Regional difference in the neurotoxicity of ochratoxin A on the developing cerebral cortex in mice

Ochratoxin A induces locomotor impairment and oxidative imbalance in adult zebrafish

Ochratoxin A (OTA) is a mycotoxin produced by species of filamentous fungi widely found as a contaminant in food and with high toxic potential. Studies have shown that this toxin causes kidney and liver damage; however, data on the central nervous system effects of exposure to OTA are still scarce. Thus, this study aimed to investigate the effects of exposure to OTA on behavioral and neurochemical parameters in adult zebrafish. The animals were treated with different doses of OTA (1.38, 2.77, and 5.53 mg/kg) with intraperitoneal injections and submitted to behavioral evaluations in the open tank and social interaction tests. Subsequently, they were euthanized, and the brains were used to assess markers associated with oxidative status. In the open tank test, OTA altered distance traveled, absolute turn angle, mean speed, and freezing time. However, no significant effects were observed in the social interaction test. Moreover, OTA also increased glutathione peroxidase (GPx), glutathione-S-transferase (GST), and glutathione reductase (GR) levels and decreased non-protein thiols (NPSH) levels in the zebrafish brain. This study showed that OTA can affect behavior and neurochemical levels in zebrafish.

Effects of probiotic supplementation on very low dose AFB1-induced neurotoxicity in adult male rats

AIMS

Aflatoxin B1 (AFB1) is the most toxic and common form of AF found in food and feed. Although AFB1 exposure has toxic effects on many organs, studies on the brain are limited. Moreover, to the best of our knowledge, there is no study on the effect of probiotics on AFB1-induced neurotoxicity. Therefore, we aimed to evaluate the possible effects of probiotics on AFB1-induced neurotoxicity in the brain.

MAIN METHODS

Thirty-two adult male Wistar rats were divided into four groups: Vehicle (VEH), Probiotic (PRO) (2.5 × 10¹⁰ CFU/day VSL#3, orally), Aflatoxin B1 (AFB1) (25 μg/kg/week AFB1, orally), and Aflatoxin B1 + Probiotic (AFB1 + PRO) (2.5 × 10¹⁰ CFU/day VSL#3 + 25 μg/kg/week AFB1, orally). At the end of eight weeks, rats were behaviorally evaluated by the open field test, novel object recognition test, and forced swim test. Then, oxidative stress and inflammatory markers in brain tissues were analyzed. Next, brain sections were processed for Hematoxylin&Eosin staining and NeuN and GFAP immunostaining.

KEY FINDINGS

Probiotic supplementation tended to decrease oxidative stress and inflammatory markers compared to the AFB1 group. Besides, brain tissues had more normal histological structures in VEH, PRO, and AFB1 + PRO groups than in the AFB1 group. Moreover, in probiotic groups, GFAP immunoreactivity intensity was decreased, while NeuN-positive cell number increased in brain tissues compared to the AFB1 group.

SIGNIFICANCE

Probiotics seem to be effective at reducing the neurotoxic effects of AFB1. Thus, our study suggested that especially Bifidobacterium and Lactobacillus species can improve AFB1-induced neurotoxicity with their antioxidant and anti-inflammatory effects.

Melatonin alleviates Ochratoxin A-induced liver inflammation involved intestinal microbiota homeostasis and microbiota-independent manner

Melatonin (MEL) shows an anti-inflammatory effect and regulates intestinal microbiota communities in animals and humans; Ochratoxin A (OTA) induces liver inflammation through intestinal microbiota. However, it remains to know whether MEL alleviates the liver inflammation induced by OTA. In this study, MEL reversed various adverse effects induced by OTA. MEL recovered the swarming and motility of intestinal microbiota, decreased the accumulation of lipopolysaccharide (LPS), enhanced the tight junction proteins of jejunum and cecum segments; ultimately alleviated OTA-induced liver inflammation in ducks. However, it is worth noting that MEL still had positive effects on the OTA-exposed ducks after antibiotic treatment. These results suggest that both the maintenance of intestinal microbiota homeostasis and intestinal microbiota-independent manner involved the MEL anti-inflammatory function in OTA-induced liver inflammation. MEL represent a promising protective approach for OTA, even other mycotoxins.

