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Drinking, but not feeding, is opiate-sensitive in hamsters
Life Sciences, Vol. 30, pp. 1639-1644 Printed in the U.S.A.
Pergamon Press
DRINKING, BUT NOT FEEDING, IS OPIATE-SENSITIVE IN HAMSTERS
Martin T. Lowy and George K. W. Yim Department of Pharmacology and Toxicology School of Pharmacy and Pharmacal Sciences Purdue University West Lafayette, Indiana 47907 (Received in final form March i, 1982) Summary The long-lasting opiate antagonist, naltrexone (NTX), was examined for its effects on various types of consummatory behavior in male golden hamsters and rats. Rat, but not hamster, 24 hr food and water intakes were significantly decreased by four daily NTX (lO.O mg/kg) injections. Hamsters displayed a minimal night to day feeding ratio compared to rats. Hamsters increased food intake following insulin (50 U/kg) administration, but not after 24 hr food depri;vation (FD) or 2-deoxy-D-glucose (2-DG; 800 mg/kg) injections. NTX (l.O and IO mg/kg) had no effect on feeding, but markedly attenuated hamster drinking induced by 48 hr water deprivation or hypertonic saline injection. Dexamethasone (DEX), a glucocorticoid whichidepletes pituitary 6-endorphin and produces anorexia in rats, had no effect on daily hamster intake. Since the normal feeding profile of the hamster is similar to that of naloxone and DEXtreated rats, hamsters appear to lack an opiate-sensitive feeding system. In contrast, stimulated drinking behavior of hamsters operates through an opiate-sensitive mechanism. Thus, there are marked species differences concerning the involvement of endogenous opioids in consummatory behavior. Endogenous opioids (EO) appear to be involved in the modulation of consummatory behavior (l, 2). Centrally injected EO, such as 6-endorphin and dynorphin stimulate feeding in satiated rats (3, 4). Opiate antagonists, such as naloxone and naltrexone (NTX), attenuate various types of feeding and drinking behaviors in rats and mice (2-9). We have observed that opiate antagonists produce a dose-related attenuation of nocturnal feeding and of the hyperphagias induced by 2-deoxy-D-glucose (2-DG) and food deprivation (FD). In contrast, insulin-lnduced eating is relatively insensitive to the anorexic effect of opiate antagonists (2, 7, lO). Dexamethasone (DEX), a synthetic glucocorticoid which inhibits the synthesis and stress-induced release of pituitary 6-endorphin (ll, 12), produced a feeding profile similar to that of naloxone-treated rats (13). This suggested that circulating plasma B-endorphin may be involved in these opiate-related hyperphagias. One important consideration concerning the involvement of EO in consummatory behavior is possible species differences. All of the above studies concerning EO and consummatory behavior utilized rats or mice. Additional studies have reported that naloxone can decrease food or water intakes of guinea pigs, cats, sheep, and monkeys (14-17), as well as subjective reports of hunger in normal human volunteers (18). The present study examines the effect of the long-lasting opiate antagonist, naltrexone, on consummatory 0024-3205/82/191639-06$03.00/0 Copyright (c) 1982 Pergamon Press Ltd.
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Opiates and Hamster Ingestive Behavior
Vol. 30, No. 19, 1982
behavior of the golden hamster CMesocricetus Auratus). Such a study was of interest since the feeding behavior of these rodents is strikingly different from that of the laboratory rat. Unlike rats, hamsters do not increase feeding following FD (19) or 2-DG administration (20, 21), yet like rats, increase feeding in response to insulin administration (20, 21). Hamsters also display a minimal circadian feeding pattern (22), eating intermittant meals every 2 hrs (23). This contrasts with the predominantly nocturnal feeding of the rat. Thus, the normal feeding behavior of the hamster is remarkably similar to that of naloxone or DEX-treated rats (7, 13), which suggests hamsters may lack an opiate-sensitive feeding system. To test this possibility, we examined the effects of repeated NTX injections on hamster and rat 24 hr food and water intakes and the effects of NTX on the feeding of FD, 2-DG, and insulin-treated hamsters. Since hypertonic saline and water deprivation-induced drinking are attenuated by opiate antagonists in rats (9), the effect of NTX on these stimulated drinking conditions in hamsters was also examined. In addition, DEX was administered to hamsters in a dosing regimen which depletes pituitary B-endorphin and produces anorexia and body weight loss in rats (12, 13). Methods Subjects and Housing. Twenty-seven male, golden hamsters (90-I00 gm) and 18 male, Sprague-Dawley rats (350-420 g) were purchased from Engle (Farmersburg, IN) and Murphy Breeding Laboratories (Plainfield, IN). Animals were housed individually in metal cages (25 x 21 x 20 cm) at least two weeks prior to testing with free access to water