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Functional Neurology: Other Molecules in Glutamate

Functional Neurology: Other Molecules in Glutamate

by | Nerve Injury, Neuropathy

Previous research studies suggest that L-aspartate, like L-glutamate, triggers excitatory activity on neurons. L-aspartate functions with L-glutamate in the synaptic vesicles of asymmetric excitatory synapses. But, the total concentration of these in the human brain (0.96-1.62 ?mol/gram wet weight), their extracellular concentrations in the cortex as measured by microdialysis (1.62 ?M for L-aspartate and 9.06 ?M for L-glutamate) and their supply according to immunohistochemistry suggest that L-aspartate is significantly less abundant than L-glutamate. Moreover, L-aspartate is a powerful agonist for NMDA receptors but not for other iGluRs with an EC50 just eight-fold higher than that of L-glutamate. EAATs which play a fundamental role in the uptake of all vesicular released L-glutamate in the central nervous system (CNS) also requires the utilization of L-aspartate. L-aspartate is perhaps as less essential as L-glutamate connected to the total excitatory activity associated with iGluRs. Along with its role as a neurotransmitter, as previously mentioned, L-aspartate is also necessary as a substrate for aspartate amino-transferase which turns into 2-oxoglutarate and L-glutamate to transport to the cortical vesicles of glutamatergic neurons which may also consequently and indirectly increase L-glutamate release. �

 

Other Molecules in Glutamate Signaling

 

One characteristic which distinguishes NMDA receptors from different iGluRs is that the activation of NMDA receptors needs the connection of a co-agonist to the glycine binding region of the receptor. By way of instance, in the retina and in the spinal cord, the origin of glycine may spillover out of glycinergic inhibitory synapses. But, in different regions of the brain with increased NMDA receptor expression, such as the hippocampal formation, reactions associated with strychnine-sensitive glycine receptors are missing, at least in adult neurons, demonstrating the absence of glycinergic inhibitory neurotransmissions. But, glycine is found in the extracellular fluid of the hippocampus at baseline amounts of roughly 1.5 ?M, which is similar to the saturation of the glycine binding region of the NMDA receptor, although these may be up- and down-regulated. The origin of extracellular glycine in the hippocampus can be neurons which release glycine through the alanine-serine-cysteine amino acid transporter 1 (asc-1). But, glycine release by astrocytes that is stimulated by depolarization and kainate, has also been demonstrated. Further research studies are required to ultimately show these outcome measures. �

 

Even in previous research studies of the NMDA receptor and its co-activation by glycine revealed that D-amino acids, particularly D-serine, are nearly as powerful as glycine. Only several years after, it became obvious that D-serine is found in rat and human brains at roughly one-third of their concentration of L-serine having an absolute concentration of more than 0.2 ?mol/g brain tissue. Utilizing an antiserum for D-serine, research studies demonstrated that D-serine from the brain is only found in astrocytes and its supply fits the expression of NMDA receptors. In addition, the same researchers demonstrated that D-serine is released from cultured astrocytes when exposed to L-glutamate or kainate. The abundance of D-serine is found by the degrading enzyme D-amino acid oxidase (DAO) which reveals increased expression in the hindbrain where D-serine levels are reduced as well as the synthetic enzyme serine racemase which creates D-serine from L-serine. D-Serine appears to be stored in cytoplasmic vesicles in astrocytes and it can be released by exocytosis. Long-term potentiation is dependent upon D-serine release from astrocytes in hippocampal slices, suggesting that this amino acid definitely plays a fundamental role in glutamatergic neurotransmission through NMDA receptors. Additionally in hippocampal slices, research studies found, utilizing D-serine and glycine degrading enzymes, which D-serine functions as a co-transmitter for synaptic NMDA receptors on CA1 neurons likewise which glycine functions as the endogenous co-agonist for extrasynaptic NMDA receptors. Synaptic NMDA receptors of dentate gyrus neurons utilize glycine rather than D-serine as the co-agonist. �

 

Taken collectively, multilayered outcome measures show that L-aspartate doesn’t simply function as an agonist on NMDA receptors but also glycine and D-serine play fundamental roles in glutamatergic neurotransmission in the human brain. But, other molecules also have been demonstrated to be relevant modulators of glutamatergic neurotransmission. �

