Taste-sickness associations in youngrats over varying delays, stimulus, and test conditions

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1 Animal Learning & Behavir 1980, 8(4), Taste-sickness assciatins in yungrats ver varying delays, stimulus, and test cnditins GERARD M. MARTIN and W. K. TIMMINS Australian Natinal University, Canberra, A.C. T., Australia We shwed, as had previus investigatrs, that yung rats frmed taste-sickness assciatins that were weaker than thse f mature rats; assciatins were nt frmed ver a delay greater than 45 min, and aversins did nt survive a 60-min test sessin. The difficulty yung rats had withhlding cnsumptin and their pr sensitivity t taste and sickness cntributed t the weak aversins. Chice tests revealed aversins that had apparently extinguished during a n-chicetest, and animals that were allwed t mature prir t the first test readily withheld cnsumptin fr 60 min. Furthermre, yung rats frmed an aversin ver a delay f 2.5 h when the cncentratins f saccharin and lithium chlride were increased. Aversins t the strnger saccharin did nt extinguish ver tw ne-bttle tests and were retained fr 52 days. The differences between experiments that have successfully demnstrated gd learned aversins in yung animals and thse that have nt are extensive. Typically, tw age grups are examined. Age f the yung grup at the time f training has varied frm 12 days (Gregg, Kittrell, Dmjan, & Amsel, 1978) t 29 days (Baker, Baker, & Kesner, 1977). Furthermre, the flavring and sickness-inducing agents used, the duratin f expsure t the taste, the mde f presenting the taste at training and test, and the interval between training and test vary quite dramatically between experiments. These differences have resulted in the cntrasting claims that animals f 23 and 29 days f age frm taste aversins with difficulty (Baker et ai., 1977; Klein, Dmat, Hallstead, Stephens, & Mikulka, 1975) and that 15-day-ld rats frm taste aversins ver a delay f 2 h (Gregg et ai., 1978). EXPERIMENT 1 In Experiment I, we determined an age at which the ability f yung rats t learn flavr aversins seemed impaired under ur labratry cnditins. In later experiments, we examined varius factrs that might be respnsible fr the impairment. Subjects. Ninety-eight female Wistar hded rats frm the The authrs thank the Department f Psychlgy at the Australian Natinal University fr financial supprt thrughut this experiment. We thank Anne Wells fr technical assistance and W. P. Bellingham fr discussin at the time f experimentatin. We als thank S. H. Revusky fr his cmments n the earlier drafts f this manuscript, Gerard M. Martin's present address is: Department f Psychlgy, Memrial University, St. Jhn's, Newfundland, Canada AlB 3X9. W. K. Timmins' present address is: D.D.LA.E., Schl f Arts, Darling Heights, Twmba, Queensland, Australia Psychlgy Department's breeding clny at Australian Natinal University were assigned t varius age and experimental cnditins as litters became available. Prcedure. Rats, which were 18, 28, 38, r 48 days f age, were mved t individual wire cages that were 21 x 21 x 20 cm high; fd and tap water were prvided ad lib. A restricted drinking schedule was intrduced n the fllwing day; animals were allwed 10 min access t tap water at 1000 hand 3 h access frm 1200 t 1500 h. The experimental grups had.1070 saccharin slutin substituted fr tap water during the IO-min drinking sessin at 1000 h (n = II, 8, 8, and 8 fr the 23-, 33-, 43-, and 53-day-ld grups, respectively). They were injected intraperitneally (ip) with.3 M LiCI (1.27 g/loo ml f distilled water), at a dsage f I ml/l g bdy weight, immediately after the bttle was remved. Animals in the saline cntrl grup als had saccharin substituted fr tap water, but were injected with an equivalent vlume f physilgical