Oral toxicity of silver ions, silver nanoparticles and colloidal silver--a review

Orally administered silver has been described to be absorbed in a range of 0.4-18% in mammals with a human value of 18%. Based on findings in animals, silver seems to be distributed to all of the organs investigated, with the highest levels being observed in the intestine and stomach. In the skin, silver induces a blue-grey discoloration termed argyria. Excretion occurs via the bile and urine. The following dose-dependent animal toxicity findings have been reported: death, weight loss, hypoactivity, altered neurotransmitter levels, altered liver enzymes, altered blood values, enlarged hearts and immunological effects. Substantial evidence exists suggesting that the effects induced by particulate silver are mediated via silver ions that are released from the particle surface. With the current data regarding toxicity and average human dietary exposure, a Margin of Safety calculation indicates at least a factor of five before a level of concern to the general population is reached.

A developmental study of serotonin-immunoreactive neurons in the embryonic brain of the marbled crayfish and the migratory locust: evidence for a homologous protocerebral group of neurons

It is well established that the brains of adult malacostracan crustaceans and winged insects display distinct homologies down to the level of single neuropils such as the central complex and the optic neuropils. We wanted to know if developing insect and crustacean brains also share similarities and therefore have explored how neurotransmitter systems arise during arthropod embryogenesis. Previously, Sintoni et al. (2007) had already reported a homology of an individually identified cluster of neurons in the embryonic crayfish and insect brain, the secondary head spot cells that express the Engrailed protein. In the present study, we have documented the ontogeny of the serotonergic system in embryonic brains of the Marbled Crayfish in comparison to Migratory Locust embryos using immunohistochemical methods combined with confocal laser-scan microscopy. In both species, we found a cluster of early emerging serotonin-immunoreactive neurons in the protocerebrum with neurites that cross to the contralateral brain hemisphere in a characteristic commissure suggesting a homology of this cell cluster. Our study is a first step towards a phylogenetic analysis of neurotransmitter system development and shows that, as for the ventral nerve cord, traits related to neurogenesis in the brain can provide valuable hints for resolving the much debated question of arthropod phylogeny.

Chlorophenylpiperazine analogues as high affinity dopamine transporter ligands

Selective σ2 ligands continue to be an active target for medications to attenuate the effects of psychostimulants. In the course of our studies to determine the optimal substituents in the σ2-selective phenyl piperazines analogues with reduced activity at other neurotransmitter systems, we discovered that 1-(3-chlorophenyl)-4-phenethylpiperazine actually had preferentially increased affinity for dopamine transporters (DAT), yielding a highly selective DAT ligand.

Rome III functional constipation and irritable bowel syndrome with constipation are similar disorders within a spectrum of sensitization, regulated by serotonin

BACKGROUND & AIMS

Patients with irritable bowel syndrome with constipation (IBS-C) and patients with functional constipation (FC) have similar symptoms, and these disorders overlap in their diagnostic features. Little is known about their overlap in physiology or the involvement of serotonin signaling. We investigated relationships between platelet-depleted plasma concentrations of serotonin, gastrointestinal symptoms, and motor-sensory function in patients with FC or IBS-C compared with healthy volunteers (controls).

METHODS

We measured platelet-depleted plasma concentrations of serotonin in fasting and fed individuals with IBS-C (n = 23; 19-50 years old), FC (n = 11; 25-46 years old), and controls (n = 23; 20-49 years old) recruited in Manchester, UK. We also quantified abdominal and bowel-related symptoms, rectal sensitivity, oro-cecal transit, and colonic (whole intestine) transit.

RESULTS

Patients with IBS-C or FC had similar baseline symptoms, bowel habits, oro-cecal and colonic transit, and fasting concentrations of serotonin and response to meal ingestion. Only patients with IBS-C had increased symptoms after ingestion of a meal (P < .001)-these patients tended to have lower sensory thresholds than patients with FC. Defecation frequency in the combined group of patients with IBS-C or FC correlated inversely with serotonin concentration (r = -0.4; P = .03). Serotonin concentration also correlated with pain threshold (r = 0.4; P = .02) and stool threshold (r = 0.5; P = .06), which correlated inversely with defecation frequency (r = -0.3; P = .10).

CONCLUSIONS

FC and IBS-C, based on Rome III criteria, are not distinct disorders, symptomatically or physiologically. Instead, they appear to lie in a spectrum of visceral sensitivity modulated by serotonin signaling. Symptom response to meal ingestion should be considered in patient classification.

