The role of allopregnanolone in depressive-like behaviors: Focus on neurotrophic proteins

Antidepressant effects of activation of infralimbic cortex via upregulation of BDNF and β-catenin in an estradiol withdrawal model

RATIONALE

Clinical and preclinical studies have demonstrated that estradiol withdrawal after delivery is one of important factors involved in the pathogenesis of postpartum depression (PPD). The infralimbic cortex (IL) is related to anxiety and mood disorders. Whether IL neurons mediate PPD is still unclear.

OBJECTIVES

This study was to observe the antidepressant effect and expression of BDNF and β-catenin in IL by allopregnanolone (ALLO) treatment or the selective activation or inhibition of IL neurons using a chemogenetic approach in a pseudopregnancy model of PPD.

METHODS

Administration of estradiol combined with progesterone and the abrupt withdrawal of estradiol simulated the pregnancy and early postpartum periods to induce depression in ovariectomized rats. The relative expression levels of β-catenin and BDNF were observed by western blotting.

RESULTS

Immobility time was significantly increased in the forced swim test and open-arm movement was reduced in the elevated plus maze test in the estradiol-withdrawn rats. After ALLO treatment, the immobility time were lower and open-arm traveling times higher than those of the estradiol-withdrawn rats. Meanwhile, the expression level of BDNF or β-catenin in the IL was reduced significantly in estradiol-withdrawn rats, which was prevented by treatment with ALLO. The hM3Dq chemogenetic activation of pyramidal neurons in the IL reversed the immobility and open-arm travel time trends in the estradiol-withdrawal rat model, but chemogenetic inhibition of IL neurons failed to affect this. Upregulated BDNF and β-catenin expression and increased c-Fos in the basolateral amygdala were found following IL neuron excitation in model rats.

CONCLUSIONS

Our results demonstrated that pseudopregnancy and estradiol withdrawal produced depressive-like behavior and anxiety. ALLO treatment or specific excitement of IL pyramidal neurons relieved abnormal behaviors and upregulated BDNF and β-catenin expression in the IL in the PPD model, suggesting that hypofunction of IL neurons may be involved in the pathogenesis of PPD.

Neuroactive Steroids, Toll-like Receptors, and Neuroimmune Regulation: Insights into Their Impact on Neuropsychiatric Disorders

Pregnane neuroactive steroids, notably allopregnanolone and pregnenolone, exhibit efficacy in mitigating inflammatory signals triggered by toll-like receptor (TLR) activation, thus attenuating the production of inflammatory factors. Clinical studies highlight their therapeutic potential, particularly in conditions like postpartum depression (PPD), where the FDA-approved compound brexanolone, an intravenous formulation of allopregnanolone, effectively suppresses TLR-mediated inflammatory pathways, predicting symptom improvement. Additionally, pregnane neurosteroids exhibit trophic and anti-inflammatory properties, stimulating the production of vital trophic proteins and anti-inflammatory factors. Androstane neuroactive steroids, including estrogens and androgens, along with dehydroepiandrosterone (DHEA), display diverse effects on TLR expression and activation. Notably, androstenediol (ADIOL), an androstane neurosteroid, emerges as a potent anti-inflammatory agent, promising for therapeutic interventions. The dysregulation of immune responses via TLR signaling alongside reduced levels of endogenous neurosteroids significantly contributes to symptom severity across various neuropsychiatric disorders. Neuroactive steroids, such as allopregnanolone, demonstrate efficacy in alleviating symptoms of various neuropsychiatric disorders and modulating neuroimmune responses, offering potential intervention avenues. This review emphasizes the significant therapeutic potential of neuroactive steroids in modulating TLR signaling pathways, particularly in addressing inflammatory processes associated with neuropsychiatric disorders. It advances our understanding of the complex interplay between neuroactive steroids and immune responses, paving the way for personalized treatment strategies tailored to individual needs and providing insights for future research aimed at unraveling the intricacies of neuropsychiatric disorders.

Neurosteroids: mechanistic considerations and clinical prospects

Like other classes of treatments described in this issue's section, neuroactive steroids have been studied for decades but have risen as a new class of rapid-acting, durable antidepressants with a distinct mechanism of action from previous antidepressant treatments and from other compounds covered in this issue. Neuroactive steroids are natural derivatives of progesterone but are proving effective as exogenous treatments. The best understood mechanism is that of positive allosteric modulation of GABAA receptors, where subunit selectivity may promote their profile of action. Mechanistically, there is some reason to think that neuroactive steroids may separate themselves from liabilities of other GABA modulators, although research is ongoing. It is also possible that intracellular targets, including inflammatory pathways, may be relevant to beneficial actions. Strengths and opportunities for further development include exploiting non-GABAergic targets, structural analogs, enzymatic production of natural steroids, precursor loading, and novel formulations. The molecular mechanisms of behavioral effects are not fully understood, but study of brain network states involved in emotional processing demonstrate a robust influence on affective states not evident with at least some other GABAergic drugs including benzodiazepines. Ongoing studies with neuroactive steroids will further elucidate the brain and behavioral effects of these compounds as well as likely underpinnings of disease.

Neurosteroid [3α,5α]-3-hydroxy-pregnan-20-one enhances IL-10 production via endosomal TRIF-dependent TLR4 signaling pathway

Background

Previous studies demonstrated the inhibitory effect of allopregnanolone (3α,5α-THP) on the activation of inflammatory toll-like receptor 4 (TLR4) signals in RAW264.7 macrophages and the brains of selectively bred alcohol-preferring (P) rats. In the current study, we investigated the impact of 3α,5α-THP on the levels of IL-10 and activation of the TRIF-dependent endosomal TLR4 pathway.

