Pregnenolone sulfate enhances neurogenesis and PSA-NCAM in young and aged hippocampus

Effects of small molecules on neurogenesis: Neuronal proliferation and differentiation

Neurons are believed to be non-proliferating cells. However, neuronal stem cells are still present in certain areas of the adult brain, although their proliferation diminishes with age. Just as with other cells, their proliferation and differentiation are modulated by various mechanisms. These mechanisms are foundational to the strategies developed to induce neuronal proliferation and differentiation, with potential therapeutic applications for neurodegenerative diseases. The most common among these diseases are Parkinson's disease and Alzheimer's disease, associated with the formation of β -amyloid (Aβ ) aggregates which cause a reduction in the number of neurons. Compounds such as LiCl, 4-aminothiazoles, Pregnenolone, ACEA, harmine, D2AAK1, methyl 3,4-dihydroxybenzoate, and shikonin may induce neuronal proliferation/differentiation through the activation of pathways: MAPK ERK, PI3K/AKT, NFκ B, Wnt, BDNF, and NPAS3. Moreover, combinations of these compounds can potentially transform somatic cells into neurons. This transformation process involves the activation of neuron-specific transcription factors such as NEUROD1, NGN2, ASCL1, and SOX2, which subsequently leads to the transcription of downstream genes, culminating in the transformation of somatic cells into neurons. Neurodegenerative diseases are not the only conditions where inducing neuronal proliferation could be beneficial. Consequently, the impact of pro-proliferative compounds on neurons has also been researched in mouse models of Alzheimer's disease.

Dual-color miniscope imaging of microvessels and neuronal activity in the hippocampus CA1 region of freely moving mice following alcohol administration

Moderate-to-heavy episodic ("binge") drinking is the most common form of alcohol consumption in the United States. Alcohol at binge drinking concentrations reduces brain artery diameter in vivo and in vitro in many species including rats, mice, and humans. Despite the critical role played by brain vessels in maintaining neuronal function, there is a shortage of methodologies to simultaneously assess neuron and blood vessel function in deep brain regions. Here, we investigate cerebrovascular responses to ethanol by choosing a deep brain region that is implicated in alcohol disruption of brain function, the hippocampal CA1, and describe the process for obtaining simultaneous imaging of pyramidal neuron activity and diameter of nearby microvessels in freely moving mice via a dual-color miniscope. Recordings of neurovascular events were performed upon intraperitoneal injection of saline versus 3 g/kg ethanol in the same mouse. In male mice, ethanol mildly increased the amplitude of calcium signals while robustly decreasing their frequency. Simultaneously, ethanol decreased microvessel diameter. In females, ethanol did not change the amplitude or frequency of calcium signals from CA1 neurons but decreased microvessel diameter. A linear regression of ethanol-induced reduction in number of active neurons and microvessel constriction revealed a positive correlation (R = 0.981) in females. Together, these data demonstrate the feasibility of simultaneously evaluating neuronal and vascular components of alcohol actions in a deep brain area in freely moving mice, as well as the sexual dimorphism of hippocampal neurovascular responses to alcohol.

Alcohol and pregnenolone interaction on cerebral arteries through targeting of vascular smooth muscle Ca2+- and voltage-gated K+ channels of big conductance

Despite the significant number of people who may be taking pregnenolone supplements while drinking alcohol (ethanol), the widely documented cerebrovascular actions of pregnenolone and ethanol, and the critical dependence of cerebrovascular function on cerebral artery diameter, there are no studies addressing the effect of pregnenolone + ethanol in combination on cerebral artery diameter. We investigated this by evaluating the effect of this combination on middle cerebral artery diameter in male and female C57BL/6J mice, both in vivo and in vitro. The use of de-endothelialized, in vitro pressurized middle cerebral artery segments allowed us to conduct a concentration-response study of constriction induced by pregnenolone ± ethanol, in which drug action could be evaluated independently of circulating and endothelial factors. In both male and female animals, pregnenolone at lower concentrations (≤1 μM) was found to synergize with 50 mM ethanol to cause vasoconstriction. In both sexes, this synergism was lost as one or both vasoconstrictors approached their maximally effective concentrations (75 mM and 10 μM for ethanol and pregnenolone, respectively), whether this was evaluated in vitro or in vivo using a cranial window. Vasoconstriction by pregnenolone + ethanol was abolished by 1 μM paxilline, indicating BK channel involvement. Moreover, cell-free recordings of BK channel activity in cerebral artery myocyte membranes showed that 10 μM pregnenolone and pregnenolone +50 mM ethanol reduced channel activity to an identical extent, suggesting that these drugs inhibit cerebrovascular BK channels via a common mechanism or mechanisms. Indeed, pregnenolone was found to disrupt allosteric coupling to C a 2 + -driven gating, as previously reported for ethanol.

Pregnenolone enhances the proliferation of mouse neural stem cells and promotes oligodendrogenesis, together with Sox10, and neurogenesis, along with Notch1 and Pax6

BACKGROUND

Pregnenolone is a precursor of various steroid hormones involved in osteoblast proliferation, microtubules polymerization and cell survival protection. Previous reports focused on the effects of pregnenolone metabolites on stem cell proliferation and differentiation; however, the effects of pregnenolone itself has not been well explored. The present study aimed to investigate the role of pregnenolone on NSC proliferation and to determine the doses required for NSC differentiation as well as the various genes involved in its mechanism of action.

METHODS

NSCs were isolated from the embryonic cortex of E14 mice, incubated for 5 days, and then treated with pregnenolone doses of 2, 5, 10, 15 and 20 μM for another 5 days. The number of neurospheres and neurosphere derived cells were then counted. Flow cytometry was used to evaluate the differentiation of NSCs into oligodendrocytes, astrocytes, and neurons. The expression level of Notch1, Pax6 and Sox10 genes were also measured by Real Time PCR after 5 days of treatment.

RESULTS

Our data suggest that treatment with 10 μM pregnenolone is optimal for NSC proliferation. In fact, this concentration caused the highest increase in the number of neurospheres and neurosphere derived cells, compared to the control group. In addition, treatment with low doses of pregnenolone (5 and 10 μM) caused a significant increase in NSC differentiation towards immature (Olig2⁺) and mature (MBP⁺) oligodendrocyte cell populations, compared to controls. However, NSC differentiation into neurons (beta III tubulin ⁺ cells) increased in all treatment groups, with the highest and most significant increase obtained at 15 μM concentration. It is worth noting that pregnenolone at the highest concentration of 15 μM decreased the number of astrocytes (GFAP+). Furthermore, there was an increase of Sox10 expression with low pregnenolone doses, leading to oligodendrogenesis, whereas Notch1 and Pax6 gene expression increased in pregnenolone groups with more neurogenesis.

CONCLUSION

Pregnenolone regulates NSCs proliferation in vitro. Treatment with low doses of pregnenolone caused an increase in the differentiation of NSCs into mature oligodendrocytes while higher doses increased the differentiation of NSCs into neurons. Oligodendrogenesis was accompanied by Sox10 while neurogenesis occurred together with Notch1 and Pax6 expression.

