Neuronal death and tumor necrosis factor-alpha response to glutamate-induced excitotoxicity in the cerebral cortex of neonatal rats

Inhibition of VEGFR-2 by SU5416 increases neonatally glutamate-induced neuronal damage in the cerebral motor cortex and hippocampus

Vascular endothelial growth factor (VEGF) exerts neuroprotective or proinflammatory effects, depending on what VEGF forms (A-E), receptor types (VEGFR1-3), and intracellular signaling pathways are involved. Neonatal monosodium glutamate (MSG) treatment triggers neuronal death by excitotoxicity, which is commonly involved in different neurological disorders, including neurodegenerative diseases. This study was designed to evaluate the effects of VEGFR-2 inhibition on neuronal damage triggered by excitotoxicity in the cerebral motor cortex (CMC) and hippocampus (Hp) after neonatal MSG treatment. MSG was administered at a dose of 4 g/kg of body weight (b.w.) subcutaneously on postnatal days (PD) 1, 3, 5, and 7, whereas the VEGFR-2 inhibitor SU5416 was administered at a dose of 10 mg/kg b.w. subcutaneously on PD 5 and 7, 30 min before the MSG treatment. Neuronal damage was assessed using hematoxylin and eosin staining, fluoro-Jade staining, and TUNEL assay. Additionally, western blot assays for some proteins of the VEGF-A/VEGFR-2 signaling pathway (VEGF-A, VEGFR-2, PI3K, Akt, and iNOS) were carried out. All assays were performed on PD 6, 8, 10, and 14. Inhibition of VEGFR-2 signaling by SU5416 increases the neuronal damage induced by neonatal MSG treatment in both the CMC and Hp. Moreover, neonatal MSG treatment increased the expression levels of the studied VEGF-A/VEGFR-2 signaling pathway proteins, particularly in the CMC. We conclude that VEGF-A/VEGFR-2 signaling pathway activation could be part of the neuroprotective mechanisms that attempt to compensate for neuronal damage induced by neonatal MSG treatment and possibly also in other conditions involving excitotoxicity.

Investigation of the Effects of Monosodium Glutamate on the Embryonic Development of the Eye in Chickens

MSG is the most ubiquitous food additive in the food industry. The aim of this report was to investigate the effects of in ovo MSG administration on embryonic chicken eye development using histological and histometric methods. A total of 410 fertilized eggs obtained from Babcock Brown laying hens (Gallus gallus domesticus) were used and divided into 5 groups: I (untreated control), II (vehicle control), III (0.12 mg/g egg MSG), IV (0.6 mg/g egg MSG), and V (1.2 mg/g egg MSG), and injections were performed via the egg yolk. At incubation day 15, 18, and 21, 6 embryos from each group were sacrificed by decapitation and pieces of eye tissue were obtained. In all MSG groups, it was determined that both corneal epithelium thickness and total corneal thickness decreased at incubation time points 15, 18, and 21 days compared with the controls (p < 0.05). The total retinal thickness, thickness of the outer nuclear layer (ONL), inner nuclear layer (INL), ganglion cell layer (GL), and nerve fibre layers (NFL), as well as the number of ganglion cells decreased significantly at incubation days 15, 18, and 21 (p < 0.05), and degenerative changes such as vacuolar degeneration and retinal pigment epithelial detachment were also observed. In conclusion, MSG in ovo administration can affect the cornea and distinct layers of retinal cells.

Determining the effects of in ovo administration of monosodium glutamate on the embryonic development of brain in chickens

Monosodium glutamate (MSG) is a popular flavor enhancer largely used in the food industry. Although numerous studies have reported the neurotoxic effects of MSG on humans and animals, there is limited information about how it affects embryonic brain development. Thus, this study aimed to determine the effects of in ovo administered MSG on embryonic brain development in chickens. For this purpose, 410 fertilized chicken eggs were divided into 5 groups as control, distilled water, 0.12, 0.6 and 1.2 mg/g egg MSG, and injections were performed via the egg yolk. On days 15, 18, and 21 of the incubation period, brain tissue samples were taken from all embryos and chicks. The mortality rates of MSG-treated groups were significantly higher than those of the control and distilled water groups. The MSG-treated groups showed embryonic growth retardation and various structural abnormalities such as abdominal hernia, unilateral anophthalmia, hemorrhage, brain malformation, and the curling of legs and fingers. The relative embryo and body weights of the MSG-treated groups were significantly lower than those of the control group on incubation days 18 and 21. Histopathological evaluations revealed that MSG caused histopathological changes such as necrosis, neuronophagia, and gliosis in brain on incubation days 15, 18, and 21. There was a significant increase in the number of necrotic neurons in the MSG-treated groups compared to the control and distilled water groups in the hyperpallium, optic tectum and hippocampus regions. Proliferating cell nuclear antigen (PCNA) positive cells in brain were found in the hyperpallium, optic tectum, and hippocampus regions; there were more PCNA(+) immunoreactive cells in MSG-treated groups than in control and distilled water groups. In conclusion, it was determined that in ovo MSG administered could adversely affect embryonic growth and development in addition to causing necrosis in the neurons in the developing brain.