 

Glutamate Activated by Other Molecules

 

L-homocysteate (L-HCA) has structural similarities with L-glutamate. The non-protein amino acid is an oxidation product of homocysteine that is biosynthesized from methionine in the elimination of its own terminal methyl group and it is also an intermediate of the transsulfuration pathway by which methionine may be converted to cysteine through cystathionine. Early research studies demonstrated that this amino acid can cause calcium influx in cultured neurons as safely and effectively as L-glutamate. Moreover, L-HCA revealed an increased affinity for NMDA receptors when compared to other iGluRs in binding assays associated with its capacity to cause NMDA receptor antagonist-inhibitable excitotoxicity and sodium influx. Additionally, L-HCA can trigger mGluR5 as efficiently as L-glutamate. L-HCA is found in the brain, however, the concentrations were demonstrated to be approximately 500-fold lesser than those of L-glutamate and even 100-fold lesser when compared to those of L-aspartate in different regions of the rat brain. Throughout potassium-induced stimulation, L-HCA discharge is triggered from brain slice preparations as demonstrated for L-aspartate and L-glutamate although the absolute release of HCA is approximately 50-fold lesser. Surprisingly, HCA is a very efficient competitive inhibitor of cystine and L-glutamate uptake through the cystine/glutamate antiporter system x?c, the activity that regulates and manages the extracellular extrasynaptic L-glutamate concentrations in the brain. Therefore, the impact of L-HCA on the activation of NMDA and other L-glutamate receptors may also rely on the L-HCA-induced trigger of L-glutamate through system x?c. L-HCA may play an important role in the overall stimulation of L-glutamate receptors. Nevertheless, this can change tremendously under certain conditions, e.g., in patients with high-dose methotrexate therapy, an anticancer drug which, by restricting dihydrofolate reductase, limits the tetrahydrofolate-catalyzed recycling of methionine from homocysteine. Here, L-HCA concentrations of more than 100 ?M have been demonstrated from the cerebrospinal fluid whereas L-HCA was undetectable in control subjects. Further research studies are still required to determine these outcome measures. �

 

Further endogenous small molecules which are believed to affect L-glutamate signaling include several intermediates of tryptophan metabolism, as shown in Figure 2. Through the activity of indoleamine 2,3-dioxygenase (IDO) or tryptophan 2,3-dioxygenase (TDO), tryptophan is turned into N-formyl-L-kynurenine which is later turned into kynurenine (KYN) by formamidase. Three pathways, two of which connect at a subsequent step, result in further metabolism. First, through the activity of kynurenine aminotransferase (KAT), KYN is converted into kynurenic acid (KYNA). KYN can also be converted to 3-hydroxykynurenine (3HK) by kynurenine monooxygenase (KMO), which can subsequently be utilized as a substrate by kynureninase for the synthesis of 3-hydroxyanthranilic acid (3HANA). Additionally, utilizing KYN as a substrate, kynureninase develops anthranilic acid (ANA), which by non-specific hydroxylation may also be converted to 3HANA. According to research studies, 3HANA finally functions as a substrate for the generation of quinolinic acid (QUIN). �

 

Figure 2 Kynurenine Metabolism | El Paso, TX Chiropractor

 

The tryptophan concentration in the rat brain is roughly 25 nmol/g wet weight and approximately 400-fold less than L-glutamate and 100-fold less than L-aspartate. The demonstrated brain levels of kynurenines are even lower with 0.4-1.6 nmol/g for QUIN, 0.01-0.07 nmol/ml for KYNA, and 0.016 nmol/g for 3HANA. Approximately 40 percent of brain KYN is locally synthesized. The metabolites of tryptophan demonstrate differential binding to plasma proteins and their transport through the barrier which is quite different. KYN and 3HK are carried through the large neutral amino acid carrier system L. Kynurenines seem to penetrate the human brain by passive diffusion. Additionally, KYNA, 3HANA, and especially ANA bind to serum proteins which then ultimately restrict and limit their diffusibility across the blood-brain barrier. �

 

