Final answer:
The neurotransmitter implicated in the development of mood disorders is serotonin, known for its crucial role in mood regulation within the CNS. So the correct answer is option (A).
Step-by-step explanation:
The neurotransmitter currently implicated in the development of mood disorders is serotonin. Alterations in serotonin (5-hydroxytryptamine, 5-HT) function are associated with mood disorders such as depression and anxiety. In the CNS, serotonin is crucial for mood regulation, and changes in its neurotransmission can lead to affective disorders. While other neurotransmitters like dopamine and GABA also play roles in the brain's function and are associated with certain neuropsychiatric conditions, serotonin is particularly known for its involvement in mood regulation.
Neurotransmitters like dopamine and acetylcholine have their own roles, such as involvement in reward and motivation systems for dopamine and muscle activation and memory functions for acetylcholine. GABA, or gamma-aminobutyric acid, is an inhibitory neurotransmitter that contributes to regulating neuronal excitability throughout the nervous system. However, for the specific question of mood disorders, serotonin is the most commonly implicated neurotransmitter.