Neurons of origin of zinc-containing pathways and the distribution of zinc-containing boutons in the hippocampal region of the rat

TSQ Incubation Enhances Autometallographic Zinc Detection in Cultured Astrocytes

Zinc is a critical ion for a large number of cellular functions. In the central nervous system, zinc ions are involved in synaptic transmission. Therefore, zinc homeostasis is essential, and cells have developed a variety of mechanisms to control cellular zinc concentration, including the zincosome formation. Alterations of free zinc levels have been associated with brain dysfunction and are present in many illnesses and syndromes. Astrocytes are implicated in the maintenance of the neuronal milleu and brain homeostasis. In this work, we have analyzed the combination of direct (TSQ) and indirect (autometallography) zinc detection methods to increase sensitivity for studying zinc uptake by rat astrocytes in vitro. Zincosome formation was visualized with the zinc fluorochrome TSQ by light microscopy. Additionally, we improved both zinc precipitation and cellular fixation methods to preserve zinc ions and make them suitable for autometallography development. Our tests pinpointed paraformaldehyde and sodium sulfide as the more adequate methods for cellular fixation and zinc precipitation, respectively. TSQ incubation and pH of the fixative were shown to be crucial for autometallography. Using this improved method, we visualized the zinc content of zincosomes at the ultrastructural level both as silver autometallographic precipitates and as electrodense sulfide-osmium zinc precipitates.

Prenatal protein malnutrition decreases neuron numbers in the parahippocampal region but not prefrontal cortex in adult rats

OBJECTIVE

Prenatal protein malnutrition produces anatomical and functional changes in the developing brain that persist despite immediate postnatal nutritional rehabilitation. Brain networks of prenatally malnourished animals show diminished activation of prefrontal areas and an increased activation of hippocampal regions during an attentional task [1]. While a reduction in cell number has been documented in hippocampal subfield CA1, nothing is known about changes in neuron numbers in the prefrontal or parahippocampal cortices.

METHODS

In the present study, we used unbiased stereology to investigate the effect of prenatal protein malnutrition on the neuron numbers in the medial prefrontal cortex and the cortices of the parahippocampal region that comprise the larger functional network.

RESULTS

Results show that prenatal protein malnutrition does not cause changes in the neuronal population in the medial prefrontal cortex of adult rats, indicating that the decrease in functional activation during attentional tasks is not due to a reduction in the number of neurons. Results also show that prenatal protein malnutrition is associated with a reduction in neuron numbers in specific parahippocampal subregions: the medial entorhinal cortex and presubiculum.

DISCUSSION

The affected regions along with CA1 comprise a tightly interconnected circuit, suggesting that prenatal malnutrition confers a vulnerability to specific hippocampal circuits. These findings are consistent with the idea that prenatal protein malnutrition produces a reorganization of structural and functional networks, which may underlie observed alterations in attentional processes and capabilities.

Metal ion content of internal organs in the calorically restricted Wistar rat

BACKGROUND

Despite the agreed principle that access to food is a human right, undernourishment and metal ion deficiencies are public health problems worldwide, exacerbated in impoverished or war-affected areas. It is known that maternal malnutrition causes growth retardation and affects behavioral and cognitive development of the newborn. Here we ask whether severe caloric restriction leads per se to disrupted metal accumulation in different organs of the Wistar rat.

METHODS

Inductively coupled plasma optical emission spectroscopy was used to determine the concentration of multiple elements in the small and large intestine, heart, lung, liver, kidney, pancreas, spleen, brain, spinal cord, and three skeletal muscles from control and calorically restricted Wistar rats. The caloric restriction protocol was initiated from the mothers prior to mating and continued throughout gestation, lactation, and post-weaning up to sixty days of age.

RESULTS

Both sexes were analyzed but dimorphism was rare. The pancreas was the most affected organ presenting a higher concentration of all the elements analyzed. Copper concentration decreased in the kidney and increased in the liver. Each skeletal muscle responded to the treatment differentially: Extensor Digitorum Longus accumulated calcium and manganese, gastrocnemius decreased copper and manganese, whereas soleus decreased iron concentrations. Differences were also observed in the concentration of elements between organs independently of treatment: The soleus muscle presents a higher concentration of Zn compared to the other muscles and the rest of the organs. Notably, the spinal cord showed large accumulations of calcium and half the concentration of zinc compared to brain. X-ray fluorescence imaging suggests that the extra calcium is attributable to the presence of ossifications whereas the latter finding is attributable to the low abundance of zinc synapses in the spinal cord.

CONCLUSION

Severe caloric restriction did not lead to systemic metal deficiencies but caused instead specific metal responses in few organs.

A Timm-Nissl multiplane microscopic atlas of rat brain zincergic terminal fields and metal-containing glia

The ability of Timm's sulphide silver method to stain zincergic terminal fields has made it a useful neuromorphological marker. Beyond its roles in zinc-signalling and neuromodulation, zinc is involved in the pathophysiology of ischemic stroke, epilepsy, degenerative diseases and neuropsychiatric conditions. In addition to visualising zincergic terminal fields, the method also labels transition metals in neuronal perikarya and glial cells. To provide a benchmark reference for planning and interpretation of experimental investigations of zinc-related phenomena in rat brains, we have established a comprehensive repository of serial microscopic images from a historical collection of coronally, horizontally and sagittally oriented rat brain sections stained with Timm's method. Adjacent Nissl-stained sections showing cytoarchitecture, and customised atlas overlays from a three-dimensional rat brain reference atlas registered to each section image are included for spatial reference and guiding identification of anatomical boundaries. The Timm-Nissl atlas, available from EBRAINS, enables experimental researchers to navigate normal rat brain material in three planes and investigate the spatial distribution and density of zincergic terminal fields across the entire brain.

Environmental Enrichment Engages Vesicular Zinc Signaling to Enhance Hippocampal Neurogenesis

Zinc is highly concentrated in synaptic vesicles throughout the mammalian telencephalon and, in particular, the hippocampal dentate gyrus. A role for zinc in modulating synaptic plasticity has been inferred, but whether zinc has a particular role in experience-dependent plasticity has yet to be determined. The aim of the current study was to determine whether vesicular zinc is important for modulating adult hippocampal neurogenesis in an experience-dependent manner and, consequently, hippocampal-dependent behaviour. We assessed the role of vesicular zinc in modulating hippocampal neurogenesis and behaviour by comparing ZnT3 knockout (KO) mice, which lack vesicular zinc, to wild-type (WT) littermates exposed to either standard housing conditions (SH) or an enriched environment (EE). We found that vesicular zinc is necessary for a cascade of changes in hippocampal plasticity following EE, such as increases in hippocampal neurogenesis and elevations in mature brain-derived neurotrophic factor (mBDNF), but was otherwise dispensable under SH conditions. Using the Spatial Object Recognition task and the Morris Water task we show that, unlike WT mice, ZnT3 KO mice showed no improvements in spatial memory following EE. These experiments demonstrate that vesicular zinc is essential for the enhancement of adult hippocampal neurogenesis and behaviour following enrichment, supporting a role for zincergic neurons in contributing to experience-dependent plasticity in the hippocampus.

Vesicular Zinc Modulates Cell Proliferation and Survival in the Developing Hippocampus

In the brain, vesicular zinc, which refers to a subset of zinc that is sequestered into synaptic vesicles by zinc transporter 3 (ZnT3), has extensive effects on neuronal signalling and modulation. Vesicular zinc-focused research has mainly been directed to its role in the hippocampus, particularly in adult neurogenesis. However, whether vesicular zinc is involved in modulating neurogenesis during the early postnatal period has been less studied. As a first step to understanding this, we used ZnT3 knockout (KO) mice, which lack ZnT3 and, thus, vesicular zinc, to evaluate cell proliferation at three different age points spanning postnatal development (P6, P14, and P28). The survival and the neuronal phenotype of these cells was also assessed in adulthood. We found that male ZnT3 KO mice exhibited lower rates of cell proliferation at P14, but a greater number of these cells survived to adulthood. Additionally, significantly more cells labelled on P6 survived to adulthood in male and female ZnT3 KO mice. We also found sex-dependent differences, whereby male mice showed higher levels of cell proliferation at P28, as well as higher levels of cell survival for P14-labelled cells, compared to female mice. However, female mice showed greater percentages of neuronal differentiation for P14-labelled cells. Finally, we found significant effects of age of BrdU injections on cell proliferation, survival, and neuronal differentiation. Collectively, our results suggest that the loss of vesicular zinc affects normal proliferation and survival of cells born at different age points during postnatal development and highlight prominent sex- and age-dependent differences. Our findings provide the foundation for future studies to further probe the role of vesicular zinc in the modulation of developmental neurogenesis.

