Signaling mechanisms mediating muscarinic enhancement of GABAergic synaptic transmission in the spinal cord

• Published in: Neuroscience 2009-02, Vol.158 (4), p.1577-1588
• Main Authors: Zhang, H.-M, Chen, S.-R, Cai, Y.-Q, Richardson, T.E, Driver, L.C, Lopez-Berestein, G, Pan, H.-L
• Format: Article
• Language: English
• Subjects: acetylcholine; Animals; Anthracenes - pharmacology; Biological and medical sciences; Biophysics; Cadmium - pharmacology; Calcium - metabolism; dorsal horn; Drug Interactions; Electric Stimulation - methods; Enzyme Inhibitors - pharmacology; Fundamental and applied biological sciences. Psychology; GABA; gamma-Aminobutyric Acid - metabolism; Gene Expression Regulation - drug effects; Gene Expression Regulation - physiology; In Vitro Techniques; Inhibitory Postsynaptic Potentials - drug effects; Inhibitory Postsynaptic Potentials - physiology; Ion Channel Gating - drug effects; Ion Channel Gating - physiology; Male; Muscarinic Agonists - pharmacology; muscarinic receptors; Neural Inhibition - drug effects; Neural Inhibition - physiology; Neurology; Neurons - drug effects; Neurons - physiology; Nickel - pharmacology; Oxotremorine - analogs & derivatives; Oxotremorine - pharmacology; Patch-Clamp Techniques - methods; Potassium Channel Blockers - pharmacology; Rats; Rats, Sprague-Dawley; Receptors, Muscarinic - classification; Receptors, Muscarinic - genetics; Receptors, Muscarinic - physiology; RNA, Messenger - metabolism; RNA, Small Interfering - pharmacology; Signal Transduction - drug effects; Signal Transduction - physiology; siRNA; spinal cord; Spinal Cord - cytology; Vertebrates: nervous system and sense organs
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2008.11.039

Abstract Activation of muscarinic acetylcholine receptors (mAChRs) inhibits spinal nociceptive transmission by potentiation of GABAergic tone through M2 , M3 , and M4 subtypes. To study the signaling mechanisms involved in this unique mAChR action, GABAergic spontaneous inhibitory postsynaptic currents (sIPSCs) of lamina II neurons were recorded using whole-cell patch clamp techniques in rat spinal cord slices. The mAChR agonist oxotremorine-M caused a profound increase in the frequency of GABAergic sIPSCs, which was abolished in the Ca2+ -free solution. Inhibition of voltage-gated Ca2+ channels with Cd2+ and Ni2+ largely reduced the effect of oxotremorine-M on sIPSCs. Blocking nonselective cation channels (NSCCs) with SKF96365 or 2-APB also largely attenuated the effect of oxotremorine-M. However, the KCNQ channel blocker XE991 and the adenylyl cyclase inhibitor MDL12330A had no significant effect on oxotremorine-M-induced increases in sIPSCs. Furthermore, the phosphoinositide-3-kinase (PI3K) inhibitor wortmannin or LY294002 significantly reduced the potentiating effect of oxotremorine-M on sIPSCs. In the spinal cord in which the M3 subtype was specifically knocked down by intrathecal small interfering RNA (siRNA) treatment, SKF96365 and wortmannin still significantly attenuated the effect of oxotremorine-M. In contrast, SKF96365 and wortmannin both failed to alter the effect of oxotremorine-M on sIPSCs when the M2 /M4 mAChRs were blocked. Therefore, our study provides new evidence that activation of mAChRs increases synaptic GABA release through Ca2+ influx and voltage-gated Ca2+ channels. The PI3K–NSCC signaling cascade is primarily involved in the excitation of GABAergic interneurons by the M2 /M4 mAChRs in the spinal dorsal horn.