BK channel-forming slo1 proteins mediate the brain artery constriction evoked by the neurosteroid pregnenolone

Pregnenolone is a neurosteroid that modulates glial growth and differentiation, neuronal firing, and several brain functions, these effects being attributed to pregnenolone actions on the neurons and glial cells themselves. Despite the vital role of the cerebral circulation for brain function and the fact that pregnenolone is a vasoactive agent, pregnenolone action on brain arteries remain unknown. Here, we obtained in vivo concentration response curves to pregnenolone on middle cerebral artery (MCA) diameter in anesthetized male and female C57BL/6J mice. In both male and female animals, pregnenolone (1 nM-100 μM) constricted MCA in a concentration-dependent manner, its maximal effect reaching ~22-35% decrease in diameter. Pregnenolone action was replicated in intact and de-endothelialized, in vitro pressurized MCA segments with pregnenolone evoking similar constriction in intact and de-endothelialized MCA. Neurosteroid action was abolished by 1 μM paxilline, a selective blocker of Ca2+ - and voltage-gated K+ channels of large conductance (BK). Cell-attached, patch-clamp recordings on freshly isolated smooth muscle cells from mouse MCAs demonstrated that pregnenolone at concentrations that constricted MCAs in vitro and in vivo (10 μM), reduced BK activity (NPo), with an average decrease in NPo reaching 24.2%. The concentration-dependence of pregnenolone constriction of brain arteries and inhibition of BK activity in intact cells were paralleled by data obtained in cell-free, inside-out patches, with maximal inhibition reached at 10 μM pregnenolone. MCA smooth muscle BKs include channel-forming α (slo1 proteins) and regulatory β1 subunits, encoded by KCNMA1 and KCNMB1, respectively. However, pregnenolone-driven decrease in NPo was still evident in MCA myocytes from KCNMB1-/- mice. Following reconstitution of slo1 channels into artificial, binary phospholipid bilayers, 10 μM pregnenolone evoked slo1 NPo inhibition which was similar to that seen in native membranes. Lastly, pregnenolone failed to constrict MCA from KCNMA1-/- mice. In conclusion, pregnenolone constricts MCA independently of neuronal, glial, endothelial and circulating factors, as well as of cell integrity, organelles, complex membrane cytoarchitecture, and the continuous presence of cytosolic signals. Rather, this action involves direct inhibition of SM BK channels, which does not require β1 subunits but is mediated through direct sensing of the neurosteroid by the channel-forming α subunit.

Responsiveness of dentate neurons generated throughout adult life is associated with resilience to cognitive aging

During aging, some individuals are resilient to the decline of cognitive functions whereas others are vulnerable. These inter-individual differences in memory abilities have been associated with differences in the rate of hippocampal neurogenesis measured in elderlies. Whether the maintenance of the functionality of neurons generated throughout adult life is linked to resilience to cognitive aging remains completely unexplored. Using the immediate early gene Zif268, we analyzed the activation of dentate granule neurons born in adult (3-month-old), middle-aged (12-month-old), or senescent (18-month-old) rats (n = 96) in response to learning when animals reached 21 months of age. The activation of neurons born during the developmental period was also examined. We show that adult-born neurons can survive up to 19 months and that neurons generated 4, 10, or 19 months before learning, but not developmentally born neurons, are activated in senescent rats with good learning abilities. In contrast, aged rats with bad learning abilities do not exhibit activity-dependent regulation of newborn cells, whatever their birthdate. In conclusion, we propose that resilience to cognitive aging is associated with responsiveness of neurons born during adult life. These data add to our current knowledge by showing that the aging of memory abilities stems not only from the number but also from the responsiveness of adult-born neurons.

The Impact of Steroid Activation of TRPM3 on Spontaneous Activity in the Developing Retina

In the central nervous system, melastatin transient receptor potential (TRPM) channels function as receptors for the neurosteroid pregnenolone sulfate (PregS). The expression and function of TRPM3 has been explored in adult retina, although its role during development is unknown. We found, during the second postnatal week in mice, TRPM3 immunofluorescence labeled distinct subsets of inner retinal neurons, including a subset of retinal ganglion cells (RGCs), similar to what has been reported in the adult. Labeling for a TRPM3 promoter-driven reporter confirmed expression of the TRPM3 gene in RGCs and revealed additional expression in nearly all Müller glial cells. Using two-photon calcium imaging, we show that PregS and the synthetic TRPM3 agonist CIM0216 (CIM) induced prolonged calcium transients in RGCs, which were mostly absent in TRPM3 knock-out (KO) mice. These prolonged calcium transients were not associated with strong membrane depolarizations but induced c-Fos expression. To elucidate the impact of PregS-activation of TRPM3 on retinal circuits we took two sets of physiological measurements. First, PregS induced a robust increase in the frequency but not amplitude of spontaneous postsynaptic currents (PSCs). This increase was absent in the TRPM3 KO mice. Second, PregS induced a small increase in cell participation and duration of retinal waves, but this modulation persisted in TRPM3 KO mice, indicating PregS was acting on wave generating circuits independent of TRPM3 channels. Though baseline frequency of retinal waves was slightly reduced in the TRPM3 KO mice, other properties of waves were indistinguishable from wildtype. Together, these results indicate that the presence of neurosteroids impact spontaneous synaptic activity and retinal waves during development via both TRPM3-dependent and independent mechanisms.

GABA-A receptor modulating steroids in acute and chronic stress; relevance for cognition and dementia?

Cognitive dysfunction, dementia and Alzheimer's disease (AD) are increasing as the population worldwide ages. Therapeutics for these conditions is an unmet need. This review focuses on the role of the positive GABA-A receptor modulating steroid allopregnanolone (APα), it's role in underlying mechanisms for impaired cognition and of AD, and to determine options for therapy of AD. On one hand, APα given intermittently promotes neurogenesis, decreases AD-related pathology and improves cognition. On the other, continuous exposure of APα impairs cognition and deteriorates AD pathology. The disparity between these two outcomes led our groups to analyze the mechanisms underlying the difference. We conclude that the effects of APα depend on administration pattern and that chronic slightly increased APα exposure is harmful to cognitive function and worsens AD pathology whereas single administrations with longer intervals improve cognition and decrease AD pathology. These collaborative assessments provide insights for the therapeutic development of APα and APα antagonists for AD and provide a model for cross laboratory collaborations aimed at generating translatable data for human clinical trials.

Widespread Cortical Thickness Is Associated With Neuroactive Steroid Levels

Background

Neuroactive steroids are endogenous molecules with regenerative and neuroprotective actions. Both cortical thickness and many neuroactive steroid levels decline with age and are decreased in several neuropsychiatric disorders. However, a systematic examination of the relationship between serum neuroactive steroid levels and in vivo measures of cortical thickness in humans is lacking.

