Low-dose lead encephalopathy in the suckling rat

Mute swans, Cygnus olor, killed from collision with electrical wires, a study of two situations in Sweden

Different studies indicate that 19-38% of the Swedish ringed Mute Swans (Cygnus olor) are killed by collision with electrical wires. The relative frequency of killed swans is not related to the density or type of electrical wires in the landscape, but to where in the landscape the wires are constructed, and to the time when mass movements of swans occur. Experience (age), bodyweight ("too heavy to raise"), breast muscle weakening ("engine problems") and heavy metal (lead) loads strongly affect the chances of birds avoiding collision; but, swans not belonging to these risk-groups are also killed. Different skeletal injuries were found in dead birds after collision but many of them were not lethal. It was proved, however, that most collision-birds ultimately died from liver damage, probably caused by their heavy bodies hitting the ground.

Decreased nerve conduction velocity in optic nerve following early post-natal low-dose lead exposure

A study was made on nerve conduction velocity of the optic nerve in rats subjected to lead exposure during the first 2 weeks of post-natal life. The rats were given intraperitoneal injections with a calculated daily exposure of 7.6 micrograms (low-dose) or 15.8 micrograms (high-dose) lead g-1 body weight. Growth retardation at 30 days was seen only with the higher dose. Littermates of low-dose exposed rat were injected with vehicle only and served as controls. Lead concentrations in blood and brain were measured in rats of 20 days of age in order to ascertain that exposure was adequate in the present litters. Nerve conduction velocity of the optic nerve was examined in 14 rats of 30 days of age taken from 10 different litters. The optic nerve(s) was prepared in anaesthetized rats and placed in a flow-through incubation chamber. One stimulating and two recording tungsten electrodes were used. In all rats, three positive-negative waves, regarded as representing three functional groups of optic nerve axons, could be recorded. The last one often had a long duration and a small amplitude without distinct peaks and hence was omitted from further analysis. The mean conduction velocities for the two faster axonal groups were 16.8 and 5.4 m s-1 in control rats, 10.3 and 5.8 m s-1 in low-dose rats and 9.4 and 5.2 m s-1 in high-dose rats. The difference in conduction velocity for the fastest axons was significant for controls versus low-dose and high-dose but not for low-dose versus high-dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of lead in the cerebellum of suckling rats following low and high dose lead exposure. A micro-PIXE analysis

The distribution of lead in the cerebellum of suckling Sprague-Dawley rats was examined using a nuclear microprobe for elemental mapping of tissue sections (particle-induced X-ray emission, 3-microns beam of 2.5 MeV protons; micro-PIXE). The rats were injected intraperitoneally with a lead-containing vehicle or vehicle only from ages 1 to 14 days. The calculated doses were 7.8 (low-dose) and 15.6 (high-dose) micrograms lead/g body weight. The rats were killed at 20 days of age. The vascular system was rinsed quickly with 0.15 M ammonium acetate to obtain determinations of intra-parenchymal lead with minimal influence of lead bound to erythrocytes and plasma proteins. Brains were frozen in propane/propylene in liquid nitrogen. Cryostat sections, 15 microns thick, were air dried on formvar coats that covered a hole, 15 mm in diameter, in a plastic disc, and were used for lead analysis by micro-PIXE. Very low concentrations of lead were found in the brain of controls. Lead levels in homogenates from cerebrum and cerebellum measured by atomic absorption spectrometry (AAS) were: low-dose 1.2-2.2 micrograms/g wet weight and high-dose 1.4-2.4 micrograms/g wet weight. The lead levels measured with the micro-PIXE method were in good agreement with the levels found with AAS. Lead was present in the cerebellar white matter in two to three times higher amounts than in the cortical grey (low-dose white matter 11-18 micrograms/g dry weight, grey matter 2.0-5.5 micrograms/g dry weight). This was true for both low and high dose exposed rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of dietary deficiency of nicotinamide on lead toxicity in young rats

The influence of dietary nicotinamide deficiency on lead intoxication in young developing rats was investigated. The Pb induced an increase in brain dopamine and noradrenaline, inhibition in blood δ-aminolevulinic acid dehydratase activity, an elevation in urinary excretion of δ-aminolevulinic acid and blood and tissue uptake of Pb were significantly more marked in animals maintained on a nicotinamide-deficient diet than those fed a nicotinamide-sufficient diet. The nicotinamide deficiency may enhance the susceptibility to Pb intoxication possible by enhancing the absorption of Pb and altering nicotinic acid metabolism.

