Peptides,Vol. 13, pp. 203-205, 1992
0196-9781/92 $5.00 + .00 Copyright© 1992 PergamonPressLtd.
Printed in the USA.
BRIEF COMMUNICATION
Activation of CCK-A Receptors Induces Elevation of Plasma Corticosterone in Rats GORO
KATSUURA, 1 NOBUHIRO
IBII A N D A K I R A M A T S U S H I T A
Shionogi Research Laboratories, Sagisu, Fukushima-ku, Osaka 553, Japan R e c e i v e d 17 J u n e 1991 KATSUURA, G., N. IBII AND A. MATSUSHITA. Activation of CCK-A receptors induces elevation of plasma corticosterone in rats. PEPTIDES 13(1) 203-205, 1992.--Cholecystokinin octapeptide (CCK-8) and ceruletide (1 #g/kg) produced a pronounced increment of plasma corticosterone levels at 30 min after intraperitoneal administration. The response to these peptides was suppressed by pretreatment with a selective antagonist for CCK-A receptors, (-)L-364,718, in a dose-related manner, but not with an antagonist for CCK-B receptors, (+)L-365,260. However, (-)L-364,718 itself had no effect on basal levels of plasma corticosterone. These results indicate that peripheral administration of CCK-8 and ceruletide stimulates the hypothalamo-pituitary adrenal axis through the activation of CCK-A receptors, but not CCK-B receptors. CCK-8 Ceruletide Plasma corticosterone
CCK-A receptors
CCK-B receptors
CHOLECYSTOKININ octapeptide (CCK-8) in the central nervous system has a wide range of central actions as neurotransmitter or neuromodulator to affect the activity of the central nervous system (3,4,12-15,17,19). Recently, CCK receptors have been classified into two subtypes, namely peripheral type (CCKA) and brain type (CCK-B), on the basis of ligand binding assay and functional studies (1,2,6). After developing and characterizing selective nonpeptide antagonists for CCK-A and CCK-B receptors (5), there is increasing evidence showing the involvement of a subtype of CCK receptors in CCK actions (l 8,20). Our previous results demonstrated that CCK-8 and ceruletide activate the hypothalamo-pituitary adrenal axis following intraperitoneal (IP) injection in rats (9,1 l). In the present study we observed which subtype of CCK receptors is involved in the activation of the hypothalamo-pituitary adrenal axis following the peripheral injection of CCK-8 and ceruletide in rat using selective nonpeptide antagonists for CCK receptors.
(-)L-364,718
(+)L-365,260
logical saline solution. Nonpeptide antagonists for CCK receptors, (+)L-365,260 and (-)L-364,718 (synthesized in Shionogi Res. Labs.), were suspended with 50% arabic gum and injected IP 30 min before the administration of peptides. The animals were sacrificed by decapitation 30 rain after the injection of peptides, and blood was collected in ice-cold test tubes containg 50/zl of heparin solution. Plasma corticosterone was determined by the fluoresence method as described previously (9). The data were statistically analyzed by Duncan's multiple range test after one-way analysis of variance. Each value represents the mean _+ SE of 7-9 rats. RESULTS IP injection of CCK-8 and ceruletide in a dose of 1 #g/kg induced pronounced elevation of plasma corticosterone levels (Fig. 1), which was consistent with our previous results (9,11). A CCK-A antagonist, (-)L-364,718, in doses over 1 #g/kg administered IP 30 min before the injection of CCK-8, significantly suppressed the elevation of plasma corticosterone levels in response to CCK-8, F(9,70) = 16.86, p < 0.01 (Fig. 1A). The response to ceruletide was also inhibited by (-)L-364,718 in doses more than 10 #g/kg, F(9,70) = 6.68, p < 0.01 (Fig. IB). The effective dose of the antagonist was approximately 3 and 30 times greater than CCK-8 and ceruletide, respectively, as based on the molecular weight. However, a CCK-B antagonist,
METHOD Male Wistar rats, weighing approximately 220 g, were housed at a constant room temperarture of 25°C under a light/dark cycle of 12:12 hours with lights turned on at 7:00. Rats were allowed access to rat biscuits and water ad lib. CCK-8 (Peptide Institute, Osaka, Japan) and ceruletide (caerulein diethylamine; Shionogi Res. Labs., Osaka, Japan) were diluted with physio-
1Requests for reprints should be addressed to Goro Katsuura, Ph.D., Shionogi Research Laboratories, 12-4, Sagisu 5-chome, Fukushima-ku, Osaka 553, Japan.
