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The actions of melanin-concentrating hormone (MCH) on passive avoidance in rats: A preliminary study
Peptides, Vol. 15, No. 4, pp. 757-759, 1994 Copyright © 1994 ElsevierScienceLtd Printed in the USA. All rights reserved 0196-9781/94 $6.00 + .00
Pergamon 0196-9781 (94)E0017-Y
BRIEF COMMUNICATION
The Actions of Melanin-Concentrating Hormone (MCH) on Passive Avoidance in Rats: A Preliminary Study ROSANNE
B. M c B R I D E , * B I L L E. B E C K W I T H , .1 R O B Y N M A C E. H A D L E Y , : ~ T E R R Y O. M A T S U N A G A §
R. SWENSON,* TOMI K. S A W Y E R , i " AND
VICTOR
J. H R U B Y §
*Psychology Department, University of North Dakota, Grand Forks, ND 58202, tParke-Davis Company, 2800 Plymouth Road, Ann Arbor, M I 48105, and Departments of ~L4natomy and §Chemistry, University of Arizona, Tucson, A Z 85721 R e c e i v e d 12 M a r c h 1993 McBRIDE, R. B., B. E. BECKWITH, R. R. SWENSON, T. K. SAWYER, M. E. HADLEY, T. O. MATSUNAGA AND V. J. HRUBY. The actions of melanin-concentratinghormone(MCH) on passive avoidance in rats:A preliminary study. PEPTIDES 15(4) 757-759, 1994.--Melanin-concentrating hormone (MCH) is a hepadecapeptide hormone that is synthesized in the CNS and is responsible for melanosome aggregation in the teleost fish. Recent evidence suggests that this peptide hormone has a unique distribution in the mammalian brain, which leads to the speculation that it may serve as a neuromodulator. The present study was undertaken to explore the comparative effects of MCH to those of a-melanocyte-stimulating Hormone (MSH) (a neuropeptide that is known to influence learning) on the rate of extinction of a passive avoidance response in rats. Both MCH and MSH were administered SC at l0 ~tg per animal. Treatment with MCH appeared to hasten, whereas treatment with MSH appeared to delay, extinction of the passive avoidance response. Behavior
Extinction
Learning
Memory
MCH
MSH
Neuropeptides
Passive avoidance
and memory. However, M S H has long been known to serve a neuromodulatory role in learning and m e m o r y (3-6). Furthermore, M S H is known to retard the extinction of passive avoidance in rats (7,8,13,14). We hypothesized that treatment with M C H would have opposite effects upon the extinction of passive avoidance to those of M S H at identical concentrations.
M E L A N I N - C O N C E N T R A T I N G hormone (MCH) is a potent cyclic hepadecapeptide hormone that was isolated and characterized from the salmon hypophysis (12) and the rat hypothalamus (15). Early work focused upon the potent melanosomeaggregating effects of M C H on pigment cells of the teleost fish-a response opposite to the melanosome-dispersing effects of aMSH (MSH) (16,17). However, subsequent studies demonstrated that M C H caused melanosome dispersion when used at high concentrations (9,10). Melanin-concentrating hormone has also been suggested to have a modulatory role in higher vertebrates (1,2). This suggestion was based on the discovery of neurons in the hypothalamus with extrahypothalamic projections that contain M C H and the demonstration that M C H inhibits release of corticotropin in response to stress (1). In an attempt to explore the possibility that M C H may act as a neuromodulatory neuropeptide, the present study was designed to examine the effects of M C H and M S H on the rate of extinction of a passive avoidance response in rats. We are aware of no other attempt to explore the influence of M C H on learning
METHOD
Animals Twenty-eight, 65-day-old male Holtzman Albino rats served as subjects. They were housed individually under conditions of controlled light-dark cycles and were provided with ad lib access to food and water in home cages.
