Analysis of Electrocardiograms and Behavior in Mice from Pregnancy to Lactation Period
Summary
A simultaneous recording of autonomic activity and detailed maternal behavior of mother mice from pregnancy to lactation was achieved using a telemetry system. This method helps to understand the dynamics of the physiological and behavioral characteristics in mothers from pregnancy to weaning.
Abstract
Changes in the mother-offspring relationship are presumably accompanied by dynamic changes in the autonomic nervous system. Although temporal measurements of autonomic activity have been performed in human mothers and infants, the analysis of long-term changes remains unexplored. Mouse mothers can form social bonds with their pups and have a short period of pregnancy and lactation, which makes them useful for the examination of physiological changes from pregnancy to pup-rearing. Therefore, a telemetry system was used for several weeks to measure the changes in the autonomic nervous system and the behavior of mouse mothers. The current results showed that an electrocardiogram (ECG) could be stably recorded regardless of the movements of mothers and parturition. ECG analysis showed that the heart rate gradually decreased from pregnancy to lactation, and sympathetic activity sharply increased as the pups developed. Furthermore, the simultaneous recording of behavior and ECG in the home cage enabled us to understand the behavior-dependent influences on the ECG, thereby revealing the characteristics of autonomic nervous activity during each behavior. Thus, the present experimental method helps to understand how the physiological characteristics of mothers change from pregnancy through pup rearing, supporting the healthy development of pups.
Introduction
The mother-offspring relationship is unique among the relationships established by various animal species owing to its great impact on the future of the offspring1. In humans, the development and internal/external behaviors of children are influenced by parenting style as well as the extent of abuse and neglect2,3. Similarly, in rodents, the quality of maternal behavior has a significant impact on pup development and behavior4,5,6. Therefore, detailed tracking and examination of the nurturing behaviors of mothers can provide insights into the mechanisms of individual differences in the development and healthy support of their offspring.
Behavioral and physiological studies have shown that mammalian mothers undergo dynamic behavioral and physiological changes from pregnancy to lactation. When female mammals become pregnant, the secretion of estrogen and other hormones changes influence maternal behavior7. As the offspring grows and the frequency of lactation decreases, hormone secretion dynamically changes toward the pre-pregnant state, putting an end to the expression of maternal behavior8,9,10. These findings suggest that the interaction between the endocrine system, maternal behavior, and offspring development plays an important role in the changes that mammalian mothers experience during pregnancy and lactation.
Behavioral and physiological changes in mammalian mothers from pregnancy to lactation are closely related not only to the endocrine system but also to the autonomic nervous system11,12. Human studies suggest that mother-infant contact induces changes in the autonomic nervous system of both mothers and infants13. Several studies have measured the electrocardiogram (ECG) and heart rate variability in human mothers and infants, showing that each behavior alters the heart rate and RR interval of the others14,15,16. However, it is not clear how the three factors-autonomic nervous system, maternal behavior, and offspring development-interact with each other from pregnancy to lactation. Moreover, it is difficult to monitor these interactions in humans over a long period of time because the human lactation period is approximately two years.
Rodents are often used instead of humans in such studies. The autonomic nervous system of rodents has been measured under anesthesia or when isolated from pups to prevent unstable recording and damage to the measuring device; hence, the measurement is temporal under behaviorally restricted situations17,18,19. It is essential to observe the autonomic nervous system in an environment where rodents can move freely and communicate with others because mother-pup interactions can alter the behavior and physiology of mothers8,9,10,15.
This experimental method was developed to allow free movement of the mother. In this method, an ECG telemeter was attached subcutaneously to a pregnant mother to prevent damage to the device and allow stable long-term ECG recording from pregnancy to lactation. Mouse mothers can exhibit general behaviors (self-grooming, food intake, etc.) and usual maternal behavior in their home cage; hence, each behavior and ECGs can be observed and compared easily in the same mouse. A drive recorder recorded the mouse's behavior for 24 h over a period of four weeks. This experimental protocol allowed us to track the dynamic changes in autonomic activity and behavior from pregnancy to the mothering period.
Protocol
Representative Results
Discussion
In this method, wherein the telemeter was implanted into pregnant mice, the ECG could be continuously tracked in the same mouse from pregnancy to lactation. The mouse exhibited ethograms that included movement, indicating wakefulness during all analysis periods (23:32-23:42) from GD 17 to PD 21. Additionally, the present results showed that the heart rate gradually decreased from pregnancy to lactation. This decrease is considered to be due to the normalization of the heart rate, as several studies have shown that heart …
Declarações
The authors have nothing to disclose.
Acknowledgements
This study was supported by JSPS KAKENHI (Grant Numbers JP 21H04981 and 30974521) and the Center for Diversity, Equity & Inclusion, Azabu University.
Materials
| 24-h repeating timer | Panasonic | WH3311BP | |
| Anesthesia box | Natsume Seisakusho Co | KN-1010 | W110×D110×H110mm |
| Anesthesia mask | Natsume Seisakusho Co | KN-1019-1 | |
| Anesthesic machine | Natsume Seisakusho Co | KN-1071-E | |
| C57BL6/J mice | Clea Japan, Inc | Pregnancy mouse at 14 day | |
| Clip light | Yazawa corporation | CLX60X02WH | |
| Configurator System | Adinstuments | TR190 | |
| drive recorder | Transcend | TS-DP250A-32G | |
| Food holder | Clea Japan, Inc | CL-2802 | |
| Isoflurane | FujiFilM | 099-06571 | |
| LabChart Pro V8 | Adinstuments | MLU260/8 | |
| LabChart8 | Adinstuments | MLS060/8 | |
| Mouse Biopotential Telemeter | Adinstuments | MT10B | |
| Needle 18 G 1 1/2 | Terumo | NN-1838R | |
| Panel heater | SANKO | 4976285145407 | |
| PowerLab 4/26 | Adinstuments | PL2604 | |
| Recordable computer | Mouse computer | mouse K7-H | |
| red light bulb | ELPA | LDG1R-G-GWP254 | |
| Rubber mask | Natsume Seisakusho Co | KN-1019-M | |
| SD card (256GB) | Transcend | TS256GUSD350V | It can record approximately 24 h |
| Silk suture 0.31 mm | Natsume Seisakusho Co | DMS2101 | |
| Suture needle 13 mm | Natsume Seisakusho Co | C-24-540-NO.0 | |
| Suture needle 7 mm | Natsume Seisakusho Co | C-24-540-NO.0000 | |
| tBase | Adinstuments | MT110 |
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