203
204
KATSUURA, IBII AND MATSUSHITA
"lo
80
60
(A) CCK-8
**
.......
-64"~*
o o
,~**
(+)L-365,260
40
o
.
~,~ 20
(-)L-364,718
"~x~m+ +
j++
T~ . . . , t r I ~
i
++
n
6 o odol o6ol olol o'1 Antagonists (mg/kg, ip)
80
(B) Ceruletide
o"
goJ 6o
~f
(÷)L-365,260
I'~)L
364,718
o
•'2- 40 o o
o odo10601obl Antagonists (mg/kg,
o'1
1'
ip)
FIG. 1. Effects of antagonists for CCK receptors on the elevation of plasma corticosterone levels induced by IP injection ofCCK-8 (A) and ceruletide (B) in rats. Horizontal lines in the figure indicate plasma corticosterone in saline control group. **p < 0.01 vs. saline control group; +p < 0.05, ++p < 0.01 vs. peptide-treated group.
(+)L-365,260, did not influence the response to both peptides (Fig. l). The antagonists (l mg/kg, IP) themselves had no effect on the basal levels of plasma corticosterone [(-)L-364,718, 19. l _+ 2.4 #g/dl; (+)L-365,260, 23.7 _+ 6.9 #g/dl] as compared with saline control (201 _+ 3.8 #g/d0, F(2,21) = 0.23, p > 0.05, when rats were killed 30 min after the injection. DISCUSSION Our previous reports showed that CCK-8 and ceruletide increased the plasma corticosterone levels following IP injection, but the intracerebroventricular (ICV) injection of the peptides
had no effect in rats (7,11). The response to the peptides was completely diminished by vagotomy and hypophysectomy in rats, and the peptides did not affect the secretion of adrenocorticotropic hormone (ACTH) in in vitro study using hemipituitary cultures (9,11). We have demonstrated that vagotomy reduces the amplitude of the circadian rhythm of plasma corticosterone, indicating the involvement of vagal neurons in activity of the hypothalamo-pituitary adrenal axis (10). Thus it is conceivable that through CCK receptors on peripheral nerves, such as vagus nerve, CCK-8 and ceruletide stimulate corticotropin-releasing horome (CRH) which, in turn, induces ACTH and then corticosterone secretion. While the presence of CCK-A receptors on the vagal neurons remains to be determined by direct binding assay at this time, the present study clearly demonstrated the involvement of CCK-A receptors in the activation of the hypothalamo-pituitary adrenal axis, because the increment of plasma corticosterone levels following the injection of the peptides was completely suppressed by the pretreatment of the selective antagonist for CCK-A receptors, (-)L-364,718, but the antagonist for CCK-B receptors, (+)L-365,260, in the same dose range of the CCK-A antagonist, was ineffective at blocking the response to CCK and ceruletide. According to numerous studies on subtypes of CCK receptors, CCK-A receptors have been demonstrated to have high affinity with a sulfated form of CCK8, but not nonsulfated CCK-8, CCK-4, pentagastrin and gastrin, and CCK-B receptors have relatively high affinity with these peptides as well as sulfated CCK-8 (1,2,6). Our previous studies demonstrated that ICV administration of sulfated CCK-8, instead of IP injection, suppressed the increment of plasma corticosterone levels induced by vasoactive intestinal peptide, and pentagastrin suppressed the activity of the hypothalamo-pituitary adrenal axis (7,8). These findings indicate that CCK-B receptors are not involved in the activation of the hypothalamo-pituitary adrenal axis. It has been reported that CCK-8 induces the secretion ofbeta-endorphin through CCK-A receptors in rats (16). It is well known that the release of both ACTH and beta-endorphin is stimulated by a common hypothalamic factor, CRH. Therefore, it seems likely that the activation of CCK-A receptors induces the secretion of CRH, which stimulates the release of ACTH and beta-endorphin from the pituitary. However, the antagonist for CCK-A receptors failed to influence the basal levels of plasma corticosterone, suggesting that the blocking effect of the antagonist is specific for CCK action. Studies using antagonists for CCK receptors might reveal the physiological and pathophysiological relevance of CCK in peripheral organs and the central nervous system.
