[Noninvasive image diagnosis of Budd-Chiari syndrome and its evaluation study].
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Budd-Chiari Syndrome↗
Biomedical subjects
Ke Ren
Publications and source records attributed to Ke Ren.
Effect of chronic inflammation on dorsal horn nociceptive neurons in aged rats.
To elucidate the effect of chronic inflammation on spinal nociceptive neurons in the elderly, we compared nocifensive behavior, peripheral inflammatory responses, and spinal dorsal horn neuronal activities between the aged (29-34 mo) and adult (7-12 mo) male rats after injection of complete Freund's adjuvant (CFA) into the hind paw. Aged rats exhibited a significantly lower mechanical paw withdrawal threshold before inflammation. However, after CFA injection mechanical allodynia developed in both adult and aged rats after CFA injection. The changes of foot temperature and thickness after CFA injection were greater and lasted longer in aged than in adult rats. Sets of 124 wide dynamic range (WDR) neurons (aged: 59, adult: 65) and 26 nociceptive specific (NS) neurons (aged: 13, adult: 13) were recorded from the lumber spinal dorsal horn. NS neurons from the inflamed adult rats showed significantly higher responses to noxious mechanical stimulation than those in aged rats, whereas WDR neurons from inflamed adult and aged rats were similar. Background activity of WDR neurons from the adult rats increased after CFA, whereas WDR neurons of aged rats and NS neurons from either group were not. The afterdischarge followed by noxious mechanical stimulation was significantly greater for WDR neurons in both adult and aged rats, whereas no significant differences were observed in NS neurons. Two days after CFA injection, Fos expression increased similarly in aged and adult rats. Thus the aged rats showed enhanced peripheral inflammatory responses to CFA injection with only a slight change in dorsal horn neuronal activity. Together with our previous finding that nociceptive neurons in aged rats exhibit hyperexcitability, these results suggest that the dorsal horn nociceptive system becomes sensitized with advancing age and its excitability cannot be further increased by inflammation.
Action Potentials↗
Cultured cell and transgenic mouse models for tau pathology linked to beta-amyloid.
The two histopathological signatures of Alzheimer's disease (AD) are amyloid plaques and neurofibrillary tangles, prompting speculation that a causal relationship exists between the respective building blocks of these abnormal brain structures: the beta-amyloid peptides (Abeta) and the neuron-enriched microtubule-associated protein called tau. Transgenic mouse models have provided in vivo evidence for such connections, and cultured cell models have allowed tightly controlled, systematic manipulation of conditions that influence links between Abeta and tau. The emerging evidence supports the view that amyloid pathology lies upstream of tau pathology in a pathway whose details remain largely mysterious. In this communication, we review and discuss published work about the Abeta-tau connection. In addition, we present some of our own previously unpublished data on the effects of exogenous Abeta on primary brain cultures that contain both neurons and glial cells. We report here that continuous exposure to 5 microM non-fibrillar Abeta40 or Abeta42 kills primary brain cells by apoptosis within 2-3 weeks, Abeta42 is more toxic and selective for neurons than Abeta40, and Abeta42, but not Abeta40, induces a transient increase in neurons that are positive for the AD-like PHF1 epitope. These findings demonstrate the greater potency of Abeta42 than Abeta40 at inducing tau pathology and programmed cell death, and corroborate and extend reports that tau-containing cells are more sensitive to Abeta peptides than cells that lack or express low levels of tau.
Amyloid beta-Peptides↗
Involvement of peripheral opioid mechanisms in electroacupuncture analgesia.
The involvement of the peripheral opioid system in modulating inflammatory pain has been well documented. This study aimed to investigate the possibility of electroacupuncture (EA)-mediated peripheral opioid release. Rats were injected with complete Freund's adjuvant in one of the hind paws to induce localized inflammatory pain. The pain behavioral changes were measured by paw withdrawal latency (PWL) to a noxious thermal stimulus. At day 5 of inflammation, rats received a second injection of saline or opioid antagonists into the inflamed paw, followed by EA at 30 Hz, 2 mA, and 0.1 ms for 30 minutes. The EA was conducted at acupuncture point GB30. A control was used in which needles were inserted at GB30 but no electrical stimulation was applied. Rats receiving EA showed a significantly longer PWL as compared with the control from 30 minutes to three hours after EA treatment. Intraplantar but not intraperitoneal injection of naloxone methiodide, a peripherally acting opioid receptor antagonist, eliminated the analgesic effect at 30 minutes after EA treatment. Intraplantar injection of an antibody against beta-endorphin and a corticotropin-releasing factor antagonist also produced a reduction in PWL in rats receiving EA. These data strongly suggest that peripheral opioids are released by EA at the inflammatory site.
