Regulation of excitation by glycine receptors

Cerebrolysin restores balance between excitatory and inhibitory amino acids in brain following concussive head injury. Superior neuroprotective effects of TiO2 nanowired drug delivery

Concussive head injury (CHI) often associated with military personnel, soccer players and related sports personnel leads to serious clinical situation causing lifetime disabilities. About 3-4k head injury per 100k populations are recorded in the United States since 2000-2014. The annual incidence of concussion has now reached to 1.2% of population in recent years. Thus, CHI inflicts a huge financial burden on the society for rehabilitation. Thus, new efforts are needed to explore novel therapeutic strategies to treat CHI cases to enhance quality of life of the victims. CHI is well known to alter endogenous balance of excitatory and inhibitory amino acid neurotransmitters in the central nervous system (CNS) leading to brain pathology. Thus, a possibility exists that restoring the balance of amino acids in the CNS following CHI using therapeutic measures may benefit the victims in improving their quality of life. In this investigation, we used a multimodal drug Cerebrolysin (Ever NeuroPharma, Austria) that is a well-balanced composition of several neurotrophic factors and active peptide fragments in exploring its effects on CHI induced alterations in key excitatory (Glutamate, Aspartate) and inhibitory (GABA, Glycine) amino acids in the CNS in relation brain pathology in dose and time-dependent manner. CHI was produced in anesthetized rats by dropping a weight of 114.6g over the right exposed parietal skull from a distance of 20cm height (0.224N impact) and blood-brain barrier (BBB), brain edema, neuronal injuries and behavioral dysfunctions were measured 8, 24, 48 and 72h after injury. Cerebrolysin (CBL) was administered (2.5, 5 or 10mL/kg, i.v.) after 4-72h following injury. Our observations show that repeated CBL induced a dose-dependent neuroprotection in CHI (5-10mL/kg) and also improved behavioral functions. Interestingly when CBL is delivered through TiO₂ nanowires superior neuroprotective effects were observed in CHI even at a lower doses (2.5-5mL/kg). These observations are the first to demonstrate that CBL is effectively capable to attenuate CHI induced brain pathology and behavioral disturbances in a dose dependent manner, not reported earlier.

Impaired "Glycine"-mia in Type 2 Diabetes and Potential Mechanisms Contributing to Glucose Homeostasis

The onset and/or progression of type 2 diabetes (T2D) can be prevented if intervention is early enough. As such, much effort has been placed on the search for indicators predictive of prediabetes and disease onset or progression. An increasing body of evidence suggests that changes in plasma glycine may be one such biomarker. Circulating glycine levels are consistently low in patients with T2D. Levels of this nonessential amino acid correlate negatively with obesity and insulin resistance. Plasma glycine correlates positively with glucose disposal, and rises with interventions such as exercise and bariatric surgery that improve glucose homeostasis. A role for glycine in the regulation of glucose, beyond being a potential biomarker, is less clear, however. Dietary glycine supplementation increases insulin, reduces systemic inflammation, and improves glucose tolerance. Emerging evidence suggests that glycine, a neurotransmitter, also acts directly on target tissues that include the endocrine pancreas and the brain via glycine receptors and as a coligand for N-methyl-d-aspartate glutamate receptors to control insulin secretion and liver glucose output, respectively. Here, we review the current evidence supporting a role for glycine in glucose homeostasis via its central and peripheral actions and changes that occur in T2D.

Glycine receptor-mediated inhibition of medial prefrontal cortical pyramidal cells

Using whole-cell patch clamp recording on medial prefrontal cortical slices of rats aged 17-33 postnatal days, we demonstrated the glycine-induced strychnine-sensitive outward currents. The amplitude of the peak current increased with the concentrations of glycine with an EC50 of 74.7 μM. Application of 1μM strychnine alone to cells caused a slight inward current without blocking the sIPSCs, indicating that GlyRs in the mPFC are activated by an endogenous ligand that can be released tonically. Glycine reversibly depressed firing rate in cells from both layer 6 and layer 3, with significantly greater inhibition on the former than the latter (EC50 12.9 vs 85.6 μM). Glycine hyperpolarized membrane potential in cells of both layer 6 and layer 3 depending on its concentrations, with an IC50 of 99.1 and 207.2 μM, respectively. We propose that GlyRs participate in a novel inhibitory mechanism in mPFC, modulating neuronal activity. This finding further supports an important role of GlyR in cortical function and dysfunction.

Ischemia induces release of endogenous amino acids from the cerebral cortex and cerebellum of developing and adult mice

Ischemia enhanced release of endogenous neuroactive amino acids from cerebellar and cerebral cortical slices. More glutamate was released in adult than developing mice. Taurine release enhanced by K⁺ stimulation and ischemia was more than one magnitude greater than that of GABA or glutamate in the developing cerebral cortex and cerebellum, while in adults the releases were almost comparable. Aspartate release was prominently enhanced by both ischemia and K⁺ stimulation in the adult cerebral cortex. In the cerebellum K⁺ stimulation and ischemia evoked almost 10-fold greater GABA release in 3-month olds than in 7-day olds. The release of taurine increased severalfold in the cerebellum of 7-day-old mice in high-K⁺ media, whereas the K⁺-evoked effect was rather small in adults. In 3-month-old mice no effects of K⁺ stimulation or ischemia were seen in the release of aspartate, glycine, glutamine, alanine, serine, or threonine. The releases from the cerebral cortex and cerebellum were markedly different and also differed between developing and adult mice. In developing mice only the release of inhibitory taurine may be large enough to counteract the harmful effects of excitatory amino acids in ischemia in both cerebral cortex and cerebellum, in particular since at that age the release of glutamate and aspartate cannot be described as massive.

Glycine receptors contribute to hypnosis induced by ethanol

BACKGROUND

Glycine is a major inhibitory neurotransmitter in the adult central nervous system (CNS), and its receptors (GlyRs) are well known for their effects in the spinal cord and the lower brainstem. Accumulating evidence indicates that GlyRs are more widely distributed in the CNS, including many supraspinal regions. Previous in vitro studies have demonstrated that ethanol potentiates the function of these brain GlyRs, yet the behavioral role of the brain GlyRs has not been well explored.

METHODS

Experiments were conducted in rats. The loss of righting reflex (LORR) was used as a marker of the hypnotic state. We compared the LORR induced by systematic administration of ethanol and of ketamine in the absence and presence of the selective glycine receptor antagonist strychnine. Ketamine is a general anesthetic that does not affect GlyRs.

RESULTS

Systemically administered (by intraperitoneal injection) ethanol and ketamine dose-dependently induced LORR in rats. Furthermore, systemically administered (by subcutaneous injection) strychnine dose-dependently reduced the percentage of rats exhibiting LORR induced by ethanol, increased the onset time, and decreased the duration of LORR. Strychnine had no effect, however, on the LORR induced by ketamine.

CONCLUSIONS

Given that hypnosis is caused by neuronal depression in upper brain areas, we therefore conclude that brain GlyRs contribute at least in part to the hypnosis induced by ethanol.