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Cell-to-cell communication is critical for the survival of an organism. Cells can communicate through a process called the signal transduction pathway. When sending a signal, different molecules, such as hormones, can bind to a receptor on or inside the cell membrane, leading to chemical reactions in the cell, ultimately reaching the target. Cells use a second messenger to transmit these messages. This article will be discussing the different types of receptors, focusing specifically on dopamine receptors, the different types of dopamine receptors, and what function each receptor has. The article will also go into different illnesses and medications that target these receptors. The dopamine receptors affect many various functions, ranging from hypertension and hormonal regulation to voluntary movement and reward.[1]

The five different dopamine receptors can subdivide into two categories. D1 and D5 receptors group together, and D2, D3, and D4 are together in a separate subgrouping. D1 and D5 receptors couple to G stimulatory sites and activate adenylyl cyclase. The activation of adenylyl cyclase leads to the production of the second messenger cAMP, which leads to the production of protein kinase A (PKA), which leads to further transcription in the nucleus. D2 through D4 receptors couple to G inhibitory sites, which inhibit adenylyl cyclase and activate K+ channels. The D1 receptor is the most abundant out of the five in the central nervous system, followed by D2, then D3, and D5, and the least abundant is D4. D1 receptors help regulate the development of neurons when the dopamine hormone binds to them. D1 and D5 receptors have high density in the striatum, nucleus accumbens, olfactory bulb, and substantia nigra. These receptors are essential in regulating the reward system, motor activity, memory, and learning. D1 and D5 receptors, along with stimulating adenyl cyclase, also activate phospholipase C, which leads to the induction of intracellular calcium release and activation of protein kinase C. Protein kinase C is a calcium-dependent protein kinase. Calcium is also involved in modulating neurotransmitter release by exocytosis. D1 and D5 receptors are also involved in the kidney by inhibiting Na/K ATPase through PKA and PKC pathways. In the kidney, these receptors correlate with an increase in electrolyte excretion and renal vasodilation. D2, D3, and D4 receptors are expressed mainly in the striatum, as well as the external globus pallidus, core of the nucleus accumbens, hippocampus, amygdala, and cerebral cortex.  These receptors also affect the postsynaptic receptor-medicated extrapyramidal activity. D2-D4 receptors are important in the signaling for the survival of human dopamine neurons and neuronal development.[4][5]