Absence of the calcium-binding protein calretinin, not of calbindin D-28k, causes a permanent impairment of murine adult hippocampal neurogenesis

Comparison of the effect of glyphosate and glyphosate-based herbicide on hippocampal neurogenesis after developmental exposure in rats

Increasing evidence indicates that glyphosate (GlyP)-based herbicides (GBHs) induce developmental neurotoxicity. The present study investigated the developmental exposure effect of GlyP and GBH on hippocampal neurogenesis in rats. Dams were treated from gestational day 6 to day 21 post-delivery on weaning with a diet containing 1.5% or 3.0% GlyP or drinking water with 1.0% GBH (containing 0.36% GlyP). Dams in the 1.5%-GlyP, 3.0%-GlyP, and GBH groups received 1.04, 2.16, and 0.25 g GlyP/kg body weight (BW)/day during gestation, and 2.27, 4.65, and 0.58 g GlyP/kg BW/day during lactation, respectively. On weaning, 3.0% GlyP- and GBH-exposed offspring decreased the BW, and the latter also decreased the brain weight. Both compounds suppressed neural progenitor cell proliferation in the neurogenic niche, and GlyP-exposed offspring showed a decreased number of TUBB3⁺ immature granule cells. In contrast, both compounds increased the number of ARC⁺ granule cells, suggesting increased synaptic plasticity. Both compounds downregulated antioxidant genes (Cat and Sod2) in the dentate gyrus, suggestive of increased sensitivity to oxidative stress, which might be related to the suppression of neurogenesis. At the adult age, GBH alone sustained decreases in body and brain weights. Both compounds increased hippocampal malondialdehyde levels and upregulated Cat in the dentate gyrus, suggesting induction of oxidative stress. Both compounds upregulated Casp9, and GBH increased neural progenitor cell apoptosis, suggesting disruption of neurogenesis related to oxidative stress. GBH increased the number of COX2⁺ granule cells, and both compounds upregulated Arc, suggesting increased synaptic plasticity. These results suggest that GlyP and GBH might cause similar effects on disruption of neurogenesis accompanying compensatory responses and induction of oxidative stress responses through the adult age in the hippocampus. However, effects on adult age were more evident with GBH, suggesting that the surfactants contained in GBH might have contributed to the enhanced neurotoxicity of GlyP, similar to the enhanced general toxicity.

Oral Exposure to Lead Acetate for 28 Days Reduces the Number of Neural Progenitor Cells but Increases the Number and Synaptic Plasticity of Newborn Granule Cells in Adult Hippocampal Neurogenesis of Young-Adult Rats

Lead (Pb) causes developmental neurotoxicity. Developmental exposure to Pb acetate (PbAc) induces aberrant hippocampal neurogenesis by increasing or decreasing neural progenitor cell (NPC) subpopulations in the dentate gyrus (DG) of rats. To investigate whether hippocampal neurogenesis is similarly affected by PbAc exposure in a general toxicity study, 5-week-old Sprague-Dawley rats were orally administered PbAc at 0, 4000, and 8000 ppm (w/v) in drinking water for 28 days. After exposure to 4000 or 8000 ppm PbAc, Pb had accumulated in the brains. Neurogenesis was suppressed by 8000 ppm PbAc, which was related to decreased number of type-2b NPCs, although number of mature granule cells were increased by both PbAc doses. Gene expression in the 8000 ppm PbAc group suggested suppressed NPC proliferation and increased apoptosis resulting in suppressed neurogenesis. PbAc exposure increased numbers of metallothionein-I/II⁺ cells and GFAP⁺ astrocytes in the DG hilus, and upregulated Mt1, antioxidant genes (Hmox1 and Gsta5), and Il6 in the DG, suggesting the induction of oxidative stress and neuroinflammation related to Pb accumulation resulting in suppressed neurogenesis. PbAc at 8000 ppm also upregulated Ntrk2 and increased the number of CALB2⁺ interneurons, suggesting the activation of BDNF-TrkB signaling and CALB2⁺ interneuron-mediated signals to ameliorate suppressed neurogenesis resulting in increased number of newborn granule cells. PbAc at both doses increased the number of ARC⁺ granule cells, suggesting the facilitation of synaptic plasticity of newborn granule cells through the activation of BDNF-TrkB signaling. These results suggest that PbAc exposure during the young-adult stage disrupted hippocampal neurogenesis, which had a different pattern from developmental exposure to PbAc. However, the induction of oxidative stress/neuroinflammation and activation of identical cellular signals occurred irrespective of the life stage at PbAc exposure.

Expression of Calbindin-D28K in the Developing and Adult Mouse Cochlea

Herein, we aimed to use double-labeling immunofluorescence to describe the expression pattern of Calbindin-D28K (CaBP28K) in the mouse cochlea from late embryonic (E) stages to the adulthood. CaBP28K was expressed in the inner hair cells (IHCs) and the greater epithelial ridge (GER) at E17. In addition, its expression was observed in the interdental cells. On postnatal day 1 (P1), CaBP28K immunoreactivity was observed in the IHCs and outer hair cells (OHCs) and was also specifically expressed in the nucleus and the cytoplasm of spiral ganglion neurons (SGNs). At P8, CaBP28K labeling disappeared from the interdental cells, and the CaBP28K-positive domain within the GER shifted from the entire cytoplasm to only the apical and basal regions. At P14, CaBP28K immunoreactivity was lost from the GER; however, its expression in the IHCs and OHCs, as well as the SGNs, persisted into adulthood. The identification of CaBP28K in the hair cells (HCs) and cuticular plates, as well as SGNs, was confirmed by its colocalization with several markers for Sox2, Myosin VIIa, Phalloidin, and Tuj1. We also detected colocalization with calmodulin in the cytoplasm of both HCs and SGNs. Western blot revealed an increase in CaBP28K postnatal expression in the mouse cochlea.

