Chronic zinc deficiency alters neuronal function of hippocampal mossy fibers

Meeting Zn Needs during Medaka Eye Development: Nanoscale Visualization of Retina by Expansion Microscopy

Fish eyes require high Zn levels to support their early development. Although numerous studies have been conducted on the nutritional and toxic effects of Zn on the eye, the Zn requirement for retinal cell development is still debatable. Moreover, due to the complexity of the retinal structure, it is difficult to clearly visualize each retinal layer and accurately separate cell morphology in vivo by conventional methods. In the present study, we for the first time have achieved nanoscale imaging of retinal anatomy affected by dietary and waterborne Zn exposure by novel expansion microscopy. We demonstrated that the fish retina showed different developmental strategies in response to dietary and aqueous Zn exposures. Excess dietary Zn produced toxicity to retinal photoreceptor cells, resulting in a reduction in cell number and cell area, and this toxicity became severe with biological development. In contrast, waterborne Zn in the natural environment probably failed to meet the Zn requirements of retinal development. Overall, our results indicated that during early development, the Zn requirement of the fish eyes was sensitive, and oversupplementation led to impaired photoreceptor cell development. Our study has provided new perspectives using the powerful and novel expansion microscopy technique in toxicity assessment, enabling ultra-clear visualization of small but complex organ development.

Severe Zinc Deficiency Causes the Loss and Apoptosis of Olfactory Ensheathing Cells (OECs) and Olfactory Deficit

Dietary zinc deficiency may lead to olfactory deficits, whose mechanism remains largely elusive. Olfactory ensheathing cells (OECs), a type of glial cells that support the function and neurogenesis in the olfactory bulb (OB), may play a pivotal role in the maintenance of the olfactory system. In the present study, we established a rat model of dietary zinc deficiency and found that severe zinc deficiency, but not marginal zinc deficiency, caused significantly reduced food intake, growth retardation, and apparent olfactory deficit in growing rats. We showed that severe zinc deficiency resulted in the loss of OECs in the olfactory nerve layer (ONL) of the olfactory bulb. In addition, we revealed that the number of TUNEL-positive cells increased markedly in the region, suggesting an involvement of apoptotic cell death in zinc deficiency-induced loss of OECs. Moreover, we found that treatment with zinc chelator N,N,N'N',-tetrakis (2-pyridylmethyl)ethylenediamine (TPEN) triggered the apoptosis of in vitro-cultured primary OECs. The apoptosis of OECs was correlated with significantly elevated expression of p53. Importantly, TUNEL and CCK-8 assays both demonstrated that treatment with p53 antagonist pifithrin-α (PFT-α) markedly attenuated TPEN-induced OEC apoptosis. These findings implicated that p53-triggered apoptosis of OECs might play an integral role in zinc deficiency-induced olfactory malfunction.

Zinc deficiency impairs the renewal of hippocampal neural stem cells in adult rats: involvement of FoxO3a activation and downstream p27(kip1) expression

Zinc plays an important role in the development and maintenance of central neural system. Zinc deficiency has been known to alter normal brain function, whose molecular mechanism remains largely elusive. In the present study, we established a zinc deficiency-exposed rat model, and, using western blot and immunohistochemical analyses, found that the expression of FoxO3a and p27(kip1) was remarkably up-regulated in the rat brain hippocampus. Immunofluorescence assay showed that FOXO3a and p27(kip1) were significantly co-localized with nestin, the marker of neural stem cells (NSCs). Furthermore, we identified that the proportion of proliferating NSCs was markedly decreased in zinc-deficient rat hippocampaus. Using C17.2 neural stem cells, it was revealed that exposure to zinc chelator N,N,N',N'-tetrakis-(2-pyridylmethy) ethylenediamine induced the expression of FoxO3a and p27(kip1) , which coincided with reduced NSC proliferation. Furthermore, depletion of FoxO3a inhibited p27(kip1) expression and restored the growth of NSCs. On the basis of these data, we concluded that FoxO3a/p27(kip1) signaling might play a significant role in zinc deficiency-induced growth impairment of NSCs and consequent neurological disorders. We describe here that zinc deficiency induces the proliferative impairment of hippocampal neural stem cells partially through the activation of FOXO3a-p27 axis in rats. Neural progenitor cells exhibited significantly up-regulated expression of FOXO3a and p27 after zinc deficiency in vivo and in vitro. Depletion of FOXO3a ameliorates zinc deficiency-induced expression of p27 and growth impairment of neural stem cells. We provide novel insight into the mechanisms underlying zinc deficiency-induced neurological deficits.

Potential roles of zinc in the pathophysiology and treatment of major depressive disorder

Incomplete response to monoaminergic antidepressants in major depressive disorder (MDD), and the phenomenon of neuroprogression, suggests a need for additional pathophysiological markers and pharmacological targets. Neuronal zinc is concentrated exclusively within glutamatergic neurons, acting as an allosteric modulator of the N-methyl D-aspartate and other receptors that regulate excitatory neurotransmission and neuroplasticity. Zinc-containing neurons form extensive associational circuitry throughout the cortex, amygdala and hippocampus, which subserve mood regulation and cognitive functions. In animal models of depression, zinc is reduced in these circuits, zinc treatment has antidepressant-like effects and dietary zinc insufficiency induces depressive behaviors. Clinically, serum zinc is lower in MDD, which may constitute a state-marker of illness and a risk factor for treatment-resistance. Marginal zinc deficiency in MDD may relate to multiple putative mechanisms underlying core symptomatology and neuroprogression (e.g. immune dysfunction, monoamine metabolism, stress response dysregulation, oxidative/nitrosative stress, neurotrophic deficits, transcriptional/epigenetic regulation of neural networks). Initial randomized trials suggest a benefit of zinc supplementation. In summary, molecular and animal behavioral data support the clinical significance of zinc in the setting of MDD.

