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Cholecystokinin-induced satiety in weanling rats
Physiology & Behavior, Vol. 17, pp. 541--543. Pergamon Press and Brain Research Publ., 1976. Printed in the U.S.A.
BRIEF COMMUNICATION Cholecystokinin-Induced Satiety in Weanling Rats' ILENE L. BERNSTEIN, 2 ELIZABETH C. L O T T E R a AND J A N E T C. ZIMMERMAN
Department of Psychology, University of Washington and Department of Psychology, Northeastern University (Received 25 November 1975) BERNSTEIN, I. L., E. C. LOTTER AND J. C. ZIMMERMAN. Cholecystokinin-induced satiety in weanlingrats. PHYSIOL. BEHAV. 17(3) 541-543, 1976. - Intraperitoneal injections fo the synthetic C-terminal octapeptide of cholecystokinin (CCK) into fasted 21-day-old weanling rats produced a significant suppression of intake of solid and liquid diets. Similar injections had no effect on water consumption of thirsty weanlings. The early appearance of CCK-induced satiety is consistent with the idea that this mechanism is responsible for the effectiveness of gastrointestinal factors in determining intake of very young rats. Feeding behavior
Satiety
Cholecystokinin
Weanlingrats
METHOD
RECENT work on neonatal rats suggests that various mechanisms which are presumed to control food intake develop at different ages. Eating in response to glucoprivation elicited by 2-deoxyglucose or insulin injections [4,6] does not appear until around the fourth or fifth week of life. On the other hand Houpt and Epstein [4] report that three-to-seven-day old suckling rats respond to food deprivation by increasing milk consumption and reduce consumption in response to gastric preloads. They conclude that although responses to glucoprivation are rather late to develop, appropriate responses to gastrointestinal fill are present almost from birth. Gibbs, Young and Smith [1] have suggested that the suppressive effects of food in the gastrointestinal tract on eating are mediated by the release of the gastrointestinal hormone cholecystokinin (CCK). They present evidence that injection of CCK into mildly deprived adult rats significantly reduces food intake in the subsequent meal. The reduced food intake which follows injections of CCK does not appear to be due to illness since similar injections do not produce conditioned taste aversions [3]. Since gastrointestinal factors appear to be of primary importance in determining food intake in suckling and weanling rats, we were interested in evaluating whether CCK injections reduce food intake in 21-day-old rats.
Wistar rats of both sexes, bred at the University of Washington vivarium were used. Three studies were performed each using a single litter of 12 pups, weaned at approximately 15 days of age. The pups were maintained on a 12:12 l i g h t - d a r k schedule and housed with their littermates except during testing, in opaque plastic cages (32 cm x 24 cm x 16 cm) with wire cage tops and sawdust bedding. The general procedure consisted of several days of habituation to a 4 - 5 hr food or water deprivation period followed by 30 min of access to food or water in individual test cages. At 21 days of age half the litter was injected intraperitoneally with either 40 Ivy dog units/kg CCK (Synthetic C terminal octapeptide dissolved i n . 15 M saline, a gift of Miguel Ordetti, Squibb) and the other half w i t h . 15 M saline, immediately before being placed in individual cages for a 30 min intake test. In the first study a palatable liquid diet (500 ml whole milk; 2 eggs; 250 g sugar) was presented in calibrated Nalgene tubes for 30 min every 4 ½ - 5 hr on a continuous basis, in both the dark and light. Food intake was recorded after 10 and 30 min of access and rats were returned to the group cage, where no food was available. On Day 21 the
t We wish to thank Stephen Woods for his helpful advice. 2Address proofs and all correspondence to: Ilene L. Bernstein, Department of Psychology NI-25, University of Washington, Seattle, WA 98195 U.S.A. a Supported by N.I.H. Grant no. AM 17122. 541
542
SATIETY IN WEANLING RATS
injection procedure preceded every other meal, with CCK and saline groups reversed. No differences were observed between food intake in the dark and light and therefore these data were combined. Each rat was tested four times; twice with saline injections and twice with CCK. In the second study a moist, solid diet and a feeding schedule similar to Gibbs, et al. [ 1] was employed. Moist Purina chow (2 parts ground chow; 3 parts water) was available in a shallow saucer. Animals were deprived of food for 4 hr at the same time each day for 4 days. On Day 21 the injection procedure was followed and food intake in the 30 min meal of the moist diet was measured by weighing the food before and after feeding. Spillage was collected and weighed. In the third study the effect of CCK injections on water intake of thirsty rats was evaluated. Purina chow pellets were available ad lib except during testing. Animals were water deprived for 5 hr before being given 30 min access to water in calibrated Nalgene tubes. On Day 21 the injection procedure was followed and water intake measured. RESULTS AND DISCUSSION
A small but significant difference was noted (Fig. 1) between the 30 min intake of liquid diet of CCK- and saline-injected rats. When I0 rain intake was considered, a greater difference was noted with CCK-injected rats consuming less food than the controls. As shown in Fig. 2, intake of moist chow diet during the 30 min access was considerably smaller following injections of CCK than following saline. Furthermore, it was noted ~ 5.04.0,
,It,
i / /
~.
