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Reduction of rapid eye movement (REM) sleep by glucose alone or glucose and insulin in rats
Life Sciences, Vol. 42, pp. 1425-1429 Printed in the U.S.A.
Pergamon Press
REDUCTION OF RAPID EYE MOVEMENT (REM) SLEEP BY GLUCOSE ALONE OR GLUCOSE AND INSULIN IN RATS Subbiah Sangiahl and Donald F. Caldwell 'Department of Physiological Sciences, College of Veterinary Medicine Oklahoma State University, Stillwater, Oklahoma 74078 2Department of Psychobiology and Sleep Center, Lafayette Clinic Detroit, MI 48207 (Received in final form February 10, 1988)
Administration of a high dose of glucose (2.5 g/kg, i.p.) thatis known to produce severe hyperglycemia in euglycemic rats suppressed rapid eye movement (REM) sleep time significantly during the first three hours of 8 hr Co-administration of total electroencephalogram (EEG) recording period. glucose (2.5 g/kg, i.p.) and a non-convulsive dose of insulin (1.0. I.U./kg, i.p.) produced a significant reduction in REM sleep time during 1st through 5th hour and an increase in slow-wave sleep (NREM) time in the 3rd and 4th hour of 8 hr total EEG recording period. However, awake, NREM and REM sleep time in the 8 hr total EEG recording period were unaffected by either glucose alone or glucose plus insulin treatments. These results strongly suggest that the insulin's effects on the sleep-awake cycle i.e. reduction in REM and a slight increase in NREM sleep times of rats is not due to indirect effects of insulin on the central nervous system via hypoglycemia as reported by us previously, but could possibily be due to its direct effects on brain chemistry of neurotransmitters such as serotonin, catecholamines and acetylcholine which are believed to modulate the sleep-awake cycle pattern in rats. The concentration and metabolism of brain serotonin is related directly to the plasma and brain concentration of its precursor, tryptophan (l-2). Both insulin and the concentration of free plasma tryptophan stimulate tryptophan uptake from blood to brain (3-5). Subconvulsive doses of insulin and insulin, endogenously secreted following the consumption of carbohydrate diet increased the concentrations of both brain tryptophan and serotonin in rats (6). Serotonin containing neurons are likely to play a role in the control of sleep, thermoregulation, motor activity, food consumption, pain perception and sexual activity (6-9). If the concentration and metabolism of serotonin in the brain is insulin dependent, the hormone should also affect serotonin dependent neurobehavioural functions including sleep-awake cycle. Our previous study showed that intraperitoneal administration of a non-convulsive dose of insulin suppressed rapid eye movement (REM) sleep time and produced a slight but significant increase in slow-wave sleep time (NREN in rats (10). These changes in sleep-awake cycle correlated with insulin induced hypoglycemia (10). Therefore, the question could be raised whether the insulin induced reduction in REM sleep time and elevation of NRF.M sleep time in rats was indirect through its hypoglycemic effects or if it was direct through changes in the chemistry of various putative neurotransmitters. such as serotonin, catecholamines and acetylcholine of sleep-awake cycle (11-19). The present study was designed to investigate the effects of glucose alone or combination of glucose and insulin on sleep-awake cycle of rats. 0024-3205/88 $3.00 + .OO Copyright (c) 1988 Pergamon Press P~C
1426
Glucose and Insulin on Sleep-Awake Cycle
Methods
Vol. 42, No. 15, 1988
and Materials