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.

Neonatal exposure to monosodium glutamate results in impaired auditory brainstem structure and function

Excitotoxic injury during the neonatal period has been shown to result in neurodegenerative changes in several different brain regions. Exposure to monosodium glutamate (MSG) during the first two postnatal weeks results in glutamate neurotoxicity in the cochlea and has been shown to result in damage to cochlear hair cells and fewer neurons in the spiral ganglion. Further, we have shown that such exposure results in fewer neurons in the cochlear nucleus and superior olivary complex and abnormal expression of the calcium binding proteins calbindin and calretinin. Based on these findings, we hypothesized that neonatal MSG exposure would result in loss of neurons at more rostral levels in the auditory brainstem, and this exposure would result in abnormal brainstem auditory evoked potentials. We identified a significantly lower density of neurons in the spiral ganglion, heterogenous loss of neurons in the globular bushy cell-trapezoid body circuit, and fewer neurons in the nuclei of the lateral lemniscus and central nucleus of the inferior colliculus. The most severe loss of neurons was found in the inferior colliculus. Click-evoked auditory brainstem responses revealed significantly higher thresholds and longer latency responses, but these did not deteriorate with age. These results, together with our previous findings, indicate that neonatal exposure to MSG results in fewer neurons throughout the entire auditory brainstem and results in abnormal auditory brainstem responses.

Tualang Honey Reduced Neuroinflammation and Caspase-3 Activity in Rat Brain after Kainic Acid-Induced Status Epilepticus

The protective effect of tualang honey (TH) on neuroinflammation and caspase-3 activity in rat cerebral cortex, cerebellum, and brainstem after kainic acid- (KA-) induced status epilepticus was investigated. Male Sprague-Dawley rats were pretreated orally with TH (1.0 g/kg body weight) five times at 12 h intervals. KA (15 mg/kg body weight) was injected subcutaneously 30 min after last oral treatment. Rats were sacrificed at 2 h, 24 h, and 48 h after KA administration. Neuroinflammation markers and caspase-3 activity were analyzed in different brain regions 2 h, 24 h, and 48 h after KA administration. Administration of KA induced epileptic seizures. KA caused significant (p < 0.05) increase in the level of tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), glial fibrillary acidic protein (GFAP), allograft inflammatory factor 1 (AIF-1), and cyclooxygenase-2 (COX-2) and increase in the caspase-3 activity in the rat cerebral cortex, cerebellum, and brainstem at multiple time points. Pretreatment with TH significantly (p < 0.05) reduced the elevation of TNF-α, IL-1β, GFAP, AIF-1, and COX-2 level in those brain regions at multiple time points and attenuated the increased caspase-3 activity in the cerebral cortex. In conclusion, TH reduced neuroinflammation and caspase-3 activity after kainic acid- (KA-) induced status epilepticus.

Glutamate Neonatal Excitotoxicity Modifies VEGF-A, VEGF-B, VEGFR-1 and VEGFR-2 Protein Expression Profiles During Postnatal Development of the Cerebral Cortex and Hippocampus of Male Rats

