Spatial and temporal expression of c-Fos protein in the spinal cord of anesthetized rat induced by subcutaneous bee venom injection

Cyclic GMP-dependent protein kinase-I localized in nociceptors modulates nociceptive cortical neuronal activity and pain hypersensitivity

Abstract

Chronic pain represents a frequent and poorly understood public health issue. Numerous studies have documented the key significance of plastic changes along the somatosensory pain pathways in chronic pain states. Our recent study demonstrated that the cGMP-dependent protein kinase I (PKG-I) specifically localized in nociceptors constitutes a key mediator of hyperexcitability of primary sensory neurons and spinal synaptic plasticity after inflammation. However, whether PKG-I in nociceptors further affects the cortical plasticity in the ascending pain pathways under pathological states has remained elusive. The immediate-early gene c-fos and phosphorylated ERK1/2 (pERK1/2) are considered reliable indicators for the neuronal activation status and it permits a comprehensive and large-scale observation of nociceptive neuronal activity along the ascending pain pathways subjected to tissue injury. In the present study, we systemically demonstrated that peripheral injury in PKG-Ifl/fl mice produced a significant upregulation of c-Fos or pERK1/2 over from the periphery to the cortex along the pain pathways, including dorsal root ganglion, spinal dorsal horn, ventral posterolateral thalamus, primary somatosensory hindlimb cortex, anterior cingulate cortex, basolateral amygdala, periaqueductal gray, and parabrachial nucleus. In contrast, very few cells in the above regions showed c-Fos or pERK1/2 induction in nociceptor-specific knockout mice lacking PKG-I (SNS-PKG-I/ mice). Our results indicate that PKG-I expressed in nociceptors is not only a key determinant of dorsal root ganglion hyperexcitability and spinal synaptic plasticity but also an important modulator of cortical neuronal activity in pathological pain states and represent what we believe to be novel targets in the periphery for pain therapeutics.

Peripheral ionotropic glutamate receptors contribute to Fos expression increase in the spinal cord through antidromic electrical stimulation of sensory nerves

Previous studies have shown that peripheral ionotropic glutamate receptors are involved in the increase in sensitivity of a cutaneous branch of spinal dorsal ramus (CBDR) through antidromic electrical stimulation (ADES) of another CBDR in the adjacent segment. CBDR in the thoracic segments run parallel to each other and no synaptic contact at the periphery is reported. The present study investigated whether the increased sensitivity of peripheral sensory nerves via ADES of a CBDR induced Fos expression changes in the adjacent segments of the spinal cord. Fos expression increased in the T8 - T12 segments of the spinal cord evoked by ADES of the T10 CBDR in rats. The increased Fos expression in the T11 and T12, but not T8 - T10 spinal cord segments, was significantly blocked by local application of either N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine maleate (MK-801) or non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) into the receptive field of T11 CBDR. The results suggest that endogenous glutamate released by ADES of sensory nerve may bind to peripheral ionotropic glutamate receptors and activate adjacent sensory nerve endings to increase the sensitivity of the spinal cord. These data reveal the potential mechanisms of neuron activation in the spinal cord evoked by peripheral sensitization.

Gastrodin protects against chronic inflammatory pain by inhibiting spinal synaptic potentiation

Tissue injury is known to produce inflammation and pain. Synaptic potentiation between peripheral nociceptors and spinal lamina I neurons has been proposed to serve as a trigger for chronic inflammatory pain. Gastrodin is a main bioactive constituent of the traditional Chinese herbal medicine Gastrodia elata Blume, which has been widely used as an analgesic since ancient times. However, its underlying cellular mechanisms have remained elusive. The present study demonstrated for the first time that gastrodin exhibits an analgesic effect at the spinal level on spontaneous pain, mechanical and thermal pain hypersensitivity induced by peripheral inflammation, which is not dependent on opioid receptors and without tolerance. This analgesia by gastrodin is at least in part mediated by depressing spinal synaptic potentiation via blockade of acid-sensing ion channels. Further studies with miniature EPSCs and paired-pulse ratio analysis revealed the presynaptic origin of the action of gastrodin, which involves a decrease in transmitter release probability. In contrast, neither basal nociception nor basal synaptic transmission was altered. This study revealed a dramatic analgesic action of gastrodin on inflammatory pain and uncovered a novel spinal mechanism that could underlie the analgesia by gastrodin, pointing the way to a new analgesic for treating chronic inflammatory pain.

Analgesic Effects of Danggui-Shaoyao-San on Various "Phenotypes" of Nociception and Inflammation in a Formalin Pain Model

Danggui-Shaoyao-San (DSS) is a traditional Chinese medicine, which has long been used for pain treatment and has been demonstrated to possess anti-oxidative, cognitive enhancement, and anti-depressant effects. In the present study, the effects of aqueous extracts of DSS on spontaneous pain behaviors and long-term hyperalgesia were examined to investigate the anti-nociceptive effects and underlying mechanisms. Single pretreatment of DSS dose-dependently reduced spontaneous flinches/licking time in the second, rather than the first, phase after subcutaneous injection of 5 % formalin into one hindpaw, in doses of 2.4 and 9.6 g/kg. DSS also dose-dependently inhibited FOS and cyclooxygenase-2 (COX-2) expression in both superficial and deep layers within the spinal dorsal horn. Further, DSS reduced hypoalgesia in the injected paw from 1 to 3 days and produced anti-hyperalgesic actions in both the injected paw after 3 days and non-injected paw. These data suggest involvement of enhancement of descending pain inhibition by suppression of 5-HTT levels in the spinal dorsal horn and reduction of peripheral long-term inflammation, including paw edema and ulcers. These findings suggest that DSS may be a useful therapeutic agent for short- and long-term inflammation induced pain, through both anti-inflammatory and suppression of central sensitization mechanisms.

