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Flavour modulates the antidipsogenic effect of substance P
334
Brain Research, 226 (1981) 334-338 Elsevier/North-Holland Biomedical Press
Flavour modulates the antidipsogenic effect of substance P
JOHN E. MORLEY*, ALLEN S. LEVINE and SAMUEL S. MURRAY Neuroendocrine Research Laboratory, Minneapolis VA Hospital Center and the Division of Endocrinology, Department of Medicine, and the Department of Food Science and Nutrition, University of Minnesota, Minneapolis and St. Paul, M N (U.S.A.)
(Accepted August 13th, 1981) Key words: substance P - - drinking - - fluid ingestion - - antidipsogenic - - flavor
Substance P reduces water intake in a dose-dependent manner. In this report we show that the antidipsogenic effect of substance P is markedly reduced when sucrose (2%), saccharine (0.2%) or quinine (0.1%) are added to the water. Addition of saline (0.8 %) has no effect on the antidipsogenic effect of substance P. These findings indicate that flavour modulates the antidipsogenic effect of parenterally administered substance P. Flavour modifies the a m o u n t o f fluid ingested by rats following a period o f water deprivation 13. The mechanism(s) by which such hedonic qualities modify fluid ingestion is not clear. It is known that various flavours can stimulate the taste buds eliciting chordatympani nerve discharges 15. Substance P, an undecapeptide which is widely distributed in the central nervous systemg,10,17, is present in the taste organs 8. The presence o f substance P in the taste organs, together with accumulating evidence that substance P is a neurotransmitter 13,~4, suggests that this peptide may play a role in the neuromodulation o f taste. Intracerebroventricular administration of substance P in the rat inhibits drinking induced by a variety o f stimuli 1,6. In this report we demonstrate that flavour modulates the antidipsogenic effect of parenterally administered substance P. Male Sprague-Dawley rats (100-150 g) maintained in a light and temperature controlled r o o m were used in these experiments. The animals were water deprived but given food ad libitum for 15 hs prior to the experiments. Substance P (Boehringer Mannheim Biochemicals) was dissolved in 0.9 % saline and injected subcutaneously (0.2 ml) in concentrations of 0.l, 1, 10 or 100 #g/kg. Control animals received saline alone. During the experiment the animals had free access to either water, saccharine (0.2 %o), saline (0.8 %), sucrose (2 %) or quinine (0.1%) for a 60 min period. F o o d was not allowed while the animals were tested. Water intake was determined to the nearest 0.1 ml. * To whom correspondence should be addressed at: Neuroendocrine Research Laboratory, Veterans Administration Medical Center, Minneapolis, MN 55417, U.S.A. 0006-8993/81/00(0)O000/$02.75 © Elsevier/North-Holland Biomedical Press
335 Substance P (10/tg/kg) reduced water intake to 44 ± 8 ~ of the control intake. No further reduction was seen with 100 #g/kg (Table I and Fig. 1). A similar reduction in saline ingestion occurred following administration of substance P. In contrast, substance P (10 and 100/~g/kg) produced no reduction in the amount of saecharineflavoured water drunk (Fig. 1). A small non-significant reduction in the amount of sucrose water (85 i 13 ~o) and quinine water (80 :k 5 ~ ) ingested was seen after administration of 10/~g/kg substance P (Fig. 2). The highest dose of substance P produced a smaller reduction in ingestion of sucrose water (63 zk 15 ~ ) and quinine water (60 :k 5 ~o) than was present when the animals had access to either tap water (48 -L 13~) or saline (40 i 10~). As can be seen from Table I, saline markedly enhanced fluid ingestion in the controls, whereas saccharine and quinine reduced intake. Animals receiving sucrose water drank slightly more than controls. It has previously been shown that rats may either drink more or less of saccharine-containing water and that this trait is genetically determined a. It is possible that the antidipsogenic effect of substance P merely reduced water intake to some minimum threshold level producing an artifactual differential in the percentage reduction. Thus, it is important to note that there were significant differences in the total amount of fluid ingested with different flavours at the 10/~g/kg level. The possibility that substance P produces its antidipsogenic effect by a generalized disruption of behaviour appears to be extremely unlikely for a number of reasons: firstly, only the highest dose of substance P (100 #g/kg) produced minor behavioural alterations such as restlessness, increased grooming and increased motor activity, while inhibition of water intake was seen at lower doses. Secondly, the differential antidipsogenic effect of substance P makes it highly unlikely that this is due to a generalized anomaly of behaviour. Finally, De Caro et al. 1 and our group li have previously shown that substance P does not suppress starvation-induced eating in doses up to 1.5 #g intraventricularly and 10/~g/kg parenterally.
