Journal of Comparative and Physiologicaz Psychology1975, Vol. 89, No. 5, 457-467

Demonstrations of Neophobia and Enhanced Neophobia in the Albino Rat

*Marilyn E. Carroll, Hatice Iffet Dine, Carolyn J. Levy, and James C. Smith Florida State University

The conditions under which neophobia and enhanced neophobia occur in the albino rat were studied. Neophobia to a .1 00 saccharin solution was demonstrated in a 10-min single-bottle test. This neophobia was enhanced by pairing water ingestion with a radiation exposure of 100 r. or an injection of lithium chloride 24 hr prior to the saccharin test. In addition, it was found that the differences in consumption of saccharin in 0 10-min single-bottle test due to neophobia and enhanced neophobia were produced by consistent differences in drinking rates which appeared early in the 10-min period. The disappearance of neophobia and enhanced neophobia in a I-hr single-bottle test suggested that the effects of neophobia and enhanced neophobia are short4ived and are best measured in a brief single-bottle test. Finally, enhanced neophobia was not found when 2 days of water drinking were interposed between LiCl poisoning and saccharin testing.

Wild rats show a pronounced hesitation in eating or drinking when presented with a novel food or fluid. Barnett (1963) discussed this protective hesitation and suggested that it is an instinctive survival mechanism which he termed "neophobia." Neophobia is conceived as the first stage in the rat's gustatory behavior in the presence of new food, followed by a second stage of acceptance or refusal based on the consequences of the initial sampling (Rzoska, 1954).

In early studies of neophobia in veild rats (Richter, 1953; Rzoska, 1953, 1954), it was observed that when rats were presented with a new food or a familiar food in a new container, the rats remained in the backs of their cages for up to 7 hr before even approaching the food. Moreover, the novel food or container was a suffcient stimulus to lower food intake for several days. Later, when domestic albino rats were tested and

This research was supported by U.S. Public Health Service Grant MH-11218 and a contract with the Division of Biology and Medicine, U.S. Atomic Energy Commission, H.

Dino is now at Hacetepe University, Ankara, 'I'urkey, and was supported during this study by a Postdoctoral Fellowship from the Agency for International Development, 1971—1972.

Requests for reprints should be sent to James C. Smith, Department of Psychology, Florida State University, Tallahassee, Florida 32306.

compared with wild rats for their response to a novel food (Barnett, 1956, 1957), the domestic rats quickly approached and consumed the novel food. On the basis of this evidence, it was concluded that domestic rats do not displa.y a neophobic response to novel foods.

More recently there have been a few demonstrations of neophobia to novel foods in domestic rats. Revusky and Bedarf (1967) noted that albino rats tended to take more time to complete 100 licks of a novel fluid than a familiar one. Other studies have also

458 CARROLL, DINC, LEVY, AND SMITHpresented data that suggest a neophobic response to novel tastæ substances by albino rats (Nachman, 1970; Nachman & Ashe, 1974; Nachman & Jones, 1974; Rolls & Rolls, 1973).

However, thus far there is no overwhelming evidence for the existence of neophobia to novel teste substances in the albino rat. Richter (1953) and Barnett (1957) may not have been able to measure a neophobic response in the albino rat because of the time scale (in days) they used. Perhaps careful observation within the first few minutes after presentation of the novel food would have revealed neophobia when the feeding patterns of these albino rats were compared with those of rats for which the food was familiar.

Both Richter (1953) and Rzoska

(1954) have reported that wild rats that have been previously poisoned

subsequently dem-onstrate suspiciousness or neophobia when other new foods are offered. Again, this effect is quite pronounced in wild rats compared with domestic rats in their studies. Rozin (1968) investigated this illness-induced neophobia by comparing the responses of half-wild and domestic rats in a threechoice preference test (a familiar, safe food vs. a novel food vs. a food associated with poisoning) after LiCl poisoning. Rozin found in both strains that poisoning that occurred about 24 hr previously caused an increase in the neophobic response to the novel food, which he called "enhanced neophobia.'

Nachxnan (1970) suggested that rats that had received earlier LiCl injections drank less saccharin in a subsequent test because of enhanced neophobia. However, the appropriate control groups were not run to allow discrimination between conditioned

taste aversion and enhanced neophobia.

Brackbill, Rosenbush, and Brookshire (1971) were unable to show neophobia or enhanced neophobia in a I-hr three-choice preference test. They criticized Rozin's (1968) demonstration of enhanced neophobia claiming that his preference test was given to animals "while they were still clearly ill" (p. 349).

