Immune cells in the brain may tune fertility hormones, animal study suggests

The kick-off signal for puberty begins in the brain. Specifically, in the hypothalamus, where specific neurons release a hormone that activates the hypophysis, at the base of the skull, which then releases other hormones to start gonad—ovaries or testicles—maturation. This mechanism leading to a fertile organism is the hypothalamic-pituitary-gonadal (HPG) axis.