Development of a Ketamine Relapse in Mice : Behavioral Dynamics and Implications

초록

Ketamine, a potent NMDA receptor antagonist, has demonstrated rapid and robust antidepressant effects in patients with treatment-resistant depression (TRD). However, sustained antidepressant efficacy requires repeated infusions, which can lead to drug dependence and a high risk of relapse. Despite increasing concerns regarding ketamine addiction, the underlying mechanisms of relapse and reinstatement remain largely unknown compared to those of opioids and psychostimulants. In this study, we established a preclinical animal model to investigate ketamine addiction and relapse susceptibility using self-administration and extinction-reinstatement paradigms in mice. This model enables the assessment of ketamine-seeking behavior following extinction and relapse responses triggered by environmental cues. To achieve this, mice were trained to self-administer ketamine in a two-lever choice task, where lever responses and infusion patterns were recorded. Following acquisition, mice were assigned to either an extinction group, in which ketamine administration was discontinued and ketamine-associated environmental cues were removed, or a cue-induced reinstatement group, where ketamine was withheld but ketamine-associated environmental stimuli remained. Behavioral analysis revealed a rapid decrease in active lever responses during extinction, whereas the reinstatement phase led to a significant increase in ketamine-seeking behavior. These findings suggest that ketamine-associated conditioning is resistant to extinction and that environmental cues serve as potent triggers for relapse. To further elucidate the neurobiological mechanisms underlying ketamine relapse, we performed c-Fos immunostaining to assess neural activation across relevant brain regions. Significant activation was observed in the hippocampus, medial prefrontal cortex (mPFC), and central amygdala (CeA), suggesting their involvement in ketamine-seeking behavior and relapse susceptibility. Additionally, to evaluate the physical symptoms of withdrawal, we analyzed withdrawal-related behaviors following extinction. Key withdrawal symptoms included rearing, exploration, scratching, genital licking, forepaw tremor, body tremor, and defecation. Notably, rearing behavior was significantly more frequent in the relapse (REL) group. Two-way repeated measures ANOVA on total withdrawal scores revealed a progressive increase in withdrawal severity over time in the REL group. Interestingly, while scratching behavior was initially more prominent in the REL group, its frequency gradually increased in the control group, possibly reflecting the prolonged effects of ketamine. These findings provide critical insights into the neural and behavioral mechanisms underlying ketamine withdrawal and relapse. By identifying key brain regions and behavioral markers associated with relapse susceptibility, this preclinical model offers a valuable framework for developing targeted interventions for ketamine use disorder.