[Polyneuropathy and encephalopathy caused by organic solvents and mixed solvent solutions. Occupational medicine and neurologic aspects of a new occupational disease]

Solvent induced polyneuropathy and encephalopathy have been acknowledged quite recently as occupational diseases in Germany. For compensation first of all the diagnosis has to be proven. For differential diagnosis other known causes as well as non-organic mental diseases must be taken into consideration. The causality between proven exposures and diagnosed disease has at least to be probable. To evaluate causation extensive experience of the experts is needed. In this context scientific criteria regarding neurotoxicity of the solvent, duration of exposure, individual aspects of non-occupational influences, time course of the disease are important within a through synoptic evaluation. Possibilities and limitations of sensitive diagnostic measures such as neurographic, neuropsychologic and neuroimaging examinations are discussed. The prognosis of toxic polyneuropathy and encephalopathy is in general favorable if exposure has stopped. Additionally, adequate therapy and rehabilitation measures are supportive for a good prognosis.

[Brain damage caused by hypotensive anesthesia? Both the anesthetic technique and the anesthetic agent must be chosen with care]

During the fifty years since hypotensive anaesthesia, induced hypotension to minimise intraoperative blood loss, became an established routine, there have been few reports of associated cerebral complications. However, evidence of disturbed cerebral function among patients undergoing orthognathic surgery under induced hypotension was obtained in a recent study where the level of adenylate kinase activity in cerebrospinal fluid was used as a highly sensitive biochemical marker of brain cell injury. Moreover, psychometric tests revealed persistent postoperative mental deterioration. The underlying cause of brain cell injury seems to be complex, and as in all likelihood it is not hypotension per se that is responsible, the effect of the anaesthetic agents used (isoflurane and propofol) has to be considered. It was also noted that hypotension did not improve the clinical outcome of orthognathic surgery, as compared with comparable operations performed under normotension.

Inhibition of iron-dependent and ischemia-induced brain damage by the alpha-tocopherol analogue MDL 74,722

Free radical-induced lipid peroxidation is an important factor in the pathogenesis of ischemic brain damage. We studied the effects of the alpha-tocopherol analogue MDL 74,722 on iron-dependent lipid peroxidation and infarct volume after transient focal cerebral ischemia. The effects of MDL 74,722 on iron-induced lipid peroxidation were tested in cerebellar granule cell cultures by means of a thiobarbituric acid reactive substances (TBARS) assay. The absorbance resulting from mitochondrial reduction of 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) was taken as a measure of cell viability. Besides, in male Wistar rats the left middle cerebral artery (MCA) was occluded for 3 h by means of an intraluminal filament. Rats were treated with vehicle (n = 19) or MDL 74,722 (n = 17), administered intravenously for 3 h in a dose of 2 mg/(kg.h), starting 105 min after MCA occlusion. Infarct volume was measured in coronal brain sections stained with hematoxylin and eosin. In cerebellar granule cell cultures, MDL 74,722 resulted in a dose-dependent inhibition of TBARS formation and prevention of cell toxicity. The compound reduced infarct volume after transient occlusion of the MCA in rats by 49%. It is concluded that MDL 74,722 is a potent inhibitor of lipid peroxidation and reduces infarct volume by about one half, even when treatment is delayed. This contributes to its potential clinical usefulness.

Selective vulnerability of the developing brain to lead

Environmental lead exposure in young children who ingest household paint dust or other sources impairs their potential intelligence in a linear, dose-dependent fashion in contrast to its far more subtle effects on other neurologic functions. Basic investigations have identified three interrelated steps in synaptic neurotransmission at which low levels of lead can disrupt signal processing. Lead enhances background transmitter release, but impairs stimulated release, inhibits function at the N-methyl-D-aspartate-type glutamate receptor and stimulates background levels of the intracellular messenger protein kinase C. Taken together these effects have the effect of diminishing the synaptic signal to noise ratio. The ability of lead to enhance 'synaptic noise' during a critical early period of postnatal development may permanently disrupt the architecture of cortical processing units by depriving them of high resolution environmental signals needed to refine synaptic connections.

Experience with a vocabulary test for workers previously and still exposed to styrene

OBJECTIVES

This study examined the possible influence of styrene exposure on the results of vocabulary tests because verbal ability is assumed to be relatively resistant to the toxic effects of organic solvents and short vocabulary tests are used as "hold tests" in many neurobehavioral epidemiologic studies,

METHODS

To evaluate the chronic neurotoxic effects of styrene, a vocabulary test was administered to a group of still-exposed workers (N=27) and an earlier exposed group of workers (N=90). A self-administered questionnaire was filled out on life events, general health, educational level, and amount of education. The still-exposed group had a mean exposure duration of 4700 hours, and that for the formerly exposed group was 3610 hours.

RESULTS

The vocabulary score of the still-exposed group was significantly lower [12.5 (SD 2.9, range 6-18)] than that of their former colleagues [14.3 (SD 3.4, range 8-22)], even though they originally belonged to the same group and had done the same tasks. The exposure duration explained a significant part of the vocabulary results, resulting in decreasing vocabulary scores even when the influence of years of education and age was taken into account. Even after correction for the possible influence of having been laid off or staying at work, there remained a negative influence on the vocabulary score for the duration of styrene exposure.

CONCLUSIONS

The use of short vocabulary tests as hold tests in cross-sectional studies of solvent-exposed workers may be limited as they seem to lack the essential toxicity-independent property.

