Effect of monosodium glutamate on some endocrine functions

Small intestine barrier function failure induces systemic inflammation in monosodium glutamate-induced chronically obese mice

Chronic obesity has increased worldwide, in conjunction with type 2 diabetes. Chronic obesity causes systemic inflammation that may result in functional deterioration of the gastrointestinal barrier. However, gastrointestinal conditions associated with chronic obesity have not been comprehensively investigated. The purpose of this study was to evaluate morphological changes in small intestine barrier structures during chronic obesity. A mouse model of chronic obesity induced by monosodium glutamate treatment was established. At postnatal week 15, pathological changes including in small intestinal epithelial cells were analyzed in chronically obese mice compared with controls. Numerous gaps were identified between small intestinal epithelial cells in chronically obese mice, and levels of both desmosomal and tight junction proteins were significantly lower in their small intestinal epithelial cells. Moreover, in chronically obese mice, a significant increase in the number of intestinal inflammatory cells, particularly macrophages, was observed; in addition, blood samples from the mouse model show an increase in markers of inflammation, tumor necrosis factor-alpha and interleukin-1-beta. These findings suggest that functional deterioration of adhesion structures between small intestinal epithelial cells causes gastrointestinal barrier function failure, leading to a rise in intestinal permeability to blood vessels and consequent systemic inflammation, characterized by macrophage infiltration.

N-Acetyl-l-Cysteine treatment efficiently prevented pre-diabetes and inflamed-dysmetabolic liver development in hypothalamic obese rats

AIM

Hypothalamic obese rats are characterized by pre-diabetes, dyslipidemia, hyperadiposity, inflammation and, liver dysmetabolism with oxidative stress (OS), among others. We studied endocrine-metabolic dysfunctions and, liver OS and inflammation in both monosodium l-glutamate (MSG)-neonatally damaged and control litter-mate (C) adult male rats, either chronically treated with N-Acetyl-l-Cysteine since weaned (C-NAC and MSG-NAC) or not.

METHODOLOGY

We evaluated circulating TBARS, glucose, insulin, triglycerides, uric acid (UA) and, aspartate and alanine amino-transferase; insulin sensitivity markers (HOMA indexes, Liver Index of Insulin Sensitivity -LISI-) were calculated and liver steps of the insulin-signaling pathway were investigated. Additionally, we monitored liver OS (protein carbonyl groups, GSH and iNOS level) and inflammation-related markers (COX-2 and TNFα protein content; gene expression level of Il1b, Tnfα and Pai-1); and carbohydrate and lipid metabolic functions (glucokinase/fructokinase activities and, mRNA levels of Srebp1c, Fas and Gpat).

KEY FINDINGS

Chronic NAC treatment in MSG rats efficiently decreased the high circulating levels of triglycerides, UA, transaminases and TBARS, as well as peripheral (high insulinemia and HOMA indexes) and liver (LISI and the P-AKT:AKT and P-eNOS:eNOS protein ratio values) insulin-resistance. Moreover, NAC therapy in MSG rats prevented liver dysmetabolism by decreasing local levels of OS and inflammation markers. Finally, NAC-treated MSG rats retained normal liver glucokinase and fructokinase activities, and Srebp1c, Fas and Gpat (lipogenic genes) expression levels.

SIGNIFICANCE

Our study strongly supports that chronic oral antioxidant therapy (NAC administration) prevented the development of pre-diabetes, dyslipidemia, and inflamed-dysmetabolic liver in hypothalamic obese rats by efficiently decreasing high endogenous OS.

Efficacy of nanoceria for periodontal tissues alteration in glutamate-induced obese rats-multidisciplinary considerations for personalized dentistry and prevention

BACKGROUND

Nowadays, we face the global epidemic of obesity, that is known to contribute to the development of many diseases, such as the oral cavity pathologies. Dental and oral pathologies are frequently caused by and overlapped with systemic multifactorial diseases such as obesity being its early indicators and risk factors. The aim was to study the influence of nanoceria on periodontal tissues alteration in glutamate (MSG)-induced obese rats.

METHODS

We included 52 Wistar rats of both genders and divided into four groups: newborn rats in group 1 (control) received subcutaneously 8 μl/g saline. Group 2 received 3 to 4 mg/g MSG subcutaneously on the second, fourth, sixth, eighth, and tenth day of life; group 3-intragastric administration of nanocrystalline cerium dioxide at a dose of 1 mg/kg volume of 2.9 ml/kg against the background of glutamate-induced obesity; the fourth group of animals was treated with a solution of sodium citrate intragastric volume of 2.9 ml/kg (solvent of nanocrystalline cerium). We determined the total proteolytic activity, the total antitrypsin activity, the content-free fucose and glycosaminoglycanes (GAG), content of TBA-active of products, the content of oxidation-modified proteins (OMB), and catalase activity in the homogenate of soft periodontal tissues of rats.

RESULTS

Intragastric injection of nanoceria prevents activation of proteolytic processes, reducing the catabolism of glycoproteins and proteoglycans of periodontal tissue in MSG-induced obese rats. Injection of nanoceria prevents activation of proteolytic processes, significantly decreases the total proteolytic activity, and inhibits the activation of free radical oxidation in periodontal tissues of rats compared with MSG-induced obesity model without corrections. Further, it significantly increases the total antitrypsin activity in periodontal tissues by 1.7 times, TBA-reagents by 1.7 times, and content of OMB by 1.4 times compared with glutamate-induced obese animals.

CONCLUSIONS

MSG-induced obesity triggers periodontal tissue alterations in the rat model. Nanoceria contributes to the corrections of pathological changes in periodontal tissues in glutamate-induced obese rats via balancing protein-inhibitory capacity and reducing the depolymerization of fucosylated proteins and proteoglycans and antioxidative activity.

Intracerebroventricular injection of ghrelin decreases wheel running activity in rats

There is an increasing interest in elucidating the molecular mechanisms by which voluntary exercise is regulated. In this study, we examined how the central nervous system regulates exercise. We used SPORTS rats, which were established in our laboratory as a highly voluntary murine exercise model. SPORTS rats showed lower levels of serum ghrelin compared with those of the parental line of Wistar rats. Intracerebroventricular and intraperitoneal injection of ghrelin decreased wheel-running activity in SPORTS rats. In addition, daily injection of the ghrelin inhibitor JMV3002 into the lateral ventricles of Wistar rats increased wheel-running activity. Co-administration of obestatin inhibited ghrelin-induced increases in food intake but did not inhibit ghrelin-induced suppression of voluntary exercise in rats. Growth hormone secretagogue receptor (GHSR) in the hypothalamus and hippocampus of SPORTS rats was not difference that in control rats. We created an arcuate nucleus destruction model by administering monosodium glutamate (MSG) to neonatal SPORTS rats. Injection of ghrelin into MSG-treated rats decreased voluntary exercise but did not increase food intake, suggesting that wheel-running activity is not controlled by the arcuate nucleus neurons that regulate feeding. These results provide new insights into the mechanism by which ghrelin regulates voluntary activity independent of arcuate nucleus neurons.

Progressive Depletion of Rough Endoplasmic Reticulum in Epithelial Cells of the Small Intestine in Monosodium Glutamate Mice Model of Obesity

Chronic obesity is a known risk factor for metabolic syndrome. However, little is known about pathological changes in the small intestine associated with chronic obesity. This study investigated cellular and subcellular level changes in the small intestine of obese mice. In this study, a mouse model of obesity was established by early postnatal administration of monosodium glutamate. Changes in body weight were monitored, and pathological changes in the small intestine were evaluated using hematoxylin-eosin and Nissl staining and light and electron microscopy. Consequently, obese mice were significantly heavier compared with controls from 9 weeks of age. Villi in the small intestine of obese mice were elongated and thinned. There was reduced hematoxylin staining in the epithelium of the small intestine of obese mice. Electron microscopy revealed a significant decrease in and shortening of rough endoplasmic reticulum in epithelial cells of the small intestine of obese mice compared with normal mice. The decrease in rough endoplasmic reticulum in the small intestine epithelial cells of obese mice indicates that obesity starting in childhood influences various functions of the small intestine, such as protein synthesis, and could impair both the defense mechanism against invasion of pathogenic microbes and nutritional absorption.

