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Bivalent effects of wheel running on taste conditioning
Behavioural Processes 89 (2012) 36–38
Contents lists available at SciVerse ScienceDirect
Behavioural Processes journal homepage: www.elsevier.com/locate/behavproc
Bivalent effects of wheel running on taste conditioning Christine Dobek, C. Donald Heth, W. David Pierce ∗ University of Alberta, Edmonton, Alberta, Canada
a r t i c l e
i n f o
Article history: Received 29 August 2011 Received in revised form 22 September 2011 Accepted 17 October 2011 Keywords: Taste avoidance Taste preference Conditioning Wheel running Rats
a b s t r a c t We replicated the finding of bivalent conditioning of tastes by wheel running by Hughes and Boakes (2008), but without pre-exposure to the wheel. Rats received six days of conditioning with a flavoured solution presented for 10 min before a 40-min placement in a running wheel and another flavoured solution presented for 10 min after. A highly palatable liquid meal replacement was used as a vehicle for the flavours to encourage consumption, allowing us to equate before and after presentation intervals. Relative to a third flavour, we found that the taste preceding wheel running was consumed less, and the taste that followed wheel running was consumed more. Novel wheel running can therefore condition both taste avoidance and taste preference. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Avoidance of tastes or flavours can be conditioned with physical activity such as wheel running. Lett and Grant (1996) allowed hungry and thirsty rats 10 min to consume either a salt or sour solution followed by 30 min of confinement in a running wheel. On separate unpaired trials, these rats were allowed 10 min to consume the other solution and confined for 30 min in home cages. After three paired trials, rats avoided the solution that had been followed by wheel running as compared to the solution followed by home cage confinement. Lett and Grant (1996) concluded that rats show conditioned taste avoidance (CTA) when the flavoured conditioned stimulus (CS) is repeatedly followed by the unconditioned stimulus (US) of wheel running, a forward conditioning procedure (Boakes and Nakajima, 2009). Salvy et al. (2004) extended the running wheel procedure to backward conditioning, in which the flavour CS followed the wheel US. Relative to unpaired controls, rats given backward pairings drank more of the CS flavour, a result suggesting that the aftereffects of wheel running produce conditioned taste preference (CTP). This aftereffect seems to involve appetitive rather than aversive conditioning (see also Lett et al., 2000). If so, wheel running has bivalent properties that produce different conditioning effects depending on the temporal placement of the CS-taste. Subsequently, Hughes and Boakes (2008, Experiment 1) showed that a flavour presented after wheel running acquired a positive
∗ Corresponding author at: Department of Sociology, University of Alberta, Edmonton, Alberta, Canada T6G 2H4. Tel.: +1 780 492 0485. E-mail address: [email protected] (W.D. Pierce). 0376-6357/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.beproc.2011.10.009
valence relative to a flavour not paired with wheel running. In another experiment (Experiment 3) they demonstrated for the first time that both aversive and appetitive conditioning could occur within subjects, a bivalent effect of wheel running. In this study, rats were given access to one flavour before, and a second flavour after, wheel running. Tests showed avoidance of the flavour that preceded running and preference for the flavour that followed. However, the bivalent effects were found only in those rats that had been given eight 3-h pre-exposures to wheel running and not in those rats without this experience. Hughes and Boakes suggested that pre-exposure to wheel running increased the effectiveness of the appetitive process related to conditioned preference, decreased the aversiveness of the process leading to conditioned avoidance, or both. We believe it is premature to conclude that pre-exposure is necessary to obtain the bivalent effects of wheel running. Notably, in the bivalent study Hughes and