[Evaluation of the risk of neuropsychological damage from lead exposure in childhood]

Potential neurotoxicity of lead in children has been explored in many recent epidemiological studies carried out all over the world. Within a multicentric European study, an investigation was carried out also in Italy on children living in an industrial area and characterised by a non steady-state exposure condition with higher exposure at the early stages of life. This peculiar feature allowed to observe interesting associations between neurobehavioural functions and the levels of Pb measured in teeth, but not in blood. Indeed, Pb in teeth was associated with the results of psychometric tests which evaluate the discriminant ability and the attention. Other associations, like those found between the intelligence quotient (IQ) scores and Pb in teeth disappeared after correction for the socioeconomical status of parents. In general, in children exposed to environmental Pb, more consistent associations were found with visual-motor integration and attention than with IQ measurements. In agreement with literature data from other countries, we suggest that the relevance of neurotoxic effects of Pb is limited, at least at the current exposure levels, but also that a threshold Pb level associated with no effect cannot be identified.

Specificity of neurobehavioral outcomes associated with prenatal alcohol exposure

A current issue in alcohol research is whether a "neurobehavioral profile" can be identified for prenatal alcohol exposure, even when dysmorphic features are not present, or whether comparable neurobehavioral deficits are detected when damage is incurred by numerous neurotoxicants to which the fetus is exposed during a common developmental period. Failure to detect such differences may, in part, be an artifact of the global developmental tests used to assess outcome. Cognitive effects of prenatal exposure to three different teratogens [polychlorinated biphenyls (PCBs), alcohol, and cocaine] are examined to determine whether exposure to each substance results in a common or different pattern of impairment on the same set of newer, more narrow band infant tests. Comparison of findings from three independent cohorts indicate that PCB exposure was related to poorer recognition memory on the Fagan Test of Infant Intelligence (FTII) in Michigan infants exposed prenatally to PCB-contaminated fish, whereas prenatal alcohol exposure was unrelated to recognition memory but to slower processing speed on a new FTII measure and slower reaction time on Haith's Visual Expectancy Paradigm (VExP) in our Detroit alcohol-exposed infants. Preliminary findings from a new study of infants recently born to Taiwanese women accidentally contaminated with sizable amounts of PCBs indicate recognition memory deficits, confirming our Michigan findings, but no processing speed effects on the FTII. Recent findings from our Detroit cohort suggest that heavy prenatal cocaine exposure is related to poorer recognition memory on the FTII, but faster reaction times on the VExP, a pattern different from that seen for either PCBs or alcohol.

Role of glutamate receptor-mediated excitotoxicity in bilirubin-induced brain injury in the Gunn rat model

Severe hyperbilirubinemia in neonates with prematurity and/or systemic illnesses such as hemolytic disease, acidosis, and hypoxemia enhances their risk for developing cerebral palsy, paralysis of ocular upgaze, and deafness. This neurologic syndrome has been associated with selective neuronal vulnerability in the basal ganglia, certain brainstem nuclei, and Purkinje cells. However, the mechanism by which bilirubin damages neurons remains unclear. In these studies, we found that intracerebral injection of N-methyl-D-aspartate (NMDA), an excitotoxic analogue of glutamate, caused greater injury in jaundiced 7-day-old Gunn (jj) rat pups than in nonjaundiced heterozygous (Nj) littermate controls. NMDA injection caused even greater injury when protein-bound bilirubin was displaced with the sulfonamide drug sulfadimethoxine in jaundiced homozygous pups. In additional experiments, the acute signs of bilirubin-mediated neuronal injury, induced in homozygous (jj) Gunn rats by treatment with sulfonamide, were reduced by concurrent treatment with the NMDA-type glutamate channel antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohept-5,10-imine (MK-801, dizocilpine). The results suggest that bilirubin may cause encephalopathy and neuronal injury, at least in part, through an NMDA receptor-mediated excitotoxic mechanism. This conclusion is consistent with clinical observations that bilirubin encephalopathy is synergistically worsened by hypoxemia, which also shares an excitotoxic mechanism of neuronal injury.

Persistent structural modifications in nucleus accumbens and prefrontal cortex neurons produced by previous experience with amphetamine

Experience-dependent changes in behavior are thought to involve structural modifications in the nervous system, especially alterations in patterns of synaptic connectivity. Repeated experience with drugs of abuse can result in very long-lasting changes in behavior, including a persistent hypersensitivity (sensitization) to their psychomotor activating and rewarding effects. It was hypothesized, therefore, that repeated treatment with the psychomotor stimulant drug amphetamine, which produces robust sensitization, would produce structural adaptations in brain regions that mediate its psychomotor activating and rewarding effects. Consistent with this hypothesis, it was found that amphetamine treatment altered the morphology of neurons in the nucleus accumbens and prefrontal cortex. Exposure to amphetamine produced a long-lasting (>1 month) increase in the length of dendrites, in the density of dendritic spines, and in the number of branched spines on the major output cells of the nucleus accumbens, the medium spiny neurons, as indicated by analysis of Golgi-stained material. Amphetamine treatment produced similar effects on the apical (but not basilar) dendrites of layer III pyramidal neurons in the prefrontal cortex. The ability of amphetamine to alter patterns of synaptic connectivity in these structures may contribute to some of the long-term behavioral consequences of repeated amphetamine use, including amphetamine psychosis and addiction.