REFERENCES 1. Chang, R. S. L.; Chen, T. B.; Bock, M. G.; Freidinger, R. M.; Chen, R.; Rosegay,A.; Lotti, V. J. Characterization of the binding of [3H]L365,260: A new potent and selective brain cholecystokinin (CCKB) and gastrin receptor antagonist radioligand. Mol. Pharmacol. 35: 803-808; 1989. 2. Chang, R. S. L.; Lotti, V. J.; Chen, T. B.; Kunkel, K. A. Characterization of the binding of [3H]-(_+)-L-364,718: A new potent, nonpeptide cholecystokinin antagonist radioligand selectivefor peripheral receptors. Mol. Pharmacol. 30:212-217; 1986. 3. Della-Fera, M. A.; Baile, C. A. Cholecystokinin octapeptide continuous picomole injections into the cerebral ventricles of sheep suppress feeding. Science 206:471-473; 1979. 4. Dockray, G. J. Immunochemical evidence of cholecystokinin-like peptides in brain. Nature 264:568-570; 1976. 5. Freidinger, R. M. Cholecystokinin and gastrin antagonists. Med. Res. Rev. 9:271-290; 1989.
6. Innis, R. B.; Snyder, S. H. Distinct cholecystokinin receptors in brain and pancreas. Proc. Natl. Acad. Sci. USA 77:6917-6921; 1980. 7. Itoh, S.; Hirota, R. Inhibitory effect of cholecystokinin octapeptide on vasoactive intestinal peptide-induced stimulation of adrenocortical secretion. Jpn. J. Physiol. 33:301-304; 1983. 8. Itoh, S.; Hirota, R.; Katsuura, G.; Odaguchi, K. Suppressive effect of pentagastrin on pituitary-adreno-cortical secretion. Endocrinol. Jpn. 26:741-744; 1979. 9. Itoh, S.; Hirota, R.; Katsuura, G.; Odaguchi, K. Adrenocortical stimulation by cholecystoldnin preparation in the rat. Life Sci. 25: 1725-1730; 1979. 10. Itoh, S.; Katsuura, G.; Hirota, R.; Botan, Y. Circadian rhythm of plasma corticosterone in vagotomized rats. Experientia 37:380-381; 1981. l 1. Itoh, S.; Katsuura, G.; Hirota, R.; Odaguchi, K. Effect of caerulein on plasma corticosterone in the rat. Life Sci. 27:2205-2210; 1980.
CCK-8 INCREASES PLASMA C O R T I C O S T E R O N E 12. Katsuura, G.; Itoh, S. Effect of cholecystokinin oactapeptide on body temperature in the rat. Jpn. J. Physiol. 31:849-858; 1980. 13. Katsuura, G.; Itoh, S. Sedative action of cholecystokinin octapeptide on behavioral excitation by thyrotropin releasing hormone and methamphetamine in the rat. Jpn. J. Physiol. 32:8391; 1982. 14. Katsuura, G.; Itoh, S. Specificity of nucleus accumbens to activities related to cholecystokinin in rats. Peptides 6:91-96; 1985. 15. Katsuura, G.; Itoh, S. Preventive effect ofcholecystokinin octapeptide on experimental amnesia in rats. Peptides 7:105-110; 1986. 16. Lavigne, G. J.; Millington, W. R.; Mueller, G. P. L-364,718 and lorglumide block the cholecystokinin-stimulated release of B-endorphin from the anterior pituitary. In: Hughes, J.; Dockray, G.;
205
17. 18. 19. 20.
Woodruff, G., eels. The neuropeptide cholecystokinin (CCK). Chichester: Ellis Horwood Limited; 1989:143-149. Magnani, M.; Florian, A.; Casamenti, F.; Pepeu, G. An analysis of cholecystokinin-induced increase in acetylcholine output from cerebral cortex of the rat. Neuropharmacology 26:1207-1210; 1987. Rattray, M.; Jordan, C. C.; De Belleroche, J. The novel CCK antagonist L364,718 abolishes caerulein- but potentiates morphineinduced antnociception. Eur. J. Pharmacol. 152:163-166; 1988. Saito, A.; Sankaran, B.; Goldfine, I. D.; Williams, J. A. Cholecystokinin receptors in brain: Characterization and distribution. Science 208:1155-1156; 1980. Weller, A.; Smith, G. P.; Gibbs, J. Endogenous cholecystokinin reduces feeding in young rats. Science 247:1589-1591; 1990.
