Zinc distribution in the brain of Nagase analbuminemic rat and enlargement of the ventricular system

Zinc-containing yeast extract promotes nonrapid eye movement sleep in mice

Zinc is an essential trace element for humans and animals, being located, among other places, in the synaptic vesicles of cortical glutamatergic neurons and hippocampal mossy fibers in the brain. Extracellular zinc has the potential to interact with and modulate many different synaptic targets, including glutamate and GABA receptors. Because of the central role of these neurotransmitters in brain activity, we examined in this study the sleep-promoting activity of zinc by monitoring locomotor activity and electroencephalogram after its administration to mice. Zinc-containing yeast extract (40 and 80 mg/kg) dose dependently increased the total amount of nonrapid eye movement sleep and decreased the locomotor activity. However, this preparation did not change the amount of rapid eye movement sleep or show any adverse effects such as rebound of insomnia during a period of 24 h following the induction of sleep; whereas the extracts containing other divalent cations (manganese, iron, and copper) did not decrease the locomotor activity. This is the first evidence that zinc can induce sleep. Our data open the way to new types of food supplements designed to improve sleep.

Zinc transporter 7 is located in the cis-Golgi apparatus of mouse choroid epithelial cells

The cellular localization of zinc transporter 7 protein in the mouse choroid plexus was examined in this study. Zinc transporter 7 immunoreactive cells were detected in the third, lateral, and fourth ventricles of CD-1 mouse brain. Distinct zinc transporter 7 immunoreactivity was concentrated in the perinuclear regions of the positive cells. The results from zinc autometallography showed that zinc-positive grains were also predominantly located in the perinuclear areas. Ultrastructural localization showed that zinc transporter 7 immunostaining was predominantly present in the membrane and cisternae of the cis-Golgi networks and some vesicle compartments. The results support the notion that zinc transporter 7 may participate in the transport of the cytoplasmic zinc into the Golgi apparatus, and may be involved in local packaging of zinc-binding proteins in the mouse choroid plexus.

[Essential trace metals and brain function]

Trace metals such as zinc, manganese, and iron are necessary for the growth and function of the brain. The transport of trace metals into the brain is strictly regulated by the brain barrier system, i.e., the blood-brain and blood-cerebrospinal fluid barriers. Trace metals usually serve the function of metalloproteins in neurons and glial cells, while a portion of trace metals exists in the presynaptic vesicles and may be released with neurotransmitters into the synaptic cleft. Zinc and manganese influence the concentration of neurotransmitters in the synaptic cleft, probably via the action against neurotransmitter receptors and transporters and ion channels. Zinc may be an inhibitory neuromodulator of glutamate release in the hippocampus, while neuromodulation by manganese might mean functional and toxic aspects in the synapse. Dietary zinc deficiency affects zinc homeostasis in the brain, followed by an enhanced susceptibility to the excitotoxicity of glutamate in the hippocampus. Transferrin may be involved in the physiological transport of iron and manganese into the brain and their utilization there. It is reported that the brain transferrin concentration is decreased in neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease and that brain iron metabolism is also altered. The homeostasis of trace metals in the brain is important for brain function and also for the prevention of brain diseases.

Dynamic zinc pools in mouse choroid plexus

We examined the presence of Zn-transporters (ZnT1, ZnT3, ZnT4, and ZnT6) proteins and zinc ions in rat choroid epithelium with immunohistochemistry and zinc selenide autometallography (ZnSe(AMG)). The four ZnT proteins were all expressed in the choroid epithelial cells. ZnT3 immunostaining was found in vesicle membranes in the apical part of the cells, associated to the microvillus membrane. Correspondingly, the ZnSe(AMG) technique revealed zinc ions in small vesicles, in microvilli, and multivesicular bodies in the epithelial cells. Traceable zinc ions were also found in lysosome-like organelles of fenestrated endothelial cells, but here no corresponding ZnT3 immunostaining was seen. The observations suggests that the choroid plexus is instrumental to regulation of the level of zinc ions in the cerebrospinal fluid.

65Zn localization in rat brain after intracerebroventricular injection of 65Zn-histidine

Previous studies have shown that 65Zn uptake in the brain expressed relative to plasma 65Zn level is enhanced by histidine infusion into the blood vessel. To study the effect of histidine on zinc uptake in the brain parenchyma via the CSF, the brains of rats injected intracerebroventricularly with 65Zn-His were subjected to autoradiography. Six days after injection, the radioactivity from 65Zn-His was distributed in the major part of the brain parenchyma higher than that from 65ZnCl(2), and relatively concentrated in the hippocampal formation, globus pallidus and hypothalamus. The radioactivity of the aqueduct was also higher in the 65Zn-His group, indicating that CSF clearance of the 65Zn-His group may be lower than that of the 65ZnCl(2) group. These results suggest an enhancement by histidine on zinc uptake in the brain parenchyma via the CSF.

109Cd transport in rat brain

The brain distribution of 109CdCl2 following administration into either the tail vein, the lateral ventricle or the olfactory bulb was studied to clarify permeability of the brain barrier system to cadmium (Cd) and Cd movement in the cerebrospinal fluid (CSF) and the brain extracellular fluid. One hour after intravenous (i.v.) injection, 109Cd was largely concentrated in the choroid plexus, and 109Cd concentration in the major part of the brain parenchyma, except for the circumventricular organs such as the pineal gland and the regions around them, was low. Six days after i.v. injection, 109Cd concentration in the choroid plexus was still high, and 109Cd was also detected highly in the pineal gland and small part around the median eminence. 109Cd concentration in the major part of the brain parenchyma was decreased in parallel with that in the blood. In the case of injection of 109CdCl2 into the lateral ventricle, a large portion of 109Cd was detected in the ventricular system 6 days after injection, and 109Cd concentration in the major part of the brain parenchyma was less than the detection limit. These results suggest that Cd cannot easily get into the brain and is blocked not only by the blood- brain and the blood-CSF barriers, but also by the ependymal and pial surfaces. In the case of injection of 109CdCl2 into the olfactory bulb, a large portion of 109Cd was detected in the injected area 24 h after injection, and, the next 24 h later, 109Cd distribution in the brain was not changed appreciably. These results suggest that Cd cannot easily move in the brain extracelular space, and is taken up into the brain parenchyma.

Release of zinc from the brain of El (epilepsy) mice during seizure induction

Brain distribution after i.v. injection of 65ZnCl2 into El mice, an animal model of genetically determined epilepsy, was studied by autoradiography to study the utilization of zinc in the brain. The distribution of 65Zn in the brain of El mice 6 days after injection was almost the same as that of ddY (normal) mice, suggesting that the uptake of zinc by the brain of El mice is normal. To study the movement of zinc in the brain in the course of seizure induction, the concentrations of 65Zn in the brain of seizure-afflicted and untreated control El mice were compared 20 days after 65Zn injection. The concentration of 65Zn in the brain of seized El mice was overall lower than that of control El mice; the concentration of 65Zn was decreased notably in the piriform cortex and amygdaloid nuclei complex during convulsion. These results suggest that the release of zinc from the El mouse brain is enhanced during convulsion. The decrease in actively functioning zinc in the brain may be associated with the increase in susceptibility to seizure in the El mouse.