Acupuncture Analgesia↗
Electroacupuncture attenuates inflammation in a rat model.
BACKGROUND: Acupuncture has traditionally been used in China and is being increasingly applied in Western countries to treat a variety of conditions, including inflammatory disease. However, clinical trials investigating the effectiveness of the anti-inflammatory effects of acupuncture have yielded inconsistent results, and the underlying mechanisms of acupuncture-produced anti-inflammation are unclear. OBJECTIVE: To evaluate the effectiveness of electroacupuncture (EA) on inflammation in a rat model. MATERIALS AND METHODS: Four experiments were conducted on male Sprague-Dawley rats (n = 8-9 per group). Inflammation was induced by injecting complete Freund's adjuvant (CFA) subcutaneously into the plantar surface of one hind paw of the rat. Experiment 1: To determine the effect of EA (10 and 100 Hz) versus sham treatment on inflammation. Experiment 2: To investigate the involvement of the adrenal glands on the effect of EA treatment using adrenalectomized (ADX) rats. Experiment 3: To determine the effects of EA on plasma levels of corticosterone. Experiment 4: To determine the effects of EA treatment versus immobilization on such stress indicators as heart rate and blood pressure. RESULTS: At 10 Hz EA significantly reduced CFA-induced hind paw edema. The effect was partially blocked in the ADX rats. EA significantly increased plasma levels of corticosterone but produced no noticeable signs of stress. CONCLUSION: At 10 Hz but not 100 Hz, EA suppresses inflammation by activating the hypothalamus-pituitary-adrenal axis (HPA) and the nervous system.
Analysis of Variance↗
Involvement of dorsal column nucleus neurons in nociceptive transmission in aged rats.
To clarify the functional role of the dorsal column nucleus (DCN) in nociception in rats with advancing age, single neuronal activity and substance P-like immunoreactivity (SP-LI) of the gracile nucleus (GN) were studied in aged rats (29 to 34 mo old) and adult rats (9 to 12 mo old). A total of 122 neurons [aged: 34 wide-dynamic-range (WDR), two nociceptive-specific (NS), and 32 low-threshold mechanical (LTM) neurons; adult: 22 WDR and 32 LTM neurons] were recorded from GN. For WDR neurons, the latency to antidromic activation of the ventral posterior lateral nucleus of the thalamus showed no difference between the aged and adult rats. Sciatic nerve stimulation with C-fiber intensity induced responses of GN with significantly longer latency in aged rats than in adults, whereas there was no difference in the response latency to A-fiber intensity stimulation. Background activity and afterdischarges were significantly higher in the aged rats than those in the adult rats. Responses to noxious mechanical and thermal stimuli were significantly greater in the aged rats during application of graded stimuli. There were no significant differences in responses to nonnoxious mechanical stimulus, mechanical response threshold, and the size of the receptive fields between neurons in the aged and adult rats. The area occupied by SP-LI fibers in the GN and the size of SP-LI dorsal root ganglia neurons were significantly larger in aged rats than in adults. The present findings suggest that the hyperexcitability of GN neurons could be involved in abnormal noxious pain sensations with advancing age.
Action Potentials↗
Activation of trigeminal intranuclear pathway in rats with temporomandibular joint inflammation.
We examined the anatomical connections of trigeminal neurons between the trigeminal subnuclei interpolaris/caudalis (Vi/Vc) transition and caudal subnucleus caudalis/upper cervical dorsal horn (Vc/C(1,2)) zones in rats, using the fluorogold (FG) retrograde tracing method combined with Fos expression, a marker of neuronal activation, following temporomandibular joint (TMJ) inflammation. The head withdrawal threshold was also measured in rats 3 days after complete Freund's adjuvant (CFA)-induced TMJ inflammation. The head withdrawal threshold on the inflamed side was significantly decreased after CFA injection into the TMJ. FG was injected into the Vi/Vc transition zone and retrogradely labeled FG-positive cells were observed in the Vc/C(1,2) region. Numerous Fos protein-expressing cells were present both in the Vi/Vc transition zone and in the laminated Vc/C(1,2) zone. A population of cells was double-labeled with Fos and FG in the Vc/C(1,2) zone. Fos/FG cells were only observed in the deep laminae of the Vc/C(1,2) zone. These findings suggest that Vi/Vc transition zone activity is modulated by activation of the caudal laminated zone after orofacial tissue injury.
