Neuromodulators synaptic modulation

H. Kimura, Y. Nagai, K. Umemure, and Y. Kimura, Physiological roles of hydrogen sulfide synaptic modulation, neuroprotection, and smooth muscle relaxation. Antioxidants Redox Signaling 7, 795-803 (2005). K. Abe and H. Kimura, The possible role of hydrogen sulfide as an endogenous neuromodulator. J. Neurosci. 16, 1066-1071 (1996). 

Some transmitters, including noradrenaline, dopamine, serotonin, and various neuropeptides, are sometimes called neuromodulators rather than neurotransmitters. These compounds may not initiate a nerve impulse but may act on adenylate cyclase to increase or decrease cAMP levels and protein kinase activity. They may also diffuse through the extracellular space to influence a region of the brain greater than a single synaptic cleft. However, the distinction between transmitters and modulators is not exact. 

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