saline (n = 9, 8, 8, and 8 fr the 23-, 33-, 43-, and 53-day-ld grups, respectively). Animals in the LiCI cntrl grup received tap water as usual and were injected with an equivalent vlume f LiCI (n=7, 8, 7, and 8 fr the 23-, 33-, 43-, and 53-day-ld grups, respectively). All animals were given access t a saccharin slutin fr I h 3 days later at 1000 h. Cnsumptin was measured after 10 min and again after 60 min. Results and Discussin One-way analyses f variance shwed that there were n differences between grups f the same age n the training day (Fs < 1). Figure 1 shws the mean amunt f saccharin cnsumed ver the 10- and 6O-min tests. All age grups differed reliably ver the 10-min test: 23 days [F(2,24) = 11.79, p <.01], 33 days [F(2,2l)=4.92, p <.05], 43 days [F(2,20) = 6.85, p <.05], and 53 days [F(2,21) = 3.33, p <.01]. Scheffe multiple cmparisns shwed that the grup that had saccharin cnsumptin paired with Liel n the training day cnsumed reliably less saccharin than the cntrl grups (all ps <.05). All grups, with the exceptin f the 23-day-ld grup [F(2,24) =.80, p >.05], als differed reliably (ps <.05) ver the 6O-mintest. Our 23-day-ld rats, like thse f Baker et al. Cpyright 1981 Psychnmic Sciety, Inc /80/ $00.75/0

2 530 MARTIN AND TIMMINS TEN MINUTE TEST EXPERIMENTAL E 160 W l4 0 :::i: U J LL 60 W :::!; Li CI CONTROL r SALINE CONTROL R I- I.':,,::',,:' "/ "",,,:" t; ":":: I, -.:_:: " [e'- \::: i, f- - ;:.:'.,-' I/; /:;; f- ",'. ly 1/ - r- ; t- -; PJ8 '/""' t- - r;; li '/ - 2 ::L: - 23 DAYS 33 DAYS 43 DAYS 53 DAYS AGE AT TRAINING Figure l. Mean amunt f saccharin cnsumed ver 60 min n the test day by the grups in Experiment 1. The lwer white prtin represents the fluid cnsumptin ver the first 10 min. (1977), maintained an aversin ver a shrt test sessin. Our findings, hwever, are nt cnsistent with thse f Klein et al. (1975), wh failed t demnstrate an aversin in yung rats when a shrt test sessin was used. Klein et al. (1975) maintained their animals n f their preexperiment fluid cnsumptin. Other investigatrs, like us, maintained their animals n a limited access schedule. Hence, the need fr fluid repletin by the yung rats in Klein's experiment may have masked the aversin. EXPERIMENT 2 The fllwing tw experiments determined whether the nature f the test and the age f the animals at the time f test cntributed t the disappearance f an aversin ver 60 min in 26-day-ld rats. In Experiment 2A, ur earlier findings n 26-day-ld rats were replicated. In additin, the yung rats were given a chice between saccharin and tap water n the day after-the apparent extinctin f the taste aversin. The presence f a saccharin aversin during the mre sensitive retest wuld indicate that the yung rat's difficulty withhlding cnsumptin cntributed t the disappearance f an aversin during the first test. In Experiment 2B, the rats were trained when 23 days ld and were tested when 33 days ld. The maintenance f a saccharin aversin in 33-dayld rats ver 60 min, in cntrast with its disappearance in 26-day-ld rats, wuld als indicate that the yung rats' difficulty withhlding cnsumptin cntributed t the apparent extinctin f the saccharin aversin. Experiment 2A. The materials used and prcedure fllwed were the same as thse emplyed in Experiment I. Eighteen I :, nimals, which were 23 days ld, were given.ll1j saccharin mtead f tap water during the looo-h drinking sessin. Half these animals were injected with Liel and the ther half were injected With an equal vlume f physilgical saline. The LiCI cntrl grp (n =) was given tap water during the I,OOO-h drinking sessin. This grup was injected with LiCI after the tap water was remved. A : 1I1J sccharin slutin was substituted fr tap water fr 60 nun dunng the looo-h drinking sessin when the rats were 26 days ld. On the fllwing day, all