Effect of zinc supplementation on neuronal precursor proliferation in the rat hippocampus after traumatic brain injury

Vitamin D3 and zinc supplements augment the antimanic efficacy of lithium and olanzapine treatments in an animal model of mania

Objective: Bipolar disorder (BD) is a challenging psychiatric disorder and a complex disease. The associated reduction in serum vitamin D3 (VitD3) levels in BD patients and the contribution of zinc (Zn) to the treatment, along with the severe side effects of lithium (Li) treatment, were encouraging to assess the efficacy of different correlated combinations of therapeutic/nutraceutical treatments such as olanzapine (Oln), VitD3, and Zn against Li. Methods: Mania was induced in C57BL/6 mice by administering methylphenidate (MPH) for 14 consecutive days. On the 8th day of MPH injection, different treatment regimens were administered, Li, Oln, VitD3/Zn, VitD3/Zn/Oln, VitD3 + Zn + Oln + Li50mg/kg (C50), and VitD3 + Zn + Oln + Li100mg/kg (C100). Both VitD3 (850 IU/kg) and Zn (180 mg/kg) were supplied with food for 2 weeks before starting the induction of mania, which continued until the end of MPH administration. Behavioral, brain oxidative stress, thyroid hormones, VitD3, Zn, GsK-3β, and Bcl2 levels, as well as brain histopathological alterations, were assessed. Results: Manic mice exhibited alterations in all tested parameters, and the histopathological examination of the cortex and hippocampus confirmed these results. The VitD3/Zn/Oln, C50, and C100 treatment regimens reversed most of the behavioral and pathophysiological alterations; however, the C50 treatment regimen was the most efficient. Conclusions: This study emphasizes the importance of combining different antimanic medications like Li and Oln with nutraceutical supplements to increase their antimanic efficacy, reduce their adverse effects, and, ideally, improve the BD patient's quality of life.

Imbalance of Essential Metals in Traumatic Brain Injury and Its Possible Link with Disorders of Consciousness

Dysfunction of the complex cerebral networks underlying wakefulness and awareness is responsible for Disorders of Consciousness (DoC). Traumatic Brain Injury (TBI) is a common cause of DoC, and it is responsible for a multi-dimensional pathological cascade that affects the proper functioning of the brainstem and brain consciousness pathways. Iron (Fe), Zinc (Zn), and Copper (Cu) have a role in the neurophysiology of both the ascending reticular activating system, a multi-neurotransmitter network located in the brainstem that is crucial for consciousness, and several brain regions. We aimed to summarize the role of these essential metals in TBI and its possible link with consciousness alterations. We found that TBI alters many neuronal molecular mechanisms involving essential metals, causing neurodegeneration, neural apoptosis, synaptic dysfunction, oxidative stress, and inflammation. This final pattern resembles that described for Alzheimer's disease (AD) and other neurological and psychiatric diseases. Furthermore, we found that amantadine, zolpidem, and transcranial direct current stimulation (tDCS)-the most used treatments for DoC recovery-seem to have an effect on essential metals-related pathways and that Zn might be a promising new therapeutic approach. This review summarizes the neurophysiology of essential metals in the brain structures of consciousness and focuses on the mechanisms underlying their imbalance following TBI, suggesting their possible role in DoC. The scenario supports further studies aimed at getting a deeper insight into metals' role in DoC, in order to evaluate metal-based drugs, such as metal complexes and metal chelating agents, as potential therapeutic options.

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.

Serum Zinc and Long-Term Prognosis after Acute Traumatic Brain Injury with Intracranial Injury: A Multicenter Prospective Study

