Functional synapses are formed between human NTera2 (NT2N, hNT) neurons grown on astrocytes

The formation of functional synapses is a late milestone of neuronal differ entiation. The establishment of functional synapses can be used to assess n euronal characteristics of different cell lines. In the present study, we e xamined the in vitro conditions that influence the ability of human neurons derived from the NT2 cell line (NT2N neurons) to establish synapses. The m orphologic, immunologic, and electrophysiologic characteristics of these sy napses was examined. In the absence of astrocytes, NT2N neurons rarely form ed synapses and their action potentials were weak and uncommon. In contrast , when plated on primary astrocytes, NT2N neurons were able to form both gl utamatergic excitatory (71%) and GABAergic inhibitory (29%) functional syna pses whose properties (kinetics, ion selectivity, pharmacology, and ultrast ructure) were similar to those of synapses of neurons in primary cultures. In addition, coculture of NT2N neurons with astrocytes modified the morphol ogy of the neurons and extended their in vitro viability to more than 1 yea r. Because astrocyte-conditioned medium did not produce these effects, we i nfer that direct contact between NT2N neurons and astrocytes is required. T hese results suggest that NT2N neurons are similar to primary neurons in th eir synaptogenesis and their requirement for glial support for optimal surv ival and maturation. This system provides a model for further investigation s into the neurobiology of synapses formed by human neurons. (C) 1999 Wiley -Liss, Inc.