Locomotor and learning deficits in adult rats exposed to monosodium-L-glutamate during early life

Neuroprotective Effect of Morin Hydrate against Attention-Deficit/Hyperactivity Disorder (ADHD) Induced by MSG and/or Protein Malnutrition in Rat Pups: Effect on Oxidative/Monoamines/Inflammatory Balance and Apoptosis

Monosodium glutamate (MSG) is one of the most widely used food additives. However, it has been linked to protein malnutrition (PM) and various forms of toxicities such as metabolic disorders and neurotoxic effects. The current study is the first to explore the association between MSG, PM, and induced brain injury similar to attention-deficit/hyperactivity disorder (ADHD). Moreover, we determined the underlying mechanistic protective pathways of morin hydrate (MH)―a natural flavonoid with reported multiple therapeutic properties. PM was induced by feeding animals with a low protein diet and confirmed by low serum albumin measurement. Subsequently, rat pups were randomized into seven groups of 10 rats each. Group I, III, and VI were normally fed (NF) and groups II, IV, V, and VII were PM fed. Group I served as normal control NF while Group II served as PM control animals. Group III received NF + 0.4 g/kg MSG, Group IV: PM + 0.4 g/kg MSG, Group V: PM + 60 mg/kg MH, Group VI: NF + 0.4 kg/g MSG + 60 mg/kg MH and Group VII: PM + 0.4 kg/kg MSG + 60 mg/kg MH. At the end of the experimental period, animals were subjected to behavioral and biochemical tests. Our results showed that treatment of rats with a combination of MSG + PM-fed exhibited inferior outcomes as evidenced by deteriorated effects on behavioral, neurochemical, and histopathological analyses when compared to rats who had received MSG or PM alone. Interestingly, MH improved animals’ behavior, increased brain monoamines, brain-derived neuroprotective factor (BDNF), antioxidant status and protein expression of Nrf2/HO-1. This also was accompanied by a significant decrease in brain MDA, inflammatory markers (NF-kB, TNF-α and IL1β), and suppression of TLR4/NLRP3/caspase-1 axis. Taken together, MSG and/or PM are associated with neuronal dysfunction. Our findings suggest MH as a potential neuroprotective agent against brain insults via targeting Nrf2/HO-1 and hindering TLR4/NLRP3 inflammasome signaling pathways.

The Effect of Monosodium Glutamate on Neuronal Signaling Molecules in the Hippocampus and the Neuroprotective Effects of Omega-3 Fatty Acids

Monosodium glutamate (MSG) is a flavoring substance added to many ready-to-eat foods and has known neurotoxic effects. This study was performed in order to examine the potential toxic effect of MSG on neurons in various regions of the hippocampus in prepubertal rats. It also investigated the protective effect of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on brain-derived neurotropic factor (BDNF), n-methyl-d-aspartate receptor (NMDA-R), and neuropeptide-Y (NPY) expression in the brain, using immunohistochemical and biochemical methods. Six female prepubertal Wistar albino rats were used in each group. Group 1, the control group, received 0.9% saline solution subcutaneously (sc) on days 1, 3, 5, 7, and 9. Group 2 received 4 mg/g MSG sc on days 1, 3, 5, 7, and 9. Group 3 received MSG + EPA (4 mg/g sc on days 1, 3, 5, 7, and 9. Oral 300 mg/kg for 9 d), while Group 4 received MSG + DHA (4 mg/g sc on days 1, 3, 5, 7, and 9 and 300 mg/kg orally for 9 d, respectively). At the end of the ninth day the hippocampal regions of the brain were removed and either fixed for immunohistochemical staining or stored at -80 °C for biochemical parameter investigation. BDNF, NMDA-R, and NPY expression results were evaluated using immunohistochemistry and an enzyme-linked immunosorbent assay. According to our findings, neurons in the control group hippocampal CA1 and DG regions exhibited strong BDNF, NPY, and NMDA-R reactions, while an expression in both regions decreased in the MSG group (p < 0.00). However, in the MSG-EPA and MSG-DHA groups, BDNF, NPY, and NMDA-R immunoreactions in neurons in the same region were similar to those of the control group (p = 0.00). No significant difference was observed in terms of expression in hippocampal neurons between the MSG-EPA and MSG-DHA groups (p > 0.00). In conclusion, since MSG caused a decrease in BDNF, NMDA-R, and NPY neural signaling molecules in the CA1 and DG regions of the hippocampus of prepubertal rats compared to the control group, care is required over the consumption of MSG, since it may affect memory-related neurons in these age groups. In addition, we concluded that the use of omega-3 fatty acids such as EPA and DHA in addition to MSG may protect against the neurotoxic effects of MSG.

Dietary glutamate and the brain: In the footprints of a Jekyll and Hyde molecule

Glutamate is a crucial neurotransmitter of the mammalian central nervous system, a molecular component of our diet, and a popular food-additive. However, for decades, concerns have been raised about the issue of glutamate's safety as a food additive; especially, with regards to its ability (or otherwise) to cross the blood-brain barrier, cause excitotoxicity, or lead to neuron death. Results of animal studies following glutamate administration via different routes suggest that an array of effects can be observed. While some of the changes appear deleterious, some are not fully-understood, and the impact of others might even be beneficial. These observations suggest that with regards to the mammalian brain, exogenous glutamate might exert a double-sided effect, and in essence be a two-faced molecule whose effects may be dependent on several factors. This review draws from the research experiences of the authors and other researchers regarding the effects of exogenous glutamate on the brain of rodents. We also highlight the possible implications of such effects on the brain, in health and disease. Finally, we deduce that beyond the culinary effects of exogenous glutamate, there is the possibility of a beneficial role in the understanding and management of brain disorders.