These discrepant results concerning enhanced neophobia in the albino rat may be attributable to the length of preference test used. Just as neophobia may be best measured in a brief test, it is possible that enhanced neophobia is short-lived in the domestic albino rat. It is possible that enhanced neophobia could appear and be overcome during

the course of an hour's contact with the novel taste substance. Therefore, if measurements were made only at the end of the hour, as Brackbill et al. (1971) did, the phenomenon of enhanced neophobia would not be evident,

It is well established that if a rat ingests a novel taste substance and is subsequently exposed to ionizing radiation or poisoned, the rat will avoid that taste substance on subsequent occasions (e.g., Nachman, 1970; Smith, 1971). This profound decrement in intake of the taste substance has been referred to as conditioned taste aversion. Based upon the rat's prior history,

the initial hesitation in drinking a taste solution has been described above as neophobia, enhanced neophobia, or conditioned taste aversion* This hesitation in drinking should result in a decrement in fluid intake when drinking is observed over a short time period. The present

457

NEOPHOBIA AND ENHANCED NEOPHOBIA 459research was designed to compare the magnitude and duration of these three phenomena.

Specifically, Sprague-Dawley rats were given a test of saccharin drinking after oneof four treatment conditions on the previous day.

1. Control-saccharin or saccharin-NaCl. Rats were given 10-min access to saccharin paired with either a control exposure to radiation or a NaCl injection. On test day these rats were considered to be normal, experienced saccharin drinkers.

2. Radiation-saccharin or saccharin-LiCl. Rats were given 10-min access to saccharin paired with either ionizing radiation or a LiCl injection. These animals represent the conditioned taste aversion group. The magnitude of the taste aversion is measured by comparing this group with the controlsaccharin or saccharin-NaCl group.

3. Radiation-H20 or H20-LiCl. Rats were given 10-min access to water paired with either ionizing radiation or a LiCl injection. This group is run to test for enhanced neophobia.

4. Control-H20 or Ho-control. Rats were given 10-min access to water paired with either a control exposure to radiation or a NaCl injection. nese animals represent the neophobia group, since the saccharin solu tion is novel on test day.

EXPERIMENT 1The purpose of this experiment

was to test for neophobia and enhanced neophobia in the albino rat. Saccharin drinking in a 10-min test by the neophobia and enhanced neophobia groups will be compared with the decreased drinking by a group that has been conditioned to avoid saccharin.

MethodSubjects. Thirty-two naive male albino rats

(CD strain, Charles River Breeding Laboratories), weighing 300-400 g, were housed in individual cages in an animal room on a 12: 12 light/dark cycle. Purina Lab Chow was available ad lib in the home cage. Water was available only at specified times.

Apparatus. Animals were irradiated or sham exposed in individual Plexiglas boxes, which were mounted on a motor-driven "Ferris wheel" rotating at a rate of 1.5 rpm. The radiation source was CO GO (Gamma Beam, 150, Atomic Energy of Canada, Ltd. In the home cage, fluids were presented to the rats in glass bottles with stainless steel drinking spouts (Girton). 'The saccharin solution used was .1% sodium saccharin (W/V).

Procedure. On Day 0 the 32 rats were deprived of water. In order to accustom the animals to drinking at a certain time each day, they were given access to water for 1 hr on Day 1, for 30 min on l)ay 2, and for 10 min on Day 3, at approximat,ely 1100 hours. Since previous research has demonstrated that optimal radiation-induced taste aversion conditioning occurs in the "backward" design (Barker & Smith, 1974; Carroll & Smith, 1974) a UCS—CS design was used, i.e., the radiation or the unconditioned stimulus (UCS) was given prior to the conditioned stimulus (CS)

i.e., saccharin or water access. Therefore, on Day 4 (treatment day) 16 rats were irradiated for 10 min for a total exposure dose of 100 r. as measured in air by a Victoreen thimble chamber; the other 16 control rats were sham exposed, i.e., rotated on the Ferris wheel but the C0 6C

source was not raised (see Table 1). Thirty minutes after these exposures, eight rats from the irradiated group were given access to saccharin for 10 min (radiation-saccharin), and the other eight were given access to tap water for 10 min (radiation-H2(_)). The control exposed animals were treated in a similar fashion, i.e., eight had access to saccharin (control-saccharin) and eight had. access to water (control--H 20). On Day 5 (test day) 24 hr after irradiation

460 CARROLL, DINC, LEVY, AND SMITHor control exposure, all rats were given

access to the saccharin solution. Fluid intakes were measured by weighing (El g) the bottles before and after the drinking period and by correcting for spillage.

