Kerchner G A, Li P, Zhuo M
Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
IUBMB Life. 1999 Sep;48(3):251-6. doi: 10.1080/713803505.
Severe tissue or nerve injury can result in a chronic and inappropriate sensation of pain, mediated in part by the sensitization of spinal dorsal horn neurons to input from primary afferent fibers. Synaptic transmission at primary afferent synapses is mainly glutamatergic. Although a functioning excitatory synapse contains both alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors in the postsynaptic membrane, recent evidence suggests that dorsal horn neurons contain some "silent" synapses, which exhibit purely NMDA receptor-mediated evoked postsynaptic currents and do not conduct signals at resting membrane potential. Serotonin, which is released onto dorsal horn neurons by descending fibers from the rostroventral medulla, potentiates sensory transmission by activating silent synapses on those neurons, i.e., by recruiting functional AMPA receptors to the postsynaptic membrane. This phenomenon may contribute to the hyperexcitability of dorsal horn neurons seen in chronic pain conditions.
严重的组织或神经损伤可导致慢性且不适当的疼痛感觉，部分是由脊髓背角神经元对初级传入纤维输入的敏化介导的。初级传入突触处的突触传递主要是谷氨酸能的。虽然一个功能正常的兴奋性突触在突触后膜中同时含有α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）和N-甲基-D-天冬氨酸（NMDA）受体，但最近的证据表明，背角神经元含有一些“沉默”突触，这些突触表现出纯粹由NMDA受体介导的诱发突触后电流，并且在静息膜电位时不传导信号。5-羟色胺由延髓嘴腹侧的下行纤维释放到背角神经元上，通过激活这些神经元上的沉默突触来增强感觉传递，即通过将功能性AMPA受体募集到突触后膜上。这种现象可能导致慢性疼痛状态下背角神经元的过度兴奋。
