go back one page go forward one page
Anatomy Cell Biology Physiology Behavior and Clinical

Behavior

The rapid nature of the synaptic transmission mediated by the nicotinic receptor is consistent with its role at the NMJ and in the ganglion of the ANS. Little is known about the role of the nicotinic receptor role in CNS behavior. Clearly, nicotine stimulation is related in some manner to reinforcement, as indicated by the prevalence of nicotine addiction among humans.

Muscarinic receptors, in contrast, are important mediators of behavior in the CNS. One example is their role in modulating motor control circuits in the basal ganglia. A second example is their participation in learning and memory. The latter is inferred from two types of observations: 1) muscarinic antagonists are amnesic agents, and 2) deterioration of the cholinergic innervation of the neocortex is associated with memory loss in Alzheimer’s disease.

Clinical

Alzheimer's disease: A disease in which a marked deterioration occurs in the CNS, the hallmark of which is a progressive dementia. One of the characteristics of this disease is a marked decrease in ACh concentrations in the cerebral cortex and caudate nucleus.

Myasthenia gravis: A disease of the neuromuscular junction in which the receptors for ACh are destroyed through the actions of the patient's own antibodies.

Cholinergic Pharmacology: Numerous drugs are used clinically to interact with the cholinergic systems. Table II summarizes the major uses for cholinergic drugs.

Cholinergic Pharmacological Agents

Table II
Cholinergic Pharmacological Agents
Drug Action Clinical Use
Atropine (and other anticholinergics) Blocks muscarinic receptors Relaxes muscle in the eye causing the pupil to dilate. Used when the eye is inflamed and during eye examinations.
Slows the activity of the stomach and intestinal track and reduces acid secretion. Therefore, used for stomach cramps, diarrhea, diverticulitis, pancreatitis, bed wetting, motion sickness.
There has been some indication of this drug for Parkinson’s disease.
Scopolamine Blocks CNS muscarinic receptors Used topically to prevent dizziness, nausea and other aspects of motion sickness.
Amantadine (Symmetrel) Blocks muscarinic receptors Antidyskinetics used to treat Parkinson’s disease and the dyskinesia associated with antipsychotic drugs
Bethanechol Mimics ACh Used to treat urinary retention, and stimulate movement of intestinal tract.
Tacrine (Cognex) Blocks ACh breakdown Treat Alzheimer’s disease
Eserine or physostigmine Blocks ACh breakdown Reduces pressure in the eye and is used to treat glaucoma
Used to diagnose and treat myasthesia gravis

Test Your Knowledge

  • Question 1
  • A
  • B
  • C
  • D
  • E

Which of the following is effective in increasing the level of acetylcholine in the synapse or neuromuscular junction? (NOTE: There is more than one correct answer.)

A. Increasing dietary acetyl coenzyme A

B. Increasing the production of acetyl coenzyme A

C. Increasing dietary choline

D. Increasing choline uptake

E. Inhibition of the enzyme, acetylcholinesterase

Which of the following is effective in increasing the level of acetylcholine in the synapse or neuromuscular junction? (NOTE: There is more than one correct answer.)

A. Increasing dietary acetyl coenzyme A This answer is INCORRECT.

The administration of treatments to enhance acetyl coenzyme A production is not effective in elevating acetylcholine neurotransmission.

B. Increasing the production of acetyl coenzyme A

C. Increasing dietary choline

D. Increasing choline uptake

E. Inhibition of the enzyme, acetylcholinesterase

Which of the following is effective in increasing the level of acetylcholine in the synapse or neuromuscular junction? (NOTE: There is more than one correct answer.)

A. Increasing dietary acetyl coenzyme A

B. Increasing the production of acetyl coenzyme A This answer is CORRECT!

Although the administration of drugs to enhance acetyl coenzyme A production are not effective in elevating acetylcholine neurotransmission, cholinergic neurons increase their coenzyme A production as a means of increasing acetylcholine availability for neurotransmission.

C. Increasing dietary choline

D. Increasing choline uptake

E. Inhibition of the enzyme, acetylcholinesterase

Which of the following is effective in increasing the level of acetylcholine in the synapse or neuromuscular junction? (NOTE: There is more than one correct answer.)

A. Increasing dietary acetyl coenzyme A

B. Increasing the production of acetyl coenzyme A

C. Increasing dietary choline This answer is INCORRECT.

Although choline availability to the cholinergic neurons is rate limiting in the synthesis of acetylcholine, studies in animals and humans indicate that the administration of choline is ineffective in elevating cholinergic neurotransmission.

D. Increasing choline uptake

E. Inhibition of the enzyme, acetylcholinesterase

Which of the following is effective in increasing the level of acetylcholine in the synapse or neuromuscular junction? (NOTE: There is more than one correct answer.)

A. Increasing dietary acetyl coenzyme A

B. Increasing the production of acetyl coenzyme A

C. Increasing dietary choline

D. Increasing choline uptake This answer is CORRECT!

Although the dietary administration of choline is ineffective as a means of increasing acetylcholine neurotransmission, cholinergic neurons increase their choline uptake as a means of increasing the synthesis of acetylcholine for neurotransmission.

E. Inhibition of the enzyme, acetylcholinesterase

Which of the following is effective in increasing the level of acetylcholine in the synapse or neuromuscular junction? (NOTE: There is more than one correct answer.)

A. Increasing dietary acetyl coenzyme A

B. Increasing the production of acetyl coenzyme A

C. Increasing dietary choline

D. Increasing choline uptake

E. Inhibition of the enzyme, acetylcholinesterase This answer is CORRECT!

Inhibitors of acetylcholinesterase are the most effective means to elevate acetylcholine either at cholinergic neurons or at the neuromuscular junction. These drugs are used to treat Alzheimer's disease, myasthenia gravis and in many other situations where the elevation of cholinergic neurotransmission is desired.



go back one page go forward one page