Other sets of brain cell cultures were developed and incubated with either estradiol (estrogen) or progesterone (the other female sex hormone). After four days, all the brain cell cultures were exposed to NMDA for 10 minutes at a concentration that was known to kill about 50 percent of the cells. Once the NMDA was washed away, the cells were bathed in a dye that can only stain dead cells and the cultures were then examined to see how many cells survived the assault. Interestingly, one observation noted by the researchers that was not prominently discussed was the fact that none of the steroids, at concentrations up to 10 µm, were toxic to the brain cell cultures before the NMDA was applied. This is strikingly different from the findings of the 2006 study, which found that testosterone at concentrations of 1-10 µm induced brain cell death. (A µm is a very, very small amount; 0.000001 mol/L. Normally, brain cells are only exposed to 20-80 nm or 1/20th that amount.) In other words, at concentrations approximately 20 to 200 times normal, none of the AAS were toxic to the brain cells. Now, some might take that sentence and decide that it is safe to use AAS at high levels, but that is premature, as the human body does not exist in a sterile lab dish.

    While it is somewhat reassuring to see that several AAS do not cause brain cell injury, even at excessively high levels, on their own, the story changed when the brain cells were subjected to NMDA. Testosterone actually protected against brain cell damage when the concentration was in the normal range of men not taking steroids (10-100 nm). However, when the concentration was increased to the µm range (20-200 times normal), the cells became more vulnerable to the toxic effects of NMDA.

    The problem was even worse for the other three AAS, as there was no protective effect at all and concentrations that presumably represent athlete use increased NMDA-induced cell death by roughly 20 percent to 80 percent. Working on the assumption that the increased damage is related to the androgen receptor, the investigators then looked at the AAS when combined with the aromatase inhibitors or the androgen receptor antagonist.