Monosodium glutamate admlinistration to the newborn reduces reproductive ability in female and male mice

Distinct effects of growth hormone deficiency and disruption of hypothalamic kisspeptin system on reproduction of male mice

Growth hormone (GH) deficiency is a common cause of late sexual maturation and fertility issues. To determine whether GH-induced effects on reproduction are associated with alterations in hypothalamic kisspeptin system, we studied the male reproduction in two distinct GH deficiency mouse models. In the first model, mice present GH deficiency secondary to arcuate nucleus of the hypothalamus (ARH) lesions induced by posnatal monosodium glutamate (MSG) injections. MSG-induced ARH lesions led to significant reductions in hypothalamic Ghrh mRNA expression and consequently growth. Hypothalamic Kiss1 mRNA expression and Kiss1-expressing cells in the ARH were disrupted in the MSG-treated mice. In contrast, kisspeptin immunoreactivity remained preserved in the anteroventral periventricular and rostral periventricular nuclei (AVPV/PeN) of MSG-treated mice. Importantly, ARH lesions caused late sexual maturation and infertility in male mice. In our second mouse model, we studied animals profound GH deficiency due to a loss-of-function mutation in the Ghrhr gene (Ghrhr^lit/lit mice). Interestingly, although Ghrhr^lit/lit mice exhibited late puberty onset, hypothalamic Kiss1 mRNA expression and hypothalamic kisspeptin fiber density were normal in Ghrhr^lit/lit mice. Despite presenting dwarfism, the majority of Ghrhr^lit/lit male mice were fertile. These findings suggest that spontaneous GH deficiency during development does not compromise the kisspeptin system. Furthermore, ARH Kiss1-expressing neurons are required for fertility, while AVPV/PeN kisspeptin expression is sufficient to allow maturation of the hypothalamic-pituitary-gonadal axis in male mice.

Gestational Exposure to Synthetic Steroid Hormones Impaired Sperm Quantity and Quality in Wistar Rats

This study was designed to investigate the effect of prenatal exposure to synthetic sex steroid on sperm quantity and quality, relative testicular and epididymal weights, and reproductive hormones level in adult Wistar rats. Forty male Wistar rats were divided into two groups: a test group (n = 20) that included mature rats that were born to dams exposed to gestational treatment with hydroxyprogesterone and a control group (n = 20) that included mature rats born to untreated dams. Compared to the control group, the test group showed a significant reduction in the sperm count, viability and motility, relative testicular and epididymal weights together with increased abnormal spermatozoa (p < 0.001). The reproductive hormonal assay revealed significantly lower serum testosterone and higher levels of FSH and LH among the test groups compared to the control (p < 0.05 for all). Prenatal exposure to synthetic progesterone negatively affected sperm production and function, relative testicular and epididymal weights, and reproductive hormone levels.

Effect of monosodium glutamate on testicular tissue of paclitaxel-treated mice: An experimental study

Background

Paclitaxel (PTX), a chemotherapeutic agent, and monosodium glutamate (MSG) have oxidative effects on testicular tissue.

Objective

In this study, the effects of MSG administration on the exacerbation of testicular tissue alterations related to PTX treatment were evaluated.

Materials and Methods

MSG (30 & 60 mg/kg i.p.) was administrated to six groups (n = 8/each) of adult mice before or after PTX treatment: control, PTX-treated, MSG30 + PTX, MSG60 + PTX, PTX + MSG30, and PTX + MSG60. Following the euthanizing, the body weight measurement, pituitary-testicular axis hormonal analysis and serum lipid peroxidation index assessment was prepared, testicular histomorphometry (tubular diameter and germinal epithelium height), immunohistochemistry of p53 was completed. Microscopic indices of spermatogenesis (tubular differentiation, spermiogenesis and repopulation indices) were studied.

Results

Body weight was not changed significantly. The levels of testosterone (p = 0.0001), follicle stimulating hormone (p = 0.019), and luteinizing hormone (p = 0.08) were decreased while the level of lipid peroxidation index was increased (p = 0.208) in the treated groups. The histomorphometry indices (p < 0.0001 and p = 0.001, respectively), germ cells population (p < 0.05) and microscopic indices of spermatogenesis (p = 0.001, p = 0.005, p < 0.0001, respectively) were significantly reduced in all treated groups. The administration of MSG before PTX treatment induces more changes. The most positive reaction to p53 was observed in MSG30 or 60 + PTX groups compared to other groups.

