Establishment of bee venom-induced contralateral heat hyperalgesia in the rat is dependent upon central temporal summation of afferent input from the site of injury

The inhibitory effect of somatostatin receptor activation on bee venom-evoked nociceptive behavior and pCREB expression in rats

The present study examined nociceptive behaviors and the expression of phosphorylated cAMP response element-binding protein (pCREB) in the dorsal horn of the lumbar spinal cord and the dorsal root ganglion (DRG) evoked by bee venom (BV). The effect of intraplantar preapplication of the somatostatin analog octreotide on nociceptive behaviors and pCREB expression was also examined. Subcutaneous injection of BV into the rat unilateral hindpaw pad induced significant spontaneous nociceptive behaviors, primary mechanical allodynia, primary thermal hyperalgesia, and mirror-thermal hyperalgesia, as well as an increase in pCREB expression in the lumbar spinal dorsal horn and DRG. Octreotide pretreatment significantly attenuated the BV-induced lifting/licking response and mechanical allodynia. Local injection of octreotide also significantly reduced pCREB expression in the lumbar spinal dorsal horn and DRG. Furthermore, pretreatment with cyclosomatostatin, a somatostatin receptor antagonist, reversed the octreotide-induced inhibition of the lifting/licking response, mechanical allodynia, and the expression of pCREB. These results suggest that BV can induce nociceptive responses and somatostatin receptors are involved in mediating the antinociception, which provides new evidence for peripheral analgesic action of somatostatin in an inflammatory pain state.

Spatial and temporal plasticity of synaptic organization in anterior cingulate cortex following peripheral inflammatory pain: multi-electrode array recordings in rats

To explore whether experiencing inflammatory pain has an impact upon intracortical synaptic organization, the planar multi-electrode array (MEA) technique and 2-dimensional current source density (2D-CSD) imaging were used in slice preparations of the anterior cingulate cortex (ACC) from rats. Synaptic activity across different layers of the ACC was evoked by deep layer stimulation through one electrode. The layer-localization of both local field potentials (LFPs) and the spread of current sink calculated by 2D-CSD analysis was characterized pharmacologically. Moreover, the induction of long-term potentiation (LTP) and changes in LTP magnitude were also evaluated. We found that under naïve conditions, the current sink was initially generated in layer VI, then spread to layer V and finally confined to layers II-III. This spatial pattern of current sink movement typically reflected changes in depolarized sites from deep layers (V-VI) to superficial layers (II-III) where intra- and extracortical inputs terminate. In the ACC slices from rats in an inflamed state (for 2 h) caused by intraplantar bee-venom injection, the spatial profile of intra-ACC synaptic organization was significantly changed, showing an enlarged current sink distribution and a leftward shift of the stimulus-response curves relative to the naïve and saline controls. The change was more distinct in the superficial layers (II-III) than in the deep site. In terms of temporal properties, the rate of LTP induction was significantly increased in layers II-III by inflammatory pain. However, the magnitude of LTP was not significantly enhanced by this treatment. Taken together, these results show that inflammatory pain results in distinct spatial and temporal plasticity of synaptic organization in the ACC, which may lead to altered synaptic transmission and modulation.

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.

The nociceptive and anti-nociceptive effects of bee venom injection and therapy: a double-edged sword

Bee venom injection as a therapy, like many other complementary and alternative medicine approaches, has been used for thousands of years to attempt to alleviate a range of diseases including arthritis. More recently, additional theraupeutic goals have been added to the list of diseases making this a critical time to evaluate the evidence for the beneficial and adverse effects of bee venom injection. Although reports of pain reduction (analgesic and antinociceptive) and anti-inflammatory effects of bee venom injection are accumulating in the literature, it is common knowledge that bee venom stings are painful and produce inflammation. In addition, a significant number of studies have been performed in the past decade highlighting that injection of bee venom and components of bee venom produce significant signs of pain or nociception, inflammation and many effects at multiple levels of immediate, acute and prolonged pain processes. This report reviews the extensive new data regarding the deleterious effects of bee venom injection in people and animals, our current understanding of the responsible underlying mechanisms and critical venom components, and provides a critical evaluation of reports of the beneficial effects of bee venom injection in people and animals and the proposed underlying mechanisms. Although further studies are required to make firm conclusions, therapeutic bee venom injection may be beneficial for some patients, but may also be harmful. This report highlights key patterns of results, critical shortcomings, and essential areas requiring further study.