Serum zinc levels in the acute stages after traumatic brain injury (TBI) may be capable of predicting cinical and functional prognoses. This study aimed to evaluate the association between serum zinc levels and long-term survival and neurological outcomes in TBI patients with intracranial injury. This multicenter prospective cohort study enrolled adult TBI patients with intracranial injury who visited emergency departments between December 2018 and June 2020. Serum zinc levels drawn within 24 h after injury were categorized into four groups: low (<80.0 mcg/dL), low−normal (80.0−100.0 mcg/dL), high−normal (100.1−120.0 mcg/dL), and high (>120.0 mcg/dL). The study outcomes were 6-month mortality and disability (Glasgow Outcome Scale, 1−3). A multilevel multivariable logistic regression analysis was conducted to estimate associations between serum zinc and study outcomes. From the eligible TBI patients (N = 487), the median (interquartile range) serum zinc level was 112.0 mcg/dL (95.0−142.0). Six-month mortality and disability were 21.1% (103/487) and 29.6% (144/487), respectively. Compared to the high−normal zinc group, there were significant associations with 6-month mortality and disability observed in the low zinc group (aORs (95% CIs): 1.91 (1.60−2.28) and 1.95 (1.62−2.36) for the low group; 1.14 (0.67−1.94) and 1.15 (0.91−1.46) for the low−normal group; and 0.72 (0.44−1.16) and 0.88 (0.61−1.27) for the high group, respectively). Among the 122 TBI patients with diabetes mellitus, the low zinc group showed a higher incidence of 6-month mortality (aOR (95% CI): 9.13 (4.01−20.81)) compared to the high−normal zinc group. Moreover, the low and low−normal groups had higher odds for 6-month disability (aORs (95% CIs): 6.63 (3.61−12.15) for the low group and 2.37 (1.38−4.07) for the low−normal group). Serum zinc deficiency is associated with a higher incidence of 6-month mortality and disability after injury for TBI patients with intracranial injury.

Current and Potential Pharmacologic Therapies for Traumatic Brain Injury

The present article reviewed the pharmacologic therapies of traumatic brain injury (TBI), including current and potential treatments. Pharmacologic therapies are an essential part of TBI care, and several agents have well-established effects in TBI care. In the acute phase, tranexamic acid, antiepileptics, hyperosmolar agents, and anesthetics are the mainstay of pharmacotherapy, which have proven efficacies. In the post-acute phase, SSRIs, SNRIs, antipsychotics, zolpidem and amantadine, as well as other drugs, have been used to manage neuropsychological problems, while muscle relaxants and botulinum toxin have been used to manage spasticity. In addition, increasing numbers of pre-clinical and clinical studies of pharmaceutical agents, including potential neuroprotective nutrients and natural therapies, are being carried out. In the present article, we classify the treatments into established and potential agents based on the level of clinical evidence and standard of practice. It is expected that many of the potential medicines under investigation will eventually be accepted as standard practice in the care of TBI patients.

Prophylactic Zinc Administration Combined with Swimming Exercise Prevents Cognitive-Emotional Disturbances and Tissue Injury following a Transient Hypoxic-Ischemic Insult in the Rat

Exercise performance and zinc administration individually yield a protective effect on various neurodegenerative models, including ischemic brain injury. Therefore, this work was aimed at evaluating the combined effect of subacute prophylactic zinc administration and swimming exercise in a transient cerebral ischemia model. The prophylactic zinc administration (2.5 mg/kg of body weight) was provided every 24 h for four days before a 30 min common carotid artery occlusion (CCAO), and 24 h after reperfusion, the rats were subjected to swimming exercise in the Morris Water Maze (MWM). Learning was evaluated daily for five days, and memory on day 12 postreperfusion; anxiety or depression-like behavior was measured by the elevated plus maze and the motor activity by open-field test. Nitrites, lipid peroxidation, and the activity of superoxide dismutase (SOD) and catalase (CAT) were assessed in the temporoparietal cortex and hippocampus. The three nitric oxide (NO) synthase isoforms, chemokines, and their receptor levels were measured by ELISA. Nissl staining evaluated hippocampus cytoarchitecture and Iba-1 immunohistochemistry activated the microglia. Swimming exercise alone could not prevent ischemic damage but, combined with prophylactic zinc administration, reversed the cognitive deficit, decreased NOS and chemokine levels, prevented tissue damage, and increased Iba-1 (+) cell number. These results suggest that the subacute prophylactic zinc administration combined with swimming exercise, but not the individual treatment, prevents the ischemic damage on day 12 postreperfusion in the transient ischemia model.

