海兔5-羟色胺能神经纤维与侧节感觉神经元的关系 Ⅱ免疫电镜研究

The Relationship between 5-HT Immunoreactive Fibers and Pleural Sensory Neurons in Aplysia——Ⅰ.Immunoelectron Microscopic Study

应用免疫细胞化学 ABC 法,研究了海兔5-羟色胺免疫反应阳性(5-HT-IR)纤维与侧节感觉神经元的空间关系。在光镜下可见5-HT-IR 纤维走向 PSN 并围绕在 PSN 胞体及轴突起始段,交织成网.5-HT-IR 膨体依据大小可分为小型、中型和大型3类。5-HT-IR 膨体与 PSN 构成轴-体和轴-轴突触.尚可见到轴-胶突触存在.各类突触可分为平坦型和内陷型.参与突触形成的膨体均为小型膨体.本文首次报道了无脊椎动物海兔神经元之间存在着轴-体突触联系,并从形态学上证明5-HT 能神经通过与 PSN 的突触联系,从而参与海兔尾回缩反射弧的组成.

The morphological properties of serotoninergic immunoreactive fibers and their spatial relationships to pleural sensory neurons of Aplysia were studied with an immunocytochemical ABC method under light and transmission electron microscopy.The data show that 5-HT- IR varicosities make apparent synaptic contacts with pleural sensory neurons of aplysia.In light microscopy,it was observed numerous 5-HT-IR fibers containing varicosities around the somata and the initial axon segment of pleural sensory neurons.Labeled varicosities(n= 574)might be classfied into three groups based on their size:i.e.small(0.2～1.2 μm, 79%),medium(1.4～2.4 μm,18%),and large(>2.6 μm,3%)groups.In electron mi- croscopy,it was observed axosomatic,axoaxonic,axoglial synaptic contacts in the pleural sen- sory clusters.Two types of synaptic contacts,flat and invaginated,were found.After mea- suring the shortest diameter of the varicosity(0.1～1.0 μm,n=42),it appeared that only the small varicosities formed synaptic contacts.These results suggest that under appropriated physiological conditions,serotonin might be released from varicosities directly onto perikayra of pleural sensory neurons eliciting the cellular changes correlated with sensitization.Two types of synaptic contacts,flat and invaginatcd,could represent two different functional states,the invaginated type more effective than the other.Thus,pleural sensory neurons con- tributing to sensitization of tail withdrawal reflex in aplysia could be activated by serotonin- ergic neurons.