Martin R. Krigman

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.

Congenital Intracranial Neoplasm

A case report with autopsy findings of a congenital neoplasm of the meninges, diagnosed as a mixed hemangiopericytoma and fibroma, and also a review of congenital intracranial neoplasms in tabular form are presented. Congenital meningeal tumors are discussed in more detail.

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).

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.

Lead encephalopathy in the developing rat: effect upon myelination.

Lead encephalopathy was induced in developing Long-Evans rats by adding lead carbonate 4% w/w to the diet of nursing mothers immediately after delivery. The suckling rats avidly accumulated lead, and by the 30th postnatal day the concentration of lead in the young-rat brain was nearly four times that in the mother. The overall effect of lead intoxication was retardation of growth of neural tissues without reduction of cell populations. The formation of myelin was altered and its cerebral content significantly reduced. Axons were reduced in size, and the number of myelin lamellae in the sheaths was also reduced. However, the relationship between axon diameter and myelin lamellae was preserved. Results of biochemical studies of the composition of the brain lipids were indistinguishable in lead-exposed and control animals. These biochemical studies included analyses of the neural constitution of phospholipids and gangliosides, the composition of the major gangliosides of the myelin subfraction, and the fatty acid composition of cerebrosides, sulfatides, and ceramides purified from brain. The effect of lead intoxication in the developing rat is one of hypomyelination. The hypomyelination appears to be primarily related to retarded growth and maturation of the neuron and not a reflection of a defect in the myelinating glia or a delay in the initiation of myelination.

Lead poisoning and reproduction: effects on pituitary and serum gonadotropins in neonatal rats.

Abstract In order to investigate the effects of neonatal lead poisoning on pituitary gonadotropic function, newborn rats were given daily doses of lead (25, 100, and 200 mg/kg) by gastric gavage. Control rats were given deionized water. Groups of animals were sacrificed at 10, 15, and 20 days of age and serum and pituitary levels of the gonadotropins follicle stimulating hormone (FSH) as well as pituitary contents of luteninizing hormone (LH) were determined by radioimmunoassay. Lead concentrations in blood, bone, brain, and pituitary tissues of similarly treated 15-day-old rats were determined by atomic absorption spectrometry. Lead content in bone (femur) and brain showed dose-dependent elevations throughout the dose range; in blood, it reached a plateau of about 1000 μg% already at the dose of 100 mg/kg/day. Lead remained at undetectable levels (

Transport of sugars into microvessels isolated from rat brain: a model for the blood-brain barrier.

Abstract— Microvessels (primarily capillaries) were isolated from the brains of rats 25‐35 days of age. This preparation was characterized by light, transmission, and scanning electron microscopy. Transmission electron microscopy revealed that the endothelial cell membranes were intact and were impermeable to horseradish peroxidase. However, scanning electron microscopy revealed that damage to the membrane occurred during isolation. The isolated microvessel preparations were metabolically competent as demonstrated by their ability to metabolize [14C]glucose.

Effects of Postnatal Trimethyltin or Triethyltin Treatment on CNS Catecholamine, GABA, and Acetylcholine Systems in the Rat