Microinjection of morphine into thalamic nucleus submedius depresses bee venom-induced inflammatory pain in the rat

Previous studies have provided evidence of the existence of a pain modulatory feedback pathway consisting of thalamic nucleus submedius (Sm)–ventrolateral orbital cortex-periaqueductal grey pathway, which is activated during acute pain and leads to depression of transmission of nociceptive information in the spinal dorsal horn. The aim of this study was to test the hypothesis that morphine microinjection into the Sm decreased spontaneous pain and bilateral thermal hyperalgesia, as well as ipsilateral mechanical allodynia, induced by subcutaneous injections of bee venom into the rat hind paw. Morphine (1.0, 2.5 or 5.0 m̀g in 0.5 μL) injected into the Sm, contralateral to the bee venominjected paw, depressed spontaneous nociceptive behaviour in a dose-dependent manner. Furthermore, morphine significantly decreased bilateral thermal hyperalgesia and ipsilateral mechanical allodynia 2 h after bee venom injection. These morphine-induced effects were antagonized by 1.0 μg naloxone (an opioid antagonist) microinjected into the Sm 5 min before morphine administration. The results provided further support for the important role of the Sm and Sm-opioid receptors in inhibiting nociceptive behaviour and indicated for the first time that Sm opioid receptors were also effective in inhibiting the hypersensitivity provoked by bee venom-induced inflammation.

Functional depletion of capsaicin-sensitive primary afferent fibers attenuates rat pain-related behaviors and paw edema induced by the venom of scorpion Buthus martensi Karch

The role of capsaicin-sensitive primary afferent fibers in rat pain-related behaviors and paw edema induced by scorpion Buthus martensi Karch (BmK) venom was investigated in this study. It was found that functional depletion of capsaicin-sensitive primary afferent fibers with a single systemic injection of resiniferatoxin (RTX) dramatically decreased spontaneous nociceptive behaviors, prevented the development of primary mechanical and thermal hyperalgesia as well as mirror-image mechanical hyperalgesia. RTX treatment significantly attenuated BmK venom-induced c-Fos expression in all laminaes of bilateral L4-L5 lumbar spinal cord, especially in superficial laminaes. Moreover, RTX treatment markedly reduced the early paw edema induced by BmK venom. Thus, the results indicate that capsaicin-sensitive primary afferent fibers play a critical role in various pain-related behaviors and paw edema induced by BmK venom in rats.

Peripheral involvement of PKA and PKC in subcutaneous bee venom-induced persistent nociception, mechanical hyperalgesia, and inflammation in rats

The roles of central protein kinases A and C (PKA and PKC) in various pain states have intensively been investigated during the past decade. The aim of the present study was to investigate the peripheral involvement of PKA and PKC in persistent nociceptive response, evoked pain behaviors, and inflammation induced by subcutaneous (s.c.) injection of bee venom (BV, 0.2mg/50 microl) in rats. The effects of intraplantar injection of H-89 (a PKA inhibitor, 5-100 microg/50 microl) and chelerythrine chloride (a PKC inhibitor, 5-100 microg/50 microl) on BV-elicited persistent nociception (nociceptive flinching reflex), mechanical hyperalgesia, and inflammation were systematically investigated. Pre-treatment with H-89 dose-dependently inhibited only BV-induced mechanical hyperalgesia, but not the persistent nociception and inflammation. In contrast, pre-treatment with chelerythrine chloride dose-dependently inhibited BV-induced sustained nociception and inflammation, but not the mechanical hyperalgesia. Topical pre-treatment of the sciatic nerve with 1% capsaicin significantly blocked the inhibitory effects of the PKC inhibitor on BV-induced inflammation, but not the persistent flinching response. These results indicate that peripheral PKA and PKC involvements in BV-induced pain behaviors differ, and capsaicin-sensitive afferents appear to participate in the pro-inflammatory role of PKC in the BV pain model. Findings from the present study also suggest that targeting specific peripheral protein kinases might prove effective in the treatment of persistent pain and inflammation.

