Cholinergic antagonist scopolamine

Figure 5. Cartoon of a cholinergic synapse showing major steps in the synthesis of acetylcholine. The two major receptor types, the ionotropic nicotinic receptor and the metabotropic muscarinic receptor, are shown (see also Chapter 1). Presynaptic muscarinic (M2) and nicotinic receptors are also depicted. Drugs which have been widely used to manipulate the cholinergic systems, and which are mentioned in the text, include the muscarinic receptor antagonists scopolamine and atropine and the nicotinic receptor agonist nicotine. Anticholinesterases (discussed elsewhere in this volume) include drugs such as physostigmine, rivastigmine, donepezil, and galanthamine.

On the other hand, 5-HT1A receptor antagonists have been shown to attenuate or reverse the cognitive deficits induced by the cholinergic blocker scopolamine, which might suggest a new therapeutic activity for this drug class (203,204). 

Cholinergic Antagonists. Atropine, which is a muscarinic antagonist that in some cases also blocks the effects of nicotinic agonists, suppresses REM sleep. The effects of the muscariniclnicotinic agonist carbachol, which facilitates REM sleep, are prevented by systemic administration of atropine. Similarly, scopolamine delays the appearance of REM sleep (35). 

The drug most commonly employed as a cholinergic antagonist is atropine, which acts at peripheral and central muscarinic sites. Other cholinergic antagonists which have been investigated include aprophen, benactyzine, scopolamine and trihexyphenidyl. ... 

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.

Scopolamine A muscarinic cholinergic receptor antagonist that has amnesic side effects. 

Acetylcholine acts at two different types of cholinergic receptors [see (1) and (2) in Fig. 2.5]. Muscarinic receptors bind ACh as well as other agonists (muscarine, pilocarpine, bethanechol) and antagonists (atropine, scopolamine). There are at least five different types of muscarinic receptors (M1-M5). 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 to open or close channels for K, Ca ", or CL (Bonner, 1989). Nicotinic receptors are less abundant than the muscarinic type in the CNS. They bind ACh as well as agonists such as nicotine or an-... 

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