Alcohol-induced exacerbation of ischemic brain injury: role of NAD(P)H oxidase

Prenatal exposure to alcohol impairs responses of cerebral arterioles to activation of potassium channels: Role of oxidative stress

BACKGROUND

Potassium channels play an important role in the basal tone and dilation of cerebral resistance arterioles in response to many stimuli. However, the effect of prenatal alcohol exposure (PAE) on specific potassium channel function remains unknown. The first goal of this study was to determine the influence of PAE on the reactivity of cerebral arterioles to activation of ATP-sensitive potassium (KATP ) and BK channels. Our second goal was to determine whether oxidative stress contributed to potassium channel dysfunction of cerebral arterioles following PAE.

METHODS

We fed Sprague-Dawley dams a liquid diet with or without alcohol (3% EtOH) for the duration of their pregnancy (21 to 23 days). We examined in vivo responses of cerebral arterioles in control and PAE male and female offspring (14 to 16 weeks after birth) to activators of potassium channels (Iloprost [BK channels] and pinacidil [KATP channels]), before and following inhibition of oxidative stress with apocynin.

RESULTS

We found that PAE impaired dilation of cerebral arterioles in response to activation of potassium channels with iloprost and pinacidil, and this impairment was similar in male and female rats. In addition, treatment with apocynin reversed the impaired vasodilation to iloprost and pinacidil in PAE rats to levels observed in control rats. This effect of apocynin also was similar in male and female rats.

CONCLUSIONS

PAE induces dysfunction in the ability of specific potassium channels to dilate cerebral arterioles which appears to be mediated by an increase in oxidative stress. We suggest that these alterations in potassium channel function may contribute to the pathogenesis of cerebral vascular abnormalities and/or behavioral/cognitive deficits observed in fetal alcohol spectrum disorders.

Rosiglitazone restores nitric oxide synthase-dependent reactivity of cerebral arterioles in rats exposed to prenatal alcohol

BACKGROUND

Prenatal exposure to alcohol leads to a greater incidence of many cardiovascular-related diseases, presumably via a mechanism that may involve increased oxidative stress. An agonist of peroxisome proliferator-activated receptor gamma (PPARγ; rosiglitazone) has been shown to suppress alcohol-induced neuroinflammation and oxidative stress. The goal of this study was to determine whether acute and chronic treatment with rosiglitazone could restore or prevent impaired nitric oxide synthase (NOS)-dependent responses of cerebral arterioles in male and female adult (14-16 weeks old) rats exposed to alcohol in utero.

METHODS

We fed Sprague-Dawley dams a liquid diet with or without 3% ethanol for the duration of their pregnancy (21-23 days). In the first series of studies, we examined the reactivity of cerebral arterioles to eNOS- (ADP), nNOS-dependent (NMDA), and NOS-independent agonists in male and female adult rats before and during acute (1 hour) topical application of rosiglitazone (1 µM). In a second series of studies, we examined the influence of chronic treatment with rosiglitazone (3 mg/kg/day in drinking water for 2-3 weeks) on the responses of cerebral arterioles in male and female adult rats exposed to alcohol in utero.

RESULTS

We found that in utero exposure to alcohol similarly reduced responses of cerebral arterioles to ADP and NMDA, but not to nitroglycerin in male and female adult rats. In addition, acute treatment of the male and female adult rats with rosiglitazone similarly restored this impairment in cerebral vascular function to that observed in controls. We also found that chronic treatment with rosiglitazone prevented impaired vascular function in male and female adult rats that were exposed to alcohol in utero.

CONCLUSIONS

PPARγ activation may be an effective and relevant treatment to reverse or prevent cerebral vascular abnormalities associated with prenatal exposure to alcohol.

Acute Alcohol Intoxication With Accompanying Neurovascular Decline in Young Adults: A Sobering Case Series

With an increase in both popularity and incidence, young adults continue to consume increasing amounts of ethanol-containing beverages at alarmingly short intervals, at times, far surpassing the threshold of binge drinking. From mixed beverages to party delights, high-concentration ethanol consumption continues to wreak havoc on the health of the younger generation. In this dual case series, we discuss two unique cases of alcohol-induced neurovascular compromise following episodes of high-volume ethanol consumption and acute neurovascular decline with varying outcomes. These cases highlight the hyperacute onset of severe pathology and the dire need for immediate medical intervention. While outcomes vary from case to case, our findings are congruent with those of vast medical literature that supports the consensus that immediate intervention to restore neurovascular flow is crucial for desired outcomes. At the end of the day, we cannot control the amount of alcohol that enters the mouths of our patients, but rather, we can educate them on safer practices while highlighting the risk and life-changing consequences of such risky behavior.