Spatiotemporal Imaging of Zinc Ions in Zebrafish Live Brain Tissue Enabled by Fluorescent Bionanoprobes

The zebrafish is a powerful model organism to study the mechanisms governing transition metal ions within whole brain tissue. Zinc is one of the most abundant metal ions in the brain, playing a critical pathophysiological role in neurodegenerative diseases. The homeostasis of free, ionic zinc (Zn²⁺) is a key intersection point in many of these diseases, including Alzheimer's disease and Parkinson's disease. A Zn²⁺ imbalance can eventuate several disturbances that may lead to the development of neurodegenerative changes. Therefore, compact, reliable approaches that allow the optical detection of Zn²⁺ across the whole brain would contribute to our current understanding of the mechanisms that underlie neurological disease pathology. We developed an engineered fluorescence protein-based nanoprobe that can spatially and temporally resolve Zn²⁺ in living zebrafish brain tissue. The self-assembled engineered fluorescence protein on gold nanoparticles was shown to be confined to defined locations within the brain tissue, enabling site specific studies, compared to fluorescent protein-based molecular tools, which diffuse throughout the brain tissue. Two-photon excitation microscopy confirmed the physical and photometrical stability of these nanoprobes in living zebrafish (Danio rerio) brain tissue, while the addition of Zn²⁺ quenched the nanoprobe fluorescence. Combining orthogonal sensing methods with our engineered nanoprobes will enable the study of imbalances in homeostatic Zn²⁺ regulation. The proposed bionanoprobe system offers a versatile platform to couple metal ion specific linkers and contribute to the understanding of neurological diseases.

Zinc deficiency and supplementation in autism spectrum disorder and Phelan-McDermid syndrome

Approximately 1 in 36 children are diagnosed with autism spectrum disorder (ASD). The disorder is four times more common in males than in females. Zinc deficiency and mutations in SHANK2 and SHANK3 (members of a family of excitatory postsynaptic scaffolding proteins) are all risk factors that may contribute to the pathophysiology of the disease. The presence of shankopathies (loss of one copy of the SHANK3 gene) can lead to the development of Phelan-McDermid syndrome (PMDS)-a rare genetic disorder characterized by developmental delay, intellectual disability, poor motor tone, and ASD-like symptoms. We reviewed the relationship between zinc, ASD, and PMDS as well as the effect of zinc supplementation in improving symptoms of ASD and PMDS based on 22 studies published within 6 years (2015-2020). Zinc deficiency (assessed by either dietary intake, blood, hair, or tooth matrix) was shown to be highly prevalent in ASD and PMDS patients as well as in preclinical models of ASD and PMDS. Zinc supplements improved the behavioral deficits in animal models of ASD and PMDS. Clinical trials are still needed to validate the beneficial therapeutic effects of zinc supplements in ASD and PMDS patients.

General Aspects of Metal Ions as Signaling Agents in Health and Disease

This review focuses on the current knowledge on the involvement of metal ions in signaling processes within the cell, in both physiological and pathological conditions. The first section is devoted to the recent discoveries on magnesium and calcium-dependent signal transduction-the most recognized signaling agents among metals. The following sections then describe signaling pathways where zinc, copper, and iron play a key role. There are many systems in which changes in intra- and extra-cellular zinc and copper concentrations have been linked to important downstream events, especially in nervous signal transduction. Iron signaling is mostly related with its homeostasis. However, it is also involved in a recently discovered type of programmed cell death, ferroptosis. The important differences in metal ion signaling, and its disease-leading alterations, are also discussed.

Micromolar concentrations of Zn2+ depress cellular excitability through a blockade of calcium current in rat adrenal slices

The present work, using chromaffin cells in rat adrenal slices (RCCs), aims to describe what type of ionic current alterations induced by zinc underlies their effects reported on synaptic transmission. Thus, Zn²⁺ blocked calcium channels of RCCs in a time- and concentration-dependent manner with an IC₅₀ of 391 μM. This blockade was partially reversed upon washout and was greater at more depolarizing holding potentials (i.e. 32 ± 5% at -110 mV, and 43 ± 6% at -50 mV, after 5 min perfusion). In ω-toxins-sensitive calcium channels (N-, P- and Q-types), Zn²⁺caused a lower blockade of I_Ca, 33.3%, than in ω-toxins-resistant ones (L-type, 55.3%; and R-type, 90%). This compound inhibited calcium current at all test potentials and shows a shift of the I-V curve to more depolarized values of about 10 mV. The sodium current was not blocked by acute application of high Zn²⁺concentrations. Voltage-dependent potassium current was marginally affected by high Zn²⁺ concentrations showing no concentration-dependence. Nevertheless, calcium- and voltage-dependent potassium current was drastically depressed in a dose-dependent manner, with an IC₅₀ of 453 μM. This blockade was related to the prevention of Ca²⁺ influx through voltage-dependent calcium channels coupled to BK channels. Under current-clamp conditions, RCCs exhibit a resting potential of -50.7 mV, firing spontaneous APs (1-2 spikes/s) generated by the opening of Na⁺ and Ca²⁺-channels, and terminated by the activation of voltage and Ca²⁺-activated K⁺-channels (BK). We found that the blockade of these ionic currents by Zn²⁺ led to a drastic alteration of cellular excitability with a depolarization of the membrane potential, the slowdown and broadening of the APs and the severe reduction of the after hyperpolarization (AHP) which led to a decrease in the APs firing frequency. Taken together, these results point to a neurotoxic action evoked by zinc that is associated with changes to cellular excitability by blocking the ionic currents responsible for both the neurotransmitter release and the action potentials firing.

Zinc modulates synaptic transmission by differentially regulating synaptic glutamate homeostasis in hippocampus

A subset of presynaptic glutamatergic vesicles in the brain co-releases zinc (Zn²⁺ ) with glutamate into the synapse. However, the role of synaptically released Zn²⁺ is still under investigation. Here, we studied the effect of Zn²⁺ on glutamate homeostasis by measuring the evoked extracellular glutamate level (EGL) and the probability of evoked action potential (P_EAP ) at the Zn²⁺ -containing or zincergic mossy fiber-CA3 synapses of the rat hippocampus. We found that the application of Zn²⁺ (ZnCl₂ ) exerted bidirectional effects on both EGL and P_EAP : facilitatory at low concentration (~1 µM) while repressive at high concentration (~50 µM). To determine the action of endogenous Zn²⁺ , we also used extracellular Zn²⁺ chelator to remove the synaptically released Zn²⁺ . Zn²⁺ chelation reduced both EGL and P_EAP , suggesting that endogenous Zn²⁺ has mainly a facilitative role in glutamate secretion on physiological condition. We revealed that calcium/calmodulin-dependent protein kinase II was integral to the mechanism by which Zn²⁺ facilitated the release of glutamate. Moreover, a glutamate transporter was the molecular entity for the action of Zn²⁺ on glutamate uptake by which Zn²⁺ decreases glutamate availability. Taken together, we show a novel action of Zn²⁺ , which is to biphasically regulate glutamate homeostasis via Zn²⁺ concentration-dependent synaptic facilitation and depression. Thus, co-released Zn²⁺ is physiologically important for enhancing weak stimulation, but potentially mitigates excessive stimulation to keep synaptic transmission within optimal physiological range.

