Serotonin in the ventral midbrain modulates the cardiovascular system in anesthetized Syrian hamsters (Mesocricetus auratus)

Serotonin (5HT) is a chemical that regulates numerous biological processes across organ systems in the body, including those in the central and cardiovascular systems. However, there is limited information regarding the role of serotonin in heart-brain interactions that may influence cardiovascular disease risk. The present study tested the hypothesis that 5HT in the ventral midbrain, in a brain region called the ventral tegmental area that regulates motivation, social behavior, and stress, modulates heart rate in the Syrian hamster (Mesocricetus auratus). Eight adult hamsters (4 males, 4 females) received 5 microinjections of 200 nl of saline (n=4) and fluoxetine (1 nM) (n=4), a selective serotonin reuptake inhibitor (SSRI), into the ventral midbrain, while under anesthesia and placed on an INDUS Rodent Surgical Monitor to collect cardiovascular data over 2 hours. There was a 24-hr inter-injection interval, and the study was conducted over 5 consecutive days. A repeated measures ANOVA revealed a significant interaction between heart rate (beats per minute, BPM, over time), drug treatment, and biological sex [F(24,96)=1.596, p=0.05]. BPM was generally stable across baseline, drug treatment, and post-treatment phases of the experiment in saline-treated subjects. In contrast, BPM decreased during the post-treatment phase in fluoxetine-treated males, whereas there was minimal change in BPM in fluoxetine-treated females. The ventral midbrain is known for its role in reward, drug addiction, learning, social behavior, and stress, and our findings indicate that 5HT in this brain region may also be involved in regulating the cardiovascular system. the biological mechanisms that underlie acute cardiovascular events, including myocardial infarctions, that are linked to psychosocial factors have not been fully characterized, and our preliminary findings provide a potential neural substrate (the midbrain) that may serve as a heart-brain interaction node. Moreover, given that many people are burdened with neuropsychiatric conditions that are associated with increased cardiovascular disease risk and some are prescribed SSRIs, our findings have translational potential and may lead to the development of interventions for psychosocial stress-associated cardiovascular disease. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.