Regulation of embryonic neurotransmitter and tyrosine hydroxylase protein levels by ascorbic acid

SCOPE

Ascorbic acid (ascorbate) is required to recycle tetrahydrobiopterin, which is necessary for neurotransmitter synthesis by the rate-limiting enzymes tyrosine and tryptophan hydroxylases. We sought to determine whether ascorbate might regulate embryonic brain cortex monoamine synthesis utilizing transgenic mouse models with varying intracellular ascorbate levels.

METHODS AND RESULTS

In embryos lacking the sodium-dependent vitamin C transporter 2 (SVCT2), very low levels of brain ascorbate decreased cortex levels of norepinephrine and dopamine by approximately 33%, but had no effect on cortex serotonin or its metabolite, 5-hydroxyindole acetic acid. This decrease in ascorbate also led to a decrease in protein levels of tyrosine hydroxylase, but not of tryptophan hydroxylase. Increased cortex ascorbate in embryos carrying extra copies of the SVCT2 resulted in increased levels of dopamine and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), as well as serotonin and 5-hydroxyindole acetic acid.

CONCLUSION

The dependence of embryonic brain cortex neurotransmitter synthesis and tyrosine hydroxylase expression on intracellular ascorbate emphasizes the importance of receiving adequate ascorbate during development.

Interactive effects of hypoxia with estradiol-17β on tryptophan hydroxylase activity and serotonin levels in the Atlantic croaker hypothalamus

Hypoxia causes a marked decline in reproductive neuroendocrine function in Atlantic croaker due to decreases in the hypothalamic expression and activities of tryptophan hydroxylase (TPH, the rate limiting enzyme in serotonin synthesis) and aromatase. In the present study, the influence of the estrogen status on hypothalamic TPH and serotonin (5-HT) regulation by hypoxia (dissolved oxygen: 1.7 mg/L for 4 weeks) was investigated in croaker. Treatment in vivo with the aromatase inhibitor, ATD (1,4,6-androstatrien-3,17-dione), significantly decreased TPH activity, TPHs (TPH-1 and TPH-2) mRNAs expression, and 5-hydroxytryptophan (5-HTP, an immediate precursor of 5-HT) and 5-HT contents in croaker hypothalamus. Treatment with estradiol-17β partially restored hypothalamic TPH activity, TPHs mRNA expression, and 5-HTP and 5-HT contents in hypoxia-exposed fish. These results suggest that the hypoxia-induced inhibition of TPH and 5-HT synthesis is dependent on the estrogen status. To our knowledge, this is the first report of a role for estrogens in modulating neural TPH and 5-HT responses to hypoxia in aquatic vertebrates.

Disruption of oral sensory relay to brain increased anxiety- and depression-like behaviours in rats

OBJECTIVE

Sensory information plays an important role to determine psycho-emotional behaviours of individuals. Lingual nerve can be damaged by dental surgery or trauma, such as physical irritation, radiation, chemotherapy, or viral infection. This study was conducted to examine the psycho-emotional effects of lingual nerve damage in which oral sensory relay to the brain is disrupted.

DESIGN

Male Sprague-Dawley rats were tested for anxiety and depression-related behaviours after bilateral transections of the lingual and chorda tympani nerves (Nx) or sham operation. Tissue contents of serotonin and its metabolite in the hippocampus, hypothalamus, and nucleus accumbens were analyzed by high-performance liquid chromatography.

RESULTS

Sucrose preference was reduced in Nx rats compared with sham rats, suggesting the development of anhedonia, decreased pleasure seeking behaviour, by the lingual nerves transection. Ambulatory activity was decreased, anxiety-related behaviours during the activity test increased, time spent in the open arms during elevated plus maze test decreased, and immobility duration during forced swim test increased in Nx rats compared with sham rats. Serotonin level in the hippocampus of Nx rats was decreased significantly compared with sham rats.

CONCLUSIONS

Results suggest that aberration of oral sensory relay to brain may lead to the development of depression- and anxiety-related disorders, and decreased serotonergic neurotransmission in the hippocampus may play a role in its underlying mechanism.

