Figure 3. Morphological and firing properties of SOM+ Htr3a-GFP-reported O-A interneurons.

(a–d) Single examples of SOM+/GFP+ interneurons located in CA1 O-A from which intrinsic membrane and firing properties were measured via whole cell patch clamp recordings in slices from Htr3a-GFP mice. Confocal images show Htr3a-GFP-driven GFP expression (top panels; green), biocytin conjugated immunofluorescence (middle panels; red), and SOM immunoreactivity (bottom panels; blue). Corresponding anatomical reconstructions of SOM+/GFP+ interneurons showing the dendritic (black) and axonal (red) arborizations are also shown. Below each reconstructed interneuron are electrophysiological membrane and action potential firing responses for hyperpolarizing, near threshold and, 2×threshold somatic current injections as indicated (single examples were taken from a total of 29 post-hoc confirmed SOM+/Htr3a-GFP+ cells recorded in 13 mice) (e–g) Representative images depicting the co-localization of 5-HT_3ARCre activity reported by tdTomato fluorescence (see methods) with somatostatin (SOM) immunoreactivity in CA1 O-A. (h) Pooled data of the percentage co-localization of 5-HT_3ARCre:tdTOM fluorescence and SOM immunoreactivity in CA1 O-A interneurons (n = 3 mice and cell counts were performed in a total of 8 hippocampal sections; total number of cells counted were 109 and 125 for black and gray data, respectively). Box-and-whisker plots are constructed as follows: circle and line within box denotes mean and median, respectively; upper and lower limits of box and capped lines indicate SEM and min/max data points, respectively.