Neuromodulators are chemical messengers released by neurons to influence the activity of other neurons. They are integral to the modulation of neuronal activity, allowing for the fine-tuning of transmission in response to changes in the environment or behavior. Neuromodulators are typically categorized as neurotransmitters or hormones, and they play a role in many physiological processes such as learning and memory, motivation, and emotion (Chiang & Aghajanian, 2018).
Neuromodulators are distinct from neurotransmitters in that they are not directly released into the synaptic cleft between neurons. Instead, they are released into the extracellular space, where they can diffuse to a variety of neurons and glial cells. This allows neuromodulators to have a much broader effect than neurotransmitters, as they can target multiple neurons and even multiple types of receptors on those neurons (Fitzgerald et al., 2020).
The types of neuromodulators vary widely, but some of the most studied are acetylcholine, dopamine, serotonin, and gamma-aminobutyric acid (GABA). Acetylcholine is involved in the control of skeletal muscle contraction and is released by neurons in the brainstem and spinal cord. It has been shown to modulate the release of neurotransmitters in the hippocampus and other brain regions, thus playing a role in learning and memory (Sotres-Bayon et al., 2019).
Dopamine is another important neuromodulator, and is involved in reward-related behavior. It is released in the nucleus accumbens and ventral tegmental area, and is thought to be involved in reward-related behavior, motivation, and movement control (Schultz, 2015).
Serotonin is an important neuromodulator in the brain, and is involved in the regulation of mood, appetite, and sleep. It is released in the dorsal raphe nucleus, and is thought to be important in the regulation of anxiety, arousal, and cognition (Puig et al., 2018).
Finally, GABA is an inhibitory neurotransmitter and neuromodulator that is released in the cortex and hippocampus. It is involved in the control of neuronal excitability, and has been shown to play a role in the control of anxiety and depression (Yamada et al., 2017).
In conclusion, neuromodulators are an important class of chemicals released by neurons to influence the activity of other neurons. They are involved in a wide variety of physiological processes, such as learning and memory, motivation, and emotion. Further research is needed to better understand the roles of neuromodulators in the brain and how they can be manipulated to treat neurological disorders.
References
Chiang, C. Y., & Aghajanian, G. K. (2018). Neurotransmitter modulation of neuronal excitability. Neuron, 97(3), 562-580.
Fitzgerald, P. J., Averill, S., & Brown, D. R. (2020). Neuromodulators of the mammalian brain. Annual Review of Neuroscience, 43, 391-414.
Puig, M. V., Celada, P., Pailhez, G., Andersen, M. L., & Artigas, F. (2018). Serotonin modulation of neuronal networks: Implications for psychiatric disorders. Frontiers in Neuroscience, 12, 479.
Schultz, W. (2015). Dopamine reward prediction error coding. Dialogues in Clinical Neuroscience, 17(3), 327-335.
Sotres-Bayon, F., Paz, R., & Quirk, G. J. (2019). Acetylcholine modulation of fear and fear extinction. Neuropsychopharmacology, 44(1), 68-84.
Yamada, K., Nakazato, A., & Noda, Y. (2017). Gamma-aminobutyric acid (GABA) as a neuromodulator in the healthy and diseased brain. Neuroscience, 344, 71-79.