Low-dose vigabatrin (gamma-vinyl GABA)-induced damage in the immature rat brain

The antiepileptic drug, vigabatrin, inhibits GABA transaminase, thus elevating GABA levels in the brain. In adult animal experiments, high-dose (200 mg/kg/day) chronic vigabatrin administration is associated with potentially reversible myelin vacuolation, a phenomenon not documented in humans. We hypothesized that vigabatrin might adversely affect myelination in the developing brain. Rats were given vigabatrin in doses comparable to those used clinically (15-50 mg/kg/day), from age 12 to 16 days. The rats were killed at age 19-20 days. We observed decreased myelin staining in the external capsule, axonal degeneration in white matter, evidence of glial cell death in the white matter, and reactive astrogliosis in the frontal cortex. We did not detect myelin vacuolation. These findings indicate that vigabatrin can have adverse and potentially irreversible effects on the developing rat brain. The mechanism of damage could be direct toxicity of vigabatrin or an indirect effect mediated through elevated GABA levels. Vigabatrin has been recommended as a treatment for some forms of childhood epilepsy; therefore, further studies are needed to assess the risks in children.

Multifocal brain damage induced by phencyclidine is augmented by pilocarpine

Phencyclidine and other antagonists of the N-methyl-D-aspartate subtype of glutamate receptor cause psychosis in humans. In low doses these agents induce a reversible neurotoxic reaction in the rat brain that is limited to the retrosplenial granular cortex. Some investigators have reported that phencyclidine at higher doses or by more prolonged treatment causes a more disseminated pattern of damage. However, it has not been clearly demonstrated whether the disseminated damage is reversible or irreversible and whether it is consistently reproducible, nor is it known how many and which neurons are at risk. In the present study we addressed these questions using several histological approaches (plastic-embedded thin sections for light microscopy and ultrathin plastic sections for electron microscopy, paraffin-embedded haematoxylin and eosin sections, 72 kDa heat shock protein immunocytochemistry and de Olmos silver impregnation) to study the lesions induced in rat brain by phencyclidine (alone or when augmented with pilocarpine). We found that phencyclidine can kill a relatively large number of neurons distributed over many cerebrocortical and limbic brain regions, but the multifocal pattern of damage occurred in only a small percentage of treated rats. The addition of a low dose of pilocarpine to phencyclidine caused the widespread pattern of damage to manifest on a much more consistent basis. Available evidence suggests that disinhibition of multiple converging excitatory pathways is the mechanism by which phencyclidine triggers widespread neuronal degeneration; however, the specific combination of excitatory inputs that contributes to the pathological process may differ from region to region.

Arthrogryposis multiplex congenita and bilateral mid-brain infarction following maternal overdose of co-proxamol

We report a case of arthrogryposis multiplex congenita secondary to fetal hypokinesia in a 41-week gestation infant following antenatal central nervous system injury. The mother's pregnancy was complicated by an episode of attempted self harm, with an overdose of co-proxamol at 22 weeks of gestational age, and by the use of cocaine in combination with excess alcohol intake. Magnetic resonance imaging showed bilateral mid-brain cysts and marked atrophy of the basal ganglia and thalami.

Cerebral complications of murine monoclonal CD3 antibody (OKT3): CT and MR findings

Treatment of acute renal allograft rejection with mouse monoclonal antibody (OKT3) is associated with systemic and neurologic side effects. We describe cerebral abnormalities in a 13-year-old boy with steroid-resistant renal allograft rejection. After treatment with OKT3, an acute neurologic syndrome developed, including seizures, lethargy, and decreased mental function. CT and MR imaging revealed confluent cerebral lesions at the corticomedullary junction. Contrast-enhanced MR images showed patchy enhancement, indicating blood-brain barrier dysfunction. The diagnosis of OKT3-induced encephalopathy with cerebral edema and capillary leak syndrome was made. Although CT and MR findings are nonspecific, neuroradiologists should be aware of this condition in transplant patients treated with OKT3.

Opioid neurotoxicity: fentanyl dose-response effects in rats

Opioids, when administered in large doses, produce brain damage, primarily in the limbic system and association areas in rats. This investigation examined the relationship between opioid dose and severity and frequency of brain damage in rats. Forty male Sprague-Dawley rats were anesthetized with halothane/N2O and underwent tracheal intubation, mechanical ventilation, arterial/venous cannulation, and insertion of a rectal temperature probe and biparietal electroencephalogram electrodes. After surgery, halothane was discontinued and O2/N2O 30%/70% was administered for 1 h. Rats were then randomly assigned to one of eight groups. The control group received a loading dose (LD) of 4 mL/kg of 0.9% normal saline solution (NSS) and a maintenance dose (MD) of 4 mL.kg-1.h-1 NSS. The other groups were given fentanyl lypophilized and reconstituted in NSS with the LD ranging from 50 to 3200 micrograms/kg and the MD from 2 to 128 micrograms.kg-1.min-1. After 2 h of fentanyl or NSS infusion; all rats received 100% O2 and, when alert, their tracheas were extubated; after 7 days the rats underwent cerebral perfusion fixation, followed by light microscopic evaluation. Histopathologic lesions (primarily eosinophilic neuron degeneration) were subjectively graded by a pathologist unaware of the experimental treatment; the grades were based on the percentage of dead neurons. There were no lesions observed in the brain areas in any of the control or 200-8 (LD, microgram/kg; MD, microgram.kg-1.min-1) groups. Eleven of 20 rats in the 400-16, 800-32, 1600-64, and 3200-18 groups showed evidence of brain damage primarily in limbic system structures and association areas (P < 0.05). Our data confirm that fentanyl produces limbic system brain damage in rats, and that the damage occurs over a broad range of doses.