The statistical treatment of the results of this experiment and of each of those to follow consists of a simple analysis of variance of intakes across all groups and of a simple repeated measures analysis of variance of intakes across water-baseline, treatment, and test days for selected groups. In cases in which there a.re significant effects (p < .05), orthogonal comparisons will be made.

Results and Discussion

The mean fluid intakes for all groups on Days 3, 4, and 5 are presented in Table 1.

TABLE 1SOLUTIONS AVAILABLE TO RATS ON BASELINE,

TREATMENT, AND TEST DAYS AND MEAN10-MIN INTAKE (IN ML) FOR EACH Gnoup

Note. Abbreviations: Rad — radiation; Sacc — saccharin;

Con = controls

Although baseline water intakes for the four groups did not differ, F(3, 28) p > .05, all four groups drank differing amounts of saccharin on test day, F (3, 28) — 81.94, p < .01 ; orthogonal F (1, 28) - 94.77, P < .01.

hom these results it can be seen that by Day 5 a conditioned taste aversion had developed in the radiation-saccharin group due to the pairing of radiation and a novel taste (saccharin) on the previous day. The control-saccharin group's Day 5

saccharin intake was elevated in contrast to the neophobia evidenced in the control-H20 group. The radiation-H20 group showed enhanced neophobia compared with the neophobia found in the control-H20 group due to the effects of radiation on the previous day.

Additional evidence for enhanced neophobia can be seen by comparing the radiation-H20 group's saccharin intake during its first saccharin exposure (Day 5) with a neophobia baseline, i.e., intakes during the first saccharin exposure for the other groups. This comparison revealed that the other three groups' intakes during their first saccharin exposure (control-H20 on Day 5, control-saccharin and radiation-saccharin on Day 4) were not significantly different from each other but were all different from that of the radiation-H20 group, F (3, 28) 4.27, p < .05; orthogonal F (1, 28) - 12.55, p < .01. The fact that these three groups were not different, even though they were first given saccharin on different days, suggests that there were no sequential effects due to differing deprivation levels*

An alternative explanation for the reduced saccharin intake on Day 5 in the radiationH20 group could be that

it resulted from a possible debilitating effect of the prior

irradiation. However, there are no overt signs of illness following a

100-1'. irradiation (Barker & Smith, 1974; Carroll & Smith, 1974)

making it an unlikely explanation. To obtain additional evidence on this

point, we ran two groups of rats (n 8) that were comparable with the

radiation-H20 and control-H20 groups except that they were

NEOPHOBIA AND ENHANCED NEOPHOBIA 461familiarized with the .1 % saccharin

solution for 10 days (10 min per day), One group was irradiated (100 r.) and the other sham exposed, and they were then allowed access to 10

min of water 30 min later. On the following day their mean saccharin

intakes were 17.1 ml and 15.6 ml, t(14) .096, p > .05, for the irradiated

and sham groups respectively. Therefore, there appeared to be no debilitating effects of the radiation

that could be measured by the amount of a familiar taste solution

ingested.Further evidence for neophobia can be

TIME ( MINUTES FIGURE l. Mean cumulative licks for

each minute of a 10-min single-bottle saccharin test given 24 hr after irradiation or sham exposure, with the best fitting straight lines drawn through the points (method of least squares). (Abbreviations: RAD = radiation; SACC saccharin ; CON = control.)

seen in the drinking pattern of the controlsaccharin group. This group's saccharin intake during the first saccharin exposure (Day 4) was significantly lower than the water intake on the day before and the

subsequent saccharin intake on the following test day. The mean saccharin intake on test day (Da,y 5) was significantly greater than the mean water intake on Day' 3, F(2, 14) 9.88, p < .01; orthogonal F(l, 14) — 19.65, p < .01.

EXPERIMENT 2In Experiment 1, enhanced

neophobia and neophobia were inferred from the reduced saccharin drinking in a 10-min singlebottle test. It was assumed that this reduction in saccharin intake in the neophobia and enhanced neophobia groups resulted from greater hesitation, i.e., longer pauses during the 10-min test. The purpose of Experiment 2 was to measure drinking continuously during the 10-min saccharin test to note how the differences among the groups developed.

