A researcher conducts an experiment where they artificially stimulate a specific nucleus within the brainstem of a nonhuman primate. The stimulation results in the animal immediately exhibiting signs of a 'fight-or-flight' response, including a rapid heart rate and heightened vigilance, which are characteristic of a panic attack. This experimental result most directly supports the conclusion that an overactivity of which neurotransmitter system is involved in generating these panic-like symptoms?

Neurobiological Basis of Panic-Like Symptoms