Conclusion

The administration of MSG could intensify testicular tissue alterations related to PTX chemotherapy.

Reviewing the Effects of L-Leucine Supplementation in the Regulation of Food Intake, Energy Balance, and Glucose Homeostasis

Leucine is a well-known activator of the mammalian target of rapamycin (mTOR). Because mTOR signaling regulates several aspects of metabolism, the potential of leucine as a dietary supplement for treating obesity and diabetes mellitus has been investigated. The objective of the present review was to summarize and discuss the available evidence regarding the mechanisms and the effects of leucine supplementation on the regulation of food intake, energy balance, and glucose homeostasis. Based on the available evidence, we conclude that although central leucine injection decreases food intake, this effect is not well reproduced when leucine is provided as a dietary supplement. Consequently, no robust evidence indicates that oral leucine supplementation significantly affects food intake, although several studies have shown that leucine supplementation may help to decrease body adiposity in specific conditions. However, more studies are necessary to assess the effects of leucine supplementation in already-obese subjects. Finally, although several studies have found that leucine supplementation improves glucose homeostasis, the underlying mechanisms involved in these potential beneficial effects remain unknown and may be partially dependent on weight loss.

Effects of monosodium-L-glutamate administration on serum levels of reproductive hormones and cholesterol, epididymal sperm reserves and testicular histomorphology of male albino rats

This study investigated the effects of administration of monosodium L-glutamate (MSG) on serum gonadotrophin-releasing hormone (GnRH), luteinising hormone (LH), testosterone and total cholesterol (TC), cauda epididymal sperm reserves (CESR) and testicular histomorphology of adult male albino rats. Eighty-four rats, randomly assigned to 7 groups of 12 rats each, were used for the study. Varying low doses (0.25, 0.50 or 1.00 g/kg body weight) of MSG were administered orally or subcutaneously at 48-h intervals for six weeks. Serum GnRH, LH, testosterone and TC, and CESR were evaluated on days 14, 28 and 42 of MSG administration. Testicular histomorphology was evaluated on day 42. The results showed that the mean serum GnRH, LH and testosterone levels, and the CESR of all the treated groups were significantly (P < 0.05) lower than those of the untreated control on days 14, 28 and 42 of MSG administration. The mean serum TC levels of all the treated groups were also significantly (P < 0.05) lower than those of the control group on days 14 and 28. No lesions were observed on sections of the testes. It was concluded that MSG administration for 14, 28 and 42 days led to significantly lower serum levels of GnRH, LH, testosterone and TC, and significantly lower CESR.

Cognitive and biochemical effects of monosodium glutamate and aspartame, administered individually and in combination in male albino mice

The present study was designed to investigate the in vivo effects of monosodium glutamate (MSG) and aspartame (ASM) individually and in combination on the cognitive behavior and biochemical parameters like neurotransmitters and oxidative stress indices in the brain tissue of mice. Forty male Swiss albino mice were randomly divided into four groups of ten each and were exposed to MSG and ASM through drinking water for one month. Group I was the control and was given normal tap water. Groups II and III received MSG (8 mg/kg) and ASM (32 mg/kg) respectively dissolved in tap water. Group IV received MSG and ASM together in the same doses. After the exposure period, the animals were subjected to cognitive behavioral tests in a shuttle box and a water maze. Thereafter, the animals were sacrificed and the neurotransmitters and oxidative stress indices were estimated in their forebrain tissue. Both MSG and ASM individually as well as in combination had significant disruptive effects on the cognitive responses, memory retention and learning capabilities of the mice in the order (MSG+ASM)>ASM>MSG. Furthermore, while MSG and ASM individually were unable to alter the brain neurotransmitters and the oxidative stress indices, their combination dose (MSG+ASM) decreased significantly the levels of neurotransmitters (dopamine and serotonin) and it also caused oxidative stress by increasing the lipid peroxides measured in the form of thiobarbituric acid-reactive substances (TBARS) and decreasing the level of total glutathione (GSH). Further studies are required to evaluate the synergistic effects of MSG and ASM on the neurotransmitters and oxidative stress indices and their involvement in cognitive dysfunctions.

Consumption of monosodium glutamate in relation to incidence of overweight in Chinese adults: China Health and Nutrition Survey (CHNS)

BACKGROUND

It has been hypothesized that monosodium glutamate (MSG), a flavor enhancer, is positively associated with weight gain, which influences energy balance through the disruption of the hypothalamic signaling cascade of leptin action.