and Wayne Lab Blox placed on the cage floor. Illumination was on a 12/12 hr schedule with light onset at 8:00 hr. Room temperature was maintained at 23-26 °C. All feeding tests were conducted in the animal's home cage. Multiple NTX Injections. To assess the effect of prolonged opiate receptor blockade on hamster and rat daily food and water intakes, NTX (l.O and lO.O mg/kg) was injected every 6 hr for 24 hr beginning at 8:00 hr. Twelve hr day and night Food and water intakes were measured, as well as body weight. NTX on Hamster Feeding. Twenty-four hr FD (water present) and administration of insulin (50 U/kg) or 2-DG (800 mg/kg) were employed in an attempt to stimulate hamster food intake. NTX (l.O and lO.O mg/kg) was injected I0-15 min prior to presentation of the preweighed food. Since insulin hyperphagia in hamsters requires 6 to 8 hr (20), NTX was administered again 4 hr post insulin injection. NTX on Hamster Drinking. NTX (l.O and lO.O mg/kg) was also tested for its effects on drinking induced by 48 hr water deprivation (WD) or by the S.C. injection of l ml of I0% NaCl (21). Food was available at all times during these drinking studies. DEX Study. Dexamethasone (Decadron, Merck) was administered in two dosing regimens: 400 or 800 ~g/kg injected at 8:00 hr, followed 24 hr later by 200 or 400 ~g, respectively. The lower dose regimen has been shown to inhibit the synthesis and stress-induced release of pituitary B-endorphin (12) and to produce anorexia and body weight loss in rats (13). Food and water intakes (12 and 24 hr), as well as body weight, of the DEX-treated hamsters were monitored for three days. General. All drugs were dissolved in 0.9% saline immediately prior to use. All injections were given subcutaneously in a volume of l ml/kg for rats and 3 ml/kg for hamsters. Control animals received saline injections. Except for the four daily NTX and DEX study, all experiments were initiated 2 to 3 hr
Vol. 30, No. 19, 1982
Opiates and Hamster Ingestive Behavior
1641
into the light cycle. Food intake was measured to the nearest O.l g by subtracting spillage collected on paper towels and uneaten food from the premeasured supply. Hamsters were examined to make sure that food pellets were not being hoarded. Water intake was measured to the nearest 0.5 ml using calibrated Richter drinking tubes. Animals were handled and given saline injections in five preliminary sessions to habituate them to the experimental procedure. Each experimental group consisted of six to seven randomly assigned animals. A recovery period of at least seven days was allowed before animals were tested again. The experiments were conducted in the order as described above. Significance was assessed by analysis of variance (ANOVA), with posthoc Newman-Keuls comparisons. Results The effect of four daily NTX injections on rat and hamster 24 hr food and water intakes is summarized in Table I. A 2-Way ANOVA (species x dose) indicated that the suppressant effect of NTX differed in rats and hamsters for both food, F (l, 24) = 20.8; p < O.OOl and water, F (l, 24) = 7.7, p < 0.01. NTX, l and lO mg/kg, attenuated rat 24 hr food intake by 23 and 28%, which was accompanied by a suppressed body weight gain (p < O.Ol). The I0.0 mg/kg dose of NTX also decreased daily water intake by 40% (p < 0.05). In contrast to rats, NTX administration did not affect 24 hr hamster food intake (p > 0.5), water intake (p > 0.3) or body weight gain (p > 0.6). Rats consumed 76 and 87% of their daily food and water intake at night, while hamsters consumed only 55 and 65% respectively (data not shown). ANOVA indicated that these differences between rats and hamsters were significant for both food and water intake (p < O.Ol). T a b l e 1.
SPECIES
Reduction by Naltrexone of 24 hr Food and Water Intake and Body Weight Gain of Rat, but not Hamster. DA I'LY INTAKE BODY WEIGHT NTX DOSE a CHANGE (g) ('mg/kg) FOOD (g) WATER (ml)
RAT
0 l lO
25.5 + 0.9 19.7 T 0.9** 18.4 +- l.l**
37.2 + 4.3 27.7 T 1.9 22.2 +- 2.8*
HAMSTER
0 l lO
9.3 + 0.4 9.0 ~ 0.4 8.7 ~ 0.4
8.9 + 0.5 7.6 ~ 0.5 7.8 T 0.8
adose injected every 6 hr for 24 hrs. each value represents mean (~ S.E.)
+ 1.8 + l.l - 8.0 T 1.2"* -14.0 ~ 1.4"* + 0.6 + 0.4 + 0.4 +- 0.5 O.0 ~- 0.5
n = 6 *p < 0.05 **p < 0.O1
The effect of NTX on the feeding of 24 hr FD, 2-DG (800 mg/kg) and insulin (50 U/kg) treated hamsters is presented in Figure I. In contrast to rats, hamsters did not increase food intake in response to FD (Figure IA) or 2-DG (Figure IB) over the 6 hr test period. Extending the feeding period to 24 hr did not improve the ability of the hamster to increase food consumption (data not shown). NTX (l.O and lO.O mg/kg) had no effect on the feeding of the FD or 2-DG treated hamsters. In contrast, insulin administration increased 6 and 8 hr food intake by 35-38% (P < 0.01; Figure IC). NTX (l.O and IO.O mg/kg) given lO min prior and 4 hr post insulin injection had no effect on the insulin-induced eating.