Apparatus The test apparatus was a standard, 40-cm-square, black Plexiglas passive avoidance chamber. A 25-W lamp placed above
Requests for reprints should be addressed to Bill E. Beckwith, 1520 Royal Palm Square Blvd., Ste 350, Fort Myers, FL 33919.
757
758
M c B R I D E ET AL.
the center of the runway was the only light in the r o o m - - t h e inside of the chamber remained dark.
400 A
u)
Procedure
o
Animals were first adapted to the apparatus by placing them in the dark chamber for 2 min. The animal was then placed on the runway facing away from the door to the dark chamber. After 10 s, the door was opened and the animal was allowed to enter the dark chamber. Ten seconds later the animal was removed and placed in its home cage. Twenty-four hours later the animal was again placed on the runway and allowed to enter the dark chamber. After two such trials, the animal was again placed on the runway and allowed to enter the dark chamber. However, upon entry into the dark chamber, the animal received a 2-s scrambled, inescapable foot shock equal to 0.5 mA. The animal was removed from the dark chamber and immediately injected with either 10 #g of M C H , 10 ttg of MSH, or an equal volume of saline. All treatments were done by experimenters who were blinded to treatment conditions. Animals were then returned to their home cages. Retention tests were administered to each animal 24, 48, and 72 h after the learning trial. The m a x i m u m duration of test trials was 600 s, with initial latency determined by the time it took the animal to place all four feet in the dark chamber.
(n
. 300
200 -I ~=
• MSH [] MCH [] PLACEBO
100
i1 24
48
Retention
72 Interval
FIG. 1. Mean latency (with SD bars) for crossing over into the dark chamber of the passive avoidance apparatus after a 24-, 48-, and 72-h retention interval. *Designates different from 24 h within treatment (p < 0.05). For each group, n = 10, 10, and 8 for treatment with the placebo, MCH, and MSH, respectively.
RESULTS To gain more statistical power (11), planned comparisons were performed among means (alpha = 0.05) for analysis of treatment effects across retention intervals. As can be seen in Fig. 1, treatment with MSH did not alter latencies to enter the dark chamber across retention intervals. Melanin-concentrating hormone decreased latency between 24 and 48 h, t(18) = 2.22, and between 24 and 72 h, t(18) = 2.87. Treatment with saline also decreased latencies between 24 and 48 h, t(18) = 2.26, and between 24 and 72 h, t(18) = 2.56. There were no statistically significant differences between treatments within retention intervals. The effect of treatments on the rate of extinction can be more clearly seen by examining the percent decrease in latency at each retention interval within treatments. Treatment with M C H , saline, and MSH produced a decrease in latency from 24 to 72 h of 87%, 51%, and 41%, respectively. Treatment with M S H decreased latency by 37% between 24 and 48 h and by 6% between 48 and 72 h; treatment with M C H reduced latency by 61% between 24 and 48 h and by 66% between 48 and 72 h. Treatment with saline decreased latency between 24 and 48 h by 28% and between 48 and 72 h by 33%.
the dark chamber of the apparatus suggest that M C H and M S H may have opposite effects on extinction of a passive avoidance response when administered at a dose of 10 #g per rat. Despite the failure to detect differences in performance within treatments at each latency, it is clear that the percent change in latency is far greater after treatment with M C H than after treatment with saline. These are the first results, to our knowledge, that peripheral administration of M C H may produce effects on learning and memory. Treatment with M S H has been shown to reduce the rate of extinction in several previous studies (8,13,14). Although the specific pattern is somewhat different in the present study, several methodological variables may account for the specific effects. O f course, these data do not resolve the issue of whether the findings are a reflection of peripheral or central effects of M C H . Future studies will need to evaluate the potential for M C H to cross the blood-brain barrier and evaluate the potential of centrally administered M C H to influence learning and memory. However, we believe these results suggest the potential for M C H to be yet another CNS active peptide.