Methods

Peripheral serum levels of seven neuroactive steroids were assayed in United States military veterans. All (n = 143) subsequently underwent high-resolution structural MRI, followed by parcellelation of the cortical surface into 148 anatomically defined regions. Regression modeling was applied to test the association between neuroactive steroid levels and hemispheric total gray matter volume as well as region-specific cortical thickness. False discovery rate (FDR) correction was used to control for Type 1 error from multiple testing.

Results

Neuroactive steroid levels of allopregnanolone and pregnenolone were positively correlated with gray matter thickness in multiple regions of cingulate, parietal, and occipital association cortices (r = 0.20–0.47; p < 0.05; FDR-corrected).

Conclusion

Positive associations between serum neuroactive steroid levels and gray matter cortical thickness are found in multiple brain regions. If these results are confirmed, neuroactive steroid levels and cortical thickness may help in monitoring the clinical response in future intervention studies of neuroregenerative therapies.

Effects of progesterone on glucose uptake in neurons of Alzheimer's disease animals and cell models

AIMS

Alzheimer's disease (AD) is closely related to abnormal glucose metabolism in the central nervous system. Progesterone has been shown to have obvious neuroprotective effects in the pathogenesis of AD, but the specific mechanism has not been fully elucidated. Therefore, the purpose of this study was to investigate the effect of progesterone on the glucose metabolism of neurons in amyloid precursor protein (APP)/presenilin 1 (PS1) mice and Aβ-induced AD cell model.

MATERIALS AND METHODS

APP/PS1 mice were treated with 40 mg/kg progesterone for 40 days and primary cultured cortical neurons were treated with 1 μM progesterone for 48 h.Then behavior tests,2-NBDG glucose uptake tests and the protein levels of glucose transporter 3 (GLUT3), GLUT4, cAMP-response element binding protein (CREB) and proliferator-activated receptor γ (PPARγ) were examined.

KEY FINDINGS

Progesterone increased the expression levels of GLUT3 and GLUT4 in the cortex of APP/PS1 mice, accompanied by an improvement in learning and memory. Progesterone increased the levels of CREB and PPARγ in the cerebral cortex of APP/PS1 mice. In vitro, progesterone increased glucose uptake in primary cultured cortical neurons, this effect was blocked by the progesterone receptor membrane component 1 (PGRMC1)-specific blocker AG205 but not by the progesterone receptor (PR)-specific blocker RU486. Meanwhile, progesterone increased the expression of GLUT3, GLUT4, CREB and PPARγ, and AG205 blocked this effect.

SIGNIFICANCE

These results confirm that progesterone significantly improves the glucose metabolism of neurons.One of the mechanisms of this effect is that progesterone upregulates protein expression of GLUT3 and GLUT4 through pathways PGRMC1/CREB/GLUT3 and PGRMC1/PPARγ/GLUT4.

Neurosteroids: non-genomic pathways in neuroplasticity and involvement in neurological diseases

Neurosteroids are neuroactive brain-born steroids. They can act through non-genomic and/or through genomic pathways. Genomic pathways are largely described for steroid hormones: the binding to nuclear receptors leads to transcription regulation. Pregnenolone, Dehydroepiandrosterone, their respective sulfate esters and Allopregnanolone have no corresponding nuclear receptor identified so far whereas some of their non-genomic targets have been identified. Neuroplasticity is the capacity that neuronal networks have to change their structure and function in response to biological and/or environmental signals; it is regulated by several mechanisms, including those that involve neurosteroids. In this review, after a description of their biosynthesis, the effects of Pregnenolone, Dehydroepiandrosterone, their respective sulfate esters and Allopregnanolone on their targets will be exposed. We then shall highlight that neurosteroids, by acting on these targets, can regulate neurogenesis, structural and functional plasticity. Finally, we will discuss the therapeutic potential of neurosteroids in the pathophysiology of neurological diseases in which alterations of neuroplasticity are associated with changes in neurosteroid levels.

Comparison of Adult Hippocampal Neurogenesis and Susceptibility to Treadmill Exercise in Nine Mouse Strains

The genetic background of mice has various influences on the efficacy of physical exercise, as well as adult neurogenesis in the hippocampus. In this study, we investigated the basal level of hippocampal neurogenesis, as well as the effects of treadmill exercise on adult hippocampal neurogenesis in 9 mouse strains: 8 very commonly used laboratory inbred mouse strains (C57BL/6, BALB/c, A/J, C3H/HeJ, DBA/1, DBA/2, 129/SvJ, and FVB) and 1 outbred mouse strain (ICR). All 9 strains showed diverse basal levels of cell proliferation, neuroblast differentiation, and integration into granule cells in the sedentary group. C57BL/6 mice showed the highest levels of cell proliferation, neuroblast differentiation, and integration into granule cells at basal levels, and the DBA/2 mice showed the lowest levels. The efficacy of integration into granule cells was maximal in ICR mice. Treadmill exercise increased adult hippocampal neurogenesis in all 9 mouse strains. These results suggest that the genetic background of mice affects hippocampal neurogenesis and C57BL/6 mice are the most useful strain to assess basal levels of cell proliferation and neuroblast differentiation, but not maturation into granule cells. In addition, the DBA/2 strain is not suitable for studying hippocampal neurogenesis.

Control of Cell Survival in Adult Mammalian Neurogenesis

The fact that continuous proliferation of stem cells and progenitors, as well as the production of new neurons, occurs in the adult mammalian central nervous system (CNS) raises several basic questions concerning the number of neurons required in a particular system. Can we observe continued growth of brain regions that sustain neurogenesis? Or does an elimination mechanism exist to maintain a constant number of cells? If so, are old neurons replaced, or are the new neurons competing for limited network access among each other? What signals support their survival and integration and what factors are responsible for their elimination? This review will address these and other questions regarding regulatory mechanisms that control cell-death and cell-survival mechanisms during neurogenesis in the intact adult mammalian brain.

Hypothalamic-pituitary-adrenal (HPA) axis and aging

Human aging is associated with increasing frailty and morbidity which can result in significant disability. Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis may contribute to aging-related diseases like depression, cognitive deficits, and Alzheimer's disease in some older individuals. In addition to neuro-cognitive dysfunction, it has also been associated with declining physical performance possibly due to sarcopenia. This article reviews the pathophysiology of HPA dysfunction with respect to increased basal adrenocorticotropic hormone (ACTH) and cortisol secretion, decreased glucocorticoid (GC) negative feedback at the level of the paraventricular nucleus (PVN) of the hypothalamus, hippocampus (HC), and prefrontal cortex (PFC), and flattening of diurnal pattern of cortisol release. It is possible that the increased cortisol secretion is secondary to peripheral conversion from cortisone. There is a decline in pregnolone secretion and C-19 steroids (DHEA) with aging. There is a small decrease in aldosterone with aging, but a subset of the older population have a genetic predisposition to develop hyperaldosteronism due to the increased ACTH stimulation. The understanding of the HPA axis and aging remains a complex area with conflicting studies leading to controversial interpretations.