Boakes provided rats with only 10 min access to the before flavour, but 30 min access to the after taste. The difference in access times equalized consumption of the before and after flavours, but may have also produced differential exposure to the two tastes, decreasing the effectiveness of the conditioning in two ways: Small sips of the flavour over the consumption interval would reduce the salience of the taste stimulus; or, sips late in the consumption interval would receive weak conditioning due to the delay between US and CS. In fact, delay between the termination of wheel running and exposure to the after taste reduces CTP (Hughes and Boakes, 2008, Experiment 2). Here, we replicate the Hughes and Boakes finding of bivalent conditioning, but without pre-exposure of the wheel running US. We used a highly palatable liquid meal replacement as a vehicle for the flavours to encourage consumption, allowing us to equate
C. Dobek et al. / Behavioural Processes 89 (2012) 36–38
before and after presentation intervals. Relative to a third flavour, we found that a taste preceding wheel running was consumed less, and a taste that followed wheel running was consumed more. That is, we obtained a bivalent effect of wheel running without pre-exposure of the wheel. 2. Method 2.1. Subjects Six male Sprague-Dawley rats, 41–45 days old at the start of the experiment and with a mean weight of 192 g, were used in the study. Rats were individually housed in clear polycarbonate cages (47 cm × 27 cm × 20 cm) with wood chip bedding. Feeding cages were identical, but without bedding. The room temperature was 22 ◦ C with lights off at 08:00 h and on at 20:00 h. Throughout the experiment animals, except as described in Section 2.3, had free access to water. Care of the animals complied with the guidelines of the University of Alberta Biological Sciences Animal Policy. 2.2. Materials Wheel running occurred in six Wahmann rat-running wheels (1.1 m circumference) with attached side cages (25 cm × 15.5 cm × 12.5 cm). Each rat was randomly assigned to a wheel. Turns were recorded at 1-min intervals by two microswitches activated by a cam situated above and below the axle of the wheel. The micro-switches, integrated with a computer system, ensured recording of only full wheel turns. Flavours were presented in solution with vanilla Ensure, a liquid meal replacement (Abbott Laboratories, Montreal Quebec). Three extracts—mint/peppermint, almond, and star anise—made by Club House (McCormick Canada, London Canada) were used as flavours. Flavoured solutions were presented in drinking bottles, with 1.5 ml of flavour extract mixed with 150 ml of Ensure. The flavours were assigned as either control, before, or after flavour with a rat randomly assigned to one of the six permutations. 2.3. Procedure The animals were acclimatized with unlimited water, but restricted food, for the first 6 days after arrival (Day 0). On Days 1, 2, and 6 each rat’s weight was recorded at 08:00 h followed by a presentation of 30 g of standard laboratory chow (Lab DietTM 5010 Rodent Diet, PMI Nutrition International, Inc., Brentwood, MO) in its home cage. At 20:00 h any remaining chow was removed and weighed. On Days 3, 4, and 5 the rats were given the control flavour. On these days, at 10:00 h, rats were weighed, transferred to feeding cages, and received 10 min of control flavour exposure. Subsequently, rats were transferred to their home cages for 40 min with no access to water, followed by another 10 min session of the control flavour, ending with a return to home cages with 30 g of chow and water. At 20:00 h, all remaining chow was removed and weighed. 2.3.1. Conditioning phase The conditioning phase started on Day 7 (Session 1) and proceeded for 6 days (to Session 6). At 10:00 h rats were weighed, placed in feeding cages with the before flavour for 10 min, and then transferred to running wheels for 40 min. Subsequently, the animals were transferred to the feeding cages where they received 10 min of access to the after flavour. Finally, they were returned to the home cages with free access to water and 14 g of chow. Water was weighed at 10:00 h and after wheel running. Any chow present at 20:00 h was removed and weighed.
