Substance P (1-7) is found to act as a very potent antagonist against the SP-induced responses and is formed locally in the nigra after SP injection. It is proposed that Substance P (1-7) is an endogenous modulator of SP actions[1]. Injection of low doses of Substance P (1-7) (1.0-4.0 pM simultaneously with SP or SP(5-11) (0.1 nM), reduce aversive behaviours induced by SP or SP(5- 11) significantly. These results indicate that SP(1-7) formed endogenously could modulate the actions of SP or SP(5-11) in the spinal cord[2].