Zinc transporters in Alzheimer's disease

Alzheimer’s disease (AD) is the most devastating neurodegenerative disorder. Due to the increase in population and longevity, incidence will triple by the middle of the twenty-first century. So far, no treatment has prevented or reversed the disease. More than 20 years of multidisciplinary studies have shown that brain zinc dyshomeostasis may play a critical role in AD progression, which provides encouraging clues for metal-targeted therapies in the treatment of AD. Unfortunately, the pilot clinical application of zinc chelator and/or ionophore strategy, such as the use of quinoline-based compounds, namely clioquinol and PBT2, has not yet been successful. The emerging findings revealed a list of key zinc transporters whose mRNA or protein levels were abnormally altered at different stages of AD brains. Furthermore, specifically modulating the expression of some of the zinc transporters in the central nervous system through genetic methods slowed down or prevented AD progression in animal models, resulting in significantly improved cognitive performance, movement, and prolonged lifespan. Although the underlying molecular mechanisms are not yet fully understood, it shed new light on the treatment or prevention of the disease. This review considers recent advances regarding AD, zinc and zinc transporters, recapitulating their relationships in extending our current understanding of the disease amelioration effects of zinc transport proteins as potential therapeutic targets to cure AD, and it may also provide new insights to identify novel therapeutic strategies for ageing and other neurodegenerative diseases, such as Huntington’s and Parkinson’s disease.

Mechanisms of zinc modulation of olfactory bulb AMPA receptors

The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype of ionotropic glutamate receptors mediates most fast excitatory transmission. Glutamate binding to AMPA receptors (AMPARs) causes most AMPARs to rapidly and completely desensitize, and their desensitization kinetics influence synaptic timing. Thus, factors that alter AMPAR desensitization influence synaptic transmission. Synaptically released zinc is such a factor. Zinc is a neuromodulator with effects on amino acid receptors and synaptic transmission in many brain regions, including the olfactory bulb (OB). We have previously shown in the OB that zinc potentiates AMPAR-mediated currents at low concentrations (30 μM, 100 μM) and inhibits them at a higher concentration (1 mM). It has been hypothesized that zinc potentiates AMPARs by decreasing receptor desensitization. Here, we used cyclothiazide (CTZ), a drug that blocks AMPAR desensitization, to determine whether zinc-mediated potentiation and/or inhibition of AMPA-evoked currents reflect(s) changes in AMPAR desensitization. Zinc largely had biphasic concentration-dependent effects at OB AMPARs. CTZ completely blocked potentiation by zinc but had no significant effect on inhibition. There was a significant negative correlation between the degree of potentiation of AMPAR-mediated currents by 100 μM zinc and a quantitative measure of the degree of AMPAR desensitization (the steady-state to peak [S:P] ratio of AMPA-evoked currents), but no correlation between the degree of current inhibition by 1 mM zinc and the S:P ratio. Together, these findings suggest that low zinc concentrations potentiate rat OB AMPARs by decreasing receptor desensitization, but that the inhibitory effects of higher zinc concentrations are mediated by a separate mechanism.

Alcohol dependence treating agent, acamprosate, prevents traumatic brain injury-induced neuron death through vesicular zinc depletion

Acamprosate, also known as N-acetyl homotaurine, is an N-methyl-d-aspartate receptor antagonist that is used for treating alcohol dependence. Although the exact mechanism of acamprosate has not been clearly established, it appears to work by promoting a balance between the excitatory and inhibitory neurotransmitters, glutamate, and gamma-aminobutyric acid, respectively. Several studies have demonstrated that acamprosate provides neuroprotection against ischemia-induced brain injury. However, no studies have been performed evaluating the effect of acamprosate on traumatic brain injury (TBI). In the present study, we sought to evaluate the therapeutic potential of acamprosate to protect against neuronal death following TBI. Rats were given oral acamprosate (200 mg/kg/d for 2weeks) and then subjected to a controlled cortical impact injury localized over the parietal cortex. Histologic analysis was performed at 3hours, 24hours, and 7days after TBI. We found that acamprosate treatment reduced the concentration of vesicular glutamate and zinc in the hippocampus. Consequently, this reduced vesicular glutamate and zinc level resulted in a reduction of reactive oxygen species production after TBI. When evaluated 24hours after TBI, acamprosate administration reduced the number of degenerating neurons, zinc accumulation, blood-brain barrier disruption, neutrophil infiltration, and dendritic loss. Acamprosate also reduced glial activation and neuronal loss at 7days after TBI. In addition, acamprosate rescued TBI-induced neurologic and cognitive dysfunction. The present study demonstrates that acamprosate attenuates TBI-induced brain damage by depletion of vesicular glutamate and zinc levels. Therefore, this study suggests that acamprosate may have high therapeutic potential for prevention of TBI-induced neuronal death.

A Brief Overview from the Physiological and Detrimental Roles of Zinc Homeostasis via Zinc Transporters in the Heart

Zinc (mostly as free/labile Zn²⁺) is an essential structural constituent of many proteins, including enzymes in cellular signaling pathways via functioning as an important signaling molecule in mammalian cells. In cardiomyocytes at resting condition, intracellular labile Zn²⁺ concentration ([Zn²⁺]_i) is in the nanomolar range, whereas it can increase dramatically under pathological conditions, including hyperglycemia, but the mechanisms that affect its subcellular redistribution is not clear. Therefore, overall, very little is known about the precise mechanisms controlling the intracellular distribution of labile Zn²⁺, particularly via Zn²⁺ transporters during cardiac function under both physiological and pathophysiological conditions. Literature data demonstrated that [Zn²⁺]_i homeostasis in mammalian cells is primarily coordinated by Zn²⁺ transporters classified as ZnTs (SLC30A) and ZIPs (SLC39A). To identify the molecular mechanisms of diverse functions of labile Zn²⁺ in the heart, the recent studies focused on the discovery of subcellular localization of these Zn²⁺ transporters in parallel to the discovery of novel physiological functions of [Zn²⁺]_i in cardiomyocytes. The present review summarizes the current understanding of the role of [Zn²⁺]_i changes in cardiomyocytes under pathological conditions, and under high [Zn²⁺]_i and how Zn²⁺ transporters are important for its subcellular redistribution. The emerging importance and the promise of some Zn²⁺ transporters for targeted cardiac therapy against pathological stimuli are also provided. Taken together, the review clearly outlines cellular control of cytosolic Zn²⁺ signaling by Zn²⁺ transporters, the role of Zn²⁺ transporters in heart function under hyperglycemia, the role of Zn²⁺ under increased oxidative stress and ER stress, and their roles in cancer are discussed.

Opposing Morphogenetic Defects on Dendrites and Mossy Fibers of Dentate Granular Neurons in CRMP3-Deficient Mice

Collapsin response mediator proteins (CRMPs) are highly expressed in the brain during early postnatal development and continue to be present in specific regions into adulthood, especially in areas with extensive neuronal plasticity including the hippocampus. They are found in the axons and dendrites of neurons wherein they contribute to specific signaling mechanisms involved in the regulation of axonal and dendritic development/maintenance. We previously identified CRMP3’s role on the morphology of hippocampal CA1 pyramidal dendrites and hippocampus-dependent functions. Our focus here was to further analyze its role in the dentate gyrus where it is highly expressed during development and in adults. On the basis of our new findings, it appears that CRMP3 has critical roles both in axonal and dendritic morphogenesis of dentate granular neurons. In CRMP3-deficient mice, the dendrites become dystrophic while the infrapyramidal bundle of the mossy fiber shows aberrant extension into the stratum oriens of CA3. This axonal misguided projection of granular neurons suggests that the mossy fiber-CA3 synaptic transmission, important for the evoked propagation of the activity of the hippocampal trisynaptic circuitry, may be altered, whereas the dystrophic dendrites may impair the dynamic interactions with the entorhinal cortex, both expected to affect hippocampal function.