Cortical tau burden and behavioural dysfunctions in mice exposed to monosodium glutamate in early life

Although monosodium glutamate (MSG)-induced neurotoxicity has been recognized for decades, the potential similarities of the MSG model to Alzheimer’s disease (AD)-type neuropathology have only recently been investigated. MSG-treated mice were examined behaviourally and histologically in relation to some features of AD. Four-week old mice received 5 subcutaneous MSG (2 g/kg) injections on alternate days, or saline. At age 10–12 weeks, they were given a battery of behavioural tests for species-typical behaviours and working memory. The mice were killed at 12 weeks and the brains excised. Accumulation of hyperphosphorylated tau protein was assessed in cortical and hippocampal neurons by immunohistochemistry, and in cerebral cortical homogenates. A 78% increase in cortical concentrations of phosphorylated tau protein was observed in the MSG mice. Intracellular hyperphosphorylated tau immunostaining was observed diffusely in the cortex and hippocampus, together with cortical atrophic neurons, extensive vacuolation and dysmorphic neuropil suggestive of spongiform neurodegeneration. Nest-building was significantly impaired, and spontaneous T-maze alternation was reduced, suggesting defective short-term working memory. Subcutaneous MSG treatment also induced a 56% reduction in exploratory head dips in a holeboard (P = 0.009), and a non-significant tendency for decreased burrowing behaviour (P = 0.085). These effects occurred in the absence of MSG-induced obesity or gross locomotor deficits. The findings point to subcutaneous MSG administration in early life as a cause of tau pathology and compromised species-typical behaviour in rodents. Determining whether MSG can be useful in modelling AD requires further studies of longer duration and full behavioural characterization.

Neonatal Monosodium Glutamate Administration Disrupts Place Learning and Alters Hippocampal-Prefrontal Learning-Related Theta Activity in the Adult Rat

Neonatal treatment with monosodium glutamate causes profound deficits in place learning and memory in adult rats evaluated in the Morris maze. Theta activity has been related to hippocampal learning, and increased high-frequency theta activity occurs through efficient place learning training in the Morris maze. We wondered whether the place learning deficits observed in adult rats that had been neonatally treated with monosodium glutamate (MSG), were related to altered theta patterns in the hippocampus and prelimbic cortex, which were recorded during place learning training in the Morris maze. The MSG-treated group had a profound deficit in place learning ability, with a marginal reduction in escape latencies during the final days of training. Learning-related changes were observed in the relative power distribution in control and MSG-treated groups in the hippocampal EEG, but not in the prelimbic cortex. Increased prefrontal and reduced hippocampal absolute power that appeared principally during the final days of training, and reduced coherence between regions throughout the training (4-12 Hz), were observed in the MSG-treated rats, thereby suggesting a misfunction of the circuits rather than a hyperexcitable general state. In conclusion, neonatal administration of MSG, which caused a profound deficit in place learning at the adult age, also altered the theta pattern both in the hippocampus and prelimbic cortex.

Patho-physiological and toxicological aspects of monosodium glutamate

Nowadays, the life-line of urban population has been formed by commercial foods due to industrialization, urbanization, and rapid increase in working class. Commercial foods are time and energy saving foods but it compromising the nutritional value of foods. The term adulteration refers to the deliberate addition of compound which is usually not present in food. These compounds are known as food additives or food adulterant. Monosodium Glutamate (MSG) is one of the most common food additives. Several studies revealed that MSG has toxic effect on fetal development/fetus, children's, adolescent, and adults. Physiological complication associated with MSG toxicity are hypertension, obesity, gastrointestinal tract troubles, and impairment of function of brain, nervous system, reproductive, and endocrine system. The effect of MSG depends upon its dose, route of administration and exposure time. Public awareness may play a major role in controlling the food adulteration by working in collaboration with National testing facilities to scrutinize each commercial food article from time to time. The aim of this review article is to highlight the deleterious impact of MSG on human health.

Monosodium glutamate impairs the contraction of uterine visceral smooth muscle ex vivo of rat through augmentation of acetylcholine and nitric oxide signaling pathways

The aim of the study was to examine the toxic effects of Monosodium glutamate (MSG), an extensively used food additive, on the contraction of uterine visceral smooth muscle (UVSM) in rat and to elucidate the probable neurocrine mechanism involved in it. MSG produced significant potentiation of the force and inhibition of frequency of uterus recorded ex vivo in chronic MSG exposure and in single dose acute experiments. MSG also produced significant potentiation of force of acetylcholine induced contraction and no alterations in atropine induced contraction of uterus. Further, MSG produced significant increase in force and frequency of contraction of neostigmine incubated uterus. We have found significant potentiation of the post pause force of contraction of uterus when MSG was applied in adrenaline incubated uterus. MSG also produced significant decrease in frequency of contraction of sodium nitroprusside incubated uterus; increase in frequency of N-ω-Nitro-l-Arginine Methyl Ester incubated uterus and no significant changes in frequency of contraction of methylene blue incubated uterus. These results indicate that MSG potentiates the force of contraction of UVSM predominantly by augmenting the activity of cholinergic intrinsic efferents and inhibits the frequency of contraction probably by augmenting the activity of nitrergic efferents. In conclusion, MSG potentiates the force and inhibits the frequency of contraction of UVSM, and the MSG induced effect is probably mediated through the augmentation of acetylcholine and nitric oxide signaling pathways.