A 3-year follow-up of the intellectual and academic functioning of children receiving central nervous system prophylactic chemotherapy for leukemia

This prospective study compared the intellectual and academic functioning of two groups of children treated for cancer over the 3 years after their diagnosis. One group consisted of children who received central nervous system (CNS) prophylactic chemotherapy, and the other group consisted of children with cancer who did not receive CNS chemotherapy. The results suggest that the children who received CNS chemotherapy experienced more adverse effects from their treatment in the area of academic functioning than the children who did not receive CNS chemotherapy. Although there were no differences in the academic functioning of the two groups of children immediately after their diagnosis, 3 years postdiagnosis, the CNS-treated children scored more poorly on academic tests of reading, spelling, and arithmetic than the non-CNS-treated children. The results suggest that CNS chemotherapy prophylaxis may impede academic achievement.

[Hypoxic brain damage after carbon monoxide poisoning. Visual agnosia, reduced initiative and memory and delayed sequelae]

Four patients with hypoxic brain damage caused by carbon monoxide poisoning are described. Three of these had attempted suicide with car exhaust fumes. Two patients had visual agnosia due to lesions in the parieto-occipital cortex. Three patients had temporary Parkinsonian symptoms. In two of these patients CT and MRI showed lesions in the globus pallidus. They also showed reduced initiative, and in one patient this was combined with minor tics and obsessive symptoms. One patient had impaired memory as the only symptom. The patient with the longest lasting exposure developed delayed sequelae; three weeks after the poisoning he became apathetic and confused, with failing memory, Parkinsonian symptoms, and urinary and faecal incontinence. MRI showed demyelination in the periventricular white matter. His condition started to improve two months after the accident.

[Delayed symptoms of hypoxic brain damage after temporary improvement]

A shipyard worker was doing welding work inside a pipe with argon as cover gas. After taking a break he fainted while controlling the weld, also inside the pipe. He was rescued after 15-20 minutes and regained consciousness after a few hours. Two days later he was discharged from hospital in apparently good health. After a week he returned to the hospital suffering from confusion, failing memory, aphasia, apraxia and urinary incontinence. MR showed elevated signal intensity bilaterally in the caudate nucleus. He improved gradually and six months later was given less demanding work. The course of his illness is consistent with delayed neuropsychiatric sequelae after hypoxia, probably due to displacement of oxygen by argon. Delayed symptoms are caused by demyelination in the subcortical white matter.

Long-term consequences of subtle stimuli during the first twenty-four hours of seizure-induced brain injury

Chronically epileptic (induced by a single systemic injection of lithium and pilocarpine about 30 days before the experiment began) male rats were trained within a radial maze while they were administered either GABA-pentin (Neurontin), or prednisolone or given no treatment. There was no significant improvement in learning or memory between the groups. Numbers of trials per day were positively correlated with the time required to display the overt stereotyped forelimb clonus after the single pilocarpine injection. The numbers of correct trials completed during the first few days of acquisition were significantly greater for the rats that had receive weak (1 microT) complex, pulsed magnetic fields over the right hemisphere during the first 24 hr. after seizure induction than for those who received the same field over the left hemisphere or that had been exposed to reference conditions. Implications of the enhanced sensitivity of limbic neurons to subtle electromagnetic interaction during electrical lability are discussed.

The effects of methylenedioxymethamphetamine (MDMA, "Ecstasy") on monoaminergic neurotransmission in the central nervous system

Methylenedioxymethamphetamine (MDMA, Ecstasy) is a popular recreationally used drug among young people in Europe and North America. The recent surge in use of MDMA and increasing concerns about possible toxic effects of the drug have inspired a great deal of research into the mechanisms by which the drug may affect the central nervous system. This paper reviews studies on the neurochemical, behavioral and neurophysiological effects of MDMA, with emphasis on MDMA effects in regions of the brain that have been implicated in reward. Experiments in awake, behaving laboratory animals have demonstrated that single injections of MDMA increase extracellular levels of the neurotransmitters dopamine (DA) and serotonin (5HT) in the nucleus accumbens and in several other brain regions that are important for reward. Most of the behavioral and electrophysiological changes that have been reported to date for single doses of MDMA appear to be mediated by this MDMA-induced increase in extracellular DA and 5HT. As an example, MDMA-induced hyperthermia and locomotor hyperactivity in laboratory animals can be blocked by administering drugs that prevent MDMA-induced 5HT release and can be attenuated by administering 5HT receptor antagonists, whereas effects of MDMA on delayed reinforcement tasks appear to be mediated by MDMA-induced increases in extracellular DA. Similarly, the effects of MDMA on neuronal excitability in the nucleus accumbens and in several other brain regions can be prevented by administering drugs that block MDMA-induced 5HT release and can be attenuated by depleting brain DA levels or by administering either DA D1 receptor antagonists or 5HT receptor antagonists. In addition to the acute effects of MDMA, it is now well established that repeated or high-dose administration of MDMA is neurotoxic to a subpopulation of 5HT-containing axons that project to the forebrain in laboratory animals. Recent studies have shown that this neurotoxic effect of MDMA is associated with long-duration changes in both DA and 5HT neurotransmission in the nucleus accumbens. Whether these long-duration changes in neurotransmission might be related to reports of depression and other psychopathologies by some frequent users of MDMA remains to be determined. Methylene-dioxymethamphetamine has been found to increase extracellular levels of norepinephrine and to alter brain levels of several neuropeptides as well as altering levels of DA and 5HT. Much additional research is required to understand the multiple ways in which this complex drug may alter neurotransmission in the brain, both acutely and in the long term.