37
2.3.2. Test phase At 10:00 h on Days 13 and 14, rats were weighed and given a two-bottle test in their feeding cages. One test (Before Test) compared consumption (g) of the control flavour to the before flavour, and the other (After Test) compared the control flavour to the after flavour. Three rats (randomly assigned) received the Before Test first while the others received the After Test first. After the first test, the animals were given 14 g of food and free access to water. Any remaining chow was removed at 20:00 h. The next day the rats received the opposite test. For the first test half of the rats, randomly chosen, received the control flavour on the left and half received it on the right. The position of the control flavour was switched to the other side for the second test. 3. Results 3.1. Acclimatization trials On the last day of acclimatization to the control flavour (Day 5), rats drank the Ensure solution before and after being placed in home cages. They drank a mean of 7.9 g (SEM ± 0.9) of the control Ensure before placement in home cages and 7.3 g (SEM ± 2.1) of the control solution after, t(5) = 0.39, n.s. 3.2. Conditioning trials Table 1 shows the mean wheel turns for each day of conditioning. Mean wheel turns significantly increased from the first day of conditioning to the last. The mean daily consumption of the before flavour and after flavour also increased significantly over the same period. On Session 6, mean consumption of the before flavour and the after flavour did not differ significantly, t(5) = 1.53, n.s. The slightly higher consumption of the before flavour is not surprising, because rats had been food restricted for 14 h at this time but only 40 min at the time they received the after flavour. 3.3. Consumption tests Fig. 1 shows the mean consumption (g) of the CS flavour and control solutions by temporal placement of the CS with respect to wheel running (US). On the Before Test, consumption of the conditioned solution was less than the control (M = 10.7, SEM ± 1.3). For the After Test, rats consumed more of the CS flavour (M = 11.2, SEM ± 1.4) than the control (M = 3.8, SEM ± 0.5). The interaction of flavour (conditioned or control) by temporal placement (before or after) was significant, F(1,5) = 34.93, MSe = 9.06, p = .002. 4. Discussion Our results show that wheel running has bivalent effects when paired with flavoured solutions. When the solution precedes the running, consumption of the flavour decreases, indicating aversive conditioning. When the solution follows running, consumption increases, showing appetitive conditioning. These effects do not depend on pre-exposure to wheel running, a result that generalizes the findings of Hughes and Boakes (2008) to situations in which wheel running is a novel stimulus. There are several differences between our study and that of Hughes and Boakes: We used younger rats, males rather than females, six rather than four sessions of conditioning, and consecutive rather than alternating sessions of conditioning. Although many of these factors are beyond the scope of our study, we did examine the possibility that our younger rats may have run at a higher rate than those of Hughes and Boakes, especially rats in the non-pre-exposed group. Estimates from the wheel running graph
38
C. Dobek et al. / Behavioural Processes 89 (2012) 36–38
Table 1 Means and (in parentheses) standard deviations for the number of wheel turns (1.1 m), and consumption (g) of the before and after flavours for sessions of the conditioning phase. Measure
F (df); MSe a
Conditioning sessions
Wheel turns Before flavour After flavour
1
2
3
4
5
6
144.8 (29.5) 7.8 (1.0) 3.8 (1.7)
195.7 (67.0) 8.0 (1.3) 8.8 (1.3)
349.3 (48.5) 8.5 (1.0) 9.0 (1.2)
347.7 (35.3) 11.5 (1.4) 9.3 (1.5)
316.2 (62.6) 10.7 (1.3) 10.3 (1.4)
398.8 (32.9) 12.2 (1.9) 9.8 (1.2)
5.90 (5,25); 10,028.2 9.89 (5,25); 2.251 13.47 (5,25); 2.502
a F-values, degrees of freedom (df) and mean squared error (MSe ) for the one-way repeated measures analysis of variance for days of conditioning. A 2 (Before vs After) by 6 (sessions) within-subjects analysis of variance of consumption showed a significant interaction F(5,25) = 4.38, MSe = 2.39. All F-tests were significant at the p < .05 level.
Control
CS Flavour
6
possible that the two additional days of conditioning, or the use of younger rats that tend to run faster, could have contributed to our findings. We suggest the use of palatable liquid meals as a useful procedure for the temporal assay of the reinforcing effects of wheel running. Lett et al. (2000) showed that the after effects of wheel running produced a condition place preference. Recently, Masaki and Nakajima (2008) obtained conditioned place aversion induced by wheel running, using a forward conditioning procedure. At this point, however, it is not clear when, or how quickly, these effects appear. Because our method allows for the presentation of short CS durations, it should be possible to use it to investigate the reinforcement process in more detail.
4
Acknowledgements
*
*
12
Consumption (g)
10 8
2 0 Before
After
A Discovery Grant (G121211127) from the Natural Sciences and Engineering Research Council of Canada (NSERC) to the authors supported this research. We thank our laboratory technician, Shannon Fischer, for her assistance in conducting this experiment.