Oral exposure to aluminum chloride for 28 days suppresses neural stem cell proliferation and increases mature granule cells in adult hippocampal neurogenesis of young-adult rats

Aluminum (Al), a common light metal, affects the developing nervous system. Developmental exposure to Al chloride (AlCl₃ ) induces aberrant neurogenesis by targeting neural stem cells (NSCs) and/or neural progenitor cells (NPCs) in the dentate gyrus (DG) of rats and mice. To investigate whether hippocampal neurogenesis is similarly affected by AlCl₃ exposure in a general toxicity study, AlCl₃ was orally administered to 5-week-old Sprague Dawley rats at dosages of 0, 4000, or 8000 ppm in drinking water for 28 days. AlCl₃ downregulated Sox2 transcript levels in the DG at the highest dosage and produced a dose-dependent decrease of SOX2⁺ cells without altering numbers of GFAP⁺ or TBR2⁺ cells in the subgranular zone, suggesting that AlCl₃ decreases Type 2a NPCs. High-dose exposure downregulated Pcna, upregulated Pvalb, and altered expression of genes suggestive of oxidative stress induction (upregulation of Nos2 and downregulation of antioxidant enzyme genes), indicating suppressed proliferation and differentiation of Type 1 NSCs. AlCl₃ doses also increased mature granule cells in the DG. Upregulation of Reln may have contributed to an increase of granule cells to compensate for the decrease of Type 2a NPCs. Moreover, upregulation of Calb2, Gria2, Mapk3, and Tgfb3, as well as increased numbers of activated astrocytes in the DG hilus, may represent ameliorating responses against suppressed neurogenesis. These results suggest that 28-day exposure of young-adult rats to AlCl₃ differentially targeted NPCs and mature granule cells in hippocampal neurogenesis, yielding a different pattern of disrupted neurogenesis from developmental exposure.

Aberrant neurogenesis and late onset suppression of synaptic plasticity as well as sustained neuroinflammation in the hippocampal dentate gyrus after developmental exposure to ethanol in rats

Drinking alcohol during pregnancy may cause fetal alcohol spectrum disorder. The present study investigated the effects of maternal oral ethanol (EtOH) exposure (0, 10, or 12.5 % in drinking water) from gestational day 6 until day 21 post-delivery (weaning) on postnatal hippocampal neurogenesis at weaning and in adulthood on postnatal day 77 in rat offspring. At weaning, type-3 neural progenitor cells (NPCs) were decreased in the subgranular zone (SGZ), accompanied by Chrnb2 downregulation and Grin2b upregulation in the dentate gyrus (DG). These results suggested suppression of CHRNB2-mediated cholinergic signaling in γ-aminobutyric acid (GABA)ergic interneurons in the DG hilus and increased glutamatergic signaling through the NR2B subtype of N-methyl-d-aspartate (NMDA) receptors, resulting in NPC reduction. In contrast, upregulation of Chrna7 may increase CHRNA7-mediated cholinergic signaling in immature granule cells, and upregulation of Ntrk2 may cause an increase in somatostatin-immunoreactive ⁽⁺⁾ GABAergic interneurons, suggesting a compensatory response against NPC reduction. Promotion of SGZ cell proliferation increased type-2a NPCs. Moreover, an increase in calbindin-d-29 K⁺ interneurons and upregulation of Reln, Drd2, Tgfb2, Il18, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor subunit genes might participate in this compensatory response. In adulthood, reduction of FOS⁺ cells and downregulation of Fos and Arc suggested suppression of granule cell synaptic plasticity, reflecting upregulation of Tnf and downregulation of Cntf, Ntrk2, and AMPA-type glutamate receptor genes. In the DG hilus, gliosis and hyper-ramified microglia, accompanying upregulation of C3, appeared at weaning, suggesting contribution to suppressed synaptic plasticity in adulthood. M1 microglia increased throughout adulthood, suggesting sustained neuroinflammation. These results indicate that maternal EtOH exposure temporarily disrupts hippocampal neurogenesis and later suppresses synaptic plasticity. Induction of neuroinflammation might initially ameliorate neurogenesis (as evident by upregulation of Tgfb2 and Il18) but later suppress synaptic plasticity (as evident by upregulation of C3 at weaning and Tnf in adulthood).