ADIOL protects against 3-NP-induced neurotoxicity in rats: Possible impact of its anti-oxidant, anti-inflammatory and anti-apoptotic actions

Huntington's disease (HD) is a progressive neurodegenerative disorder with a wide spectrum of cognitive, behavioral and motor abnormalities. The mitochondrial toxin 3-nitropropionic acid (3-NP) effectively induces specific behavioral changes and selective striatal lesions similar to that observed in HD. Some neurosteroids, synthesized in neurons and glial cells, previously showed neuroprotective abilities. 5-Androstene-3β-17β-diol (ADIOL) is a major metabolite of dehydroepiandrosterone (DHEA) with previously reported anti-inflammatory, anti-apoptotic and neuroprotective activities. The neuroprotective potential of ADIOL in HD was not previously investigated. Therefore, the present study investigated the neuroprotective effects of ADIOL against 3-NP-induced behavioral changes, oxidative stress, inflammation and apoptosis. Intraperitoneal administration of 3-NP (20mg/kg) for 4 consecutive days in rats caused significant loss in body weight, reduced prepulse inhibition (PPI) of acoustic startle response, locomotor hypoactivity with altered cortical/striatal histological structure, increased cortical/striatal oxidative stress, inflammation and apoptosis. Administration of ADIOL (25mg/kg, s.c.) for two days before 3-NP significantly attenuated the reduction in body weights and PPI, increased locomotor activity and restored cortical/striatal histological structure nearly to normal. Moreover, it displayed anti-oxidant, anti-inflammatory and anti-apoptotic activities as evidenced by the elevation of cortical and striatal reduced glutathione levels, reductions of cortical and striatal malondialdehyde, striatal tumor necrosis factor alpha and interleukin-6 levels. Only a small number of iNOS and caspase-3 positive cells were detected in sections from rats pretreated with ADIOL. This study suggests a potential neuroprotective role of ADIOL against 3-NP-induced Huntington's disease-like manifestations. Such neuroprotection can be attributed to its anti-oxidant, anti-inflammatory and anti-apoptotic activities.

Interaction between Neurogenesis and Hippocampal Memory System: New Vistas

During the last decade, the questions on the functionality of adult neurogenesis have changed their emphasis from if to how the adult-born neurons participate in a variety of memory processes. The emerging answers are complex because we are overwhelmed by a variety of behavioral tasks that apparently require new neurons to be performed optimally. With few exceptions, the hippocampal memory system seems to use the newly generated neurons for multiple roles. Adult neurogenesis has given the dentate gyrus new capabilities not previously thought possible within the scope of traditional synaptic plasticity. Looking at these new developments from the perspective of past discoveries, the science of adult neurogenesis has emerged from its initial phase of being, first, a surprising oddity and, later, exciting possibility, to the present state of being an integral part of mainstream neuroscience. The answers to many remaining questions regarding adult neurogenesis will come along only with our growing understanding of the functionality of the brain as a whole. This, in turn, will require integration of multiple levels of organization from molecules and cells to circuits and systems, ultimately resulting in comprehension of behavioral outcomes.

Frontiers in therapeutic development of allopregnanolone for Alzheimer's disease and other neurological disorders

Allopregnanolone (Allo), a neurosteroid, has emerged as a promising promoter of endogenous regeneration in brain. In a mouse model of Alzheimer’s disease, Allo induced neurogenesis, oligodendrogenesis, white matter generation and cholesterol homeostasis while simultaneously reducing β-amyloid and neuroinflammatory burden. Allo activates signaling pathways and gene expression required for regeneration of neural stem cells and their differentiation into neurons. In parallel, Allo activates systems to sustain cholesterol homeostasis and reduce β-amyloid generation. To advance Allo into studies for chronic human neurological conditions, we examined translational and clinical parameters: dose, regimen, route, formulation, outcome measures, and safety regulations. A treatment regimen of once per week at sub-sedative doses of Allo was optimal for regeneration and reduction in Alzheimer’s pathology. This regimen had a high safety profile following chronic exposure in aged normal and Alzheimer’s mice. Formulation of Allo for multiple routes of administration has been developed for both preclinical and clinical testing. Preclinical evidence for therapeutic efficacy of Allo spans multiple neurological diseases including Alzheimer’s, Parkinson’s, multiple sclerosis, Niemann-Pick, diabetic neuropathy, status epilepticus, and traumatic brain injury. To successfully translate Allo as a therapeutic for multiple neurological disorders, it will be necessary to tailor dose and regimen to the targeted therapeutic mechanisms and disease etiology. Treatment paradigms conducted in accelerated disease models in young animals have a low probability of successful translation to chronic diseases in adult and aged humans. Gender, genetic risks, stage and burden of disease are critical determinants of efficacy. This review focuses on recent advances in development of Allo for Alzheimer’s disease (AD) that have the potential to accelerate therapeutic translation for multiple unmet neurological needs.

Inflammatory Response in Patients under Coronary Artery Bypass Grafting Surgery and Clinical Implications: A Review of the Relevance of Dexmedetomidine Use

Despite the fact that coronary artery bypass grafting surgery (CABG) with cardiopulmonary bypass (CPB) prolongs life and reduces symptoms in patients with severe coronary artery diseases, these benefits are accompanied by increased risks. Morbidity associated with cardiopulmonary bypass can be attributed to the generalized inflammatory response induced by blood-xenosurfaces interactions during extracorporeal circulation and the ischemia/reperfusion implications, including exacerbated inflammatory response resembling the systemic inflammatory response syndrome (SIRS). The use of specific anesthetic agents with anti-inflammatory activity can modulate the deleterious inflammatory response. Consequently, anti-inflammatory anesthetics may accelerate postoperative recovery and better outcomes than classical anesthetics. It is known that the stress response to surgery can be attenuated by sympatholytic effects caused by activation of central (α-)2-adrenergic receptor, leading to reductions in blood pressure and heart rate, and more recently, that they can have anti-inflammatory properties. This paper discusses the clinical significance of the dexmedetomidine use, a selective (α-)2-adrenergic agonist, as a coadjuvant in general anesthesia. Actually, dexmedetomidine use is not in anesthetic routine, but this drug can be considered a particularly promising agent in perioperative multiple organ protection.

Allopregnanolone as regenerative therapeutic for Alzheimer's disease: Translational development and clinical promise

Herein, we review a translational development plan to advance allopregnanolone to the clinic as a regenerative therapeutic for neurodegenerative diseases, in particular Alzheimer's. Allopregnanolone, an endogenous neurosteroid that declines with age and neurodegenerative disease, was exogenously administered and assessed for safety and efficacy to promote neuro-regeneration, cognitive function and reduction of Alzheimer's pathology. Allopregnanolone-induced neurogenesis correlated with restoration of learning and memory function in a mouse model of Alzheimer's disease and was comparably efficacious in aged normal mice. Critical to success was a dosing and treatment regimen that was consistent with the temporal requirements of systems biology of regeneration in brain. A treatment regimen that adhered to regenerative requirements of brain was also efficacious in reducing Alzheimer's pathology. With an optimized dosing and treatment regimen, chronic allopregnanolone administration promoted neurogenesis, oligodendrogenesis, reduced neuroinflammation and beta-amyloid burden while increasing markers of white matter generation and cholesterol homeostasis. Allopregnanolone meets three of the four drug-like physicochemical properties described by Lipinski's rule that predict the success rate of drugs in development for clinical trials. Pharmacokinetic and pharmacodynamic outcomes, securing GMP material, development of clinically translatable formulations and acquiring regulatory approval are discussed. Investigation of allopregnanolone as a regenerative therapeutic has provided key insights into mechanistic targets for neurogenesis and disease modification, dosing requirements, optimal treatment regimen, route of administration and the appropriate formulation necessary to advance to proof of concept clinical studies to determine efficacy of allopregnanolone as a regenerative and disease modifying therapeutic for Alzheimer's disease.