Chronic Glucocorticoid-Rich Milieu and Liver Dysfunction

We investigated the impact of chronic hypercorticosteronemia (due to neonatal monosodium L-glutamate, MSG, and treatment) on liver oxidative stress (OS), inflammation, and carbohydrate/lipid metabolism in adult male rats. We evaluated the peripheral concentrations of several metabolic and OS markers and insulin resistance indexes. In liver we assessed (a) OS (GSH and protein carbonyl groups) and inflammatory (IL-1b, TNFa, and PAI-1) biomarkers and (b) carbohydrate and lipid metabolisms. MSG rats displayed degenerated optic nerves, hypophagia, low body and liver weights, and enlarged adipose tissue mass; higher peripheral levels of glucose, triglycerides, insulin, uric acid, leptin, corticosterone, transaminases and TBARS, and peripheral and liver insulin resistance; elevated liver OS, inflammation markers, and glucokinase (mRNA/activity) and fructokinase (mRNA). Additionally, MSG liver phosphofructokinase-2, glucose-6-phosphatase (mRNA and activity) and glucose-6-phosphate dehydrogenase, Chrebp, Srebp1c, fatty acid synthase, and glycerol-3-phosphate (mRNAs) were increased. In conclusion adult MSG rats developed an insulin-resistant state and increased OS and serious hepatic dysfunction characterized by inflammation and metabolic signs suggesting increased lipogenesis. These features, shared by both metabolic and Cushing's syndrome human phenotypes, support that a chronic glucocorticoid-rich endogenous environment mainly impacts on hepatic glucose cycle, displacing local metabolism to lipogenesis. Whether correcting the glucocorticoid-rich environment ameliorates such dysfunctions requires further investigation.

Oral Metformin Treatment Counteracts Adipoinsular Axis Dysfunction in Hypothalamic Obese Rats

Rats neonatally treated with monosodium L-glutamate (MSG) are deeply dysfunctional in adulthood. We explored the effect of an oral low dose of metformin treatment in male MSG rats on adipoinsular axis and visceral adipose tissue (VAT) dysfunctions, in both basal (nonfasting) and endotoxemia conditions. MSG rats, treated or not treated with metformin (30 days prior to experimentation), and control litter-mates (CTR) were studied at 90 days of age. Peripheral concentrations of glucose, lipids, and hormones were determined in basal and post-lipopolysaccharide (LPS) treatment conditions. Food intake and body weight (BW) were recorded and VAT mass and leptin mRNA levels were evaluated. Data indicated that MSG rats were lighter and displayed hypercorticosteronemia, hypophagia, adipoinsular axis hyperactivity, and enhanced VAT mass associated with an increased leptin gene expression. Interestingly, metformin-treated MSG rats corrected BW catch-up and counteracted VAT (mass and leptin mRNA level) and adipoinsular axis (basal and post-LPS) dysfunctions. Thus metformin treatment in MSG rats is able to correct several VAT and metabolic-endocrine dysfunctions. Our study suggests that a low-dose metformintherapy is effective to correct, at least in part, adipoinsular axis dysfunction in hypertrophic obese phenotypes, such as that of the human Cushing syndrome.

Metformin reduces the Walker-256 tumor development in obese-MSG rats via AMPK and FOXO3a

AIMS

Studies have associated obesity with a wide variety of cancers. Metformin, an anti-diabetic drug, has recently received attention as a potentially useful therapeutic agent for treating cancer. Therefore, the objective of this study was to analyze the mechanisms involved in the increase in tumor development and the reduction of it by metformin in obesity using an experimental breast tumor model.

MATERIAL AND METHODS

Newborn male Wistar rats were subcutaneously injected with 400mg/kg monosodium glutamate (MSG) (obese) or saline (control) at 2, 3, 4, 5 and 6 days of age. After 16 weeks, 1 × 10(7) Walker-256 tumor cells were subcutaneously injected in the right flank of the rats and concomitantly the treatment with metformin 300 mg/kg/15 days, via gavage, started. The rats were divided into 4 groups: control tumor (CT), control tumor metformin (CTM), obese-MSG tumor (OT) and obese-MSG tumor metformin (OTM). On the 18th week the tumor development and metformin effect were analyzed.

KEY FINDINGS

Tumor development was higher in OT rats compared with CT rats. Activation of insulin-IR-ERK1/2 pathway and an anti-apoptotic effect might be the mechanisms involved in the higher development of tumor in obesity. The effect of metformin reducing the tumor development in obese rats might involve increased mRNA expression of pRb and p27, increased activity of AMPK and FOXO3a and decreased expression of p-ERK1/2 (Thr202/Tyr204) in Walker-256 tumor.

SIGNIFICANCE

Our data allow us to suggest that metformin, reducing the stimulatory effect of obesity on tumor development, has a potential role in the management of cancers.

Hyperleptinemia directly affects testicular maturation at different sexual stages in mice, and suppressor of cytokine signaling 3 is involved in this process

BACKGROUND

Leptin plays an important role in reproductive function, and the mechanism of this phenomenon primarily focuses on the hypothalamic-pituitary-gonadal axis. However, until now, the direct effects of leptin on the testes during development from infancy to adulthood remained unclear. The aim of the present study was to explore the effects and molecular mechanisms that underlie leptin's action in the testes during sexual maturation.

METHODS

We used a monosodium glutamate (MSG)-treated mouse model to assess the effects of endogenous hyperleptinemia on the development of the testes from infancy to adulthood. Then, a variety of reproductive parameters were measured, including the concentration of testosterone, the weight and volume of the testicles, the diameter of the seminiferous tubules, and numbers of spermatogonia, spermatocytes, sperm, Leydig cells and offspring. In addition, we assessed the direct role of leptin and suppressor of cytokine signalling 3 (SOCS3)/phosphorylated signal transducer and activator of transcription 3 (pSTAT3) on the testes in vitro.

RESULTS

Testosterone secretion exhibited a diverse response: a low concentration of leptin induced testosterone secretion, and a high concentration inhibited testosterone secretion both in vivo and in vitro. A variety of reproductive parameters decreased in hyperleptinemic mice, including the weight and volume of the testicles, the diameter of the seminiferous tubules, and the numbers of spermatocytes, sperm, Leydig cells and offspring. The amount of spermatogonia was also elevated. The development of the testes was partially recovered after hyperleptinemia withdrawal. A high concentration of leptin induced SOCS3 expression and inhibited pSTAT3 expression in the testes.

CONCLUSIONS

The results indicated that MSG-induced hyperleptinemia directly affects testicular structure and function and that SOCS3/pSTAT3 played an important role in this process. These results also indicated the importance of monitoring and controlling leptin levels in obese male children. SOCS3 is a potential therapeutic target for leptin-induced dysgenesis.

The efficacy of probiotics for monosodium glutamate-induced obesity: dietology concerns and opportunities for prevention

Introduction

Obesity becomes endemic today. Monosodium glutamate was proved as obesogenic food additive. Probiotics are discussed to impact on obesity development.

Aims and objectives

The aim was to study the effects of probiotics on the development of monosodium glutamate (MSG)-induced obesity in rats.

Material and methods

We included 45 Wistar male rats and divided into three groups (n = 15). Newborn rats of group 1 (control) received subcutaneously 8 μl/g saline. Group 2 received 3 to 4 mg/g MSG subcutaneously on the second, fourth, sixth, eighth and tenth day of life. Within 4 months after birth, rats were on a standard diet. Group 3 received an aqueous solution of probiotics mixture (2:1:1 Lactobacillus casei IMVB-7280, Bifidobacterium animalis VKL, B. animalis VKB) at the dose of 5 × 10⁹ CFU/kg (50 mg/kg) intragastrically. Administration of probiotics was started at the age of 4 weeks just after weaning and continued for 3 months during 2-week courses. Group 2 received intragastrically 2.5 ml/kg water. Organometric and biochemical parameters in all groups of rats were analyzed over 4 months. The concentration of adiponectin was determined in serum, and leptin - in adipose tissue.

