Cadmium-induced selective lesions of sensory ganglia

Barriers in the developing brain and Neurotoxicology

The brain develops and grows within a well-controlled internal environment that is provided by cellular exchange mechanisms in the interfaces between blood, cerebrospinal fluid and brain. These are generally referred to by the term "brain barriers": blood-brain barrier across the cerebral endothelial cells and blood-CSF barrier across the choroid plexus epithelial cells. An essential component of barrier mechanisms is the presence of tight junctions between the endothelial and epithelial cells of these interfaces. This review outlines historical evidence for the presence of effective barrier mechanisms in the embryo and newborn and provides an up to date description of recent morphological, biochemical and molecular data for the functional effectiveness of these barriers. Intercellular tight junctions between cerebral endothelial cells and between choroid plexus epithelial cells are functionally effective as soon as they differentiate. Many of the influx and efflux mechanisms are not only present from early in development, but the genes for some are expressed at much higher levels in the embryo than in the adult and there is physiological evidence that these transport systems are functionally more active in the developing brain. This substantial body of evidence supporting the concept of well developed barrier mechanisms in the developing brain is contrasted with the widespread belief amongst neurotoxicologists that "the" blood-brain barrier is immature or even absent in the embryo and newborn. A proper understanding of the functional capacity of the barrier mechanisms to restrict the entry of harmful substances or administered therapeutics into the developing brain is critical. This knowledge would assist the clinical management of pregnant mothers and newborn infants and development of protocols for evaluation of risks of drugs used in pregnancy and the neonatal period prior to their introduction into clinical practice.

Developmental neuropathology in DNT-studies—A sensitive tool for the detection and characterization of developmental neurotoxicants

Developmental neurotoxicity (DNT-) studies are the first reproduction toxicity studies for which an extended histopathological examination of developing structures is required by the current EPA and OECD guidelines. The morphological screening includes a macroscopic evaluation of the brain and nervous tissue, brain weight parameters, gross morphometry of the brain, neurohistological examinations and a quantitative analysis of major brain areas. This review is intended to give an overview about the needs according to guideline requirements, practical approaches for a successful developmental neuropathology and its preconditions and does include examples of background data on the value and functional meaning of morphological data. A selection of experimental data from literature is also presented in the light of their contribution for the understanding of important, neurodevelopmental disorders in humans.

Strain differences in the toxicity of cadmium to trigeminal ganglia in mice

Cadmium (Cd) is toxic to sensory ganglia in many animal species. Cadmium uptake is low in the central nervous system, but it distributes preferentially to peripheral sensory and autonomic ganglia. Strain differences have been demonstrated in the sensitivity of mice to Cd-induced hepatotoxicity, testicular toxicity, and teratogenicity. To study the sensitivity of different mouse strains to Cd toxicity in sensory ganglia, eight strains of mice (four sensitive to testicular toxicity: 129/SVIM, AKR/J, DBA/1J, and C57BR/J; and four resistant: Balb/C, C3H/HeJ, A/J, and C57BL/6J) were given 15 micromol CdCl(2)/kg iv. Trigeminal ganglia (TG) were harvested 24 h later and examined by light microscopy for pathologic lesions. Cadmium induced degeneration of ganglion cells in five strains, namely 129/SVIM, AKR/J, DBA/1J, C57BR/J, and C3H/HeJ mice. These are the same strains that show sensitivity to testicular toxicity, except for C3H/HeJ, which is resistant to testicular toxicity. Cd also induced focal hemorrhages around the ganglion cells and nerve fibers in two of these strains (129/SVIM and AKR/J) and scattered foci of necrosis in C3H/HeJ and 129/SVIM strains. There was no morphologic abnormality in three strains, namely Balb/C, A/J, and C57BL/6J. To examine the mechanism of these strain differences in toxicity, all eight strains of mice were given a nontoxic dose of Cd (0.4 micromol CdCl(2)/kg, 20 microCi (109)Cd/kg iv). Cadmium distribution to the brain and trigeminal ganglia was determined 30 min later by gamma scintillation spectrometry. Cadmium content in the brain was very low and did not differ among the eight strains. In contrast, Cd content was higher in trigeminal ganglia of four of the five strains showing trigeminal ganglia sensitivity than in the three strains showing resistance. In conclusion, the toxicity of Cd to trigeminal ganglia is different among various strains of mice. This strain difference in toxicity appears to be due, at least in part, to differences in the distribution of Cd to the ganglia, but it is clearly not the only factor.

