**Core Concept**
GABA-B receptors are a type of metabotropic receptor that modulates neurotransmitter release in response to the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). These receptors are ionotropic, meaning they do not directly open ion channels, but instead, they are coupled to G-proteins that regulate various downstream signaling pathways.

**Why the Correct Answer is Right**
GABA-B receptors are a type of metabotropic receptor that is activated by the binding of GABA to its receptor complex. This binding causes a conformational change in the receptor, which activates a G-protein that triggers a signaling cascade. The activation of GABA-B receptors leads to the inhibition of adenylate cyclase, which in turn reduces the production of cyclic AMP (cAMP) and results in the closure of voltage-gated calcium channels. This ultimately leads to the reduction of excitatory neurotransmitter release.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because GABA-A receptors are a type of ionotropic receptor, whereas GABA-B receptors are metabotropic.
**Option B:** This option is incorrect because AMPA receptors are a type of ionotropic glutamate receptor, whereas GABA-B receptors are metabotropic.
**Option C:** This option is incorrect because NMDA receptors are a type of ionotropic glutamate receptor, whereas GABA-B receptors are metabotropic.

**Clinical Pearl / High-Yield Fact**
GABA-B receptors play a critical role in the regulation of neurotransmitter release in the brain, particularly in the regulation of inhibitory neurotransmission. The activation of GABA-B receptors can lead to a reduction in excitatory neurotransmitter release, which can have a profound impact on neuronal activity.

**Correct Answer: D. Metabotropic receptor.**