Influence of lead exposure on catecholamine metabolism in discrete rat brain nuclei

1. Using the rat exposed both acutely and chronically to lead as a model of lead neurotoxicity, various parameters of catecholamine metabolism were investigated. 2. The steady-state concentrations of noradrenaline, adrenaline and dopamine together with the activities of tyrosine hydroxylase and phenylethanolamine N-methyl transferase were measured in discrete brain nuclei--periventricular, paraventricular, median eminence, posterior and anterior hypothalamus, caudate putamen and globus pallidus. 3. Lead exposure resulted in significant fall in the activity of the rate-limiting enzyme of catecholamine synthesis, tyrosine hydroxylase which was associated with alterations in concentrations of catecholamines in the median eminence, periventricular nucleus and anterior hypothalamus. 4. No other brain nuclei investigated exhibited any effect of lead on the catecholaminergic nervous system and, therefore, the effect of lead on rat brain can be considered to be regionally specific.     

Alterations in some membrane properties in rat brain following exposure to lead

The effect of lead exposure on intracellular calcium levels, membrane fluidity, lipid peroxidation, acetylcholinesterase and monoamine oxidase activity and its accumulation in different regions of the brain were studied to understand the molecular mechanism of lead induced neurotoxicity. Lead treatment (20 mg/kg lead nitrate, intraperitoneally, once daily for 15 days) resulted in a significant accumulation of lead in all brain regions with the maximum being in the hippocampus. Levels of glutathione, lipid peroxidation, intracellular calcium and membrane fluidity, as well as the activity of the membrane bound enzymes, acetylcholinesterase and monoamine oxidase, increased to a significant level in certain areas of the rat brain. The results suggest that lead exerts neurotoxic effects by altering certain membrane bound enzymes and may cause oxidative stress.     

Influence of chronic inorganic lead exposure on regional dopamine and 5-hydroxytryptamine turnover in rat brain

The results of previous behavioral studies utilizing chronic exposure to low amounts of inorganic lead (Pb) have suggested alterations in the function of biogenic amine neuronal systems. The following study was performed to provide evidence for the possible bases of these changes in pharmacological responsiveness in exposed animals. Dams were administered 0.2% Pb acetate in drinking water to expose their offspring to Pb via the maternal milk. Males were weaned to the same drinking solution. At 120–140 days a tracer dose of 1.0 mCil-[³H]2,6-tyrosine (³H-TYR) and 0.5 mCil-[³H(G)]tryptophan (³H-TRP) was injected through an indwelling jugular catheter, and norepinephrine (NE), dopamine (DA), 5-hydroxytryptamine (5-HT) and their respective precursors and metabolites were quantified by liquid chromatography with electrochemical detection with column eluate collected for liquid scintillation counting. At this level of exposure (blood lead (PbB) at day 90 in exposed animals=43.1±1.7 g/dl) no changes were observed in concentration Nf NE or DA mr DA metabolites in any brain region. However, DA turnover was decreased in Pb-exposed animals in nucleus accumbens and frontal cortex. No changes in 5-HT content and turnover were observed in any brain region, but 5-hydroxyindoleacetic acid (5-HIAA) levels were decreased in 6 of the 9 brain regions examined. These findings are consistent with observations of an attenuated behavioral responsiveness to d-amphetamine (AMPH) in exposed animals, and suggest that the changes in DA and 5-HT neurons noted by other workers at higher levels of exposure persist when PbBs are in the range of 40 g/dl.     

Effect of inorganic lead exposure on myelination in the rat

The effect of defined lead burdens on myelination of the central and peripheral nervous systems was studied in neonatal Long-Evans rats. Pups were exposed to inorganic lead (100 or 400 mg Pb as lead acetate/kg body wt/day by gastric intubation) from day 2 following birth to 30 days of age. Accumulation of myelin in forebrain was not affected by the 100-mg dosage, but at the 400 mg/kg dosage level, myelin accumulation was reduced by approximately 42% on a per gram forebrain basis relative to vehicle-intubated animals. The deficit was over 50% on a per forebrain basis, since there was also a slight reduction in brain weight. This lead effect was observed at both 15 and 30 days of age. Accumulation of myelin in optic nerve (determined on the basis of proteolipid protein concentration) was also reduced by 30% relative to controls by this dosage level. However, myelination in sciatic nerve (determined on the basis of P₀ protein concentration) was not affected by this exposure regimen. Myelin deficits were greater than could be accounted for by undernutrition arising secondary to lead exposure and were not due to a developmental delay in the onset of myelination.     