Research studies demonstrated that QUIN, when ionophoretically utilized in rat cells, caused neuronal firing which has been prevented by an NMDA receptor antagonist, suggesting that QUIN may function as an NMDA receptor agonist. However, the EC50 for QUIN to trigger NMDA receptor currents has been shown to be roughly 1000-fold higher than the EC50 of L-glutamate. Intracerebral injection of QUIN was proven to cause ultrastructural, neurochemical, and behavioral changes similar to those caused by NMDA receptor agonists. The fact that QUIN concentrations are about 5000- to 15,000-fold lower than cerebral L-glutamate concentrations makes it unlikely that modulation of NMDA receptor signaling by QUIN plays an essential role. KYNA was demonstrated to function as an NMDA receptor antagonist. But, although infusion with the KMO inhibitor Ro 61-8048 improved cerebral extracellular KYNA concentrations 10-fold, this didn’t result in an inhibition of NMDA-mediated neuronal depolarization, a finding which challenges the belief that KYNA at near-physiological amounts directly modulates NMDA receptors. In comparison, increased KYNA in the brain induced from the KMO inhibitor JM6 decreased the extracellular cerebral L-glutamate concentration. Additionally, KYNA levels from the extracellular cerebral fluid have been associated with L-glutamate levels suggesting that even at physiological or near physiological levels, KYNA modulates L-glutamate metabolism. Both the activation of the G-protein-coupled receptor GPR35 and the inhibition of presynaptic ?7 nicotinic acetylcholine receptors are suggested in the KYNA-induced reduction in L-glutamate release. To summarize, although QUIN and L-HCA are present in the human brain, their concentrations discuss against them with roles in regulating and maintaining neurotransmission. In contrast, even though the pathways have to be defined in greater detail, evidence supports levels and the opinion that discharge can be modulated by KYNA and neurotransmission. �

 

El Paso Chiropractor Dr. Alex Jimenez

Glutamate, together with aspartate and other molecules, are several of the main excitatory neurotransmitters in the human brain. Although these play a fundamental role in the overall structure and function of the central nervous system, including the brain and the spinal cord, excessive amounts of other molecules can ultimately trigger glutamate receptors. Excess glutamate can cause excitotoxicity which may lead to a variety of health issues, such as Alzheimer’s disease and other types of neurological diseases. The following article describes how other molecules can activate glutamate receptors. – Dr. Alex Jimenez D.C., C.C.S.T. Insight – Dr. Alex Jimenez D.C., C.C.S.T. Insight

 

Research studies suggest that L-aspartate, like L-glutamate, triggers excitatory activity. L-aspartate functions with L-glutamate in the synaptic vesicles of asymmetric excitatory synapses. But, the total concentration of these in the human brain suggest that L-aspartate is significantly less abundant than L-glutamate. Moreover, L-aspartate is a powerful agonist for NMDA receptors but not for other iGluRs with an EC50 just eight-fold higher than that of L-glutamate. The scope of our information is limited to chiropractic, musculoskeletal and nervous health issues as well as functional medicine articles, topics, and discussions. We use functional health protocols to treat injuries or chronic disorders of the musculoskeletal system. To further discuss the subject matter above, please feel free to ask Dr. Alex Jimenez or contact us at 915-850-0900 . �

 

Curated by Dr. Alex Jimenez �

 

References �

 

  1. Lewerenz, Jan, and Pamela Maher. �Chronic Glutamate Toxicity in Neurodegenerative Diseases-What Is the Evidence?� Frontiers in Neuroscience, Frontiers Media S.A., 16 Dec. 2015, www.ncbi.nlm.nih.gov/pmc/articles/PMC4679930/.

 

 

Additional Topic Discussion: Chronic Pain

 

Sudden pain is a natural response of the nervous system which helps to demonstrate possible injury. By way of instance, pain signals travel from an injured region through the nerves and spinal cord to the brain. Pain is generally less severe as the injury heals, however, chronic pain is different than the average type of pain. With chronic pain, the human body will continue sending pain signals to the brain, regardless if the injury has healed. Chronic pain can last for several weeks to even several years. Chronic pain can tremendously affect a patient’s mobility and it can reduce flexibility, strength, and endurance.

