多巴胺的抑制作用？
Dopamine is an important transmitter in the brain that mediates many physiological effects， including motor control. Dopaminergic neurons are abundant in the substantia nigra pars compacta (SNc) of the basal ganglia， where they project to several structures in the cerebral cortex and hippocampus. In addition， some dopaminergic cells are located in the mesopontine tegmentum， a region at the base of the midbrain that is associated with sleep regulation.
The major biological functions of dopamine are mediated by two families of receptors：DA1和 DA2 . There are seven known subtypes within each family（Dαl/ α1、 Dβl/ α2 和 Dγl）， which differ in their affinity for neurotransmitters or agonists， as well as selectivity patterns for other receptors.
Both types of receptors are G-protein coupled receptors． When activated by an agonist， these receptors facilitate the production of inositol trisphosphate（IP3） ， which triggers intracellular free calcium ions（Ca2+［i］） increase， thereby initiating intracellular signaling cascades that ultimately lead to cellular responses such as increased cyclic AMP（cAMP） generation or protein kinase A activation， or phosphatidylinositide turnover， or the formation of protein complexes that regulate transcription.
A variety of drugs can activate either DA1 or DA2 receptors； however， this article will restrict discussion of the physiological consequences of those receptor subtypes normally thought to be primarily regulated by endogenous dopamines. The most extensively characterized effect of DA1receptor stimulation is the inhibition of adenylate cyclase，the enzyme responsible for generating cAMP. As noted above，cAMP has important regulatory functions on gene expression and cell growth in all eukaryotic cells. Therefore，dopamine’s ability to inhibit adenylate cyclase activity represents a critical step toward regulating multiple aspects of neural and cellular function.
The second largest known effector of dopamine is the metabotropic glutamate receptor，which acts as a Ca2+channel when stimulated by L-glutamate. This receptor was initially believed to be involved solely in excitatory synaptic transmission but it now apparent that these receptors also play a