2-Minute Neuroscience: Glutamate

Glutamate is the primary excitatory neurotransmitter of the human nervous system. It is an amino acid neurotransmitter that interacts with both ionotropic and metabotropic receptors. There are 3 identified ionotropic glutamate receptors: NMDA, AMPA, and kainate receptors, and 3 identified metabotropic glutamate receptors. Glutamate is removed from the synaptic cleft by excitatory amino acid transporters, or EAATs. Glutamate that is transported into glial cells is converted to glutamine before being sent back to the neuron to be converted back to glutamate, a process referred to as the glutamate-glutamine cycle.

TRANSCRIPT:

Welcome to 2 minute neuroscience, where I explain neuroscience topics in 2 minutes or less. In this installment I will discuss glutamate.

Glutamate is an amino acid that also functions as a neurotransmitter. Although glutamate is obtained through the diet, it cannot pass the blood-brain barrier and thus must be synthesized in the brain. It can be synthesized from alpha ketoglutarate, an intermediate product in the citric acid cycle.

Glutamate generally has excitatory actions, meaning that when it interacts with the receptors of a neuron it makes that neuron more likely to fire an action potential. It is, in fact, used at the vast majority of excitatory connections in the brain and at more than half of all synapses in the brain.

Glutamate interacts with several different types of receptors. There are 3 identified ionotropic glutamate receptors, named for substances that activate them: NMDA, AMPA, and kainate receptors. When activated, all 3 allow positively charged sodium ions to flow into a postsynaptic neuron, depolarizing the neuron and making it more likely to fire an action potential. NMDA receptors have unique characteristics that make them well-suited to be involved in synaptic plasticity, or synaptic changes that occur in response to experience, which are an important component of learning and memory.

There are also 3 identified types of metabotropic glutamate receptors. These receptors have more varied effects than ionotropic glutamate receptors, and may be involved with excitatory or inhibitory actions.

Glutamate is removed from the synaptic cleft by a class of transporter proteins called the excitatory amino acid transporters, or EAATs. EAATs carry glutamate into neurons and glial cells. Glutamate taken into glial cells is converted to the amino acid glutamine by the enzyme glutamine synthetase. Glutamine is then transported back into neurons, where it is converted back to glutamate. This process is referred to as the glutamate-glutamine cycle.

Reference:

Purves D, Augustine GJ, Fitzpatrick D, Hall WC, Lamantia AS, McNamara JO, White LE. Neuroscience. 4th ed. Sunderland, MA. Sinauer Associates; 2008.

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