Upregulation of Ih expressed in IB4-negative Aδ nociceptive DRG neurons contributes to mechanical hypersensitivity associated with cervical radiculopathic pain

Cervical radiculopathy represents aberrant mechanical hypersensitivity. Primary sensory neuron’s ability to sense mechanical force forms mechanotransduction. However, whether this property undergoes activity-dependent plastic changes and underlies mechanical hypersensitivity associated with cervical radiculopathic pain (CRP) is not clear. Here we show a new CRP model producing stable mechanical compression of dorsal root ganglion (DRG), which induces dramatic behavioral mechanical hypersensitivity. Amongst nociceptive DRG neurons, a mechanically sensitive neuron, isolectin B4 negative Aδ-type (IB4⁻ Aδ) DRG neuron displays spontaneous activity with hyperexcitability after chronic compression of cervical DRGs. Focal mechanical stimulation on somata of IB4^- Aδ neuron induces abnormal hypersensitivity. Upregulated HCN1 and HCN3 channels and increased I_h current on this subset of primary nociceptors underlies the spontaneous activity together with neuronal mechanical hypersensitivity, which further contributes to the behavioral mechanical hypersensitivity associated with CRP. This study sheds new light on the functional plasticity of a specific subset of nociceptive DRG neurons to mechanical stimulation and reveals a novel mechanism that could underlie the mechanical hypersensitivity associated with cervical radiculopathy.

Helminthes and insects: maladies or therapies

By definition, parasites cause harm to their hosts. But, considerable evidence from ancient traditional medicine has supported the theory of using parasites and their products in treating many diseases. Maggots have been used successfully to treat chronic, long-standing, infected wounds which failed to respond to conventional treatment by many beneficial effects on the wound including debridement, disinfection, and healing enhancement. Maggots are also applied in forensic medicine to estimate time between the death and discovery of a corpse and in entomotoxicology involving the potential use of insects as alternative samples for detecting drugs and toxins in death investigations. Leeches are segmented invertebrates, famous by their blood-feeding habits and used in phlebotomy to treat various ailments since ancient times. Leech therapy is experiencing resurgence nowadays in health care principally in plastic and reconstructive surgery. Earthworms provide a source of medicinally useful products with potential antimicrobial, antiviral, and anticancer properties. Lumbrokinases are a group of fibrinolytic enzymes isolated and purified from earthworms capable of degrading plasminogen-rich and plasminogen-free fibrin and so can be used to treat various conditions associated with thrombotic diseases. Helminth infection has been proved to have therapeutic effects in both animal and human clinical trials with promising evidence in treating many allergic diseases and can block the induction of or reduce the severity of some autoimmune disorders as Crohn's disease or ulcerative colitis. What is more, venomous arthropods such as scorpions, bees, wasps, spiders, ants, centipedes, snail, beetles, and caterpillars. The venoms and toxins from these arthropods provide a promising source of natural bioactive compounds which can be employed in the development of new drugs to treat diseases as cancer. The possibility of using these active molecules in biotechnological processes can make these venoms and toxins a valuable and promising source of natural bioactive compounds. The therapeutic use of helminthes and insects will be of great value in biomedicine and further studies on insect toxins will contribute extensively to the development of Biomedical Sciences.

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.

Neuronal Activity Stimulated by Liquid Substrates Injection at Zusanli (ST36) Acupoint: The Possible Mechanism of Aquapuncture

Aquapuncture is a modified acupuncture technique and it is generally accepted that it has a greater therapeutic effect than acupuncture because of the combination of the acupoint stimulation and the pharmacological effect of the drugs. However, to date, the mechanisms underlying the effects of aquapuncture remain unclear. We hypothesized that both the change in the local spatial configuration and the substrate stimulation of aquapuncture would activate neuronal signaling. Thus, bee venom, normal saline, and vitamins B1 and B12 were injected into a Zusanli (ST36) acupoint as substrate of aquapuncture, whereas a dry needle was inserted into ST36 as a control. After aquapuncture, activated neurons expressing Fos protein were mainly observed in the dorsal horn of the spinal cord in lumbar segments L3–5, with the distribution nearly identical among all groups. However, the bee venom injection induced significantly more Fos-expressing neurons than the other substrates. Based on these data, we suggest that changes in the spatial configuration of the acupoint activate neuronal signaling and that bee venom may further strengthen this neuronal activity. In conclusion, the mechanisms for the effects of aquapuncture appear to be the spatial configuration changes occurring within the acupoint and the ability of injected substrates to stimulate neuronal activity.

The Possible Neuronal Mechanism of Acupuncture: Morphological Evidence of the Neuronal Connection between Groin A-Shi Point and Uterus

Somatovisceral reflex suggested that the somatic stimulation could affect visceral function like acupuncture which treats diseases by stimulating acupoints. The neuronal connection between somatic point and visceral organ was not clear. Uterine pain referred to the groin region has long been recognized clinically. Wesselmann, using neurogenic plasma extravasation method, showed that uterine pain was referred to the groin region through a neuronal mechanism (Wesselmann and Lai 1997). This connection could be considered through the somatovisceral reflex pathway. However, the relay center of this pathway is still not clearly identified. In the present study, bee venom was injected in the groin region to induce central Fos expression to map the sensory innervation of groin region. Pseudorabies virus (PrV), a transneuronal tracer, was injected in the uterus to identify the higher motor control of the uterus. Immunohistochemistry staining revealed the Fos expression and PrV-infected double-labeled neurons in the nucleus of solitary tract (NTS), the dorsal motor nucleus of vagus (DMX), and the paraventricular hypothalamic nucleus (PVN). These results suggest a somatoparasympathetic neuronal connection (groin-spinal dorsal horn-NTS/DMX-uterus) and a somatosympathetic neuronal connection (groin-spinal dorsal horn-NTS-PVN-uterus). These two neuronal connections could be the prerequisites to the neuronal basis of the somatovisceral reflex and also the neuronal mechanism of acupuncture.