Re-evaluation of acute neurotoxic effects of Cd2+ on mesencephalic trigeminal neurons of the adult rat

The mechanism of Cd2+ neurotoxicity, which is considered to be secondary to changes in blood vessels, was re-evaluated in dissociated mesencephalic trigeminal (Me5) neurons of the adult rat. Cd2+ induced morphological changes in Me5 neurons at 0.1 and 1 mM but not at 0.01 mM. The changes appeared predominantly in the cytoplasm: destruction of the cytoplasmic organelles, swelling and vacuolization of the cell body, and finally resulted in cell lysis. These observations indicate necrosis rather than apoptosis, and no sign of degraded nuclear DNA, characteristic to apoptosis, was detected by the TUNEL technique. Using a Ca2+-sensitive dye Indo-1, Cd2+ was found to elevate the intracellular Ca2+ concentration [Ca2+](i) (both in the cytoplasm and the nucleus). Both the elevation in [Ca2+](i) and the morphological alteration were inhibited either by removing Ca2+-from the bathing medium or by the application of BAPTA/AM (10 microM), a membrane-permeable intracellular Ca2+ chelator. Furthermore, neither morphological changes nor elevation in [Ca2+](i) by Cd2+ occurred in the presence of Zn2+. It is concluded that (1) Cd2+ can directly affect nerve cells, (2) toxicity of Cd2+ on Me5 neurons is mediated by continuous elevation in [Ca2+](i), (3) Cd2+ induces necrotic cell death, and (4) Cd2+ neurotoxicity can be antagonized by Zn2+.

Neurobehavioural effects of occupational exposure to cadmium: a cross sectional epidemiological study

BACKGROUND

A patient with unexplained minor behavioural changes associated with an axonal sensorimotor polyneuropathy had a history of chronic occupational exposure to cadmium (Cd). Although animal studies have shown that Cd is a potent neurotoxicant, little is known about its toxicity for the human central nervous system. The aim of this study was to investigate the toxic potential of chronic occupational exposure to Cd on neurobehavioural functions.

METHODS

A cross sectional epidemiological study was conducted ina group of Cd workers and an age matched control group. Eighty nine adult men (42 exposed to Cd and 47 control workers) were given a blinded standardised examination that consisted of computer assisted neurobehavioural tests (neurobehavioural examination system), a validated questionnaire to assess neurotoxic complaints (neurotoxicity symptom checklist--60, NSC-60), and a standardised self administered questionnaire to detect complaints consistent with peripheral neuropathy and dysfunction of the autonomic nervous system. Historical and current data on biomonitoring of exposure to Cd, either the highest value of Cd in urine (CdU in microgram Cd/g creatinine) of each Cd worker during work (CdUmax) or the current value (CdUcurrent) of each control, were available as well as data on microproteinuria.

RESULTS

Cd workers (CdUmax: mean (range), 12.6 (0.4-38.4)) performed worse than the controls (CdUcurrent: mean (range), 0.7 (0.1-2.0)) on visuomotor tasks, symbol digit substitution (p = 0.008), and simple reaction time to direction (p = 0.058) or location (p = 0.042) of a stimulus. In multiple linear regression analysis, symbol digit substitution, simple direction reaction time test, and simple location reaction time test were significantly related to CdUmax, (beta = 0.35 (p < 0.001), beta = 0.25 (p = 0.012), and beta = 0.23 (p = 0.021) respectively). More complaints consistent with peripheral neuropathy (p = 0.004), complaints about equilibrium (p = 0.015), and complaints about concentration ability (p = 0.053) were found in the group exposed to Cd than in the control group, and these variables correlated positively with CdUmax (peripheral neuropathy: beta = 0.38, p < 0.001; equilibrium: beta = 0.22, p = 0.057; concentration ability: beta = 0.27, p = 0.020).

CONCLUSION

Slowing of visuomotor functioning on neurobehavioural testing and increase in complaints consistent with peripheral neuropathy, complaints about equilibrium, and complaints about concentration ability were dose dependently associated with CdU. Age, exposure to other neurotoxicants, or status of renal function could not explain these findings. The present study also indicates that an excess of complaints may be detected in Cd workers before signs of microproteinuria induced by Cd occur.

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.