Serum reference levels of selenium, zinc and copper in healthy pregnant women at a prenatal screening program in southeastern Mediterranean region of Turkey

PROJECT

The aim of the study was to investigate the serum reference range for Selenium (Se), Zinc (Zn) and Copper (Cu) levels in women of 10-14 (group I) and 16-20 (group II) weeks of gestation and compare them with those in non-pregnant healthy women and healthy men.

PROCEDURE

This cross-sectional study was performed in 351 pregnant women [group I (n: 177) and group II (n: 174)], 30 non-pregnant women and 30 men as controls. The levels of Se, Zn and Cu levels were determined on flame and furnace atomic absorption spectrophotometer using Zeeman background correction.

RESULTS

In the 10-14 weeks of gestation Se, Zn and Cu serum levels were 44.85+/-9.23, 81.30+/-31.94 and 132.33+/-38.24 microg/dl, in 16-20 weeks of gestation were 47.18+/-10.92, 74.25+/-22.47 and 164.86+/-39.69 microg/dl, in non-pregnant women were 55.38+/-8.81, 121.41+/-29.22 and 104.75+/-39.14 microg/dl also in men 72.24+/-9.28, 134.85+/-15.95 and 78.29+/-20.90 microg/dl, respectively.

CONCLUSION

A significant low level of serum Se, Zn and a high level of Cu in the pregnant women in the 10-14 and 16-20 weeks of gestation were detected when compared with that of non-pregnant women and men.

Zn2+ ions: modulators of excitatory and inhibitory synaptic activity

The role of Zn(2+) in the CNS has remained enigmatic for several decades. This divalent cation is accumulated by specific neurons into synaptic vesicles and can be released by stimulation in a Ca(2+)-dependent manner. Using Zn(2+) fluorophores, radiolabeled Zn(2+), and selective chelators, the location of this ion and its release pattern have been established across the brain. Given the distribution and possible release under physiological conditions, Zn(2+) has the potential to act as a modulator of both excitatory and inhibitory neurotransmission. Excitatory N-methyl-D-aspartate (NMDA) receptors are directly inhibited by Zn(2+), whereas non-NMDA receptors appear relatively unaffected. In contrast, inhibitory transmission mediated via GABA(A)receptors can be potentiated via a presynaptic mechanism, influencing transmitter release; however, although some tonic GABAergic inhibition may be suppressed by Zn(2+), most synaptic GABA receptors are unlikely to be modulated directly by this cation. In the spinal cord, glycinergic transmission may also be affected by Zn(2+) causing potentiation. Recently, the penetration of synaptically released Zn(2+) into neurons suggests that this ion has the potential to act as a direct transmitter, by affecting postsynaptic signaling pathways. Taken overall, present studies are broadly supportive of a neuromodulatory role for Zn(2+) at specific excitatory and inhibitory synapses.

Zinc translocation accelerates infarction after mild transient focal ischemia

Excess release of chelatable zinc (Zn(2+)) from central synaptic vesicles may contribute to the pathogenesis of selective neuronal cell death following transient forebrain ischemia, but a role in neurodegeneration after focal ischemia has not been defined. Adult male Long-Evans rats subjected to middle cerebral artery occlusion (MCAO) for 30 min followed by reperfusion developed delayed cerebral infarction reaching completion 3 days after the insult. One day after the insult, many degenerating cerebral neurons exhibited increased intracellular Zn(2+), and some labeled with the antibody against activated caspase-3. I.c.v. administration of the Zn(2+) chelator, EDTA saturated with equimolar Ca(2+) (CaEDTA), 15 min prior to ischemia attenuated subsequent Zn(2+) translocation into cortical neurons, and reduced infarct volume measured 3 days after ischemia. Although the protective effect of CaEDTA at this endpoint was substantial (about 70% infarct reduction), it was lost when insult severity was increased (from 30 to 60 min MCAO), or when infarct volume was measured at a much later time point (14 days instead of 3 days after ischemia). These data suggest that toxic Zn(2+) translocation, from presynaptic terminals to post-synaptic cell bodies, may accelerate the development of cerebral infarction following mild transient focal ischemia.

Zinc and cognitive development

Cognition is a field of thought processes by which an individual processes information through skills of perception, thinking, memory, learning and attention. Zinc deficiency may affect cognitive development by alterations in attention, activity, neuropsychological behavior and motor development. The exact mechanisms are not clear but it appears that zinc is essential for neurogenesis, neuronal migration, synaptogenesis and its deficiency could interfere with neurotransmission and subsequent neuropsychological behavior. Studies in animals show that zinc deficiency during the time of rapid brain growth, or during the juvenile and adolescent period affects cognitive development by decreasing activity, increasing emotional behavior, impairing memory and the capacity to learn. Evidence from human studies is limited. Low maternal intakes of zinc during pregnancy and lactation were found to be associated with less focused attention in neonates and decreased motor functions at 6 months of age. Zinc supplementation resulted in better motor development and more playfulness in low birth weight infants and increased vigorous and functional activity in infants and toddlers. In older school going children the data is controversial but there is some evidence of improved neuropsychological functions with zinc supplementation. Additional research is required to determine the exact biological mechanisms, the critical periods, the threshold of severity and the long-term effects of zinc deprivation on cognitive development.