Direct synaptic excitation between hilar mossy cells revealed with a targeted voltage sensor

The dentate gyrus not only gates the flow of information into the hippocampus, it also integrates and processes this information. Mossy cells (MCs) are a major type of excitatory neuron strategically located in the hilus of the dentate gyrus where they can contribute to this processing through networks of synapses with inhibitory neurons and dentate granule cells. Some prior work has suggested that MCs can form excitatory synapses with other MCs, but the role of these synapses in the network activity of the dentate gyrus has received little attention. Here, we investigated synaptic inputs to MCs in mouse hippocampal slices using a genetically encoded hybrid voltage sensor (hVOS) targeted to MCs by Cre-lox technology. This enabled optical recording of voltage changes from multiple MCs simultaneously. Stimulating granule cells and CA3 pyramidal cells activated well-established inputs to MCs and elicited synaptic responses as expected. However, the weak blockade of MC responses to granule cell layer stimulation by DCG-IV raised the possibility of another source of excitation. To evaluate synapses between MCs as this source, single MCs were stimulated focally. Stimulation of one MC above its action potential threshold evoked depolarizing responses in neighboring MCs that depended on glutamate receptors. Short latency responses of MCs to other MCs did not depend on release from granule cell axons. However, granule cells did contribute to the longer latency responses of MCs to stimulation of other MCs. Thus, MCs transmit their activity to other MCs both through direct synaptic coupling and through polysynaptic coupling with dentate granule cells. MC-MC synapses can redistribute information entering the dentate gyrus and thus shape and modulate the electrical activity underlying hippocampal functions such as navigation and memory, as well as excessive excitation during seizures.

NRSF deficiency leads to abnormal postnatal development of dentate gyrus and impairment of progenitors in subgranular zone of hippocampus

Neuron-restrictive silencing factor (NRSF) is a zinc-finger transcription factor that regulates expression of a diverse set of genes. However, NRSF function in brain development still remains elusive. In the present study, we generated NRSF-conditional knockout (NRSF-cKO) mice by hGFAP-Cre/loxp system to study the effect of NRSF deficiency on brain development. Results showed that NRSF conditional knockout caused a smaller hippocampus and a thinner granule cell layer (GCL) in mice. Moreover, the reduction and disarrangement of GFAP+ cells in subgranular zone (SGZ) of NRSF-cKO mice was accompanied with the decreased number of premature neurons, neural stem cells (NSCs) and neural progenitor cells (NPCs), as well as compromising the majority of mitotically active cells. The analysis of postnatal development of hippocampus indicated the existence of an abnormality at postnatal day (P) 8, rather than at P1, in NRSF-cKO mice, although the densities of Ki67+ cells with mitotic ability in dentate gyrus were relatively unaffected at P1 and P8. Meanwhile, NRSF deficiency led to abnormal organization of SGZ at P8 during postnatal development. RNA-Seq analysis revealed 79 deregulated genes in hippocampus of NRSF-cKO mice at P8, which were involved in p53 signal transduction, neuron migration and negative regulation of cell proliferation, etc. The deregulation of p53 pathway in NRSF-cKO mice at P1 and P8 was evidenced, of which p21/Cdkn1a was accumulated in a portion of NSCs and NPCs in hippocampus during postnatal development. Together, these results, for the first time, revealed that NRSF could significantly influence the postnatal development of hippocampus, especially the formation of SGZ.

Hippocampal GABAergic interneurons and their co-localized neuropeptides in stress vulnerability and resilience

Studies in humans and rodents suggest a critical role for the hippocampal formation in cognition and emotion, but also in the adaptation to stressful events. Successful stress adaptation promotes resilience, while its failure may lead to stress-induced psychopathologies such as depression and anxiety disorders. Hippocampal architecture and physiology is shaped by its strong control of activity via diverse classes of inhibitory interneurons that express typical calcium binding proteins and neuropeptides. Celltype-specific opto- and chemogenetic intervention strategies that take advantage of these biochemical markers have bolstered our understanding of the distinct role of different interneurons in anxiety, fear and stress adaptation. Moreover, some of the signature proteins of GABAergic interneurons have a potent impact on emotion and cognition on their own, making them attractive targets for interventions. In particular, neuropeptide Y is a promising endogenous agent for mediating resilience against severe stress. In this review, we evaluate the role of the major types of interneurons across hippocampal subregions in the adaptation to chronic and acute stress and to emotional memory formation.

Proteomics-based screening of the target proteins associated with antidepressant-like effect and mechanism of nimesulide

Nimesulide is an inhibitor of COX-2 with antioxidant and anti-inflammatory effects. However, few studies have explored the antidepressant mechanism of nimesulide. Here, we evaluated the therapeutic effects of nimesulide on CUMS rats. iTRAQ technology was used to identify the differentially expressed protein in the hippocampus between CUMS and nimesulide-treated rats to identify the possible molecular mechanism of its effects. We found that nimesulide had positive effects on depressive-like behaviors and inflammatory factors in depressed rats. Using proteomics technologies, we screened 16 differentially expressed proteins in CUMS-exposed rats after nimesulide treatment, 5 of which were related to inflammation. Overall, these results show that nimesulide might mediate its antidepressant effect on depressed rats through the inhibition of oxidative stress inflammatory response.

Cytosolic Ca2+ Buffers Are Inherently Ca2+ Signal Modulators

For precisely regulating intracellular Ca²⁺ signals in a time- and space-dependent manner, cells make use of various components of the "Ca²⁺ signaling toolkit," including Ca²⁺ entry and Ca²⁺ extrusion systems. A class of cytosolic Ca²⁺-binding proteins termed Ca²⁺ buffers serves as modulators of such, mostly short-lived Ca²⁺ signals. Prototypical Ca²⁺ buffers include parvalbumins (α and β isoforms), calbindin-D9k, calbindin-D28k, and calretinin. Although initially considered to function as pure Ca²⁺ buffers, that is, as intracellular Ca²⁺ signal modulators controlling the shape (amplitude, decay, spread) of Ca²⁺ signals, evidence has accumulated that calbindin-D28k and calretinin have additional Ca²⁺ sensor functions. These other functions are brought about by direct interactions with target proteins, thereby modulating their targets' function/activity. Dysregulation of Ca²⁺ buffer expression is associated with several neurologic/neurodevelopmental disorders including autism spectrum disorder (ASD) and schizophrenia. In some cases, the presence of these proteins is presumed to confer a neuroprotective effect, as evidenced in animal models of Parkinson's or Alzheimer's disease.

