Figure 3. CA3 associative network activation differs across investigated mouse strains. (A) Hippocampal Schaffer collaterals were electrically stimulated, and evoked local field potential recordings were obtained from CA3 and CA1 pyramidal layers. Antidromic and orthodromic population spike (PS) areas (ms.mV) were calculated for stimulation intensities ranging from 0 to 50 µA.(b) Representative antidromic and orthodromic population spikes in the CA3. Note the strong reduction of orthodromic responses in 129 mouse strain. CA3 IO curves (B6J: N=5 mice, n=18 slices; B6N: N=5 mice, n=14 slices; 129, N=5 mice, n=16 slices) (c) of antidromic and(d) orthodromic population spikes showing a slight reduction in antidromic population spikes and a strong reduction of orthodromic population spikes of 129 strains in comparison to B6J strain.(e) Reduced CA3 associative network activation in 129 mouse strain calculated via normalized orthodromic population spike responses. For this purpose, orthodromic responses were divided to corresponding antidromic responses and were averaged across 5 stimulation strengths.(f) Representative orthodromic population spikes in the CA1.(g) CA1 IO curves (B6J: N=5 mice, n=13 slices; B6N: N=5 mice, n=12 slices; 129, N=5 mice, n=12 slices) showing similar population spike areas across investigated strains. Statistical comparison for(c), (d), (g): two-way repeated measures ANOVA followed by posthoc comparison using Fisher LSD Method with Greenhouse–Geisser correction. Statistical comparison for (e): Kruskal-Wallis One Way Analysis of Variance on Ranks followed by posthoc comparison using Dunn´s Method. Post-hoc statistical differences between strains B6J and 129 are indicated via #p<0.05 and ###p<0.001. Post-hoc statistical differences between substrains B6J and B6N are indicated via *p<0.05. Data are presented ± standard error of mean (SEM). Empty circles represent individual data points.