 

 

 

Neural Zoomer Plus for Neurological Disease

 

Neural Zoomer Plus | El Paso, TX Chiropractor �

Dr. Alex Jimenez utilizes a series of tests to help evaluate neurological diseases. The Neural ZoomerTM Plus is an array of neurological autoantibodies which offers specific antibody-to-antigen recognition. The Vibrant Neural ZoomerTM Plus is designed to assess an individual�s reactivity to 48 neurological antigens with connections to a variety of neurologically related diseases. The Vibrant Neural ZoomerTM Plus aims to reduce neurological conditions by empowering patients and physicians with a vital resource for early risk detection and an enhanced focus on personalized primary prevention. �

 

Formulas for Methylation Support

 

Xymogen Formulas - El Paso, TX

 

XYMOGEN�s Exclusive Professional Formulas are available through select licensed health care professionals. The internet sale and discounting of XYMOGEN formulas are strictly prohibited

 

Proudly,�Dr. Alexander Jimenez makes XYMOGEN formulas available only to patients under our care.

 

Please call our office in order for us to assign a doctor consultation for immediate access.

 

If you are a patient of Injury Medical & Chiropractic�Clinic, you may inquire about XYMOGEN by calling 915-850-0900.

xymogen el paso, tx

 

For your convenience and review of the XYMOGEN products please review the following link.*XYMOGEN-Catalog-Download �

* All of the above XYMOGEN policies remain strictly in force.

 

 

�

Functional Neurology: The Role of Glutamate in the Brain

Functional Neurology: The Role of Glutamate in the Brain

by | Nerve Injury, Neuropathy

L-glutamate is one of the main excitatory neurotransmitters in the human brain and it plays an essential role in practically all activities of the nervous system. In the following article, we will discuss the general principles of L-glutamate signaling in the brain. Then, we will demonstrate this scheme by describing the different pools of extracellular glutamate, including the synaptic, the perisynaptic, and the extrasynaptic, resulting from vesicular and non-vesicular sources or abnormally located glutamate receptors outside of synapses as well as discuss their possible physiological functions in the human brain. �

 

Glutamate Signaling in the Brain

 

According to research studies, the human brain has about a 6 to 7 ?mol/g wet weight of L-glutamate. L-glutamate, together with glutamine, is one of the most abundant free amino acids in the central nervous system (CNS). More than five decades ago, several research studies demonstrated that L-glutamate has an excitatory response on nerve cells. Since then, its role as an excitatory neurotransmitter as well as its cerebral metabolism has been evaluated in numerous research studies. �

 

L-glutamate is commonly found throughout synaptic vesicles in the presynaptic terminal through the process of vesicular glutamate transporters. Additionally, several of the L-glutamate in the vesicles may develop by a vesicle-associated aspartate amino-transferase from 2-oxoglutarate utilizing L-aspartate as the amino group donor. During the depolarization of the presynaptic membrane, L-glutamate is released into the synaptic cleft and connects to ionotropic glutamate receptors, known as iGluRs, at the postsynaptic membrane, as shown in Figure 1. According to research studies, iGluRs are characterized as ligand-gated ion channels which include receptors of the ?-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), kainate, and N-methyl-D-aspartic acid (NMDA) types. While AMPA and kainate receptors primarily regulate and maintain sodium influx, NMDA receptors actually have a high calcium conductivity. Moreover, the activation of NMDA receptors plays a fundamental role in synaptic plasticity and learning. In contrast to the other iGluRs, the activity of NMDA receptors is ultimately restricted by an Mg+2 block at the regular membrane potential, however, the ion channel is immediately unblocked by membrane depolarization which eliminates Mg+2 from the pore. Furthermore, NMDA receptors are tetramers that have two NR1 subunits and two NR2 or NR3 subunits, according to several research studies. �

 

Figure 1 Glutamate Metabolism in the Brain | El Paso, TX Chiropractor

 