TABLE I Meanamoun~(i S.~M.)offluMingestedover~mmmthe~salsm~andafterlO~g/~ofsubsmnceP
Water Saccharine (0.2~) Saline (0.8~) Sucrose (2~) Quinine (0.1%) * P < 0.05. ** P < 0.005. *** P < 0.001.
Basal
Substance P (10 ~g/ke)
4.8 zk 0.6 3.3 zk 0.4* 8.1 -4- 0.7** 5.2 -4- 0.5 2.0 ~z 0.2***
2.1 ± 0.4 3.4 ± 0.4* 3.7 zk 0.8 4.4 ± 0.7** 1.6 ± 0.1
336
A. Water
g.
ioo _°2
75
75 ~: Iz
,~ 5 0 F-* Z
~ z5 0
C. Saline (0.8%)
I00
I00 v
Saccharine (0.2 oYoj~
v
50
Q:
I0
I
5O
z
~ 2s
o
0.1
75
0.I
I00
I
lO
0
I00
0.1
I
I0
I00
SUBSTANCE P DOSE (nug/kg)
E. Quinine (0.1%)
D. Sucrose ( 2 % ) I00
I00 ~
g,
~
75
75
g~
,-,-
50
z o o
25
I-z
50
o z5 0
0 I
I0
I00 SUBSTANCE PDOSE
, nM
0.I
I
I0
IO0
(pg/kg)
Fig. 1. The effect of different flavours on the suppression of fluid ingestion by substance P. All results are expressed as a percentage of the control ± S.E.M. for a particular flavour to allow direct comparison between groups. Numbers in parentheses and at the bottom of the bars represent the number of animals in each group. Results in each group were compared using one-way analysis of variance and Tukey's honor significance test. *P < 0.01.
O u r results confirm the finding that substance P is a p o t e n t antidipsogenic agent in the rat 1,6. This is in c o n t r a s t to the dipsogenic effect o f substance P in pigeons ~ a n d ducksL W e further d e m o n s t r a t e d that p a r e n t e r a l a d m i n i s t r a t i o n o f substance P is effective in p r o d u c i n g its antidipsogenic effect. This suggests that, like angiotensin, it m a y be exerting its effect on the circumventricular organs which lie outside the b l o o d - b r a i n barrier 4. The d e m o n s t r a t i o n by D e C a r o et al. 1 t h a t substance P strongly antagonizes angiotensin l I - i n d u c e d d r i n k i n g is further circumstantial evidence that these substances m a y act o n the same central area. The concept that drugs m a y exert a differential effect on flavour sensitivity was first suggested in 1892 when it was shown t h a t g y m n e m i c acid, a n extract o f the leaves o f a n I n d i a n plant, Gymmema sylvestre, reduces sensitivity for sweet a n d bitter but leaves salt a n d sour relatively uninfluenced 18. O u r o b s e r v a t i o n represents the first d e m o n s t r a t i o n that a n e n d o g e n o u s l y occurring n e u r o p e p t i d e with antidipsogenic p r o p e r t i e s can have its effect m o d u l a t e d b y flavour. It is o f interest that substance P selectively reduces sensitivity to sweet a n d bitter but leaves salt a n d sour unaffected. A n u m b e r o f other p h a r m a c o l o g i c a l substances such as stovaine, cocaine a n d the Sudanese plant, Bumelia dulcifica, have been d e m o n s t r a t e d to show a similar differential effect on taste with the effects on sweet a n d bitter being c o u p l e d a n d being
337 120 t
I00
t 8O
4O 2O ii!i!i!iiii::ililili:ili 0
Water
Satine Saccharine Sucrose Quinine
Fig. 2. Direct comparison of the suppression of fluid ingestion produced by 10/~g/kg substance P as modified by different flavours. All groups were compared to the effect seen when drinking water using one-way analysis of variance and Tukey's honor significance test. *P < 0.01 and tP < 0.05.
