There is indeed quite a bit of evidence suggesting that astrocytes can secrete glutamate, however, it is surrounded by much controversy still and there is not a definite consensus on the topic yet. The following papers suggest that glutamate is indeed secreted by astrocytes:

https://www.ncbi.nlm.nih.gov/pubmed/9753099 (1998)

https://www.ncbi.nlm.nih.gov/pubmed/10632596 (2000)

https://www.ncbi.nlm.nih.gov/pubmed/28130845 (2017)

This paper suggests that glial cells can release glutamate by reversal of the glutamate transporter: https://www.ncbi.nlm.nih.gov/pubmed/2247147?dopt=Abstract&holding=npg (1990)

and that this may be important in ischemia: https://www.ncbi.nlm.nih.gov/pubmed/10659851 (2000)

The findings to date are well summarized in the following three reviews:

https://www.ncbi.nlm.nih.gov/pubmed/20300101 (2010)

https://www.ncbi.nlm.nih.gov/pubmed/24559669 (2014)

and most recently: https://www.ncbi.nlm.nih.gov/pubmed/26814587 (2016)

Dear Rajan,

Glutamate is one of the most abundant amino acids in the body, and under ordinary conditions enough is obtained from the diet. In the central nervous system, glutamate is synthesized from glutamine as part of the glutamate-glutamine cycle by the enzyme glutaminase in the presynaptic neuron or in neighboring glial cells.

Best wishes,

Refik

In the nervous tissue there are complex neuro-glial relationships for the metabolism of glutamate. Thanks to the harmony of these processes, the signal role of the glutamate molecule is preserved under natural conditions. In violation of the relationship between neurons and glia, pathological processes develop, for example, because of the excess glutamate toxicity.

Please have a look an attachment.

Rodriguez M. et al. The role of non-synaptic extracellular glutamate. Brain Res. Bull. 2013. Vol.93. P. 17-26.

Thanks for your kind and elaborative suggestive explanation Prof. Refik Kanjhan and Prof. Vladimir A. Kulchitsky.

Sir but I want to know that whether neurons are the only cells which can produce Glutamate or Glia too can do this.

There are about 106 glutamatergic neurons in the central nervous system. The bodies of neurons lie in the cerebral cortex, the olfactory bulb, the hippocampus, the black substance, the cerebellum. In the spinal cord - in the primary afferents of the dorsal roots.

In the presence of glucose in the mitochondria of the nerve endings, glutamine is deaminated to glutamate by the glutamine enzyme. Also, in the aerobic oxidation of glucose, glutamate is reversibly synthesized from alpha-ketoglutarate (formed in the Krebs cycle) by means of an aminotransferase.

The neuron-synthesized glutamate is pumped into the vesicles. This process is a proton-conjugate transport. The H+ ions are pumped into the vesicle using proton-dependent ATPase. When protons leave the gradient, glutamate molecules enter the vesicle using a vesicular glutamate transporter (VGLUTs).

Glutamate is excreted into the synaptic cleft, from where it enters the astrocytes, where it transaminates to glutamine. Glutamine is removed again into the synaptic cleft and only then is captured by the neuron. According to some reports, glutamate is not directly returned by re-capture.

Thank You, Prof. Grigoriy Mikhaiylovich Palatnikov for your elaborative reply.

Sir, I want to ask whether astrocyte can produce glutamate or not?

There is indeed quite a bit of evidence suggesting that astrocytes can secrete glutamate, however, it is surrounded by much controversy still and there is not a definite consensus on the topic yet. The following papers suggest that glutamate is indeed secreted by astrocytes:

https://www.ncbi.nlm.nih.gov/pubmed/9753099 (1998)

https://www.ncbi.nlm.nih.gov/pubmed/10632596 (2000)

https://www.ncbi.nlm.nih.gov/pubmed/28130845 (2017)

This paper suggests that glial cells can release glutamate by reversal of the glutamate transporter: https://www.ncbi.nlm.nih.gov/pubmed/2247147?dopt=Abstract&holding=npg (1990)

and that this may be important in ischemia: https://www.ncbi.nlm.nih.gov/pubmed/10659851 (2000)

The findings to date are well summarized in the following three reviews:

https://www.ncbi.nlm.nih.gov/pubmed/20300101 (2010)

https://www.ncbi.nlm.nih.gov/pubmed/24559669 (2014)

and most recently: https://www.ncbi.nlm.nih.gov/pubmed/26814587 (2016)

Thank You, Prof. Dr. Anusha Mishra.

Mam Your answers are really helpful.