Vascular endothelial growth factor (VEGF) exerts both neuroprotective and proinflammatory effects in the brain, depending on the VEGF (A-E) and VEGF receptor (VEGFR1-3) types involved. Neonatal monosodium glutamate (MSG) treatment triggers an excitotoxic degenerative process associated with several neuropathological conditions, and VEGF messenger RNA (mRNA) expression is increased at postnatal day (PD) 14 in rat hippocampus (Hp) following the treatment. The aim of this work was to establish the changes in immunoreactivity to VEGF-A, VEGF-B, VEGFR-1 and VEGFR-2 proteins induced by neonatal MSG treatment (4 g/kg, subcutaneous, at PD1, 3, 5 and 7) in the cerebral motor cortex (CMC) and Hp. Samples collected from PD2 to PD60 from control and MSG-treated male Wistar rats were assessed by western blotting for each protein. Considering that immunoreactivity measured by western blotting is related to the protein expression level, we found that each protein in each cerebral region has a specific expression profile throughout the studied ages, and all profiles were differentially modified by MSG. Specifically, neonatal MSG treatment significantly increased the immunoreactivity to the following: (1) VEGF-A at PD8-PD10 in the CMC and at PD6-PD8 in the Hp; (2) VEGF-B at PD2, PD6 and PD10 in the CMC and at PD8-PD9 in the Hp; and (3) VEGFR-2 at PD6-PD8 in the CMC and at PD21-PD60 in the Hp. Also, MSG significantly reduced the immunoreactivity to the following: (1) VEGF-B at PD8-PD9 and PD45-PD60 in the CMC; and (2) VEGFR-1 at PD4-PD6 and PD14-PD21 in the CMC and at PD4, PD9-PD10 and PD60 in the Hp. Our results indicate that VEGF-mediated signalling is involved in the excitotoxic process triggered by neonatal MSG treatment and should be further characterized.

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.

Neuronal Damage Induced by Perinatal Asphyxia Is Attenuated by Postinjury Glutaredoxin-2 Administration

The general disruption of redox signaling following an ischemia-reperfusion episode has been proposed as a crucial component in neuronal death and consequently brain damage. Thioredoxin (Trx) family proteins control redox reactions and ensure protein regulation via specific, oxidative posttranslational modifications as part of cellular signaling processes. Trx proteins function in the manifestation, progression, and recovery following hypoxic/ischemic damage. Here, we analyzed the neuroprotective effects of postinjury, exogenous administration of Grx2 and Trx1 in a neonatal hypoxia/ischemia model. P7 Sprague-Dawley rats were subjected to right common carotid ligation or sham surgery, followed by an exposure to nitrogen. 1 h later, animals were injected i.p. with saline solution, 10 mg/kg recombinant Grx2 or Trx1, and euthanized 72 h postinjury. Results showed that Grx2 administration, and to some extent Trx1, attenuated part of the neuronal damage associated with a perinatal hypoxic/ischemic damage, such as glutamate excitotoxicity, axonal integrity, and astrogliosis. Moreover, these treatments also prevented some of the consequences of the induced neural injury, such as the delay of neurobehavioral development. To our knowledge, this is the first study demonstrating neuroprotective effects of recombinant Trx proteins on the outcome of neonatal hypoxia/ischemia, implying clinical potential as neuroprotective agents that might counteract neonatal hypoxia/ischemia injury.

Intrinsic apoptosis and proinflammatory cytokines regulated in human astrocytes infected with enterovirus 71

Enterovirus 71 (EV71) has emerged as a clinically important neurotropic virus following poliovirus eradication. However, the mechanism of EV71-induced neurological manifestation remains largely unclear. In this study, we showed that human astrocytes were susceptible to EV71 and viral RNA was first detected at 12 h post-infection (p.i.), whilst viral proteins were detected at 36 h p.i. EV71-infected astrocytes underwent apoptosis, in which cytochrome c was released from mitochondria to the cytosol and caspase-9 was activated. Interestingly, caspase-2 and -8 were not cleaved or activated during the infection, whilst a selective inhibitor of caspase-9, Z-LEHD-FMK, blocked the cleavage of caspase-3 and -7, indicating that only the mitochondria-mediated intrinsic apoptotic pathway was activated in EV71-infected astrocytes. EV71 infection also induced proinflammatory cytokines, including IL-6, IL-8, CCL5 and IFN-γ-inducible protein (IP)-10 in astrocytes, which may play a critical role in EV71-induced neuroinflammation and neurological complications. By using inhibitors of mitogen-activated protein kinases (MAPKs), we demonstrated that the induction of the cytokines was mainly regulated by the MAPK p38 signalling pathway as a significant reduction of the cytokines was observed when treated with p38 inhibitors. This study demonstrated that human astrocytes were susceptible to EV71, and the infection led to intrinsic apoptosis and induction of p38-regulated proinflammatory cytokines. These findings further our understanding of the neuropathogenesis in severe cases of EV71 infection.