Methods

The amygdala and nucleus accumbens (NAc) of P rats, which exhibit innately activated TLR4 pathways as well as RAW264.7 cells, were used. Enzyme-linked immunosorbent assays (ELISA) and immunoblotting assays were used to ascertain the effects of 3α,5α-THP on the TRIF-dependent endosomal TLR4 pathway and endosomes were isolated to examine translocation of TLR4 and TRIF. Additionally, we investigated the effects of 3α,5α-THP and 3α,5α-THDOC (0.1, 0.3, and 1.0 µM) on the levels of IL-10 in RAW264.7 macrophages. Finally, we examined whether inhibiting TRIF (using TRIF siRNA) in RAW264.7 cells altered the levels of IL-10.

Results

3α,5α-THP administration facilitated activation of the endosomal TRIF-dependent TLR4 pathway in males, but not female P rats. 3α,5α-THP increased IL-10 levels (+13.2 ± 6.5%) and BDNF levels (+21.1 ± 11.5%) in the male amygdala. These effects were associated with increases in pTRAM (+86.4 ± 28.4%), SP1 (+122.2 ± 74.9%), and PI(3)K-p110δ (+61.6 ± 21.6%), and a reduction of TIRAP (-13.7 ± 6.0%), indicating the activation of the endosomal TRIF-dependent TLR4 signaling pathway. Comparable effects were observed in NAc of these animals. Furthermore, 3α,5α-THP enhanced the accumulation of TLR4 (+43.9 ± 11.3%) and TRIF (+64.8 ± 32.8%) in endosomes, with no significant effect on TLR3 accumulation. Additionally, 3α,5α-THP facilitated the transition from early endosomes to late endosomes (increasing Rab7 levels: +35.8 ± 18.4%). In RAW264.7 cells, imiquimod (30 µg/mL) reduced IL-10 while 3α,5α-THP and 3α,5α-THDOC (0.1, 0.3, and 1.0 µM) restored IL-10 levels. To determine the role of the TRIF-dependent TLR4 signaling pathway in IL-10 production, the downregulation of TRIF (-62.9 ± 28.2%) in RAW264.7 cells led to a reduction in IL-10 levels (-42.3 ± 8.4%). TRIF (-62.9 ± 28.2%) in RAW264.7 cells led to a reduction in IL-10 levels (-42.3 ± 8.4%) and 3α,5α-THP (1.0 µM) no longer restored the reduced IL-10 levels.

Conclusion

The results demonstrate 3α,5α-THP enhancement of the endosomal TLR4-TRIF anti-inflammatory signals and elevations of IL-10 in male P rat brain that were not detected in female P rat brain. These effects hold significant implications for controlling inflammatory responses in both the brain and peripheral immune cells.

Reduced urine pregnenolone concentration after clinical response in patients with depression: An open-label short-term prospective study

BACKGROUND

Identifying biological alterations in patients with depression, particularly those that differ between responders and non-responders, is of interest to clinical practice. Biomarker candidates involve neuroactive steroids, including pregnenolone (PREG) and allopregnanolone (ALLO). However, alterations in PREG and ALLO associated with treatment response are understudied. This study's main aim was to evaluate the effects of antidepressant treatment, clinical response, and treatment duration on PREG and ALLO in depression.

MATERIALS AND METHODS

In a 4-week, open-label trial, participants were allocated randomly to the venlafaxine (n = 27) or mirtazapine (n = 30) group. Urine concentrations of PREG and ALLO were assessed through gas chromatography-mass spectrometry. Participants collected night urine between 10:30 p.m. and 8:00 a.m. Two primary outcomes were analyzed. Firstly, the effect of treatment (mirtazapine or venlafaxine), clinical response (operationalized through the Hamilton Depression Rating Scale), and time (baseline compared to 28 days) on the urine concentrations of PREG or ALLO in depression. Finally, the effect of clinical response and time on the urine concentration of PREG or ALLO, independently of the antidepressant given (mirtazapine or venlafaxine). Linear mixed models were carried out.

RESULTS

There was no significant difference in PREG and ALLO concentrations between baseline and 28 days in responders and non-responders when investigating the venlafaxine or the mirtazapine group. However, we found a significant reduction of urine PREG concentration after 28 days of treatment in responders who received either venlafaxine or mirtazapine (estimate = -0.56; p = 0.016; 95CI [-1.003; -0.115]; Cohen's d = -0.61).

CONCLUSIONS

Our main results indicate that responders in depression show reduced urinary PREG concentrations after 4-weeks of therapy, independently of the antidepressant used. More studies are needed to confirm these findings.

