Alterations in serum and brain trace element levels after antidepressant treatment

We have studied the effect of chronic treatment with imipramine, citalopram and electroconvulsive shock (ECS) on serum and brain zinc levels in rats. Chronic treatment with citalopram (but not with imipramine or ECS) significantly (approx 20%) increased the serum zinc level. Chronic treatment with both drugs slightly (by approx 10%) increase the zinc level in the hippocampus and slightly decreased it in the cortex, cerebellum and basal forebrain. Calculation of the ratio hippocampus/brain region within each group demonstrated a significantly (approx 20%) higher value after treatment with either imipramine or citalopram. Moreover, chronic ECS induced a significant increase (by 30%) in the zinc level in the hippocampus and also a slight increase (by 11–15%) in the other brain regions. Thus, these different antidepressant therapies induced an elevation of the hippocampal zinc concentration, which indicates a significant role of zinc in the mechanism of antidepressant therapy.     

Ultrasonic neuromodulation by brain stimulation with transcranial ultrasound

Brain stimulation methods are indispensable to the study of brain function. They have also proven effective for treating some neurological disorders. Historically used for medical imaging, ultrasound (US) has recently been shown to be capable of noninvasively stimulating brain activity. Here we provide a general protocol for the stimulation of intact mouse brain circuits using transcranial US, and, using a traditional mouse model of epilepsy, we describe how to use transcranial US to disrupt electrographic seizure activity. The advantages of US for brain stimulation are that it does not necessitate surgery or genetic alteration, but it confers spatial resolutions superior to other noninvasive methods such as transcranial magnetic stimulation. With a basic working knowledge of electrophysiology, and after an initial setup, ultrasonic neuromodulation (UNMOD) can be implemented in less than 1 h. Using the general protocol that we describe, UNMOD can be readily adapted to support a broad range of studies on brain circuit function and dysfunction.     

Zinc homeostasis and functions of zinc in the brain

The brain barrier system, i.e., the blood-brain and blood-cerebrospinal fluid barriers, is important for zinc homeostasis in the brain. Zinc is supplied to the brain via both barriers. A large portion of zinc serves as zinc metalloproteins in neurons and glial cells. Approximately 10% of the total zinc in the brain, probably ionic zinc, exists in the synaptic vesicles, and may serve as an endogenous neuromodulator in synaptic neurotransmission. The turnover of zinc in the brain is much slower than in peripheral tissues such as the liver. However, dietary zinc deprivation affects zinc homeostasis in the brain. Vesicular zinc-enriched regions, e.g., the hippocampus, are responsive to dietary zinc deprivation, which causes brain dysfunctions such as learning impairment and olfactory dysfunction. Olfactory recognition is reversibly disturbed by the chelation of zinc released from amygdalar neuron terminals. On the other hand, the susceptibility to epileptic seizures, which may decrease vesicular zinc, is also enhanced by zinc deficiency. Therefore, zinc homeostasis in the brain is closely related to neuronal activity. Even in adult animals and probably adult humans, adequate zinc supply is important for brain functions and prevention of neurological diseases.     

Influence of maternal dietary zinc intake on in vitro tubulin polymerization in fetal rat brain

The hypothesis that one of the biochemical lesions underlying zinc deficiency-induced teratogenicity is altered microtubule formation was tested. Day 19 fetuses from zinc-deficient Sprague-Dawley dams were characterized by low brain supernate zinc concentrations and slow brain tubulin polymerization rates compared to controls. Brain supernate tubulin and protein concentrations were similar in zinc-deficient and control fetuses. In vitro brain tubulin polymerization rates were increased following addition of zinc to either control or zinc-deficient brain supernates; however, the stimulatory effect of added zinc on polymerization was significantly higher in brain supernates obtained from zinc-deficient fetuses compared to controls. These results support the idea that one effect of fetal zinc deficiency is a reduction in tubulin polymerization, which in turn may result in altered microtubule function.     

