Which neurotransmitter is primarily released in the VLPO to promote sleep?

The correct answer is GABA, which stands for gamma-aminobutyric acid. In the ventrolateral preoptic nucleus (VLPO) of the hypothalamus, GABA serves as the primary inhibitory neurotransmitter that promotes sleep. The neurons in the VLPO release GABA to inhibit wake-promoting centers in the brain, thereby facilitating the transition from wakefulness to sleep. This action is crucial for initiating and maintaining sleep states, making GABA a vital player in the regulation of sleep.

In contrast, dopamine is primarily associated with wakefulness and alertness, serotonin is involved in various functions including mood regulation and the sleep-wake cycle but is not the main neurotransmitter released in the VLPO specifically for sleep promotion, and acetylcholine is mainly linked to the promotion of arousal and is more involved in the regulation of REM sleep rather than directly promoting sleep onset.