A morphological analysis of growth cones of DRG neurons combining atomic force and confocal microscopy.

We have analyzed the morphology of growth cones of differentiating neurons from rat dorsal root ganglia (DRG) with conventional Laser Scanning Confocal Microscopy (LSCM) and Atomic Force Microscopy (AFM). Images of immunofluorescent DRG growth cones colabeled for actin and tubulin were superimposed to images obtained with AFM at different scanning forces. In order to reduce changes of the image surface caused by the pressure of the AFM tip, we have developed a procedure to obtain 0pN AFM images. Further analysis of these images revealed topographical structures with nanoscale dimensions, referred to as "invaginations" or "holes". These holes had an area varying from 0.01 to 3.5 microm(2) with a depth varying from 2 to 178 nm. Comparative analysis with LSCM images showed that these holes correspond to regions where staining of both actin and tubulin was negligible. Filopodia height varied from 40 to 270 nm and their diameter from 113 to 887 nm. These results show that the combination of LSCM and AFM reveal structural details with a nanoscale dimension of DRG growth cones, difficult to resolve with conventional microscopy.