Effects of zinc on spatial reference memory and brain dopamine (D1) receptor binding kinetics in rats

1. The present study was designed to evaluate the effects of zinc on spatial reference memory and brain dopamine (D1) receptor binding kinetics in rats. Male Sprague-Dawley rats (120-150 g), adapted 12 hour light: 12 hour dark illumination cycle were used. Treated animals were given zinc chloride (25 mg/kg, 50 mg/kg, or 100 mg/kg) by oral gavage for 15 days at 11:00 hr. Controlrats received an equivalent volume of saline. 2. Spatial reference memory was evaluated in treated and control rats on days 10 through 15 using the Morris Water Maze. The time to find the platform (latency) was significantly increased in the 50 mg/kg and 100-mg/kg zinc treated animals as compared to the controls. One hour after the last spatial reference memory testing, the animals were sacrificed by decapitation; their brains were removed and dissected into various regions. 3. D1 receptor binding kinetics were measured using the ligand [3H] SCH23390. Results obtained indicate that zinc chloride administration resulted in a statistically significant decline in the binding affinity (increased Kd) of the D1 receptors in the frontal cortex, hypothalamus, hippocampus, and midbrain. However, there was a significant increase in the D1 receptor binding capacity (Bmax) in these same brain regions following zinc chloride administration. 4. These findings clearly indicate that administration of high doses of zinc to rats resulted in spatial reference memory deficit, which may in part be explained by alterations in dopamine receptor binding kinetics.

The actions of synaptically released zinc at hippocampal mossy fiber synapses

Zn2+ is present at high concentrations in the synaptic vesicles of hippocampal mossy fibers. We have used Zn2+ chelators and the mocha mutant mouse to address the physiological role of Zn2+ in this pathway. Zn2+ is not involved in the unique presynaptic plasticities observed at mossy fiber synapses but is coreleased with glutamate from these synapses, both spontaneously and with electrical stimulation, where it exerts a strong modulatory effect on the NMDA receptors. Zn2+ tonically occupies the high-affinity binding site of NMDA receptors at mossy fiber synapses, whereas the lower affinity voltage-dependent Zn2+ binding site is occupied during action potential driven-release. We conclude that Zn2+ is a modulatory neurotransmitter released from mossy fiber synapses and plays an important role in shaping the NMDA receptor response at these synapses.

Causes of iron and zinc deficiencies and their effects on brain

Low consumption of foods rich in bioavailable iron (Fe) and zinc (Zn) such as meat, particularly red meat, and high consumption of foods rich in inhibitors of Fe and Zn absorption, such as phytate, certain dietary fibers and calcium, cause Fe and Zn deficiencies. Neuropsychologic impairment is one of several potential outcomes of these deficiencies.

History of zinc as related to brain function

Zinc (Zn) is essential for synthesis of coenzymes that mediate biogenic-amine synthesis and metabolism. Zn from vesicles in presynaptic terminals of certain glutaminergic neurons modulates postsynaptic N-methyl-D-aspartate (NMDA) receptors for glutamate. Large amounts of Zn released from vesicles by seizures or ischemia can kill postsynaptic neurons. Acute Zn deficiency impairs brain function of experimental animals and humans. Zn deficiency in experimental animals during early brain development causes malformations, whereas deficiency later in brain development causes microscopic abnormalities and impairs subsequent function. A limited number of studies suggest that similar phenomena can occur in humans.

Zinc modulation of AMPA receptors may be relevant to splice variants in carp retina

With the use of the whole-cell patch clamp technique, we examined effects of zinc on AMPA receptors of isolated carp retinal horizontal cells, predominantly consisting of flop splice variants. We found that zinc ranging from 30 microM to 1 mM failed to modulate glutamate-induced currents of these cells, which is clearly distinct from the results previously obtained in superior colliculus neurons and Xenopus ooctyes. Furthermore, glutamate responses remained unchanged when zinc was co-applied with PEPA, a flop variant-preferential AMPA receptor potentiator. With the co-application of cyclothiazide, a flip variant-preferential AMPA receptor potentiator, however, a dual effect could be observed: zinc potentiated glutamate responses at low concentrations, but inhibited them at higher concentrations. These results suggest that the action of zinc on AMPA receptors may be splice variant-relevant.

Zinc deficiency and child development

Zinc is a trace metal that is present in the brain and contributes to its structure and function. Limited evidence from both animal and human studies suggests that zinc deficiency may lead to delays in cognitive development. Although the mechanisms linking zinc deficiency with cognitive development are unclear, it appears that zinc deficiency may lead to deficits in children's neuropsychologic functioning, activity, or motor development, and thus interfere with cognitive performance. In this article a model is presented that incorporates the influence of social context and the caregiving environment and suggests that the relation between zinc deficiency and cognitive development may vary by age in children and may be mediated by neuropsychologic functioning, activity, and motor development. Suggestions for further research are provided.