Role for calcium signaling in manganese neurotoxicity

BACKGROUND

Calcium is an essential macronutrient that is involved in many cellular processes. Homeostatic control of intracellular levels of calcium ions [Ca²⁺] is vital to maintaining cellular structure and function. Several signaling molecules are involved in regulating Ca²⁺ levels in cells and perturbation of calcium signaling processes is implicated in several neurodegenerative and neurologic conditions. Manganese [Mn] is a metal which is essential for basic physiological functions. However, overexposure to Mn from environmental contamination and workplace hazards is a global concern. Mn overexposure leads to its accumulation in several human organs particularly the brain. Mn accumulation in the brain results in a manganism, a Parkinsonian-like syndrome. Additionally, Mn is a risk factor for several neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. Mn neurotoxicity also affects several neurotransmitter systems including dopaminergic, cholinergic and GABAergic. The mechanisms of Mn neurotoxicity are still being elucidated.

AIM

The review will highlight a potential role for calcium signaling molecules in the mechanisms of Mn neurotoxicity.

CONCLUSION

Ca²⁺ regulation influences the neurodegenerative process and there is possible role for perturbed calcium signaling in Mn neurotoxicity. Mechanisms implicated in Mn-induced neurodegeneration include oxidative stress, generation of free radicals, and apoptosis. These are influenced by mitochondrial integrity which can be dependent on intracellular Ca²⁺ homeostasis. Nevertheless, further elucidation of the direct effects of calcium signaling dysfunction and calcium-binding proteins activities in Mn neurotoxicity is required.

The effect of electroconvulsive seizure on survival, neuronal differentiation, and expression of the maturation marker in the adult mouse hippocampus

Electroconvulsive seizure (ECS), a model of electroconvulsive therapy in rodents, strongly increases neurogenesis in the adult hippocampus. Neurogenesis is a multi-step process that spans proliferation, survival, neuronal differentiation, and functional maturation. Our previous study demonstrated that ECS stimulates the proliferation of neural stem-like cells. However, the contribution of ECS to survival, neuronal differentiation, and maturation in newborn cells remains unknown. To evaluate the effect of ECS on these processes, we labeled newborn cells with bromodeoxyuridine (BrdU) before ECS treatment to determine the cell age and examined the survival rate and expression of cellular markers in the BrdU-labeled cells. Our results revealed that exposure to ECS (11 repetitions) during the differentiation phase significantly increased survival and promoted neuronal differentiation of newborn cells in the dentate gyrus. Four of ECS repetitions during the early differentiation phase were sufficient to promote dendritic outgrowth in immature neurons and enhance the expression of the immature neuronal marker, calretinin, in newborn cells. In contrast, exposure to ECS (11 repetitions) during the late maturation phase significantly suppressed the expression of the mature neuronal marker, calbindin, in newborn neurons. These results demonstrate that ECS during the differentiation phase promoted survival and neuronal differentiation and, in contrast, suppressed mature marker expression during the late maturation phase, suggesting that ECS has multiple effects on the different stages of adult neurogenesis.

Bumetanide Prevents Brain Trauma-Induced Depressive-Like Behavior

Brain trauma triggers a cascade of deleterious events leading to enhanced incidence of drug resistant epilepsies, depression, and cognitive dysfunctions. The underlying mechanisms leading to these alterations are poorly understood and treatment that attenuates those sequels are not available. Using controlled-cortical impact as an experimental model of brain trauma in adult mice, we found a strong suppressive effect of the sodium-potassium-chloride importer (NKCC1) specific antagonist bumetanide on the appearance of depressive-like behavior. We demonstrate that this alteration in behavior is associated with an impairment of post-traumatic secondary neurogenesis within the dentate gyrus of the hippocampus. The mechanism mediating the effect of bumetanide involves early transient changes in the expression of chloride regulatory proteins and qualitative changes in GABA(A) mediated transmission from hyperpolarizing to depolarizing after brain trauma. This work opens new perspectives in the early treatment of human post-traumatic induced depression. Our results strongly suggest that bumetanide might constitute an efficient prophylactic treatment to reduce neurological and psychiatric consequences of brain trauma.

JNK Isoforms Are Involved in the Control of Adult Hippocampal Neurogenesis in Mice, Both in Physiological Conditions and in an Experimental Model of Temporal Lobe Epilepsy