Behavioural and biochemical changes after simultaneous and post-treatment of vitamin A and D on cadmium toxicity

In the present study, an investigation was undertaken to assess the protective efficacy in cadmium toxicity of vitamins administered simultaneously as well as post-treatment. Rats were treated with cadmium 1 mg/kg body weight (bw) powdered vitamin A chewable tablet 500 IU/kg bw/day and injectable vitamin D(3) (made into a suspension with gum tragacanth in 100 ml distilled water) 100 IU/kg bw/day, mixed with powdered pellet feed and fed to experimental animals. Spontaneous motor activity and Rota Rod Endurance time was recorded after both simultaneous (for 21 days) and post-treatment (42 days). Vitamin treated animals by themselves behaved like controls but attenuated the cadmium effect when given Cd simultaneously or as post-treatment. While the biochemical changes were assayed, vitamins which did not have any influence on their own, given simultaneously and as post-treatment, antagonized the cadmium effect on heart, liver tissues and serum. Both simultaneous and post-cadmium and -vitamin treatments significantly increased the activities of the enzymes aspartic amino transferase, alanine aminotransferase, acid phosphatase and alkaline phosphatase in tissues and serum. Simultaneous and post-vitamin treatment with Cd had an effect of bringing back the activity of the enzymes closer to control values. These data suggest that treatment with vitamin A and D can minimise the Cd effect when given to the population exposed to Cd.

Functional impairment of blood-brain barrier following pesticide exposure during early development in rats

1. The effect of certain pesticides on the functional integrity of the developing blood-brain barrier (BBB) was studied following single and repeated exposure, and after subsequent withdrawal in rats. 2. Ten-day-old rat pups exposed orally to quinalphos (QP, organophosphate), cypermethrin (CM, pyrethroid) and lindane (LD, organochlorine) at a dose of 1/50th of LD50, showed a significant increase in the brain uptake index (BUI) for a micromolecular tracer, sodium fluorescein (SF), by 97, 37 and 72%, respectively, after 2 h. Residual increases in the BUI were found even after 3 days of the single treatment of QP (28%) and LD (23%). 3. Repeated exposure for 8 days (postnatal days (PND) 10-17) with QP, CM and LD increased the BBB permeability by 130, 80 and 50%, respectively. Recovery from these changes was complete in QP and LD-treated animals after 13 days (PND 18-30) of withdrawal. However, CM showed persistent effects that were normalized only after 43 days (PND 18-60) of withdrawal. 4. A single dose reduced to 1/100th of LD50 also increased BUI in 10-day-old rat pups following QP (20%) and CM (28%) exposure at 2 h. 5. An age-dependent effect of these pesticides was evident from the study showing higher magnitude of BUI changes in 10-day-old rats as compared to that in 15-day-old rats. Furthermore, adult rats did not show any effect on BBB permeability even at a higher dose (1/25th of LD50) of these pesticides given alone or in combination with piperonyl butoxide (600 mg/kg, i.p.) for 3 consecutive days. 6. This study showed that developing BBB is highly vulnerable to single or repeated exposure of certain pesticides. The observed persistent effects during brain development even after withdrawal of the treatment may produce some neurological dysfunction at later life as well.

Slow closed-state inactivation: a novel mechanism underlying ramp currents in cells expressing the hNE/PN1 sodium channel

To better understand why sensory neurons express voltage-gated Na+ channel isoforms that are different from those expressed in other types of excitable cells, we compared the properties of the hNE sodium channel [a human homolog of PN1, which is selectively expressed in dorsal root ganglion (DRG) neurons] with that of the skeletal muscle Na+ channel (hSkM1) [both expressed in human embryonic kidney (HEK293) cells]. Although the voltage dependence of activation was similar, the inactivation properties were different. The V1/2 for steady-state inactivation was slightly more negative, and the rate of open-state inactivation was approximately 50% slower for hNE. However, the greatest difference was that closed-state inactivation and recovery from inactivation were up to fivefold slower for hNE than for hSkM1 channels. TTX-sensitive (TTX-S) currents in small DRG neurons also have slow closed-state inactivation, suggesting that hNE/PN1 contributes to this TTX-S current. Slow ramp depolarizations (0.25 mV/msec) elicited TTX-S persistent currents in cells expressing hNE channels, and in DRG neurons, but not in cells expressing hSkM1 channels. We propose that slow closed-state inactivation underlies these ramp currents. This conclusion is supported by data showing that divalent cations such as Cd2+ and Zn2+ (50-200 microM) slowed closed-state inactivation and also dramatically increased the ramp currents for DRG TTX-S currents and hNE channels but not for hSkM1 channels. The hNE and DRG TTX-S ramp currents activated near -65 mV and therefore could play an important role in boosting stimulus depolarizations in sensory neurons. These results suggest that differences in the kinetics of closed-state inactivation may confer distinct integrative properties on different Na+ channel isoforms.