Brain Lateralization in Mice Is Associated with Zinc Signaling and Altered in Prenatal Zinc Deficient Mice That Display Features of Autism Spectrum Disorder

A number of studies have reported changes in the hemispheric dominance in autism spectrum disorder (ASD) patients on functional, biochemical, and morphological level. Since asymmetry of the brain is also found in many vertebrates, we analyzed whether prenatal zinc deficient (PZD) mice, a mouse model with ASD like behavior, show alterations regarding brain lateralization on molecular and behavioral level. Our results show that hemisphere-specific expression of marker genes is abolished in PZD mice on mRNA and protein level. Using magnetic resonance imaging, we found an increased striatal volume in PZD mice with no change in total brain volume. Moreover, behavioral patterns associated with striatal lateralization are altered and the lateralized expression of dopamine receptor 1 (DR1) in the striatum of PZD mice was changed. We conclude that zinc signaling during brain development has a critical role in the establishment of brain lateralization in mice.

Impact of Labile Zinc on Heart Function: From Physiology to Pathophysiology

Zinc plays an important role in biological systems as bound and histochemically reactive labile Zn²⁺. Although Zn²⁺ concentration is in the nM range in cardiomyocytes at rest and increases dramatically under stimulation, very little is known about precise mechanisms controlling the intracellular distribution of Zn²⁺ and its variations during cardiac function. Recent studies are focused on molecular and cellular aspects of labile Zn²⁺ and its homeostasis in mammalian cells and growing evidence clarified the molecular mechanisms underlying Zn²⁺-diverse functions in the heart, leading to the discovery of novel physiological functions of labile Zn²⁺ in parallel to the discovery of subcellular localization of Zn²⁺-transporters in cardiomyocytes. Additionally, important experimental data suggest a central role of intracellular labile Zn²⁺ in excitation-contraction coupling in cardiomyocytes by shaping Ca²⁺ dynamics. Cellular labile Zn²⁺ is tightly regulated against its adverse effects through either Zn²⁺-transporters, Zn²⁺-binding molecules or Zn²⁺-sensors, and, therefore plays a critical role in cellular signaling pathways. The present review summarizes the current understanding of the physiological role of cellular labile Zn²⁺ distribution in cardiomyocytes and how a remodeling of cellular Zn²⁺-homeostasis can be important in proper cell function with Zn²⁺-transporters under hyperglycemia. We also emphasize the recent investigations on Zn²⁺-transporter functions from the standpoint of human heart health to diseases together with their clinical interest as target proteins in the heart under pathological condition, such as diabetes.

Zinc as a Neuromodulator in the Central Nervous System with a Focus on the Olfactory Bulb

The olfactory bulb (OB) is central to the sense of smell, as it is the site of the first synaptic relay involved in the processing of odor information. Odor sensations are first transduced by olfactory sensory neurons (OSNs) before being transmitted, by way of the OB, to higher olfactory centers that mediate olfactory discrimination and perception. Zinc is a common trace element, and it is highly concentrated in the synaptic vesicles of subsets of glutamatergic neurons in some brain regions including the hippocampus and OB. In addition, zinc is contained in the synaptic vesicles of some glycinergic and GABAergic neurons. Thus, zinc released from synaptic vesicles is available to modulate synaptic transmission mediated by excitatory (e.g., N-methyl-D aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)) and inhibitory (e.g., gamma-aminobutyric acid (GABA), glycine) amino acid receptors. Furthermore, extracellular zinc can alter the excitability of neurons through effects on a variety of voltage-gated ion channels. Consistent with the notion that zinc acts as a regulator of neuronal activity, we and others have shown zinc modulation (inhibition and/or potentiation) of amino acid receptors and voltage-gated ion channels expressed by OB neurons. This review summarizes the locations and release of vesicular zinc in the central nervous system (CNS), including in the OB. It also summarizes the effects of zinc on various amino acid receptors and ion channels involved in regulating synaptic transmission and neuronal excitability, with a special emphasis on the actions of zinc as a neuromodulator in the OB. An understanding of how neuroactive substances such as zinc modulate receptors and ion channels expressed by OB neurons will increase our understanding of the roles that synaptic circuits in the OB play in odor information processing and transmission.

Complementary Modular Microcircuits of the Rat Medial Entorhinal Cortex

The parahippocampal region is organized into different areas, with the medial entorhinal cortex (MEC), presubiculum and parasubiculum prominent in spatial memory. Here, we also describe a region at the extremity of the MEC and bordering the subicular complex, the medial-most part of the entorhinal cortex. While the subdivisions of hippocampus proper form more or less continuous cell sheets, the superficial layers of the parahippocampal region have a distinct modular architecture. We investigate the spatial distribution, laminar position, and putative connectivity of zinc-positive modules in layer 2 of the MEC of rats and relate them to the calbindin-positive patches previously described in the entorhinal cortex. We found that the zinc-positive modules are complementary to the previously described calbindin-positive patches. We also found that inputs from the presubiculum are directed toward the zinc-positive modules while the calbindin-positive patches received inputs from the parasubiculum. Notably, the dendrites of neurons from layers 3 and 5, positive for Purkinje Cell Protein 4 expression, overlap with the zinc modules. Our data thus indicate that these two complementary modular systems, the calbindin patches and zinc modules, are part of parallel information streams in the hippocampal formation.

Methionine Sulfoxide Reductase-B3 (MsrB3) Protein Associates with Synaptic Vesicles and its Expression Changes in the Hippocampi of Alzheimer's Disease Patients

Genome-wide association studies (GWAS) identified susceptibility loci associated with decreased hippocampal volume, and found hippocampal subfield-specific effects at MSRB3 (methionine sulfoxide reductase-B3). The MSRB3 locus was also linked to increased risk for late onset Alzheimer's disease (AD). In this study, we uncovered novel sites of MsrB3 expression in CA pyramidal layer and arteriolar walls by using automated immunohistochemistry on hippocampal sections from 23 individuals accompanied by neuropathology reports and clinical dementia rating scores. Controls, cognitively intact subjects with no hippocampal neurofibrillary tangles, exhibited MsrB3 signal as distinct but rare puncta in CA1 pyramidal neuronal somata. In CA3, however, MsrB3-immunoreactivity was strongest in the neuropil of the pyramidal layer. These patterns were replicated in rodent hippocampi where ultrastructural and immunohistofluorescence analysis revealed MsrB3 signal associated with synaptic vesicles and colocalized with mossy fiber terminals. In AD subjects, the number of CA1 pyramidal neurons with frequent, rather than rare, MsrB3-immunoreactive somatic puncta increased in comparison to controls. This change in CA1 phenotype correlated with the occurrence of AD pathological hallmarks. Moreover, the intensity of MsrB3 signal in the neuropil of CA3 pyramidal layer correlated with the signal pattern in neurons of CA1 pyramidal layer that was characteristic of cognitively intact individuals. Finally, MsrB3 signal in the arteriolar walls in the hippocampal white matter decreased in AD patients. This characterization of GWAS-implicated MSRB3 protein expression in human hippocampus suggests that patterns of neuronal and vascular MsrB3 protein expression reflect or underlie pathology associated with AD.