Animals Thirty adult, male, Spraugue-Dawley rats weighing between 300-350 g were individually housed in environmentally controlled rooms, with 12 hr light and dark cycles. They were given free access to food and water. Evaluation of Electroencephalogram (EEG) Sleep in Rats Rats were divided into three groups of 10 each. They were anesthetized (40 mg/kg, i.p.). with sodium pentobarbital Atropine sulphate and methoxyflurane were used as preanesthetic and supplemental anesthetic agents respectively. Stainless steel round head screw (O-80" x 3x32") electrodes were stereotaxically implanted in the skull over the frontal (A-P = 5.0 mm, lateral = -2.5 mm) and occipital (A-P = -6.5 mm, lateral = -3.5 mm) lobes using bregma and the dura as reference (20). A third screw electrode implanted equidistant from the first two (A-P = -1.2 mm, lateral = 2.0 mm) served as a reference electrode. Two (I/O)stainless steel washers, soldered to Teflon insulated 30 ga stranded copper wire, bilaterally sutured to the neck muscles, served as a bipolar muscle electrode. All electrode leads were connected to an amphenol plug which was connected to the skull. A post-operative recovery period of two weeks proceeded EEG sleep studies. EEG sleep was evaluated in a 1.5 x 2.0 M temperaturechamber controlled, sound proof environmental (Labline humidity Environ-Room). A 12 hr diurnal cycle was maintained with lights on at 7:00 a.m. and off at 7:00 p.m. with temperature (23°C) and humidity (28% R.H.) held constant. The environmental chamber contained two activity recording boxes (Lafayette, Instrument A-501). Each box had three aluminum walls, one clear Plexiglas wall and a 30 x 30 cm Formica floor. After being placed in an activity box, EGG, EMG and body movement (activity) of individual rats within the group were monitored as described previously (10). Rats were Sleep was monitored with fasted overnight before EEG sleep recording. continuous polygraphic recordings for an 8 hr period from 8:30 a.m. to 4:30 p.m. Groups of 10 rats each, received intraperitoneal injection of either normal saline (0.1 ml), glucose (2.5 g/kg body weight) or the same dose of glucose plus insulin (Regular-Iletin, Lilly; 1.0, I.U./kg body weight) respectively. Polygraph records were scored in 30 sec. time epochs, immediately after each treatment for 8 hr periods, following standard criteria (21-24) and were assigned to one of 3 possible sleep-awake stages: awake, slow-wave (NREM), and paradoxical, (REM), (Table 1). Using each rat's total time (min) in the sleep-awake stages, percentages of each of 3 stages in each hr beginning 0 - 8 hrs and 8 hrs total were calculated for saline, glucose, and glucose plus insulin treated rats. Statistical Analysis Differences between control and treatment groups were determined by analysis of variance with Duncan's multiple range test. A probability level of 0.05 was accepted as significant. Results
The sequential hourly, mean f S.E. awake, NRRM and RRM sleep times in minutes of various groups of rats are presented in Table 1. Following glucose (2.5 g/kg, i.p.) administration, mean REM sleep time during the lst, 2nd and 3rd hour was 0.40 + 0.80, 1.70 + 2.14 and 5.60 f 3.92 min or 90, 77 and 45 percent less than the saline treated controls 3.8 f 1.21, 7.45 ? 1.21 and 10.20 + 1.46 min respectively. However, the mean awake time during the 2nd hr was 32.40 + 5.21 min or 41 percent more than that of saline treated controls (22.95 f 5.20 min). There was no change either in the hourly mean NREM or awake, NRRM and REM sleep time in the 8 hr total measurement period
Vol. 42, No. 15, 1988
Glucose and Insulin on Sleep-Awake Cycle
1427
in glucose treated rats compared to saline controls. Administration of glucose (2.5 g/kg, i.p.) plus insulin (1.0, I.U./kg, i.p.> produced 86, 84, 75, 31 and 44 percent reduction in RRM sleep time during the 1st through 5th hr periods respectively, returning to saline treated levels by the 6th hr. However, there was a 64% increase in awake time during the 5th hr period. In addition, there was a 26 and 16 percent increase in NRRM sleep time during 3rd and 4th hr respectively in glucose plus insulin treated animals, compared to saline treated ones. Awake, NREM and REM sleep time in the 8 hr total EEG recording period were unaffected by glucose plus insulin treatment. TABLE1 sequentia1Ehur1ylleanAwate,llRIpland RRI Slea!p'lEiresofvariouSGroupaofIoRatSmchAfteAr anIntzr+aritonaaI~trrtion ofSaline,Glmose (2.5 g/k&. and Glucose (2.5 g/w Plus Insulin (1.0, I.lJ./kg).
