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R M Caudle

Publications and source records attributed to R M Caudle.

At least 19 recordsLinked to original sources
PubMed2005

Diverse immunocytochemical expression of opioid receptors in electrophysiologically defined cells of rat dorsal root ganglia.

The development of opiate analgesics that do not produce adverse side effects is hampered by the difficulty in developing drugs that are tissue/sensory cell-specific. Previously, our laboratory has demonstrated that small- and medium-diameter dorsal root ganglia (DRG) cells can be subclassified into at least nine distinct cell types based upon their patterns of voltage activated currents [Petruska, J.C., Napaporn, J., Johnson, R.D., Gu, J.G., Cooper, B.Y., 2000. Subclassified acutely dissociated cells of rat DRG: histochemistry and patterns of capsaicin-, proton-, and ATP-activated currents. J. Neurophysiol. 84 (5), 2365-2379; Petruska, J.C., Napaporn, J., Johnson, R.D., Cooper, B.Y., 2002. Chemical responsiveness and histochemical phenotype of electrophysiologically classified cells of the adult rat dorsal root ganglion. Neuroscience 115 (1), 15-30.] Based on their responses to algesic compounds and histochemical phenotype, eight of the nine subtypes are likely nociceptors. In the present study, we examined the immunoreactivity (IR) of delta-, kappa- and mu-opioid receptors (DOR, KOR and MOR, respectively), in 164 electrophysiologically subclassified DRG neurons. The expression of opioid receptors in the DRG cell types was diverse. Type 1 (25-30 microm cell diameter) and type 9 (35-45 microm) expressed MOR-IR, but were negative for DOR-IR and KOR-IR. Type 2 (25-30 microm) co-expressed DOR-IR and MOR-IR, but did not express KOR-IR. Type 3 (15-20 microm), the non-nociceptive cell type, was not immunoreactive. Type 4 (35-45 microm), type 6 (35-45 microm), and type 7 (15-20 microm) expressed all three opioid receptors. Type 5 (35-45 microm) and type 8 (35-45 microm), co-expressed KOR-IR and MOR-IR, but did not express DOR-IR. The co-expression of opioid receptors in some of the cell types suggests that these sensory afferents might contain heteromeric opioid receptors. Additionally, the diverse expression patterns of opioid receptors between cell types and the consistency of these patterns maintained within each cell type provides further evidence of distinct functional properties of DRG nociceptors.

Afferent Pathways↗
PubMed2005

Expression of the receptor of advanced glycation end products in gingival tissues of type 2 diabetes patients with chronic periodontal disease: a study utilizing immunohistochemistry and RT-PCR.

OBJECTIVES: Relationship between diabetes and periodontal disease is well established. It has been shown that advanced glycation end-products (AGEs) might exert noxious effects on gingival tissues through its receptor. Evidence for the role of receptors of AGE (RAGE) in periodontal disease was verified in a murine model for diabetes. However, the presence of RAGE in human gingival tissues has not been demonstrated previously. In this study we demonstrate the presence of RAGE in human periodontium in patients with chronic periodontitis with and without type 2 diabetes. MATERIAL AND METHODS: Gingival biopsies from eight patients with both type 2 diabetes and chronic periodontitis and 14 healthy control subjects with chronic periodontitis were immunohistochemically stained for RAGE. Five samples from the study groups and four controls were subjected to reverse transcriptase coupled to polymerase chain reaction (RT-PCR) for quantitative determination of mRNA for RAGE. RESULTS: On immunohistochemistry, positive staining for RAGE was seen in the endothelium and the basal and spinous layer of the inflamed gingival epithelium in both type 2 diabetes and non-diabetes tissue with no statistically significant difference between both groups. RT-PCR, however, showed a 50% increase in mRNA for RAGE in the gingiva of diabetic patients when compared with controls (p<0.05). CONCLUSIONS: Although there was no change in the staining intensity for RAGE between both groups, the increase in the mRNA for RAGE in the type 2 diabetes gingival epithelium may indicate a possible involvement of this receptor in the periodontal destruction in type 2 diabetes.

