How to optimize the concentration and time of EDTA free trypsin for primary neuron digestion?

Primary digestion of rat cortical neurons, without EDTA trypsin, I would start at 0.05% and do not recommend directly increasing to 0.125%, as high concentrations can easily cut off cell surface proteins in a short period of time, affecting subsequent adhesion and axonal growth. 2-3 embryonic brain tissues can be digested at 37 ℃ for 10-15 minutes with a small tissue volume, using 0.05% DNase I at a concentration of approximately 0.1mg/mL to reduce the viscosity caused by DNA release. If the tissue block is still relatively intact after 10 minutes, it can be gently blown and digested for 15-20 minutes, gradually establishing a fixed time for its own batch.

EDTA mainly chelates divalent cations to promote intercellular dissociation. Trypsin without EDTA is milder, but digestion efficiency may also decrease. Suggest conducting a parallel trial of 0.05% and 0.125% first to compare the cell viability, adhesion rate, and neuronal purity after digestion. If 0.05% can achieve a survival rate of over 80%, there is no need to go up to 0.125%. The EDTA free version is more wall friendly, especially for primary cells such as neurons, but it is also important to pay attention to the concentration of calcium and magnesium ions and avoid using dilutions containing these ions.

At 37°C, I usually set three observation time points: 10 min, 15 min, and 20 min. Do not wait until the tissue is completely dissociated into single cells before stopping. Once the tissue edges look loose and the liquid is slightly cloudy, terminate with serum-containing medium. For the termination solution, medium containing 10% FBS is sufficient; the inhibitors in serum can effectively neutralize trypsin. Even for the EDTA-free version, termination is still recommended to avoid residual activity. After termination, pipette gently 8-12 times, and do not pipette too many times. If cell viability is low, switch to digestion on ice or shorten the time.

For small packaging, you can first ask the brand or distributor to apply for a trial sample. Many EDTA-free trypsins come in 100 ml or even smaller aliquots, or you can buy a 100 ml ready-to-use bottle. For the first test, it is recommended to keep an old protocol using the EDTA-containing version as a control in parallel, and evaluate it from several perspectives, including digestion time, viability, attachment number, and neuronal markers such as βIII-tubulin. If the teacher is concerned about enzyme lot-to-lot variation, you can request small packaging from the same lot and store aliquots at -20°C to avoid repeated freeze-thaw cycles.