Alteration of pentylenetetrazole-induced seizure threshold by chronic administration of ginger (Zingiber officinale) extract in male mice

CONTEXT

Zingiber officinale Roscoe (Zingiberaceae), or ginger, used in traditional Chinese medicine, has antioxidant activity and neuroprotective effects. The effects of this plant on clonic seizure have not yet been studied.

OBJECTIVE

The present study evaluated the anticonvulsant effect of ginger in a model of clonic seizures induced with pentylenetetrazole (PTZ) in male mice.

MATERIALS AND METHODS

The anticonvulsant effect of Z. officinale was investigated using i.v. PTZ-induced seizure models in mice. Different doses of the hydroethanolic extract of Z. officinale (25, 50, and 100 mg/kg) were administered intraperitonal (i.p.), daily for 1 week before induction of PTZ. Phenobarbital sodium (30 mg/kg), a reference standard, was also tested for comparison. The effect of ginger on to the appearance of three separate seizure endpoints, e.g., myoclonic, generalized clonic, and tonic extension phase, was recorded.

RESULTS

Hydroethanolic extract of Z. officinale significantly increased the onset time of myoclonic seizure at doses of 25-100 mg/kg (55.33 ± 1.91 versus 24.47 ± 1.33 mg/kg, p < 0.001) and significantly prevented generalized clonic (74.64 ± 3.52 versus 47.72 ± 2.31 mg/kg, p < 0.001) and increased the threshold for the forelimb tonic extension (102.6 ± 5.39 versus 71.82 ± 7.82 mg/kg, p < 0.01) seizure induced by PTZ compared with the control group.

DISCUSSION AND CONCLUSION

Based on the results, the hydroethanolic extract of ginger has anticonvulsant effects, possibly through an interaction with inhibitory and excitatory systems, antioxidant mechanisms, and oxidative stress inhibition.

High dosage of monosodium glutamate causes deficits of the motor coordination and the number of cerebellar Purkinje cells of rats

Monosodium glutamate (MSG) has been widely used throughout the world as a flavoring agent of food. However, MSG at certain dosages is also thought to cause damage to many organs, including cerebellum. This study aimed at investigating the effects of different doses of MSG on the motor coordination and the number of Purkinje cells of the cerebellum of Wistar rats. A total of 24 male rats aged 4 to 5 weeks were divided into four groups, namely, control (C), T2.5, T3, and T3.5 groups, which received intraperitoneal injection of 0.9% sodium chloride solution, 2.5 mg/g body weight (bw) of MSG, 3.0 mg/g bw of MSG, and 3.5 mg/g bw of MSG, respectively, for 10 consecutive days. The motor coordination of the rats was examined prior and subsequent to the treatment. The number of cerebellar Purkinje cells was estimated using physical fractionator method. It has been found that the administration of MSG at a dosage of 3.5 mg/g bw, but not at lower dosages, caused a significant decrease of motor coordination and the estimated total number of Purkinje cells of rats. There was also a significant correlation between motor coordination and the total number of Purkinje cells.

Excitotoxicity triggered by neonatal monosodium glutamate treatment and blood-brain barrier function

It is likely that monosodium glutamate (MSG) is the excitotoxin that has been most commonly employed to characterize the process of excitotoxicity and to improve understanding of the ways that this process is related to several pathological conditions of the central nervous system. Excitotoxicity triggered by neonatal MSG treatment produces a significant pathophysiological impact on adulthood, which could be due to modifications in the blood-brain barrier (BBB) permeability and vice versa. This mini-review analyzes this topic through brief descriptions about excitotoxicity, BBB structure and function, role of the BBB in the regulation of Glu extracellular levels, conditions that promote breakdown of the BBB, and modifications induced by neonatal MSG treatment that could alter the behavior of the BBB. In conclusion, additional studies to better characterize the effects of neonatal MSG treatment on excitatory amino acids transporters, ionic exchangers, and efflux transporters, as well as the role of the signaling pathways mediated by erythropoietin and vascular endothelial growth factor in the cellular elements of the BBB, should be performed to identify the mechanisms underlying the increase in neurovascular permeability associated with excitotoxicity observed in several diseases and studied using neonatal MSG treatment.