Chronic Disease↗
PubMed2004

Receptor of advanced glycation end product (RAGE) expression in the minor salivary glands of patients with Sjögren's syndrome: a preliminary study.

OBJECTIVE: Receptor for advanced glycation end product (RAGE) is a cell-surface receptor with ligands capable of inducing proinflammatory responses in autoimmunity. We investigated the immunohistochemical expression and immunoblotting of RAGE in labial salivary glands from Sjögren's syndrome (SS) patients. MATERIAL AND METHODS: Ten minor salivary glands from SS and 15 from normal salivary tissue adjacent to mucocele were stained immunohistochemically using an antibody to RAGE. Immunoblotting was performed on four SS biopsies and four controls from normal gland. RESULTS: Immunohistochemistry showed all sections positive for RAGE. The SS sections did not statistically differ from controls. In immunoblotting, SS samples expressed approximately 100% more RAGE than controls [probability (p)<0.03, Student's t-test]. CONCLUSIONS: RAGE is present in the labial salivary glands of both normal and SS patients, with preliminary data suggesting over-expression in SS tissues. The role of RAGE in the pathogenesis of SS has yet to be determined.

Aged↗
PubMed2001

Intrathecally administered cholera toxin blocks allodynia and hyperalgesia in persistent pain models.

In persistent pain, the spinal cord concentration of the opioid peptide dynorphin increases dramatically, yet the function of dynorphin remains unknown. If prodynorphin expression could be manipulated in vivo, it might be possible to determine what role dynorphin plays in persistent pain. Previous work in our laboratory showed that prodynorphin expression is regulated through the cyclic adenosine monophosphate pathway. Therefore, we attempted to enhance prodynorphin expression in the spinal cord of rats by stimulating adenylate cyclase with cholera toxin; however, contrary to our hypothesis, intrathecally administered cholera toxin did not enhance prodynorphin expression. Rather, cholera toxin suppressed the increase in prodynorphin produced by inflammation. Cholera toxin also inhibited the allodynia and hyperalgesia associated with inflammation and nerve injury. Interestingly, the antiallodynic and antihyperalgesic actions of cholera toxin were reversed with the opioid receptor antagonist, naloxone. These findings suggest that cholera toxin enhances or unmasks an endogenous opioid pathway to produce its antiallodynic and antihyperalgesic effects. Furthermore, these data indicate that the suppression of the inflammation-induced increase in spinal cord prodynorphin is caused by the opioid-mediated decrease in the nociceptive stimulus.

Journal Article↗
PubMed2000

Ligand-induced dynamic membrane changes and cell deletion conferred by vanilloid receptor 1.

The real time dynamics of vanilloid-induced cytotoxicity and the specific deletion of nociceptive neurons expressing the wild-type vanilloid receptor (VR1) were investigated. VR1 was C-terminally tagged with either the 27-kDa enhanced green fluorescent protein (eGFP) or a 12-amino acid epsilon-epitope. Upon exposure to resiniferatoxin, VR1eGFP- or VR1epsilon-expressing cells exhibited pharmacological responses similar to those of cells expressing the untagged VR1. Within seconds of vanilloid exposure, the intracellular free calcium ([Ca(2+)](i)) was elevated in cells expressing VR1. A functional pool of VR1 also was localized to the endoplasmic reticulum that, in the absence of extracellular calcium, also was capable of releasing calcium upon agonist treatment. Confocal imaging disclosed that resiniferatoxin treatment induced vesiculation of the mitochondria and the endoplasmic reticulum ( approximately 1 min), nuclear membrane disruption (5-10 min), and cell lysis (1-2 h). Nociceptive primary sensory neurons endogenously express VR1, and resiniferatoxin treatment induced a sudden increase in [Ca(2+)](i) and mitochondrial disruption which was cell-selective, as glia and non-VR1-expressing neurons were unaffected. Early hallmarks of cytotoxicity were followed by specific deletion of VR1-expressing cells. These data demonstrate that vanilloids disrupt vital organelles within the cell body and, if administered to sensory ganglia, may be employed to rapidly and selectively delete nociceptive neurons.

Animals↗
PubMed2000

Co-localization of N-methyl-D-aspartate receptors and substance P (neurokinin-1) receptors in rat spinal cord.

