Intrathecally-administered histamine facilitates nociception through tachykinin NK₁ and histamine H₁ receptors: A study in histidine decarboxylase gene knockout mice

Intrathecal injection of histamine elicited behavioral responses consisting of scratching, biting and licking in conscious mice. To study the participation of histamine in pain perception, histidine decarboxylase knockout mice were examined for pain threshold by means of three different kinds of noxious stimuli: thermal nociception (hot-plate, tail-flick, and paw-withdrawal), mechanical nociception (tail-pressure), and chemical nociception (formalin test and capsaicin test). Mutant mice lacking histidine decarboxylase showed significantly fewer nociceptive responses to the hot-plate, tail-flick, paw-withdrawal, tail-pressure, formalin and capsaicin tests. Sensitivity to noxious stimuli in the histidine decarboxylase knockout mice was significantly lower when compared to the wild-type mice. The intrathecally-administered histamine (400 pmol) significantly shortened the latency in the histidine decarboxylase knockout mice, but not in the wild-type mice in tail-flick tests. Pyrilamine, a histamine H₁ receptor antagonist, but not ranitidine, a histamine H₂ receptor antagonist, produced inhibition of the induced behavioral responses in the tail-flick test when co-administered with histamine. Sendide, a tachykinin NK₁ receptor antagonist, inhibited histamine-induced nociceptive behavior in the histidine decarboxylase knockout mice. In contrast, the treatment with d-(-)-2 amino-5-phosponovaleric acid (d-APV), an N-methyl-d-aspartate (NMDA) receptor antagonist, did not prevent the induction of the behavioral responses by histamine. These studies substantiate the evidence that nociceptive behavior induced by intrathecal injection of histamine is largely mediated through tachykinin NK₁ and histamine H₁ receptors in the spinal cord.