Effect of alcohol on Brain-Derived Neurotrophic Factor (BDNF) blood levels: a systematic review and meta-analysis

Brain-Derived Neurotrophic Factor (BDNF) is a vital protein involved in neuronal development, survival, and plasticity. Alcohol consumption has been implicated in various neurocognitive deficits and neurodegenerative disorders. However, the impact of alcohol on BDNF blood levels remains unclear. This systematic review and meta-analysis aimed to investigate the effect of alcohol consumption on BDNF blood levels. A comprehensive search of electronic databases was conducted to identify relevant studies. Eligible studies were selected based on predefined inclusion criteria. Data extraction was performed, and methodological quality was assessed using appropriate tools. A meta-analysis was conducted to estimate the overall effect size of alcohol consumption on BDNF levels. A total of 25 studies met the inclusion criteria and were included in the final analysis. Alcohol use and BDNF blood levels were significantly correlated, according to the meta-analysis (p = 0.008). Overall, it was discovered that drinking alcohol significantly decreased BDNF levels (SMD: - 0.39; 95% CI: - 0.68 to - 0.10; I2: 93%). There was a non-significant trend suggesting that alcohol withdrawal might increase BDNF levels, with an SMD of 0.26 (95% CI: - 0.09 to 0.62; I2: 86%; p = 0.14). Subgroup analysis based on the source of BDNF demonstrated significant differences between the subgroups (p = 0.0008). No significant publication bias was observed. This study showed that alcohol consumption is associated with a significant decrease in BDNF blood levels. The findings suggest a negative impact of alcohol on BDNF levels regardless of alcohol dosage. Further studies are needed to strengthen the evidence and elucidate the underlying mechanisms.

The efficacy and safety of some new GABAkines for treatment of depression: A systematic review and meta-analysis from randomized controlled trials

Positive allosteric modulators of γ-aminobutyric acid-A (GABAA) receptors, or GABAkines, play important roles in the treatment of depression, epilepsy, insomnia, and other disorders. Recently, some new GABAkines (zuranolone and brexanolone) have been administrated to patients with major depressive disorder (MDD) or postpartum depression (PPD) in randomized controlled trials (RCTs). This study aims to systematically review and examine the efficacy and safety of zuranolone or brexanolone for treatment of depression. A systematic literature retrieval was conducted through August 20, 2023. RCTs evaluating the efficacy and safety of zuranolone or brexanolone for treatment of depression were included. Eight studies (nine reports) were identified in the study. The percentages of patients with PPD achieving Hamilton Depression Rating Scale (HAM-D) response and remission were significantly higher after brexanolone or zuranolone administration compared with placebo at different points. The percentages of patients with MDD achieving HAM-D response and remission were significantly increased during the zuranolone treatment period compared with placebo. In addition, zuranolone caused more adverse events in patients with MDD compared with placebo. Our findings support the effects of brexanolone on improving the core symptoms of depression in patients with PPD, and the potential of zuranolone in treating patients with MDD or PPD.

Efficacy and safety of zuranolone in Japanese adults with major depressive disorder: A double-blind, randomized, placebo-controlled, phase 2 clinical trial

AIM

To evaluate the efficacy and safety of an oral, once-daily, 14-day treatment course of zuranolone in Japanese patients with major depressive disorder (MDD).

METHODS

This multicenter, randomized, double-blind, placebo-controlled study randomized eligible patients (1:1:1) to receive oral zuranolone 20 mg, zuranolone 30 mg, or placebo once daily for 14 days (treatment-period), followed by two 6-week follow-up periods. The primary endpoint was change from baseline in the 17-item Hamilton Depression Rating Scale (HAMD-17) total score on Day 15.

RESULTS

Overall, 250 patients (enrolled: 07/07/2020-05/26/2021) were randomized to receive placebo (n = 83), zuranolone 20 mg (n = 85), or zuranolone 30 mg (n = 82). The demographic and baseline characteristics were balanced between groups. The adjusted mean (standard error) change from baseline in the HAMD-17 total score on Day 15 was -6.22 (0.62), -8.14 (0.62), and - 8.31 (0.63) in the placebo, zuranolone 20-mg, and zuranolone 30-mg groups, respectively. Significant differences in the adjusted mean (95% confidence interval [CI]) for zuranolone 20 mg versus placebo (-1.92; [-3.65, -0.19]; P = 0.0296) and zuranolone 30 mg versus placebo (-2.09; [-3.83, -0.35]; P = 0.0190) groups were observed on Day 15, and also as early as Day 3. A nonsignificant yet distinct drug-placebo separation was observed during follow-up. Somnolence (placebo [3.7%], zuranolone 20 mg [10.6%], and zuranolone 30 mg [20.7%]) and dizziness (3.7%, 9.4%, and 9.8%, respectively) were more common with zuranolone.

CONCLUSION

Oral zuranolone was safe and demonstrated significant improvements in depressive symptoms, as assessed by HAMD-17 total score change from baseline over 14 days in Japanese patients with MDD.

Nucleus accumbens deep brain stimulation improves depressive-like behaviors through BDNF-mediated alterations in brain functional connectivity of dopaminergic pathway

