**Core Concept**
The inhibitory neurotransmitter in CNS neurons is a key concept in understanding the regulation of neuronal activity. **GABA (Gamma-Aminobutyric Acid)** is the primary inhibitory neurotransmitter in the central nervous system, responsible for reducing the excitability of neurons and promoting a calming effect on neural activity.

**Why the Correct Answer is Right**
GABA acts on GABA_A receptors, which are ligand-gated chloride channels. When GABA binds to these receptors, it leads to an influx of chloride ions into the neuron, resulting in hyperpolarization and a decrease in the likelihood of action potential firing. This inhibitory effect is crucial for maintaining a balance between excitation and inhibition in the CNS, allowing for proper neural communication and regulation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, so we'll move on to the next one.
**Option B:** This option is also not provided, so we'll move on to the next one.
**Option C:** This option is incorrect because while glycine is an inhibitory neurotransmitter, it primarily acts in the spinal cord and brainstem, rather than the entire CNS.
**Option D:** This option is incorrect because glutamate is an excitatory neurotransmitter, not an inhibitory one.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that GABA is not only an inhibitory neurotransmitter but also a key player in the regulation of sleep, anxiety, and muscle tone. Imbalances in GABA levels or function have been implicated in various neurological and psychiatric disorders.

**Correct Answer: GABA. Gamma-Aminobutyric Acid**