Effects of vagotomy on immune response
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Effects of vagotomy on immune response
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[post_date] => 2024-12-23 18:07:43
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[post_content] => Practice Passage (Question 1-6)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
The vagus nerve is part of the parasympathetic division of the autonomic nervous system and influences many biological processes, such as digestion, heart rate, and immune function.
Scientists performed an experiment to explore the relationship between vagal activity and rats’ immune response to lipopolysaccharide (LPS), an antigen found in the outer membrane of Gram-negative bacteria. LPS normally elicits a strong immune response in animals, because the O-antigen is a target for recognition by host antibodies.
For this experiment, 40 rats were collected and separated into two groups. The vagal trunks were removed from the rats in one group (vagotomy, Vx). The other group was subjected to a surgery in which the rats’ vagus nerve was exposed but not cut (sham). Both groups were given one month to recover from their surgery, and the weight of both groups was measured.
After weighing, rats from both groups were given injections of either saline or LPS. Two hours after injection, the rats were decapitated, and concentrations of interleukin-1β (IL-1β) mRNA were measured in the hippocampus, hypothalamus, and pituitary. Neither group had significant levels of IL-1β mRNA in the pituitary. Levels of IL-1β mRNA in the hippocampus and hypothalamus are shown in Figure 1.
Figure 1 Effects of vagotomy on interleukin concentrations in the hippocampus (A) or hypothalamus (A)
The stomachs of the rats were also removed and weighed. This information, along with the original body weights after surgery, is shown in Table 1.
Table 1 Body weight and stomach weight of vagotomized and sham-operated rats.
Source: Bluthe, R. Combe, C. Dantzer, R. Keith, K. Kent, S. Laye, S. Medina, C. Parnet, P. (1995).
[post_title] => Effects of vagotomy on immune response
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[quiz_unique_key] => 602779517
[question] => Why did the researchers measure IL-1β levels in mice?
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[answer] => 3
[description] => Reason for Correct Answer:
This question tests your understanding of why and how this experiment was performed.
According to Paragraph 1, researchers “performed an experiment to explore the relationship between vagal activity and rats’ immune response to lipopolysaccharide (LPS).”
Researchers measured immune responses in mice that underwent vagotomy, versus mice who did not.
In these mice, they used IL-1β levels to quantify immune response to one particular antigen, LPS, in both of these groups. The primary function of interleukins is to modulate cellular processes during inflammatory and immune responses, and IL-1β is evidently involved in the immune response of mice to LPS, or else its levels would not be helpful in assessing this response and comparing groups of mice.
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[each_answer] => A. They served as a marker for immune response in the hypothalamus specifically.
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[each_answer] => B. They allowed researchers to determine immune responses to vagotomy.
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[2] => Array
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[each_answer] => C. They allowed researchers to quantify immune responses to LPS.
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[each_answer] => D. IL-1β increases the immunogenicity of LPS in rats.
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[1] => Array
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[quiz_unique_key] => 1403770772
[question] => What is a plausible reason for having one group undergo sham surgery?
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[answer] => 1
[description] => Reason for Correct Answer:
A sham surgery is a surgical intervention in which the experimental step is omitted.
Putting the rats to sleep, or anesthetizing them, and actually operating on them is part of the sham surgery. Having a sham-operated group would account for any unexpected effects of these activities.
In other words, the purpose of a sham surgery is to serve as a control to account for the effects of surgery, ensuring that differences between groups are due to vagus nerve removal and not the effects of surgery itself.
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[answers] => Array
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[0] => Array
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[each_answer] => A. To account for effects of surgery that may affect the physiological results
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[each_answer] => B. To provide more insight into how vagotomy affects immune response
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[each_answer] => C. To evaluate the hypothesis that surgery also affects IL-1β levels
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[each_answer] => D. To evaluate the baseline variation in IL-1β levels
)
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[2] => Array
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[quiz_unique_key] => 1403770772
[question] => Which research finding would strengthen the data presented in this research?
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[answer] => 2
[description] => Reason for Correct Answer:
The data demonstrates that vagotomy results in a decreased immune response, since interleukin responses to LPS decreased in these mice. This means that vagus nerve activity is important for the immune response.