Monosodium glutamate suppresses the female reproductive function by impairing the functions of ovary and uterus in rat

The aim of the present study was to examine the effect of monosodium glutamate (MSG) on the functions of ovary and uterus in rat. Virgin female rats of Charles Foster strain (120 gms approximately) were administrated MSG by oral gavage at a dose level of 0.8, 1.6, 2.4 gm/kgBW/day, respectively for 30 and 40 days duration. We observed a significant decrease in the duration of proestrus, estrus and metestrus phases, and increase in the duration of diestrus phase and diestrus index compared to control. We found significant increase in the levels of serum LH, FSH and estradiol in test groups of rat. We also observed significant increase in the number of primary and primordial follicles, increase in the size of graafian follicle, and decrease in the size of corpus luteum. Further, we have seen significant increase in the activities SOD, CAT and GST, decrease in the activities GR and GPx, and decrease MDA level in MSG exposed groups. These results suggest that MSG impairs the functions of the ovary probably by augmenting the release of FSH, LH and estradiol; promoting the follicular maturation and improving the biochemical mechanism for antioxidant defense. We also observed significant potentiation of the force of contraction of uterus in estrus, metestrus and diestrus phases. This result suggests that MSG potentiates the contraction of uterus probably by stimulating the estradiol sensitivity to oxytocin. From the results it is concluded that MSG suppresses the female reproductive function in rat probably by impairing the functions of ovary and uterus.

Ginger and Propolis Exert Neuroprotective Effects against Monosodium Glutamate-Induced Neurotoxicity in Rats

Central nervous system cytotoxicity is linked to neurodegenerative disorders. The objective of the study was to investigate whether monosodium glutamate (MSG) neurotoxicity can be reversed by natural products, such as ginger or propolis, in male rats. Four different groups of Wistar rats were utilized in the study. Group A served as a normal control, whereas group B was orally administered with MSG (100 mg/kg body weight, via oral gavage). Two additional groups, C and D, were given MSG as group B along with oral dose (500 mg/kg body weight) of either ginger or propolis (600 mg/kg body weight) once a day for two months. At the end, the rats were sacrificed, and the brain tissue was excised and levels of neurotransmitters, ß-amyloid, and DNA oxidative marker 8-OHdG were estimated in the brain homogenates. Further, formalin-fixed and paraffin-embedded brain sections were used for histopathological evaluation. The results showed that MSG increased lipid peroxidation, nitric oxide, neurotransmitters, and 8-OHdG as well as registered an accumulation of ß-amyloid peptides compared to normal control rats. Moreover, significant depletions of glutathione, superoxide dismutase, and catalase as well as histopathological alterations in the brain tissue of MSG-treated rats were noticed in comparison with the normal control. In contrast, treatment with ginger greatly attenuated the neurotoxic effects of MSG through suppression of 8-OHdG and β-amyloid accumulation as well as alteration of neurotransmitter levels. Further improvements were also noticed based on histological alterations and reduction of neurodegeneration in the brain tissue. A modest inhibition of the neurodegenerative markers was observed by propolis. The study clearly indicates a neuroprotective effect of ginger and propolis against MSG-induced neurodegenerative disorders and these beneficial effects could be attributed to the polyphenolic compounds present in these natural products.

Selenofuranoside improves long-term memory deficits in rats after exposure to monosodium glutamate: Involvement of Na+, K+-ATPase activity

Monosodium glutamate (MSG) is the most widely used additive in the food industry; however, some adverse effects of this additive, including functional, learning, and behavioral alterations, have been observed in experimental animals and humans. Studies have shown learning and memory impairment in adult animals exposed to MSG. However, studies relating exposure to MSG to acetylcholinesterase (AChE) and Na⁺, K⁺-ATPase activities and memory damage are still scarce in the literature. The aim of the present study was to assess the possible protective effects of selenofuranoside, an organoselenium compound, against the impairment of long-term memory, Na⁺, K⁺-ATPase and AChE activities, and oxidative stress after MSG exposure in rats. MSG (2g/kg) and/or selenofuranoside (5mg/kg) were administered orally to 5-week-old male Wistar rats for 10days. On the 10th day, after the administration of last dose of the drug(s), the rats were subjected to behavioral tests: the open-field test and step-down passive avoidance task (SDPA). The blood, liver, kidney, cortex, and hippocampus were removed to determine the oxidative stress parameters, such as the levels of reactive species, lipid peroxidation, antioxidant enzyme activities, and endogenous nonenzymatic antioxidant content. Furthermore, the cortex and hippocampus were used to determine the Na⁺, K⁺-ATPase and AChE activities. The results demonstrate that the administration of MSG led to long-term memory impairment, as shown in the SDPA task, and also hippocampal and cortical Na⁺, K⁺-ATPase inhibition. There were no alterations in the AChE activity and oxidative stress parameters. Treatment with selenofuranoside attenuated memory impairment associated with MSG exposure by improving the hippocampal Na⁺, K⁺-ATPase activity.