Major depressive disorder (MDD), a common psychiatric condition, adversely affects patients' moods and quality of life. Despite the development of various treatments, many patients with MDD remain vulnerable and inadequately controlled. Since anhedonia is a feature of depression and there is evidence of leading to metabolic disorder, deep brain stimulation (DBS) to the nucleus accumbens (NAc) might be promising in modulating the dopaminergic pathway. To determine whether NAc-DBS alters glucose metabolism via mitochondrial alteration and neurogenesis and whether these changes increase neural plasticity that improves behavioral functions in a chronic social defeat stress (CSDS) mouse model. The Lab-designed MR-compatible neural probes were implanted in the bilateral NAc of C57BL/6 mice with and without CSDS, followed by DBS or sham stimulation. All animals underwent open-field and sucrose preference testing, and brain resting-state functional MRI analysis. Meanwhile, we checked the placement of neural probes in each mouse by T2 images. By confirming the placement location, mice with incorrect probe placement (the negative control group) showed no significant therapeutic effects in behavioral performance and functional connectivity (FC) after receiving electrical stimulation and were excluded from further analysis. Western blotting, seahorse metabolic analysis, and electron microscopy were further applied for the investigation of NAc-DBS. We found NAc-DBS restored emotional deficits in CSDS-subjected mice. Concurrent with behavioral amelioration, the CSDS DBS-on group exhibited enhanced FC in the dopaminergic pathway with increased expression of BDNF- and NeuN-positive cells increased dopamine D1 receptor, dopamine D2 receptors, and TH in the medial prefrontal cortex, NAc, ventral hippocampus, ventral tegmental area, and amygdala. Increased pAMPK/total AMPK and PGC-1α levels, functions of oxidative phosphorylation, and mitochondrial biogenesis were also observed after NAc-DBS treatment. Our findings demonstrate that NAc-DBS can promote BDNF expression, which alters FC and metabolic profile in the dopaminergic pathway, suggesting a potential strategy for ameliorating emotional processes in individuals with MDD.

Pharmacokinetics, safety, and tolerability of single and multiple doses of zuranolone in Japanese and White healthy subjects: A phase 1 clinical trial

AIM

This phase 1 study assessed the pharmacokinetics, safety, and tolerability of zuranolone in Japanese and White healthy adults, and Japanese healthy elderly subjects.

METHODS

This single-center study consisted of three parts. In Part A (randomized, double-blind), the safety, tolerability, and pharmacokinetics of single dose and 7-day consecutive multiple doses of zuranolone 10, 20, and 30 mg and placebo were assessed in 36 Japanese adults, 24 White adults, and 12 Japanese elderly (aged 65-75 years) subjects. In Part B (randomized, open-label, crossover), the effect of food intake on the pharmacokinetics and safety of single-dose zuranolone 30 mg was evaluated in 12 Japanese adults. In Part C (randomized, double-blind, crossover), the effects of single-dose zuranolone 10 and 30 mg and placebo on electroencephalography parameters were evaluated in eight Japanese adults.

RESULTS

Single and multiple doses of zuranolone were safe and well tolerated in all subjects. Linear pharmacokinetics were observed in the studied dose range. Time to steady-state plasma concentration was within 72 h for Japanese and White adults. Pharmacokinetic profiles were comparable between Japanese and White adults and between Japanese adults and Japanese elderly subjects. Plasma exposures of zuranolone were greater in the fed versus fasted state. Single-dose zuranolone 30 mg increased low-beta electroencephalography power.

CONCLUSION

In healthy Japanese subjects, zuranolone was well tolerated; pharmacokinetic profile was unaffected by ethnicity or age; plasma exposures were greater in the fed state. The increased low-beta electroencephalography power with the 30-mg dose is consistent with γ-aminobutyric acid receptor type A activation by zuranolone.

Effects of Antidepressant Medication on Brain-derived Neurotrophic Factor Concentration and Neuroplasticity in Depression: A Review of Preclinical and Clinical Studies

Depression is the most prevalent and debilitating disease with great impact on societies. Evidence suggests Brain-Derived Neurotrophic Factor (BDNF) plays an important role in pathophysiology of depression. Depression is associated with altered synaptic plasticity and neurogenesis. BDNF is the main regulatory protein that affects neuronal plasticity in the hippocampus. A wealth of evidence shows decreased levels of BDNF in depressed patients. Important literature demonstrated that BDNF-TrkB signaling plays a key role in therapeutic action of antidepressants. Numerous studies have reported anti-depressant effects on serum/plasma levels of BDNF and neuroplasticity which may be related to improvement of depressive symptoms. Most of the evidence suggested increased levels of BDNF after antidepressant treatment. This review will summarize recent findings on the association between BDNF, neuroplasticity, and antidepressant response in depression. Also, we will review recent studies that evaluate the association between postpartum depression as a subtype of depression and BDNF levels in postpartum women.

Hippocampus-based behavioral, structural, and molecular dynamics across the estrous cycle

The activity of neurons in the rodent hippocampus contributes to diverse behaviors, with the activity of ventral hippocampal neurons affecting behaviors related to anxiety and emotion regulation, and the activity of dorsal hippocampal neurons affecting performance in learning- and memory-related tasks. Hippocampal cells also express receptors for ovarian hormones, estrogen and progesterone, and are therefore affected by physiological fluctuations of those hormones that occur over the rodent estrous cycle. In this review, we discuss the effects of cycling ovarian hormones on hippocampal physiology. Starting with behavior, we explore the role of the estrous cycle in regulating hippocampus-dependent behaviors. We go on to detail the cellular mechanisms through which cycling estrogen and progesterone, through changes in the structural and functional properties of hippocampal neurons, may be eliciting these changes in behavior. Then, providing a basis for these cellular changes, we outline the epigenetic, chromatin regulatory mechanisms through which ovarian hormones, by binding to their receptors, can affect the regulation of behavior- and synaptic plasticity-related genes in hippocampal neurons. We also highlight an unconventional role that chromatin dynamics may have in regulating neuronal function across the estrous cycle, including in sex hormone-driven X chromosome plasticity and hormonally-induced epigenetic priming. Finally, we discuss directions for future studies and the translational value of the rodent estrous cycle for understanding the effects of the human menstrual cycle on hippocampal physiology and brain disease risk.