Assessment of Toxic Effects of Ochratoxin A in Human Embryonic Stem Cells

Ochratoxin A (OTA) is a mycotoxin produced by different Aspergillus and Penicillium species, and it is considered a common contaminant in food and animal feed worldwide. On the other hand, human embryonic stem cells (hESCs) have been suggested as a valuable model for evaluating drug embryotoxicity. In this study, we have evaluated potentially toxic effects of OTA in hESCs. By using in vitro culture techniques, specific cellular markers, and molecular biology procedures, we found that OTA produces mild cytotoxic effects in hESCs by inhibiting cell attachment, survival, and proliferation in a dose-dependent manner. Thus, we suggest that hESCs provide a valuable human and cellular model for toxicological studies regarding preimplantation stage of human fetal development.

Ochratoxin A at nanomolar concentration perturbs the homeostasis of neural stem cells in highly differentiated but not in immature three-dimensional brain cell cultures

Ochratoxin A (OTA), a fungal contaminant of basic food commodities, is known to be highly cytotoxic, but the pathways underlying adverse effects at subcytotoxic concentrations remain to be elucidated. Recent reports indicate that OTA affects cell cycle regulation. Therefore, 3D brain cell cultures were used to study OTA effects on mitotically active neural stem/progenitor cells, comparing highly differentiated cultures with their immature counterparts. Changes in the rate of DNA synthesis were related to early changes in the mRNA expression of neural stem/progenitor cell markers. OTA at 10nM, a concentration below the cytotoxic level, was ineffective in immature cultures, whereas in mature cultures it significantly decreased the rate of DNA synthesis together with the mRNA expression of key transcriptional regulators such as Sox2, Mash1, Hes5, and Gli1; the cell cycle activator cyclin D2; the phenotypic markers nestin, doublecortin, and PDGFRα. These effects were largely prevented by Sonic hedgehog (Shh) peptide (500ngml(-1)) administration, indicating that OTA impaired the Shh pathway and the Sox2 regulatory transcription factor critical for stem cell self-renewal. Similar adverse effects of OTA in vivo might perturb the regulation of stem cell proliferation in the adult brain and in other organs exhibiting homeostatic and/or regenerative cell proliferation.

Pathological outcomes in kidney and brain in male Fischer rats given dietary ochratoxin A, commencing at one year of age

Malignant renal carcinoma, manifest in morbid ageing rats, is the striking component of an otherwise silent response after about nine months of exposure to ochratoxin A in the first year of life (daily intake ~100-250 µg/kg body weight). Reasons for the long latency are unclear, as is whether there would be a similar carcinogenic response if toxin exposure started at one year of age. Therefore, 24 male Fischer rats were given 100 µg ochratoxin A as a daily dietary contaminant for 35 weeks from age 50 weeks. Plasma ochratoxin A concentration reached a maximum value of ~8 µg/mL within one month of starting the toxin regimen. No renal carcinomas occurred. Four renal adenomas, two of which were only microscopic, were found among the six rats surviving for 110 weeks. The findings raise new questions about a difference between young adults and mature adults in sensitivity of male rats to the ochratoxin A-induced DNA damage necessary for renal carcinogenesis. A pilot histological study of perfuse-fixed brains of the toxin-treated rats showed no gross abnormalities, correlating with the consistent absence of behavioral or neurological disorders from chronic ochratoxin A exposure regimens in the range 100-250 µg/kg/day during the second half of life. Reasoned questioning concerning ochratoxin A as a neurotoxic mycotoxin is made.

Neurotoxicant-induced inflammatory response in three-dimensional brain cell cultures

Brain inflammatory response is triggered by the activation of microglial cells and astrocytes in response to various types of CNS injury, including neurotoxic insults. Its outcome is determined by cellular interactions, inflammatory mediators, as well as trophic and/or cytotoxic signals, and depends on many additional factors such as the intensity and duration of the insult, the extent of both the primary neuronal damage and glial reactivity and the developmental stage of the brain. Depending on particular circumstances, the brain inflammatory response can promote neuroprotection, regeneration or neurodegeneration. Glial reactivity, regarded as the central phenomenon of brain inflammation, has also been used as an early marker of neurotoxicity. To study the mechanisms underlying the glial reactivity, serum-free aggregating brain cell cultures were used as an in vitro model to test the effects of conventional neurotoxicants such as organophosphate pesticides, heavy metals, excitotoxins and mycotoxins. This approach was found to be relevant and justified by the complex cell-cell interactions involved in the brain inflammatory response, the variability of the glial reactions and the multitude of mediators involved. All these variables need to be considered for the elucidation of the specific cellular and molecular reactions and their consequences caused by a given chemical insult.