Abstract: The effects on brain neurochemistry of two neurotoxic tin compounds, trimethyltin (TMT) hydroxide and triethyltin (TET) sulfate, were examined. Long‐Evans rats were treated with TMT hydroxide (1 mg/kg, i.p.) on alternate days from day 2 to 29 of life. These treatments caused a weight deficit of 10–20% by the time the animals were killed on day 55 by head‐focused microwave irradiation. These TMT treatments are known to cause severe neuronal loss in the hippocampus and lesser damage in other brain regions. Accordingly, the concentration of γ‐aminobutyric acid (GABA) was decreased in the hippocampus; however, acetylcholine and choline concentrations were unaffected. These data suggest that TMT‐induced effects on GABA systems are greater than that due simply to generalized neuronal loss. The TMT treatments also caused a significant decrease in dopamine concentrations in the striatum, but did not alter the concentrations of dihydroxyphenylacetic acid or homovanillic acid, the acidic metabolites of dopamine. Conversely, concentrations of dopamine and norepinephrine in the brain stem and norepinephrine in the cerebellum were not altered. Despite reports in the literature of TMT‐induced neuronal damage in areas of the cortex, no effects on GABA, acetylcholine, or choline levels were found in the cortical areas examined, or in the hypothalamus. TET sulfate (0.3 mg/kg/day) was administered for 6 consecutive days of every week during days 2–29 of life. This dose is lower than that needed to cause intramyelin edema, yet it does result in long‐term behavioral changes. Despite this, no changes in the concentration of any of the measured neurotransmitters or their metabolites were detected. In concert, these data demonstrate that neurochemical methods should not be used as neurological “screens,” but rather to define specific mechanisms suggested by detailed behavior, pharmacological, and/or physiological studies.

Chronic effects of lead on schedule-controlled pigeon behavior

Abstract Pigeons were trained to peck a response key under a multiple fixed ratio 30 response (FR 30) fixed-interval 5-min (FI 5) schedule of food presentation. When rates of responding stabilized, lead acetate (6.25, 12.5, and 25 mg/kg body weight) or sodium acetate solutions were given daily by gastric intubation. Blood-lead concentrations were measured weekly by atomic absorption spectrometry, and responding under the multiple schedule was measured Monday through Friday. Control intubations of sodium acetate did not affect responding under either component of the schedule. The 25-mg/kg dose of lead decreased rates of responding after 3 to 10 days of administration and usually was lethal between 18 and 35 days. Post mortem examination of the birds showed obvious esophageal dilatation, damage to the crop, weight loss, and subarachnoid hemorrhages. Administration of the 25-mg/kg dose was discontinued in some birds after responding had ceased. Responding gradually began to recover, but rates of responding remained low and variable under both components of the schedule for many days. Daily administration of the 12.5-mg/kg dose of lead caused one death, but no obvious signs of intoxication occurred in the other birds. However, three of the four birds surviving daily 12.5-mg/kg doses of lead showed decreased rates of responding under both schedule components within 30 days of the initial intubation. The fourth bird showed a highly variable rate under the FI component of the schedule during lead administration; however, when lead administration was discontinued, dramatic increases in rates of responding above lead pretreatment levels occurred, particularly under the FI component. These rate increases persisted for 75 days thereafter. The 6.25-mg/kg dose of lead produced only small changes in rates of responding during 70 days of intubation. Blood-lead concentrations were very high (150–3470 μg/dl) during treatment with all doses of lead. Increasing doses produced increasing blood concentrations which were correlated with increasing behavioral effects, although correlations between blood-lead concentrations and behavioral changes were low within individual birds.

Lead encephalopathy in the developing rat: effect on cortical ontogenesis.

The effect of lead intoxication on postnatal cortical ontogenesis was studied in the 30-day-old rat. Lead encephalopathy was induced in developing Long-Evans rats by adding lead carbonate (4% w/w) to the diet of nursing mothers immediately after delivery. A segment of somatosensory neocortex was prepared for light and electron microscopy, and the neurons and the neuropil, including the synapses, were subjected to a morphometric analysis. Lead intoxication resulted in an overall reduction of gray matter which was characterized by an astrocytosis and by the preservation of the neuronal population. However, growth and maturation of the neurons in the lead rats were altered. The neurons were smaller, and, more important, the proliferation of neurite processes in the neuropil was retarded. There was also an apparent reduction in the number of synapses per neuron. However, in terms of its biochemical and morphological features, lead intoxication does not affect the maturation of the synaptic complex. The apparent effect of lead intoxication on cortical development is one of retarded neuronal maturation. This defect in neuronal maturation is proposed to be a reduction in the dendritic field and a concomitant reduction in synaptic connections.