Zinc in taste function

Zinc has been associated with taste function in humans at several levels of organization—the taste bud, the nerves transmitting taste information, and the brain. Zinc plays specific yet varied roles at each organizational level, although many of these roles have not been clearly identified. They include participation in the structural architecture of the cell, maintenance of cell membrane integrity, and control of activity of several cytoplasmic and membrane enzymes. Early investigators noted that some patients given drugs that altered zinc metabolism or who experienced disease processes associated with abnormalities of zinc metabolism exhibited taste dysfunction. Because of these findings zinc was given to a variety of patients as treatment for taste dysfunction. Initial treatment success was observed, but was quickly tempered by more extensive studies that yielded widely variable results leading to confusion about the role of zinc in both taste function and taste treatment. Further studies revealed that taste disorders were diverse and complex with multiple underlying pathophysiologies that were little understood. Subsequent work by several investigators revealed that patients with zinc deficiency, of any etiology, exhibited taste dysfunction and that treatment of these patients with zinc usually produced improvement of clinical symptoms. These results raised the question of how to define zinc deficiency, for zinc treatment in patients without zinc deficiency was unsuccessful and these patients represent more than three-quarters of all patients with taste dysfunction. New clinical techniques for the definition of human zinc deficiency have been achieved through the use of binding and displacement of⁶⁵Zn on specific sites on erythrocyte membranes; these results offer a guide to the identification of patients (i.e., those with zinc deficiency) who may benefit from zinc treatment.     

Effects of marginal zinc deficiency on microtubule polymerization in the developing rat brain

One of the possible mechanisms that has been proposed to underlie the deleterious effects of zinc deficiency on brain development is an impairment in the normal formation of the cytoskeletal network. In the current study, in vivo microtubule polymerization was characterized in brain supernatant fluids, from 20-d-old pups whose dams were fed diets containing control (50 micrograms zinc/g) or marginal levels of zinc (10 micrograms zinc/g) throughout pregnancy and lactation. Pup brain and body weights were similar between the groups; however, plasma zinc concentrations were lower (27%) in pups fed the marginal zinc diet than in controls. Tubulin concentrations in 100,000 g brain supernates were similar between the groups; however, tubulin polymerization in the brain supernates was significantly lower in pups fed the marginal zinc diet compared to controls. Primarily, the early events of polymerization were affected; the lag period of the reaction was doubled, and the initial velocity was slower (26%) in supernates from pups fed the marginal zinc diet than in controls. These findings support the idea that some of the negative effects of marginal zinc deficiency on brain development and function may be mediated by an alteration in microtubule formation.     

The importance of boron nutrition for brain and psychological function

Boron (B) nutriture has been related to bone, mineral and lipid metabolism, energy utilization, and immune function. As evidence accumulates that B is essential for humans, it is important to consider possible relationships between B nutriture and brain and psychological function. Five studies conducted in our laboratory are reviewed. Assessments of brain electrical activity in both animals and humans found that B deprivation results in decreased brain electrical activity similar to that observed in nonspecific malnutrition. Assessments of cognitive and psychomotor function in humans found that B deprivation results in poorer performance on tasks of motor speed and dexterity, attention, and short-term memory. However, little support was found for anecdotal reports that supplementation with physiologic amounts of B helps alleviate the somatic and psychological symptoms of menopause. Parallels between nutritional and toxicological effects of B on brain and psychological function are presented, and possible biological mechanisms for dietary effects are reviewed. Findings support the hypothesis that B nutriture is important for brain and psychological function in humans. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable. The US Department of Agriculture, Agricultural Research Service, Northern Plains Area, is an equal opportunity/affirmative action employer, and all agency services are available without discrimination.     

Zinc deficiency decreases the activity of calmodulin regulated cyclic nucleotide phosphodiesterases in vivo in selected rat tissues

The effect of zinc deficiency on calmodulin function was investigated by assessing the in vivo activity of two calmodulin regulated enzymes, adenosine 3′,5′-monophosphate (c-AMP) and guanosine 3′,5′-monophosphate (c-GMP) phosphodiesterase (PDE) in several rat tissues. Enzymatic activities in brain, heart, and testis of rats fed a zinc deficient diet were compared with activities in these tissues from pair fed, zinc supplemented rats. In testis, a tissue in which zinc concentration decreased with zinc deficient diet, enzyme activities were significantly decreased over those in rats who were pair fed zinc supplemented diets. In brain and heart, tissues in which zinc concentrations did not change with either diet, enzymatic activities between the groups were not different. These results indicate that zinc deficiency influences the activity of calmodulin-regulated phosphodiesterases in vivo supporting the hypothesis that zinc plays a role in calmodulin function in vivo in zinc sensitive tissues.     

