Neurotransmitter
A neurotransmitter is a type of molecule that carries signals between neurons (nerve cells) at synapses in the nervous system.
Neurotransmitters may be either excitatory (EPSPs) or inhibitory (IPSPs). That is, they may foster the initiation of a nerve impulse in the receiving neuron, or they may inhibit such an impulse. GABA and glycine are well-known inhibitory neurotransmitters.
Within the cells, neurotransmitter molecules are packaged in vesicles and released by rapid exocytosis upon the arrival of a nerve impulse. Then they diffuse across the synaptic gap to bind neurotransmitter receptors or other ligand gated ion channels, and stimulate or inhibit the firing of the postsynaptic neuron.
Many neurotransmitters are removed from the synaptic gap by transport proteins residing in neuronal and glial plasma membranes. This process is called reuptake (or often simply uptake).
Without reuptake, the molecules might (counterproductively) continue to stimulate or inhibit the firing of the postsynaptic neuron.
Another mechanism for removal of a neurotransmitter is destruction by an enzyme. For example, at cholinergic synapses (where acetylcholine is the neurotransmitter) the enzyme acetylcholinesterase destroys the acetylcholine.
Drugs may alter the way neurotransmitters function. Cocaine, for example, blocks the reuptake of dopamine, leaving it in the synaptic gap longer. AMPT prevents the conversion of tyrosine to L-DOPA; reserpine prevents dopamine storage within vesicles; and deprenyl inhibits monoamine oxidase B and thus increases dopamine levels.
Common neurotransmitters
See also