Immunohistochemical investigation of the internal structure of the mouse subiculum

The subiculum is the output component of the hippocampal formation and holds a key position in the neural circuitry of memory. Previous studies have demonstrated the subiculum's connectivity to other brain areas in detail; however, little is known regarding its internal structure. We investigated the cytoarchitecture of the temporal and mid-septotemporal parts of the subiculum using immunohistochemistry. The border between the CA1 region and subiculum was determined by both cytoarchitecture and zinc transporter 3 (ZnT3)-immunoreactivity (IR), whereas the border between the subiculum and presubiculum (PreS) was partially indicated by glutamate receptor 1 (GluR1)-IR. The subiculum was divided into proximal and distal subfields based on cytoarchitecture and immunohistochemistry for calbindin (CB), nitric oxide synthase (NOS) and Purkinje cell protein 4 (PCP4). The proximal subiculum (defined here as subiculum 2) was composed of five layers: the molecular layer (layer 1), the medium-sized pyramidal cell layer (layer 2) that contained NOS- and PCP4-positive neurons, the large pyramidal cell layer (layer 3) characterized by the accumulation of ZnT3- (more proximally) and vesicular glutamate transporter 2-positive (more distally) boutons, layer 4 containing polymorphic cells, and the deepest layer 5 composed of PCP4-positive cells with long apical dendrites that reached layer 1. The distal subiculum (subiculum 1) consisting of smaller neurons did not show these features. Quantitative analyses of the size and numerical density of somata substantiated this delineation. Both the proximal-distal division and five-layered structure in the subiculum 2 were confirmed throughout the temporal two-thirds of the subiculum. These findings will provide a new structural basis for hippocampal investigations.

Zinc-specific Autometallographic In Vivo Selenium Methods: Tracing of Zinc-enriched (ZEN) Terminals, ZEN Pathways, and Pools of Zinc Ions in a Multitude of Other ZEN Cells

In vivo-applied sodium selenide or sodium selenite causes the appearance of zinc-selenium nanocrystals in places where free or loosely bound zinc ions are present. These nanocrystals can in turn be silver enhanced by autometallographic (AMG) development. The selenium method was introduced in 1982 as a tool for zinc-ion tracing, e.g., in vesicular compartments such as synaptic vesicles of zinc-enriched (ZEN) terminals in the central nervous system, and for visualization of zinc ions in ZEN secretory vesicles of, e.g., somatotrophic cells in the pituitary, zymogene granules in pancreatic acinar cells, beta-cells of the islets of Langerhans, Paneth cells of the crypts of Lieberkühn, secretory cells of the tubuloacinar glands of prostate, epithelium of parts of ductus epididymidis, and osteoblasts. If sodium selenide/selenite is injected into brain, spinal cord, spinal nerves containing sympathetic axons, or intraperitoneally, retrograde axonal transport of zinc-selenium nanocrystals takes place in ZEN neurons, resulting in accumulation of zinc-selenium nanocrystals in lysosomes of the neuronal somata. The technique is, therefore, also a highly specific tool for tracing ZEN pathways. The present review includes an update of the 1982 paper and presents evidence that only zinc ions are traced with the AMG selenium techniques if the protocols are followed to the letter.

A possible significant role of zinc and GPR39 zinc sensing receptor in Alzheimer disease and epilepsy

Zinc the essential trace element, plays a significant role in the brain development and in the proper brain functions at every stage of life. Misbalance of zinc (Zn(2+)) ions in the central nervous system is involved in the pathogenesis of numerous neurodegenerative disorders such as Alzheimer's disease, Depression, and Epilepsy. In brain, Zn(2+) has been identified as a ligand, capable of activating and inhibiting the receptors including the NMDA-type glutamate receptors (NMDARs), GABAA receptors, nicotinic acetylcholine receptors (nAChRs), glycine receptors (glyR) and serotonin receptors (5-HT3). Recently GPR39 has been identified as a zinc-specific receptor, widely expressed in brain tissues including the frontal cortex, amygdala, and hippocampus. GPR39, when binding with Zn(2+) has shown promising therapeutic potentials. This review presents current knowledge regarding the role of GPR39 zinc sensing receptor in brain, with a focus on Alzheimer's disease and Epilepsy. Although the results are encouraging, further research is needed to clarify zinc and GPR39 role in the treatment of Alzheimer's disease and Epilepsy.

Topological organization of CA3-to-CA1 excitation

The CA1-projecting axons of CA3 pyramidal cells, called Schaffer collaterals, constitute one of the major information flow routes in the hippocampal formation. Recent anatomical studies have revealed the non-random structural connectivity between CA3 and CA1, but little is known regarding the functional connectivity (i.e. how CA3 network activity is functionally transmitted downstream to the CA1 network). Using functional multi-neuron calcium imaging of rat hippocampal slices, we monitored the spatiotemporal patterns of spontaneous CA3 and CA1 burst activity under pharmacological GABAergic blockade. We found that spatially clustered CA3 activity patterns were transformed into layered CA1 activity sequences. Specifically, synchronized bursts initiated from multiple hot spots in CA3 ensembles, and CA1 neurons located deeper in the pyramidal cell layer were recruited during earlier phases of the burst events. The order of these sequential activations was maintained across the bursts, but the sequence velocity varied depending on the inter-burst intervals. Thus, CA3 axons innervate CA1 neurons in a highly topographical fashion.

Allosteric modulation of GABAA receptors by extracellular ATP

Background

The γ-aminobutyric acid type A receptor (GABA_AR) is the primary receptor mediating fast synaptic inhibition in the brain and plays a critical role in modulation of neuronal excitability and neural networks. Previous studies have demonstrated that ATP and its nucleotide analogs may regulate the function of GABA_ARs via Ca²⁺-dependent intracellular mechanisms, which require activation of purinergic 2 (P2) receptors or cross-talk between two receptors.

Results

Here, we report a potentiation of GABA_ARs by extracellular ATP via a previously un-recognized allosteric mechanism. Using cultured hippocampal neurons as well as HEK293 cells transiently expressing GABA_ARs, we demonstrate that extracellular ATP potentiates GABA_AR mediated currents in a dose-dependent manner with an EC50 of 2.1 ± 0.2 mM. The potentiation was mediated by a postsynaptic mechanism that was not dependent on activation of either ecto-protein kinase or P2 receptors. Single channel recordings from cell-free excised membrane patches under outside-out mode or isolated membrane patches under cell-attached mode suggest that the ATP modulation of GABA currents is achieved through a direct action of ATP on the channels themselves and manifested by increasing the single channel open probability without alteration of its conductance. Moreover, this ATP potentiation of GABA_AR could be reconstituted in HEK293 cells that transiently expressed recombinant rat GABA_ARs.

Conclusions

Our data strongly suggest that extracellular ATP allosterically potentiates GABA_AR-gated chloride channels. This novel mode of ATP-mediated modulation of GABA_ARs may play an important role in regulating neuronal excitability and thereby in fine-tuning the excitation-inhibition balance under conditions where a high level of extracellular ATP is ensured.

The effects of zinc treatment on the blood-brain barrier permeability and brain element levels during convulsions

We evaluated the effect of zinc treatment on the blood-brain barrier (BBB) permeability and the levels of zinc (Zn), natrium (Na), magnesium (Mg), and copper (Cu) in the brain tissue during epileptic seizures. The Wistar albino rats were divided into four groups, each as follows: (1) control group, (2) pentylenetetrazole (PTZ) group: rats treated with PTZ to induce seizures, (3) Zn group: rats treated with ZnCl(2) added to drinking water for 2 months, and (4) Zn + PTZ group. The brains were divided into left, right hemispheres, and cerebellum + brain stem regions. Evans blue was used as BBB tracer. Element concentrations were analyzed by inductively coupled plasma optical emission spectroscopy. The BBB permeability has been found to be increased in all experimental groups (p < 0.05). Zn concentrations in all brain regions in Zn-supplemented groups (p < 0.05) showed an increase. BBB permeability and Zn level in cerebellum + brain stem region were significantly high compared to cerebral hemispheres (p < 0.05). In all experimental groups, Cu concentration decreased, whereas Na concentrations showed an increase (p < 0.05). Mg content in all the brain regions decreased in the Zn group and Zn + PTZ groups compared to other groups (p < 0.001). We also found that all elements' levels showed hemispheric differences in all groups. During convulsions, Zn treatment did not show any protective effect on BBB permeability. Chronic Zn treatment decreased Mg and Cu concentration and increased Na levels in the brain tissue. Our results indicated that Zn treatment showed proconvulsant activity and increased BBB permeability, possibly changing prooxidant/antioxidant balance and neuronal excitability during seizures.