Activation of spinal ERK signaling pathway contributes to pain-related responses induced by scorpion Buthus martensi Karch venom

It has been demonstrated that spontaneous nociceptive behaviors, cutaneous hyperalgesia and paw edema can be induced by intraplantar injection of scorpion Buthus martensi Karch (BmK) venom in rats. In the present study, activation of spinal extracellular signal-regulated kinase (ERK) signaling pathway and its contribution to pain-related responses induced by scorpion BmK venom were investigated. It was found that ERK was activated not only in the superficial layers but also in deep layers of L4-L5 spinal cord dorsal horn, which started at 2 min, peaked at 30-60 min and almost disappeared at 4h following intraplantar injection of BmK venom. Intrathecal injection of U0126 (0.1, 1.0 and 10 microg), a widely used specific MAP kinase kinase (MEK) inhibitor, suppressed spontaneous nociceptive responses and reduced primary heat hyperalgesia and bilateral mechanical hyperalgesia induced by BmK venom. In addition, BmK venom-induced spinal c-Fos expression could be inhibited by U0126 dose-dependently. Intrathecal delivery of NMDA receptor antagonist (5R, 10S)-(+)-5-methyl-10, 11-dihydro-5H-dibenzo [a,d]-cyclohepten-5-10-imine hydrogen maleate (MK-801) and the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) could partially inhibit activation of spinal ERK induced by BmK venom at 30 min. Thus, activation of ERK in spinal cord dorsal horn, partially mediated by NMDA and non-NMDA receptor, potentially contributes to BmK venom-induced pain-related behaviors.

Roles of peripheral mitogen-activated protein kinases in melittin-induced nociception and hyperalgesia

Recently, we have reported that melittin, a major toxic peptide of the whole bee venom, plays a central role in production of local inflammation, nociception and hyperalgesia following the experimental honeybee's sting. However, the exact peripheral mechanisms underlying melittin-induced multiple pain-related behaviors are still less characterized. In the present study, we sought to investigate the potential roles of peripheral mitogen-activated protein kinases (MAPKs) in melittin-induced nociception and hyperalgesia by pre- and post-administration of three MAPK inhibitors, namely U0126 (1 mug, 10 mug) for extracellular signal-regulated kinase (ERK), SP600125 (10 mug, 100 mug) for c-Jun N-terminal kinase (JNK) and SB239063 (10 mug, 100 mug) for p38 MAPK, into the local inflamed area of one hind paw of rats. Both pre- and post-treatment with three drugs significantly suppressed the occurrence and maintenance of melittin-evoked persistent spontaneous nociception (PSN) and primary heat hyperalgesia, with little antinociceptive effect on mechanical hyperalgesia. In vehicle-treated group, ipsilateral injection of melittin produced no impact on thermal and mechanical sensitivity of the other hind paw, suggesting no occurrence of contralateral heat and mechanical hyperalgesia in the melittin test. In addition, local administration of each inhibitor into the contralateral hind paw exerted no significant influence on either PSN or heat/mechanical hyperalgesia tested in the primary injured hind paw, excluding the systemically pharmacological effects of the three drugs. Furthermore, local administration of the three compounds in naïve animals, respectively, did not change the basal pain sensitivity to either thermal or mechanical stimuli, suggesting lack of peripherally functional roles of the three MAPK subfamily members in normal pain sensitivity under the physiological state. Taken together, we conclude that activation of peripheral MAPKs, including ERK, JNK and p38, might contribute to the induction and maintenance of persistent ongoing pain and primary heat hyperalgesia in the melittin test. However, they are not likely to be involved in the processing of melittin-induced primary mechanical hyperalgesia, implicating a mechanistic separation between mechanical and thermal hyperalgesia in the periphery.

