A class of neuropeptides (i.e., peptides produced by cells of the nervous system; neurons) which includes neurokinin A, neurokinin B, eledoisin, physalaemin, kassinin, substance P, and substance K. Some of these neuropeptides (e.g.. Substance P) are picked up by mast cells, lymphocytes, and/or monocytes; and cause those three types of immune system cells to release certain lymphokines (e.g., tumor necrosis factor, interleukin-1 etc.), thus activating the immune system.
Any of a large family of peptides that function as neurotransmitters in the central and peripheral nervous systems. They have extraneuronal activity in other body tissues. Their diverse biological actions are mediated through cellular G proteins.