5.0-
t / i / / J f / / f / / i / #
~
2.0
i / /
e F / J i / J / / J / / / / / / / / /
1.0
/'// f// /// fJJ
0 Saline 0-30
CCK M in,
Saline
n CCK
0 - 1 0 Min.
FIG. 1. Consumption of liquid diet (X in ml +_SEM) 10 and 30 min after intraperitoneal injection of saline or 40 U/kg of cholecystokinin (CCK). (* indicates p<~0.05; ** indicates p~<0.01)
4.0-
t
,
~ 3.0
,•5.0
I
ElY /// i i / i / i i 1 1 i 1 1 1 1 1 # # #
~ 2.O
2.0 i / /
~-'o I.O-
~ O ,o~o
/ / /
~ 1.0'
® Saline
CCK
0
# / J
/// //J ///
Saline
CCK
FIG. 2. Consumption of moist chow (X in g -+SEM) and water (X in ml +- SEM) in the 30 min after intraperitoneal injection of saline or CCK. (** indicates p~<0.01) that 3 to 5 min after injection and introduction into the testing cage all saline control animals were engaged in eating while all animals that had received CCK were not eating. This observation was similar to the results obtained using a liquid diet, showing an almost immediate effect of the CCK injections on feeding behavior. Gibbs, et al. [1 ] state that CCK-injected adult rats begin to eat normally but stop eating sooner than control animals. The observation made on weanlings that CCK effects were greatest immediately after injection suggested that the mechanism responsible for reduced intake in weanlings might differ from that seen in adult rats. In order to test the possibility that CCK effects in weanlings were due to general tranquilization rather than a specific satiety effect we tested for drinking in response to water deprivation. Gibbs, et al. [1] indicate that CCK injections do not affect water intake in adult rats. Figure 2 indicates that water intake of weanling rats is likewise unaffected by injections of CCK. Consumption of water in a 30 min test does not differ for the saline and CCKinjected groups. This finding supports the idea that CCK effects on the food intake of weanlings, as in adults, is a specific satiety effect and not one of general behavioral suppression. Weaned rats show evidence of short term satiety in response to CCK injections at 21 days of age. Suckling rats were not tested since the design of these experiments involved a habituation period and ingestion of measured quantities of food and water. It is therefore possible that CCI( injections can induce satiety in even younger rats than those observed in these studies. The early appearance of CCK-induced satiety is consistent with the possibility that this mechanism is responsible for the effectiveness of gastrointestinal factors in determining intake of very young rats, as observed by Houpt and Epstein [4] and Houpt and Houpt [5]. Details of the developmental aspects of endogenous CCK production and release would be needed in order to evaluate this further, since it appears that general intestinal function undergoes important developmental changes from 1 5 - 3 0 days of age in the rat [2].
REFERENCES 1.
Gibbs, J., R. C. Young and G. P. Smith. Cholecytokinin decreases food intake in rats. J. comp. physiol. Psychol. 84: 488-495, 1973.
2.
Hahn, P. and O. Koldovsky. Utilization of Nutrients during Postnatal Development. London: Pergamon Press, 1966.
BERNSTEIN, LOTTER AND ZIMMERMAN 3. 4.
Holt, J., J. Antin, J. Gibbs, R. C. Young and G. P. Smith. Cholecystokinin does not produce produce bait shyness in rats. Physiol. Behav. 12: 497-498, 1974. Houpt, K. A. and A. N. Epstein. Ontogeny of controls of food intake in the rat: GI fill and glucoprivation. Am. J. Physiol. 225: 58-66, 1973.
543 5. 6.
Houpt, K. A. and T. R. Houpt. Effects of gastric loads and food deprivation on subsequent food intake in suckling rats. J. comp. physiol. Psychol. 88: 764-772, 1975. Lytle, L. D., W. H. Moorcroft and B. A. Campbell. Ontogeny of amphetamine anorexia and insulin hyperphagia in the rat. J. comp. physiol. Psych. 77: 388-393, 1971.