Antinociceptive effects of systemic paeoniflorin on bee venom-induced various ‘phenotypes’ of nociception and hypersensitivity

Paeoniflorin (PF), one of the active chemical compounds identified from the root of Paeonia lactiflora Pall, has been well-established to exhibit various neuroprotective actions in the central nervous system (CNS) after long-term daily administration. In the present study, by using the bee venom (BV) model of nociception and hypersensitivity, antinociceptive effects of PF were evaluated by intraperitoneal administration in conscious rats. When compared with saline control, systemic pre- and post-treatment with PF resulted in an apparent antinociception against both persistent spontaneous nociception and primary heat hypersensitivity, while for the primary mechanical hypersensitivity only pre-treatment was effective. Moreover, pre- and early post-treatment with PF (5 min after BV injection) could successfully suppress the occurrence and maintenance of the mirror-image heat hypersensitivity, whereas late post-treatment (3 h after BV) did not exert any significant impact. In the Rota-Rod treadmill test, PF administration did not affect the motor coordinating performance of rats. Furthermore, systemic PF application produced no significant influence upon BV-induced paw edema and swelling. Finally, the PF-produced antinociception was likely to be mediated by endogenous opioid receptors because of its naloxone-reversibility. Taken together, these results provide a new line of evidence showing that PF, besides its well-established neuroprotective actions in the CNS, is also able to produce analgesia against various 'phenotypes' of nociception and hypersensitivity via opioid receptor mediation.

Degranulation of mast cells and histamine release involved in rat pain-related behaviors and edema induced by scorpion Buthus martensi Karch venom

In the present study, it was investigated whether the degranulation of mast cells and histamine release were involved in rat pain-related behaviors and edema induced by the venom of scorpion Buthus martensi Karch (BmK) or not. It was found that the obvious degranulation of mast cells could be triggered in rat hindpaw skin by BmK venom. The chronic degranulation of mast cells using compound 48/80 relieved the spontaneous nociceptive responses, the primary thermal and bilateral mechanical hyperalgesia and the rat paw edema, as well as partially reduced c-Fos expression in superficial layers (laminae I-II) of bilateral spinal cord induced by BmK venom. In addition, individual peripheral co-administration of either 100 nmol chlorpheniramine or 100 nmol pyrilamine (histamine H(1) receptor antagonist) or 500 nmol cimetidine (histamine H(2) receptor antagonist) and BmK venom suppressed the spontaneous nociceptive responses, partially the primary thermal and bilateral mechanical hyperalgesia and rat paw edema induced by BmK venom. Thus, these results suggest that the peripheral cellular incidents of mast cells degranulation and histamine release are involved in BmK venom-induced pain-related behaviors and inflammation.

Roles of different subtypes of opioid receptors in mediating the ventrolateral orbital cortex opioid-induced inhibition of mirror-neuropathic pain in the rat

