The Role of the Nucleus Reuniens in Regulating Contextual Conditioning with the Predator Odor TMT

Rationale Experiencing intrusive distressing memories of a traumatic event(s) is a prominent symptom profile for post-traumatic stress disorder (PTSD). Understanding the neurobiological mechanisms associated with this symptom profile can be invaluable for effective treatment for PTSD. Objectives Here, we investigated the functional role of the nucleus reuniens (RE), a midline thalamic in modulating stressor-related memory. Methods Female Long Evans rats were implanted with a cannula aimed at the RE. The RE was pharmacologically inactivated via muscimol (0.5 mM) prior to exposure to the predator odor stressor trimethylthiazoline (TMT; synthetically derived fox feces component) or water (controls) in a distinct context with bedding material ([Experiment 1][1]) or no bedding ([Experiment 2][2]). To measure context reactivity, the index of the contextual memory, 2 weeks following exposure to TMT, rats were re-exposed to the TMT-paired context (in the absence of TMT). Results In [Experiment 1][1], during context re-exposure (with bedding), inactivation of the RE had no effect on context reactivity. In [Experiment 2][2], during context re-exposure (no bedding), rats previous exposed to TMT showed decreased immobility compared to controls, indicating reactivity to the context and likely related to increased exploration of the environment. Rats in the TMT group that received RE inactivation showed increased immobility relative to rats that received aCSF, suggesting that muscimol pre-treatment blunted context reactivity. Conclusion In conclusion, recruitment of the RE in stressor-related contextual memory appears to be dependent on the contextual environment and whether the animal is able to engage in different stress coping strategies. ### Competing Interest Statement The authors have declared no competing interest. [1]: #sec-19 [2]: #sec-20