rats were given a chice fr 60 min between tap water and.ll1j saccharin during the I,OOO-h drinking sessin. Experiment 2B. This experiment was the same as Experiment I up t and including when the rats were 23 days f age. There were eight rats each in the experimental, the LiCI, and the saline cntrl grups. The rats were allwed ad lib access t fd and water frm 24 (Q 29 days f age. The deprivatin prcedure was then reinstated. A.1% saccharin slutin was substituted fr tap water during the I,OOO-h drinking sessin when the rats were 33 days f age. Results and Discussin Experiment 2A. The findings frm the first test day replicated thse bserved in Experiment 1. A reliable difference was btained n the first test day ver the 10-min test [F(2,23) = 5.49, p <.05]. Scheffe multiple cmparisns shwed that the experimental (mean = 2.7 ml) grup drank less than the saline (mean = 3.9 ml) and LiCl (mean = 4.1 ml) cntrl grups (ps <.05). A reliable difference between grups was nt btained when the analysis was carried ut n the 6O-min saccharin cnsumptin (F < 1). The retest data were cnverted t suppressin ratis (retest saccharin cnsumptin/retest saccharin + retest tap water cnsumptin). The grups differed reliably ver the lo-min retest sessin [F(2,23) = 13.35, p <.01] and ver the whle f the 6O-min sessin [F(2,23) = 7.87, p <.01]. Scheffe multiple cmparisns shwed that the experimental grup had a lwer saccharin preference than bth cntrl grups ver bth the lo-min (mean =.42 fr the experimental vs. mean =.72 and mean =.69 fr the LiCI and saline cntrl grups, respectively) and the 6O-min (mean =.45 fr the experimental vs. mean =.71 and mean =.68 fr the LiCl and saline cntrl grups, respectively) tests (all ps <.05). Apparently, the mre sensitive chice test is required t demnstrate an aversin in yung rats when the test sessin is 60 min in duratin. Experiment 2B. The rats retained the saccharin aversin ver 10 days, and the aversin did nt extinguish during the 6O-min test sessin. There were reliable differences between the grups ver bth the 10-min [F(2,2l) = 25.30, p <.01] and 60-min sessins [F(2,21) = 15.69, p <.01]. Scheffe multiple cmparisns shwed that the experimental grup drank reliably less saccharin (means = 2.1 and 7.5 ml fr 10 and 60 min, respectively) than either the saline (means = 5.8 and 10.9 ml fr 10 and 60 min, respectively) r the LiCI (means = 7.5 and 14.0 ml fr 10 and 60 min, respectively) cntrl grup (all ps <.05).

3 TASTE SICKNESS ASSOCIATIONS IN YOUNG RATS 531 EXPERIMENT 3 Twenty-three-day-ld rats shwed a strng aversin t.1fjl saccharin when a chice test was emplyed. The fllwing experiment assessed further the ability f yung rats t frm taste-sickness assciatins under ur stimulus cnditins. We varied the delay between the saccharin and the injectin f the LiCI and measured the aversin frmed by the yung rats. Frmatin f a tastesickness assciatin ver a lng delay wuld indicate that the aversins frmed by yung rats were cmparable t thse bserved in adults when the difficulty yung rats have withhlding cnsumptin was taken int accunt. Failure t frm taste-sickness assciatins ver lng delays wuld indicate that ther factrs als cntribute t the weak aversins bserved in yung rats l2i EXPERIMENTAL [', '1 LiCI CONTROL 60 MINUTE TEST 10 MINUTE TEST Water was prvided frm tw bttles thrughut the experiment and the prcedure was the same as in Experiment I. Frty-eight rats were given a slutin f.11ji saccharin instead f tap water when they were 23 days ld. They were injected with LiCl 0 (n = 7), 15 (n = 8), 30 (n = 8), 45 (n = 8), 60 (n = 9), r 120 min (n = 8) after the saccharin was remved. Seven LiCI cntrl rats drank tap water when 23 days ld and were injected with an equivalent vlume f LiCI immediately after the fluid was remved. Three days later, all rats were