0196-9781/92 $5.00 + .00 Copyright© 1992 PergamonPressLtd.
Printed in the USA.
BRIEF COMMUNICATION
Activation of CCK-A Receptors Induces Elevation of Plasma Corticosterone in Rats GORO
KATSUURA, 1 NOBUHIRO
IBII A N D A K I R A M A T S U S H I T A
Shionogi Research Laboratories, Sagisu, Fukushima-ku, Osaka 553, Japan R e c e i v e d 17 J u n e 1991 KATSUURA, G., N. IBII AND A. MATSUSHITA. Activation of CCK-A receptors induces elevation of plasma corticosterone in rats. PEPTIDES 13(1) 203-205, 1992.--Cholecystokinin octapeptide (CCK-8) and ceruletide (1 #g/kg) produced a pronounced increment of plasma corticosterone levels at 30 min after intraperitoneal administration. The response to these peptides was suppressed by pretreatment with a selective antagonist for CCK-A receptors, (-)L-364,718, in a dose-related manner, but not with an antagonist for CCK-B receptors, (+)L-365,260. However, (-)L-364,718 itself had no effect on basal levels of plasma corticosterone. These results indicate that peripheral administration of CCK-8 and ceruletide stimulates the hypothalamo-pituitary adrenal axis through the activation of CCK-A receptors, but not CCK-B receptors. CCK-8 Ceruletide Plasma corticosterone
CCK-A receptors
CCK-B receptors
CHOLECYSTOKININ octapeptide (CCK-8) in the central nervous system has a wide range of central actions as neurotransmitter or neuromodulator to affect the activity of the central nervous system (3,4,12-15,17,19). Recently, CCK receptors have been classified into two subtypes, namely peripheral type (CCKA) and brain type (CCK-B), on the basis of ligand binding assay and functional studies (1,2,6). After developing and characterizing selective nonpeptide antagonists for CCK-A and CCK-B receptors (5), there is increasing evidence showing the involvement of a subtype of CCK receptors in CCK actions (l 8,20). Our previous results demonstrated that CCK-8 and ceruletide activate the hypothalamo-pituitary adrenal axis following intraperitoneal (IP) injection in rats (9,1 l). In the present study we observed which subtype of CCK receptors is involved in the activation of the hypothalamo-pituitary adrenal axis following the peripheral injection of CCK-8 and ceruletide in rat using selective nonpeptide antagonists for CCK receptors.
(-)L-364,718
(+)L-365,260
logical saline solution. Nonpeptide antagonists for CCK receptors, (+)L-365,260 and (-)L-364,718 (synthesized in Shionogi Res. Labs.), were suspended with 50% arabic gum and injected IP 30 min before the administration of peptides. The animals were sacrificed by decapitation 30 rain after the injection of peptides, and blood was collected in ice-cold test tubes containg 50/zl of heparin solution. Plasma corticosterone was determined by the fluoresence method as described previously (9). The data were statistically analyzed by Duncan's multiple range test after one-way analysis of variance. Each value represents the mean _+ SE of 7-9 rats. RESULTS IP injection of CCK-8 and ceruletide in a dose of 1 #g/kg induced pronounced elevation of plasma corticosterone levels (Fig. 1), which was consistent with our previous results (9,11). A CCK-A antagonist, (-)L-364,718, in doses over 1 #g/kg administered IP 30 min before the injection of CCK-8, significantly suppressed the elevation of plasma corticosterone levels in response to CCK-8, F(9,70) = 16.86, p < 0.01 (Fig. 1A). The response to ceruletide was also inhibited by (-)L-364,718 in doses more than 10 #g/kg, F(9,70) = 6.68, p < 0.01 (Fig. IB). The effective dose of the antagonist was approximately 3 and 30 times greater than CCK-8 and ceruletide, respectively, as based on the molecular weight. However, a CCK-B antagonist,
METHOD Male Wistar rats, weighing approximately 220 g, were housed at a constant room temperarture of 25°C under a light/dark cycle of 12:12 hours with lights turned on at 7:00. Rats were allowed access to rat biscuits and water ad lib. CCK-8 (Peptide Institute, Osaka, Japan) and ceruletide (caerulein diethylamine; Shionogi Res. Labs., Osaka, Japan) were diluted with physio-
1Requests for reprints should be addressed to Goro Katsuura, Ph.D., Shionogi Research Laboratories, 12-4, Sagisu 5-chome, Fukushima-ku, Osaka 553, Japan.
