Lead exposure during infancy permanently increases lithium-induced polydipsia.

Lead (200 milligrams per kilogram) was administered daily by intubation to Long-Evans rats on days 3 through 30 of life. Thirty to 180 days after cessation of lead administration, the lead-treated rats were consistently more polydipsic after lithium administration (2 millimoles per kilogram per day) than were pair-treated controls. Lithium increased the plasma renin activity equally in both the lead treated and the control groups. These data are evidence that there may be permanent neural changes induced by postnatal exposure to lead that are manifested by pharmacological challenge with lithium.

Trimethyltin retinopathy. Relationship of subcellular response to neuronal subspecialization.

Retinal neurons from rats acutely intoxicated with trimethyltin (TMT) were examined by light and electron microscopy to determine if there is a relationship between the subcellular response of a neuron to TMT and its morphologic subspecialization. Subcellular pathologic alterations were present in neurons from all three cellular layers of the sensory retina. However, the type and degree of subcellular response varied among the highly subspecialized neurons of the different retinal layers. Clusters of dense-cored vesicles and tubules were mainly limited to neurons of the ganglion-cell layer, large accumulations of dense bodies were mainly limited to neurons of the inner nuclear layer, and neuronal necrosis was mainly limited to the photoreceptor cells. The inner segment of the photoreceptor cell shared with the perikaryon of more conventional neurons a special vulnerability to TMT cytotoxicity. Our results suggest that the morphologic subspecialization of neurons affects the type and the degree of subcellular response to TMT.

Schwann cell vulnerability to demyelination is associated with internodal length in tellurium neuropathy.

The frequency of demyelinated fibers in mixed nerve and cutaneous nerve and the relationship of the frequency of demyelination to internodal length were assessed in a model of tellurium neuropathy in the rat. Twenty-day-old Long-Evans rats were fed chow containing 1.25% elemental tellurium for seven days and subsequently killed at 34 or 41 days of age. Teased-fiber preparations revealed a higher frequency of demyelinated fibers in sciatic nerve (mixed nerve) than in sural nerve (cutaneous nerve). The frequency of demyelinated fibers was positively associated with internodal length in both nerves. The type of nerve (mixed or cutaneous) was not a significant predictor of the frequency of demyelinated fibers once internodal length had been taken into account. These data indicate that there is a hierarchy of vulnerability within the population of myelinating Schwann cells to tellurium toxicity, and that this hierarchy is related to internodal length. The hierarchy of vulnerability may reflect intrinsic differences among Schwann cells, such as the volume of myelin each cell is synthesizing and maintaining, or a gradient of unrecognized axonal abnormalities.

Effect of lead on the developing peripheral nervous system.

The effect of lead on the developing nervous system was studied in the Long-Evans rat. Pups were intoxicated with lead from day 2 through the 20th day of life with a dosage of 1 gm Pb/kg body weight. Doses were administered via gastric gavage on the second and third days of life, and bidaily thereafter. Lead-treated and age-matched controls were then studied at selected intervals up to and including 20 days of age. Central and peripheral nervous systems were examined by light and electron microscopy. Morphometric analysis focused on defined segments of proximal and distal sciatic nerves and the 6th dorsal and ventral lumbar roots. For teased fiber studies, a segment of the contralateral proximal sciatic nerve was used. The investigation revealed that during the period studied, the myelin formed is stable. Multiple lead effects, however, were found: the Schwann cell is initially swollen but this effect gradually wanes during the 20 day period; myelin compaction is initially delayed, particularly in the ventral roots; axonal segregation proceeds, but appears to be accelerated in the ventral roots of the lead-treated pups where the larger bundles of naked axons disappear by five days of life. All of the changes noted, except axonal segregation, are reversed in the face of continued lead intoxication. While the hallmarks of "classical" lead neuropathy--segmental demyelination and the selective involvement of large fibers were not observed--the sensitivity of the somatic efferent fibers to lead was apparent in the accentuation of the lead effects in the ventral roots.

Apolipoprotein E is released by rat sciatic nerve during segmental demyelination and remyelination.