Previous studies have demonstrated that opioid receptors in the prefrontal ventrolateral orbital cortex (VLO) are involved in anti-nociception. The aim of this current study was to examine whether opioid receptors in the VLO have effects on the hypersensitivity induced by contralateral L5 and L6 spinal nerve ligation (SNL), termed as mirror neuropathic pain (MNP) in the male rat. Morphine (1.0, 2.5, 5.0 microg) microinjected into the VLO contralateral to the SNL depressed the mechanical paw withdrawal assessed by von Frey filaments and the cold plate (4 degrees C)-induced paw lifting in a dose-dependent manner on the side without SNL. These effects were antagonized by microinjection of the non-selective opioid receptor antagonist naloxone (1.0 mug) into the same VLO site. Microinjection of endomorphin-1 (5.0 microg), a highly selective mu-opioid receptor agonist, and [d-Ala(2), d-Leu(5)]-enkephalin (DADLE, 10 microg), a delta-/mu-receptor agonist, also depressed the MNP. The effects of both drugs were blocked by selective mu-receptor antagonist beta-funaltrexamine (beta-FNA, 3.75 microg), but the effect of the DADLE was not influenced by the selective delta-receptor antagonist naltrindole (5.0 microg). Microinjection of the kappa-opioid receptor agonist spiradoline mesylate salt (U-62066) (100 microg) had no effect on the MNP. These results suggest that the VLO is involved in opioid-induced inhibition of the MNP and the effect is mediated by mu- (but not delta- and kappa-) opioid receptors.

Pivotal involvement of neurogenic mechanism in subcutaneous bee venom-induced inflammation and allodynia in unanesthetized conscious rats

The bee venom (BV) model is a valid inflammatory pain model in animals and has been extended to human studies using its principle protein, mellitin. After subcutaneous (s.c.) injection of BV, long-lasting spontaneous nociception followed by thermal hyperalgesia, static allodynia, and local inflammatory response (edema) can be observed in rats. We hypothesize that (1) neurogenic components may contribute to the BV-induced inflammatory response and (2) static and dynamic mechanical allodynia may exist simultaneously in the BV model. Using different approaches including sciatic nerve transection (SCT), L4-L6 dorsal rhizotomy (DRT) and local treatment of the sciatic nerve with capsaicin, we found that SCT, DRT, and local capsaicin onto the sciatic nerve produced a significant inhibition of the BV-induced increase in volume of the injected paw, with a stronger effect of the SCT and the local capsaicin treatments than that of the DRT treatment. Static and dynamic mechanical allodynia in the BV test was assessed by measuring the paw withdrawal mechanical threshold and the paw withdrawal latency before and after the BV injection, respectively. Local capsaicin onto the sciatic nerve produced a significant inhibition of the BV-induced decrease in the paw withdrawal mechanical threshold, but not the paw withdrawal latency, of the injected paw. These findings suggest that neurogenic components, via dorsal root reflex and axon reflex mechanisms, are probably involved in the maintenance and the development of the BV-induced inflammation. In addition, the capsaicin-sensitive primary afferents may play differential roles in the development of the BV-induced static and dynamic mechanical allodynia.

Altered pain-related behaviors and spinal neuronal responses produced by s.c. injection of melittin in rats

Recently, we have reported that following s.c. injection of a solution containing the whole bee-venom (BV; Apis mellifera), into one hind paw of a rat, the experimentally produced honeybee's sting, the animal shows altered pain-related behaviors and inflammation relevant to pathological pain state. To see whether melittin, the major (over 50%) toxic component of the BV, is responsible for the above abnormal pain behavioral changes, the present study was designed to investigate the effects of s.c. melittin on either nociceptive behaviors in conscious rats or spinal dorsal horn neuronal responses in anesthetized rats. In the behavioral surveys, s.c. injection of three doses of both melittin (5, 25 and 50 microg) and BV (10, 50 and 100 microg) into the posterior surface of one hind paw of rats produced an immediate tonic nociceptive response displaying as persistent spontaneous paw flinching reflex. Similar to the BV test, the melittin response was also monophasic and dose-dependent in terms of both intensity and time course. As an accompanied consequence, both heat and mechanical hypersensitivity (hyperalgesia and allodynia) and inflammatory responses (paw swelling and plasma extravasation) were induced by s.c. melittin injections. In the electrophysiological recordings, s.c. injection of the same three doses of melittin into the cutaneous receptive field produced an immediate, dose-dependent increase in spontaneous spike discharges of spinal dorsal horn wide-dynamic-range (WDR) neurons which are believed to be responsible for the spinally-organized nociceptive flexion reflex. The melittin-induced ongoing spike responses are similar to the behavioral flinching reflex in terms of both duration and frequency. Furthermore, the responsiveness of the WDR neurons to both heat (42 degrees C, 45 degrees C, 47 degrees C and 49 degrees C) and mechanical (brush, pressure and pinch) stimuli was significantly enhanced by s.c. injection of melittin shown as a leftward shift of the stimulus-response functional curves. Taken together, the present results suggest that melittin, the major toxin of the whole BV, is likely to be responsible for production of the long-term spinal neuronal changes as well as persistent spontaneous nociception, heat/mechanical hypersensitivity and inflammatory responses that are produced by experimental honeybee's sting.