Influence of Chronic Ethanol Consumption on Apoptosis and Autophagy Following Transient Focal Cerebral Ischemia in Male Mice

Stroke remains one of the leading causes of permanent disability and death worldwide. Apoptosis and autophagy are two key elements involved in ischemic brain damage. Ethanol is a commonly used and abused chemical substance that affects the prognosis of ischemic stroke. We determined the influence of chronic ethanol consumption on apoptosis and autophagy following transient focal cerebral ischemia. Male C57BL/6 J mice were randomly divided into three groups and gavage fed with 0.7 and 2.8 g/kg/day ethanol or volume-matched water daily for 8 weeks. DNA fragmentation, TUNEL-positive neurons, cleaved caspase-3-positive neurons, translocation of mitochondrial cytochrome C and apoptosis inducing factor (AIF), LC3B-positive neurons, and expression of LC3B, Beclin-1 and Bcl-2 in peri-infarct cortex were evaluated at 24 hours of reperfusion after a 90-minute unilateral middle cerebral artery occlusion (MCAO). Cerebral ischemia/reperfusion (I/R) injury was significantly improved in the 0.7 g/kg/d ethanol group but worsened in the 2.8 g/kg/d ethanol group. DNA fragmentation was significantly increased at 24 hours of reperfusion in all groups. However, the magnitude of the increase was significantly less in the 0.7 g/kg/d ethanol group. In addition, both cleaved caspase-3-positive neurons and TUNEL-positive neurons were significantly less in 0.7 g/kg/d ethanol group. Furthermore, translocation of mitochondrial cytochrome C and AIF was significantly alleviated in the 0.7 g/kg/d ethanol group. On the other hand, baseline expression of LC3B was significantly reduced in the 2.8 g/kg/d ethanol group. Post-ischemic expression of LC3B and LC3B-positive neurons were significantly attenuated in both 0.7 and 2.8 g/kg/d ethanol groups. Moreover, although post-ischemic expression of Beclin-1 was not altered in the ethanol groups, post-ischemic expression of Bcl-2 was significantly greater in both 0.7 and 2.8 g/kg/d ethanol groups. Our findings suggest that light ethanol consumption may protect against cerebral I/R injury by suppressing post-ischemic apoptosis, whereas heavy ethanol consumption may exacerbate cerebral I/R injury by suppressing autophagy.

In Utero Exposure to Alcohol Impairs Reactivity of Cerebral Arterioles and Increases Susceptibility of the Brain to Damage Following Ischemia/Reperfusion in Adulthood

BACKGROUND

Maternal consumption of alcohol produces abnormalities in the developing fetus and can contribute to an increased incidence of many cardiovascular-related diseases. The first goal of this study was to determine whether in utero exposure to alcohol influences reactivity of cerebral arterioles in adult (12 to 15 weeks old) rats. The second goal of this study was to examine whether in utero exposure to alcohol increased the susceptibility of the brain to damage following an ischemic event in adult rats.

METHODS

We fed Sprague Dawley dams a liquid diet with or without alcohol (3% ethanol) for the duration of their pregnancy (21 to 23 days). In the first series of studies, we examined reactivity of cerebral arterioles to endothelial nitric oxide synthase (eNOS)- (adenosine diphosphate [ADP]) and neuronal nitric oxide synthase (nNOS)-dependent N-methyl-D-aspartate (NMDA, and NOS-independent agonists in adult rats before and during application of l-NMMA. In another series of studies, we examined infarct volume following middle cerebral artery occlusion in adult offspring exposed to alcohol in utero. In both series of studies, we also determined the role for an increase in oxidative stress by feeding dams apocynin for the duration of their pregnancy.

RESULTS

We found that in utero exposure to alcohol reduced responses of cerebral arterioles to ADP and NMDA, but not to nitroglycerin in adult rats. In addition, treatment of the dams with apocynin prevented this impairment in cerebral vascular function. We also found that in utero exposure to alcohol worsened brain damage following ischemia/reperfusion in adult rats and that treatment of dams with apocynin prevented this increase in brain damage following ischemia/reperfusion.