Low-level cadmium exposure of lactating rats causes alterations in brain serotonin levels in the offspring

Effects on monoaminergic and cholinergic transmitter systems as well as neurotrophins were characterized in developing Sprague-Dawley rats directly exposed to 5 ppm cadmium in the drinking water or indirectly via exposed dams. Cadmium was given to dams during the lactation period, from parturition to postnatal day 17, and/or to the offspring until postnatal day 42. Cresyl violet staining and glial fibrillary acidic protein immunohistochemistry did not reveal any obvious neuropathology after cadmium exposure. Following high-power microwave fixation, concentrations of acetylcholine (ACh) and monoamines were determined in cerebral cortex, striatum, and hippocampus using HPLC with electro-chemical detection. ACh, dopamine, and noradrenaline levels were not significantly affected after the different cadmium exposures. Cortical levels of serotonin were significantly reduced in rats exposed to cadmium during lactation as well as in rats exposed to cadmium during both lactation and postweaning. A major decrease in 5-hydroxyindoleacetic acid was found in cortex and hippocampus in rats exposed to cadmium during lactation. The regional characteristics of cadmium toxicity as reflected in changes of neurotrophins were studied using in situ hybridization histochemistry with oligonucleotide probes and phosphoimaging evaluation. No significant changes in the mRNA expression of brain-derived neurotrophic factor (BDNF), neurotrophin-3, and the high-affinity tyrosine kinase receptor of BDNF, trkB, were detected. The present results demonstrate that exposure to levels of cadmium as low as 5 ppm in the drinking water leads to neurochemical disturbances of the serotonergic system in the offspring during the lactational period.

Cadmium-induced alterations in blood-brain barrier permeability and its possible correlation with decreased microvessel antioxidant potential in rat

1. Male albino rats of 21 days age were exposed to 10 p.p.m. cadmium (CdCl2 salt) in drinking water, ad libitum, for 90 days. It increased the brain cadmium levels by 76% (P < 0.05) and 165% (P < 0.001) respectively at 30 and 90 days of exposure compared to controls. 2. Cadmium increased blood-brain barrier permeability of fluoroscein dye (24%, P < 0.02) and the levels of brain microvessel malondialdehyde (31%, P < 0.01) at 90 days of exposure. However, these parameters did not alter significantly at 30 days of exposure. 3. Increased activities of microvessel superoxide dismutase (18%, P < 0.02), glutathione peroxidase (20%, P < 0.01) and catalase (28%, P < 0.01) were observed at 30 days of exposure. 4. The continuation of the Cd treatment for 90 days decreased the levels of superoxide dismutase (30%, P < 0.001), glutathione peroxidase (23%, P < 0.005), catalase (25%, P < 0.005), glutathione reductase (18%, P < 0.02), vitamin E (20%, P < 0.01), glutathione (26%, P < 0.01), ascorbic acid (18%, P < 0.05) and ceruloplasmin (13%, P < 0.05) in the microvessal preparation compared to controls. 5. It appears that Cd-induced blood-brain barrier dysfunction may be related to the depletion of microvessel antioxidant substances along with increase in lipid peroxidation at 90 days of exposure.

Cadmium accumulation and metallothionein expression in brain of mice at different stages of development

Cadmium accumulation and metallothionein (MT) expression were studied in brains of adult mice as well as at different stages of development. MT expression was also studied in the eye of adult mice as well as at different stages of development. Using northern blot analysis with total RNA, MT mRNAs were not detected in day 16 through day 18 embryos or in postnatal animals up to day 14. Detectable expression of MT-I, -II, and -III mRNAs was obtained in brains of 30- and 60-day-old-mice. The expression of MT-III mRNA appeared to be much stronger in adults (12 weeks old or more) than in 30- and 60-day-old animals. In contrast, there was similar expression of MT-I and -II in 30- and 60-day-old mice. Cd distribution to brain was found to decrease with age; the brains of 7-day-old mice contained about 4-times more Cd than that of adult mice. Thus, an inverse correlation was observed between MT expression and Cd accumulation in brain.

