Differential Dependence of GABAergic and Glutamatergic Neurons on Glia for the Establishment of Synaptic Transmission

In the mammalian cortex, GABAergic and glutamatergic neurons represent 2 major neuronal classes, which establish inhibitory and excitatory synapses, respectively. Despite differences in their anatomy, physiology and developmental origin, both cell types require support from glial cells, particularly astrocytes, for their growth and survival. Recent experiments indicate that glutamatergic neurons also depend on astrocytes for synapse formation. However, it is not clear if the same holds true for GABAergic neurons. By studying highly pure GABAergic cell cultures, established through fluorescent activated cell sorting, we find that purified GABAergic neurons are smaller and have reduced survival, nevertheless they establish robust synaptic transmission in the absence of glia. Support from glial cells reverses morphological and survival deficits, but does little to alter synaptic transmission. In contrast, in cultures of purified glutamatergic neurons, morphological development, survival and synaptic transmission are collectively dependent on glial support. Thus, our results demonstrate a fundamental difference in the way GABAergic and glutamatergic neurons depend on glia for the establishment of synaptic transmission, a finding that has important implications for our understanding of how neuronal networks develop