MethodSubjects. Twenty-four naive male albino

rats, weighing 300—400 g, were housed and fed as in Experiment 1.

Apparatus. The conditions for the radiation exposure were the same as described in Experiment 1. Rats licked on a stainless steel drinking tube recessed behind a 2.5 X. 1 cm vertical slot. Licking was measured as the rat's tongue broke a beam of light that was imaged on a Clairex 903L photocell. The output from the photocell operated printout counters through a high-speed relay. The counters were set to print out once each minute.

Procedure. The procedure followed was identical to that of Experiment 1 except that a control-H20 group was not included (see Table 1) and drinking was: measured in the experimental box rather than in the home cage. Cumulative licks were recorded for each rat on Days 4 and 5 during each minute of the 10-min test.

Results and DiscussionFigure 1 shows Day 5 mean

cumulative licks as a function of time for each of the three groups. The data points for each group were fitted with

106

462 CARROLL, DINC, LEVY, AND SMITHa straight line using the method of least squares. It can be seen that early in the I()-min period the rates of licking develop in linear patterns but the slopes are distinctly different for each group, F(2, 21) = 26.04, p < .01* Thus, it appears from these data that the differences among groups observed in Experiment 1 after 10 min of saccharin drinking were produced by consistent differences in drinking rates that appeared early in the drinking period.

In order to show that the neophobia seen in the radiation-H20 group in Figure 1 was enhanced by the previous radiation treatment, the drinking rates (slopes) of the three groups were compared on the day when they first received saccharin (see Figure 2). The Day 4 slopes for the radiation-saccharin and control-saccharin groups were the same; however, they both were markedly greater than the Day 5 slope for the radiation-H20 group, F (2, 21) 4.68, p < .05; orthogonal F (1, 21) — 9.35, p < .01 e

Since local licking rates have been shown to be constant at approximately 5—7 licks/ sec (Corbit & Luschei, 1969), the dif-

o 2 4 6 8TIME MINUTES )

FIGURE 2. Mean cumulative licks for each minute during rats' first 10-min single-bottle exposure to saccharin (I)ay 4 for the Rad-Sacc and Con-Sacc groups and Day 5 for the Rad-H20 group), with the best fitting straight lines drawn through the points (method of least squares). (Abbreviations: RAD radiation; SACC saccharin; CON = control.)

ferences in drinking rates observed in this experiment must be explained by differences in the lengths of pauses between bouts. Longer pauses due to the hesitancy associated with neophobia would thus produce lower overall drinking rates. However, a more fine-grained picture of drinking will be necessary before differences in pauses after bouts can be analyzed,

EXPERIMENT 3Brackbill et al. (1971), in a I-hr

drinking test, failed to find enhanced neophobia in rats previously poisoned by apomorphine. However, in Experiment 2 of the present research, enhanced neophobia as a result of previous radiation exposure was shown to appear early in a 10-min drinking test. This discrepancy in results suggests that enhanced neophobia may be short-lived, and this "fear" of the novel solution may possibly be overcome during a 60-min drinking test. The purpose of this experiment was to measure periodically the saccharin intake of previously irradiated rats to determine at what time neophobia or enhanced neophobiaIS overcome.

MethodSubjects. Thirty-two naive male albino

rats, weighing 250—350 g, were housed and fed as in Experiment 1.

Procedure. The procedure followed on Days 0-4 was identical to that in Experiment 1 (see Table 1). On Day 5 (test

NEOPHOBIA AND ENHANCED NEOPHOBIA 463day) all rats were given 60-min access to a . 1 co sodium saccharin solution. The saccharin was presented to the rats in 100-ml graduated cylinders so that fluid intakes could be measured (±.5 ml) every 10 min. At the end of 60 min, a 24-hr two-bottle (saccharin vs. water) test was begt..m.

Results and DiscussionA comparison of the amount of

saccharin consumed during each 10-min interval for the four groups revealed that the only interval in which there were significant differences among groups was the first 10-min interval, F(3, 28) — 13.9, p < .01. At the end of this first 10-min period, each group had consumed a different amount of saccharin, orthogonal F (1, 28) = 40.67, p < .01.

