The results from the first experiment showed that downregulation of Prdm2 in the prelimbic cortex can increase the risks to develop fear-related behaviour in a model of posttraumatic stress disorder, even if it did not affect baseline anxiety levels. This finding is consistent with the literature that supports a crucial role of prelimbic cortex in fear expression.

Moreover, previous studies showed that Prdm2 was downregulated in the prefrontal cortex of alcohol dependent rats. So a defecit of this enzyme in this brain region might suggest an increasing susceptibility to develop alcohol use disorders and anxiety disorders. 

However, the study was limited to male subjects and it is hard to rule out possible sex differences. Moreover, interindividual differences among the treatment groups were not investigated. Evidence in literature reports pre-existing factors that make rats more susceptible or more resistent to stress exposure. Prdm2 downregulation might have affected these subpopulations differently. Further studies are needed to elucidate these specific effects.

Despite the absence of any significant effect, the study showed that witnesses and stressed animals had a tendency for higher anxiety-like behaviour than control. This was consistent with results coming from more validated models, showing that the psychological component of social stressor is sufficient alone to develop anxiety and fear-related behaviour. So, witnessing somebody else's trauma can lead to high stress responses.

However, some studies in the literature showed differential behavioural responses from physical and psychological stress. For example, witnesses tend to be hyperactive in an open field whereas physically harmed rats tend to be hypoactive. In our study, both witnesses and stressed animals showed a similar pattern instead.

Results from our lab in previous studies showed that rats witnessing conspecifics exposed to social defeat stress even escalated alcohol consumption, as a model for comorbid phenotype in humans. If our model manages to replicate the findings from social defeat stress, this will be an useful tool in studying comorbidity of alcohol use and anxiety disorders in a more controllable experimental set up.

However, it is important to implement our model and find more consistent results with larger sample sizes. Additionally, since the model aims to study sex differences, it is important to include female individuals in future as well. 

Summing up, in this project I showed that overlapping molecular mechanisms might mediate alcohol use disorders (AUDs) and anxiety disorders. This will help the preclinical research to find possible pharmacological targets for eventual treatments of comorbid phenotypes. Sex differences and interindividual differences need to be investigated in this respect. 

I also showed the promising results from a new behavioural model to study witness stress in a more controllable set up and that has the potentiality to investigate sex-specific effects. However, more studies are needed to implement this model and to get more consistent results to validate it. Once validated, this model will represent a useful tool for preclinical research of risk factors of comorbid AUDs and anxiety disorders.