The novel steroidal alkaloids dendrogenin A and B promote proliferation of adult neural stem cells

Dendrogenin A (DDA) and dendrogenin B (DDB) are new aminoalkyl oxysterols which display re-differentiation of tumor cells of neuronal origin at nanomolar concentrations. We analyzed the influence of dendrogenins on adult mice neural stem cell proliferation, sphere formation and differentiation. DDA and DDB were found to have potent proliferative effects in neural stem cells. Additionally, they induce neuronal outgrowth from neurospheres during in vitro cultivation. Taken together, our results demonstrate a novel role for dendrogenins A and B in neural stem cell proliferation and differentiation which further increases their likely importance to compensate for neuronal cell loss in the brain.

Glycogen synthase kinase 3 inhibition promotes adult hippocampal neurogenesis in vitro and in vivo

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase originally identified as a regulator of glycogen metabolism but it also plays a pivotal role in numerous cellular functions, including differentiation, cell cycle regulation, and proliferation. The dentate gyrus of the hippocampus, together with the subventricular zone of the lateral ventricles, is one of the regions in which neurogenesis takes place in the adult brain. Here, using a chemical genetic approach that involves the use of several diverse inhibitors of GSK-3 as pharmacological tools, we show that inhibition of GSK-3 induces proliferation, migration, and differentiation of neural stem cells toward a neuronal phenotype in in vitro studies. Also, we demonstrate that inhibition of GSK-3 with the small molecule NP03112, called tideglusib, induces neurogenesis in the dentate gyrus of the hippocampus of adult rats. Taken together, our results suggest that GSK-3 should be considered as a new target molecule for modulating the production and integration of new neurons in the hippocampus as a treatment for neurodegenerative diseases or brain injury and, consequently, its inhibitors may represent new potential therapeutic drugs in neuroregenerative medicine.

Metallocenes as Target Specific Drugs for Cancer Treatment

The application use of organometallic compounds into the cancer research was established in the late 1970s by Köpf-Maeir and Köpf. This new research area has been developed for the past thirty years. In the early 1980s, Jaouen and coworkers recognized the potential application of organometallic compounds vectorized with pendant groups that can deliver the drug to certain specific receptors. This is what is called nowdays Target Specific Drugs. This review will focus on metallocenes vectorized with steroids derivatives of hormones, nonsteroidal and selective endrocrine modulator.

Loss of the mu opioid receptor on different genetic backgrounds leads to increased bromodeoxyuridine labeling in the dentate gyrus only after repeated injection

The endogenous opioid system is involved in various physiological processes, including neurogenesis in the dentate gyrus (DG) of the hippocampus. In the current study, we investigated the role of the mu opioid receptor (MOR-1) on DG neurogenesis and measured glucocorticoid levels following several injection paradigms to supplement the neurogenesis experiments. MOR-1 knockout (KO) mice on C57BL/6 and 129S6 backgrounds were injected with bromodeoxyuridine (BrdU) using either a single injection or two different repeated injection protocols and then sacrificed at different time points. The total number of BrdU and proliferating cell nuclear antigen (PCNA) positive cells in the DG is significantly increased in MOR-1 KO mice compared with wild type (WT) on both strains after repeated injection, but not after a single injection. Plasma corticosterone (CORT) levels increased similarly in MOR-1 KO and WT mice following both single and repeated injection, indicating that the stress response is activated following any injection protocol, but that the mechanism responsible for the increase in BrdU labeling in MOR-1 KO mice is CORT-level independent. Finally, WT 129S6 mice, independent of genotype, showed higher levels of plasma CORT compared with WT C57BL/6 mice in both noninjected controls and following injection at two separate time points; these levels were inversely correlated with low numbers of BrdU cells in the DG in 129S6 mice compared with C57BL/6 mice. In summary, these data demonstrate that loss of MOR-1 increases BrdU labeling in the DG independent of CORT levels, but only following a repeated injection, illustrating the capability of injection paradigms to influence cell-proliferative responses in a genotype-dependent manner.

Cannabidiol reduces Aβ-induced neuroinflammation and promotes hippocampal neurogenesis through PPARγ involvement

Peroxisome proliferator-activated receptor-γ (PPARγ) has been reported to be involved in the etiology of pathological features of Alzheimer's disease (AD). Cannabidiol (CBD), a Cannabis derivative devoid of psychomimetic effects, has attracted much attention because of its promising neuroprotective properties in rat AD models, even though the mechanism responsible for such actions remains unknown. This study was aimed at exploring whether CBD effects could be subordinate to its activity at PPARγ, which has been recently indicated as its putative binding site. CBD actions on β-amyloid-induced neurotoxicity in rat AD models, either in presence or absence of PPAR antagonists were investigated. Results showed that the blockade of PPARγ was able to significantly blunt CBD effects on reactive gliosis and subsequently on neuronal damage. Moreover, due to its interaction at PPARγ, CBD was observed to stimulate hippocampal neurogenesis. All these findings report the inescapable role of this receptor in mediating CBD actions, here reported.

Neuroregenerative mechanisms of allopregnanolone in Alzheimer's disease

The proliferative pool and regenerative potential of neural stem cells diminishes with age, a phenomenon that may be exacerbated in prodromal and mild Alzheimer's disease (AD) brains. In parallel, the neuroactive progesterone metabolite, allopregnanolone (APα), along with a host of other factors, is decreased in the AD brain. Results of preclinical analyses demonstrate that APα is a potent inducer of neural progenitor proliferation of both rodent and human derived neural progenitor cells in vitro. In vivo, APα significantly increased neurogenesis within the subgranular zone of the dentate gyrus and subventricular zone of the 3xTgAD mouse model. Functionally, APα reversed the learning and memory deficits of 3xTgAD mice prior to and following the onset of AD pathology and was comparably efficacious in aged normal mice. In addition to inducing regenerative responses in mouse models of AD, APα significantly reduced beta-amyloid burden, beta-amyloid binding alcohol dehydrogenase load, and microglial activation. In parallel, APα increased markers of white matter generation and cholesterol homeostasis. Analyses to determine the optimal treatment regimen in the 3xTgAD mouse brain indicated that a treatment regimen of APα once per week was optimal for both inducing neurogenesis and reducing AD pathology. Pharmacokinetic analyses indicated that APα is rapidly increased in both plasma and brain following a single dose. APα is most efficacious when administered once per week which will contribute to its margin of safety. Further, analyses in both animals and humans have provided parameters for safe APα dosage exposure in humans. From a translational perspective, APα is a small molecular weight, blood brain barrier penetrant molecule with substantial preclinical efficacy data as a potential Alzheimer's therapeutic with existing safety data in animals and humans. To our knowledge, APα is the only small molecule that both promotes neural progenitor regeneration in brain and simultaneously reduces AD pathology burden.