Results

Administration of MSG led to the development of obesity in rats; body weight had increased by 7.9% vs controls (p < 0.05); body length had increased by 5.4% (p < 0.05). Body mass index and Lee index and visceral fat mass had increased (p < 0.001). Under the neonatal injection of MSG, the concentration of total cholesterol, triglycerides, VLDL cholesterol and LDL cholesterol significantly increased (p < 0.001), in comparison with controls. Adipose-derived hormones changed in MSG obesity rats: adiponectin decreased by 58.8% (p < 0.01), and leptin concentration in adipose tissue had increased by 74.7% (p < 0.01). The probiotic therapy of rats from group 3 prevented obesity development. Parameters of rats treated with probiotic mixture did not differ from that in the control.

Conclusions

The introduction of MSG to newborn rats caused the obesity in adulthood. Periodic administration of probiotic mixture to rat injected with MSG neonatally resulted in recovery of lipid metabolism and prevention of the obesity development.

Analysis of angiotensin II- and ACTH-driven mineralocorticoid functions and omental adiposity in a non-genetic, hyperadipose female rat phenotype

The hypothalamic damage induced by neonatal treatment with monosodium L -glutamate (MSG) induces several metabolic abnormalities, resulting in a rat hyperleptinemic-hyperadipose phenotype. This study was conducted to explore the impact of the neonatal MSG treatment, in the adult (120 days old) female rat on: (a) the in vivo and in vitro mineralocorticoid responses to ACTH and angiotensin II (AII); (b) the effect of leptin on ACTH- and AII-stimulated mineralocorticoid secretions by isolated corticoadrenal cells; and (c) abdominal adiposity characteristics. Our data indicate that, compared with age-matched controls, MSG rats displayed: (1) enhanced and reduced mineralocorticoid responses to ACTH and AII treatments, respectively, effects observed in both in vivo and in vitro conditions; (2) adrenal refractoriness to the inhibitory effect of exogenous leptin on ACTH-stimulated aldosterone output by isolated adrenocortical cells; and (3) distorted omental adiposity morphology and function. This study supports that the adult hyperleptinemic MSG female rat is characterized by enhanced ACTH-driven mineralocorticoid function, impaired adrenal leptin sensitivity, and disrupted abdominal adiposity function. MSG rats could counteract undesirable effects of glucocorticoid excess, by developing a reduced AII-driven mineralocorticoid function. Thus, chronic hyperleptinemia could play a protective role against ACTH-mediated allostatic loads in the adrenal leptin resistant, MSG female rat phenotype.

Prenatal Monosodium Glutamate (MSG) Treatment Given Through the Mother's Diet Causes Behavioral Deficits in Rat Offspring

The present study reports various developmental and behavioral changes in the offspring of rat dams that received monosodium glutamate (MSG) in the drinking water all through the second and third trimesters of pregnancy. Three main effects were observed in the MSG exposed offspring: (1) juvenile obesity; (2) reduced general activity levels; (3) a specific type of learning disability in discrimination learning involving choice between simultaneously present positive and negative stimuli.

Testis structure and function in a nongenetic hyperadipose rat model at prepubertal and adult ages

There are few data for hormonal levels and testis structure and function during postnatal development in rats neonatally treated with monosodium L-glutamate (MSG). In our study, newborn male pups were ip injected with MSG (4 mg/g body weight) every 2 d up to 10 d of age and investigated at prepubertal and adult ages. Plasma levels of leptin, LH, FSH, prolactin, testosterone (T), corticosterone, and free T4 (FT4) were measured. MSG rats displayed elevated circulating levels of corticosterone and hyperadiposity/hyperleptinemia, regardless of the age examined; conversely, circulating prolactin levels were not affected. Moreover, prepubertal MSG rats revealed a significant (P < 0.05) reduction in testis weight and the number of Sertoli (SC) and Leydig cells per testis. Leptin plasma levels were severalfold higher (2.41 vs. 8.07; P < 0.05) in prepubertal MSG rats, and these animals displayed plasma LH, FSH, T, and FT4 levels significantly decreased (P < 0.05). Taken together, these data indicate that testis development, as well as SC and Leydig cell proliferation, were disturbed in prepubertal MSG rats. Adult MSG rats also displayed significantly higher leptin plasma levels (7.26 vs. 27.04; P < 0.05) and lower (P < 0.05) LH and FSH plasma levels. However, T and FT4 plasma levels were normal, and no apparent alterations were observed in testis structure of MSG rats. Only the number of SCs per testis was significantly (P < 0.05) reduced in the adult MSG rats. In conclusion, although early installed hyperadipose/hyperleptinemia phenotype was probably responsible for the reproductive axis damages in MSG animals, it remains to be investigated whether this condition is the main factor for hypothalamus-pituitary-gonadal axis dysfunction in MSG rats.

Impact of transient correction of increased adrenocortical activity in hypothalamo-damaged, hyperadipose female rats

OBJECTIVE

To explore the effects of transient correction of enhanced corticoadrenal activity in monosodium L-glutamate (MSG)-damaged female rats on peripheral insulin sensitivity and in vitro retroperitoneal (RP) adipocyte function.

DESIGNS

A dose of 4 mg/g body weight (BW) of MSG or vehicle (CTR) was i.p. injected, once every 2 days, between days 2 and 10 of age, in female rats. Intact and 21 day-operated (sham or adrenal enucleation (AE)) rats from both (CTR and MSG) groups were used for experimentation on day 120 of age. Circulating levels of several hormones, in basal and after i.v. high-glucose load conditions, and RP adiposity morphology and function were then evaluated.

RESULTS

MSG rats developed increased adrenocortical function, hyperadiposity, hyperleptinemia, hyperinsulinemia and decreased peripheral insulin sensitivity. These characteristics were fully reversed after transient correction of corticoadrenal hyperactivity induced by AE. In addition, in vitro experimentation with isolated RP adipocytes indicated that cells from intact MSG animals displayed decreased sensitivity to insulin and dexamethasone stimulation of leptin secretion. Interestingly, adipocyte dysfunction in MSG rats was fully abrogated after AE-induced transient correction of insulinemia, leptinemia and adrenocortical activity. Importantly, the reversion of these metabolic abnormalities, induced by AE for 21 days, in MSG animals did occur, despite no significant changes in BW values.

CONCLUSION

Our results support that the changes in adipocyte characteristics and peripheral insulin resistance, developed in this pseudo-obese female rat model, are mainly due to increased glucocorticoid production. Importantly, appropriate correction of the enhanced adrenocortical activity fully reversed these abnormal functions.

Relationship between pituitary and adipose tissue after hypothalamic denervation in the female rat. A morphometric immunohistochemical study

Neonatal administration of monosodium glutamate (MSG) to rats produces severe lesions in certain hypothalamic nuclei, with repercussions in different neuroendocrine axes, and serves as a model for their study. In addition, adipose tissue, as a target organ, is known to be directly related to several neurondocrine axes. We used 21-day-old female Sprague-Dawley rats that had received a neonatal treatment with MSG (4 mg/g body weight, i.p., from day 2 up to day 10 of age) in addition to control rats (injected with 10% NaCl solution, on a similar schedule). We performed a specific immunohistochemical study on each anterior-pituitary cell population, along with the morphometry of these cells and of the parietal and visceral adipose tissue, and measured the levels of serum leptin and triglycerides. The MSG animals evinced significant changes in volume density (VD), cell density (CD), and cell size (CS) in the corticotropes, thyrotropes, and LH gonadotropes, but not in the somatotropes, lactotropes, and FSH gonadotropes. The modification common to the three cell types was a hyperplasia, but with different results depending on cell size. Furthermore, in the MSG rats significant changes were also observed in the VD, CD, and CS of the adipose tissue, consisting of adipogenesis and decrease of adipocyte size in visceral fat, together with probable lipogenesis as judged by an increase in adipocyte size in the parietal fat. The serum levels of leptin and triglycerides appeared significantly higher in MSG animals. For the first time in this animal model, and at the level of three neuroendocrine axes, our results suggest changes that correlate hypothalamic damage, cellular pituitary alterations, and the response of the adipose tissue as a target organ for MSG insult.