Glutamate, substance P (SP), and their receptors have been implicated in the initiation and maintenance of persistent pain through an interaction at second order spinal cord neurons. Employing well-characterized antibodies to the SP receptor and the N-methyl-D-aspartate receptor (NR1 subunit, splice variant missing exon 22), we demonstrate co-localization of these receptors on second order neurons at cervical, thoracic, lumbar, and sacral spinal cord levels. The co-localization was marked in lamina I of the dorsal horn at all levels and in the intermediolateral nucleus of the thoraco-lumbar spinal cord nuclei associated with autonomic function.

Amino Acid Sequence↗
PubMed1999

Actions of intrathecal diphtheria toxin-substance P fusion protein on models of persistent pain.

Substance P (SP) plays a central role in the transduction of second messenger signals from primary afferent nociceptive terminals to second-order neurons in the spinal cord. We have tested a recombinant engineered diphtheria toxin/SP fusion protein (DAB389SP) in acute and chronic pain models in the rat. DAB389SP binds to the SP receptor (SPR) and is internalized and kills SPR-expressing cells by blocking cellular protein synthesis. DAB389SP delivery was by intrathecal infusion, of varying duration, at the lumbar level. In the chronic constriction injury model of neuropathic pain a significant reduction in mechanically induced hyperalgesia was obtained. This effect was less marked in an acute carageenan inflammation model. Although other pain characteristics (mechano-allodynia, cold-allodynia, and heat-hyperalgesia) showed some improvement, these were less pronounced. Immunocytochemistry revealed a toxin-induced reduction in lamina I, of SPR and of NMDA NR1 subunit receptor expressing neurons, and of c-Fos, an inducible molecular marker of persistent nociceptive activity. The use of cytotoxic fusion proteins to target specific cell types may be of considerable benefit in the study of nociception and the treatment of chronic pain.

Acute Disease↗
PubMed1999

The kappa opioid agonist GR89,696 blocks hyperalgesia and allodynia in rat models of peripheral neuritis and neuropathy.

Previous work demonstrated that, in rats, intrathecal GR89696, a putative kappa-2 opioid receptor agonist, inhibited hyperalgesia to noxious heat in an inflamed hind paw (anti-hyperalgesic effect). Non-inflamed paws were not influenced by kappa-2 receptor activation. The question addressed in this study was whether GR89696 was as effective in blocking hyperalgesia and allodynia in nerve injury models as it was in the inflammation model. GR89696 (6 nmoles, i.t.) completely reversed the hyperalgesia and allodynia observed in both the neuropathy and neuritis models in all sensory tests. However, it did not alter sensory function in non-injured limbs nor in sham operated animals. Naloxone (1 mg/kg, i.p.) reversed the anti-hyperalgesic and anti-allodynic effects of GR89696. The mu agonist DAMGO (6 nmoles, i.t.) and the kappa-1 agonist U69593 (100 nmoles, i.t.) only partially reversed hyperalgesia and allodynia. These findings suggest that kappa-2 opioid receptors may be a useful target for the pharmacological control of hyperalgesia and allodynia.

Analgesics, Non-Narcotic↗
PubMed1998

Spinal kappa1 and kappa2 opioid binding sites in rats, guinea pigs, monkeys and humans.

Several lines of work demonstrate that there are two subtypes of kappa opioid receptors. Intrathecally administered agonists for the kappa1 subtype are not effective in treating pain, whereas agonists for the kappa2 receptor are anti-hyperalgesic and anti-allodynic. The question addressed here was whether the ratio of spinal kappa1 to kappa2 receptors was conserved across species. Thus, binding experiments were performed on spinal cord membranes from rats, guinea pigs, monkeys and humans. We found that kappa2 receptors were approximately ten times more abundant than kappa1 receptors in all species tested. This suggests that the anti-hyperalgesic and anti-allodynic properties of kappa2 agonists may also be conserved. Therefore, selective kappa2 agonists may be effective in treating chronic pain in humans.

Analgesics↗
PubMed1998

Adenoviral gene transfer to spinal-cord neurons: intrathecal vs. intraparenchymal administration.

