Contribution of peripheral vanilloid receptor to the nociception induced by injection of spermine in mice

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Polyamines (putrescine, spermidine and spermine) are important endogenous regulators of ion channels, such as vanilloid (TRPV1), glutamatergic (NMDA or AMPA/kainate) and acid-sensitive (ASIC) receptors. In the present study, we have investigated the possible nociceptive effect induced by polyamines and the mechanisms involved in this nociception in vivo. The subcutaneous (s.c.) injection of capsaicin (as positive control), spermine, spermidine or putrescine produced nociception with ED50 of 0.16 (0.07–0.39)nmol/paw, 0.4 (0.2–0.7)μmol/paw, 0.3 (0.1–0.9)μmol/paw and 3.2 (0.9–11.5)μmol/paw, respectively. The antagonists of NMDA (MK801, 1nmol/paw), AMPA/kainate (DNQX, 1nmol/paw) or ASIC receptors (amiloride, 100nmol/paw) failed to reduce the spermine-trigged nociception. However, the TRPV1 antagonists capsazepine or SB366791 (1nmol/paw) reduced spermine-induced nociception, with inhibition of 81±10 and 68±9%, respectively. The previous desensitization with resiniferatoxin (RTX) largely reduced the spermine-induced nociception and TRPV1 expression in the sciatic nerve, with reductions of 82±9% and 67±11%, respectively. Furthermore, the combination of spermine (100nmol/paw) and RTX (0.005fmol/paw), in doses which alone were not capable of inducing nociception, produced nociceptive behaviors. Moreover, different concentrations of spermine (3–300μM) enhanced the specific binding of [3H]-RTX to TRPV1 receptor. Altogether, polyamines produce spontaneous nociceptive effect through the stimulation of TRPV1, but not of ionotropic glutamate or ASIC receptors.