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Chapter 6: Cholinergic Pharmacology

A 35-year-old man has ingested Amanita muscaria mushrooms. He is experiencing a heart rate of 40 beats per minute. This bradycardia is most likely due to an interaction of the chemical(s) in the mushrooms with which receptors at the sinoatrial node?

a. α1 Adrenergic

b. β1 Adrenergic

c. β2 Adrenergic

d. M2 muscarinic

e. Nicotinic

Answer is d. Although the concentration of muscarine is low in these mushrooms, the symptom of bradycardia observed in this patient is most likely attributable to muscarine. Other chemicals that may be involved in the neurotoxicity of mushrooms of the Amanita species are muscimol, ibotenic acid, and other isoxazole derivatives. The receptors in the sinoatrial node innervated by parasympathetic nerves are M2 muscarinic receptors (see Table 5-1).

A 49-year-old woman is treated with pilocarpine hydrochloride for xerostomia (dry mouth) following head and neck radiation treatments. As a result of taking this drug she may experience which of the following side effects?

a. Sweating

b. Dry eyes

c. Dry skin

d. Confusion

e. Tachycardia

Answer is a. Side effects with pilocarpine treatment typify cholinergic stimulation, with sweating being the most common complaint. The other answers would be side effects seen after treatment with a muscarinic receptor antagonist.

A 54-year-old woman is receiving Botox injections to remove facial wrinkles. Botox (botulinum toxin) acts by

a. stimulating the release of ACh.

b. stimulating the release of norepinephrine.

c. blocking the release of ACh.

d. blocking the release of norepinephrine.

e. blocking muscarinic receptors.

Answer is c. Botulinum toxins act peripherally to reduce muscle contraction. The anaerobic bacterium Clostridium botulinum produces a family of toxins targeted to presynaptic proteins that block the release of ACh (see Figure 6-1). By blocking ACh release, BOTOX produces flaccid paralysis of skeletal muscle and diminished activity of parasympathetic and sympathetic cholinergic synapses. The FDA has issued a safety alert for BOTOX, warning of respiratory paralysis from unexpected spread of the toxin from the site of injection.


Figure 6-1. A cholinergic neuroeffector junction showing features of the synthesis, storage, and release ...

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