Final answer:
The sleeping aid ramelteon works by binding to melatonin receptors, mimicking the hormone melatonin's role in regulating sleep. It is thus tied to melatonin receptor systems, not to acetylcholine, GABA-A, histamine, or norepinephrine systems.
Step-by-step explanation:
The mechanism of action of the sleeping aid ramelteon involves binding to melatonin receptors. Specifically, it binds to the MT1 and MT2 receptors in the brain which are involved in the regulation of the sleep-wake cycle. This action of ramelteon mimics the naturally occurring hormone melatonin, which typically increases at night to promote sleep and decreases in presence of light to promote wakefulness. Therefore, among the options given, the correct answer is D. Melatonin.
On the broader topic, substances that affect the autonomic system often interact with various neurotransmitters. A drug that affects both divisions of the autonomic system might bind to or block nicotinic receptors, as these are common in both the parasympathetic and sympathetic divisions of the autonomic nervous system.