Fig. 1.

Leptin increases the density of dendritic filopodia in hippocampal neurons. (A) Confocal images of actin staining in hippocampal neurons (6–8 DIC) labeled with Alexa 488-conjugated phalloidin. (Ai) Control neurons display relatively few actin-rich protrusions or growth cones. Exposure of neurons to leptin (50 nM) for 30 min stimulated an increase in the number of filopodia (ii) and growth cones (iii) extending from processes (indicated by arrows). (B) Confocal images of hippocampal neurons (9DIC) dual labeled with Alexa 488-conjugated phalloidin (green) and the somatodendritic marker, MAP2 (red). Leptin (50 nM; 30 min) increased the number of filopodia protruding from dendritic (MAP2-positive) processes (ii) compared to control (i). (C) Histogram illustrating the pooled data of the mean number of dendritic filopodia in control and leptin treated neurons. Leptin stimulates circa a 3-fold increase in the density of filopodia. (D) Histogram illustrating the pooled data of the mean number of dendritic filopodia after 10 min, 20 min, 30 min, 3 h and 18 h exposures to leptin (50 nM). The leptin-induced increase in filopodial density is apparent after only 10 min exposure to leptin and reaches a peak after 3 h. (F) Representative confocal images (i–iii) of leptin receptor (ObR; i) and synapsin-1 (ii) immunoreactivity in 9-day-old hippocampal cultures. The merged image (iii) shows that leptin receptor labeling is highly localized to synapses.