3500 Market Street, Philadelphia, PA 19104. Received 17 June 1983. STEWART ... chased from Perfection Breeders, Inc., Douglassville, PA),. 25-35 g, housed ...
Physiology & Behavior, Vol. 32, pp. 955--959. Copyright e> Pergamon Press Ltd., 1984. Printed in the U.S.A.
0031-8384/84 $3.00 + .00
Disparity Between Formation of Conditioned Flavor Aversions and Neophobia During Grooming in 1 Rats and Mice CHARLES N. STEWART2 * AND RUSSELL F. REIDINGER, JR.t *Whitely Psychology Laboratories, Franklin and Marshall College, Lancaster, PA 17604 tU.S. Fish and Wildlife Service, c/o Monell Chemical Senses Center 3500 Market Street, Philadelphia, PA 19104
Received 17 June 1983 STEWART, C. N. AND R. F. REIDINGER, JR. Disparity between formation of conditioned flavor aversions and neophobia during grooming in rats and mice. PHYSIOL BEHAV 32(6) 955-959, 1984._.:Mice (Mus musculus) allowed to groom a paste containing saccharin from their fur before injection with lithium chloride displayed a saccharin aversion in subsequent drinking preference tests. No attenuation of neophobia was observed in mice grooming saccharin because the animals failed to display a neophobia towards saccharin in drinking tests. Rattus norvegicus displayed neophobia towards saccharin in two- and single-bottle drinking tests but this neophobia was not attenuated by grooming experience with the saccharin paste. Rats apparently learn that if a taste is hazardous in the grooming context it is also likely hazardous in an appetitive context. Learned safety in grooming, however, does not generalize into the appetitive context. The results support the view that neophobia and learned taste aversion depend upon different mechanisms. Conditioned flavor aversion
Grooming
Mice
Neophobia
GROOMING in rodents has been studied intensively and is generally viewed as a stereotyped behavior that is primarily "self organized" [6] and, thus, under endogenous control. Depending on the animal's behavioral state, grooming is also influenced by peripheral stimulation such as irritants to the fur [8,11), auditory stimulation from conspecifics [l], as well as by placement in a strange environment [2,5). Rats [1) groomed selectively on the flank which had been soiled by 2% aqueous agar solution. When aroused by hearing tape recordings of a conspecific being attacked, however, the rats groomed both flanks indiscriminantly, suggesting that attention to peripheral stimulation during grooming occurs only under lower levels of arousal in this species. A conditioned flavor aversion (CF A) method has also been used [11) to determine if rats attend to peripheral stimulation while grooming. In this study a gelatinous paste containing saccharin was applied to the fur of rats, who were then allowed to groom themselves, following which they were injected with LiCl. The rats subsequently avoided saccharin in two-bottle preferene;e tests. The CFA was taken as evidence that the rats had attended to the taste qualities of the paste while grooming it from the fur. An attempt to demon-
Rats
Saccharin
strate a CF A to saccharin presented on the fur of pine voles (Microtus pinetorum) was not successful; i.e., when given two-bottle preference tests, no significant differences were found between sham and LiCl injected groups (L. A. Geyer and C. Komet, personal communication). In this study, however, sham injected controls did not show a stable and strong saccharin preference. Thus, it remains unclear whether these rodents do form a CFA when the substance to be tasted is applied to the fur. Deer mice (Peromyscus maniculatus), another cricetid species, readily form a CFA when the tastant is presented while they are drinking [12). In the present Experiment 1, we determined whether another species of Muridae, Mus musculus, like Rattus norvegicus, would readily form a CFA to saccharin groomed from the fur before LiCl injection. In addition, we designed the experiment to address whether exposure to a substance on the fur would influence the relative neophobia displayed by animals towards a novel solution encountered in a two bottle preference test. As numerous studies have shown [10), such prior exposure attenuates neophobia when the pre-exposure and test occur in the drinking situation. At issue is whether information regarding the flavor of a substance obtained dur-
'This research was conducted while the senior author was a Visiting Scientist at the Monell Chemical Senses Center and was supported by the U.S. Fish and Wildlife Service, Department of the Interior, and Franklin and Marshall College. 2 Requests for reprints should be addressed to Charles N. Stewart, Whitely Psychology Laboratories, Franklin and Marshall College, P.O. Box 3003, Lancaster, PA 17604.
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ing grooming will transfer into an appetitive situation (drinking) when neophobia is the only mediating process and illness-induced aversion is not involved as it was in previous work [ 11]. Experiments 2 and 3 addressed this same question using rats instead of mice and measuring the neophobia attenuation in both a two-bottle and single-bottle preference test. Previous work [4] has indicated that the latter is more sensitive as a measure of neophobia attenuation. EXPERIMENT I
Method
Sixty male mice (M. nwsrn/11s-Swiss Webster) (purchased from Perfection Breeders, Inc., Douglassville, PA), 25-35 g, housed individually in plastic cages, (28x 18x 15 cm) were fed ad lib (Wayne Lab-Blox) throughout the experiment. The room was maintained at 21-23°C with lights on from 0800-2000 hr. On days one and two of the experiment, following 23 hr of water deprivation, the mice were given access to a single 10 ml drinking tube containing tapwater for one hr per day. On the third day, 2 ml of carboxymethylcellulose (CMC; 3.55% w/v in water) was applied to the flank fur of 30 of these animals. The CMC was a gelatinous material that tastes neutral to humans. The remaining 30 animals were also smeared on both flanks with 2 ml of CMC to which had been added 0.35% w/w sodium saccharin. Thirty min after the applications to the fur, during which time the animals invariably groomed the soiled fur, intraperitoneal injections of LiCI (0.15 M) or NaCl (0.15 M) in the amount of 2% of body weight were administered to two groups of 20 mice. A third group of 20 received no injections. Each of these groups of mice contained 10 who had groomed plain CMC and 10 who had groomed the CMC containing saccharin. At 30 min after injections the animals were given free access to tapwater for 23 hr to allow them to be fully hydrated during recovery from the· LiCl injection. They were then fluid deprived again for 23 hr in preparation for a one hr, two-bottle preference test between sodium saccharin (0.2% w/v) and tapwater. The preference tests were carried out over three successive days with the position of the 10 ml tube containing the saccharin alternated to prevent a confounding of taste preference with position preference. The design followed was therefore a 2 x 3 x 3 factorial with type of conditioned stimulus (CS; i.e., saccharin in plain CMC vs. plain CMC) as one factor, the type of unconditioned stimulus (US; i.e., LiCl vs. NaCl vs. no injection) as the second factor and the day of testing (I vs. 2 vs. 3) as the third and repeated measure factor. Percentage preference for saccharin (i.e., the volume of saccharin consumed divided by the total volume of water and saccharin consumed during the one hour test period) was used as the dependent variable. Results
Overall, the saccharin solution was preferred during the 3 days of testing (mean=76.3%). However, preferences for the saccharin solution were influenced by all three factors; i.e., type of CS, F(l,54)=10.8, p
