Fig. 5
Selective hyperexcitability of SSt INs in 16p11.2+/- rat hippocampus, but with no change in IN number. A Overview micrograph of Gad1 mRNA and NeuN protein expression in the rat hippocampus and cortex at P21. Gad1 expressing INs (red) and NeuN expressing, Gad1 negative excitatory neurons (green) can be observed in the cortex and hippocampus. Scale bars 400 µm B Quantification of Gad1-positive IN (IN) number through the somatosensory cortex in WT (black, n = 5) and 16p11.2+/- (pink, n = 5) rats. Counting areas indicated yellow in A with cortical bins numbered from 1 at the ventricular edge to 10 at the pial surface. C Quantification of the combined total number of Gad1-positive neurons in the str.oriens (Str. ori) and str. pyramidale (Str pyr.) of the CA1 region of the hippocampus in WT (N = 5) and 16p11.2+/- (N = 5) rats. Counting area indicated in (A). D example reconstruction of a recorded CA1 SST IN. Dendrites are shown in black and axons shown in red. Hippocampal layers are indicated (dashed grey lines) with respect to the alveus, Str. Ori, Str. Pyr, Str. Radiatum (Rad.), and Str. Lacunosum-moleculare (L-M). D, inset immunoreactivity for SST (green) from the same cell shown in comparison to the biocytin filled soma. E Representative action potential discharge in response to hyper- to depolarising current steps in SST-INs, from the str. oriens of CA1 from WT (top) and 16p11.2+/- rats (bottom). F Summary current-frequency plots from identified SSt INs from WT (N = 15 rats) and 16p11.2+/- (N = 10 rats). G Measured slope of individual current-frequency (F/I) plots from all cells. H Quantification of rheobase current in identified SSt-INs from WT (n = 30 cells) and 16p11.2+/- (n = 28 cells) rats. (I) Measurement of the voltage threshold of the first action potential elicited at rheobase for the same cells in (F). J Representative micrographs showing immunohistochemical labelling for SSt (green), the AIS marker AnkyrinG (AnkG, magenta), and their overlap (merge). The SSt soma is indicated with an asterisk (*) and the start and end of the AIS localised to that IN indicated (arrows). Scale bar: 10 µm. K Quantification of the AIS length of SSt INs from WT (N = 6 rats, n = 162 AIS) and 16p11.2+/- (N = 6 rats, n = 151 AIS). L Quantification of AIS lengths of putative CA1 pyramidal cells from WT (N = 6 rats, n = 150 AIS) and 16p11.2+/- (N = 6 rats, n = 155 AIS) rats. Statistics shown: ns – p > 0.05, *—p < 0.05, from Linear Mixed Effects modelling