The mean cumulative intakes on test day (Day 5) for all groups at the end of each

TABLE 2MEAN CUMULATIVE SACCHARIN INTAKE (IN ML)

AT THE END OF SIX 10-MIN INTERVALSON TEST DAY FOR EACH GROUP

Group

10

2.448,565.75

Minutes of saccharin

9.9416.4413.63

intake

50

11.69 18.50 16.06

60

15.8720E0019.44

Rad-SaccRad-H20 Con-SaccCon.H20

Note. Abbreviations: Rad — radiation; Sacc saccharin; Con control.

10-min interval are presented in Table 2. An analysis of cumulative saccharin intake at the end of each of the 10-min intervals indicated that all groups were different for the first 50 min of drinking (p < .01). On the other hand, the 60-min cumulative intakes for the four groups did not differ because of subtle changes in intakes throughout the 60-min period, F (3, 28) 2.72 p > .05. These results may explain Brackbill et al.'s (1971) failure to produce enhanced

neophobia in a I-hr test; however, no direct comparison can be made since there were many procedural differences between their study and the present one. In addition, the fact that the effects of enhanced neophobia disappeared within the I-hr test provides further evidence against lingering debilitation as an explanation for the radiation-H20 group's decrement in saccharin intake.

The use of a I-hr single-bottle test as a dependent measure in this experiment resulted in an apparent extinction of the saccharin aversion by the end of 1 hr of saccharin access. Therefore, a 24-hr two-bottle(saccharin vs. water) test was initiated at the end of the one-bottle test to determine whether the conditioned taste aversion and enhanced neophobia were still present after 24 hr. The two-bottle test data were converted into saccharin-preference scores which were the percentage of saccharin solution intake of the total fluid intake. The radiation-saccharin group showed a significantly decreased preference for the saccharin solution (.50) when compared with the radiation-H20 (.80), control-saccharin (.81), and control-H20 (.83) groups, F (3, 28) 0.0, p < .01; orthogonal F (l, 28)

.01. These results indicate that the conditioned taste aversion was longer lasting than the effects of neophobia and of enhanced neophobia as measured by a two-bottle 24hr drinking test.

EXPERIMENT 4The first three experiments have

demonstrated neophobia in the albino rat and the enhancement of this neophobia due to a previous

exposure to ionizing radiation. However, a large number of

conditioned taste aversion experiments have used poisons rather than ionizing radiation as the

10.06 11.93

464 CARROLL, DINC, LEVY, AND SMITHaversive stimuli (e.g., Garcia & Koelling, 1967 ; Nachman, 1970). Radiation-produced taste aversions have been reported to be stronger and more resistant to extinction than aversions produced by poisons (Barker & Smith, 1974; Garcia & Koelling, 1967). Because of these differences it was necessary to test for enhanced neophobia after poisoning. In this experiment, LiCl, which has been widely used as a stimulus to produce taste aversions, was selected as the toxic agent.Ilethod

Subjects. Forty-eight naive male albino rats, weighing 300-400 g, were housed and fed as in Experiment 1.

Procedure. The procedure was similar to that in Experiment 1. On Day 0 the 48 rats were deprived of water. In order to accustom the animals to drinking at a certain time each day, they were given access to water for 1 hr on Day l, for 30 min on Day 2, and for 10 min on Day 3 at approximately 1100 hours* On Day 4 (treatment day) 24 rats were given 10-min access to *1 0 0 sodium saccharin (see Table 3). Immediately after drinking, 12 rats were given a 2% body weight ip injection of .15 M LiCl (saccharin-LiCl), and 12 rats were given a 2% body weight ip injection of .15 M Na,Cl (saccharin-NaCl). The other 24 rats were given 10-min access to tap water, followed immediately by a 2% body weight ip injection of .15 LiCl (H20-LiC1) for 12 rats and of .15 M NaCl (H20NaCl) for the remaining 12 rats. On I)ay 5 all rats were given 10-min access to saccharin solution.

Results and DiscussionThe mean fluid intakes for all

groups on Days 3, 4, and 5 are presented in Table 3. Although baseline water intakes for the four

NEOPHOBIA ENHANCED NEOPHOBIA 465AND

groups did not differ, F (3, 44) 1.55, p > .05, all four groups drank differing amounts of saccharin on test day, F (3, 44)

102.4, p < .01; orthogonal F (1, 44)

These results are similar to those produced in Experiment 1 in which ionizing radiation was used as the aversive stimulus. On test day the saccharin-LiCl groups showed a profound taste aversion due to the pairing of lithium poisoning and a novel taste (saccharin) on the previous day. The H2()LiCl group showed marked enhanced neophobia, compared with the neophobia in the H20-NaCl group, due to the aversive effects of poisoning on the previous day. Saccharin drinking for the H20-NaCl group's first saccharin exposure (Day 5) reflected neophobia in contrast with the saccharin intake for the saccharin-NaCl group's second saccharm exposure (Day 5).

