Electroconvulsive seizures activate anorexigenic signals in the ventromedial nuclei of the hypothalamus

Prolactin-Releasing Peptide System as a Potential Mechanism of Stress Coping: Studies in Male Rats

Prolactin-releasing peptide (PrRP) has a regulatory role in both acute and chronic stress, suggesting its potential contribution to stress-related disorders such as depression. However, not all individuals with depression respond equally to stressors. We aimed to determine whether the PrRP system could underlie stress coping, an important aspect of depression. The forced swim test was used both as a stressor and as a method to assess coping strategy. Based on immobility time, active coping and passive coping subgroups were identified, and 10 brain regions were studied using qPCR to measure the mRNA expression levels of PrRP and its receptors (specific: GPR10; non-specific: NPFFR2). Passive coping animals spent more time in an immobile posture and exhibited altered mRNA expression levels in the medullary A1 region, the habenula, and the arcuate nucleus than control or active coping rats. Additionally, we identified corticotropin-releasing hormone and vesicular glutamate transporter 2 positive neurons in the A1 medullary region that contained Prrp, suggesting a modulatory role of PrRP in these excitatory neurons involved in stress regulation. Our findings reinforce the hypothesis that PrRP plays a role in stress coping, a process closely linked to depression. However its effect is brain region-specific.

Neuroimmune crosstalk through brain-derived neurotrophic factor and its precursor pro-BDNF: New insights into mood disorders

Mood disorders are the most common mental disorders, affecting approximately 350 million people globally. Recent studies have shown that neuroimmune interaction regulates mood disorders. Brain-derived neurotrophic factor (BDNF) and its precursor pro-BDNF, are involved in the neuroimmune crosstalk during the development of mood disorders. BDNF is implicated in the pathophysiology of psychiatric and neurological disorders especially in antidepressant pharmacotherapy. In this review, we describe the functions of BDNF/pro-BDNF signaling in the central nervous system in the context of mood disorders. In addition, we summarize the developments for BDNF and pro-BDNF functions in mood disorders. This review aims to provide new insights into the impact of neuroimmune interaction on mood disorders and reveal a new basis for further development of diagnostic targets and mood disorders.

Electroconvulsive shock increases neurotrophy and neurogenesis: Time course and treatment session effects

Increasing evidence suggests that hippocampal neurotrophy may be related to the development of major depressive disorders. Neurogenesis, which can be regulated by neurotrophic factors, is also involved in antidepressant efficacy. This paper reviewed literature on neurotrophic signaling and cell proliferation after electroconvulsive shock (ECS) treatment. All articles were from PubMed, Web of Science, and Scopus databases between 2000 and 2020. The keywords used in the literature search are: "ECS," "ECT," "electroconvulsive seizure," "electroconvulsive shock," "electroconvulsive therapy," "neurotrophic factor," "nerve growth factor," "neurotrophins," "neurogenesis," and "cell proliferation." Eighty-two articles were included in the final analysis. It was shown that compared with acute ECS, repeated ECS increased neurotrophin expression in more brain regions at higher levels and was maintained for a longer time. Similarly, ECS increased cell proliferation in a dose- and time-dependent manner. The increase in cell proliferation was positively correlated with the amount of ECS administered and the newly born cells survived for a long time. The effects of ECS in inducing increases in neurotrophin levels and neurogenesis may contribute to brain function changes and antidepressant effects. Future research may focus on optimal sessions of ECT treatment to obtain the best therapeutic effect.

Electroconvulsive seizures lead to lipolytic-induced gene expression changes in mediobasal hypothalamus and decreased white adipose tissue mass

Aims

Electroconvulsive seizure (ECS) therapy is highly effective in the treatment of several psychiatric disorders, including depression. Past studies have shown that the rodent model of ECS reveals the activation of multiple brain regions including the hypothalamus, suggesting that this method of brain stimulation broadly regulates central neuronal function, which results in peripheral function. The ventromedial nucleus of the hypothalamus (VMH) plays an important role in feeding and energy homeostasis. Our previous study showed that ECS increases the expression of anorexigenic factors in the VMH and has an anorexigenic effect in a mouse model. Since the VMH is also suggested to play a critical role in the peripheral lipid metabolism of white adipose tissue (WAT), we hypothesized that ECS alters lipid metabolism via activation of the VMH.

Methods and Results

Here, we demonstrate that repeated ECS suppresses the fat mass of epididymal WAT and significantly increases the expression levels of lipolytic and brown adipose tissue markers such as Adrb3, Hsl/Lipe, and Ppargc1a. In the VMH, ECS increased the expression of multiple genes, notably Bdnf, Adcyap1, and Crhr2, which are not only anorexigenic factors but are also modulators of lipid metabolism. Furthermore, gold‐thioglucose‐induced hypothalamic lesions affecting the VMH abolished the effect of ECS on the WAT, indicating that hypothalamus activation is required for the phenotypic changes seen in the epididymal WAT.

Conclusion

Our data demonstrates a new effect of ECS on the lipid metabolism of WAT via induction of hypothalamic activity involving the VMH.