Effects of sub-chronic low-level lead exposure on the homeostasis of copper and zinc in rat tissues

Information about the health risks or the subtle adverse health effects that might be associated with low-level lead exposure on micronutrient metabolism are scarce in the literature. The present work investigated the subtle adverse health effects of exposure to progressively low levels of lead on the metabolism of two micronutrients, copper and zinc in different tissues of the rat. Rats were exposed to 200, 300 and 400 ppm lead in their drinking water for 12 weeks. Lead, copper and zinc concentrations were determined in blood, liver, kidney, heart, spleen and brain of the animals. While the imbalance in zinc metabolism was characterized by a deposition of zinc in the kidney and to a lesser extent in the heart of the animals, imbalance in copper metabolism was characterized by a depletion of blood and splenic copper concentrations as well as renal and cardiac accumulation of copper. Hepatic and brain copper and zinc contents, together with blood zinc were not affected by the 12-week lead exposure. A linear relationship was observed between lead dose and lead accumulation in the spleen, whereas a non-linear relationship was observed between lead dose and lead accumulation in blood, liver, kidney and heart. Our findings indicate that exposure to progressively low-level lead concentrations results in imbalance in copper and zinc in the organism and this might be a factor in propensity toward behavioral disorders observed in lead exposure.     

Alterations in calcium homeostasis on lead exposure in rat synaptosomes

The effects of lead on Ca²⁺ homeostasis in nerve terminals was studied. Incubation with leadin vitro stimulated the activity of calmodulin and the maximum effect was observed at 30 M lead, higher concentrations had an inhibitory effect.In vivo exposure to lead increased the activity of calmodulin by 45%. Lead had an inhibitory effect on Ca²⁺ ATPase activity in both calmodulin-rich and calmodulin-depleted synaptic plasma membranes, the IC₅₀ values for inhibition being 13.34 and 16.69 M respectively. Exogenous addition of calmodulin (5 g) and glutathione (1 mM) to calmodulin rich synaptic plasma membranes reversed the inhibition by IC₅₀ concentration of lead.In vivo exposure of lead also significantly reduced the Ca²⁺ ATPase activity, resulting in an increase in intrasynaptosomal calcium. Concomitant with the increase in intrasynaptosomal calcium, lipid peroxidation values also increased significantly in lead-treated animals. In addition lead also had an inhibitory effect on depolarization induced Ca²⁺ uptake and the inhibition was found to be a competitive one. The results sugest that lead exerts its toxic effects by modifications of the intracellular calcium messenger system which would have serious consequences on neuronal functioning.     

Decreased brain volume in adults with childhood lead exposure

Background

Although environmental lead exposure is associated with significant deficits in cognition, executive functions, social behaviors, and motor abilities, the neuroanatomical basis for these impairments remains poorly understood. In this study, we examined the relationship between childhood lead exposure and adult brain volume using magnetic resonance imaging (MRI). We also explored how volume changes correlate with historic neuropsychological assessments.

Methods and Findings

Volumetric analyses of whole brain MRI data revealed significant decreases in brain volume associated with childhood blood lead concentrations. Using conservative, minimum contiguous cluster size and statistical criteria (700 voxels, unadjusted p < 0.001), approximately 1.2% of the total gray matter was significantly and inversely associated with mean childhood blood lead concentration. The most affected regions included frontal gray matter, specifically the anterior cingulate cortex (ACC). Areas of lead-associated gray matter volume loss were much larger and more significant in men than women. We found that fine motor factor scores positively correlated with gray matter volume in the cerebellar hemispheres; adding blood lead concentrations as a variable to the model attenuated this correlation.