eansLk!B!E~~
B!m
i!!m
E!%
&!em
!!m
!m
1
34.50 21.70 3x? f 5.44 f 4.56 f 1.21
40.90 f 9.42
18.70 f 8.76
0.40b f 0.80
34.96 f 6.83
22.50 f 6.41
o.54b f 0.99
2
22.9? 29.60 7.45a f 5.30 f 4.27 f 1.21
32.40b 25.90 f 5.21 f 4.37
1.70c f 2.14
24.08a 34.71 f 4.76 f 4.70
1.21b f 1.20
3
18.20 31.60a 10.20a f 3.79 f 2.65 f 1.46
17.40 f 6.90
5.60b 37.00a f 5.56 f 3.92
17.54 f 7.99
39.88b f 7.18
2.58' f 2.14
4
20.00 32.20a 7.80a f 3.29 f 2.71 t 1.42
21.10 f11.84
7.00a 31.90a f 4.06 f 8.44
17.12 f 7.70
37.54b f 6.58
5.3Sd f 2.94
5
12.90a 37.10 10.00= f 2.59 f 1.99 f 1.06
9.30a 41.00 f 3.91 f 2.79
9.70a f 4.02
21.21b 32.92 f 6.35 f 5.42
5.88d f 1.72
6
20.15 29.25 10.60 f 4.28 f 2.63 f 1.80
14.70 f 3.35
34.00 f 6.09
11.30 f 6.09
14.34 f 6.29
35.34 f 4.39
10.34 f 3.36
7
11.90 37.05 11.05 f 3.22 f 2.90 t 0.76
9.10 f 5.14
38.30 f 1.75
12.60 f 4.40
8.38 f 3.61
39.88 f 3.21
11.71 f 3.36
8
14.95 32.30 12.75 f 4.16 f 2.90 f 2.18
10.00 f 7.36
39.20 f 7.39
10.80 f 6.71
10.58 f 6.73
37.25 f 5.24
11.34 f 3.11
19.36 f 6.40
33.25 f 1.90
7.39 f 2.56
18.78 f 2.49
35.00 f 2.09
6.12 f 1.18
8 Hr. Avg. 19.44 31.35 9.21 f 1.42 f 1.08 f 0.49
abed
Means within each time interval for each component of sleep-awake cycle with unlike superscripts are different (p < 0.05).
1428
Glucose and Insulin on Sleep-Awake Cycle
Vol. 42, No. 15, 1988
Discussion
It has been previously reported that intraperitoneal administration of a non-convulsive dose of insulin (1.0, I.U./kg) in rats produced a significant reduction of REM sleep time during the first five hours and an elevation of NREM sleep in the second and third hour of a total 8 hr EEG recording period (10). The time course and magnitude of REM sleep time coincided with insulin induced hypoglycemia. The data presented in this study indicate that co-administration of a high glucose dose (2.5 g/kg, i.p.), known to produce severe hyperglycemia in euglycemic rats and prevent insulin induced hypoglycemia, failed to prevent insulin induced reduction in REM and elevation in NREM sleep time of rats. In fact, co-administration of both glucose and insulin altered sleep-awake cycle: i.e. reduction in REM and elevation of NREM sleep, very similar to that observed in rats treated with insulin alone (IO). Thus, reduction in REM and increase in NREM sleep time of insulin treated rats is not due to indirect effects of insulin on the central nervous system via hypoglycemia but could possibily be due to its direct effects on brain chemistry of neurotransmitters such as serotonin, catecholamines and acetylcholine, believed to modulate the sleep-awake cycle pattern of mammalian species (11-19). Further more, glucose alone significantly reduced REM sleep in rats. It is well established that such a high dose of glucose as used in this study would increase insulin secretion (25). These results strongly suggest that the changes in sleep-awake cycles were caused by insulin, independent of changes in plasma glucose concentrations. The notion of insulin having direct effects on sleep-awake cycles is strengthened by findings, demonstrating insulin receptors in the central nervous system and brain sequestering of plasma insulin (26). There is substantial evidence from neurophysiological and neuropharmacological studies that REM sleep could be modified by alternations in protein synthesis and neurotransmitters functions (11-19, 27-32). Enhanced brain cholinergic transmission and decreased catecholaminergic transmission or proteins synthesis have increased REM sleep in animals (11-19, 27-32). Thus, the inhibitory effects of insulin on REM sleep could have been insulin stimulation of brain protein synthesis or mediated by catecholaminergic synaptic transmission and/or insulin inhibition of central cholinergic pathways. It is further known that growth hormone, an insulin antagonist, increased protein synthesis and REM sleep (32). Thus, the reduction in REM sleep of insulin treated rats is compatible with recent reports that insulin Further inhibits growth hormone secretion in vitro in rats. (33-34). studies are necessary to understand the precise relationship between insulin, growth hormone and their effects on sleep-awake cycles of mammalian species under normal and diabetic conditions.
1. 2. 3. 4. 5. 6. 7.
