EXPERIMENTAL
NEUHOLOGY
Hypothalamic
62, 191-199
Lesion
Glutamate
(1978)
Induced
by Injection
in Suckling
Period
Development KAZUHIKO
Department
TANAKA,
of Pediatrics, Rcceivcd
.4pril
SHIMADA, KUSUNOE;I
Prcfrcfrwal
4, 1978;
Subsequent
of Obesity
MORIMI TOMOICHI
ICyoto
and
of Monosodium
Uilizcrsity
revision
rcccivrd
KOJI
NAKAO,
AND
l of Mediciitc, J~tm
Kyoto,
Japart
9, 1978
The relationship between the hypothalamic lesion, which was induced by injecting monosodium glutamate (MSG) in a suckling mouse, and subsequent growth of the mouse was studied. Hypothalamic lesions were localized mainly in the preoptic region and a region surrounding the median eminence. The severity and extent of these lesions varied according to the time of MSG injection. When 2 mgMSG/g body weight was given subcutaneously to mice successively from 1 to 5 days of age (group I), the hypothalamic lesions included not only the preoptic and arcuate nuclei but also two-thirds of the ventromedial nucleus and a part of some other nuclei. Whereas in the mice in group 2, which had five successive injections of 2. mg/g MSG from 6 to 10 days of age, the hypothalamic lesion was milder than that in group 1 and the ventromedial nucleus was spared. When the difference of body weight gain of the mice was evaluated by a ratio of weight: length, 92% of the mice in group 1 developed overt obesity at 15 weeks of age, whereas only 22% of mice in group 2 and 370 of the control mice developed overt obesity. It is suggested that the development of overt obesity in mice treated with MSG is intimately related to damage in the ventromedial nucleus in addition to that in the arcuate nucleus. Abbreviations : MSG-monosodium glutamate ; na-n. arcuatus ; ndm-n. dorsomedialis ; nha-n. anterior ; nhp-n. posterior ; nml-n. mamillaris lateralis ; nmmn. mamillaris medialis ; npe-n. periventricularis ; npmd-n. premamillaris dorsalis ; npmv-n. premamillaris ventralis ; npv-n. paraventricularis ; nsc-n. suprachiasmaticus ; nvm-n. ventromedialis ; porn-n. preopticus medialis ; pop-n. preopticus periventricularis ; pos-n. preopticus suprachiasmaticus ; td-tractus diagonalis Broca. 1Doctors Shimada and Nakao are now at the Department of Pediatrics, Shiga University of Medical Science, Otsu, Japan. 191 0014-4886/78/0621-0191$02.00/O All
Copyright 0 1978 rights of reproduction
b;
Academic Press, Inc. in any form reserved.
192
TANAKA
ET
AL.
INTRODUCTION Data from a number of laboratories have indicated that an excess amount of monosodium glutamate (MSG) causes extensive damage to the hypothalamus of a mouse when this chemical is given in the suckling period (2, 5, 12, 16, 18, 19). S ome authors also mentioned that a mouse thus treated subsequently develops obesity and/or endocrinological abnormalities (4, 11, 15, 17, 20, 21). There are, however, few papers dealing with the relationship between the extent of hypothaIamic lesion and subsequent physical and endocrinological development. This study was intended to throw light upon the effect of excess amounts of MSG on a suckling mouse brain, with special reference to the relationship between the extent, of hypothalamic lesion and subsequent development of obesity. MATERIALS
AND
METHODS
The animals used in this experiment were a strain of ICR-JCL mice. Monosodium glutamate (Merck Inc.) was used in a 10% aqueous solution. To study the relationship between the age at time of administration of MSG and the extent of brain damage, 78 mice were injected with a single dose of 2 mgMSG/g body weight at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, or 30 days after birth. These mice were killed 6 h after the injection. To examine the relationship between the extent of hypothalamic lesion and subsequent physical growth, 77 newborn male mice were divided into three groups. A group of 24 mice (group 1) had five successive injections of 2 mgMSG/g body weight from 1 to 5 days of age. The 23 mice in group 2 had five successive injections of 2 mgMSG/g body weight from 6 to 10 days of age. The remaining 30 mice, which were injected with the same amount of saline, served as the control. MSG was injected subcutaneously on the back in each animal. The animals in each group were weaned at 21 days of age. After weaning, four to five mice in each group were placed in a cage and given free access to mouse chow. Body lengths (from nose to anus) and weights were measured at weekly intervals until 15 weeks of age. A ratio of body weight: length was then calculated from these values. Data on daily food consumption were evaluated during the 5th and 15th weeks of age. Mice in this study were given free access to mouse chow in a cage designed to avoid food loss by spillage. Several animals were killed at different days after MSG injection. Brains were fixed by Bouin’s solution, dehydrated, and embedded in paraffin. Serial sections were cut at 6 pm both in the parasagittal and coronal planes and stained with hematoxylin-eosin. Livers from each group were fixed in 10% formalin.
