Titanium mesh implantation--a method to stabilize the spine and protect the spinal cord following a multilevel laminectomy in the adult rat.

The development of clinically relevant larger spinal cord injury models is in part limited by the possibility of a widened or multilevel laminectomy causing a spinal cord injury from an unstable spine or from compression of the spinal cord by adjacent soft tissues. In the adult rat, we have developed a method to protect the spinal cord and stabilize the spinal column using a titanium mesh implant following a bilateral, multilevel lumbar laminectomy. For this purpose, bilateral and expanded L1-4 laminectomies were performed with or without the use of a titanium mesh to protect the spinal cord and stabilize the spine. Without titanium mesh protection, the rats developed a severe paraparesis or paraplegia, urinary retention, gross anatomical signs of cord compression, and motoneuron loss. In the titanium mesh treatment group, the rats typically maintained a normal gait and lower urinary tract function, normal gross anatomical features of the spinal cord, and normal motoneuron counts. We propose that the use of a titanium mesh implant may assist in the development of clinically relevant larger spinal cord injury and repair models.

Differential distribution of growth associated protein (GAP-43) in the motor nuclei of the adult rat conus medullaris.

GAP-43 is normally produced by neurons during developmental growth and axonal regeneration, but it is also expressed in specific regions of the normal adult nervous system. We studied the protein expression of GAP-43 within the conus medullaris portion of the spinal cord in adult male rats. Immunohistochemistry for choline acetyltransferase (ChAT) was first performed to identify specific efferent autonomic and motor nuclei in lumbosacral segments of the spinal cord. Adjacent sections were then processed for GAP-43 immunoreactivity (IR). We show GAP-43 IR in the superficial portion of the dorsal horn, the intermediolateral nucleus, and the dorsal commissural tract. We also demonstrate a differential distribution of GAP-43 IR between different motor nuclei of the conus medullaris. Using densitometry, the most prominent GAP-43 IR was detected in the dorsolateral and dorsomedial motor nuclei, which represent the human Onuf's nucleus homologue. Confocal microscopy of double immunofluorescent labeling for ChAT and GAP-43 demonstrate GAP-43 IR in the neuropil of the autonomic and motor nuclei, and many of the GAP-43 IR arbors are in close apposition with the efferent cholinergic neurons. We note that the efferent neurons of both the autonomic and somatic nuclei, which are ultimately responsible for the integrated normal control of the lower urinary tract, bowel and sexual functions, are heavily innervated by GAP-43 enriched projections. We speculate that these functionally related neurons retain a physiological GAP-43-associated synaptic plasticity throughout adult life.