203
204
KATSUURA, IBII AND MATSUSHITA
"lo
80
60
(A) CCK-8
**
.......
-64"~*
o o
,~**
(+)L-365,260
40
o
.
~,~ 20
(-)L-364,718
"~x~m+ +
j++
T~ . . . , t r I ~
i
++
n
6 o odol o6ol olol o'1 Antagonists (mg/kg, ip)
80
(B) Ceruletide
o"
goJ 6o
~f
(÷)L-365,260
I'~)L
364,718
o
•'2- 40 o o
o odo10601obl Antagonists (mg/kg,
o'1
1'
ip)
FIG. 1. Effects of antagonists for CCK receptors on the elevation of plasma corticosterone levels induced by IP injection ofCCK-8 (A) and ceruletide (B) in rats. Horizontal lines in the figure indicate plasma corticosterone in saline control group. **p < 0.01 vs. saline control group; +p < 0.05, ++p < 0.01 vs. peptide-treated group.
(+)L-365,260, did not influence the response to both peptides (Fig. l). The antagonists (l mg/kg, IP) themselves had no effect on the basal levels of plasma corticosterone [(-)L-364,718, 19. l _+ 2.4 #g/dl; (+)L-365,260, 23.7 _+ 6.9 #g/dl] as compared with saline control (201 _+ 3.8 #g/d0, F(2,21) = 0.23, p > 0.05, when rats were killed 30 min after the injection. DISCUSSION Our previous reports showed that CCK-8 and ceruletide increased the plasma corticosterone levels following IP injection, but the intracerebroventricular (ICV) injection of the peptides
had no effect in rats (7,11). The response to the peptides was completely diminished by vagotomy and hypophysectomy in rats, and the peptides did not affect the secretion of adrenocorticotropic hormone (ACTH) in in vitro study using hemipituitary cultures (9,11). We have demonstrated that vagotomy reduces the amplitude of the circadian rhythm of plasma corticosterone, indicating the involvement of vagal neurons in activity of the hypothalamo-pituitary adrenal axis (10). Thus it is conceivable that through CCK receptors on peripheral nerves, such as vagus nerve, CCK-8 and ceruletide stimulate corticotropin-releasing horome (CRH) which, in turn, induces ACTH and then corticosterone secretion. While the presence of CCK-A receptors on the vagal neurons remains to be determined by direct binding assay at this time, the present study clearly demonstrated the involvement of CCK-A receptors in the activation of the hypothalamo-pituitary adrenal axis, because the increment of plasma corticosterone levels following the injection of the peptides was completely suppressed by the pretreatment of the selective antagonist for CCK-A receptors, (-)L-364,718, but the antagonist for CCK-B receptors, (+)L-365,260, in the same dose range of the CCK-A antagonist, was ineffective at blocking the response to CCK and ceruletide. According to numerous studies on subtypes of CCK receptors, CCK-A receptors have been demonstrated to have high affinity with a sulfated form of CCK8, but not nonsulfated CCK-8, CCK-4, pentagastrin and gastrin, and CCK-B receptors have relatively high affinity with these peptides as well as sulfated CCK-8 (1,2,6). Our previous studies demonstrated that ICV administration of sulfated CCK-8, instead of IP injection, suppressed the increment of plasma corticosterone levels induced by vasoactive intestinal peptide, and pentagastrin suppressed the activity of the hypothalamo-pituitary adrenal axis (7,8). These findings indicate that CCK-B receptors are not involved in the activation of the hypothalamo-pituitary adrenal axis. It has been reported that CCK-8 induces the secretion ofbeta-endorphin through CCK-A receptors in rats (16). It is well known that the release of both ACTH and beta-endorphin is stimulated by a common hypothalamic factor, CRH. Therefore, it seems likely that the activation of CCK-A receptors induces the secretion of CRH, which stimulates the release of ACTH and beta-endorphin from the pituitary. However, the antagonist for CCK-A receptors failed to influence the basal levels of plasma corticosterone, suggesting that the blocking effect of the antagonist is specific for CCK action. Studies using antagonists for CCK receptors might reveal the physiological and pathophysiological relevance of CCK in peripheral organs and the central nervous system.