DISCUSSION
ACKNOWLEDGEMENTS
Treatment with MSH retarded extinction of a passive avoidance response whereas treatment with M C H and saline allowed reduction of latencies after retention intervals of 24, 48, and 72 h. Comparisons of the percent reduction of latencies to enter
This work was supported, in part, by grants from the Upjohn Company and U.S. Public Health Service AM 17420. We acknowledge the assistance of Mike Cicha with this project.
REFERENCES 1. Baker, B. I.; Bird, D. J.; Buckingham, J. C. Salmonidmelanin-concentrating hormone inhibits corticotropin release. J. Endocrinol. 106: R5-R8; 1985. 2. Barber, L. D.; Baker, B. I.; Penny, J. C.; Eberle, A. N. Melanin concentrating hormone inhibits the release of alpha-MSH from teleost pituitary glands. Gen. Comp. Endrocrinol. 65:79-86; 1987. 3. Beckwith, B. E. The melanotropins, leaning and memory. In: Hadley, M. E., ed. The melanotropic peptides: Biological roles, vol. 2. Boca Raton: CRC Press; 1988:43-72.
4. Beckwith, B. E.; Kastin, A. J. Central actions of melanocyte-stimulating hormone (MSH). In: Negro-Vilar, A.; Conn, P. M., eds. Peptide hormones: Effects and mechanisms of action. Boca Raton: CRC Press; 1988:195-218. 5. Beckwith, B. E.; Sandman, C. A. Behavioral influences of the neuropeptides ACTH and MSH: A methodological review. Neurosci. Biobehav. Rev. 2:311-338; 1978. 6. Bohus, B. Effects of ACTH-Iike neuropeptides on animal behavior and man. Pharmacology 18:113-122; 1979. 7. Datta, P. C.; King, M. G. Effects of alpha-MSH and melatonin on
EFFECTS OF MCH
8. 9. 10. 1 I. 12. 13.
PA-induced defecation and plasma 11-OHCS in hypophysectomized rats. Peptides 1:147-153; 1980. Dempsey, G. L.; Kastin, A. J.; Schally, A. V. The effects of MSH on a restricted passive avoidance response. Horm. Behav. 3:333-337; 1972. Eberle, A. N. J. Peptide synthesis. Part 9. Solid phase synthesis of melanin concentrating hormone using a continuous flow polyamine method. Chem. Soc. Perkin. Trans. 1:361-367; 1986. Hadley, M. E.; Zechel, C.; Wilkes, B. C.; et al. Differential structural requirements for the MSH and MCH activities of melanin concentrating hormone. Life Sci. 40:1139-1145; 1987. Hays, W. L. Statistics. New York: Holt, Rinehart, Winston; 1963. Kawauchi, W.; Kawozoe, I.; Tsubokawa, M.; Kishida, M.; Baker, B. Characterization of melanin concentrating hormone in chum salmon pituitaries. Nature 305:321-323; 1983. Sandman, C. A.; Kastin, A. J.; Schally, A. V. Behavioral inhibition
759
14.
15. 16.
17.
as modified by melanocyte-stimulating hormone (MSH) and lightdark conditions. Physiol. Behav. 6:45-48; 1971. Segal, A.; Wright, C.; Edwardson, J. A.; Keith, A. B. Corticotropin releasing factor is more potent than some corticotropin-related peptides in affecting passive avoidance behavior in rats. Neurosci. Lett. 36:81-86; 1983. Vaughan, J. M.; Fischer, W. H.; Hoeger, C.; Rivier, J.: Vale, W. Characterization of melanin-concentrating hormone from rat hypothalamus. Endocrinology 125:1660-1665; 1989. Wilkes, B. C.; Hruby, V. J.; Castrucci, A. M. L.; Sherbrooke, W. C.; Hadley, M. E. Synthesis of a cyclic melanotropic peptide exhibiting both melanin concentrating and dispersing activities. Science 224: 1111-1113; 1984. Wilkes, B. C.; Hruby, V. J.; Sherbrooke, W. C.; Castrucci, A. M. L.; Hadley, M. E. Biochem. Biophys. Res. Commun. 122:613-619; 1984.