CONCLUSIONS

We suggest that our findings may have important implications for the pathogenesis of brain abnormalities associated with fetal alcohol exposure.

Dose-Dependent Influences of Ethanol on Ischemic Stroke: Role of Inflammation

Chronic ethanol consumption dose-dependently affects both incidence and prognosis of ischemic stroke. Our goal was to determine whether the influence of chronic ethanol consumption on ischemic stroke is related to an altered inflammatory profile in the brain. Male C57BL/6J mice were divided into six groups and gavage fed with 0.175, 0.35, 0.7, 1.4, 2.8 g/kg/day ethanol or volume-matched water once a day for 8 weeks. Adhesion molecules, microglial activation, neutrophil infiltration, pro- and anti-inflammatory cytokines/chemokines, blood-brain barrier (BBB) permeability, and matrix metallopeptidases (MMPs) in the cerebral cortex before and following a 90-min unilateral middle cerebral artery occlusion (MCAO)/24-h reperfusion were evaluated. Brain ischemia/reperfusion (I/R) injury was significantly reduced in 0.7 g/kg/day ethanol group (peak blood ethanol concentration: 9 mM) and worsened in 2.8 g/kg/day ethanol group (peak blood ethanol concentration: 37 mM). Baseline E-selectin was downregulated in all ethanol groups, whereas baseline intercellular adhesion molecule-1 (ICAM-1) was only downregulated in 0.35 and 0.7 g/kg/day ethanol groups. Interestingly, baseline vascular cell adhesion molecule-1 (VCAM-1) was upregulated in 0.35, 0.7, and 1.4 g/kg/day ethanol groups. Post-ischemic upregulation of ICAM-1 and E-selectin were suppressed in all ethanol groups. Post-ischemic neutrophil infiltration and microglial activation were significantly less in the low-moderate (0.175–1.4 g/kg/day) ethanol groups but greater in the 2.8 g/kg/day ethanol group compared to the vehicle group. At basal conditions, ethanol increased one pro- and two anti-inflammatory cytokines/chemokines at the 0.7 g/kg/day dose, and 13 pro- and eight anti-inflammatory cytokines/chemokines at the 2.8 g/kg/day dose. After ischemia, 0.7 g/kg/day ethanol suppressed post-ischemic pro-inflammatory cytokines/chemokines and enhanced post-ischemic anti-inflammatory cytokines/chemokines. Moreover, 0.7 g/kg/day ethanol significantly reduced baseline MMP-9 activity and alleviated post-ischemic BBB breakdown. On the other hand, 2.8 g/kg/day ethanol worsened post-ischemic BBB breakdown. Our findings suggest that low-moderate ethanol consumption may prevent ischemic stroke and reduce brain I/R injury by suppressing inflammation, whereas heavy alcohol consumption may induce ischemic stroke and worsen brain I/R injury by aggravating inflammation.

Platelet Endothelial Cell Adhesion Molecule-1 and Oligodendrogenesis: Significance in Alcohol Use Disorders

Alcoholism is a chronic relapsing disorder with few therapeutic strategies that address the core pathophysiology. Brain tissue loss and oxidative damage are key components of alcoholism, such that reversal of these phenomena may help break the addictive cycle in alcohol use disorder (AUD). The current review focuses on platelet endothelial cell adhesion molecule 1 (PECAM-1), a key modulator of the cerebral endothelial integrity and neuroinflammation, and a targetable transmembrane protein whose interaction within AUD has not been well explored. The current review will elaborate on the function of PECAM-1 in physiology and pathology and infer its contribution in AUD neuropathology. Recent research reveals that oligodendrocytes, whose primary function is myelination of neurons in the brain, are a key component in new learning and adaptation to environmental challenges. The current review briefly introduces the role of oligodendrocytes in healthy physiology and neuropathology. Importantly, we will highlight the recent evidence of dysregulation of oligodendrocytes in the context of AUD and then discuss their potential interaction with PECAM-1 on the cerebral endothelium.

Effects of Chronic Alcohol Exposure on the Modulation of Ischemia-Induced Glutamate Release via Cannabinoid Receptors in the Dorsal Hippocampus

BACKGROUND

Chronic alcohol consumption is a critical contributing factor to ischemic stroke, as it enhances ischemia-induced glutamate release, leading to more severe excitotoxicity and brain damage. But the neural mechanisms underlying this phenomenon are poorly understood.