Upper thoracic postsynaptic dorsal column neurons conduct cardiac mechanoreceptive information, but not cardiac chemical nociception in rats

Postsynaptic dorsal column (PSDC) neurons transmit noxious visceral information from the lower thoracic and lumbosacral spinal cord. Cuneothalamic neurons in the PSDC pathway and upper thoracic (T(3)-T(4)) spinal neurons ascending through the ventrolateral funiculus (VLF) have been shown to transmit nociceptive cardiac information. Therefore, we hypothesized that upper thoracic PSDC neurons transmit noxious cardiac information. Neuronal responses to intrapericardially injected mechanical (1.0 ml saline) and noxious chemical (0.2 ml algogenic chemicals) stimuli were recorded from antidromically activated PSDC and VLF neurons in the T(3)-T(4) spinal cord of anesthetized Sprague-Dawley rats. Of the PSDC neurons, 43% responded to mechanical stimulation, but only one responded to noxious chemical stimuli. Fifty-eight percent of VLF neurons responded to mechanical stimulation and all responded to noxious chemical stimulation. Fluoro-Ruby (FR)-labeled PSDC neurons in the T(3)-T(4) spinal cord of Sprague-Dawley rats were processed for c-fos immunohistochemistry following intrapericardial stimulation with mechanical, chemical, or control stimuli. Sections were viewed under epifluorescence and light microscopy to detect FR-labeled neurons containing a c-fos immunoreactive (IR) nucleus. An average of 6 PSDC neurons per rat was found in the T(3) and T(4) spinal segments. The average number of c-fos-IR neurons per segment varied by type of stimulus: 12 (control), 67 (chemical) and 85 (mechanical) for T(3) and 8 (control), 37 (chemical) and 62 (mechanical) for T(4). None of the 200 PSDC neurons examined expressed c-fos-IR regardless of stimulus. Together, these results suggest that thoracic PSDC neurons transmit mechanical cardiac information, but they play a minimal role in cardiac nociception.

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.

Spatiotemporal characteristics of pain-associated neuronal activities in primary somatosensory cortex induced by peripheral persistent nociception

The primary somatosensory cortex (S1 area) is one of the key brain structures for central processing of somatic noxious information to produce pain perception. However, so far, the spatiotemporal characteristics of neuronal activities associated with peripheral persistent nociception have rarely been studied. In the present report, we used c-Fos as a neuronal marker to analyze spatial and temporal patterns of pain-related neuronal activities within the S1 area of rats subjecting to subcutaneous (s.c.) injection of bee venom (BV) solution, a well-established animal model of persistent pain. In naïve and saline-treated rats, c-Fos-labeled neurons were diffusely and sparsely distributed in the hindlimb region of S1 area. Following s.c. BV injection, c-Fos-labeled neurons became densely increased in superficial layers (II-III) and less increased in deep layers (IV-VI). The mean number of c-Fos positive neurons in the layers II-III began to increase at 1h and reached a peak at 2h after BV treatment that was followed by a gradual decrease afterward. The time course of c-Fos expression in the layers IV-VI was in parallel with that of the superficial layers, but with a much lower density and magnitude. The present results demonstrated that BV-induced peripheral persistent nociception could evoke increased neuronal activities in the S1 area with predominant localization in layers II-III.

Region- or state-related differences in expression and activation of extracellular signal-regulated kinases (ERKs) in naïve and pain-experiencing rats

BACKGROUND

Extracellular signal-regulated kinase (ERK), one member of the mitogen-activated protein kinase (MAPK) family, has been suggested to regulate a diverse array of cellular functions, including cell growth, differentiation, survival, as well as neuronal plasticity. Recent evidence indicates a role for ERKs in nociceptive processing in both dorsal root ganglion and spinal cord. However, little literature has been reported to examine the differential distribution and activation of ERK isoforms, ERK1 and ERK2, at different levels of pain-related pathways under both normal and pain states. In the present study, quantitative blot immunolabeling technique was used to determine the spatial and temporal expression of ERK1 and ERK2, as well as their activated forms, in the spinal cord, primary somatosensory cortex (SI area of cortex), and hippocampus under normal, transient pain and persistent pain states.

RESULTS

In naïve rats, we detected regional differences in total expression of ERK1 and ERK2 across different areas. In the spinal cord, ERK1 was expressed more abundantly than ERK2, while in the SI area of cortex and hippocampus, there was a larger amount of ERK2 than ERK1. Moreover, phosphorylated ERK2 (pERK2), not phosphorylated ERK1 (pERK1), was normally expressed with a high level in the SI area and hippocampus, but both pERK1 and pERK2 were barely detectable in normal spinal cord. Intraplantar saline or bee venom injection, mimicking transient or persistent pain respectively, can equally initiate an intense and long-lasting activation of ERKs in all three areas examined. However, isoform-dependent differences existed among these areas, that is, pERK2 exhibited stronger response than pERK1 in the spinal cord, whereas ERK1 was more remarkably activated than ERK2 in the S1 area and hippocampus.

CONCLUSION

Taken these results together, we conclude that: (1) under normal state, while ERK immunoreactivity is broadly distributed in the rat central nervous system in general, the relative abundance of ERK1 and ERK2 differs greatly among specific regions; (2) under pain state, either ERK1 or ERK2 can be effectively phosphorylated with a long-term duration by both transient and persistent pain, but their response patterns differ from each other across distinct regions; (3) The long-lasting ERKs activation induced by bee venom injection is highly correlated with our previous behavioral, electrophysiological, morphological and pharmacological observations, lending further support to the functional importance of ERKs-mediated signaling pathways in the processing of negative consequences of pain associated with sensory, emotional and cognitive dimensions.

Contusive spinal cord injury evokes localized changes in NADPH-d activity but extensive changes in Fos-like immunoreactivity in the rat

The histological detection of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d), a marker for nitric oxide-producing cells, was used to evaluate ongoing changes in the neural biochemistry of the rat spinal cord 1 week following contusive spinal cord injury (SCI). In addition, the immunohistochemical detection of the immediate-early gene c-fos was used to identify basal patterns of neural activity at this time. The numbers and laminar locations of NADPH-d- and c-fos-positive cells were examined in spinal segments adjacent to the site of injury (T12-S3) as well as those distant from the injury (C3-C5) in both SCI and un-injured rats. Our data show that contusive SCI results in a significant reduction in NADPH-d labelling in the superficial dorsal horn, and a significant increase in NADPH-d expression in small bipolar neurons and large motoneurons in the ventral horn at the site of the injury. In spinal segments distant to the injury site (C3-C5), NADPH-d activity did not differ from that of uninjured controls. Furthermore, significant reductions in the levels of c-fos expression were observed in SCI rats, in spinal segments both at and distant to the site of injury for all spinal laminae. The only exception was a dramatic increase observed in the sacral parasympathetic nucleus. These data suggest that increased NADPH-d expression is related to conditions specific to the site of injury, whereas the changes in c-fos expression probably indicate more global changes in neuronal activity following SCI.