Conclusions

Childhood lead exposure is associated with region-specific reductions in adult gray matter volume. Affected regions include the portions of the prefrontal cortex and ACC responsible for executive functions, mood regulation, and decision-making. These neuroanatomical findings were more pronounced for males, suggesting that lead-related atrophic changes have a disparate impact across sexes. This analysis suggests that adverse cognitive and behavioral outcomes may be related to lead''s effect on brain development producing persistent alterations in structure. Using a simple model, we found that blood lead concentration mediates brain volume and fine motor function.     

Effects of whole body microwave exposure on the rat brain contents of biogenic amines.

The effects of whole body microwave exposure on the central nervous system (CNS) of the rat were investigated. Rats weighing from 250 to 320 g were exposed for 1 h to whole body microwave with a frequency of 2450 MHz at power densities of 5 and 10 mW.cm-2 at an ambient temperature of 21-23 degrees C. The rectal temperatures of the rats were measured just before and after microwave exposure and mono-amines and their metabolites in various discrete brain regions were determined after microwave exposure. Microwave exposure at power densities of 5 and 10 mW.cm-2 increased the mean rectal temperature by 2.3 degrees C and 3.4 degrees C, respectively. The noradrenaline content in the hypothalamus was significantly reduced after microwave exposure at a power density of 10 mW.cm-2. There were no differences in the dopamine (DA) content of any region of the brain between microwave exposed rats and control rats. The dihydroxyphenyl acetic acid (DOPAC) content, the main metabolite of DA, was significantly increased in the pons plus medulla oblongata only at a power density of 10 mW.cm-2. The DA turnover rates, the DOPAC:DA ratio, in the striatum and cerebral cortex were significantly increased only at a power density of 10 mW.cm-2. The serotonin (5-hydroxytryptamine, 5-HT) content in all regions of the brain of microwave exposed rats was not different from that of the control rats. The 5-hydroxyindoleacetic acid (5-HIAA) content in the cerebral cortex of microwave exposed rats was significantly increased at power densities of 5 and 10 mW.cm-2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Human brain neurochemistry - some postmortem problems

Neurochemical analyses of postmortem human brain tissue is currently a challenging and expanding area of research. Many groups are now concentrating on mapping central neuronal pathways or identifying biochemical abnormalities in neurological and psychiatric diseases. In investigations of this kind a number of more or less obvious problems have to be tackled and this article provides some idea of current, and often controversial, issues associated with sampling postmortem brain material and with some of the variable factors which may influence neurochemical data.     

Effects of dysthyroidism on central catecholaminergic neurons

After 15 years of research, it is clear that alterations in thyroidal status affect catecholaminergic neurons in the developing as well as in the adult brain. Experiments on fetal catecholaminergic brain areas grafted into the anterior eye chamber of adult thyroidectomized rat have shown the thyroid hormone dependency of the morphological differentiation of catecholaminergic neurons originating from the substantia nigra and the locus coeruleus. Furthermore, thyroid hormones also affect the metabolism of catecholaminergic neurons. Neonatal hypothyroidism induced either by ¹³¹I or by an antithyroid drug decreases the concentration of dopamine, noradrenaline and the activity of tyrosine hydroxylase at least in whole brain studies. Treatments with l-thyroxine of neonatally thyroidectomized rats reverse these neurochemical changes in a both time and dose dependent manner. These presynaptic modifications are associated with a decrease in the number of catecholaminergic receptors in different brain areas. On the opposite, experimental neonatal hyperthyroidism induced by daily administration of l-triiodothyronine increases the synthesis as well as the utilization of catecholamines. These changes are also associated with an alteration of catecholaminergic receptors. Despite numerous studies, there is, so far, no clear conclusion on the effects of neonatal dysthyroidism on the development of each catecholaminergic group. However, from these studies, it appears that the intensity of neonatal dysthyroidism greatly varies, depending of the monoamine and the brain area studied. The utilization of fetal brain cell cultures growing in a chemically defined medium has permitted to demonstrate the direct effect of thyroid hormones on fetal brain cells and the morphological effects of triiodothyronine on the size and the neurite length and arborization of fetal hypothalamic dopaminergic neurons.In the adult brain, hypothyroidism induced by surgical thyroidectomy, decreases the rate of catecholamines synthesis, decreases the number of alpha noradrenergic receptors and has no effect on striatal dopaminergic receptors. In contrast, hyperthyroidism increases the rate of catecholamines synthesis and induced an hypersensitivity of noradrenergic receptors. The intensity of the effects of dysthyroidism seems to be dependent on the monoamine and the brain area studied.In conclusion, it can be proposed that in the neonate thyroid hormones act on CA neuron activity mostly through a morphogenetic effect whereas in the adulthood they directly affect CA metabolism.     