Oroxylin A, a flavonoid, stimulates adult neurogenesis in the hippocampal dentate gyrus region of mice

Previously, we reported the cognitive enhancing effects of oroxylin A in unimpaired mice and its memory ameliorating activity in various memory impaired mice. To elucidate the mechanism mediating the cognitive effects of oroxylin A, this study examined the consequences of oroxylin A administration on neurogenesis in the hippocampal dentate gyrus using immunostaining for 5-bromo-2-deoxyuridine (BrdU) incorporation. In addition, we determined whether the new cells adopted a neuronal or glial fate by examining the co-localization of BrdU staining with neuronal or glial markers. Administration of oroxylin A in a dose-dependent and time-dependent manner increased the number of BrdU-incorporating cells. Moreover, the percentage of BrdU-incorporating cells co-localized with neuronal markers, neuronal nuclei, was significantly increased by the oroxylin A administration. These results suggest that the increased neurogenesis induced by the administration of oroxylin A could be, at least in part, associated with its positive effects on cognitive processing.

Synthesis and cytotoxicity studies of steroid-functionalized titanocenes as potential anticancer drugs: sex steroids as potential vectors for titanocenes

Six titanocenyls functionalized with steroidal esters have been synthesized and characterized by infrared, (1)H, and (13)C NMR spectroscopy and elemental analysis. Among those steroids, dehydroepiandrosterone, trans-androsterone, and androsterone are androgens and pregnenolone is a progesterone precursor. Clionasterol is a natural steroid compound. These steroid-functionalized titanocenyls were tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for in vitro cytotoxicity for MCF-7 breast cancer and HT-29 colon cancer cells. All complexes exhibited more cytotoxicity than titanocene dichloride. The titanocenyls containing androgen and progesterone derivatives as pendant groups had higher antiproliferative activities than those with cholesterol steroid compounds. Of particular significance is titanocenyl-dehydroepiandrosterone complex, which is 2 orders of magnitude more cytotoxic than titanocene dichloride and also shows much more sensitivity and selectivity for the MCF-7 cell line.

Steroidal and gonadal effects on neural cell proliferation in vitro in an adult songbird

Neurogenesis in the adult songbird brain occurs along the ventricular zone (VZ), a specialized cell layer surrounding the lateral ventricles. To examine the acute effects of sex steroids on VZ cell proliferation, male and female adult zebra finch brain slices containing the VZ were exposed to 5-bromo-2'-deoxyuridine-5'-monophosphate (BrdU) in vitro. Slices from one hemisphere served as the control, while contralateral slices were treated with steroids, steroidogenic enzyme inhibitors or gonadal tissue itself. There were no significant effects on VZ cell proliferation in either sexes by acute exposure to 17beta-estradiol (E2), dihydrotestosterone (DHT), a cocktail of four sex steroids, and inhibitors of sex steroid synthesis (aminoglutethimide, ketoconazole, and fadrozole), or by activation of a mitochondrial cholesterol transporter. By contrast, dehydroepiandrosterone (DHEA) suppressed VZ cell proliferation in males, but not females, replicating previous observations involving treatments with corticosterone and RU-486. This suggests that DHEA suppresses proliferation in males via a glucocorticoid receptor-related mechanism. These results suggest that neurosteroidogenesis per se has little effect on acute VZ cell proliferation. Co-incubation with an ovary of female, but not male, slices significantly increased VZ cell proliferation; testicular tissue had no impact on proliferation in males or females. This suggests a role for a non-steroidal ovarian factor on adult female VZ cell proliferation. We also have evidence that previously reported sex-differences in BrdU-labeling along the adult VZ (males>females) result from a more rapid loss of cells in females. Sex differences in steroid action and cell death along the VZ may contribute to the maintenance of the sexually dimorphic song system.

Progesterone promotes the survival of newborn neurons in the dentate gyrus of adult male mice

This study investigated the effects of progesterone (P4) on the production and survival of neurons in the hippocampal dentate gyrus of adult male mice. The administration of P4 (4 mg/kg) for 3 consecutive days beginning on the 0-2nd day after the first BrdU-injection (BrdU-D(0-2)) produced an approximately twofold increase in the number of 28- and 56-day-old BrdU(+) cells in comparison to the controls, whereas it did not alter the number of 24/48-h-old BrdU(+) cells. P4 preferentially promoted the survival of newborn neurons when administered at BrdU-D(5-7), but not at BrdU-D(10-12) and BrdU-D(15-17). Androstenedione (Ad), testosterone (TE), or estradiol (E2) at the same-dose of P4, when administered at BrdU-D(0-2), could not replicate the effect of P4, while the inhibition of 5alpha-reductase by finasteride did not affect the P4-action, indicating that the P4-effect is exerted by P4 itself but not by its metabolites. On the other hand, the P4R antagonist RU486 partially suppressed the P4-effect, while inhibitors for Src, MEK, or PI3K totally suppressed the P4-effect. Finally, the P4-enhanced survival of newborn neurons was accompanied by a potentiation of spatial learning and memory, which was P4R-dependent. These findings suggest that P4 enhances the survival of newborn neurons through P4R and/or the Src-ERK and PI3K pathways independent of its influence on cell proliferation, which is well correlated with the potentiated spatial cognitive function of P4-treated animals.

Hippocampal adult neurogenesis is enhanced by chronic eszopiclone treatment in rats

The adult hippocampal dentate gyrus (DG) exhibits cell proliferation and neurogenesis throughout life. We examined the effects of daily administration of eszopiclone (Esz), a commonly used hypnotic drug and gamma-aminobutyric acid (GABA) agonist, compared with vehicle, on DG cell proliferation and neurogenesis, and on sleep-wake patterns. Esz was administered during the usual sleep period of rats, to mimic typical use in humans. Esz treatment for 7 days did not affect the rate of cell proliferation, as measured by 5-bromo-2'-deoxyuridine (BrdU) immunostaining. However, twice-daily Esz administration for 2 weeks increased survival of newborn cells by 46%. Most surviving cells exhibited a neuronal phenotype, identified as BrdU-neuronal nuclei (NeuN) double-labeling. NeuN is a marker of neurons. Non-rapid eye movement sleep was increased on day 1, but not on days 7 or 14 of Esz administration. Delta electroencephalogram activity was increased on days 1 and 7 of treatment, but not on day 14. There is evidence that enhancement of DG neurogenesis is a critical component of the effects of antidepressant treatments of major depressive disorder (MDD). Adult-born DG cells are responsive to GABAergic stimulation, which promotes cell maturation. The present study suggests that Esz, presumably acting as a GABA agonist, has pro-neurogenic effects in the adult DG. This result is consistent with evidence that Esz enhances the antidepressant treatment response of patients with MDD with insomnia.