Intrinsic electrophysiological properties of entorhinal cortex stellate cells and their contribution to grid cell firing fields

The medial entorhinal cortex (MEC) is an increasingly important focus for investigation of mechanisms for spatial representation. Grid cells found in layer II of the MEC are likely to be stellate cells, which form a major projection to the dentate gyrus. Entorhinal stellate cells are distinguished by distinct intrinsic electrophysiological properties, but how these properties contribute to representation of space is not yet clear. Here, we review the ionic conductances, synaptic, and excitable properties of stellate cells, and examine their implications for models of grid firing fields. We discuss why existing data are inconsistent with models of grid fields that require stellate cells to generate periodic oscillations. An alternative possibility is that the intrinsic electrophysiological properties of stellate cells are tuned specifically to control integration of synaptic input. We highlight recent evidence that the dorsal-ventral organization of synaptic integration by stellate cells, through differences in currents mediated by HCN and leak potassium channels, influences the corresponding organization of grid fields. Because accurate cellular data will be important for distinguishing mechanisms for generation of grid fields, we introduce new data comparing properties measured with whole-cell and perforated patch-clamp recordings. We find that clustered patterns of action potential firing and the action potential after-hyperpolarization (AHP) are particularly sensitive to recording condition. Nevertheless, with both methods, these properties, resting membrane properties and resonance follow a dorsal-ventral organization. Further investigation of the molecular basis for synaptic integration by stellate cells will be important for understanding mechanisms for generation of grid fields.

Basket cell dichotomy in microcircuit function

A diversity of GABAergic cell types exist within each brain area, and each cell type is thought to play a unique role in the modulation of principal cell output. Basket cells, whose axon terminals surround principal cell somata and proximal dendrites, have a privileged and influential position for regulating the firing of principal cells. This review explores the dichotomy of the two basket cell classes, cholecystokinin- (CCK) and parvalbumin (PV)-containing basket cells, beginning with differences at the level of the individual cell and subsequently focusing on two ways in which this intrinsic dichotomy is enhanced by extrinsic factors. Neuromodulatory influences, exemplified by the effects of the peptide CCK, dynamically enhance the differential functions of the two cell types. Specifications at the level of the postsynaptic principal cell, including input-specific differences in chloride handling and differences in long-range projection patterns of the principal cell targets, also enhance the distinct network function of basket cells. In this review, new findings will be highlighted concerning the roles of neuromodulatory control and postsynaptic long-range projection pattern in the definition of basket cell function.

New dimensions of interneuronal specialization unmasked by principal cell heterogeneity

Although the diversity of neocortical and hippocampal GABAergic interneurons is recognized in terms of their anatomical, molecular and functional properties, principal cells are usually assumed to constitute homogenous populations. However, even within a single layer, subpopulations of principal cells can often be differentiated by their distinct long-range projection targets. Such subpopulations of principal cells can have different local connection properties and excitatory inputs, forming subnetworks that may serve as separate information-processing channels. Interestingly, as reviewed here, recent evidence has revealed specific instances where interneuron cell types selectively innervated distinct subpopulations of principal cells, targeting only those with particular long-distance projection targets. This organization represents a novel form of interneuron specialization, providing interneurons with the potential to selectively regulate specific information-processing streams.

Fluorophilia: fluorophore-containing compounds adhere non-specifically to injured neurons

Ionic (free) zinc (Zn(2+)) is implicated in apoptotic neuronal degeneration and death. In our attempt to examine the effects of Zn(2+) in neurodegeneration following brain injury, we serendipitously discovered that injured neurons bind fluorescein moieties, either alone or as part of an indicator dye, in histologic sections. This phenomenon, that we have termed "fluorophilia", is analogous to the ability of degenerating neuronal somata and axons to bind silver ions (argyrophilia - the basis of silver degeneration stains). To provide evidence that fluorophilia occurs in sections of brain tissue, we used a wide variety of indicators such as Fluoro-Jade (FJ), a slightly modified fluorescein sold as a marker for degenerating neurons; Newport Green, a fluorescein-containing Zn(2+) probe; Rhod-5N, a rhodamine-containing Ca(2+) probe; and plain fluorescein. All yielded remarkably similar staining of degenerating neurons in the traumatic brain-injured tissue with the absence of staining in our sham-injured brains. Staining of presumptive injured neurons by these agents was not modified when Zn(2+) in the brain section was removed by prior chelation with EDTA or TPEN, whereas staining by a non-fluorescein containing Zn(2+) probe, N-(6-methoxy-8-quinolyl)-p-toluenesulfonamide (TSQ), was suppressed by prior chelation. Thus, certain fluorophore-containing compounds nonspecifically stain degenerating neuronal tissue in histologic sections and may not reflect the presence of Zn(2+). This may be of concern to researchers using indicator dyes to detect metals in brain tissue sections. Further experiments may be advised to clarify whether Zn(2+)-binding dyes bind more specifically in intact neurons in culture or organotypic slices.

Modulation of neuronal signal transduction and memory formation by synaptic zinc

The physiological role of synaptic zinc has remained largely enigmatic since its initial detection in hippocampal mossy fibers over 50 years ago. The past few years have witnessed a number of studies highlighting the ability of zinc ions to regulate ion channels and intracellular signaling pathways implicated in neuroplasticity, and others that shed some light on the elusive role of synaptic zinc in learning and memory. Recent behavioral studies using knock-out mice for the synapse-specific zinc transporter ZnT-3 indicate that vesicular zinc is required for the formation of memories dependent on the hippocampus and the amygdala, two brain centers that are prominently innervated by zinc-rich fibers. A common theme emerging from this research is the activity-dependent regulation of the Erk1/2 mitogen-activated-protein kinase pathway by synaptic zinc through diverse mechanisms in neurons. Here we discuss current knowledge on how synaptic zinc may play a role in cognition through its impact on neuronal signaling.

Hippocampal pyramidal cells: the reemergence of cortical lamination

The increasing resolution of tract-tracing studies has led to the definition of segments along the transverse axis of the hippocampal pyramidal cell layer, which may represent functionally defined elements. This review will summarize evidence for a morphological and functional differentiation of pyramidal cells along the radial (deep to superficial) axis of the cell layer. In many species, deep and superficial sublayers can be identified histologically throughout large parts of the septotemporal extent of the hippocampus. Neurons in these sublayers are generated during different periods of development. During development, deep and superficial cells express genes (Sox5, SatB2) that also specify the phenotypes of superficial and deep cells in the neocortex. Deep and superficial cells differ neurochemically (e.g. calbindin and zinc) and in their adult gene expression patterns. These markers also distinguish sublayers in the septal hippocampus, where they are not readily apparent histologically in rat or mouse. Deep and superficial pyramidal cells differ in septal, striatal, and neocortical efferent connections. Distributions of deep and superficial pyramidal cell dendrites and studies in reeler or sparsely GFP-expressing mice indicate that this also applies to afferent pathways. Histological, neurochemical, and connective differences between deep and superficial neurons may correlate with (patho-) physiological phenomena specific to pyramidal cells at different radial locations. We feel that an appreciation of radial subdivisions in the pyramidal cell layer reminiscent of lamination in other cortical areas may be critical in the interpretation of studies of hippocampal anatomy and function.

Myosins and DYNLL1/LC8 in the honey bee (Apis mellifera L.) brain

Honey bees have brain structures with specialized and developed systems of communication that account for memory, learning capacity and behavioral organization with a set of genes homologous to vertebrate genes. Many microtubule- and actin-based molecular motors are involved in axonal/dendritic transport. Myosin-Va is present in the honey bee Apis mellifera nervous system of the larvae and adult castes and subcastes. DYNLL1/LC8 and myosin-IIb, -VI and -IXb have also been detected in the adult brain. SNARE proteins, such as CaMKII, clathrin, syntaxin, SNAP25, munc18, synaptophysin and synaptotagmin, are also expressed in the honey bee brain. Honey bee myosin-Va displayed ATP-dependent solubility and was associated with DYNLL1/LC8 and SNARE proteins in the membrane vesicle-enriched fraction. Myosin-Va expression was also decreased after the intracerebral injection of melittin and NMDA. The immunolocalization of myosin-Va and -IV, DYNLL1/LC8, and synaptophysin in mushroom bodies, and optical and antennal lobes was compared with the brain morphology based on Neo-Timm histochemistry and revealed a distinct and punctate distribution. This result suggested that the pattern of localization is associated with neuron function. Therefore, our data indicated that the roles of myosins, DYNLL1/LC8, and SNARE proteins in the nervous and visual systems of honey bees should be further studied under different developmental, caste and behavioral conditions.

