**Core Concept**
GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter in the central nervous system, playing a crucial role in regulating neuronal excitability and synaptic plasticity. As an amino acid, GABA is synthesized from glutamate through the action of the enzyme glutamic acid decarboxylase (GAD).

**Why the Correct Answer is Right**
GABA acts on GABA receptors, which are ligand-gated chloride channels, to hyperpolarize neurons and reduce their excitability. This inhibitory effect helps to balance the excitatory actions of other neurotransmitters, such as glutamate and aspartate. GABA is the primary inhibitory neurotransmitter in the adult brain, and its dysfunction has been implicated in various neurological and psychiatric disorders.

**Why Each Wrong Option is Incorrect**
**Option A:** Acetylcholine is a choline-based neurotransmitter, not an amino acid, and is primarily involved in excitatory neurotransmission.
**Option C:** Lignocaine (lidocaine) is a local anesthetic and antiarrhythmic medication, not a neurotransmitter.
**Option D:** Epinephrine (adrenaline) is a catecholamine neurotransmitter and hormone, primarily involved in the 'fight or flight' response, not an amino neurotransmitter.

**Clinical Pearl / High-Yield Fact**
GABA receptors are divided into two main subtypes: GABA_A and GABA_B. GABA_A receptors are ligand-gated chloride channels, whereas GABA_B receptors are metabotropic receptors that activate G-proteins.

**✓ Correct Answer: B. GABA**