In the present study, we demonstrated that ECS exerts effects on adipose tissue and suggest the requirement of the hypothalamus, including the VMH, for the lipolytic effect of ECS.

Rapid and stable changes in maturation-related phenotypes of the adult hippocampal neurons by electroconvulsive treatment

Electroconvulsive therapy (ECT) is a highly effective and fast-acting treatment for depression. Despite a long history of clinical use, its mechanism of action remains poorly understood. Recently, a novel cellular mechanism of antidepressant action has been proposed: the phenotype of mature brain neurons is transformed to immature-like one by antidepressant drug treatments. We show here that electroconvulsive stimulation (ECS), an animal model of ECT, causes profound changes in maturation-related phenotypes of neurons in the hippocampal dentate gyrus of adult mice. Single ECS immediately reduced expression of mature neuronal markers in almost entire population of dentate granule cells. After ECS treatments, granule cells showed some of physiological properties characteristic of immature granule cells such as higher somatic intrinsic excitability and smaller frequency facilitation at the detate-to-CA3 synapse. The rapid downregulation of maturation markers was suppressed by antagonizing glutamate NMDA receptors, but not by perturbing the serotonergic system. While single ECS caused short-lasting effects, repeated ECS induced stable changes in the maturation-related phenotypes lasting more than 2 weeks along with enhancement of synaptic excitation of granule cells. Augmentation of synaptic inhibition or blockade of NMDA receptors after repeated ECS facilitated regaining the initial mature phenotype, suggesting a role for endogenous neuronal excitation in maintaining the altered maturation-related phenotype probably via NMDA receptor activation. These results suggest that brief neuronal activation by ECS induces "dematuration" of the mature granule cells and that enhanced endogenous excitability is likely to support maintenance of such a demature state. The global increase in neuronal excitability accompanying this process may be relevant to the high efficacy of ECT.

Brain-Derived Neurotrophic Factor and Antidepressive Effect of Electroconvulsive Therapy: Systematic Review and Meta-Analyses of the Preclinical and Clinical Literature

Emerging data suggest that Electro-Convulsive Treatment (ECT) may reduce depressive symptoms by increasing the expression of Brain-Derived Neurotrophic Factor (BDNF). Yet, conflicting findings have been reported. For this reason we performed a systematic review and meta-analysis of the preclinical and clinical literature on the association between ECT treatment (ECS in animals) and changes in BDNF concentrations and their effect on behavior. In addition, regional brain expression of BDNF in mouse and human brains were compared using Allen Brain Atlas. ECS, over sham, increased BDNF mRNA and protein in animal brain (effect size [Hedge’s g]: 0.38―0.54; 258 effect-size estimates, N = 4,284) but not in serum (g = 0.06, 95% CI = -0.05―0.17). In humans, plasma but not serum BDNF increased following ECT (g = 0.72 vs. g = 0.14; 23 effect sizes, n = 281). The gradient of the BDNF increment in animal brains corresponded to the gradient of the BDNF gene expression according to the Allen brain atlas. Effect-size estimates were larger following more ECT sessions in animals (r = 0.37, P < .0001) and in humans (r = 0.55; P = 0.05). There were some indications that the increase in BDNF expression was associated with behavioral changes in rodents, but not in humans. We conclude that ECS in rodents and ECT in humans increase BDNF concentrations but this is not consistently associated with changes in behavior.

Role of the 5-HT4 receptor in chronic fluoxetine treatment-induced neurogenic activity and granule cell dematuration in the dentate gyrus

Background

Chronic treatment with selective serotonin (5-HT) reuptake inhibitors (SSRIs) facilitates adult neurogenesis and reverses the state of maturation in mature granule cells (GCs) in the dentate gyrus (DG) of the hippocampus. Recent studies have suggested that the 5-HT₄ receptor is involved in both effects. However, it is largely unknown how the 5-HT₄ receptor mediates neurogenic effects in the DG and, how the neurogenic and dematuration effects of SSRIs interact with each other.

Results

We addressed these issues using 5-HT₄ receptor knockout (5-HT4R KO) mice. Expression of the 5-HT₄ receptor was detected in mature GCs but not in neuronal progenitors of the DG. We found that chronic treatment with the SSRI fluoxetine significantly increased cell proliferation and the number of doublecortin-positive cells in the DG of wild-type mice, but not in 5-HT4R KO mice. We then examined the correlation between the increased neurogenesis and the dematuration of GCs. As reported previously, reduced expression of calbindin in the DG, as an index of dematuration, by chronic fluoxetine treatment was observed in wild-type mice but not in 5-HT4R KO mice. The proliferative effect of fluoxetine was inversely correlated with the expression level of calbindin in the DG. The expression of neurogenic factors in the DG, such as brain derived neurotrophic factor (Bdnf), was also associated with the progression of dematuration. These results indicate that the neurogenic effects of fluoxetine in the DG are closely associated with the progression of dematuration of GCs. In contrast, the DG in which neurogenesis was impaired by irradiation still showed significant reduction of calbindin expression by chronic fluoxetine treatment, suggesting that dematuration of GCs by fluoxetine does not require adult neurogenesis in the DG.

