Nicotinic type

There are two major types of receptor which are activated by neurotransmitters. These are the ionotropic and metabotropic receptors. The former receptor type is illustrated by the amino acid neurotransmitter receptors for glutamate, gamma-aminobutyric acid (GABA) and glycine, and the acetylcholine receptors of the nicotinic type. These are examples of fast transmitters in that they rapidly open and close the ionic channels in... 

Nicotine Nicotiana tabacum L.) (11), an agonist of the nicotinic-type acetylchoUne receptor (nAChR), has long been known for its mechanism of action. Nicotine-like compounds offer much potential in the treatment... 

Cytisine (30), from Cytisus scoparius L., has been found to be a selective and specific probe for the nicotinic-type acetylcholine receptor (nAChR) as a partial agonist and has served as the lead compound... 

The laboratory of the Government Chemist in London undertakes the analysis of tobacco smokes in order to produce league tables (Fig. 20) of the tar and nicotine content of all cigarette brands available in the UK, on behalf of the British government. In this context tar is defined as the total particulate matter present in the main-stream smoke (inhaled smoke), adjusted for its content of water and nicotine alkaloids. Nicotine is defined as the total nicotine-type alkaloids present in the mainstream smoke both are expressed in mg per cigarette. The tar and nicotine league tables are published every six months, and include details of approximately 130 brands of cigarette. 

A simple synthesis of alkaloids of the nicotine type is exemplified by that of myosmine (41) and is outlined in Scheme 8. It employs l-vinyl-2-pyrrolidone as... 

Striatum, Flippocampus, Thalamus Relatively few studies have investigated the expression of AChRs outside the cortex in schizophrenia ( Table 4.2-7). However, studies done in the striatum, the hippocampus, and the thalamus have identified changes similar to those in the cortex including increased (striatum), unaltered (thalamus), or decreased (striatum, hippocampus) binding of [3H] nicotine to 4P2 type nAChRs in schizophrenia (Leonard et al., 1998 Court et al., 1999 Breese et al., 2000 Court et al., 2000). Supporting decreased expression of nicotinic type receptor in the striatum and the hippocampus, [3H]cytosine and [3H]epibatidine were similarly reported decreased in schizophrenia (Freedman et al., 1995 Breese et al., 2000 Durany et al., 2000). Additionally, a7 receptor binding in the hippocampus and the thalamus, as well as a.7 protein expression in the striatum, was reported to be decreased in this illness (Freedman et al., 1995 Leonard et al., 1998 Court et al., 1999). 

Acetylcholine receptors (AChRs) are of two types muscarinic (mAChR) and nicotinic (nAChR) based on the agonist activities of the natural alkaloids, muscarine and nicotine, respectively. These receptors are functionally different. The muscarinic type being G-protein coupled receptors mediate a slow metabolic response via second messenger cascades, while the nicotinic type are ligand-gated ion channels, which mediate a fast synaptic transmission of the neurotransmitter. Skeletal muscles are enriched with nAChRs and are devoid of mAChRs. 

ACh acts at two different types of cholinergic receptors Muscarinic and Nicotinic receptors. Muscarinic receptors (1) bind ACh as well as other agonists (muscarine, pilocarpine, bethan-echol) and antagonists (atropine, scopolamine). There are at least 5 different types of muscarinic receptors (M1-M5) and all have slow response times. They are coupled to G-proteins and a variety of second messenger systems. When activated, the final effect can be an opening or closing of channels for K", Ca ", or Cl . Presynaptic cholinergic receptors are of the muscarinic or nicotinic type and can modulate the release of several neurotransmitters. 

Relief of symptoms of Parkinson s disease. Acetylcholine receptors of the nicotinic type have been implicated in the Parkinsonian syndrome (7-9). 

A new photometric determination of volatile bases in tobacco and tobacco smoke in terms of nicotine, which compares quantitatively with mass spectral and g.c. methods, has been developed.27 A colorimetric method for the estimation of nicotine alkaloids in tobacco by reaction with cyanogen bromide and 4,4 -di-aminostilbene-2,2 -disulphonic acid has also been reported.28 Dilute sulphuric acid extraction of nicotine and anabasine from autopsy tissue appears to be a more efficient method than extraction with acidified ethanol, aqueous oxalic acid, and steam distillation.29 Thin-layer chromatography has been effective in the analysis of nicotine and other alkaloids and drugs.30 Two reports on the isolation of anabasine from anabasine-lupinine mixtures have appeared.31 The P a values of some nicotine-type compounds have been determined.32... 

Upon stimulation, acetylcholine (Ach) is released at the parasympathetic nerve endings and displays activity on a number of different cell types, mediated by two major classes of receptors. While muscarine, an alkaloid of the fly agaric Amanita muscaria) and other mushrooms, binds more selectively than acetylcholine at certain ACh-receptors, these are called muscarinic receptors or mAChRs. On the other hand, nicotinic-type AChRs function as ligand-gated ion channels and show selectivity for nicotine over ACh. 

The nicotinic effects of ACh are its excitatory action on the autonomic ganglia and the suprarenal glands and its capacity to stimulate the skeletal striated musdes. The nicotinic effects of ACh are reproduced by nicotine and are not abolished by atropine. Nicotinic action on ganglia and suprarenal glands is blocked by hexa-methonium and tetraethylammonium. The nicotinic action of ACh on the skeletal muscles is blocked by tubocurarine. The action of ACh on central nervous system neurons may be of the nicotinic type (for example, Renshaw cells) or of the muscarinic type (certain brain neurons). 

The cholinergic synapses in autonomic ganglia are more complex Each ganglionic cell has many synaptic inputs. The receptors on the postsynaptic membrane differ qualitatively. The ChR principally responsible for the transmission is of the nicotinic type (N-ChR). In addition, there are receptors of muscarinic type (M-ChR see p. 242). 

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