Effects of intracellular treatment with 5- or 40-nm AuNPs on the passive electrical properties of hippocampal CA1 neurons from a mouse hippocampal slice.

(A) DIC images of a brain slice (left, 50×) and hippocampal CA1 layer (middle, 630×), and a fluorescence image of CA1 neurons (right, 630×) loaded with fluorophore-conjugated AuNPs through a patch pipette (middle) after breaking the gigaohm seal. The fluorescence signal indicates the infusion of AuNPs into the cell. (B) Representative traces of membrane potential changes and APs elicited by step-current injections for 1 sec from AuNP-treated and untreated (no AuNPs) hippocampal CA1 neurons. (C) AuNPs of both sizes considerably increased the changes in membrane potential. (D) Input resistance was significantly increased by AuNPs of both sizes. (E) The 5- or 40-nm AuNPs increased the number of APs substantially at low current intensity (at 30- or 60-pA depolarizing current injection). *p<0.05, **p<0.01, Student's t-test, No AuNPs vs. 40-nm AuNPs; ^#p<0.05, Student's t-test, No AuNPs vs. 5-nm AuNPs; ⁺p<0.05, Student's t-test, 5-nm AuNPs vs. 40-nm AuNPs.