Effects of insulin on rat brain noradrenaline

A single intracardial injection of streptozotocin produced a significant increase in rat hypothalamic noradrenaline while no changes were observed in the olfactory tubercles. The parenteral administration of a single dose of insulin decreased rat hypothalamic noradrenaline; the effect had a rapid onset and lasted for at least six hours. Similar noradrenaline reductions were observed in the olfactory tubercles but in this tissue the depletion started later and recovered earlier. In addition, in olfactory tubercles after insulin injection, tyrosine level and dopamine metabolism were increased. The results show that the increases in hypothalamic NA observed in streptozotocin diabetic rats are counteracted by insulin administration and possibly the consequence of changes in noradrenaline turnover.     

The influence of phentolamine on the fluorescence of catecholaminergic structures in selected areas of rat brain.

Wistar rats were given phentolamine into the ventriculus lateralis. The D1 group of rats received a larger dose than the D2 group. The animals were decapitated within 2 hours after phentolamine injection. The FALCK fluorescence technique was applied to demonstrate the fluorescence of catecholaminergic structures. The results in rat brain areas selected according to KONIG and KLIPPEL are shown in figs 10-46. Whereas earlier biochemical experiments did not show any phentolamine-induced changes in the NA level of the whole brain, the present histochemical experiments carried out with the fluorescence technique revealed the influence of phentolamine on individual structures and areas of the NA system. In comparison with the control material in 5 out of 11 areas the fluorescence was much weaker, in 3 it was similar to the control group, and in 3 (1 with a larger dose and 2 with a smaller dose of phentolamine) it was slightly stronger. The simultaneous increase of fluorescence in 6 out of 7 areas of the DA system may indicate a compensatory interaction of these areas as a response to the neuromediator decrease in the NA system. The paper discusses the increase in the intensity of fluorescence induced by a small dose of phentolamine in some brain areas, or by a large dose in others, both these alternatives depending on the neuromediator turnover.     

Effects of acute manganese chloride exposure on lipid peroxidation and alteration of trace metals in rat brain

Although manganese (Mn) is an essential element, exposure to excessive levels of Mn and its accumulation in the brain can cause neurotoxicity and extrapyramidal syndrome. We have investigated the differences in the accumulated levels of Mn, the degree of lipid peroxidation, and its effects on the levels of trace elements (Fe, Cu, and Zn) in various regions in the brain of rats having undergone acute Mn exposure. The rats in the dose—effect group were injected intraperitoneally (ip) with MnCl₂ (25, 50, or 100 mg MnCl₂/kg) once a day for 24 h. The Mn significantly accumulated (p<0.05) in the frontal cortex, corpus callosum, hippocampus, striatum, hypothalamus medulla, cerebellum, and spinal cord in each case. The rats in the timecourse group were ip injected with MnCl₂ (50 mg MnCl₂/kg) and then monitored 12, 24, 48, and 72 h after exposure. The Mn accumulated in the frontal cortex, corpus callosum, hippocampus, striatum hypothalamus, medulla, cerebellum, and spinal cord after these periods of time, In both the dose—effect and time-course studies, we observed that the concentration of malondialdehyde, an end product of lipid peroxidation, increased significantly in the frontal cortex, hippocampus, striatum, hypothalamus, medulla, and cerebellum. However, no relationship between the concentrations of Mn in the brain and the extent of lipid peroxidation was observed. In addition, we found that there was a significant increase (p<0.05) in the level of Fe in the hippocampus, striatum, hypothalamus, medulla, and cerebellum, but the Cu and Zn levels had not changed significantly. These findings indicated that Mn induces an increase in the iron level, which provides direct evidence for Fe-mediated lipid peroxidation in the rats' brains; these phenomena might play important roles in the mechanisms of Mn-induced neurotoxicology.     