opposite to the effects o n salt 16. The high c o n c e n t r a t i o n s of substance P i n the taste organs s t a k e n together with the observations reported here, suggest a possible physiological n e u r o m o d u l a t o r y role of substance P i n the central a n d peripheral integration of taste with fluid intake. M u c h evidence has been a c c u m u l a t e d to suggest a similar n e u r o m o d u l a t o r y role for substance P i n the control of p a i n t r a n s m i s s i o n7,12 a n d recently we have d e m o n s t r a t e d the substance P modulates stress-induced eating 11. 1 DeCaro, G., Massi, M. and Micossi, L. G., Antidipsogenic effect of intracranial injections of substance P in rats, J. Physiol. (Lond.), 17 (1978) 925-929. 2 DeCaro, G., Mariotti, M., Massi, M. and Micossi, L. G., Dipsogenic effect of angiotensin II, bombesin and tachykinins in the duck, Pharmacol. Biochem. Behav., 13 (1980) 229-233. 3 Epstein, A. N., Oropharyngeal factor in feeding and drinking. In C. F. Code (Ed.), Handbook oj Physiology: Alimentary Canal, 1Iol. 1, American Physiology Society, Washington, 1967, pp. 197-218. 4 Epstein, A. N., Concensus, controversies, and curiosities, Fed. Proc., 37 (1978) 2711-2716. 5 Evered, M. D., Fitzsimmons, J. T. and DeCaro, G., Drinking behavior induced by intracranial injections of eledoisin and substance P in the pigeon, Nature (Lond.), 268 (1977) 332-333. 6 Fitzsimmons, I. T. and Evered, M. D., Eledosin, substance P and related peptides: intracranial dipsogens in the pigeon and antidipsogens in the rat, Brain Research, 150 (1978) 533-542. 7 Frederickson, R. C. A., Burgis, V., Harrell, C. E. and Edwards, J. D., Dual actions of substance P on nociception: possible role of endogenous opioids, Science, 199 (1978) 1359-1361. 8 H6kfelt, T., Johansson, O., Ljungdahl A., Lundberg, J. M. and Schutzberg, M., Peptidergic neurons, Nature (Lond.), 284 (1980) 515-521. 9 Kanazawa, I. and Jessell, T., Postmortem changes and regional distribution of substance P in the rat and the mouse nervous system, Brain Research, 117 (1976) 362-367. 10 Morley, J. E., Yamada, T., Walsh, J. H., Lamers, C. B., Wong, H., Shulkes, A., Damassa, D. A., Gordon, J., Carlson, H. E. and Hershman, J. M., Morphine addiction and withdrawal alters brain peptide concentrations, Life ScL, 26 (1980) 2239-2244. 11 Morley, J. E. and Levine, A. S., Substance P suppresses stress-induced eating, Europ. J. Pharmacol., 67 (1980) 309-311. 12 Oehme, P., Helse, H., Morgenstern, E. and Gores, E. Substance P: does it produce analgesia or hyperalgesia? Science, 208 (1980) 305-307. 13 Otsuka, M., Konishi, S. and Takahashi, T., Hypothalamic substance P as a candidate for transmitter of primary afferent neurons, Fed. Proc., 34 (1975) 1922-1928. 14 Otsuka, M. and Takahashi, T., Putative peptide neurotransmitters, Ann. Rev. Pharmacol. ToxicoL, 17 (1977) 425439.
338 15 Pfaffmann, C., Gustatory nerve impulses in rat, cat and rabbit, J. Neurophysiol., 18 (1955) 429-440. 16 Pfaffmann, C., The sense of taste. In J. Field (Ed.), Handbook of Physiology: Neurophysiology VoL 1, American Physiology Society, Washington, 1959, pp. 507-533. 17 Powell, D., Leeman, S., Treager, G. W., Niall, M. D. and Potts, J. T., Radioimmunoassay for substance P, Nature New. Biol., 241 (1973) 252-254,. 18 Shore, L. E., A contribution to our knowledge of taste sensation, J. Physiol. (Lond.), 13 (1892) 191-217.