Regional cerebral blood flow measurements with Xenon-CT in the prediction of delayed encephalopathy after carbon monoxide intoxication

Reported evaluations of CBF with Xe/CT were performed in 11 patients during the lucid interval following CO intoxication. Results were compared with clinical and SPECT data. Two patients developed neuropsychiatric behavior (delayed encephalopathy) one month following the initial recovery. The symptoms persisted in one of them 15 months later. Their CBF values as well as those in most of the other patients, monitored at the basal ganglia and white matter areas, were in relation with the clinical outcome, However, further studies with a larger number of patients, are needed to confirm the predictive significance of Xe/CT measurements for the long term sequelae of CO poisoning.

Chronic elemental mercury intoxication: neuropsychological follow-up case study

In initial and follow-up investigations of neuropsychological function in a patient with elemental mercury intoxication, his scores were compared with those of a group of normal control subjects matched for sex, age and education. Each subject received a comprehensive neuropsychological examination including a personality inventory. On the initial examination the results indicated that the patient had a significant depression of performance intellectual functioning, impairments of attention, non-verbal short-term memory and visual judgement of angles and directions, psychomotor retardation and personality changes including depression, anxiety, desire to be alone, lack of interest and sensitivity to physical problems. Such an impairment picture is compatible with the previous observations of individuals with chronic exposure to elemental, organic or inorganic mercury. The follow-up study was undertaken about 1.5 years later. The results show that the patient's cognitive and personality functions were fully recovered. Our findings thus suggest a reversibility of impaired neuropsychological function in persons with elemental mercury poisoning if a prompt removal from the toxic environment is accomplished, together with proper medical treatment.

Reinduction of hyponatremia improves survival in rats with myelinolysis-related neurologic symptoms

Brain myelinolysis occurs after excessive correction (delta SNa > 20 mEq/1/24 hours) of chronic hyponatremia. However, we showed recently that the mechanisms leading to brain myelinolysis remain reversible. Indeed, reinduction of the hyponatremia by water administration despite 12 hours of sustained excessive correction could prevent the development of demyelination in rats still asymptomatic at that time. Whether this therapeutic maneuver could be also beneficial to rats with preexisting myelinolysis-related neurologic symptoms is unknown. Therefore we evaluated here the effect of reinduction of the hyponatremia on the survival and on brain damage in rats presenting obvious neurologic symptoms after excessive correction of hyponatremia. After 3 days of severe hyponatremia induced by 2.5 D-glucose in water and continuous infusion of AVP, rats were submitted to a large correction (delta SNa approximately 30 mEq/l) by 2 i.p. injections of hypertonic saline given over 24 hours. In group I (n = 15) the rats developing neurologic symptoms during the first 24 hours of correction received one i.p. injection of distilled water which rapidly decreased the natremia to a final correction gradient <20 mEq/l/24 hour. In group II (n = 13, controls) the symptomatic rats were left permanently overcorrected. In group I, after water administration, the neurological manifestations were generally attenuated or disappeared. Seven of the 15 rats (47%) in this group survived up to day 10 with a mean survival time of 7.5 +/- 2 days, an outcome clearly improved as compared to group II (controls): only 1 of the 13 rats (7%, p < 0.03) was still alive on day 10 and the mean survival time was 3.3 +/- 2 days (p < 0.001) in this group II. The duration of the symptoms also influences the prognosis. In group I, in 9 rats the water administration was performed 4 hours after symptoms onset. These rats had a better outcome than the 6 rats with more sustained (8-10 hours) neurologic symptoms before water loading. Brain analysis in the 7 surviving rats of group I demonstrated demyelinating lesions in only 2 of them, suggesting the reversibility of the process even when neurologic manifestation developed. In conclusion, after exposure to an excessive correction of chronic hyponatremia, even when rats have developed myelinolysis-related neurologic symptoms, hypotonic fluids administration could improve survival and could prevent the subsequent development of brain myelinolysis.

A neurological dissociation between shape from shading and shape from edges

We studied the ability of a neurological patient, who has deficits in various aspects of form perception, to perform region segregation tasks requiring discriminations based on several image properties that are related to the three-dimensional structure of objects. The patient could discriminate the apparent three-dimensional structure and orientation of shapes defined by shading gradients, but could not make such discriminations for shapes in which edges were depicted as lines or as luminance discontinuities. These results suggest that the neural pathways that compute shape from shading gradients may be independent of those that compute shape based on edges, and, based on the patient's pattern of brain damage, they also indicate a relatively early functional separation in the requisite inputs.

Cannabis and the brain

OBJECTIVE

The aim of the paper is to review the effects of Cannabis sativa on the human brain.

METHOD

A selective literature review was undertaken.

