Re: Why does chloroform increase the heart rate of Daphnia?

Hello Cole! Thank you for your question.

You asked: “Why does chloroform increase the heart rate of Daphnia? I'm working on a lab about the effects of different drugs on the heart rate of Daphnia, and although I have searched for information regarding chloroform and the heart rate of Daphnia, I can't seem to find anything indicating whether or not my results were correct.”

Chloroform, also known as trichloromethane (CHCl3), is a gas that causes anesthesia when inhaled. Dr. John Snow used chloroform on Queen Victoria back in 1853 to ease the pain of childbirth. Chloroform is not used anymore due to its carcinogenic properties on the liver and kidney. The evolution of Anesthesiology has led to many more forms of inhalation anesthetics which are much safer on the patient and the doctor administrating them!

So, why are you seeing an increased heart rate in your Daphnia?

One idea: Chloroform depresses the central nervous system (CNS). Anesthesiologists classify the stages of general anesthesia into four steps:

1. Stage of voluntary movement. People and animals can become excited, with increases in heart rate. Perhaps your Daphnia are in this stage...

2. Stage of delirium. This is an exaggerated phase of Stage 1, but without conscious movements. Patients and animals still have increased heart rates and may hyperventilate and thrash unconsciously. Your Daphnia may also be in this stage...

3. Plane of surgical anesthesia. At this point, reflexes depress, breathing becomes steady, the heart rate comes down, and the muscles relax --- adequate relaxation and analgesia for surgical procedures to be performed.

4. At this stage, the CNS is very depressed --- breathing stops, blood pressure drops, and the patient will die unless resuscitative measures are taken.

But, if your Daphnia are sufficiently anesthetized with chloroform and you are pretty sure that they are not in stage 1 or 2 as described above, what else could be going on?

Another idea: Chloroform can affect the cardiovascular system: 1. Depresses the ability of the heart to contract and pump blood 2. Can trigger arrhythmias (irregular heart beats)

Since chloroform is a depressant, you might think it would automatically result in a slower heart rate. This is not always the case, though. There are other things that chloroform does to the rest of the body which then results in an altered heart rate:

Depressing the CNS means that neuronal signals to the heart are reduced. The heart does not beat as strongly and the heart rate decreases. This results in a decrease in cardiac output, and less blood pumped out by the heart per beat leads to a lower blood pressure. This is a problem, because the rest of the body is expecting to receive that original blood volume for oxygenation. What does the heart do in order to provide the body with its standard volume of blood during a period of low pressures? It simply beats faster. This is a reflexive response, called Reflex Tachycardia (“tachycardia” simply means a fast heart rate, around 100-180 beats per min. for humans), which is triggered by a complex network of baroreceptors in the body that sense pressure variations.

So, chloroform could result in an increased heart rate this way, but it is a reflexive response due to a decrease in blood pressure. Of course, this is all assuming Daphnia have cardiovascular systems and responses similar to humans...

I was also reading up on the chemical properties of chloroform and supposedly it is a strong irritant, causing sores on the skin upon contact. If these properties hold true when chloroform is dissolved in water (if that is how you’re administering it to your Daphnia), then you may be seeing increased heart rates due to a stress response by their environment if their little bodies are irritated by the chloroform. :( Please always study your Daphnia with the utmost kindness and respect.

Hope these ideas helped!

Sincerely,

G. Monreal