Allopregnanolone: Metabolism, Mechanisms of Action, and Its Role in Cancer

Allopregnanolone (3α-THP) has been one of the most studied progesterone metabolites for decades. 3α-THP and its synthetic analogs have been evaluated as therapeutic agents for pathologies such as anxiety and depression. Enzymes involved in the metabolism of 3α-THP are expressed in classical and nonclassical steroidogenic tissues. Additionally, due to its chemical structure, 3α-THP presents high affinity and agonist activity for nuclear and membrane receptors of neuroactive steroids and neurotransmitters, such as the Pregnane X Receptor (PXR), membrane progesterone receptors (mPR) and the ionotropic GABA_A receptor, among others. 3α-THP has immunomodulator and antiapoptotic properties. It also induces cell proliferation and migration, all of which are critical processes involved in cancer progression. Recently the study of 3α-THP has indicated that low physiological concentrations of this metabolite induce the progression of several types of cancer, such as breast, ovarian, and glioblastoma, while high concentrations inhibit it. In this review, we explore current knowledge on the metabolism and mechanisms of action of 3α-THP in normal and tumor cells.

Sex steroid hormones in depressive disorders as a basis for new potential treatment strategies

The sex steroid hormones (SSHs) such as testosterone, estradiol, progesterone, and their metabolites have important organizational and activational impacts on the brain during critical periods of brain development and in adulthood. A variety of slow and rapid mechanisms mediate both organizational and activational processes via intracellular or membrane receptors for SSHs. Physiological concentrations and distribution of SSHs in the brain result in normal brain development. Nevertheless, dysregulation of hormonal equilibrium may result in several mood disorders, including depressive disorders, later in adolescence or adulthood. Gender differences in cognitive abilities, emotions as well as the 2-3 times higher prevalence of depressive disorders in females, were already described. This implies that SSHs may play a role in the development of depressive disorders. In this review, we discuss preclinical and clinical studies linked to SSHs and development of depressive disorders. Our secondary aim includes a review of up-to-date knowledge about molecular mechanisms in the pathogenesis of depressive disorders. Understanding these molecular mechanisms might lead to significant treatment adjustments for patients with depressive disorders and to an amelioration of clinical outcomes for these patients. Nevertheless, the impact of SSHs on the brain in the context of the development of depressive disorders, progression, and treatment responsiveness is complex in nature, and depends upon several factors in concert such as gender, age, comorbidities, and general health conditions.

An enriched environment reduces hippocampal inflammatory response and improves cognitive function in a mouse model of stroke

An enriched environment is used as a behavioral intervention therapy that applies sensory, motor, and social stimulation, and has been used in basic and clinical research of various neurological diseases. In this study, we established mouse models of photothrombotic stroke and, 24 hours later, raised them in a standard, enriched, or isolated environment for 4 weeks. Compared with the mice raised in a standard environment, the cognitive function of mice raised in an enriched environment was better and the pathological damage in the hippocampal CA1 region was remarkably alleviated. Furthermore, protein expression levels of tumor necrosis factor receptor-associated factor 6, nuclear factor κB p65, interleukin-6, and tumor necrosis factor α, and the mRNA expression level of tumor necrosis factor receptor-associated factor 6 were greatly lower, while the expression level of miR-146a-5p was higher. Compared with the mice raised in a standard environment, changes in these indices in mice raised in an isolated environment were opposite to mice raised in an enriched environment. These findings suggest that different living environments affect the hippocampal inflammatory response and cognitive function in a mouse model of stroke. An enriched environment can improve cognitive function following stroke through up-regulation of miR-146a-5p expression and a reduction in the inflammatory response.

The Fibrinolytic System in Peripartum Depression

The relationship between depression and reduced fibrinolytic activity reflects the role of tissue plasminogen activator and plasmin in brain remodeling underlying resilience, depression remission, and reward processing, rather than the dissolution of fibrin clots. Individuals who experience depression demonstrate hippocampal and prefrontal cortex atrophy, as well as impaired neuronal connectivity. Brain-derived neurotrophic factor (BDNF), synthesized as a precursor that is activated through cleavage by tissue plasminogen activator and plasmin, influences adult neurogenesis and neuronal plasticity in the hippocampus and prefrontal cortex. Depression is associated with decreased brain levels of BDNF, due to reduced activity of tissue plasminogen activator and plasmin. Tissue plasminogen activator and plasmin also mediate the release of dopamine, a neurotransmitter implicated in motivation and reward. Peripartum depression defines a depressive episode that occurs during pregnancy or in the first month after delivery, reinforcing the concept that postpartum depression may be a continuum of antenatal depression. This article describes the fibrinolytic status in the healthy brain, in stress and depression, emphasizing the links between biological markers of depression and defective fibrinolysis. It also discusses the association between hypofibrinolysis and risk factors for perinatal depression, including polycystic ovary syndrome, early miscarriage, preeclampsia, stressful life events, sedentariness, eating habits, gestational and type 2 diabetes, and antithyroid peroxidase antibodies. In addition, it reviews the evidence that antidepressant medications and interventions as diverse as placebo, psychotherapy, massage, video game playing, regular exercise, dietary modifications, omega 3 fatty acid supplementation, neurohormones, and cigarette smoking may reduce depression by restoring the fibrinolytic activity. Last, it suggests new directions for research.

