Is 5% fetal bovine serum sufficient for primary neuron culture?

5% is somewhat tight for primary neuron attachment, but it is workable. My approach is to use 10% for the first 12-24 hours to let cortical neurons attach first, then switch to 5% or the Neurobasal+B27 system, which greatly reduces glial cells. A density of 5×10^4 per well in a 24-well plate is not low; the key is sufficient coating. PDL or PDL plus laminin should be pre-coated, otherwise the number of attached cells will drop under low serum conditions. In a 500 μl system, the amount of 5% serum is small, so pipetting should be gentle during medium changes. Within one week, 5% can be maintained, but if by day 5-7 there are many floating cells or broken processes, perform a half-volume medium change or supplement antioxidants in a timely manner.

Reducing to 5% does help inhibit glial proliferation, but lowering serum alone is not enough. It is recommended to use 10% for the first 2-4 hours after coating, then switch to 5%, and on day 3 treat with Ara-C for 24 hours; glial cells will be significantly reduced. 5% is not extremely low; the key lies in the serum lot. Primary neurons are sensitive to endotoxin and hormones, and at 5% lot-to-lot variation will be amplified. It is best to use the same lot for pilot experiments, set up 5% and 10% controls in a 24-well plate, and assess adhesion rate and neurite length at 48 hours and 72 hours separately; do not rely on just one image. If you want to switch to a low-serum-specific brand, first obtain a small package and perform a side-by-side comparison before deciding.

I have cultured primary cortical neurons at 5% and 2% serum. Maintaining them at 5% for one week is generally not a problem, but do not drop the serum concentration too low on the day of plating. You can initially plate in 10% serum, then switch to 5% after 2 hours; if you plate directly in 5%, some neurons will adhere slowly, and shaking the culture plate within 24 hours can easily cause them to detach. A 500 μl volume is on the low side; it is recommended to supplement with 100–150 μl at 48 hours or perform a half-volume medium change rather than a full-volume change, to avoid pH and temperature fluctuations. When glial contamination is high, low serum is the right direction, but a serum-free neuronal medium is more effective, as the glial background will be much lower and the neuronal state more uniform. Before switching, first use one 24-well plate to compare survival rates.