Neuropeptides
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To evaluate the roles of spinal neurokinin receptors in the development of persistent nociception and hyperalgesia to thermal and mechanical stimuli induced by subcutaneous (s.c.) bee venom injection, effects of intrathecal (i.t.) pre- or post-treatment with a non-selective antagonist of (NK1/2) receptors, [D-Arg1,D-Trp7,9,Leu11] substance P (spantide), and a selective NK3 receptor antagonist, (S)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl) piperidin-3-yl)propyl)-4-phenylpiperidin-4-yl)-N-methyl acetamide (SR142801) were assessed in conscious rat. Injection of bee venom s.c. into the plantar surface of one hind paw resulted in a pathological pain phenomenon characterized by a 1-2 h single phase of persistent spontaneous nociceptive behaviors (continuously flinching the injected paw) and a 72-96 h profound primary thermal and mechanical hyperalgesia in the injection site and a secondary thermal hyperalgesia in the non-injected hindpaw. Pre-treatment with spantide i.t. at 0.05 microg, 0.5 microg and 5 microg produced a dose-related suppression of the bee venom-induced flinching reflex during the whole time course and the inhibitory rate was 24 +/- 12.60% (35.38 +/- 4.12 flinches/5 min, n=5), 48 +/- 6.75% (24.53 +/- 2.90 flinches/5 min, n=5) and 60 +/- 7.69% (18.88 +/- 3.58 flinches/5 min, n=5) respectively when compared with the saline control group (46.80 +/- 2.60 flinches/5 min, n=5). ⋯ Pre and post-treatment of SR142801 did not produce any significant effect on the bee venom-induced spontaneous pain and thermal and mechanical hyperalgesia. Our present result suggests that activation of spinal NK1/2 receptors is involved in both induction and maintenance of the persistent spontaneous nociception, while it is only involved in induction of the primary and secondary thermal, but not primary mechanical hyperalgesia induced by s.c. bee venom injection. The spinal NK3 receptor seems not likely to be involved in the bee venom-induced behavioral response characterized by spontaneous pain and thermal and mechanical hyperalgesia.