Stress-induced sleep-like inactivity modulates stress susceptibility in mice.

Severe environmental and social stress induces dysregulation of sleep along with mood and cognitive disturbances. However, the role and mechanism of this sleep dysregulation remain elusive. Here we evaluated sleep-like inactivity measured by voluntary movements and its relationship to social behaviors in mice without or with social defeat stress as well as the stressed mice with subsequent sleep deprivation. Social defeat stress immediately induced sleep-like inactivity with decreased body temperature. In the social interaction test, the control mice showed high social interest and its correlation with social sniffing intensity, the latter of which indicates positive valence of social sniffing. After the stress, these social characteristics were maintained in stress-resilient mice, but disrupted in stress-susceptible mice, leading to social avoidance. Sleep deprivation after the stress decreased social sniffing intensity along with reduced social interest, but enhanced the exploratory activity with the positive valence of social sniffing. We also found by c-Fos immunohistochemistry that the stress activated sleep-related brain regions, the dorsomedial hypothalamus and ventrolateral periaqueductal gray. Collectively, these findings show that stress activates sleep-related brain regions and induces sleep-like inactivity, contributing to multiple roles of stress-induced sleep for social behaviors.

Social defeat stress-specific increase in c-Fos expression in the extended amygdala in mice: Involvement of dopamine D1 receptor in the medial prefrontal cortex.

We recently reported that dopamine D1 receptor in the medial prefrontal cortex (mPFC) is activated by subthreshold social defeat stress and suppresses the induction of depressive-like behavior in mice. However, which mPFC projection(s) mediates this antidepressant-like effect remains poorly understood. Here we show that social defeat stress specifically increased c-Fos expression, a marker for neuronal activity, in distinct brain regions involved in emotional regulation, relative to novelty-induced exploration. Among these brain areas, D1 knockdown in the mPFC decreased social defeat stress-induced c-Fos expression in the interstitial nucleus of the posterior limb of the anterior commissure (IPAC), a subregion of the extended amygdala. Using retrograde adeno-associated virus vectors and transgenic mice expressing Cre recombinase under the D1 promoter, we also found that D1-expressing deep-layer pyramidal neurons in the mPFC send direct projections to the IPAC. These findings indicate that social defeat stress specifically activates neurons in distinct brain areas, among which the IPAC is regulated by dopamine D1 receptor in the mPFC perhaps through direct projections. Thus, this study provides hints toward identifying neural circuits that underlie antidepressant-like effects of stress-induced dopamine D1 receptor signaling in the mPFC.

Social defeat stress induces phosphorylation of extracellular signal-regulated kinase in the leptomeninges in mice.

AIMS: Animal studies using various stress models have shown that excessive environmental stress induces depression? and anxiety?like behaviors through inflammatory responses in the brain and periphery. Although the leptomeningeal cells have multiple functions related to inflammatory responses in the brain, whether environmental stress influences the leptomeninges remains unknown. In this study, we aimed to examine phosphorylation of the extracellular signal-regulated kinase (ERK) in the leptomeninges. METHODS: We subjected C57BL/6 male mice to a single episode of social defeat stress and analyzed the expression of phosphorylated ERK in the leptomeninges by immunohistochemistry. RESULTS: Social defeat stress in mice induced phosphorylation of ERK in the leptomeninges, adjacent to vascular endothelial cells and the glia limitans. This ERK phosphorylation was maintained for at least one hour after the stress. CONCLUSIONS: This study shows the effect of environmental stress on the leptomeninges for the first time and paves the way for elucidating its functional role in stress-induced changes in neural functions.

Differential S-palmitoylation of the human and rodent ß3-adrenergic receptors.

With few reported exceptions, G protein-coupled receptors (GPCRs) are modified by Cys palmitoylation (S-palmitoylation). In multiple GPCRs, S-palmitoylation targets a canonical site within the C-terminal cytoplasmic tail adjacent to the C terminus of the seventh transmembrane domain, but modification of additional sites is exemplified by the ß-adrenergic receptors (ßARs). The ß1AR is S-palmitoylated at a second, more distal site within the C-terminal tail, and the ß2AR is modified at a second site within the third intracellular loop, neither of which is conserved in other ßAR isoforms. The functional roles of S-palmitoylation of disparate sites are incompletely characterized for any GPCR family. Here, we describe S-palmitoylation of the ß3AR. We compared mouse and human ß3ARs and found that both were S-palmitoylated at the canonical site within the C-terminal tail, Cys-358 and Cys-361/363 in mouse and human ß3ARs, respectively. Surprisingly, the human ß3AR was S-palmitoylated at two additional sites, Cys-153 and Cys-292 within the second and third intracellular loops, respectively. Cys-153 is apparently unique to the human ß3AR, and Cys-292 is conserved primarily in primates. Mutational substitution of C-tail Cys in human but not mouse ß3ARs resulted in diminished ligand-induced cAMP production. Substitution of Cys-153, Cys-292, or Cys-361/363 within the human ß3AR diminished membrane-receptor abundance, but only Cys-361/363 substitution diminished membrane-receptor half-life. Thus, S-palmitoylation of different sites differentially regulates the human ß3AR, and differential S-palmitoylation distinguishes human and rodent ß3ARs, potentially contributing to species-specific differences in the clinical efficacy of ß3AR-directed pharmacological approaches to disease.