Enhanced neophobia can also be seen by comparing the intake of the H20-LiCl group on test day with a neophobia baseline. This comparison revealed that the other three groups' intakes during their first saccharin exposure on Day 5, saccharinNaCl and saccharin-LiCl on Day 4) were significantly different from that of the H20LiCl group, F(3, 47) 14.95, p < .01; orthogonal F (1, 47) 43.47, P < .01. As was observed in Experiment 1, although the three groups were exposed to saccharin on different days, there appeared to be no effect due to differing deprivation levels.

Additional evidence for neophobia was found in the saccharin-NaCl group. The saccharin intake on Day 4 i„vas significantly lower than the water intake on the day before and the subsequent saccharin intake on the following test day. The test day (Day 5) saccharin intake was not, however, different from the baseline water intake, F ('2, 22)

14.3, p < .01; orthogonal F(l, 22)

It is possible that the H20-LiCl group's decrement in saccharin intake on Day 5 was due to a debilitation lingering '24 hr after the LiC1 injection. Hmvever, Nachman's (1970) data suggested that there are no lingering sickness effects that affect a short-term test of fluid intake given 24 hr

TABLE 3SOLUTIONS AVAILABLE TO RATS ON BASELINE,

TREATMENT, AND TEST DAYS AND MEAN 10-MIN INTAKE (IN ML) FOR EACH GROUP

Note. Abbreviation: Sacc — saccharin,

after the LiCl injection. To test for the possibility of a lingering debilitation in the present experiment, two additional groups were run (n — 8). These groups were familiarized with the .1 % saccharin solution for 8 days (10 min/day) and were then allowed ad-lib access to saccharin for 1 day. They were then put on a saccharin-deprivation schedule similar to the water-deprivation schedule described above. On treatment day they received 10 min of access to tap water; then one group was given a 2% body weight injection ip of LiCl and the other an equal volume of NaCl. the next day (test day) each group was given a 10-min saccharin test. Their intakes on test day were 18.4 (LiCl group) and 18.8 (NaCl group), and this difference was not significant, t(14) = 0.17, p > .05.

EXPERIMENT 5Nachman (1970) conditioned taste

aversions in rats by injecting them with LiCl after saccharin ingestion. He found that as the delay between saccharin consumption and LiCl injection increased, the strength of the saccharin aversion decreased, up to 8 hr, The aversions observed in the 8-hr and 12-hr

466 CARROLL, DINC, LEVY, AND SMITHdelay groups did not differ, but they were significantly different from that of the control rats. Nachman suggested that the decrement in saccharin consumption observed in the. 8- and 12-hr delay groups relative to the NaCl-injected controls may be an example of enhanced neophobia rather than conditioned saccharin aversion. He did not, however, run the appropriate control groups to test this hypothesis. In Experiment 4 of the present research, enhanced neophobia has been demonstrated in a 10-min onebottle test as a result of LiCl poisoning on the previous day, Since Nachman also used a 10-min one-bottle test to measure the taste aversion, it is possible that he did indeed observe enhanced neophobia in his 8- and 12-hr delay groups. It is also possible that enhanced neophobia cannot be demonstrated with Nachman's procedure because his 10min test for aversion was not given until 3 days after his conditioning day. The purpose of this experiment was to determine whether enhanced neophobia could be demonstrated using Nachman's procedure and whether it accounted for the saccharin aversion noted in his 8- and 12-hr-delav groups.

MethodSubjects. Twenty-four naive male rats,

weighing 250-330 g, were fed and housed as in Experiment 1.