1642
Opiates and Hamster Ingestive Behavior
~
5.0
v
~
c.-.-oCON HFD ~--a FD~-N-IO m-.--mFD÷N-I00
v
20
<[ I--Z
Vol. 30, No. 19, 1982
o-oCON
/,l;~
e-~ INS
--
4 o -c-o INS÷N-IO
z
IO
H
IN-
/./-'~2
~
//"/
3o
0 0 kl_
o 2o
CON >
<~
Fj
g
20
T I M E (hr)
(.3
TIME (hr)
Figure I. Lack of effect of naltrexone on feeding of (A) 24 hr FD, (B) 2-DG (800 mg/kg) or (C) insulin (INS; 50 U/kg) treated hamsters. Naltrexone (l.O and I0 mg/kg) was injected lO-15 min prior to presentation of the preweighed food. Control (CON) hamsters received saline injections. Points represent mean cumulative intake of lab chow in gm (+ S.E.). b = p < O.Ol vs. INS. group, n = 6. NTX, l.O and lO mg/kg, decreased 4 hr water intake of the 48 hr WD hamsters by 27 and 46% (p < O.Ol; Figure 2A). These same doses of NTX also markedly depressed NaCl-induced drinking by 40 and 75%, respectively (p < 0.01;
Figure 2B).= A
B
w 8
~6
b w
6
4 w m2
2
b
I
CON
WD
LO
IO.O
DOSE NALTREXONE(mg/kg)
CON $AL I.O IO.0 DOSE NALTREXONE (rng/kg)
Figure 2. Reduction by naltrexone of (A) 48 hr water deprivation (WD) and (B) hypertonic saline (SAL)-induced drinking in hamsters. Naltrexone (l.O and lO.O mg/kg) was injected lO-15 min prior to presentation of water or injection of l ml lO~ NaC]. Bars represent mean 4 hr intake of water in ml (+ S.E.). b = p < O.Ol vs. WD or SAL group. n
~
6°
Neither dose of DEX affected the 24 hr daily food intake of the hamster over the three day test period (Table 2). ANOVA (treatment x days) revealed a significant effect of days (p > O.Ol), but not treatment (p > 0.2). However, DEX administration produced a small loss in hamster body weight over the three test days, which was most pronounced at 12 hr following the initial DEX injection. This body weight loss occurred in the absence of any decreases in 12 hr food or water intake.
Vol. 30, No. 19, 1982
Opiates and Hamster Ingestive Behavior
1643
Table 2.
DEXa TOTAL DOSE
Lack of Effect of DEX on Hamster Daily Food Intake, But Not, Bo,d,y,,Wei,ght Change Food Intake 12 hr
Day I
Day 2
Day 3
9.4 + 0.8
10.0 + 0.4
I0.6 ~-"0..4 9.9 +~0.4
10.9 + 0.3 11.65-0.6
0 0.6 mg/kg 1.2 mg/kg
4.5 + 0.2 4.4 T 0.2 4.2 ~-0.3
9.7;0.5 9.4 +___0.4
0 0.6 mg/kg 1.2 mg/kg
1.6 + 0.5 -2.9 + 0.5"* -3.9 + 0.4"*
0.8 + 0.4 -0.6 +-0.8 -I .6 T 0.4*
II.4 +--0.9
Body Weight Change m
1.0 + 0.3 -0.3 T 0 . 5 -2.0 • 0.5**
a2/3 dose given on day I; I/3 dose given on day 2. each value represents ~ S.E. in g for 7 hamsters
1.8 + 0.4 I.I T 0 . 7 -0.7 ~ 0.5*
*p < 0.05 **p < 0.01 vs. c o n t r o l
Discussion The present r e s u l t s confirm p r e v i o u s l y reported d i f f e r e n c e s between the c i r c a d i a n feeding p a t t e r n s o f the r a t and hamster (23), as w e l l as the f a i l u r e o f FD (19) and 2-DG (20, 21), to increase the food intake o f hamsters. In a d d i t i o n , DEX-induced a n o r e x i a , which is r e a d i l y produced in rats (13), could not be induced in hamsters. More important, m u l t i p l e i n j e c t i o n s o f NTX f a i l e d to depress the d a i l y food and water intakes o f hamsters but not t h a t o f rats. However, the present study also demonstrated c e r t a i n s i m i l a r i t i e s in the consummatory behaviors o f these two rodents. F i r s t , i n s u l i n - i n d u c e d hyperphagala, which has been induced in both species, was also found to be r e s i s t a n t to a t t e n u a t i o n by n a l t r e x o n e in the hamster (2, 7). Secondly, DEX a d m i n i s t r a t i o n decreased body weight gain of both rodents (13). The absence o f concommitant anorexia in the hamster suggests t h a t the weight loss is mainly due to d i r e c t c a t a b o l i c e f f e c t s o f the g l u c o c o r t i c o i d . Final]y, opiate antagonists decreased d r i n k i n g induced by WD or h y p e r t o n i c s a l i n e in both rats (9) and hamsters. The ]ast f i n d i n g suggests t h a t the observed i n e f f e c t i v e n e s s o f n a l t r e x o n e in reducing hamster feeding cannot be a t t r i b u t e d to enhanced metabolism and/or e x c r e t i o n of n a l t r e x o n e , nor to the absence of o p i a t e receptors in the hamster. In t h i s regard, low doses o f naloxone awakens h i b e r n a t i n g hamsters (24) and reverse the behavioral e f f e c t s o f i n j e c t e d ~-endorphin (25). For a number of reasons, i t appears t h a t the