Valproic acid affects which neurotransmission mechanism?

Valproic acid predominantly acts by inhibiting GABA transaminase, which is the enzyme responsible for the degradation of GABA (gamma-aminobutyric acid), the main inhibitory neurotransmitter in the brain. By inhibiting this enzyme, Valproic acid effectively increases the levels of GABA in the synaptic cleft, enhancing its inhibitory effects. This mechanism is particularly beneficial in the treatment of conditions such as epilepsy and bipolar disorder, where increased GABAergic activity can help stabilize mood and suppress seizures.

The other options reflect mechanisms that do not accurately describe Valproic acid's pharmacological profile. For instance, the idea that it decreases GABA levels contradicts its primary action of increasing GABA availability; additionally, claiming it increases presynaptic Na+ levels does not align with the established understanding of its effects, which are more focused on GABA modulation than on sodium channel activity. Lastly, while Valproic acid can have various effects on neurotransmitter systems, enhancing dopamine secretion is not a primary or well-documented action associated with this medication.