Release of zinc sulphide accumulations into synaptic clefts after in vivo injection of sodium sulphide

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.

Age-related changes of sulphide-silver staining in the rat hippocampus

The influence of ageing on sulphide-silver positive zinc stores was assessed in the stratum radiatum of the CA1-CA3 sub fields of the rat hippocampus and in the molecular layer of the dentate gyrus using a silver amplification histochemical technique associated with microdensitometry. The volume of areas examined for microdensitometry was evaluated as well by quantitative image analysis. Male Sprague-Dawley rats aged 3 months (considered to be young), 12 months (considered to be adult) and 24 months (considered to be old) were used. Microdensitometric analysis of values of sulphide-silver staining corrected for the volume of hippocampal areas investigated revealed no age-dependent changes of staining in the CA1 sub field of the hippocampus. In the CA2 sub field a decrease of sulphide-silver staining was noticeable in aged rats in comparison with younger cohorts. A progressive reduction in the intensity of sulphide-silver staining was observed in the CA3 sub field of the hippocampus. In the molecular layer of the dentate gyrus, the intensity of staining was decreased in adult and old rats in comparison with young animals. These findings indicate a different sensitivity to ageing of histochemically detectable zinc stores of rat hippocampus. The possibility of a specific sensitivity to senescence of different zinc-containing pathways of the hippocampus is discussed.

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.

Autometallographic silver enhancement of zinc sulfide crystals created in cryostat sections from human brain biopsies: a new technique that makes it feasible to demonstrate zinc ions in tissue sections from biopsies and early autopsy material

We present a new technique that allows zinc ions in synaptic and secretory vesicles of biopsy and early autopsy material (< 2 hr post mortem) to be transformed to nanometer-sized zinc sulfide crystal lattices for subsequent autometallographic (AMG) development. Human brain biopsies, or other tissue samples containing zinc-enriched (ZEN) cells, are frozen in liquid nitrogen or by CO2 gas immediately after removal. The tissue blocks are cut in a cryostat and the sections placed on glass slides. The slides are transferred to an H2S exposure chamber placed in a -15 C freezer. After 1-24 hr of gas exposure the sections are removed from the chamber, fixed while thawing, and dehydrated. The sections are then exposed to an AMG developer. AMG causes silver enhancement of zinc sulfide crystal lattices created in the tissues through the H2S exposure, making them visible. It is imperative that the tissues are frozen instantaneously after removal, because loosely bound or free zinc ions start leaving their vesicular compartment soon after death. The AMG technique can, despite inadequate fixation and damage to the tissue caused by freezing, also be used to trace zinc ions at ultrastructural levels, and it is demonstrated that zinc ions in the human neocortex are located in synaptic vesicles. In the few human biopsies analyzed thus far, the light microscopic pattern created by the silver-enhanced ZEN terminals resembles that seen in the neocortex of rat brain. The technique has been applied to cryostat sections from neocortex biopsies of five individuals undergoing brain surgery. Biopsies from three patients resulted in satisfactory AMG-stained sections. Rat brains removed and frozen immediately after decapitation constituted the material on which the present technique was developed. Such material results in an almost uniform high quality of staining, and we found that unexposed sections can be stored for at least 5 months at -80 C without ensuing significant loss of AMG staining intensity.

Increased amount of zinc in the hippocampus and amygdala of Alzheimer's diseased brains: a proton-induced X-ray emission spectroscopic analysis of cryostat sections from autopsy material

Zinc has been implicated as a contributing cause of the neuropathology of Alzheimer's disease (AD), but consensus on the zinc content of AD brains has not yet been established. In the present study, multi-element PIXE was used to measure zinc in cryostat sections of brain tissue from AD patients and from normal control subjects. Compared to their age-matched controls, the AD patients showed an increase in zinc in the hippocampal and amygdalar regions. The instrumental PIXE assays do not show whether the zinc changes are due to altered zinc in the boutons of Zinc-ENriched (ZEN) neurons, i.e., zinc ions in synaptic vesicles, or to changes in the amount of zinc tightly bound to macromolecules. We hypothesise that the increased zinc level is caused by an increase in the amount of ZEN terminals. Such an increase could be the result of a sprout of ZEN terminals in diseased areas of the brain.