most l i k e l y e x p l a n a t i o n f o r the above noted d i f f e r e n c e s in hamster and rat feeding behavior is t h a t the system t h a t generates the e p i s o d i c (~2 hr) feeding p a t t e r n of the hamster is o p i a t e independent, whereas the rat has c r i t i c a l o p i a t e l i n k s in i t s feeding c o n t r o l system. F i r s t , the v a r i o u s types o f hyperphagic c o n d i t i o n ~ which the hamster f a i l e d to respond to ( i . e . , FD, 2-DG, and nocturnal feeding~ are a l ] hyperphagic c o n d i t i o n s which, in r a t s , are r e a d i l y a t t e n u a t e d in a doser e l a t e d fashion by o p i a t e a n t a g o n i s t s (2, 7). In c o n t r a s t , i n s u l i n - i n d u c e d hyperphagia, which is present in both species, is u n a f f e c t e d by o p i a t e a n t a g o n i s t s in e i t h e r rats (2, 7), or hamsters. Second, o p i a t e independence of hamster feeding system would be c o n s i s t e n t w i t h the i n a b i l i t y of m u l t i p l e
1644
Opiates and Hamster Ingestive Behavior
Vol. 30, No. 19, 1982
injections of NTX to decrease the food intake and cause weight loss in hamsters. In contrast, the NTX regimen did produce anorexia and body weight loss in the rats. Third, morphine and ketocyclazoclne, opiate agonists which stimulate feeding and drinking in rats (26) do not increase food or water intake of hamsters (unpub. observations). Finally, DEX administration which produces anorexia and selectively attenuates naloxone-sensitive hyperphagias in rats (7, 13) failed to decrease daily hamster food intake. Thus, these findings demonstrate that there are marked species differences in the importance of endogenous opioids in feeding behavior. They also provide another example indicating that 2-DG and insulin-induced hyperphagias are useful tools to monitor the function of the opiate link in feeding control (2, 7, IO, 13). Ackn9wledgments We thank Endo Laboratory for the gift of naltrexone. Supported in part by NIGMS Training Grant GM-07095 and American Cancer Society Grant #CH-194. References I. 2. 3. 4. 5. 6. 7. 8. 9. lO.
II. 12. 13. 14. 15. 16. 17. 18.
19. 20. 21. 22. 23. 24. 25. 26.
J. E. MORLEY, Life Sci. 27 355-368 (1980). M. T. LOWY, C. STARKEY and G. K. W. YIM, Pharmac. Biochem. Behav. 15 591-596 (1981). L. GRANDISON and A. GUIDOTTI, Neuropharmacology 16 533-536 (1977). J. E. MORLEY and A. S. LEVlNE, Life Sci. 29 ]90]-/-1903 (1981). D. R. BROWN and S. G. HOLTZMAN, Pharmac. Bi---ochem. Behav. l] 567-573 (1979). B. BRANDS, J. A. THORNHILL, M. HIRST and C. W. GOWDY, tife---Sci. 24 1773-1778 (1979). M. T. LOWY, R. P. MAICKEL and G. K. W. YIM, Life Sci. 26 2113-2118 (1980). J. E. MORLEY and A. S. LEVINE, Science 209 1259-126] -(]-980). D. R. BROWN, M. S. BLAND and S. G. HOLTZMAN, Life Sci. 26 1535-1542 (]980). G. K. W. YIM, M. T. LOWY, J. M. DAVIS, D. R. LAMB and P. V. MALVEN, The Neural Basis of Feeding and Reward, (B. Hoebel and D. Novin, eds.), in press. R. SIMANTOV, Nature 280 684-685 (1979). J. ROSSIER, E. FRENCH, C. RIVIER, T. SHIBASAKI, R. GUILLEMIN and F. E. BLOOM, Proc. Natl. Acad. Sci. USA 77: 666-669 (1980). M. T. LOWY and G. K. W. YIM, Life S~i. 27 2553-2558 (1980). R. SCHULZ, M. WUSTER and A. HERZ, Europea---n J. Pharmacol. 63 313-319 (1980). J. A. FOSTER, M. MORRISON, S. J. DEAN, M. HILL and H. FRENK, Pharmacol. Biochem. Behav. 14: 419-421 (1981). C. A. BAILE, D. A--~-KEIM, M. A. DELLA-FERA and C. L. MCLAUGHLIN, Physiol. Behav. 26 I019-I023 (1981). D. R. BRO---WNand S. G. HOLTZMAN, Life Sci. 28 1287-1294 (1981). R. T. JONES and R. I. HERNING, Endorphins i~Mental Health Research, E. Usdin, W. E. Bunney, Jr. and N. S. Kline, eds., 484-491, Oxford University Press, N.Y. (1979). H. J. SILVERMAN and I. ZUCKER, Physiol. Behav. 17 271-285 (1976). N. ROWLAND, Physiol. Behav. 21 291-294 (1978) -R. C. RITTER and O. K. BALCH,---Am. J. Physiol. 234(I): E20-E24 (1978). I. ZUCKER and F. STEPHAN, Physiol. Behav. II 239"250 (1973). K. T. BORER, N. ROWLAND, A. MIROW, R. C. BORER, JR. and R. P. KELCH, Am. J. Physiol. 236(2) ElO3-Ell2 (1979). D. L. MARGULES, B. GOLDMAN and A. FINCK, Brain Res. Bull. 4: 721-724 (1979). L.-F. TSENG, T. J. OSTWALD, H. H. LOH and C. H. LI, Psychopharmacology 64 215-218 (1979) • G. K. W. YIM, M. T. LOWY, M. P. HOLSAPPLE and W. B. NICHOLS, Soc. Neurosci. Abstr. 6 528 (1980).
