Isolated hippocampal neurons in cryopreserved long-term cultures: Development of neuroarchitecture and sensitivity to NMDA

Isolated neurons in long-term culture provide a unique opportunity to address important problems in neuronal development. In the present study we established conditions for cryopreservation and long-term primary culture of isolated embryonic hippocampal neurons. This culture system was then used for initial characterizations of the development of neuroarchitecture and neurotransmitter response systems. Cryoprotection with 8% dimethylsulfoxide, slow freezing, and rapid thawing provided high-yield cultures which appeared normal in terms of cell types, mitotic ability, axonal and dendritic outgrowth, and sensitivity to glutamate neurotoxicity. A reduced medium volume and moderate elevation in extracellular K⁺ to 20 mM promoted survival of isolated neurons through 3 weeks of culture. The outgrowth of axons and dendrites in pyramidal-like neurons was found to differ over a 3-week culture period such that axons continued to grow at a relatively constant rate while dendritic outgrowth slowed during the second week and ceased by the end of week 3. Developmental changes were also observed in the sensitivity of pyramidal neurons to glutamate neurotoxicity; functional kainate/ quisqualate receptors were present during the first week of culture, while responses to N-methyl-d-aspartic acid (NMDA) did not appear until the second week. The technologies for cryopreservation and long-term culture of isolated hippocampal neurons reported here provide a useful system in which to address a variety of problems in developmental neuroscience.