Repeated Antibiotic Treatment Affects Social Behaviors In Siberian Hamsters (Phodopus Sungorus)
Authors: Sylvia Kristyn E. , Rendon Nikki M. , St. John Emma A. , Demas Gregory E. 
Published: November 2023

Antibiotics are an important resource, saving the lives of humans and other animals throughout the world. The effects of antibiotics on a host's microbiome, however, can be extremely detrimental to the animal's well‐being. Recent studies have shown that early‐life antibiotics affect the microbial diversity of the gut microbiome and may subsequently affect anxiety‐like behaviors in several model systems (e.g., mouse and rat species). The effects of repeated antibiotic treatment in adulthood and its consequences on social behavior in a non‐model species (e.g., the Siberian hamster) however, have yet to be explored. We have recently shown that a 7‐day treatment of the broad‐spectrum antibiotic, enrofloxacin (Baytril) 10% solution, a fluoroquinolone antimicrobial agent that inhibits DNA synthesis, produces a decrease in microbial diversity in the gut microbiome of Siberian hamsters. To further investigate how changes in microbial diversity affect behavior, this study sought to determine the influence of antibiotic treatment on social behavior. Specifically, we tested the effects of short‐term vs. repeated antibiotic treatment on aggressive and investigative behaviors. To address this, male hamsters were either administered sterilized water or an antibiotic (0.3 μl of Baytril 10% oral solution per gram of body mass) orally via sterile pipette for seven days during two treatment periods (D1–7 and again on D15–21). Each treatment period was followed by a 7‐day recovery period (D8–14 and D22–28). On the last day of each treatment and recovery period (D7, D14, D21, and D28), social behavioral trials were conducted. To assess behavior, we used a resident‐intruder model by which a non‐aggressive intruder was introduced into the home cage of an experimental animal for five minutes, and aggression and investigation were scored by an unbiased observer. At the end of the experiment, all animals were euthanized and organs were harvested and weighed. No significant change in aggressive behavior (e.g., attacks and chases) was seen after one antibiotic treatment. Following the second antibiotic treatment, however, hamsters showed a decrease in overall aggression, as well as in the number of attacks and chases. Additionally, there was a significant difference in the level of total investigation across behavioral trials for both the treatment and control groups, however, there were no significant differences in either anogenital or head‐neck investigation between groups within these time periods. Lastly, there was no significant change in body mass throughout the experiment, and liver, spleen, and testes mass did not differ across groups. These data further our understanding of the effects of antibiotics on behavior and particularly how the gut microbiome works as an important player in the interaction of both of these systems in a non‐model species. This is particularly valuable in making meaningful comparisons between organisms to understand the diversity in host strategies used to cope with environmental and immunological pressures. Future studies will investigate how the use of multiple, prolonged antibiotic treatments affect behavior in a sex‐specific manner in our non‐model species.