Zinc and brain injury

Zinc is an essential catalytic or structural element of many proteins, and a signaling messenger that is released by neural activity at many central excitatory synapses. Growing evidence suggests that zinc may also be a key mediator and modulator of the neuronal death associated with transient global ischemia and sustained seizures, as well as perhaps other neurological disease states. Manipulations aimed at reducing extracellular zinc accumulation, or cellular vulnerability to toxic zinc exposure, may provide a novel therapeutic approach toward ameliorating pathological neuronal death in these settings.

Learning/memory impairments in rat offspring prenatally exposed to phenytoin

Phenytoin (PHT) was orally administered in dosages of 50 and 100 mg/kg/day to pregnant rats on days 7-18 of gestation. Offspring were tested on the negative geotaxis test, a figure-eight maze (F8), the Biel water maze (BM), the Morris maze (MM), and the radial maze (RM). In addition, a delayed nonmatching-to-sample (DNMTS) test was employed. The levels of neuropeptides in brain and brain weights were determined. The maturation of negative geotaxis was delayed in both PHT groups. PHT groups showed no differences in F8, BM, and MM. In the RM, the total number of choices was high, whereas the number of correct choices was low. In the DNMTS, PHT groups showed low for correct choices with a long interval. The concentrations of neuropeptides were changed in the mesolimbic cortex, hippocampus, and amygdala. Brain weights were lower at 6 weeks of age in the 100 mg/kg/day PHT group, but were comparable at 16 weeks of age. This study suggests that the RM is a detectable task for the learning/memory impairments induced by PHT. In addition, it is surmised that the learning deficit is due to a working memory impairment arising from abnormal changes in neuropeptides and an injury in the fetal hippocampus.

Zinc metabolism in the brain: relevance to human neurodegenerative disorders

Zinc is an important trace element in biology. An important pool of zinc in the brain is the one present in synaptic vesicles in a subgroup of glutamatergic neurons. In this form it can be released by electrical stimulation and may serve to modulate responses at receptors for a number of different neurotransmitters. These include both excitatory and inhibitory receptors, particularly the NMDA and GABA(A) receptors. This pool of zinc is the only form of zinc readily stained histochemically (the chelatable zinc pool), but constitutes only about 8% of the total zinc content in the brain. The remainder of the zinc is more or less tightly bound to proteins where it acts either as a component of the catalytic site of enzymes or in a structural capacity. The metabolism of zinc in the brain is regulated by a number of transport proteins, some of which have been recently characterized by gene cloning techniques. The intracellular concentration may be mediated both by efflux from the cell by the zinc transporter ZrT1 and by complexing with apothionein to form metallothlonein. Metallothionein may serve as the source of zinc for incorporation into proteins, including a number of DNA transcription factors. However, zinc is readily released from metallothionein by disulfides, increasing concentrations of which are formed under oxidative stress. Metallothionein is a very good scavenger of free radicals, and zinc itself can also reduce oxidative stress by binding to thiol groups, decreasing their oxidation. Zinc is also a very potent inhibitor of nitric oxide synthase. Increased levels of chelatable zinc have been shown to be present in cell cultures of immune cells undergoing apoptosis. This is very reminiscent of the zinc staining of neuronal perikarya dying after an episode of ischemia or seizure activity. Thus a possible role of zinc in causing neuronal death in the brain needs to be fully investigated. intraventricular injections of calcium EDTA have already been shown to reduce neuronal death after a period of ischemia. Pharmacological doses of zinc cause neuronal death, and some estimates indicate that extracellular concentrations of zinc could reach neurotoxic levels under pathological conditions. Zinc is released in high concentrations from the hippocampus during seizures. Unfortunately, there are contrasting observations as to whether this zinc serves to potentiate or decrease seizure activity. Zinc may have an additional role in causing death in at least some neurons damaged by seizure activity and be involved in the sprouting phenomenon which may give rise to recurrent seizure propagation in the hippocampus. In Alzheimer's disease, zinc has been shown to aggregate beta-amyloid, a form which is potentially neurotoxic. The zinc-dependent transcription factors NF-kappa B and Sp1 bind to the promoter region of the amyloid precursor protein (APP) gene. Zinc also inhibits enzymes which degrade APP to nonamyloidogenic peptides and which degrade the soluble form of beta-amyloid. The changes in zinc metabolism which occur during oxidative stress may be important in neurological diseases where oxidative stress is implicated, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS). Zinc is a structural component of superoxide dismutase 1, mutations in which give rise to one form of familiar ALS. After HIV infection, zinc deficiency is found which may be secondary to immune-induced cytokine synthesis. Zinc is involved in the replication of the HIV virus at a number of sites. These observations should stimulate further research into the role of zinc in neuropathology.

Differences of CA3 bursting in DBA/1 and DBA/2 inbred mouse strains with divergent shuttle box performance

The CA3 bursting activity was compared in slices from two genetically closely related inbred mouse strains with divergent shuttle box performance (low level performing DBA/1 and high performing DBA/2 strains) and a control, behaviorally untested inbred strain, NMRI. Spontaneous population bursts of hippocampal CA3 pyramidal cells (measured extracellularly as field potentials) occurred more frequently in slices of the DBA/2 strain (in 62.5% of the slices in DBA/2 mice) than in the DBA/1 strain (in 33.3% of the slices in DBA/1 mice) and the control NMRI strain (in 33.3% of the slices), whereas the ratio of bursting and nonbursting cells was not different. The resting membrane potential of spontaneously bursting and nonbursting cells was hyperpolarized and the frequency of spontaneous cell bursts were higher in DBA/2 mice compared with both other strains. Slices from the high performing DBA/2 strain had significantly lower thresholds for population bursts evoked by mossy fiber (but not perforant path) stimulation. Electrophysiological properties and bursting patterns of CA3 pyramidal cells are shown to correlate with learning behavior in three different mouse strains. This result is in keeping with an important role of CA3 bursting in memory trace formation.