Temporal Placement of CS References Fig. 1. Mean (with SEM bars) consumption (g) on test days for the CS flavours presented before and after wheel running compared to the non-paired control flavour. Horizontal bar with asterisk indicates significant within subject t-test between flavour and control. For the before flavour, t(5) = −3.78, p = .013; for the after flavour t(5) = 5.30, p = .003.
of Experiment 3 from Hughes and Boakes, however, indicated that our rats did not run faster. We were able to obtain the bivalent effect by using a highly palatable liquid meal replacement that was readily consumed by the rats, regardless of whether it was presented before or after the wheel running. Consequently, the temporal duration of consumption before and after wheel running was equated, allowing for conditioning of the flavours without the enhancement by wheel pre-exposure that Hughes and Boakes found necessary. It is also
Boakes, R.A., Nakajima, S., 2009. Conditioned taste aversions based on running or swimming. In: Reilly, S., Schachtman, T.R. (Eds.), Conditioned Taste Aversion: Behavioral and Neural Processes. Oxford University Press, New York, NY, pp. 159–178. Hughes, S.C., Boakes, R.A., 2008. Flavour preferences produced by backward pairing with wheel running. Journal of Experimental Psychology: Animal Behavior Processes 34, 283–293. Lett, B.T., Grant, V.L., 1996. Wheel running induces conditioned taste aversion in rats trained while hungry and thirsty. Physiology and Behavior 59, 699–702. Lett, B.T., Grant, B.L., Byrne, M.J., Koh, M.T., 2000. Pairings of a distinctive chamber with the aftereffect of wheel running produce conditioned place preference. Appetite 34, 87–94. Masaki, T., Nakajima, S., 2008. Forward conditioning with wheel running causes place aversion in rats. Behavioural Processes 79, 43–47. Salvy, S.-J., Pierce, W.D., Heth, D.C., Russell, J.C., 2004. Taste avoidance induced by wheel running: effects of backward pairings and robustness of conditioned taste aversion. Physiology and Behavior 82, 303–308.
Contents lists available at SciVerse ScienceDirect
Behavioural Processes journal homepage: www.elsevier.com/locate/behavproc
Bivalent effects of wheel running on taste conditioning Christine Dobek, C. Donald Heth, W. David Pierce ∗ University of Alberta, Edmonton, Alberta, Canada
a r t i c l e
i n f o
Article history: Received 29 August 2011 Received in revised form 22 September 2011 Accepted 17 October 2011 Keywords: Taste avoidance Taste preference Conditioning Wheel running Rats
a b s t r a c t We replicated the finding of bivalent conditioning of tastes by wheel running by Hughes and Boakes (2008), but without pre-exposure to the wheel. Rats received six days of conditioning with a flavoured solution presented for 10 min before a 40-min placement in a running wheel and another flavoured solution presented for 10 min after. A highly palatable liquid meal replacement was used as a vehicle for the flavours to encourage consumption, allowing us to equate before and after presentation intervals. Relative to a third flavour, we found that the taste preceding wheel running was consumed less, and the taste that followed wheel running was consumed more. Novel wheel running can therefore condition both taste avoidance and taste preference. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Avoidance of tastes or flavours can be conditioned with physical activity such as wheel running. Lett and Grant (1996) allowed hungry and thirsty rats 10 min to consume either a salt or sour solution followed by 30 min of confinement in a running wheel. On separate unpaired trials, these rats were allowed 10 min to consume the other solution and confined for 30 min in home cages. After three paired trials, rats avoided the solution that had been followed by wheel running as compared to the solution followed by home cage confinement. Lett and Grant (1996) concluded that rats show conditioned taste avoidance (CTA) when the flavoured conditioned stimulus (CS) is repeatedly followed by the unconditioned stimulus (US) of wheel running, a forward conditioning procedure (Boakes and Nakajima, 2009). Salvy et al. (2004) extended the running wheel procedure to backward conditioning, in which the flavour CS followed the wheel US. Relative to unpaired controls, rats given backward pairings drank more of the CS flavour, a result suggesting that the aftereffects of wheel running produce conditioned taste preference (CTP). This aftereffect seems to involve appetitive rather than aversive conditioning (see also Lett et al., 2000). If so, wheel running has bivalent properties that produce different conditioning effects depending on the temporal placement of the CS-taste. Subsequently, Hughes and Boakes (2008, Experiment 1) showed that a flavour presented after wheel running acquired a positive
∗ Corresponding author at: Department of Sociology, University of Alberta, Edmonton, Alberta, Canada T6G 2H4. Tel.: +1 780 492 0485. E-mail address: [email protected] (W.D. Pierce). 0376-6357/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.beproc.2011.10.009