OBJECTIVE

The objective was to examine the longitudinal association between MSG consumption and incidence of overweight.

DESIGN

Data were collected from the China Health and Nutrition Survey (CHNS), a prospective open-cohort, ongoing nationwide health and nutrition survey, consisting of 10,095 apparently healthy Chinese adults aged 18-65 y at entry from 1991 to 2006. Diet, including MSG and other condiments, was assessed with a weighed food inventory in combination with three 24-h recalls. Incident overweight was defined as a body mass index (BMI; in kg/m(2)) ≥ 25 or ≥23 based on World Health Organization recommendations for Asian populations. Multilevel mixed-effects models were constructed to estimate change in BMI, and Cox regression models with gamma shared frailty were used to determine the incidence of overweight.

RESULTS

The mean follow-up was 5.5 y. The cumulative mean (±SD) MSG intake of 2.2 ± 1.6 g/d was positively associated with BMI after adjustment for potential confounders and cluster effects at different levels (individual, household, and community). The adjusted hazard ratio of overweight was 1.33 (95% CI: 1.01, 1.75; P for trend < 0.01) for participants in the highest quintile of MSG intake compared with those in the lowest quintile after adjustment for age, physical activity, total energy intake, and other major lifestyle factors.

CONCLUSIONS

MSG consumption was positively, longitudinally associated with overweight development among apparently healthy Chinese adults. Additional studies are needed to elucidate mechanisms of action and to establish causal inference.

Effect of the oral administration of monosodium glutamate during pregnancy and breast-feeding in the offspring of pregnant Wistar rats

PURPOSE

Determine the effects of the MSG (monosodium glutamate) in the offspring of pregnant rats through the comparison of the weight, NAL (nasal-anal length) and IL (Index of Lee) at birth and with 21 days of life.

METHODS

Pregnant Wistar rats and their offspring were divided into 3 groups: GC, G10 and G20. Each of the groups received 0%, 10% and 20% of MSG, respectively from coupling until the end of the weaning period.

RESULTS

Neither weight nor NAL were different among the groups at birth. The group G20 at birth had an IL lower than the group GC (p<0,05) and with 21 days of life presented weight and NAL lower than the groups G10 and this lower than the GC (p<0,01). Otherwise the G20 at 21 days of life had the IL similar to the other two groups. The weight profit percentage from birth to the 21st day of life was lower in the G20 regarding the other two groups (p<0,01). The G20 had a NAL increase percentage from birth to the 21st day of life lower than the G10 and this lower than the GC (p<0,01).

CONCLUSIONS

MSG presented a dose-dependent relation in the variables weight and NAL. It caused a decrease in the growth pattern as well as in the weight gain pattern until the 21st day of life. The IL of the group 20% had an increased in relation to the control group after 3 weeks of follow up.

Association of monosodium glutamate intake with overweight in Chinese adults: the INTERMAP Study

Animal studies indicate that monosodium glutamate (MSG) can induce hypothalamic lesions and leptin resistance, possibly influencing energy balance, leading to overweight. This study examines the association between MSG intake and overweight in humans. We conducted a cross-sectional study involving 752 healthy Chinese (48.7% women), aged 40-59 years, randomly sampled from three rural villages in north and south China. The great majority of participants prepared their foods at home, without use of commercially processed foods. Diet was assessed with four in-depth multipass 24-h recalls. Participants were asked to demonstrate MSG amounts added in food preparation. Amounts shaken out were weighed by trained interviewers. Overweight was defined as BMI > or =25.0 or > or =23.0 kg/m(2)(based on World Health Organization recommendations for Asian populations). Eighty-two percent of participants were MSG users. Average intake was 0.33 g/day (s.d. = 0.40). With adjustment for potential confounders including physical activity and total energy intake, MSG intake was positively related to BMI. Prevalence of overweight was significantly higher in MSG users than nonusers. For users in the highest tertile of MSG intake compared to nonusers, the multivariable-adjusted odds ratios of overweight (BMI > or =23.0 and > or =25.0) were 2.10 (95% confidence interval, 1.13-3.90, P for trend across four MSG categories = 0.03) and 2.75 (95% confidence interval, 1.28-5.95, P = 0.04). This research provides data that MSG intake may be associated with increased risk of overweight independent of physical activity and total energy intake in humans.

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.

