Social hierarchy differentially influences the anxiety-like behaviors and dendritic spine density in prefrontal cortex and limbic areas in male rats.

Social hierarchy is a fundamental feature of social organization that can influence brain and emotional processing regarding social ranks. Several areas, including the medial prefrontal cortex (mPFC), the hippocampus, and the basolateral nucleus of the amygdala (BLA), are recognized to be involved in the regulation of emotional processing. However, its delicate structural correlates in brain regions are poorly understood. To address this issue, social hierarchy in home-caged sibling Wistar rats (three male rats/cage) was determined by employing a social confrontation tube test (postnatal weeks 9-12). Then, locomotor activity and anxiety-like behaviors were evaluated using an open-field test (OFT) and elevated plus-maze (EPM) at 13 weeks of age. The rapid Golgi impregnation method was conducted to quantify the spine density of the first secondary branch of the primary dendrite in 20 µm length. The results indicated that dominant rats had significantly higher anxiety-like behaviors compared to subordinates, as was evident by lower open-arm entries and time spent in the EPM and lower entries and time spent in the center of OFT. The spine density analysis revealed a significantly higher number of spines in subordinates compared to the dominant rats in dmPFC pyramidal neurons and the apical and basal dendrites of hippocampal CA1 pyramidal neurons. However, the spine density of pyramidal-like neurons in the BLA was higher in dominant rats. Our findings suggest that dominant social rank is associated with higher anxiety and differential density of the dendritic spine in the prefrontal cortex and limbic regions of the brain in male rats.

Electrical impulses evoked activity patterns in ventral tegmental area and locus coeruleus modulate endogenous and learning-dependent disparity of cell proliferation along the mouse dentate gyrus.

This study aimed to examine the effects of the ventral tegmental area (VTA) and the locus coeruleus (LC) patterned electrical stimulation on hippocampal-dependent learning and hippocampal neurogenesis in adult mouse. For this, mice were given unilateral electrical stimulation of VTA or LC using phasic or tonic stimulation protocols. Behavior acquisition rates were evaluated using the Barnes maze (BM) and a passive avoidance (PA) task. Cell proliferation was measured in the dorsal (dDG), intermediate (iDG) and ventral (vDG) dentate gyrus (DG) using Ki67 immunohistochemistry. We showed that the levels of cell proliferation were significantly different in three highlighted parts of the DG. The behavioral testing paradigms themselves were sufficient to alter cell proliferation indices along the dentate gyrus. The phasic LC modulation treatment enhanced behavioral acquisition of the BM and cell proliferation in the dDG, while tonic VTA stimulation improved PA acquisition and increased cell proliferation in the iDG. It is concluded that electrical impulses-evoked phasic or tonic activity patterns in the LC and VTA could modulate endogenous and learning dependent disparity of cell proliferation along the adult mouse DG.