Exp. Clin. Endocrinol. Vol. 96, No. 1, 1990, pp. 113-116
J. A. Barth, Leipzig
Department of Physiology (Chairman: Prof. K. Seto), Kochi Medical School, Nankoku, and Department of Physiology (Chairman: Prof. F. Kimura)1), Yokohama City University School of Medicine, Yokohama, Japan
H. SAlTO, H. KABA, T. SATO, K. N0JmIA, C.-S. Li, K. SETO, F. KIMURA1) and M. KAWAKAMI1)
Summary. We examined the effects of stimulation of the dorsal hippocampus and lesions of the dorsal fornix on glucose metabolism in liver slices of rabbits. Hippocampal stimulation decreased the '4C transfer rates from '1C-glucose into CO0, ketone bodies, cholesterol ester and free fatty acids,
but increased the rates into triglyceride, phospholipids and glycogen. Fornix lesions had various effects on glucose metabolism, and the effects of hippocampal stimulation on glucose metabolism were abolished by fornix lesions. These observations support the hypothesis that the hippocampus is an integral part of the brain regulator system in the hepatic glucose metabolism.
Key words: Hippocampus - Glucose metabolism - Rabbit's liver
Introduction A considerable body of evidence has accumulated showing that the hypothalamus participates in the metabolic regulation of glucose in the liver. Among them, stimulation of the ventromedial hypothalamus caused an increase in the activities of enzymes concerning glycogenolysis and gluconeogenesis but resulted in marked suppression of glycolytic enzymes; stimulation of the lateral hypothalamic area caused an increase in the activity of glycogen synthase and suppressed the glyconeogenesis in the rat's liver (Shimazu, 1970; Shimazu and Saito, 1984). In this point of view, our previous experiments indicated that the glucose formation from acetate and pyruvate was altered by lesions of various sites of limbic-hypothalamic structures including the dorsal fornix, a neural pathway from the dorsal hippocampus to the hypothalamus, in the rabbit's liver (Seto et al., 1983 ;Seto et al., 1985). More recently, it was shown that the injection of neostigmine, an inhibitor of acetylcholine esterase, into the dorsal hippocampus caused a dose-dependent increase in the hepatic venous plasma glucose concentrations in rats (Uemura et al., 1989). These findings suggest that the dorsal hippocampus is involved in the regulation of hepatic glucose metabolism. In order to explore this possibility, we examined the effects of electrical stimulation of the dorsal hippocampus and lesions of the dorsal fornix on the glucose metabolism in liver slices of rabbits.
Downloaded by: University of Pittsburgh. Copyrighted material.
Influence of Dorsal Hippocampal Stimulation and Dorsal Fornix Lesions on Hepatic Glucose Metabolism in Rabbits
114
Exp. Clin. Endocrinol. 96 (1990) 1
Material and Methods Materials and methods have been described elsewhere (Kawakami et al., 1967; Kawakami et al., 1968; Seto et al., 1973; Seto et al., 1983a; Seto et al., 1983b; Shimazu et al., 1984; Seto et al., 1985).