Bee venom injection significantly reduces nociceptive behavior in the mouse formalin test via capsaicin-insensitive afferents

Peripheral bee venom (BV) administration produces 2 contrasting effects, nociception and antinociception. This study was designed to evaluate whether the initial nociceptive effect induced by BV injection into the Zusanli acupoint is involved in producing the more prolonged antinociceptive effect observed in the mouse formalin test, and whether capsaicin-sensitive primary afferents are involved in these effects. BV injection into the Zusanli point increased spinal Fos expression but not spontaneous nociceptive behavior. BV pretreatment 10 minutes before intraplantar formalin injection dose-dependently attenuated nociceptive behavior associated with the second phase of the formalin test. The destruction of capsaicin-sensitive primary afferents by resiniferatoxin (RTX) pretreatment selectively decreased BV-induced spinal Fos expression but did not affect BV-induced antinociception. Furthermore, BV injection increased Fos expression in tyrosine hydroxylase immunoreactive neurons in the locus caeruleus, and this expression was unaltered by RTX pretreatment. Finally, BV's antinociception was blocked by intrathecal injection of 10 microg idazoxan, and this effect was not modified by RTX pretreatment. These findings suggest that subcutaneous BV stimulation of the Zusanli point activates central catecholaminergic neurons via capsaicin-insensitive afferent fibers without induction of nociceptive behavior. This in turn leads to the activation of spinal alpha2-adrenoceptors, which ultimately reduces formalin-evoked nociceptive behaviors.

PERSPECTIVE

This study demonstrates that BV acupuncture produces a significant antinociception without nociceptive behavior in rodents, which is mediated by capsaicin-insensitive afferents and involves activation of central adrenergic circuits. These results further suggest that BV stimulation into this acupuncture point might be a valuable alternative to traditional electrical or mechanical acupoint stimulation.

Unilateral subcutaneous bee venom but not formalin injection causes contralateral hypersensitized wind-up and after-discharge of the spinal withdrawal reflex in anesthetized spinal rats

This study aimed to investigate the effect of tonic nociception on spinal withdrawal reflexes including (1) long lasting spontaneous responses elicited by subcutaneous (s.c.) administration of formalin (2.5%, 50 microl) and bee venom (BV, 0.2 mg/50 microl) into the hind paw and (2) corresponding ipsilateral (primary) and contralateral (secondary) hypersensitivity to noxious pinch and repetitive supra-threshold (1.5 x T) electrical stimuli at different frequencies (3 Hz: wind-up; 20 Hz: after-discharge) in anesthetized spinal rats. Spinal withdrawal reflexes were studied by simultaneously assessing single motor units (SMUs) electromyographic (EMG) activities from the bilateral medial gastrocnemius (MG) muscles. Subcutaneous formalin-induced persistent spontaneous SMU EMG responses were in typical biphasic manner with an apparent silent period (about 13-18 min), but in contrast, BV elicited monophasic long lasting (about 1 h) SMU EMG responses without any resting state. The mechanically and electrically evoked responsiveness of SMUs were enhanced significantly by ipsilateral BV injection, whereas enhanced electrically, but not mechanically, evoked responses (including wind-up and after-discharge) were found at the non-injection site of the contralateral hind paw. However, s.c. administration of formalin was only able to establish ipsilateral hypersensitivity of the SMUs to repeated electrical, not mechanical, stimulation. Neither mechanically nor electrically evoked contralateral hypersensitivity of the SMUs was found during the ipsilateral formalin-induced nociception. For pharmacological intervention, intrathecal administration of the non-N-methyl-d-aspartate (non-NMDA) receptor antagonist CNQX (40 nmol/10 microl), but not the non-competitive NMDA receptor antagonist MK-801 (40 nmol/10 microl), significantly depressed BV-induced contralateral hypersensitivity of the SMUs to repeated 3 Hz (wind-up) and 20 Hz (after-discharge) frequencies of electrical stimulation. Using the extracellular SMU recording technique, we found that s.c. administration of formalin and BV shows a significant difference in long lasting spontaneous firing of SMUs. This is consistent with previous observations in animal behavioral studies. Additionally, contralateral electrically evoked hypersensitivity of the SMUs was found only following BV injection, not in the formalin test. The maintenance and development of BV-induced contralateral hypersensitivity of the spinal withdrawal reflex to noxious electrical stimulation indeed depend on different central pharmacological receptors. The spinal non-NMDA, but not the NMDA, receptors may play important role in BV-induced contralateral central hyperexcitability and sensitization.

Microarray analysis of gene expression in chondrosarcoma cells treated with bee venom

Bee venom (BV) has a broad array of clinical applications in Korean medicine, including treatment of inflammatory conditions such as arthritis. The final common pathway of many arthropathies is the destruction of articular cartilage and consequent loss of articular function. Chondrocyte dysfunction plays a key role in the pathogenesis of such disorders. To explore the global gene expression profiles in a human chondrocyte-like cell line treated with BV, microarray analysis was performed. The HTB-94 human chondrosarcoma cells were treated with BV, lipopolysaccharide (LPS), or both. Of the 344 genes profiled in this study, with a cut-off level of 4-fold change in the expression, (1) 35 were downregulated following BV treatment, (2) 16 were upregulated and 7 downregulated following LPS treatment, and (3) 32 were downregulated following co-stimulation of BV and LPS. The results of the present study shows that treatment of BV reversed the LPS-induced upregulation of such genes as interleukin-6 (IL-6) receptor, matrix metalloproteinase 15 (MMP-15), tumor necrosis factor (ligand) superfamily-10, caspase-6 and tissue inhibitor of metalloproteinase-1 (TIMP-1). It is thought that microarrays will play an ever-growing role in the advance of our understanding of the pharmacologic actions of BV in the treatment of arthritis.

