The hormone CRH seems to be most responsible for this effect. As you’ll recall, the hormone not only starts the glucocorticoid cascade by stimulating ACTH release from the pituitary, but it is also the neurotransmitter that activates all sorts of fear, anxiety, and arousal pathways in the brain. Infuse CRH into a sleeping rat’s brain and you suppress sleep—it’s like throwing ice water onto those happily dozing neurons.