Imaging free zinc in synaptic terminals in live hippocampal slices

Some glutamatergic synapses in the mammalian central nervous system exhibit high levels of free ionic zinc in their synaptic vesicles. The precise role of this vesicular zinc remains obscure, despite suggestive evidence for zinc as a neuromodulator. As a step towards elucidating the role of free zinc in the brain we have developed a method for imaging zinc release in live brain slices. A newly synthesized zinc-sensitive fluorescent probe, N-(6-methoxy-8-quinolyl)-p-carboxybenzoylsulphonamide (TFLZn), was used to monitor intracellular zinc in live rat hippocampal slices. The dye loaded into the zinc-rich synaptic vesicles of the mossy fibre terminals in the hippocampal formation. Direct electrical stimulation of the mossy fibre pathway diminished the fluorescence in the mossy fibre terminals, consistent with a stimulus-dependent zinc release. The synaptic release of zinc was followed by the rapid replenishment of the zinc levels in vesicles from an as yet unidentified intracellular zinc source. Furthermore, we present evidence that zinc may play a role in a form of long-term potentiation exhibited by the mossy fibre pathway.

Voltage- and GABA-evoked currents from Müller glial cells of the baboon retina

The electrophysiological features of isolated baboon Müller cells was investigated using the whole-cell voltage-clamp technique. Application of depolarizing voltage steps evoked transient inward and delayed outward currents. The transient currents disappeared when extracellular Na+ was replaced by choline+ and were substantially decreased by application of tetrodotoxin (1 microM). The outward currents were strongly diminished by extracellular Ba2+ (1 mM), and the hyperpolarization-generated inward currents disappeared following application of Ba2+. The recently described gamma-aminobutyric acid A (GABAA) receptor currents were increased by flunitrazepam, nordiazepam, pentobarbital and Zn2+, as well as by the inverse agonist DMCM. These results suggest that the baboon Müller cells possess the same voltage-dependent current pattern as those from other species, e.g. humans, whereas their GABAA receptors react in an uncharacteristic manner to DMCM and Zn2+, when compared with neuronal GABAA receptors.

The autometallographic zinc-sulphide method. A new approach involving in vivo creation of nanometer-sized zinc sulphide crystal lattices in zinc-enriched synaptic and secretory vesicles

A new version of Timm's sulphide silver method involving in vivo binding of zinc ions in zinc enriched terminals is presented. By injecting sodium sulphide into the vena cava of deeply anaesthetized animals, it is possible to bind chemically the vesicular zinc, i.e. chelatable zinc (zinc ions), in secretory and synaptic vesicles, in the form of zinc sulphide crystal lattices. Four minutes after the intravenous injection the animal is perfused transcardially with a phosphate-buffered solution of glutaraldehyde, glutaraldehyde and formaldehyde, or with a saline solution. The nanometer-sized catalytic crystals can then be silver-amplified in cryostat and vibratome sections by exposure to an autometallographic developer. It is demonstrated that contemporaneously with silver enhancement, the zinc sulphide crystals are transformed to the corresponding silver sulphide crystals. For ultrastructural studies, autometallographic development of vibratome sections is recommended. From these sections tissue blocks are cut from the areas of interest, blockstained with osmium tetroxide and embedded in Epon. This approach results in a zinc-specific autometallographic staining of the sections of a hitherto unseen, high technical quality.

Expression and regulation of brain metallothionein

Many, but not all, zinc-containing neurons in the brain are a subclass of the glutamatergic neurons, and they are found predominantly in the telencephalon. These neurons store zinc in their presynaptic terminals and release it by a calcium-dependent mechanism. These "vesicular" pools of zinc are viewed as endogenous modulators of ligand- and voltage-gated ion channels. Metallothioneins (MTs) are low molecular weight zinc-binding proteins consisting of 25-30% cysteine, with no aromatic amino acids or disulfide bonds. The areas of the brain containing high contents of zinc such as the retina, the pineal gland, and the hippocampus synthesize unique isoforms of MT on a continuous basis. The four MT isoforms are thought to provide the neurons and glial elements with mechanisms to distribute, donate, and sequester zinc at presynaptic terminals; or buffer the excess zinc at synaptic junctions. In this cause, glutathione disulfide may participate in releasing zinc from MT. A similar nucleotide and amino acid sequence has made it difficult to obtain cDNA probes and antibodies capable of distinguishing indisputably among MT isoforms. MT-I and MT-II isoforms are found in the brain and in the peripheral tissues; MT-III isoform, possessing an additional seven amino acids, is expressed mostly in the brain and to a very minute extent in the intestine and pancreas; whereas MT-IV isoform is found in tissues containing stratified squamous epithelial cells. Since MTs are expressed in neurons that sequester zinc in their synaptic vesicles, the regulation of the expression of MT isoforms is extremely important in terms of maintaining the steady-state level of zinc and controlling redox potentials. The concentration of zinc has been shown to be altered in an extensive number of disorders of the central nervous system, including alcoholism. Alzheimer-type dementia, amyotrophic lateral sclerosis, Down's syndrome, epilepsy, Friedreich's ataxia, Guillaine-Barré syndrome, hepatic encephalopathy, multiple sclerosis, Parkinson's disease, Pick's disease, retinitis pigmentosa, retinal dystrophy, schizophrenia, and Wernicke-Korsakoff syndrome. The status of MT isoforms and other low molecular weight zinc-binding proteins in these conditions, diseases, disorders, or syndromes is being delineated at this time. Since several of these disorders, such as amyotrophic lateral sclerosis, are associated with oxidative stress, and since MT is able to prevent the formation of free radicals, it is believed that cytokine-induced induction of MT provides a long-lasting protection to avert oxidative damage.

