Well, I wanted to write this post back in December, shortly after my trip to Duke ended, but now it’s already February somehow! Better late than never, right?
I am very excited about a new collaboration that I have begun with Dr. Nick Grebe, a postdoc at Duke University in the lab of Dr. Christine Drea. Christine’s lab studies a variety of different species in which the females are the dominant sex, including hyenas, meerkats, and lemurs. They have been able to conduct studies of captive, free-ranging lemurs at the Duke Lemur Center, which is an incredible facility that’s been in operation for over 50 years. They have 15 different species of lemur, as well as two additional prosimian primate species (the pygmy slow loris and the thick-tailed bush baby), which they report is the “largest and most diverse population of lemurs” in the World, outside of their native home of Madagascar.
This lovely, nocturnal lady is housed in a reverse light cycle, so that her active period (in the dark) occurs during the daytime hours when most of her care staff is on duty. This photo was taken in the last minutes of the light period, when she was first waking up to start her “day” as the lights go out.
This facility promotes research on lemurs in a variety of disciplines with a focus on conservation. I was very happy to learn that I would be able to tour the facility during my visit to Duke, and I was overwhelmingly impressed with their facilities, animals, and staffing expertise. The highlight of the tour was being able to see an Aye-Aye (right), which is an endangered, nocturnal species of lemur that I’ve known about for years (thanks, David Attenborough!), but that I never dreamed I would be able to see up close with my own eyes!
There is a high degree of diversity in the behavior, diet, body size, coat color, and other features of lemurs. Of specific interest to Nick was the fact that some species of lemur are monogamous and form long-lasting bonds between adult male-female pairs, and some species are not. So when he came to start his postdoc at Duke, he wanted to investigate the neurobiological and hormonal basis for this difference in mating structure across lemur species.
There is evidence from other species, especially monogamous and non-monogamous voles, that the social hormones oxytocin and vasopressin are two of the primary biological players in this difference. The distribution of oxytocin and vasopressin receptors in the brain parallel the differences in mating strategy; specifically, the brains of the monogamous species have high levels of these receptors in the regions of the brain that underlie the rewarding properties of stimuli, and the brains of non-monogamous voles do not have receptors in these areas. Behavioral work has followed up on these comparative, neuroanatomical findings to show that receptors in these areas are necessary and sufficient for pair-bonding in monogamous prairie voles. This work from nearly 15 years ago has set a precedent for the patterns of oxytocin and vasopressin receptor expression in the brain to inform our understanding of the behavior of a species, especially when investigating monogamy.
This figure (adapted from Lim et al. 2004) shows the dense areas of oxytocin and vasopressin receptor expression in the monogamous prairie vole brain (left column), which are reduced or absent in the brain of the non-monogamous meadow vole (right column).
In my career, I have mapped out the distributions of these receptors in brain tissue from four species of primate: rhesus macaques, titi monkeys, and marmosets. There is a great diversity in the behaviors and receptor distributions across these species, and I have dedicated a large part of my research career in describing these differences in and effort to better understand how they contribute to the diversity of primate behavior. Of course, all brain tissue from monkeys is collected opportunistically, when the animals die of natural causes or need to be euthanized at the recommendation of a veterinarian.
Three coronal blocks of a lemur brain, resting safely on dry ice.
Based on my experience working with this precious tissue and visualizing oxytocin and vasopressin receptors, Nick sought me out to see if I wanted to start a collaboration in order to map out these receptors in brains from monogamous and non-monogamous lemurs. The Duke Lemur Center maintains an extensive brain and tissue bank of postmortem specimens, which are available for research. These tissues are also acquired opportunistically; these animals are NEVER euthanized for research purposes. It’s wonderful that these animals provide researchers with resources for scientific inquiry during their lives AND after they die.
After almost a year of planning, grant writing, and organization, Nick and the Drea lab flew me out to Raleigh-Durham, NC for a week to get this new project off the ground. This project would also not be possible without the generous assistance of Dr. Heather Patisaul at NC State, who provided the lab space and necessary equipment (including the ever precious freezer space!). First, we had to prepare the brain tissues, which were mostly frozen whole, by carefully blocking them into smaller, more manageable pieces. Nick had no previous experience working with brain tissue, so I taught him everything he needed to know in order to carry out this work in my absence, from handling and storage to ultrathin cryosectioning of the brain blocks into slices for neuroanatomical analysis. In one week, we were able to organize and prepare all the tissues and get Nick proficient on sectioning primate brain tissue on the cryostat. It was a busy but enjoyable trip getting a new project off the ground and meeting new people at Duke and NC State.
Sometime later this year, the tissue will be ready and I will return to NC to help them carry out the visualization experiments and start the analysis! Can’t wait for my next trip back!
Sara M. Freeman, PhD 