Differential effect of beta-N-oxalylamino-L-alanine, the Lathyrus sativus neurotoxin, and (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate on the excitatory amino acid and taurine levels in the brain of freely moving rats

Proteomic Changes in Chick Brain Proteome Post Treatment with Lathyrus Sativus Neurotoxin, β-N-Oxalyl-L-α,β-Diaminopropionic Acid (L-ODAP): A Better Insight to Transient Neurolathyrism

Neurolathyrism is a neurodegenerative disorder characterized by spastic paraplegia resulting from the excessive consumption of Lathyrus sativus (Grass pea). β-N-Oxalyl-L-α,β-diaminopropionic acid (L-ODAP) is the primary neurotoxic component in this pea. The present study attempted to evaluate the proteome-wide alterations in chick brain 2 hr and 4 hr post L-ODAP treatment. Proteomic analysis of chick brain homogenates revealed several proteins involved in cytoskeletal structure, signaling, cellular metabolism, free radical scavenging, oxidative stress and neurodegenerative disorders were initially up-regulated at 2 hr and later recovered to normal levels by 4 hr. Since L-ODAP mediated neurotoxicity is mainly by excitotoxicity and oxidative stress related dysfunctions, this study further evaluated the role of L-ODAP in apoptosis in vitro using human neuroblastoma cell line, IMR-32. The in vitro studies carried out at 200 μM L-ODAP for 4 hr indicate minimal intracellular ROS generation and alteration of mitochondrial membrane potential though not leading to apoptotic cell death. L-ODAP at low concentrations can be explored as a stimulator of various reactive oxygen species (ROS) mediated cell signaling pathways not detrimental to cells. Insights from our study may provide a platform to explore the beneficial side of L-ODAP at lower concentrations. This study is of significance especially in view of the Government of India lifting the ban on cultivation of low toxin Lathyrus varieties and consumption of this lentil.

The Role of Primary Motor Cortex (M1) Glutamate and GABA Signaling in l-DOPA-Induced Dyskinesia in Parkinsonian Rats

Long-term treatment of Parkinson's disease with l-DOPA almost always leads to the development of involuntary movements termed l-DOPA-induced dyskinesia. Whereas hyperdopaminergic signaling in the basal ganglia is thought to cause dyskinesia, alterations in primary motor cortex (M1) activity are also prominent during dyskinesia, suggesting that the cortex may represent a therapeutic target. The present study used the rat unilateral 6-hydroxydopamine lesion model of Parkinson's disease to characterize in vivo changes in GABA and glutamate neurotransmission within M1 and determine their contribution to behavioral output. 6-Hydroxydopamine lesion led to parkinsonian motor impairment that was partially reversed by l-DOPA. Among sham-lesioned rats, l-DOPA did not change glutamate or GABA efflux. Likewise, 6-hydroxydopamine lesion did not impact GABA or glutamate among rats chronically treated with saline. However, we observed an interaction of lesion and treatment whereby, among lesioned rats, l-DOPA given acutely (1 d) or chronically (14-16 d) reduced glutamate efflux and enhanced GABA efflux. Site-specific microinjections into M1 demonstrated that l-DOPA-induced dyskinesia was reduced by M1 infusion of a D1 antagonist, an AMPA antagonist, or a GABAA agonist. Overall, the present study demonstrates that l-DOPA-induced dyskinesia is associated with increased M1 inhibition and that exogenously enhancing M1 inhibition may attenuate dyskinesia, findings that are in agreement with functional imaging and transcranial magnetic stimulation studies in human Parkinson's disease patients. Together, our study suggests that increasing M1 inhibitory tone is an endogenous compensatory response designed to limit dyskinesia severity and that potentiating this response is a viable therapeutic strategy.

SIGNIFICANCE STATEMENT

Most Parkinson's disease patients will receive l-DOPA and eventually develop hyperkinetic involuntary movements termed dyskinesia. Such symptoms can be as debilitating as the disease itself. Although dyskinesia is associated with dynamic changes in primary motor cortex physiology, to date, there are no published studies investigating in vivo neurotransmitter release in M1 during dyskinesia. In parkinsonian rats, l-DOPA administration reduced M1 glutamate efflux and enhanced GABA efflux, coincident with the emergence of dyskinetic behaviors. Dyskinesia could be reduced by local M1 modulation of D1, AMPA, and GABAA receptors, providing preclinical support for the notion that exogenously blunting M1 signaling (pharmacologically or with cortical stimulation) is a therapeutic approach to the treatment of debilitating dyskinesias.

