For children the holidays are filled with joy and fun, but as we age, this time often demands more of us. The pressures of gift shopping, hosting family and friends, attending parties, cooking, and cleaning can lead to feelings of anxiety and depression.1 Some find comfort spending time with loved ones, but for others this season awakens a sense of loneliness. In addition, many people experience seasonal affective disorder in the winter as we hibernate in our homes, lacking mood boosting vitamin D from sunlight. The ability to manage stress and feelings of depression varies from person to person. Some experience these feelings at certain times of the year, while others live with them every day.
The major challenges in studying affective disorders, such as anxiety and depression, include efficient and timely disease diagnosis and the development of more effective pharmacological and non-pharmacological treatments. As each case is unique, treatment often involves a delicate balance of multiple medications and therapy. Affective disorders can also have physical consequences which may require treatment including, but not limited to, cardiovascular disease, obesity, digestive issues, and sleep disturbances.4
To better understand the mechanisms behind affective disorders and search for new treatments, researchers often look at physiologic changes related to common biomarkers such as heart rate variability, sleep, and thermoregulation. DSI offers solutions to measure the key physiologic endpoints within these biomarkers including electrocardiogram (ECG), blood pressure, electroencephalogram (EEG), electromyogram (EMG), electrooculogram (EOG), and temperature.
The following are 4 recent publications from studies looking at stress and affective disorders in animal models using DSI technology.
Essential Role of Ovarian Hormones in Susceptibility to the Consequences of Witnessing Social Defeat in Female Rats
As women have a greater risk of developing depression and comorbid disorders such as cardiovascular disease, especially between puberty and menopause, this study looked to understand the role of hormones in the development of depression. A female rat model of psychosocial witness stress was used to look at hormonal stress responses. The research team used DSI’s PhysioTel™ HD-S11 telemetry implant to measure mean arterial pressure and heart rate. From these measurements they also calculated heart rate variability. The results indicate ovarian hormones are key in the behavioral, inflammatory, and cardiovascular responses to stress in females.5
REM sleep: unique associations with behavior, corticosterone regulation and apoptotic pathways in chronic stress in mice
Although stress is known to cause sleep disturbances, little is known about whether REM (rapid eye movement) or non-REM sleep are more affected or how changes in sleep correlate with stress hormone or behavioral and transcriptomic responses. This study indicated REM sleep is most vulnerable to stress. It also showed these changes correlate with diminished regulation of corticosterone, a hormone which plays a large role in energy regulation as well as immune and stress responses. To reach this conclusion, the research team exposed mice to unpredictable chronic mild stress and studied their sleep using DSI’s PhysioTel™ F20-EET telemetry implant to look at EEG and EMG.6
Physical versus psychological social stress in male rats reveals distinct cardiovascular, inflammatory and behavioral consequences
This study aimed to understand how stress responses differ in relation to physical and psychosocial stress. To accomplish this, the research team exposed rats to either social defeat stress with an intruder or had them witness another male rat being defeated. To measure stress responses, the team used DSI’s HD-S11-F0 and HD-S11-F2 implants to measure ECG and blood pressure in pair housed animals. Analysis was completed with DSI’s Ponemah™ software. The research team saw almost identical increases in blood pressure and heart rate between the two experiences. Despite these similarities, there were differences in the long-term consequences of the stressful events. The research indicated those who experience physical stress may be more likely to develop inflammatory disorders, where those who experience psychological stress are more likely to have long-term cardiovascular dysfunction.7
Differential mGluR5 expression in response to the same stress causes individually adapted hippocampal network activity
As mentioned, some individuals are very vulnerable to stress and can develop psychiatric disorders, while other are able to manage stress. This study aimed to better understand why these variations in vulnerability exist. In particular, they were looking for novel pathways and molecular targets in the brain for new treatments to help patients maintain neurological homeostasis. They found individual differences in responses to stress lead to distinct changes in the methylation of the mGluR5 locus, which, in turn, causes changes in hippocampal mGluR5 mRNA expression. The resulting high and low levels of mGluR5 expression alter theta EEG activity in the hippocampus, which is likely important in stress adaptation. The team measured EEG activity of the rats with DSI’s PhysioTel™ ETA-F20 telemetry implant.8
DSI offers a variety of solutions to measure the physiologic endpoints of interest for each of the three common biomarkers of affective disorders in species ranging in size from mouse to primate.