given a chice between tap water and saccharin fr 60 min. Results Preference ratis frm the test day are presented in Figure 2. An analysis f variance shwed that the grups differed reliably ver the lo-min test sessin [F(6,48) = 2.30, p <.05]. Scheffe multiple cmparisns shwed that the grup that was pisned immediately and 15 min after saccharin remval had lwer saccharin preference ratis than did the cntrl grup (all ps <.05). The remaining grups did nt differ reliably frm the cntrl grup (all ps >.05). The grups differed reliably ver the 60-min test sessin [F(6,48) = 4.49, P <.01]. Scheffe multiple cmparisns shwed that the grups that were injected 0, 15, 30, r 45 min after saccharin remval had lwer saccharin preference ratis than the cntrl grup (all ps <.01). The remaining grups did nt (all ps >.05). The shrt taste-sickness delay cntrasts with the delays f 8 and 12 h that have been btained with adult rats (Nachman, 1970). One cannt argue that the yung rats did nt shw an aversin because they culd nt withhld cnsumptin. Apparently, cnditins that are favrable t taste aversin learning in ld rats are nt apprpriate fr yung rats. 15 TEST IN MINUTES Figure 2. Mean saccharin preference ratis f grups that were injected with LiCI after saccharin cnsumptin (EXPERIMEN TALl r tap water cnsumptin (CONTROl.) in Experiment EXPERIMENT ONTROL Findings frm several experiments indicate that increases in the intensity f the flavr and sickness wuld help vercme the apparent weak aversins bserved in ur 23-day-ld rats. A lw dsage f LiCI that prduces a weak aversin in adult rats (Nachman & Ashe, 1973) des nt prduce an aversin in yung rats (Franchina, Dmat, & McCleese, 1979). Furteen-day-ld rats frm taste-sickness assciatins ver a delay f 2 h when the cncentratin f saccharin is.5% (Gregg et al., 1978), and they shw better retentin f a taste aversin with high, rather than lw, flavr cncentratins (Campbell & Alberts, 1979). We determined whether ur rats frmed strnger taste aversins under ur training and test cnditins when the cncentratin f saccharin was increased t 1.0fJI and the dsage f LiCI was increased t.65 M. The strength f a saccharin aversin was measured in three ways: Experiment 4A examined the extinctin f the aversin in rats that were trained when 23 days ld and tested when 26 days ld. Experiment 4B examined the extinctin f the aversin in rats that were trained when 23 days f age and tested when 72 days ld, and Experiment 4C determined whether 23-day-ld rats culd frm a

4 532 MARTIN AND TIMMINS taste-sickness assciatin ver a delay lnger than the 45 min bserved in Experiment 3. In all three experiments, the deprivatin prcedure was the same as that used in Experiment I. Rats in the experimental and saline grups had saccharin substituted fr tap water during the IO-min drinking sessin at 1000 h when they were 23 days ld. After saccharin remval, the experimental grup was injected with.65 M LiCI at a dsage f I ml/ioo g bdy weight, and the saline cntrl grup was injected with an equivalent vlume f physilgical saline. The LiCI cntrl grup was given tap water when 23 days f age and was injected with LiCl at a dsage equivalent t that given the experimental grup. All animals were tested n saccharin during the looo h drinking sessin. Measures f fluid cnsumptin were taken at the end f 10 and 60 min. Experiment 4A. The experimental, saline cntrl, and LiCl cntrl grups had 9, II, and 12 rats, respectively. The rats were tested n saccharin when 26, 27, and 28 days f age. Experiment 48. The experimental, the saline cntrl, and LiCI cntrl grups each cntained eight rats. After training, the rats were mved t grup cages. They were returned t individual cages and the deprivatin prcedure was reinstated when they were 72 days f age. The rats were tested n saccharin, when