REFERENCES 1. Chang, R. S. L.; Chen, T. B.; Bock, M. G.; Freidinger, R. M.; Chen, R.; Rosegay,A.; Lotti, V. J. Characterization of the binding of [3H]L365,260: A new potent and selective brain cholecystokinin (CCKB) and gastrin receptor antagonist radioligand. Mol. Pharmacol. 35: 803-808; 1989. 2. Chang, R. S. L.; Lotti, V. J.; Chen, T. B.; Kunkel, K. A. Characterization of the binding of [3H]-(_+)-L-364,718: A new potent, nonpeptide cholecystokinin antagonist radioligand selectivefor peripheral receptors. Mol. Pharmacol. 30:212-217; 1986. 3. Della-Fera, M. A.; Baile, C. A. Cholecystokinin octapeptide continuous picomole injections into the cerebral ventricles of sheep suppress feeding. Science 206:471-473; 1979. 4. Dockray, G. J. Immunochemical evidence of cholecystokinin-like peptides in brain. Nature 264:568-570; 1976. 5. Freidinger, R. M. Cholecystokinin and gastrin antagonists. Med. Res. Rev. 9:271-290; 1989.
6. Innis, R. B.; Snyder, S. H. Distinct cholecystokinin receptors in brain and pancreas. Proc. Natl. Acad. Sci. USA 77:6917-6921; 1980. 7. Itoh, S.; Hirota, R. Inhibitory effect of cholecystokinin octapeptide on vasoactive intestinal peptide-induced stimulation of adrenocortical secretion. Jpn. J. Physiol. 33:301-304; 1983. 8. Itoh, S.; Hirota, R.; Katsuura, G.; Odaguchi, K. Suppressive effect of pentagastrin on pituitary-adreno-cortical secretion. Endocrinol. Jpn. 26:741-744; 1979. 9. Itoh, S.; Hirota, R.; Katsuura, G.; Odaguchi, K. Adrenocortical stimulation by cholecystoldnin preparation in the rat. Life Sci. 25: 1725-1730; 1979. 10. Itoh, S.; Katsuura, G.; Hirota, R.; Botan, Y. Circadian rhythm of plasma corticosterone in vagotomized rats. Experientia 37:380-381; 1981. l 1. Itoh, S.; Katsuura, G.; Hirota, R.; Odaguchi, K. Effect of caerulein on plasma corticosterone in the rat. Life Sci. 27:2205-2210; 1980.
CCK-8 INCREASES PLASMA C O R T I C O S T E R O N E 12. Katsuura, G.; Itoh, S. Effect of cholecystokinin oactapeptide on body temperature in the rat. Jpn. J. Physiol. 31:849-858; 1980. 13. Katsuura, G.; Itoh, S. Sedative action of cholecystokinin octapeptide on behavioral excitation by thyrotropin releasing hormone and methamphetamine in the rat. Jpn. J. Physiol. 32:8391; 1982. 14. Katsuura, G.; Itoh, S. Specificity of nucleus accumbens to activities related to cholecystokinin in rats. Peptides 6:91-96; 1985. 15. Katsuura, G.; Itoh, S. Preventive effect ofcholecystokinin octapeptide on experimental amnesia in rats. Peptides 7:105-110; 1986. 16. Lavigne, G. J.; Millington, W. R.; Mueller, G. P. L-364,718 and lorglumide block the cholecystokinin-stimulated release of B-endorphin from the anterior pituitary. In: Hughes, J.; Dockray, G.;
205
17. 18. 19. 20.
Woodruff, G., eels. The neuropeptide cholecystokinin (CCK). Chichester: Ellis Horwood Limited; 1989:143-149. Magnani, M.; Florian, A.; Casamenti, F.; Pepeu, G. An analysis of cholecystokinin-induced increase in acetylcholine output from cerebral cortex of the rat. Neuropharmacology 26:1207-1210; 1987. Rattray, M.; Jordan, C. C.; De Belleroche, J. The novel CCK antagonist L364,718 abolishes caerulein- but potentiates morphineinduced antnociception. Eur. J. Pharmacol. 152:163-166; 1988. Saito, A.; Sankaran, B.; Goldfine, I. D.; Williams, J. A. Cholecystokinin receptors in brain: Characterization and distribution. Science 208:1155-1156; 1980. Weller, A.; Smith, G. P.; Gibbs, J. Endogenous cholecystokinin reduces feeding in young rats. Science 247:1589-1591; 1990.
