Fig. 2.

Schematic of excitatory and inhibitory synapses. (A) The tripartite glutamate synapse. In the presynaptic pyramidal neuron, glutamine is converted to glutamate by glutaminase and packaged into synaptic vesicles by the vesicular glutamate transporter (vGLUT). Following release into the synaptic cleft, glutamate binds to postsynaptic glutamate receptors located on a postsynaptic neuron. Glutamate is then cleared from the synaptic space through excitatory amino acid transporters (EAATs) on nearby astrocytes. Within the astrocyte, glutamate is converted to glutamine by glutamine synthetase before being transported to presynaptic neurons and beginning the process again. (B) The inhibitory GABA synapse. In the presynaptic terminal of a GABA neuron, GABA is synthesized from glutamate by the enzymes glutamic acid decarboxylase 67 and 65 (GAD67 and GAD65, respectively). GABA is packaged into vesicles via the vesicular GABA transporter (vGAT). After release into the synaptic cleft, GABA acts on GABAA receptors located on the postsynaptic neuron, opening chloride channels and hyperpolarizing the membrane. The action of GABA in the synapse is terminated, in part, by the reuptake of GABA into the presynaptic axon by GABA membrane transporter 1 (GAT1).