**Core Concept**
The sympathetic nervous system plays a crucial role in regulating sweat gland function, particularly in response to heat and emotional stimuli. This is mediated by the release of specific neurotransmitters from sympathetic nerve terminals. In sweat glands, the sympathetic neurotransmitter is responsible for stimulating sweat secretion.

**Why the Correct Answer is Right**
The correct answer is Acetylcholine (ACh). ACh is the primary neurotransmitter released by the sympathetic nervous system in sweat glands. This is in contrast to the parasympathetic nervous system, which releases ACh in other glands, such as salivary and lacrimal glands, to stimulate secretion. In sweat glands, ACh binds to muscarinic receptors, leading to an increase in sweat secretion. This is an example of a sympathetic cholinergic response, where the sympathetic nervous system uses ACh as its neurotransmitter.

**Why Each Wrong Option is Incorrect**
**Option A:** Norepinephrine - Norepinephrine is the primary neurotransmitter released by the sympathetic nervous system in other tissues, such as the heart and blood vessels, but not in sweat glands.
**Option B:** Dopamine - Dopamine is not a primary neurotransmitter released by the sympathetic nervous system in sweat glands.
**Option C:** GABA - GABA (Gamma-Aminobutyric Acid) is an inhibitory neurotransmitter and is not involved in sweat gland function.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the sympathetic nervous system uses ACh as its neurotransmitter in sweat glands, which is a unique characteristic of this system in this specific tissue.

**Correct Answer: C. Acetylcholine**