Peripheral nervous system nicotinic acetylcholine receptors

As we have seen [in a previous chapter], acetylcholine occurs in s niapses in both the somatic and the autonomic nervous system. The nicotinic acetylcholine receptor is found in the motor endplate of the skeletal muscle, and in both the sympathetic and the parasympathetic ganglia of the peripheral autonomic system. Muscarinic acetylcholine receptors are found at the endings of all secondary neurons within the parasympathetic part of the peripheral autonomous system. In addition, acetylcholine receptors of both types also occur in the brain. Drugs with a useful degree of selectivity for each of these targets are available and used in practical medicine. Selectivity is based on two principles ... 

Cholinergic Transmission is the process of synaptic transmission which uses mainly acetylcholine as a transmitter. Cholinergic transmission is found widely in the peripheral and central nervous system, where acetylcholine acts on nicotinic and muscarinic receptors. 

Diazinon, an anticholinesterase organophosphate, inhibits acetylcholinesterase in the central and peripheral nervous system. Inhibition of acetylcholinesterase results in accumulation of acetylcholine at muscarinic and nicotinic receptors leading to peripheral and central nervous system effects. These effects... 

Nicotine is known to bind to acetylcholine receptors (the receiving areas on cells) that are located throughout the central nervous system as well as the peripheral nervous system. Acetylcholine is a neurotransmitter it transmits nerve impulses from one nerve fiber to another. The pleasurable effects of nicotine are a... 

Nicotinic acetylcholine receptors (uAChRs) are ligand-gated ion channels, and one of the best-studied of the ionotropic receptors. They are found in both the CNS and the peripheral nervous system, as well as in the neuromuscular junctions of somatic muscles. 

Acetylcholine is the endogenous neurotransmitter at cholinergic synapses and neuroeffector junctions in the central and peripheral nervous systems. The actions of acetylcholine are mediated through nicotinic and muscarinic cholinergic receptors, which transduce signals via distinct mechanisms. 

FIGURE 10-5. Organization of neurotransmitters of the peripheral nervous system and site of acetylcholinesterase action. (Ach, acetylcholine Ach-ase, acetylcholinesterase NE, norepinephrine M, muscarinic receptor N, nicotinic receptor.)... 

Nicotinic acetylcholine receptors (nAChRs) are a family of ligand-gated ion channels that are found in abundance at the neuromuscular junction, and are widely distributed throughout the central and peripheral nervous systems. They comprise five subunit proteins that combine to form a cation permeable pore at the cell surface. In neuronal tissues, multiple nAChR subtypes may be assembled from a diverse array of subunits (a2-a9 32-p4) and their... 

The nicotinic acetylcholine (ACh) receptor mediates neurotransmission postsynaptically at the neuromuscular junction and peripheral autonomic ganglia in the central nervous system (CNS), it largely controls release of neurotransmitters from presynaptic sites. The receptor is called the nicotinic acetylcholine receptor because it is stimulated by both the neurotransmitter ACh and the alkaloid nicotine. 

Not surprisingly, different ligands exhibit a characteristic individual affinity profile at the subtypes of the nicotinic acetylcholine receptors (Tab. 8.2). [131] These compounds served as suitable tools to investigate the tissue distribution of such receptors in the central and peripheral nervous systems. 

Mecfianism of Action A cholinergic-receptor agonist that binds to acetylcholine receptors, producing both stimulating and depressant effects on the peripheral and central nervous systems. Therapeutic Effect Provides a source of nicotine during nicotine withdrawal and reduces withdrawal symptoms. 

As with the mental effects of nicotine, the physiological effects are brought about by its actions on the nervous system, both peripheral and central. Nicotine changes the transmission of nerve impulses by binding to acetylcholine receptors, and induces the release of several chemical messengers, which in turn affect several body systems. 

In the peripheral (Wessler 1989) as well as central (Wonnacott 1997) nervous system, presynaptic nicotinic autoreceptors were reported to control the release of acetylcholine. In both locations, the consequence of presynaptic nAChR activation most commonly is an increase in both spontaneous and evoked acetylcholine release (MacDermott et al. 1999), whereas presynaptic muscarinic receptors mediate the opposite effect, an autoinhibition. Recent studies have focused on the composition of presynaptic nAChRs (Table 2). In the hippocampus, nicotinic autoreceptors were suggested to be a3/p4 receptors (Tani et al. 1998), but a role of p2 subunits has also been implicated (Lloyd et al. 1998). Likewise, in the neocortex, presynaptic nicotinic autoreceptors are likely to be 04/ p2 receptors (Marchi et al. 2002). In contrast, in the interpeduncular nucleus the autoreceptors were suggested to mainly contain a3 and p4 subunits (Grady et al. 2001). 

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