Behavioral deficits in adult rats treated neonatally with glutamate

The present study evaluated long-term behavioral consequences of neonatal monosodium-l-glutamate (MSG) treatment in rats. The pups received MSG (3 mg/g sc) daily from postnatal day (PD) 5-12. Data from an automatic activity monitor showed that locomotion of MSG-treated females and males aged 56 and 84 days was significantly reduced. Beginning PD 120, three behavioral tests were performed. As compared to the controls, in the elevated plus maze test, modified to evaluate the adaptive form of spatial memory, MSG-treated animals of both sex had significantly prolonged start and transfer latencies. In the social recognition test, assessing olfactory working memory, MSG-treated males displayed a reduced interest in the juvenile conspecific as the stimulus partner during both the initial exposure and re-exposure performed 30 min later. In the open field test, a significant decrease in the habituation rate was found in MSG-treated animals. Sex-dependent differences in behavioral performance were suggested in the open field and elevated plus maze tests. Behavioral changes are discussed in light of the deficits in perception and processing of visual and olfactory stimuli.

Orexin a stimulates hypothalamic-pituitary-adrenal (HPA) axis function, but not food intake, in the absence of full hypothalamic NPY-ergic activity

Neonatal monosodium L-glutamate (MSG) treatment destroys hypothalamic arcuate nucleus neuronal bodies, thus inducing several metabolic abnormalities. As a result, rats develop a phenotype characterized by hyperleptinemia and by impaired NPY but normal preproorexin hypothalamic mRNAs expression. Thus, our study was designed to explore whether hypothalamic effects of orexin A on food intake and glucocorticoid production develop in the absence of full hypothalamic NPY-ergic activity. For this purpose we evaluated, in control and MSG-treated rats, the consequences of intracerebroventricular (icv) orexin A administration on food intake and changes in circulating levels of ACTH and glucocorticoid. Our results indicate that orexin A icv treatment stimulated hypothalamic-pituitary-adrenal (HPA) axis activity in both MSG-damaged and normal animals, with this response even more pronounced in neurotoxin-damaged rats. Conversely, food intake was only enhanced by icv orexin A injection in normal rats. Our study further supports that acute hypothalamic effects of orexin A on food intake and glucocorticoid production are due to independent neuronal systems. While intact arcuate nucleus activity is needed for the orexinergic effect induced by icv orexin A administration, conversely, orexin A-stimulated HPA axis function takes place even in the absence of full NPY-ergic activity.

Turnover of acinar and islet cells in the pancreas of monosodium glutamate-treated obese mice

OBJECTIVE

Subcutaneous administrations of monosodium glutamate (MSG) to neonatal animals result in obesity and induce the toxicity on the central nervous system, and furthermore, have an effect on entero-pancreatic hormone. The effect of MSG on the cell turnover of organs, especially the pancreas, has received little attention until now. This study was designed to examine the effect of MSG on pancreatic cell turnover by immunohistochemistry and [(3)H]thymidine autoradiography.

RESEARCH METHODS AND PROCEDURES

Male JcI-ICR strain mice were SC injected with MSG (2 mg/g body weight daily) for 5 days after birth, received 112 repeated injections of [(3)H]thymidine at 6-hour intervals for 28 days after birth, and then were killed immediately thereafter, or 30, 60, or 120 days after the last injection. Autoradiography was performed on sections immunostained for glucagon, insulin, and somatostatin.

RESULTS

After continuous labeling, most pancreatic cells were labeled, and thereafter, labeling of cells decreased in control and MSG-treated mice. The mean grain counts of acinar cells in MSG-treated mice decreased more slowly than those in control mice. On the other hand, those of islet cells, including glucagon, insulin, and somatostatin cells, decreased more rapidly in MSG-treated mice than those in control mice.

DISCUSSION

Cell turnover of acinar cells was decelerated and that of islet cells including glucagon, insulin, and somatostatin cells was accelerated in MSG-treated mice pancreas. MSG-induced hypothalamic lesions exert the contrary influences on the cell turnover of acinar and islet cells.

Glutamate and aspartate impair memory retention and damage hypothalamic neurons in adult mice

We examined the effects of systemic administration of monosodium glutamate (MSG) or aspartate (ASP) on the memory retention and neuronal damage in the brains of adult mice. Compared with the control mice, a single intraperitoneal injection of either 4.0 mg/g MSG or 0.5 mg/g ASP after acquisition trial significantly shortened the response latency in the passive avoidance test, accompanying by the transient weight loss. Histopathological analysis of the brains of these mice revealed that neurons in the arcuate nucleus of hypothalamus were damaged markedly by MSG (4.0 mg/g) or ASP (0.5 mg/g). Other brain areas including cerebral cortex and hippocampus did not show any pathological changes. These findings suggest that systemic administration of MSG or ASP could impair memory retention and damage hypothalamic neurons in adult mice.

Neural transplants. effects On startle responses in neonatally MSG-treated rats

Neonatal monosodium glutamate (MSG) treatment has been associated with dysfunctions in stress responses. Therefore, the present study aimed at examining the acoustic startle response (ASR) in MSG-treated rats and the effects of fetal neural transplantation. Male and female rats were given MSG (4 mg/g) or saline on alternate days from days 2-10 after birth. To determine whether fetal transplants could reverse behavioral impairments observed in MSG-treated rats, at 12 days of age MSG-treated rats received either arcuate nucleus (AN), cortical fetal grafts, or sham surgery into the third ventricle. ASR amplitude was measured at 35-40 days of age, and again in adulthood. MSG produced the expected decrease in the density of hypothalamic neuropeptide Y (NPY) and tyrosine hydroxylase (TH) in the AN area. Corticotropin-releasing factor (CRF) neurons/fibers were not affected by MSG. Pituitary atrophy was observed in all MSG rats. We report a permanent increase in the amplitude and reduction in short-term habituation of ASR in all MSG-treated rats. No effect was observed on long-term habituation in male rats. Cortical, but not AN tissue significantly reduced the magnitude of ASR in MSG animals. The results are discussed in terms of the central pathways mediating ASR, in particular hypothalamo-amygdala connections. It is considered that nonspecific factors mediate recovery produced by cortical tissue grafts, as observed in other models of neural transplantation.

Monosodium glutamate lesions inhibit the N-methyl-D-aspartate-induced growth hormone but not prolactin release in rats

Large doses of glutamate administered to newborn rats damage permanently the neurones in the hypothalamic arcuate nucleus containing the growth hormone releasing hormone and the prolactin inhibiting dopamine neuron cell bodies. Since adult animals that underwent neonatal glutamate treatment still have a relatively well functioning growth hormone and prolactin system, we tested whether in the adults the excitatory amino acid sensibility is changed. After i.v. injection of different doses (10 or 30 mg/kg) of N-methyl-D-aspartate (excitatory amino acid receptor subtype agonist) growth hormone levels were significantly increased in the control groups but there was no rise in neonatally glutamate treated male and female rats. The level of prolactin was increased by N-methyl-D-aspartate, too, but the glutamate treatment had no effect on the rise. Our study suggests that systemic administration of N-methyl-D-aspartate increases plasma growth hormone level by activating the growth hormone releasing cells in the arcuate nucleus, but the intact tuberoinfundibular dopaminergic pathway is not essential for its prolactin stimulatory effect.

Quinolinic acid: effect on the nucleus arcuatus of the hypothalamus in the rat (ultrastructural evidence)

Quinolinic acid was administered intraperitoneally to male Wistar rats in a dose of 60 mmol, once daily for 8 days. By electron microscopy, in quinolinic acid-treated rats, the neuronal cell bodies in the arcuate nucleus had features of increased cellular activity, but some damage of neuronal cell bodies was also evident.