Unusual astrocyte reactivity caused by the food mycotoxin ochratoxin A in aggregating rat brain cell cultures

Ochratoxin A (OTA), a mycotoxin and widespread food contaminant, is known for its patent nephrotoxicity and potential neurotoxicity. Previous observations in vitro showed that in the CNS, glial cells were particularly sensitive to OTA. In the search for the molecular mechanisms underlying OTA neurotoxicity, we investigated the relationship between OTA toxicity and glial reactivity, in serum-free aggregating brain cell cultures. Using quantitative reverse transcriptase-polymerase chain reaction to analyze changes in gene expression, we found that in astrocytes, non cytotoxic concentrations of OTA down-regulated glial fibrillary acidic protein, while it up-regulated vimentin and the peroxisome proliferator-activated receptor-gamma expression. OTA also up-regulated the inducible nitric oxide synthase and the heme oxygenase-1. These OTA-induced alterations in gene expression were more pronounced in cultures at an advanced stage of maturation. The natural peroxisome proliferator-activated receptor-gamma ligand, 15-deoxy-delta(12,14) prostaglandin J2, and the cyclic AMP analog, bromo cyclic AMP, significantly attenuated the strong induction of peroxisome proliferator-activated receptor-gamma and inducible nitric oxide synthase, while they partially reversed the inhibitory effect of OTA on glial fibrillary acidic protein. The present results show that OTA affects the cytoskeletal integrity of astrocytes as well as the expression of genes pertaining to the brain inflammatory response system, and suggest that a relationship exists between the inflammatory events and the cytoskeletal changes induced by OTA. Furthermore, these results suggest that, by inducing an atypical glial reactivity, OTA may severely affect the neuroprotective capacity of glial cells.

Fate of ochratoxin a during cooking of naturally contaminated polished rice

Ochratoxin A (OTA), a mycotoxin widespread in cereals, occurs in polished rice that is consumed as cooked rice after washing and steaming. Cooking decreases OTA levels in food to varying extents, but little is known about how cooking changes the biological activity of this mycotoxin. We therefore evaluated the fate of OTA during rice cooking to determine the OTA residues and cytotoxic potential in vitro. Water-washed rice, ordinary cooked rice, and pressure-cooked rice were prepared from three polished rice lots naturally contaminated with OTA. Residual OTA in each sample was analyzed by high-performance liquid chromatography (HPLC), whereas in vitro cytotoxicity of OTA to C6 glioma cells, susceptible to low levels (nanograms per milliliter) of OTA, was used to confirm the chemical analysis. OTA concentration, as determined by HPLC analysis, in the cooked rice by both types of cookers was significantly lower than (59 to 75%) in the raw polished rice and water-washed rice. The cytotoxicity of the OTA that remained in the pressure-cooked rice from three lots was markedly decreased (approximately 20%, P < 0.05) when compared with other samples in respective lots. This confirms that cooking lowers OTA residues. Although washing polished rice with water had little effect on OTA levels, pressure steaming appeared to be the critical cooking step not only to reduce OTA residues in polished rice before reaching the consumer as the dietary staple of cooked rice, but also to diminish cytotoxicity of OTA.

Application of the physical disector to the central nervous system: estimation of the total number of neurons in subdivisions of the rat hippocampus

Stereology is a group of mathematical and statistical methods that allows the extrapolation of three-dimensional structural information from two-dimensional sections (or slices). This allows researchers to derive important quantitative structural information, such as the volume, surface area or numbers of particular particles (e.g. cells) within defined regional boundaries. The need for such quantitative information in biology is of particular importance when evaluating the influence of various experimental treatments on specific organs, tissues and cells in the body. Knowledge of such changes has given important insights into the neural substrates that may be responsible for the functional and behavioral consequences of a disparate range of experimental treatments. Here, we describe some of these methods as applied to quantifying the total numbers of cells in defined regions of the hippocampal formation. The methods used for this evaluation were, first, the Cavalieri principle, which was used to determine the volumes of the various subdivisions of the rat hippocampus, and, second, the 'physical disector' method, which was used to estimate the numerical density of neurons within each subdivision. Once these values were derived, it was but a simple task to multiply them together to obtain estimates for the total numbers of cells in the given hippocampal region. We found that 16-and 30-day-old normal male rats had 176 800 and 152 700 pyramidal cells in the CA1 region, respectively. This decrease in the neuronal number was statistically significant. However, in the CA2 + CA3 region, there were approximately 169 300 and 149 600 pyramidal cells in 16- and 30-day-old normal male rats, respectively, which was not significantly different. In the dentate gyrus, there were approximately 36 700 neurons in the hilus region and 483 000 granule cells in the granule cell layer, irrespective of the age of the rats. There were no significant differences between these estimates of hilus neurons and granule cells.