The spinal cord is the site of many chronic, debilitating, neurological disorders that may be amenable to gene therapy. The present study, using quantitative and anatomical methods, examines the ability of replication deficient adenovirus to transfer a transcription cassette composed of the cytomegalovirus promoter driving the expression of the LacZ reporter gene (AdCMVbetagal) to spinal-cord neurons. Rats were microinjected with AdCMVbetagal into the spinal-cord parenchyma or subarachnoid space and sacrificed between 1 and 60 days post-infusion. The spinal cord was assayed for beta-galactosidase (beta-gal) activity fluorometrically (MUG). Intraparenchymal injection resulted in significant beta-gal activity at day 1, which peaked at day 7, and decreased at day 14 (21-, 57- and 9.8-fold of control respectively). The spatial distribution of beta-gal activity on day 7 was confined to the 1-cm section containing the injection site but was detected 2 cm caudal to this section by day 14. Histochemical staining and immunocytochemistry revealed a prominent reaction product in neurons, particularly motor neurons, and glia within the ventral grey matter bilaterally. Intrathecal viral injections showed comparatively modest, yet significant increases in beta-gal activity throughout the spinal cord with the greatest activity (170% control) closest to the catheter tip. This study demonstrates that AdCMVbetagal injected into the ventral spinal cord results in extensive in vivo neuronal gene transfer with beta-gal activity reaching a peak by day 7 and remaining detectable at 60 days. Intrathecal viral injections result in greater spatial distribution but a comparatively lower level of expression.

Adenoviridae↗
PubMed1998

Ifenprodil blocks the excitatory effects of the opioid peptide dynorphin 1-17 on NMDA receptor-mediated currents in the CA3 region of the guinea pig hippocampus.

This study found that dynorphin had a biphasic concentration response relationship on N-methyl-D-aspartate (NMDA) receptor-mediated currents in the CA3 region of the guinea pig hippocampal slice. A previous study demonstrated that the inhibitory effect was mediated by a kappa 2 opioid receptor. In the present study, the polyamine site antagonist ifenprodil converted dynorphin's biphasic concentration response relationship to a monophasic inhibitory curve. The polyamine diethylenetriamine also blocked dynorphin's excitatory actions. The combination of dynorphin 1-17 and naloxone produced neurotoxicity, presumably as a result of dynorphin's excitatory actions on NMDA receptors. In addition, the release of endogenous dynorphin from mossy fibers in the presence of naloxone injured the cells. Ifenprodil prevented the neurotoxicity of both applied and released dynorphin. These findings suggest that dynorphin acts at a polyamine site to produce its excitatory effects and, further, suggest that dynorphin may mediate some neuropathologies through its interaction at this site.

Animals↗
PubMed1997

Putative kappa-2 opioid agonists are antihyperalgesic in a rat model of inflammation.

It has been demonstrated that kappa-2 opioid receptor agonists can inhibit the current that flows through the N-methyl-o-aspartate (NMDA) subclass of excitatory amino acid receptor. NMDA receptor antagonists have been shown to be effective antihyperalgesic agents when administered intrathecally into rats. Antihyperalgesia is defined as the ability to block enhanced sensitivity, usually produced by nerve injury or inflammation, to nociceptive stimuli. Thus, the hypothesis was proposed that kappa-2 opioid receptor agonists would be antihyperalgesic when injected intrathecally into rats with an inflamed hind paw. The kappa agonists bremazocine and GR89,696 were effective at reversing the hyperalgesia associated with the inflamed hind paw but did not influence the sensitivity of the noninflamed hind paw to noxious heat. The kappa-1-selective agonist U69,593 had no effect on the heat sensitivity of either the inflamed paw or the noninflamed paw. Intrathecal injection of the mu-selective agonist [D-Ala2,N-MePhe4,Gly5-ol]enkephalin or the delta-selective agonist [D-Pen(2,5)]enkephalin elevated paw withdrawal latencies to heat in both hind paws. These findings indicate that activation of presumed kappa-2 receptors in the rat spinal cord results in suppression of the hyperalgesic state without influencing normal sensitivity to noxious stimuli. It is proposed that the antihyperalgesic effect of kappa-2 receptor activation is mediated by the ability of the opioid receptor to reduce the flow of current through the NMDA receptor ionophore.