Apolipoprotein E (apo E) is synthesized and released in greatly increased amounts by peripheral nerve following Wallerian degeneration; it has been suggested that this protein may function in the transport of degenerated myelin lipid. The purpose of this study was to determine if the amount of apo E released by rat peripheral nerve is increased following selective demyelination, in the absence of significant axonopathy. Using an immunoturbidimetric assay, release of apo E from excised sciatic nerve segments was measured during the phases of acute demyelination and remyelination caused by tellurium (Te) toxicity, during segmental demyelination in chronic lead (Pb) poisoning, and during Wallerian degeneration following nerve crush. Morphologic changes were examined in contralateral sciatic nerves by nerve-fiber teasing or by light and electron microscopy of transverse sections. As in previous studies, the amount of apo E released from the nerves was greatly increased following Wallerian degeneration due to nerve crush. In Te neuropathy, increased release of apo E was first detected on the fourth day of Te exposure, corresponding temporally to the acute onset of paralysis and segmental demyelination. Apolipoprotein E release rose steeply to a maximum of ten times the control values by day 9 and then gradually waned during the next five weeks, corresponding to a period of active remyelination and resolution of the neuropathy. In the demyelinating neuropathy of chronic lead poisoning, apo E release was increased four times over control animals after seven weeks of exposure, with less than 10% of teased fibers showing early paranodal demyelination and no evidence of remyelination.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential vulnerability of mixed and cutaneous nerves in lead neuropathy.

The prevalence of demyelinated fibers in mixed nerve (sciatic) and cutaneous nerve (sural) and the change in lead levels in various tissues over time were assessed in a model of lead neuropathy in the rat. Long-Evans rats were given drinking water containing 4% lead acetate and killed between one and 213 days of exposure. Lead levels in blood, brain, kidney, and femur increased over the 213-day period. Lead levels in sciatic nerve appeared to increase rapidly during the first few weeks of exposure and then decline to a lower plateau. The neuropathy was characterized by segmental demyelination and remyelination; neither axonal degeneration nor a microangiopathy was found. Sciatic nerve had a significantly greater prevalence of demyelinated fibers than sural nerve; the prevalence of demyelinated fibers was similar in proximal and distal sciatic nerve. The variable, brain-lead concentration times days on lead, which is an indicator of cumulative brain exposure, was the best predictor of the prevalence of demyelination. The differential involvement of sciatic and sural nerves in lead neuropathy may either indicate that Schwann cells myelinating different nerve-fiber populations have different susceptibilities to lead toxicity, or that lead preferentially enters sciatic nerve.

Neuropathology of heavy metal intoxication.

The basis for utilizing altered morphology, i.e., pathology, in defining diseases of the nervous system is presented. The importance of recognizing the dynamics of pathologic processes is emphasized, particularly in understanding the pathogenesis of neural diseases. Demonstrative examples of the neuropathology of human heavy metal toxicity are presented. The limitations of descriptive pathology are considered, and the potentials of quantitative (morphometric) analysis for studying pathologic processes are introduced.

Effect of lead intoxication on the postnatal growth of the rat nervous system.

Lead encephalopathy was induced in developing Long-Evans rats by adding lead carbonate (4% w/w) to the diet of nursing mother immediately after delivery. The morphological and biochemical features of cerebral ontogenesis were studied in 30-day-old rats. By the 30th postnatal day, the overall effect of lead intoxication was retardation of brain growth. The mass of both the cerebral gray and white matter was appreciably reduced in the lead rats without any reduction in cell populations. While the neuronal population was preserved, the growth of neurons was reduced and their maturation retarded. The retarded neuronal growth was characterized by the limited proliferation of processes in the neuropil and by the reduction in the number of synapses per neuron. However, synaptogenesis was neither delayed nor perturbed but reduced by the limited development of neuronal dendritic fields. The myelination was altered and its cerebral content significantly reduced. The effect of lead on myelination was one of hypomyelination. The hypomyelination appears to be primarily related to retarded growth and maturation of the neuron and is not a reflection of a defect in the myelinating glia or a delay in the initiation of myelination.

Blood-brain barrier dysfunction in acute lead encephalopathy: a reappraisal.

Acute lead encephalopathy was induced in adult guinea pigs by administering daily oral doses of lead carbonate. During the development of the encephalopathy, the structural and functional integrity of the blood-brain barrier was evaluated with electron microscopy and tracer probes. Blood, cerebral gray matter, liver, and kidney were analyzed for lead, calcium, and magnesium content. The animals regularly developed an encephalopathy after four doses of lead. There were no discernible pathomorphologic alterations in the cerebral capillaries or perivascular glial sheaths. Furthermore, no evidence of blood-brain barrier dysfunction was demonstrated with Evans blue-albumin complex or horseradish peroxidase. Blood-brain barrier permeability to radiolead was not increased in the intoxicated animals. During the development of the encephalopathy there was a progressive rise in the lead concentration in all tissues. Concurrently, there was a significant rise in brain calcium. These results suggest that the encephalopathic effects of lead may be mediated directly at the neuronal level.

