**Core Concept**
Miazapine, also known as mirtazapine, is an atypical antidepressant that exhibits a unique pharmacological profile. It primarily functions as an antagonist of central presynaptic α2-adrenergic receptors, which are involved in the modulation of norepinephrine release.

**Why the Correct Answer is Right**
Mirtazapine's action as an α2-adrenergic receptor antagonist increases the release of norepinephrine and serotonin in the central nervous system. This leads to an enhancement of neurotransmission, ultimately contributing to its antidepressant effects. The blockade of α2-adrenergic receptors inhibits the negative feedback mechanism that normally limits the release of norepinephrine, resulting in an increase in its availability for synaptic transmission. This mechanism is distinct from other antidepressants that primarily target serotonin or norepinephrine reuptake.

**Why Each Wrong Option is Incorrect**
**Option A:** Beta receptors are primarily involved in the regulation of heart rate and blood pressure, and are not a primary target for mirtazapine's antidepressant effects.
**Option B:** D2 receptors are primarily associated with the dopaminergic system and are not a primary target for mirtazapine.
**Option D:** While mirtazapine does have some affinity for 5-HT receptors, its primary mechanism of action is not as a direct antagonist of these receptors.

**Clinical Pearl / High-Yield Fact**
Mirtazapine's unique mechanism of action as an α2-adrenergic receptor antagonist sets it apart from other antidepressants and makes it a useful option for patients who have not responded to other treatments. Its ability to increase the release of both norepinephrine and serotonin also contributes to its efficacy in treating anxiety and insomnia.

**✓ Correct Answer: C. Alpha 2 receptors**