Cholinergic receptors receptor Nicotinic

Cholinergic receptors Receptors for acetylcholine are classified into muscarinic (muscarine is a selective agonist) and nicotinic (nicotine is a selective agonist). There are five muscarinic (mj to m5) and two nicotinic (neuronal, or ganglionic, and skeletal muscular) subtypes. 

In the sympathetic system the preganglionic cholinergic receptors are nicotinic while the postganglionic are adrenergic variations called a and p receptors. These receptors are also subdivided and indicated by subscripts in order to specify the tissues where they are found. 

Acetylcholine receptors are classified as either muscarinic cholinergic receptors or nicotinic cholinergic receptors. The alkaloid muscarine mimics the effects produced by stimulation of the parasympathetic system. These effects are postganglionic and are exerted on exocrine glands, cardiac muscle, and smooth muscle. The alkaloid nicotine mimics the actions of acetylcholine, which include stimulation of all autonomic ganglia, stimulation of the adrenal medulla, and contraction of skeletal muscle. 

The actions of nicotine relate to its ability to activate one of the two groups of cholinergic receptors, the nicotinic receptors. Nicotine and a second substance, muscarine, a mushroom toxin, were known long before acetylcholine was identified as a neurotransmitter, and the receptors in the PNS were initially distinguished by... 

Abbreviations AON, anterior olfactory nucleus mAChR, muscarinic cholinergic receptor nAChR, nicotinic cholinergic receptor alpha and beta adrenergic receptors NMDA, N-methyl-D-Aspartate receptor AMPA, a-amino-hydroxy-5-methyl-4-isoxazolepropionic acid receptor GABAa/b, gamma aminobutyric acidreceptor. 

Nicotinic Receptor Agonists. There has been significant activity in the development of muscarinic cholinergic receptor agonists for dementia. In addition, agents that interact with nicotinic cholinergic receptors may also have therapeutic value. Nicotinic receptors have been reported to be... 

Acetyl choline is the natural neurotransmitter for the cholinergic receptor. Two distinct receptor subtypes have been characterized based on their binding affinity for either nicotine (189) and (190) or muscarine (191). 

In contrast to all this negativity, it must be acknowledged that more is known about the structure and function of cholinergic receptors and synapses, especially the nicotinic ones, than for the receptors of any other NT. It is unfortunate that nicotinic synapses are not very common in the CNS. 

Figure 13.3. An overview of the chemical events at a cholinergic synapse and agents commonly used to alter cholinergic transmission acetyl CoA, acetyl coenzyme A Ch, choline. Nicotine and scopolamine bind to nicotinic and muscarinic receptors, respectively (nicotine is an agonist while scopolamine is an antagonist). Most anti-Alzheimer drugs inhibit the action of the enzyme cholinesterase.

Isoreceptors Different receptor proteins that recognise and bind the same neurotransmitter (e.g., muscarinic and nicotinic cholinergic receptors). 

Muscle-relaxant A drug that relaxes skeletal (voluntary) muscle either directly by blocking nicotinic cholinergic receptors or indirectly through the activation of inhibitory spinal cord interneurons. 

The intrinsic complexity and the multiplicity of cholinergic receptors became evident upon elucidation of their primary structures. In the CNS, at least nine different sequences of a subunits and three different sequences of (3 subunits of the nicotinic receptor have been identified [10, 11]. Expression of the cloned genes encoding certain subunit combinations yields functional receptors with different sensitivities toward various toxins and agonists. 

Thus, cholinergic receptor classification can be considered in terms of three stages of development. Initially, Dale [2] distinguished nicotinic and muscarinic receptor subtypes with crude alkaloids. Then, chemical synthesis and structure-activity relationships clearly revealed that nicotinic and muscarinic receptors were heterogeneous, but chemical selectivity could not come close to uncovering the true diversity of receptor subtypes. Lastly, analysis of subtypes came from molecular cloning, making possible the classification of receptors on the basis of primary structure (Fig. 11-2). 

Elgoyhen, A., Vetter, D., Katz, E. etal. Alpha 10 a determinant of nicotinic cholinergic receptor function in mammalian vestibular and cochlear mechanosensory hair cells. Proc. Natl Acad. Sci. U.S.A. 98,3501-3506, 2001. 

Acetylcholine. Most of the acetylcholine in the basal ganglia is found in the striatum, as the neurotransmitter of the large spiny interneurons, which account for about 3% of all striatal neurons. Both muscarinic and nicotinic cholinergic receptors are found in the striatum. Postsynaptic muscarinic receptors may inhibit transmitter release from... 

Acetylcholine Binds to cholinergic receptor, which are of two types— muscarinic and nicotinic. 

Spinella M, Schaeffer LA, Bodnar RJ. (1997). Ventral medullary mediation of mesencephalic morphine analgesia by muscarinic and nicotinic cholinergic receptor antagonists in rats. Analgesia. 3 119-30. 

The Road to Discovery of Neuronal Nicotinic Cholinergic Receptor Subtypes... 

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