Dissociated adult Rana pipiens motoneuron growth cones turn up concentration gradients of denervated peripheral nerve-released factors

A novel method for establishing daily in vivo concentration gradients of soluble nerve growth factor (NGF)

Despite the capacity for spontaneous axonal regeneration, recovery following injuries to the peripheral nervous system (PNS) following transection are often incomplete and limited to short distances. Nerve growth factor (NGF) has been previously shown to support neuron survival, and direct growth of both developing and regenerating nerve fibers along a concentration gradient, based largely on in vitro studies. Here, we present a novel in vivo model of administering daily concentration gradients of NGF by directly manipulating the placement of the catheter-nerve conduit junction. Our results show that a dose of 800 pg NGF can be reliably used to establish a chemotactic concentration gradient over both a transient time period, and chronically through repeated daily administrations of the drug. Results from these studies may lead to a better mechanistic understanding of how concentration gradients of soluble NGF influence in vivo peripheral nerve regeneration.

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.