Commons K G, Milner T A
Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021, USA.
J Comp Neurol. 1995 Jul 31;358(3):324-42. doi: 10.1002/cne.903580303.
Opioid peptides, including leu-enkephalin (LE), are important neuromodulators in the hippocampal formation where they may play a role in learning and memory as well as epileptogenesis. We examined the cellular substrates that underlie the function of LE in each lamina of the rat hippocampal formation by immunocytochemistry at the electron microscopic level in single section analysis. LE-like immunoreactivity (LE-LI) was primarily associated with large dense-core vesicles (80-100 nm), usually found in axons and axon terminals, but was also observed in perikarya and occasionally in dendrites. The morphology and synaptic associations of LE-LI-containing terminals were strikingly distinct in each region of the hippocampal formation. In the molecular layer of the dentate gyrus, terminals with LE-LI were typically small (0.6 microns) and formed primarily asymmetric (excitatory type) synapses on single dendritic spines, which is consistent with the presence of LE in the lateral perforant path. In the hilus of the dentate gyrus, two types of LE-containing terminals were present: (1) small round terminals that were heterogeneous in size (0.4-1 microns) and in type of contact formed and (2) larger (3-5 microns) terminals exhibiting the characteristic morphology of mossy fiber boutons that formed asymmetric synapses on spines. This variation in morphology and the type of contact suggests LE may have a heterogeneous influence on diverse hilar interneurons. In the CA3 region of the hippocampus, LE-LI was localized to large mossy fiber boutons (3-7 microns) that formed multiple asymmetric synapses on complex spiny dendritic processes and often formed puncta adherentia with the shafts of large CA3 pyramidal cell dendrites, indicating that this peptide may be directly released onto pyramidal cells. At the border of stratum radiatum and lacunosum moleculare in the CA1 region of the hippocampus, LE-labeled terminals averaged 0.8 microns in diameter and often formed symmetric (inhibitory type) synapses on dendritic shafts, which is consistent with a role in disinhibition. In conclusion, these heterogeneous cellular interactions indicate that LE has diverse functional roles and mechanisms of action within each lamina of the hippocampal formation and may directly and indirectly modulate hippocampal cell activity.
阿片肽，包括亮氨酸脑啡肽（LE），是海马结构中的重要神经调质，它们可能在学习、记忆以及癫痫发生过程中发挥作用。我们通过单切片分析的电子显微镜免疫细胞化学方法，研究了大鼠海马结构各层中LE功能的细胞基础。类LE免疫反应性（LE-LI）主要与大的致密核心囊泡（80-100纳米）相关，这些囊泡通常存在于轴突和轴突终末，但也在胞体中观察到，偶尔在树突中也有。含LE-LI终末的形态和突触联系在海马结构的每个区域都有显著差异。在齿状回分子层，含LE-LI的终末通常较小（0.6微米），主要在单个树突棘上形成不对称（兴奋性类型）突触，这与外侧穿通路径中存在LE一致。在齿状回门区，存在两种含LE的终末：（1）大小（0.4-1微米）和形成的接触类型各异的小圆形终末，以及（2）较大（3-5微米）的终末，呈现苔藓纤维终扣的特征形态，在棘上形成不对称突触。这种形态和接触类型的差异表明LE可能对不同的门区中间神经元有不同的影响。在海马的CA3区，LE-LI定位于大的苔藓纤维终扣（3-7微米），这些终扣在复杂的多棘树突过程上形成多个不对称突触，并且经常与大的CA3锥体细胞树突轴形成粘着斑，表明这种肽可能直接释放到锥体细胞上。在海马CA1区辐射层和分子层空洞交界处，LE标记的终末平均直径为0.8微米，经常在树突轴上形成对称（抑制性类型）突触，这与去抑制作用一致。总之，这些不同的细胞相互作用表明LE在海马结构的各层中具有多种功能作用和作用机制，并且可能直接和间接调节海马细胞活性。