Analysis of Variance↗
Group I metabotropic glutamate receptor NMDA receptor coupling and signaling cascade mediate spinal dorsal horn NMDA receptor 2B tyrosine phosphorylation associated with inflammatory hyperalgesia.
Hindpaw inflammation induces tyrosine phosphorylation (tyr-P) of the NMDA receptor (NMDAR) 2B (NR2B) subunit in the rat spinal dorsal horn that is closely related to the initiation and development of hyperalgesia. Here, we show that in rats with Freund's adjuvant-induced inflammation, the increased dorsal horn NR2B tyr-P is blocked by group I metabotropic glutamate receptor (mGluR) antagonists [7-(hydroxyimino)cyclopropa[b] chromen-1a-carboxylate ethyl ester (CPCCOEt) and 2-methyl-6-(phenylethynyl)-pyridine (MPEP), by the Src inhibitor CGP 77675, but not by the MAP kinase inhibitor 2'-amino-3'-methoxyflavone. Analysis of the calcium pathways shows that the in vivo NR2B tyr-P is blocked by an IP3 receptor antagonist 2-aminoethoxydiphenylborate (2APB) but not by antagonists of ionotropic glutamate receptors and voltage-dependent calcium channels, suggesting that the NR2B tyr-P is dependent on intracellular calcium release. In a dorsal horn slice preparation, the group I (dihydroxyphenylglycine), but not group II [(2R,4R)-4-aminopyrrolidine-2,3-dicarboxylate] and III [L-AP 4 (L-(+)-2-amino-4-phosphonobutyric acid)], mGluR agonists, an IP3 receptor (D-IP3) agonist, and a PKC (PMA) activator, induces NR2B tyr-P similar to that seen in vivo after inflammation. Coimmunoprecipitation indicates that Shank, a postsynaptic density protein associated with mGluRs, formed a complex involving PSD-95 (postsynaptic density-95), NR2B, and Src in the spinal dorsal horn. Double immunofluorescence studies indicated that NR1 is colocalized with mGluR5 in dorsal horn neurons. mGluR5 also coimmunoprecipitates with NR2B. Finally, intrathecal pretreatment of CPCCOEt, MPEP, and 2APB attenuates inflammatory hyperalgesia. Thus, inflammation and mGluR-induced NR2B tyr-P share similar mechanisms. The group ImGluR-NMDAR coupling cascade leads to phosphorylation of the NMDAR and appears necessary for the initiation of spinal dorsal horn sensitization and behavioral hyperalgesia after inflammation.
Animals↗
A parametric study of electroacupuncture on persistent hyperalgesia and Fos protein expression in rats.
We previously reported the anti-hyperalgesia of electroacupuncture (EA) on persistent inflammatory pain in an unrestrained, unsedated, and conscious rat model. Using this model, induced by injecting complete Freund's adjuvant (CFA) into one hind paw, we systematically evaluated the anti-hyperalgesia of EA stimulation parameters (frequency, intensity, treatment duration, and pulse width). We assessed hyperalgesia by paw withdrawal latency (PWL) to a noxious thermal stimulus and found that 10- and 100-Hz EA frequencies at a current intensity of 3 mA produced the greatest anti-hyperalgesia, when compared to other parameters. Both frequencies significantly increased PWL in the early phases of hyperalgesia (2.5 and 24 h; p < 0.05), and 10 Hz EA also significantly increased PWL in later phases (5 to 7 days; p < 0.05). A sufficient but tolerable intensity of 3 mA was more effective than lower intensities (1-2 mA). A 20-min treatment produced better anti-hyperalgesia than longer and shorter (10 and 30 min) treatments. Acupoint specificity study demonstrated that GB30 produced significant EA anti-hyperalgesia, while Waiguan (TE5) and sham points, an abdominal point and a point at the opposite aspect of GB30, did not. The spinal Fos protein expression study demonstrated that the optimal EA selectively suppressed Fos expression in superficial laminae (I/II) and activated it in deeper laminae (III/IV) of the spinal dorsal horn. The results suggest that the EA anti-hyperalgesia is parameter-dependent and point-specific, and they provide important information for designing further clinical acupuncture research on persistent inflammatory pain.
Analysis of Variance↗
Involvement of opioid receptors in electroacupuncture-produced anti-hyperalgesia in rats with peripheral inflammation.
