The effects of intra-arterial bradykinin, histamine, acetylcholine and prostaglandin E1 on nociceptive and non-nociceptive dorsal horn neurones of the cat.

The effects of peripherally administered algesic agents were investigated on the firing of cat dorsal horn interneurones classified as nociceptive or non-nociceptive according to the peripheral stimuli that excited them. A small amount of bradykinin injected into the blood supplying the receptive fields of cells was a potent specific stimulus causing activation of nociceptive cells and slowly conducting nerve fibres. Larger amounts of bradykinin and large amounts of histamine, 5-hydroxytryptamine and acetylcholine activated both nociceptive and non-nociceptive cells. Prostaglandin E1 enhanced the effects of bradykinin and histamine on nociceptive cells. Prostaglandin E1 also increased the response of these cells to the application of noxious heat whilst aspirin reduced this response. These results support a chemosensitive theory of nociceptor activation and show bradykinin to be the most potent and specific of the suggested endogenous algesic agents in causing activation of CNS nociceptive pathways.