Neurobiology of zinc and its role in neurogenesis

BACKGROUND

Zinc (Zn) has a diverse role in many biological processes, such as growth, immunity, anti-oxidation system, homeostatic, and repairing. It acts as a regulatory and structural catalyst ion for activities of various proteins, enzymes, and signal transcription factors, as well as cell proliferation, differentiation, and survival. The Zn ion is essential for neuronal signaling and is mainly distributed within presynaptic vesicles. Zn modulates neuronal plasticity and synaptic activity in both neonatal and adult stages. Alterations in brain Zn status results in a dozen neurological diseases including impaired brain development. Numerous researchers are working on neurogenesis, however, there is a paucity of knowledge about neurogenesis, especially in neurogenesis in adults. Neurogenesis is a multifactorial process and is regulated by many metal ions (e.g. Fe, Cu, Zn, etc.). Among them, Zn has an essential role in neurogenesis. At the molecular level, Zn controls cell cycle, apoptosis, and binding of DNA and several proteins including transcriptional and translational factors. Zn is needed for protein folding and function and Zn acts as an anti-apoptotic agent; organelle stabilizer; and an anti-inflammatory agent. Zn deficiency results in aging, neurodegenerative disease, immune deficiency, abnormal growth, cancer, and other symptoms. Prenatal deficiency of Zn results in developmental disorders in humans and animals.

CONCLUSION

Both in vitro and in vivo studies have shown an association between Zn deficiency and increased risk of neurological disorders. This article reviews the existing knowledge on the role of Zn and its importance in neurogenesis.

Zinc and Traumatic Brain Injury: From Chelation to Supplementation

With a worldwide incidence rate of almost 70 million annually, traumatic brain injury (TBI) is a frequent cause of both disability and death. Our modern understanding of the zinc-regulated neurochemical, cellular, and molecular mechanisms associated with TBI is the result of a continuum of research spanning more than three decades. This review describes the evolution of the field beginning with the initial landmark work on the toxicity of excess neuronal zinc accumulation after injury. It further shows how the field has expanded and shifted to include examination of the cellular pools of zinc after TBI, identification of the role of zinc in TBI-regulated gene expression and neurogenesis, and the use of zinc to prevent cognitive and behavioral deficits associated with brain injury.

Adult Neurogenesis, Glia, and the Extracellular Matrix

In the adult mammalian hippocampus, new neurons arise from stem and progenitor cell division, in a process known as adult neurogenesis. Adult-generated neurons are sensitive to experience and may participate in hippocampal functions, including learning and memory, anxiety and stress regulation, and social behavior. Increasing evidence emphasizes the importance of new neuron connectivity within hippocampal circuitry for understanding the impact of adult neurogenesis on brain function. In this Review, we discuss how the functional consequences of new neurons arise from the collective interactions of presynaptic and postsynaptic neurons, glial cells, and the extracellular matrix, which together form the "tetrapartite synapse."

Zinc homeostasis and zinc signaling in white matter development and injury

Zinc is an essential dietary micronutrient that is abundant in the brain with diverse roles in development, injury, and neurological diseases. With new imaging tools and chelators selectively targeting zinc, the field of zinc biology is rapidly expanding. The importance of zinc homeostasis is now well recognized in neurodegeneration, but there is emerging data that zinc may be equally important in white matter disorders. This review provides an overview of zinc biology, including a discussion of clinical disorders of zinc deficiency, different zinc pools, zinc biomarkers, and methods for measuring zinc. It emphasizes our limited understanding of how zinc is regulated in oligodendrocytes and white matter. Gaps in knowledge about zinc transporters and zinc signaling are discussed. Zinc-induced oligodendrocyte injury pathways relevant to white matter stroke, multiple sclerosis, and white matter injury of prematurity are reviewed and examples of zinc-dependent proteins relevant to myelination highlighted. Finally, a novel ratiometric zinc sensor is reviewed, revealing new information about mobile zinc during oligodendrocyte differentiation. With a better understanding of zinc biology in oligodendrocytes, new therapeutic targets for white matter disorders may be possible and the necessary tools to appropriately study zinc are finally available.

