Ovariectomy and chronic stress lead toward leptin resistance in the satiety centers and insulin resistance in the hippocampus of Sprague-Dawley rats

Impact of leptin or melatonin on Sema4D overexpression-related bone metabolism

PURPOSE

The current study aims to investigate the regulatory impact of leptin or melatonin on bone metabolism as well as the underlying mechanism in conjunction with Sema4D (monoclonal antibody to semaphorin 4D).

METHODS

Rats were used to create the osteoporosis model utilizing the OVX (OVariectomize) technique. Rat tibial specimens from each side were collected for three-dimensional reconstruction and Micro-CT scanning examination. The Hematoxylin-osinstaining (HE) staining technique was used to determine the pathological condition of bone tissues. The ELISA (Enzyme-Linked Immunosorbent Assay) assay was used to measure the amount of estradiol present in the serum. In the current study, there were six groups: control, OVX, OVX + NL (no load group), OVX + Sema4D, OVX + Sema4D + leptin, and OVX + Sema4D + MT (melatonin). Rats were given injections of the Sema4D or leptin overexpressing vectors via the tail vein in accordance with the aforementioned classification. By using a high-resolution micro-CT technology, 3D bone structure was discovered. The activity of tartrate-resistant acid phosphatase-5b (TRAP-5b) and bone-derived alkaline phosphatase (BALP) in serum was assessed using an ELISA. The number of osteoclasts in the metaphysis of the upper tibia was determined using TRAP (tartrate-resistant acid phosphatase) staining. Immunohistochemistry was used to find leptin and bone morphogenetic protein-2 (BMP-2) expressions in bone tissue.

RESULTS

The BV/TV (Bone volume/Tissue volume), Tb.N (Trabecular number), BMD (Bone Mineral Density), and BMC (Bone Mineral Content) levels were significantly higher in the OVX + Sema4D + leptin and OVX + Sema4D + MT groups compared to OVX + NL, while Tb.Sp (Trabecular separation) levels were significantly lower. In contrast to the OVX group, the bone trabeculae in the OVX + Sema4D + leptin and OVX + Sema4D + MT groups had a relatively complete structure and tended to be organized closely. The amount of bone trabeculae grew drastically, whereas the proportion of TRAP-positive osteoclasts declined dramatically. BMP-2 and leptin were also elevated, while BALP and TRAP-5b activity was reduced.

CONCLUSION

Leptin or melatonin improved Sema4d's role in trabecular bone microstructure, bone production, and repairment of trabecular bone loss in osteoporosis rats.

Behavioral, neuroplasticity and metabolic effects of 7,8-dihydroxy-4-methylcoumarin associated with physical activity in mice

The search for strategies to develop resilience against metabolic and neuropsychiatric disorders has motivated the clinical and experimental assessment of early life interventions such as lifestyle-based and use of unconventional pharmacological compounds. In this study, we assessed the effects of voluntary physical activity and 7,8-Dihydroxy-4-methylcoumarin (DHMC), independently or in combination, over mice physiological and behavioral parameters, adult hippocampal and hypothalamic neurogenesis, and neurotrophic factors expression in the hypothalamus. C57Bl/6J mice were submitted to a 29-day treatment with DHMC and allowed free access to a running wheel. We found that DHMC treatment alone reduced fasting blood glucose levels. Moreover, physical activity showed an anxiolytic effect in the elevated plus maze task and DHMC produced additional anxiolytic behavior, evidenced by reduced activity during the light cycle in the physical activity group. Although we did not find any differences in hypothalamic or hippocampal adult neurogenesis, DHMC increased gene expression levels of VEGF, which was correlated to the reduced fasting glucose levels. In conclusion, our data emphasize the potential of physical activity in reducing development of neuropsychiatric conditions, such as anxiety, and highlights DHMC as an attractive compound to be investigated in future studies addressing neuropsychiatric disorders associated with metabolic conditions.

Chronic Stress and Gonadectomy Affect the Expression of Cx37, Cx40 and Cx43 in the Spinal Cord

The study aimed to determine whether the exposure to chronic stress and/or performance of gonadectomy might lead to disturbance in the expression of connexin (Cx) 37, 40 and 43 in the spinal cord (SC), as a potential explanation for sex differences in stress-related chronic pain conditions. After the rats were sham-operated or gonadectomized, three 10-day sessions of sham or chronic stress were applied. Immunohistochemistry and transmission electron microscopy (TEM) were used to examine Cx localization and expression in the SC. The gonadectomy resulted in an increase of Cx37 expression in the dorsal horn (DH) of the female rats, but chronic stress suppressed the effects of castration. In male rats, only the combined effects of castration and chronic stress increased Cx37 expression. The influence of chronic stress on the DH Cx40 expression was inversely evident after the castration: increased in the ovariectomized female rats, while decreased in the orchidectomized male rats. We did not find any effect of chronic stress and castration, alone or together, on Cx43 expression in the DH, but the percentage of Cx43 overlapping the astrocyte marker glial fibrillary acidic protein (gfap) increased in the male stressed group after the castration. In conclusion, the association of the chronic stress with sex hormone depletion results in disturbances of the SC Cx expression and might be a possible mechanism of disturbed pain perception after chronic stress exposure.

