GABAergic regulation of cell proliferation within the adult mouse spinal cord

Manipulation of neural stem cell proliferation and differentiation in the postnatal CNS is receiving significant attention due to therapeutic potential. In the spinal cord, such manipulations may promote repair in conditions such as multiple sclerosis or spinal cord injury, but may also limit excessive cell proliferation contributing to tumours such as ependymomas. Here we show that when ambient GABA is increased in vigabatrin-treated or decreased in glutamic acid decarboxylase67-green fluorescent protein (GAD67-GFP) mice, the numbers of proliferating cells respectively decreased or increased. Thus, intrinsic spinal cord GABA levels are correlated with the extent of cell proliferation, providing important evidence for the possibility of manipulating these levels. Diazepam binding inhibitor, an endogenous protein that interacts with GABA receptors and its breakdown product, octadecaneuropeptide, which preferentially activates central benzodiazepine (CBR) sites, were highly expressed in the spinal cord, especially in ependymal cells surrounding the central canal. Furthermore, animals with reduced CBR activation via treatment with flumazenil or Ro15-4513, or with a G2F77I mutation in the CBR binding site had greater numbers of Ethynyl-2’-deoxyuridine positive cells compared to control, which maintained their stem cell status since the proportion of newly proliferated cells becoming oligodendrocytes or astrocytes was significantly lower. Altering endogenous GABA levels or modulating GABAergic signaling through specific sites on the GABA receptors therefore influences NSC proliferation in the adult spinal cord. These findings provide a basis for further study into how GABAergic signaling could be manipulated to enable spinal cord self-regeneration and recovery or limit pathological proliferative activity.