Brain Research, 226 (1981) 334-338 Elsevier/North-Holland Biomedical Press
Flavour modulates the antidipsogenic effect of substance P
JOHN E. MORLEY*, ALLEN S. LEVINE and SAMUEL S. MURRAY Neuroendocrine Research Laboratory, Minneapolis VA Hospital Center and the Division of Endocrinology, Department of Medicine, and the Department of Food Science and Nutrition, University of Minnesota, Minneapolis and St. Paul, M N (U.S.A.)
(Accepted August 13th, 1981) Key words: substance P - - drinking - - fluid ingestion - - antidipsogenic - - flavor
Substance P reduces water intake in a dose-dependent manner. In this report we show that the antidipsogenic effect of substance P is markedly reduced when sucrose (2%), saccharine (0.2%) or quinine (0.1%) are added to the water. Addition of saline (0.8 %) has no effect on the antidipsogenic effect of substance P. These findings indicate that flavour modulates the antidipsogenic effect of parenterally administered substance P. Flavour modifies the a m o u n t o f fluid ingested by rats following a period o f water deprivation 13. The mechanism(s) by which such hedonic qualities modify fluid ingestion is not clear. It is known that various flavours can stimulate the taste buds eliciting chordatympani nerve discharges 15. Substance P, an undecapeptide which is widely distributed in the central nervous systemg,10,17, is present in the taste organs 8. The presence o f substance P in the taste organs, together with accumulating evidence that substance P is a neurotransmitter 13,~4, suggests that this peptide may play a role in the neuromodulation o f taste. Intracerebroventricular administration of substance P in the rat inhibits drinking induced by a variety o f stimuli 1,6. In this report we demonstrate that flavour modulates the antidipsogenic effect of parenterally administered substance P. Male Sprague-Dawley rats (100-150 g) maintained in a light and temperature controlled r o o m were used in these experiments. The animals were water deprived but given food ad libitum for 15 hs prior to the experiments. Substance P (Boehringer Mannheim Biochemicals) was dissolved in 0.9 % saline and injected subcutaneously (0.2 ml) in concentrations of 0.l, 1, 10 or 100 #g/kg. Control animals received saline alone. During the experiment the animals had free access to either water, saccharine (0.2 %o), saline (0.8 %), sucrose (2 %) or quinine (0.1%) for a 60 min period. F o o d was not allowed while the animals were tested. Water intake was determined to the nearest 0.1 ml. * To whom correspondence should be addressed at: Neuroendocrine Research Laboratory, Veterans Administration Medical Center, Minneapolis, MN 55417, U.S.A. 0006-8993/81/00(0)O000/$02.75 © Elsevier/North-Holland Biomedical Press
335 Substance P (10/tg/kg) reduced water intake to 44 ± 8 ~ of the control intake. No further reduction was seen with 100 #g/kg (Table I and Fig. 1). A similar reduction in saline ingestion occurred following administration of substance P. In contrast, substance P (10 and 100/~g/kg) produced no reduction in the amount of saecharineflavoured water drunk (Fig. 1). A small non-significant reduction in the amount of sucrose water (85 i 13 ~o) and quinine water (80 :k 5 ~ ) ingested was seen after administration of 10/~g/kg substance P (Fig. 2). The highest dose of substance P produced a smaller reduction in ingestion of sucrose water (63 zk 15 ~ ) and quinine water (60 :k 5 ~o) than was present when the animals had access to either tap water (48 -L 13~) or saline (40 i 10~). As can be seen from Table I, saline markedly enhanced fluid ingestion in the controls, whereas saccharine and quinine reduced intake. Animals receiving sucrose water drank slightly more than controls. It has previously been shown that rats may either drink more or less of saccharine-containing water and that this trait is genetically determined a. It is possible that the antidipsogenic effect of substance P merely reduced water intake to some minimum threshold level producing an artifactual differential in the percentage reduction. Thus, it is important to note that there were significant differences in the total amount of fluid ingested with different flavours at the 10/~g/kg level. The possibility that substance P produces its antidipsogenic effect by a generalized disruption of behaviour appears to be extremely unlikely for a number of reasons: firstly, only the highest dose of substance P (100 #g/kg) produced minor behavioural alterations such as restlessness, increased grooming and increased motor activity, while inhibition of water intake was seen at lower doses. Secondly, the differential antidipsogenic effect of substance P makes it highly unlikely that this is due to a generalized anomaly of behaviour. Finally, De Caro et al. 1 and our group li have previously shown that substance P does not suppress starvation-induced eating in doses up to 1.5 #g intraventricularly and 10/~g/kg parenterally.