Additionally to iGluRs, there are also eight isoforms of metabotropic glutamate receptors (mGluRs) which belong to the family of G-protein-coupled receptors, where they don’t develop ion channels but instead signal through a variety of second messenger systems. L-glutamate-associated depolarization causes a postsynaptic excitatory potential which eases the development of an action potential at the axon hillock. The glutamatergic synapse is activated by astrocytic processes that demonstrate high levels of excitatory amino acid transporters (EAATs). There are five different EAATs, EAAT1 to 5, of which EAAT1 and 2 are the primary astrocytic EAATs, whereas EAAT3 shows a predominantly neuronal expression. Approximately 90 percent of the L-glutamate transport is regulated and maintained by EAAT2 such as GLT-1 in rodent models. These transporters then co-transport 2 or 3 molecules of Na+ and a proton with each molecule of L-glutamate or L-aspartate together with the counter-transport of a K+ ion. Therefore, by utilizing the electrochemical gradient of these ions throughout the plasma membrane as an energy source, the transporters are able to safely and effectively accumulate L-glutamate and L-aspartate in cells against their sudden intra- to extracellular concentration gradients. This allows the brain to control a very low extracellular L-glutamate concentration in the low micromolar range. It is generally believed that L-glutamate taken up by astrocytes is turned to glutamine by the enzyme glutamine synthetase, the glutamine is then released, taken up by neurons and turned to L-glutamate, where it is ultimately utilized once again for neurotransmission. �

 

Extrasynaptic Glutamate in the Brain

 

Aside from the essential role of L-glutamate as the primary excitatory neurotransmitter released from glutamatergic presynapses, as previously mentioned above, it has become evident that L-glutamate receptors outside the synaptic cleft also play an essential role in brain physiology. In the cerebellum, it was demonstrated by evaluating AMPA receptor-mediated currents in Bergmann glia that synaptically released L-glutamate concentrations can reach extrasynaptic concentrations of up to 190 ?M while concentrations in the synaptic cleft can exceed 1 mM. Moreover, several mGluRs have been shown to demonstrate a different localization in proximity to the postsynaptic density which would allow them to immediately recognize L-glutamate escaping from the synaptic cleft, as shown in Figure 1. However, current research studies have demonstrated that iGluRs, especially of the NMDA type, are also found at extrasynaptic regions in the neuronal cell membrane. Utilizing light and electron microscopy, other research studies also demonstrated that extrasynaptic NMDA receptors gather at different regions of close contact in the dendritic shaft with axons, axon terminals, or astrocytic processes. The proportion of extrasynaptic NMDA receptors was estimated to be as high as 36 percent of the dendritic NMDA receptor pool in rat hippocampal slices. Although extrasynaptic NMDA receptors were associated with similar scaffolding proteins as synaptic NMDA receptors, an in vitro research study suggested that extrasynaptic and synaptic NMDA receptors may ultimately activate different downstream signaling pathways with a variety of results, including the suppression of CREB activity by extrasynaptic NMDA receptor activation as well as activation by synaptic NMDA receptors. Furthermore, NMDA receptors localized extrasynaptically on dendritic shafts connect extrasynaptic L-glutamate as well as regulate and maintain Ca2+ influx during the elimination of the Mg+2 block by dendrite depolarization throughout the backfiring of action potentials. Research studies demonstrated that L-glutamate release from astrocytes can activate slow inward currents through extrasynaptic NMDAR receptors in CA1 neurons which can also be ultimately synchronized. The mechanisms through which glial cells release L-glutamate as well as how the extrasynaptic L-glutamate concentrations are controlled are vital towards understanding how the activity of extrasynaptic NMDA receptors is controlled. �

 

Different mechanisms through which astrocytes can release L-glutamate have been suggested, including vesicular L-glutamate release and non-vesicular release through anion channels as well as connexin hemichannels and release through the cystine/glutamate antiporter system x?c. Several research studies strongly suggest that vesicular release from astrocytes plays a minor role because the Ca+2-associated release of L-glutamate was still present in astrocytes created from dominant-negative SNARE mice where vesicular release can be blocked by doxycycline withdrawal. System x?c is a cystine/glutamate antiporter which is characterized as heterodimeric amino acid transporters, made up of xCT as the specific subunit and 4F2hc as the promiscuous heavy chain. This transporter is demonstrated in the brain, especially in astroglial and microglial cells, as shown in Figure 1. The fact that extrasynaptic L-glutamate levels in different regions of the human brain are downregulated by approximately 60 percent to 70 percent in xCT knock out mice, research studies demonstrated that system x?c releases L-glutamate into the extrasynaptic space and suggests that this transporter is essential in the regulation of extrasynaptic L-glutamate levels. This is further supported by the observation that when measured by in vivo microdialysis, the increase in extrasynaptic L-glutamate developed by EAAT inhibitors is neutralized by blocking system x?c while blocking neuronal vesicular L-glutamate release is ineffective. Further research studies are still required. �

 

Taken together, glutamatergic neurotransmissions don’t simply happen through classical excitatory synapses but also through extrasynaptic L-glutamate receptors, as shown in Figure 1. Finally, the levels of extrasynaptic L-glutamate are determined, at least partially, by glial non-vesicular L-glutamate release, as also shown in Figure 1. However, the regulation of extrasynaptic L-glutamate levels, as well as its temporal-spatial dynamics and its effect on neuronal function, neurodegeneration, and behavior, are far from being fully understood by researchers, healthcare professionals, and patients. �

 

El Paso Chiropractor Dr. Alex Jimenez

Glutamate, together with aspartate, is one of the main excitatory neurotransmitters in the human brain. Although it plays a fundamental role in the overall structure and function of the nervous system, excessive amounts of glutamate can ultimately cause excitotoxicity which may lead to a variety of health issues, such as Alzheimer’s disease and other types of neurological diseases. The following article describes the role of glutamate in the human brain. – Dr. Alex Jimenez D.C., C.C.S.T. Insight

 

L-glutamate is one of the main excitatory neurotransmitters in the human brain and it plays an essential role in practically all activities of the nervous system. In the article above, we discussed the general principles of L-glutamate signaling in the brain. Then, we demonstrated this scheme by describing the different pools of extracellular glutamate, including the synaptic, the perisynaptic, and the extrasynaptic, resulting from vesicular and non-vesicular sources or abnormally located glutamate receptors outside of synapses as well as discussed their possible physiological functions in the human brain. The scope of our information is limited to chiropractic, musculoskeletal and nervous health issues as well as functional medicine articles, topics, and discussions. We use functional health protocols to treat injuries or chronic disorders of the musculoskeletal system. To further discuss the subject matter above, please feel free to ask Dr. Alex Jimenez or contact us at 915-850-0900 . �

 

Curated by Dr. Alex Jimenez �

 

References �

 

  1. Lewerenz, Jan, and Pamela Maher. �Chronic Glutamate Toxicity in Neurodegenerative Diseases-What Is the Evidence?� Frontiers in Neuroscience, Frontiers Media S.A., 16 Dec. 2015, www.ncbi.nlm.nih.gov/pmc/articles/PMC4679930/.

 

 

Additional Topic Discussion: Chronic Pain

 

Sudden pain is a natural response of the nervous system which helps to demonstrate possible injury. By way of instance, pain signals travel from an injured region through the nerves and spinal cord to the brain. Pain is generally less severe as the injury heals, however, chronic pain is different than the average type of pain. With chronic pain, the human body will continue sending pain signals to the brain, regardless if the injury has healed. Chronic pain can last for several weeks to even several years. Chronic pain can tremendously affect a patient’s mobility and it can reduce flexibility, strength, and endurance.

 

 

 

Neural Zoomer Plus for Neurological Disease

Neural Zoomer Plus | El Paso, TX Chiropractor �

Dr. Alex Jimenez utilizes a series of tests to help evaluate neurological diseases. The Neural ZoomerTM Plus is an array of neurological autoantibodies which offers specific antibody-to-antigen recognition. The Vibrant Neural ZoomerTM Plus is designed to assess an individual�s reactivity to 48 neurological antigens with connections to a variety of neurologically related diseases. The Vibrant Neural ZoomerTM Plus aims to reduce neurological conditions by empowering patients and physicians with a vital resource for early risk detection and an enhanced focus on personalized primary prevention. �

 

Formulas for Methylation Support

 

Xymogen Formulas - El Paso, TX

 

XYMOGEN�s Exclusive Professional Formulas are available through select licensed health care professionals. The internet sale and discounting of XYMOGEN formulas are strictly prohibited.

 

Proudly,�Dr. Alexander Jimenez makes XYMOGEN formulas available only to patients under our care.

 

Please call our office in order for us to assign a doctor consultation for immediate access.

 

If you are a patient of Injury Medical & Chiropractic�Clinic, you may inquire about XYMOGEN by calling 915-850-0900.

xymogen el paso, tx

 

For your convenience and review of the XYMOGEN products please review the following link.*XYMOGEN-Catalog-Download �

 

* All of the above XYMOGEN policies remain strictly in force.

 

 