RISC;,
~lTl’OTIItlLA&~IC
LESIONS,
ANL)
OEWSITY
193
RESULTS Relationship bctzceen .4ge at Administration of MSG arld Extent of Brain Lesion. The severity and extent of the lesion in the brains of mice which were injected with MSG at different days of life are shown in Fig. 1. Severity and extent of brain damage were most prominent in the youngest mice. Though the hypothalamus of the youngest animals was the site most vulnerable to MSG, different numbers of degenerating neurons were found in various regions in the brain, such as the neocortex, subfornical organ, olfactory lobe, and area postrema. When mice were injected with MSG on the fourth day of life and killed 6 h later, the extent of the lesion was reduced significantly (Fig. 2) compared to that of the youngest mice. The hypothalamus, however, showed severe damage. In the preoptic area of the hypothalamus (Figs. 2A, B), degenerating neurons were confined to the suprachiasmatic preoptic nucIeus. Around the median eminence, the arcuate nucleus was the site of the severest damage (Figs. 2E, F). A few neurons in the ventromedial and ventral premamillar nuclei showed necrosis. The severity and the extent of lesion in the mouse brain decreased in proportion to the age at which the MSG was given. However, a few pyknotic nuclei and nuclear debris were found in the arcuate nucleus of the mice which were treated on the 30th day of life. Hypotlzalamic Lcsiojls and Subsequent Growth Evaluafed by Body Length and K7eiglzt. When the mice in group 1 were killed at 105 days of
FIG. 1. Camera lucida drawing of frontal sections at different levels of a l-day-old mouse cerebrum 6 h after injection of 2 mg monosodium glutamate/g body weight. The regions painted out contained a number of pyknotic nuclei. The hatched regions contained a moderate number of pyknotic nuclei.
194
TANAKA
ET
AL,
FIG. 2. Camera lucida drawing of frontal sections at different levels of a 4-day-old mouse cerebrum 6 h after injection of 2 mg monosodium glutamate/g body weight. Lesion was almost entirely confined to the preoptic area and the arcuate nucleus.
age, the preoptic area, arcuate nucleus, and ventral two-thirds of the ventromedial nucleus were scanty in cellularity and showed severe atrophy (Fig. 3B), whereas the hypothalamic lesions of mice in group 2 were confined mostly to the arcuate nucleus (Fig. 3C). The body lengths and body weights of animals in each group are shown in Figs. 4 and 5. The mean increase in body length of mice in groups 1 and 2 was stunted and became significantly shorter (P < 0.05) than that of the controls by 42 days of age. When the mice in each group were weighed at 21 days after birth, the mean body weights of the mice in both experimental groups were significantly less (P < 0.001) than those of the control group. After 21 days of age, the rate of body weight gain of mice in group 1 was accelerated and their mean body weight exceeded that of the controls at 91 days after birth. After 98 days of age the mean body weight of group 1 was significantly larger than the control (P < 0.05). There was, however, no significant difference in mean body weights between group 2 and the control. Figure 6 shows the ratio of mean body weight and mean length of mice in each group. The ratio in group 1 exceeded that in the control by 63 days of age and the difference in the ratio between group 1 and the control group became statistically significant after 77 days of age (P < 0.05). The ratio of mean body weight and mean length of mice in group 2 was significantly smaller than that of the control until 63 days of age (P < 0.05), and then the difference became insignificant. If a mouse whose ratio exceeds two standard deviations (J4'/L = 3.48) of the control group is regarded as obese,92% of the mice in group 1 exceeded two standard deviations after
195
-
196
TANAKA
ET
AL,
control
:j_
I
2
3
4
5
6
oge
FIG.
4. Measurements
7
6
in
weeks
9 IO I I 12 13 14 15
of nasoanal length. The vertical lines represent 1 SD.