Neurogenesis in the adult dentate gyrus (DG) of the hippocampus allows the continuous generation of new neurons. This cellular process can be disturbed under specific environmental conditions, such as epileptic seizures; however, the underlying mechanisms responsible for their control remain largely unknown. Although different studies have linked the JNK (c-Jun-N-terminal-kinase) activity with the regulation of cell proliferation and differentiation, the specific function of JNK in controlling adult hippocampal neurogenesis is not well known. The purpose of this study was to analyze the role of JNK isoforms (JNK1/JNK2/JNK3) in adult-hippocampal neurogenesis. To achieve this goal, we used JNK-knockout mice (Jnk1^-/-, Jnk2^-/-, and Jnk3^-/-), untreated and treated with intraperitoneal injections of kainic acid (KA), as an experimental model of epilepsy. In each condition, we identified cell subpopulations at different stages of neuronal maturation by immunohistochemical specific markers. In physiological conditions, we evidenced that JNK1 and JNK3 control the levels of one subtype of early progenitor cells (GFAP⁺/Sox2⁺) but not the GFAP⁺/Nestin⁺ cell subtype. Moreover, the absence of JNK1 induces an increase of immature neurons (Doublecortin⁺; PSA-NCAM⁺ cells) compared with wild-type (WT). On the other hand, Jnk1^-/- and Jnk3^-/- mice showed an increased capacity to maintain hippocampal homeostasis, since calbindin immunoreactivity is higher than in WT. An important fact is that, after KA injection, Jnk1^-/- and Jnk3^-/- mice show no increase in the different neurogenic cell subpopulation analyzed, in contrast to what occurs in WT and Jnk2^-/- mice. All these data support that JNK isoforms are involved in the adult neurogenesis control.

Melatonin Influences Structural Plasticity in the Axons of Granule Cells in the Dentate Gyrus of Balb/C Mice

Melatonin, the main product synthesized by the pineal gland, acts as a regulator of the generation of new neurons in the dentate gyrus (DG). Newborn neurons buffer the deleterious effects of stress and are involved in learning and memory processes. Furthermore, melatonin, through the regulation of the cytoskeleton, favors dendrite maturation of newborn neurons. Moreover, newborn neurons send their axons via the mossy fiber tract to Cornu Ammonis 3 (CA3) region to form synapses with pyramidal neurons. Thus, axons of newborn cells contribute to the mossy fiber projection and their plasticity correlates with better performance in several behavioral tasks. Thus, in this study, we analyzed the impact of exogenous melatonin (8 mg/kg) administered daily for one- or six-months on the structural plasticity of infrapyramidal- and suprapyramidal mossy fiber projection of granule cells in the DG in male Balb/C mice. We analyzed the mossy fiber projection through the staining of calbindin, that is a calcium-binding protein localized in dendrites and axons. We first found an increase in the number of calbindin-positive cells in the granular cell layer in the DG (11%, 33%) after treatment. Futhermore, we found an increase in the volume of suprapyramidal (>135%, 59%) and infrapyramidal (>128%, 36%) mossy fiber projection of granule neurons in the DG after treatment. We also found an increase in the volume of CA3 region (>146%, 33%) after treatment, suggesting that melatonin modulates the structural plasticity of the mossy fiber projection to establish functional synapses in the hippocampus. Together, the data suggest that, in addition to the previously reported effects of melatonin on the generation of new neurons and its antidepressant like effects, melatonin also modulates the structural plasticity of axons in granule cells in the DG.

Circuit development in the master clock network of mammals

Daily rhythms are generated by the circadian timekeeping system, which is orchestrated by the master circadian clock in the suprachiasmatic nucleus (SCN) of mammals. Circadian timekeeping is endogenous and does not require exposure to external cues during development. Nevertheless, the circadian system is not fully formed at birth in many mammalian species and it is important to understand how SCN development can affect the function of the circadian system in adulthood. The purpose of the current review is to discuss the ontogeny of cellular and circuit function in the SCN, with a focus on work performed in model rodent species (i.e., mouse, rat, and hamster). Particular emphasis is placed on the spatial and temporal patterns of SCN development that may contribute to the function of the master clock during adulthood. Additional work aimed at decoding the mechanisms that guide circadian development is expected to provide a solid foundation upon which to better understand the sources and factors contributing to aberrant maturation of clock function.

Antidepressant but Not Prophylactic Ketamine Administration Alters Calretinin and Calbindin Expression in the Ventral Hippocampus

Ketamine has been found to have rapid, long-lasting antidepressant effects in treatment-resistant (TR) patients with major depressive disorder (MDD). Recently, we have also shown that ketamine acts as a prophylactic to protect against the development of stress-induced depressive-like behavior in mice, indicating that a preventative treatment against mental illness using ketamine is possible. While there is significant investigation into ketamine’s antidepressant mechanism of action, little is known about ketamine’s underlying prophylactic mechanism. More specifically, whether ketamine’s prophylactic action is molecularly similar to or divergent from its antidepressant action is entirely unknown. Here, we sought to characterize immunohistochemical signatures of cell populations governing ketamine’s antidepressant and prophylactic effects. 129S6/SvEv mice were treated with saline (Sal) or ketamine (K) either before a social defeat (SD) stressor as a prophylactic, or after SD as an antidepressant, then subsequently assessed for depressive-like behavior. Post-fixed brains were processed for doublecortin (DCX), calretinin (CR) and calbindin (CB) expression. The number of DCX⁺ neurons in the dentate gyrus (DG) of the hippocampus (HPC) was not affected by prophylactic or antidepressant ketamine treatment, while the number of CR⁺ neurons in the ventral hilus increased with antidepressant ketamine under SD conditions. Moreover, antidepressant, but not prophylactic ketamine administration significantly altered CR and CB expression in the ventral HPC (vHPC). These data show that while antidepressant ketamine treatment mediates some of its effects via adult hippocampal markers, prophylactic ketamine administration does not, at least in 129S6/SvEv mice. These data suggest that long-lasting behavioral effects of prophylactic ketamine are independent of hippocampal DCX, CR and CB expression in stress-susceptible mice.