Interactions between carnosine and zinc and copper: implications for neuromodulation and neuroprotection

This review examines interactions in the mammalian central nervous system (CNS) between carnosine and the endogenous transition metals zinc and copper. Although the relationship between these substances may be applicable to other brain regions, the focus is on the olfactory system where these substances may have special significance. Carnosine is not only highly concentrated in the olfactory system, but it is also contained in neurons (in contrast to glia cells in most of the brain) and has many features of a neurotransmitter. Whereas the function of carnosine in the CNS is not well understood, we review evidence that suggests that it may act as both a neuromodulator and a neuroprotective agent. Although zinc and/or copper are found in many neuronal pathways in the brain, the concentrations of zinc and copper in the olfactory bulb (the target of afferent input from sensory neurons in the nose) are among the highest in the CNS. Included in the multitude of physiological roles that zinc and copper play in the CNS is modulation of neuronal excitability. However, zinc and copper also have been implicated in a variety of neurologic conditions including Alzheimer's disease, Parkinson's disease, stroke, and seizures. Here we review the modulatory effects that carnosine can have on zinc and copper's abilities to influence neuronal excitability and to exert neurotoxic effects in the olfactory system. Other aspects of carnosine in the CNS are reviewed elsewhere in this issue.     

The Presence of Zinc-Binding Proteins in Brain

Abstract: Zinc is one of the most abundant divalent metal ions in the brain, its concentration being greater than those of copper and manganese. Since free zinc ion is a potent inhibitor of sulfhydryl enzymes, we postulated that zinc in the brain most probably exists bound to macromolecules. As zinc-binding proteins in brain have not been characterized, we attempted to discover the occurrence and properties of these proteins. By using Sephadex G-75 column chromatography calibrated with proteins of known molecular weights, and by other techniques, we detected separate zinc-binding proteins, with apparent estimated molecular weights ranging from 15,000 to 210,000. Unlike the hepatic or renal zinc thioneins, the zinc-binding proteins in brain are not inducible following administration of zinc. Our interpretation of the results is that the major portion of the existing zinc in the brain is bound, and does not exist in free form.     

Effect of dietary zinc deficiency on brain metallothionein-I and -III mRNA levels during stress and inflammation

Zinc is an essential heavy metal for the normal function of the central nervous system (CNS), but the knowledge of its metabolism and functions is scarce. In this report we have studied the effect of a zinc deficient diet on the regulation of brain metallothioneins (MTs). In situ hybridization analysis revealed that brain MT-I induction by restraint stress was significantly blunted in some but not all brain areas in the mice fed the zinc deficient diet compared to normally fed mice. In contrast, brain MT-I induction by the administration of bacterial lipopolysaccharide (LPS) was not significantly lower in the mice fed the zinc deficient diet. In contrast to MT-I, MT-III mRNA levels were minimally affected by either stress or LPS. Yet, significant decreasing effects of the zinc deficient diet were observed in areas such as the neocortex, CA1-CA3 neuronal layer and dentate gyrus of the hippocampus, and the Purkinje neuronal layer of the cerebellum. These results demonstrate that dietary zinc deficiency impairs the response of brain MTs during both stress and LPS-elicited inflammatory response in a highly specific manner.     

Zinc in maturing rat brain: hippocampal concentration and localization

—Alterations in the localization and concentration of zinc in the hippocampus and in other regions of rat brain were studied during postnatal maturation. Histochemical observations indicated increasing levels of zinc in the hippocampal mossy fibre layer at about 20 days of age. Between 18 and 22 days, hippocampal levels of zinc increased by 35 per cent to reach adult levels (121 ng/mg of protein). After subcellular fractionation, more than one-half of the hippocampal zinc was found in the first pellet (P₁; 1085 g– 10 min), where large boutons would be expected. Autoradiographic evidence, revealing the sequential location of positron tracks first in the granular cell layer and later in the mossy fibre layer, raises the possibility of axoplasmic transport of zinc from granule cell perikarya to their terminal boutons. Our data suggest that zinc may be involved in the maturation and function of the mossy fibre pathway.     