Zinc-containing innervation of the subicular region in the rat

The subiculum is densely innervated by zinc-containing axonal terminals, but the cells of origin of those zinc-containing afferents have not previously been identified. In the present work the zinc-specific retrograde tracing method was employed to locate the zinc-containing neurons afferent to the subicular complex. Following microinfusions into the subicular region, the somata of zinc-containing neurons were found in the hippocampus, the pre- and para subiculum, retrosplenial, cingulate, and perirhinal cortices, and in the anterodorsal nucleus of the thalamus. The results show another component of the zinc-containing associational network that interconnects the cerebral cortex and amygdalohippocampal systems of the brain.

Heterogeneous and compartmental distribution of zinc in the striatum and globus pallidus of the rat

The distribution of vesicular or chelatable zinc was analysed in the dorsal and ventral subdivisions of the striatum and globus pallidus of the rat with Danscher's selenium method. Acetylcholinesterase and Calbindin-D28k were used as striatal and pallidal markers in order to analyse the possible compartmentalization of the distribution of zinc in the striatum and globus pallidus. The main findings of this study are the following: (1) The distribution of vesicular zinc in the dorsal striatum was heterogeneous. A peripheral rim of tissue heavily stained for zinc was detected in the medial, dorsal and lateral striatal areas, along most of the rostrocaudal extent of the striatum. addition, patch-like zones intensely stained for zinc were prominent in the rostral half of the caudate-putamen complex. (2) In some regions of the rostral half of the caudate-putamen complex, the staining for zinc appeared to follow the well-known striatal patches (striosomes)/matrix organization. However, in other regions of the rostral half of the striatum such a relation was not detected. (3) The ventral striatum also showed a heterogeneous staining for zinc. Thus, in the most ventral part of the caudate-putamen complex, both subdivisions of the nucleus accumbens and parts of the olfactory tubercle displayed different patterns of compartmentalized distribution of zinc. In the dorsal half of the shell of the nucleus accumbens, some patches with an intense reaction for zinc seemed to overlap with acetylcholinesterase-poor patches. (4) There was a remarkable absence of staining for zinc in the globus pallidus. This histochemical study illustrates, on the one hand, the high content of vesicular zinc in the dorsal and ventral subdivisions of the striatum, which was distributed following different patterns of chemical compartmentalization, and on the other hand, the absence of vesicular zinc in the globus pallidus of the rat.

Histochemical localization of synaptic zinc in the developing cat visual cortex

The terminal boutons of many neurons in the telencephalon are known to contain a vesicle-bound, chelatable pool of zinc (Zn2+) that can be selectively visualized with histochemical procedures. In this paper, the normal laminar, areal, and ultrastructural distribution of histochemically reactive zinc in the visual cortex of the adult cat as well as its development from birth are described. In the adult cat visual cortex, intense zinc staining was found in layers I, II, III, and V, with layer VI staining only lightly. The primary geniculostriate input zone, layer IV, was conspicuously distinguished by the relative absence of zinc. This distinct pattern was restricted only to areas 17 and 18 and differentiated them from adjacent cortical area 19 laterally and the subadjacent cingulate cortex. The earliest zinc-positive staining in visual cortical areas 17 and 18 was first apparent by postnatal day 2 (P2) and was characterized by staining of a thin layer at the bottom of the cortical plate. By P10, and continuing through P20, synaptic zinc formed a trilaminar pattern of dense staining in areas 17 and 18, which included the top of layer I, and layers III and V. The laminar pattern of synaptic zinc in visual cortex appeared mature by P30, except that the distribution of zinc in layer IV was not uniform. This was most apparent around P50 in tangential sections through layer IV from opened and flattened cortex, where columnar patches of increased zinc staining were apparent in area 17. These columns were approximately 400 microns in diameter, with a centre-to-centre spacing of approximately 900 microns. The distribution of synaptic zinc apparently reflects the process of synaptic maturity of the cat visual cortex and appears to demarcate a particular form of columnar organization in visual cortex.