valence relative to a flavour not paired with wheel running. In another experiment (Experiment 3) they demonstrated for the first time that both aversive and appetitive conditioning could occur within subjects, a bivalent effect of wheel running. In this study, rats were given access to one flavour before, and a second flavour after, wheel running. Tests showed avoidance of the flavour that preceded running and preference for the flavour that followed. However, the bivalent effects were found only in those rats that had been given eight 3-h pre-exposures to wheel running and not in those rats without this experience. Hughes and Boakes suggested that pre-exposure to wheel running increased the effectiveness of the appetitive process related to conditioned preference, decreased the aversiveness of the process leading to conditioned avoidance, or both. We believe it is premature to conclude that pre-exposure is necessary to obtain the bivalent effects of wheel running. Notably, in the bivalent study Hughes and Boakes provided rats with only 10 min access to the before flavour, but 30 min access to the after taste. The difference in access times equalized consumption of the before and after flavours, but may have also produced differential exposure to the two tastes, decreasing the effectiveness of the conditioning in two ways: Small sips of the flavour over the consumption interval would reduce the salience of the taste stimulus; or, sips late in the consumption interval would receive weak conditioning due to the delay between US and CS. In fact, delay between the termination of wheel running and exposure to the after taste reduces CTP (Hughes and Boakes, 2008, Experiment 2). Here, we replicate the Hughes and Boakes finding of bivalent conditioning, but without pre-exposure of the wheel running US. We used a highly palatable liquid meal replacement as a vehicle for the flavours to encourage consumption, allowing us to equate
C. Dobek et al. / Behavioural Processes 89 (2012) 36–38
before and after presentation intervals. Relative to a third flavour, we found that a taste preceding wheel running was consumed less, and a taste that followed wheel running was consumed more. That is, we obtained a bivalent effect of wheel running without pre-exposure of the wheel. 2. Method 2.1. Subjects Six male Sprague-Dawley rats, 41–45 days old at the start of the experiment and with a mean weight of 192 g, were used in the study. Rats were individually housed in clear polycarbonate cages (47 cm × 27 cm × 20 cm) with wood chip bedding. Feeding cages were identical, but without bedding. The room temperature was 22 ◦ C with lights off at 08:00 h and on at 20:00 h. Throughout the experiment animals, except as described in Section 2.3, had free access to water. Care of the animals complied with the guidelines of the University of Alberta Biological Sciences Animal Policy. 2.2. Materials Wheel running occurred in six Wahmann rat-running wheels (1.1 m circumference) with attached side cages (25 cm × 15.5 cm × 12.5 cm). Each rat was randomly assigned to a wheel. Turns were recorded at 1-min intervals by two microswitches activated by a cam situated above and below the axle of the wheel. The micro-switches, integrated with a computer system, ensured recording of only full wheel turns. Flavours were presented in solution with vanilla Ensure, a liquid meal replacement (Abbott Laboratories, Montreal Quebec). Three extracts—mint/peppermint, almond, and star anise—made by Club House (McCormick Canada, London Canada) were used as flavours. Flavoured solutions were presented in drinking bottles, with 1.5 ml of flavour extract mixed with 150 ml of Ensure. The flavours were assigned as either control, before, or after flavour with a rat randomly assigned to one of the six permutations. 2.3. Procedure The animals were acclimatized with unlimited water, but restricted food, for the first 6 days after arrival (Day 0). On Days 1, 2, and 6 each rat’s weight was recorded at 08:00 h followed by a presentation of 30 g of standard laboratory chow (Lab DietTM 5010 Rodent Diet, PMI Nutrition International, Inc., Brentwood, MO) in its home cage. At 20:00 h any remaining chow was removed and weighed. On Days 3, 4, and 5 the rats were given the control flavour. On these days, at 10:00 h, rats were weighed, transferred to feeding cages, and received 10 min of control flavour exposure. Subsequently, rats were transferred to their home cages for 40 min with no access to water, followed by another 10 min session of the control flavour, ending with a return to home cages with 30 g of chow and water. At 20:00 h, all remaining chow was removed and weighed. 2.3.1. Conditioning phase The conditioning phase started on Day 7 (Session 1) and proceeded for 6 days (to Session 6). At 10:00 h rats were weighed, placed in feeding cages with the before flavour for 10 min, and then transferred to running wheels for 40 min. Subsequently, the animals were transferred to the feeding cages where they received 10 min of access to the after flavour. Finally, they were returned to the home cages with free access to water and 14 g of chow. Water was weighed at 10:00 h and after wheel running. Any chow present at 20:00 h was removed and weighed.