Briefly, for unilateral stimulation of the dorsal hippocampus monophasic square wave pulses of 0.1 msec duration and 80 A intensity were delivered at 100 Hz from an isolation unit for 60 min. 5 sec on and 55 sec off; for bilateral lesions of the dorsal fornix a direct current of 4 mA was delivered
Results and Discussion Table 1 shows that stimulation of the dorsal hippocampus of intact rabbits significantly decreased the rates of 14C transfer from 14C-glucose into 002, ketone bodies, cholesterol ester and fatty acids, but significantly increased the rates of 140 transfer into triglyceride, phospholipids and glycogen. Table 1 also shows that lesions of the dorsal fornix significantly increased the rates of transfer into CO2, ketone bodies, cholesterol ester and free fatty acids, but significantly decreased the rates of 140 transfer into triglyceride, phospholipids and glycogen. These results suggest that the dorsal hippocampus-fornix-hy-pothalamic system acts to inhibit the formation of 002, ketone bodies, cholesterol ester and free fatty acids from glucose but to enhance the formation of triglyceride, phospholipids and glycogen from glucose in the rabbit's liver. However, the rates of 1C transfer into free cholesterol were significantly increased by lesions of the dorsal fornix, but the '4C transfer rates were not altered by stimulation of the dorsal hippocampus. The role of the dorsal hippocampus-fornix-hypothalamic system in the formation of free cholesterol from glucose still remains a mystery. Table 1 shows that in rabbits subjected to electrolytic lesioning of the dorsal fornix three weeks before, stimulation of the dorsal hippocampus had no effects on the rates of '4C transfer from '4C-glucose into 002, ketone bodies, cholesterol ester, triglyceride, free cholesterol, free fatty acids, phospholipids or glycogen. The effects of stimulation of the dorsal hippocampus on the hepatic glucose metabolism were abolished by lesions of the dorsal fornix, suggesting that these hippocampal effects on the hepatie glucose metabolism are exerted via the hypothalamus. Our present results suggest that the dorsal hippocampus-fornix-hypothalamic system plays some role in the regulation of hepatic glucose metabolism Our previous study indicated that electrical stimulation of the dorsal hippocampus facilitated the formation of glucocorticoid and increased the circulating levels of insulin but decreased the glucagon levels in rabbits (Kawakami et al., 1968; Seto et al., 1983; Kaba et al., 1987). Taken together, it might be suggested that the action of the dorsal hippocampus on hepatic glucose metabolism was mediated by the secretion of these metabolic hormones. However the effect of stimulation of the hypothalamus on glycogenolysis and glycogen synthesis in the rat's liver was exerted through direct innervation of the autonomie nervous system to the liver (Shimazu, 1979; Shimazu and Saito, 1984). Further studies are needed to determine as to what extent metabolic hormones or direct innervation to the liver contributes to the response of hepatic glucose metabolism to hippocampal stimulation presented here. In conclusion, our present results indicate that the dorsal hippocampus is involved in the central nervous system-mediated regulation of hepatic glucose metabolism through the hypothalamus.
Downloaded by: University of Pittsburgh. Copyrighted material.
for 30 sec. Animals were killed by decapitation on the end of stimulation or 3 weeks after lesions; livers were rapidly removed from the decapitated carcasses; 2 g of liver slices was incubated with '4C-U-glueose (100 moles, 1 PCi) in 10 ml of KRB buffer for 3 h at 38°C and rates of 14C transfer from '4C-ghicose into various fractions were determined. The values were expressed as the mean mCi/3 hJ 100 mg tissue protein nitrogen ± SD (Standard deviation). Statistical evaluation of the data was performed by Student's t-test; differences with p < 0.05 were regarded as significant.
+
+
1.9 ± 0.1*
1.9±0.1
8.3±0.4
2.0±0.1
8.4 ± Ø4*
637.6±38.1
644.1 ± 31.7*
2.0 ± 0.1*
6.6±0.3
6.5 ± 0.3*
6.0±0.3
6.1 ± 0.3*
1.8±0.0
2.3±0.1
3.7±0.1
2.8±0.1
0.3±0.0
234.4±10.3
1.9±0.0 0.6 ± 0.0*
1.5 ± 0.0*
2.4 ± 0.1
2.9±0.1
0.4±0.0 2.5±0.1
Fraction F
5.1 ± 0.2*
Fraction E
3.6±0.1
Fraction D
0.1 ± 0.0*
Fraction C
102.2 ± 3.6*
Fraction B
240.3±9.5
Fraction A
'C transfer rates from '4C-glucose into
47.2 ± 2.0*
46.7±2.2
48.6±2.4
96.3±2.6
212.6 ± 7.1*
98.8±2.9
Fraction H
49.4 ± 2.1w'
78.7±3.1
139.4 ± 4.1*
79.7±2.9
Fraction G
Downloaded by: University of Pittsburgh. Copyrighted material.