R.J. WURTMAN and J.D. FERNSTROM, Amer. J. Clin. Nutr. 28 638-647 (1975). J.D. FERNSTROM and R.J. WURTMAN, Science 178 414-416 (1972). J.D. FERNSTROM and R.J. WURTMAN, Sci. Amer. 230 84-91 (1974). A. TAGLIAMONTE, M.G. DFMONTIS, M. OLIANAS, P.L. ONALI and G.L. GESSA, Advances In Experimental Medicine and Biology 69 89-94 (1975). J.D. FERNSTROM and R.J. WURTMAN, Metabolism _ 337-342 (1972). J.D. FERNSTROM and R.J. WURTMAN, Science 174 1023-1025 (1975). R. SAHANIN, T. MENINI and S. GARATTINI, Prog. Neuropsychopharmacol. 4 363-369, (1980).
vol. 42, No. 15, 1988
8. 9. 10. 11. 12. 13.
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19 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.
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31. 32.
33. 34.
Glucose and Insulin on Sleep-Awake Cycle
1429
M.J. BAUM and M.S. STARR, Pharmacol. Biochem. Behav. 13 57-67, (1980). S.G. DENNIS and R. MELZACK, Exp. Neurol. 69 260-270, (1980). S. SANGIAH, D.F. CALDWELL, M.J. VILLENEUVE and J.J. CLANCY, Life Sciences 31 763-769 (1982). M. JOUVET, Science 163 32-41 (1969). M. JOUVET, Ergebn. Phsiol. 64 166-307 (1976). M. JOWET and J.F. PUJOL, InSerotonin - New Vistas: Biochemistry and Behavioural and Clinical Studies, (E. Costa, G.L. Gressa and M. Sander, eds.) pp 169-179. Raven Press, New York (1974). J.M. MONTI, Life Sci, 30 1145-1157 (1982). J.M. MONTI, Life Sci, 32 1401-1415 (1983). 225 667-674 C. FORNAL and M. RADULOVACKI, J. Pharmacol. Exp. Ther., (1983). C. FORNAL and M. RADULOVACKI, J. Pharmacol. Exp. Ther., 225 675-681 (1983). K. SAKAI, In Brain Mechanisms of Sleep, (D. McGinty, A. Morrison, R.R. Ducker-Colin, P.L. Parmeggiani, eds.) pp 111-138. Spectrum, New York (1985). P.J. SHIROMANI and J.C. GILLIN, Ann. Rev. Pharmacol. 27 137-156, (1987). L.J. PELLEGRINO and A.J. CUSHMAN, Stereotaxic Atlas of the Rat Brain, Appleton-Century-Crofts (1987). E. TAKEUCHI, Jap. J. Psychol. 41 248-256 (1970). C. TIMO-IARIA, N. NEGRO, W.-ii:SCHMIDEK, K. HOSHINO, C.E. LABATO DEMENZES and T. LEME DAROCHA, Physiol. Behav. 5 1057-1062 (1970). H. VAN TWYVER, Physiol. Behav. 4 901-905 (1969). J.P. MOURET, P. BOBILLER and M. JOWET, Eur. J. Pharmacol. 5 17-22, 1968). E. CERASI, Quart. Rev. Biophys. 8 l-41 (1975). D.G. BASKIN, D.P. FIGLEWICZ, S.C. WOODS, D. PORTE,JR, and D.M. DORSA, Ann. Rev. Physiol. 49 335-347 (1987). IAN OSWALD, Pharmacol. Reviews 20 (4) 273-303 (1986). J.C. GILLN, W.B. MENDELSON, N. SITARAM and R.J. WYATT, Ann. Rev. Pharmacol. Toxicol. 18 563-579 (1978). R.R.DRUCKER-COLIN, C.W. SPANIS, C.W. COTMAN and G.L. MCGRAUGH, In Sleep 1974: Instinct, Neurophysiology, Endocrinology, Episodes, Dreams, Epilepsy and Intracranial Pathology, (W.P. Koella and P. Levin, eds.) pp 55-59, Karger, Basle (1975). 55-59 (1975). R.R. DRUCKER-COLIN, In Sleep, Dreams and Memory: Advances in Sleep Research, (Fishbein, eds.) pp 73-93, Spectrum, Flushing, New York (1981). 0. BELSITO, M.N. SHOUSE and S.S. BOWERSOX, Behavioural Neural biol. 41 209-216, (1984). W.C. STERN and P.J. MORGANE, In Neurobiology of Sleep and Memory, (R.R. Drucker-Colin and J.L. McGaugh, eds.) pp 373-400, Acad. Press, New York (1977). S. YAMASHITA and S. MELMED, Diabetes 35 440-447 (1986). S. YAMASHITA and S. MELMED, J. Clin. Invest. -78 1008-1014 (1986).