Mercury (Hg2+) and zinc (Zn2+): two divalent cations with different actions on voltage-activated calcium channel currents

1. We examined the actions of mercury (Hg2+) and zinc (Zn2+) on voltage-activated calcium channel currents of cultured rat dorsal root ganglion (DRG) neurons, using the whole-cell patch clamp technique. 2. Micromolar concentrations of both cations reduced voltage-activated calcium channel currents. Calcium channel currents elicited by voltage jumps from a holding potential of -80 to 0 mV (mainly L- and N-currents) were reduced by Hg2+ and Zn2+. The threshold concentration for Hg2+ effects was 0.1 microM and that for Zn2+ was 10 microM. Voltage-activated calcium channel currents were abolished (> 80%) with 5 microM Hg2+ or 200 microM Zn2+. The peak calcium current was reduced to 50% (IC50) by 1.1 microM Hg2+ or 69 microM Zn2+. While Zn2+ was much more effective in reducing the T-type calcium channel current--activated by jumping from -80 to -35 mV--Hg2+ showed some increased effectiveness in reducing this current. 3. The effects of both cations occurred rapidly and a steady state was reached within 1-3 min. While the action of Zn2+ was not dependent on an open channel state, Hg2+ effects depended partially on channel activation. 4. While both metal cations reduced the calcium channel currents over the whole voltage range, some charge screening effects were detected with Hg2+ and with higher concentrations (> 100 microM) of Zn2+. 5. As Zn2+ in the concentration range used had no influence on resting membrane currents, Hg2+ caused a clear inward current at concentrations > or 2 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Zinc deficiency and corticosteroids in the pathogenesis of alcoholic brain dysfunction--a review

Chronic alcoholism is associated with hypercortisolemia and low serum zinc (Zn). Hypercortisolemia could be responsible for alcoholic cerebral atrophy and is also associated with enhanced NMDA neurotoxicity. It is hypothesized that low brain Zn, noted in chronic alcoholics, enhances NMDA excitotoxicity and ethanol withdrawal seizure susceptibility. Also, Zn deficiency can produce neuronal damage through increased free radical formation. Clinically, Zn replacement therapy may be a rational approach to the treatment of alcohol withdrawal seizures and alcohol-related brain dysfunction.

Modulation of GABA-mediated synaptic transmission by endogenous zinc in the immature rat hippocampus in vitro

1. Intracellular recordings from postnatal 2- to 12-day-old (P2-12) rat hippocampal CA3 pyramidal neurones exhibited spontaneous synaptic potentials mediated by GABAA receptors. These potentials can be separated on the basis of amplitude into two classes which are referred to as small and large. 2. The large depolarizing potentials were reversibly inhibited by the Zn2+ chelator 1,2-diethyl-3-hydroxypyridin-4-one (CP94). The small inhibitory postsynaptic potentials. (IPSPs) were apparently unaffected. 3. Stimulation of the mossy fibre pathway evoked composite excitatory postsynaptic potentials (EPSPs) and IPSPs. Threshold stimulus-evoked synaptic potentials were mediated by GABAA receptors and were reversibly blocked by CP94. The responses evoked by suprathreshold stimulation and persisting in the presence of bicuculline or CP94 were partially inhibited by 2-amino-5-phosphonopropionic acid (AP5) and were completely blocked with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). 4. L-Histidine, which preferentially forms complexes with Cu2+ > Zn2+ > Fe2+ > Mn2+, inhibited both naturally occurring spontaneous and evoked GABAA-mediated large synaptic potentials without affecting the neuronal resting membrane properties. Exogenously applied Zn2+ induced large spontaneous synaptic potentials and prolonged the duration of the evoked potentials. These effects were reversibly blocked by histidine. 5. The metal chelating agent diethyldithiocarbamate had little effect on the large amplitude synaptic potentials. 6. The transition metal divalent cations Fe2+ and Mn2+ did not initiate large synaptic potentials in CA3 neurones; however, Cu2+ depolarized the membrane and enhanced both excitatory and inhibitory synaptic transmission, resulting in a transient increase in the frequency of the large amplitude events. In comparison, zinc increased the frequency of the large potentials and also induced such events in neurons (P4-21) where innate potentials were absent. The postsynaptic response to ionophoretically applied GABA was either unaffected or slightly enhanced by Zn2+. 7. Under conditions favouring the activation of non-NMDA receptors, excitatory synaptic transmission was unaffected by CP94 but was depressed by Zn2+. Responses to ionophoretically applied glutamate were not inhibited by Zn2+, indicating that Zn2+ affects excitatory synaptic transmission via a presynaptic mechanism. 8. We conclude that the naturally occurring large synaptic potentials in young CA3 neurones are apparently induced by endogenous Zn2+ which can promote or synchronize the release of GABA in the immature hippocampus.