Fractions A, B, C, D, E, F, G and H represent CO2, ketone bodies, cholesterol ester, triglyceride, free cholesterol, free fatty acids, phospholipids and glycogen, respectively. Each value represents the mean mCi per 100 mg liver protein-N ± SD of 10 rabbits. * p < 0.05.
+
+ -
Stimulation Lesion
Table 1 Effects of stimulation of the dorsal hippocampus and lesion of the dorsal fornix on glucose metabolism in liver slices of rabbits
F
o
o n
I
118
Exp. Clin. Endocrinol. 96 (1990) 1
Ac kno wie dg eme rit s. Grateful acknowledgements were made to Prof. S. Roberts, UCLA School
of Medicine, Dr. K. Yoshida, Yokohama City University, Prof. Y. Sasaki, Tohoku University, and to Miss A. Ohri, Kochi Medical School, for their helpful advice, criticism, collaboration and secre tary work. This study was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (Grant No. 01570086).
References KABA, H.; SAlTo, H.; KAWARAMI, T.; KITAOKA, K.; SETO, K.; YAMAMOTO, H.; KAWAKAaII, M.:
Influence of electrical stimulation of the limbic structure on glucagon level in rabbit's plasma. Exp. Clin. Endocrinol. 89 (1987) 233-236. KAWAKAMI, M.; SETO, K.; TERASAWA, E.; YOsHIDA, K.: Mechanisms in the limbic system con-
trolling reproductive functions of the ovary with special reference to positive feedback of progestin to the hippocampus. Progr. Brain Res. 27 (1967) 69-102. SETO, K.; TERASAWA, E.; YOSIITDA, K.; MIYAMOTO, T.; SEKIOEEJCHI, M.; HATTORI, Y.: Influence of electrical stimulation and lesion in limbic structure upon biosynthesis of adrenocorticoid in the rabbit. Neuroendocrinology 3 (1968) 337-348. SETO, K.; OTSUKA, K.; YANASE, M.; SAKUMA, Y.; KAWAKAMI, M.; BLACK, A. L.: Relation-
ship between acetate metabolism and glycolysis in liver slices of normal, starved and alloxan diabetic sheep. Clin. Chem. 2 (1973) 121-128. SETO, K.; SAlTo, H.; OTSUKA, K.; KAWAKAMI, M.: Influence of electrical stimulation of the limbic structure on insulin level in rabbit's plasma. Exp. Clin. Endocrinol. 81 (1983a) 347-349. SETO, K.; SAlTO, H.; OTSUKA, K.; KAWAKAMI, M.: Influence of lesion of the limbic-hypothalamic system on metabolic responses of acetate to daily repeated cold exposures in rabbits. Exp.
Clin. Endocrinol. 82 (1983b) 275-284. SETO, K.; SAlTo, H.; OTSUKA, K.; SATO, T.; OTSTJKA, K.; KAWAKAMI, M.: Influence of lesions
in the limbic-hypothalamic system on metabolic response of pyruvate to daily repeated cold exposure in rabbits. Exp. Clin. Endocrinol. 86 (1985) 223-232. SHhia&zu, T.: The hypothalamus and metabolic regulation- Metabolism and Disease 16 (1979)
21-33. SHIMAZU, T.; SAlTO, M.: Methods for stimulation and lesion of the brain and their application to metabolic research. Metabolism and Disease 21 (1984) 577-592. UEMURA, K.; Iciuciu, A.; YATOMI, A.; MIURA, H.; HONMURA, A.; YANASE, M.; SAXAMOTO, N.:
Involvement of the lippocampus in central nervous system-mediated glucoregulation in rats. Endocrinology 124 (1989) 2449-2455. (Accepted 12 September 1989)
Author's address: Prof. K. SETO, Department of Physiology, Kochi Medical School, Kochi 781-51/Japan
Nankoku,
Downloaded by: University of Pittsburgh. Copyrighted material.