Effects of zinc on SN56 cholinergic neuroblastoma cells

Zinc is a trace element necessary for proper development and function of brain cells. However, excessive accumulation of zinc exerts several cytotoxic effects in the brain. The aim of this work was to see whether cytotoxic effects of zinc are quantitatively correlated with changes in acetyl-CoA metabolism. The zinc levels up to 0.20 mmol/L caused concentration-dependent inhibition of pyruvate dehydrogenase (PDH) activity that correlated with the increase in trypan blue-positive fraction and the decrease in cultured cell number (r = 0.96, p = 0.0001). Chronic exposure of cells to 0.15 mmol/L zinc decreased choline acetyltransferase and aconitase activities, cytoplasmic acetyl-CoA and whole cell ATP level by 38%, 57%, 35%, and 62%, respectively but caused no change in mitochondrial acetyl-CoA level and activities of other enzymes of glycolytic and tricarboxylic acid cycle. dl-alpha-lipoamide when added simultaneously with zinc to cultured cells or their homogenates attenuated its chronic or acute suppressive effects. In homogenates of chronically Zn-treated cells, lipoamide overcame PDH but not aconitase inhibition. Presented data indicate that acute-transient elevation of zinc caused reversible inhibition of PDH, aconitase activities and acetyl-CoA metabolism, which when prolonged could lead to irreversible enzyme inactivation yielding decrease in cell viability and secondary suppression of their cholinergic phenotype.     

Zinc protection against lipid peroxidation from cadmium.

Effect of zinc and cadmium on lipid peroxidation and catalase activity in liver, heart, brain and testis was determined in order to characterise the interaction of zinc with cadmium. Zinc and cadmium both increased lipid peroxidation significantly in the tissues studied. In animals pretreated with zinc prior to cadmium administration, significant decrease in lipid peroxidation in liver was observed. Lipid peroxidation was not affected significantly in testis but a significant increase was observed in heart and brain tissues. Catalase activity in testis increased significantly by zinc treatment with or without cadmium administration.     

Isolation of GIF from porcine brain and studies of its zinc transfer kinetics with apo-carbonic anhydrase

Neuronal growth inhibitory factor (GIF) of porcine brain, was isolated and purified by a similar procedure which was used on the isolation of human and bovine GIF. The native porcine protein with stoichiometry of 4Cu⁺, 3Zn²⁺ was obtained for the first time. The kinetics of zinc transfer from Cu₄Zn₃MT-3 to apo-carbonic anhydrase were studied, and zinc transfer rate constants and thermodynamic parameters were obtained. It is found that like other MTs, porcine Cu₄Zn₃MT-3 can also transfer its zinc atom to apoCA, even much easier than other MTs. A possible association mechanism has been proposed, the formation of Cu₄Zn₃MT3-apoCA complex may be the rate-determining step. The obtained data indicate besides its neuronal growth inhibitory function, GIF might play a role in cellular Zn homeostasis in brain.     

Direct visualization of mitochondrial zinc accumulation reveals uniporter-dependent and -independent transport mechanisms

Current evidence suggests that zinc kills neurons by disrupting energy production, specifically by inhibiting mitochondrial function. However it is unclear if the inhibitory effect requires zinc accumulation, and if so, precisely how zinc enters mitochondria. Here, using fluorescence microscopy to visualize individual rat brain mitochondria, we detected matrix zinc uptake using the fluorophore FluoZin-3. Fluorescence increased rapidly in mitochondria treated with micromolar free zinc, and was quickly returned to baseline by membrane permeant chelation. Zinc uptake occurred through the calcium uniporter, because depolarization or uniporter blockade reduced fluorescence changes. However, increased fluorescence under these conditions suggests that zinc can enter through a uniporter-independent pathway. Fluorescence steadily declined over time and was unaffected by acidification or phosphate depletion, suggesting that zinc precipitation is not a mechanism for reducing matrix zinc. Uniporter blockade with ruthenium red also did not change the rate of zinc loss. Instead, zinc appears to exit the matrix through a novel efflux pathway not yet identified. Interestingly, dye-loaded mitochondria showed no fluorescence increase after treatment with strong oxidants, arguing against oxidant-labile intra-mitochondrial zinc pools. This study is the first to directly demonstrate zinc accumulation in individual mitochondria and provides insight about mechanisms mediating mitochondrial zinc uptake and efflux.     

Maternal hair zinc concentration in neural tube defects in Turkey

Hair zinc concentration was measured in samples taken from 57 mothers who delivered infants with neural tube defects (NTD) (mainly anencephaly). Control groups consisted of 30 healthy mothers with normal offspring and 37 nonpregnant women from middle-income backgrounds. Zinc concentration was also measured in the hair of eight infants with NTD (four being anencephalic). The mean maternal hair zinc concentration in the NTD group (128.2 +/- 38.9 micrograms/g) was lower than that of the control women (p less than 0.001), whereas the mean hair zinc level of malformed babies (250.4 +/- 85.2 micrograms/g) was significantly higher than that of normal infants (193.4 +/- 39.2 micrograms/g) (p less than 0.05). Maternal nutritional zinc deficiency was thought to be one of the factors responsible for NTD in Turkey.