Pergamon 0196-9781 (94)E0017-Y
BRIEF COMMUNICATION
The Actions of Melanin-Concentrating Hormone (MCH) on Passive Avoidance in Rats: A Preliminary Study ROSANNE
B. M c B R I D E , * B I L L E. B E C K W I T H , .1 R O B Y N M A C E. H A D L E Y , : ~ T E R R Y O. M A T S U N A G A §
R. SWENSON,* TOMI K. S A W Y E R , i " AND
VICTOR
J. H R U B Y §
*Psychology Department, University of North Dakota, Grand Forks, ND 58202, tParke-Davis Company, 2800 Plymouth Road, Ann Arbor, M I 48105, and Departments of ~L4natomy and §Chemistry, University of Arizona, Tucson, A Z 85721 R e c e i v e d 12 M a r c h 1993 McBRIDE, R. B., B. E. BECKWITH, R. R. SWENSON, T. K. SAWYER, M. E. HADLEY, T. O. MATSUNAGA AND V. J. HRUBY. The actions of melanin-concentratinghormone(MCH) on passive avoidance in rats:A preliminary study. PEPTIDES 15(4) 757-759, 1994.--Melanin-concentrating hormone (MCH) is a hepadecapeptide hormone that is synthesized in the CNS and is responsible for melanosome aggregation in the teleost fish. Recent evidence suggests that this peptide hormone has a unique distribution in the mammalian brain, which leads to the speculation that it may serve as a neuromodulator. The present study was undertaken to explore the comparative effects of MCH to those of a-melanocyte-stimulating Hormone (MSH) (a neuropeptide that is known to influence learning) on the rate of extinction of a passive avoidance response in rats. Both MCH and MSH were administered SC at l0 ~tg per animal. Treatment with MCH appeared to hasten, whereas treatment with MSH appeared to delay, extinction of the passive avoidance response. Behavior
Extinction
Learning
Memory
MCH
MSH
Neuropeptides
Passive avoidance
and memory. However, M S H has long been known to serve a neuromodulatory role in learning and m e m o r y (3-6). Furthermore, M S H is known to retard the extinction of passive avoidance in rats (7,8,13,14). We hypothesized that treatment with M C H would have opposite effects upon the extinction of passive avoidance to those of M S H at identical concentrations.
M E L A N I N - C O N C E N T R A T I N G hormone (MCH) is a potent cyclic hepadecapeptide hormone that was isolated and characterized from the salmon hypophysis (12) and the rat hypothalamus (15). Early work focused upon the potent melanosomeaggregating effects of M C H on pigment cells of the teleost fish-a response opposite to the melanosome-dispersing effects of aMSH (MSH) (16,17). However, subsequent studies demonstrated that M C H caused melanosome dispersion when used at high concentrations (9,10). Melanin-concentrating hormone has also been suggested to have a modulatory role in higher vertebrates (1,2). This suggestion was based on the discovery of neurons in the hypothalamus with extrahypothalamic projections that contain M C H and the demonstration that M C H inhibits release of corticotropin in response to stress (1). In an attempt to explore the possibility that M C H may act as a neuromodulatory neuropeptide, the present study was designed to examine the effects of M C H and M S H on the rate of extinction of a passive avoidance response in rats. We are aware of no other attempt to explore the influence of M C H on learning
METHOD
Animals Twenty-eight, 65-day-old male Holtzman Albino rats served as subjects. They were housed individually under conditions of controlled light-dark cycles and were provided with ad lib access to food and water in home cages.
Apparatus The test apparatus was a standard, 40-cm-square, black Plexiglas passive avoidance chamber. A 25-W lamp placed above
Requests for reprints should be addressed to Bill E. Beckwith, 1520 Royal Palm Square Blvd., Ste 350, Fort Myers, FL 33919.