Myelin basic protein in brains of rats with low dose lead encephalopathy

Postnatal exposure of rats to lead has been shown previously to cause CNS hypo-myelination. Since rats intoxicated with lead often show retarded growth, the superimposed malnutrition, which as such can cause hypomyelination, may contribute to myelin deficit. In the present study control rats and lead exposed rats which did not have any retardation of growth were examined by radioimmunological assay of myelin basic protein (MBP) of homogenates of cerebrum and cerebellum at 30, 60 and 120 days of age. Lead was administered on postnatal days 1-15 by daily intraperitoneal injections of 10 mg lead nitrate/kg body weight. This lead dose results in light microscopically discernible hemorrhagic encephalopathy in the cerebellum of 15-day old rats, but does not induce growth retardation (Sundström et al. 1983). The controls were injected with vehicle only. The amount of lead in the blood and brain homogenates of lead-exposed and control rats 15-200 days old was estimated by atomic absorption spectrophotometry. Significant differences between the lead-exposed and control rats were not found in the cerebral or cerebellar content of MBP. Considering the results of previous investigations, the findings do not exclude a hypo-myelinating effect of lead, but they suggest that exposure to lead without concomitant malnutrition does not cause hypo-myelination in the cerebrum and cerebellum of the developing rat.

Extracellular edema and glial response to it in the cerebellum of suckling rats with low-dose lead encephalopathy. An electron microscopic and immunohistochemical study

Newborn rats were exposed to daily intraperitoneal injections of 10 mg lead nitrate per kg body weight for the first 15 postnatal days. The growth and mortality of the lead-exposed animals did not differ from their control litter-mates, injected with vehicle only. In our previous studies, focal hemorrhages and spongy areas as well as breakdown of blood-brain barrier to plasma proteins were shown by light microscopy in the cerebellar parenchyma of 15-day-old rats exposed to this dose. In spite of these signs of edema, measurements of brain tissue specific gravity did not show increased water content. In the present investigation we examined the ultrastructure of the brain lesions in these rats with low-dose lead encephalopathy, focusing on signs of edema, and evaluated astroglial reaction by immunocytochemical staining for glial fibrillary acidic protein (GFAP). The electron microscopic findings were compatible with extracellular edema in the cerebellum of 15-day-old lead exposed rats. The number of GFAP-positive cell bodies in the gray substance of the cerebellar cortex was increased in the 15-day-old lead-exposed rats as compared with the controls of the same age, a finding which is presumably related to the leakage of plasma proteins. Both these findings were lacking at 20 days of age, suggesting reversibility of the lead-induced changes.

Changes in the integrity of the blood-brain barrier in suckling rats with low dose lead encephalopathy

Previous studies on the toxic effects of lead on the brains of young animals have shown damage to the blood-brain barrier (BBB) which in severe forms appears as hemorrhagic encephalopathy. In those studies the doses of lead have been of such magnitude that lead-induced anorexia resulting in growth retardation has contributed to the extent of the injury (Sundström et al. 1984). The growth retardation can be prevented by using low lead doses (Sundström et al. 1983). Consequently, we have examined to which extent the BBB is injured in suckling rats with low dose lead encephalopathy. This was done by testing the permeability of the BBB to plasma proteins and assessing the possible occurrence of vasogenic edema by measuring the specific gravity of brain tissue. Low dose lead encephalopathy was induced by daily i.p. injections of lead nitrate 10 mg/kg body weight (b.wt.) for the first 15 days. The lead contents of the blood and homogenates of the cerebrum and cerebellum were assayed by atomic absorption spectrophotometry. The brains were examined at 15, 20, or 30 days of age. When Evans blue-albumin (EBA) was injected i.v. 2 h before killing, most 15-day-old rats exposed to lead displayed a bluish discoloration in their cerebellum. Microscopically, red fluorescence of EBA was seen in the blue-stained regions. Immunohistochemically, extravasation of albumin, fibrinogen, and fibronectin was demonstrated as positive staining in the cerebellar cortex, with diffuse spread to the white matter of the corresponding folium.(ABSTRACT TRUNCATED AT 250 WORDS)

Vulnerability to lead in protein-deprived suckling rats

Most studies on lead toxicity in the suckling rat have been performed with doses leading to growth retardation. In a previous paper ( Sundstr öm et al. 1983), the effects of different lead doses on normal suckling rats were described. The dose of 10 mg/kg body weight daily given on days 1-15 pp produced minute hemorrhagic lesions on day 15 in the cerebellum, whereas rats given 5 mg/kg body weight daily lacked microscopically discernible pathologic changes in the brain. None of these groups exhibited growth retardation. To further elucidate the association between lead encephalopathy and malnutrition, lead was administered to protein-deprived suckling rats. Protein deprivation was achieved by a diet with 50% reduction of protein content. The mothers of the pups were fed this diet from 2 weeks before conception throughout the experiment. Experimental animals were injected i.p. with 5 mg or 10 mg lead nitrate/kg b.wt. daily. Littermates, injected with vehicle without lead nitrate served as controls. Protein-deprived rats without either treatment were "external" controls. Animals were killed at 10, 15, and 20 days age for determination of lead content in blood and brain and for light-microscopic examination. The protein-deprived rats given 10 mg/kg b.wt. daily were growth-retarded as compared to unexposed protein-deprived rats. The mortality was almost 100% at 15-20 days pp. At 15 days, the cerebellum of these rats showed abundant hemorrhages, and the cerebrum was also hemorrhagically discolored. Protein-deprived rats given 5 mg/kg b.wt. daily did not differ significantly from unexposed protein-deprived rats with regard to body weight gain.(ABSTRACT TRUNCATED AT 250 WORDS)