A morphometric analysis of trimethyltin-induced change in rat brain using the Timm technique

Rats were given a single gavage of trimethyltin chloride (TMT) providing a dose of 0, 4.3, or 6.7 mg/kg of alkyltin. Gross changes in brain structures were quantified and analyzed statistically. Behavioral and functional measures were taken to verify efficacy of TMT dose. The high dose produced transient weight loss and seizures. In the fourth week after gavage, the high dose produced hyperactivity in the residential maze and activity wheel. High and low TMT doses decreased auditory startle responsiveness. Estrus cycle was normal in all groups. Brains were sectioned and stained with the Timm stain which delimited subregions of hippocampus and connected structures and also revealed mossy fibers. Linear and areal measures were made at three positions along the septotemporal axis of Ammon's horn. The low dose produced reductions in size in a few isolated subareas of the brain. The high dose produced, at the three planes studied, extensive (15-40%) loss of tissue in Ammon's horn and structures to which Ammon's horn is interconnected--subiculum, entorhinal cortex, dentate gyrus, hilus, CA3, and CA1 region. Neocortex and caudate-putamen were unaffected. These findings suggest that a single TMT gavage may disrupt brain structures important to linking neocortex with subcortex via structures in the hippocampal region.

Growth hormone augments superoxide anion secretion of human neutrophils by binding to the prolactin receptor

Recombinant human growth hormone (HuGH) and human prolactin (HuPRL), but not GH of bovine or porcine origin, prime human neutrophils for enhanced superoxide anion (O2-) secretion. Since HuGH, but not GH of other species, effectively binds to the HuPRL receptor (HuPRL-R), we used a group of HuGH variants created by site-directed mutagenesis to identify the receptor on human neutrophils responsible for HuGH priming. A monoclonal antibody (MAb) directed against the HuPRL-R completely abrogated O2- secretion by neutrophils incubated with either HuGH or HuPRL, whereas a MAb to the HuGH-R had no effect. The HuGH variant K172A/F176A, which has reduced affinity for both the HuGH-binding protein (BP) and the HuPRL-BP, was unable to prime human neutrophils. This indicates that priming is initiated by a ligand-receptor interaction, the affinity of which is near that defined for receptors for PRL and GH. Another HuGH variant, K168A/E174A, which has relatively low affinity for the HuPRL-BP but slightly increased affinity for the HuGH-BP, had much reduced ability to prime neutrophils. In contrast, HuGH variant E56D/R64M, which has a similar affinity as wild-type HuGH for the HuPRL-BP but a lower affinity for the HuGH-BP, primed neutrophils as effectively as the wild-type HuGH. Finally, binding of HuGH to the HuPRL-BP but not to the HuGH-BP has been shown to be zinc dependent, and priming of neutrophils by HuGH was also responsive to zinc. Collectively, these data directly couple the binding of HuGH to the HuPRL-R with one aspect of functional activation of human target cells.

Cephaloconiosis: a free radical perspective on the proposed particulate-induced etiopathogenesis of Alzheimer's dementia and related disorders

By analogy to the etiology of the pneumoconioses, exogenous dust-induced diseases of the lung, and endogenous crystal-induced arthropathies such as gout, it is proposed that Alzheimer's dementia and allied disorders are causally related to the accumulation of fibriform inorganic deposits within the brain. Hence the neonosological term 'Cephaloconiosis'. It is proposed that: 1) either by the extrinsic migration or intrinsic formation and deposition of insoluble and persistent inorganic reactive nidi, the particle-induced generation of tissue-damaging free-radical oxygen metabolites by stimulated brain glial macrophage-type and allied phagocytic cells, provides a rationale for the etiopathogenesis of neurodegenerative processes; 2) the modulation of the injurious oxidative metabolic reaction by micronutrient and pharmacological antioxidant agents is a rational and potentially feasible strategy for future therapeutic clinical investigations.

A physiological role for endogenous zinc in rat hippocampal synaptic neurotransmission

The mammalian central nervous system (CNS) contains an abundance of the transition metal zinc, which is highly localized in the neuronal parenchyma. Zinc is actively taken up and stored in synaptic vesicles in nerve terminals, and stimulation of nerve fibre tracts that contain large amounts of zinc, such as the hippocampal mossy fibre system, can induce its release, suggesting that it may act as a neuromodulator. The known interaction of zinc with the major excitatory and inhibitory amino-acid neurotransmitter receptors in the CNS supports this notion. That zinc has a role in CNS synaptic transmission, however, has so far not been shown. Here we report a physiological role for zinc in the young rat hippocampus (postnatal, P3-P14 days). Our results indicate that naturally occurring spontaneous giant depolarizing synaptic potentials (GDPs) in young CA3 pyramidal neurones, mediated by the release of GABA (gamma-aminobutyric acid), are induced by endogenously released zinc. These synaptic potentials are inhibited by specific zinc-chelating agents. GDPs are apparently generated by an inhibitory action of zinc on both pre- and postsynaptic GABAB receptors in the hippocampus. Our study implies that zinc modulates synaptic transmission in the immature hippocampus, a finding that may have implications for understanding benign postnatal seizures in young children suffering with acute zinc deficiency.