Re-evaluation of glutamic acid (E 620), sodium glutamate (E 621), potassium glutamate (E 622), calcium glutamate (E 623), ammonium glutamate (E 624) and magnesium glutamate (E 625) as food additives

The EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) provides a scientific opinion re-evaluating the safety of glutamic acid-glutamates (E 620-625) when used as food additives. Glutamate is absorbed in the intestine and it is presystemically metabolised in the gut wall. No adverse effects were observed in the available short-term, subchronic, chronic, reproductive and developmental studies. The only effect observed was increased kidney weight and increased spleen weight; however, the increase in organ weight was not accompanied by adverse histopathological findings and, therefore, the increase in organ weight was not considered as an adverse effect. The Panel considered that glutamic acid-glutamates (E 620-625) did not raise concern with regards to genotoxicity. From a neurodevelopmental toxicity study, a no observed adverse effect level (NOAEL) of 3,200 mg monosodium glutamate/kg body weight (bw) per day could be identified. The Panel assessed the suitability of human data to be used for the derivation of a health-based guidance value. Although effects on humans were identified human data were not suitable due to the lack of dose-response data from which a dose without effect could be identified. Based on the NOAEL of 3,200 mg monosodium glutamate/kg bw per day from the neurodevelopmental toxicity study and applying the default uncertainty factor of 100, the Panel derived a group acceptable daily intake (ADI) of 30 mg/kg bw per day, expressed as glutamic acid, for glutamic acid and glutamates (E 620-625). The Panel noted that the exposure to glutamic acid and glutamates (E 620-625) exceeded not only the proposed ADI, but also doses associated with adverse effects in humans for some population groups.

Altered behavior of adult obese rats by monosodium l-glutamate neonatal treatment is related to hypercorticosteronemia and activation of hypothalamic ERK1 and ERK2

OBJECTIVES

Obesity is a metabolic and hormonal disorder with serious social and psychological impacts. There is a close relationship among obesity, neuroendocrine homeostasis and behavioral patterns. However, few data are available in the literature regarding this subject. This study assessed behavior and memory of adult obese rats by monosodium l-glutamate (MSG) neonatal treatment or highly palatable dietary treatment.

METHODS

MSG obesity was induced by subcutaneous injections of MSG (4 mg/g) during the first 5 days of life (Ob-MSG); control group (C-MSG), received saline solution equimolar. Both groups were fed with commercial chow. To induce dietary obesity, 21-day-old rats were assigned to two experimental diets: highly palatable diet (Ob-Diet) and control diet (C-Diet) composed of commercial chow. Ninety-day-old animals were submitted to behavioral assessment by the open-field test and short- and long-term memory by the object recognition test. Biometric variables were obtained, the Lee index was calculated and mass of retroperitoneal and perigonadal fat pads was measured. Furthermore, an altered behavioral profile was investigated by quantification of plasmatic corticosterone, expression, and activity of hypothalamic extracellular signal-regulated kinase protein (ERK) 1 and 2.

RESULTS

Increased Lee index and fat pads were observed in Ob-MSG and Ob-Diet groups. Ob-MSG presented a higher level of anxiety and impaired long-term memory compared to C-MSG, while there was no difference between Ob-Diet and C-Diet. The Ob-MSG group presented a higher level of plasmatic corticosterone and increased phosphorylation of hypothalamic ERK1 and 2.

DISCUSSION

Both treatments induced obesity but only Ob-MSG showed altered behavioral parameters, which is related to increased concentration of corticosterone and hypothalamic ERK1 and 2 activation.

The Neuroprotective Effect of Dark Chocolate in Monosodium Glutamate-Induced Nontransgenic Alzheimer Disease Model Rats: Biochemical, Behavioral, and Histological Studies

The vulnerability to oxidative stress and cognitive decline continue to increase during both normal and pathological aging. Dietary changes and sedentary life style resulting in mid-life obesity and type 2 diabetes, if left uncorrected, further add to the risk of cognitive decline and Alzheimer disease (AD) in the later stages of life. Certain antioxidant agents such as dietary polyphenols, taken in adequate quantities, have been suggested to improve the cognitive processes. In this study, we examined the effect of oral administration of dark chocolate (DC) containing 70% cocoa solids and 4% total polyphenol content for three months at a dose of 500 mg/Kg body weight per day to 17-month-old monosodium glutamate treated obese Sprague-Dawley rats, earlier characterized as a nontransgenic AD (NTAD) rat model after reversal of obesity, diabetes, and consequent cognitive impairments. The results demonstrated that DC reduced the hyperglycemia, inhibited the cholinesterase activity in the hippocampal tissue homogenates, and improved the cognitive performance in spatial memory related Barnes maze task. Histological studies revealed an increase in cell volume in the DC treated rats in the CA3 region of the hippocampus. These findings demonstrated the benefits of DC in enhancing cognitive function and cholinergic activity in the hippocampus of the aged NTAD rats while correcting their metabolic disturbances.

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.

Effects of maternally exposed coloring food additives on receptor expressions related to learning and memory in rats

Exposure to artificial food colors and additives (AFCAs) has been implicated in the induction and severity of some childhood behavioral and learning disabilities. N-methyl-D-aspartate receptors (NMDARs) and nicotinic acetylcholine receptors (nACHRs) are thought to be effective in the learning and memory-generating process. In this study, we investigated the effects of intrauterine exposure to AFCAs on subunit concentrations of NMDARs and nAChRs isoforms in rats. We administered a mixture of AFCAs (Eritrosin, Ponceau 4R, Allura Red AC, Sunset Yellow FCF, Tartrazin, Amaranth, Brilliant Blue, Azorubin and Indigotin) to female rats before and during gestation. The concentration of NR2A and NR2B subunits and nAChR α7, α4β2 isoforms in their offspring's hippocampi were measured by Western Blotting. Expressions of NR2B and nAChR β2 were significantly increased (17% and 6.70%, respectively), whereas expression of nAChR α4 was significantly decreased (5.67%) in male experimental group compared to the male control group (p<0.05). In the female experimental group, AFCAs caused a 14% decrease in NR2B expression when compared to the female control group (p<0.05). Our results indicate that exposure to AFCAs during the fetal period may lead to alterations in expressions of NMDARs and nAChRs in adulthood. These alterations were different between male and female genders.