Analgesics↗
PubMed1997

GR89,696 is a kappa-2 opioid receptor agonist and a kappa-1 opioid receptor antagonist in the guinea pig hippocampus.

Receptor binding studies and electrophysiological studies demonstrated the existence of at least two kappa opioid receptors, which have been designated kappa-1 and kappa-2. Several agonists and antagonists are selective for the kappa-1 receptor whereas no known ligands are selective for the kappa-2 receptor. In this study, the kappa opioid GR89,696 was tested in the guinea pig hippocampal slice preparation for kappa-1 versus kappa-2 activity. The perforant path-evoked population spike in the dentate was use to evaluate activity at the kappa-1 receptor, and the Schaffer collateral-evoked N-methyl-D-aspartate (NMDA) receptor-mediated synaptic current in CA3 pyramidal cells was used to measure kappa-2 receptor activation. GR89,696 had no effect on the perforant path-evoked dentate population spike; however, it did reverse the effects of the selective kappa-1 agonist U69,593 when co-perfused over the slices. In the CA3, GR89,696 inhibited the NMDA receptor-mediated synaptic current. The inhibition was antagonized by naloxone. The EC50 for GR89,696 on the NMDA current was 41.7 nM (95% CL, 7.0-248 nM). These findings indicate that GR89,696 is an agonist for kappa-2 opioid receptors and an antagonist at kappa-1 receptors in the guinea pig hippocampus.

Animals↗
PubMed1994

Kappa 2 opioid receptors inhibit NMDA receptor-mediated synaptic currents in guinea pig CA3 pyramidal cells.

The role of the endogenous opioid peptide dynorphin (1-17) in regulating NMDA receptor-mediated synaptic currents was examined in guinea pig hippocampus. Schaffer collateral/commissural fiber-evoked NMDA synaptic currents were recorded using whole-cell patch-clamp techniques in CA3 pyramidal cells. Dynorphin was found to have dual effects on NMDA synaptic currents, increasing currents at low concentrations and decreasing currents at high concentrations. Only the inhibitory action of dynorphin was sensitive to naloxone, indicating that this effect was mediated by an opioid receptor. The inhibitory effect was mimicked by bremazocine, but not by U69,593, U50,488, [D-Ala2, N-Me-Phe4, Gly-ol]-enkephalin, or [D-Pen2,5]-enkephalin. Bremazocine's effect was blocked by naloxone, but not by nor-binaltorphimine, cyprodime, or naltrindole. These findings suggest that bremazocine's effect was mediated by the kappa 2 subtype of opioid receptor. In addition, 1 microM naloxone and antisera to dynorphin (1-17) were found to increase NMDA-mediated synaptic currents. Nor-binaltorphimine, cyprodime, naltrindole, and antisera to met-enkephalin did not increase the NMDA synaptic current. These findings suggest that endogenous dynorphin was acting at kappa 2 receptors to inhibit NMDA receptor-mediated synaptic currents. Overall, these findings indicate that dynorphin is an endogenous agonist for kappa 2 receptors in the CA3 region of the guinea pig hippocampus and that these receptors regulate NMDA receptor function.

Animals↗
PubMed1993

The demonstration of long latency potentials in the CA1 region of the rat hippocampal slice.

Shaffer collateral evoked extracellular DC potentials with latencies greater than 100 ms are demonstrated in the CA1 region of the rat hippocampal slice preparation. The most prominent potential following the population spike is a positive potential peaking between 150 and 400 ms after the stimulus. The amplitude of the potential is approximately two orders of magnitude smaller than the population spike. This potential shares several characteristics with the P300 from electroencephalogram studies of evoked potentials. Thus, it was dubbed the in vitro P3. One of the most distinguishing characteristics of the in vitro P3 is a negative potential that immediately follows it. The negative potential is smaller in amplitude than the in vitro P3, but lasts for several seconds. A similar potential also follows the P300 in electroencephalogram studies. These data suggest that the in vitro P3 is an in vitro version of the long latency evoked potential known as the P300 in electroencephalogram studies.

Animals↗