Distribution of histochemically reactive zinc in the forebrain of the rat

The major cytoarchitectonic regions of the rat brain that stain with the Timm-Danscher metal stain were tested with the fluorescent probe for zinc, 6-methoxy 8-para toluene sulfonamide quinoline (TSQ). Throughout most of the striatum, cerebral cortex and limbic system, the diffuse, even neuropil staining produced by the Timm-Danscher method was mirrored by comparable fluorescence in TSQ-stained sections. Blockade of the TSQ fluorescence by prior treatment with sulphide indicated that the Timm-Danscher and the TSQ procedures both labeled the same pool of endogenous metal, which is inferred to be the zinc that is in axonal boutons. It is concluded that the Timm-Danscher staining generally indicates zinc-containing axonal boutons. The distribution of the zinc-containing axonal boutons throughout the forebrain is described.

Changes in free radicals, trace elements, and neurophysiological function in rats with liver damage induced by D-galactosamine

The changes in trace elements, free radicals, and neurophysiological function were investigated in rats with liver damage induced by D-galactosamine (GalN). The elevated results showed that all the parameters related to free radical metabolism changed after administration of GalN. Relative free radical concentration, malonaldehyde (MDA), and oxidized glutathione (GSSG) elevated, but reduced glutathione (GSH) decreased. Concurrently, zinc, copper, manganese, and selenium contents in liver were significantly reduced, whereas iron was elevated. In rats with hepatic encephalopathy (HE) owing to fulminant hepatic failure (FHF) induced by a high dosage of GalN, the latencies of VEPs were delayed. Moreover, there is a correlation between Zn content of brain and the latencies of VEPs. The results of this study suggested that lipid peroxidation by free radicals might be responsible for GalN-induced liver damage in which trace elements were involved, and that change in brain Zn might play a role in the neural inhibition of HE owing to FHF.

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

Recent methods allow the study of neurons that contain zinc in synaptic vesicles of their boutons (Timm-stainable boutons) by the intravital precipitation (local or throughout the CNS) of the vesicular zinc with selenium compounds and its subsequent retrograde transport to the parent neurons, where the precipitate can be silver enhanced. The present study is a description of the distribution of zinc-containing neurons, their possible connections and their terminal fields within the hippocampal region of the rat. Problems inherent to the methods are addressed. Finally, based on the results and a review of literature, the possible function of zinc in the hippocampal region is considered. Neurons which contain silver-enhanced precipitates were observed in layers II, V and VI of the lateral entorhinal area and in layers V and VI of the medial entorhinal area. In the parasubiculum, labeled cells were seen in layer II/III of the parasubiculum a and in layer V. Labeled cells in the presubiculum were concentrated in layers III and V, in the hippocampal pyramidal cell layer and the dentate granule cell layer, but neurons containing precipitates were largely absent from the subiculum. Zinc-containing axonal boutons defined subpopulations within principal hippocampal neuron populations. Within layer II of the lateral entorhinal cortex and the pyramidal cell layer for regio inferior deeply situated neurons were labeled, whereas superficially placed pyramidal cells were labeled in regio superior. The neuropil staining described in the present study corresponded to that found in earlier studies. However, glial and vascular staining or unspecific background were largely absent, and the neuropil staining could unequivocally be identified light microscopically. Methodological problems are most prominently reflected in unstained mossy fibers in some animals. Based on series from animals treated with decreasing doses of sodium selenite and increased survival times, this problem can be related to small amounts of circulating reactive selenium and a competition of zinc compartments (vesicles) for the selenium. Staining will fail where the competition prevents individual compartments from reaching a threshold amount of zinc precipitate for silver amplification. A guide to evaluate histological material is provided. The distribution of zinc-containing boutons and their cells of origin indicate that zinc-containing and zinc-negative projections are not organized as parallel pathways. The mossy fibers provide an example of a pure zinc-containing pathway. Projections from regio superior to the dorsal presubiculum are likely to be zinc-negative while projections from the same area to the subiculum are zinc-containing.(ABSTRACT TRUNCATED AT 400 WORDS)