Differential Expression of Ca2+-buffering Protein Calretinin in Cochlear Afferent Fibers: A Possible Link to Vulnerability to Traumatic Noise

The synaptic contacts of cochlear afferent fibers (CAFs) with inner hair cells (IHCs) are spatially segregated according to their firing properties. CAFs also exhibit spatially segregated vulnerabilities to noise. The CAF fibers contacting the modiolar side of IHCs tend to be more vulnerable. Noise vulnerability is thought to be due to the absence of neuroprotective mechanisms in the modiolar side contacting CAFs. In this study, we investigated whether the expression of neuroprotective Ca²⁺-buffering proteins is spatially segregated in CAFs. The expression patterns of calretinin, parvalbumin, and calbindin were examined in rat CAFs using immunolabeling. Calretinin-rich fibers, which made up ~50% of the neurofilament (NF)-positive fibers, took the pillar side course and contacted all IHC sides. NF-positive and calretinin-poor fibers took the modiolar side pathway and contacted the modiolar side of IHCs. Both fiber categories juxtaposed the C-terminal binding protein 2 (CtBP2) puncta and were contacted by synaptophysin puncta. These results indicated that the calretinin-poor fibers, like the calretinin-rich ones, were afferent fibers and probably formed functional efferent synapses. However, the other Ca²⁺-buffering proteins did not exhibit CAF subgroup specificity. Most CAFs near IHCs were parvalbumin-positive. Only the pillar-side half of parvalbumin-positive fibers coexpressed calretinin. Calbindin was not detected in any nerve fibers near IHCs. Taken together, of the Ca²⁺-buffering proteins examined, only calretinin exhibited spatial segregation at IHC-CAF synapses. The absence of calretinin in modiolar-side CAFs might be related to the noise vulnerability of the fibers.

Sex differences in associations between maternal deprivation and alterations in hippocampal calcium-binding proteins and cognitive functions in rats

Background and objective

Adverse early-life experiences have been suggested as one of the key contributors to neurodevelopmental disorders, such that these experiences influence brain development, cognitive ability and mental health. Previous studies indicated that hippocampal levels of the calcium-binding proteins calretinin (CALR) and calbindin-D28k (CALB) changed in response to maternal deprivation (MD), a model for adverse early-life experiences. We investigated the effects of MD on hippocampal CALR and CALB protein levels and cognitive behaviors, and explored whether these effects were sex-related.

Methods

From postnatal day 2 (PND-2) to PND-14, rat pups in the MD group were separated from their mothers for 3 h/day for comparison with pups raised normally (control). To determine hippocampal CALR and CALB levels, fluorescent immunostaining of hippocampal sections and Western blot analysis of hippocampal tissues were employed at various timepoints (PND-21, -25, -30, -35 and -40). Behavioral and cognitive changes were determined by open field test (PND-21) and Morris water maze (PND-25).

Results

Western blot analysis showed changes in the hippocampal CALR and CALB levels in both male and female MD groups, compared with controls. The open field test showed reduced exploration only in male MD groups but not female MD groups. The Morris water maze tests indicated that MD caused spatial memory impairment both in male and female rats, but there was a sex difference in CALR and CALB levels.

Conclusions

Male rats are relatively more vulnerable to MD stress than female rats, but both male and female rats demonstrate spatial learning impairment after exposure to MD stress. Sex difference in CALR and CALB levels may reveal the different mechanisms behind the behavioral observations.

Calcium signaling orchestrates glioblastoma development: Facts and conjunctures

While it is a relatively rare disease, glioblastoma multiform (GBM) is one of the more deadly adult cancers. Following current interventions, the tumor is never eliminated whatever the treatment performed; whether it is radiotherapy, chemotherapy, or surgery. One hypothesis to explain this poor outcome is the "cancer stem cell" hypothesis. This concept proposes that a minority of cells within the tumor mass share many of the properties of adult neural stem cells and it is these that are responsible for the growth of the tumor and its resistance to existing therapies. Accumulating evidence suggests that Ca(2+) might also be an important positive regulator of tumorigenesis in GBM, in processes involving quiescence, maintenance, proliferation, or migration. Glioblastoma tumors are generally thought to develop by co-opting pathways that are involved in the formation of an organ. We propose that the cells initiating the tumor, and subsequently the cells of the tumor mass, must hijack the different checkpoints that evolution has selected in order to prevent the pathological development of an organ. In this article, two main points are discussed. (i) The first is the establishment of a so-called "cellular society," which is required to create a favorable microenvironment. (ii) The second is that GBM can be considered to be an organism, which fights to survive and develop. Since GBM evolves in a limited space, its only chance of development is to overcome the evolutionary checkpoints. For example, the deregulation of the normal Ca(2+) signaling elements contributes to the progression of the disease. Thus, by manipulating the Ca(2+) signaling, the GBM cells might not be killed, but might be reprogrammed toward a new fate that is either easy to cure or that has no aberrant functioning. This article is part of a Special Issue entitled: Calcium and Cell Fate. Guest Editors: Jacques Haiech, Claus Heizmann, Joachim Krebs, Thierry Capiod and Olivier Mignen.

Calretinin and parvalbumin in schizophrenia and affective disorders: a mini-review, a perspective on the evolutionary role of calretinin in schizophrenia, and a preliminary post-mortem study of calretinin in the septal nuclei

OBJECTIVE

The septal nuclei are important limbic regions that are involved in emotional behavior and connect to various brain regions such as the habenular complex. Both the septal nuclei and the habenular complex are involved in the pathology of schizophrenia and affective disorders.