Chronic inflammation and compression of the dorsal root contribute to sciatica induced by the intervertebral disc herniation in rats

The pathophysiological mechanisms underlying sciatica and back pain are not well understood. In the present study, a sciatica model was developed to investigate the contributions of inflammation and compression of the dorsal root (DR). The procedure used autologous disc to apply direct pressure to the L5 DR (disc compression, DC group). For control, five additional groups were included: (1). mechanical compression of L5 DR without disc (compression, CP group); (2). epidurally placed disc without mechanical compression (disc group); (3). epidurally placed nucleus pulposus (NP) without mechanical compression (NP group); (4). epidurally placed annulus fibrosus (AF) without mechanical compression (AF group) and (5). sham group. The paw withdrawal latency to heat stimulation, paw withdrawal threshold to mechanical stimulation, body weight, and motor function were determined pre- and post-surgery. It was observed that all experimental groups with the exception of the sham group showed a progressive and prolonged mechanical hyperalgesia with the DC group having the strongest effect. Furthermore, the disc group showed a greater mechanical hyperalgesia with earlier onset in comparison with the CP group and disc, AF, and NP groups developed thermal hyperalgesia in addition to mechanical hyperalgesia following surgery. Finally, rats in all groups showed normal motor function and body weight increase. These data suggest that this model is suitable to investigate the mechanisms of sciatica and inflammation as well as mechanical compression is involved in the pathogenesis of this condition. Moreover, AF and NP may contribute similarly to the development of sciatica and back pain.

Acupoint stimulation using bee venom attenuates formalin-induced pain behavior and spinal cord fos expression in rats

In two previous reports, we have demonstrated that injection of bee venom (BV) into an acupoint produces a significant antinociceptive and anti-inflammatory effect in both a mouse model of visceral nociception and a rat model of chronic arthritis. The present study was designed to evaluate the potential antinociceptive effect of BV pretreatment on formalin-induced pain behavior and it associated spinal cord Fos expression in rats. Adult Sprague-Dawley rats were injected with BV directly into the Zusanli (ST36) acupoint or into an arbitrary non-acupoint located on the back. BV pretreatment into the Zusanli acupoint significantly decreased paw-licking time in the late phase of the formalin test. In contrast, BV injected into a non-acupoint in the back region did not suppress the paw-licking time. In addition, BV pretreatment into the Zusanli acupoint markedly inhibited spinal cord Fos expression induced by formalin injection. These findings indicate that BV pretreatment into the Zusanli acupoint has an antinociceptive effect on formalin-induced pain behavior.

Behavioral evidence supporting a differential role for spinal group I and II metabotropic glutamate receptors in inflammatory hyperalgesia in sheep