Spinal c-fos expression associated with spontaneous biting in a mouse model of dry skin pruritus

As a model of dry skin pruritus in mice, one hind paw was treated twice daily with a mixture of acetone/diethylether/water (AEW); controls received water only. A protective collar prevented the animals from accessing the treatment area. At 16 days, the collar was removed and AEW-treated mice exhibited marked biting of the treated paw; the number and cumulative duration of bites was significantly greater than in controls. After 3 additional treatment days (collars intact), animals were perfused for c-fos immunohistochemistry. There was significantly more fos-like immunoreactivity in the ipsilateral lumbar spinal cord of AEW-treated animals, with the majority in superficial laminae. It is proposed that biting of the dry skin reflects pruritus, and that neurons predominantly in superficial laminae of the dorsal horn may signal itch sensation.

Genetic evidence for the correlation of deep dorsal horn Fos protein immunoreactivity with tonic formalin pain behavior

The formalin test is commonly used as a model of persistent pain. Besides producing pain behavior, hind paw formalin injection induces the expression of the immediate-early gene, c-fos. A current controversy is whether noxious stimulus-induced Fos protein immunoreactivity can be considered a proxy (biomarker) of nociception in the spinal cord. We investigated this issue by exploiting our recent demonstration of genotype-dependent behavioral differences in response to formalin injection among inbred mouse strains. Accordingly, 6 inbred and 2 outbred strains were administered formalin (5% in 25 microL) into the ventral hind paw, monitored for licking behavior, and then sacrificed at 90 minutes after injection for Fos protein immunocytochemistry. Significant strain differences were observed in both licking behavior and Fos counts in superficial and deep laminae. We observed a significant correlation among strains between licking behavior in the late phase (10 to 60 minutes) of the formalin test and Fos expression in laminae V-VI (but not laminae I-II) of the dorsal horn (r = 0.94). These findings reinforce the use of the Fos technique to study the neuronal processing underlying pain but suggest that Fos labeling reliably reflects tonic pain behavior only in neurons located in the neck of the dorsal horn in mice.

Opioid modulation of scratching and spinal c-fos expression evoked by intradermal serotonin

We investigated a spinal site for opioid modulation of itch-related scratching behavior in rats. Intradermal 5-HT (2%, 10 microl) elicited intermittent bouts of hindlimb scratching directed toward the injection site (nape of neck) beginning within minutes and lasting >1 hr. 5-HT-evoked scratching was significantly reduced by systemic administration of the opiate antagonist naltrexone but was not affected by systemic morphine at a dosage (3 mg/kg) that induces analgesia. Intradermal 5-HT elicited a significant increase in c-fos-like immunoreactivity (FLI) in superficial laminas I-III at the lateral aspect of the cervical C3-C6 dorsal horn compared with controls receiving intradermal saline. Neither systemic morphine nor naltrexone significantly affected counts of 5-HT-evoked FLI. The lack of effect of morphine suggests that intradermal 5-HT activates dorsal horn neurons, signaling itch but not pain. Attenuation of 5-HT-evoked scratching but not spinal FLI by naltrexone suggests a supraspinal site for its antipruritic action. In contrast, morphine significantly attenuated FLI elicited by intradermal capsaicin, a chemical that induces pain but not scratching.

Fos expression in rat spinal cord induced by peripheral injection of BmK I, an α-like scorpion neurotoxin

In this paper, the central neuronal activities elicited by BmK I, a specific voltage-gated Na+ channel modulator, were examined by monitoring the c-Fos expression pattern of rat spinal cord. c-Fos protein in laminae I-II, V-VI, and VII-X could be detected at 0.5 h, increased steadily at 1 h, reached a peak at 2 h, and then decreased rapidly from 4 to 24 h after Bmk I was subcutaneously injected into the rat hind paw. However, c-Fos expression in laminae III-IV was activated to a peak at 0.5 h and then declined gradually from 0.5 to 24 h. Furthermore, c-Fos expression could be induced by BmK I in a dose-dependent manner. In addition, the increase of c-Fos expression in laminae I-II, V-VI, and VII-X induced by BmK I, and not in laminae III-IV, could be partially inhibited by systemic morphine in a dose-dependent manner. The results suggested that peripheral administration of BmK I could evoke a profound change of spinal neuronal activities manifested as specific patterns of c-Fos expression, which may be partially attributed to the selective modulation of BmK I on voltage-gated Na+ channels located in peripheral nociceptors.

c-fos expression in superficial dorsal horn of cervical spinal cord associated with spontaneous scratching in rats with dry skin

Using a dry skin model in rats, we assessed spontaneous itch-related scratching behavior and associated c-fos expression in the superficial dorsal horn of the spinal cord. The number of spontaneous bouts of hind limb scratching directed toward the nape of the neck was significantly higher after 5 days of topical application of acetone-diethylether-water (AEW) compared to pre-treatment levels or to control animals treated with water only. In AEW-treated animals, neurons expressing Fos-like immunoreactivity (FLI) were observed in superficial laminae of the dorsal horn at C3-C5 levels. There was a significant, positive correlation between the number of neurons in lamina I expressing FLI and the number and cumulative duration of spontaneous scratching bouts. These results suggest that this model may be useful to assess mechanisms of dry skin pruritus, and that lamina I neurons are activated as a consequence of itching and/or scratching in this model.

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.

The anti-inflammatory effect of bee venom stimulation in a mouse air pouch model is mediated by adrenal medullary activity

Cutaneous electrical or chemical stimulation can produce an anti-inflammatory effect, which is dependent on adrenal medullary-sympathetic activation. We have previously shown that peripheral injection of bee venom (BV) also produces a significant anti-inflammatory effect that is neurally mediated. In the present study, we examined whether this anti-inflammatory effect is also dependent on the adrenal gland using the mouse inflammatory air pouch model. Subcutaneous (s.c.) BV injection produced a marked suppression of leucocyte migration and tumour necrosis factor (TNF)-alpha concentration induced by zymosan injection into the air pouch. The role of the adrenal gland in this suppression was evaluated in adrenalectomized mice. Adrenalectomy significantly reversed the suppression of leucocyte migration and TNF-alpha elevation caused by BV. Serum concentrations of corticosteroid were increased in mice with zymosan-induced air-pouch inflammation and this increase was reduced by BV administration, suggesting that adrenal corticosteroid release is not involved in mediating the anti-inflammatory effects of BV. To test this hypothesis, the corticosteroid receptor antagonist (RU486) was administered and found not to affect the BV-induced inhibition of leucocyte migration. By contrast, pretreatment with the beta-adrenergic antagonist propranolol reversed the BV-induced inhibitory effect on leucocyte migration. These results suggest that the anti-inflammatory effect of s.c. BV administration is mediated in part by the release of catecholamines from the adrenal medulla.