Acute administration of ginger (Zingiber officinale rhizomes) extract on timed intravenous pentylenetetrazol infusion seizure model in mice

PURPOSE

Zingiber officinale (Zingiberaceae) or ginger, which is used in traditional medicine has antioxidant activity and neuroprotective effects. The effects of this plant on clonic seizure have not yet been studied. The present study evaluated the anticonvulsant effect of ginger in a model of clonic seizures induced with pentylenetetrazole (PTZ) in male mice.

MATERIALS AND METHODS

The anticonvulsant effect of Z. officinale was investigated using i.v. PTZ-induced seizure models in mice. Different doses of the hydroethanolic extract of Z. officinale (25, 50, and 100mg/kg) were administered intraperitonal (i.p.), 2 and 24h before induction of PTZ. Phenobarbital sodium (30mg/kg), a reference standard, was also tested for comparison. The effect of ginger on to the appearance of three separate seizure endpoints (myoclonic, generalized clonus and forelimb tonic extension phase) was recorded.

RESULTS

The results showed that the ginger extract has anticonvulsant effects in all the experimental treatment groups of seizure tested as it significantly increased the seizure threshold. Hydroethanolic extract of Z. officinale significantly increased the onset time of myoclonic seizure at doses of 25-100mg/kg (p<0.001) and significantly prevented generalized clonic (p<0.001) and increased the threshold for the forelimb tonic extension (p<0.01) seizure 2 and 24h before induction of PTZ compared with control group.

CONCLUSION

Based on the results the hydroethanolic extract of ginger has anticonvulsant effects, possibly through an interaction with inhibitory and excitatory system, antioxidant mechanisms, oxidative stress and calcium channel inhibition.

Proposed toxic and hypoxic impairment of a brainstem locus in autism

Electrophysiological findings implicate site-specific impairment of the nucleus tractus solitarius (NTS) in autism. This invites hypothetical consideration of a large role for this small brainstem structure as the basis for seemingly disjointed behavioral and somatic features of autism. The NTS is the brain's point of entry for visceral afference, its relay for vagal reflexes, and its integration center for autonomic control of circulatory, immunological, gastrointestinal, and laryngeal function. The NTS facilitates normal cerebrovascular perfusion, and is the seminal point for an ascending noradrenergic system that modulates many complex behaviors. Microvascular configuration predisposes the NTS to focal hypoxia. A subregion--the "pNTS"--permits exposure to all blood-borne neurotoxins, including those that do not readily transit the blood-brain barrier. Impairment of acetylcholinesterase (mercury and cadmium cations, nitrates/nitrites, organophosphates, monosodium glutamate), competition for hemoglobin (carbon monoxide, nitrates/nitrites), and higher blood viscosity (net systemic oxidative stress) are suggested to potentiate microcirculatory insufficiency of the NTS, and thus autism.

Exposure to enriched environment decreases neurobehavioral deficits induced by neonatal glutamate toxicity

Environmental enrichment is a popular strategy to enhance motor and cognitive performance and to counteract the effects of various harmful stimuli. The protective effects of enriched environment have been shown in traumatic, ischemic and toxic nervous system lesions. Monosodium glutamate (MSG) is a commonly used taste enhancer causing excitotoxic effects when given in newborn animals. We have previously demonstrated that MSG leads to a delay in neurobehavioral development, as shown by the delayed appearance of neurological reflexes and maturation of motor coordination. In the present study we aimed at investigating whether environmental enrichment is able to decrease the neurobehavioral delay caused by neonatal MSG treatment. Newborn pups were treated with MSG subcutaneously on postnatal days 1, 5 and 9. For environmental enrichment, we placed rats in larger cages, supplemented with different toys that were altered daily. Normal control and enriched control rats received saline treatment only. Physical parameters such as weight, day of eye opening, incisor eruption and ear unfolding were recorded. Animals were observed for appearance of reflexes such as negative geotaxis, righting reflexes, fore- and hindlimb grasp, fore- and hindlimb placing, sensory reflexes and gait. In cases of negative geotaxis, surface righting and gait, the time to perform the reflex was also recorded daily. For examining motor coordination, we performed grid walking, footfault, rope suspension, rota-rod, inclined board and walk initiation tests. We found that enriched environment alone did not lead to marked alterations in the course of development. On the other hand, MSG treatment caused a slight delay in reflex development and a pronounced delay in weight gain and motor coordination maturation. This delay in most signs and tests could be reversed by enriched environment: MSG-treated pups kept under enriched conditions showed no weight retardation, no reflex delay in some signs and performed better in most coordination tests. These results show that environmental enrichment is able to decrease the neurobehavioral delay caused by neonatal excitotoxicity.