Environmental endocrine modulators and human health: an assessment of the biological evidence

Recently, a great deal of attention and interest has been directed toward the hypothesis that exposure, particularly in utero exposure, to certain environmental chemicals might be capable of causing a spectrum of adverse effects as a result of endocrine modulation. In particular, the hypothesis has focused on the idea that certain organochlorine and other compounds acting as weak estrogens have the capability, either alone or in combination, to produce a variety of adverse effects, including breast, testicular and prostate cancer, adverse effects on male reproductive tract, endometriosis, fertility problems, alterations of sexual behavior, learning disability or delay, and adverse effects on immune and thyroid function. While hormones are potent modulators of biochemical and physiological function, the implication that exposure to environmental hormones (e.g., xenoestrogens) has this capability is uncertain. While it is reasonable to hypothesize that exposure to estrogen-like compounds, whatever their source, could adversely affect human health, biological plausibility alone is an insufficient basis for concluding that environmental endocrine modulators have adversely affected humans. Diethylstilbestrol (DES) is a potent, synthetic estrogen administered under a variety of dosing protocols to millions of women in the belief (now known to be mistaken) that it would prevent miscarriage. As a result of this use, substantial in utero exposure to large numbers of male and female offspring occurred. Numerous studies have been conducted on the health consequences of in utero DES exposure among the adult offspring of these women. There are also extensive animal data on the effects of DES and there is a high degree of concordance between effects observed in animals and humans. The extensive human data in DES-exposed cohorts provide a useful basis for assessing the biological plausibility that potential adverse effects might occur following in utero exposure to compounds identified as environmental estrogens. The effects observed in both animals and humans following in utero exposure to sufficient doses of DES are consistent with basic principles of dose response as well as the possibility of maternal dose levels below which potential non-cancer effects may not occur. Significant differences in estrogenic potency between DES and chemicals identified to date as environmental estrogens, as well as an even larger number of naturally occurring dietary phytoestrogens, must be taken into account when inferring potential effects from in utero exposure to any of these substances. The antiestrogenic properties of many of these same exogenous compounds might also diminish net estrogenic effects. Based on the extensive data on DES-exposed cohorts, it appears unlikely that in utero exposure to usual levels of environmental estrogenic substances, from whatever source, would be sufficient to produce many of the effects (i.e., endometriosis, adverse effects on the male reproductive tract, male and female fertility problems, alterations of sexual behavior, learning problems, immune system effects or thyroid effects) hypothesized as potentially resulting from exposure to chemicals identified to date as environmental estrogens.

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.

Glutamate neurotoxicity in the developing rat cochlea is antagonized by kynurenic acid and MK-801

Glutamate (Glu) is neurotoxic in the neonatal rat cochlea, producing hearing impairment which is largely due to the death of spiral ganglion cells, whereas the receptor hair cells are spared. Dendritic processes of the spiral ganglion are postsynaptic to the primary afferent synapse of the auditory system. The experiments reported here were designed to test whether this apparent excitotoxicity can be blocked by Glu antagonists. The broad-spectrum antagonist kynurenic acid (KYNA) was coadministered with Glu initially to determine whether the high-frequency hearing deficit caused by Glu may be mediated by excitatory amino acid receptors. Subsequently, the N-methyl-D-aspartate (NMDA)-specific receptor blocker MK-801 was used to test whether NMDA receptors may be involved in the effect. Both antagonists partially blocked the high-frequency hearing impairment caused by Glu. The blocker-alone control groups exhibited mid-frequency effects of unknown origin. The significant antagonism of Glu-induced impairment is consistent with the hypothesis that Glu or a similar excitatory amino acid is an important afferent transmitter in the cochlea.

Glutamate neurotoxicity in the developing rat cochlea: physiological and morphological approaches

The neurotoxic effects of exogenous glutamate were studied in the rat cochlea. Glutamate-treated rats (4 g/kg/day i.p., postnatal days 2-9) exhibited electrophysiologically-measured elevations in high frequency thresholds usually associated with hair cell loss in the basal region of the cochlea. While surface preparations of the organ of Corti revealed no loss of hair cells, there was a dramatic and selective reduction of neurons in the basal, high frequency-related portion of the spiral ganglion. This sensitivity of developing spiral ganglion cells to the neurotoxicity of glutamate is consistent with the hypothesis that glutamate or a structurally related substance is a neurotransmitter at afferent synapses of cochlear hair cells.