Densitometric analysis of the local bleaching of the Neo-Timm staining pattern following intrahippocampal injection of diethyldithiocarbamate

Treatment with certain metal chelating agents causes a time-dependent bleaching of the Neo-Timm staining pattern of zinc visualized in synaptic vesicles. In the present study, the extent and time course of the reversible chelation of hippocampal vesicular zinc was investigated following intrahippocampal injection of the chelating agent diethyldithiocarbamate. The carbamate (1.0 microliters 45 mg ml-1, 200 mM) was injected unilaterally into the hippocampal region of adult rats, which were allowed to survive 15 min-6 h before sacrifice. Control animals either received injections of distilled water or were untreated. Computerized optical densitometry was performed on cryostat sections of brains stained with the Neo-Timm method. Injection of diethyldithiocarbamate into the hippocampal region resulted in a localized bleaching of the Neo-Timm staining pattern. The extent of the bleaching varied with time being most pronounced at 15 min survival and gradually decreasing with time. After 6 h survival, a faint bleaching of the injected hippocampal region was barely seen. Computerized optical densitometry confirmed and extended the observations providing a semi-quantitative measure of zinc in synaptic vesicles.

The neurotoxicity of zinc in the rat hippocampus

Intrahippocampal injections of zinc chloride (5-10 nmol) caused a discrete lesion in the rat hippocampus, involving all neuronal perikarya. In addition to the necrosis, the lesion was also characterized by a decrease in staining of the neuropil, the presence of pyknotic neurons, and occasionally infarction. Pathological changes occurred within 8 h of an injection, and neuronal loss, as judged by the loss of Nissl staining, was complete within 24 h. On the other hand, the loss of acidophilic staining of the neurons was more gradual, as acid fuchsin staining was still present in neurons in the periphery of the damaged area 4 days later. In comparison with an excitotoxic lesion, glial infiltration into the damaged area was minimal, even up to 3 weeks later, suggesting that some glial cell toxicity also occurred.

Effects of dietary zinc status on seizure susceptibility and hippocampal zinc content in the El (epilepsy) mouse

The effects of dietary zinc status on the development of convulsive seizures, and zinc concentrations in discrete hippocampal areas and other parts of the limbic system were studied in the El mouse model receiving zinc-adequate, zinc-deficient or zinc-loaded diets. Seizure susceptibility of the El mouse was increased by zinc deficiency, and decreased by zinc loading, while an adequate diet had no effect. Zinc loading was accompanied by a marked increase in hippocampal zinc content in the El mouse. Conversely, hippocampal zinc content declined in the El mouse fed a zinc-deficient diet. These results suggest that zinc may have a preventive effect on the development of seizures in the El mouse, and hippocampal zinc may play an important role in the pathophysiology of convulsive seizures of epilepsy.

Hearing loss related to zinc deficiency in rats

Based on the observation that the zinc concentration in the cochlea of guinea pigs is very high, Shambaugh in North America has suggested that zinc plays an important role in hearing. Zinc deficiency is not infrequently present in growing children and elderly people, and thus might result in a hearing loss, which should be treated with zinc supplementation. The present experiment examined the effects of a zinc-deficient diet on hearing in 7-week-old rats. The auditory brainstem response threshold was measured in four rats before, during and after a zinc-deficient diet. Concentrations of zinc in the brain and in several other organs were measured, and the cochleas were examined microscopically. No hearing loss or morphological change in the cochlea of these animals was detected, although a clear zinc-deficient status was reached.

Hypozincemia during fever may trigger febrile convulsion

Febrile convulsions are generally thought to be induced by metabolic changes during the rise-phase of body temperature. The mechanism by which convulsions are induced, however, is not fully elucidated. In this article, we propose a new hypothesis about the induction mechanism of febrile convulsions that takes into account the hypozincemia during fever. This hypozincemia activates the NMDA receptor, one of the glutamate family of receptors, which may play an important role in the induction of epileptic discharge.

Zinc has opposite effects on NMDA and non-NMDA receptors expressed in Xenopus oocytes

Pharmacological characterization of Zn2+ effects on glutamate ionotropic receptors was investigated in Xenopus oocytes injected with rat brain mRNA, using a double microelectrode, voltage-clamp technique. At low concentration, Zn2+ inhibited NMDA currents (IC50 = 42.9 +/- 1.3 microM) and potentiated both AMPA (EC50 = 30.0 +/- 1.2 microM) and desensitized kainate responses (EC50 = 13.0 +/- 0.1 microM). At higher concentrations, Zn2+ inhibited non-NMDA responses with IC50 values of 1.3 +/- 0.1 mM and 1.2 +/- 0.3 mM for AMPA and kainate, respectively. The potentiation of AMPA or quisqualate currents by Zn2+ was more than 2-fold, whereas that of the kainate current was only close to 30%. This potentiating effect of Zn2+ on AMPA current modified neither the affinity of the agonist for its site nor the current-voltage relationship. In addition, 500 microM Zn2+ differentially affected NMDA and non-NMDA components of the glutamate-induced response. The possible physiological relevance of Zn2+ modulation is discussed.

Unification of the findings in schizophrenia by reference to the effects of gestational zinc deficiency

The hypothesis presented here suggests that schizophrenia is caused by the action of gestational zinc deficiency on genetically susceptible foetuses. The psychosis seen is suggested to be due to a combination of dietary or otherwise induced zinc deficiency and lack of zinc releasing capacity in the hippocampus. A non genetic but transmissable immune defect is suggested to be relevant to psychosis and to the nonmendelian pattern of inheritance of the disorder.