Undernutrition in the developing rat: effect upon myelination.

Long-Evans rats were undernourished from birth by removing the mother from the sucling rats for part of each day; the undernutrition was continued after weaning till 60 days of age by restricting the daily food intake. Brain development was monitored by histologic and selected biochemical analyses coordinated with an ultrastructural morphometric analysis of the pyramidal tract of 30-day-old rats. Brain and body growth were already reduced after 10 days of undernutrition. At 20 days of age, the peak of myelination in the controls, the body and brain weights of the undernourished rats, compared to the controls, were reduced by 25 and 60%, respectively, and by the end of the study (60 days), the brain and body weights were reduced by 30 and 70%, respectively. Morphometric analysis indicated that the proportion of myelinated axons was significantly reduced in starved (34%) relative to control (43%) animals. Fiber analysis revealed that not only were the myelin sheaths thinner in the undernourished rats, but that the sheath was disproportionately reduced relative to the axon diameter. Chemical analysis on a whole brain basis demonstrated a greater than 60% deficit in the relatively myelin-specific galactolipids. (Whole brain analysis included regions more severely affected than the morphometrically analyzed pyramidal tract.) We also obtained evidence for both a delay in the initiation and a general retardation of myelinogenesis. The promyelinating fibers (axons with one or two non-compacted myelin lamellae) still constituted 4.5% of the myelinated fibers in the undernourished animals at 30 days but had declined to 0.3% in the controls. Analysis of the fabtty acids of cerebroside and sulfatide (lipids enriched in myelin) demonstrated in the undernourished group a pattern characteristic of a younger animal. Thus, the effect of undernutrition on the developing rat appears to be one of inhibited and somewhat retarded myelination. These effects were most likely due to a reduction in the number of myelinating glia formed and the restricted capacity of those which form to generate myeline lamellae.

Developmental studies of the uptake of choline, GABA and dopamine by crude synaptosomal preparations after in vivo or in vitro lead treatment.

The kinetics of sodium dependent, high affinity uptake of choline and dopamine by striatal synaptosomal preparations and of GABA (gamma-aminobutyric acid) by cortical synaptosomal preparations have been examined during the development of Long-Evans control and lead-treated rats. Choline uptake was very low until 12 days postnatally, then the Vmax increased and approached adult values of 29 pmol/mg prot./min within a week. GABA uptake was somewhat elevated at birth and only after three weeks did it decrease to the adult value of 0.7 nmol/mg prot./min. Dopamine uptake was low at birth, developed linearly with age and by 30 days postnatally approached the adult value of 68 pmoles/mg prot./min. The high affinity uptake constants (choline, 0.66 microM; GABA, 4.4 muM; and dopamine, 0.31 muM) did not change markedly during development. Similar studies were conducted with rats treated at the highest lead dosage which did not result in weight loss (100 microgram lead as lead acetate/g body weight/day via intubation). Blood and brain lead determinations confirmed a substantial lead exposure. Such chronic exposure did not markedly affect the amount or developmental pattern of uptake of the putative neurotransmitters. The effect of 2.5 x 10(-5) M lead acetate in vitro on the kinetics of high affinity uptake of these compounds into preparations from 20-26-day-old rats was investigated. When uptake was assayed in the absence of calcium, lead caused a 20% increase in the Vmax for dopamine. This stimulation was reduced if samples were assayed in the presence of n mM CaCl2. The Km for high affinity uptake of these neurotransmitter-related compounds was not affected by lead. In other studies, crude synaptosomal preparations were preloaded with neurotransmitter by preincubation with radioactive choline, GABA, or dopamine. Release of radioactive neurotransmitter, either spontaneous or in response to potassium depolarization, was quantitated and correlated with the presence or absence of 2.5 x 10(-5) M lead and/or 10(-3) M calcium ions. Lead slightly inhibited calcium dependent spontaneous release of dopamine. Lead also appeared to partially substitute for calcium in the potassium depolarized release of dopamine and GABA, although subtraction of the spontaneous (potassium independent) component reduced the magnitude of the lead effect.