Neonatal MSG reduces hypothalamic DA, beta-endorphin, and delays weight gain in genetically obese (A viable yellow/alpha) mice

Neonatal treatment with monosodium glutamate (MSG) decreases proopiomelanocortin (POMC) peptides and results in obesity. The yellow mouse is a model of obesity induced by the viable yellow (Avy) gene at the agouti locus on Chromosome 2, which results in overproduction of a POMC receptor antagonist. Thus we hypothesized that MSG, when imposed on the genetically susceptible model, would alter the development of obesity. Both yellow obese (Avy) and black lean (alpha/alpha) males were injected on Postnatal Days 1, 3, 5, 7, and 9 with 2.0 mg/g body weight MSG or saline SC. Their food intake, growth parameters, and neurochemical status were examined. Paradoxically, MSG interacted with the yellow phenotype to delay the rapid rate of weight gain characteristic of this model (p < 0.05). Food intake was decreased (p < 0.05) in both phenotypes treated with MSG, as was hypothalamic content of dopamine (p < 0.05) and of the POMC peptide, beta-endorphin (p < 0.001). The yellow obese phenotype was more sensitive than the black lean phenotype to the neurochemical effect of early postnatal MSG administration. Recent reports suggest the agouti locus protein is an antagonist of the receptor for another POMC peptide, melanocyte-stimulating hormone (MSH). Therefore, the balance of functional activity between various POMC peptides appears to be an important factor in the development of both acquired and genetic obesity.

Immunohistochemical evidence of neurons with GHRH or LHRH in the arcuate nucleus of male mice and their possible role in the postnatal development of adenohypophysial cells

BACKGROUND

The neonatal administration of monosodium L-glutamate (MSG) has been used in investigations of the possible role of the arcuate nucleus in neuroendocrine regulation during postnatal development. We used this method to examine whether the mouse arcuate contained cell bodies immunoreactive with antisera to growth hormone releasing hormone (GHRH) or luteinizing hormone releasing hormone (LHRH), and whether these hypothalamic peptides affect synthesis and secretion of growth hormone and gonadotropin and the testis.

METHODS

The hypothalamus, pituitary, and testes of adult male mice treated with MSG during the neonatal period were fixed in Bouin's fluid or 10% neutral formalin. The hypothalamus was used in immune staining, the pituitary was used in both morphometry and immune staining, and the testis was stained with hematoxylin and eosin.

RESULTS

Body weights in control and treated mice were not different. The treated mice had more subcutaneous adipose tissue and a shorter body than the control mice. The testes were heavier in the controls. Many perikarya immunoreactive with antisera to GHRH or LHRH were found in the arcuate nucleus in control mice, but few such perikarya were found in this nucleus in treated mice. The size of the anterior lobe and the number and size of GH cells, follicle stimulating hormone (FSH) cells, and prolactin (PRL) cells in treated mice were less than those of control mice.

CONCLUSIONS

GHRH and LHRH neurons in the arcuate nucleus in male mice may cause body and testis weight to increase via GH and LH cells, respectively, in the adenohypophysis during postnatal development. There are some differences in the hypothalamo-pituitary-testis axis of mice and rats.

Body fat and RNA content of the VMH cells in rats neonatally treated with monosodium glutamate

The RNA content of the ventromedial hypothalamus (VMH), the lateral hypothalamic area (LHA), and the cortical neurons of male and female rats, neonatally treated with monosodium glutamate (MSG), were investigated. MSG (2 g/kg b.wt.) was injected subcutaneously to male and female rat pups daily for 5 days after birth. At 12 weeks of age a significant decrease of RNA content in the VMH cells and significantly increased body fat in neonatally MSG-treated animals were found. Correlation of these data showed a significant negative correlation between the body fat content and the RNA content in VMH neurons. The results a) confirm a closed relationship between the body fat content and the functional activity of VMH, b) indicate that obesity of neonatally MSG-treated animals should be due to decreased functional activity of the VMH cells.

A report of the proceedings of an MSG workshop held August 1991

This report of the proceedings of a workshop on monosodium glutamate (MSG) represents the output of an exchange of scientific information, discussed and debated, by a group of experts representing a variety of disciplines. Experts in the areas of food science, potential adverse reactions to foods, pharmacology, neuroscience, biochemistry, nutrition, pediatrics, and anatomy reviewed the current scientific literature relative to the safe use of MSG in foods. These proceedings supplement the extensive literature compiled by various prestigious international expert committees since the flavor-enhancing properties of MSG were identified around the turn of the century,

Central effects of monosodium glutamate on feeding behavior in adult Long-Evans rats

Monosodium glutamate (MSG) is known as a neurotoxic molecule when injected neonatally in rats, where it produces a marked decrease in food intake and an increase in adipose tissue mass. But, in adult rats subcutaneous injections of MSG produce a small, dose-dependent increase in food intake. It is not known if this action is centrally or systemically mediated. Therefore, the feeding pattern of adult rats injected intracerebroventricularly with MSG was measured. Seven days after installation of a cannula in the right lateral ventricle, rats were injected either with artificial cerebrospinal fluid or twice with 3 mg/brain MSG within a 3-day interval. The feeding pattern was recorded via a complete computerized system during 24 h. Feeding behavior was significantly modified by MSG treatments. These effects were observed immediately after drug injections, that is, upon the first meal, as well as during the 24 h that followed. For the first meal, modifications in meal size (+285%; p = 0.0001), meal duration (x10; p = 0.0005), postmeal interval (x4; p = 0.0005), and the satiety ratio (-50%; p = 0.01) were observed. During the 24-h postinjection period, modifications in meal number (-3; p = 0.0007), total amount of food eaten (+21%,; p = 0.007), time spent eating (+40%; p = 0.007), meal duration (+53%; p = 0.005), and meal size (+44%; p = 0.01) were noted. When the two MSG injections were compared, differences were also noted. For the first meal, postmeal interval (-50%; p < 0.005) and satiety ratio (-50%; p < 0.005) were decreased after the second injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of neonatal administration of monosodium glutamate and castration on neurokinin A levels in the hypothalamus and anterior pituitary of rats

The effects of neonatal administration of monosodium glutamate (MSG) and castration on hypothalamic and anterior pituitary levels of neurokinin A (NKA) were studied in male and female rats killed at 46 days of age. In male rats treated neonatally with MSG, body, anterior pituitary, testis, ventral prostate, and seminal vesicle weights and serum testosterone levels were significantly lower than in saline-injected controls. Hypothalamic NKA was significantly lower in MSG-treated male rats as compared with the controls, and no apparent changes were recorded in anterior pituitary NKA. Orchidectomy was followed by a significant decrease in hypothalamic NKA in saline controls, but not in MSG-treated rats. In female rats treated with MSG, there was a significant decrease in body, anterior pituitary, and ovarian weights, as compared with saline-injected controls, but no significant differences were observed in uterine weights and serum estradiol levels. Hypothalamic NKA was lower, although not significantly, in MSG-treated rats as compared with the respective controls, and no differences were recorded in anterior pituitary NKA levels. Ovariectomy was followed by a significant decrease in hypothalamic NKA in both MSG-treated and control rats, but NKA in the anterior pituitary was significantly increased after ovariectomy only in saline-treated controls, whereas MSG-treated females failed to show this response. It is concluded that neonatal MSG treatment resulted in a decrease of hypothalamic NKA, which was particularly pronounced in male rats without any significant change in anterior pituitary NKA levels. The response of hypothalamic NKA to castration and the response of anterior pituitary NKA to ovariectomy were also altered in MSG-treated rats; this may reflect a functional block of some neuroendocrine functions of the hypothalamus that resulted from the neuronal lesions induced by MSG.

