Increased expression of glutamate decarboxylase (GAD67) in feline lumbar spinal cord after complete thoracic spinal cord transection

To determine changes in γ‐aminobutyric acid (GABA) in the spinal cord in response to a complete transection, we examined the cellular and tissue changes of the two forms of GABA synthetic enzyme glutamate decarboxylase (GAD65 and GAD67). In situ hybridization, immunohistochemistry, and Western blot analyses show that spinal cord transection between thoracic segments 12 and 13 results in an increase of GAD67, but not GAD65, protein and mRNA in the lumbar spinal cord. This increase occurs mainly in the dorsal horn and persists for at least 12 months. In addition, there was relatively high GAD67‐immunoreactivity around the central canal, with dorsolateral GAD67‐immunoreactive fibers extending toward the ependyma and into the central canal in the transected animals. We suggest that an increase in GAD67 leads to increased GABA production in spinal neurons below the injury site, resulting in altered inhibition and trophic support during posttrauma recovery and adaptation. Increased GABA synthesis around the central canal, in the vicinity of ependymal cells, may represent part of a regenerative process in the mammalian spinal cord, reminiscent of that observed in lower vertebrates. J. Neurosci. Res. 60:219–230, 2000 © 2000 Wiley‐Liss, Inc.