METHODS

We evaluated the effects of chronic alcohol exposure on the modulation of ischemia-induced glutamate release via CB1 and CB2 cannabinoid receptors during middle cerebral artery occlusion, using in vivo microdialysis coupled with high-performance liquid chromatography, in alcohol-naïve rats or rats after 1 or 30 days of withdrawal from chronic ethanol intake (6% v/v for 14 days).

RESULTS

Intra-dorsal hippocampus (DH) infusions of ACEA or JWH133, selective CB1 or CB2 receptor agonists, respectively, decreased glutamate release in the DH in alcohol-naïve rats in a dose-dependent manner. Such an effect was reversed by co-infusions of SR141716A or AM630, selective CB1 or CB2 receptor antagonists, respectively. After 30 days, but not 1 day of withdrawal, ischemia induced an enhancement in glutamate release in the DH, as compared with non-alcohol-treated control group. Intra-DH infusions of JWH133, but not ACEA, inhibited ischemia-induced glutamate release in the DH after 30 days of withdrawal. Finally, 1 day of withdrawal did not alter the protein level of CB1 or CB2 receptors in the DH, as compared to non-alcohol-treated control rats. Whereas 30 days of withdrawal robustly decreased the protein level of CB1 receptors, but failed to alter the protein level of CB2 receptors, in the DH, as compared to non-alcohol-treated control rats.

CONCLUSIONS

Together, these findings suggest that loss of expression/function of CB1 receptors, but not CB2 receptors in the DH, is correlated with the enhancement of ischemia-induced glutamate release after prolonged alcohol withdrawal.

NOX2 As a Target for Drug Development: Indications, Possible Complications, and Progress

SIGNIFICANCE

NOX2 is important for host defense, and yet is implicated in a large number of diseases in which inflammation plays a role in pathogenesis. These include acute and chronic lung inflammatory diseases, stroke, traumatic brain injury, and neurodegenerative diseases, including Alzheimer's and Parkinson's Diseases.

RECENT ADVANCES

Recent drug development programs have targeted several NOX isoforms that are implicated in a variety of diseases. The focus has been primarily on NOX4 and NOX1 rather than on NOX2, due, in part, to concerns about possible immunosuppressive side effects. Nevertheless, NOX2 clearly contributes to the pathogenesis of many inflammatory diseases, and its inhibition is predicted to provide a novel therapeutic approach.

CRITICAL ISSUES

Possible side effects that might arise from targeting NOX2 are discussed, including the possibility that such inhibition will contribute to increased infections and/or autoimmune disorders. The state of the field with regard to existing NOX2 inhibitors and targeted development of novel inhibitors is also summarized.

FUTURE DIRECTIONS

NOX2 inhibitors show particular promise for the treatment of inflammatory diseases, both acute and chronic. Theoretical side effects include pro-inflammatory and autoimmune complications and should be considered in any therapeutic program, but in our opinion, available data do not indicate that they are sufficiently likely to eliminate NOX2 as a drug target, particularly when weighed against the seriousness of many NOX2-related indications. Model studies demonstrating efficacy with minimal side effects are needed to encourage future development of NOX2 inhibitors as therapeutic agents.

Pathophysiology and Treatments of Oxidative Injury in Ischemic Stroke: Focus on the Phagocytic NADPH Oxidase 2

SIGNIFICANCE

Phagocytes play a key role in promoting the oxidative stress after ischemic stroke occurrence. The phagocytic NADPH oxidase (NOX) 2 is a membrane-bound enzyme complex involved in the antimicrobial respiratory burst and free radical production in these cells.

RECENT ADVANCES

Different oxidants have been shown to induce opposite effects on neuronal homeostasis after a stroke. However, several experimental models support the detrimental effects of NOX activity (especially the phagocytic isoform) on brain recovery after stroke. Therapeutic strategies selectively targeting the neurotoxic ROS and increasing neuroprotective oxidants have recently produced promising results.

CRITICAL ISSUES

NOX2 might promote carotid plaque rupture and stroke occurrence. In addition, NOX2-derived reactive oxygen species (ROS) released by resident and recruited phagocytes enhance cerebral ischemic injury, activating the inflammatory apoptotic pathways. The aim of this review is to update evidence on phagocyte-related oxidative stress, focusing on the role of NOX2 as a potential therapeutic target to reduce ROS-related cerebral injury after stroke.