Differential effects of neonatally administered glutamate on the ultradian pattern of circulating growth hormone regulating expression of sex-dependent forms of cytochrome P450

Neonatal male rats were treated with monosodium glutamate (MSG) at either 0.5, 1.0, 2.0, 3.0 or 4.0 mg/g body weight on alternate days during the first 9 days of life. As adults, rats were catheterized to obtain unstressed, serial blood samples for the determination of ultradian patterns of circulating growth hormone. In addition, the levels of drug-metabolizing enzymes (i.e. hexobarbital hydroxylase, cytochromes P450 and b5, NADPH-cytochrome P450 reductase and ethoxyresorufin O-deethylase) as well as sex-dependent forms of cytochrome P450 [i.e. male-dependent cytochromes P450 2c (IIC11), 2a (IIIA2) and RLM2 (IIA2) and female-dependent cytochromes P450 2d (IIC12) and 3 (IIA1)] and/or their catalytic activities were measured in the hepatic microsomes of the treated rats. The results demonstrated a dose-dependent, graded response to MSG treatment. As the dose of MSG increased from 0.5 to 4.0 mg, there was a concurrent decline in the amplitudes of the characteristically masculine, episodic bursts of growth hormone, until at the highest dose (4 mg), the pulses were no longer detectable. Associated with this dose-dependent alteration in the ultradian pattern of growth hormone secretion was a measurable change in the activities of the sex-dependent hepatic enzymes. As the pulse heights of the hormone declined to 10-20% of their normal amplitudes, the levels of the male-dependent enzymes (i.e. the drug-metabolizing enzymes, as well as the male forms of cytochrome P450 and their specific steroid hydroxylases) were maintained, and in some cases, exceeded the levels normally found in males. However, as the hormone pulse heights declined, there appeared an accompanying increase in the activities of some of the female-dependent enzymes. Finally, with the loss of all detectable levels of circulating growth hormone, the normal masculine profile of hepatic enzymes was reversed to an apparently normal (with the exception of cytochrome P450 2d) feminine profile. Summarizing, the results indicate that (1) neonatal administration of MSG can produce dose-dependent, graded, long-term developmental defects in the ultradian rhythm of circulating growth hormone and associated sex-dependent hepatic enzymes, and (2) while the male-dependent hepatic enzymes can be maintained at normal or even higher levels in the face of an up to 90% reduction in the pulse heights of plasma growth hormone, the activities of the female-dependent enzymes may begin to increase.

Sex- and dose-dependent effects of neonatally administered aspartate on the ultradian patterns of circulating growth hormone regulating hexobarbital metabolism and action

Rats, neonatally treated with monosodium aspartate (MSA), exhibited developmental defects through adulthood that were characterized by stunted growth, obesity, and reduced size of the liver, kidney, adrenals, and pituitary. Adult male and female rats treated with 4 mg of MSA had no detectable plasma growth hormone as determined from serial blood samples taken every 15 min for 8 consecutive hr. Associated with this loss of circulating growth hormone in the males was a dramatic decline in in vivo and in vitro hexobarbital metabolism and hepatic cytochrome P450 to female levels. The loss of plasma growth hormone in the females had no effect on the already low levels of hepatic monooxygenases. At 2 mg/g body weight, MSA produced both sex- and dose-dependent effects that were far more subtle than the full-blown obesity and growth retardation associated with the larger 4-mg dose. While the mean concentration of circulating growth hormone was reduced 70 to 90% in 2-mg-MSA-treated rats, the sexually dimorphic, ultradian patterns of growth hormone secretion were undisturbed. Affected males continued to secrete a pulse of growth hormone every 3 hr, albeit at greatly reduced amplitudes, interposed by normally undetectable baselines. Similarly, 2-mg-MSA-treated females had greatly reduced mean levels of plasma growth hormone, but with the usual secretion of multiple pulses never dropping to baseline. Surprisingly, the sex-dependent, hepatic monooxygenases, which are normally regulated by the ultradian secretions of growth hormone, were unaffected by the 2-mg MSA treatment. Our results suggest that while an ultradian pulse of circulating growth hormone is necessary for the characteristically male profile of hepatic monooxygenases, neither the amplitude of the secretory peaks nor their total growth hormone content is critical.

Are neurons of the arcuate nucleus necessary for pathfinding by GnRH fibers arising from third ventricular grafts?

The hypogonadal (hpg) mouse lacks GnRH due to a severe truncation of the gene by which it is encoded. This results in an infertile animal with an infantile reproductive system. When fetal or 1-day postnatal septal/preoptic area of a normal mouse is grafted into the third ventricle of an hpg mouse, GnRH-containing fibers grow out of the grafts and innervate the host median eminence (ME), a normal target of these fibers. GnRH axons exiting the graft course follow a very stereotyped pathway through host tissue. They are observed passing through the ependymal wall of the ventricle directly into the ME or arching through the host arcuate nucleus to terminate in the host ME. Given the fixed pattern of outgrowth, we wanted to determine if the neurons of the arcuate nucleus, which lie between the graft and its target, are exerting an influence on the growth and direction of these fibers. The excitotoxin monosodium glutamate (MSG) has been shown to destroy the vast majority of arcuate neurons when administered neonatally. Mutant host animals treated with MSG received fetal grafts of normal septal/preoptic area. Brains were examined for GnRH fiber outgrowth 30 days later to assess early outgrowth which preferentially uses the arcuate route. We report here that the pattern of outgrowth is virtually identical to that observed in saline-injected, grafted animals. There is also no difference in the success rate of grafts placed in control vs MSG-treated hosts nor in the stimulation of testicular growth. The results of this experiment imply that axonal outgrowth to the ME does not rely on arcuate neurons for guidance information or trophic substances. These functions may be subserved by glia, tanycytes/ependyma, or the target.

Glutamate in the mammalian CNS

The excitatory amino acid glutamate plays an important role in the mammalian CNS. Studies conducted from 1940 to 1950 suggested that oral administration of glutamate could have a beneficial effect on normal and retardate intelligence. The neurotoxic nature of glutamate resulting in excitotoxic lesions (neuronal death) is thought possibly to underlie several neurological diseases including Huntington's disease, status epilepticus. Alzheimer's dementia and olivopontocerebellar atrophy. This neurodegenerative effect of glutamate also appears to regulate the formation, modulation and degeneration of brain cytoarchitecture during normal development and adult plasticity, by altering neuronal outgrowth and synaptogenesis. In addition to its function as a neurotransmitter in several regions of the CNS, glutamate seems to be specifically implicated in the memory process. Long-term potentiation (LTP) and long-term depression (LTD), two forms of synaptic plasticity associated with learning and memory, both involve glutamate receptors. Studies with antagonists of glutamate receptors reveal a highly selective dependency of LTP and LTD on the N-methyl-D-aspartate and quisqualate receptors respectively. The therapeutic value of glutamate receptor antagonists is being actively investigated. The most promising results have been obtained in epilepsy and to some extent in ischaemia and stroke. The major drawback remains the inability of antagonists to permeate the blood-brain barrier when administered systemically. Efforts should be directed towards finding antagonists that are lipid soluble and able to cross the blood-brain barrier and to find precursors that would yield the antagonist intracerebrally.

A pharmacological analysis of food intake regulation in rats treated neonatally with monosodium L-glutamate (MSG)

Studies were conducted to examine deficits in food intake regulation in MSG-treated rats that result from known or suspected damage to neurotransmitter systems involved in feeding. Male rats were injected with either MSG (4 mg/g) or sodium chloride on postnatal days 2 and 4 (MSG-Lo) or postnatal days 2, 4, 6 and 8 (MSG-Hi). As adults, MSG-treated and control rats (n = 12/group) were examined for deficits in pharmacologically elicited feeding and other measures of food intake regulation. A second group of MSG-treated (n = 9/group) and control rats (n = 12) were used to measure basal blood pressure and nociceptive reactivity in adulthood. Organ weights, body weight and neuropeptide Y (NPY) content in brain regions were determined at the end of the study. MSG-Hi rats consumed significantly less food than controls during the dark part of the light cycle. Both MSG-Hi and MSG-Lo groups ate significantly less food than controls after a 48-hour fast. MSG-Hi and MSG-Lo rats consumed significantly less food than controls in response to 1.0 mg/kg morphine. MSG-Hi rats consumed significantly less food than controls during the dark phase and significantly more food than controls during the light phase in response to naloxone (1.0 mg/kg). MSG-Lo ate significantly more than controls in response to 0.1 mg/kg guanfacine. MSG-Hi and MSG-Lo showed a significant attenuation in diazepam-stimulated feeding when compared to controls. Blood pressure was significantly lower in both MSG-Hi and MSG-Lo rats compared to controls. Tail flick latencies were not altered by MSG-treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotoxin effects on oxytocin, vasopressin and somatostatin in discrete rat brain areas

Monosodium-L-Glutamate (MSG) produces lesions to monoaminergic and peptidergic neurons in several brain areas. The present study examined the effect of neonatal MSG treatment on oxytocin (OXY), arginine-vasopressin (AVP) and somatostatin (SRIF) concentrations in several discrete brain areas of adult rats. OXY increased in the suprachiasmatic and arcuate nuclei and median eminence (ME) and decreased in the paraventricular nucleus of MSG-treated rats. MSG treatment caused AVP to increase in the arcuate nucleus and ME and decrease in the supraoptic nucleus. SRIF decreased following neonatal MSG treatment in both the ME and neurointermediate pituitary lobe. The results demonstrate that the effects of neonatal MSG treatment on neuropeptide content are not just limited to the arcuate nucleus. Furthermore, taken together with previous results, the data suggest that these changes may be indicative of functional deficits in the neuronal activity of some of these peptidergic neurons which, in turn, may be responsible for the abnormal secretion of several pituitary hormones observed in MSG-treated animals.

