Fig. 4

Morphology features and locations of CA2 M1⁺RGS14⁻ neurons. A Representative image of apical dendrites (AD) in CA2 stratum lucidumis (SLu) infected with AAV9/M1-EGFP (n = 5 mice). Dashed rectangular boxes show RGS14⁻EGFP⁺ AD of complex spines. Arrow indicates simple AD on CA2 RGS14⁺ neurons like previous research. B1 magnified images of simple spines in AD of most M1⁺RGS14⁺ neurons in SLu layer from area as indicated by the white arrow in A. B2 magnified images of complex and simple spines in main apical dendrites (left) and apical dendrites tuft (right) of some M1⁺RGS14⁻ neurons in SLu layer from dashed rectangular enclosed regions of A. C1, C2 Dil stained typical CA2 simple spines and CA3 complex spines. D Representative images of a M1⁺RGS14⁻ neuron in AAV9/M1-EGFP infected CA2 region. E1–E3 Representative images of a group of pyramidal neurons displaying similar triangle cell bodies but can be divided into M1⁺RGS14⁺ and M1⁺RGS14⁻ neurons in CA2 area close to CA3. F1–F5 Z-projected IHC images displaying thorny excrescences of RGS14⁺ neurons apical dendrites tuft in SLu. Dashed rectangular boxes show M1⁺RGS14⁺ and M1⁺RGS14⁻ neurons co-stained with CaMKII-α (F1). Images shows RGS14⁺ or RGS14⁻ M1-EGFP complex apical dendrites tuft (F4) G Scatter chart (left) displaying soma size of M1⁺RGS14⁻ in CA2-Z4 and CA2. Pie chart (right) displaying the proportions of different located neurons with complex or simple spines in total M1⁺RGS14⁻ (n = 5 mice). H Diagram summarizing the features and locations of M1⁺RGS14⁻ neurons in CA2 Py layer. M1⁺RGS14⁻ neurons with simple spine can be detected in the CA2b region (Fig. 3B1–B4, 3E1 and H are the good examples). M1⁺RGS14⁻ neurons can be detected in both the deep and superficial layers of the CA2b Py region (Fig. 3B1), and its cell morphology will be more like the isosceles triangle. It shows neurons with complex spine in CA2-CA3 mixed border (black) supposed be CA3-like neurons. Scale bars: 2 μm (B1, B2, C1, C2, F4), 50 μm (A, D), 20 μm (E1–E3, F1–F3, F5)