37
2.3.2. Test phase At 10:00 h on Days 13 and 14, rats were weighed and given a two-bottle test in their feeding cages. One test (Before Test) compared consumption (g) of the control flavour to the before flavour, and the other (After Test) compared the control flavour to the after flavour. Three rats (randomly assigned) received the Before Test first while the others received the After Test first. After the first test, the animals were given 14 g of food and free access to water. Any remaining chow was removed at 20:00 h. The next day the rats received the opposite test. For the first test half of the rats, randomly chosen, received the control flavour on the left and half received it on the right. The position of the control flavour was switched to the other side for the second test. 3. Results 3.1. Acclimatization trials On the last day of acclimatization to the control flavour (Day 5), rats drank the Ensure solution before and after being placed in home cages. They drank a mean of 7.9 g (SEM ± 0.9) of the control Ensure before placement in home cages and 7.3 g (SEM ± 2.1) of the control solution after, t(5) = 0.39, n.s. 3.2. Conditioning trials Table 1 shows the mean wheel turns for each day of conditioning. Mean wheel turns significantly increased from the first day of conditioning to the last. The mean daily consumption of the before flavour and after flavour also increased significantly over the same period. On Session 6, mean consumption of the before flavour and the after flavour did not differ significantly, t(5) = 1.53, n.s. The slightly higher consumption of the before flavour is not surprising, because rats had been food restricted for 14 h at this time but only 40 min at the time they received the after flavour. 3.3. Consumption tests Fig. 1 shows the mean consumption (g) of the CS flavour and control solutions by temporal placement of the CS with respect to wheel running (US). On the Before Test, consumption of the conditioned solution was less than the control (M = 10.7, SEM ± 1.3). For the After Test, rats consumed more of the CS flavour (M = 11.2, SEM ± 1.4) than the control (M = 3.8, SEM ± 0.5). The interaction of flavour (conditioned or control) by temporal placement (before or after) was significant, F(1,5) = 34.93, MSe = 9.06, p = .002. 4. Discussion Our results show that wheel running has bivalent effects when paired with flavoured solutions. When the solution precedes the running, consumption of the flavour decreases, indicating aversive conditioning. When the solution follows running, consumption increases, showing appetitive conditioning. These effects do not depend on pre-exposure to wheel running, a result that generalizes the findings of Hughes and Boakes (2008) to situations in which wheel running is a novel stimulus. There are several differences between our study and that of Hughes and Boakes: We used younger rats, males rather than females, six rather than four sessions of conditioning, and consecutive rather than alternating sessions of conditioning. Although many of these factors are beyond the scope of our study, we did examine the possibility that our younger rats may have run at a higher rate than those of Hughes and Boakes, especially rats in the non-pre-exposed group. Estimates from the wheel running graph
38
C. Dobek et al. / Behavioural Processes 89 (2012) 36–38
Table 1 Means and (in parentheses) standard deviations for the number of wheel turns (1.1 m), and consumption (g) of the before and after flavours for sessions of the conditioning phase. Measure
F (df); MSe a
Conditioning sessions
Wheel turns Before flavour After flavour
1
2
3
4
5
6
144.8 (29.5) 7.8 (1.0) 3.8 (1.7)
195.7 (67.0) 8.0 (1.3) 8.8 (1.3)
349.3 (48.5) 8.5 (1.0) 9.0 (1.2)
347.7 (35.3) 11.5 (1.4) 9.3 (1.5)
316.2 (62.6) 10.7 (1.3) 10.3 (1.4)
398.8 (32.9) 12.2 (1.9) 9.8 (1.2)
5.90 (5,25); 10,028.2 9.89 (5,25); 2.251 13.47 (5,25); 2.502
a F-values, degrees of freedom (df) and mean squared error (MSe ) for the one-way repeated measures analysis of variance for days of conditioning. A 2 (Before vs After) by 6 (sessions) within-subjects analysis of variance of consumption showed a significant interaction F(5,25) = 4.38, MSe = 2.39. All F-tests were significant at the p < .05 level.
