Enzyme activities involved in the glutamate–glutamine cycle are altered to reduce glutamate after spinal cord injury in rats

Quantitative Nano-amperometric Measurement of Intravesicular Glutamate Content and its Sub-Quantal Release by Living Neurons

Quantitative measurements of intravesicular glutamate (Glu) and of transient exocytotic release contents directly from individual living neurons are highly desired for understanding the mechanisms (full or sub-quantal release?) of synaptic transmission and plasticity. However, this could not be achieved so far due to the lack of adequate experimental strategies relying on selective and sensitive Glu nanosensors. Herein, we introduce a novel electrochemical Glu nanobiosensor based on a single SiC nanowire that can selectively measure in real-time Glu fluxes released via exocytosis by large Glu vesicles (ca. 125 nm diameter) present in single hippocampal axonal varicosities as well as their intravesicular content before exocytosis. These measurements revealed a sub-quantal release mode in living hippocampal neurons, viz., only ca. one third to one half of intravesicular Glu molecules are released by individual vesicles during exocytotic events. Importantly, this fraction remained practically the same when hippocampal neurons were pretreated with L-Glu-precursor L-glutamine, while it significantly increased after zinc treatment, although in both cases the intravesicular contents were drastically affected.

Amantadine prevented hypersensitivity and decreased oxidative stress by NMDA receptor antagonism after spinal cord injury in rats

BACKGROUND

Neuropathic pain (NP) after spinal cord injury (SCI) is a disabling condition, without an effective treatment. Hyperexcitability of N-methyl-D-aspartate (NMDA) receptors and oxidative stress have been reported to be associated with pain development. Amantadine, an NMDA receptor antagonist, has been proposed as a potential therapy for NP. However, its use has not been tested for NP after SCI.

METHODS

To produce SCI, 120 female Wistar rats were used, a contusion injury to the T10 and T12 thoracic vertebrae was performed from heights of 6.25 mm and 12.5 mm. Nociceptive behaviour, was evaluated with the use of von Frey filaments for 31 days. The final products of lipid peroxidation (LP) and concentration of reduced glutathione (GSH) in the injured tissue were quantified by fluorescence spectrophotometry. The antinociceptive effect of the acute (15 days after the injury) and chronic (once daily for three days immediately after the injury) with amantadine (6.25-50 mg/Kg. I.p.) was determined. Finally, the LP and GSH were quantified in the injured tissue.

RESULTS

Acute treatment with amantadine reduced nociceptive behaviour. Concomitantly, LP was decreased by Amantadine treatment while GSH increased in the injured tissue. Similar effects were observed with chronic treatment with amantadine.

CONCLUSIONS

Data from this study suggested that the antinociceptive effects of amantadine treatment are modulated through oxidative stress and excitotoxicity reduction associated with N-methyl-D-aspartate receptors activation.

SIGNIFICANCE

This study suggests that acute treatment with amantadine decreases hypersensitivity threshold and frequency of hypersensitivity response in a dose-dependent manner, in rats with SCI, by decreasing oxidative stress. Since amantadine is an easily accessible drug and has fewer adverse effects than current treatments for hypersensitivity threshold and frequency of hypersensitivity response, amantadine could represent a safe and effective therapy for the treatment of neuropathic pain. However, further research is required to provide evidence of the effectiveness and feasibility.

Longitudinal [18F]FDG and [13N]NH3 PET/CT imaging of brain and spinal cord in a canine hemisection spinal cord injury model

To further understand the neurological changes induced by spinal cord injury (SCI) in its acute and subacute stages, we evaluated longitudinal changes in glucose and glutamate metabolism in the spinal cord and brain regions of a canine hemisection SCI model. [18F]FDG and [13N]NH3 positron-emission tomography (PET) with computed tomography (CT) was performed before SCI and at 1, 3, 7, 14, and 21 days after SCI. Spinal cord [18F]FDG uptake increased and peaked at 3 days post SCI. Similar changes were observed in the brain regions but were not statistically significant. Compared to the acute phase of SCI, [13N]NH3 uptake increased in the subacute stage and peaked at 7 days post SCI in all analyzed brain regions. But in spinal cord, no [13N]NH3 uptake was detected before SCI when the blood-spinal cord barrier (BSCB) was intact, then gradually increased when the BSCB was damaged after SCI. [13N]NH3 uptake was significantly correlated with plasma levels of the BSCB disruption marker, monocyte chemoattractant protein-1 (MCP-1). Overall, we showed that SCI induced in vivo changes in glucose uptake in both the spinal cord and the examined brain regions, and changes in glutamine synthetase activity in the latter. Moreover, our results suggest that [13N]NH3 PET may serve as a potential method for assessing BSCB permeability in vivo.