Procedure. The procedure was identical to that described by Nachman (1970)E On Day 0 all rats were deprived of water; they were given 10-min daily access to water on Days 1—4 in their home cages. 'I'he procedure for Days 5—8 is illustrated in Table 4. On Day 5 (treatment day) 12 rats were given 10-min access to .25% sodium saccharin. Immediately after this drinking period, six rats

were given a 2% body weight ip injection of .15 M LiCl (saccharin-LiCl), and six rats were given a 2% body weight ip injection of .15 M NaCl (saccharin-NaCl). The remaining 12 rats were given 10-min access to water. Immediately after this drinking period, six rats were given a 2% body weight ip injection of .15 M LiCl (H20-LiCl), and six rats were given a 2% body weight ip injection of M NaC1 (H20-NaC1). On Days 6 and 7 811 rats were given 10-rnin access to water

followed by an additional 20-min access to ensure drinking. The water intakes of rats in the H20-NaCl group were limited to the mean intake of rats in the H*O-LiCl group, since the water intakes of the rats in the H20-LiCl group were depressed because of a water aversion. On Day 8 (test day) all rats were given 10-min access to the .25% sodium saccharin solution.

Results and Discussion

Mean fluid intakes for all groups on Days 4—8 are presented in Table 4. Although baseline water intakes for the four groups did not differ, F (3, 20) - .738, p < .05, there were differences among the groups on test day. The H20-LiCl and H20-NaCl groups were not different from each other, but they were each different from the saccharin-LiCl and saccharin-NaCl groups which were also different from each other, F(3, 20) = 17.8, p < .01 ; orthogonal F (1, 20) = 62.76, p < .01.

Since the test day intakes of the H20-LiCl and H20-NaCl groups did not differ, it appears that enhanced neophobia was not produced in this study, using Nachman's procedure in which testing is postponed for 3 days. In Nachman's study the decreased saccharin consumption in the 8- and 12-hrdelay groups relative to the NaCl-injected controls must be conditioned saccharin

NEOPHOBIA AND ENHANCED NEOPHOBIA 467aversion, even after these long delays, rather than enhanced neophobia. If one observes intakes during the first saccharin exposure for all four groups, i.e., saccharinLiCl and saccharin-NaCl on Day 5 and H20-LiC1 and H20-NaC1 on Day 8, it appears that the H20-LiCl group drank less than all the others; however,

the four groups' intakes were not significantly different, .869, p > .05. Although the groups that had received saccharin for the first time on Day 8 had been subjected to a different deprivation sequence than those that received their first exposure on Day 5, this factor did not produce a difference in intakes among the groups in a 10-min test.

In addition to the neophobic effect found in the H20-LiCl and the H20-NaCl group on test day (Day 8), a comparison of the four groups' intakes on treatment day (Day 5) also revealed that the two groups that received saccharin drank significantly less than the two groups that received water, F (3, 20) = 4.0, p < .05; orthogonal F(1, 2()) 9.1'2, p < .01. Further evidence for neophobia was found in a comparison of 10-min intakes for the saccharin-NaCl group on Days 4, 5, and 8. This group's intake during its first saccharin exposure (Day 5) was significantly lower than its water intake on Day 4 or

saccharin intake on Day 8, and there was no difference in intake on Day 4 and Day 8, F (2, 15) 10.23, p < .01; orthogonal F(1, 15) - 19.71, p < .01.

An interesting result of this experiment was the decrement in water intake in the H20LiCl group on Days 6 and 7. A comparison of 10-min water

intakes on Day 6 for saccharin-LiCl, H20-LiCl, and saccharin-NaCl

groups revealed that the intake of the H20LiCl group was significantly lower

than the other two groups because of a water aversion, 22.04,

p < .01; orthogonal = 41.86, p < .01. Since intake was limited in the H20-NaCl group, this group was not included in the analysis. A similar companson of the 30-min intake on Day 6 produced the same results; i.e., the 1-120LiCA group's intake was significantly lower than the other two groups, F(2, 15)16.87, p < .01; orthogonal F (1, 15) 33.73, p < .01. These comparisons were also made for the three groups' 10- and 30-min water intakes on Day 7; however, only the H,O-LiCl group showed a significant water aversion during the 10-min test, F(2, 15) = 5S1, p < .05 ; orthogonal F(1, 15) - 10.96, < .01.

TABLE 4SOLUTIONS AVAILABLE TO RAT,s ON Days 4-8 AND MEAN 10-MIN FLUID

The water intakes of the H20-NaCl group were limited to the mean intakes of the H20-LiCl groups on Days 6 and 7. 'Thus the two groups' deprivation levels were comparable prior to testing on Day 8.

