This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Substance P belongs to the tachykinin family of peptides. Which of the following peripheral tissues contain substance P? \nSelect and explain. \nA. Plasma cell, B. Mast cell, C. Nerve terminal, D. Vascular endothelium', 'role': 'user'}, {'content': "Answer: C \nExplanation: Substance P is found in high concentrations in the endings of primary afferent neurons in the spinal cord, and it is probably the mediator at the first synapse in the pathways for pain transmission in the dorsal horn. It is also found in high concentrations in the nigrostriatal system, where its concentration is propoional to that of dopamine, and in the hypothalamus, where it may play a role in neuroendocrine regulation. It is responsible for the axon reflex and in the intestine, it is involved in peristalsis. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 7. Neurotransmitters & Neuromodulators. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.", 'role': 'assistant'}]