Structural and functional aberrations in the cerebral cortex of tenascin-C deficient mice

The extracellular matrix glycoprotein tenascin-C (TNC) has been implicated in neural development and plasticity but many of its functions in vivo remain obscure. Here we addressed the question as to whether the constitutive absence of TNC in mice affects cortical physiology and structure. Defined major cell populations (neurons and inhibitory neuronal subpopulations, astrocytes, oligodendrocytes and microglia) were quantified in the somatosensory and motor cortices of adult TNC deficient (TNC-/-) and wild-type (TNC+/+) mice by immunofluorescence labelling and stereology. In both areas studied we found abnormally high neuronal density, astrogliosis, low density of parvalbumin-positive interneurons and reduced ratios of oligodendrocytes to neurons and of inhibitory to excitatory neurons in the TNC deficient as opposed to the non-deficient animals. Analysis of Golgi-impregnated layer V pyramidal neurons in TNC-/- animals showed aberrant dendrite tortuosity and redistribution of stubby spines within first- to third-order dendritic arbors. Significantly enhanced responses upon whisker stimulation were recorded epicranially over the barrel and the motor cortices of TNC-/- as compared to TNC+/+ animals, and this effect might be associated with the diminished inhibitory circuitry. These results indicate that TNC is essential for normal cortical development and function.

Inhibitory effects of ochratoxin A on nerve growth factor-induced neurite extension through downregulation of p38 MAP kinase and AP-1 activation in cultured pheochromocytoma cells

Ochratoxin A (OTA) induces microcephaly in animals and in vitro cultured whole embryos. Inhibition of neuronal cell differentiation was proposed as underlying mechanisms responsible for OTA-induced microcephaly. Previously it was found that OTA inhibited differentiation of cultured rat embryonic midbrain cells into neurons. In this study, the influence of OTA on differentiation in PC-12 cells, a widely accepted model cells for study of neuronal differentiation was examined. Cell differentiation was assessed by measurement of neurite extension and quantified by the number of neurites extended. OTA decreased serum and nerve growth factor (NGF)-induced neurite extension in a concentration-dependent manner. Since MAP kinase and transcription factors have been implicated in cell differentiation of neuronal cells, and our previous study demonstrated that p38 MAP kinase and AP-1 are activated during PC 12 cell differentiation, the effect of OTA on NGF-induced p38 MAP kinase and transcription factor activation was examined. Co-treatment of OTA with NGF resulted in inhibition of NGF-induced p38 MAP kinase and AP-1 activation. Moreover, SB203580, a specific inhibitor of p38 MAP kinase blocked p38 MAP kinase and AP-1 activation accompanied by further inhibition of neurite extension. The present study shows that OTA inhibited cell differentiation of PC-12 cells, and this inhibitory effect may be related to inhibition of the activation of the p38 MAP kinase in conjunction with transcription factors AP-1. This finding suggests that the inhibitory effect on neuronal cell differentiation by OTA might be a mechanism responsible for OTA-induced microcephaly.

Indoor mold, toxigenic fungi, and Stachybotrys chartarum: infectious disease perspective

