aversion is a powerful experimental tool to modify animal diets. We have also investigated it as a potential management tool to prevent livestock from grazing poisonous plants such as tall larkspur (Delphinium barbeyi), white locoweed (Oxytropis sericea) and ponderosa pine (Pinus ponderosa) on western US rangelands. The following principles pertain to increasing the strength and longevity of aversions: mature animals retain aversions better than young animals; novelty of the plant is important, although aversions can be created to familiar plants; LiCl is the most effective emetic, and the optimum dose for cattle is 200 mg/kg body weight; averted animals should be grazed separately from non-averted animals to avoid the influence of social facilitation which can rapidly extinguish aversions. Social facilitation is the most important factor preventing widespread application of aversive conditioning. When averted animals see other animals eat the target food they will sample it, and if there is no adverse reaction they will continue eating and extinguish the aversion. However, if averted animals can be grazed separately, aversions will persist. Aversive conditioning may provide an effective management tool to prevent animals from eating palatable poisonous plants that cause major economic loss.

Taste preference of the adult rat as a function of prenatal exposure to ethanol

Two groups of pregnant rats (n = 10) received exposure to either 10% ethanol or water. All male offspring (n = 43) received a six-day preference test (ethanol vs water) at 90 days of age. Fluid consumption scores indicated a significant preference for water by all Ss. However, those animals receiving prenatal ethanol exposure consumed significantly more ethanol during preference testing than did the animals receiving prenatal water exposure.

The effect of CS-preexposure on conditioned taste aversion in young and adult rats

Young and adult rats were given nonreinforced exposures to the flavor-CS prior to a taste aversion conditioning session. CS-preexposure prevented the conditioning of a taste aversion in young rats but only attenuated conditioning in adults. These results suggest that an enhanced CS-preexposure effect may account for the previously reported weaker conditioned taste aversion observed in young rats, as compared to adults, when there is a protracted interstimulus interval.