Effects of the insecticide fipronil on reproductive endocrinology in the fathead minnow

Gamma-aminobutyric acid (GABA) and GABA receptors play an important role in neuroendocrine regulation in fish. Disruption of the GABAergic system by environmental contaminants could interfere with normal regulation of the hypothalamic-pituitary-gonadal axis, leading to impaired fish reproduction. The present study used a 21-d fathead minnow (Pimephales promelas) reproduction assay to investigate the reproductive toxicity of fipronil (FIP), a broad-spectrum phenylpyrazole insecticide that acts as a noncompetitive blocker of GABA receptor-gated chloride channels. Continuous exposure up to 5 µg FIP/L had no significant effect on most of the endpoints measured, including fecundity, secondary sexual characteristics, plasma steroid and vitellogenin concentrations, ex vivo steroid production, and targeted gene expression in gonads or brain. The gonad mass, gonadosomatic index, and histological stage of the gonad were all significantly different in females exposed to 0.5 µg FIP/L compared with those exposed to 5.0 µg FIP/L; however, there were no other significant effects on these measurements in the controls or any of the other treatments in either males and females. Overall, the results do not support a hypothesized adverse outcome pathway linking FIP antagonism of the GABA receptor(s) to reproductive impairment in fish.

Neurotransmitter-mediated control of neurogenesis in the adult vertebrate brain

It was long thought that no new neurons are added to the adult brain. Similarly, neurotransmitter signaling was primarily associated with communication between differentiated neurons. Both of these ideas have been challenged, and a crosstalk between neurogenesis and neurotransmitter signaling is beginning to emerge. In this Review, we discuss neurotransmitter signaling as it functions at the intersection of stem cell research and regenerative medicine, exploring how it may regulate the formation of new functional neurons and outlining interactions with other signaling pathways. We consider evolutionary and cross-species comparative aspects, and integrate available results in the context of normal physiological versus pathological conditions. We also discuss the potential role of neurotransmitters in brain size regulation and implications for cell replacement therapies.

Fundamental research progress of mild hypothermia in cerebral protection

Through the years, the clinical application of mild hypothermia has been carried out worldwide and is built from the exploration and cognition of neuroprotection mechanisms by hypothermia. However, within the last decade, extensive and fundamental researches in this area have been conducted. In addition to aspects of the previous findings, scholars have discovered several new contents and uncertain results. This article reviews and summarizes this decade’s progression of mild hypothermia in lowering the cerebral oxygen metabolism, protecting the blood–brain-barrier, regulating the inflammatory response, regulating the excessive release of neurotransmitters, inhibiting calcium overload, and reducing neuronal apoptosis. In many aspects, particularly in regulating inflammatory reverse reaction, various results have been reported and therefore guide scholars to conduct more detailed analysis and investigation in order to discover the inherent theories surrounding the effect of mild hypothermia, and for better clinical services.

Surface modified fluorescent quantum dots with neurotransmitter ligands for potential targeting of cell signaling applications

The possibility of combining nanotechnology with nanomedicine opens a broad field of research which may truly revolutionize our society. The neural system plays a crucial role in the human body, and most related diseases can dramatically change the quality of life. Thus, the present study reports a novel approach for using neurotransmitters as ligands in the synthesis of surface-modified fluorescent nanocrystals for potential use in cell labeling applications. Briefly, CdS quantum dots (QDs) were prepared using L-glutamic and L-aspartic as surface capping agents via a one-step chemical processing method, which resulted in stable aqueous colloidal systems at room temperature and ambient pressure. UV-visible spectroscopy, photoluminescence spectroscopy (PL), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM) were used to characterize the synthesis and relative stability of peptide-capped CdS nanocrystals. The results demonstrate that both ligands were effective in nucleating and stabilizing CdS quantum dots in colloidal aqueous suspensions, with an estimated dimension below 3.3 nm and with fluorescence activity. Thus, novel nanohybrids were developed based on QDs bioconjugated to surface-active neurotransmitter moieties suitable for investigation as potential biomarkers in cell targeting and signaling applications.

The neurobiology of suicide - A Review of post-mortem studies

The neurobiology of suicidal behaviour, which constitutes one of the most serious problems both in psychiatry and general medical practice, still remains to a large degree unclear. As a result, scientists constantly look for new opportunities of explaining the causes underlying suicidality. In order to elucidate the biological changes occurring in the brains of the suicide victims, studies based on post-mortem brain tissue samples are increasingly being used. These studies employ different research methods to provide an insight into abnormalities in brain functioning on various levels, including gene and protein expression, neuroplasticity and neurotransmission, as well as many other areas. The aim of this paper to summarize the available data on the post-mortem studies, to provide an overview of main research directions and the most up-to-date findings, and to indicate the possibilities of further research in this field.