Heart rate variability (HRV) is the physiologic phenomenon of variation in the time interval between heartbeats and indicates autonomic nervous system dysregulation. HRV is typically derived from the R-R intervals of ECG signals or inter-beat-intervals from blood pressure signals. DSI offers several technologies to measure ECG and blood pressure signals including implantable telemetry, external telemetry, and hardwired options.
Sleep is determined by physiologic changes in EEG together with EMG (muscle movement) and EOG (eye movement). DSI solutions for measuring these biopotentials include telemetry and hardwired options. Within the line of PhysioTel™ implantable telemetry, researchers have the option to measure biopotentials, pressure, and temperature within one device. Paired housing options are also available for studies looking to understand stressful interactions or coping mechanisms.
Changes in body temperature and temperature regulation are common responses to stress. Researchers can measure temperature with DSI’s implantable telemetry. Researchers also have the flexibility to measure temperature simultaneously with biopotentials and blood pressure within one telemetry implant.
Data Collection and Analysis
DSI also offers software solutions for collecting and analyzing data in affective disorder research. Researchers can use Ponemah™ to collect, analyze, and summarize data from a wide range of physiologic endpoints and applications. NeuroScore™ allows neuroscience researchers to quickly analyze large, continuous data sets common to sleep and seizure studies.
Help is Available
Over 300 million people suffer from depression globally, and someone dies by suicide every 40 seconds.2,9 If you experience symptoms of depression or other mood disorders, don’t be afraid to ask for help! Whether it’s simply planning ahead for the holiday season, talking with a friend or family member, learning yoga or meditation, or seeking professional assistance through therapy and medication, there are ways of coping with these feelings. If you notice a friend or family member showing symptoms of an affective disorder, let them know they can talk to you, refrain from judgement, and encourage them to seek professional assistance if necessary.
To learn more about DSI solutions for affective disorders, download our free neuroscience whitepaper.
1Mayo Clinic. (2017). “Stress, depression and the holidays: Tips for coping”. https://www.mayoclinic.org/healthy-lifestyle/stress-management/in-depth/stress/art-20047544
2World Health Organization. (2018). “Depression”. http://www.who.int/news-room/fact-sheets/detail/depression
3NIMH. (2018). “Depression”. https://www.nimh.nih.gov/health/topics/depression/index.shtml
4WebMD. (2018). “Depression: Recognizing the Physical Signs”. https://www.webmd.com/depression/physical-symptoms
5Finnell JE, Muniza BL, Padi AR, Lombarda CM, Moffitt CM, Wood CS, Wilson LB, Reagan LP, Wilson MA, Wood SK. (2018). “Essential Role of Ovarian Hormones in Susceptibility to the Consequences of Witnessing Social Defeat in Female Rats”. Biological Psychiatry, 84(5), 372-382. https://doi.org/10.1016/j.biopsych.2018.01.013
6Nollet M, Hicks H, McCarthy AP, Wu H, Möller-Levet CS, Laing EE, Malki K, Lawless N, Wafford KA, Dijk DJ, Winsky-Sommerer R. (2018). “REM sleep: unique associations with behavior, corticosterone regulation and apoptotic pathways in chronic stress in mice”. bioRxiv. https://www.biorxiv.org/content/biorxiv/early/2018/11/07/460600.full.pdf
7Finnell JE, Lombard CM, Padi AR, Moffitt CM, Wilson LB, Wood CS, Wood SK. (2017). “Physical versus psychological social stress in male rats reveals distinct cardiovascular, inflammatory and behavioral consequences”. PLoS ONE 12(2): e0172868. https://doi.org/10.1371/journal.pone.0172868
8Yim YS, Han W, Seo J, Kim CH, Kim DG. (2018). “Differential mGluR5 expression in response to the same stress causes individually adapted hippocampal network activity”. Biochemical and Biophysical Research Communications, 495(1), 1305-1311. https://doi.org/10.1016/j.bbrc.2017.11.172
9World Health Organization. (2018). “Suicide data”. http://www.who.int/mental_health/prevention/suicide/suicideprevent/en/