Damp buildings often have a moldy smell or obvious mold growth; some molds are human pathogens. This has caused concern regarding health effects of moldy indoor environments and has resulted in many studies of moisture- and mold-damaged buildings. Recently, there have been reports of severe illness as a result of indoor mold exposure, particularly due to Stachybotrys chartarum. While many authors describe a direct relationship between fungal contamination and illness, close examination of the literature reveals a confusing picture. Here, we review the evidence regarding indoor mold exposure and mycotoxicosis, with an emphasis on S. chartarum. We also examine possible end-organ effects, including pulmonary, immunologic, neurologic, and oncologic disorders. We discuss the Cleveland infant idiopathic pulmonary hemorrhage reports in detail, since they provided important impetus for concerns about Stachybotrys. Some valid concerns exist regarding the relationship between indoor mold exposure and human disease. Review of the literature reveals certain fungus-disease associations in humans, including ergotism (Claviceps species), alimentary toxic aleukia (Fusarium), and liver disease (Aspergillys). While many papers suggest a similar relationship between Stachybotrys and human disease, the studies nearly uniformly suffer from significant methodological flaws, making their findings inconclusive. As a result, we have not found well-substantiated supportive evidence of serious illness due to Stachybotrys exposure in the contemporary environment. To address issues of indoor mold-related illness, there is an urgent need for studies using objective markers of illness, relevant animal models, proper epidemiologic techniques, and examination of confounding factors.

Inhibitory effect of peroxisome proliferator-activated receptor gamma agonist on ochratoxin A-induced cytotoxicity and activation of transcription factors in cultured rat embryonic midbrain cells

The effects of 15-deoxy-delta12,14-prostaglandin J2 (15-deoxy PGJ2) on ochratoxin A (OTA)-induced neurotoxicity and on the activation of transcription factors activator protein-1 (AP-1) and nuclear factor-kappa B (NF-kappaB) were investigated in cultured rat embryonic midbrain cells. Twelve-day rat embryo midbrain cells were cultured for 48 h. OTA (0.5 or 1 microg/ml) and/or 1.5-deoxy PGJ2 (0.5 microM) were then added for 48 h. Cell number and neurite outgrowth were determined to assess the neurotoxicity of OTA. AP-1 and NF-kappaB activation was determined by gel mobility shift assay after 3 h of exposure to OTA and/or 15-deoxy PGI2. OTA caused concentration-dependent reductions in neurite outgrowth and cell number, and induced AP-1 and NF-kappaB activation. Cotreatment with 15-deoxy PGJ2 (0..5 microM) blocked OTA-induced decrease in neurite outgrowth and cell number and inhibited AP-1 and NF-kappaB activation. 15-Deoxy PGJ2 (0.5 microM) caused the expression of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) in the cells. Results show that 1.5-deoxy PGJ2 blocked OTA-induced neurotoxicity by inhibiting AP-1 and NF-kappaB activation in cultured rat embryonic midbrain cells.

Behavioral screening of two mouse lines selected for different brain weight

1. Several behavioral tests were used to compare two lines of mice selected for large (LB) and small brain (SB) weight on the basis of brain/body weight ratio values. 2. An elevated pain sensitivity as well more intense startle response was shown in SB mice in comparison with LB mice. 3. In inescapable situations of slip funnel and tail suspension tests, analogues of the Porsolt swim test, higher immobility scores in SB mice suggest an increased level of fear and/or anxiety the stress situations. 4. The SB mice demonstrated higher levels of locomotion in open field and cross-maze tests. In the latter test, the SB mice also showed increased tendency for stereotyped alternation of two arms during maze exploration. 5. Acute administration of a moderate dose of ethanol (3 g/kg) had opposite effects on the total time of cross-maze exploration: this measure increased in the SB and decreased in the LB line. By contrast, the tendency for stereotypy was similarly increased and the efficacy of maze exploration decreased in both lines.

Age-related differences in the toxicity of ochratoxin A in female rats

Ochratoxin A (OTA) is a mycotoxin found in food and feedstuffs of plant and animal origin. OTA exposure is related to nephropathy in humans. Age-related differences, especially in nephro- and immunotoxicity of OTA, were investigated in young adult (aged 12 weeks) and old (aged 27-30 months) female SPF Wag rats, treated by gavage with 0, 0.07, 0.34 or 1.68 mg OTA/kg body weight for 4 weeks. In both age groups, survival was significantly decreased in the highest dose group. Clinical condition, body weight, clinical chemistry parameters (ALAT, ASAT, creatinin and urea) and target organs (as identified by weight and pathology - kidney, liver, adrenals, forestomach and brain) were affected by age and dose, but often more severely in old than in young rats. OTA induced primarily nephropathy. Old rats were more sensitive to induction of tubular karyomegaly and vacuolation/necrosis. In young rats, OTA induced a dose-related thickening of the basement membrane and reduction in splenic T-cell fraction. Decreased IgG levels were seen at 0.34 mg/kg OTA (young and old rats) and 1.68 mg/kg OTA (young rats). Vacuolation of the white brain matter (cerebellar medulla and ventral parts of the brain stem) was significantly increased in young rats at 0.34 and 1.68 mg/kg OTA and in old rats at 0.07 and 0.34 mg/kg OTA. It was concluded that: (1) the profiles of OTA toxicity for both age groups are similar, with the kidney and possibly the brain being primary target organs; (2) based on clinical and pathological data old rats are more sensitive to OTA than young rats; and (3) the immune system is probably not the primary target of OTA toxicity.