Ischemia-Triggered Glutamate Excitotoxicity From the Perspective of Glial Cells

A plethora of neurological disorders shares a final common deadly pathway known as excitotoxicity. Among these disorders, ischemic injury is a prominent cause of death and disability worldwide. Brain ischemia stems from cardiac arrest or stroke, both responsible for insufficient blood supply to the brain parenchyma. Glucose and oxygen deficiency disrupts oxidative phosphorylation, which results in energy depletion and ionic imbalance, followed by cell membrane depolarization, calcium (Ca²⁺) overload, and extracellular accumulation of excitatory amino acid glutamate. If tight physiological regulation fails to clear the surplus of this neurotransmitter, subsequent prolonged activation of glutamate receptors forms a vicious circle between elevated concentrations of intracellular Ca²⁺ ions and aberrant glutamate release, aggravating the effect of this ischemic pathway. The activation of downstream Ca²⁺-dependent enzymes has a catastrophic impact on nervous tissue leading to cell death, accompanied by the formation of free radicals, edema, and inflammation. After decades of “neuron-centric” approaches, recent research has also finally shed some light on the role of glial cells in neurological diseases. It is becoming more and more evident that neurons and glia depend on each other. Neuronal cells, astrocytes, microglia, NG2 glia, and oligodendrocytes all have their roles in what is known as glutamate excitotoxicity. However, who is the main contributor to the ischemic pathway, and who is the unsuspecting victim? In this review article, we summarize the so-far-revealed roles of cells in the central nervous system, with particular attention to glial cells in ischemia-induced glutamate excitotoxicity, its origins, and consequences.

Maternal cigarette smoke exposure disturbs glutamate/GABA balance in pFRG of neonatal rats

We previously found that maternal cigarette smoke (CS) exposure resulted in impairment of central chemoreception and oxidative stress and mitochondrial dysfunction of parafacial respiratory group (pFRG, a critical site for mammalian central chemoreception) in neonatal rats. The present work was carried out to identify if maternal CS exposure could disturb the glutamate (GLU)-ergic and γ-aminobutyric acid (GABA)-ergic balance in pFRG of neonatal rats. We found that maternal CS exposure induced a decrease in GLU content and consequently in GLU/GABA ratio in pFRG of neonatal rats. Maternal CS exposure also decreased glutamine content and glutaminase and glutamine synthetase activity in offspring pFRG. In addition, expression of vesicular glutamate transporter 2 was depressed, and those of glutamate transporter 1 and GABA transporter 3 were elevated by maternal CS exposure. These results indicate that maternal CS exposure leads to a disturbance of GLU/GABA balance in pFRG of the neonatal rats, which might contribute to the suppression of central chemoreception in maternal CS-exposed offspring.

Vesicular glutamate transporter isoforms: The essential players in the somatosensory systems

In nervous system, glutamate transmission is crucial for centripetal conveyance and cortical perception of sensory signals of different modalities, which necessitates vesicular glutamate transporters 1-3 (VGLUT 1-3), the three homologous membrane-bound protein isoforms, to load glutamate into the presysnaptic vesicles. These VGLUTs, especially VGLUT1 and VGLUT2, selectively label and define functionally distinct neuronal subpopulations at each relay level of the neural hierarchies comprising spinal and trigeminal sensory systems. In this review, by scrutinizing each structure of the organism's fundamental hierarchies including dorsal root/trigeminal ganglia, spinal dorsal horn/trigeminal sensory nuclear complex, somatosensory thalamic nuclei and primary somatosensory cortex, we summarize and characterize in detail within each relay the neuronal clusters expressing distinct VGLUT protein/transcript isoforms, with respect to their regional distribution features (complementary distribution in some structures), axonal terminations/peripheral innervations and physiological functions. Equally important, the distribution pattern and characteristics of VGLUT1/VGLUT2 axon terminals within these structures are also epitomized. Finally, the correlation of a particular VGLUT isoform and its physiological role, disclosed thus far largely via studying the peripheral receptors, is generalized by referring to reports on global and conditioned VGLUT-knockout mice. Also, researches on VGLUTs relating to future direction are tentatively proposed, such as unveiling the elusive differences between distinct VGLUTs in mechanism and/or pharmacokinetics at ionic/molecular level, and developing VGLUT-based pain killers.

Baicalin effects on rats with spinal cord injury by anti-inflammatory and regulating the serum metabolic disorder

Baicalin had neuroprotective effects on inhibiting neuronal cell apoptosis induced by spinal cord ischemic injury. This study aimed to explore the protective effects of Baicalin on rats with spinal cord injury (SCI) and its mechanism of action. The recovery of spinal cord nerve function in rats was evaluated by the Basso, Beattie, and Bresnahan (BBB) score and the combine behavioral score (CBS). The expressions of cytokines tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), and IL-6 were detected by the enzyme-linked immunosorbent assay method. Expressions of inflammation-related proteins were detected by Western blot. Multivariate statistical analysis was performed for serum metabolites. The BBB and CBS score results showed that Baicalin had a certain improvement on rats with SCI. SCI symptoms were significantly improved in low-dose and high-dose groups. The levels of TNF-α, IL-1β, and IL-6 in the SCI group were significantly increased. The expressions of NF-κB p65, NF-κB p50, p-IκBα, and IKKα in the SCI group showed the opposite trend compared with the low-dose and high-dose groups. Compared with the sham group, glutamine, levels of 3-OH-butyrate, N-acetylaspartate, and glutathione were significantly reduced, and the levels of glutamate and betaine were significantly increased in the SCI group. When Baicalin was administered, the contents of glutamine synthase (GS) and glutaminase (GLS) were significantly reduced, indicating that Baicalin had the effect of improving GS and GLS. Baicalin has protective effects on improving SCI and lower extremity motor function, has a significant anti-inflammatory effect, and regulates the serum metabolic disorder caused by SCI in rats.