The neurotoxicity of intrahippocampal kainic acid injection in rats is not accompanied by a reduction of Timm stain.

Histopathological changes induced by intrahippocampal injections of low doses of kainic acid (17.5 ng/site) were investigated in rats. Kainic acid produced a selective loss of CA3 pyramidal and hilar neurons. The development of kainic acid-induced neuronal injury was not accompanied by any detectable loss of histologically demonstrable zinc as assessed by means of a modified Timm's sulphide-silver method. It is suggested that the selective injury of hippocampal neurons induced by kainic acid is not contingent on the release of zinc from mossy-fiber terminals.

The use of Synapsin I as a biochemical marker for neuronal damage by trimethyltin.

The content of Synapsin I (Protein I) was examined in brain regions of adult rats exposed to trimethyltin (TMT), and in control animals. Long Evans hooded rats were intragastrically dosed with 4 mg TMT hydroxide/kg body weight for 4 days. No perturbations in Synapsin I levels were evident by 24 h following the fourth dose; however, by 36 h, a significant decrease of 28% in Synapsin I level was present in the hippocampus of TMT treated animals. This decrease was selective, no other brain region examined was affected. As determined by regional analysis of inorganic tin, this specificity was not due to a profound preferential accumulation of tin in the hippocampus. Despite the absence of an alteration in Synapsin I levels at 24 h, morphological examination revealed perturbation in the normal uniform arrangement of granule cell neurons, with dead neurons diffusely distributed throughout the facia dentata. At 36 h, these changes were only slightly more extensive. In contrast, examination of the terminal projection area of these cells, the mossy boutons, showed to be unaffected at 24 h after the 4th dose of TMT. However, by 36 h, many of the mossy boutons contained dense bodies and showed signs of degeneration. This result suggested that the loss of Synapsin I coincides with degeneration of the nerve terminal region. In order to better establish the temporal correlation, a less severe dosing regimen (only 3 days of exposure to 4 mg TMT/kg body wt) was utilized to attenuate the time course of necrosis. Again, necrotic changes were visible in the perikaryon by 1 day after termination of toxicant dosing.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental lead encephalopathy in the suckling rat: concentration of lead in cellular fractions enriched in brain capillaries.

Five-day old rats subjected to short-term (2-day) lead exposure by gastric gavage of aqueous lead acetate at the highest non-lethal dosage (1mgPb/g body weight/day) developed a hemorrhagic encephalopathy. Capillaries and microvessels isolated from brains of these rats showed abnormal morphology consisting of an increased number of irregularly dispersed endothelial nuclei and swollen, vacuolated endothelial cells. Lead was concentrated in isolated brain capillary-microvessel fractions, as demonstrated by both atomic absorption and 210Pb tracer methods. When lead exposure was continued for 20 days (at the maximal dosage regime compatible with a 60% survival rate), the rats recovered from the initial encephalopathy and capillaries and microvessels isolated from brains of these rats appeared morphologically normal. This recovery occurred despite continued high levels of lead in the blood and in the isolated capillary-microvessel fractions, suggesting that, as capillary endothelial cells mature, they are able to adapt to the presence of large amounts of lead.

The effects of lead administration during development on lithium-induced polydipsia and dopaminergic function.

Previous studies have demonstrated that postnatal (days 2-29 of life) administration of lead (200 mg/kg/day by gavage) to Long-Evans rats caused permanent increases in lithium-induced polydipsia (LIP). These lead-induced increases in LIP were apparently not of renal origin, did not occur in animals treated with lead after day 30, and persisted for at least 6 months. The present studies have narrowed the dose-time window for lead-induced increases in LIP. The first study showed that continuous administration of lead (200 mg/kg/day, p.o.) in the form of lead acetate during days 2-9 of life caused increases in LIP (P = 0.022). Although lead-induced increases in LIP were not statistically significant (P = 0.084) for the group administered lead from days 9 to 19, the lack of a significant difference between the 2-9- and 9-19-day groups suggested that lead treatment during either of these time periods would result in LIP increases. Lead administration between days 19 and 29 of life was not effective in increasing LIP (P = 0.8). In the second study, a single dose of lead (200 mg/kg/day) was administered either on day 5 or 15 of life. Concentrations of lead in the blood on day 30 of life averaged 23.2 micrograms/100 ml for treated rats versus 4.8 micrograms/100 ml for controls. When tested at approximately 90 days of age, both groups showed significant increases in LIP (P = 0.028). The rats from this second study were also examined for changes in nigrostriatal dopamine function, since this pathway is known to be essential for LIP.(ABSTRACT TRUNCATED AT 250 WORDS)

Myelin synthesis during postnatal nutritional deprivation and subsequent rehabilitation.