FUTURE DIRECTIONS

Radical scavenger compounds (such as Ebselen and Edaravone) are under clinical investigation as a therapeutic approach against stroke. On the other hand, NOX inhibition might represent a promising strategy to prevent the stroke-related injury. Although selective NOX inhibitors are not yet available, nonselective compounds (such as apocynin and fasudil) provided encouraging results in preclinical studies. Whereas additional studies are needed to better evaluate this therapeutic potential in human beings, the development of specific NOX inhibitors (such as monoclonal antibodies, small-molecule inhibitors, or aptamers) might further improve brain recovery after stroke.

Which NADPH oxidase isoform is relevant for ischemic stroke? The case for nox 2

Significance and Recent Advances: Ischemic stroke is the leading cause of disability and third in mortality in industrialized nations. Immediate restoration of cerebral blood flow is crucial to salvage brain tissue, but only few patients are eligible for recanalization therapy. Thus, the need for alternative neuroprotective strategies is huge, and antioxidant interventions have long been studied in this context. Reactive oxygen species (ROS) physiologically serve as signaling molecules, but excessive amounts of ROS, as generated during ischemia/reperfusion (I/R), contribute to tissue injury.

CRITICAL ISSUES

Nevertheless and despite a strong rational of ROS being a pharmacological target, all antioxidant interventions failed to improve functional outcome in human clinical trials. Antioxidants may interfere with physiological functions of ROS or do not reach the crucial target structures of ROS-induced injury effectively.

FUTURE DIRECTIONS

Thus, a potentially more promising approach is the inhibition of the source of disease-promoting ROS. Within recent years, NADPH oxidases (Nox) of the Nox family have been identified as mediators of neuronal pathology. As, however, several Nox homologs are expressed in neuronal tissue, and as many of the pharmacological inhibitors employed are rather unspecific, the concept of Nox as mediators of brain damage is far from being settled. In this review, we will discuss the contribution of Nox homologs to I/R injury at large as well as to neuronal damage in particular. We will illustrate that the current data provide evidence for Nox2 as the most important NADPH oxidase mediating cerebral injury.

Method parameters' impact on mortality and variability in rat stroke experiments: a meta-analysis

Background

Even though more than 600 stroke treatments have been shown effective in preclinical studies, clinically proven treatment alternatives for cerebral infarction remain scarce. Amongst the reasons for the discrepancy may be methodological shortcomings, such as high mortality and outcome variability, in the preclinical studies. A common approach in animal stroke experiments is that A) focal cerebral ischemia is inflicted, B) some type of treatment is administered and C) the infarct sizes are assessed. However, within this paradigm, the researcher has to make numerous methodological decisions, including choosing rat strain and type of surgical procedure. Even though a few studies have attempted to address the questions experimentally, a lack of consensus regarding the optimal methodology remains.

Methods

We therefore meta-analyzed data from 502 control groups described in 346 articles to find out how rat strain, procedure for causing focal cerebral ischemia and the type of filament coating affected mortality and infarct size variability.

Results

The Wistar strain and intraluminal filament procedure using a silicone coated filament was found optimal in lowering infarct size variability. The direct and endothelin methods rendered lower mortality rate, whereas the embolus method increased it compared to the filament method.

Conclusions

The current article provides means for researchers to adjust their middle cerebral artery occlusion (MCAo) protocols to minimize infarct size variability and mortality.

Nutraceutical strategies for ameliorating the toxic effects of alcohol

Rodent studies reveal that oxidative stress, much of it generated via induction/activation of NADPH oxidase, is a key mediator of a number of the pathogenic effects of chronic ethanol overconsumption. The highly reactive ethanol metabolite acetaldehyde is a key driver of this oxidative stress, and doubtless works in other ways to promote alcohol-induced pathology. Effective antioxidant measure may therefore be useful for mitigating the adverse health consequences of alcohol consumption; spirulina may have particular utility in this regard, as its chief phycochemical phycocyanobilin has recently been shown to function as an inhibitor of certain NADPH oxidase complexes, mimicking the physiological role of its chemical relatives biliverdin/bilirubin in this respect. Moreover, certain nutraceuticals, including taurine, pantethine, and lipoic acid, may have the potential to boost the activity of the mitochondrial isoform of aldehyde dehydrogenase, ALDH-2, accelerating conversion of acetaldehyde to acetate (which arguably has protective health effects). Little noticed clinical studies conducted nearly three decades ago reported that pre-ingestion of either taurine or pantethine could blunt the rise in blood acetaldehyde following ethanol consumption. Other evidence suggests that lipoic acid may function within mitochondria to maintain aldehyde dehydrogenase in a reduced active conformation; the impact of this agent on ethanol metabolism has however received little or no study. Studies evaluating the impact of nutracetical strategies on prevention of hangovers - which likely are mediated by acetaldehyde - may represent a quick, low-cost way to identify nutraceutical regimens that merit further attention for their potential impact on alcohol-induced pathology. Measures which boost or preserve ALDH-2 activity may also have important antioxidant potential, as this enzyme functions physiologically to protect cells from toxic aldehydes generated by oxidant stress.

