Neuromodulator

A neuromodulator is a chemical messenger that modulates the activity of neural circuits rather than conveying specific information through fast synaptic transmission alone. Neuromodulators are often released by certain neurons into the extracellular space and can diffuse to nearby cells, influencing a broad population of neurons rather than a single synapse. Their effects tend to build up over time and last from seconds to hours, shaping network states and the probability of neuronal firing.

Neuromodulation generally occurs through receptors that activate intracellular signaling cascades, such as G-protein-coupled receptors, leading to changes in ion channel activity, neurotransmitter release, or gene expression. Because their action is diffuse and long-lasting, neuromodulators can alter the strength and timing of synaptic responses and modulate learning, attention, arousal, mood, and stress responses. They can be released alongside classical neurotransmitters or from specialized pathways that influence many targets.

Common examples include neuropeptides (such as substance P and neuropeptide Y), endocannabinoids, and nitric oxide. Monoamines like dopamine, norepinephrine, and serotonin can also function as neuromodulators in addition to acting as neurotransmitters, depending on context. Neuromodulators are distinct from classical neurotransmitters, which mediate rapid, point-to-point signaling, and from hormones, which primarily travel through the bloodstream to act at distant sites.

In summary, neuromodulators regulate the excitability and plasticity of neural networks, providing a higher-order level of control over brain function.