White blood cells are cells of the immune system.
If stimulating the vagus nerve increases white blood cell count, that would be additional confirmation that the vagus nerve contributes to immune system responses.
)
[answers] => Array
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[0] => Array
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[each_answer] => A. Increased concentrations of IL-1β cause a decrease in vagus nerve activity.
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[1] => Array
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[each_answer] => B. Stimulation of the vagus nerve of healthy rats results in an increased white blood cell count.
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[2] => Array
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[each_answer] => C. Digestive hormones are released in response to a vagotomy.
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[3] => Array
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[each_answer] => D. Hyperactivity of the vagus nerve is linked to obesity in young adults.
)
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[3] => Array
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[quiz_unique_key] => 1403770772
[question] => What is another potential result of vagotomy in a rat?
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[answer] => 4
[description] => Reason for Correct Answer:
The passage states that the vagus nerve is anatomically classified as part of the parasympathetic system and has effects on digestion, heart rate, and immune function.
The parasympathetic system is involved in conserving energy and resting the body. It works antagonistically with the sympathetic nervous system. Here are some functions of both:
https://upload.wikimedia.org/wikipedia/commons/c/c5/The_Autonomic_Nervous_System.jpg
Vagotomy would remove or lessen effects of the parasympathetic nervous system on the heart and digestive system and enhance the effects of the sympathetic nervous system.
By reducing parasympathetic input to the heart, vagotomy would cause increased heart rate.
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[each_answer] => A. Stimulation of digestion
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[each_answer] => B. Pupillary constriction
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[each_answer] => C. Bronchial constriction
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[each_answer] => D. Increased heart rate
)
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[quiz_unique_key] => 1403770772
[question] => Which of the following is a plausible explanation for the results shown in Table 1?
[value] => Array
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[answer] => 3
[description] => Reason for Correct Answer:
First, you want to look at what Table 1 actually shows. It seems to show that vagotomy actually INCREASES stomach weight.
We know that vagotomy causes loss of parasympathetic innervation, so you need to choose an answer that either pairs loss of parasympathetic innervation with greater stomach weight or intact parasympathetic innervation with lower stomach weight. This means you can eliminate Choices A and D.
We can also eliminate Choice B, because we should know that parasympathetic activity increases digestive activity.
The only answer choice that makes sense is therefore Choice C, which says that the loss of parasympathetic activity caused by the vagotomy may have resulted in decreased stomach emptying leading to bloating and increased stomach weight.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Intact parasympathetic innervation caused increased gastric muscle tone and weight, leading to increased stomach weight.
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[each_answer] => B. Intact parasympathetic innervation lessened digestive activity and tone in the stomach, leading to decreased stomach weight.
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[each_answer] => C. Loss of parasympathetic innervation inhibited gastric emptying, resulting in bloating and increased stomach weight.
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[each_answer] => D. Loss of parasympathetic innervation inhibited digestive activity and tone in the stomach, leading to decreased stomach weight.
)
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[quiz_unique_key] => 1325138223
[question] => What technique could the researchers use to measure the levels of IL-1β mRNA?
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[answer] => 1
[description] => Reason for Correct Answer:
mRNA is a nucleic acid. Western blots measure the levels of proteins.
Southern and western blots are used to detect DNA and protein molecules, respectively.
Mass spectrometry measures the weights of molecules. (Although it can also be used to measure the levels of proteins, it is not useful for the measurement of levels of nucleic acids, which often have very similar weights and are present at low concentrations).
The polymerase chain reaction (PCR) is a method of increasing the concentration of specific DNA sequences. This can be done quantitatively, which allows for the levels of certain DNA sequences to be measured.
Reverse transcription is the process of converting RNA to DNA. When combined with the polymerase chain reaction (RT-PCR), it allows for the levels of certain RNAs to be measured.
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[each_answer] => A. RT-PCR
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[each_answer] => B. Southern blot
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[each_answer] => C. Western blot
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[each_answer] => D. Mass spectrometry
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[554599|1] => C
[554599|2] => A
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[554599|5] => C
[554599|6] => A
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Figure 1