Changes in open-field activity and novelty-seeking behavior in periadolescent rats neonatally treated with monosodium glutamate

Monosodium glutamate (MSG) treatment of neonatal rodents leads to degeneration of the neurons in the arcuate nucleus, inner retinal layers and various other brain areas. It also causes various changes in the motor activity, sensory performance and learning abilities. We have previously shown that MSG treatment delays the appearance of some reflexes during neurobehavioral development and leads to temporary changes in reflex performance and motor coordination. Investigation of novelty-seeking behavior is of growing importance for its relationship with sensitivity to psychomotor stimulants. Perinatal administration of numerous toxic agents has been shown to influence novelty-seeking behavior in rats, but little is known about the influence of neonatal MSG treatment on the novelty-seeking behavior. The aim of the present study was to compare changes in locomotor, spontaneous exploratory and novelty-seeking behavior in periadolescent rats neonatally treated with MSG. Newborn rats were treated with 4 mg/g MSG subcutaneously on postnatal days 1, 3, 5, 7 and 9. Open-field behavior was tested at 2, 3, 4, 6 and 8 weeks of age. We found that MSG administration led to only temporary increases in locomotor behavior, which was more pronounced during the first few postnatal weeks, followed by a subtle hypoactivity at 2 months of age. Novelty-seeking was tested in four 5-min trials at 3 weeks of age. Trial 1 was in an empty open-field, two identical objects were placed in the arena during trial 2 and 3, and one of them was replaced to a novel object during trial 4. We found that the behavioral pattern of MSG-treated rats was the opposite in all tested signs in the novelty exploration test compared to control pups. In summary, our present study shows that neonatal MSG treatment leads to early temporary changes in the locomotor activity followed by hypoactivity at 2 months of age. Furthermore, MSG-treated rats show a markedly disturbed novelty-seeking behavior represented by altered activity when subjected to a novel object.

Integrated digital image and accelerometer measurements of rat locomotor and vibratory behaviour

This study developed a combined IC-type accelerometer and video camera system to simultaneously measure vibration and locomotion activities in rats. A personal computer, adopted as an image frame grabber, was combined with a digital image processing algorithm to measure the precise location of an animal in an experimental cage. An accelerometer-based vibration subsystem, based on an 89C51 single-chip microprocessor, was designed. The acceleration sensor module was attached directly to the shaved back of the rat's body to directly measure the animal's vibration. This module can detect a wide range of vibrations from movements of the entire body to micro-tremors. Along with hardware, this study also proposes novel software for video enhancement and data analysis to calculate the behaviour parameters from recorded movements. In normal mode, three vibration activities (locomotor activity, tremor and twitch) are auto-analyzed every 10 min. The results are saved, and various display, statistical and data organization options are available. The primary merits of this system are the ability to simultaneously record locomotion and vibrational data, the rapid set-up and operation, the low cost, the reduced illumination requirements, the reduction of environmental noise and the high precision. The proposed method will be of interest to researchers in various behavioural, biological and medical fields.

Temporal and spatial expression of preprotachykinin A mRNA in the developing filial mice brain after maternal administration of monosodium glutamate at a late stage of pregnancy

In the early stages of brain development, exposure of excessive monosodium glutamate (MSG) to neurons causes animal functional and behavioral disorders in adulthood. To investigate the effects of excessive MSG during pregnancy on the neurons in the developing brain, in situ hybridization was used. In mice, the expression of preprotachykinin A mRNA (PPT A mRNA) was assessed in neurons of in the brain after MSG treatment. Brain tissue sections were hybridized with specific digoxigenin-labeled RNA probes. The number of cells that expressed PPT A mRNA gradually decreased from 10-day-old (10d) to 60-day-old (60d) MSG-treated and normal animals. In the MSG-treated and normal mice, the PPT A mRNA-positive neurons almost disappeared in 90-day-old (90d) mice. The expression of PPT A mRNA significantly decreased at 10d in most of the brain regions of MSG-treated mice including the cerebral cortex (CC), hippocampal subregions of CA1, CA2 (CA1, CA2), habenula nucleus (HAB), hypothalamic periventricular nucleus (PE), hypothalamic arcuate nucleus (AR), median eminence (ME), amygdala nucleus (AMY), endopiriform nucleus (EN), and hypothalamic ventromedial nucleus (VMH) and dorsomedial nucleus (DMH). In the hippocampal CA4 subregions (CA4), paraventricular nucleus (PV) and caudate putamen (CPU), however, they were not significantly altered. Furthermore, in CC, hippocampal CA3 subregion (CA3), PE and EN regions the number of PPT A mRNA-positive neurons decreased at 20 days old (20d), but increased significantly in CA2 and CPU. At 30 days old (30d), the positive neuron number decreased in AMY, and they did not change in other regions. At 60d, the number of positive neurons significantly decreased in PV and ME, but increased in AMY. In the other observed regions, no changes were found. These results show that maternal administration of excessive MSG at a late stage of pregnancy significantly decreases PPT A mRNA expression in most of the brain regions of filial mice. This suggests that glutamate-induced excitotoxicity may affect the metabolism of precursors of substance P in developing brain neurons. The present study provides insights into the plasticity and vulnerability of neuron in different brain regions to glutamate excitotoxicity.