TABLE I Meanamoun~(i S.~M.)offluMingestedover~mmmthe~salsm~andafterlO~g/~ofsubsmnceP
Water Saccharine (0.2~) Saline (0.8~) Sucrose (2~) Quinine (0.1%) * P < 0.05. ** P < 0.005. *** P < 0.001.
Basal
Substance P (10 ~g/ke)
4.8 zk 0.6 3.3 zk 0.4* 8.1 -4- 0.7** 5.2 -4- 0.5 2.0 ~z 0.2***
2.1 ± 0.4 3.4 ± 0.4* 3.7 zk 0.8 4.4 ± 0.7** 1.6 ± 0.1
336
A. Water
g.
ioo _°2
75
75 ~: Iz
,~ 5 0 F-* Z
~ z5 0
C. Saline (0.8%)
I00
I00 v
Saccharine (0.2 oYoj~
v
50
Q:
I0
I
5O
z
~ 2s
o
0.1
75
0.I
I00
I
lO
0
I00
0.1
I
I0
I00
SUBSTANCE P DOSE (nug/kg)
E. Quinine (0.1%)
D. Sucrose ( 2 % ) I00
I00 ~
g,
~
75
75
g~
,-,-
50
z o o
25
I-z
50
o z5 0
0 I
I0
I00 SUBSTANCE PDOSE
, nM
0.I
I
I0
IO0
(pg/kg)
Fig. 1. The effect of different flavours on the suppression of fluid ingestion by substance P. All results are expressed as a percentage of the control ± S.E.M. for a particular flavour to allow direct comparison between groups. Numbers in parentheses and at the bottom of the bars represent the number of animals in each group. Results in each group were compared using one-way analysis of variance and Tukey's honor significance test. *P < 0.01.
O u r results confirm the finding that substance P is a p o t e n t antidipsogenic agent in the rat 1,6. This is in c o n t r a s t to the dipsogenic effect o f substance P in pigeons ~ a n d ducksL W e further d e m o n s t r a t e d that p a r e n t e r a l a d m i n i s t r a t i o n o f substance P is effective in p r o d u c i n g its antidipsogenic effect. This suggests that, like angiotensin, it m a y be exerting its effect on the circumventricular organs which lie outside the b l o o d - b r a i n barrier 4. The d e m o n s t r a t i o n by D e C a r o et al. 1 t h a t substance P strongly antagonizes angiotensin l I - i n d u c e d d r i n k i n g is further circumstantial evidence that these substances m a y act o n the same central area. The concept that drugs m a y exert a differential effect on flavour sensitivity was first suggested in 1892 when it was shown t h a t g y m n e m i c acid, a n extract o f the leaves o f a n I n d i a n plant, Gymmema sylvestre, reduces sensitivity for sweet a n d bitter but leaves salt a n d sour relatively uninfluenced 18. O u r o b s e r v a t i o n represents the first d e m o n s t r a t i o n that a n e n d o g e n o u s l y occurring n e u r o p e p t i d e with antidipsogenic p r o p e r t i e s can have its effect m o d u l a t e d b y flavour. It is o f interest that substance P selectively reduces sensitivity to sweet a n d bitter but leaves salt a n d sour unaffected. A n u m b e r o f other p h a r m a c o l o g i c a l substances such as stovaine, cocaine a n d the Sudanese plant, Bumelia dulcifica, have been d e m o n s t r a t e d to show a similar differential effect on taste with the effects on sweet a n d bitter being c o u p l e d a n d being
337 120 t
I00
t 8O
4O 2O ii!i!i!iiii::ililili:ili 0
Water
Satine Saccharine Sucrose Quinine
Fig. 2. Direct comparison of the suppression of fluid ingestion produced by 10/~g/kg substance P as modified by different flavours. All groups were compared to the effect seen when drinking water using one-way analysis of variance and Tukey's honor significance test. *P < 0.01 and tP < 0.05.
