Fig. 8
Neuroinflammatory responses, changes of NSC activity in HPC, and reduction of NTR2 expression in BLA after SCI. The DG (in red rectangle) of the hippocampal formation (Bregma − 4.80 mm; A) of a SCI rat showed markedly augmented reactive astrogliosis assessed by GFAP IHC stain (B1 and inset), relative to a control image (B2 and inset). Moreover, the mean IRL of Iba1 (red) expressed by hypertrophic microglia (C1 inset: lower left column) concentrated mostly in the neurogenic SGZ of the DG in SCI rats (C1 inset of upper left column: Iba1 images in SGZ versus those in Gr) was higher than the controls (C2); the difference was statistically significant (C3; **P < 0.01; Student’s t test; n = 4/group). SCI DG sections exhibited much more nuclear SOX2 (green, D1) and cytosol nestin immunostains (red, D2; DAPI in D3) compared to those of control tissue (E1–3). The merged z-stack images (D4) showed that some NSCs had SOX2 (green) and DAPI (blue) co-stained nuclei (cyan in D5). The differences between the IRL means of the two groups were significant (F; *P < 0.05; Mann–Whitney U test; n = 4/group for both SOX2 and nestin). The SCI HPC sections (G1–3), relative to controls (G4), exhibited significantly stronger BDNF immunosignal (green, G1) in cells that were mostly negative for DCX (red, G2). Some DCX+ NSCs also expressed BDNF (yellow cells in G3). The mean IRLs of BDNF, not DCX, were significantly different between the two groups (*P < 0.05 or ns, Mann–Whitney U test, respectively; n = 4/group; H). SCI-triggered neuroinflammatory impacts were evaluated in the BLA (Bregma − 2.30 mm; I). Mean IRL of NTR2 (red) or GFAP (green) in the SCI group (K1–3) was significantly lower or higher than the control group (L1–L3), respectively (J; ***P < 0.001 for NTR2; **P < 0.01 for GFAP; Student’s t test; n = 4/group). The NTR2 immunostain was mainly located in the cytosol fractions of GFAP− cells, suggesting the cells were BLA interneurons (see morphologic differences between NTR2+ cells/L4 and GFAP+ astrocytes/K4). Scale bars:100 µm except for K4 and L4 where they were 20 µm. BLA basolateral amygdala, DCX doublecortin, DG dentate gyrus, ec external capsule, Gr granular layer of DG, HPC hippocampus, Mo molecular layer of DG, ns not significant, NSC neural stem cell, NTR2 neurotensin receptor type 2, Po polymorphic layer of DG (i.e., hilus), SGZ subgranular zone of DG