105 days of age, thus showing overt obesity. Only 22% of the mice in group 2 and 3% of the control mice developed overt obesity. Histological findings obtained at 105 days of age revealed massive accumulations of adipose tissue in mice belonging to group 1 compared to those in the control. Livers of most mice in group 1 showed fatty changes.
40
-
QmJP I
‘---,I
aroup
-
CMtrOl
2
30
20
IO. t
I
2
3 4
5 age
FIG.
6 7 in
6
9
IO I I I2 13 14 15
weeks
5. Measurements of bodv weight. The vertical lines represent 1 SD.
MSG,
HTI’OTHALAMIC
LESIONS,
AND
197
OUESITY
YL 4.00
3.00
2.00
1.00. ,p I
2
3
4
5
6
age
FIG.
6. Ratios
of body
weight
to body
7 in
6
9
IO II
12 13 14 15
weeks
length.
The
vertical
lines
represent
1 SD,
The daily intake of diet was measured for selected mice in each group, and the data are shown in Fig. 7. Although mice in group 1 ate slightly more food than those in the control group between 42 and 84 days of age, the difference between these two groups was statistically insignificant. The daily dietary intake of mice in group 2 was slightly less than that of those in the control group throughout the entire period tested. The difference between these two groups was, however, statistically insignificant. DISCUSSION As reported by Inouye and Murakami (11) and Lemkey-Johnston Reynolds (12), the severity and extent of brain damage of suckling
6
0
9muP
I
llama
group
2
B
control
”
.
T
4 ” 2.
5
FIG. 7. Measurements
6
7
8
9
of food consumption.
IO
II
I2
The
vertical
I3
lines
I4
I5
represent
1 SD
and mice
198
TANAKA
ET
AL.
in this experiment also largely depended on the age of the animals when MSG was given. In the cerebrums of mice in group 2, which were injected with MSG at 6 to 10 days of age, the hypothalamic lesion was confined almost entirely to the arcuate nucleus. Although the damage was mild, the cerebral lesion in the mice belonging to group 1, which had successive injections of MSG from 1 to 5 days of age, was extended even to the neocortex, hypocampus, and habenular nucleus. The hypothalamic lesion in this group was also extended to the preoptic area, the mamillary nucleus, and the ventral two-thirds of the ventromedial nucleus. Most animals in group 1 subsequently developed overt obesity by the 10th week of age as evaluated by the ratio of mean weight and length, whereas most animals in group 2 and the control group remained unchanged. Considering the increasing evidence (9, 10, 14, 22, 23) that selective damage of the ventromedial nucleus results in overt obesity in adult animals, it is most probable that neuronal damage in the ventral two-thirds of the ventromedial nucleus played an important role in the development of overt obesity in group 1. Anand and Brobeck ( 1) and Brobeck et al. (3) reported that adult animals which had electrolytic lesions in both sides of the ventromedial nucleus increased their food intake and subsequently developed obesity. Debons and co-workers (&8) and Mayer and Marshall (13) also found that the adult mouse whose ventromedial nucleus was destroyed by injection of gold thioglucose became hyperphagic and subsequently developed obesity. According to those data, the hyperphagia and obesity were considered to be associated with the pathology of the lesion of the ventromedial nucleus of the hypothalamus. However, the food consumption study in the present experiment disclosed that the obese mice in group 1 did not show a significant increase in their food intake throughout the entire period tested, in spite of bilateral lesions of the ventromedial nucleus. Olney (17) and Bunyan et al. (4) also found that an obese mouse treated with MSG is rather hypophagic. Further studies will be required to conclude whether this difference in food consumption derives from the difference in the age of animals when the treatment is started or the difference in the extent of the hypothalamic lesions. REFERENCES 1. ANAND, B. K., AND J. R. BROBECK. 1951. Hypothalamic control of food intake in rats and cats. Yale J. Biol. Med. 24: 123-140. 2. AREES, E., AND J. MAYER. 1970. Monosodium glutamate-induced brain lesions: Electron microscopic examination. Science 170 : 549-550. 3. BROBECK, J. R., J. TEPPERMAN, AND C. N. H. LONG. 1943. Experimental hypothalamic hyperphagia in the albino rat. Yule J. Physiol. 15 : 831-853. 4. BUNYAN, J., E. A. MURRELL, AND P. P. SHAH. 1976. The induction of obesity in rodents by means of monosodium glutamate. Br. J. Nfrtr. 35 : 25-39.
