Neural damage can arise from trauma, disease states, a side effect of certain therapeutic agents, or normal aging and can result in impaired motor, sensory, autonomic, and/or cognitive functions. A major problem in recovery from CNS damage is the general failure of axons to regenerate after injury. In contrast, peripheral neurons respond to nerve injury by axonal regeneration. This difference has been attributed to the environment through which the injured neurons must grow and the neurons'""""""""intrinsic growth properties"""""""". The latter is believed to reside in the ability of axotomized peripheral neurons to make adaptive changes in gene expression. These changes may underlie the observation that regeneration of peripheral neurons is enhanced by a conditioning lesion. We are interested in the signals that trigger the conditioning lesion effect. During the previous grant period, we made the intriguing observation that treatment of animals with an antiserum to NGF produces a conditioning lesion-like effect in sympathetic neurons in culture. This finding has led us to hypothesize that """"""""a reduction in the availability of target-derived trophic factors after injury is a stimulus for regeneration"""""""". We propose to test this hypothesis further by (a) examining the specificity of this effect using highly specific antibodies to NGF and the related neurotrophin NT-3, (b) blocking NGF's action by injecting antibodies directly into a sympathetic target tissue, (c) blocking NGF's actions by a second approach, i.e., administration of receptor bodies, (d) determining whether the antibody treatment promotes regeneration in vivo, and (e) determining the impact of overexpressing NGF in sympathetic ganglia using a viral construct. We have further hypothesized that anti-NGF produces its effects on the intrinsic growth properties of sympathetic neurons by down-regulating BDNF- and p75-mediated inhibition of neurite outgrowth, and we will test this hypothesis by (a) determining the impact of antibodies to NGF on BDNF levels in sympathetic neurons, (b) determining whether antibodies to BDNF by themselves trigger a conditioning lesion-like effect, and (c) seeing if the conditioning lesion effect is absent or reduced in p75 -/- mice. Work from other laboratories has established that elevation of cAMP plays a critical role in mediating the conditioning lesion effect. One of the genes that is elevated after nerve injury in sensory, motor, and sympathetic neurons is pituitary adenylate cyclase activating polypeptide (PACAP). PACAP stimulates cAMP synthesis and its own expression is elevated by cAMP. We propose to test the hypothesis that PACAP is involved in the conditioning lesion effect either upstream or downstream of cAMP or both using PACAP -/- mice. The proposed experiments will significantly further our understanding of the role of neurotrophins and neuropeptides in promoting nerve regeneration and how these agents might be used to enhance clinical recovery both in the peripheral nervous system and, hopefully, in the CNS.
following nerve damage, nerve cells in the peripheral nervous system are able to regenerate, while nerve cells in the central nervous system (i.e., the brain and spinal cord) are not. This proposal focuses on identifying molecules that trigger regeneration with the idea that they might be used to enhance regeneration in the periphery and promote regeneration in the central nervous system.
Showing the most recent 10 out of 43 publications