Influence of pinealectomy on sexual behavior of normal and monosodium L-glutamate-treated rats

Subcutaneous injections of monosodium L-glutamate (MSG) were administered, as a neurotoxin, at a dose of 4 mg/g body weight to rat pups on days 1 and 3 postnatally. Pinealectomy was performed at 6 weeks of age, and animals were allowed to mature. The intact MSG-treated rats showed a decrease of lordosis quotient in females and a reduction of ejaculation frequency and an increase in mount frequency in males. Pinealectomy caused no significant improvement on sexual behavior of the saline-treated normal rats, but it caused a marked improvement of the sexual receptivity in MSG-treated female rats and reinstated ejaculation in MSG-treated males. The circulatory sex steroid levels, estrogen in females and androgen in males, were not significantly different between the intact and pinealectomized MSG-treated groups in the respective sexes, whereas the progesterone level in females was significantly elevated in the pinealectomized MSG-treated group compared with the intact MSG-treated group. These findings suggest that the pineal gland plays an inhibitory role on the sexual behavior of MSG-treated rats and the improvement of sexual behavior following pinealectomy may be dependent on certain mechanisms other than the actions of circulatory androgens or estrogens.

Monosodium glutamate neurotoxicity: a sex-specific impairment of blood pressure but not vasopressin in developing rats

Neonatal administration of monosodium glutamate (MSG) results in severe adenohypophyseal endocrine malfunction as a result of hypothalamic neurotoxic lesioning. The present study examined the effects of administration of MSG on the neurohypophyseal vasopressinergic (AVP) system and systolic blood pressure (SBP) in adulthood. Monosodium glutamate or hypertonic sodium chloride was administered to male and female rat pups on days 1, 3, 5, 7 and 9 after birth. MSG treatment produced several features characteristic of the MSG-toxicity syndrome, including obesity, anterior pituitary dysgenesis and hypogonadism. However, MSG did not alter neurohypophyseal AVP profiles: AVP content of the posterior pituitary and microdissected regions of the hypothalamus and brainstem were similar in MSG-treated and control rats. Furthermore, MSG treatment did not alter water intake, serum AVP concentration, or the ability to reduce urine output in response to water deprivation. Thus, despite insult to adenohypophyseal function by neonatal administration of MSG, the neurohypophyseal AVP system remained functionally intact. In contrast, neonatal treatment with MSG altered SBP in a sex dependent manner. Female MSG-treated rats, unlike male MSG-treated rats, exhibited consistent systolic hypotension when compared with the NaCl-treated or non-treated control rats at 6, 9 and 12 weeks of age. Despite this chronic hypotension in MSG-treated female rats, heart rate was not altered and serum AVP was not elevated. These observations suggest a resetting of the baroreflex, attributable to neonatal administration of MSG.

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.

Flavor potentiators

This review provides extensive presentation and evaluation of data relative to flavor potentiation, including the historical, chemical, organoleptic, metabolic, physiological, and consumptive properties of the commonly available flavor potentiators, which are primarily monosodium glutamate and 5'-nucleotides. In addition, their food occurrences, mode of action, manufacturing procedures, and methods of analyses will be discussed. Also, attention will be given to miscellaneous compounds that possess flavor potentiating properties.

Acute effects of N-methyl-DL-aspartate on the release of pituitary gonadotropins and prolactin in the adult female rhesus monkey

The acute effects of an aspartic acid analogue, N-methyl-DL-aspartate (NMA), upon the release of several anterior pituitary hormones were examined in adult female rhesus monkeys. Intravenous injection of NMA (15 mg kg body weight) induced a large and rapid rise in plasma levels of luteinizing hormone, follicle stimulating hormone, and prolactin. Thyroid stimulating hormone concentrations were not altered. Thus, in primates, as in rodents, systemically administered NMA is capable of eliciting pituitary hormone secretion, although the site of its action in the rhesus monkey remains to be established.

The distribution of enkephalin in the mediobasal hypothalamus of the mouse brain: effects of neonatal administration of MSG

The immunocytochemical distribution of the pentapeptides, methionine- and leucine-enkephalin (Enk) were examined in the mediobasal hypothalamus of control mice with a neurotoxic lesion of the arcuate nucleus due to neonatal treatment of monosodium glutamate (MSG). In control mice immunoreactive Enk cells and fibers were present in the arcuate nucleus. Enk fibers were found in the subependymal, internal and external layers of the median eminence. At 60 days of age, mice receiving neonatal injections of MSG displayed symptoms of neuroendocrine deficiencies. Histochemical methods revealed a loss of Enk immunoreactivity from the arcuate nucleus and all layers of the median eminence. These results suggest that the lack of Enk cells and fibers in the mediobasal hypothalamus of MSG-treated animals is partially responsible for the endocrine dysfunctions exhibited by these animals.