opposite to the effects o n salt 16. The high c o n c e n t r a t i o n s of substance P i n the taste organs s t a k e n together with the observations reported here, suggest a possible physiological n e u r o m o d u l a t o r y role of substance P i n the central a n d peripheral integration of taste with fluid intake. M u c h evidence has been a c c u m u l a t e d to suggest a similar n e u r o m o d u l a t o r y role for substance P i n the control of p a i n t r a n s m i s s i o n7,12 a n d recently we have d e m o n s t r a t e d the substance P modulates stress-induced eating 11. 1 DeCaro, G., Massi, M. and Micossi, L. G., Antidipsogenic effect of intracranial injections of substance P in rats, J. Physiol. (Lond.), 17 (1978) 925-929. 2 DeCaro, G., Mariotti, M., Massi, M. and Micossi, L. G., Dipsogenic effect of angiotensin II, bombesin and tachykinins in the duck, Pharmacol. Biochem. Behav., 13 (1980) 229-233. 3 Epstein, A. N., Oropharyngeal factor in feeding and drinking. In C. F. Code (Ed.), Handbook oj Physiology: Alimentary Canal, 1Iol. 1, American Physiology Society, Washington, 1967, pp. 197-218. 4 Epstein, A. N., Concensus, controversies, and curiosities, Fed. Proc., 37 (1978) 2711-2716. 5 Evered, M. D., Fitzsimmons, J. T. and DeCaro, G., Drinking behavior induced by intracranial injections of eledoisin and substance P in the pigeon, Nature (Lond.), 268 (1977) 332-333. 6 Fitzsimmons, I. T. and Evered, M. D., Eledosin, substance P and related peptides: intracranial dipsogens in the pigeon and antidipsogens in the rat, Brain Research, 150 (1978) 533-542. 7 Frederickson, R. C. A., Burgis, V., Harrell, C. E. and Edwards, J. D., Dual actions of substance P on nociception: possible role of endogenous opioids, Science, 199 (1978) 1359-1361. 8 H6kfelt, T., Johansson, O., Ljungdahl A., Lundberg, J. M. and Schutzberg, M., Peptidergic neurons, Nature (Lond.), 284 (1980) 515-521. 9 Kanazawa, I. and Jessell, T., Postmortem changes and regional distribution of substance P in the rat and the mouse nervous system, Brain Research, 117 (1976) 362-367. 10 Morley, J. E., Yamada, T., Walsh, J. H., Lamers, C. B., Wong, H., Shulkes, A., Damassa, D. A., Gordon, J., Carlson, H. E. and Hershman, J. M., Morphine addiction and withdrawal alters brain peptide concentrations, Life ScL, 26 (1980) 2239-2244. 11 Morley, J. E. and Levine, A. S., Substance P suppresses stress-induced eating, Europ. J. Pharmacol., 67 (1980) 309-311. 12 Oehme, P., Helse, H., Morgenstern, E. and Gores, E. Substance P: does it produce analgesia or hyperalgesia? Science, 208 (1980) 305-307. 13 Otsuka, M., Konishi, S. and Takahashi, T., Hypothalamic substance P as a candidate for transmitter of primary afferent neurons, Fed. Proc., 34 (1975) 1922-1928. 14 Otsuka, M. and Takahashi, T., Putative peptide neurotransmitters, Ann. Rev. Pharmacol. ToxicoL, 17 (1977) 425439.
338 15 Pfaffmann, C., Gustatory nerve impulses in rat, cat and rabbit, J. Neurophysiol., 18 (1955) 429-440. 16 Pfaffmann, C., The sense of taste. In J. Field (Ed.), Handbook of Physiology: Neurophysiology VoL 1, American Physiology Society, Washington, 1959, pp. 507-533. 17 Powell, D., Leeman, S., Treager, G. W., Niall, M. D. and Potts, J. T., Radioimmunoassay for substance P, Nature New. Biol., 241 (1973) 252-254,. 18 Shore, L. E., A contribution to our knowledge of taste sensation, J. Physiol. (Lond.), 13 (1892) 191-217.