3.4. Altered GABAergic interneuron populations in the hippocampus of B6N and 129 strains
Inhibition mediated via hippocampal GABAergic interneurons is indispensable for generation and propagation of network oscillations along the hippocampal CA3-CA1 axis (Le Duigou et al. , 2014; Çalişkan et al. , 2016). Thus, we compared the number of three major population of interneurons (GAD67+, PV+ and SST+) in the hippocampal CA3 and CA1 subregions. Interestingly, a major strain effect was detected in the number of GAD67+ interneurons (Figure 4a-b) with a significant increase in both CA3 (F(2,19)=40.627, p<0.001) and CA1 subregions (F(2,19)=28.756, p<0.001) of 129 strain (For both CA3 and CA1: B6J vs. 129: p<0.001, B6N vs. 129: p<0.001).
Next, we observed a significant strain effect in the number of CA3 PV+ interneurons (Figure 3c-d: F(2,19)=4.229, p=0.03) with a significant reduction in the B6N strain in comparison to the other two strains (B6N vs. 129: p=0.014, B6N vs. B6J: p=0.043). Interestingly, the strain effect was further present in the CA1 subregion (Figure 3c-d: F(2,19)=7.494, p=0.004). Both B6N (p=0.002) and 129 (p=0.009) showed a significant reduction in comparison to B6J strain.
Last, a significant strain effect was detected in the number of CA3 SST+ interneurons (Figure 3e-f) with a significant increase in the 129 strain compared to the other mouse strains (B6J vs. 129: p<0.001, B6N vs. 129: p<0.001). No strain effect was found in the CA1 subregion (F(2,20)=0.105, p=0.901). These data demonstrate that 129 strain shows remarkable differences in the number of hippocampal interneurons in comparison to the C57/BL6 substrains in a cell-type-specific manner. Furthermore, there is a mild but significant change in the number of PV+ interneurons that are instrumental for generation of network oscillations, when C57/BL6 substrains are compared.