Effects of fast-acting antidepressant drugs on a postpartum depression mice model

Postpartum depression (PPD) is a severe psychiatric disorder with devastating consequences on child development and mother's health. Dysregulation of glutamatergic and GABAergic signalling has been described in the corticolimbic system of PPD patients, who also show a downregulation of allopregnanolone levels in serum. Consequently, a synthetic allopregnanolone-based treatment is the current eligible drug to treat PPD patients. Alternatively, ketamine appears to be a promising medication for preventing PPD, nevertheless the differences in efficacy between both treatments remains unknown due to the lack of comparative studies. On this basis, the present study aims to compare the effectiveness of allopregnanolone and ketamine on a PPD-like mouse model. Our results show that postpartum females undergoing a maternal separation with early weaning (MSEW) protocol show increased despair-like behaviour, anhedonia and disrupted maternal care. Such symptoms are accompanied by lower allopregnanolone serum levels, reduction of vesicular transporters of GABA (VGAT) and glutamate (VGLUT1) in the infralimbic cortex (IL), as well as decreased hippocampal cellular proliferation. Furthermore, both drugs prevent despair-like behaviour while only ketamine reverts anhedonia. Both treatments increase hippocampal neurogenesis, while only allopregnanolone raises VGAT and VGLUT1 markers in IL. These findings suggest that ketamine might be even more effective than allopregnanolone, which points out the necessity of including ketamine in clinical studies for PPD patients. Altogether, we propose a new mice model that recapitulates the core symptomatology and molecular alterations shown in PPD patients, which allows us to further investigate both the neurobiology of PPD and the therapeutic potential of antidepressant drugs.

Allopregnanolone in Postpartum Depression

Postpartum depression (PPD) is a debilitating psychiatric disorder characterized by a high worldwide prevalence and serious long-term negative outcomes for both mothers and children. The lack of a specific treatment and overreliance on pharmacotherapy with limited efficacy and delayed treatment response has constituted a complication in the management of PPD. Recently, the Food and Drug Administration (FDA) in the USA approved a synthetic formulation of the GABAergic neurosteroid allopregnanolone, administered intravenously (brexanolone) for the rapid, long-lasting and effective treatment of PPD. Hereinafter, we review findings on allopregnanolone biosynthesis and GABA_A receptor plasticity in the pathophysiology of PPD. We also discuss evidence supporting the efficacy of brexanolone for the treatment of PPD, which opens a promising new horizon for neurosteroid-based therapeutics for mood disorders.

The effects of neurosteroid allopregnanolone on synaptic dysfunction in the hippocampus in experimental parkinsonism rats: An electrophysiological and molecular study

The dopaminergic system is a powerful candidate targeted for changes of synaptic plasticity in the hippocampus. Higher incidence of Parkinson's disease (PD) in men than women indicates the influence of sex hormones on the PD development. Previous studies have shown that neurodegenerative diseases such as PD are related to the decline of Allopregnanolon (Allo), a metabolite of progesterone; it is also well known that learning and memory are influenced by oscillations in steroidal hormones. Although abnormalities in hippocampal plasticity have been observed in the toxic models of PD, effects of Allo on hippocampal LTP and hippocampal synaptic protein levels, which play an important role in maintaining the integrity of neural connections, have never been analyzed thus far. Experimental groups subjected to the long-term potentiation (LTP) were studied in the CA1 area of the hippocampus. In addition, the levels of hippocampal postsynaptic density protein 95 (PSD-95), neurexin-1 (Nrxn1) and neuroligin (Nlgn) as synaptic molecular components were determined by immunoblotting. Although dopamine denervation did not alter basal synaptic transmission and pair-pulse facilitation of field excitatory postsynaptic potentials (fEPSPs), the induction and maintenance of LTP were impaired in the CA1 region. In addition, the levels of PSD-95, Nrxn1 and Nlgn were significantly decreased in the hippocampus of 6-OHDA-treated animals. Such abnormalities in synaptic electrophysiological aspects and protein levels were abolished by the treatment with Allo. These findings showed that partial dopamine depletion led to unusual synaptic plasticity in the CA1 as well as the decrease in synaptic proteins in the hippocampus. Our results demonstrated that Allo ameliorated these deficits and preserved pre- and post-synaptic proteins. Therefore, Allo may be an effective factor in maintaining synaptic integrity in the mesolimbic pathway.

Relating neurosteroid modulation of inhibitory neurotransmission to behaviour

Studies in the 1980s revealed endogenous metabolites of progesterone and deoxycorticosterone to be potent, efficacious, positive allosteric modulators (PAMs) of the GABA_A receptor (GABA_A R). The discovery that such steroids are locally synthesised in the central nervous system (CNS) promoted the thesis that neural inhibition in the CNS may be "fine-tuned" by these neurosteroids to influence behaviour. In preclinical studies, these neurosteroids exhibited anxiolytic, anticonvulsant, analgesic and sedative properties and, at relatively high doses, induced a state of general anaesthesia, a profile consistent with their interaction with GABA_A Rs. However, realising the therapeutic potential of either endogenous neurosteroids or synthetic "neuroactive" steroids has proven challenging. Recent approval by the Food and Drug Administration of the use of allopregnanolone (brexanolone) to treat postpartum depression has rekindled enthusiasm for exploring their potential as new medicines. Although neurosteroids are selective for GABA_A Rs, they exhibit little or no selectivity across the many GABA_A R subtypes. Nevertheless, a relatively minor population of receptors incorporating the δ-subunit (δ-GABA_A Rs) appears to be an important contributor to their behavioural effects. Here, we consider how neurosteroids acting upon GABA_A Rs influence neuronal signalling, as well as how such effects may acutely and persistently influence behaviour, and explore the case for developing selective PAMs of δ-GABA_A R subtypes for the treatment of psychiatric disorders.