Differences in neurotoxic effects of ochratoxin A, ochracin and ochratoxin-alpha in vitro

The mycotoxin ochratoxin A (OTA) is a chlorinated dihydroisocoumarin derivative connected through an amide-bond to L-phenylalanine. In a previous study we could show that competition with L-phenylalanine-dependent processes does not play a role in OTA neurotoxicity. To test whether the isocoumarin part is responsible for the neurotoxic effects, we determined in the present study the effects of the hydrolysis product of OTA, ochratoxin-alpha (OTalpha), and of ochracin on embryonic chick brain cell cultures. In addition, we investigated the interaction between OTA and ochracin regarding the neurotoxic effects. We report here that OTalpha did not affect brain cell cultures at concentrations up to 15 microM. With the exception of a small (20%) but significant reduction in cell culture, cellular protein at concentrations above 0.3 microM, in our cell cultures' cell function, as defined by neutral red uptake and MTT-dehydrogenase activity, was only reduced by high OTalpha concentrations (1 mM). Addition of 0.1 microM OTA increased ochracin cytotoxicity as defined by latter parameters. No effects on cell culture NF68kD content could be detected. The results are discussed with regard to the existence of an OTA target interaction binding site.

Subchronic effects of ochratoxin A on young adult rat brain and partial prevention by aspartame, a sweetener

1. Ochratoxin A (OTA) is a mycotoxin produced by several fungi, especially Aspergillus and Penicillium species. Many food and foodstuffs can be contaminated by ochratoxin A, which is consequently found in blood of animals and humans. 2. The distribution into the brain of young adult rats fed OTA for 1 to 6 weeks and some consequences have been investigated in the present study. 3. Our results on rats given OTA (289 microg/kg/48 h) indicated that OTA accumulated in the whole brain as function of time according to a regression curve, Y=-8.723 a+16.72 with a correlation coefficient of r=0.989, where Y-axis is the OTA concentration in ng/g of brain and X-axis is the duration of the treatment in weeks. The brain OTA contents was 11.95 +/- 2.2, 23.89 +/- 4.4, 39.9 +/- 4.5, 50.3 +/- 7.3, 78.8 +/- 6.3, 94 +/- 16 ng/g of brain in the mycotoxin-treated animals for respectively 1, 2, 3, 4, 5 and 6-weeks treatment. OTA induced modifications of free amino-acid concentrations in the brain, mainly, Tyrosine (Tyr) and phenylalanine (Phe). Tyr decreased significantly as compared to control (p < 0.05). Phe increased significantly as compared to control (p < 0.05). 4. Aspartame, (25 mg/kg/48 h) a structural analogue of OTA largely modified the distribution and prevented the accumulation of OTA in the brain since the respective brain OTA contents decreased respectively to 9.6 +/- 7.9, 19.2 +/- 3.0, 26.8 +/- 4.2, 19.7 +/- 1.9, 13.7 /- 5.6 and 11.0 +/- 6.0 ng/g of tissue, for the same duration of treatment. It also prevented the modifications of Tyr and Phe levels. 5. The histological investigations showed several necrotic cells with pyknotic nucleus, detected in OTA treated animals with higher frequency as compared to the controls and Aspartame treated ones. Aspartame appeared to significantly prevent this nuclear effect as well, the meaning of which is discussed.

