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Bombesin effects on responding maintained by a fixed interval schedule of food reinforcement
Peptides, Vol. 12, pp. 1435-1436. ~ Pergamon Press plc, 1991. Printed in the U.S.A.
0196-9781/91 $3.00 + .00
BRIEF COMMUNICATION
Bombesin Effects on Responding Maintained by a Fixed Interval Schedule of Food Reinforcement I R O B I N L. B O W E R S 2 A N D C H R I S T O P H E R D. H E R Z O G
The College of Charleston, Charleston, SC 29424 R e c e i v e d 27 June 1991 BOWERS, R. L. AND C. D. HERZOG. Bombesin effects on responding maintained by a fixed interval schedule of food reinforcement. PEPTIDES 12(6) 1435-1436, 1991.--The present experiment examined rats' responding maintained by a fixed interval two-min schedule of food reinforcement following IP injections of bombesin (4, 6, 16, 32 ~g/kg). The results showed that bombesin's effects were rate dependent where the responses per minute emitted during the early portion of the fixed interval were reduced, but responding during the latter portion was unaffected. Bombesin did not reduce overall session responses per minute, pause after reinforcement, or amount of water consumed in the test chamber. The results are in accord with prior research examining the effects of bombesin and cholecystokinin on operant behavior. Together, the data challenge the notion that bombesin affects food-motivated behavior generally; rather, the results indicate that bombesin's effect may interact with the demands required of the animal for reinforcement. Bombesin
Operant responding
Fixed interval schedule of reinforcement
INTRAPERITONEAL injections of bombesin (BBS) decrease food intake in hungry animals [for a review see (8)]. Recent operant research, however, indicates that BBS may play a more complex role in regulating food-motivated behavior (1,2). The aim of the present study was to extend this research by examining BBS's effects on behavior maintained by a fixed interval (FI) schedule of reinforcement. The primary concern here was the extent to which BBS alters a number of FI behaviors, including: session responses per minute, responding within the interval, and the pause after reinforcement.
CCK8
after IP injections of BBS (Sigma Co., 4, 6, 16, and 32 i~g/kg) administered on odd days. On even-numbered sessions, animals were injected with 0.9% saline (1 ml/kg). The order of BBS dose was randomized across subjects, and only one administration of each dose was given to each animal.
RESULTS Figure 1 shows the mean number of responses emitted per minute during the successive 20-s periods within the FI 120 s after injection of saline or doses of BBS. As illustrated, responding was maintained with all doses and responses per minute accelerated positively with the FI. More importantly, the figure shows that BBS reduced the number of responses that occurred immediately following reinforcement, but increased the number of responses that occurred prior to reinforcement. An ANOVA performed on the data (5 Doses × 6 Successive Time Periods) revealed a significant main effect for Periods, F(5,25)=26.69, p<0.001, and a reliable interaction between Dose and Periods, F(20,100) = 2.73, p<0.01. Newman-Keuls post hoc tests showed that BBS reliably reduced responding 60-80 s into the interval and increased responding during the last 20 s of the interval, particularly with the 4-16 p,g/kg doses. Although BBS slightly reduced responses per minute and water consumed, and appeared to increase the pause after reinforcement, F-tests failed to support the reliability of these effects (Fs>0.05).
METHOD
Subjects Six experimentally naive, male Sprague-Dawley rats weighing 300--400 g served as subjects. All animals were maintained at approximately 85% of their ad lib weight and given free access to water throughout the experiment.
Apparatus One standard operant conditioning chamber was used that contained a response lever and a calibrated (ml) drinking spout filled with tap water.
Procedure Rats were shaped to bar press and were then exposed to a FI 2-min schedule for 30 days. FI performance was then examined
~Portions of the data were presented at the 1991 conference for the Eastern Psychological Association, New York, NY. 2Requests for reprints should be addressed to Robin L. Bowers, Ph.D., Psychology Department, The College of Charleston, Charleston, SC 29424. 1435
1436
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FIG. 1. Shown are mean responses per min across successive 20-s periods within the FI 2-rain period after IP injection of saline (filled circles) and BBS (4 I~g unfilled circle, 6 ~g triangle, 16 Ixg square, 32 I~g/kg inverted triangle).
little effect on other FI characteristics, such as overall responses per minute, pause after reinforcement, and water consumption. The finding that BBS altered FI responding is consistent with prior research examining the effects of BBS on schedule behavior (1,2). For example, Bowers et al. showed that BBS altered DRL responding by decreasing the number of short interresponse times, while the number of long IRTs increased. The results are also consistent with the findings of Cohen (4), indicating that CCK8 produces rate-dependent effects in temporally based schedules. Since both peptides are viewed as putative mediators of short-term satiety [see (8,9)], it is interesting that the peptides failed to reduce responding generally; rather, the effects are rate dependent. Additional research may determine whether BBS's effects on FI responding involve changes in internal clock processes (3, 10, 11) and/or varying the nature of FI behavior (5). Nevertheless, the data indicate that the once held view that BBS decreases food-motivated behavior generally is too simple. BBS's role in regulating food-motivated behavior appears to be complex, and may interact with the task required of the animal. ACKNOWLEDGEMENTS
DISCUSSION The major finding was that BBS decreased the number of responses made in the early portion of the fixed interval, but had
A portion of the research was funded by a Pew Science grant, and a College of Charleston faculty research grant awarded to the first author. Thanks are extended to David G. Gentry, Daniel Weeks and Peter Kivisto.
