Dopamine is a crucial monoamine neurotransmitter in the brain, playing a pivotal role in movement, learning, memory, reward, and motivation [1]. Disruptions in the dopamine system lead to a variety of psychiatric and neurological disorders, including Parkinson’s disease, addiction, and schizophrenia. Pioneering studies using formaldehyde-induced fluorescence revealed multiple dopamine-rich neuronal nuclei in the brain, distributed from the mesencephalon to the olfactory bulb, designated as A8-A16 [2]. Among these, the substantia nigra (A9) and ventral tegmental area (VTA) (A10) in the mesencephalon have received the most extensive research attention. These dopaminergic neurons project to various brain regions, with the densest projections to the dorsal striatum and nucleus accumbens and sparser projections to the cortex and amygdala.

Unlike classical neurotransmitters, dopamine functions as a neuromodulator, lacking the formation of classical synaptic structures 3, 4. Dopamine terminals form varicosities and often fail to establish typical postsynaptic structures. Upon release from presynaptic terminals, dopamine acts on dopamine receptors located on nearby neuronal cell bodies, dendrites, or even axons through volume transmission. In vertebrates, dopamine exerts its effects through two major classes of dopamine receptors: the Gs/olf-coupled D1-like (D1 and D5) receptors and the Gi/o-coupled D2-like (D2, D3, and D4) receptors.