The Influence of Ectopic Migration of Granule Cells into the Hilus on Dentate Gyrus-CA3 Function
Figure 8
Effects of hEGCs on action potential generation of GCs.
Results are shown from a single representative simulation run with the Standard (black), Intermediate (blue) and New (red) models. A. To determine effects of the perforant path on GC action potential generation (firing), 10 patterns, each with 10% active elements, were presented as input (from the perforant path). The GCs that were active (discharged action potentials), averaged across patterns, are expressed as a percentage of each GC subtype. For the Standard model (black), a small percentage (about 2%) of mature GCs became active in response to the input patterns, consistent with the relatively high threshold of mature GCs. In the Intermediate model (blue), a similar percentage of mature (dark blue) and immature GCs (light blue) became active (all, p>0.50; n.s. = not significant; asterisks denote p<0.05). A smaller percentage of mature GCs in the New model (dark red) were active compared to the Standard or Intermediate models (p<0.05). hEGCs in the New model (white outlined in red) were very active, significantly more than the mature or immature GCs in the Standard or Intermediate models; hEGCs were also more active than mature GCs in the New model (p<0.0001). When CA3 backprojections were removed from the New model (red with asterisk), hEGCs (white outlined in red) were effectively silenced, and firing of mature GCs (dark red) was restored to the activity of mature GCs in the Standard model (p>0.50). B. GC firing, expressed as the absolute number of each GC subtype. Most results were similar to part A. The only difference was the relative activity of mature and immature GCs in the Intermediate model. In part A, there were similar percentages of mature and immature GCs that were active, but in absolute numbers (B), there were significantly more active mature GCs than active immature GCs in the Intermdediate model. The reason for the similarity in percentages – but not absolute numbers - is that the number of active GCs is always small relative to all GCs. C. Total GC firing, expressed as the absolute number of all GCs (the sum of mature, immature, and hEGCs). Total GC firing did not differ significantly among Standard, Intermediate, and the New model without backprojections (all p>0.100), but was significantly higher in the New model with backprojections (p<0.0001).