Trajectory of leptin and leptin receptor in vertebrates: Structure, function and their regulation

The present review provides a comparative insight into structure, function and control of leptin system in fishes, herptiles, birds and mammals. In general, leptin acts as an anorexigenic hormone since its administration results in decrease of food intake in vertebrates. Nonetheless, functional paradox arises in fishes from contradictory observations on level of leptin during fasting and re-feeding. In addition, leptin is shown to modulate metabolic functions in fishes, reptiles, birds and mammals. Leptin also regulates reproductive and immune functions though more studies are warranted in non-mammalian vertebrates. The expression of leptin and its receptor is influenced by numerous factors including sex steroids, stress and stress-induced catecholamines and glucocorticoids though their effect in non-mammalian vertebrates is hard to be generalized due to limited studies.

Increased expression of dendrin in the dorsal horn of the spinal cord during stress is regulated by sex hormones

Chronic stress has various effects on organisms and is sex-specific. The aim of the study was to describe the expression of synapse strengthening protein, dendrin, in the spinal cord (SC) and the dependence of its expression on chronic stress and sex hormones. Thirteen-month-old female and male rats were castrated (ovariectomy [F-OVX] or orchidectomy [M-ORX]) or sham-operated (F-SH or M-SH), respectively. At age 15 months, three 10-day-sessions of sham stress (control, C) or chronic stress (S) were conducted. Dendrin expression was present in the thoracic SC segments and the dorsal root ganglia (DRG). In the SC, dendrin expression was prominent in superficial laminae of the dorsal horn and lamina X (central canal). The M-ORX-S group had the highest dendrin expression in the dorsal horn, being significantly higher than the M-ORX-C or M-SH-S groups (P < 0.05). Dendrin expression was significantly higher in the F-SH-S group than the F-SH-C group (P < 0.05), as well as in the F-SH-S than the M-SH-S (P < 0.05). Co-localization with the α-d-galactosyl-specific isolectin B4 (IB4) in central projections of the DRG neurons in the dorsal horn of the SC was 7.43 ± 3.36%, while with the calcitonin gene-related peptide (CGRP) was 8.47 ± 4.45%. Localization of dendrin was observed in soma and nuclei of neurons in the dorsal horn. Dendrin expression in pain-processing areas of the SC, the DRG neurons and their peripheral projections suggest possible roles in pain perception and modulation. Stress-induced increase in dendrin expression and its dependence on sex hormones may partially explain sex-specific pain hypersensitivity induced by stress.

Impact of subchronic variable stress on ovariectomy and dendritic spine density in prefrontal cortex in mice

Major depressive disorder affects both women and men but females are two times more susceptible to the incidence of depression. The majority of stress models used male rodents, whereas fewer studies included females. Volumetric reductions have been reported in brain areas critical for the stress response, such as prefrontal cortex, and remodeling of dendritic spines has been proposed as an underlying factor. The aim of this study was to determine the effects of subchronic variable stress (SCVS) in males, sham, and specifically in ovariectomized (OVX) female mice. Here, we used 6 days SCVS model to induce depressive-like behavior, and only the OVX female mice showed the depressive-like behavior, while males showed resilient type behavior. Only OVX female mice showed significant increase in dendritic spine density in SCVS paradigm. Overall, this study suggests that (1) the effects SCVS produced on the behavior of males and OVX females and (2) SCVS may induce rapid and sustained changes of PL neurons, which highlights the importance of gonadal hormones in studying depression.

Gene expression alterations in the medial prefrontal cortex and blood cells in a mouse model of depression during menopause

Aims

The prevalence of major depressive disorder (MDD) is higher in women than in men, and this may be due to the decline in estrogen levels that occurs during the menopausal transition. We studied the biological alterations in the medial prefrontal cortex (mPFC), which is a region that is highly implicated in the neurobiology of MDD, and the blood cells (BCs) of ovariectomized (OVX) mice subjected to chronic mild stress (CMS), which represents a mouse model of depression during menopause.

Main methods

The mPFC and the BCs were obtained from the same individuals. Gene expression levels were analyzed by microarray. The data were used for the Ingenuity Pathway Analysis and the Gene Ontology analysis.

Key findings

The gene expression alterations (GEAs) induced by OVX were mainly associated with ribosomal and mitochondrial functions in both the mPFC and the BCs. Rapamycin-insensitive companion of mTOR (RICTOR) was identified as a possible upstream regulator of the OVX-induced GEAs in both tissues. The CMS-induced GEAs were associated with retinoic acid receptor signaling, inflammatory cytokines and post-synaptic density in the mPFC, but not in the BCs.

Significance

OVX and CMS independently affect biological pathways in the mPFC, which is involved in the development of the depression-like phenotype. Because a subset of the OVX-induced GEAs in the mPFC also occurred in the BCs, the GEAs in the BCs might be a useful probe to predict biological pathways in the corresponding brain tissue under specific conditions such as OVX in females.