757
758
M c B R I D E ET AL.
the center of the runway was the only light in the r o o m - - t h e inside of the chamber remained dark.
400 A
u)
Procedure
o
Animals were first adapted to the apparatus by placing them in the dark chamber for 2 min. The animal was then placed on the runway facing away from the door to the dark chamber. After 10 s, the door was opened and the animal was allowed to enter the dark chamber. Ten seconds later the animal was removed and placed in its home cage. Twenty-four hours later the animal was again placed on the runway and allowed to enter the dark chamber. After two such trials, the animal was again placed on the runway and allowed to enter the dark chamber. However, upon entry into the dark chamber, the animal received a 2-s scrambled, inescapable foot shock equal to 0.5 mA. The animal was removed from the dark chamber and immediately injected with either 10 #g of M C H , 10 ttg of MSH, or an equal volume of saline. All treatments were done by experimenters who were blinded to treatment conditions. Animals were then returned to their home cages. Retention tests were administered to each animal 24, 48, and 72 h after the learning trial. The m a x i m u m duration of test trials was 600 s, with initial latency determined by the time it took the animal to place all four feet in the dark chamber.
(n
. 300
200 -I ~=
• MSH [] MCH [] PLACEBO
100
i1 24
48
Retention
72 Interval
FIG. 1. Mean latency (with SD bars) for crossing over into the dark chamber of the passive avoidance apparatus after a 24-, 48-, and 72-h retention interval. *Designates different from 24 h within treatment (p < 0.05). For each group, n = 10, 10, and 8 for treatment with the placebo, MCH, and MSH, respectively.
RESULTS To gain more statistical power (11), planned comparisons were performed among means (alpha = 0.05) for analysis of treatment effects across retention intervals. As can be seen in Fig. 1, treatment with MSH did not alter latencies to enter the dark chamber across retention intervals. Melanin-concentrating hormone decreased latency between 24 and 48 h, t(18) = 2.22, and between 24 and 72 h, t(18) = 2.87. Treatment with saline also decreased latencies between 24 and 48 h, t(18) = 2.26, and between 24 and 72 h, t(18) = 2.56. There were no statistically significant differences between treatments within retention intervals. The effect of treatments on the rate of extinction can be more clearly seen by examining the percent decrease in latency at each retention interval within treatments. Treatment with M C H , saline, and MSH produced a decrease in latency from 24 to 72 h of 87%, 51%, and 41%, respectively. Treatment with M S H decreased latency by 37% between 24 and 48 h and by 6% between 48 and 72 h; treatment with M C H reduced latency by 61% between 24 and 48 h and by 66% between 48 and 72 h. Treatment with saline decreased latency between 24 and 48 h by 28% and between 48 and 72 h by 33%.
the dark chamber of the apparatus suggest that M C H and M S H may have opposite effects on extinction of a passive avoidance response when administered at a dose of 10 #g per rat. Despite the failure to detect differences in performance within treatments at each latency, it is clear that the percent change in latency is far greater after treatment with M C H than after treatment with saline. These are the first results, to our knowledge, that peripheral administration of M C H may produce effects on learning and memory. Treatment with M S H has been shown to reduce the rate of extinction in several previous studies (8,13,14). Although the specific pattern is somewhat different in the present study, several methodological variables may account for the specific effects. O f course, these data do not resolve the issue of whether the findings are a reflection of peripheral or central effects of M C H . Future studies will need to evaluate the potential for M C H to cross the blood-brain barrier and evaluate the potential of centrally administered M C H to influence learning and memory. However, we believe these results suggest the potential for M C H to be yet another CNS active peptide.
DISCUSSION
ACKNOWLEDGEMENTS
Treatment with MSH retarded extinction of a passive avoidance response whereas treatment with M C H and saline allowed reduction of latencies after retention intervals of 24, 48, and 72 h. Comparisons of the percent reduction of latencies to enter
This work was supported, in part, by grants from the Upjohn Company and U.S. Public Health Service AM 17420. We acknowledge the assistance of Mike Cicha with this project.
