The anti-nociceptive effect and the possible mechanism of acupoint stimulation caused by chemical irritants in the bee venom pain model.

Many studies have demonstrated the anti-nociceptive and anti-inflammatory effects of injecting bee venom (BV) into the Zusanli (ZSL) acupoint in rats. The present study was designed to determine whether the injection of other chemical irritants, such as formalin and complete Freund's adjuvant (CFA), into the ZSL acupoint can produce anti-nociceptive and anti-inflammatory effects in the BV pain model and to determine the possible mechanisms underlying these effects. First, the effects of injecting BV, formalin, CFA, or saline into the ZSL acupoint on intraplantar BV-induced persistent spontaneous pain, mechanical hyperalgesia, and inflammatory swelling of the injected paw were observed. BV, formalin, CFA, and saline injection into the ZSL acupoint significantly inhibited intraplantar BV-induced persistent spontaneous nociception (PSN) and mechanical hyperalgesia but had no effect on intraplantar BV-induced inflammatory swelling. Next, the effects of pretreatment with naloxone (5mg/kg, ip) or injection of 0.15% capsaicin into the ZSL acupoint on the anti-nociceptive effect of BV acupuncture (BVA) were observed. Pretreatment with naloxone had no effect on the BVA-induced anti-nociceptive effect, intraplantar BV-induced PSN, and mechanical hyperalgesia. Pretreatment with capsaicin produced partial blockage of the BVA-induced anti-nociceptive effect on PSN, but it had no effect on BVA-induced anti-nociception of mechanical hyperalgesia. These results suggest that (1) chemical irritant acupuncture produces the anti-nociceptive effect but not the anti-inflammatory effect in the BV pain model, and (2) chemical irritant acupuncture-induced analgesia is a common mechanism that is not specific to BV acupuncture. Our results also suggest that the BVA-induced anti-nociceptive mechanism is partially mediated by capsaicin-sensitive primary afferent fibers but not by endogenous mu opioid receptors in the BV pain model.

Differential roles of peripheral metabotropic glutamate receptors in bee venom-induced nociception and inflammation in conscious rats.

UNLABELLED: Intraplantar injection of bee venom (BV) produces persistent spontaneous nociception (PSN), hyperalgesia, and inflammatory swelling of the injected paw. The present study was designed to determine the roles of peripheral metabotropic glutamate receptors (mGluRs) in BV-induced nociception and inflammation. We determined the effects of the group I mGluR antagonist AIDA, the group II mGluR agonist ADPC, and the group III mGluR agonist L-AP4 on BV-induced PSN, mechanical hyperalgesia, and inflammatory swelling. Pretreatment with intraplantar injections of AIDA, ADPC or L-AP4 at different doses significantly inhibited BV-induced PSN over the 1-hour observational period. The inhibitory effects of ADPC and L-AP4 were completely abolished by pretreatment with the group II mGluR antagonist LY341495 and the group III mGluR antagonist MSOP, respectively. Pretreatment with ADPC prevented the BV-induced decrease in paw-withdrawal mechanical threshold (PWMT) in a dose-dependent manner, while pretreatment with AIDA or L-AP4 had no effect. The antihyperalgesic effect of ADPC was completely abolished by pretreatment with LY341495. Pretreatment with AIDA, ADPC or L-AP4 at different doses had no effect on the BV-induced increase in the paw volume (PV), a measurement of inflammatory swelling. All contralateral drug treatments at the highest doses had no effect on BV-induced PSN, decreases in PWMT or increases in PV, eliminating the possibility of drug-induced systemic effects. These data suggest that the activation of mGluRs in the periphery may play a differential role in BV-induced nociception and inflammation. PERSPECTIVE: The present study demonstrated that the intraplantar injection of antagonists or agonists of different mGluRs produced differential effects on bee venom-induced persistent spontaneous nociception and mechanical hyperalgesia. However, no effects on inflammation were observed, suggesting that mGluRs in the periphery have differential roles. Thus, therapies specifically targeting metabotropic glutamate receptors may improve the treatment of patients with persistent spontaneous nociception and hyperalgesia.

Differential roles of peripheral mitogen-activated protein kinase signal transduction pathways in bee venom-induced nociception and inflammation in conscious rats.

UNLABELLED: Intraplantar injection of bee venom (BV) produces persistent spontaneous nociception (PSN) and hyperalgesia, as well as obvious inflammatory swelling, in the paws of injected rats. The present study was designed to determine the peripheral roles of mitogen-activated protein kinase (MAPK) signal transduction pathways in BV-induced nociception and inflammation. We examined the effect of intraplantar injection of an ERK1/2 inhibitor, PD98059, and a p38 inhibitor, SB202190, on BV-induced PSN, mechanical hyperalgesia, and inflammatory swelling. We found that (1) pretreatment with SB202190 (0.1 to 10 microg) had no effect on BV-induced PSN, whereas pretreatment with PD98059 (0.1 to 100 microg) produced a significant and dose-dependent inhibition of BV-induced PSN; (2) pretreatment with PD98059 (0.1 to 100 microg) had no effect on BV-induced decreases in paw withdrawal mechanical threshold (PWMT), while pretreatment with SB202190 (0.1 to 10 microg) produced an obvious prevention of the BV-induced decrease in PWMT; and (3) pretreatment with PD98059 (0.1 to 100 microg) had no effect on BV-induced increase in paw volume (PV), whereas pretreatment with SB202190 (0.1 to 10 microg) produced a dose-related inhibition of BV-induced increases in PV. No contralateral drug treatments, even at the highest dose, had any effect on BV-induced PSN, PWMT or PV, ruling out the systemic effect of these drugs. These results suggest that peripheral MAPK signal transduction pathways may play differential roles in bee venom-induced nociception and inflammation. Targeting specific peripheral MAPKs might prove effective in the treatment of persistent pain and inflammation. PERSPECTIVE: The present article showed that intraplantar injection of different MAPK inhibitors produced differential effects on bee venom-induced nociception and inflammation, suggesting that the peripheral MAPK signal transduction pathways have differential roles. Targeting specific peripheral MAPKs might prove effective in the treatment of persistent pain and inflammation.