KAWAKAMI, M.;
J. A. Barth, Leipzig
Department of Physiology (Chairman: Prof. K. Seto), Kochi Medical School, Nankoku, and Department of Physiology (Chairman: Prof. F. Kimura)1), Yokohama City University School of Medicine, Yokohama, Japan
H. SAlTO, H. KABA, T. SATO, K. N0JmIA, C.-S. Li, K. SETO, F. KIMURA1) and M. KAWAKAMI1)
Summary. We examined the effects of stimulation of the dorsal hippocampus and lesions of the dorsal fornix on glucose metabolism in liver slices of rabbits. Hippocampal stimulation decreased the '4C transfer rates from '1C-glucose into CO0, ketone bodies, cholesterol ester and free fatty acids,
but increased the rates into triglyceride, phospholipids and glycogen. Fornix lesions had various effects on glucose metabolism, and the effects of hippocampal stimulation on glucose metabolism were abolished by fornix lesions. These observations support the hypothesis that the hippocampus is an integral part of the brain regulator system in the hepatic glucose metabolism.
Key words: Hippocampus - Glucose metabolism - Rabbit's liver
Introduction A considerable body of evidence has accumulated showing that the hypothalamus participates in the metabolic regulation of glucose in the liver. Among them, stimulation of the ventromedial hypothalamus caused an increase in the activities of enzymes concerning glycogenolysis and gluconeogenesis but resulted in marked suppression of glycolytic enzymes; stimulation of the lateral hypothalamic area caused an increase in the activity of glycogen synthase and suppressed the glyconeogenesis in the rat's liver (Shimazu, 1970; Shimazu and Saito, 1984). In this point of view, our previous experiments indicated that the glucose formation from acetate and pyruvate was altered by lesions of various sites of limbic-hypothalamic structures including the dorsal fornix, a neural pathway from the dorsal hippocampus to the hypothalamus, in the rabbit's liver (Seto et al., 1983 ;Seto et al., 1985). More recently, it was shown that the injection of neostigmine, an inhibitor of acetylcholine esterase, into the dorsal hippocampus caused a dose-dependent increase in the hepatic venous plasma glucose concentrations in rats (Uemura et al., 1989). These findings suggest that the dorsal hippocampus is involved in the regulation of hepatic glucose metabolism. In order to explore this possibility, we examined the effects of electrical stimulation of the dorsal hippocampus and lesions of the dorsal fornix on the glucose metabolism in liver slices of rabbits.
Downloaded by: University of Pittsburgh. Copyrighted material.
Influence of Dorsal Hippocampal Stimulation and Dorsal Fornix Lesions on Hepatic Glucose Metabolism in Rabbits
114
Exp. Clin. Endocrinol. 96 (1990) 1
Material and Methods Materials and methods have been described elsewhere (Kawakami et al., 1967; Kawakami et al., 1968; Seto et al., 1973; Seto et al., 1983a; Seto et al., 1983b; Shimazu et al., 1984; Seto et al., 1985).