Zinc containing projections to the bed nucleus of the stria terminalis

A retrograde tracing method that selectively labels the perikarya of zinc-containing neurons was used to identify the neurons that supply zinc-containing fibers to the bed nucleus of the stria terminalis in the rat. In agreement with prior lesion studies, retrograde tracing indicates that neurons in amygdalar and periamygdalar regions are the major sources of the zinc-containing innervation of the bed nucleus complex. Zinc-containing neurons in the presubiculum and prosubiculum were also retrogradely labeled from the BNST, whereas cells of the subiculum proper did not label. Light and occasional retrograde labeling of some CA1 and CA2 neurons and limbic cortical neurons was also observed, but the possibility of transport from regions bordering BNST injections (septum, caudate-putamen) could not be excluded in the latter cases.

Functional and molecular distinction between recombinant rat GABAA receptor subtypes by Zn2+

gamma-Aminobutyric acid receptor (GABAAR) channels in different neurons display heterogeneous functional properties. Molecular cloning revealed a large number of GABAAR subunits that assemble into GABAAR subtypes with different functional properties, suggesting that the subunit combination determines the functional properties of the receptor. In this study, the subunit composition of GABAARs is related to a functional distinction between Zn2(+)-sensitive and Zn2(+)-insensitive receptor subtypes. GABAARs reconstituted in transiently transfected fibroblasts from combinations of cDNAs encoding alpha and beta subunits are potently blocked by Zn2+. The presence of a gamma subunit in any combination with the other subunits leads to the formation of GABAARs that are almost insensitive to Zn2+. These data provide a structural correlate to the functional heterogeneity of the action of Zn2+ on GABAARs in native membranes and show that Zn2+ insensitivity of GABA-activated currents indicates the presence of a gamma-subunit in the assembled GABAAR channel.

A retrograde transport method for mapping zinc-containing fiber systems in the brain

A method for selectively labeling the CNS neurons that give rise to zinc-containing axonal boutons is described. Focal intracerebral infusions of selenium anions are used to produce a precipitate (presumably ZnSe) in zinc-containing axonal boutons at the injection site, and within 24-48 h, the precipitate is transported to the neurons of origin of those boutons. Silver enhancement is used to render the ZnSe visible in sections prepared for the light or electron microscope. No evidence of retrograde labeling is apparent in neurons that do not contain zinc in their boutons. Thus, the method provides a chemically specific technique for retrograde tracing of zinc-containing pathways in the CNS.

In situ binding of bouton zinc reversibly disrupts performance on a spatial memory task

Neurons with zinc in the presynaptic vesicles innervate much of the telencephalon, but the functional significance of the vesicular zinc has never been established. The present work shows that reversible binding of zinc by drug infusion into the hippocampus produces a time-locked and selective disruption of hippocampal-dependent spatial-working memory. A role for vesicular zinc in neurotransmission or neuromodulation is implied.

Zinc-containing neurons in hippocampus and related CNS structures

Recent advances in metallohistochemistry have substantiated the identification of a distinct class of neurons in the brain, the zinc-containing neurons. These neurons sequester peculiar amounts of zinc in their presynaptic boutons and show both high-affinity uptake and calcium- and impulse-dependent release of the cation. It is thought that the zinc may act to stabilize the storage of certain macromolecules in presynaptic vesicles, but there is also mounting evidence that zinc released from vesicles can produce a broad spectrum of neuromodulatory effects upon target cells. Zinc-containing neurons are found predominantly in limbic and cerebrocortical regions, and a possible role of these neurons in the modification of synaptic strength is considered.

Amygdaloid efferents through the stria terminalis in the rat give origin to zinc-containing boutons

Many regions of the basal forebrain are innervated by zinc-containing axonal boutons. In the present work, the lesion/degeneration method, coupled with histochemical staining for zinc-containing boutons, was used to determine the origins and efferent pathways of these zinc-containing projections to the basal forebrain. Knife cuts of the stria terminalis or extensive electrolytic lesions of the amygdala resulted in the bleaching of the staining for zinc (Timm stain) and terminal degeneration (Fink-Heimer method) ipsilaterally in the following areas: granule cell layer of the accessory olfactory bulb, shell of nucleus accumbens, bed nucleus of the stria terminalis, striohypothalamic nucleus, retrochiasmatic area, ventromedial hypothalamic nucleus (in the cell-sparse shell), medial tuberal nucleus, terete hypothalamic nucleus, and ventral premammillary nucleus. Small lesions made with ibotenic acid in the posteromedial part of the amygdalohippocampal area caused bleaching of the stain for zinc in the accessory olfactory bulb, in the medial zone of the bed nucleus of the stria terminalis, and in the ventral premammillary nucleus. Lesions in either the ventral subiculum or the anterolateral part of the amygdalohippocampal area caused bleaching in the ventromedial hypothalamic nucleus. Lesions in the hippocampus or in the neocortex did not produce bleaching of the stain for zinc in the above-mentioned terminal fields. The present results agree with previous studies on amygdaloid efferents and suggest that neurons in the amygdalohippocampal area and, possibly, in the ventral subiculum give origin to zinc-containing boutons.

