A little bit about rats
Rats are pretty cool. Yet, they are typically seen as pesky sewer-dwelling nuisances that infest buildings with the intention of eating all the food inside and leaving their droppings as a reminder of their presence. This gives them a pretty bad rap, especially when one considers how important they have been in the advancement of many fields of science. Rats have been used as a model organism in labs for decades, and studies conducted on them have led to numerous scientific breakthroughs; the knowledge gained from rat studies has in turn led to a much better understanding of everything from psychological disorders to advanced cancer treatments.
I therefore feel quite privileged to be able to work in a lab that uses a rat model for its studies. Here in Dr. Siviy’s lab, the focus of our research is differences in play behavior between specific strains of rats. One of the reasons why the rat is such a useful model organism is that many of its behaviors can be translated to humans, including play behaviors. While it might sound odd, juvenile rats, much like human children, love to have bouts of rough-and-tumble social play. Rats and humans may go about this play in slightly different manners, but the end goal of the play is still the same: social and cognitive development. Social play can help an individual become better acquainted with other individuals of their species, help develop social skills, help develop emotion-processing skills, and teach an individual important survival skills for the environment they live in. The absence of social play during critical periods of development could therefore lead to deficits in such skills, which in turn makes individuals less fit to live in their environment. As such, it is important to develop a better understanding of the neurological, physiological, and genetic factors behind social play such that deficits in play can be addressed effectively.
Much of our research focuses on a particular inbred strain of rat called the Fischer 344, or F344, rat. F344 rats were originally bred to look at things like inflammation and immune responses, but in subsequent years have been found to have other unique traits, such as heightened anxiety. In addition to anxiety, however, the F344 rats have also been found to consistently play less with other rats. This makes them a perfect subject for our research, as we hope to tease apart the reasons for why these rats do not play as much as their outbred counterparts (essentially what would be considered “normal” or control rats). How do we know they play less you may ask? Well, we record F344 rats playing with other rats and watch back the footage to look for specific behaviors associated with play: chasing, boxing, pouncing, and pinning. These are all hallmark characteristics of juvenile rats having a good old romp around the examination box. Most juvenile rats are always down for a bout of play, but F344 rats consistently exhibited less behaviors associated with play when in a social situation. As mentioned, our lab’s overarching goal is to determine why this is the case. Do the F344 rats have irregular brain chemistry? Is nature vs. nurture an important aspect in this occurrence? Do the F344 rats simply not have enough energy to bother with play? Are their brains wired differently? Through various finished and ongoing experiments, our lab has worked to answer some of these questions.
The project I’m currently working on is looking into the possibility of differences in oxytocin expression in the hypothalamus of F344 rats. Oxytocin (OT) is a neuropeptide that has gained a fair deal of popularity in the scientific community over the past couple of decades, largely because of its connections to the formation of trust and love between humans (it’s even started to just be called the love hormone). OT is produced in the hypothalamus and acts on many different parts of the brain. Trust and bonding are an important part of social play, so it seems logical that differences in OT expression could lead to differences in play behavior. Thus, the end goal of this project is to see if F344 rats have altered OT expression (less OT producing cells) in the hypothalamus.
Back in 2014, past lab-mates Lana McDowell, Sam Eck, and Jenn Soroka did behavioral testing on F344 rats that were raised by either F344 mothers or cross-fostered by a rat mother from a different strain. This study looked into the concept of “nature vs. nurture” with the F344 rat, to see if its upbringing by an equally as un-playful mother had any difference on its play compared to a playful, control mother. After behavioral testing, these rats had their brains removed, sliced on what is essentially a very expensive and precise deli meat slicer, and stored in a preservation solution. These brain slices are what I’ve been working with for the summer. I performed an immunohistochemistry staining procedure on the brain slices, which involved attaching an OT-specific antibody to any OT present in the brain slices followed by the attachment of a secondary antibody onto the primary antibody. After doing a few other chemical reactions, the brain slices turned brown-ish, with the stained OT-positive cells turning very dark brown. I then prepared microscope slides of the stained brain slices and took pictures of them using a microscope with an attached camera. I then began the arduous process of going back through every single slice on every slide to determine the volume of stained cells in the hypothalamus on each slice and the number of cells in this volume, to get a density of OT-positive cells. I use a program called Image-J (shout out to Bio 111 lab) to do this; the process involves clicking on every stained cell I see on a slice (lots of clicking). The cell densities for the F344 rats will then be compared to the densities from control/more playful rats to see if there is a difference. If there is a difference, then we could conclude that OT may be involved in the process of social play.
This OT project is only one half of my summer, however. The other half will be spent examining the mitochondria of the F344 rat. While social play is important during development, it is not essential to a rat’s survival. Thus, if a rat needs to expend more energy on surviving (defending itself/maintaining homeostasis), it will probably let playing fall to the wayside. As anyone who has taken high school biology would know, the mitochondria is the powerhouse of the cell. Well, F344 rats have been found to be more sensitive to mitochondrial toxins that disrupt or prevent mitochondrial function. This could suggest that F344 rats have irregular mitochondria, which in turn could mean they do not produce as much energy or do not produce it as efficiently. Having less energy could in turn translate into less play. The experiment I will be performing later in the summer, under the guidance of Dr. Brandauer, will examine the mitochondria of the F344 rat to look for any differences from mitochondria of control rats, in an effort to see if this is in fact a reason for why F344 rats play less.
Rats are love, rats are life.