RESULTS/CONCLUSIONS

Cannabis sativa causes an acute and, with regular heavy ingestion, a subacute encephalopathy. There is no evidence of irreversible cerebral damage resulting from its use, although impairment of information processing might be a long-term consequence of heavy prolonged use. The precise relationship of cannabis to the functional psychoses such as schizophrenia has yet to be clarified.

Cortical hyperintensity on proton density-weighted images: An MR sign of cyclosporine-related encephalopathy

PURPOSE

To describe cortical hyperintensities in proton density-weighted images in six patients with presumed cyclosporine-induced neurotoxicity.

METHODS

In six patients with clinical evidence of cyclosporine-related encephalopathy, MR imaging was performed after the onset of symptoms and signs (mean, 24 days after liver transplantation). Five of these patients had serial MR imaging for a period that varied from 2 to 20 months. Along with the imaging studies, the patients' clinical status was evaluated and various laboratory parameters, including blood pressure and levels of cyclosporine, cholesterol, and magnesium, were monitored.

RESULTS

In all six patients, initial MR studies showed hyperintensity of several cerebral gyri that was unequivocal only on proton density-weighted images. Although in five patients these signal abnormalities were limited to the cortex, one patient had increased signal in the subjacent white matter as well. In one patient, the images were also remarkable for areas of cortical hyperintensities on T1-weighted images. In another patient, cortical enhancement occurred after administration of gadopentetate dimeglumine, with a normal cortical signal on the precontrast images. The abnormal cortical signal began to fade after cyclosporine reduction, but in two patients it remained visible for at least 20 months. The neurologic symptomatology associated with cyclosporine-induced neurotoxicity included seizures (three patients), speech disorder (three patients), and disturbance of consciousness (three patients).

CONCLUSION

Cyclosporine-induced neurotoxicity occurring in patients after liver transplantation appears to affect the cerebral cortex preferentially. Because its MR equivalent resembles changes resulting from hypoxic injury or cortically centered vasculitis, we suspect the underlying mechanism may be a vascular injury that results in cortical hypoperfusion.

MR in trichloroethane poisoning

We present a case of acute trichloroethane intoxication caused by inhalation of typewriter correction fluid. CT and MR findings revealed lesions in the basal ganglia and cortex similar to those observed in patients with methanol and carbon monoxide poisoning.

Carmofur-induced leukoencephalopathy: MRI

Carmofur, a derivative of 5-fluorouracil, has recently been noted to have an infrequent but serious association with leukoencephalopathy. To our knowledge, there has been no report of early MRI findings in this leukoencephalopathy. We describe a case in which diffuse high signal intensity of the entire cerebral white matter, including the corpus callosum, was seen on T2-weighted magnetic resonance images. Although similar findings can be seen in many other diseases, carmofur-induced leukoencephalopathy should be suspected in a patient treated with carmofur. It is important to know the clinical and MRI characteristics of this condition, for early diagnosis and better prognosis.

Focal cerebral ischemia during anesthesia with etomidate, isoflurane, or thiopental: a comparison of the extent of cerebral injury

An investigation was performed to compare the cerebral protective properties of etomidate, isoflurane, and thiopental. In separate groups of spontaneously hypertensive rats, etomidate, isoflurane, or thiopental was administered to achieve and maintain burst-suppression of the electroencephalogram (3-5 bursts/min) for the duration of the experiment. A fourth group received 1.2 minimal alveolar concentration halothane. All groups underwent 3 hours of middle cerebral artery occlusion and then 2 hours of reperfusion. Thereafter, the animals were killed and the volume of injured brain was determined by staining with 2,3,5-triphenyltetrazolium. Physiological parameters did not differ among the four groups during the investigation, with the exception that hemolysis occurred in the etomidate group (free hemoglobin levels, approximately 0.4 g.dl-1). The volume of injured brain in the thiopental group (56 +/- 10 mm3) was significantly smaller than that in the halothane control group (99 +/- 13 mm3). The volumes of injured brain in the etomidate and isoflurane groups (145 +/- 11 mm3 and 139 +/- 14 mm3, respectively) were significantly larger than those in the control and thiopental groups. We speculate that the apparently detrimental effect of etomidate may be the result of the binding of nitric oxide of cerebral endothelial origin by the iron component of free hemoglobin. Intracranial pressure was not recorded, and in the isoflurane group, there may have been adverse effects on cerebral perfusion pressure associated with vasodilation caused by high concentrations of isoflurane. The results are consistent with a protective effect by barbiturates.

Cerebral and cerebellar diaschisis following carbamazepine therapy

1. The regional cerebral blood flow was studied by SPECT in patients with partial epilepsy before and after 30 days of monotherapy with carbamazepine (CBZ). 2. Both a qualitative visual interpretation and a semiquantitative analysis of SPECT was performed. All patients underwent EEG, CT scan, and MRI studies. The CBZ serum concentrations were assayed. 3. After therapy, in three patients with focal epilepsy, both a crossed cerebral and cerebellar diaschisis were observed, with respect to the side of the epileptic focus in the opposite hemisphere. No morphologic changes were detected at MRI in the cerebral or cerebellar remote hypometabolic areas found at SPECT. 4. CBZ may have a depressant action on the corticopontocerebellar pathways and on the corticocallosal connections.

White matter changes caused by chronic solvent abuse

PURPOSE

To examine the brain damage of solvent abusers in Japan, where pure industrial toluene is frequently abused.

