Theodosis D T, Poulain D A
Neuroscience. 1984 Jan;11(1):183-93. doi: 10.1016/0306-4522(84)90222-7.
Supraoptic nuclei of lactating rats present a particular anatomical organization that could serve to facilitate the synchronization of neuronal firing observed during suckling-induced reflex milk ejections. Although magnocellular neurones are usually separated by neuropil elements, particularly glial fibers, in lactating rats, numerous neurosecretory soma and dendritic profiles are in direct apposition, without glial interposition. Concomitantly, there is also a higher incidence of presynaptic terminals contacting two neurosecretory elements in the same plane of section ("double" synapses). In the present study, a quantitative ultrastructural analysis was used to trace the evolution of the structural reorganization of the nucleus at different stages of the reproductive cycle. The percentage of neurosecretory soma and dendritic profiles in direct apposition was low two weeks after the beginning of pregnancy, but the day prior to parturition, as during lactation, over 40% of all neurosecretory profiles were directly in contact and involved about 10% of the total neuronal surface membrane measured (a 5-fold increase over the corresponding frequencies recorded in virgin rats at oestrus). The contiguous neuronal membranes and associated intercellular space appeared unmodified, except for the presence of attachment plaques, that also increased in frequency at late gestation and lactation. The incidence of "double" synapses also increased by late gestation, so that at lactation, they bridged 8% of all the recorded neurosecretory somata and dendrites, (as compared to 1% in the virgin rats). Similar changes were observed during a first and second gestation and lactation. The incidence of direct appositions and "double" synapses then diminished gradually after weaning: 2 months after the end of lactation, the ultrastructure of the nucleus resembled that of virgin animals. These observations demonstrate a plasticity in the structural organization of the supraoptic nucleus that appears closely related to changing physiological states of the animal and that involves both neurone-glial relationships and the neurones' synaptic configuration.
哺乳期大鼠的视上核呈现出一种特殊的解剖结构，这种结构可能有助于促进在哺乳诱导的反射性乳汁排出过程中观察到的神经元放电同步。尽管在哺乳期大鼠中，大细胞神经元通常被神经毡成分（特别是胶质纤维）分隔，但许多神经分泌性胞体和树突轮廓直接相邻，中间没有胶质成分。同时，在同一截面平面上接触两个神经分泌元件的突触前终末（“双”突触）的发生率也更高。在本研究中，采用定量超微结构分析来追踪在生殖周期不同阶段视上核结构重组的演变。怀孕开始两周后，直接相邻的神经分泌性胞体和树突轮廓的百分比很低，但在分娩前一天，与哺乳期一样，所有神经分泌轮廓中超过40%直接接触，涉及测量的神经元总表面膜的约10%（比发情期未孕大鼠记录的相应频率增加了5倍）。相邻的神经元膜和相关的细胞间隙除了存在附着斑外似乎没有改变，附着斑的频率在妊娠后期和哺乳期也增加了。“双”突触的发生率在妊娠后期也增加，因此在哺乳期，它们连接了所有记录的神经分泌性胞体和树突的8%（相比之下，未孕大鼠为1%）。在第一次和第二次妊娠及哺乳期观察到类似的变化。断奶后，直接相邻和“双”突触的发生率逐渐降低：哺乳结束后2个月，视上核的超微结构类似于未孕动物。这些观察结果表明视上核结构组织具有可塑性，这似乎与动物生理状态的变化密切相关，并且涉及神经元与胶质细胞的关系以及神经元的突触构型。