Development of brain free radical scavenging system and lipid peroxidation under the influence of gestational and lactational cadmium exposure

1. Rat pups were exposed to cadmium (Cd) gestationally and lactationally through mothers receiving 20 ppm Cd in drinking water, ad libitum, from zero day of pregnancy. 2. The sequential measurement of brain lipid peroxidation showed an increase in thiobarbituric acid reactive substances at 1 (73%), 7 (30%), 14 (22%) and 21 (354%) days of age compared to respective controls. 3. A marked variation in reduced glutathione levels was observed at different postnatal ages of both control and Cd-treated groups. The levels of brain total sulphydryls were increased significantly in experimental animals at 1 (30%) and 7 (12%) days of age. 4. Cd exposure increased the activities of superoxide dismutase and glutathione peroxidase by 45% and 104%, respectively, at day one. However, the continuous exposure inhibited them at 7, 14 and 21 postnatal days. 5. Cadmium treatment elevated the levels of brain catalase and glutathione reductase at all the studied ages with a maximum alteration of 66% and 50%, respectively, at 21 days of age. 6. The data indicate that the exposure of pregnant mothers to low doses of Cd produced changes in the brain antioxidant defence mechanisms at critical periods of development which may have serious implications in later life.

Lipid peroxidation and antioxidant defense enzymes in various regions of adult rat brain after co-exposure to cadmium and ethanol

Effect of cadmium (1 mg/kg body weight) and ethanol (2 g/kg body weight) exposure, alone as well as in combination, on essential trace metal homeostasis, lipid peroxidation and antioxidant defense enzymes in various regions of the adult rat brain was investigated. It was observed that cadmium when administered along with ethanol accumulated significantly in corpus striatum (3.5 fold) and cerebral cortex (3.0 fold) compared to the cadmium treated group. The ethanol induced accumulation of cadmium led to significant depletion in the levels of essential trace metals like zinc and copper in these regions of the brain. Further, cadmium or ethanol alone did not show any significant effect on lipid peroxidation and antioxidant defense enzymes in any of the regions of the adult brain but when given in combination, caused a significant increase in lipid peroxidation and markedly decreased the activities of antioxidant defense enzymes like glutathione peroxidase, superoxide dismutase and catalase particularly in corpus striatum and cerebral cortex. Structural alterations produced by increased lipid peroxidation after cadmium and ethanol co-exposure may have profound effect on the activities of membrane bound enzymes and hence may lead to functional impairment. The results of the present study imply that ethanol renders the adult brain more susceptible to the neurotoxic effects of cadmium. Corpus striatum and cerebral cortex are more vulnerable to the toxic effects of cadmium under the influence of ethanol than other regions of the brain.

Central nervous system lesions in the Wistar rat fetus following direct fetal injections of cadmium

During embryogenesis, maternal administration of cadmium (Cd) produces teratogenic effects, including hydrocephalus (HC), whereas later in gestation (during the fetal period), such effects have not been reported. Since there is little placental transfer of Cd late in gestation, such differences in response could be due to a lower Cd concentration in the fetus compared with the embryo after maternal Cd exposure, or could be due to a decreased sensitivity of the fetal central nervous system (CNS) to Cd. To test the susceptibility of the late gestational CNS to Cd, day 19 (sperm plug = day 0) rat fetuses were directly injected i.p. with CdCl2 (165, 100, 50 nmoles/fetus in 5 microliters saline). All fetuses in one horn were treated with Cd, while fetuses in the other horn were treated with saline. Fetuses were collected on day 21, grossly examined, weighed, fixed in Bouin's fixative, and later razor sectioned. Cd did not affect fetal viability or body weight. However, Cd caused a dose-dependent increase in hydrocephalus, with the total number of fetuses showing moderate to severe HC being 0/45, 0/11, 6/10, and 18/20 for controls, low, medium, and high doses, respectively. Mild HC was noted in one control and two low Cd fetuses. Brain necrosis was correlated with hydrocephalus, being observed in 0/45, 0/11, 5/10, and 16/20 fetuses, respectively. In medium-dose fetuses without HC or brain necrosis, extravasation of erythrocytes was noted histologically within the cortical parenchyma, suggesting that hemorrhaging may lead to brain necrosis and hydrocephalus in Cd-exposed fetuses. Thus, the fetal CNS is susceptible to the toxic effects of Cd.

Effect of cadmium on lipid peroxidation and antioxidant enzymes in undernourished weanling rat brain

The effect of early postnatal cadmium exposure on lipid peroxidation and antioxidant enzymes in undernourished weanling rat brain has been studied. The results suggest that undernutrition makes the weanling rat brain more susceptible to the neurotoxic effects of cadmium. Cadmium at a low dose of 1 mg/kg body weight did not produce any changes in lipid peroxidation and antioxidant enzymes in normal weanling rat brain, but caused a significant increase in lipid peroxidation and markedly decreased the activities of antioxidant enzymes like glutathione peroxidase, superoxide dismutase and catalase when subjected to undernutrition.