Behavior and neurotoxic consequences of lead on rat brain followed by recovery

Long-term exposure to lead has been shown to produce behavioral disturbances in human and animal models. These disturbances are shown to be associated with alterations in cholinergic and dopaminergic neurotransmission in the central nervous system. The present experiment was designed to study the effect of lead exposure on neurotransmitters like dopamine, serotonin, norepinephrine, and activity of acetyl cholinesterase along with alterations seen in memory and locomotor functions. Lead was administrated orally in a dose of 50 mg/kg for 8 wks on alternate days and a study was done at the end of exposure and also after 8 wk of recovery. Lead exposure reduced the brain and body weight, which, however, did not improve even after recovery of 8 wk. The alterations seen in the various transmitters also remain unchanged at the end of recovery. Lead exposure for 8 wk affected the locomotor and cognitive functions as assessed by the rota rod treadmill and active avoidance test. However, following a recovery period, a significant improvement was seen in locomotor as well as cognitive behavior. The short-term memory as assessed by the passive avoidance test remains unchanged both following lead exposure as well as recovery.     

Bee venom acupoint stimulation increases Fos expression in catecholaminergic neurons in the rat brain

Fos immunocytochemistry was combined with tyrosine hydroxylase (TH) or dopamine-beta-hydroxylase (DBH) immunolabeling to examine brainstem catecholaminergic neuronal activation resulting from bee venom (BV) stimulation of the Zusanli acupoint (ST36) in Sprague-Dawley rats. BV injection into the Zusanli acupoint caused increased Fos expression in catecholaminergic neurons located in the hypothalamic arcuate nucleus (Arc), the dorsal raphe (DR), the A5 cell group (A5) and the locus coeruleus (LC). BV acupoint stimulation significantly increased Fos-TH double-labeled neurons in the Arc, LC and DR. Fos-DBH positive neurons were also increased by BV acupoint stimulation in the LC and A5. In contrast BV stimulation of a non-acupoint only increased Fos expression and Fos-TH double-labeled neurons in the Arc. These data indicate that BV acupoint stimulation activates brainstem catecholaminergic neurons and that this activation underlies BV acupoint-induced antinociception.     

Effects of sub-chronic aluminum chloride exposure on rat ovaries

Aims

This experiment investigated the effects of sub-chronic aluminum chloride (AlCl₃) exposure on rat ovaries.

Main methods

Eighty female Wistar (5 weeks old) rats, weighed 110–120 g, were randomly divided into four treatment groups: control group (CG), low-dose group (LG, 64 mg/kg BW AlCl₃), mid-dose group (MG, 128 mg/kg BW AlCl₃) and high-dose group (HG, 256 mg/kg BW AlCl₃). The AlCl₃ was administered in drinking water for 120 days. The ovarian ultrastructure was observed. The activities of acid phosphatase (ACP), alkaline phosphatase (ALP), succinate dehydrogenase (SDH), Na⁺–K⁺-ATPase, Mg^2 +-ATPase and Ca^2 +-ATPase, the contents of Fe, Cu and Zn, and the protein expression of follicle-stimulating hormone receptor (FSHR) and luteinizing hormone receptor (LHR) in the ovary were determined.

Key findings

The results showed that the structure of the ovary was disrupted, the activities of ALP, ACP, SDH, Na⁺–K⁺-ATPase, Mg^2 +-ATPase and Ca^2 +-ATPase, the contents of Zn, Fe and the protein expression of FSHR and LHR were lowered, and the content of Cu was increased in AlCl₃-treated rats than those in control.

Significance

The results indicate that sub-chronic AlCl₃ exposure caused the damage of the ovarian structure, the disturbed metabolism of Fe, Zn and Cu and the decreased activities of Na⁺–K⁺-ATPase, Mg^2 +-ATPase and Ca^2 +-ATPase in the ovary, which could result in suppressed energy supply in the ovary. A combination of suppression of energy supply and reduction of expression of FSHR and LHR could inhibit ovulation and corpus luteum development, leading to infertility in female rats.     

