Area CA3 in the hippocampus is traditionally thought to act as a homogeneous neural circuit that is vital for spatial navigation and episodic memories. However, recent studies have revealed that CA3 pyramidal neurons in dorsal hippocampus display marked anatomical and functional heterogeneity along the proximodistal (transverse) axis. The hippocampus is also known to be functionally segregated along the dorsoventral (longitudinal) axis, with dorsal hippocampus strongly involved in spatial navigation and ventral hippocampus associated with emotion and anxiety. Surprisingly, however, relatively little is known about CA3 functional heterogeneity along the dorsoventral axis. Here we carried out mouse brain slice patch clamp recordings and morphological analyses to examine the heterogeneity of CA3 cellular properties along both proximodistal and dorsoventral axes. We find that CA3 pyramidal neurons exhibit considerable heterogeneity of somatodendritic morphology and intrinsic membrane properties, with ventral CA3 (vCA3) displaying more elaborate somatodendritic morphology, lower intrinsic excitability, smaller input resistance, greater cell capacitance, and more prominent I_h than dCA3. Furthermore, although both dCA3 and vCA3 exhibit proximal-to-distal gradients in intrinsic properties and neuronal morphology, these proximal-to-distal gradients in vCA3 are more moderate than those in dCA3. Taken together, our results extend previous findings on the proximodistal heterogeneity of dCA3 function and uncover a complex, yet orderly, pattern of topographic organization of CA3 neuronal features that extend to multiple anatomical dimensions and may contribute to its in vivo functional diversity.

中文翻译：

---

小鼠海马 CA3 锥体神经元内在兴奋性的地形异质性。

海马体中的 CA3 区传统上被认为是一个对空间导航和情景记忆至关重要的同质神经回路。然而，最近的研究表明，背侧海马中的 CA3 锥体神经元沿着近距（横向）轴显示出显着的解剖和功能异质性。还已知海马体在功能上沿背腹（纵向）轴分离，背侧海马体强烈参与空间导航，腹侧海马体与情绪和焦虑相关。然而，令人惊讶的是，对沿背腹轴的 CA3 功能异质性知之甚少。在这里，我们进行了小鼠脑切片膜片钳记录和形态学分析，以检查沿近侧轴和背腹轴的 CA3 细胞特性的异质性。我们发现 CA3 锥体神经元表现出相当大的体树突形态和内在膜特性的异质性，腹侧 CA3 (vCA3) 显示出更精细的体树突形态、更低的内在兴奋性、更小的输入电阻、更大的细胞电容和更突出的 I_h比 dCA3。此外，尽管 dCA3 和 vCA3 在内在特性和神经元形态方面都表现出近端到远端的梯度，但 vCA3 中的这些近端到远端的梯度比 dCA3 中的更温和。总之，我们的结果扩展了先前关于 dCA3 功能近端异质性的发现，并揭示了 CA3 神经元特征的复杂而有序的地形组织模式，这些特征扩展到多个解剖维度，并可能有助于其体内功能的多样性。