they were 75,76, and 77 days f age. Experiment 4C. There were eight rats in the LiCl cntrl grup and 40 rats in the experimental grup. The animals in the experimental grup were divided equally amng five grups and were injected with LiCI.5, 1.0, 1.5, r 2.5 h after the saccharin was remved. All animals were tested n saccharin when they were 26 and 27 days f age. One rat in the 1.5-h grup died prir t testing. Resultsand Discussin The grups differed reliably n the training day in Experiments 4A [F(2,29) = 5.72, p <.025], 4B [F(2,2l)=29.11, P <.01], and 4C [F(5,4l) = 8.90, p <.01]. Scheffe multiple cmparisns shwed that the experimental grups' saccharin cnsumptin in Experiments 4A (mean = 2.2 ml), 4B (mean = 2.4 ml), and 4C (means=2.l, 2.5, 1.9, 2.2, and 1.7 ml) and the saline cntrl grups' saccharin cnsumptin in Experiments 4A (mean = 2.1 ml) and 4B (mean = 2.3 ml) were reliably less (all ps <.05) than the tap water cnsumptin f the LiCI cntrl grups in Experiments 4A (mean=3.5 ml), 4B (mean =4.2 ml), and 4C (mean = 4.9 ml). Furthermre, crrelated t tests revealed that the cntrl grups' saccharin cnsumptin increased reliably (all ps <.05) between the first and the secnd test in Experiments 4A (mean = 4.8 t 7.9 ml and mean = 4.3 t 7.2 rnl, by the LiCI and saline cntrl grups, respectively), 4B (mean = 14.2 t 18.0 ml and mean = 14.0 t 18.1 ml, by the LiCI and saline cntrl grups, respectively), and 4C (mean = 4.3 t 8.0 ml, by the LiCI cntrl grup). These bservatins indicate that the 23-day-ld rats nticed the saccharin and that their fear f it disappeared ver repeated presentatins. A similar bservatin has been made n adult, but nt yung, rats by several investigatrs (e.g., Dmjan, 1977). The aversins bserved in Experiments 4A, 4B, and 4C were strnger than thse bserved t.1010 saccharin in the first three experiments. The grups differed reliably ver 60 min in Experiment 4A during Test 1 [F(2,29) = 4.03, p <.05] and Test 2 [F (2,29) = 6.19, p <.01], but nt Test 3 [F(2,29) = 1.68, p >.05]. Scheffe multiple cmparisns shwed that the experimental grup (means = 2.5 and 4.9 ml fr Tests 1 and 2, respectively) drank reliably less (all ps <.05) saccharin than did the LiCI (means = 4.8 and 8.0 ml fr Tests I and 2, respectively) and the saline (means = 4.5 and 7.5 ml fr Tests I and 2, respectively) cntrl grups. In Experiment 4B, the grups differed reliably ver 60 min during Tests I [F(2,21) = 22.60, p <.01], Test 2 [F(2,21) = 11.55, p <.01], and Test 3 [F(2,21) =4.5, p <.05]. Scheffe multiple cmparisns shwed that the experimental grup (means = 4.2, 10.0, and 15.6 ml fr Tests I, 2, and 3, respectively) drank reliably less saccharin (all ps <.05) than did the LiCI (means = 14.2, 18.0, and 20.1 ml fr Tests I, 2, and 3, respectively) and the saline (means = 14.0, 18.1, and 21.0 ml fr Tests 1, 2, and 3, respectively) cntrl grups. In Experiment 4C, the grups differed reliably ver 60 min during Test I [F(5,41) = 4.30, p <.01] and Test 2 [F(5,41) = 4.12, p <.01]. Scheffe multiple cmparisns revealed that all experimental grups drank reliably less (all ps <.01) saccharin than did the LiCI cntrl grup during Test 1 and that all grups, with the exceptin f the 2.5-h grup, drank reliably (all ps <.05) less than the LiCI cntrl grup during Test 2 (see Figure 3 fr a summary f the means). One ther difference between the findings f these experiments and the first three experiments was the absence f any differences between the grups during the first 10 min f Test 1 in Experiments 4A [F(2,29)= 1.76, p>.05] and 4C [F(5,41)= 1.63, n >.05]. Apparently, grup differences were masked by the absence f drinking during the first 10 min f the initial test. GENERAL DISCUSSION Our findings indicate that any attempt t draw cnclusins abut the ability f yung rats t frm a taste-sickness assciatin is fraught with difficulties. The perfrmance f yung rats varied as a functin f manipulatins in stimulus parameters and test prcedures. The imprtance f these manipulatins indicates that any experiment that fails t btain learned aversins in yung rats may have selected the wrng parameters. Furthermre, the manipulatins required t demnstrate learned aversins in yung rats may reflect differences between them and ld rats in assciative ability r in sensitivity