Effect of resource availability on biparental care, and offspring neural and behavioral development in the California mouse (Peromyscus californicus)

Maternal care influences cognitive function in humans, primates and rodents; however, little is known about the effect of biparental care. Environmental factors such as resource availability play an important role in modulating parental investment strategies with subsequent effects on the offspring. Thus, we examined the interaction between foraging demand and biparental care on hippocampal development and novel object recognition in the monogamous, biparental California mouse. We characterized biparental behavior for 15 days in families exposed to either control (ad libitum feeding) or a high-foraging demand across the weaning period. Adult male offspring were then tested in the open field, and for novel object and place recognition, as well as for hippocampal synaptic density and the expression of genes encoding for subunits of the N-methyl-D-aspartate (NMDA) receptor complex, and the postsynaptic density (PSD)-95 scaffolding protein. Under high-foraging demand, the mothers' body weight was decreased at weaning and fathers spent significantly less time in contact with pups. Offspring reared under high-foraging demand weighed less at weaning and, as adults, were more fearful in the open field and showed profound deficits in both novel object and place recognition. While synaptic density and NR1 mRNA expression were unaffected, offspring reared under high-foraging demand showed increased NR2A and decreased NR2B mRNA expression. Further, PSD-95 protein expression was decreased in mice reared under high-foraging demand. Together, the results suggest that resource availability affects biparental investment strategies, with subsequent effects on hippocampal development and novel object recognition in the offspring.

Development of neurological reflexes and motor coordination in rats neonatally treated with monosodium glutamate

Monosodium glutamate (MSG) treatment of neonatal rats causes neuronal degeneration in various brain areas and leads to several neurochemical, endocrinological and behavioral alterations. However, relatively little is known about the development of neurological reflexes and motor coordination of these animals. Therefore, the aim of the present study was to examine the neurobehavioral development of newborn rats treated with MSG. Rats received MSG at postnatal days 1, 3, 5, 7, and 9. Appearance of neural reflexes and reflex performance as well as motor coordination were examined for 5 weeks after birth. The efficacy of MSG treatment was confirmed by histological examination of the arcuate nucleus. We found that MSG treatment delayed the appearance of forelimb placing, forelimb grasp and righting reflexes, besides the retarded somatic development. The treated pups performed surface righting in significantly longer times. Also, worse performance was observed in the foot-fault and rota-rod tests. However, MSG-treated rats reached control levels by the end of the fifth postnatal week. These results show that MSG treatment does not cause permanent alterations in the neurobehavioral development, only delays the appearance of some reflexes and leads to temporary changes in reflex performance and motor coordination signs.

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.

Effect of pretreatment of cytochrome P450 (P450) modifiers on neurobehavioral toxicity induced by deltamethrin

To investigate the involvement of cytochrome P450 (P450) enzyme induction and the effect of different P450 modifiers in the neurobehavioral toxicity of deltamethrin, deltamethrin (10 mg/kg; orally for 1 day) was administered to young male albino Wistar rats, or in rats pretreated with phenobarbital (PB; 80 mg/kg, ip for 5 days), an inducer of P450 2B1/2B2 or 3-methylcholanthrene (MC; 30 mg/kg, ip for 5 days), an inducer of P450 1A1/1A2 or cobalt chloride (CoCl(2); sc for 2 days), a depletor of P450s. The administration of PB or MC or CoCl(2) alone did not produced any symptoms of neurobehavioral toxicity. While a single oral administration of deltamethrin produced tremors in two out of 10 rats and decreased the spontaneous locomotor activity, pretreatment with MC or PB potentiated the deltamethrin induced neurobehavioral toxicity with 50% of the treated rats exhibiting tremors. Half of the animals pretreated with MC prior to exposure to deltamethrin also exhibited choreoathetosis. The decrease in the spontaneous locomotor activity was found to be much more significant in PB- or MC-pretreated animals exposed to deltamethrin. In contrast to the pretreatment with inducers, rats pretreated with CoCl(2) exhibited no symptoms of tremors or choreoathetosis, indicating that a reactive metabolite of deltamethrin is formed by P450 catalysed reactions which is involved in the neurobehavioral toxicity of deltamethrin.

Modulation of anxiety through blockade of anandamide hydrolysis

The psychoactive constituent of cannabis, Delta(9)-tetrahydrocannabinol, produces in humans subjective responses mediated by CB1 cannabinoid receptors, indicating that endogenous cannabinoids may contribute to the control of emotion. But the variable effects of Delta(9)-tetrahydrocannabinol obscure the interpretation of these results and limit the therapeutic potential of direct cannabinoid agonists. An alternative approach may be to develop drugs that amplify the effects of endogenous cannabinoids by preventing their inactivation. Here we describe a class of potent, selective and systemically active inhibitors of fatty acid amide hydrolase, the enzyme responsible for the degradation of the endogenous cannabinoid anandamide. Like clinically used anti-anxiety drugs, in rats the inhibitors exhibit benzodiazepine-like properties in the elevated zero-maze test and suppress isolation-induced vocalizations. These effects are accompanied by augmented brain levels of anandamide and are prevented by CB1 receptor blockade. Our results indicate that anandamide participates in the modulation of emotional states and point to fatty acid amide hydrolase inhibition as an innovative approach to anti-anxiety therapy.