Mechanisms affecting brain remodeling in depression: do all roads lead to impaired fibrinolysis?

Fibrinolysis occurs when plasminogen activators, such as tissue plasminogen activator (tPA), convert plasminogen to plasmin, which dissolves the fibrin clot. The proteolytic activity of tPA and plasmin is not restricted to fibrin degradation. In the extravascular space, these two proteases modify a variety of substrates other than fibrin, playing a crucial role in physiological and pathological tissue remodeling. In the brain, for example, tPA and plasmin mediate the conversion of brain-derived neurotrophic factor precursor (proBDNF) to mature brain-derived neurotrophic factor precursor (BDNF). Thus, the fibrinolytic system influences processes reported to be dysfunctional in depression, including neurogenesis, synaptic plasticity, and reward processing. The hypothesis that decreased fibrinolytic activity is an important element in the pathogenesis of depression is supported by the association between depression and increased levels of plasminogen activator inhibitor (PAI)-1, the main inhibitor of tPA. Also, various biochemical markers of depression induce PAI-1 synthesis, including hypercortisolism, hyperinsulinemia, hyperleptinemia, increased levels of cytokines, and hyperhomocysteinemia. Moreover, hypofibrinolysis provides a link between depression and emotional eating, binge eating, vegetarianism, and veganism. This paper discusses the role of reduced fibrinolytic activity in the bidirectional interplay between depression and its somatic manifestations and complications. It also reviews evidence that abnormal fibrinolysis links heterogeneous conditions associated with treatment-resistant depression. Understanding the role of hypofibrinolysis in depression may open new avenues for its treatment.

Adult Neurogenesis and Antidepressant Treatment: The Surprise Finding by Ron Duman and the Field 20 Years Later

Of Duman's many influential findings, the finding that long-term treatment with antidepressant drugs produces an increase in neurogenesis in the subgranular zone of the adult hippocampus may be one of the most enduring and far-reaching. This novel discovery and his decades of continued research in the field led to a new hypothesis about the mechanism of action of antidepressants, providing a critical step in our understanding of the neurotrophic hypothesis of depression and synaptic plasticity. It is now accepted that antidepressant treatments can oppose and even reverse the effects of stress on the brain and on newly born hippocampal cells, possibly via neurotrophic factors, which Duman had continued to explore. Furthermore, ablation studies have shown preclinically that hippocampal neurogenesis may be necessary for some of the clinical effects of antidepressant drugs. Duman's laboratory continued to interrogate neurotrophins and synaptic plasticity, demonstrating that newer clinically approved antidepressant compounds also affect neurogenesis and synaptic plasticity. In this review, we summarize Duman's original findings and discuss the current state of the field of neurogenesis with respect to animal models and human studies and the implications of those findings on the field of drug discovery.

The Role of HPA Axis and Allopregnanolone on the Neurobiology of Major Depressive Disorders and PTSD

Under stressful conditions, the hypothalamic-pituitary-adrenal (HPA) axis acts to promote transitory physiological adaptations that are often resolved after the stressful stimulus is no longer present. In addition to corticosteroids (e.g., cortisol), the neurosteroid allopregnanolone (3α,5α-tetrahydroprogesterone, 3α-hydroxy-5α-pregnan-20-one) participates in negative feedback mechanisms that restore homeostasis. Chronic, repeated exposure to stress impairs the responsivity of the HPA axis and dampens allopregnanolone levels, participating in the etiopathology of psychiatric disorders, such as major depressive disorder (MDD) and post-traumatic stress disorder (PTSD). MDD and PTSD patients present abnormalities in the HPA axis regulation, such as altered cortisol levels or failure to suppress cortisol release in the dexamethasone suppression test. Herein, we review the neurophysiological role of allopregnanolone both as a potent and positive GABAergic neuromodulator but also in its capacity of inhibiting the HPA axis. The allopregnanolone function in the mechanisms that recapitulate stress-induced pathophysiology, including MDD and PTSD, and its potential as both a treatment target and as a biomarker for these disorders is discussed.

Effect of Allopregnanolone on Spatial Memory and Synaptic Proteins in Animal Model of Metabolic Syndrome

Metabolic Syndrome (MetS) is considered a common disorder, especially with a sedentary lifestyle and unhealthy food consumption. Cognitive impairment is one of the MetS consequences that worsens the quality of life of the patients. The study aimed to assess the therapeutic effect of the neurosteroid Allopregnalonone on spatial memory and, therefore, the expression of two synaptic plasticity markers in the hippocampus. Thirty-two male rats were divided into four groups: control groups, MetS, and MetS + Allopregnalone. Spatial memory has been evaluated by the Y-maze task and blood pressure measured by the rat tail method. Biochemical evaluation of serum glucose, insulin, lipid profile, and hippocampal expression of Synaptophysin and Associated Protein 43 (GAP-43) were performed for assessing Allopregnanolone on serum and hippocampal markers. Allopregnanolone therapy improved working spatial memory, hypertension, and biochemical markers measured in the serum and hippocampus.