Age-related effects on hippocampal precursor cell subpopulations and neurogenesis

Hippocampal neurogenesis continuously declines in the aging brain but only little is known about age-related alterations in the subgranular zone (SGZ) of the dentate gyrus which accommodates different subpopulations of precursor cells. Here, we examined the age-related effects on total number and proliferation rate of distinct precursor cell populations in the dentate gyrus of 3 and 16 months old transgenic pNestin-GFP mice. Following a single injection of bromodeoxyuridine (BrdU) we observed a significant reduction of all proliferating precursor subtypes in aged mice compared to young controls. Stereological analysis further revealed that this decreased proliferation was not only caused by a general reduction in total number of precursor subtypes but also by a subtype-specific alteration of the proliferation rate. Whereas radial glia-like and early neuronal precursor cells demonstrate decreased proliferation rates, no difference was found for doublecortin-positive precursors. Additional long-term experiments further revealed that these age-related alterations in the proliferative zone were accompanied by a strongly decreased neurogenesis while hippocampal function was not impaired.

Proof-of-concept trial with the neurosteroid pregnenolone targeting cognitive and negative symptoms in schizophrenia

The neurosteroid pregnenolone and its sulfated derivative enhance learning and memory in rodents. Pregnenolone sulfate also positively modulates NMDA receptors and could thus ameliorate hypothesized NMDA receptor hypofunction in schizophrenia. Furthermore, clozapine increases pregnenolone in rodent hippocampus, possibly contributing to its superior efficacy. We therefore investigated adjunctive pregnenolone for cognitive and negative symptoms in patients with schizophrenia or schizoaffective disorder receiving stable doses of second-generation antipsychotics in a pilot randomized, placebo-controlled, double-blind trial. Following a 2-week single-blind placebo lead-in, patients were randomized to pregnenolone (fixed escalating doses to 500 mg/day) or placebo, for 8 weeks. Primary end points were changes in BACS and MCCB composite and total SANS scores. Of 21 patients randomized, 18 completed at least 4 weeks of treatment (n=9/group). Pregnenolone was well tolerated. Patients receiving pregnenolone demonstrated significantly greater improvements in SANS scores (mean change=10.38) compared with patients receiving placebo (mean change=2.33), p=0.048. Mean composite changes in BACS and MCCB scores were not significantly different in patients randomized to pregnenolone compared with placebo. However, serum pregnenolone increases predicted BACS composite scores at 8 weeks in the pregnenolone group (r(s)=0.81, p=0.022). Increases in allopregnanolone, a GABAergic pregnenolone metabolite, also predicted BACS composite scores (r(s)=0.74, p=0.046). In addition, baseline pregnenolone (r(s)=-0.76, p=0.037), pregnenolone sulfate (r(s)=-0.83, p=0.015), and allopregnanolone levels (r(s)=-0.83, p=0.015) were inversely correlated with improvements in MCCB composite scores, further supporting a possible role for neurosteroids in cognition. Mean BACS and MCCB composite scores were correlated (r(s)=0.74, p<0.0001). Pregnenolone may be a promising therapeutic agent for negative symptoms and merits further investigation for cognitive symptoms in schizophrenia.

Effects of the hypnotic drug zolpidem on cell proliferation and survival in the dentate gyrus of young and old rats

Sleep loss/disruption has been shown to suppress adult hippocampal neurogenesis. Whether the administration of hypnotic drugs, by promoting sleep, especially in older subjects, who typically exhibit poor sleep, has a beneficial effect on neurogenesis parameters is unknown. We examined the effects of zolpidem, a widely prescribed nonbenzodiazepine hypnotic, on cell proliferation and survival in the dentate gyrus of young ( approximately 2 1/2 months) and old ( approximately 13 months) male Sprague-Dawley rats. Zolpidem (5, 10 or 20 mg/kg, i.p.) or vehicle was administered twice daily, at the beginning and middle of the sleep period, for either 2 days (acute study) or 21 days (chronic study). Proliferation and cell survival were measured by staining for Ki67 or 5-bromo-2'-deoxyurdine (BrdU), respectively. Acute administration of zolpidem produced a suppression of cell proliferation, which attained statistical significance only in the aged animals. The magnitude of the suppressive effect was larger in the hilus than in the subgranular zone (SGZ). In contrast, chronic administration of zolpidem produced little or no effect on proliferation in either age group, despite marked differences in basal proliferation levels between the two age groups. Similarly, there was little change in cell survival following chronic zolpidem administration in young versus old animals. A slight reduction of cell survival in the granular cell layer (GCL)/SGZ was observed in young animals and a slight augmentation in aged animals. To the extent that zolpidem improves sleep, these data suggest little or no benefit of hypnotic drug treatment on neurogenesis parameters in young or old rats.

Sex differences in cell proliferation and glucocorticoid responsiveness in the zebra finch brain

Neural proliferation is a conserved property of the adult vertebrate brain. In mammals, stress reduces hippocampal neuronal proliferation and the effect is stronger in males than in females. We tested the effects of glucocorticoids on ventricular zone cell proliferation in adult zebra finches where neurons are produced that migrate to and incorporate within the neural circuits controlling song learning and performance. Adult male zebra finches sing and have an enlarged song circuitry; females do not sing and the song circuit is poorly developed. Freshly prepared slices from adult males and females containing the lateral ventricles were incubated with the mitotic marker BrdU with or without steroid treatments. BrdU-labeled cells were revealed immunocytochemically and all labeled cells within the ventricular zone were counted. We identified significantly higher rates of proliferation along the ventricular zone of males than in females. Moreover, acute administration of corticosterone significantly reduced proliferation in males with no effects in females. This effect in males was replicated by RU-486, which appears to act as an agonist of the glucocorticoid receptor in the songbird brain. The corticosterone effect was reversed by Thiram, which disrupts corticosterone action on the glucocorticoid receptor. Sex differences in proliferation and responses to stress hormones may contribute to the sexually dimorphic and seasonal growth of the neural song system of songbirds.