Lentiviral vector-mediated stable expression of sTNFR-Fc in human macrophage and neuronal cells as a potential therapy for neuroAIDS

Background

Human immunodeficiency virus type 1 (HIV-1) infection frequently causes neurologic disease, which is the result of viral replication and activation of macrophages and microglia in the CNS, and subsequent secretion of high levels of neurotoxic products, including tumor necrosis factor-α (TNF-α). We therefore hypothesized that a soluble TNF-α antagonist might have potential utility as a neuroprotective effecter molecule, and conducted proof-of-concept studies to test this hypothesis.

Methods

To develop novel therapeutics for the treatment of neuroAIDS, we constructed and characterized a soluble TNF receptor (sTNFR)-Fc fusion protein with the goal of neutralizing TNF-α, and tested the stability of expression of this gene following delivery by a lentiviral vector.

Results

High-titer lentiviral vectors were prepared, allowing efficient transduction of macrophage/glial and neuronal cell lines, as well as primary rat cerebellar neurons. Efficient, stable secretion of sTNFR-Fc was demonstrated in supernatants from transduced cell lines over 20 passages, using both western blot and ELISA. Biological activity of the secreted sTNFR-Fc was confirmed by TNF-specific in vitro protein binding and functional blocking assays. Finally, the secreted protein was shown to protect neuronal cells from TNF-α, HIV-1 Tat-, and gp120-mediated neurotoxicity.

Conclusions

These results demonstrate that lentiviral vector mediated expression of sTNFR-Fc may have potential as a novel therapy for neuroAIDS.

TNF-α potentiates glutamate-induced spinal cord motoneuron death via NF-κB

Besides glutamate excitotoxicity, the neuroinflammatory response is emerging as a relevant contributor to motoneuron loss in amyotrophic lateral sclerosis (ALS). In this regard, high levels of circulating proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) have been shown both in human patients and in animal models of ALS. The aim of this work was to study the effects of TNF-α on glutamate-induced excitotoxicity in spinal cord motoneurons. In rat spinal cord organotypic cultures chronic glutamate excitotoxicity, induced by the glutamate-uptake inhibitor threohydroxyaspartate (THA), resulted in motoneuron loss that was associated with a neuroinflammatory response. In the presence of TNF-α, THA-induced excitotoxic motoneuron death was potentiated. Co-exposure to TNF-α and THA also resulted in down-regulation of the astroglial glutamate transporter 1 (GLT-1) and in increased extracellular glutamate levels, which were prevented by nuclear factor-kappaB (NF-κB) inhibition. Furthermore, TNF-α and THA also cooperated in the induction of oxidative stress in a mechanism involving the NF-κB signalling pathway as well. The inhibition of this pathway abrogated the exacerbation of glutamate-mediated motoneuron death induced by TNF-α. These data link two important pathogenic mechanisms, excitotoxicity and neuroinflammation, suggested to play a role in ALS and, to our knowledge, this is the first time that TNF-α-induced NF-κB activation has been reported to potentiate glutamate excitotoxicity on motononeurons.

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.

TNFalpha and TNF receptor 1 expression in the mixed neuronal-glial cultures of hippocampal dentate gyrus exposed to glutamate or trimethyltin

We examined the expression and cellular localization of tumor necrosis factor alpha (TNFalpha) and its type 1 receptor (TNFR1) in mixed neuronal-glial cultures of rat hippocampal dentate gyrus exposed to glutamate (GLU) or trimethyltin (TMT). Our previous studies demonstrated that both pathogenic factors evoked neuronal apoptosis, however, TMT was more potent and caused cell death in almost 90% of neurons. Observed neurodegeneration was accompanied by morphological changes of microglia. In the current study, using RT-PCR and Western blotting analysis, we found that GLU and TMT induced increase in TNFalpha mRNA and protein levels. The induction of transcription was stronger following GLU treatment, however the protein production was much more intensive after TMT exposure. Double fluorescent labeling for TNFalpha, TNFR1 and cellular markers revealed cytokine expression in microglia and some neurons. On the other hand, majority of neuronal cells displayed TNFR1 immunoreactivity, in control and in treated cultures. Moreover, TMT led to a strong increase in TNFR1 expression in astrocytes, which displayed remarkable, granular staining for the cytokine receptor. Western blotting for TNFR1 revealed enhanced protein expression only in cultures treated with TMT. This is the first report demonstrating the changes of expression of TNFalpha and TNFR1 in hippocampal dentate gyrus cultures treated with GLU or TMT. Our results indicate that TNFalpha may be involved in the mechanism of neurotoxic effects evoked by both pathogenic factors and suggest that astrocytes via TNFR1 may enhance TMT-induced injury.

