Muscarinic effects acetylcholine receptors

Antagonists of muscarinic acetylcholine receptors had widely been used since 1860 for the treatment of Parkinson s disease, prior to the discovery of l-DOPA. They block receptors that mediate the response to striatal cholinergic interneurons. The antiparkinsonian effects of drugs like benzatropine, trihexyphenidyl and biper-iden are moderate the resting tremor may sometimes respond in a favorable manner. The adverse effects, e.g., constipation, urinary retention, and mental confusion, may be troublesome, especially in the elderly. 

A G-protein-mediated effect has an absolute requirement for GTP. Reference has already been made to the requirement for GTP in reconstituting hormone-stimulated adenylate cyclase activity. A similar requirement can be demonstrated when the effector is an ion channel, such as the cardiac atrial inward-rectifier K+ channel which is activated following stimulation of the M2 muscarinic acetylcholine receptor. Thus, in the experiment illustrated in Figure 7.8, the channel recorded with a cell-... 

List the side effects of imipramine that result from its blockade of muscarinic acetylcholine receptors. 

The answer is a. (Katzung, p 499.) Of the listed a n tide press ants, only amitriptyline, a tricyclic, causes adverse effects related to blockade of muscarinic acetylcholine receptors. Both trazodone and amitriptyline cause adverse effects related to a-adrenoreceptor blockade... 

Areca (Areca catechu) is a tall palm tree that yields a nut, commonly chewed in Asia for its stimulant effects. It is discussed at greater length in chapter 4, but is mentioned here briefly for its cognitive effects. Areca s psychoactive constituents (arecoline, arecaidine, guvacoline, and guvacine) are agonists at muscarinic acetylcholine receptors. They also directly inhibit reuptake of GABA. 

Acetyichoiine Muscarine is an agonist at muscarinic acetylcholine receptors, for which the receptor was named. It is not certain what role this plays in the psychoactive effects of amanita. 

Certain plants of the family Solanaceae, such as Atropa belladonna L., Hyoscyamus niger L., and Datura stramonium L., have been used medicinally for centuries in Europe because they contain tropane-type alkaloids.For example, atropine (1) [a racemic mixture of (+)- and (—)-hyoscyamine (2)] and (-)-hyoscyamine are competitive antagonists at the muscarinic acetylcholine receptor site, leading to antispasmodic and antiallergic effects. Scopolamine [(—)-hyoscine)] (3) is used in a transdermal patch for the prevention of motion sickness. Since these tropane alkaloids penetrate the blood-brain barrier, they also have psychoactive effects. ... 

Atropine, an alkaloid from Atropa belladonna, is the classical parasympatholytic compound. It competes with acetylcholine for the binding at the muscarinic receptor. Its affinity towards nicotinic receptors is very low, so that it does not interfere with the ganglionic transmission or the neuromotor transmission, at least in therapeutic dosages. However, in the central nervous system muscarinic receptor do play an important role and while atropine can penetrate the blood-brain barrier it exerts pronounced central effects. Atropine, like all other antagonists of the muscarinic acetylcholine receptor inhibit the stimulatory influence of the parasympathetic branch of the autonomous nervous system. All excretory glands (tear, sweat, salivary, gasto-intestinal, bronchi) are... 

Mechanism of Action A urinary antispasmodic t hat act s as a direct antagonist at muscarinic acetylcholine receptors in cholinergically innervated organs. Reduces tonus (elastictension) of smooth muscle in the bladder and slows parasympathetic contractions. Therapeutic Effect Decreases urinary bladder contractions, increases residual urine volume, and decreases detrusor muscle pressure. 

Mode of action. The precise mode of action of carbamazepine has not been fully established. It has been shown to stabilize both pre- and postsynaptic neurons by blocking the use and frequency-dependent sodium channels. While this is probably its main action, the blockade of the glutamate NMDA ionotropic receptors also leads to a reduction in the influx of sodium and calcium ions into the neuron. The net effect of these changes is a reduction in the sustained high-frequency repetitive firing of the action potentials which characterize epileptic activity. There is also evidence that carbamazepine blocks purine, noradrenaline, serotonin and muscarinic acetylcholine receptors which probably accounts for the use of carbamazepine as a mood stabilizing agent. 

Terry AV Jr, Gearhart DA, Mahadik SP, Warsi S, Waller JL. 2006. Chronic treatment with first or second generation antipsychotics in rodents Effects on high affinity nicotinic and muscarinic acetylcholine receptors in the brain. Neuroscience 140 1277-1287. 

The modes of action of different alkaloids are diverse. For example, nicotine binds to and affects nicotinic acetylcholine receptors and shows toxicity. A recent molecular 3D model suggests that both acetylcholine and nicotine bind to the same pocket formed in a nicotinic acetylcholine receptor.15 Morphine binds to and activates opioid receptors, transmembrane-spanning G protein-coupled receptors, in the central nervous system of humans.16 Caffeine, which is structurally similar to adenine, inhibits cyclic AMP phosphodiesterase activity and inhibits the degradation of cAMP, thus exerting a toxic effect on insects 17 in human beings, binding of caffeine to the adenosine A2A receptor induces wakefulness.18 Atropine binds to muscarinic acetylcholine receptors, competing with acetylcholine, and blocks neurotransmission.1... 

Welch SP, Huffman JW, Lowe J (1998) Differential blockade of the antinociceptive effects of centrally administered cannabinoids by SR14176A. J Pharmacol Exp Ther 286 1301-1308 Wen HL, Mehal ZD, Ong BH, Ho WKK, Wen DYK (1985) Intrathecal administration of beta-endorphin and dynorphin-(l-13) for the treatment of intractable pain. Life Sd 37 1213-1220 Wess J (1996) Molecular biology of muscarinic acetylcholine receptors. Grit Rev Neurobiol 10 69-99... 

---