Colonic enteric nervous system analysis during parenteral nutrition

INTRODUCTION

Parenteral nutrition (PN) is a necessary therapy used to feed patients with gastrointestinal dysfunction. Unfortunately, PN results in intestinal atrophy and changes to host immune function. PN may also induce additional effects on gut motility that we hypothesized would result from changes in the enteric nervous system.

METHODS

Mice received an intravenous (i.v.) catheter and were randomized to chow (n = 5), i.v. PN (n = 6), or i.v. PN + bombesin (BBS, 15 μg/kg, 3×/d) (n = 6) for 5 d. Colons were removed and dissected to measure the length and circumference. Enteric neuronal density and neurotransmitter expression were determined by co-immunostaining whole-mount tissue with Hu and neuronal nitric oxide synthase (nNOS).

RESULTS

The number of myenteric neurons expressing Hu and nNOS increased per unit length in the mid-colon during PN treatment compared with chow. This increase was abrogated by the addition of BBS to the PN regimen. However, the percentage of nNOS-expressing neurons was not significantly altered by PN. Morphometric analysis revealed a decrease in the length and circumference of the colon during PN administration that was partially normalized by supplementation of PN with BBS. A significant reduction in total fecal output was observed in PN animals compared with chow and was increased by mice receiving BBS in addition to PN.

CONCLUSIONS

PN causes a constriction of the bowel wall, reducing not only the length but also the circumference of the colon. These changes cause a condensation of enteric neurons but no difference in neurotransmitter expression. BBS supplementation partially restores the constriction and increases the fecal output during PN treatment compared with PN treatment alone.

Advances in research on mechanism of Chinese medicine treatment of functional constipation

Functional constipation is a common disease affecting patients' health and quality of life. Chinese medicine has certain advantages in the treatment of functional constipation. In this article we review the literature and summarize the mechanisms on Chinese medicine treatment of functional constipation. Main mechanisms include lubricating the intestinal tract and increasing intestinal contents, promoting gastrointestinal motility and defecation, increasing the number of interstitial cells of Cajal in the colon and regulating the amount of intestinal neurotransmitters and hormones. We also put forward ideas and suggestions for future research.

AADC deficiency: occurring in humans, modeled in rodents

Aromatic l-amino acid decarboxylase (AADC) is a homodimeric pyridoxal phosphate-dependent enzyme responsible for the syntheses of dopamine and serotonin. Defects in the AADC gene result in neurotransmitter deficiencies. Patients with AADC deficiency have severe motor and autonomic dysfunctions. A mouse model of AADC deficiency was recently established. These mice grow poorly and move awkwardly during infancy. They also show high anxiety when they grow up. Because drug therapy provides little or no benefit for many patients with AADC deficiency, a gene therapy has been attempted. The gene therapy employed an adeno-associated virus viral vector that can express the human AADC protein. The vector was injected to the brain of several children with AADC deficiency. The therapy was well tolerated, and all treated patients showed improvement. In the future, the mouse model will also help the development of treatments for AADC deficiency.

Severe Hypoxia: Consequences to Neural Stem Cells and Neurons

BACKGROUND

Multiple neurological diseases result from a pathological hypoxia in the brain, resulting in various motor, sensory or cognitive sequelae. Understanding the response of neural stem cells (NSCs) and differentiated neurons to hypoxia will help better treat such diseases.

METHODS

We exposed mouse embryonic primary neurons (PN) and neural stem cells to 1% O₂ in vitro.

RESULTS

Both cell types survived and retained their immunocyto-chemical markers, and neurons showed no obvious morphological changes. Microarray analysis showed that the number of genes with significantly altered expression levels was almost five-fold higher in NSCs compared to PN. NSCs displayed a clear block in G1/S phase of the cell cycle and a number of down-regulated cytokine genes. Various growth factors (e.g. neural growth factor, prolactin), involved in survival and proliferation, genes of the Notch pathway, and genes involved in glial differentiation, and cell-matrix adhesion were up-regulated. PN displayed a down-regulation of a number of genes involved in neuron-specific functions, in particular, transmitter-related (e.g. synaptic transmission, neurotransmitter transport and release, learning, adult behavior).

CONCLUSIONS

We conclude that hypoxia 1-down-regulates genes involved in multiple neuronal functions which can negatively impact learning and memory; 2-induces a cell cycle block in NSCs; 3-can precondition NSC towards a particular differentiation potential while maintaining them fully undifferentiated.