Neuroendocrine alterations impair enamel mineralization, tooth eruption and saliva in rats

Neonatal administration of monosodium glutamate (MSG) in rats causes definite neuroendocrine disturbances which lead to alterations in many organ systems. The possibility that MSG could affect tooth and salivary gland physiology was examined in this paper. Male and female pups were injected subcutaneously with MSG (4 mg/g BW) once a day at the 2nd, 4th, 6th, 8th and 10th day after birth. Control animals were injected with saline, following the same schedule. Lower incisor eruption was determined between the 4th and the 10th postnatal days, and the eruption rate was measured between the 43rd and the 67th days of age. Pilocarpine-stimulated salivary flow was measured at 3 months of age; protein and amylase contents were thereby determined. The animals treated with MSG showed significant reductions in the salivary flow (males, -27%; females, -40%) and in the weight of submandibular glands (about -12%). Body weight reduction was only about 7% for males, and did not vary in females. Saliva of MSG-treated rats had increased concentrations of total proteins and amylase activity. The eruption of lower incisors occurred earlier in MSG-treated rats than in the control group, but on the other hand the eruption rate was significantly slowed down. The incisor microhardness was found to be lower than that of control rats. Our results show that neonatal MSG treatment causes well-defined oral disturbances in adulthood in rats, including salivary flow reduction, which coexisted with unaltered protein synthesis, and disturbances of dental mineralization and eruption. These data support the view that some MSG-sensitive hypothalamic nuclei have an important modulatory effect on the factors which determine caries susceptibility.

Comparative effect of dietary administration of Lathyrus sativus pulse on behaviour, neurotransmitter receptors and membrane permeability in rats and guinea pigs

Neurolathyrism, an upper motor neuron disease, has been thought to be caused by long-term dietary consumption of lathyrus pulse, which contains the toxin beta-N-oxalyl-L-alpha,beta-diaminopropionic acid. Earlier behavioural studies employing oral feeding of lathyrus pulse to animals has been conducted without evaluating the biochemical toxicity potential. In the present investigation the effect of dietary feeding of 10%, 50% and 80% lathyrus pulse to rats and guinea pigs for 3 months on neurobehavioural parameters, including locomotor activity, inclined plain test and neurotoxicological parameters such as neurotransmitter receptor binding, Ca(2+) influx and membrane fluidity, was investigated. Exposure of 50% low and high toxin lathyrus to rats did not cause any significant change in locomotor activity, whereas guinea pigs at the same dosage regimen of high toxin lathyrus showed significant lowering of inclined plain test scores. Furthermore, studies of neuroreceptor binding in rats fed 50% low and high toxin lathyrus showed significant changes in glutamate, dopamine and muscarinic receptors, whereas the benzodiazepine receptor elicited no change. Guinea pigs, on the other hand, fed 50% and 80% lathyrus in the diet showed significant changes in glutamate, dopamine, muscarinic and benzodiazepine receptors. Interestingly, significant elevation in intracellular calcium with a concomitant increase in membrane fluidity was observed in rats (50% low and high toxin) and guinea pigs (50% and 80%) fed a lathyrus diet. These results indicate that although both species (rats and guinea pigs) are susceptible to neurochemical changes on exposure to lathyrus, locomotor changes are only noticed in guinea pigs. Thus, guinea pigs may be more prone to lathyrus toxicity and may serve as a sensitive animal model compared with rats.

Neonatal exposure to monosodium L-glutamate induces loss of neurons and cytoarchitectural alterations in hippocampal CA1 pyramidal neurons of adult rats

Glutamatergic post-synaptic receptors are closely related to the known excitotoxic effects of high doses of L-glutamate. Several behavioral abnormalities, glial reaction, and an increase of expression of the NMDA receptor sub-units have been observed in the rat hippocampus after early monosodium glutamate exposure. Thus, a quantitative morphological study was carried out to determine the effects of early exposure to monosodium glutamate on post-synaptic structures that mediate glutamate excitatory neurotransmission in the hippocampal CA1 field. Four milligrams per gram body weight of monosodium glutamate was subcutaneously injected into neonatal Wistar rats, at 1, 3, 5, and 7 days. Cell loss and several cytoarchitectonic parameters were evaluated in pyramidal cells from the hippocampal CA1 field in the treated rats at 60 days of age. An untreated group of rats were used as controls. Cell number in the hippocampus of experimental rats was 11.5% less than that in control animals. In addition, both dendritic arborization and dendritic spine density were adversely affected, and thin and mushroom-shaped spines became proportionally more numerous, while the opposite occurred to stubby spines. These results strongly suggest the occurrence of cell death and also show some cytoarchitectural modifications in the surviving neurons. These could lead to functional alterations in the hippocampal integrative activity, due to an early cytoexcitotoxic effect of monosodium glutamate.

Deficit in hippocampal long-term potentiation in monosodium glutamate-treated rats

Rats subjected to monosodium glutamate (MSG) administration during the neonatal period present chronic neuroendocrine dysfunction associated with marked cognitive deficits. Long-term potentiation (LTP) in the hippocampus provides a model suited for the study of mammalian brain plasticity and memory formation. In the present work, we used the LTP protocol to investigate the synaptic plasticity in the hippocampal CA1 area of adult rats subjected to MSG treatment during the first 10 days of life. Synaptic transmission in CA1 area was analyzed using extracellular field recordings in response to Schaffer's collateral fiber stimulation in hippocampal slices. Animals injected with MSG exhibited a dramatic decrement of LTP field excitatory postsynaptic potentials (fEPSPs) compared to control group. Analysis of percent enhancement of fEPSP slope at 2 min after high frequency stimulation (HFS) increased by 189.3 +/- 33.2% in slices from control rats and 129.45 +/- 18.5% (p < 0.01) in slices from MSG-treated rats. Additionally, MSG-treated animals failed to maintain or consolidate LTP as revealed by a significant reduction in fEPSP slope enhancement over time after HFS. The mean fEPSP slope, 60 min after HFS, was 154.28 +/- 21% of the average baseline slope in control slices versus only 124.4 +/- 15% in MSG-treated rats (p < 0.01). At 90 min after HFS, slices from controls reached a potentiation of 44.5 +/- 2.9%, whereas the MSG group displayed an overall response enhancement of 17.65 +/- 2.7% of basal levels (p < 0.01). These findings indicate that MSG-treated rats display a chronic impairment of CA1 synaptic plasticity.

