Intrinsic properties inhibit axonal outgrowth from neonatal rat spinal cord explant.

Lumbar spinal cord explants, harvested from neonatal rat pups aged between postnatal day 0 (P0) and P6, were cultured for a period of 48 hrs in the chemically defined medium R(12) on a poly-ethylene-imine (PEI) and on poly-D-lysin (PDL) coated surface. The outgrowth outside the explant was quantified. Lumbar explants from the same rat and embedded in a collagen matrix, and cortical explants from a P0 rat were used as controls. Statistical analysis demonstrated a clear relation between age-at-explantation and the number of neurites in the corona surrounding the explant. The number of outgrowing neurites decreased sharply with age-at-explantation. The average number of neurites per explant obeyed to the expression log (n) = -0.736x + 3.294 on PEI, and log (n) = -0.721x + 2.295 on PDL; x epsilon in [P0 - P6] (n, the number of neurites per explant; x, the age-at-explantation expressed in postnatal days). A similar observed age-related decrease of outgrowth has been described when culturing the lumbar explant inside a collagen matrix. The phenomenon appears to be an intrinsic property of the explant. We review growth inhibitory properties in different models and propose that the phenomenon occurs here at the interface explant-world.