Simplified and probably somehwat inaccurate explanation:
The currently believed theory about this effect it's that the number of nuclei in your muscle cells increase, along with the actuall volume of the cell. Cell volume decreases quite fast, but the number of nuclei stays more or less constant, allowing you tor egain cell volume quite fast.
Anabolic drugs push the natural upper limits of myonuclei per cell, which can remain higher than natural even years after stopping exercise/dosing.
So once you have reached a certain level of hypertrophy
Yes, in long muscle fibers and in the syncytiotrophoblast of the placenta. This involves repurposed viral DNA. Viruses use that DNA to spread directly from cell to cell. The placenta makes a giant multi-nucleated cell to block any gaps.
Anabolic drugs push the natural upper limits of myonuclei per cell, which can remain higher than natural even years after stopping exercise/dosing.
So once you have reached a certain level of hypertrophy