Rodent models of chronic restraint stress (CRS) are often used as simple models of depressive disorder. However, these models of stress have been mainly developed in rats, and the behavioral phenotypes of CRS models are still controversial. In this study, we compared the physiological and behavioral responses of C57BL/6J (B6) and BALB/c mice, which are commonly used in genetic and behavioral studies, to CRS. In addition to measuring physiological parameters and the levels of corticosterone (a stress hormone) in response to stress, we also examined changes in the levels of testosterone (an anti-stress hormone), which have rarely been studied in stressed mice. The mice were exposed to CRS for 6 h a day for 21 days. In both B6 and BALB/c mice, CRS elicited several physiological stress responses, including decreased body weight gain and changes in the tissue weights of stress-related organs. Accumulated corticosterone in the hair was measured, and BALB/c mice had significantly greater levels than control mice and B6 mice after CRS. On the other hand, in the case of accumulated testosterone in the hair, both B6 mice and BALB/c mice showed significantly higher concentrations than control mice, but the degree of change was not different between the two strains. In the sucrose preference test, BALB/c mice, but not B6 mice, showed anhedonia-like behavior after CRS. However, neither strain showed depressive-like behavior in the forced swim or tail suspension test. Our results show that the physiological and behavioral stress responses of BALB/c mice are greater than those of B6 mice, although anti-stress responses to CRS are similar in both strains. This suggests that BALB/c mice are likely to be advantageous for use as a CRS-induced depression model.

Wide-field optical imaging of the animal brain is a useful technique for measuring brain dynamics, including spatial structure. However, quantitative inter-animal comparison is difficult due to lack of the common cortical space that can normalize individually imaged brains as done in human functional MRI studies. Here, by using wide-field functional Ca2+ imaging on anesthetized transgenic mice expressing G-CaMP7 in astrocytes and excitatory neutrons, we attempted to establish the common cortical space in mice, which can be useful as a standard of functional brain map. We initially reconstructed cortical areas embedded within spontaneous activity as the functional connectivity maps for the individual mice, then matched them in size, shape, and location across mice by geometric transformation. Finally, we assigned all the recorded signals into the transformed space, to make spatially normalized signals in the common cortical space. Using this method, we managed to extract activity patterns commonly observed across mice. These results suggest that the presented method is available to facilitate inter-animal comparison of brain dynamics, and has the potential to identify common brain activity across animals.

Sirtuin 6 (SIRT6), a member of the Sirtuin family, acts as nicotinamide adenine dinucleotide (NAD)-dependent protein deacetylase, mono-adenosine diphosphate (ADP)-ribosyltransferase, and fatty acid deacylase, and plays critical roles in inflammation, aging, glycolysis, and DNA repair. Accumulating evidence has suggested that SIRT6 is involved in brain functions such as neuronal differentiation, neurogenesis, and learning and memory. However, the precise molecular roles of SIRT6 during neuronal circuit formation are not yet well understood. In this study, we tried to elucidate molecular roles of SIRT6 on neurite development by using primary-cultured hippocampal neurons. We observed that SIRT6 was abundantly localized in the nucleus, and its expression was markedly increased during neurite outgrowth and synaptogenesis. By using shRNA-mediated SIRT6-knockdown, we show that both dendritic length and the number of dendrite branches were significantly reduced in the SIRT6-knockdown neurons. Microarray and subsequent gene ontology analysis revealed that reducing SIRT6 caused the downregulation of immediate early genes (IEGs) and alteration of several biological processes including MAPK (ERK1/2) signaling. We found that nuclear accumulation of phosphorylated ERK1/2 was significantly reduced in SIRT6-knockdown neurons. Overexpression of SIRT6 promoted dendritic length and branching, but the mutants lacking deacetylase activity had no significant effect on the dendritic morphology. Collectively, the presented findings reveal a role of SIRT6 in dendrite morphogenesis, and suggest that SIRT6 may act as an important regulator of ERK1/2 signaling pathway that mediates IEG expression, which leads to dendritic development.

Substance P (SP) regulates inhibitory synaptic transmission mediated by GABAA receptors in the cerebral cortex; however, SP-mediated regulation of excitatory synaptic transmission remains poorly understood. We performed whole-cell patch-clamp recordings from pyramidal neurons to examine the effects of SP on excitatory postsynaptic currents (EPSCs) mediated via AMPA receptors in the insular cortex (IC), which is involved in nociceptive information processing. First, EPSCs evoked by minimal electrical stimulation (eEPSCs) including stepwise EPSCs and failure events, were examined. SP dose-dependently suppressed mean eEPSC amplitude, partially due to an increase in the failure rate of eEPSCs. The SP-induced suppression of eEPSCs was accompanied by an increase in the paired-pulse ratio and was inhibited by the preapplication of SR140333, an NK1 receptor antagonist. [Sar9,Met(O2)11]-substance P, an NK1 receptor-selective agonist, mimicked the effects of SP on eEPSCs and decreased the frequency of miniature EPSCs (mEPSCs) without changing the average mEPSC amplitude. Considering that most NK1 receptors in the cerebral cortex are expressed in nitric oxide synthase (NOS)-positive GABAergic neurons, the SP-induced suppressive effect on EPSCs may be mediated by nitric oxide (NO) in this subtype of GABAergic neurons. NO imaging using the fluorescent probe DAX-J2 Red supports this hypothesis: SP increased the fluorescence intensity of DAX-J2 Red in some GABAergic neurons. Furthermore, both L-NAME, an NOS inhibitor, and PTIO, an NO scavenger, diminished the SP-induced suppression of eEPSCs. These results suggest that the activation of presynaptic NK1 receptors contributes to SP-induced eEPSC suppression by activating the NO synthesis pathway in GABAergic neurons. (246 words).