Fig. 5. Primary neurons were isolated from neonatal rodent brains at postnatal day 1–3 and grown in vitro for 5–7 days. Neurons were then transfected for 72 h with increasing doses of a lentiviral (LV) vector that expresses p75NTRdriven by a neuronal-specific synapsin promoter (LV-syn-p75NTR). (A ) Immunoblot analysis shows an increase in p75NTRexpression with increasing doses of LV-syn-p75NTR. (B ) Quantitation of the data are represented in the graph. These data demonstrate that, in vitro , primary neurons from neonatal rodents transfected for 72 h with LV-syn-p75NTRexhibits a dose-dependent increase in p75NTRexpression. (C ) Polymerase chain reactor confirmed that rodents used for primary neuronal cultures were p75NTRknockout genotype (-/-). On day in vitro 4, p75NTRknockout neurons were transfected with LV-syn-p75NTRfor 72 h. LV-syn-GFP served as a control. On day in vitro 7 neurons were exposed to propofol 3.0 μM for 6 h and apoptosis was evaluated by cleaved caspase-3 immunofluorescence microscopy. (D ) Immunofluorescence microscopy shows an increase in cleaved caspase-3 in p75NTRknockout neurons transfected with LV-syn-p75NTRand exposed to propofol versus LV-syn-GFP transfected neurons exposed to propofol. (E ) Quantitation of the data are represented in the graph (n = 10; P = 0.0002). Sample size is indicated above the error bars ± SEM. These data demonstrate that, in vitro , reexpression of p75NTRin p75NTRknockout neurons reestablishes propofol-mediated apoptosis. Cl-Csp3 = cleaved caspase-3; DAPI = 4′,6-diamidino-2-phenylindole; GAPDH = glyceraldehyde 3-phosphate dehydrogenase; GFP = green fluorescent protein; LV-syn-p75NTR= a neuronal-specific synapsin promoter.