Age-dependent patterns and rates of neurite outgrowth from CNS neurons on Schwann cell-derived basal lamina and laminin substrata

Abstract

In the present study, we have examined the growth characteristics of CNS neurons on type I collagen, detergent-treated collagen (dColl), Schwann cell-derived basal lamina (SC-BL), and purified laminin substrata. Neurons from the cerebral cortex, septal basal forebrain, and lumbosacral spinal cord were obtained from embryonic age (E) 15 and E18 rats and grown in vitro as explants on the test substrata. Neurons from either embryonic age displayed radial neurite outgrowth on collagen and dColl substrata. However, pretreatment of collagen with detergents slightly diminished its ability to support neurite outgrowth, as evidence by the 20-40% decrease in the rate of neurite growth on dColl versus the rate calculated for neurons on collagen. In contrast to the similar growth characteristics of E15 and E18 neurons on collagen and dColl, the pattern of neurite outgrowth for CNS neurons on SC-BL and laminin substrata was age dependent. Most E15 neurons grown on SC-BL extended neurites that grew identically to those observed on dColl; these 'non-orienting' neurites maintained a radial orientation to their outgrowth despite encountering interposing channels of SC-BL and grew at rates equal to that calculated for neurons on dColl. E15 neurons placed on laminin substrata showed similar growth patterns and rates equal to that calculated for neurons on dColl. E15 neurons placed on laminin substrata showed similar growth patterns and rates to neurons on collagen. In contrast, neurons from E18 rats exhibited neurites that preferentially grew in intimate association with SC-BL channels once contact with the channels was established. These 'orienting' neurites faithfully elongated within the SC-BL and demonstrated a 1.4- to 2.0-fold increase in growth rate compared with the sister cultures of neurons grown on dColl. Furthermore, E18 neurons exhibited a 1.4-fold increase in growth on laminin compared with E18 neurons grown on collagen. A minor population of neurites exhibiting similar characteristics to orienting neurites was also observed in E15 cultures. It is hypothesized that orienting and non-orienting neurites reflect the outgrowth of 'regenerating' and 'developing' neurons, respectively, and may indicate an inherent difference in the ability of regenerating and developing neurons to recognize and respond to the same guidance signals.