Glycine- and GABA-activated currents in identified glial cells of the developing rat spinal cord slice

In the neonatal rat spinal cord, four types of glial cells, namely astrocytes, oligodendrocytes and two types of precursor cells, can be distinguished based on their membrane current patterns and distinct morphological features. In the present study, we demonstrate that these cells respond to the inhibitory neurotransmitters glycine and GABA, as revealed with the whole-cell recording configuration of the patch-clamp technique. All astrocytes and glial precursor cells and a subpopulation of oligodendrocytes responded to glycine. The involvement of glycine receptors was inferred from the observation that the response was blocked by strychnine and that the induced current reversed close to the Cl- equilibrium potential. GABA induced large membrane currents in astrocytes and precursor cells while oligodendrocytes showed only small responses. The GABA-activated current was due to the activation of GABAA receptors since muscimol mimicked and bicuculline blocked the response; moreover, the reversal potential was close to the Cl- equilibrium potential. Besides the increase in a Cl- conductance, GABAA receptor activation also induced a block of the resting K+ conductance, as observed previously in Bergmann glial cells. Our experiments show that while glial GABAA receptors are found in many brain regions and the spinal cord, glial glycine receptors have so far been detected only in the spinal cord. The restricted coexpression of glial and neuronal glycine receptors in a defined central nervous system grey matter area implies that such glial receptors may be involved in synaptic transmission.