May 14, 2018
Written by: Rebecca Somach
Mother’s Day and Father’s Day give us the opportunity to thank parents for all of their hard work in raising their children. Over brunch, people gather together to recognize and celebrate this hard work, as well as the special bond between children and their parents. While we are all familiar with parenting, you might not have thought of it as a ‘behavior’ that can be studied. Scientists, however, are very interested in parenting, since it is a behavior that is conserved among many species and takes an enormous amount of time and effort. For animals that need to constantly forage for food, protect themselves from enemies, and find shelter, having an almost useless baby that just wants to eat, sleep, and cry is not the most optimal way to survive. One wrong cry from a baby and a predator could spot an otherwise hidden family. Parenting animals will not only take care of their young, but will even sacrifice themselves to protect them. If we look at the big picture, we can recognize that these animals are protecting their young to pass on their genetic material. However, the individual animals don’t recognize this fact. There must be something intrinsic that drives the almost paradoxical parenting behavior we see in so many animals. But how do researchers study the neuroscience of parenting?
For many diseases and behaviors, scientists will use animals in controlled experiments in a laboratory, and this is also true of parenting studies. When scientists observe mother mice in a lab, they will predictably perform the same behaviors, such as grooming their babies and keeping them in one place in a nest1. If one pup is left out of the nest, the pup will cry for its mother. If that happens, the mother mouse will retrieve the pup and bring it back into the nest. Grooming and retrieval behaviors are some of the ways scientists can measure how well a mouse parents. These behavioral studies aren’t all warm and fuzzy; a significant part of studying these behaviors is also observing aggression. If a male mouse encounters pups that aren’t his, he will actually attack them. However, once a male mouse has a litter of his own with a female, a switch happens and the male mouse will begin to act as a model parent and retrieve his pups. Scientists are interested in this switch in behavior and the neural circuits involved in parenting behavior as a whole.
There are many different neurons and hormones that have been associated with parenting behaviors, but in 2014, a group of scientists from Dr. Catherine Dulac’s lab identified a particular group of neurons that have a profound effect on parenting behavior2. To identify these neurons, this group examined which regions of the brain were activated by parenting behaviors as opposed to other behaviors, such as interacting with new bedding materials in their cages. When compared to these control animals, the scientists found an increase in activity in a group of cells in an area called the hypothalamus after parenting behaviors. The hypothalamus is a brain region with many different parts and is usually associated with making hormones, controlling your body temperature and blood pressure, and determining if you are hungry or thirsty. The scientists found that neurons in a region of the hypothalamus called the Medial Preoptic Area, or MPOA, were active when the mice were parenting (Figure 1). Even more specifically, they found that these parenting-activated neurons express a protein called galanin, which allowed the researchers to target these specific neurons in their next experiments.
How did these scientists know that the galanin-expressing MPOA neurons are the ones that actually cause the parenting behaviors, and aren’t just more active by chance? By destroying only the galanin-expressing MPOA neurons in female mice, they were able to observe how parenting behaviors changed after these neurons were gone. If these neurons are actually responsible for producing parenting behaviors, the mice should be much worse at parenting once these neurons are gone. In fact, this is exactly what they saw. The female mice did not do the things that they should have been doing as mothers: they showed reduced levels of building nests, grooming and retrieving their pups (Figure 2).
The scientists were also able to do the opposite. If these MPOA neurons are responsible for parenting, then activating them should produce better parenting behaviors. The scientists specifically activated the galanin neurons in male mice that were not parents yet. These mice would normally attack pups since they aren’t parents themselves. When the galanin neurons were activated, the male mice would instead groom pups (Figure 2). Even though these pups must be from another male mouse, the activation of these neurons made it much less likely that they would attack these stranger pups. Together, these experiments tell us that the activation of galanin neurons is an essential part of parenting behavior in these mice. Without these neurons, females don’t act as parents and by activating these neurons males are much less aggressive towards pups.
These studies just the beginning for exploring this neural behavior and understanding something that is so essential for many different species on the planet. When you are out and celebrating all parents in the next few weeks, it is definitely important to acknowledge how hard they work, but it can also be a fun opportunity to think about how essential neurobiology is in our everyday lives.
References:
- Kohl, Johannes et al. “The neurobiology of parenting: A neural circuit perspective.” BioEssays : news and reviews in molecular, cellular and developmental biology 39,1 (2016): 1-11. doi:10.1002/bies.201600159
- Wu, Zheng et al. “Galanin neurons in the medial preoptic area govern parental behaviour.” Nature 509,7500 (2014): 325-30. doi:10.1038/nature13307
Image References:
Cover Image from Pixabay https://pixabay.com/photos/baby-parents-father-child-hand-1321548/
Figures 1 and 2 created with BioRender
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