Substance P

Abstract

In spite of the considerable amount of data on the distribution and actions of SP being accumulated, our knowledge of the function of SP in various organs is still incomplete. The multiplicity and overlap of different systems containing SP and other peptides in various parts of the nervous systems have made it difficult to elucidate the functional role of each of these peptides. The recent finding of a coexistence between SP (and other peptides) and classical neurotransmitters probably requires an expansion of our present concept of chemical transmission. The results so far reached point towards a role of these peptides as modulators rather than conventional transmitters. Thus, observations on an interaction of SP with nicotinic responses seem to indicate that neuropeptides may modulate synaptic transmission by interacting at the receptor level and potentiate the effect of coexisting classical neurotransmitters. SP has been attributed a role as a transmitter or modulator in many parts of the central and peripheral nervous system. The evidence that SP, released from axon collaterals of primary afferents in prevertebral ganglia, serves as a transmitter that generates noncholinergic, slow excitatory postsynaptic potentials seems to be the most convincing so far, and it is possible that similar mechanisms operate also in the spinal cord. Th importance of SP in transmission of nociceptive information has been extensively studied, The is still unclear. The recent observation that highly specific SP receptor antagonists are potent anti-nociceptive agents, however, strongly suggests that SP is involved in this mechanism. The discoveries of these antagonists as well as of stable SP analogues constitute important progress and these new compounds have already proven to be effective tools in the study of the physiological significance of SP and possibly also in developing new types of drugs.