Semilunar granule cells (SGCs) have been proposed as a morpho-functionally distinct class of hippocampal dentate projection neurons contributing to feedback inhibition and memory processing in juvenile rats. However, the structural and physiological features that can reliably classify granule cells (GCs) from SGCs through postnatal development remain unresolved. Focusing on postnatal days 11-13, 28-42, and >120, corresponding with human infancy, adolescence, and adulthood, we examined the somatodendritic morphology and inhibitory regulation in SGCs and GCs to determine the cell-type specific features. Unsupervised cluster analysis confirmed that morphological features reliably distinguish SGCs from GCs irrespective of animal age. SGCs maintain higher spontaneous inhibitory postsynaptic current (sIPSC) frequency than GCs from infancy through adulthood. Although sIPSC frequency in SGCs was particularly enhanced during adolescence, sIPSC amplitude and cumulative charge transfer declined from infancy to adulthood and were not different between GCs and SGCs. Extrasynaptic GABA current amplitude peaked in adolescence in both cell types and was significantly greater in SGCs than in GCs only during adolescence. Although GC input resistance was higher than in SGCs during infancy and adolescence, input resistance decreased with developmental age in GCs while it progressively increased in SGCs. Consequently, GCs input resistance was significantly lower than SGCs in adults. The data delineate the structural features that can reliably distinguish GCs from SGCs through development. The results reveal developmental differences in passive membrane properties and steady state inhibition between GCs and SGCs which could confound their use in classifying the cell types.

中文翻译：

---

树突形态学和抑制性调节通过产后发育的不同阶段从颗粒细胞中区分齿状半月形颗粒细胞。

已提出半月粒细胞（SGC）作为海马齿状投射神经元的形态功能不同的一类，有助于幼年大鼠的反馈抑制和记忆处理。但是，仍无法解决可以通过出生后发育可靠地将SGC中的颗粒细胞（GC）分类的结构和生理特征。着重于出生后的11-13、28-42和> 120天（与人类婴儿，青春期和成年期相对应），我们检查了SGC和GC中的树突形态和抑制调控，以确定细胞类型的特定特征。无监督聚类分析证实，无论动物年龄大小，形态特征都能可靠地将SGC与GC区分开。从婴儿期到成年期，SGC的自发抑制突触后电流（sIPSC）频率要高于GC。尽管SGCs的sIPSC频率在青春期特别增加，但sIPSC振幅和累积电荷转移从婴儿期到成年期均下降，GC和SGC之间没有差异。两种细胞类型的突触外GABA电流振幅均在青春期达到峰值，并且仅在青春期期间，SGC中的GABA电流幅度明显大于GC。尽管在婴儿期和青春期，GC的输入阻力高于SGC，但随着年龄的增长，GC的输入阻力降低，而在SGC中则逐渐增加。因此，成人的GC输入阻力显着低于SGC。数据描述了可以通过开发可靠地区分GC和SGC的结构特征。