Defensive burying as an ethological approach to studying anxiety: Influence of juvenile methamphetamine on adult defensive burying behavior in rats

The defensive burying test is an ethological approach that has both pharmacological and physiological validity in studying rodent anxiety-like behaviors. The defensive burying test measures the naturally occurring behavior of displacing bedding toward a noxious stimulus. Exposure to psychostimulants can alter anxiety behaviors in children and adults, however few studies have investigated the long-term effects of chronic juvenile stimulant exposure on anxiety behaviors in adulthood. Therefore, the current experiment tested the effects of juvenile methamphetamine exposure on defensive burying behavior in adulthood. Juvenile (PD20-34) male and female rats were either given intraperitoneal injections of 2.0 mg/kg methamphetamine or saline or were not handled, and then all groups were left undisturbed until adulthood. As adults, rats' anxiety-like behavior was assessed after exposure to a single shock probe in a defensive burying paradigm. Adult male rats that were exposed to methamphetamine as juveniles showed a significant increase in the latency to begin burying following the shock, indicative of decreased behavioral reactivity towards the shock. However, there were no other differences between treatment groups. Interestingly, there were no sex differences in any measure. These findings suggest that early exposure to the stimulant drug methamphetamine has limited effects on defensive burying behaviors when measured in adulthood. Defensive burying is an important ethological approach to assess rodent anxiety and can increase our understanding of coping behaviors in rodents following stimulant drug exposure.