Maternal Distress and Offspring Neurodevelopment: Challenges and Opportunities for Pre-clinical Research Models

Pre-natal exposure to acute maternal trauma or chronic maternal distress can confer increased risk for psychiatric disorders in later life. Acute maternal trauma is the result of unforeseen environmental or personal catastrophes, while chronic maternal distress is associated with anxiety or depression. Animal studies investigating the effects of pre-natal stress have largely used brief stress exposures during pregnancy to identify critical periods of fetal vulnerability, a paradigm which holds face validity to acute maternal trauma in humans. While understanding these effects is undoubtably important, the literature suggests maternal stress in humans is typically chronic and persistent from pre-conception through gestation. In this review, we provide evidence to this effect and suggest a realignment of current animal models to recapitulate this chronicity. We also consider candidate mediators, moderators and mechanisms of maternal distress, and suggest a wider breadth of research is needed, along with the incorporation of advanced -omics technologies, in order to understand the neurodevelopmental etiology of psychiatric risk.

Neurosteroids and Neurotrophic Factors: What Is Their Promise as Biomarkers for Major Depression and PTSD?

Even though major depressive disorder (MDD) and post-traumatic stress disorder (PTSD) are among the most prevalent and incapacitating mental illnesses in the world, their diagnosis still relies solely on the characterization of subjective symptoms (many of which are shared by multiple disorders) self-reported by patients. Thus, the need for objective measures that aid in the detection of and differentiation between psychiatric disorders becomes urgent. In this paper, we explore the potential of neurosteroids and neurotrophic proteins as biomarkers for MDD and PTSD. Circulating levels of the GABAergic neuroactive steroid, allopregnanolone, are diminished in MDD and PTSD patients, which corroborates the finding of depleted neurosteroid levels observed in animal models of these disorders. The neurotrophic protein, brain-derived neurotropic factor (BDNF), is also reduced in the periphery and in the brain of MDD patients and depressed-like animals that express lower neurosteroid levels. Although the role of BDNF in PTSD psychopathology seems less clear and merits more research, we propose a causal link between allopregnanolone levels and BDNF expression that could function as a biomarker axis for the diagnosis of both MDD and PTSD.

The Effect of Allopregnanolone on Enzymatic Activity of the DNA Base Excision Repair Pathway in the Sheep Hippocampus and Amygdala under Natural and Stressful Conditions

The neurosteroid allopregnanolone (AL) has many beneficial functions in the brain. This study tested the hypothesis that AL administered for three days into the third brain ventricle would affect the enzymatic activity of the DNA base excision repair (BER) pathway in the hippocampal CA1 and CA3 fields and the central amygdala in luteal-phase sheep under both natural and stressful conditions. Acute stressful stimuli, including isolation and partial movement restriction, were used on the last day of infusion. The results showed that stressful stimuli increased N-methylpurine DNA glycosylase (MPG), thymine DNA glycosylase (TDG), 8-oxoguanine glycosylase (OGG1), and AP-endonuclease 1 (APE1) mRNA expression, as well as repair activities for 1,N6-ethenoadenine (εA), 3,N4-ethenocytosine (εC), and 8-oxoguanine (8-oxoG) compared to controls. The stimulated events were lower in stressed and AL-treated sheep compared to sheep that were only stressed (except MPG mRNA expression in the CA1 and amygdala, as well as TDG mRNA expression in the CA1). AL alone reduced mRNA expression of all DNA repair enzymes (except TDG in the amygdala) relative to controls and other groups. DNA repair activities varied depending on the tissue-AL alone stimulated the excision of εA in the amygdala, εC in the CA3 and amygdala, and 8-oxoG in all tissues studied compared to controls. However, the excision efficiency of lesioned bases in the AL group was lower than in the stressed and stressed and AL-treated groups, with the exception of εA in the amygdala. In conclusion, the presented modulating effect of AL on the synthesis of BER pathway enzymes and their repair capacity, both under natural and stressful conditions, indicates another functional role of this neurosteroid in brain structures.

Enriched Environment and Social Isolation Affect Cognition Ability via Altering Excitatory and Inhibitory Synaptic Density in Mice Hippocampus

The purpose of the study was to examine whether the underlying mechanism of the alteration of cognitive ability and synaptic plasticity induced by the housing environment is associated with the balance of excitatory/inhibitory synaptic density. Enriched environment (EE) and social isolation (SI) are two different housing environment, and one is to give multiple sensory environments, the other is to give monotonous and lonely environment. Male 4-week-old C57 mice were divided into three groups: CON, EE and SI. They were housed in the different cage until 3 months of age. Morris water maze and novel object recognition were performed. Long term potentiation (LTP), depotentiation (DEP) and local field potentials were recorded in the hippocampal perforant pathway and dentate gyrus (DG) region. The data showed that EE enhanced the ability of spatial learning, reversal learning and memory as well as LTP/DEP in the hippocampal DG region. Meanwhile, SI reduced those abilities and the level of LTP/DEP. Moreover, there were higher couplings of both phase-amplitude and phase-phase in the EE group, and lower couplings of them in the SI group compared to that in the CON group. Western blot and immunofluorescence analysis showed that EE significantly enhanced the level of PSD-95, NR2B and DCX; however, SI reduced them but increased GABA_AR_α1 and decreased DCX levels. The data suggests that the cognitive functions, synaptic plasticity, neurogenesis and neuronal oscillatory patterns were significantly impacted by housing environment via possibly changing the balance of excitatory and inhibitory synaptic density.