A Statistical Analysis of the Effect of Mycobacterium vaccae on Rat Behavior and its Correlation to Electrode Placement

By: Amaris Bouchard

The Mycobacterium That Could Treat Anxiety Disorders

Where Panic is Processed

• peri = surrounding
• gray = region of brain with high concentration of neurons and few myelinated axons

The PAG, Pain, and Panic

Research Questions

• Since Mycobacterium vaccae inhibits responses related to PTSD, would it be able to also inhibit behaviors associated with another type of anxiety disorder, such as panic?

​

To investigate if M. vaccae induces a panicolytic-like effect, members of the Chris Lowry lab at CU Boulder used the animal model: electrical stimulation of the dPAG.

​

• If Mycobacterium vaccae inhibits panic-like behavior, will a more medial placement of the electrode, which induces a panic-like behavior, in the rat’s dPAG be associated with a more robust panicolytic-like effect of M. vaccae?

​

How to Measure Panic-like Behavior in Rats

• 10 sec of 20 microamperes (𝝻A)
• 10 sec of rest
• 10 sec of 24 microamps
• 10 sec of rest
• 10 sec of 28 microamps
• 10 sec of rest
• … Continue until rat “escapes”/runs, then repeat two more times using the same current.
• If the rat escapes when exposed to the same current three consecutive times, record microamps reached as rat’s “escape threshold”.

My Hypothesis

If Mycobacterium vaccae is panicolytic, the escape thresholds of rats injected with M. vaccae will have a negative correlation with the distance the electrode from the rat’s dorsal medial periaqueductal gray.

​

What is “Bregma”?

Data for Rats Injected with M. vaccae

Mean Escape Threshold: 127.3333333 Microamperes

​

Mean Distance of Electrode: 0.3888888889 Millimeters

Data for Rats Injected with Borate Buffered Saline

The other six rats either displayed no escape behavior, or died during surgery/of infection.

Mean Escape Threshold: 107 Microamperes

​

Mean Distance of Electrode: 0.2 Millimeters

There was no significant difference between the escape thresholds of both groups.

​

In other words, M. vaccae did not have a panicolytic-like effect.

​

​

Mycobacterium vaccae Injected Rats - Graphs and Analysis

• Coefficient of Determination (How well does the line of best fit account for variation?)

​

r^2 = 0.0006892528

​

Approximately 0% of variation in the escape thresholds recorded is accounted for by the LSRL.

​

​

• Correlation Coefficient (How strong is the correlation?)

​

r = - 0.0262536242

​

Because r is negative, the correlation is negative. Because r is significantly below 0.5, there is a very weak correlation between the distance of the electrode from 0mm in the dorsal medial periaqueductal gray.

Equation of the LSRL:

ŷ= 129.6853104 - 6.047940996x

Borate Buffered Saline Injected Rats - Graphs and Analysis

r^2 = 0.0400911162

Approximately 4% of variation in the escape thresholds recorded is accounted for by the LSRL.

r = 0.2002276609

Because r is positive, the correlation is positive. Because r is below 0.5, there is a weak correlation between the distance of the electrode from 0mm in the dorsal medial periaqueductal gray.

​

Equation of the LSRL:

ŷ= 99 + 40x

Conclusion

Mycobacterium vaccae did not have a panicolytic effect on the rats injected with it.

The correlation between escape threshold and distance of the electrode for both groups of rats were weak/very weak, so it appears that the two variables are not related.

Measurements/observations were subject to human error. Also, the small sample size could have limited my ability to find a correlation between the variables.

In the future, more testing of M. vaccae’s panicolytic effect on symptoms of PTSD, generalized anxiety, and panic should continue, as many other studies have shown promising results. The scientific community have found evidence that M. Vaccae decreases inflammation, an immune system response caused by PTSD and anxiety; thereby decreasing behavior associated with those disorders. Lastly, finding treatments for mental health disorders is vital to the well being of millions!

​

Thank you for your time!

And a special thank you to James Hassell and Paula Yamashita. I couldn’t have done this without you!