Quantitative electron microscopic analysis of postnatal development of zinc-positive nerve endings in the rat amygdala using Timm's sulphide silver technique

The distribution and quantitation of zinc during postnatal development of the rat amygdala were investigated by light and electron microscopy with Timm's sulphide silver method. The adult rat amygdala could be divided into basolateral, basomedial, central, cortical, intercalated, lateral and medial subnuclei on the basis of Timm's plus Toluidine blue staining. Only a very weakly positive Timm's reaction could be observed in newborns, and a positive reaction was seen on the 5th postnatal day. The reaction became stronger with development, and reached adult levels by the 30th postnatal day. Electron microscopically, we investigated the basolateral subnucleus of the amygdala. The electron-dense deposits of silver grains from the Timm's reaction were only seen in nerve fibers endings containing many small clear vesicles. The results are similar to those described for mossy fiber endings in the rat hippocampus and in boutons of other telencephalic structures. The number of deposits of silver grains increased with age, and reached that of the adult between the 20th and 30th postnatal days. A significant increase in the number of silver grains per micron 2 area of the Timm's-positive nerve terminals occurred between the 10th and 20th postnatal days. Based on the available literature, these findings suggest that zinc exists in nerve fiber endings in the rat amygdala and that the amount increases with postnatal age. The findings are consistent with an important role for zinc in synaptic transmission.

Histochemical demonstration of zinc in the hippocampal region of the domestic pig: I. Entorhinal area, parasubiculum, and presubiculum

A detailed description is given of the distribution of zinc in three areas of the domestic pig hippocampal region, viz., the entorhinal area, the parasubiculum, and the presubiculum. Zinc was demonstrated histochemically with use of the Neo-Timm method, a recent modification of the sulphide silver procedure. Each of the studied areas showed a distinctly stratified staining pattern, which has been correlated in detail to fields and layers defined on the basis of cyto- and fibroarchitecture, providing a combined chemo- and cytoarchitectonic map. The staining was primarily confined to the neuropil, although stained nerve cell bodies were encountered in all three parts of the hippocampal region. Two main subfields were identified in the entorhinal area that have been designated pars medialis and pars lateralis, in accordance with their topographical positions, but both the cytoarchitecture and Neo-Timm staining pattern are indicative of further subdivision. In pars medialis, the deep half of layer I, the interstices between the stellate cell bodies in layer II, and layer III were medium to heavily stained, whereas layer IV stained weakly. Layers V-VI were slightly darker than layer IV and were inseparable on the basis of the Neo-Timm staining. The staining of pars lateralis differed in many respects from that of pars medialis, the most conspicuous feature being a much lighter layer III. In the parasubiculum, the deep half of layer I together with layers II-III had the appearance of an intensely stained triangle wedged in between the entorhinal area and the presubiculum. The latter showed moderate staining of the inner half of layer I and posterior part of layer II, while layer IV was stained intensely. Layers III and V-VI exhibited only weak staining. The distribution of zinc in the pig was compared with that in the guinea pig and rat, described previously. Although many histochemical features are shared by the staining patterns of the three species, striking differences exist in the pig, the most notable being the virtually reverse staining of the entorhinal layer IV. The possible functional implications of zinc in synaptic vesicles are considered.

The distribution of zinc in the forebrain and midbrain of the lizard Gekko gecko. A histochemical study

The distribution of zinc in the forebrain and midbrain of the lizard Gekko gecko was studied with the recently modified Timm method. Areas with a high intensity of staining are almost exclusively found in the telencephalon, although also some structures in the diencephalon display notable staining. Cortical areas that stain heavily are the deep zone of the subcortical layer of the small-celled medial cortex, the longitudinal association bundle that encompasses the large-celled medial cortex, and the dorsal cortex. Of the subcortical areas, particularly the anterior septal nucleus shows a high intensity of staining. Moderate to dense Timm staining is further observed in the ventral part of the anterior lateral cortex, the lateral septal nucleus, the striatum, the amygdaloid complex, and the dorsal ventricular ridge. Staining in the diencephalon is primarily confined to the stria terminalis and the ventromedial hypothalamic nucleus, whereas in the midbrain weak staining is observed in the ventral tegmental area and the periventricular layers of the tectum and the tegmentum. The presence of zinc in the gekkonid brain is discussed in relation to connections and neurotransmitters as studied in same species. Moreover, similarities in pattern of staining for zinc in mammals and reptiles and possible evolutionary implications are mentioned.