Reduced Neuroinflammation and Improved Functional Recovery after Traumatic Brain Injury by Prophylactic Diet Supplementation in Mice

Currently, there are no approved therapeutic drugs for the treatment of traumatic brain injury (TBI), and new targets and approaches are needed to provide relief from the long-term effects of TBI. Recent studies suggest that nutrition plays a critical role in improving the outcome from TBI in both civilians and military personnel. We have previously shown that GrandFusion^® (GF) diets improved recovery from cerebral ischemia and enhanced physical activity and endurance in rodent models. We, therefore, sought to determine the impact of a prophylactic diet enriched in fruits and vegetables on recovery from TBI in the controlled cortical impact rodent model. Results demonstrated that mice fed the diets had improved neuromotor function, reduced lesion volume, increased neuronal density in the hippocampus and reduced inflammation. As previously shown, TBI increases cathepsin B as part of the inflammasome complex resulting in elevated inflammatory markers like interleukin-1β (IL-1β). Consumption of the GF diets attenuated the increase in cathepsin B levels and prevented the increase in the proapoptotic factor Bax following TBI. These data suggest that prior consumption of diets enriched in fruits and vegetables either naturally or through powdered form can provide protection from the detrimental effects of TBI.

Variability and uncertainty in the rodent controlled cortical impact model of traumatic brain injury

BACKGROUND

Controlled cortical impact (CCI) has emerged as one of the most flexible and clinically applicable approaches for the induction of traumatic brain injury (TBI) in rodents and other species. Although this approach has been shown to model cognitive and functional outcomes associated with TBI in humans, recent work has shown that CCI is limited by excessive variability in lesion size despite attempts to control velocity, impact depth, and dwell time.

NEW METHOD

Thus, this work used high-speed imaging to evaluate the delivery of cortical impact and permit the identification of specific parameters associated with technical variability in the CCI model.

RESULTS

Variability is introduced by vertical oscillations that result in multiple impacts of varying depths, lateral movements after impact, and changes in velocity, particularly at the prescribed impact depth.

CONCLUSIONS

Together these data can inform future work to design modifications to commonly used CCI devices that produce TBI with less variability in severity and lesion size.

The phosphodiesterase-4 inhibitor Rolipram promotes cognitive function recovery in prenatal Escherichia coli infected offspring

Objective: Preterm infants are especially vulnerable to intrauterine infection-induced brain injury, which is closely relevant with cognitive deficits and cerebral palsy. Rolipram, a phosphodiesterase-4 inhibitor, can improve cognition in rodents. However, the underlying roles and mechanisms are not well investigated.Methods: In the present study, we used intrauterine Escherichia coli (E. coli) infected model. Escherichia coli was inoculated into pregnant rats' uterine cervix at embryonic day 15 (E15) while the control group was given normal saline. Rolipram was administered by intraperitoneal (i.p.) injection once daily from postnatal day (P) 1-7. Morris water maze test was used for cognitive behavior test. Hippocampal neural stem/precursor cells (NSPCs) proliferation and neuronal differentiation were studied by immunofluorescent staining. The expressions of p-CREB, p-Akt, TrkB and BDNF were estimated by western-blot analysis.Results: The data showed that Rolipram could ameliorate cognitive deficits and enhance NSPCs proliferation and neuronal differentiation in intrauterine infected offspring. Additionally, Rolipram could significantly increase p-CREB/CREB, p-Akt/Akt, TrkB and BDNF levels.Conclusions: These results suggested that Rolipram might play a neuroprotective role to promote cognitive function recovery after intrauterine infection. And hippocampal NSPCs proliferation and neuronal differentiation might be enhanced via CREB/Akt/BDNF signal transduction.

Total Number Is Important: Using the Disector Method in Design-Based Stereology to Understand the Structure of the Rodent Brain

The advantages of using design-based stereology in the collection of quantitative data, have been highlighted, in numerous publications, since the description of the disector method by Sterio (1984). This review article discusses the importance of total number derived with the disector method, as a key variable that must continue to be used to understand the rodent brain and that such data can be used to develop quantitative networks of the brain. The review article will highlight the huge impact total number has had on our understanding of the rodent brain and it will suggest that neuroscientists need to be aware of the increasing number of studies where density, not total number, is the quantitative measure used. It will emphasize that density can result in data that is misleading, most often in an unknown direction, and that we run the risk of this type of data being accepted into the collective neuroscience knowledge database. It will also suggest that design-based stereology using the disector method, can be used alongside recent developments in electron microscopy, such as serial block-face scanning electron microscopy (SEM), to obtain total number data very efficiently at the ultrastructural level. Throughout the article total number is discussed as a key parameter in understanding the micro-networks of the rodent brain as they can be represented as both anatomical and quantitative networks.