MSG,
HYPOTHALAMIC
LESIONS,
AND
OBESITY
199
5. BURDE, R. M., J3. SCIIAINKER, AND J. KAYES. 1971. Monosodium glutamate: Acute effect of oral and subcutaneous administration on the arcuate nucleus of hypothalamus in mice and rats. Nature (London) 233: 58-60. 6. DEBONS, A. F., I. KRIMSKY, H. J. LIKVSICI, A. FROM, AND R. J. CLovrIEa. 1968. Gold thioglucose damage to the satiety center. A*J~. J. Pl~ysiol. 214 : 652-658. 7. DEBON~, A. F., I. KRIMSKY, A. FROM, AND R. J. CLOUTIER. 1970. Site of action c,f gold thioglucose in the hypothalamic satiety center. .-flrr. J. Plrssiul. 219: 13971402. 8. DEBONS, A. F., I. KRIMSZGY, A. FRO&I, AND R. J. CLOUTIER. 1970. Gold thioglucose induction of obesity: significance of focal gold deposits in hypothalamus. -4~1. J. Physiol. 219: 1403-1408. 9. HOEBEL. B. G., AND P. TIETP;LBAV~~. 1966. Weight regulation in normal and hypothalamic hyperphagic rats. /. Co~rp. Physiol. Psyzl~ol. 61: 189-193. 10. HOEBEL, B. G. 1969. Feeding and self-stimulation. .4~lr. N.Y. .4cod. .?ci. 157: 758-778. 11. INOUYE, M., AND U. MURAE(AMI. 1971. Brain lesions in the mouse fetus caused by maternal administration of monosodium glutamate. C‘olrg. ,4110?11. 11 : 171-177. 12. LEMKEY-JOHNSTON, N., AND W. A. REYNOLDS. 1974. Nature and extent of brain lesions in mice related to ingestion of monosodium glutamate. J. Neztropathol. Exp. Nrwol. 33 : 74-97. 13. MAYER, J., AND N. B. MARSHALL. 1956. Specificity of gold thioglucose for ventromedial hypothalamic lesions and hyperphagia. Nntzrvc (Lo&otz) 178: 13991400. 14. MOGENSON, G. J. 1974. Changing views of the role of the hypothalamus in the control of ingestive behaviors. Pages 268-293 in Rcccrlt Stztdirs of Hypothalamic Furrcfiorc Znt. Sv*np. Calgary, 1973. Larger, Basel. 15. NAGASAWA, H., R. YANAI, AND S. K~KUYAMA. 1974. Irreversible inhibition of pituitary prolactin and growth hormone secretion and of mammary gland development in mice by monosodium glutamate administration neonatally. A4cta Endocrinol. 75: 249-259. 16. OLNEY, J. W., AND L. G. SHARPE. 1969. Brain lesions in an infant rhesus monkey treated with monosodium glutamate. Science 166 : 386-388. 17. OLNEY, J. W. 1969. Brain lesions, obesity, and other disturbances in mice treated with monosodium glutamate. Scicfzce 164 : 719-721. 18. OLNEY, J. W. 1971. Glutamate-induced neuronal necrosis in the infant mouse hypothalamus : an electron microscopic studies. J. Ncuropathol. Exp. NclkYD/. 30 : 75-90. 19. OLNEy, J. W., L. G. SHARPE, AND R. D. FEIGIN. 1972. Glutamate-induced brain damage in infant primates. J. Ncwopathol. Exp. NCUW~. 31 : 464-488. 20. I+zz, W. J., J. E. BARKHART, AND D. J. FAPGSLOW. 1977. Monosodium glutamate administration to the newborn : Reduces reproductive ability in female and male mice. Scicnsr 1%: 452-454. 21. REDDING, T. W., A. V. SCHALLY, A. ARIMURA, AND I. WAKABAYASHI. 1971. Effect of monosodium glutamate on some endocrine functions. Nrzlroe&ocrinology 8 : 245-255. 22. STEVENSON, J. A. F. 1949. Effects of hypothalamic lesions on water and energy metabolism in the rat. IZcrolt Prvqr. H~rrr~ottp h’cs. 4: 363-394. 23. STEVENSON, J. A. I;. 1969. Pages 524-621 in HAYXIAI;EK, E., A. ANI)F.R~ON, *xl) W. NAVTA, The I-lypothnlasrttls. Thomas, Springfield, Ill.