Pergamon Press
DRINKING, BUT NOT FEEDING, IS OPIATE-SENSITIVE IN HAMSTERS
Martin T. Lowy and George K. W. Yim Department of Pharmacology and Toxicology School of Pharmacy and Pharmacal Sciences Purdue University West Lafayette, Indiana 47907 (Received in final form March i, 1982) Summary The long-lasting opiate antagonist, naltrexone (NTX), was examined for its effects on various types of consummatory behavior in male golden hamsters and rats. Rat, but not hamster, 24 hr food and water intakes were significantly decreased by four daily NTX (lO.O mg/kg) injections. Hamsters displayed a minimal night to day feeding ratio compared to rats. Hamsters increased food intake following insulin (50 U/kg) administration, but not after 24 hr food depri;vation (FD) or 2-deoxy-D-glucose (2-DG; 800 mg/kg) injections. NTX (l.O and IO mg/kg) had no effect on feeding, but markedly attenuated hamster drinking induced by 48 hr water deprivation or hypertonic saline injection. Dexamethasone (DEX), a glucocorticoid whichidepletes pituitary 6-endorphin and produces anorexia in rats, had no effect on daily hamster intake. Since the normal feeding profile of the hamster is similar to that of naloxone and DEXtreated rats, hamsters appear to lack an opiate-sensitive feeding system. In contrast, stimulated drinking behavior of hamsters operates through an opiate-sensitive mechanism. Thus, there are marked species differences concerning the involvement of endogenous opioids in consummatory behavior. Endogenous opioids (EO) appear to be involved in the modulation of consummatory behavior (l, 2). Centrally injected EO, such as 6-endorphin and dynorphin stimulate feeding in satiated rats (3, 4). Opiate antagonists, such as naloxone and naltrexone (NTX), attenuate various types of feeding and drinking behaviors in rats and mice (2-9). We have observed that opiate antagonists produce a dose-related attenuation of nocturnal feeding and of the hyperphagias induced by 2-deoxy-D-glucose (2-DG) and food deprivation (FD). In contrast, insulin-lnduced eating is relatively insensitive to the anorexic effect of opiate antagonists (2, 7, lO). Dexamethasone (DEX), a synthetic glucocorticoid which inhibits the synthesis and stress-induced release of pituitary 6-endorphin (ll, 12), produced a feeding profile similar to that of naloxone-treated rats (13). This suggested that circulating plasma B-endorphin may be involved in these opiate-related hyperphagias. One important consideration concerning the involvement of EO in consummatory behavior is possible species differences. All of the above studies concerning EO and consummatory behavior utilized rats or mice. Additional studies have reported that naloxone can decrease food or water intakes of guinea pigs, cats, sheep, and monkeys (14-17), as well as subjective reports of hunger in normal human volunteers (18). The present study examines the effect of the long-lasting opiate antagonist, naltrexone, on consummatory 0024-3205/82/191639-06$03.00/0 Copyright (c) 1982 Pergamon Press Ltd.
1640
Opiates and Hamster Ingestive Behavior
Vol. 30, No. 19, 1982
behavior of the golden hamster CMesocricetus Auratus). Such a study was of interest since the feeding behavior of these rodents is strikingly different from that of the laboratory rat. Unlike rats, hamsters do not increase feeding following FD (19) or 2-DG administration (20, 21), yet like rats, increase feeding in response to insulin administration (20, 21). Hamsters also display a minimal circadian feeding pattern (22), eating intermittant meals every 2 hrs (23). This contrasts with the predominantly nocturnal feeding of the rat. Thus, the normal feeding behavior of the hamster is remarkably similar to that of naloxone or DEX-treated rats (7, 13), which suggests hamsters may lack an opiate-sensitive feeding system. To test this possibility, we examined the effects of repeated NTX injections on hamster and rat 24 hr food and water intakes and the effects of NTX on the feeding of FD, 2-DG, and insulin-treated hamsters. Since hypertonic saline and water deprivation-induced drinking are attenuated by opiate antagonists in rats (9), the effect of NTX on these stimulated drinking conditions in hamsters was also examined. In addition, DEX was administered to hamsters in a dosing regimen which depletes pituitary B-endorphin and produces anorexia and body weight loss in rats (12, 13). Methods Subjects and Housing. Twenty-seven male, golden hamsters (90-I00 gm) and 18 male, Sprague-Dawley rats (350-420 g) were purchased from Engle (Farmersburg, IN) and Murphy Breeding Laboratories (Plainfield, IN). Animals were housed individually in metal cages (25 x 21 x 20 cm) at least two weeks prior to testing with free access to water and Wayne Lab Blox placed on the cage floor. Illumination was on a 12/12 hr schedule with light onset at 8:00 