Modulation of extracellular d-serine content by calcium permeable AMPA receptors in rat medial prefrontal cortex as revealed by in vivo microdialysis

In mammalian brains, d-serine has been shown to be required for the regulation of glutamate neurotransmission as an endogenous co-agonist for the N-methyl-d-aspartate type glutamate receptor that is essential for the expression of higher-order brain functions. The exact control mechanisms for the extracellular d-serine dynamics, however, await further elucidation. To obtain an insight into this issue, we have characterized the effects of agents acting at the α-amino-3-hydroxy-5-methyl-4-isoxazolepropioinic acid (AMPA) type glutamate receptor on the extracellular d-serine contents in the medial prefrontal cortex of freely moving rats by an in vivo microdialysis technique in combination with high-performance liquid chromatography with fluorometric detection. In vivo experiments are needed in terms of a crucial role of d-serine in the neuron-glia communications despite the previous in vitro studies on AMPA receptor-d-serine interactions using the separated preparations of neurons or glial cells. Here, we show that the intra-cortical infusion of (S)-AMPA, an active enantiomer at the AMPA receptor, causes a significant and concentration-dependent reduction in the prefrontal extracellular contents of d-serine, which is reversed by an AMPA/kainate receptor antagonist, 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide disodium salt, and a calcium permeable AMPA receptor antagonist, 1-naphthyl acetyl spermine. The d-serine reducing effects of (S)-AMPA are augmented by co-infusion of cyclothiazide that prevents AMPA receptor desensitization. Our data support the view that a calcium permeable AMPA receptor subtype may exert a phasic inhibitory control on the extracellular d-serine release in the mammalian prefrontal cortex in vivo.

Comparison of alterations in amino acids content in cultured astrocytes or neurons exposed to methylmercury separately or in co-culture

Methylmercury (MeHg) is an environmental toxicant that induces enduring neuropsychological deficits in humans. Although the mechanisms associated with MeHg-induced neurotoxicity have not yet been fully elucidated, some lines of evidence point out to excitatory amino acids dyshomeostasis as an important outcome of MeHg exposure. The present study was designed to characterize the effects of MeHg on amino acid content in co-cultured astrocytes and neurons or in each cell type under solitary conditions. The results showed that glutamate concentrations significantly decreased in neurons, but not in astrocyte cultures exposed to 10 microM MeHg. The decrease in neurons was fully reversed when these cells were co-cultured with astrocytes. The content of other amino acids (aspartate, alanine, glycine and serine) decreased upon exposure to 10 microM MeHg in both neurons and astrocytes cultured in solitary conditions, although the effect was generally smaller in astrocytes than in neurons. However, the content of these amino acids in each of the cell types was indistinguishable from controls when co-cultures were treated with MeHg. Overall, the results indicate that astrocytes, which are more resistant to amino acid modulation by MeHg, can (i) mitigate the effects of MeHg that occur in neurons cultured in solitary conditions and (ii) become themselves more MeHg resistant in the presence of neurons. Delineating the mechanisms underlying the mutual neuroprotective effects of astrocytes and neurons in co-culture to MeHg-induced amino acid imbalance requires further investigation.

Lathyrus sativus (grass pea) and its neurotoxin ODAP

Lathyrus sativus (grass pea) is a high-yielding, drought-resistant legume consumed as a food in Northern India and neighboring countries as well as in Ethiopia. Its development into an important food legume, however, has been hindered by the presence of the neurotoxin - beta-N-oxalyl-L-alpha,beta-diaminopropionic acid (beta-ODAP) in seeds which, if consumed in large quantities for prolonged periods, can cause irreversible paralysis. Recently, some low-toxin lines have been developed that may prove safe for both animal and human foods. Cultivation of L. sativus should thus be considered in suitable regions because the demand for legume animal feed protein products is expected to increase. This paper addresses advances in understanding L. sativus from the perspective of its taxonomy, genetics, ecology, chemistry, nutrition, medicine, biology and for animal nutrition.