Neuronal cell death due to glutamate excitotocity is mediated by P38 activation in the rat cerebral cortex

Excitotoxic neuronal death occurs through the activation of NMDA and non-NMDA glutamatergic receptors in the CNS. Glutamate also induces strong activation of p38 and indeed, cell death can be prevented by inhibitors of the p38 pathway. Furthermore, intracellular signals generated by AMPA receptors activate the stress sensitive MAP kinases implicated in apoptotic neuronal death, such as JNK and p38. To investigate the relationship between these elements, we have used immunohistochemistry to analyze the expression of GluR2 in the cerebral cortex of postnatal rats (postnatal Day [PD] 8 and 14) after administering them with monosodium glutamate (MSG; 4 mg/g body weight on PD1, 3, 5, and 7). Similarly, the expression of REST, Fas-L and Bcl-2 mRNA transcripts in animals exposed to a p38 inhibitor, SB203580 (0.42 microg/g body weight, administered subcutaneously) was determined by reverse transcriptase-PCR. The enhanced GluR2-expression in the cerebral cortex at PD8 and the down regulation of this receptor at PD14 was correlated with neuronal damage induced by excitotoxicity. In addition, the enhanced expression of REST at PD8 and PD14 suggests that the induction of REST transcription contributes to glutamate-induced excitotoxic neurodegeneration, possibly by modulating GluR2 expression. Fas-L and Bcl-2 over expression at PD8 and their subsequent down regulation at PD14 also suggests that Fas-L could be the direct effector of apoptosis in the cerebral cortex. On the other hand, the presence of Bcl-2 at PD8 could attenuate certain survival signals in neurons under these neurotoxic conditions. Thus, a change in glutamate receptor composition, and enhanced Fas-L and Bcl-2 expression, coupled with activation of the p38/SAPK pathway appear to be events involved in the neuronal apoptosis induced under neurotoxic conditions.

Role of the pro-inflammatory cytokines TNF-alpha and IL-1beta in HIV-associated dementia

Human immunodeficiency virus-1 (HIV-1)-infected and immune-activated macrophages and microglia secrete neurotoxins. Two of these neurotoxins are the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta), which are thought to play a major role in inducing neuronal death. Both TNF-alpha and IL-1beta increase the permeability of the blood-brain barrier, through which subsequently HIV-infected monocytes can enter the brain. They both induce over-stimulation of the NMDA-receptor via several pathways, resulting in a lethal neuronal increase in Ca(2+) levels. Additionally, TNF-alpha co-operates with several other proinflammatory mediators to enhance their toxic effects. Although most research has focused on the neurotoxic effects of TNF-alpha and IL-1beta in HAD, there is also evidence that these cytokines can be neuroprotective. In this paper the effect of TNF-alpha and IL-1beta on neuronal life and death in HAD is discussed.

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.

Inflammation in areas of remote changes following focal brain lesion

Focal brain lesions can lead to metabolic and structural changes in areas distant from but connected to the lesion site. After focal ischemic or excitotoxic lesions of the cortex and/or striatum, secondary changes have been observed in the thalamus, substantia nigra pars reticulata, hippocampus and spinal cord. In all these regions, inflammatory changes characterized by activation of microglia and astrocytes appear. In the thalamus, substantia nigra pars reticulata and hippocampus, an expression of proinflammatory cytokine like tumor necrosis factor-alpha and interleukin-1beta is induced. However, time course of expression and cellular localisation differ between these regions. Neuronal damage has consistently been observed in the thalamus, substantia nigra and spinal cord. It can be present in the hippocampus depending on the procedure of induction of focal cerebral ischemia. This secondary neuronal damage has been linked to antero- and retrograde degeneration. Anterograde degeneration is associated with somewhat later expression of cytokines, which is localised in neurons. In case of retrograde degeneration, the expression of cytokines is earlier and is localised in astrocytes. Pharmacological intervention aiming at reducing expression of tumor necrosis factor-alpha leads to reduction of secondary neuronal damage. These first results suggest that the inflammatory changes in remote areas might be involved in the pathogenesis of secondary neuronal damage.