REFERENCES 1. Babcock, A. M.; Livosky, M.; Avery, D. D. Cholecystokinin and bombesin suppress operant responding for food reward. Pharmacol. Biochem. Behav. 22:893-895; 1985. 2. Bowers, R. L.; Harris-Peterson, M.; Mollenhauer, M. S.; Devolder, C.; Avery, D. D.; Richards, R. W. Bombesin improves rats' responding maintained by a differential-reinforcement-of-low-ratesschedule of food reinforcement. Psychol. Rep. 66:131-138; 1990. 3. Church, R. M. The internal clock. In: Hulse, S. H.; Fowler, H.; Honig, W. K., eds. Cognitive processes in animal behavior. Hillsdale, NJ: Erlbaum; 1978:277-310. 4. Cohen, S. L. A pharmacological examination of the resistance-tochange hypothesis of response strength. J. Exp. Anal. Behav. 46: 363-379; 1986. 5. Gentry, D. G.; Weiss, B.; Laties, V. G. The microanalysis of fixed-interval responding. J. Exp. Anal. Behav. 39:327-343; 1983.
6. Gibbs, J. D.; Fauser, D. J.; Rowe, E. A.; Rolls, B. J.; Rolls, E, T.; Maddison, S. P. Bombesin suppresses feeding in rats. Nature 282:208-210; 1979. 7. Kulkosky, P. J.; Gibbs, J.; Smith, G. D. Behavioral effects of bombesin administration in rats. Physiol. Behav. 28:505-512; 1982. 8. McCoy, J. G.; Avery, D. D. Bombesin: Potential integrative peptide for feeding and satiety. Peptides 11:595-607; 1990. 9. Martin, C. F.; Gibbs, J. Bombesin elicits satiety in sham feeding in rats. Peptides 1:131-134; 1981. 10. Meck, W. H. Selective adjustment of the speed of internal clock and memory processes. J. Exp. Psychol. (Anim. Behav.)9:171210; 1983. 11. Meck, W. H.; Komeily-Zadeh, F. N.; Church, R. M. Two-step acquisition: Modification of an internal clock criterion. J. Exp. Psychol. (Anim. Behav.) 10:297-306; 1984.
0196-9781/91 $3.00 + .00
BRIEF COMMUNICATION
Bombesin Effects on Responding Maintained by a Fixed Interval Schedule of Food Reinforcement I R O B I N L. B O W E R S 2 A N D C H R I S T O P H E R D. H E R Z O G
The College of Charleston, Charleston, SC 29424 R e c e i v e d 27 June 1991 BOWERS, R. L. AND C. D. HERZOG. Bombesin effects on responding maintained by a fixed interval schedule of food reinforcement. PEPTIDES 12(6) 1435-1436, 1991.--The present experiment examined rats' responding maintained by a fixed interval two-min schedule of food reinforcement following IP injections of bombesin (4, 6, 16, 32 ~g/kg). The results showed that bombesin's effects were rate dependent where the responses per minute emitted during the early portion of the fixed interval were reduced, but responding during the latter portion was unaffected. Bombesin did not reduce overall session responses per minute, pause after reinforcement, or amount of water consumed in the test chamber. The results are in accord with prior research examining the effects of bombesin and cholecystokinin on operant behavior. Together, the data challenge the notion that bombesin affects food-motivated behavior generally; rather, the results indicate that bombesin's effect may interact with the demands required of the animal for reinforcement. Bombesin
Operant responding
Fixed interval schedule of reinforcement
INTRAPERITONEAL injections of bombesin (BBS) decrease food intake in hungry animals [for a review see (8)]. Recent operant research, however, indicates that BBS may play a more complex role in regulating food-motivated behavior (1,2). The aim of the present study was to extend this research by examining BBS's effects on behavior maintained by a fixed interval (FI) schedule of reinforcement. The primary concern here was the extent to which BBS alters a number of FI behaviors, including: session responses per minute, responding within the interval, and the pause after reinforcement.
CCK8
after IP injections of BBS (Sigma Co., 4, 6, 16, and 32 i~g/kg) administered on odd days. On even-numbered sessions, animals were injected with 0.9% saline (1 ml/kg). The order of BBS dose was randomized across subjects, and only one administration of each dose was given to each animal.
RESULTS Figure 1 shows the mean number of responses emitted per minute during the successive 20-s periods within the FI 120 s after injection of saline or doses of BBS. As illustrated, responding was maintained with all doses and responses per minute accelerated positively with the FI. More importantly, the figure shows that BBS reduced the number of responses that occurred immediately following reinforcement, but increased the number of responses that occurred prior to reinforcement. An ANOVA performed on the data (5 Doses × 6 Successive Time Periods) revealed a significant main effect for Periods, F(5,25)=26.69, p<0.001, and a reliable interaction between Dose and Periods, F(20,100) = 2.73, p<0.01. Newman-Keuls post hoc tests showed that BBS reliably reduced responding 60-80 s into the interval and increased responding during the last 20 s of the interval, particularly with the 4-16 p,g/kg doses. Although BBS slightly reduced responses per minute and water consumed, and appeared to increase the pause after reinforcement, F-tests failed to support the reliability of these effects (Fs>0.05).