Evidence from dithizone and selenium zinc histochemistry that perivascular mossy fiber boutons stain preferentially "in vivo"

This paper describes a perivascular staining pattern that is obtained when dithizone or sodium selenite are used to label zinc intravitally. Our observations indicate that the perivascular staining is a result of zinc labeling in mossy fiber boutons adjacent to capillaries and suggest that there might be a special blood brain barrier in the mossy fiber regions.

Zinc-containing fiber systems in the cochlear nuclei of the rat and mouse

Zinc-containing neurons are cells which sequester zinc in the vesicles of their axonal boutons; such zinc-containing fiber systems have been previously shown to innervate many limbic and cerebrocortical brain regions. The present study of rats and mice shows that zinc-containing axons also innervate the cochlear nuclei, forming two morphologically-distinct projection systems. One zinc-containing pathway innervates the molecular stratum of the dorsal nucleus, supplying a diffuse, even band of neuropil staining throughout the stratum. The other pathway projects sparsely to the various small cell (granule cell) regions of the nuclei where the zinc-positive elements form scattered clusters and threads of bouton-like puncta amidst the granule neuron somata. Preliminary observations indicate that the pattern is the same in the cat as in the rat and mouse.

Glutamate and dynorphin release from a subcellular fraction enriched in hippocampal mossy fiber synaptosomes

A procedure is described for the isolation of intact hippocampal mossy fiber synaptosomes. Electron microscopic examination revealed numerous synaptosomal profiles which are clearly of mossy fiber origin, indicated by their large size (2-6 micron diameter) and characteristic morphology. Furthermore, this fraction is enriched in zinc and dynorphin B which appear to be concentrated in mossy fiber terminals in vivo. Synaptosomes isolated by this procedure accumulated 2-deoxyglucose and retained 88% of total lactate dehydrogenase activity after incubation at 30 degrees C for 60 minutes, indicating a high degree of membrane integrity. Oxygen consumption was stimulated 4-fold by veratridine (0.1 mM) and inhibited 90% by ouabain (1 mM), suggesting that synaptosomal metabolism remained tightly coupled to ouabain-sensitive ATPase activity. Potassium-stimulated (45 mM) release of dynorphin B was completely dependent upon the presence of extrasynaptosomal calcium, while only 30% of the evoked release of glutamate was calcium-dependent. D-aspartate, which exchanges glutamate out of the cytoplasmic pool, virtually eliminated the calcium-independent component of glutamate release. This synaptosomal preparation will be useful in identifying the factors that modulate the release of amino acid and opioid neurotransmitters from hippocampal nerve terminals and in the investigation of their presynaptic mechanisms of action.

Loss of zinc staining from hippocampal mossy fibers during kainic acid induced seizures: a histofluorescence study

A quinoline fluorescence method for staining zinc in axonal boutons was used to study the effects of kainic acid (KA) induced seizures upon zinc in the boutons of hippocampal mossy fibers. Compared to untreated rats, rats given KA (10-12 mg/kg) and undergoing sustained seizures showed a marked loss of zinc fluorescence in the mossy fiber regions. The reduced fluorescence was detectable within 3 h of KA administration, was most pronounced at 12-24 h, and was still noticeable up to 48 h after KA. The findings suggest that zinc is released rapidly from mossy fiber boutons during seizures.