Elucidating opportunities and pitfalls in the treatment of experimental traumatic brain injury to optimize and facilitate clinical translation

The aim of this review is to discuss the research presented in a symposium entitled "Current progress in characterizing therapeutic strategies and challenges in experimental CNS injury" which was presented at the 2016 International Behavioral Neuroscience Society annual meeting. Herein we discuss diffuse and focal traumatic brain injury (TBI) and ensuing chronic behavioral deficits as well as potential rehabilitative approaches. We also discuss the effects of stress on executive function after TBI as well as the response of the endocrine system and regulatory feedback mechanisms. The role of the endocannabinoids after CNS injury is also discussed. Finally, we conclude with a discussion of antipsychotic and antiepileptic drugs, which are provided to control TBI-induced agitation and seizures, respectively. The review consists predominantly of published data.

The Impact of Synaptic Zn2+ Dynamics on Cognition and Its Decline

The basal levels of extracellular Zn²⁺ are in the range of low nanomolar concentrations and less attention has been paid to Zn²⁺, compared to Ca²⁺, for synaptic activity. However, extracellular Zn²⁺ is necessary for synaptic activity. The basal levels of extracellular zinc are age-dependently increased in the rat hippocampus, implying that the basal levels of extracellular Zn²⁺ are also increased age-dependently and that extracellular Zn²⁺ dynamics are linked with age-related cognitive function and dysfunction. In the hippocampus, the influx of extracellular Zn²⁺ into postsynaptic neurons, which is often linked with Zn²⁺ release from neuron terminals, is critical for cognitive activity via long-term potentiation (LTP). In contrast, the excess influx of extracellular Zn²⁺ into postsynaptic neurons induces cognitive decline. Interestingly, the excess influx of extracellular Zn²⁺ more readily occurs in aged dentate granule cells and intracellular Zn²⁺-buffering, which is assessed with ZnAF-2DA, is weakened in the aged dentate granule cells. Characteristics (easiness) of extracellular Zn²⁺ influx seem to be linked with the weakened intracellular Zn²⁺-buffering in the aged dentate gyrus. This paper deals with the impact of synaptic Zn²⁺ signaling on cognition and its decline in comparison with synaptic Ca²⁺ signaling.

Effects of Chronic and Acute Zinc Supplementation on Myocardial Ischemia-Reperfusion Injury in Rats

The present study aims to explore the effects of chronic and acute zinc sulfate supplementation on myocardial ischemia-reperfusion injury in rats. The study registered 50 adult male rats which were divided into five groups in equal numbers as follows: group 1, normal control; group 2, sham; group 3, myocardial ischemia reperfusion (My/IR): the group which was fed on a normal diet and in which myocardial I/R was induced; group 4, myocardial ischemia reperfusion + chronic zinc: (5 mg/kg i.p. zinc sulfate for 15 days); and group 5, myocardial ischemia reperfusion + acute zinc: the group which was administered 15 mg/kg i.p. zinc sulfate an hour before the operation and in which myocardial I/R was induced. The collected blood and cardiac tissue samples were analyzed using spectrophotometric method to determine levels of MDA, as an indicator of tissue injury, and GSH, as an indicator of antioxidant activity. The highest plasma and heart tissue MDA levels were measured in group 3 (p < 0.05). Group 5 had lower MDA values than group 3, while group 4 had significantly lower MDA values than groups 3 and 5 (p < 0.05). The highest erythrocyte GSH values were found in group 4 (p < 0.05). Erythrocyte GSH values in group 5 were higher than those in group 3 (p < 0.05). The highest GSH values in heart tissue were measured in group 4 (p < 0.05). The results of the study reveal that the antioxidant activity inhibited by elevated oxidative stress in heart ischemia reperfusion in rats is restored partially by acute zinc administration and markedly by chronic zinc supplementation.

