Smeeth et al., 2021: Investigating the Impact of Sex Hormones on Neurogenesis
Written by Liam Ruel
A recent focus of cognitive research has been how hormones impact neurogenesis, the process of neuron generation in the brain (Smeeth et al., 2021). Neurogenesis is a difficult area of study that relies on tissue donated to science and research. Smeeth et al. (2021) investigated neurogenesis in humans by testing the hippocampal cells of medically terminated fetuses. Previous research on neurogenesis has identified the hippocampus as one of the main areas neurogenesis occurs, so hippocampal cells were selected with hopes of observing more activity. The extracted cells were placed under conditions that would foster the growth of the culture, a group of cells kept outside the body, allowing it to stabilize itself and begin reproduction.
Smeeth et al. (2021) focused on the impacts of different levels of sex hormones; prolactin, testosterone, and estrogen, on the process of neurogenesis. The extracted cell line was divided into 12 subcultures, with 4 receiving each hormone treatment (prolactin, testosterone, and estrogen). The researchers assigned each hormone to one of four experimental conditions: 1-day incubation, 2-day incubation; 3-day incubation; 7-day incubation. Researchers watched for changes in two phases of neurogenesis: proliferation and differentiation. Proliferation is the initial stage of neuron development when cells reproduce rapidly, and differentiation is when the cells begin to mature into neurons and form connections in the brain (Smeeth et al., 2021).
The researchers found that prolactin had no observable impact on proliferation, but that it did stimulate the beginning of differentiation (Smeeth et al., 2021). The hormone appeared to increase the rate of neuronal differentiation after 3 days of incubation. However, after 7 days there was a significant decrease in the number of cells in the proliferation phase, indicating that neurogenesis was slowing down. Both estradiol and testosterone increased the production of cells during proliferation but appeared to have no impact on neuron maturation during differentiation.
Overall, the study supports the current research on the topic which indicates that sex hormones influence neurogenesis in humans. This is important because research has indicated that neurogenesis may play a key role in several cognitive processes including forgetting and pattern separation (which allows people to distinguish between incoming stimuli; Oomen, 2014). In forgetting, the introduction of new neurons through neurogenesis is thought to trigger an evaluation of the established neural structure. This evaluation provides an opportunity for the existing neural networks to be changed or removed, resulting in the loss or distortion of memories. Research in the area is promising, but is currently focused on non-human subjects because it uses invasive methods that could cause permanent damage to subjects. Additionally, research on pattern separation suggests that the dentate gyrus, part of the hippocampus, is responsible for distinguishing between similar incoming signals. The hippocampus is known to be an active site of neurogenesis, and it holds a lot of neurons created in adulthood. It is speculated that because neurogenesis creates these adult-born neurons, it also plays an important role in pattern separation. However, the exact role that neurogenesis plays in brain development has yet to be identified. This speculation mainly stems from the theory that neurons become less active as they mature. Thus, the production of neurons in adulthood may be necessary to sustain some brain functions, including activity in the dentate gyrus.
It is important to note that Smeeth et al.’s study has several limitations (2021). Since it was conducted outside the body, this study may not have accurately portrayed the environment in which neurogenesis takes place. It is unclear whether the amount of each hormone used reflects what would naturally occur, and there is a chance that the presence of other chemicals in the body could also influence neurogenesis. If the sex hormones were to interact with other chemicals, or were present in different amounts, the results of the study could have varied greatly. Such a process would make it difficult to accurately identify the role of each hormone. Furthermore, some of the hormones had little impact during the incubation period but may have had a greater effect if exposed to the neurons for a longer time (Smeeth et al., 2021). Overall, while the study provides interesting ideas on neurogenesis in humans, further advancements in technology and scientific knowledge could bring more reliable results.
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References
Oomen, C. A., Bekinschtein, P., Kent, B. A., Saksida, L. M., & Bussey, T. J. (2014). Adult
hippocampal neurogenesis and its role in cognition. WIREs Cognitive Science, 5, 573-587. doi:10.1002/wcs.1304
Smeeth, D. M., Kourouzidou, I., Duarte, R. R., Powell, T. R., & Thuret, S. (2021). Prolactin, Estradiol and Testosterone
differentially impact human Hippocampal neurogenesis in an In Vitro model. Neuroscience, 454, 15-39.
doi:https://doi.org/10.1016/j.neuroscience.2019.12.021
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The blog posts are for informational and educational purposes only. The posts should not be considered as any type of advice (medical, mental health, legal, and/or religious advice). All blog posts have been researched, written, and edited by the undergraduate students and alumni of the Lifespan Cognition Lab. As a teaching and research-based lab, we encourage all lab members to help make knowledge more accessible to all communities through these posts.