Prevention of cadmium-induced effects on regional glutathione status of rat brain by vitamin E

The effect of vitamin E on the cadmium-induced changes of glutathione metabolism was investigated in different brain regions. Daily intraperitoneal injection of cadmium (0.4 mg/kg) for 30 days significantly decreased the concentration of reduced glutathione (GSH), and the activities of glutathione reductase (GR) and glucose-6-phosphate dehydrogenase (GPDH) in the cerebellum, cerebral hemispheres and brain stem of rats. Cadmium elevated the levels of oxidized glutathione (GSSG) in cerebellum and cerebral hemisphere regions only, while the GSH/GSSG ratio decreased in all three brain regions. The only effect of intramuscular injections of vitamin E (5 mg/kg) given on alternate days for 30 days was a slight increase in GSH and GR in the cerebral hemispheres. The simultaneous administration of vitamin E and cadmium prevented cadmium-induced changes in GSH and GSSG levels and in the GSH/GSSG ratio, but the cerebellar GSH remained lowered. Furthermore, vitamin E, with the exception of GR in the cerebral hemispheres, did not prevent cadmium-induced changes in enzyme activities. As the simultaneous injections of vitamin E reduced cadmium-induced alterations in glutathione concentration without having any appreciable effect on the activity of related enzymes, it is suggested that the preventive effect of vitamin E is mediated through its antioxidative effect, saving GSH from oxidative destruction in the brain of cadmium-exposed rats.

Cadmium exposure results in decreased responsiveness to ethanol

Adult male Sprague-Dawley rats were maintained on an ad lib diet containing 100 ppm cadmium (Group Cadmium-Diet) or a control diet with no added cadmium. On Day 61, all animals (N = 10/group) were challenged with a single hypnotic dose of ethanol (3.5 g/kg IP), prepared from a 20% v/v solution of tap water and a stock solution of 95% ethanol. The latency from the time of the injection until the loss of the righting reflex was recorded, as well as the latency for recovery of the reflex. The results showed a nonsignificant trend for animals exposed to cadmium to lose the righting reflex less rapidly than controls, and Cadmium-Diet animals regained the righting reflex significantly more rapidly than controls. These findings suggest that the pharmacologic effectiveness of ethanol is altered by chronic exposure to dietary cadmium. The implications of these data for other studies of cadmium/ethanol interactions are discussed.

Possible role of regional superoxide dismutase activity and lipid peroxide levels in cadmium neurotoxicity: in vivo and in vitro studies in growing rats

Cd2+ (0.4 mg/kg) administration to growing rats (45 +/- 5 g) intraperitoneally, daily for 30 days was found to decrease the activity of superoxide dismutase (SOD) in all the brain regions, except hippocampus. The concentrations of lipid peroxides were significantly elevated in the cerebellum, cerebral cortex, corpus striatum and midbrain. A 100% inhibition in SOD activity was observed by 14 microM and 50 microM of Cd2+ in bovine blood and rat brain preparations, respectively. Cadmium-induced strong inhibitory effect on brain and purified bovine blood SOD suggested a direct effect of the metal on enzyme molecule. Furthermore, in vitro addition of a wide range of Cd2+ (1-100 microM) increased the rate of lipid peroxidation (LPO) reaction in fresh brain homogenate, however, did not affect boiled homogenate. The studies on LPO in reconstituted homogenate resulting from mixing of fresh and/or heated different subcellular fractions indicated the presence of some heat-labile Cd2+ -sensitive factor in 15000 x g pellet fraction. It is suggested that Cd2+ directly and indirectly through inhibition of SOD, increases the LPO of cell membranes and thus produces damage to the associated physiological functions leading to central nervous dysfunctions.