Briefly, for unilateral stimulation of the dorsal hippocampus monophasic square wave pulses of 0.1 msec duration and 80 A intensity were delivered at 100 Hz from an isolation unit for 60 min. 5 sec on and 55 sec off; for bilateral lesions of the dorsal fornix a direct current of 4 mA was delivered
Results and Discussion Table 1 shows that stimulation of the dorsal hippocampus of intact rabbits significantly decreased the rates of 14C transfer from 14C-glucose into 002, ketone bodies, cholesterol ester and fatty acids, but significantly increased the rates of 140 transfer into triglyceride, phospholipids and glycogen. Table 1 also shows that lesions of the dorsal fornix significantly increased the rates of transfer into CO2, ketone bodies, cholesterol ester and free fatty acids, but significantly decreased the rates of 140 transfer into triglyceride, phospholipids and glycogen. These results suggest that the dorsal hippocampus-fornix-hy-pothalamic system acts to inhibit the formation of 002, ketone bodies, cholesterol ester and free fatty acids from glucose but to enhance the formation of triglyceride, phospholipids and glycogen from glucose in the rabbit's liver. However, the rates of 1C transfer into free cholesterol were significantly increased by lesions of the dorsal fornix, but the '4C transfer rates were not altered by stimulation of the dorsal hippocampus. The role of the dorsal hippocampus-fornix-hypothalamic system in the formation of free cholesterol from glucose still remains a mystery. Table 1 shows that in rabbits subjected to electrolytic lesioning of the dorsal fornix three weeks before, stimulation of the dorsal hippocampus had no effects on the rates of '4C transfer from '4C-glucose into 002, ketone bodies, cholesterol ester, triglyceride, free cholesterol, free fatty acids, phospholipids or glycogen. The effects of stimulation of the dorsal hippocampus on the hepatic glucose metabolism were abolished by lesions of the dorsal fornix, suggesting that these hippocampal effects on the hepatie glucose metabolism are exerted via the hypothalamus. Our present results suggest that the dorsal hippocampus-fornix-hypothalamic system plays some role in the regulation of hepatic glucose metabolism Our previous study indicated that electrical stimulation of the dorsal hippocampus facilitated the formation of glucocorticoid and increased the circulating levels of insulin but decreased the glucagon levels in rabbits (Kawakami et al., 1968; Seto et al., 1983; Kaba et al., 1987). Taken together, it might be suggested that the action of the dorsal hippocampus on hepatic glucose metabolism was mediated by the secretion of these metabolic hormones. However the effect of stimulation of the hypothalamus on glycogenolysis and glycogen synthesis in the rat's liver was exerted through direct innervation of the autonomie nervous system to the liver (Shimazu, 1979; Shimazu and Saito, 1984). Further studies are needed to determine as to what extent metabolic hormones or direct innervation to the liver contributes to the response of hepatic glucose metabolism to hippocampal stimulation presented here. In conclusion, our present results indicate that the dorsal hippocampus is involved in the central nervous system-mediated regulation of hepatic glucose metabolism through the hypothalamus.
Downloaded by: University of Pittsburgh. Copyrighted material.
for 30 sec. Animals were killed by decapitation on the end of stimulation or 3 weeks after lesions; livers were rapidly removed from the decapitated carcasses; 2 g of liver slices was incubated with '4C-U-glueose (100 moles, 1 PCi) in 10 ml of KRB buffer for 3 h at 38°C and rates of 14C transfer from '4C-ghicose into various fractions were determined. The values were expressed as the mean mCi/3 hJ 100 mg tissue protein nitrogen ± SD (Standard deviation). Statistical evaluation of the data was performed by Student's t-test; differences with p < 0.05 were regarded as significant.
+
+
1.9 ± 0.1*
1.9±0.1
8.3±0.4
2.0±0.1
8.4 ± Ø4*
637.6±38.1
644.1 ± 31.7*
2.0 ± 0.1*
6.6±0.3
6.5 ± 0.3*
6.0±0.3
6.1 ± 0.3*
1.8±0.0
2.3±0.1
3.7±0.1
2.8±0.1
0.3±0.0
234.4±10.3
1.9±0.0 0.6 ± 0.0*
1.5 ± 0.0*
2.4 ± 0.1
2.9±0.1
0.4±0.0 2.5±0.1
Fraction F
5.1 ± 0.2*
Fraction E
3.6±0.1
Fraction D
0.1 ± 0.0*
Fraction C
102.2 ± 3.6*
Fraction B
240.3±9.5
Fraction A
'C transfer rates from '4C-glucose into
47.2 ± 2.0*
46.7±2.2
48.6±2.4
96.3±2.6
212.6 ± 7.1*
98.8±2.9
Fraction H
49.4 ± 2.1w'
78.7±3.1
139.4 ± 4.1*
79.7±2.9
Fraction G
Downloaded by: University of Pittsburgh. Copyrighted material.