c-Fos expression in rat spinal cord induced by scorpion BmK venom via plantar subcutaneous injection

The aim of this study was to assess the cell-type and distribution of highly activated neurons in rat spinal cord underlying nociceptive responses induced by scorpion BmK venom using Fos immunohistochemistry. BmK venom was intraplantarly injected into one hind paw of a conscious rat. Fos-like immunoreactive neurons were found to predominantly distribute at L4-5 segments in the rat spinal cord after BmK venom application. c-Fos labeling was most dense in the medial half portion of laminae I-II, moderately dense in laminae V-VI and less dense in laminae III-IV, VII-X. c-Fos labeling could be detected at 0.5 h, reached the peak at 2 h, decreased steeply from 4 h and then almost disappeared at 24 h. Ten to fifty micrograms of BmK venom was deemed to be a sufficient dosage to evoke c-Fos expression. On the other hand, c-Fos expression induced by BmK venom could be suppressed partially by systemic morphine in a dose-dependent manner. The results suggest that the different extent of activities of neuronal subpopulation in the spinal cord involved in nociceptive transmission manifesting as c-Fos expression, were mainly correlated with mechanisms underlying the generation, maintenance and/or modulation of spontaneous pain and hyperalgesia evoked by BmK venom.

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.

Dynamic determination and possible mechanism of amino acid transmitter release from rat spinal dorsal horn induced by the venom and a neurotoxin (BmK I) of scorpion Buthus martensi Karsch

In the present communication, we determined the dynamic release of amino acid transmitters from spinal dorsal horn induced by scorpion Buthus martensi Karsch (BmK) venom and a neurotoxin (BmK I). The results found that glutamate and aspartate release could be evoked significantly within the initial 30 min with the applied doses of either 0.05 and 0.01 mg BmK venom or 0.01 and 0.002 mg BmK I. However, gamma-aminobutyric acid (GABA) release could be largely evoked during the second 30 min by the venom, but not by BmK I. The result suggested that nociceptive afferent fibers could be activated to induce excitatory amino acid release from spinal dorsal horn by nociceptive factors such as BmK I, but the delayed release of GABA might be attributed to the modulating role of some antinociceptive components in the venom.

The analgesic efficacy of bee venom acupuncture for knee osteoarthritis: a comparative study with needle acupuncture

The aim of this investigation was to determine whether bee venom (BV) administered directly into an acupoint was a clinically effective and safe method for relieving the pain of patients with knee osteoarthritis (OA) as compared to traditional needle acupuncture. We evaluated the efficacy of BV acupuncture using both pain relief scores and computerized infrared thermography (IRT) following 4 weeks of BV acupuncture treatment. We observed that a significantly higher proportion of subjects receiving BV acupuncture reported substantial pain relief as compared with those receiving traditional needle acupuncture therapy. Furthermore, the IRT score was significantly improved and paralleled the level of pain relief.

Pivotal role of capsaicin-sensitive primary afferents in development of both heat and mechanical hyperalgesia induced by intraplantar bee venom injection

To investigate the roles of primary afferent fibers in development of the bee venom (BV)-induced persistent spontaneous nociception (PSN) and hyperalgesia (HA), the sciatic nerve or both the sciatic and saphenous nerves of rats were topically treated with capsaicin respectively under pentobarbital anesthesia to destroy the capsaicin-sensitive primary afferent (CSPA) fibers. Effect of the sciatic nerve capsaicin on the formalin-induced PSN was also evaluated. Destruction of the CSPA fibers of the sciatic nerve or both the sciatic and saphenous nerves only produced 34 or 69% inhibition of the mean total number of 1 h BV-induced paw flinches. However, the total number of 1 h formalin-induced paw flinches was inhibited by 90% (85% for phase 1 and 91% for phase 2). In naïve rats, destruction of the CSPA fibers of the sciatic nerve caused 237 and 60% increase in paw withdrawal thermal latency (PWTL) to radiant heat in the injection site (paw pad) and at the heel of the treated hind paw compared to the baseline values. However, it was without significant influence upon the PWTL in the non-treated side or the paw withdrawal mechanical threshold (PWMT) to von Frey filament stimuli in both hind paws. In the BV-treated rats, the CSPA fiber destruction of the sciatic nerve completely blocked development of the heat and mechanical HA in the BV injection site. However, the reduction in either PWTL (drop to baseline level) or PWMT (drop by 56% from the baseline level) at the heel of the BV-treated side was not affected by this treatment. However, destruction of the CSPA fibers of both the sciatic and saphenous nerves was able to block development of both heat and mechanical HA in the whole BV-treated hind paw and heat hyperalgesia in the non-injected hind paw. Taken together, we conclude that: (1) the CSPA (C- and A delta-) fibers play a pivotal role in mediation of either the heat or the mechanical hyperalgesia induced by s.c. BV; (2) the CSPA fibers may play a crucial role in mediation of the formalin-induced PSN, but play a partial role in the BV-induced nociceptive process; (3) in addition to the sciatic nerve, the saphenous nerve is also involved in mediation of the BV-induced PSN as well as heat and mechanical hyperalgesia, while it is not likely to be involved in the formalin-induced nociception.