METHODS

We characterized the number and density of calretinin-immunoreactive neurons in the lateral, medial, and dorsal subregions of the septal nuclei in three groups of subjects: healthy control subjects (N = 6), patients with schizophrenia (N = 10), and patients with affective disorders (N = 6).

RESULTS

Our mini-review of the combined role of calretinin and parvalbumin in schizophrenia and affective disorders summarizes 23 studies. We did not observe significant differences in the numbers of calretinin-immunoreactive neurons or neuronal densities in the lateral, medial, and dorsal septal nuclei of patients with schizophrenia or patients with affective disorders compared to healthy control subjects.

CONCLUSIONS

Most post-mortem investigations of patients with schizophrenia have indicated significant abnormalities of parvalbumin-immunoreactive neurons in various brain regions including the hippocampus, the anterior cingulate cortex, and the prefrontal cortex in schizophrenia. This study also provides an explanation from an evolutionary perspective for why calretinin is affected in schizophrenia.

Septo-temporal distribution and lineage progression of hippocampal neurogenesis in a primate (Callithrix jacchus) in comparison to mice

Adult born neurons in the hippocampus show species-specific differences in their numbers, the pace of their maturation and their spatial distribution. Here, we present quantitative data on adult hippocampal neurogenesis in a New World primate, the common marmoset (Callithrix jacchus) that demonstrate parts of the lineage progression and age-related changes. Proliferation was largely (∼70%) restricted to stem cells or early progenitor cells, whilst the remainder of the cycling pool could be assigned almost exclusively to Tbr2+ intermediate precursor cells in both neonate and adult animals (20–122 months). Proliferating DCX+ neuroblasts were virtually absent in adults, although rare MCM2+/DCX+ co-expression revealed a small, persisting proliferative potential. Co-expression of DCX with calretinin was very limited in marmosets, suggesting that these markers label distinct maturational stages. In adult marmosets, numbers of MCM2+, Ki67+, and significantly Tbr2+, DCX+, and CR+ cells declined with age. The distributions of granule cells, proliferating cells and DCX+ young neurons along the hippocampal longitudinal axis were equal in marmosets and mice. In both species, a gradient along the hippocampal septo-temporal axis was apparent for DCX+ and resident granule cells. Both cell numbers are higher septally than temporally, whilst proliferating cells were evenly distributed along this axis. Relative to resident granule cells, however, the ratio of proliferating cells and DCX+ neurons remained constant in the septal, middle, and temporal hippocampus. In marmosets, the extended phase of the maturation of young neurons that characterizes primate hippocampal neurogenesis was due to the extension in a large CR+/DCX- cell population. This clear dissociation between DCX+ and CR+ young neurons has not been reported for other species and may therefore represent a key primate-specific feature of adult hippocampal neurogenesis.

Chronic high-dose creatine has opposing effects on depression-related gene expression and behavior in intact and sex hormone-treated gonadectomized male and female rats

Creatine is an antioxidant, neuromodulator and key regulator of energy metabolism shown to improve depressive symptoms in humans and animals, especially in females. To better understand the pharmacological effects of creatine, we examined its influence on depression-related hippocampal gene expression and behaviors in the presence and absence of sex steroids. Sham-operated and gonadectomized male and female rats were fed chow alone or chow blended with either 2% or 4% w/w creatine monohydrate for five weeks before forced swim, open field, and wire suspension tests, or seven weeks total. Before supplementation, males were chronically implanted with an empty or a testosterone-filled (T) capsule (10-mm surface release), and females were administered progesterone (P, 250 μg), estradiol benzoate (EB, 2.5 μg), EB+P, or sesame oil vehicle weekly. Relative to non-supplemented shams, all hippocampal plasticity-related mRNAs measured, including brain-derived neurotrophic factor (BDNF), tyrosine kinase B, doublecortin, calretinin, and calbindin, were downregulated in sham males given 4% creatine, and BDNF, doublecortin, and calbindin mRNAs were downregulated in sham females given 4% creatine. In contrast, combined 4% creatine+T in castrates prevented downregulation of BDNF, doublecortin, and calretinin mRNAs. Similarly, combined 4% creatine+EB+P in ovariectomized females attenuated downregulation of BDNF and calbindin mRNA levels. Moderate antidepressant and anxiolytic-like behaviors were observed in EB+P-treated ovariectomized females fed creatine, with similar trends in T-treated castrates fed creatine. Altogether, these data show that chronic, high-dose creatine has opposing effects on neuroplasticity-related genes and depressive behavior in intact and gonadectomized male and female rats. The dose and schedule of creatine used negatively impacted hippocampal neuronal integrity in otherwise healthy brains, possibly through negative compensatory changes in energy metabolism, whereas combined creatine and sex steroids acted in a neuroprotective manner in gonadectomized rats, potentially by reducing metabolic complications associated with castration or ovariectomy.

