Axotomy enhances the outgrowth of neurites from embryonic rat septal-basal forebrain neurons on a laminin substratum.

Previous studies have suggested that embryonic (nonaxotomized) and regenerating central nervous system neurons differentially respond to the same substrata. In the present study, we have used an in vitro model to test the ability of laminin and type I collagen to promote the outgrowth of neurites from nonaxotomized and axotomized, embryonic septal-basal forebrain (SBF) neurons. Neurons within explants derived from Embryonic Day (E) 15 rats extended neurites that demonstrated similar growth characteristics on a collagen or laminin substratum. E15 neurons could be induced to extend longer neurites on laminin if they were axotomized in vitro and subsequently replated onto a laminin substratum. The carbocyanine dye DiI indicated that neurons which were axotomized could survive and regenerate processes. These regenerating neurites grew 27% longer on laminin than they did on collagen. Similarly, neurons that were axotomized in situ, i.e., E18 SBF neurons, extended neurites that were 29% longer on a laminin substratum. In contrast, E15 explants that were maintained in suspension culture prior to being plated onto a substratum exhibited similar growth on laminin or collagen. The increase in regeneration by E15 neurons on laminin was augmented, by 22%, if nerve growth factor was supplemented to the culture medium. These results demonstrate that laminin is a better substratum, as compared to collagen, for the elongation of neurites from axotomized SBF neurons. Nonaxotomized neurites, on the other hand, do not appear to prefer one substratum over the other. Furthermore, regeneration from embryonic, SBF neurons on laminin is augmented if NGF is used simultaneously.