Organization of zinc-containing terminal fields in the brain of the lizard Podarcis hispanica: a histochemical study

The Timm method for the histochemical detection of metals defines accurately many terminal fields in the brain of mammals. This pattern is based on the presence of zinc within the synaptic vesicles of some boutons. The aim of this study was to use the Timm method for the anatomical description of the brain in a reptile. In the telencephalon, zinc staining was observed in the inner layer of the medial cortex, the inner and outer layers of both dorsomedial and dorsal cortices, the inner layer of the lateral cortex pars anterior ventralis, the lateral cortex pars profunda, the intermediate and caudal aspects of the anterior dorsal ventricular ridge, the marginal layer and hilus of the nucleus sphericus, the perifascicular nucleus of the accessory olfactory tract, the striatum pars medialis, the olfactory tubercle, the septum pars anterior, and embedded in the fibres of both pallial and anterior commissures. In the diencephalon, staining was observed in the ventromedial hypothalamic nucleus and among the fibers of the stria terminalis. Stained somata and dendrites were observed in the infundibulum. In the mesencephalon and rhombencephalon, sparse staining was observed in the central gray, torus semicircularis, nucleus interpeduncularis, raphe, reticular formation, Purkinje and granular cell layers in the cerebellum, and nucleus cerebellaris medialis. The present results suggest that the histochemical detection of zinc may be a useful method for the accurate definition of terminal fields in the brain of reptiles also. The presence of zinc-containing terminal fields is discussed in relation to the connections and histochemistry in the reptilian brain. Similarities in the pattern of staining for zinc between mammals and reptiles are mentioned.

Zinc neurotoxicity in cortical cell culture

Large amounts of zinc are endogenously present in synaptic vesicles of mammalian central excitatory boutons, and are likely released during synaptic activity; transient elevations in extracellular zinc concentration exceeding several hundred micromolar may accompany intense neuronal excitation. Exposure of mature cortical cell cultures, in mice, to similar concentrations of zinc for several minutes resulted in widespread neuronal injury; the extent of injury was dependent on both the concentration of zinc, and the length of exposure. Quantitative neuronal cell counts suggested an approximate neurotoxic ED50 of 600 microM for a 15 min zinc exposure, and 225 microM for an 18-24 h exposure. High zinc concentrations or long exposure times resulted in the addition of glial injury to the neuronal injury; this glial injury could also be demonstrated in neuron-free glial cell cultures, and hence likely represented a direct effect of zinc rather than a consequence of neuronal injury. Neurons in immature cultures were relatively resistant to zinc-induced injury, suggesting that neuronal vulnerability to zinc increases with maturation in vitro. An early event associated with toxic exposure to zinc was gross neuronal swelling. This swelling was dependent on the presence of extracellular sodium, and, interestingly, could be delayed by the continued presence of zinc itself. Zinc-induced neuronal cell loss, however, occurred even when both sodium and calcium were absent during the exposure to zinc. The present results provide direct evidence that zinc might be a relatively potent, rapidly acting neurotoxin, and somewhat less potent gliotoxin, in the mammalian central nervous system. We suggest that zinc should be included on the growing list of endogenous toxins which may be involved in the acute pathogenesis of central neuronal, and possibly glial, cell loss in some disease states.

A quinoline fluorescence method for visualizing and assaying the histochemically reactive zinc (bouton zinc) in the brain

A histochemical method for staining CNS zinc by the stoichiometric formation of zinc: quinoline fluorescent chelates is described. Four congeners of quinoline have been tested, and two found to be useful for histochemistry. The procedure is a one-step method, suitable for fresh-frozen and fixed tissue sections alike. The quinoline fluorescence selectively labels the CNS regions (such as hippocampus, amygdala) shown by prior histochemical procedures to be rich in histochemically reactive zinc in axon boutons and therefore appears to be a specific marker for the bouton zinc. Microfluorometric data indicate that the fluorochrome can be used for quantitative estimates of CNS zinc pools as well as qualitative studies of localization.

Zinc selectively blocks the action of N-methyl-D-aspartate on cortical neurons

Large amounts of zinc are present in synaptic vesicles of mammalian central excitatory boutons and may be released during synaptic activity, but the functional significance of the metal for excitatory neurotransmission is currently unknown. Zinc (10 to 1000 micromolar) was found to have little intrinsic membrane effect on cortical neurons, but invariably produced a zinc concentration-dependent, rapid-onset, reversible, and selective attenuation of the membrane responses to N-methyl-D-aspartate, homocysteate, or quinolinate. In contrast, zinc generally potentiated the membrane responses to quisqualate or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate and often did not affect the response to kainate. Zinc also attenuated N-methyl-D-aspartate receptor-mediated neurotoxicity but not quisqualate or kainate neurotoxicity. The ability of zinc to specifically modulate postsynaptic neuronal responses to excitatory amino acid transmitters, reducing N-methyl-to-aspartate receptor-mediated excitation while often increasing quisqualate receptor-mediated excitation, is proposed to underlie its normal function at central excitatory synapses and furthermore could be relevant to neuronal cell loss in certain disease states.