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Receptors

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psychology

research papers

published 13/11/2007

review : Completed

level : Advanced

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Summary

Ultimately the effects of monoamines on CNS function and behavior depend upon their interactions with receptor molecules. The binding of monoamines to these plasma membrane proteins initiates a series of intracellular events that modulate neuronal excitability. Unlike the transporters, multiple receptor subtypes exist for each monoamine transmitter. The initial classification of many receptor subtypes was based on radioligand binding studies. Receptor binding sites were identified on the basis of the rank order of binding affinities for a number of agonist and antagonist compounds. More recently, the molecular cloning of monoamine receptors has confirmed that many of the sites initially defined by these binding studies did indeed correspond to distinct receptor proteins encoded by unique genes. Molecular cloning has also led to the identification of previously unknown receptors, and to the introduction of powerful tools to characterize receptor structure and function.

Neurotransmitter receptors produce intracellular effects by one of two basic mechanisms:
In the wake of the recent proliferation of known receptors subtypes, much work needs to be done to determine the functional roles of individual receptors.
The 5-HT1 receptors comprise the largest serotonin receptor subfamily, with human subtypes designated:
At least three receptor subtypes mediate the effects previously attributed to a single 5HT2 receptor subtype.
The 5-HT3 receptor is unique among monoaminergic receptors in its membership within the ligand-gated ion channel superfamily.
The D1 receptor was initially distinguished from the D2 subtype by its high affinity for the antagonist SCH 23390 and its relatively low affinity for butyrophenones such as haloperidol
The dopamine D2 receptor was initially distinguished from the D1 receptor on the basis of its high affinity for butyrophenones.
The D3 and D4 receptors are considered to be D2-like on the basis of similarities in their gene structures, sequence homologies, and pharmacology.
Like the a-adrenergic receptors described, b-adrenergic receptors (designated including subtypes b1, b2, and b3) are found both in the brain and in many peripheral tissues.
Unlike H1 and H2 histamine receptors, H3 receptors are located presynaptically on axon terminals.
Within the human brain, nicotinic acetylcholine receptors are found at highest densities within the hippocampal formation, neocortex, substantia nigra, ventral tegmental area, dorsal raphe nucleus, periaqueductal gray, and the basal forebrain cholinergic complex.