The effect of arcuate nucleus transplantation on the development of the anterior pituitary in monosodium glutamate-treated rats

Treatment with monosodium glutamate (MSG) during the neonatal period is known to produce a selective lesion of the arcuate nucleus in rat brain, which is the major site of production of growth hormone releasing-hormone (GRH), followed by a secondary reduction in growth hormone (GH) synthesis in the anterior pituitary. Normal arcuate nuclei from hypothalamic areas of newborn rats were transplanted into the third ventricles of 27-day-old rats which were treated with MSG on alternate days for the first 10 days of life. Ninety days after birth, the anterior pituitaries were examined for GH synthesis by immunohistochemical staining with GH antiserum. The results indicated that the impaired GH synthesis in the anterior pituitary treated with MSG was partially restored in some recipients by grafts of arcuate nuclei in which the GRH-containing neurons were clearly detected by immunohistochemical staining with GRH antiserum.

Follicle-stimulating hormone secretion in monosodium glutamate-lesioned rats: response to unilateral gonadectomy or porcine follicular fluid (inhibin)

The purpose of this study is to determine the acute response of pituitary FSH and LH release to unilateral gonadectomy in the MSG-treated rat, and to determine whether pFF (inhibin) can act effectively on pituitary FSH secretion in the MSG-lesioned rat. MSG (4 mg/kg B.W.) or saline was injected subcutaneously on postnatal days 2, 4, 6, 8, and 10 to male and female littermates which were used in the experiments after postnatal day 60. In the first experiment male and female littermates were bilaterally gonadectomized and bled serially for the next 72 h. At 0 h plasma FSH concentrations in MSG-treated rats were lower (p less than 0.05) than those in saline-treated controls, and for the 72 h immediately following bilateral gonadectomy FSH levels increased parallel to those of the controls, but after a significant delay. In the second experiment, MSG-treated male and female littermates were injected with 0.5 ml of pFF at several intervals following bilateral gonadectomy and decapitated 6 hours later. Injection of pFF significantly suppressed circulating FSH titers in all groups without affecting LH levels. In a third experiment, rats were unilaterally gonadectomized and blood samples were obtained at various intervals for 48 h. Following unilateral gonadectomy there was a significant transient increase in FSH levels in male or female MSG-treated rats as compared to their 0 h values; however, the absolute levels attained were barely equal to the basal concentrations observed in the saline-treated control rats. The conclusions from these data are: insufficient FSH secretion in response to unilateral gonadectomy may be responsible for the lack of compensatory gonadal hypertrophy in MSG-lesioned rats, pituitary response to inhibin is apparently unaltered by MSG toxicity, and the MSG-lesioned rat is a useful model to study the differential control mechanisms of FSH and LH secretion.

Effects of neonatal administration of monosodium glutamate on plasma growth hormone (GH) response to GH-releasing factor in adult male and female rats

Female and male rats were treated with monosodium glutamate (MSG; 4 mg/g b. wt.) as neonates and the capability of the pituitary gland to secrete growth hormone (GH) in response to an intravenous injection of human GH-releasing factor (GRF) was evaluated under pentobarbital anesthesia on 109 days of life. Immunoreactive GRF content in the pituitary stalk-median eminence tissue in MSG-treated rats was less than 20% of that of control. A significant dose-dependent plasma GH response was observed after the administration of two doses of human GRF (0.25 and 1 microgram/kg b. wt., i.v.) in both control and MSG-treated rats. The responses between MSG-treated and control rats were comparable in female rats, but they were significantly reduced in male MSG-treated rats. These results show that the pituitary's responsiveness to exogenous GRF is well preserved in MSG-treated rats despite prolonged and severe depletion of endogenous GRF and there exists a sex difference in the effect of MSG on GH secretion elicited by GRF.

Effects of monosodium L-glutamate administration on neuropeptide Y-containing neurons in the rat hypothalamus

Immunocytochemical localization of neuropeptide Y (NPY) was performed in the hypothalamus of rats of which the arcuate nucleus had been destroyed with monosodium L-glutamate in the neonatal period. The treatment produced a disappearance of most of the NPY cell bodies normally found in the arcuate nucleus. The concentration of fibers was decreased in the paraventricular nucleus, but not in the other hypothalamic nuclei. The treatment also induced the appearance of a large number of immunoreactive cell bodies in the paraventricular nucleus. These results strongly suggest that arcuate NPY neurons are projecting to the paraventricular nucleus and that the arcuate nucleus probably exerts some inhibitory tonic influence on NPY paraventricular neurons.

Suppression of normal and preneoplastic mammary growth and uterine adenomyosis with reduced growth hormone level in SHN mice given monosodium glutamate neonatally

As a step in the evaluation of the role of growth hormone (GH) in mammary tumorigenesis, the effects of neonatal treatment with monosodium glutamate (MSG) on normal and neoplastic mammary growth, plasma levels of GH and prolactin (PRL) and the pattern of estrous cycles were determined in SHN virgin mice. The development of uterine adenomyosis, which is under similar hormonal control, was also examined in these mice. The formation of precancerous mammary hyperplastic alveolar nodules (HAN) was markedly inhibited and the number of 'ghosts', the remnants of regressed HAN, was increased by the single injection of 4 mg MSG on the day of birth, although spontaneous mammary tumorigenesis was not inhibited. The incidence of adenomyosis was suppressed by MSG treatment. Plasma GH level was chronically lower in the MSG-treated mice than in the controls. In contrast, plasma PRL levels and the pattern of estrous cycles were little affected by the treatment. These results indicate an involvement of GH in the development of HAN and uterine adenomyosis in mice.

Effect of hypothalamic ventromedial lesions on plasma growth hormone response to growth hormone-releasing factor in rats

The effect of ventromedial-arcuate (VMH-ARC) nuclei lesions on plasma growth hormone (GH) response to human growth hormone-releasing factor (GRF, 1 microgram/kg b.wt., i.v.) was studied in conscious rats after they had received chlorpromazine (CPZ) or CPZ plus antiserum against somatostatin (ASS). When rats were pretreated with CPZ alone, there was no difference in basal plasma GH level between VMH-ARC lesioned rats and controls. The magnitude of plasma GH response to GRF in 5 out of 6 VMH-ARC lesioned rats exceeded that of controls. When the same observation was repeated using the same rats after they had received ASS and CPZ, basal plasma GH levels of controls were significantly higher than those of VMH-ARC lesioned rats, and the magnitude of the plasma GH response to GRF was augmented in both groups of rats. The plasma GH response to GRF was comparable between two groups, though the peak plasma GH response to GRF was slightly but significantly lower in VMH-ARC lesioned rats as compared to controls. Pituitary GH content was reduced significantly in VMH-ARC lesioned rats as compared to controls. The results demonstrate that the pituitary responsiveness to GRF does not appear to be altered significantly in rats bearing bilateral VMH-ARC lesions. In addition, the placement of electrolytic lesions in VMH-ARC regions causes reduced SS secretion into the hypophyseal portal vessels and leads to an augmentation of plasma GH response to GRF.