A differential role for metabotropic glutamate receptors (mGluRs) in spinal nociception in normal animals has previously been identified. The present study examined the contribution of group I and group II mGluRs to the development and maintenance of inflammatory hyperalgesia produced by unilateral intradermal injection of carrageenan into the lower forelimb in sheep. Carrageenan (7.5 mg in 500 micro l) produced a significant bilateral reduction in forelimb mechanical withdrawal thresholds. Intrathecal administration of saline-vehicle or the group II mGluR antagonist (2S)-alpha-ethylglutamate (EGLU; 570 nmol) had no effect on either the development or maintenance of hyperalgesia. However, intrathecal administration of the group I mGluR antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA; 450 nmol) before carrageenan blocked the development of ipsilateral hyperalgesia, and when given 2 h after carrageenan, reversed both ipsilateral and contralateral hyperalgesia. Intrathecal administration of the group II mGluR agonist (2S,1S,2S)-2-(carboxycyclopropyl)glycine (L-CCG-I; 620 nmol) given either before or after carrageenan treatment produced analgesia and anti-hyperalgesia, an effect abolished by co-administration of EGLU (570 nmol). The magnitude of the analgesic response, assessed by the area under the response curve, was significantly greater than that produced by LCCG-I in normal animals. These data demonstrate that the development and maintenance of inflammatory hyperalgesia is dependent on activation of group I mGluRs in spinal cord. In addition, the analgesic and anti-hyperalgesic actions of group II mGluRs suggest that these receptors play a crucial role in modulating acute inflammatory hyperalgesia.

Effect of honey bee venom on proliferation of K1735M2 mouse melanoma cells in-vitro and growth of murine B16 melanomas in-vivo

Bee venom has been reported to exhibit antitumour activity in-vitro and in-vivo. Apoptosis, necrosis and lysis of tumour cells were suggested as possible mechanisms by which bee venom inhibited tumour growth. The aim of this study was to investigate potential mechanisms by which bee venom inhibits K1735M2 mouse melanoma cells in-vitro and B16 melanoma, a transplantable solid melanoma in C57BL/6 mice, in-vivo. The proliferation of K1735M2 cells in-vitro was inhibited by bee venom in a concentration- and time-dependent manner. The inhibition was indicated by the arrest of the cell cycle at the G1 stage, as detected by flow cytometric measurements. The bee venom induced apoptosis-like cell death as identified by histological observations and by DNA fragmentation. In the in-vivo experiments, the bee venom (1.0, 3.0, 9.0 mg kg-1 of body weight, on days 1-12) was injected intraperitoneally into mice 24 h after the mice were inoculated with B16 cells. Inhibition of the solid tumour was observed. Apoptosis of the K1735M2 cells was suggested as the possible mechanism by which bee venom inhibited cell proliferation and induced K1735M2 cell differentiation in-vitro. The in-vivo experiment indicated that bee venom could be used as a chemotherapeutic agent against malignant tumours.

Heritability of nociception. III. Genetic relationships among commonly used assays of nociception and hypersensitivity

We and others have previously demonstrated that nociception in the mouse is heritable. A genetic correlation analysis of 12 common measures of nociception among a common set of inbred strains revealed three major clusters (or 'types') of nociception in this species. In the present study, we re-evaluated the major types of nociception and their interrelatedness using ten additional assays of nociception and hypersensitivity, including: three thermal assays (tail withdrawal from 47.5 degrees C water or -15 degrees C ethanol; tail flick from radiant heat), two chemical assays of spontaneous nociception (bee venom test; capsaicin test) and their subsequent thermal hypersensitivity states (including contralateral hypersensitivity in the bee venom test), a mechanical nociceptive assay (tail-clip test), and a mechanical hypersensitivity assay (intrathecal dynorphin). Confirming our earlier findings, the results demonstrate distinct thermal and chemical nociceptive types. It is now clear that mechanical hypersensitivity and thermal hypersensitivity are genetically dissociable phenomena. Furthermore, we now see at least two distinct types of thermal hypersensitivity: afferent-dependent, featuring a preceding significant period of spontaneous nociceptive behavior associated with afferent neural activity, and non-afferent-dependent. In conclusion, our latest analysis suggests that there are at least five fundamental types of nociception and hypersensitivity: (1) baseline thermal nociception; (2) spontaneous responses to noxious chemical stimuli; (3) thermal hypersensitivity; (4) mechanical hypersensitivity; and (5) afferent input-dependent hypersensitivity.