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Low doses of D-Pro2-D-Phe7-D-Trp9-substance P, as specific substance P antagonist, depressed the scratching and biting behaviors elicited by intrathecal injections of substance P, and cutaneous application of algesic substances. Higher antagonist doses caused hindlimb paralysis. This suggests that substance P is a neurotransmitter for primary nociceptor afferents and may also have an important function in motor control.
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Piercey et al. (1981) studied this question.
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