METHODS

Twenty solvent abusers 17 to 33 years of age with 7.2 +/- 4.0 years of abuse were examined with a 1.5-T MR imaging system.

RESULTS

White matter hyperintensities in cerebrum, brain stem, and cerebellum on T2-weighted images were found in seven cases. The extent of white matter change was most clearly shown on proton density-weighted images. The patients with restricted white matter change and intermediate white matter change showed white matter hyperintensities in the brain stem and cerebellum on T2-weighted images, in some cases, with additional hypointensities in the corresponding T1-weighted images. These patients had mainly abused pure toluene. The patients with diffuse white matter change showed obvious brain atrophy, including hippocampal atrophy and thinning of the corpus callosum. These patients had mainly abused lacquer thinner.

CONCLUSION

There are some patients with restricted but severe enough change to cause the neurologic symptoms in specific regions, such as the brain stem and/or cerebellum, before the brain atrophy becomes apparent. This suggests that the restricted white matter change represents not only an early change of diffuse white matter change, but at least in some cases also represents a qualitatively different change than that of diffuse white matter change. We suggest that pure toluene has a possible relation to this qualitative difference.

Neurobehavioral effects of developmental methylmercury exposure

Methylmercury (MeHg) is a global environmental problem and is listed by the International Program of Chemical Safety as one of the six most dangerous chemicals in the world's environment. Human exposure to MeHg primarily occurs through the consumption of contaminated food such as fish, although catastrophic exposures due to industrial pollution have occurred. The fetus is particularly sensitive to MeHg exposure and adverse effects on infant development have been associated with levels of exposure that result in few, if any, signs of maternal clinical illness or toxicity. High levels of prenatal exposure in humans result in neurobehavioral effects such as cerebral palsy and severe mental retardation. Prenatal exposure to MeHg in communities with chronic low-level exposure is related to decreased birthweight and early sensorimotor dysfunction such as delayed onset of walking. Neurobehavioral alterations have also been documented in studies with nonhuman primates and rodents. Available information on the developmental neurotoxic effects of MeHg, particularly the neurobehavioral effects, indicates that the fetus and infant are more sensitive to adverse effects of MeHg. It is therefore recommended that pregnant women and women of childbearing age be strongly advised to limit their exposure to potential sources of MeHg. Based on results from human and animal studies on the developmental neurotoxic effects of methylmercury, the accepted reference dose should be lowered to 0.025 to 0.06 MeHg microgram/kg/day. Continued research on the neurotoxic effects associated with low level developmental exposure is needed.

Cranial MRI in chronic thinner intoxication

We studied a 19-year-old man with thinner and toluene poisoning for 5 years by CT and MRI. Symmetrical lesions were seen in the basal ganglia and cingulate gyri.

Leukoencephalopathy in childhood hematopoietic neoplasm caused by moderate-dose methotrexate and prophylactic cranial radiotherapy--an MR analysis

PURPOSE

The main purpose of this study was to determine influential factors related to minor leukoencephalopathy (LEP) caused by moderate-dose methotrexate (MTX) and prophylactic cranial radiotherapy (CRT) in childhood hematopoietic malignancies. We also compared the incidence of LEP following this treatment to that reported in the literature following treatment with high-dose MTX alone.

METHODS AND MATERIALS

Thirty-eight pediatric patients of hematopoietic malignancies (37 acute lymphoblastic leukemias, 1 non-Hodgkin lymphoma) who were given CRT (18-24 Gy) as well as prophylactic intrathecal and per os MTX were studied for leukoencephalopathy by magnetic resonance (MR) imaging. All the patients were free from grave neuropsychiatric disturbances. The data were examined to elucidate the influential ones of five factors (patients' age, doses of intrathecal and per os MTX, dose of CRT, interval between treatment, and MR study) to develop LEP using multiple regression analysis. To compare the effect of moderate-dose MTX and prophylactic CRT on LEP to that of high-dose MTX alone, we conducted literature review.

RESULTS

Seven out of 38 patients (18%) developed LEP. From multiple regression analysis and partial correlation coefficients, the age and CRT dose seemed influential in the subsequent development of LEP. The incidence of LEP following treatment with moderate-dose MTX and prophylactic CRT appears to be less than that reported in the literature following treatment with intravenous high-dose MTX. However, even moderate-dose MTX in combination with CRT can result in a significant incidence of MR-detectable LEP, particularly in children 6 years of age or younger receiving 24 Gy.

CONCLUSION

Leukoencephalopathy was caused by moderate-dose MTX and prophylactic CRT in pediatric patients, probably less frequently than by high-dose MTX treatment alone. The influential factors were patient's age and CRT dose.

[Late effects of occupational organic brain damage in painters 6-8 years after diagnosis. Occurrence of mental and psychosomatic health problems and utilization of health services]

With the object of illustrating effects on health and social functions of occupational organic brain damage, a questionnaire study was carried out in 1986 concerning 192 brain-damaged painters and a reference group of 341 other painters. The study was repeated in 1990 to elucidate effects six to eight years after diagnosis. In 1986 a high prevalence of mental and psychosomatic symptoms was found among the brain-damaged painters. The prevalence correlated with severity of the disease, occupational situation and social network. In 1990 the same level of symptoms was found. In the reference group the prevalence of symptoms increased from 1986 to 1990. Besides the major difference in the prevalence of symptoms between the two groups, the level of symptoms correlated to the occupational situation in both groups. Twenty-seven percent of the brain-damaged painters were still at work in 1990. The high symptom level among the brain-damaged painters is considered to be chronic.

