Substance P N-terminal fragment SP(1-7) attenuates chronic morphine tolerance and affects dynorphin B and nociceptin in rats

► Peripheral administration of substance P (1-7) inhibits the expression of morphine tolerance in the rat. ► SP(1-7)-morphine treated rats display altered levels of dynorphin B in brain areas involved in opioid tolerance and dependence. ► SP(1-7)-morphine treated rats display altered levels of nociceptin in brain areas involved in opioid tolerance and dependence.