REFERENCES 1. Baker, B. I.; Bird, D. J.; Buckingham, J. C. Salmonidmelanin-concentrating hormone inhibits corticotropin release. J. Endocrinol. 106: R5-R8; 1985. 2. Barber, L. D.; Baker, B. I.; Penny, J. C.; Eberle, A. N. Melanin concentrating hormone inhibits the release of alpha-MSH from teleost pituitary glands. Gen. Comp. Endrocrinol. 65:79-86; 1987. 3. Beckwith, B. E. The melanotropins, leaning and memory. In: Hadley, M. E., ed. The melanotropic peptides: Biological roles, vol. 2. Boca Raton: CRC Press; 1988:43-72.
4. Beckwith, B. E.; Kastin, A. J. Central actions of melanocyte-stimulating hormone (MSH). In: Negro-Vilar, A.; Conn, P. M., eds. Peptide hormones: Effects and mechanisms of action. Boca Raton: CRC Press; 1988:195-218. 5. Beckwith, B. E.; Sandman, C. A. Behavioral influences of the neuropeptides ACTH and MSH: A methodological review. Neurosci. Biobehav. Rev. 2:311-338; 1978. 6. Bohus, B. Effects of ACTH-Iike neuropeptides on animal behavior and man. Pharmacology 18:113-122; 1979. 7. Datta, P. C.; King, M. G. Effects of alpha-MSH and melatonin on
EFFECTS OF MCH
8. 9. 10. 1 I. 12. 13.
PA-induced defecation and plasma 11-OHCS in hypophysectomized rats. Peptides 1:147-153; 1980. Dempsey, G. L.; Kastin, A. J.; Schally, A. V. The effects of MSH on a restricted passive avoidance response. Horm. Behav. 3:333-337; 1972. Eberle, A. N. J. Peptide synthesis. Part 9. Solid phase synthesis of melanin concentrating hormone using a continuous flow polyamine method. Chem. Soc. Perkin. Trans. 1:361-367; 1986. Hadley, M. E.; Zechel, C.; Wilkes, B. C.; et al. Differential structural requirements for the MSH and MCH activities of melanin concentrating hormone. Life Sci. 40:1139-1145; 1987. Hays, W. L. Statistics. New York: Holt, Rinehart, Winston; 1963. Kawauchi, W.; Kawozoe, I.; Tsubokawa, M.; Kishida, M.; Baker, B. Characterization of melanin concentrating hormone in chum salmon pituitaries. Nature 305:321-323; 1983. Sandman, C. A.; Kastin, A. J.; Schally, A. V. Behavioral inhibition
759
14.
15. 16.
17.
as modified by melanocyte-stimulating hormone (MSH) and lightdark conditions. Physiol. Behav. 6:45-48; 1971. Segal, A.; Wright, C.; Edwardson, J. A.; Keith, A. B. Corticotropin releasing factor is more potent than some corticotropin-related peptides in affecting passive avoidance behavior in rats. Neurosci. Lett. 36:81-86; 1983. Vaughan, J. M.; Fischer, W. H.; Hoeger, C.; Rivier, J.: Vale, W. Characterization of melanin-concentrating hormone from rat hypothalamus. Endocrinology 125:1660-1665; 1989. Wilkes, B. C.; Hruby, V. J.; Castrucci, A. M. L.; Sherbrooke, W. C.; Hadley, M. E. Synthesis of a cyclic melanotropic peptide exhibiting both melanin concentrating and dispersing activities. Science 224: 1111-1113; 1984. Wilkes, B. C.; Hruby, V. J.; Sherbrooke, W. C.; Castrucci, A. M. L.; Hadley, M. E. Biochem. Biophys. Res. Commun. 122:613-619; 1984.