Impaired adult neurogenesis in the dentate gyrus of a triple transgenic mouse model of Alzheimer's disease

It has become generally accepted that new neurones are added and integrated mainly in two areas of the mammalian CNS, the subventricular zone and the subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus, which is of central importance in learning and memory. The newly generated cells display neuronal morphology, are able to generate action potentials and receive functional synaptic inputs, i.e. their properties are similar to those found in mature neurones. Alzheimer's disease (AD) is the primary and widespread cause of dementia and is an age-related, progressive and irreversible neurodegenerative disease that deteriorates cognitive functions. Here, we have used male and female triple transgenic mice (3xTg-AD) harbouring three mutant genes (beta-amyloid precursor protein, presenilin-1 and tau) and their respective non-transgenic (non-Tg) controls at 2, 3, 4, 6, 9 and 12 months of age to establish the link between AD and neurogenesis. Using immunohistochemistry we determined the area density of proliferating cells within the SGZ of the DG, measured by the presence of phosphorylated Histone H3 (HH3), and their possible co-localisation with GFAP to exclude a glial phenotype. Less than 1% of the HH3 labeled cells co-localised with GFAP. Both non-Tg and 3xTg-AD showed an age-dependent decrease in neurogenesis. However, male 3xTg-AD mice demonstrated a further reduction in the production of new neurones from 9 months of age (73% decrease) and a complete depletion at 12 months, when compared to controls. In addition, female 3xTg-AD mice showed an earlier but equivalent decrease in neurogenesis at 4 months (reduction of 63%) with an almost inexistent rate at 12 months (88% decrease) compared to controls. This reduction in neurogenesis was directly associated with the presence of beta-amyloid plaques and an increase in the number of beta-amyloid containing neurones in the hippocampus; which in the case of 3xgTg females was directly correlated. These results suggest that 3xTg-AD mice have an impaired ability to generate new neurones in the DG of the hippocampus, the severity of which increases with age and might be directly associated with the known cognitive impairment observed from 6 months of age onwards . The earlier reduction of neurogenesis in females, from 4 months, is in agreement with the higher prevalence of AD in women than in men. Thus it is conceivable to speculate that a recovery in neurogenesis rates in AD could help to rescue cognitive impairment.

The effect of prolonged anesthesia with isoflurane, propofol, dexmedetomidine, or ketamine on neural cell proliferation in the adult rat

BACKGROUND

Recent evidence indicates that new neurons are produced in the adult hippocampus, and play a functional role in cognitive processes such as learning and memory. In animals, new neuron production is suppressed by increasing age, gamma-aminobutyric acid receptor activity, reductions in basal forebrain activity and brain norepinephrine levels, and decreased environmental stimuli. Similarities between these effects and those of anesthetic administration suggest that anesthetics may modulate new cell production, and raise the possibility that postoperative cognitive dysfunction may result, in part, from anesthetic-induced suppression of adult neurogenesis. To test this hypothesis, we investigated the effects of prolonged anesthesia with four different anesthetics on hippocampal cell proliferation in young and older rats.

METHODS

Young (approximately 3 mo) and older, middle-aged (approximately 12 mo) male Sprague-Dawley rats received one of four anesthetics (propofol, isoflurane, dexmedetomidine, and ketamine) for 8 h. Rats breathed spontaneously, and anesthesia was titrated to loss of righting reflex and tolerance of clip-style pulse oximetry. Six hours into the anesthetic, rats received 200 mg/kg bromodeoxyuridine (BrdU) intraperitoneally and were killed hours later. Frozen hippocampal sections were collected and processed for BrdU using an immunoperoxidase technique. BrdU(+) cells in the dentate gyrus were then counted, and compared with unanesthetized controls to determine the degree of new cell production. All four anesthetics were given to young rats. Older rats received isoflurane and ketamine, and also received isoflurane during their dark phase.

RESULTS

Forty-two young, and 26 older, middle-aged rats were studied. When compared with controls, prolonged anesthesia in young rats with any drug had no effect on the number of BrdU(+) cells. BrdU labeling was also unaffected in older rats given isoflurane for 8 h during the light phase. Older rats had significantly lower BrdU(+) cell counts than younger rats. In older rats, ketamine anesthesia reduced BrdU(+) cell counts by 26% when compared with unanesthetized controls. Older rats given isoflurane for 8 h during their dark phase demonstrated no difference in BrdU labeling when compared with unanesthetized controls.

CONCLUSION

Despite using multiple, mechanistically distinct drugs, we found no effect of prolonged anesthesia on adult hippocampal cell proliferation in young rats, a slight suppressive effect of ketamine in older rats, and no circadian effect with isoflurane. These data indicate that anesthetics are unlikely to alter cell proliferation, and by extension that anesthetic-induced inhibition of cell proliferation is unlikely to play a major role in postoperative cognitive impairment. The contrast between our findings, current concepts of anesthetic action, and known modifiers of cell proliferation suggest an incomplete understanding of the pharmacological and behavioral factors governing new neuron production.

Neuroactive steroids, mood stabilizers, and neuroplasticity: alterations following lithium and changes in Bcl-2 knockout mice

Many neuroactive steroids (NS) demonstrate neurotrophic and neuroprotective actions, including protection against apoptosis via Bcl-2 protein. NS are altered in post-mortem brain tissue from subjects with bipolar disorder, and several agents with efficacy in mania elevate NS in rodents. We therefore hypothesized that lithium and valproate may elevate NS, and compensatory NS increases may occur in Bcl-2 knockout mice. NS levels (allopregnanolone, pregnenolone) were determined in frontal cortex by negative ion chemical ionization gas chromatography/mass spectrometry in male Wistar Kyoto rats treated chronically with lithium, valproate, or vehicle. NS were also investigated in heterozygous Bcl-2 knockout mice. Allopregnanolone levels are significantly elevated in lithium-treated (p<0.05), but not in valproate-treated, rats. Pregnenolone levels also tend to be higher following lithium treatment (p=0.09). Knockout of Bcl-2 significantly increases pregnenolone levels in mice (p<0.01), while allopregnanolone levels are unaltered. NS induction may be relevant to mechanisms contributing to lithium therapeutic efficacy and neuroprotection.

Spatial learning depends on both the addition and removal of new hippocampal neurons

The role of adult hippocampal neurogenesis in spatial learning remains a matter of debate. Here, we show that spatial learning modifies neurogenesis by inducing a cascade of events that resembles the selective stabilization process characterizing development. Learning promotes survival of relatively mature neurons, apoptosis of more immature cells, and finally, proliferation of neural precursors. These are three interrelated events mediating learning. Thus, blocking apoptosis impairs memory and inhibits learning-induced cell survival and cell proliferation. In conclusion, during learning, similar to the selective stabilization process, neuronal networks are sculpted by a tightly regulated selection and suppression of different populations of newly born neurons.

The birth of adult hippocampal neurons is associated with enhanced learning and memory performance. In particular, spatial learning increases the survival and the proliferation of newborn cells, but surprisingly, it also decreases their number. Here, we hypothesized that spatial learning also depends upon the death of newborn hippocampal neurons. We examined the effect of spatial learning in the water maze on cell birth and death in the rodent hippocampus. We then determined the influence of an inhibitor of cell death on memory abilities and learning-induced changes in cell death, cell proliferation, and cell survival. We show that learning increases the elimination of the youngest newborn cells during a specific developmental period. The cell-death inhibitor impairs memory abilities and blocks the learning-induced cell death, the survival-promoting effect of learning on older newly born neurons, and the subsequent learning-induced proliferation of neural precursors. These results show that spatial learning induces cell death in the hippocampus, a phenomenon that subserves learning and is necessary for both the survival of older newly born neurons and the proliferation of neural precursors. These findings suggest that during learning, neuronal networks are sculpted by a tightly regulated selection of newly born neurons and reveal a novel mechanism mediating learning and memory in the adult brain.

Spatial learning-induced cell death in the hippocampus is necessary for the survival of newly born cells, the proliferation of neural precursors, and the retention of spatial memories.