在内源性痛调制系统中

中缝大核(NRM)及邻近结构的神经元轴突行向脊髓后角

其释放的5-羟色胺(5-HT)可能对后角内痛敏神经元

中间神经元以及初级传入5

6-dihydroxytryptamine was microinjected into the nucleus raphe magus (NRM)of rate. The sections of upper cervical segments were processed for immunoreaclive substance P (SP). The degenerated axon terminals and immunoreactive fibers were identified by electron microscopy. The results show that the degenerated axon terminals and immunoreactive positive dendrites and axons were found in the laminae I and II of the dorsal horn. The electron-dense axon terminals were in contact with unlabelled dendrites

some also in contract with immunoreactive dendrites. In lamina II

one of degenerated axon terminals as a center was contacted by several unlabellcd axonal boutons. SP labelled terminals were synapsed with unlabelled dendrites and dendritic spinej in addition

unlabelled axo-axonal synapse was found in lamina II. These results suggest that 5-HT axon terminals from NRM directly innervate SP and non-SP neurons in the laminae I and II.