Role of the anterior and posterior Paraventricular Nucleus of the Thalamus on Sign-Tracking in inbred C57BL/6J and DBA/2J mice

Aims: Sign-tracking (ST) behavior is a model of overwhelming attraction to rewards-associated stimuli due to incentive salience attribution as measured by the Pavlovian Conditioned Approach (PCA) paradigm. Previous studies suggested different strain-specific neurobiological substrates underlying ST behavior. This study was aimed at investigating the genotype-dependent networks mediating ST phenotype in C57BL/6J (C57) andDBA/2J (DBA) mice. Methods: In experiment 1 quantification of the c-fos protein was a marker of neural activation of strain-specific circuits during expression of ST behavior. After training, Paired (CS-food presentation) and Unpaired(random CS and food presentation) mice underwent a short exposure only to the lever-CS and then sacrificed for the immunohistochemistry. According to the results, in experiment 2 an excitotoxic lesion by NMDA infusion within the anterior and posterior Paraventricular Nucleus of the Thalamus (PVT) was performed before PCA training. Results: PVT was the only area expressing c-fos immunostaining in both strains though with opposite direction. Indeed, when compared to the respective Unpaired mice, c-fos expression was increased in C57Paired and decreased in DBA Paired mice. Moreover, while the aPVT showed to be more involved in ST expression for DBA mice, any antero-posterior gradient was found relative to the activation for C57 mice. However, lesion of the aPVT selectively reduced ST behavior in DBA mice, while the pPVT lesion selectively reduced ST behavior in C57 mice. Conclusions: This strain-dependent functional role of the PVT and its anatomical division confirm the hypothesis that ST phenotype may be mediated by different networks in these strains.