Astrocyte

Excitotoxic Injury

Death by over-stimulation. Glutamate opens calcium channels, calcium floods in past what the mitochondria can hold, and the cell triggers its own destruction. It is the final common path for a large share of neuronal death, and it is the exact process estrogen defends against.

BDNF Signalling

Brain-derived neurotrophic factor acting at TrkB. The growth signal behind new synapses and behind the kind of memory that needs sleep to form. It is suppressed by sustained cortisol and by lost deep sleep, which is how a compound with no direct action in the brain still reaches memory.

Local Brain Estrogen Synthesis

The brain makes its own estradiol from testosterone, in neurons and astrocytes, independently of what the testes supply. This single fact is why a blood estradiol reading does not tell you what the brain has, and why an aromatase inhibitor is a different kind of intervention from simply having low testosterone.