Newborn Long-Evans rats were undernourished by maternal deprivation so that by 20 days of age their body and brain weights were about 45 and 80%, respectively, of the values obtained for control (well-nourished) values. Proteins from myelin of undernourished and control rats were separated by polyacrylamide gel electrophoresis in buffers containing sodium dodecyl sulfate. At 15 and 20 days of age the proportion of basic and proteolipid protein was reduced in the starved animals relative to controls, indicative of a delay in maturation. However, by 30 days of age the composition of myelin from starved and control animals appeared similar. At all ages the yield of myelin from brains of starved rats was less than 25% of that obtained from control animals. A series of isotope labeling experiments, using a double label design, was carried out to compare relative rates of incorporation of radioactive amino acids into individual proteins of various brain subcellular fractions. In 20-day-old rats the incorporation of [3H] OR [14C] leucine or glycine into myelin proteins, relative to incorporation into proteins of other subcellular fractions, is preferentially depressed (about 60%) in starved animals. Synthesis of all the myelin proteins was depressed, supporting the hypothesis that the high molecular weight proteins isolated with myelin are true myelin constituents. Similar experiments were conducted using [3H]-and [14C] acetate, choline, or glycerol as precursors of lipids. Incorporation of isotope into lipids of myelin, relative to lipids of other subcellular fractions, was also depressed by about 60% in starved animals. In several experiments we studied synthesis during rehabilitation (ad libitum feeding) following 20 days of postnatal starvation. After 6 days of rehabilitation, incorporation of radioactive precursors into myelin, relative to other subcellular fractions, was still depressed. This result was true for both proteins and lipids, and was interpreted as evicence against the initiation of a process leading to a net recovery of myelin (i.e., an irreversible deficit of myelin synthesis is induced by this regime of nutritional deprivation).

Post-natal ontogenesis of calmodulin and cyclic AMP-dependent protein kinase subunits in the Purkinje cell using immunofluorescence.

Specific immunofluorescent techniques were utilized to demonstrate the regulatory (RI and RII) and catalytic (C) subunits of cyclic AMP-dependent protein kinase, and calmodulin, in the rat cerebellar Purkinje cell during post-natal ontogenesis. Whereas these second messenger receptor proteins were not detectable at 5 days, an increase in staining intensity occurred from this time until adult levels and distribution were attained at 25 days. Differences in immunofluorescent staining were noted between these proteins during ontogenesis. The relationship of these immunocytochemical changes to synaptogenesis and cellular maturation are discussed, including possible interactions between cyclic AMP and calcium messenger systems.

CT recognition of subcortical hematomas.

Subcortical hematomas develop in brain trauma and less commonly in hypertensive intracerebral hemorrhage. Six cases are reported that exhibit a spectrum of computed tomographic (CT) findings in this entity. Pathologic correlates in four cases are presented. It is theorized that subcortical hematomas form in trauma secondary to shearing stresses in the brain. Differential movement of gray and white matter may disrupt cortical medullary vessels. Rupture of degenerative vessels at this junction may account for hypertensive hematomas.

Morphological evidence for 6-hydroxydopamine-induced sprouting or noradrenergic neurons in the cerebellum.

Intracisternal injection of 6-hydroxydopamine (6-OHDA) into young rats during the first 24 hours after birth resulted in a significant elevation of cerebellar norepinephrine by day 9. This elevation continued through 120 days. Fluorescence microscopy demonstrated an increased fluorescence in all layers of the cerebellar cortex in treated rats from 9 days after treatment through 120 days. This was considerably greater than the normal developmental change observed in control rats and appeared to be due to an increased number of fluorescent terminals. Quantitative electron-microscopic analysis indicated that all layers of the cerebellar cortex of treated rats contained significantly more boutons with small dense-cored vesicles (SGV), a morphologic marker for catecholamines, than controls. No significant difference in the number of SGVs per bouton was observed in 6-OHDA treated rats.