Secondary heat, but not mechanical, hyperalgesia induced by subcutaneous injection of bee venom in the conscious rat: effect of systemic MK-801, a non-competitive NMDA receptor antagonist

Subcutaneous (s.c.) administration of bee venom into the plantar surface of one hind paw in rats has been found to produce an immediate single phase of persistent spontaneous nociceptive responses (continuously flinching, licking or lifting the injected paw) for 1-2 h accompanied by a 72-96 hour period of primary heat and mechanical hyperalgesia in the injection site and a spread of heat, but not mechanical, hyperalgesia in the non-injected hind paw (Chen et al., 1999b). To gain insight into the underlying mechanisms of the bee venom-induced hyperalgesia in particular, we further identified a heat, but not mechanical, hyperalgesia in an area (paw pad) distant from the injection site induced by s.c. injection of bee venom into the posterior leg 0.8-1.2 cm proximal to the heel measured by paw withdrawal reflex to radiant heat or von Frey monofilament stimuli in conscious rats. In the bee venom-treated hind limb, however, significant reduction in both thermal latency and mechanical threshold of withdrawal reflex was identified for a period of more than 96 h in the heel with a similar characteristic to the primary heat and mechanical hyperalgesia identified in the injection site previously. The time course of the heat hyperalgesia identified in the paw pad of the bee venom-treated side was shorter and lasted for less than 48 h, which was in parallel with the reduction in thermal latency of the withdrawal reflex identified in the non-injected hind paw. Moreover, pre- or post-treatment with a single dose of MK-801 (0.01 mg/kg, i.p.), a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, completely blocked the occurrence, and reversed the established process of the heat hyperalgesia identified in either the bee venom-treated or non-treated paw pads, while the same treatments with the drug did not produce any influence upon the development and maintaining of the heat and mechanical hyperalgesia identified in the heel of the injected hind limb. Taken together with our previous results following s.c. intraplantar bee venom injection, we conclude that: (1) in addition to the well-identified primary heat and mechanical hyperalgesia in the injection site and its adjacent area, s.c. bee venom is also able to produce a secondary heat hyperalgesia in a region distant from the injection site which has a similar characteristic to the contralateral heat hyperalgesia; (2) NMDA receptors are involved in either development or maintenance of the secondary and the contralateral heat hyperalgesia, but without any role in those processes of the primary heat and mechanical hyperalgesia; (3) the secondary heat hyperalgesia seen in the injected hind limb is likely to share the same neural mechanisms with that identified in the non-injected side via co-activation of NMDA receptors.

Bee venom pretreatment has both an antinociceptive and anti-inflammatory effect on carrageenan-induced inflammation

Although the injection of bee venom (BV) has been reported to evoke tonic pain and hyperalgesia, there is conflicting evidence in the literature indicating that BV can also exert an anti-inflammatory and antinociceptive effects on inflammation. In this regard, BV has been traditionally used in Oriental medicine to relieve pain and to treat chronic inflammatory diseases such as rheumatoid arthritis. The present study was designed to test the hypothesis that BV induces acute nociception under normal conditions, but that it can serve as a potent anti-inflammatory and antinociceptive agent in a localized inflammatory state. The experiments were designed to evaluate the effect of BV pretreatment on carrageenan (CR)-induced acute paw edema and thermal hyperalgesia. In addition, spinal cord Fos expression induced by peripheral inflammation was quantitatively analyzed. In normal animals subcutaneous BV injection into the hindlimb was found to slightly increase Fos expression in the spinal cord without producing detectable nociceptive behaviors or hyperalgesia. In contrast pretreatment with BV (0.8 mg/kg) 30 min prior to CR injection suppressed both the paw edema and thermal hyperalgesia evoked by CR. In addition, there was a positive correlation between the percent change in paw volume and the expression of Fos positive neurons in the spinal cord. These results indicate that BV pretreatment has both antinociceptive and anti-inflammatory effects in CR-induced inflammatory pain. These data also suggest that BV administration may be useful in the treatment of the pain and edema associated with chronic inflammatory diseases.

Bee venom injection into an acupuncture point reduces arthritis associated edema and nociceptive responses

Bee venom (BV) has traditionally been used in Oriental medicine to relieve pain and to treat inflammatory diseases such as rheumatoid arthritis (RA). While several investigators have evaluated the anti-inflammatory effect of BV treatment, the anti-nociceptive effect of BV treatment on inflammatory pain has not been examined. Previous studies in experimental animals suggest that the therapeutic effect of BV on arthritis is dependent on the site of administration. Because of this potential site specificity, the present study was designed to evaluate the anti-nociceptive effect of BV injections into a specific acupoint (Zusanli) compared to a non-acupoint in an animal model of chronic arthritis. Subcutaneous BV treatment (1 mg/kg per day) was found to dramatically inhibit paw edema caused by Freund's adjuvant injection. Furthermore, BV therapy significantly reduced arthritis-induced nociceptive behaviors (i.e. the nociceptive scores for mechanical hyperalgesia and thermal hyperalgesia). These anti-nociceptive/anti-inflammatory effects of BV were observed from 12 days through 21 days post-BV treatment. In addition, BV treatment significantly suppressed adjuvant-induced Fos expression in the lumbar spinal cord at 3 weeks post-adjuvant injection. Finally, injection of BV into the Zusanli acupoint resulted in a significantly greater analgesic effect on arthritic pain as compared to BV injection in to a more distant non-acupoint. The present study demonstrates that BV injection into the Zusanli acupoint has both anti-inflammatory and anti-nociceptive effects on Freund's adjuvant-induced arthritis in rats. These findings raise the possibility that BV acupuncture may be a promising alternative medicine therapy for the long-term treatment of rheumatoid arthritis.

Differential roles of spinal neurokinin 1/2 receptors in development of persistent spontaneous nociception and hyperalgesia induced by subcutaneous bee venom injection in the conscious rat

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). Post-treatment of spantide i.t. at the highest dose (5 microg) used in the present study 5 min after bee venom injection also produced a 49% suppression of the flinching reflex in the control group [post-spantide vs saline: 19.42 +/- 3.15 (n=5) vs 38.42 +/- 3.25 flinches/5 min (n=5)]. Moreover, i.t. pre-treatment with 5 microg spantide partially prevented the primary and secondary thermal hyperalgesia from occurring, while it did not show any influence on the development of primary mechanical hyperalgesia. Neither the established thermal nor mechanical hyperalgesia identified in the above sites was affected by i.t. post-treatment with the same dose of spantide 3 h after bee venom injection. 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.

