Figure 4.

Cre-mediated inactivation of p75NTR in single PV cells induces the formation of more complex innervations. A, Control PV cell transfected with P_g67-GFP in EP18 organotypic cultures from p75^flx/flx mice shows immature perisomatic innervation with one terminal, axonal branching, and small boutons. B, PV cells transfected with P_G67-Cre/GFP from EP10–EP18 (p75^−/− PV cells) show exuberant perisomatic innervation characterized by multiple terminal axonal branches (B2) bearing numerous clustered boutons (B3; arrowheads) around neuronal somata (NeuN immunostaining, blue). Stars indicate NeuN-positive somata that are not innervated. A3, B3, From regions in A2 and B2. Scale bars: A1, B1, 50 μm; A2, B2, 5 μm; A3, B3, 3 μm. Perisomatic bouton density (C), terminal branching (D), and percentage of innervated cells (E) of p75^flx/flx and p75^−/− PV cells transfected at EP10–EP18 or EP16–EP24 (C) EP10–EP18: unpaired t test, df = 13, t = 8.835, p < 0.0001, EP16–EP24: Mann–Whitney test, p = 0.0022. D, EP10–EP18: Mann–Whitney test: at 5, 6 μm: p = 0.0037; at 7–9 μm: p = 0.0003; EP16–EP24: unpaired t test: at 6 μm: df = 10, t = 2.513, p = 0.0307; at 7 μm: df = 10, t = 4.908, p = 0.0006; at 8 μm: df = 10, t = 5.065, p = 0.0005; at 9 μm: df = 10, t = 6.063, p = 0.0001. E, EP10–EP18: unpaired t test, df = 13, t = 7.017, p < 0.0001; EP16–EP24: unpaired t test, df = 10, t = 1.642, p = 0.1315. EP10–EP18: n = 8 p75^−/− PV cells, n = 7 p75^flx/flx PV cells. EP16–EP24: n = 6 p75^−/− PV cells, n = 6 p75^flx/flx PV cells. * indicate p < 0.05.