Our previous study showed that electroacupuncture (EA) significantly attenuated inflammatory hyperalgesia. It has also been reported that EA analgesia in uninjured animals is mediated by mu and delta opioid receptors at 2-15 Hz and by kappa opioid receptor at 100 Hz. Because persistent pain changes neural response to external stimulation, we hypothesized that (1) the mechanisms of EA anti-hyperalgesia may be different under conditions of persistent pain and that (2) combining EA with a sub-effective dose of morphine could enhance EA anti-hyperalgesia. Hyperalgesia, decreased paw withdrawal latency (PWL) to a noxious thermal stimulus, was induced by subcutaneously injecting complete Freund's adjuvant (CFA) into the hind paws of rats. Selective antagonists against mu (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-ThrNH2, CTOP), delta (naltrinodole, NTI) and kappa (nor-binaltorphimine, BNI) opioid receptors were administered intrathecally 10 min before each of two EA treatments at acupoint Huantiao (GB30), one immediately post and the other 2 h post-CFA. Morphine was given (i.p.) 40 min before the second EA treatment. PWL was measured before and 2.5 and 5 h post-CFA. Both 10 and 100 Hz EA-produced anti-hyperalgesia were blocked spinally by mu- and delta- but not kappa-receptor antagonists. EA combined with a sub-threshold dose of morphine (2.5 mg/kg) enhanced anti-hyperalgesia additively (10 Hz EA) or synergistically (100 Hz EA) compared to that produced by each component alone. These results suggest selective involvement of mu and delta, but not kappa, receptors in EA-produced anti-hyperalgesia in rats. A combined EA and opioid drug protocol may provide an improved treatment strategy for inflammatory pain.
Analgesics, Opioid↗
Changes in AMPA receptor phosphorylation in the rostral ventromedial medulla after inflammatory hyperalgesia in rats.
To study the glutamatergic mechanisms underlying changes in excitability in the brain stem pain modulatory circuitry after injury, we examined GluR1 serine 831 phosphorylation in the rostral ventromedial medulla (RVM) after complete Freund's adjuvant-induced hindpaw inflammation. Western blots indicated a rapid and prolonged (30 min and 7 days post-inflammation) increase in phosphoserine 831 GluR1 protein levels in the RVM. The upregulated GluR1 phosphorylation was blocked by pretreatment, but not by post-treatment, with the local anesthetic, lidocaine, at the site of inflammation. The upregulation of phosphoserine 831 GluR1 was attenuated by pretreatment with chelerythrine, a selective PKC inhibitor, KN-93, a selective CaMKII inhibitor, and two NMDA receptor antagonists, MK-801 and APV. These findings provide new evidence linking in vivo AMPA receptor phosphorylation in the RVM pain modulatory circuitry to the enhanced descending pain modulation after inflammation.
Animals↗
Alteration of the second branch of the trigeminal nerve activity following inferior alveolar nerve transection in rats.
After transection of the inferior alveolar nerve (IAN), the whisker pad area, which is innervated by the infraorbital nerve (ION) that was not injured, showed hypersensitivity to mechanical stimulation. Two days after IAN transection, threshold intensity for escape behavior to mechanical stimulation of the ipsilateral whisker pad area was less than 4.0 g, indicating mechanical allodynia. A total of 68 single fiber discharges were recorded from ION fibers at 3 days after IAN transection. The responses of C- and A-fibers were classified according to their conduction velocity. The C-fiber activities were not affected by IAN transection, whereas A-fiber activities were significantly enhanced by IAN transection as indicated by an increase in background activity and mechanically evoked response. Since the A-fiber responses were significantly affected by IAN transection, patch clamp recording was performed from middle to large diameter retrogradely labeled and acutely dissociated trigeminal ganglion (TRG) neurons. The I(K) (sustained) and I(A) (transient) currents were significantly smaller and hyperpolarization-activated current (I(h)) was significantly larger in TRG neurons of rats with IAN transection as compared to those of naive rats. Furthermore, current injection into TRG neurons induced high frequency spike discharges in rats with IAN transection. These data suggest that changes in K(+) current and I(h) observed in the uninjured TRG neurons reflect an increase in excitability of TRG neurons innervated by the ION after IAN transection, resulting in the development of mechano-allodynia in the area adjacent to the injured IAN innervated region.
Action Potentials↗
Electroacupuncture combined with indomethacin enhances antihyperalgesia in inflammatory rats.