Control
CS Flavour
6
possible that the two additional days of conditioning, or the use of younger rats that tend to run faster, could have contributed to our findings. We suggest the use of palatable liquid meals as a useful procedure for the temporal assay of the reinforcing effects of wheel running. Lett et al. (2000) showed that the after effects of wheel running produced a condition place preference. Recently, Masaki and Nakajima (2008) obtained conditioned place aversion induced by wheel running, using a forward conditioning procedure. At this point, however, it is not clear when, or how quickly, these effects appear. Because our method allows for the presentation of short CS durations, it should be possible to use it to investigate the reinforcement process in more detail.
4
Acknowledgements
*
*
12
Consumption (g)
10 8
2 0 Before
After
A Discovery Grant (G121211127) from the Natural Sciences and Engineering Research Council of Canada (NSERC) to the authors supported this research. We thank our laboratory technician, Shannon Fischer, for her assistance in conducting this experiment.
Temporal Placement of CS References Fig. 1. Mean (with SEM bars) consumption (g) on test days for the CS flavours presented before and after wheel running compared to the non-paired control flavour. Horizontal bar with asterisk indicates significant within subject t-test between flavour and control. For the before flavour, t(5) = −3.78, p = .013; for the after flavour t(5) = 5.30, p = .003.
of Experiment 3 from Hughes and Boakes, however, indicated that our rats did not run faster. We were able to obtain the bivalent effect by using a highly palatable liquid meal replacement that was readily consumed by the rats, regardless of whether it was presented before or after the wheel running. Consequently, the temporal duration of consumption before and after wheel running was equated, allowing for conditioning of the flavours without the enhancement by wheel pre-exposure that Hughes and Boakes found necessary. It is also
Boakes, R.A., Nakajima, S., 2009. Conditioned taste aversions based on running or swimming. In: Reilly, S., Schachtman, T.R. (Eds.), Conditioned Taste Aversion: Behavioral and Neural Processes. Oxford University Press, New York, NY, pp. 159–178. Hughes, S.C., Boakes, R.A., 2008. Flavour preferences produced by backward pairing with wheel running. Journal of Experimental Psychology: Animal Behavior Processes 34, 283–293. Lett, B.T., Grant, V.L., 1996. Wheel running induces conditioned taste aversion in rats trained while hungry and thirsty. Physiology and Behavior 59, 699–702. Lett, B.T., Grant, B.L., Byrne, M.J., Koh, M.T., 2000. Pairings of a distinctive chamber with the aftereffect of wheel running produce conditioned place preference. Appetite 34, 87–94. Masaki, T., Nakajima, S., 2008. Forward conditioning with wheel running causes place aversion in rats. Behavioural Processes 79, 43–47. Salvy, S.-J., Pierce, W.D., Heth, D.C., Russell, J.C., 2004. Taste avoidance induced by wheel running: effects of backward pairings and robustness of conditioned taste aversion. Physiology and Behavior 82, 303–308.