dizocilpine-maleate and fluorocitrate

In this study, we examined the relationship between astrocyte activation in the cuneate nucleus (CN) and behavioral hypersensitivity after chronic constriction injury (CCI) of the median nerve. In addition, we also examined the effects of pre-emptive treatment with a number of drugs on astrocyte activation and hypersensitivity development in this model. Using immunohistochemistry and immunoblotting, little glial fibrillary acidic protein (GFAP; an astrocyte marker) immunoreactivity was detected in the CN of the normal rats. As early as 3 days after CCI, there was a significant increase in GFAP immunoreactivity in the lesion side of CN, and this reached a maximum at 7 days, and was followed by a decline. Counting of GFAP-immunoreactive astrocytes revealed that astrocytic hypertrophy, but not proliferation, contributes to increased GFAP immunoreactivity. Furthermore, microinjection of the glial activation inhibitor, fluorocitrate, into the CN at 3 days after CCI attenuated injury-induced behavioral hypersensitivity in a dose-dependent manner. These results suggest that median nerve injury-induced astrocytic activation in the CN modulated the development of behavioral hypersensitivity. Animals received MK-801 (glutamate N-methyl-d-aspartate (NMDA) receptor antagonist), clonidine (alpha(2)-adrenoreceptor agonist), tetrodotoxin (TTX, sodium channel blocker) or lidocaine (local anesthetic) 30 min prior to median nerve CCI. Pre-treatment with MK-801, TTX, and 2% lidocaine, but not clonidine, attenuated GFAP immunoreactivity and behavioral hypersensitivity following median nerve injury. In conclusion, suppressing reactions to injury, such as the generation of ectopic discharges and activation of NMDA receptors, can decrease astrocyte activation in the CN and attenuate neuropathic pain sensations.

Topics: Adrenergic alpha-Agonists; Animals; Astrocytes; Citrates; Clonidine; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glial Fibrillary Acidic Protein; Hyperalgesia; Lidocaine; Male; Median Neuropathy; Medulla Oblongata; Pain Threshold; Rats; Rats, Sprague-Dawley; Sodium Channel Blockers; Tetrodotoxin; Time Factors; Up-Regulation

Bradykinin is one of the most potent endogenous algesic substances and its role in pain transmission has been intensively studied in the periphery. However, the action of this peptide in central structures involved in pain transmission remains unclear. Administration of bradykinin (0.25 nmol/site) into the right amygdala of adult male Wistar rats induced thermal hyperalgesia, evaluated in the paw-flick test. Bradykinin-induced hyperalgesia was abolished by co-administration with the B(2) receptor antagonist Hoe 140 (5 pmol/site), the NMDA antagonist MK-801 (5 nmol/site), the cyclooxygenase inhibitor indomethacin (10 nmol/site) and the glial metabolic inhibitor fluorocitrate (1 nmol/site). Since the intra-amygdala administration of bradykinin did not alter spontaneous locomotion in the open-field test, it is unlikely that the current described hyperalgesic effect of bradykinin is due to an unspecific action on motor activity. These findings provide evidence that bradykinin, through activation of amygdalar B(2) receptors induces hyperalgesia and that glutamatergic- and prostanoid-mediated mechanisms are involved in such effect.

Topics: Amygdala; Animals; Behavior, Animal; Bradykinin; Bradykinin Receptor Antagonists; Citrates; Cyclooxygenase Inhibitors; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Hyperalgesia; Indomethacin; Male; Motor Activity; Neuroglia; Pain Measurement; Rats; Rats, Wistar

The major local symptom of Phoneutria nigriventer envenomation is an intense pain, which can be controlled by infiltration with local anesthetics or by systemic treatment with opioid analgesics. Previous work showed that intraplantar (i.pl) injection of Phoneutria nigriventer venom in rats induces hyperalgesia, mediated peripherally by tachykinin and glutamate receptors. The present study examined the spinal mechanisms involved in pain-enhancing effect of this venom. Intraplantar injection of venom into rat hind paw induced hyperalgesia. This phenomenon was inhibited by intrathecal (i.t.) injection of tachykinin NK1 (GR 82334) or NK2 (GR 94800) receptor antagonists, a calcitonin gene-related peptide (CGRP) receptor antagonist (CGRP8-37) and N-methyl-D-aspartate (NMDA; MK 801 and AP-5), non-NMDA ionotropic (CNQX), or metabotropic (AIDA and MPEP) glutamate receptor antagonists, suggesting the involvement of spinal neurokinins and excitatory amino acids. The role of proinflammatory cytokines, nitric oxide (NO), and prostanoids in spinally mediated pain facilitation was also investigated. Pharmacological blockade of tumour necrosis factor-alpha (TNFalpha) or interleukin-1beta (IL-1beta) reduced the hyperalgesic response to venom. Intrathecal injection of L-N6-(1-iminoethyl)lysine (L-NIL), but not of 7-nitroindazole (7-NI), inhibited hyperalgesia induced by the venom, indicating that NO, generated by the activity of the inducible form of nitric oxide synthase, also mediates this phenomenon. Furthermore, indomethacin, an inhibitor of cyclooxigenases (COX), or celecoxib, a selective inhibitor of COX-2, abolished venom-induced hyperalgesia, suggesting the involvement of spinal prostanoids in this effect. These data indicate that the spinal mechanisms of pain facilitation induced by Phoneutria nigriventer venom involves a plethora of mediators that may cooperate in the genesis of venom-induced central sensitization.