Estimation of the numerical densities of neurons and synapses in cerebral cortex

In this paper we discuss a stereological technique, 'the unfolding method', for a quantitative study of the nervous system [1,31]. Stereology implies a geometric analysis of structures and textures, and is a method to derive directly metric properties of structures from two-dimensional sections on the basis of geometrico-statistical reasoning [36,37]. Recent advances in the stereological method allow quantitative analysis [8,19,27,32]. Images on sections provide only two-dimensional information, but the stereological method can offer three-dimensional and quantitative information [19]. The need for quantitative analysis is more important and useful in the central nervous system (CNS) than in other organs. Two functional units, neurons and synapses, are of particular interest in evaluating CNS function. Numerical densities of neurons and synapses in rat visual cortex were estimated using the unfolding method at light and electron microscopic levels, respectively. Once the numerical densities of neurons and synapses were obtained, synapse-to-neuron ratios could be calculated. The ratios are interpreted as a means to obtain an index of interneuronal connectivity [9]. The unfolding method may become a powerful strategy in neuroscience research when numerical estimates are performed in restricted areas such as cortical layers II-IV, because this method is less time-consuming than other stereological methods [6,21,22].

The neurotoxic effects of ochratoxin-A are reduced by protein binding but are not affected by l-phenylalanine

Recent in vivo investigations indicate that the mycotoxin ochratoxin A (OTA) is a neurotoxicant during prenatal stages. In line with in vivo data, in our embryonic chick brain and neural retina cell cultures the markers for neuritic outgrowth and differentiation (NF68 and 160 kDa, MAP2 and MAP5) were especially negatively affected. In vivo OTA is nearly completely bound to serum constituents. In our culture system binding of OTA to BSA evoked a significant shift of the concentration-effect relationships in meningeal and brain cell cultures. As a result of the albumin binding the OTA IC5 and IC50 values of all parameters increased by nearly the same value (about 15-fold in brain and 32-fold in meningeal cell cultures). One of the mechanisms responsible for OTA toxicity is thought to be the competitive inhibition versus Phe of Phe-dependent enzymes. Therefore, in addition, we investigated the effects of l-phenylalanine (Phe) and its influence on OTA toxicity in brain and neural retina cell cultures. Phe itself was found to differently affect brain and neural retina cell cultures. However, in both cultures OTA toxicity is not diminished by Phe. Therefore, our data indicate that at least in our cultures competition with Phe-dependent processes does not play a role in OTA toxicity.

Reduction of ochratoxin A toxicity by heat-induced epimerization. In vitro effects of ochratoxins on embryonic chick meningeal and other cell cultures

The widespread contamination of food by mycotoxins may present a serious hazard to human and animal health. The present study was designed to determine the toxic potential of three structurally related ochratoxins: ochratoxin A (OTA), ochratoxin B (OTB) and the heat-induced 3S-epimer of OTA (3S-OTA) recently discovered in roasted coffee and human serum. The toxicity was determined using serum-free cell cultures of embryonic chick meningeal fibroblasts, taking the effects on mitochondrial and lysosomal activity and culture protein content as an index for toxicity. OTA, OTB and 3S-OTA were toxic. However, the concentration necessary to induce comparable effects were nearly 19- and 10-fold higher for OTB and 3S-OTA, respectively, than those for OTA. In a next step the sensitivity of serum-free cell cultures of embryonic chick neural retina and brain were compared in relation to meningeal cell cultures. In the present study, no indications for differences in sensitivity could be detected. Furthermore, our study suggest that the OTA-induced toxic effects are not due to the inhibition by OTA of phenylalanine-tRNA synthetase.

A quantitative study of the effects of prenatal X-irradiation on the development of cerebral cortex in rats

Pregnant rats were exposed to a single whole body X-irradiation on day 15 of gestation at a dose of 1.0 Gy. The offspring showed microcephaly at 7 weeks of age. Their body weight, brain weight, cortical thickness and the numerical density of neurons and synapses in the somatosensory and visual cortex were examined. Significant decreases in cortical thickness in both somatosensory (25%) and visual (16%) cortex were observed. However, there were no significant changes in the numerical density of neurons and synapses, nor in synapse-to-neuron ratios in both cortical regions between control and X-irradiated groups. These results suggest that prenatal X-irradiation can decrease the number of neurons, and the neurons which survive X-irradiation proliferate and elaborate connections in a normal fashion. This is in contrast to the animals exposed to ochratoxin A, in which numerical density of neurons in the somatosensory cortex is increased, with normal numerical density of synapses, resulting in low synapse-to-neuron ratios. The discrepancy in the synapse-to-neuron ratios between the X-irradiation and ochratoxin A-treatment might derive from a different effect on the developing neurons.