Dose-related effects of dichloromethane on rat brain in short-term inhalation exposure

Male Wistar rats were exposed to 500, 1000 or 100 ppm as time-weighted average (t.w.a.) concentrations of dichloromethane vapour. The 1000 (t.w.a.) ppm exposure consisted of two 1-h peak concentrations (2800 ppm) on a basal exposure of 100 ppm. All exposures lasted for 6 h, 5 days weekly and for 2 weeks. The solvent burdens were analyzed in the perirenal fat samples which showed a relation to the dose with the highest values in the 1000 (t.w.a.) ppm exposures. The solvent concentrations increased in the perirenal fat between the two weeks of exposure. Blood carbon monoxide concentrations did not accurately reflect the body solvent burdens. Neurochemical effects also displayed a dose relationship, and included decreased succinate dehydrogenase activity in the cerebellum at the two higher doses and increased acid proteinase activity at 1000 ppm in the cerebrum. Withdrawal of the animals for 7 days from the 2-week exposure showed that the biochemical changes were largely abolished with the exception of decreased succinate dehydrogenase activity at 1000 ppm (t.w.a.).     

Effects of lead and hyperthermia on prenatal brain growth of guinea pigs

The effects of lead at blood levels of 100 micrograms/100ml or less on the brains of young animals have not been clearly defined, and little is known of its effects and interactions with other agents on prenatal brain development. This study examined the effects of subclinical doses of lead acetate given to pregnant guinea pigs on the development of the embryo brain. At 9 A.M. on day 20 or 21 of pregnancy, guinea pigs were given 6, 12.5, or 25 mg/kg body weight of 0.5% lead acetate in distilled water by intraperitoneal injection. Some of the animals at each dose rate were also exposed to hyperthermia at 11 A.M. on the day of injection and the following day. Another group was exposed to hyperthermia without lead treatment. A saline-treated control group was used for comparison. Mean levels of lead in blood 1 hour after dosing ranged between 65 and 128 micrograms/100 ml and at 24 and 72 hours between 65 and 96 micrograms/100 ml. Brain weights of newborn guinea pigs in the 12.5- and 25-mg lead acetate group were significantly reduced compared with control values. Body weights of all groups receiving lead were not significantly different from those of controls. There was no indication of interaction between hyperthermia and lead acetate in doses of 6 or 12.5 mg/kg. At 25 mg/kg plus hyperthermia, there appeared to be a strong synergistic response, with an incidence of 88% micrencephaly compared with 5% in the group given 25 mg/kg without hyperthermia and 46% in the hyperthermia without lead group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of lead poisoning on properties of brain mitochondria in young rats

When the litters were 14 days old, wistar rat pups received lead ions. The suckling mother was fed by a powdered laboratory chow containing lead carbonate (1%, 2%, 4%). The intoxication was going on for 3 days to 9 weeks. While lead-fed pups showed a decrease in body-weight gain and in neurologic development, lead ions were without effects on oxygen consumption, ADP-phosphorylation and activity of several enzymes of cerebral mitochondria. On the other hand, the important lead accumulation into cerebral mitochondria was in a straight ratio with lead doses in the feedings. To explain the in vivo data, the effects of lead acetate were investigated in vitro on brain mitochondria of young male wistar rats. Our findings indicate that lead ions alter mitochondrial respiration and ADP-phosphorylation and that inorganic phosphate has a protective effect.     

Monoamine oxidase activity of rat brain under cold exposure

Cold stress and cold adaptation were studied for their effect on the activity and substrate specificity of the monoamine oxidase A and B and on the Km of serotonin deamination in the rat brain mitochondria and supernatant. Mitochondrial monoamine oxidase Km with serotonin is established to increase more than twice under cold stress and decrease considerably in cold adapted rats. The lowering of the mitochondrial monoamine oxidase A activity is accompanied by the appearance of serotonin and the glucosamine deaminating activity in supernatant. The data suggest that decrease in the monoamine oxidase activity under cold stress may be caused by both release of the enzyme from mitochondrial membrane and changes in its catalytic property alteration.