Principles of tachykininergic co-transmission in the peripheral and enteric nervous system

The tachykinins substance P (SP) and neurokinin A (NKA) are synthesized and released from nerves in the peripheral and enteric nervous system (PNS and ENS). They act as nonadrenergic noncholinergic (NANC) excitatory transmitt ers in mammalian airways, and the genitourinary and gastrointestinal tract. At the postjunctional level, both NK1 (SP-prefening) and NK2 (NKA-preferri ng) receptors are often co-expressed by target cells innervated by TKergic nerves. Thus an issue of duplication seems to exists with regard to periphe ral tachykininergic co-transmission, the duplication involving both messeng ers (the peptides) and effecters (the receptors). By using receptor selecti ve antagonists it has been possible to dissect the relative contribution of different receptors to TKergic co-transmission: the available results indi cate that multiple arrangements exist involving both summation, cooperation and specialization of different messengers/effectors in producing the over all response. (C) 2000 Elsevier Science B.V. All rights reserved.