ABSTRACT
Furthermore, neuro-transmitter peptides with powerful actions are not confined to the higher levels of the brain-stem. Forty-six years ago von Euler & Gaddum (I) discovered a hypotensive and oxytocic principle in brain and spinal cord, naming it Substance-P, and later it was found to be concentrated in the dorsal roots of cord segments much more than in the ventral roots. This led Lembeck (I) to suggest, a couple of decades later, that substance-P might be a neuro-transmitter of sensory and pain-conducting dorsal root fibres; but further progress hung fire until the isolation and identification of substance-P as an undeca-peptide by M. M. Chang and his collaborators in 1971.b There is indeed about a thousand times more of it in the dorsolateral part of the dorsal horns than there is in the ventral or motor horns, and the experiments of Otsuka & Konishi (I, 2) now clearly indicate that it should be regarded as the excitatory transmitter of primary afferent sensory neurons (cf. Fig. 52).c The antagonist lioresal, for example, which blocks dorsal root transmission, also completely inhibits the effects of substance-P.' Thus yet another peptide is involved in the transmission of pain impulses, and hence in the general system where acupuncture intervenes. The control of its release could constitute a further inhibitory or gating phenomenon.