Research progress of enteric nervous system in esophagus

The functions of esophageal peristalsis and contraction were regulated and controlled by both neural and humoral system at all levels. Esophageal function depends on coordination of all the effectors regulated by enteric nervous system (ENS). Esophageal neurons are generally divided into two groups: the excitatory neurons and the inhibitory neurons. They regulate the tone, peristalsis and contraction of esophagus by interaction of various neurotransmitters. This article reviews recent research advancement of ENS in esophagus.

Research progress in intestinal motility during ulcerative colitis

Ulcerative colitis, which is fairly difficult to be treated, has an extended course and frequent recurrent rate. As a new direction in the pathogenesis of ulcerative colitis, the role of intestinal motility is being recognized and becoming a hotspot. It is reported that the changes of number and structure in interstitial cells of Cajal and colonic manometry, the abnormity of electrophsiology in the intestine and the expression of neurotransmitters, including acetylcholine (Ach), vasoactive intestinal peptide (VIP), nitric oxide (NO), and carbon monoxide (CO), are associated with the pathogenesis of ulcerative colitis. Further investigation of intestinal motility has an important significance in realizing the pathogenic mechanism of ulcerative colitis.

Contributions to the field of neurotransmitters by Japanese scientists, and reflections on my own research

PART I DESCRIBES IMPORTANT CONTRIBUTIONS MADE BY SOME JAPANESE PIONEERS IN THE FIELD OF NEUROTRANSMITTERS: (their achievements in parentheses) J. Takamine (isolation and crystallization of adrenaline); K. Shimidzu (early hint for acetylcholine as a neurotransmitter); F. Kanematsu (donation of the Kanematsu Memorial Institute in Sydney); T. Hayashi (discovery of the excitatory action of glutamate and the inhibitory action of GABA); and I. Sano (discovery of a high concentration of dopamine in striatum, its reduction in a patient with Parkinson's disease and the treatment with DOPA). In Part II, I present some of my reflections on my research on neurotransmitters. The work of my colleagues and myself has made some significant contributions to the establishment of neurotransmitter roles played by GABA and substance P, the first amino acid and the first peptide neurotransmitters, respectively. By the early 1960s, 3 substances, i.e., acetylcholine, noradrenaline, and adrenaline, had been established as neurotransmitters. Now the number of neurotransmitters is believed to be as many as 50 or even more mainly due to the inclusion of several amino acids and a large number of peptide transmitters.

Changes in the amounts of neurotransmitters released from the striatum and spontaneous motor activity in rats exposed to high doses of toluene

We studied the neurotoxicological effects of high-dose toluene exposure by measuring neurotransmitter release from the striatum and spontaneous motor activity in freemoving Tokai High Avoider (THA) male rats. The rats were exposed to 1,000, 2,000, and 4,000ppm toluene for 4 hours. During the 4-hour exposure period and each one hour pre- and post-exposure periods, acetylcholine (ACh), 3, 4-dihydroxyphenylacetic acid (DOPAC), homovanilic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in the microdialysate from kthe striatum of each rat were measured continuously using microdialysis. Simultaneously, spontaneous motor activity of each rat was monitored using an Aimex device. The amounts of neurotransmitters released and spontaneous motor activity showed similar changes for every concentration of toluene exposure during those periods. Although minimal changes in neurotransmitters and motor activity were observed in the 1,000 ppm group, increases in neurotransmitter release and motor activity were observed in the 2,000 ppm group during the entire exposure period and also in the 4,000 ppm group during the early period of exposure. On the other hand, decreases in neurotransmitter release and motor activity were observed in the 4,000 ppm group during the late period of exposure. These findings indicate that the striatum influences motor activity via changes in the amounts of neurotransmitters released during the period of high-dose toluene exposure.

The Geschwind-Behan-Galaburda model (GBGM) of cerebral lateralization: a critique and prospective

In the wake of, and as a complement to, a recently published major meta-analytic review of empirical support of the Geschwind-Behan-Galaburda model (GBGM) of cerebral lateralization (CL) the present brief essay attempts to present a critical assessment of the theoretical approach underlying the GBGM. The GBGM is criticized for having been misguided in its representation of the cerebral basis of handedness, and of the links between testosterone and immune function. Some guidelines are presented for the development of a general theory of CL, emphasizing animal research, greater interdisciplinary communication, a hierarchical model-building approach, and the relevance of neuropharmacology and psychiatry.