hr. Room temperature was maintained at 23-26 °C. All feeding tests were conducted in the animal's home cage. Multiple NTX Injections. To assess the effect of prolonged opiate receptor blockade on hamster and rat daily food and water intakes, NTX (l.O and lO.O mg/kg) was injected every 6 hr for 24 hr beginning at 8:00 hr. Twelve hr day and night Food and water intakes were measured, as well as body weight. NTX on Hamster Feeding. Twenty-four hr FD (water present) and administration of insulin (50 U/kg) or 2-DG (800 mg/kg) were employed in an attempt to stimulate hamster food intake. NTX (l.O and lO.O mg/kg) was injected I0-15 min prior to presentation of the preweighed food. Since insulin hyperphagia in hamsters requires 6 to 8 hr (20), NTX was administered again 4 hr post insulin injection. NTX on Hamster Drinking. NTX (l.O and lO.O mg/kg) was also tested for its effects on drinking induced by 48 hr water deprivation (WD) or by the S.C. injection of l ml of I0% NaCl (21). Food was available at all times during these drinking studies. DEX Study. Dexamethasone (Decadron, Merck) was administered in two dosing regimens: 400 or 800 ~g/kg injected at 8:00 hr, followed 24 hr later by 200 or 400 ~g, respectively. The lower dose regimen has been shown to inhibit the synthesis and stress-induced release of pituitary B-endorphin (12) and to produce anorexia and body weight loss in rats (13). Food and water intakes (12 and 24 hr), as well as body weight, of the DEX-treated hamsters were monitored for three days. General. All drugs were dissolved in 0.9% saline immediately prior to use. All injections were given subcutaneously in a volume of l ml/kg for rats and 3 ml/kg for hamsters. Control animals received saline injections. Except for the four daily NTX and DEX study, all experiments were initiated 2 to 3 hr
Vol. 30, No. 19, 1982
Opiates and Hamster Ingestive Behavior
1641
into the light cycle. Food intake was measured to the nearest O.l g by subtracting spillage collected on paper towels and uneaten food from the premeasured supply. Hamsters were examined to make sure that food pellets were not being hoarded. Water intake was measured to the nearest 0.5 ml using calibrated Richter drinking tubes. Animals were handled and given saline injections in five preliminary sessions to habituate them to the experimental procedure. Each experimental group consisted of six to seven randomly assigned animals. A recovery period of at least seven days was allowed before animals were tested again. The experiments were conducted in the order as described above. Significance was assessed by analysis of variance (ANOVA), with posthoc Newman-Keuls comparisons. Results The effect of four daily NTX injections on rat and hamster 24 hr food and water intakes is summarized in Table I. A 2-Way ANOVA (species x dose) indicated that the suppressant effect of NTX differed in rats and hamsters for both food, F (l, 24) = 20.8; p < O.OOl and water, F (l, 24) = 7.7, p < 0.01. NTX, l and lO mg/kg, attenuated rat 24 hr food intake by 23 and 28%, which was accompanied by a suppressed body weight gain (p < O.Ol). The I0.0 mg/kg dose of NTX also decreased daily water intake by 40% (p < 0.05). In contrast to rats, NTX administration did not affect 24 hr hamster food intake (p > 0.5), water intake (p > 0.3) or body weight gain (p > 0.6). Rats consumed 76 and 87% of their daily food and water intake at night, while hamsters consumed only 55 and 65% respectively (data not shown). ANOVA indicated that these differences between rats and hamsters were significant for both food and water intake (p < O.Ol). T a b l e 1.
SPECIES
Reduction by Naltrexone of 24 hr Food and Water Intake and Body Weight Gain of Rat, but not Hamster. DA I'LY INTAKE BODY WEIGHT NTX DOSE a CHANGE (g) ('mg/kg) FOOD (g) WATER (ml)
RAT
0 l lO
25.5 + 0.9 19.7 T 0.9** 18.4 +- l.l**
37.2 + 4.3 27.7 T 1.9 22.2 +- 2.8*
HAMSTER
0 l lO
9.3 + 0.4 9.0 ~ 0.4 8.7 ~ 0.4
8.9 + 0.5 7.6 ~ 0.5 7.8 T 0.8
adose injected every 6 hr for 24 hrs. each value represents mean (~ S.E.)
+ 1.8 + l.l - 8.0 T 1.2"* -14.0 ~ 1.4"* + 0.6 + 0.4 + 0.4 +- 0.5 O.0 ~- 0.5
n = 6 *p < 0.05 **p < 0.O1
The effect of NTX on the feeding of 24 hr FD, 2-DG (800 mg/kg) and insulin (50 U/kg) treated hamsters is presented in Figure I. In contrast to rats, hamsters did not increase food intake in response to FD (Figure IA) or 2-DG (Figure IB) over the 6 hr test period. Extending the feeding period to 24 hr did not improve the ability of the hamster to increase food consumption (data not shown). NTX (l.O and lO.O mg/kg) had no effect on the feeding of the FD or 2-DG treated hamsters. In contrast, insulin administration increased 6 and 8 hr food intake by 35-38% (P < 0.01; Figure IC). NTX (l.O and IO.O mg/kg) given lO min prior and 4 hr post insulin injection had no effect on the insulin-induced eating.
