PMC

At the infusion site, (A) BDNF immunolabeling and (B) GFP immunolabeling are predominantly observed in neurons labeled with (C) NeuN. (D), overlay. On quantification, 88.2 ± 3.8% of GFP-expressing cells co-label for NeuN. Scale bar = 50 μm.

(A) BDNF immunolabeling in an AAV2-BDNF infusion site in the entorhinal cortex. (B) Map of individual cells immunolabeled for BDNF, and (C) zone of BDNF-containing cells used to quantify volume of vector distribution. (D–E) The volume of AAV2-BDNF vector infused significantly correlates with volume of tissue containing BDNF-labeled neurons (p<0.001) and with number of BDNF labeled neurons (p<0.001).

The major projections from the entorhinal cortex (layers II–III) are to the outer molecular layer of the dentate gyrus (DG) and CA3 region of the hippocampus. The CA1 region projects back to the deeper layers of the entorhinal cortex. The entorhinal cortex also directly projects to cortical regions that are sites of long-term memory storage.

Schematic diagrams (adopted from Paxinos et al., 1989) of entorhinal cortex across four coronal planes from −2.7 to −14.85 mm relative to bregma (A, C–E). The entorhinal cortex is located on the ventral and medial surface of the temporal lobe, with local landmarks that include the rhinal fissure (RF), perirhinal cortex (PR), amygdala (Am), subicular area (S), and hippocampus (Hp). T1 and T2 MRI scans (B, F–H) with the visible landmark of the rhinal fissure (RF) indicated on the T2 image (arrows in A,B,D,G).

(A) BDNF immunoreactivity in hippocampus of control subject shows endogenous expression of BDNF in the mossy fiber terminal fields of the CA3 lucidum and hilus region. (B) Following AAV2-BDNF infusion into entorhinal cortex, BDNF immunoreactivity is visible in the hippocampal outer molecular layers (arrowheads). (C) Fluorescent labeling illustrates BDNF immunoreactive fibers in the outer molecular layer (OML) and not in the inner molecular layer (IML) or granule cell layer (GC) of hippocampus. (D) Scatterplot showed that even smaller volumes of AAV2-BDNF infused into the entorhinal cortex can lead to a widespread (~70%) increase of BDNF expression in the OML of dentate gyrus. Scale bar A, B 1 mm; C, 200 μm.

(A) An MR-compatible needle is present passing through the cortex and striatum (arrowhead) to reach the ventral and medial entorhinal cortex (arrow). The spread of gadoteridol in the infusion site is visible (arrow). Inset show gadoteridol signal at higher magnification. (B) A matching histological section from the same animal shows the spread of BDNF by immunolabeling in the same region predicted by MR imaging. (C) Pattern of gadolinium spread in a different subject within the entorhinal cortex on MR, and (D) the matching histological section. (E) Vector spread on MR in a 3^rd subject, with gadolinium spread along cortical surface (green arrows), and (F) the matching BDNF immunolabeled section. Green arrows indicate a band of BDNF-containing, layer II entorhinal cells. Hp, hippocampus. Scale Bar, D = 0.5 mm, E–F = 1 mm.