neurotransmittersbinding

Neurotransmitter binding is the interaction in which a chemical messenger binds to its receptor at a synapse, initiating a signal that propagates neuronal communication.

Binding is characterized by affinity and specificity. Affinity is the strength of the interaction, often summarized by a dissociation constant (Kd). Binding is reversible and governed by kinetics—association rate (k_on) and dissociation rate (k_off).

Receptors fall into two broad classes: ionotropic receptors, which are ligand-gated ion channels producing rapid postsynaptic currents, and metabotropic receptors, which are G protein-coupled and trigger slower intracellular signaling cascades.

Common neurotransmitters include acetylcholine, binding to nicotinic and muscarinic receptors; glutamate, binding NMDA, AMPA, and kainate receptors; GABA, binding GABA-A and GABA-B receptors; and monoamines such as dopamine, norepinephrine, and serotonin binding their respective receptors.

Termination of binding and signaling is achieved through reuptake of the neurotransmitter, enzymatic degradation (for example acetylcholinesterase for acetylcholine), diffusion away from the synapse, and presynaptic autoreceptors that modulate release. Receptor desensitization can reduce responsiveness during sustained exposure.

In pharmacology and research, ligands include agonists, antagonists, partial agonists, inverse agonists, and allosteric modulators. Binding can be competitive or noncompetitive, and binding assays (often radioligand-based) estimate affinity and capacity (Kd and Bmax). Imaging methods like PET and SPECT visualize receptor binding in vivo.