Monosodium glutamate: acute and chronic effects on rhythmic growth hormone and prolactin secretion, and somatostatin in the undisturbed male rat

The present in investigation was designed to determine the chronic effects of neonatal monosodium glutamate (MSG) administration (4 g/kg s.c.) and the acute effects of MSG (1 g/kg i.p.) on episodic growth hormone (GH) and prolactin (PRL) secretion and brain somatostatin (SRIF) in unanesthetized, chronically cannulated male rats. Adult rats showed the typical physical characteristics that result from neonatal MSG administration. Analysis of episodic GH secretion showed a significant reduction in : (1) the amplitude of GH secretory peaks. and (2) the mean 5.5-h plasma level of GH. Bursts of plasma PRL were inhibited by MSG, but the mean 5.5-h plasma levels were not affected. SRIF concentrations in the medial basal hypothalamus were reduced by 60% after neonatal MSG. Acute administration of MSG to adult rats caused an immediate, long-lasting suppression of rhythmic GH secretion and a rapid, transient release of PRL. These results suggest: (1) neonatally administered MSG causes a marked disturbance in episodic GH and PRL secretion in adult rats; (2) MSG induces a decrease in hypothalamic SRIF and possibly GH-releasing factor; and (3) the acute effects of MSG on GH and PRL may be due to the inhibition and/or excitation of a complex neuronal network involving monoaminergic and peptidergic systems.

alpha-Melanocyte-stimulating hormone: reduction in adult rat brain after monosodium glutamate treatment of neonates

Intraperitoneal injection of monosodium glutamate in neonatal rates resulted in a 90 percent loss of alpha-melanocyte-stimulating hormone in hypothalamic and extrahypothalamic areas of the brain, whereas the amount of hormone in the pituitary gland did not change. The dramatic reduction of alpha-melanocyte-stimulating hormone in the brain suggests that is primary source there is the neuronal perikarya of the arcuate nucleus.

Somatic, behavioral, and reproductive disturbances in mice following neonatal administration of sodium L-aspartate

Sodium L-aspartate (ASP) was administered to neonatal mice according to an increasing dose schedule from Days 2--11 after birth. Adult ASP-treated animals showed large increases in body weight over controls along with stunted body length. The ASP group also showed decreases in locomotor and exploratory behavior. Reproductive dysfunction occurred in both female and male ASP-treated animals. Among treated animals, females had fewer pregnancies and smaller litters while males showed reduced fertility. Evidence of multiple endocrine dysfunction in ASP-treated animals was reflected by decreased pituitary, thyroid, ovaries and tested weights, along with delayed onset of puberty in females. These results demonstrate that sodium L-aspartate produces a syndrome similar to that seen following the administration of monosodium L-glutamate.

The effect of parenteral glutamate treatment on the localization of neurotransmitters in the mediobasal hypothalamus

The localization of cholinergic, aminergic and amino acid-ergic neurones in the mediobasal hypothalamus has been studied in normal rat brain and in brains where neurones in nucleus arcuatus were destroyed by repeated administration of 2 mg/g body weight monosodium glutamate to newborn animals. In normal animals acetylcholinesterase staining, choline acetyltransferase and aromatic L-amino acid decarboxylase were concentrated in the median eminence and the arcuate nucleus. Glutamate decarboxylase was concentrated at the boundary between the ventromedial and the arcuate nuclei, with lower activity in the arcuate nucleus and very low activity in the median eminence. Nucleus arcuatus contained an intermediate level of high affinity glutamate uptake. In the lesioned animals, there were significant decreases in choline acetyltransferase, acetylcholinesterase staining and glutamate decarboxylase in the median eminence, whereas choline acetyltransferase activity and acetylcholinesterase staining, but not glutamate decarboxylase activity, were decreased in nucleus arcuatus. Aromatic L-amino acid decarboxylase was unchanged in all regions studied. The high affinity uptakes of glutamate, dopamine and noradrenaline, and the endogenous amino acid levels were also unchanged in the treated animals. The results indicate the existence of acetylcholine- and GABA-containing elements in the tuberoinfundibular tract. They further indicate that the dopamine cells in the arcuate nucleus are less sensitive to the toxic effect of glutamate than other cell types, possibly because they contain less glutamate receptors.