As meat eaters, protein is foundational for cats. Proteins are obtained through meat sources. Protein supports the role of serotonin in both dogs and cats. Without sufficient levels of protein intake, there will be an eventual decline in serotonin, which can manifest as hyperactivity, aggression, hypersensitivity or restless sleep. As with us, cats are what they eat: garbage in = garbage out. I can’t stress enough the major role hydration and clean, good food plays in the behavior of your cat.