Kirov S A, Sorra K E, Harris K M
Division of Neuroscience in the Department of Neurology, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
J Neurosci. 1999 Apr 15;19(8):2876-86. doi: 10.1523/JNEUROSCI.19-08-02876.1999.
Hippocampal slices have long been used to investigate properties of synaptic transmission and plasticity. Here, for the first time, synapses in slices have been compared quantitatively with synapses occurring in perfusion-fixed hippocampus, which is presumed to represent the natural in vivo state. Relative to perfusion-fixed hippocampus, a remarkable 40-50% increase in spine number occurs in adult hippocampal slices, and a 90% increase occurs in slices from postnatal day 21 rats. Serial EM shows that all of the dendritic spines have normal synapses with presynaptic and postsynaptic elements; however, not all spine types are affected uniformly. Stubby and mushroom spines increase in the adult slices, and thin, mushroom, and branched spines increase in the immature slices. More axonal boutons with multiple synapses occur in the slices, suggesting that the new synapses form on preexisting axonal boutons. The increase in spine and synapse number is evident within a couple of hours after preparing the slices. Once the initial spine induction has occurred, no further change occurs for up to 13 hr in vitro, the longest time investigated. Thus, the spine increase is occurring during a period when there is little or no synaptic activity during the first hour, and the subsequent stabilization in spine synapse numbers is occurring after synaptic activity returns in the slice. These findings suggest that spines form in response to the loss of synaptic activity when slices are removed from the rest of the brain and during the subsequent 1 hr recovery period.
海马体切片长期以来一直被用于研究突触传递和可塑性的特性。在此，首次对切片中的突触与灌注固定海马体中的突触进行了定量比较，灌注固定海马体被认为代表了自然的体内状态。相对于灌注固定海马体，成年海马体切片中的棘突数量显著增加了40 - 50%，出生后第21天大鼠的切片中增加了90%。连续电子显微镜显示，所有树突棘都与突触前和突触后元件形成正常突触；然而，并非所有棘突类型都受到均匀影响。成年切片中短粗型和蘑菇型棘突增加，未成熟切片中细型、蘑菇型和分支型棘突增加。切片中出现了更多具有多个突触的轴突终扣，这表明新突触在预先存在的轴突终扣上形成。在制备切片后的几个小时内，棘突和突触数量的增加就很明显。一旦最初的棘突诱导发生，在长达13小时的体外培养时间内（这是研究的最长时间），不会再发生进一步变化。因此，棘突增加发生在最初一小时内几乎没有或没有突触活动的时期，而随后棘突突触数量的稳定是在切片中突触活动恢复之后发生的。这些发现表明，当切片从大脑其他部分分离出来以及在随后的1小时恢复期内，棘突是对突触活动丧失的反应而形成的。