NEUHOLOGY
Hypothalamic
62, 191-199
Lesion
Glutamate
(1978)
Induced
by Injection
in Suckling
Period
Development KAZUHIKO
Department
TANAKA,
of Pediatrics, Rcceivcd
.4pril
SHIMADA, KUSUNOE;I
Prcfrcfrwal
4, 1978;
Subsequent
of Obesity
MORIMI TOMOICHI
ICyoto
and
of Monosodium
Uilizcrsity
revision
rcccivrd
KOJI
NAKAO,
AND
l of Mediciitc, J~tm
Kyoto,
Japart
9, 1978
The relationship between the hypothalamic lesion, which was induced by injecting monosodium glutamate (MSG) in a suckling mouse, and subsequent growth of the mouse was studied. Hypothalamic lesions were localized mainly in the preoptic region and a region surrounding the median eminence. The severity and extent of these lesions varied according to the time of MSG injection. When 2 mgMSG/g body weight was given subcutaneously to mice successively from 1 to 5 days of age (group I), the hypothalamic lesions included not only the preoptic and arcuate nuclei but also two-thirds of the ventromedial nucleus and a part of some other nuclei. Whereas in the mice in group 2, which had five successive injections of 2. mg/g MSG from 6 to 10 days of age, the hypothalamic lesion was milder than that in group 1 and the ventromedial nucleus was spared. When the difference of body weight gain of the mice was evaluated by a ratio of weight: length, 92% of the mice in group 1 developed overt obesity at 15 weeks of age, whereas only 22% of mice in group 2 and 370 of the control mice developed overt obesity. It is suggested that the development of overt obesity in mice treated with MSG is intimately related to damage in the ventromedial nucleus in addition to that in the arcuate nucleus. Abbreviations : MSG-monosodium glutamate ; na-n. arcuatus ; ndm-n. dorsomedialis ; nha-n. anterior ; nhp-n. posterior ; nml-n. mamillaris lateralis ; nmmn. mamillaris medialis ; npe-n. periventricularis ; npmd-n. premamillaris dorsalis ; npmv-n. premamillaris ventralis ; npv-n. paraventricularis ; nsc-n. suprachiasmaticus ; nvm-n. ventromedialis ; porn-n. preopticus medialis ; pop-n. preopticus periventricularis ; pos-n. preopticus suprachiasmaticus ; td-tractus diagonalis Broca. 1Doctors Shimada and Nakao are now at the Department of Pediatrics, Shiga University of Medical Science, Otsu, Japan. 191 0014-4886/78/0621-0191$02.00/O All
Copyright 0 1978 rights of reproduction
b;
Academic Press, Inc. in any form reserved.
192
TANAKA
ET
AL.
INTRODUCTION Data from a number of laboratories have indicated that an excess amount of monosodium glutamate (MSG) causes extensive damage to the hypothalamus of a mouse when this chemical is given in the suckling period (2, 5, 12, 16, 18, 19). S ome authors also mentioned that a mouse thus treated subsequently develops obesity and/or endocrinological abnormalities (4, 11, 15, 17, 20, 21). There are, however, few papers dealing with the relationship between the extent of hypothaIamic lesion and subsequent physical and endocrinological development. This study was intended to throw light upon the effect of excess amounts of MSG on a suckling mouse brain, with special reference to the relationship between the extent, of hypothalamic lesion and subsequent development of obesity. MATERIALS
AND
METHODS
The animals used in this experiment were a strain of ICR-JCL mice. Monosodium glutamate (Merck Inc.) was used in a 10% aqueous solution. To study the relationship between the age at time of administration of MSG and the extent of brain damage, 78 mice were injected with a single dose of 2 mgMSG/g body weight at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, or 30 days after birth. These mice were killed 6 h after the injection. To examine the relationship between the extent of hypothalamic lesion and subsequent physical growth, 77 newborn male mice were divided into three groups. A group of 24 mice (group 1) had five successive injections of 2 mgMSG/g body weight from 1 to 5 days of age. The 23 mice in group 2 had five successive injections of 2 mgMSG/g body weight from 6 to 10 days of age. The remaining 30 mice, which were injected with the same amount of saline, served as the control. MSG was injected subcutaneously on the back in each animal. The animals in each group were weaned at 21 days of age. After weaning, four to five mice in each group were placed in a cage and given free access to mouse chow. Body lengths (from nose to anus) and weights were measured at weekly intervals until 15 weeks of age. A ratio of body weight: length was then calculated from these values. Data on daily food consumption were evaluated during the 5th and 15th weeks of age. Mice in this study were given free access to mouse chow in a cage designed to avoid food loss by spillage. Several animals were killed at different days after MSG injection. Brains were fixed by Bouin’s solution, dehydrated, and embedded in paraffin. Serial sections were cut at 6 pm both in the parasagittal and coronal planes and stained with hematoxylin-eosin. Livers from each group were fixed in 10% formalin.
