Part I—"Poisoned!" Human Anatomy and Physiology Edition by James A. Hewlett Science and Technology Department Finger Lakes Community College

One evening during a recent trip to Indonesia, Dr. Marshall Westwood from the Montana Technical Institute sat down to a meal of pufferfish and rice.  Within an hour of returning to his hotel room, Dr. Westwood felt numbness in his lips and tongue, which quickly spread to his face and neck.  Before he could call the front desk, he began to feel pains in his stomach and throat, which produced feelings of nausea and eventually severe vomiting.

Fearing that he had eaten some "bad fish" for dinner, Dr. Westwood called a local hospital to describe his condition.  The numbness in his lips and face made it almost impossible for him to communicate, but the hospital staff managed to at least understand the address he gave them and sent an ambulance in response.  As Dr. Westwood was rushed to the hospital, his breathing became increasingly difficult.

Doctor's Notes

The patient presented in the ED with severe headache, diaphoresis, motor dysfunction, paresthesias, nausea, and an ascending paralysis that spread to the upper body, arms, face, and head.  The patient was cyanotic and was hypoventilating.  Within 30 minutes of presenting in the ED, Dr. Westwood developed bradycardia with a BP of 90/50.  Atropine was administered in response to the bradycardia.  IV hydration, gastric lavage, and activated charcoal followed a presumptive diagnosis of tetrodotoxin poisoning based on the clinical presentation in the ED.  Five hours after intervention, the following vitals were noted:

• BP 125/79
• HR 78bpm
• Oxygen saturation:  97% on room air

Follow-up

Within a few hours, Dr. Westwood's condition improved and he was on his way to a full recovery.  After discussing his case with his physician, he learned that he had probably been the victim of a pufferfish poisoning.  The active toxin in the tissues of this fish is a chemical called tetrodotoxin.  Tetrodotoxin is in a class of chemicals known as neurotoxins due to the fact that it has its effects on nerve cells (neurons).  Specfically, tetrodotoxin blocks voltage-gated sodium ion channels on neurons.

Questions

1. Present the "Doctor's Notes" portion of the case with a description of the following terms or concepts:
   
   • diaphoresis
   • motor dysfunction
   • paresthesias
   • cyanotic
   • hypoventilating
   • bradycardia
   • gastric lavage
   • oxygen saturation
2. How many different elements are contained in a molecule of tetrodotoxin?  What are the names of these elements?
3. What type of chemical bonds are found in this molecule?  Describe the structure of those bonds.
4. As mentioned in the case description, tetrodotoxin is a molecule that blocks voltage-gated sodium ion channels.  Describe the structure of a sodium ion.
5. What is a voltage-gated sodium ion channel?  What is it made of?  What is its function?
6. Why do sodium ions need channels in order to move into and out of cells?
7. Describe the process involved in the movement of ions through these channels.
8. When nerve cells are at rest, there is an unequal amount of positive and negative charges on either side of a nerve cell membrane.  This charge difference is called an electrical potential.  Describe this "potential" when the neuron is at rest (resting potential).
9. What is happening to the electrical potential of a neuron when it generates an action potential?  What is the function of the action potential in neurons?
10. Describe the role of sodium ions and sodium channels in the action potential.
11. What would happen to a neuron if it were exposed to tetrodotoxin?  Be specific regarding its effect on the ability of a neuron to communicate.
12. Now that you have addressed some of the basic biology of this case, explain why Dr. Westwood experienced numbness after eating the pufferfish meal.
13. Paralysis is a term used to describe the loss of function of muscle.  If tetrodotoxin's effect is on neurons, why did Dr. Westwood experience paralysis?
14. Explain how tetrodotoxin is involved in the development of hypotension and hypoventilation.
15. Briefly describe the role of the autonomic nervous system in human physiology.  What are the two divisions of this system?
16. Atropine was administered in the ED as part of Dr. Westwood's care.  What effect did it have on his vitals after it was administered?  Atropine acts as an antagonist within the central nervous system, which means it acts as a blocker of specific cellular functions.  What part of the autonomic nervous system does atropine block to produce its effect on Dr. Westwood?

Image Credit:  Photograph of Arothron meleagris © John E. Randall.  Used with permission.
Date Posted:  04/10/03 nas
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