ABSTRACT
Mounting evidence supports an important role of chemokines, produced by spinal cord astrocytes, in promoting central sensitization and chronic pain. In particular, CCL2 (C-C motif chemokine ligand 2) has been shown to enhance N-methyl-D-aspartate (NMDA)-induced currents in spinal outer lamina II (IIo) neurons. However, the exact molecular, synaptic, and cellular mechanisms by which CCL2 modulates central sensitization are still unclear. We found that spinal injection of the CCR2 antagonist RS504393 attenuated CCL2- and inflammation-induced hyperalgesia. Single-cell RT-PCR revealed CCR2 expression in excitatory vesicular glutamate transporter subtype 2-positive (VGLUT2) neurons. CCL2 increased NMDA-induced currents in CCR2/VGLUT2 neurons in lamina IIo; it also enhanced the synaptic NMDA currents evoked by dorsal root stimulation; and furthermore, it increased the total and synaptic NMDA currents in somatostatin-expressing excitatory neurons. Finally, intrathecal RS504393 reversed the long-term potentiation evoked in the spinal cord by C-fiber stimulation. Our findings suggest that CCL2 directly modulates synaptic plasticity in CCR2-expressing excitatory neurons in spinal lamina IIo, and this underlies the generation of central sensitization in pathological pain.
Subject(s)
Animals , Female , Male , Mice , Benzoxazines , Pharmacology , Therapeutic Uses , Chemokine CCL2 , Genetics , Metabolism , Pharmacology , Excitatory Amino Acid Agents , Pharmacology , Excitatory Amino Acid Agonists , Pharmacology , Freund's Adjuvant , Toxicity , Hyperalgesia , Metabolism , Long-Term Potentiation , Physiology , Luminescent Proteins , Genetics , Metabolism , Mice, Inbred C57BL , Mice, Transgenic , Myelitis , Drug Therapy , Metabolism , Neurons , Pain Management , Somatostatin , Genetics , Metabolism , Spinal Cord , Cell Biology , Spiro Compounds , Pharmacology , Therapeutic Uses , Vesicular Glutamate Transport Protein 2 , Genetics , Metabolism , Vesicular Inhibitory Amino Acid Transport Proteins , Genetics , MetabolismABSTRACT
Recent studies have provided several lines of evidence that peripheral administration of oxytocin induces analgesia in human and rodents. However, the exact underlying mechanism of analgesia still remains elusive. In the present study, we aimed to identify which receptor could mediate the analgesic effect of intraperitoneal injection of oxytocin and its cellular mechanisms in thermal pain behavior. We found that oxytocin-induced analgesia could be reversed by d(CH₂)₅[Tyr(Me)²,Dab⁵] AVP, a vasopressin-1a (V1a) receptor antagonist, but not by desGly-NH₂-d(CH₂)₅[DTyr², Thr⁴]OVT, an oxytocin receptor antagonist. Single cell RT-PCR analysis revealed that V1a receptor, compared to oxytocin, vasopressin-1b and vasopressin-2 receptors, was more profoundly expressed in dorsal root ganglion (DRG) neurons and the expression of V1a receptor was predominant in transient receptor potential vanilloid 1 (TRPV1)-expressing DRG neurons. Fura-2 based calcium imaging experiments showed that capsaicin-induced calcium transient was significantly inhibited by oxytocin and that such inhibition was reversed by V1a receptor antagonist. Additionally, whole cell patch clamp recording demonstrated that oxytocin significantly increased potassium conductance via V1a receptor in DRG neurons. Taken together, our findings suggest that analgesic effects produced by peripheral administration of oxytocin were attributable to the activation of V1a receptor, resulting in reduction of TRPV1 activity and enhancement of potassium conductance in DRG neurons.
Subject(s)
Humans , Analgesia , Calcium , Diagnosis-Related Groups , Electrophysiology , Fura-2 , Ganglia, Spinal , Injections, Intraperitoneal , Neurons , Oxytocin , Potassium , Receptors, Oxytocin , Receptors, Vasopressin , Rodentia , Spinal Nerve RootsABSTRACT
BACKGROUND/AIMS: This study was aimed to examine if FB1 induced-hepatotoxicity involves apoptosis, and cholesteryl hemisuccinate (CS) pre-treatment would selectively interfere with FB1 induced-apoptosis of hepatocytes. METHODS: Sprague-Dawley rats were intravenousely injected with FB1 (1.25 mg/kg/day) for two days, and were sacrificed at 3, 6, 12, 24 and 48 hours after injection. Another experiment group was composed of rats with pretreatment of CS (100 mg/kg/day, i.p.) before FB1 injection. RESULTS: This study demonstrated that administration of hepatotoxic dose of FB1 to Sprague-Dawley rats resulted in liver injury leading to cell death by apoptosis. FB1-induced apoptosis was preceded by early elevation in serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), total cholesterol, and appearance of injured pre-apoptotic cells at 12 hours was followed by massive fragmentation and margination of heterochromatin at 24 hours. CS pre-treatment prior to FB1 injection ameliorated serum biochemistry and hepatic injury with apoptosis, demonstrated by histological, ultrastructural and TUNEL (terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling) methods. In addition, there was remarkable decrease in number of PCNA (proliferative cell nuclear antigen)-positive proliferating hepatocytes compared to that of FB1 treated group. CONCLUSION: This study suggests that apoptosis significantly contributes to FB1-induced hepatotoxicity in vivo, and pre-exposure of rat to CS prevents FB1-induced hepatic apoptosis and proliferation.