Pergamon Press
REDUCTION OF RAPID EYE MOVEMENT (REM) SLEEP BY GLUCOSE ALONE OR GLUCOSE AND INSULIN IN RATS Subbiah Sangiahl and Donald F. Caldwell 'Department of Physiological Sciences, College of Veterinary Medicine Oklahoma State University, Stillwater, Oklahoma 74078 2Department of Psychobiology and Sleep Center, Lafayette Clinic Detroit, MI 48207 (Received in final form February 10, 1988)
Administration of a high dose of glucose (2.5 g/kg, i.p.) thatis known to produce severe hyperglycemia in euglycemic rats suppressed rapid eye movement (REM) sleep time significantly during the first three hours of 8 hr Co-administration of total electroencephalogram (EEG) recording period. glucose (2.5 g/kg, i.p.) and a non-convulsive dose of insulin (1.0. I.U./kg, i.p.) produced a significant reduction in REM sleep time during 1st through 5th hour and an increase in slow-wave sleep (NREM) time in the 3rd and 4th hour of 8 hr total EEG recording period. However, awake, NREM and REM sleep time in the 8 hr total EEG recording period were unaffected by either glucose alone or glucose plus insulin treatments. These results strongly suggest that the insulin's effects on the sleep-awake cycle i.e. reduction in REM and a slight increase in NREM sleep times of rats is not due to indirect effects of insulin on the central nervous system via hypoglycemia as reported by us previously, but could possibily be due to its direct effects on brain chemistry of neurotransmitters such as serotonin, catecholamines and acetylcholine which are believed to modulate the sleep-awake cycle pattern in rats. The concentration and metabolism of brain serotonin is related directly to the plasma and brain concentration of its precursor, tryptophan (l-2). Both insulin and the concentration of free plasma tryptophan stimulate tryptophan uptake from blood to brain (3-5). Subconvulsive doses of insulin and insulin, endogenously secreted following the consumption of carbohydrate diet increased the concentrations of both brain tryptophan and serotonin in rats (6). Serotonin containing neurons are likely to play a role in the control of sleep, thermoregulation, motor activity, food consumption, pain perception and sexual activity (6-9). If the concentration and metabolism of serotonin in the brain is insulin dependent, the hormone should also affect serotonin dependent neurobehavioural functions including sleep-awake cycle. Our previous study showed that intraperitoneal administration of a non-convulsive dose of insulin suppressed rapid eye movement (REM) sleep time and produced a slight but significant increase in slow-wave sleep time (NREN in rats (10). These changes in sleep-awake cycle correlated with insulin induced hypoglycemia (10). Therefore, the question could be raised whether the insulin induced reduction in REM sleep time and elevation of NRF.M sleep time in rats was indirect through its hypoglycemic effects or if it was direct through changes in the chemistry of various putative neurotransmitters. such as serotonin, catecholamines and acetylcholine of sleep-awake cycle (11-19). The present study was designed to investigate the effects of glucose alone or combination of glucose and insulin on sleep-awake cycle of rats. 0024-3205/88 $3.00 + .OO Copyright (c) 1988 Pergamon Press P~C
1426
Glucose and Insulin on Sleep-Awake Cycle
Methods
Vol. 42, No. 15, 1988
and Materials