RISC;,
~lTl’OTIItlLA&~IC
LESIONS,
ANL)
OEWSITY
193
RESULTS Relationship bctzceen .4ge at Administration of MSG arld Extent of Brain Lesion. The severity and extent of the lesion in the brains of mice which were injected with MSG at different days of life are shown in Fig. 1. Severity and extent of brain damage were most prominent in the youngest mice. Though the hypothalamus of the youngest animals was the site most vulnerable to MSG, different numbers of degenerating neurons were found in various regions in the brain, such as the neocortex, subfornical organ, olfactory lobe, and area postrema. When mice were injected with MSG on the fourth day of life and killed 6 h later, the extent of the lesion was reduced significantly (Fig. 2) compared to that of the youngest mice. The hypothalamus, however, showed severe damage. In the preoptic area of the hypothalamus (Figs. 2A, B), degenerating neurons were confined to the suprachiasmatic preoptic nucIeus. Around the median eminence, the arcuate nucleus was the site of the severest damage (Figs. 2E, F). A few neurons in the ventromedial and ventral premamillar nuclei showed necrosis. The severity and the extent of lesion in the mouse brain decreased in proportion to the age at which the MSG was given. However, a few pyknotic nuclei and nuclear debris were found in the arcuate nucleus of the mice which were treated on the 30th day of life. Hypotlzalamic Lcsiojls and Subsequent Growth Evaluafed by Body Length and K7eiglzt. When the mice in group 1 were killed at 105 days of
FIG. 1. Camera lucida drawing of frontal sections at different levels of a l-day-old mouse cerebrum 6 h after injection of 2 mg monosodium glutamate/g body weight. The regions painted out contained a number of pyknotic nuclei. The hatched regions contained a moderate number of pyknotic nuclei.
194
TANAKA
ET
AL,
FIG. 2. Camera lucida drawing of frontal sections at different levels of a 4-day-old mouse cerebrum 6 h after injection of 2 mg monosodium glutamate/g body weight. Lesion was almost entirely confined to the preoptic area and the arcuate nucleus.
age, the preoptic area, arcuate nucleus, and ventral two-thirds of the ventromedial nucleus were scanty in cellularity and showed severe atrophy (Fig. 3B), whereas the hypothalamic lesions of mice in group 2 were confined mostly to the arcuate nucleus (Fig. 3C). The body lengths and body weights of animals in each group are shown in Figs. 4 and 5. The mean increase in body length of mice in groups 1 and 2 was stunted and became significantly shorter (P < 0.05) than that of the controls by 42 days of age. When the mice in each group were weighed at 21 days after birth, the mean body weights of the mice in both experimental groups were significantly less (P < 0.001) than those of the control group. After 21 days of age, the rate of body weight gain of mice in group 1 was accelerated and their mean body weight exceeded that of the controls at 91 days after birth. After 98 days of age the mean body weight of group 1 was significantly larger than the control (P < 0.05). There was, however, no significant difference in mean body weights between group 2 and the control. Figure 6 shows the ratio of mean body weight and mean length of mice in each group. The ratio in group 1 exceeded that in the control by 63 days of age and the difference in the ratio between group 1 and the control group became statistically significant after 77 days of age (P < 0.05). The ratio of mean body weight and mean length of mice in group 2 was significantly smaller than that of the control until 63 days of age (P < 0.05), and then the difference became insignificant. If a mouse whose ratio exceeds two standard deviations (J4'/L = 3.48) of the control group is regarded as obese,92% of the mice in group 1 exceeded two standard deviations after
195
-
196
TANAKA
ET
AL,
control
:j_
I
2
3
4
5
6
oge
FIG.
4. Measurements
7
6
in
weeks
9 IO I I 12 13 14 15
of nasoanal length. The vertical lines represent 1 SD.