BRIEF COMMUNICATION Cholecystokinin-Induced Satiety in Weanling Rats' ILENE L. BERNSTEIN, 2 ELIZABETH C. L O T T E R a AND J A N E T C. ZIMMERMAN
Department of Psychology, University of Washington and Department of Psychology, Northeastern University (Received 25 November 1975) BERNSTEIN, I. L., E. C. LOTTER AND J. C. ZIMMERMAN. Cholecystokinin-induced satiety in weanlingrats. PHYSIOL. BEHAV. 17(3) 541-543, 1976. - Intraperitoneal injections fo the synthetic C-terminal octapeptide of cholecystokinin (CCK) into fasted 21-day-old weanling rats produced a significant suppression of intake of solid and liquid diets. Similar injections had no effect on water consumption of thirsty weanlings. The early appearance of CCK-induced satiety is consistent with the idea that this mechanism is responsible for the effectiveness of gastrointestinal factors in determining intake of very young rats. Feeding behavior
Satiety
Cholecystokinin
Weanlingrats
METHOD
RECENT work on neonatal rats suggests that various mechanisms which are presumed to control food intake develop at different ages. Eating in response to glucoprivation elicited by 2-deoxyglucose or insulin injections [4,6] does not appear until around the fourth or fifth week of life. On the other hand Houpt and Epstein [4] report that three-to-seven-day old suckling rats respond to food deprivation by increasing milk consumption and reduce consumption in response to gastric preloads. They conclude that although responses to glucoprivation are rather late to develop, appropriate responses to gastrointestinal fill are present almost from birth. Gibbs, Young and Smith [1] have suggested that the suppressive effects of food in the gastrointestinal tract on eating are mediated by the release of the gastrointestinal hormone cholecystokinin (CCK). They present evidence that injection of CCK into mildly deprived adult rats significantly reduces food intake in the subsequent meal. The reduced food intake which follows injections of CCK does not appear to be due to illness since similar injections do not produce conditioned taste aversions [3]. Since gastrointestinal factors appear to be of primary importance in determining food intake in suckling and weanling rats, we were interested in evaluating whether CCK injections reduce food intake in 21-day-old rats.
Wistar rats of both sexes, bred at the University of Washington vivarium were used. Three studies were performed each using a single litter of 12 pups, weaned at approximately 15 days of age. The pups were maintained on a 12:12 l i g h t - d a r k schedule and housed with their littermates except during testing, in opaque plastic cages (32 cm x 24 cm x 16 cm) with wire cage tops and sawdust bedding. The general procedure consisted of several days of habituation to a 4 - 5 hr food or water deprivation period followed by 30 min of access to food or water in individual test cages. At 21 days of age half the litter was injected intraperitoneally with either 40 Ivy dog units/kg CCK (Synthetic C terminal octapeptide dissolved i n . 15 M saline, a gift of Miguel Ordetti, Squibb) and the other half w i t h . 15 M saline, immediately before being placed in individual cages for a 30 min intake test. In the first study a palatable liquid diet (500 ml whole milk; 2 eggs; 250 g sugar) was presented in calibrated Nalgene tubes for 30 min every 4 ½ - 5 hr on a continuous basis, in both the dark and light. Food intake was recorded after 10 and 30 min of access and rats were returned to the group cage, where no food was available. On Day 21 the
t We wish to thank Stephen Woods for his helpful advice. 2Address proofs and all correspondence to: Ilene L. Bernstein, Department of Psychology NI-25, University of Washington, Seattle, WA 98195 U.S.A. a Supported by N.I.H. Grant no. AM 17122. 541
542
SATIETY IN WEANLING RATS
injection procedure preceded every other meal, with CCK and saline groups reversed. No differences were observed between food intake in the dark and light and therefore these data were combined. Each rat was tested four times; twice with saline injections and twice with CCK. In the second study a moist, solid diet and a feeding schedule similar to Gibbs, et al. [ 1] was employed. Moist Purina chow (2 parts ground chow; 3 parts water) was available in a shallow saucer. Animals were deprived of food for 4 hr at the same time each day for 4 days. On Day 21 the injection procedure was followed and food intake in the 30 min meal of the moist diet was measured by weighing the food before and after feeding. Spillage was collected and weighed. In the third study the effect of CCK injections on water intake of thirsty rats was evaluated. Purina chow pellets were available ad lib except during testing. Animals were water deprived for 5 hr before being given 30 min access to water in calibrated Nalgene tubes. On Day 21 the injection procedure was followed and water intake measured. RESULTS AND DISCUSSION
A small but significant difference was noted (Fig. 1) between the 30 min intake of liquid diet of CCK- and saline-injected rats. When I0 rain intake was considered, a greater difference was noted with CCK-injected rats consuming less food than the controls. As shown in Fig. 2, intake of moist chow diet during the 30 min access was considerably smaller following injections of CCK than following saline. Furthermore, it was noted ~ 5.04.0,
,It,
i / /
~.