Conclusions

We demonstrated that the 5-HT₄ receptor plays an important role in fluoxetine-induced adult neurogenesis in the DG in addition to GC dematuration, and that these phenomena are closely associated. Our results suggest that 5-HT₄ receptor-mediated phenotypic changes, including dematuration in mature GCs, underlie the neurogenic effect of SSRIs in the DG, providing new insight into the cellular mechanisms of the neurogenic actions of SSRIs in the hippocampus.

Chronic all-trans retinoic acid administration induces CRF over-expression accompanied by AVP up-regulation and multiple CRF-controlling receptors disturbance in the hypothalamus of rats

Clinical reports suggest a potential link between excess retinoids and development of depression. Corticotropin-releasing factor (CRF) produced in the hypothalamic paraventricular nucleus (PVN) is considered the central driver of the hypothalamic-pituitary-adrenal (HPA) axis and plays a key role in the pathogenesis of depression. Although we had shown that chronic all-trans retinoic acid (ATRA) administration induced hypothalamic CRF over-expression and hyperactivity of HPA axis in rats, further insight into how ATRA modulate CRF expression is lacking. The activity of CRF neurons is under close control of vasopressinergic system and three-paired receptors (corticosteroid receptors, sex hormone receptors and CRF receptors). Here we show that ATRA-induced CRF over-expression is accompanied by arginine-vasopressin (AVP) up-regulation and apparent gene expression disturbances of CRF-controlling receptors. ATRA was applied to rats by daily intraperitoneal injection for 6 weeks. Chronic ATRA treatment induced significantly increased expression of CRF and AVP in the PVN. Moreover, the transcript levels of CRF receptor 1 (CRFR1), estrogen receptor-β (ERβ) and mineralocorticoid receptor (MR), three genes involved in the activation of CRF neurons, were significantly increased in the hypothalamus, and the expression ratio of GRα/MR was markedly decreased. Correlation analysis indicated that the alteration of multiple CRF-controlling receptors is highly correlated with depression-related behaviors of rats in the forced swimming test. These findings support that in addition to the 'classic' retinoic acid receptor α-mediated transcriptional control of CRF expression, disruption in CRF-modulating systems constitutes a novel pathway that underlies ATRA-induced HPA axis hyperactivity in vivo.

Regional specific regulation of steroid receptor coactivator-1 immunoreactivity by orchidectomy in the brain of adult male mice

Androgens including testosterone and dihydrotestosterone play important roles on brain structure and function, either directly through androgen receptor or indirectly through estrogen receptors, which need coactivators for their transcription activation. Steroid receptor coactivator-1 (SRC-1) has been shown to be multifunctional potentials in the brain, but how it is regulated by androgens in the brain remains unclear. In this study, we explored the effect of orchidectomy (ORX) on the expression of SRC-1 in the adult male mice using nickel-intensified immunohistochemistry. The results showed that ORX induced dramatic decrease of SRC-1 immunoreactivity in the olfactory tubercle, piriform cortex, ventral pallidum, most parts of the septal area, hippocampus, substantia nigra (compact part), pontine nuclei and nucleus of the trapezoid body (p<0.01). Significant decrease of SRC-1 was noticed in the dorsal and lateral septal nucleus, medial preoptical area, dorsomedial and ventromedial hypothalamic nucleus and superior paraolivary nucleus (p<0.05). Whereas in other regions examined, levels of SRC-1 immunoreactivity were not obviously changed by ORX (p>0.05). The above results demonstrated ORX downregulation of SRC-1 in specific regions that have been involved in sense of smell, learning and memory, cognition, neuroendocrine, reproduction and motor control, indicating that SRC-1 play pivotal role in the mediating circulating androgenic regulation on these important brain functions. It also indicates that SRC-1 may serve as a novel target for the central disorders caused by the age-related decrease of circulating androgens.

A new method to model electroconvulsive therapy in rats with increased construct validity and enhanced translational value

Electroconvulsive therapy is the most effective therapy for major depressive disorder (MDD). The remission rate is above 50% in previously pharmacoresistant patients but the mechanisms of action are not fully understood. Electroconvulsive stimulation (ECS) in rodents mimics antidepressant electroconvulsive therapy (ECT) in humans and is widely used to investigate the underlying mechanisms of ECT. For the translational value of findings in animal models it is essential to establish models with the highest construct, face and predictive validity possible. The commonly used model for ECT in rodents does not meet the demand for high construct validity. For ECT, cortical surface electrodes are used to induce therapeutic seizures whereas ECS in rodents is exclusively performed by auricular or corneal electrodes. However, the stimulation site has a major impact on the type and spread of the induced seizure activity and its antidepressant effect. We propose a method in which ECS is performed by screw electrodes placed above the motor cortex of rats to closely simulate the clinical situation and thereby increase the construct validity of the model. Cortical ECS in rats induced reliably seizures comparable to human ECT. Cortical ECS was more effective than auricular ECS to reduce immobility in the forced swim test. Importantly, auricular stimulation had a negative influence on the general health condition of the rats with signs of fear during the stimulation sessions. These results suggest that auricular ECS in rats is not a suitable ECT model. Cortical ECS in rats promises to be a valid method to mimic ECT.