5 10 0 r , 80 z 60 a. :E 40 ::::> en z 20 U ii: 80 I U 60 U en 40 W 20 :E TEN MINUTE TEST EXPERIMENTAL [:'::':.:J LiCI CONTROL TEST 'L..---'---'-_...L...L.._.J...1-_'--JL..---'---'-_-'--l TEST J CONTROL TIME OF INJECTION (h) Figure 3. Mean amunts f saccharin cnsumed n the 2 test days by the grups in Experiment 4C. The lwer white prtin represents the fluid cnsumed in the first 10 min. t stimulus parameters and deprivatin prcedures emplyed. Klein et al. (1975) shwed that a chice test was required t demnstrate an aversin in yung rats. We cnfirmed this and shwed that yung rats still frmed weaker aversins than did ld rats when this difficulty was taken int accunt and the delay between the taste and sickness was increased. The latter finding was cnsistent with the bservatin that yung rats frm taste-sickness assciatins ver shrt, but nt lng, delays (Baker et ai., 1977). This was nt the case, hwever, when the cncentratins f saccharin and Liel were increased. Hence, ur findings agreed with thse f Gregg et al. (1978), wh reprted that 15-day-ld rats frm taste-sickness assciatins ver a delay f 2 h. They did nt btain taste-sickness assciatins ver a delay greater than 30 min when the rats were 12 days ld. Such a fail- TASTE SICKNESS ASSOCIATIONS IN YOUNG RATS 533 ure, in the light f ur findings, culd reflect either an inability f 12-day-ld rats t frm such assciatins r inapprpriate stimulus parameters. Similarly. Campbell and Alberts (1979) fund that W and 12-day-ld rats shwed retentin deficits when tested 5 r 10 days later. Such deficits culd reflect prblems with retentin r differences in sensitivity t the stimuli invlved. Furthermre, ur findings indicate that manipulatins in stimulus intensity alne are nt adequate t ensure an accurate assessment f the ability f yung rats t frm taste-sickness assciatins. Fr example, we fund an aversin t.lltj saccharin was revealed with a 1O-min, but nt a 6O-min, test. The reverse was true when 1.0ltJ saccharin was emplyed. REFERENCES BAKER, L. J., BAKER, T. B., & KESNER, R. P. Taste aversin learning in yung and adult rats. Jurnal fcmparative and Physilgical Psychlgy, 1977,91, CAMPBELL, B. A., & ALBERTS, J. R. Ontgeny f lng-term memry fr learned taste aversins. Behaviral and Neural Bilgy, 1979,25, DOMJAN, M. Attenuatin and enhancement f nephbia fr edible substances. In L. M. Barker, M. R. Best, & M. Drnjan (Eds.), Learning mechanisms in fd selectin. Wac, Tex: Baylr University Press, FRANCHINA, J. J., DOMATO. G. C., & MCCLESSE, D. Learning and retentin f sucrse taste aversin in weanling rats. Bulletin fthe PsychnmicSciety, 1979, ]4, GREGG, B., KITTRELL, E. M. W., DOMJAN, M., & AMSEL, A. 1ngestinal aversin learning in preweanling rats. Jurnal f Cmparative and Physilgical Psychlgy, 1978,92, KLEIN, S. B., DOMATO, G. G., HALLSTEAD, C., STEPHENS, I., & MIKULKA, P. J. Acquisitin f a cnditined aversin as a functin f age and measurement technique. Physilgical Psychlgy, 1975,3, NACHMAN, M. Learned taste and temperature aversins due t lithium chlride sickness after tempral delays. Jurnal f Cmparative and Physilgical Psychlgy, 1970, 73, NACHMAN, M., & ASHE, J. H. Learned taste aversins in rats as a functin f dsage, cncentratin, and rute f administratin f Lie!. Physilgy & Behavir, 1973, 10, (Received fr publicatin March 4, 1980; revisin accepted July 29, 1980.)