Our previous study showed that electroacupuncture (EA), an adjuvant to conventional medicine, significantly attenuated hyperalgesia and inflammation. The present study is an evaluation of the potential synergism of EA and a subeffective dosage of indomethacin (INDO) in a rat model. Inflammation and hyperalgesia, manifesting as edema and decreased paw withdrawal latency (PWL) to a noxious stimulus, were induced by injecting complete Freund's adjuvant (CFA) subcutaneously into the plantar surface of one hind paw of the rat. EA treatments were given at acupoint GB30 immediately and 2 h post-CFA. INDO at 2 mg/kg was given (intraperitoneally) 40 min before the second EA. PWL and edema were measured prior to CFA and 2.5 and 5 h post-CFA. Ten and 100 Hz EA significantly inhibited CFA-induced hind paw hyperalgesia. Both low- and high-frequency EA combined with INDO enhanced antihyperalgesia compared to each component alone, and 10 Hz but not 100 Hz EA significantly reduced CFA-induced hind paw edema. A combination of low-frequency EA and INDO did not show synergistic inhibitory effects on edema. The results demonstrate that EA combined with INDO synergistically inhibits hyperalgesia and suggest an improved treatment strategy for inflammatory pain.
Animals↗
Trigeminal neuronal recording in animal models of orofacial pain.
The electrical signal associated with nerve cells, mainly as a result of changes in the membrane potential during functional activity, can be recorded extracellularly to study central mechanisms underlying sensory processing. The secondary neurons in the spinal trigeminal complex receive inputs from peripheral neurons that innervate the orofacial region and forward information to the higher levels of the nervous system. Analyzing activity patterns of trigeminal neurons related to pain perception has proven to be an efficient method in studying orofacial pain mechanisms. Here we describe some basic techniques and tips for extracellular single neuron recording from the subnucleus caudalis of the trigeminal spinal nucleus in rats with orofacial injury. Two different rat models with temporomandibular joint inflammation and inferior alveolar nerve transection are described.
Action Potentials↗
Central neuronal changes after nerve injury: neuroplastic influences of injury and aging.
Peripheral nerve injury produces a hyperexcitability of primary afferents and neurons in the spinal cord that is considered important in the development of nerve injury-induced pain. The authors recently developed a nerve injury model in the trigeminal region of the rat to study the neuronal mechanism of neuropathic pain in the trigeminal system. The escape thresholds to mechanical stimulation applied to the whisker pad area were significantly lower in rats with an inferior alveolar nerve (IAN) transection than those evoked from the contralateral, sham-operated whisker pad. Also, background activity and mechanically evoked responses in infraorbital nerve (ION) afferents and hyperpolarization-activated current (Ih) in trigeminal ganglion ION neurons were increased following IAN transection. Background activity and mechanically evoked responses of wide dynamic range (WDR) neurons in trigeminal subnucleus caudalis on the ipsilateral side relative to the transection were also significantly increased after the operation. A large number of cells expressed c-Fos-like immunoreactivity in the caudal medulla and upper cervical spinal cord following non-noxious mechanical stimulation of the faces of rats with IAN transection. The effect of aging on spinal dorsal horn neurons and the involvement of nerve injury in producing abnormal pain sensation in rats with advancing age were also studied. The incidence of licking behavior in response to noxious radiant heat stimulation of the hind paw was lower in the aged rats than in younger adults, but paw withdrawal latency was shorter and the activities of spinal dorsal horn neurons were higher in the aged rats. Furthermore, the descending inhibitory systems were impaired in the aged rats. These observations suggest that the changes in neuronal activity in the aged rats likely corresponded to the changes observed in the rat model of peripheral nerve injury.
Aging↗
Brainstem mechanisms of persistent pain following injury.
Nerve signals arising from sites of tissue or nerve injury lead to long-term changes in the central nervous system and contribute to hyperalgesia and the amplification and persistence of pain. These nociceptor activity-dependent changes are referred to as central sensitization. Central sensitization involves an increase in the excitability of medullary dorsal horn (subnucleus caudalis) and spinal dorsal horn neurons brought about by a series of events including neuronal depolarization; removal of the voltage-dependent magnesium block of the N-methyl-D-aspartate (NMDA) receptor; release of calcium from intracellular stores; phosphorylation of the NMDA, alpha amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA), and neurokinin (NK) 1 receptors via activation of protein kineses; a change in the neuron's excitability; and an increase in synaptic strength. Central sensitization occurs in trigeminal nociceptive pathways, and more robust neuronal hyperexcitability occurs following deep tissue stimulation than cutaneous stimulation. Utilizing Fos protein immunocytochemistry, it has been found that 2 distinct regions are activated in the trigeminal brainstem sensory nuclei, the subnuclei interpolaris/caudalis transition zone (Vi/Vc) and the caudal part of the subnucleus caudalis. The latter is very similar to the spinal dorsal horn and is involved in the sensory discriminative aspects of pain. In contrast, the ventral pole of the Vi/Vc is unique. In addition to its role in the nociceptive sensory processing of deep tissues, it is involved bilaterally in somatovisceral and somatoautonomic processing, activation of the pituitary-adrenal axis, and descending modulatory control. The findings support our overall hypothesis that the ventral pole of Vi/Vc is involved in the coordination of bilateral sensorimotor functions of the trigeminal system associated with the response to deep tissue injury.