Consequences of monosodium glutamate or goldthioglucose arcuate nucleus lesions on ethanol-induced locomotion

It has been suggested that the endogenous opioid system, especially beta-endorphins, may play an important role in the behavioral effects of ethanol. The main site of beta-endorphin synthesis in the brain is the hypothalamic arcuate nucleus (ARC). In the present study, we used the neurotoxins monosodium glutamate (MSG) or goldthioglucose (GTG) to produce a selective ARC lesion and to assess its effects on the locomotion observed after ethanol administration. The results show that MSG or GTG pre-treatment produces a blockade of the increased locomotion produced by the injection of low and moderate doses of ethanol (0.5 and 1.5 g/kg, respectively). These effects were observed in the absence of any change in blood ethanol levels. On the other hand, MSG (but not GTG) pre-treatment enhanced the locomotor depression produced by higher doses of this alcohol (2.5 g/kg). Finally, caffeine (10 mg/kg)-induced locomotion was unaffected by the aforementioned neurotoxic agents. Thus, taken together, the present results suggest that MSG and GTG administration produce a blockade of the stimulating effects of ethanol on locomotion in mice and thus provides further support for a role of the ARC in the behavioral effects observed after ethanol administration.

Astrocytic and microglia cells reactivity induced by neonatal administration of glutamate in cerebral cortex of the adult rats

Recent studies confirm that astrocytes and neurons are associated with the synaptic transmission, particularly with the regulation of glutamate (Glu) levels. Therefore, they have the capacity to modulate the Glu released from neurons into the extracellular space. It has also been demonstrated an intense astrocytic and microglia response to physical or chemical lesions of the central nervous system. However, the persistence of the response of the glial cells in adult brain had not been previously reported, after the excitotoxic damage caused by neonatal dosage of monosodium glutamate (MSG) to newborn rats. In this study, 4 mg/g body weight of MSG were administered to newborn rats at 1, 3, 5, and 7 days after birth, at the age of 60 days the astrocytes and the microglia cells were analyzed with immunohistochemical methods in the fronto-parietal cortex. Double labeling to glial fibrillary acidic protein (GFAP) and BrdU, or isolectin-B(4) and BrdU identified astrocytes or microglia cells that proliferated; immunoblotting and immunoreactivity to vimentin served for assess immaturity of astrocytic intermediate filaments. The results show that the neonatal administration of MSG-induced reactivity of astrocytes and microglia cells in the fronto-parietal cortex, which was characterized by hyperplasia; an increased number of astrocytes and microglia cells that proliferated, hypertrophy; increased complexity of the cytoplasm extension of both glial cells and expression of RNAm to vimentin, with the presence of vimentin-positive astrocytes. This glial response to neuroexcitotoxic stimulus of Glu on the immature brain, which persisted to adulthood, suggests that the neurotransmitter Glu could trigger neuro-degenerative illnesses.

Induction of rat brain cytochrome P450s (P450s) by deltamethrin: regional specificity and correlation with neurobehavioral toxicity

Oral administration of 5 mg/kg body weight of deltamethrin, an alpha-cyano type II pyrethroid insecticide once a day for 1, 7, 15 and 21 consecutive days to young Druckerey rats (6- 8 weeks old) produced a time dependent increase in the activity of cytochrome P450 (P450) dependent 7-ethoxyresorufin-O-deethylase (EROD) and 7-pentoxyresorufin-O-dealkylase (PROD) in rat brain microsomes. A significant induction was observed on prolonged exposure of deltamethrin for 15 or 21 days. The induction in the activity of cerebral P450 enzymes was associated with the time dependent increase in the spontaneous locomotor activity indicating accumulation of deltamethrin or its metabolites in brain with the increase in the duration of exposure. Administration of deltamethrin (5 mg/kg) for 21 days produced region specific changes in the dealkylation of ethoxyresorufin and pentoxyresorufin in rat brain with significant induction occurring in the activity of P450 1A1/2 dependent EROD in cerebellum, hippocampus, hypothalamus and medulla-pons and that of P450 2B1/2 mediated PROD in hippocampus, hypothalamus, corpus striatum and mid brain. The data suggests that the differences in the induction of individual P450 isoenzymes in diverse brain regions could play a role in regulating the response of brain to pyrethroid insecticides by modulating their concentration per se or their active metabolites at the target site(s).

Neonatal exposure to monosodium glutamate induces cell death and dendritic hypotrophy in rat prefrontocortical pyramidal neurons

Monosodium glutamate was administered subcutaneously to male neonate rats, and the effects on cell number and cytoarchitecture of third-layer pyramidal neurons from the prefrontal cerebral cortex were studied in the adult. Monosodium glutamate treatment (4 mg/g of body weight, on post-natal days 1, 3, 5 and 7) resulted in fewer neurons, and shorter and less ramified dendritic processes, than those observed in control animals. Both density and proportional shapes of dendritic spines were not modified. We propose a dual effect of neonatal exposure to glutamate: an excitotoxic effect leading to cell death, and; a secondary neuroprotective effect, arising from the proliferation of glial cells and their subsequent uptake of glutamate, that favors the survival of the remaining neurons, and leads to a further hypotrophic effect on their dendritic processes.