Opening the blood-brain barrier to zinc

Sheep with guide tubes implanted over the brain lateral ventricles, in order to facilitate episodic sampling of cerebrospinal fluid (CSF), were used to determine the effects of increasing cranial blood osmolality or electroconvulsive shock (ECS) on the permeability of the blood-brain barrier (BBB) to zinc. Zinc acetate solution (1 mg Zn/ml) was infused intravenously (i.v.) at 1.0 ml/min for 30 min and then continuously at 0.125 ml/min. This infusion increased plasma total zinc concentration (pZn) approximately 10-fold without altering CSF zinc concentration (CSFZn). After 1.5-3.5 h, 4 M NaCl was infused at 5-10 ml/min for 10 min into one carotid artery with the other carotid artery occluded, or the animals were anaesthetized and given an ECS (140 V, 2 s). Paired samples of blood and CSF were collected before and after these treatments. Results were: (i) CSFZn was approximately one tenth of pZn; (ii) zinc administered i.v. was almost completely excluded from the CSF; (iii) increased cranial blood osmolality or ECS increased CSFZn in all experiments, but the time course and extent of the rise were variable. CSFZn reached the concentrations of zinc in normal sheep plasma in some experiments; (iv) CSFZn subsequently fell towards the low values of zinc in normal CSF; (v) the animals suffered no evident ill-effects from either procedure. The procedures may, therefore, be used for reversible opening of the BBB to particles such as zinc in conscious or anaesthetized sheep with no troublesome sequelae.

Diethyldithiocarbamate and dithizone augment the toxicity of kainic acid

Male Fischer-344 rats were injected i.p. with diethyldithiocarbamate or dithizone 15 min after kainic acid (KA), s.c. Diethyldithiocarbamate and dithizone reduced both the number of wet dog shakes and the latency to onset of seizures induced by KA. Moreover, they increased the severity of seizures. These compounds may be useful tools for investigating the role of zinc in central nervous system excitatory transmission and/or convulsive phenomena.

Dietary zinc deficiency has no effect on auditory brainstem responses in the rat

Zinc has been shown to effect--in vitro--a number of processes associated with neurotransmission. We have tested whether the rate of impulse conduction--in vivo--as measured from the latencies of auditory brainstem responses (ABR), is influenced by dietary zinc deficiency in the rat. Dietary zinc deficiency for up to 26 wk had no effect on the wave I-IV interval compared to zinc-adequate fed animals. The results are discussed in relation to the observed constancy of brain overall and extracellular fluid zinc concentrations under conditions of dietary zinc deficiency.

Prenatal ethanol exposure decreases hippocampal mossy fiber zinc in 45-day-old rats

The long-term consequences of prenatal ethanol exposure on histochemically detectable hippocampal mossy fiber zinc was examined using a recently developed quantitative histofluorescence procedure. Pregnant Sprague-Dawley rats were maintained throughout gestation on one of three dietary regimens: (a) a liquid diet containing either 3.35% ethanol, (b) an isocalorically matched liquid diet pair-fed to the 3.35% ethanol group, or (c) lab chow ad libitum. At 45 days of age, offspring from each of the three diet groups were sacrificed for determination of hippocampal mossy fiber zinc and zinc analysis of selected tissues by atomic absorption spectroscopy. Hippocampal mossy fiber zinc was reduced by 36% in dorsal and 20% in ventral hippocampal formation stratum lucidum of rats exposed to the 3.35% ethanol diet compared to the offspring of the pair-fed control and ad libitum control dams. No significant differences in zinc:TS-Q histofluorescence were observed between the ad libitum and pair-fed control groups. No significant differences were observed among groups in tissue wet weight or tissue zinc concentration in any of the brain or other body regions analyzed. These results indicate a long lasting prenatal ethanol exposure-induced reduction in hippocampal mossy fiber zinc in the absence of changes in any indices of total body zinc nutriture. These results suggest that prenatal exposure to relatively low blood ethanol levels (30-40 mg/dl) has subtle, yet long-lasting effects in the hippocampal formation, a brain region important in the process of memory consolidation.

Identification of Zn2+-dependent and Mg2+/Triton X-100-dependent tyrosine protein kinases in ethylenediaminetetraacetate-treated P2 membrane fraction of monkey brain basal ganglia

Tyrosine phosphorylation of a 55- and 60-kDa protein was observed when EDTA-treated P2 membrane fraction from monkey basal ganglia was incubated with [gamma-32P]-ATP in the presence of Zn2+. Other metal ions were less effective in this phosphorylation. The effect of Zn2+ did not appear to be due to its inhibition of a tyrosine phosphatase. In the presence of Mg2+/Triton X-100 instead of Zn2+, phosphorylation on tyrosine residues of a 17-kDa protein and the external substrate poly(Glu, Tyr) 4:1 copolymer was observed. Both Mg2+ and Triton X-100 were essential for this and Zn2+ inhibited both of these phosphorylations. Convincing evidence for the existence of Zn2+-dependent and Mg2+/Triton X-100-dependent tyrosine protein kinases was obtained when the two kinases could be separated by extraction of the membranes by Triton X-100. The Zn2+-dependent phosphorylation was present exclusively in the Triton-solubilized supernatant whereas the Mg2+/Triton X-100-dependent phosphorylation was found associated with the Triton-insoluble membrane fractions. Externally added histone could also be phosphorylated on tyrosine residues in a Zn2+- or Mg2+/Triton X-100-dependent manner by the supernatant or membrane fraction, respectively.