Conflict between Threat Sensitivity and Sensation Seeking in the Adolescent Brain: Role of the Hippocampus, and Neurobehavioural Plasticity Induced by Pleasurable Early Enriched Experience

The impact of social isolation on depression-like behavior in carioca high- and low-conditioned freezing rats

This study investigated the impact of social isolation in Carioca High-Conditioned Freezing (CHF) rats, an animal model of generalized anxiety disorder (GAD). Animals selected for high (CHF), low trait anxiety (Carioca Low-Conditioned Freezing, CLF), and control rats from randomly bred populations (CTL) were housed in groups or kept isolated in their cages for 14 consecutive days. On the fifteenth day, all animals underwent the Forced Swimming Test (FST), where the latency to immobility was assessed as a depressive-like measure. Under standard grouping conditions, CHF rats showed a shorter latency to immobility in the FST compared to CTL and CLF animals, indicating depressive-like characteristics and possible GAD comorbidity. Social isolation decreased the latency to immobility in CLF and CTL animals, while it paradoxically increased this measure in CHF animals. Therefore, social isolation exerted a depressive-like action in CTL and CLF rats, but had a protective or "antidepressant-like" effect in CHF animals. Since, CHF rats are housed with other animals with high trait anxiety, such protective action induced by social isolation might have been due to the mitigation of what has been referred to as "social stress contagion". These results are discussed regarding the association between depressive-like behaviors and reduced social engagement.

Contribution of the Roman rat lines/strains to personality neuroscience: neurobehavioral modeling of internalizing/externalizing psychopathologies

The Roman high-avoidance (RHA) and low-avoidance (RLA) rat lines/strains were established in Rome through bidirectional selection of Wistar rats for rapid (RHA) or extremely poor (RLA) acquisition of a two-way active avoidance task. Relative to RHAs, RLA rats exhibit enhanced threat sensitivity, anxiety, fear and vulnerability to stress, a passive coping style and increased sensitivity to frustration. Thus, RLA rats' phenotypic profile falls well within the "internalizing" behavior spectrum. Compared with RLAs and other rat strains/stocks, RHAs present increased impulsivity and reward sensitivity, deficits in social behavior and attentional/cognitive processes, novelty-induced hyper-locomotion and vulnerability to psychostimulant sensitization and drug addiction. Thus, RHA rats' phenotypes are consistent with a "disinhibiting externalizing" profile. Many neurobiological/molecular traits differentiate both rat lines/strains. For example, relative to RLA rats, RHAs exhibit decreased function of the prefrontal cortex (PFC), hippocampus and amygdala, increased functional tone of the mesolimbic dopamine system, a deficit of central metabotropic glutamate-2 (mGlu2) receptors, increased density of serotonin 5-HT2A receptors in the PFC, impairment of GABAergic transmission in the PFC, alterations of several synaptic markers and increased density of pyramidal immature dendrític spines in the PFC. These characteristics suggest an immature brain of RHA rats and are reminiscent of schizophrenia features like hypofrontality and disruption of the excitation/inhibition cortical balance. We review evidence supporting RLA rats as a valid model of anxiety/fear, stress and frustration vulnerability, whereas RHA rats represent a promising translational model of neurodevelopmental alterations related to impulsivity, schizophrenia-relevant features and comorbidity with drug addiction vulnerability.

Social preference in Roman rats: age and sex variations relevance for modeling negative schizophrenia-like features

Social withdrawal is one of the most relevant negative symptoms of schizophrenia. Animal models that mimic schizophrenia's symptoms, in general, and negative symptoms, in particular, are difficult to develop because of the high complexity of symptoms and neurochemical disturbances that schizophrenia patients display throughout their lives. In recent years we have shown that Roman High- Avoidance (RHA) rats exhibit some phenotypes that are thought to represent positive symptoms, cognitive/attentional symptoms, as well as some negative symptoms of the disease. In the present study, we aimed at elucidating whether the social interaction (SI) deficits exhibited by adult male RHA rats, compared to their Roman Low-Avoidance (RLA) counterparts, are also present during adolescence, as well as whether there are between-strain differences in adolescent and adult female rats. The results of the present study show that adult male RHA rats exhibited a deficit in social preference compared to their RLA counterparts. Such a deficit was not observed in adolescent RHA rats or female rats of any age. The results also show that the adult male rats of both strains had significant decreases in social preference compared to the adolescent male rats. Additionally, we also show that female adult RHA rats have greater social preference than their male counterparts. These results seem to be in line with previous rodent and human studies and add face validity to the RHA rats as a model of schizophrenia.