Abstract
Small vasoactive neurotransmitter molecules with a long evolutionary history of involvement in biological defense and inflammation play important roles in the up-regulation and down-regulation of the immune response and with similar effects on neuronal and lymphocyte transmembrane signaling molecules and mechanisms. The longest acting of these stimulatory molecules on lymphocyte traffic, substance P and bradykinin, also are transmitters of impulses relating to heat and pain. Heat and pain have been primordial stimuli to learning and memory--immunological as well as CNS.
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