What mechanism is associated with D2 receptors in terms of G protein and second messenger?

Dopamine D2 receptors are primarily associated with the Gi protein. When dopamine binds to D2 receptors, it activates the Gi protein, which subsequently inhibits adenylate cyclase. This inhibition leads to a decrease in the production of cyclic AMP (cAMP) in the cell. Reduced levels of cAMP affect various downstream signaling pathways that can influence neurotransmitter release and cellular response.

The mechanism of Gi-coupled receptors, such as D2, is crucial for understanding their role in the nervous system and their pharmacological significance in treating conditions like schizophrenia, where dopamine pathways are involved. The interaction between D2 receptors and Gi proteins is a classic example of how neurotransmitter signaling can modulate synaptic transmission without stimulating cAMP production, differentiating it from Gs-coupled receptors which increase cAMP levels.

Other mechanisms described in the options involve distinct receptor types or actions, but they do not pertain to the D2 receptor's functionality. For example, Gs proteins increase cAMP production, Gq proteins typically lead to increased inositol trisphosphate (IP3) levels, and G12 proteins are involved in different signaling pathways altogether. Therefore, option B accurately represents the inhibitory mechanism linked to D2 receptors in the