Ethanol self-administration in rats following exposure to dietary cadmium

Rats were maintained on an ad lib diet containing 100 ppm cadmium (Group Cadmium-Diet) or a control diet with no added cadmium (Group Control-Diet). After 55 days of exposure to their respective diets, animals were tested for fluid intake using a nonchoice procedure that presented a 15% ethanol solution in the home cage for 5 days. Subsequently, all animals were offered a 10% ethanol solution or tap water in a 3-bottle, 2-fluid choice test in the home cage. This fluid intake test was conducted for a 5 day baseline period, and then again concurrently with avoidance acquisition (14 days) and extinction (4 days) training on a free operant (Sidman) avoidance task that required animals to lever press to avoid electric footshock. After training was terminated the choice test was continued further in the home cage for a 15 day post-avoidance period. Ethanol intake was greater for animals exposed to cadmium on all tests of fluid consumption, and all animals consumed more ethanol during the periods following termination of the stressor (avoidance extinction, post-avoidance) than during the actual period of stress (avoidance acquisition). Interpretive comments focus on the effects of cadmium on stress reactivity, sensory processing, and metabolism.

The vascular endothelium as a target tissue in acute cadmium toxicity

Sensitivity of tissues to the acute toxicity of cadmium is reviewed. It is concluded that the initial effect of acute cadmium administration is on the integrity and permeability of the vascular endothelium; other necrotic changes occur secondarily to this effect. In a sensitive tissue, not all of the endothelial cells are susceptible to cadmium. Furthermore, after necrosis of the sensitive cells, the resistant cells proliferate and result in regeneration of the vasculature and subsequent acquired resistance to the metal. It is found that sex hormones are probably important in determining susceptibility and response of tissues to cadmium. The role of metallothionein in these phenomena remains to be elucidated.

Effect of cadmium on lipid composition of the weanling rat brain

The effect of early postnatal cadmium exposure (cadmium injected at dose levels of 1 and 2 mg cadmium/kg body weight on 3rd, 10th and 17th day after birth) on various lipid fractions of the weanling rat brain was studied. The results suggest that cadmium treatment (a dose of only 2 mg Cd/kg) results in an appreciable decrease in myelin-specific lipids like nonesterified cholesterol, ethanolamine-containing lipids, cerebrosides and sulfatides leading to hypomyelination. The lower dose of cadmium (1 mg Cd/kg) did not have any significant effect.

Effects of cadmium exposure on zinc and copper distribution in neonatal rats

Tissue zinc and copper concentrations undergo marked changes in the neonatal rat during the first several weeks of life and it was of considerable interest to study the effect of cadmium exposure on these ontogenic changes. Long evans rats received either 2 or 10 mumol cadmium chloride per kg SC at 9 days of age and were sacrificed at 20 or 36 days of age. Tissue copper and zinc concentrations in cadmium-treated rats were compared to those of age-matched controls for statistically significant changes. The tissue affected, the element altered and the direction of change in concentration, increased (+) or decreased (-), are summarized for the two dosing groups (age at dosing, age at sacrifice in days): 2 mumol/kg (9, 20): kidney Zn (+), blood Zn (-), cerebral Cu (-), cerebellar Cu (+); 2 mumol/kg (9, 36): blood Zn (-); 10 mumol/kg (9, 20); liver, kidney, cerebral and cerebellar and blood Zn (-), cerebellar Cu (+); 10 mumol/kg (9, 36): liver and heart Zn (+), blood Zn (-); liver and heart Zn (+), blood Zn (-); kidney, cerebral, cerebellar and heart Cu (+). Changes in tissue zinc or copper concentrations produced by cadmium treatment could not be accounted for by the direct replacement of these elements by cadmium and may be due to alterations in transport of these elements. These results indicate that early life exposure to low levels of cadmium can have large and persistent effects on the distribution of the essential metals, copper and zinc.

Retrograde axonal transport of cadmium in the rat hypoglossal nerve

A small volume of radioactively labelled cadmium was injected into the tongue of rats. Two weeks later, the rats were killed and the lower brainstem with the hypoglossal nuclei was dissected out and sectioned in a cryostat. Autoradiography of freeze-dried sections showed accumulation of cadmium in both hypoglossal nuclei. When unilateral nerve section was performed prior to the injection, only the contralateral nucleus was labelled. The results are interpreted as strong evidence for retrograde axonal transport of cadmium in the hypoglossal nerve.

Influence of age on the development of cadmium-induced vascular lesions in rat sensory ganglia

It is known from previous investigations that parenteral administration of single large doses of cadmium salts causes hemorrhagic lesions in the sensory ganglia of adult rats, whereas the ganglia of immature rats remain unaffected. The present study was undertaken to determine more precisely the age at which vascular lesions occur in the sensory ganglia of rats. At the age of 10 days, thrombocytes accumulated and adhered to the endothelial cells in vessels of the trigeminal ganglion, and at the age of 12 days focal hemorrhages occurred in the vicinity of nerve cells. After the age of 12 days, ultrastructural changes in endothelial cells were present in the trigeminal ganglia, with condensation of the cytoplasm, nuclear pyknosis, and discontinuities of the endothelial lining. Intravascular thrombus formation was also observed. In the dorsal root ganglia, there were no hemorrhages before the age of 22 days. The vascular lesions were then similar to those in the trigeminal ganglia. The possible relation between the structure and permeability of endothelial cells and the development of hemorrhagic lesions is discussed.

