Astrocytes in the Ventromedial Hypothalamus Involve Chronic Stress-Induced Anxiety and Bone Loss in Mice

Ventromedial hypothalamus relays chronic stress inputs and exerts bidirectional regulation on anxiety state and related sympathetic activity

Chronic stress can induce negative emotion states, including anxiety and depression, leading to sympathetic overactivation and disturbed physiological homeostasis in peripheral tissues. While anxiety-related neural circuitry integrates chronic stress information and modulates sympathetic nervous system (SNS) activity, the critical nodes linking anxiety and sympathetic activity still need to be clarified. In our previous study, we demonstrated that the ventromedial hypothalamus (VMH) is involved in integrating chronic stress inputs and exerting influence on sympathetic activity. However, the underlying synaptic and electrophysiological mechanisms remain elusive. In this study, we combined in vitro electrophysiological recordings, behavioral tests, optogenetic manipulations, and SNS activity analyses to explore the role of VMH in linking anxiety emotion and peripheral SNS activity. Results showed that the VMH played an important role in bidirectionally regulating anxiety-like behavior and peripheral sympathetic excitation. Chronic stress enhanced excitatory inputs into VMH neurons by strengthening the connection with the paraventricular hypothalamus (PVN), hence promoting anxiety and sympathetic tone outflow, an important factor contributing to the development of metabolic imbalance in peripheral tissues and cardiovascular diseases.

Correlation analysis of positron emission tomography/computed tomography-magnetic resonance imaging of cannabinoid type 1 receptor in the lumbar spine and brain of aged osteoporosis female cynomolgus monkeys

Background

Although cannabinoid receptor 1 (CB1R) antagonists can inhibit bone loss in osteoporosis mouse models, different strains of mice show different bone mass phenotypes after knock out the CB1R gene. The relationship between CB1R and bone metabolism is complex, and its regulatory role in bone metabolism and as a therapeutic target for osteoporosis requires further investigation.

Methods

Based on lumbar spine volumetric bone mineral density (vBMD) data of healthy female cynomolgus monkeys aged 1-25 years, naturally aged postmenopausal female osteoporotic monkeys and normal young monkeys were screened by detecting lumbar vertebrae vBMD and estradiol levels in this study. Positron emission tomography-computed tomography (PET/CT) and magnetic resonance imaging (MRI) scans were performed on the lumbar spine and brain of the two groups of monkeys using the probe [11C]OMAR, which specifically targets CB1R, and the difference in the CB1R expression of osteoporotic monkeys was evaluated.

Results

The vBMD values of two standard deviations (SDs) below the peak bone value (428.1±53.8 g/cm3) were set as the reference standard for osteoporosis vBMD. Of the 49 healthy female cynomolgus monkeys, 4 postmenopausal older osteoporotic monkeys (18-26 years) and 5 young control monkeys (6-7 years) were selected, and the mean vBMD of the lumbar spine of the two groups was 295.07±19.11 and 419.72±16.14 g/cm3, respectively (P<0.0001). Radioactive uptake in the lumbar spine was linearly and negatively correlated with vBMD (r=-0.7977; P=0.01). Dynamic PET/MR imaging of the brains showed that CB1R was upregulated in the osteoporosis group, and there was a negative linear correlation between the vBMD and area under the time-radioactivity curve (AUC) of the thalamus (r=-0.8506; P=0.0153) and prefrontal cortex (r=-0.8306; P=0.0207).

Conclusions

In this study, PET/CT-MRI molecular imaging technology revealed that CB1R was upregulated in the lumbar spine and brain of the osteoporosis monkeys and that CB1R may be regulated by the brain-bone axis. CB1R antagonist may be a potential drug for the treatment of osteoporosis.

Astrocyte Heterogeneity in Regulation of Synaptic Activity

Our awareness of the number of synapse regulatory functions performed by astroglia is rapidly expanding, raising interesting questions regarding astrocyte heterogeneity and specialization across brain regions. Whether all astrocytes are poised to signal in a multitude of ways, or are instead tuned to surrounding synapses and how astroglial signaling is altered in psychiatric and cognitive disorders are fundamental questions for the field. In recent years, molecular and morphological characterization of astroglial types has broadened our ability to design studies to better analyze and manipulate specific functions of astroglia. Recent data emerging from these studies will be discussed in depth in this review. I also highlight remaining questions emerging from new techniques recently applied toward understanding the roles of astrocytes in synapse regulation in the adult brain.