| a small peptide released upon stimulation in the nervous system and involved in regulation of the pain threshold. |

| substance P n. A short-chain polypeptide that functions as a neurotransmitter especially in the transmission of pain impulses from peripheral receptors to the central nervous system. [From p(ain).] |
substance P n.
A short-chain polypeptide that functions as a neurotransmitter especially in the transmission of pain impulses from peripheral receptors to the central nervous system.