5.0-
t / i / / J f / / f / / i / #
~
2.0
i / /
e F / J i / J / / J / / / / / / / / /
1.0
/'// f// /// fJJ
0 Saline 0-30
CCK M in,
Saline
n CCK
0 - 1 0 Min.
FIG. 1. Consumption of liquid diet (X in ml +_SEM) 10 and 30 min after intraperitoneal injection of saline or 40 U/kg of cholecystokinin (CCK). (* indicates p<~0.05; ** indicates p~<0.01)
4.0-
t
,
~ 3.0
,•5.0
I
ElY /// i i / i / i i 1 1 i 1 1 1 1 1 # # #
~ 2.O
2.0 i / /
~-'o I.O-
~ O ,o~o
/ / /
~ 1.0'
® Saline
CCK
0
# / J
/// //J ///
Saline
CCK
FIG. 2. Consumption of moist chow (X in g -+SEM) and water (X in ml +- SEM) in the 30 min after intraperitoneal injection of saline or CCK. (** indicates p~<0.01) that 3 to 5 min after injection and introduction into the testing cage all saline control animals were engaged in eating while all animals that had received CCK were not eating. This observation was similar to the results obtained using a liquid diet, showing an almost immediate effect of the CCK injections on feeding behavior. Gibbs, et al. [1 ] state that CCK-injected adult rats begin to eat normally but stop eating sooner than control animals. The observation made on weanlings that CCK effects were greatest immediately after injection suggested that the mechanism responsible for reduced intake in weanlings might differ from that seen in adult rats. In order to test the possibility that CCK effects in weanlings were due to general tranquilization rather than a specific satiety effect we tested for drinking in response to water deprivation. Gibbs, et al. [1] indicate that CCK injections do not affect water intake in adult rats. Figure 2 indicates that water intake of weanling rats is likewise unaffected by injections of CCK. Consumption of water in a 30 min test does not differ for the saline and CCKinjected groups. This finding supports the idea that CCK effects on the food intake of weanlings, as in adults, is a specific satiety effect and not one of general behavioral suppression. Weaned rats show evidence of short term satiety in response to CCK injections at 21 days of age. Suckling rats were not tested since the design of these experiments involved a habituation period and ingestion of measured quantities of food and water. It is therefore possible that CCI( injections can induce satiety in even younger rats than those observed in these studies. The early appearance of CCK-induced satiety is consistent with the possibility that this mechanism is responsible for the effectiveness of gastrointestinal factors in determining intake of very young rats, as observed by Houpt and Epstein [4] and Houpt and Houpt [5]. Details of the developmental aspects of endogenous CCK production and release would be needed in order to evaluate this further, since it appears that general intestinal function undergoes important developmental changes from 1 5 - 3 0 days of age in the rat [2].
REFERENCES 1.
Gibbs, J., R. C. Young and G. P. Smith. Cholecytokinin decreases food intake in rats. J. comp. physiol. Psychol. 84: 488-495, 1973.
2.
Hahn, P. and O. Koldovsky. Utilization of Nutrients during Postnatal Development. London: Pergamon Press, 1966.
BERNSTEIN, LOTTER AND ZIMMERMAN 3. 4.
Holt, J., J. Antin, J. Gibbs, R. C. Young and G. P. Smith. Cholecystokinin does not produce produce bait shyness in rats. Physiol. Behav. 12: 497-498, 1974. Houpt, K. A. and A. N. Epstein. Ontogeny of controls of food intake in the rat: GI fill and glucoprivation. Am. J. Physiol. 225: 58-66, 1973.
543 5. 6.
Houpt, K. A. and T. R. Houpt. Effects of gastric loads and food deprivation on subsequent food intake in suckling rats. J. comp. physiol. Psychol. 88: 764-772, 1975. Lytle, L. D., W. H. Moorcroft and B. A. Campbell. Ontogeny of amphetamine anorexia and insulin hyperphagia in the rat. J. comp. physiol. Psych. 77: 388-393, 1971.