Alterations in insulin and glucagon secretion by monosodium glutamate lesions of the hypothalamic arcuate nucleus

This study was performed to determine the effects of monosodium glutamate (MSG) induced lesions of the hypothalamic arcuate nucleus (ARC) on glucose tolerance and insulin and glucagon secretion in male golden hamsters. Eight day old hamsters were given a single s.c. injection of 5.8 mg/g BW MSG or hypertonic saline (controls). Studies were initiated when the hamsters were 3 months of age. At this age there were no body weight differences. Glucose (180 mg/100 g BW) was administered via stomach tube to 18 control and 18 MSG-treated hamsters. Animals were anesthetized with ether and a single blood sample from the portal vein was taken either before or at 30 or 60 min after glucose administration (n = 6/group). Glucose concentrations were similar in both groups at all time periods. Insulin concentrations in the MSG group were significantly (P less than 0.05) elevated in MSG-treated hamsters compared to controls at the 60 min time point. Glucose suppressed glucagon (P less than 0.05) in control but not in MSG-treated hamsters. The MSG group had significantly more glucagon (P less than 0.05) in portal vein blood at 30 min after glucose administration than did the control hamsters. Molar insulin/glucagon ratios did not differ between the 2 groups which likely accounts for the lack of differences in blood glucose levels. These results suggest a role for the ARC in regulating pancreatic function.

The modifying influence of aging on behavior in mice neonatally injected with monosodium glutamate

Newborn mice were injected with monosodium glutamate (MSG), and behavioral testing and physical development in neonatal, juvenile, adult, and aged mice were observed by means of a battery of appropriate tests. Early exposure to MSG resulted in altered behavioral performances postnatally, which were transitory and reflected the neurotoxicity of the chemical. Although behavioral deficits were not observed in mice neonatally treated with MSG at 1 month of age, a definite decline was manifested at 12 months and 34 months of age.

Reduction of pituitary GnRH receptors in immature rats treated with monosodium glutamate

The number of pituitary gonadotropin-releasing hormone (GnRH) receptors increases during sexual maturation in the rat and probably reflects changes in hypothalamic GnRH secretion. As GnRH is synthesized in various hypothalamic nuclei, including the arcuate nucleas (ARC), we investigated the effects of monosodium glutamate (MSG)-induced lesions of the ARC in the rat. In males and females treated with MSG during the first 10 days of life, GnRH receptor content (GnRH-RC) was unchanged from controls at 10 days but was decreased at 20 and 30 days of age (P less than 0.01). Serum concentrations of luteinizing hormone (LH) were similar in MSG-treated and control males but were significantly lower in 10-day-old females (P less than 0.01). Injections of GnRH (3 micrograms every 8 h on days 18 and 19) restored GnRH-RC to control values in MSG-treated rats. Both MSG and untreated control rats showed similar LH responses to acute injections of GnRH, but responses were attenuated (P less than 0.05) after 2 days pretreatment with GnRH in rats that had received MSG. Ovarian GnRH-RC was similar in both MSG-treated and untreated controls. These data indicate that MSG-induced lesions of the ARC reduce pituitary GnRH-RC in immature rats, and the more marked effects in females suggest a more significant role in the ARC in the control of GnRH secretion during maturation in females. The lack of MSG-induced changes in ovarian GnRH-RC indicates that GnRH from the arcuate nucleus is not responsible for the increase in ovarian GnRH receptors seen during sexual maturation.

A decrease in thymus-mediated immune responses as a result of treatment of neonatal rats with glutamate

We investigated whether administration of monosodium 1-glutamate (MSG) to neonatal rats would disrupt immune responses in intact and orchidectomized adult male rats. Neonatal male rats were treated with saline or MSG which causes severe endocrine abnormalities. Half of each group of animals were orchidectomized as adults and killed one week later along with intact rats. MSG treatment resulted in suppressed serum LH levels in intact rats. Thymus weight and spleen cellularity in intact animals were not affected by MSG treatment, but thymus weight increased within one week after orchidectomy in both saline- and MSG-treated groups. In intact rats, lymphocyte stimulation by the T cell specific mitogens (concanavalin A or phytohemagglutinin) or the B cell specific mitogen (lipopolysaccharide) was unaffected by prior treatment with MSG. However, MSG treatment blocked the decrease attributable to orchidectomy in concanavalin A and phytohemagglutinin stimulation of lymphocyte blastogenesis. The results suggest that administration of MSG to neonatal male rats can alter some immune responses in the adult animal.

Normal pancreatic and intestinal enzymes in hypophagic growth-retarded rats that received dorsomedial hypothalamic lesions shortly after weaning

Male weanling Sprague-Dawley rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats). Sham-operated rats served as controls. After being fed lab chow for two postoperative weeks, the animals were divided into four groups. One group of DMNL rats and controls received a high-caloric diet (high-fat diet, chocolate chip cookies, 32% sucrose solution, potato chips and marshmallows), whereas another group of DMNL rats and controls continued to receive lab chow. The experiment was terminated on the 185th postoperative day. In accordance with previous findings, DMNL rats, irrespective of diet, were lighter and shorter than controls. In addition, DMNL rats fed junk food were lighter than DMNL rats fed lab chow, and junk-fed controls weighed as much as chow-fed controls. Both DMNL rats and controls fed junk food were also shorter and showed higher carcass fat than their chow-fed counterparts. Also, DMNL rats fed junk food had less carcass fat than junk-fed sham-operated controls, whereas in accordance with previous findings, there was no difference between chow-fed DMNL rats and chow-fed sham-operated controls. Irrespective of diet, DMNL rats ate less calories than their respective sham-operated controls. Both absolute and percent pancreas weight and protein/pancreas were unaffected in DMNL rats but were reduced in both junk-fed groups in comparison with their chow-fed counterparts. Both concentrations and contents of pancreatic trypsinogen, amylase and lipase were unaffected in DMNL rats but total activities of all three enzymes were dramatically reduced in the junk-fed compared with the chow-fed DMNL rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Steroid-monoamine feedback interactions in discrete brain regions using as a model the monosodium glutamate (MSG)-lesioned rat

The present studies examine the effects of neonatal treatment with monosodium glutamate (MSG) on dopamine (DA), 5-hydroxytryptamine (5-HT) and norepinephrine (NE) metabolism in discrete brain regions and correlate them with steroid receptor kinetics in the anterior pituitary (PIT), preoptic hypothalamus (POA) and caudal hypothalamus (HYP), and with steroid negative and positive feedback effects on luteinizing hormone (LH) secretion. Substantial decreases in the neuronal activity of all three amines in the arcuate nucleus, decreased DA and 5-HT metabolism in the suprachiasmatic nucleus and, surprisingly, increased metabolism of 5-HT and NE in the median eminence was observed in adult ovariectomized (OVX), MSG-treated versus OVX, vehicle-treated litter mate controls. Measurement of estradiol receptors in the nuclear and cytosolic fractions of the POA, HYP and PIT from MSG- and vehicle-treated rats killed during diestrus or 2 weeks after OVX revealed no differences. Similarly, no differences in cytosolic progestin receptors between control and MSG unprimed or estradiol-primed, OVX rats or on progestin receptor translocation induced by progesterone in Eb-primed rats were observed. Negative and positive feedback effects of estradiol or the positive feedback of progesterone on LH secretion were not significantly impaired in MSG rats, and indeed, MSG animals actually were hyper-responsive to the administration of the steroids or of luteinizing hormone-releasing hormone. These results indicate that the MSG-induced damage to DA, 5-HT and NE elements observed within several preoptic and hypothalamic nuclei does not impair estrogen and progestin receptor kinetics, nor does it prevent adequate negative or positive steroid feedback responses, if appropriate steroid regimens are employed, and that the impaired gonadal function reported in these animals does not result primarily from inadequate steroid feedback mechanisms.

Effects of excitotoxic amino acids on pituitary hormone secretion in the rat

The acute effects of administration of 4 excitatory amino acids (n-methyl-DL-aspartic acid (NMA), kainic acid (KA), ibotenic acid (IA) and quinolinic acid (QA] on the serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH) and prolactin (PRL) were studied in the rat. NMA-treated rats exhibited increased serum LH and GH concentrations while KA-treated rats-showed increases only in serum GH concentrations. Neither IA nor QA altered adenohypophyseal hormone levels. These endocrine alterations induced by NMA and KA are different from those previously reported after administration of glutamate, another excitatory amino acid. The finding that all of the excitatory amino acids studied did not produce identical effects on anterior pituitary hormone secretion may be due to differential permeability of these substances into the central nervous system or because they act at different subtypes of excitatory amino acid receptors.