The interaction of human fetal neurons and epidermal cells in vitro.

The interaction of autologous human fetal neurons with epidermal cells was studied by culturing fetal dorsal root ganglia (DRG) in the center of a dual chamber system with epidermal explants in the outer chamber. The two chambers were separated by two concentric stainless steel annular rings adherent to the substratum by silicon grease and agarose. Axons from the DRG penetrated the agarose barrier, growing into the exterior chamber by 10 d in vitro (DIV) and extended past sparse peripheral fibroblasts to interact specifically with epidermal cells by 12 to 16 DIV. Scanning electron microscopy (SEM) showed single or multiple neuronal fascicles terminating on epidermal cells with spatular, veillike or bulbous axon termini. Transmission electron microscopy (TEM) showed fine axonal termini between epidermal cells, separated by an intercellular gap. The specificity of axonal targeting for epidermal cells rather than fibroblasts was also demonstrated by infecting the DRG with Herpes simplex virus type-1 (HSV-1). Specific anterograde transport of HSV-1 along axons to keratin-expressing epidermal cells was demonstrated by immunofluorescence and immunoperoxidase staining using monoclonal antibodies to viral glycoprotein D. This model allows the study of the mechanism of the specific interactions between neurons and epidermal cells analogous to those in fetal development and after cutaneous nerve regeneration.