Analysis of Electrocardiograms and Behavior in Mice from Pregnancy to Lactation Period

Our research focus on the physiological changes in mothers from pregnancy to lactation, and how they impact maternal behavior and the development of her pups. We seek to determine how a mother's physiology adapts to support the healthy growth and development of her offspring. Implementing territories in pregnant mouse enable to continuous ECG tracking from pregnancy to lactation, providing an insight into automatic activity during a reproductive event. This method results in more natural behavior observations and simultaneous ECG recordings offer a clear understanding of changing maternal physiology.

Our research has improved surgery methods and mouse observation methods, making it possible to monitor mice for a long time.

Our research helps us understand how mother's physical response during pregnancy and lactation in terms of automatic activity. Our research could lead to improved maternal care and support for pup development, and may inspire new approaches to study reproduction, not only in animals, but also in humans.

In the future, we plan to investigate where the mothers who have committed infanticide or neglect in the natural environment have differences in autonomic activity and maternal behavior from pregnancy to lactation compared to normal mothers. We believe this protocol will also be helpful in understanding the factors behind neglect and infanticide.

[Instructor] To begin, place the anesthetized mouse in a prone position on the panel heater. Using scissors, make a skin incision between the ears, then insert forceps into the incision to separate the skin and muscle around the neck and ventral side, creating a space for telemeter placement. Now insert the telemeter through the incision between the ears and place it in the created space on the ventral side. Use forceps to roll and bundle the positive and negative leads of the telemeter and place these leads in the neck space. To close the incision, use a 13 millimeter needle and a 20 centimeter suture. Next, place the mouse in a supine position. Using scissors, make a small incision around the clavicle skin and separate the muscles from the neck skin. With forceps, extract the positive and negative leads from the back of the neck. Then gently separate the salivary glands to expose the V-shaped appearance of the sternocleidomastoid muscle. Afterwards, adjust the length of the negative lead to reach the sternocleidomastoid muscle near the clavicle, and carefully remove the lead tubing from the negative lead. Now pass the stitching needle with a 10 centimeter suture through the V-shaped bend of the sternocleidomastoid muscle to create a loop. Thread the stainless steel electrode from the negative lead through this loop and position it under the muscle near the clavicle. Lightly tie the loop to secure the stainless steel electrode without damaging the sternocleidomastoid muscle. Further, position a second suture on the cranial side of the muscle, and tie it around the tubing of the negative lead to secure it. Afterwards, section around the xiphoid process and carefully separate the skin from the muscle between the xiphoid process to the clavicle. Then extend the positive lead to reach the xiphoid process. Remove the lead tubing from the positive lead, ensuring the coiled stainless steel electrode inside is stretched using fine tweezers. Next, use an 18 gauge needle to create a tunnel under the muscle around the xiphoid process. Then place the stainless steel electrode in a needle and pass it through the muscle around the xiphoid process. After the needle is removed, use a stitching needle with a 10 centimeter suture to lightly suture the coiled stainless steel electrode to the muscle around the xiphoid process. To further secure the positive lead, position a second suture on the cranial side of the xiphoid process and tie it around the tubing of the positive lead. Using a stitching needle with a 20 centimeter suture, close all incisions. After implantation, place the mouse in a clean cage. To start, place the mouse with the telemeter into the cage and position the cage on the T-Base which acts as the receiver for mouse telemetry. Turn on the recordable computer and use the installed data analysis software application to collect electrocardiogram data from the mouse. Then, using the lab chart application on the recordable computer, record the electrocardiogram. To analyze the electrocardiogram data, start LabChart and open the data file for the recording period. Click on the HRV button and adjust the beat detection settings accordingly to analyze heart rate variability. Then click the HRV button and select the Beat Classifier view. Choose all beats on the Beat Classifier view and select the Report View from the HRV button. Copy the data from the Report View and paste it into Excel for further analysis. Electrocardiogram analysis showed that the heart rate decreased gradually while the respiratory rate interval increased gradually from GD 17 to PD 21. The HRV analysis showed that the low to high frequency ratio increased sharply from PD 0 to PD 21.