1642
Opiates and Hamster Ingestive Behavior
~
5.0
v
~
c.-.-oCON HFD ~--a FD~-N-IO m-.--mFD÷N-I00
v
20
<[ I--Z
Vol. 30, No. 19, 1982
o-oCON
/,l;~
e-~ INS
--
4 o -c-o INS÷N-IO
z
IO
H
IN-
/./-'~2
~
//"/
3o
0 0 kl_
o 2o
CON >
<~
Fj
g
20
T I M E (hr)
(.3
TIME (hr)
Figure I. Lack of effect of naltrexone on feeding of (A) 24 hr FD, (B) 2-DG (800 mg/kg) or (C) insulin (INS; 50 U/kg) treated hamsters. Naltrexone (l.O and I0 mg/kg) was injected lO-15 min prior to presentation of the preweighed food. Control (CON) hamsters received saline injections. Points represent mean cumulative intake of lab chow in gm (+ S.E.). b = p < O.Ol vs. INS. group, n = 6. NTX, l.O and lO mg/kg, decreased 4 hr water intake of the 48 hr WD hamsters by 27 and 46% (p < O.Ol; Figure 2A). These same doses of NTX also markedly depressed NaCl-induced drinking by 40 and 75%, respectively (p < 0.01;
Figure 2B).= A
B
w 8
~6
b w
6
4 w m2
2
b
I
CON
WD
LO
IO.O
DOSE NALTREXONE(mg/kg)
CON $AL I.O IO.0 DOSE NALTREXONE (rng/kg)
Figure 2. Reduction by naltrexone of (A) 48 hr water deprivation (WD) and (B) hypertonic saline (SAL)-induced drinking in hamsters. Naltrexone (l.O and lO.O mg/kg) was injected lO-15 min prior to presentation of water or injection of l ml lO~ NaC]. Bars represent mean 4 hr intake of water in ml (+ S.E.). b = p < O.Ol vs. WD or SAL group. n
~
6°
Neither dose of DEX affected the 24 hr daily food intake of the hamster over the three day test period (Table 2). ANOVA (treatment x days) revealed a significant effect of days (p > O.Ol), but not treatment (p > 0.2). However, DEX administration produced a small loss in hamster body weight over the three test days, which was most pronounced at 12 hr following the initial DEX injection. This body weight loss occurred in the absence of any decreases in 12 hr food or water intake.
Vol. 30, No. 19, 1982
Opiates and Hamster Ingestive Behavior
1643
Table 2.
DEXa TOTAL DOSE
Lack of Effect of DEX on Hamster Daily Food Intake, But Not, Bo,d,y,,Wei,ght Change Food Intake 12 hr
Day I
Day 2
Day 3
9.4 + 0.8
10.0 + 0.4
I0.6 ~-"0..4 9.9 +~0.4
10.9 + 0.3 11.65-0.6
0 0.6 mg/kg 1.2 mg/kg
4.5 + 0.2 4.4 T 0.2 4.2 ~-0.3
9.7;0.5 9.4 +___0.4
0 0.6 mg/kg 1.2 mg/kg
1.6 + 0.5 -2.9 + 0.5"* -3.9 + 0.4"*
0.8 + 0.4 -0.6 +-0.8 -I .6 T 0.4*
II.4 +--0.9
Body Weight Change m
1.0 + 0.3 -0.3 T 0 . 5 -2.0 • 0.5**
a2/3 dose given on day I; I/3 dose given on day 2. each value represents ~ S.E. in g for 7 hamsters
1.8 + 0.4 I.I T 0 . 7 -0.7 ~ 0.5*
*p < 0.05 **p < 0.01 vs. c o n t r o l
Discussion The present r e s u l t s confirm p r e v i o u s l y reported d i f f e r e n c e s between the c i r c a d i a n feeding p a t t e r n s o f the r a t and hamster (23), as w e l l as the f a i l u r e o f FD (19) and 2-DG (20, 21), to increase the food intake o f hamsters. In a d d i t i o n , DEX-induced a n o r e x i a , which is r e a d i l y produced in rats (13), could not be induced in hamsters. More important, m u l t i p l e i n j e c t i o n s o f NTX f a i l e d to depress the d a i l y food and water intakes o f hamsters but not t h a t o f rats. However, the present study also demonstrated c e r t a i n s i m i l a r i t i e s in the consummatory behaviors o f these two rodents. F i r s t , i n s u l i n - i n d u c e d hyperphagala, which has been induced in both species, was also found to be r e s i s t a n t to a t t e n u a t i o n by n a l t r e x o n e in the hamster (2, 7). Secondly, DEX a d m i n i s t r a t i o n decreased body weight gain of both rodents (13). The absence o f concommitant anorexia in the hamster suggests t h a t the weight loss is mainly due to d i r e c t c a t a b o l i c e f f e c t s o f the g l u c o c o r t i c o i d . Final]y, opiate antagonists decreased d r i n k i n g induced by WD or h y p e r t o n i c s a l i n e in both rats (9) and hamsters. The ]ast f i n d i n g suggests t h a t the observed i n e f f e c t i v e n e s s o f n a l t r e x o n e in reducing hamster feeding cannot be a t t r i b u t e d to enhanced metabolism and/or e x c r e t i o n of n a l t r e x o n e , nor to the absence of o p i a t e receptors in the hamster. In t h i s regard, low doses o f naloxone awakens h i b e r n a t i n g hamsters (24) and reverse the behavioral e f f e c t s o f i n j e c t e d ~-endorphin (25). For a number of reasons, i t appears t h a t