Contralateral heat hyperalgesia induced by unilaterally intraplantar bee venom injection is produced by central changes: a behavioral study in the conscious rat

In a previous study, we found that subcutaneous (s.c.) intraplantar injection of bee venom unilaterally could produce bilateral heat hyperalgesia. However, the bee venom-induced heat hyperalgesia identified in the injection site was presumed to be different from that identified in the contralateral hindpaw, since the former co-existed with the mechanical hyperalgesia while the latter did not. The aim of the present study was to testify whether the contralateral heat hyperalgesia identified in the bee venom model was a consequence of central changes. The radiant heat and von Frey-type filaments were applied to both the injection site and the contralateral pawpad of conscious rats prior to and 4 h after s.c. bee venom injection. After confirmation of the development of primary heat and mechanical hyperalgesia and contralateral heat hyperalgesia following s.c. bee venom, the sciatic nerve of the injection side was transected. After axotomy, the bee venom-induced heat hyperalgesia in the non-injected hindpaw was not altered at all compared with that prior to axotomy. Moreover, intrathecal pre-treatment with either N-methyl-D-aspartate (NMDA) or non-NMDA receptor antagonist could prevent the development of the contralateral heat hyperalgesia. The present results suggest that central sensitization contributes to development of the bee venom-induced contralateral heat hyperalgesia and activation of both NMDA and non-NMDA receptors in the spinal cord is involved in the processing.

Involvement of peripheral NMDA and non-NMDA receptors in development of persistent firing of spinal wide-dynamic-range neurons induced by subcutaneous bee venom injection in the cat

To study the roles of peripheral excitatory amino acids receptor subtypes N-methyl-D-aspartate (NMDA) and non-NMDA receptors in persistent nociception, extracellular single unit recording technique was used to assess the effects of a single dose NMDA and non-NMDA receptor antagonists, AP(5) (5-aminophosphonovaleric acid) and CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) or DNQX (6,7-dinitroquinoxaline-2,3-dione), on s.c. bee venom-induced increase in firing of wide-dynamic-range (WDR) neurons in the spinal dorsal horn of the urethane-chloralose anesthetized cats. Subcutaneous bee venom injection into the cutaneous receptive field resulted in a single phase of increased firing of WDR neurons over the background activity for more than 1 h. Local pre-administration of AP(5) (200 microg/100 microl) or CNQX (8.3 microg/100 microl) into the bee venom injection site produced 94% (1.01+/-0.96 spikes/s, n=5) or 76% (2.97+/-0.58 spikes/s, n=4) suppression of the increased neuronal firing when compared with local saline (16.32+/-4.55 spikes/s, n=10) or dimethyl sulfoxide (DMSO) (12.37+/-6.36 spikes/s, n=4) pre-treated group, respectively. Local post-administration of the same dose of AP(5) produced a similar result to the pre-treatment group with a 67% inhibition of the mean firing rate, however, the same treatment with CNQX and even a higher dose of DNQX (100 microg/100 microl) did not produce any inhibition of the neuronal firing induced by s.c. bee venom injection (DNQX vs. DMSO: 23.91+/-0. 25 vs. 22.14+/-0.04 spikes/s, P=0.0298, n=5). In the control experiments, local pre-administration of the same dose of AP(5) or CNQX into a region on the contralateral hindpaw symmetrical to the bee venom injection site produced no significant influence on the increased firing of the WDR neurons [contralateral AP(5) vs. saline: 14.17+/-6.27 spikes/s (n=5) vs. 16.32+/-4.55 spikes/s (n=10), P0.05; contralateral CNQX vs. DMSO: 12.85+/-6.38 spikes/s (n=4) vs. 12. 37+/-6.36 spikes/s (n=4), P0.05], implicating that the suppressive action of local AP(5) or CNQX was not the result of systemic effects. The present results suggest that activation of the peripheral NMDA receptors is involved in both induction and maintenance, while activation of non-NMDA receptors is only involved in induction, but not in the maintenance of persistent firing of the dorsal horn WDR neurons induced by s.c. bee venom injection.

Primary hyperalgesia to mechanical and heat stimuli following subcutaneous bee venom injection into the plantar surface of hindpaw in the conscious rat: a comparative study with the formalin test

To elucidate the underlying mechanisms of pathological pain, it is important and necessary to develop an animal model characterized by both spontaneous tonic pain and hyperalgesia with a prolonged duration post-tissue injury. In this report, we investigated whether the two animal models of spontaneous tonic pain (the formalin test and the bee venom test) could develop a hyperalgesia to mechanical and thermal stimuli in the injured area following subcutaneous (s.c. ) administration of the two chemical agents into the plantar surface of one hindpaw in the conscious rats. It was found that the persistent nociceptive response (flinching and lifting/licking the injected hindpaw) was monophasic and lasted for 1-2 h followed by a 72-96 h period of reduction in mechanical threshold and heat latency of withdrawal reflex in the bee venom injection area; however, in contrast, the spontaneous pain-related response was biphasic followed by a permanent hypoalgesia or analgesia in the formalin injection area although the duration and response intensity of spontaneous pain was comparable with those following bee venom treatment. Subcutaneous. bee venom injection also produced a distinct reduction of heat latency on the contralateral hindpaw, while s.c. formalin did not. On the other hand, s.c. bee venom injection produced a striking edema and redness of the plantar surface for nearly the same period as the development of hyperalgesia, while the edema and redness could not be obviously observed after the formalin treatment. In the control study, repetitive suprathreshold mechanical or heat stimuli applied to the plantar surface with or without saline treatment did not significantly influence the mechanical threshold or heat latency, suggesting that the phenomena of mechanical and heat hyperalgesia were not the effects of vehicle treatment or those of the stimulus modalities themselves. Taken together, our present results showed that in contrast to s.c. formalin injection, subcutaneous. bee venom injection produced little tissue damage but a striking inflammation accompanied by a prolonged spontaneous pain and a pronounced primary hyperalgesia to mechanical and heat stimuli in the treated hindpaw and a heat, but not mechanical, hyperalgesia in the contralateral hindpaw, implicating that bee venom model may have more advantages over the formalin test and probably other chemoirritants to study the neural mechanisms underlying pathological pain and, especially, the relationship between spontaneous pain and development of hyperalgesia.