Hippocampal CA1 pyramidal cells form functionally distinct sublayers

Hippocampal CA1 pyramidal neurons have frequently been regarded as a homogeneous cell population in biophysical, pharmacological and modeling studies. Here we report robust differences between pyramidal neurons residing in the deep and superficial CA1 sublayers in the rat. Compared to their superficial peers, deep pyramidal cells fired at higher rates, burst more frequently, were more likely to have place fields and were more strongly modulated by slow oscillations of sleep. Both deep and superficial pyramidal cells fired preferentially at the trough of theta oscillations during maze exploration, yet during Rapid eye movement (REM) sleep, deep pyramidal cells shifted their preferred phase of firing to the peak of theta. Furthermore, whereas in waking, the majority of REM theta phase-shifting cells fired at the ascending phase of gamma oscillations, non-shifting cells preferred the trough. Thus, CA1 pyramidal cells in adjacent sublayers can address their targets jointly or differentially, depending on brain states.

Impact of synaptic neurotransmitter concentration time course on the kinetics and pharmacological modulation of inhibitory synaptic currents

The time course of synaptic currents is a crucial determinant of rapid signaling between neurons. Traditionally, the mechanisms underlying the shape of synaptic signals are classified as pre- and post-synaptic. Over the last two decades, an extensive body of evidence indicated that synaptic signals are critically shaped by the neurotransmitter time course which encompasses several phenomena including pre- and post-synaptic ones. The agonist transient depends on neurotransmitter release mechanisms, diffusion within the synaptic cleft, spill-over to the extra-synaptic space, uptake, and binding to post-synaptic receptors. Most estimates indicate that the neurotransmitter transient is very brief, lasting between one hundred up to several hundreds of microseconds, implying that post-synaptic activation is characterized by a high degree of non-equilibrium. Moreover, pharmacological studies provide evidence that the kinetics of agonist transient plays a crucial role in setting the susceptibility of synaptic currents to modulation by a variety of compounds of physiological or clinical relevance. More recently, the role of the neurotransmitter time course has been emphasized by studies carried out on brain slice models that revealed a striking, cell-dependent variability of synaptic agonist waveforms ranging from rapid pulses to slow volume transmission. In the present paper we review the advances on studies addressing the impact of synaptic neurotransmitter transient on kinetics and pharmacological modulation of synaptic currents at inhibitory synapses.

Chronic treatment with zinc and antidepressants induces enhancement of presynaptic/extracellular zinc concentration in the rat prefrontal cortex

Zinc exhibits antidepressant-like activity in preclinical tests/models. Moreover, zinc homeostasis is implicated in the pathophysiology of affective disorders. The aim of the present study was to examine the effect of chronic zinc, citalopram and imipramine intraperitoneal administration on the presynaptic and extracellular zinc concentration in the rat prefrontal cortex and hippocampus. We used two methods: zinc-selenium histochemistry (which images the pool of presynaptic-vesicle zinc) and anodic stripping voltammetry (ASV) for zinc determination in microdialysate (which assays the extracellular zinc concentration). We report that chronic (14 ×) zinc (hydroaspartate, 10 and 65 mg/kg) and citalopram (20 mg/kg) administration increased the pool of presynaptic zinc (by 34, 50 and 37%, respectively) in the rat prefrontal cortex. The 21% increase induced by imipramine (20 mg/kg) was marginally significant. Likewise, zinc (hydroaspartate, 65 mg/kg), citalopram and imipramine increased the extracellular zinc (although with a different pattern: time point, area under the curve and/or basal level) in this brain region. Furthermore, zinc induced an increase in presynaptic (by 65%) and extracellular zinc (by 90%) in the hippocampus, while both citalopram and imipramine did not. These results indicate that all of the treatments increase presynaptic/extracellular zinc concentrations in the rat prefrontal cortex, which may then contribute to their antidepressant mechanisms. Alterations induced by zinc (but not antidepressants) administration in the hippocampus may be related to specific zinc mechanisms. All the data (previous and present) on the effect of antidepressant treatments on the presynaptic/extracellular zinc concentrations suggest the involvement of this biometal presynaptic/synaptic homeostasis in the antidepressant mechanism(s).

In vivo imaging with a cell-permeable porphyrin-based MRI contrast agent

Magnetic resonance imaging (MRI) with molecular probes offers the potential to monitor physiological parameters with comparatively high spatial and temporal resolution in living subjects. For detection of intracellular analytes, construction of cell-permeable imaging agents remains a challenge. Here we show that a porphyrin-based MRI molecular imaging agent, Mn-(DPA-C(2))(2)-TPPS(3), effectively penetrates cells and persistently stains living brain tissue in intracranially injected rats. Chromogenicity of the probe permitted direct visualization of its distribution by histology, in addition to MRI. Distribution was concentrated in cell bodies after hippocampal infusion. Mn-(DPA-C(2))(2)-TPPS(3) was designed to sense zinc ions, and contrast enhancement was more pronounced in the hippocampus, a zinc-rich brain region, than in the caudate nucleus, which contains relatively little labile Zn(2+). Membrane permeability, optical activity, and high relaxivity of porphyrin-based contrast agents offer exceptional functionality for in vivo imaging.

Chemical blocking of zinc ions in CNS increases neuronal damage following traumatic brain injury (TBI) in mice

Background

Traumatic brain injury (TBI) is one of the leading causes of disability and death among young people. Although much is already known about secondary brain damage the full range of brain tissue responses to TBI remains to be elucidated. A population of neurons located in cerebral areas associated with higher cognitive functions harbours a vesicular zinc pool co-localized with glutamate. This zinc enriched pool of synaptic vesicles has been hypothesized to take part in the injurious signalling cascade that follows pathological conditions such as seizures, ischemia and traumatic brain injury. Pathological release of excess zinc ions from pre-synaptic vesicles has been suggested to mediate cell damage/death to postsynaptic neurons.

Methodology/Principal Findings

In order to substantiate the influence of vesicular zinc ions on TBI, we designed a study in which damage and zinc movements were analysed in several different ways. Twenty-four hours after TBI ZnT3-KO mice (mice without vesicular zinc) were compared to littermate Wild Type (WT) mice (mice with vesicular zinc) with regard to histopathology. Furthermore, in order to evaluate a possible neuro-protective dimension of chemical blocking of vesicular zinc, we treated lesioned mice with either DEDTC or selenite. Our study revealed that chemical blocking of vesicular zinc ions, either by chelation with DEDTC or accumulation in zinc-selenium nanocrystals, worsened the effects on the aftermath of TBI in the WT mice by increasing the number of necrotic and apoptotic cells within the first 24 hours after TBI, when compared to those of chemically untreated WT mice.

Conclusion/Significance

ZnT3-KO mice revealed more damage after TBI compared to WT controls. Following treatment with DEDTC or selenium an increase in the number of both dead and apoptotic cells were seen in the controls within the first 24 hours after TBI while the degree of damage in the ZnT3-KO mice remained largely unchanged. Further analyses revealed that the damage development in the two mouse strains was almost identical after either zinc chelation or zinc complexion therapy.