Nutrients, neurogenesis and brain ageing: From disease mechanisms to therapeutic opportunities

Appreciation of the physiological relevance of mammalian adult neurogenesis has in recent years rapidly expanded from a phenomenon of homeostatic cell replacement and brain repair to the current view of a complex process involved in high order cognitive functions. In parallel, an array of endogenous or exogenous triggers of neurogenesis has also been identified, among which metabolic and nutritional cues have drawn significant attention. Converging evidence from animal and in vitro studies points to nutrient sensing and energy metabolism as major physiological determinants of neural stem cell fate, and modulators of the whole neurogenic process. While the cellular and molecular circuitries underlying metabolic regulation of neurogenesis are still incompletely understood, the key role of mitochondrial activity and dynamics, and the importance of autophagy have begun to be fully appreciated; moreover, nutrient-sensitive pathways and transducers such as the insulin-IGF cascade, the AMPK/mTOR axis and the transcription regulators CREB and Sirt-1 have been included, beside more established "developmental" signals like Notch and Wnt, in the molecular networks that dictate neural-stem-cell self-renewal, migration and differentiation in response to local and systemic inputs. Many of these nutrient-related cascades are deregulated in the contest of metabolic diseases and in ageing, and may contribute to impaired neurogenesis and thus to cognition defects observed in these conditions. Importantly, accumulating knowledge on the metabolic control of neurogenesis provides a theoretical framework for the trial of new or repurposed drugs capable of interfering with nutrient sensing as enhancers of neurogenesis in the context of neurodegeneration and brain senescence.

Neurotoxicity of Zinc

Zinc-induced neurotoxicity has been shown to play a role in neuronal damage and death associated with traumatic brain injury, stroke, seizures, and neurodegenerative diseases. During normal firing of "zinc-ergic" neurons, vesicular free zinc is released into the synaptic cleft where it modulates a number of postsynaptic neuronal receptors. However, excess zinc, released after injury or disease, leads to excitotoxic neuronal death. The mechanisms of zinc-mediated neurotoxicity appear to include not only neuronal signaling but also regulation of mitochondrial function and energy production, as well as other mechanisms such as aggregation of amyloid beta peptides in Alzheimer's disease. However, recent data have raised questions about some of our long-standing assumptions about the mechanisms of zinc in neurotoxicity. Thus, this review explores the most recent published findings and highlights the current mechanistic controversies.

Significance of synaptic Zn2+ signaling in zincergic and non-zincergic synapses in the hippocampus in cognition

A portion of zinc concentrates in the synaptic vesicles in the brain and is released from glutamatergic (zincergic) neuron terminals. It serves as a signaling factor (in a form of free Zn²⁺). Both extracellular Zn²⁺ signaling, which predominantly originates in Zn²⁺ release from zincergic neuron terminals, and intracellular Zn²⁺ signaling, which is often linked to extracellular Zn²⁺ signaling, are involved in hippocampus-dependent memory. At mossy fiber-CA3 pyramidal cell synapses and Schaffer collateral-CA1 pyramidal cell synapses, which are zincergic, extracellular Zn²⁺ signaling leads to intracellular Zn²⁺ signaling and is involved in learning and memory. At medial perforant pathway-dentate granule cell synapses, which are non-zincergic, intracellular Zn²⁺ signaling, which originates in the internal stores containing Zn²⁺, is involved in learning and memory. The blockade of Zn²⁺ signaling with Zn²⁺ chelators induces memory deficit, while the optimal amount range of Zn²⁺ signaling is unknown. It is possible that the degree and frequency of Zn²⁺ signaling, which determine the increased Zn²⁺ levels, modulates learning and memory as well as intracellular Ca²⁺ signaling. To understand the precise role of synaptic Zn²⁺ signaling in the hippocampus, the present paper summarizes the current knowledge on Zn²⁺ signaling at zincergic and non-zincergic synapses in the hippocampus in cognition and involvement of zinc transporters and zinc-binding proteins in synaptic Zn²⁺ signaling.