Animals↗
Differential rostral projections of caudal brainstem neurons receiving trigeminal input after masseter inflammation.
To understand the functional significance of orofacial injury-induced neuronal activation, this study examined the rostral projection of caudal brainstem neurons that were activated by masseteric inflammation. Rats were injected with a retrograde tracer, Fluorogold, into the nucleus submedius of the thalamus (Sm), parabrachial nucleus (PB), lateral hypothalamus (LH), or medial ventroposterior thalamic nucleus (VPM) 7 days before injection of an inflammatory agent, complete Freund's adjuvant (CFA), into the masseter muscle. Rats were perfused at 2 hours after inflammation, and brainstem tissues were processed for Fos-Fluorogold double immunocytochemistry. Although there was no difference in Fos expression among the four groups (n=4 per site), the rostral projection of Fos-positive neurons showed dramatic differences. In the ventral portion of the trigeminal subnuclei interpolaris/caudalis (Vi/Vc) transition zone, the percentage of Fos-positive neurons projecting to the Sm (39.7%) was significantly higher than that projecting to the LH (5.4%) or VPM (5.6%; P<.001). The anesthesia alone also induced Fos expression in ventral Vi/Vc neurons, but these neurons did not project to Sm. In the caudal laminated Vc and dorsal Vi/Vc, the PB was the major site of rostral projection of Fos-positive neurons. In the caudal ventrolateral medulla and nucleus tractus solitarius, Fos-positive neurons projected to the Sm, PB, and LH. Most VPM-projecting neurons examined did not show Fos-like immunoreactivity after masseter inflammation. These findings emphasize the importance of the trigeminal Vi/Vc transition zone in response to orofacial deep tissue injury. Furthermore, the results differentiate the ventral and dorsal portions of the Vi/Vc transition zone, in that the Sm received projection mainly from activated neurons in the ventral Vi/Vc. The activation of Vi/Vc neurons and associated ascending pathways may facilitate somatoautonomic and somatovisceral integration and descending pain modulation after orofacial deep tissue injury.
Anesthetics, Local↗
Inflammation-induced upregulation of AMPA receptor subunit expression in brain stem pain modulatory circuitry.
Our previous study demonstrated an increase in alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor sensitivity in the rostral ventromedial medulla (RVM) associated with enhanced net descending inhibition after inflammatory hyperalgesia. The present study further studied the time-dependent changes in AMPA-produced inhibition after inflammation and the underlying molecular mechanisms. Inflammation was induced by intraplantar injection of complete Freund's adjuvant (CFA, 0.2ml). There was a significant increase in AMPA-produced inhibition at 5h that was further enhanced at 24h (P<0.05), as compared to that at 3h post-inflammation. The AMPA-produced inhibition returned to the control level at 14 days post-inflammation. We analyzed mRNA and protein levels of the GluR1 and GluR2 AMPA receptor subunits in the RVM at 2h to 14 days post-inflammation. AMPA receptor subunits exist in the two 'flip' and 'flop' isoforms that differentially affect the desensitization properties of the receptor. Reverse transcription-polymerase chain reaction analysis indicated that there was a significant upregulation of mRNAs encoding the GluR1-flip (5-24h), GluR2-flip (24h) and GluR2-flop (24h) isoforms in the RVM after inflammation, whereas the levels of GluR1-flop mRNAs showed no significant change. Western blots demonstrated that the GluR1 protein levels were significantly upregulated at 24h-3 days (P<0.05) post-inflammation, compared to that of naive animals. GluR2 protein levels remained unchanged. Immunohistochemistry further demonstrated an increase in GluR1-like immunoreactivity localized to the RVM at 24h post-inflammation. These findings suggest that AMPA receptors in the RVM undergo selective transcriptional and translational modulation following inflammation and may contribute to activity-dependent plasticity in descending pain modulatory systems after prolonged noxious input.
Animals↗