Pathway-specific utilization of synaptic zinc in the macaque ventral visual cortical areas

Synaptic zinc is an activity-related neuromodulator, enriched in hippocampal mossy fibers and a subset of glutamatergic cortical projections, exclusive of thalamocortical or corticothalamic. Some degree of pathway specificity in the utilization of synaptic zinc has been reported in rodents. Here, we use focal injections of the retrograde tracer sodium selenite to identify zinc-positive (Zn+) projection neurons in the monkey ventral visual pathway. After injections in V1, V4, and TEO areas, neurons were detected preferentially in several feedback pathways but, unusually, were restricted to deeper layers without involvement of layers 2 or 3. Temporal injections resulted in more extensive labeling of both feedback and intratemporal association pathways. The Zn+ neurons had a broader laminar distribution, similar to results from standard retrograde tracers. After anterograde tracer injection in area posterior TE, electron microscopic analysis substantiated that a proportion of feedback synapses was co-labeled with zinc. Nearby injections, Zn+ intrinsic neurons concentrated in layer 2, but in temporal areas were also abundant in layer 6. These results indicate considerable pathway and laminar specificity as to which cortical neurons use synaptic zinc. Given the hypothesized roles of synaptic zinc, this is likely to result in distinct synaptic properties, possibly including differential synaptic plasticity within or across projections.

Localization of zip1 and zip4 mRNA in the adult rat brain

The localization of two members of the Slc39a (zip1 and zip4) family of zinc transporters was examined in the brains of adult mice. Zip1 was highly enriched in brain regions with high densities of neuronal cell bodies, including the hippocampus, thalamus, and perifontal cortex. Zip1 was also expressed in commissural fiber tracts such as the corpus callosum and anterior commissure, but little was found in the internal and external capsules. Also, very low amounts of zip1 mRNA were detected in resting astrocytes and reactive astrocytes that were examined at 14 days after inflicting a stab wound. Zip1 mRNA was detected in ependymal cells lining the third and lateral ventricles and epithelium cells in the choroid plexus. Interestingly, zip4 mRNA was detected in the choroid plexus but not in the ependymal cells or other neural elements. Zip4 mRNA was also detected in brain capillaries, but zip1 mRNA was not. In zip4 knockout heterozygotes that express green fluorescent protein regulated by the zip4 promoter, green fluorescent protein was detected in brain capillaries. Because zip4 levels are regulated by dietary Zn, our studies suggest that the brain has the potential of adapting to changes in Zn status.

Zinc: the brain's dark horse

Zinc is a life-sustaining trace element, serving structural, catalytic, and regulatory roles in cellular biology. It is required for normal mammalian brain development and physiology, such that deficiency or excess of zinc has been shown to contribute to alterations in behavior, abnormal central nervous system development, and neurological disease. In this light, it is not surprising that zinc ions have now been shown to play a role in the neuromodulation of synaptic transmission as well as in cortical plasticity. Zinc is stored in specific synaptic vesicles by a class of glutamatergic or "gluzinergic" neurons and is released in an activity-dependent manner. Because gluzinergic neurons are found almost exclusively in the cerebral cortex and limbic structures, zinc may be critical for normal cognitive and emotional functioning. Conversely, direct evidence shows that zinc might be a relatively potent neurotoxin. Neuronal injury secondary to in vivo zinc mobilization and release occurs in several neurological disorders such as Alzheimer's disease and amyotrophic lateral sclerosis, in addition to epilepsy and ischemia. Thus, zinc homeostasis is integral to normal central nervous system functioning, and in fact its role may be underappreciated. This article provides an overview of zinc neurobiology and reviews the experimental evidence that implicates zinc signals in the pathophysiology of neuropsychiatric diseases. A greater understanding of zinc's role in the central nervous system may therefore allow for the development of therapeutic approaches where aberrant metal homeostasis is implicated in disease pathogenesis.

Hippocampal zinc infusion delays the development of afterdischarges and seizures in a kindling model of epilepsy

PURPOSE

Zinc occurs in high concentration in synaptic vesicles of glutamatergic terminals including hippocampal mossy fibers. This vesicular zinc can be synaptically released during neuronal activity, including seizures. Zinc inhibits certain subtypes of N-methyl-D-aspartate (NMDA) and gamma-aminobutyric acid (GABA)(A) receptors. By blocking NMDA excitation or GABA inhibition, an excess of zinc may alter the excitability of hippocampal circuits, which contribute to the development of seizures.

METHODS

Twenty-one adult Wistar rats were implanted under anesthesia with Alzet pumps releasing vehicle, 10 microM ZnCl(2) or 1,000 microM ZnCl(2), at a rate of 0.25 microl/h continuously into the hippocampal hilus for 4 weeks. Kindling was performed by daily awake commissural stimulation at 60 Hz and afterdischarges were recorded from a dentate gyrus electrode. Development of behavioral Racine seizure stages was recorded by a blinded investigator.

RESULTS

The development of behavioral Racine seizure stages was delayed only in rats infused with 1,000 microM ZnCl(2) (p < 0.02). With completion of kindling at stimulation number 20, all groups had reached the same maximum level of behavioral seizures. The expected increased progression of afterdischarge duration was inhibited by both 10 microM ZnCl(2) and 1,000 microM ZnCl(2) infusion compared to control animals (p < 0.01). At stimulation number 18, all groups had reached the same maximum duration of afterdischarges.

DISCUSSION

We conclude that excess infused zinc delayed the development of behavioral seizures in a kindling model of epilepsy. These data support the hypothesis that zinc synaptically released during seizures may alter hippocampal excitability similar to zinc infused in our experiment.

Inflammation, genes and zinc in Alzheimer's disease

Alzheimer's disease (AD) is a heterogeneous and progressive neurodegenerative disease which in Western society mainly accounts for clinical dementia. AD has been linked to inflammation and metal biological pathway. Neuro-pathological hallmarks are senile plaques, resulting from the accumulation of several proteins and an inflammatory reaction around deposits of amyloid, a fibrillar protein, Abeta, product of cleavage of a much larger protein, the beta-amyloid precursor protein (APP) and neurofibrillary tangles. Amyloid deposition, due to the accumulation of Abeta peptide, is the main pathogenetic mechanism. Inflammation clearly occurs in pathologically vulnerable regions of AD and several inflammatory factors influencing AD development, i.e. environmental factors (pro-inflammatory phenotype) and/or genetic factors (pro-inflammatory genotype) have been described. At the biochemical level metals such as zinc are known to accelerate the aggregation of the amyloid peptide and play a role in the control of inflammatory responses. In particular, zinc availability may regulate mRNA cytokine expression, so influencing inflammatory network phenotypic expression.

Differential modes of termination of amygdalothalamic and amygdalocortical projections in the monkey

The amygdala complex participates in multiple systems having to do with affective processes. It has been implicated in human disorders of social and emotional behavior, such as autism. Of the interconnected functional networks, considerable research in rodents and primates has focused on connections between the amygdala and orbitofrontal cortex (OFC). The amygdala projects to OFC by both a direct amygdalocortical (AC) pathway and an indirect pathway through mediodorsal thalamus. In the rat, retrograde tracer experiments indicate that the AC and amygdalothalamic (AT) pathways originate from separate populations, and may therefore convey distinctive information, although the characteristics of these pathways remain unclear. To investigate this issue in monkeys we made anterograde tracer injections in the basolateral amygdala complex (BLC; n = 3). Three distinctive features were found preferentially associated with the AT or AC pathways. First, AT terminations are large (average diameter = 3.5 microm; range = 1.2-7.0 microm) and cluster around proximal dendrites, in contrast with small-bouton AC terminations. Second, AT terminations form small arbors (diameter approximately 0.1 mm), while AC are widely divergent (often >1.0 mm long). The AT terminations features are reminiscent of large bouton, "driver" corticothalamic terminations. Finally, AC but not AT terminations are positive for zinc (Zn), a neuromodulator associated with synaptic plasticity. From these results we suggest that AC and AT terminations originate from distinct populations in monkey as well as in rodent. Further work is necessary to determine the degree and manner of their segregation and how these subsystems interact within a broader connectivity network.