Targeting NOX enzymes in the central nervous system: therapeutic opportunities

Among the pathogenic mechanisms underlying central nervous system (CNS) diseases, oxidative stress is almost invariably described. For this reason, numerous attempts have been made to decrease reactive oxygen species (ROS) with the administration of antioxidants as potential therapies for CNS disorders. However, such treatments have always failed in clinical trials. Targeting specific sources of reactive oxygen species in the CNS (e.g. NOX enzymes) represents an alternative promising option. Indeed, NOX enzymes are major generators of ROS, which regulate progression of CNS disorders as diverse as amyotrophic lateral sclerosis, schizophrenia, Alzheimer disease, Parkinson disease, and stroke. On the other hand, in autoimmune demyelinating diseases, ROS generated by NOX enzymes are protective, presumably by dampening the specific immune response. In this review, we discuss the possibility of developing therapeutics targeting NADPH oxidase (NOX) enzymes for the treatment of different CNS pathologies. Specific compounds able to modulate the activation of NOX enzymes, and the consequent production of ROS, could fill the need for disease-modifying drugs for many incurable CNS pathologies.

The neuroprotective effects of apocynin

The recognition of health benefits of phytomedicines and herbal supplements lead to an increased interest to understand the cellular and molecular basis of their biological activities. Apocynin (4-hydroxy-3-methoxy-acetophenone) is a constituent of the Himalayan medicinal herb Picrorhiza kurroa which is regarded as an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, a superoxide-producing enzyme. NADPH oxidase appears to be especially important in the modulation of redox-sensitive signaling pathways and also has been implicated in neuronal dysfunction and degeneration, and neuroinflammmation in diseases ranging from stroke, Alzheimer's and Parkinson's diseases to psychiatric disorders. In this review, we aim to give an overview of current literature on the neuroprotective effects of apocynin in the prevention and treatment of neurodegenerative disorders. Particular attention is given to in vivo studies.

Up-regulation of neurosteroid biosynthesis as a pharmacological strategy to improve behavioural deficits in a putative mouse model of post-traumatic stress disorder

Benzodiazepines remain the most frequently used psychotropic drugs for the treatment of anxiety spectrum disorders; however, their use is associated with the development of tolerance and dependence. Another major hindrance is represented by their lack of efficacy in many patients, including patients with post-traumatic stress disorder (PTSD). For these nonresponders, the use of selective serotonin reuptake inhibitors (SSRIs) has been the therapy of choice. In the past decade, clinical studies have suggested that the pharmacological action of SSRIs may include the ability of these drugs to normalise decreased brain levels of neurosteroids in patients with depression and PTSD; in particular, the progesterone derivative allopregnanolone, which potently, positively and allosterically modulates the action of GABA at GABA(A) receptors. Preclinical studies using the socially-isolated mouse as an animal model of PTSD have demonstrated that fluoxetine and congeners ameliorate anxiety-like behaviour, fear responses and aggressive behaviour expressed by such mice by increasing corticolimbic levels of allopregnanolone. This is a novel and more selective mechanism than serotonin reuptake inhibition, which, for half a century, has been considered to be the main molecular mechanism for the therapeutic action of SSRIs. Importantly, this finding may shed light on the high rates of SSRI resistance among patients with PTSD and depression, comprising disorders in which there appears to be a block in allopregnanolone synthesis. There are several different mechanisms by which such a block may occur, and SSRIs may only be corrective under some conditions. Thus, the up-regulation of allopregnanolone biosynthesis in corticolimbic neurones may offer a novel nontraditional pharmacological target for a new generation of potent nonsedating, anxiolytic medications for the treatment of anxiety, depression, and PTSD: selective brain steroidogenic stimulants.