INTAKE (IN ML) FOR EACH GROUP

468 CARROLL, DINC, LEVY, AND SMITHThe conditioned water aversion found

in this study agrees with previous findings (Garcia & Koelling, 1967; Nachman, 1970; Nachman & Jones, 1974). However, others have shown that conditioning with nonnovel solutions resulted in weakened or attenuated taste aversions (Elkins, 1973 ; Farley, McLaurin, Scarborough, & Rawlings, 1964; McLaurin, Farley, & Scarborough, 1963; Revusky & Bedarf, 1967).

On Day 6, it is interesting to note that the saccharin-LiCl and saccharin-NaCl groups consumed identical quantities of water in 30 min, This is further evidence that there are no lingering "sickness" effects 24 hr after a LiCl injection that are reflected in a diminution of intake.

GENERAL DISCUSSION

In the present series of experiments it has been reliably demonstrated that neophobia and enhanced neophobia occur in the albino rat. In Experiments 1 and 4 it was shown that rats drinking a .1 % saccharin solution for the first time during a 10-min test showed a significant decrease in consumption when compared with either the previous day's water consumption or the following day's saccharin consumption. Furthermore, it was shown that the magnitude of the neophobia could be enhanced when the rat was either irradiated or given LiCl poisoning on the previous day.

In Experiments 2 and 3 the development and extinction of neophobia and enhanced neophobia were studied. In Experiment 2 it was showm that the differences in saccharin consumption among the groups that displayed neophobia, enhanced neophobia, and conditioned taste aversion in Experiment 1 were due to differences in the drinking rates that appeared very early and were present throughout the 10-min drinking test. InExperiment 3 differences among the fourtreatment groups used in Experiment 1 were again found in the first 10 min of saccharin drinking. However, the most surprising finding was that in subsequent 10-min

intervals of this test, no differences in saccharin intakes were observed* Differences in intakes that occurred during the first 10 min resulted in significantly different cumulative intakes for each of the four groups up to 50 min of drinking. However, cumulative intakes did not differ after 60 min of drinking.

Experiment 5 demonstrated that interposing 2 days of water drinking between LiCl poisoning and the first saccharin exposure eliminated enhanced neophobia in a 10-min test. It is assumed, based on the results from Experiment 4, that enhanced neophobia would have been seen if the test had been given 24 hr after lithium poisoning. The interaction of longer delays between LiCl poisoning and saccharin exposure and the effect of interposed water drinking using the Nachman (1970) procedure has not yet been studied; for example, it is not known whether a significant effect due to enhanced neophobia u-ould have been produced with 1 day of interposed water drinking.

The present results have described neophobia and enhanced neophobia in the albino rat as short-lived phenomena, which are present during the first 50 min of a singlebottle test with fluid-deprived rats. Since Richter (1953) and Barnett (1957) compared the neophobic response of wild rats in tests of daily food intake with the responses of albino rats, it is possible that by the time food intake was first measured, effects due to neophobia and enhanced neophobia in the albino rat had already disappeared* More sensitive tests would be needed to make an accurate comparison of neophobia and enhanced neophobia in wild and albino rats.

Assuming that the present results obtained with saccharin can be generalized to other solutions, the existence of neophobia and enhanced neophobia in the albino rat has important implications for feeding and drinking studies that employ short-term dependent measures. In designing such studies, one should be careful to include the appropriate control groups to allow

NEOPHOBIA AND ENHANCED NEOPHOBIA 469measurement of the effects due to neophobia and/or enhanced neophobia, If long-term tests are used, it seems from Experiment 3 that these controls are not necessary since the effects of neophobia and enhanced neophobia are overcorne during this longer period of time (at least 1 hr).

Another implication of the present findings is specifically related to research involving taste aversion conditioning. There is some recent evidence that suggests that neophobia may play an important role in the formation of conditioned taste aversions (Nachman & Ashe, 1974). Several studies have already demonstrated that rats do not learn a taste aversion to a solution that does not evoke a neophobic response as well as to one that does (Kalat & Rozin, 1973; Nachman & Jones, 1974; Revusky & Bedarf, 1967). It would be expected that the degree of neophobia resulting from the initial presentation of a taste solution, as measured by tests similar to those reported in this article, might be a good predictor of a subsequent taste aversion resulting from the pairing of that taste with an aversive stim-

Since wild rats appear to exhibit much more profound neophobia than albino rats, one would expect to see a stronger taste aversion in wild rats if the degree of neophobia is indeed a good predictor of aversion. The taste aversions in wild versus albino rats may differ in terms of aversion strength as well as the maximum CS—UCS delays over which conditioning can take place.

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(Received July 29, 1974)