Metabolism of dietary ODAP in humans may be responsible for the low incidence of neurolathyrism

OBJECTIVES

The reasons for the very low incidence of the disease neurolathyrism in humans even after excessive consumption of the pulse, Lathyrus sativus, under severe drought and famine conditions, and its continued consumption by large populations during normal periods without any deleterious effects have been examined in the context of a possible metabolism or detoxification of beta-N-oxalyl-L-alpha, beta-diaminopropionic acid (ODAP), the major neurotoxic amino acid of L. sativus.

DESIGN AND METHODS

ODAP in urine samples from 54 subjects habitually consuming the pulse and in three volunteers on an L. sativus diet was determined by the OPT method following clean up of the samples on an alumina column. Urinary oxalate was also determined in these individuals.

RESULTS

Twenty-five subjects showed no excretion of ODAP and it was only less than 0.7% of the dietary intake in the remaining 29 subjects. Urinary excretion of ODAP in three volunteers was also less than 1% with a peak excretion in the 4-h sample. The 4-h blood sample from one volunteer had a maximum ODAP concentration of 177 microM. The urinary oxalate content in the volunteers was nearly 3-fold higher compared to controls.

CONCLUSIONS

The low excretion of dietary ingested ODAP in humans is in sharp contrast to that seen in animals and indicates a metabolism or detoxification of ODAP which may be unique to humans and may explain the low incidence of neurolathyrism.

Neuroactive and other free amino acids in seed and young plants of Panax ginseng

The seeds and one to three years old plants of Asian ginseng (Panax ginseng C.A. Meyer) were analyzed for their free amino acid contents. The neuro-excitatory beta-ODAP (beta-N-oxalyl-L-alpha,beta-diaminopropionic acid), suggested to be the cause of the crippling neurolathyrism, was the major component in the seed extract (70% of the total free amino acids detected) and showed the highest concentration (0.43% by wt) compared to that in the different parts of young plants. beta-ODAP concentration was higher in the shoots as compared to roots and declined in older plants. The amount of beta-ODAP in the roots may be considered as an indirect measure of age and quality. Another neuro-active non-protein amino acid, GABA (gamma-aminobutyric acid), increased dramatically after germination and reached highest concentration in different parts of 3 year-old plants. Glutamine and arginine were the two major free proteinogenic amino acids in the ginseng plants and together they constituted over 50% of all the free amino acids detected in the root.

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.

The non-competitive AMPA receptor antagonist (GYKI 52466) blocks quisqualate-induced acetylcholine release from the rat hippocampus and striatum: an in vivo microdialysis study

The effects of the non-N-methyl-D-aspartate (NMDA) agonist quisqualate (QUIS) and selective AMPA/kainate receptor antagonist 1-(aminophenyl)-methyl-7, 8-methyilendioxy-5H-2,3-benzodiazepine (GYKI 52466) on the release of acetylcholine (ACh) from the hippocampus and striatum of freely moving rats were studied by transversal microdialysis. Acetylcholine level in the dialisate was measured by the high performance liquid chromatography (HPLC) method with an electrochemical detector. The QUIS (100 microM) perfused through the striatum induced an increase of extracellular ACh level (250%) which lasted for over 1h and gradually returned to basal values. Local perfusion of GYKI 52466 (10-100 microM) to the striatum did not change the basal release of ACh. GYKI 52466 (10 microM) administered together with QUIS (100 microM) in he striatum antagonized the stimulant effect of QUIS on the ACh release. Local administration of the QUIS (100 microM) through the microdialysis fiber implanted in the hippocampus, caused a long lasting increase of extracellular hippocampal ACh level (360%) which was reversed when the drug was withdrawn from the perfusion solution. The stimulant effect of QUIS was antagonized by concomitant perfusion of GYKI (10 microM). No effect was seen on the basal ACh release when GYKI (10-100 microM) was perfused through the hippocampus. Local perfusion with tetrodotoxin (1 microM) decrease the basal release of ACh and prevented the QUIS-induced increase of ACh both in the hippocampus and striatum. Our in vivo neurochemical results indicate that hippocampal and striatal cholinergic systems are regulated by non-NMDA (probably AMPA) glutamatergic receptors located in the hippocampus and striatum.