Melatonin maintains calcium-binding calretinin-positive neurons in the dentate gyrus during aging of Balb/C mice

Melatonin, the main product synthesized by the pineal gland, modulates several brain functions through different mechanisms, some of them involving the activation or participation of calcium binding intracellular proteins, such as the alpha calcium dependent protein kinase C and calmodulin. Another calcium-binding protein is calretinin, which exerts an essential role for adult hippocampal neurogenesis. Melatonin favors calretinin-positive neurons in the dentate gyrus (DG) of young mice but hippocampal neurogenesis and plasma levels of melatonin decrease during aging. Thus, in this study, we analyzed the impact of exogenous supplementation with melatonin in calretinin-neurons and their distribution along the dorsal-ventral DG in the hippocampus at three different time points (1, 3, or 6 months) after daily treatment with melatonin (8 mg/kg) in male Balb/C mice. We found an increase in the number of calretinin-positive neurons in the DG after treatment (>66%). Although a significant decline in the number of calretinin-neurons was found in both treated (~60.46-69.56%) and untreated mice (~68.81-70.34%) with respect to the youngest mice analyzed, melatonin still maintained higher number of cells in the DG. Also, the distribution of calretinin-neurons along the dorsal-ventral DG significantly showed more cells in the ventral-DG of mice treated with melatonin. Together, the data suggest that melatonin also acts on calretinin in the DG, supporting it as a molecule connecting calcium signaling and neuronal development.

Calretinin: from a "simple" Ca(2+) buffer to a multifunctional protein implicated in many biological processes

The hexa-EF-hand Ca(2+)-binding protein calretinin (CR) is predominantly expressed in specific neurons of the central and peripheral nervous system. However, CR expression is also observed in non-neuronal cells, e.g., during embryonic development and in mesothelioma cells. Of the 6 EF-hand domains, 5 are functional; the first 4 domains form 2 pairs showing high cooperativity within a pair that results in non-linear modulation of intracellular Ca(2+) signals by CR. EF-hand domain 5 has a low affinity and represents the identified interaction site with CR-binding partners present in mouse cerebellar granule cells. CR binding to other targets including the pore-forming α1 subunit of the Ca(2+) channel Ca V 2.1, as well as to huntingtin indicates additional Ca(2+) sensor functions besides the well-known Ca(2+)-buffering functions. The absence of CR in cerebellar granule cells of CR(-/-) mice results in increased excitability and altered firing of Purkinje cells and promotes cerebellar 160-Hz oscillations impairing motor coordination. The putative role of CR in neuroprotection is still highly discussed. Altogether, CR emerges as a multi-functional protein also associated with development, i.e., cell proliferation, differentiation, and cell death.

Untangling the influences of voluntary running, environmental complexity, social housing and stress on adult hippocampal neurogenesis

Environmental enrichment (EE) exerts powerful effects on brain physiology, and is widely used as an experimental and therapeutic tool. Typical EE paradigms are multifactorial, incorporating elements of physical exercise, environmental complexity, social interactions and stress, however the specific contributions of these variables have not been separable using conventional housing paradigms. Here, we evaluated the impacts of these individual variables on adult hippocampal neurogenesis by using a novel "Alternating EE" paradigm. For 4 weeks, adult male CD1 mice were alternated daily between two enriched environments; by comparing groups that differed in one of their two environments, the individual and combinatorial effects of EE variables could be resolved. The Alternating EE paradigm revealed that (1) voluntary running for 3 days/week was sufficient to increase both mitotic and post-mitotic stages of hippocampal neurogenesis, confirming the central importance of exercise; (2) a complex environment (comprised of both social interactions and rotated inanimate objects) had no effect on neurogenesis itself, but enhanced depolarization-induced c-Fos expression (attributable to social interactions) and buffered stress-induced plasma corticosterone levels (attributable to inanimate objects); and (3) neither social isolation, group housing, nor chronically increased levels of plasma corticosterone had a prolonged impact on neurogenesis. Mouse strain, handling and type of running apparatus were tested and excluded as potential confounding factors. These findings provide valuable insights into the relative effects of key EE variables on adult neurogenesis, and this "Alternating EE" paradigm represents a useful tool for exploring the contributions of individual EE variables to mechanisms of neural plasticity.

S100A6 (calcyclin) is a novel marker of neural stem cells and astrocyte precursors in the subgranular zone of the adult mouse hippocampus

S100A6 (calcyclin), an EF-hand calcium binding protein, is considered to play various roles in the brain, for example, cell proliferation and differentiation, calcium homeostasis, and neuronal degeneration. In addition to some limbic nuclei, S100A6 is distributed in the rostral migratory stream, one of the major neurogenic niches of the adult brain. However, the potential involvement of S100A6 in adult neurogenesis remains unclear. In this study, we aimed to elucidate the role of S100A6 in the other major neurogenic niche, the subgranular zone of the dentate gyrus in the adult mouse hippocampus. Immunofluorescent multiple labeling showed that S100A6 was highly expressed in neural stem cells labeled by sex determining region Y-box 2, brain lipid-binding protein protein and glial fibrillary acidic protein. S100A6+ cells often extended a long process typical of radial glial morphology. In addition, S100A6 was found in some S100β+ astrocyte lineage cells. Interestingly, proliferating cell nuclear antigen was detected in a fraction of S100A6+/S100β+ cells. These cells were considered to be lineage-restricted astrocyte precursors maintaining mitotic potential. On the other hand, S100A6 was rarely seen in neural lineage cells labeled by T-box brain protein 2, doublecortin, calretinin and calbindin D28K. Cell fate-tracing experiment using BrdU showed that the majority of newly generated immature astrocytes were immunoreactive for S100A6, while mature astrocytes lacked S100A6 immunoreactivity. Administration of S100 protein inhibitor, trifluoperazine, caused a reduction in production of S100β+ astrocyte lineage cells, but had no impact on neurogenesis. Overall, our data provide the first evidence that S100A6 is a specific marker of neural stem cells and astrocyte precursors, and may be especially important for generation of astrocytes in the adult hippocampus.