Principle neurons (PNs) give rise to distinct excitatory synaptic inputs onto the 2 basket cell (BC) types.

<p>(A) Panoramic images showing a cholecystokinin-expressing basket cell (CCKBC)→PN (left) and a parvalbumin-containing basket cell (PVBC)→PN (right) pair in the anterior part of the basal amygdala (BA). Interneurons were filled with Cascade Blue and PNs with biocytin. Insets show a higher magnification of the cell pairs recorded. Scales: 250 μm. (B) Representative traces of unitary excitatory postsynaptic currents (EPSCs) evoked by action potentials in a PN→CCKBC (upper traces) and a PN→PVBC pair (lower traces). Ten superimposed consecutive traces are in gray, and averages are in blue and orange. Scales: x: 2 ms; PN→CCKBC, y: 80 mV/8 pA; PN→PVBC, y: 90 mV/30 pA. (C) PVBCs receive unitary excitatory postsynaptic currents (uEPSCs) from local PNs with larger amplitude and lower failure rate than CCKBCs (potency, CCKBC: 21.5 ± 1.6 pA, PVBC: 94.25 ± 15.08 pA; failure rate, CCKBC: 0.58 ± 0.04, PVBC: 0.25 ± 0.04; Mann–Whitney <i>U</i> test, ***<i>p</i> < 0.001) (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2001421#pbio.2001421.s016" target="_blank">S6 Data</a>). Each data point on the plots represents an average obtained in a pair recording, and lines represent means. (D) Schematic illustration of the experimental design to excite PNs using blue light. mCherry-containing construct was injected into the BA of transgenic mice (bottom drawing illustrates a horizontal slice showing the expression site in red). Among adeno-associated virus (AAV)-infected PNs (red circles), a CCKBC (blue) was recorded in whole-cell mode, while its excitatory input from neighboring PNs was tested by light illumination and/or whole-cell recording. BA, basal amygdala; Hip, hippocampus. (E) Connectivity map. Concentric circles indicate Δ100 μm distance from the interneuron in the center (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2001421#pbio.2001421.s016" target="_blank">S6 Data</a>). Each dot represents a tested PN soma location. (F) PVBCs receive excitatory synaptic inputs from their neighboring PNs with high probability, while CCKBCs are innervated by PNs via their local collaterals with low probability, independently of the inter-somatic distance (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2001421#pbio.2001421.s016" target="_blank">S6 Data</a>).