METHOD
Subjects Six experimentally naive, male Sprague-Dawley rats weighing 300--400 g served as subjects. All animals were maintained at approximately 85% of their ad lib weight and given free access to water throughout the experiment.
Apparatus One standard operant conditioning chamber was used that contained a response lever and a calibrated (ml) drinking spout filled with tap water.
Procedure Rats were shaped to bar press and were then exposed to a FI 2-min schedule for 30 days. FI performance was then examined
~Portions of the data were presented at the 1991 conference for the Eastern Psychological Association, New York, NY. 2Requests for reprints should be addressed to Robin L. Bowers, Ph.D., Psychology Department, The College of Charleston, Charleston, SC 29424. 1435
1436
BOWERS AND HERZOG
6O
@
z
/ ,S'
5O b3 £1_
(/3 Z
4O
©
3o
a:
20
12_ (/3 k,J
[]
Z
I
I
I
I
I
I
20
40
60
80
1O0
120
SUCCESSIVE 20 SECOND PERIODS
FIG. 1. Shown are mean responses per min across successive 20-s periods within the FI 2-rain period after IP injection of saline (filled circles) and BBS (4 I~g unfilled circle, 6 ~g triangle, 16 Ixg square, 32 I~g/kg inverted triangle).
little effect on other FI characteristics, such as overall responses per minute, pause after reinforcement, and water consumption. The finding that BBS altered FI responding is consistent with prior research examining the effects of BBS on schedule behavior (1,2). For example, Bowers et al. showed that BBS altered DRL responding by decreasing the number of short interresponse times, while the number of long IRTs increased. The results are also consistent with the findings of Cohen (4), indicating that CCK8 produces rate-dependent effects in temporally based schedules. Since both peptides are viewed as putative mediators of short-term satiety [see (8,9)], it is interesting that the peptides failed to reduce responding generally; rather, the effects are rate dependent. Additional research may determine whether BBS's effects on FI responding involve changes in internal clock processes (3, 10, 11) and/or varying the nature of FI behavior (5). Nevertheless, the data indicate that the once held view that BBS decreases food-motivated behavior generally is too simple. BBS's role in regulating food-motivated behavior appears to be complex, and may interact with the task required of the animal. ACKNOWLEDGEMENTS
DISCUSSION The major finding was that BBS decreased the number of responses made in the early portion of the fixed interval, but had
A portion of the research was funded by a Pew Science grant, and a College of Charleston faculty research grant awarded to the first author. Thanks are extended to David G. Gentry, Daniel Weeks and Peter Kivisto.
REFERENCES 1. Babcock, A. M.; Livosky, M.; Avery, D. D. Cholecystokinin and bombesin suppress operant responding for food reward. Pharmacol. Biochem. Behav. 22:893-895; 1985. 2. Bowers, R. L.; Harris-Peterson, M.; Mollenhauer, M. S.; Devolder, C.; Avery, D. D.; Richards, R. W. Bombesin improves rats' responding maintained by a differential-reinforcement-of-low-ratesschedule of food reinforcement. Psychol. Rep. 66:131-138; 1990. 3. Church, R. M. The internal clock. In: Hulse, S. H.; Fowler, H.; Honig, W. K., eds. Cognitive processes in animal behavior. Hillsdale, NJ: Erlbaum; 1978:277-310. 4. Cohen, S. L. A pharmacological examination of the resistance-tochange hypothesis of response strength. J. Exp. Anal. Behav. 46: 363-379; 1986. 5. Gentry, D. G.; Weiss, B.; Laties, V. G. The microanalysis of fixed-interval responding. J. Exp. Anal. Behav. 39:327-343; 1983.
6. Gibbs, J. D.; Fauser, D. J.; Rowe, E. A.; Rolls, B. J.; Rolls, E, T.; Maddison, S. P. Bombesin suppresses feeding in rats. Nature 282:208-210; 1979. 7. Kulkosky, P. J.; Gibbs, J.; Smith, G. D. Behavioral effects of bombesin administration in rats. Physiol. Behav. 28:505-512; 1982. 8. McCoy, J. G.; Avery, D. D. Bombesin: Potential integrative peptide for feeding and satiety. Peptides 11:595-607; 1990. 9. Martin, C. F.; Gibbs, J. Bombesin elicits satiety in sham feeding in rats. Peptides 1:131-134; 1981. 10. Meck, W. H. Selective adjustment of the speed of internal clock and memory processes. J. Exp. Psychol. (Anim. Behav.)9:171210; 1983. 11. Meck, W. H.; Komeily-Zadeh, F. N.; Church, R. M. Two-step acquisition: Modification of an internal clock criterion. J. Exp. Psychol. (Anim. Behav.) 10:297-306; 1984.