Fractions A, B, C, D, E, F, G and H represent CO2, ketone bodies, cholesterol ester, triglyceride, free cholesterol, free fatty acids, phospholipids and glycogen, respectively. Each value represents the mean mCi per 100 mg liver protein-N ± SD of 10 rabbits. * p < 0.05.
+
+ -
Stimulation Lesion
Table 1 Effects of stimulation of the dorsal hippocampus and lesion of the dorsal fornix on glucose metabolism in liver slices of rabbits
F
o
o n
I
118
Exp. Clin. Endocrinol. 96 (1990) 1
Ac kno wie dg eme rit s. Grateful acknowledgements were made to Prof. S. Roberts, UCLA School
of Medicine, Dr. K. Yoshida, Yokohama City University, Prof. Y. Sasaki, Tohoku University, and to Miss A. Ohri, Kochi Medical School, for their helpful advice, criticism, collaboration and secre tary work. This study was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (Grant No. 01570086).
References KABA, H.; SAlTo, H.; KAWARAMI, T.; KITAOKA, K.; SETO, K.; YAMAMOTO, H.; KAWAKAaII, M.:
Influence of electrical stimulation of the limbic structure on glucagon level in rabbit's plasma. Exp. Clin. Endocrinol. 89 (1987) 233-236. KAWAKAMI, M.; SETO, K.; TERASAWA, E.; YOsHIDA, K.: Mechanisms in the limbic system con-
trolling reproductive functions of the ovary with special reference to positive feedback of progestin to the hippocampus. Progr. Brain Res. 27 (1967) 69-102. SETO, K.; TERASAWA, E.; YOSIITDA, K.; MIYAMOTO, T.; SEKIOEEJCHI, M.; HATTORI, Y.: Influence of electrical stimulation and lesion in limbic structure upon biosynthesis of adrenocorticoid in the rabbit. Neuroendocrinology 3 (1968) 337-348. SETO, K.; OTSUKA, K.; YANASE, M.; SAKUMA, Y.; KAWAKAMI, M.; BLACK, A. L.: Relation-
ship between acetate metabolism and glycolysis in liver slices of normal, starved and alloxan diabetic sheep. Clin. Chem. 2 (1973) 121-128. SETO, K.; SAlTo, H.; OTSUKA, K.; KAWAKAMI, M.: Influence of electrical stimulation of the limbic structure on insulin level in rabbit's plasma. Exp. Clin. Endocrinol. 81 (1983a) 347-349. SETO, K.; SAlTO, H.; OTSUKA, K.; KAWAKAMI, M.: Influence of lesion of the limbic-hypothalamic system on metabolic responses of acetate to daily repeated cold exposures in rabbits. Exp.
Clin. Endocrinol. 82 (1983b) 275-284. SETO, K.; SAlTo, H.; OTSUKA, K.; SATO, T.; OTSTJKA, K.; KAWAKAMI, M.: Influence of lesions
in the limbic-hypothalamic system on metabolic response of pyruvate to daily repeated cold exposure in rabbits. Exp. Clin. Endocrinol. 86 (1985) 223-232. SHhia&zu, T.: The hypothalamus and metabolic regulation- Metabolism and Disease 16 (1979)
21-33. SHIMAZU, T.; SAlTO, M.: Methods for stimulation and lesion of the brain and their application to metabolic research. Metabolism and Disease 21 (1984) 577-592. UEMURA, K.; Iciuciu, A.; YATOMI, A.; MIURA, H.; HONMURA, A.; YANASE, M.; SAXAMOTO, N.:
Involvement of the lippocampus in central nervous system-mediated glucoregulation in rats. Endocrinology 124 (1989) 2449-2455. (Accepted 12 September 1989)
Author's address: Prof. K. SETO, Department of Physiology, Kochi Medical School, Kochi 781-51/Japan
Nankoku,
Downloaded by: University of Pittsburgh. Copyrighted material.
KAWAKAMI, M.;