105 days of age, thus showing overt obesity. Only 22% of the mice in group 2 and 3% of the control mice developed overt obesity. Histological findings obtained at 105 days of age revealed massive accumulations of adipose tissue in mice belonging to group 1 compared to those in the control. Livers of most mice in group 1 showed fatty changes.
40
-
QmJP I
‘---,I
aroup
-
CMtrOl
2
30
20
IO. t
I
2
3 4
5 age
FIG.
6 7 in
6
9
IO I I I2 13 14 15
weeks
5. Measurements of bodv weight. The vertical lines represent 1 SD.
MSG,
HTI’OTHALAMIC
LESIONS,
AND
197
OUESITY
YL 4.00
3.00
2.00
1.00. ,p I
2
3
4
5
6
age
FIG.
6. Ratios
of body
weight
to body
7 in
6
9
IO II
12 13 14 15
weeks
length.
The
vertical
lines
represent
1 SD,
The daily intake of diet was measured for selected mice in each group, and the data are shown in Fig. 7. Although mice in group 1 ate slightly more food than those in the control group between 42 and 84 days of age, the difference between these two groups was statistically insignificant. The daily dietary intake of mice in group 2 was slightly less than that of those in the control group throughout the entire period tested. The difference between these two groups was, however, statistically insignificant. DISCUSSION As reported by Inouye and Murakami (11) and Lemkey-Johnston Reynolds (12), the severity and extent of brain damage of suckling
6
0
9muP
I
llama
group
2
B
control
”
.
T
4 ” 2.
5
FIG. 7. Measurements
6
7
8
9
of food consumption.
IO
II
I2
The
vertical
I3
lines
I4
I5
represent
1 SD
and mice
198
TANAKA
ET
AL.
in this experiment also largely depended on the age of the animals when MSG was given. In the cerebrums of mice in group 2, which were injected with MSG at 6 to 10 days of age, the hypothalamic lesion was confined almost entirely to the arcuate nucleus. Although the damage was mild, the cerebral lesion in the mice belonging to group 1, which had successive injections of MSG from 1 to 5 days of age, was extended even to the neocortex, hypocampus, and habenular nucleus. The hypothalamic lesion in this group was also extended to the preoptic area, the mamillary nucleus, and the ventral two-thirds of the ventromedial nucleus. Most animals in group 1 subsequently developed overt obesity by the 10th week of age as evaluated by the ratio of mean weight and length, whereas most animals in group 2 and the control group remained unchanged. Considering the increasing evidence (9, 10, 14, 22, 23) that selective damage of the ventromedial nucleus results in overt obesity in adult animals, it is most probable that neuronal damage in the ventral two-thirds of the ventromedial nucleus played an important role in the development of overt obesity in group 1. Anand and Brobeck ( 1) and Brobeck et al. (3) reported that adult animals which had electrolytic lesions in both sides of the ventromedial nucleus increased their food intake and subsequently developed obesity. Debons and co-workers (&8) and Mayer and Marshall (13) also found that the adult mouse whose ventromedial nucleus was destroyed by injection of gold thioglucose became hyperphagic and subsequently developed obesity. According to those data, the hyperphagia and obesity were considered to be associated with the pathology of the lesion of the ventromedial nucleus of the hypothalamus. However, the food consumption study in the present experiment disclosed that the obese mice in group 1 did not show a significant increase in their food intake throughout the entire period tested, in spite of bilateral lesions of the ventromedial nucleus. Olney (17) and Bunyan et al. (4) also found that an obese mouse treated with MSG is rather hypophagic. Further studies will be required to conclude whether this difference in food consumption derives from the difference in the age of animals when the treatment is started or the difference in the extent of the hypothalamic lesions. REFERENCES 1. ANAND, B. K., AND J. R. BROBECK. 1951. Hypothalamic control of food intake in rats and cats. Yale J. Biol. Med. 24: 123-140. 2. AREES, E., AND J. MAYER. 1970. Monosodium glutamate-induced brain lesions: Electron microscopic examination. Science 170 : 549-550. 3. BROBECK, J. R., J. TEPPERMAN, AND C. N. H. LONG. 1943. Experimental hypothalamic hyperphagia in the albino rat. Yule J. Physiol. 15 : 831-853. 4. BUNYAN, J., E. A. MURRELL, AND P. P. SHAH. 1976. The induction of obesity in rodents by means of monosodium glutamate. Br. J. Nfrtr. 35 : 25-39.
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