Topics: Animals; Antibodies; Calcitonin Gene-Related Peptide Receptor Antagonists; Celecoxib; Citrates; Cyclooxygenase Inhibitors; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Hyperalgesia; Indazoles; Interleukin-1; Lysine; Male; Neurokinin-1 Receptor Antagonists; Nitric Oxide Synthase; Pain; Physalaemin; Prostaglandins; Pyrazoles; Rats; Rats, Wistar; Receptors, Calcitonin Gene-Related Peptide; Receptors, Neurokinin-1; Spider Venoms; Spinal Cord; Sulfonamides; Tumor Necrosis Factor-alpha

Glial cells are relatively resistant to energy impairment, although little is known of the extent to which glial metabolism is affected during partial energy impairment and how this influences neurons. Fluorocitrate has been shown to be a glial specific metabolic inhibitor. Its selective effect on chick retinal Müller cells was verified by measuring incorporation of radiolabel from 3H-acetate and U-14C-glucose into glutamate and glutamine following exposure of isolated embryonic day 15-18 chick retina to 20 microm fluorocitrate. Fluorocitrate significantly reduced the incorporation of radiolabel from acetate and glucose into glutamine, with less effect on incorporation of label from acetate into glutamate and no reduction of label from glucose into glutamate. The relative specific activity (RSA; ratio of glutamine to glutamate) increased between embryonic day 15 and 18 consistent with the increase in glutamine synthetase activity that occurs in Müller cells at this time in chick retinal development. As with previous findings, mild energy stress produced by inhibiting glycolysis with the general inhibitor iodoacetate (IOA) for up to 45 min, caused acute neuronal damage that was predominately NMDA receptor mediated and occurred in the absence of a net efflux of excitatory amino acids. Acute NMDA-mediated toxicity in this preparation is characterized by the selective damage to amacrine and ganglion cells and quantitatively, by GABA release into the medium. When IOA was combined with fluorocitrate, acute toxicity was potentiated and temporally accelerated. Acute damage was first noted at 15 min, occurred throughout all retinal layers and was accompanied by an overflow of excitatory amino acids at 30 and 45 min. Blocking NMDA receptors with MK-801 during IOA plus fluorocitrate exposure attenuated the rise in excitatory amino acids and prevented the swelling in neuronal, but not Müller cells. Following incorporation of radiolabel from acetate and glucose into glutamate and glutamine after different times of exposure to IOA showed that while the effects of incorporation of label from glucose were immediate, glutamine synthesis from acetate was preserved for a longer period of time. These findings suggest that during a partial energy impairment, neuronal metabolism is affected to a greater extent than is glial metabolism. Glial cells may play a protective role in this situation, and can delay the onset of acute neuronal damage.

Topics: Animals; Chick Embryo; Citrates; Dizocilpine Maleate; Energy Metabolism; gamma-Aminobutyric Acid; Glutamic Acid; Glutamine; Glycolysis; In Vitro Techniques; Iodoacetates; Neuroglia; Receptors, N-Methyl-D-Aspartate; Retina

We investigated electrophysiological responses induced by ischemia-like insult (anoxia and aglycemia, AA) in the rat hippocampal CA1 pyramidal cells in an in vitro slice preparation devoid of glial metabolism. In the slice treated with fluorocitrate (100 microM), a glia-specific metabolic inhibitor, 10 min AA induced hyperexcitation as evidenced by an appearance of multiple population spikes evoked by stimulation of the Schaffer collateral/commissural pathway in the CA1 region prior to elimination of the response. Readministration of oxygen and glucose failed to restore the population spike amplitude. Intracellular recordings revealed that 10 min AA induced slow EPSPs with relative long duration. The induction of the slow EPSPs was followed by a rapid membrane depolarization with a large amplitude. When the fluorocitrate-treated slice was exposed to MK-801 (10 microM), a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, 10 min AA failed to induce either the hyperexcitation of synaptic responses or the rapid depolarization. Furthermore, synaptic responses were fully restored after readministration of oxygen and glucose. In contrast, neither the synaptic hyperexcitation nor the rapid depolarization was observed during 10 min AA in the hippocampal CA1 pyramidal cells of the control slice. In addition, an irreversible synaptic failure associated with AA was not induced in the control slice. These results strongly suggest that fluorocitrate increases NMDA receptor-dependent AA-induced damage in the hippocampal slice by interfering glial spatial buffering of K+.

Topics: Animals; Brain Ischemia; Citrates; Dizocilpine Maleate; Evoked Potentials; Excitatory Amino Acid Antagonists; Hippocampus; Hypoxia, Brain; In Vitro Techniques; Male; Membrane Potentials; Neuroglia; Neuroprotective Agents; Pyramidal Cells; Rats; Rats, Wistar; Synaptic Transmission