Altered expression of PICK1 in cultured striatal medium spiny neurons dynamically affects intracellular accumulation of TAMRA-conjugated TAT-P4-(DATC5)2 (5nM). (A) Representative confocal images of striatal medium spiny neurons identified by dopamine and cAMP-regulated neuronal phosphoprotein (DARPP-32) marker. Medium spiny neurons were transduced with the control viral vector encoding GFP (top), the short hairpin 18 silencing PICK1 (GFP-sh18, middle) coupled to GFP expression and the over-expressing vector encoding sh18 as well as shRNA-resistant GFP-PICK1 (WT, bottom). Images show: DARPP-32 in grey, GFP, GFP-sh18, GFP-PICK1WT in green, and TAMRA-conjugated TAT-P4-(DATC5)2 in magenta, as well as the three images merged. Scale bar: 10μm. (B) Quantification of TAMRA-conjugated TAT-P4-(DATC5)2 intensity values of each viral-transduced neuron from (A) normalized to the mean TAMRA-conjugated TAT-P4-(DATC5)2 intensity of the GFP control viral vector. Each dot represents a single neuron, (GFP n =34, GFP-sh18 n=38, GFP-PICK1 WT n=48, all data expressed as means ± S.E.M.). A significant reduction in the TAMRA-conjugated TAT-P4-(DATC5)2 intensity is observed by silencing PICK1 (GFP-sh18) versus both GFP control and GFP-PICK1 WT overexpressing neurons (one way ANOVA with Tukey’s multiple comparisons test * p< 0.05, **** p< 0.0001).