Placental toxicity of cadmium in the rat: an ultrastructural study

Pregnant rats on day 18 of gestation were injected s.c. with 40 mumol/kg CdCl2 which caused fetal death and placental necrosis. The placental changes were studied by electron microscopy and indicate that there is a direct placental toxic effect of cadmium which appears targeted at the trophoblast and, in particular, trophoblast cell layer II. Findings in cell layer II which suggest a toxic effect were lysosomal vesiculation, 'buckshot' nuclear chromatin clumping, nucleolar changes and apparent mitochondrial calcification. Furthermore, the selectivity of the effect on cell layer II and the rapidity of the necrosis are also consistent with a toxic effect. Trophoblast cell layer II first undergoes necrosis, but is rapidly followed by the rest of the trophoblast. Many of the changes at this necrotic stage suggest a secondary ischaemic effect or a combined ischaemic and toxic effect. Therefore it appears that cadmium induces placental necrosis via a direct effect on the trophoblast, especially on layer II.

Aggressive behavior of the rat induced by repeated administration of cadmium

Muricidal behavior of the rat was induced by repeated s.c. administration of cadmium (Cd) for 15 weeks. The number of muricidal rats increased with increase in the duration of Cd administration in association with greater accumulation of Cd in the olfactory bulb than in any other region of the brain. The whole brain norepinephrine (NE) level of the rats which had been given Cd for 15 weeks was significantly greater than that of the control rats; neither dopamine (DA) nor serotonin (5-HT) level was changed. The Cd-induced muricide is discussed.

Crohn's disease: transmission electron microscopic studies. III. Target tissues. Proliferation of and injury to smooth muscle and the autonomic nervous system

Transmission electron microscopy was done on surgical specimens from 12 patients with Crohn's disease and three control subjects. Nonulcerated involved areas of ileum as well as proximal, grossly uninvolved resection margins were chosen for study. Specimens for transmission electron microscopy were prepared by a variety of techniques and 112 blocks were examined by electron microscopy. The study was concentrated on two target tissues of the gut: the autonomic nervous system and the smooth muscle. Proliferative and injurious changes were found in each. Proliferation, myofibroblastic transformation, hypercontraction, and necrosis characterized the smooth muscle changes seen in Crohn's disease of the ileum. Autonomic nervous system changes included proliferation of axons containing dense core granules (catecholamines) and axonal necrosis. The possible pathogenetic significance of these changes is discussed here and in the accompanying article beginning on page 606 of this issue.

An ultrastructural study of chronic cadmium chloride-induced neuropathy

After the long-term exposure to cadmium chloride in drinking water, the Wistar rats developed peripheral polyneuropathy. The main lesion was of myelin degeneration. Ultrastructural examination of the roots and sciatic nerves revealed segmental demyelination beginning from the node of Ranvier. There was the active autophagocytosis of Schwann cells which contained a number of myelin remnants and dense bodies. There was, on the other hand, the evidence of remyelination with toxic damage, in which the thinner myelin sheaths and abnormal myelinations were observed with increase of Schwann cells containing rich ribosomes. Axoplasmic changes were minimal, but consisted of accumulation of glycogen particles which very often produced glycogenosomes in characteristic appearance with axoplasmal dysfunction.

Quantitative and electron microscopic studies of sensory ganglion cells of the Sprawling mouse

The L4-6 sensory root ganglia of young and adult Sprawling (Swl) and normal mice were studied. Cell counts showed a great reduction in the total number of ganglion cells in Swl. Cell degeneration was observed in young Swl animals but not in normal littermates. Most of the remaining ganglion cells showed morphological abnormalities very similar to those seen in chromatolytic neurons-enlarged nucleolus, eccentric nucleus with an infolded nuclear membrane, loss of juxtanuclear Nissl bodies and an increase in neurofilaments, Golgi membranes, autophagic vacuoles, and dense bodies. In contrast to the classical changes of chromatolysis the abnormalities in Swl neurons persisted throughout the lifespan of the animals. Reconstructions from serial sections showed that ganglion cells in Swl were highly irregular in shape.