Proinflammatory cytokines and apoptosis following glutamate-induced excitotoxicity mediated by p38 MAPK in the hippocampus of neonatal rats

The proinflammatory cytokines TNF-alpha, IL-1beta, and IL-6 rise during neuronal damage and activate the apoptotic mitogen-activated protein kinase p38. We studied apoptosis, the levels of TNF-alpha, IL-1beta, and IL-6, and the cell type producing TNF-alpha in rats at 8, 10, and 14 days of age after neonatal exposure to glutamate, which induces neuronal damage. TNF-alpha production was significantly increased by glutamate, but inhibited by SB203580 (a p38 inhibitor). TNF-alpha, IL-1beta, and IL-6 mRNA levels increased, but SB203580 did not modify their expression. Thus, the p38 signaling pathway influences the expression of inflammatory genes and its inhibition may offer anti-inflammatory therapy.

Regulation of cytokine-induced neuron death by ovarian hormones: involvement of antiapoptotic protein expression and c-JUN N-terminal kinase-mediated proapoptotic signaling

Mechanisms underlying the divergent effects of ovarian hormones on neuron death induced by TNFalpha were investigated in differentiated PC12 cells (dPC12). dPC12 cells were exposed to 17beta-estradiol (E, 1.0 nm), progesterone (P, 100 nm), or a combination of both hormones for 0-72 h before treatment with TNFalpha (0-150 ng) to induce cell death. Cells undergoing apoptosis were identified by a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling assay and fluorescence-activated cell sorting after 18 h. Cell death induced by TNFalpha was decreased 89% after E treatment and increased 2-fold after P treatment compared with cells treated with TNFalpha alone. Treatment with E for 24 h before TNFalpha exposure was required for maximum neuroprotection, whereas P-enhanced death was maximal after a 30-min P treatment. TNFalpha induced a 3-fold increased activity of c-JUN-N-terminal kinase (JNK) 1 in d PC12 cells within 20 min that could be increased 5- to 8-fold by P together with TNFalpha. A peptide inhibitor of JNK1 abrogated P enhancement of TNFalpha-mediated dPC12 death but had only a minimal effect on cell death by TNFalpha alone. Inhibition of caspase-8 activation reduced death induced by TNFalpha alone but was much less effective for P+TNF. P alone did not activate caspase-8. E increased estrogen receptor alpha (ERalpha) and Bcl-xL expression and all but abolished TNFalpha receptor 1 (TNFR1) expression. P decreased ERalpha and Bcl-xL expression and doubled TNFR1 expression. These data suggest that P regulates apoptosis or survival through augmentation of JNK signaling and altered TNFR1 expression, whereas E mainly affects the expression of BCL-xL, TNFR1, and ERalpha.

Tumor necrosis factor-alpha at the crossroads of neuronal life and death during HIV-associated dementia

Human immunodeficiency type-1 (HIV-1) infection is known to cause disorders of the CNS, including HIV-associated dementia (HAD). It is suspected that tumor necrosis factor-alpha (TNF-alpha) released by infected microglia and macrophages play a role in neuronal injury seen in HAD patients. Accordingly, studies suggest that the level of TNF-alpha mRNA increases with increasing severity of dementia in patients, and that inhibitors of TNF-alpha release reduces neuronal injury in murine model of HAD. However, the exact role of TNF-alpha in relation to neuronal dysfunction is a matter of ongoing debate. One school of thought hails TNF-alpha as the inducer and mediator of neurodegeneration and their evidence suggest that TNF-alpha kill neurons directly by recruiting caspases or may kill indirectly by various means. In sharp contrast to this, another concept theory envisages a role for TNF-alpha in negotiating neuroprotection during HAD. The current compilation examines these contradictory concepts, and evaluates their efficacy in the light of TNF-alpha signaling. It also attempts to elaborate the current consensus outlook of TNF-alpha's role during HAD.