The metabolic gate, and the brain above it

Kisspeptin neurons carry receptors for leptin and read the body's fuel state, which is how starvation, heavy training and body fat all reach the reproductive axis: through this one node. That is why men with type 2 diabetes and low testosterone still answered kisspeptin-10 normally, with LH and testosterone both rising, which located their problem above the pituitary rather than in the testis. It also acts in the amygdala and limbic system, where it changes how sexual and emotional cues are processed. The same signal therefore links fuel, desire and fertility.