NbActiv4® neuron culture medium without phenol red is an improved version of Neurobasaltm / B27tm. NbActiv4 grows neurons with twice as many synapses and up to 8x higher spike rates than Neurobasal/B27. NbActiv4 minus phenol red was optimized for maximum spike rates by addition of 3 new components to Neurobasal/B27: creatine, estrogen and cholesterol. Measures of respiration indicated that neurons in NbActiv4 were under less metabolic stress and operated more efficiently under demand loading from glutamate. These results suggest that NbActiv4 will be a convenient and useful serum-free neuron culture medium for electrophysiology, developmental synaptic plasticity, neuronal network analyses, pharmacology, toxicology and drug discovery. Synapses and spiking activity develop earlier, starting at 1 week in NbActiv4 compared to Neurobasal/B27 (Brewer et al. 2008. Neuron network activity scales exponentially with synapse density. J. Neural Eng., in press) Brewer,GJ., Boehler, MD; Jones, TT, Wheeler, BC. 2008. NbActiv4 medium for neurons increases synaptic densities and network spike rates on multielectrode arrays compared to Neurobasal/B27. J. Neurosci. meth. 170:181-187 (PM 18308400) Strategies for switching to NbActiv4® from Neurobasal/B27 NbActiv4 contains all the ingredients in Neurobasal + B27 +Glutamax (all Invitrogen). It can be stored at 4 °C for up to 6 months if unopened. It should not be frozen. Both media (Neurobasal/B27 and NbActiv4) are designed for use at 37 °C in a 5% CO2 incubator. Neurons are subject to less oxidative stress if the oxygen is also regulated at 9%. To evaluate NbActiv4 in the context of current experiments, we suggest a side-by-side comparison. For new lines of study, experiments can begin directly with NbActiv4. Beginning cultures in Neurobasal/B27 followed by a switch to NbActiv4 shows no indication of being better than use of NbActiv4 from the start. One-Half medium changes with incubator temperature equilibrated medium should be performed at least once a week, with more frequent changes at cell densities above 300 cells/mm2. NBActiv4 must be shipped overnight. Click here for our Primary Neuronal Culturing Protocol. Please do not hesitate to contact us with questions.