**Core Concept**
Lithium is a mood stabilizer used in the treatment of bipolar disorder, primarily due to its ability to modulate neurotransmitter release and neuronal excitability. It exerts its effects by influencing various signaling pathways, including the glycogen synthase kinase-3 (GSK-3) pathway and the inositol signaling pathway.

**Why the Correct Answer is Right**
Lithium inhibits GSK-3, which in turn leads to an increase in the activity of protein kinase B (Akt). This results in the inhibition of glycogen breakdown and an increase in glycogen synthesis. Additionally, lithium decreases the activity of inositol monophosphatase, leading to a decrease in the levels of inositol and its downstream metabolites, which are involved in the signaling of various neurotransmitters. This action helps to stabilize mood and prevent manic episodes.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because lithium does not primarily act through the dopamine or serotonin systems, although it may have some indirect effects on these neurotransmitters.
**Option B:** Incorrect because while lithium may have some effects on the GABA system, this is not its primary mechanism of action.
**Option C:** Incorrect because lithium is not primarily used as an antipsychotic, although it may be used in conjunction with antipsychotics in some cases.

**Clinical Pearl / High-Yield Fact**
Lithium has a narrow therapeutic index, and monitoring of serum levels is essential to prevent toxicity, which can cause symptoms such as tremors, ataxia, and in severe cases, renal failure.

**Correct Answer:** A.