Animals Thirty adult, male, Spraugue-Dawley rats weighing between 300-350 g were individually housed in environmentally controlled rooms, with 12 hr light and dark cycles. They were given free access to food and water. Evaluation of Electroencephalogram (EEG) Sleep in Rats Rats were divided into three groups of 10 each. They were anesthetized (40 mg/kg, i.p.). with sodium pentobarbital Atropine sulphate and methoxyflurane were used as preanesthetic and supplemental anesthetic agents respectively. Stainless steel round head screw (O-80" x 3x32") electrodes were stereotaxically implanted in the skull over the frontal (A-P = 5.0 mm, lateral = -2.5 mm) and occipital (A-P = -6.5 mm, lateral = -3.5 mm) lobes using bregma and the dura as reference (20). A third screw electrode implanted equidistant from the first two (A-P = -1.2 mm, lateral = 2.0 mm) served as a reference electrode. Two (I/O)stainless steel washers, soldered to Teflon insulated 30 ga stranded copper wire, bilaterally sutured to the neck muscles, served as a bipolar muscle electrode. All electrode leads were connected to an amphenol plug which was connected to the skull. A post-operative recovery period of two weeks proceeded EEG sleep studies. EEG sleep was evaluated in a 1.5 x 2.0 M temperaturechamber controlled, sound proof environmental (Labline humidity Environ-Room). A 12 hr diurnal cycle was maintained with lights on at 7:00 a.m. and off at 7:00 p.m. with temperature (23°C) and humidity (28% R.H.) held constant. The environmental chamber contained two activity recording boxes (Lafayette, Instrument A-501). Each box had three aluminum walls, one clear Plexiglas wall and a 30 x 30 cm Formica floor. After being placed in an activity box, EGG, EMG and body movement (activity) of individual rats within the group were monitored as described previously (10). Rats were Sleep was monitored with fasted overnight before EEG sleep recording. continuous polygraphic recordings for an 8 hr period from 8:30 a.m. to 4:30 p.m. Groups of 10 rats each, received intraperitoneal injection of either normal saline (0.1 ml), glucose (2.5 g/kg body weight) or the same dose of glucose plus insulin (Regular-Iletin, Lilly; 1.0, I.U./kg body weight) respectively. Polygraph records were scored in 30 sec. time epochs, immediately after each treatment for 8 hr periods, following standard criteria (21-24) and were assigned to one of 3 possible sleep-awake stages: awake, slow-wave (NREM), and paradoxical, (REM), (Table 1). Using each rat's total time (min) in the sleep-awake stages, percentages of each of 3 stages in each hr beginning 0 - 8 hrs and 8 hrs total were calculated for saline, glucose, and glucose plus insulin treated rats. Statistical Analysis Differences between control and treatment groups were determined by analysis of variance with Duncan's multiple range test. A probability level of 0.05 was accepted as significant. Results
The sequential hourly, mean f S.E. awake, NRRM and RRM sleep times in minutes of various groups of rats are presented in Table 1. Following glucose (2.5 g/kg, i.p.) administration, mean REM sleep time during the lst, 2nd and 3rd hour was 0.40 + 0.80, 1.70 + 2.14 and 5.60 f 3.92 min or 90, 77 and 45 percent less than the saline treated controls 3.8 f 1.21, 7.45 ? 1.21 and 10.20 + 1.46 min respectively. However, the mean awake time during the 2nd hr was 32.40 + 5.21 min or 41 percent more than that of saline treated controls (22.95 f 5.20 min). There was no change either in the hourly mean NREM or awake, NRRM and REM sleep time in the 8 hr total measurement period
Vol. 42, No. 15, 1988
Glucose and Insulin on Sleep-Awake Cycle
1427
in glucose treated rats compared to saline controls. Administration of glucose (2.5 g/kg, i.p.) plus insulin (1.0, I.U./kg, i.p.> produced 86, 84, 75, 31 and 44 percent reduction in RRM sleep time during the 1st through 5th hr periods respectively, returning to saline treated levels by the 6th hr. However, there was a 64% increase in awake time during the 5th hr period. In addition, there was a 26 and 16 percent increase in NRRM sleep time during 3rd and 4th hr respectively in glucose plus insulin treated animals, compared to saline treated ones. Awake, NREM and REM sleep time in the 8 hr total EEG recording period were unaffected by glucose plus insulin treatment. TABLE1 sequentia1Ehur1ylleanAwate,llRIpland RRI Slea!p'lEiresofvariouSGroupaofIoRatSmchAfteAr anIntzr+aritonaaI~trrtion ofSaline,Glmose (2.5 g/k&. and Glucose (2.5 g/w Plus Insulin (1.0, I.lJ./kg).