the most l i k e l y e x p l a n a t i o n f o r the above noted d i f f e r e n c e s in hamster and rat feeding behavior is t h a t the system t h a t generates the e p i s o d i c (~2 hr) feeding p a t t e r n of the hamster is o p i a t e independent, whereas the rat has c r i t i c a l o p i a t e l i n k s in i t s feeding c o n t r o l system. F i r s t , the v a r i o u s types o f hyperphagic c o n d i t i o n ~ which the hamster f a i l e d to respond to ( i . e . , FD, 2-DG, and nocturnal feeding~ are a l ] hyperphagic c o n d i t i o n s which, in r a t s , are r e a d i l y a t t e n u a t e d in a doser e l a t e d fashion by o p i a t e a n t a g o n i s t s (2, 7). In c o n t r a s t , i n s u l i n - i n d u c e d hyperphagia, which is present in both species, is u n a f f e c t e d by o p i a t e a n t a g o n i s t s in e i t h e r rats (2, 7), or hamsters. Second, o p i a t e independence of hamster feeding system would be c o n s i s t e n t w i t h the i n a b i l i t y of m u l t i p l e
1644
Opiates and Hamster Ingestive Behavior
Vol. 30, No. 19, 1982
injections of NTX to decrease the food intake and cause weight loss in hamsters. In contrast, the NTX regimen did produce anorexia and body weight loss in the rats. Third, morphine and ketocyclazoclne, opiate agonists which stimulate feeding and drinking in rats (26) do not increase food or water intake of hamsters (unpub. observations). Finally, DEX administration which produces anorexia and selectively attenuates naloxone-sensitive hyperphagias in rats (7, 13) failed to decrease daily hamster food intake. Thus, these findings demonstrate that there are marked species differences in the importance of endogenous opioids in feeding behavior. They also provide another example indicating that 2-DG and insulin-induced hyperphagias are useful tools to monitor the function of the opiate link in feeding control (2, 7, IO, 13). Ackn9wledgments We thank Endo Laboratory for the gift of naltrexone. Supported in part by NIGMS Training Grant GM-07095 and American Cancer Society Grant #CH-194. References I. 2. 3. 4. 5. 6. 7. 8. 9. lO.
II. 12. 13. 14. 15. 16. 17. 18.
19. 20. 21. 22. 23. 24. 25. 26.
J. E. MORLEY, Life Sci. 27 355-368 (1980). M. T. LOWY, C. STARKEY and G. K. W. YIM, Pharmac. Biochem. Behav. 15 591-596 (1981). L. GRANDISON and A. GUIDOTTI, Neuropharmacology 16 533-536 (1977). J. E. MORLEY and A. S. LEVlNE, Life Sci. 29 ]90]-/-1903 (1981). D. R. BROWN and S. G. HOLTZMAN, Pharmac. Bi---ochem. Behav. l] 567-573 (1979). B. BRANDS, J. A. THORNHILL, M. HIRST and C. W. GOWDY, tife---Sci. 24 1773-1778 (1979). M. T. LOWY, R. P. MAICKEL and G. K. W. YIM, Life Sci. 26 2113-2118 (1980). J. E. MORLEY and A. S. LEVINE, Science 209 1259-126] -(]-980). D. R. BROWN, M. S. BLAND and S. G. HOLTZMAN, Life Sci. 26 1535-1542 (]980). G. K. W. YIM, M. T. LOWY, J. M. DAVIS, D. R. LAMB and P. V. MALVEN, The Neural Basis of Feeding and Reward, (B. Hoebel and D. Novin, eds.), in press. R. SIMANTOV, Nature 280 684-685 (1979). J. ROSSIER, E. FRENCH, C. RIVIER, T. SHIBASAKI, R. GUILLEMIN and F. E. BLOOM, Proc. Natl. Acad. Sci. USA 77: 666-669 (1980). M. T. LOWY and G. K. W. YIM, Life S~i. 27 2553-2558 (1980). R. SCHULZ, M. WUSTER and A. HERZ, Europea---n J. Pharmacol. 63 313-319 (1980). J. A. FOSTER, M. MORRISON, S. J. DEAN, M. HILL and H. FRENK, Pharmacol. Biochem. Behav. 14: 419-421 (1981). C. A. BAILE, D. A--~-KEIM, M. A. DELLA-FERA and C. L. MCLAUGHLIN, Physiol. Behav. 26 I019-I023 (1981). D. R. BRO---WNand S. G. HOLTZMAN, Life Sci. 28 1287-1294 (1981). R. T. JONES and R. I. HERNING, Endorphins i~Mental Health Research, E. Usdin, W. E. Bunney, Jr. and N. S. Kline, eds., 484-491, Oxford University Press, N.Y. (1979). H. J. SILVERMAN and I. ZUCKER, Physiol. Behav. 17 271-285 (1976). N. ROWLAND, Physiol. Behav. 21 291-294 (1978) -R. C. RITTER and O. K. BALCH,---Am. J. Physiol. 234(I): E20-E24 (1978). I. ZUCKER and F. STEPHAN, Physiol. Behav. II 239"250 (1973). K. T. BORER, N. ROWLAND, A. MIROW, R. C. BORER, JR. and R. P. KELCH, Am. J. Physiol. 236(2) ElO3-Ell2 (1979). D. L. MARGULES, B. GOLDMAN and A. FINCK, Brain Res. Bull. 4: 721-724 (1979). L.-F. TSENG, T. J. OSTWALD, H. H. LOH and C. H. LI, Psychopharmacology 64 215-218 (1979) • G. K. W. YIM, M. T. LOWY, M. P. HOLSAPPLE and W. B. NICHOLS, Soc. Neurosci. Abstr. 6 528 (1980).