eansLk!B!E~~
B!m
i!!m
E!%
&!em
!!m
!m
1
34.50 21.70 3x? f 5.44 f 4.56 f 1.21
40.90 f 9.42
18.70 f 8.76
0.40b f 0.80
34.96 f 6.83
22.50 f 6.41
o.54b f 0.99
2
22.9? 29.60 7.45a f 5.30 f 4.27 f 1.21
32.40b 25.90 f 5.21 f 4.37
1.70c f 2.14
24.08a 34.71 f 4.76 f 4.70
1.21b f 1.20
3
18.20 31.60a 10.20a f 3.79 f 2.65 f 1.46
17.40 f 6.90
5.60b 37.00a f 5.56 f 3.92
17.54 f 7.99
39.88b f 7.18
2.58' f 2.14
4
20.00 32.20a 7.80a f 3.29 f 2.71 t 1.42
21.10 f11.84
7.00a 31.90a f 4.06 f 8.44
17.12 f 7.70
37.54b f 6.58
5.3Sd f 2.94
5
12.90a 37.10 10.00= f 2.59 f 1.99 f 1.06
9.30a 41.00 f 3.91 f 2.79
9.70a f 4.02
21.21b 32.92 f 6.35 f 5.42
5.88d f 1.72
6
20.15 29.25 10.60 f 4.28 f 2.63 f 1.80
14.70 f 3.35
34.00 f 6.09
11.30 f 6.09
14.34 f 6.29
35.34 f 4.39
10.34 f 3.36
7
11.90 37.05 11.05 f 3.22 f 2.90 t 0.76
9.10 f 5.14
38.30 f 1.75
12.60 f 4.40
8.38 f 3.61
39.88 f 3.21
11.71 f 3.36
8
14.95 32.30 12.75 f 4.16 f 2.90 f 2.18
10.00 f 7.36
39.20 f 7.39
10.80 f 6.71
10.58 f 6.73
37.25 f 5.24
11.34 f 3.11
19.36 f 6.40
33.25 f 1.90
7.39 f 2.56
18.78 f 2.49
35.00 f 2.09
6.12 f 1.18
8 Hr. Avg. 19.44 31.35 9.21 f 1.42 f 1.08 f 0.49
abed
Means within each time interval for each component of sleep-awake cycle with unlike superscripts are different (p < 0.05).
1428
Glucose and Insulin on Sleep-Awake Cycle
Vol. 42, No. 15, 1988
Discussion
It has been previously reported that intraperitoneal administration of a non-convulsive dose of insulin (1.0, I.U./kg) in rats produced a significant reduction of REM sleep time during the first five hours and an elevation of NREM sleep in the second and third hour of a total 8 hr EEG recording period (10). The time course and magnitude of REM sleep time coincided with insulin induced hypoglycemia. The data presented in this study indicate that co-administration of a high glucose dose (2.5 g/kg, i.p.), known to produce severe hyperglycemia in euglycemic rats and prevent insulin induced hypoglycemia, failed to prevent insulin induced reduction in REM and elevation in NREM sleep time of rats. In fact, co-administration of both glucose and insulin altered sleep-awake cycle: i.e. reduction in REM and elevation of NREM sleep, very similar to that observed in rats treated with insulin alone (IO). Thus, reduction in REM and increase in NREM sleep time of insulin treated rats is not due to indirect effects of insulin on the central nervous system via hypoglycemia but could possibily be due to its direct effects on brain chemistry of neurotransmitters such as serotonin, catecholamines and acetylcholine, believed to modulate the sleep-awake cycle pattern of mammalian species (11-19). Further more, glucose alone significantly reduced REM sleep in rats. It is well established that such a high dose of glucose as used in this study would increase insulin secretion (25). These results strongly suggest that the changes in sleep-awake cycles were caused by insulin, independent of changes in plasma glucose concentrations. The notion of insulin having direct effects on sleep-awake cycles is strengthened by findings, demonstrating insulin receptors in the central nervous system and brain sequestering of plasma insulin (26). There is substantial evidence from neurophysiological and neuropharmacological studies that REM sleep could be modified by alternations in protein synthesis and neurotransmitters functions (11-19, 27-32). Enhanced brain cholinergic transmission and decreased catecholaminergic transmission or proteins synthesis have increased REM sleep in animals (11-19, 27-32). Thus, the inhibitory effects of insulin on REM sleep could have been insulin stimulation of brain protein synthesis or mediated by catecholaminergic synaptic transmission and/or insulin inhibition of central cholinergic pathways. It is further known that growth hormone, an insulin antagonist, increased protein synthesis and REM sleep (32). Thus, the reduction in REM sleep of insulin treated rats is compatible with recent reports that insulin Further inhibits growth hormone secretion in vitro in rats. (33-34). studies are necessary to understand the precise relationship between insulin, growth hormone and their effects on sleep-awake cycles of mammalian species under normal and diabetic conditions.
1. 2. 3. 4. 5. 6. 7.
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