Mechanisms in the induction of neuronal heterotopiae following prenatal cytotoxic brain damage

Prenatal exposure to several neuroteratogens, such as ionizing radiation, ethanol, and cytotoxic drugs, induces the development of clusters of abnormally positioned neurons within the brain. These abnormalities have always been presumed to result from interference with normal neuronal migration, presumably via effects on radial glia. In our study, pregnant rats were injected with methylazoxymethanol acetate (MAM) on either E13, E14, or E15. Computerised reconstruction techniques, Golgi and immunocytochemical staining as well as electron microscopy were used to detect structural abnormalities of radial glia which might be responsible for the production of heterotopiae. Several structural abnormalities such as microcavitation, involvement of radial glial elements in rosettes, disturbance of the normal ventricular lining, and disruption of the attachment of radial glial endfeet to the pial surface were identified. We propose that periventricular heterotopiae result from disruption of the palisade arrangement of neuroepithelial cells in the ventricular zone and the involvement of radial glial elements in rosettes. Layer I heterotopiae may arise from abnormalities of the distal segments of radial glia and their attachment to the pia. No prenatal abnormalities in radial glia of the hippocampus were noted following MAM exposure at any of the 3 ages, consistent with the proposition that hippocampal heterotopiae arise by postnatal movements of pyramidal neurons without radial glial involvement.

Multiple choice vocabulary test MWT as a valid and short test to estimate premorbid intelligence

The discrepancy between current and premorbid ability is a relevant indicator of acquired mental impairment, which itself is closely related to general cerebral dysfunction. The use of tests sensitive to cerebral dysfunction, raises relatively few problems compared with tests being resistant that are used to estimate premorbid mental ability. For premorbid ability, verbal tests assessing knowledge, especially vocabulary, have been shown to be valid. A test, possibly more insensitive to brain dysfunction than the ones usually administered, is the multiple choice vocabulary test (MWT = Mehrfachwahl-Wortschatz-Test). At present only German versions are available. They are presented in some detail because of their advantages. Construction of the MWT is simple, and it can be easily administered in about five minutes. The results correlate fairly well with global IQ in healthy adults (median of r = 0.72 in 22 samples) and are more insensitive to current disturbances than such tests as the WAIS vocabulary test. The limitations of premorbid tests with respect to diagnostic validity are discussed. It is concluded, that studies which do not control premorbid intelligence have to be considered as a "malpractice" and should not be accepted by scientists.

Congenital brain damage spares the basic patterns of parental behavior in affected mice

Pregnant albino mice were treated with 5-azacytidine so that the embryonic brains were affected late in their morphological ontogeny. The offspring showed retarded body growth and a conspicuous reduction in the size of the cerebral hemispheres as measured at the end of development. Histological alterations were found in the hippocampus and the cingulate cortex. No behavioral alterations were detected during development, with the exception of the hyperactivity which probably caused the better performance of treated offspring observed in a self-feeding test. This functional abnormality, attributed by previous authors to retardation in telencephalic development, persisted into adulthood. The parental behavior of virgin females towards a weak stimulus-object was robust. Treated subjects were non-neophobic, seldom aggressive and showed clearcut parental responses. In addition, although the frequency of overall parental tendency was lower in the treated subjects, it gradually approached that of the controls across repeated trials. The brain structures affected by this treatment seem influential on behavioral organization and habituation to novelty, not on basic patterns of behavior, which are probably rooted in phylogenetically more ancient structures.

MR of toxic effects of accelerated fractionation radiation therapy and carboplatin chemotherapy for malignant gliomas

PURPOSE

To present MR findings of parenchymal brain injury after accelerated fractionation radiation therapy combined with carboplatin chemotherapy in the treatment of malignant brain gliomas.

METHODS

Eighty-one evaluable subjects in an ongoing treatment protocol for malignant gliomas form the patient base for this report. After surgical resection of tumors, patients underwent a course of accelerated fractionation radiation therapy to a total dose of 60 Gy. Carboplatin was infused intravenously before each radiation treatment. Precontrast and postcontrast MR scans were obtained before treatment and at 4-week intervals afterward and were analyzed retrospectively.

RESULTS

Posttreatment MR imaging in 20 of the 81 patients showed development of unusual parenchymal lesions or enlarging masses needing debulking, and these patients underwent second operations. Two groups emerged: those with tumor and necrotic brain (n = 11) and those with necrosis and reactive gliosis but no definitive tumor (n = 9). Enhancing lesions in the tumor-negative group appeared later than those in the tumor-positive group, were often multiple, and were usually located several centimeters away from the tumor resection site or even contralaterally. Common locations were the corpus callosum and corticomedullary junctions. Lesions in the tumor-positive group were more often solitary and located immediately adjacent to the surgical site. Positive and negative results of positron emission tomography with fludeoxyglucose F 18 were obtained in both groups. The incidence of brain necrosis without associated tumor was 11%.

CONCLUSIONS

A pattern of unusual enhancing parenchymal brain lesions was seen on MR imaging after accelerated fractionation radiation therapy and concomitant carboplatin chemotherapy. The abnormalities seem more extensive than focal necrotic lesions on enhanced CT or MR imaging after conventional radiation therapy, and they may mimic recurrent tumor.

The residual neuropsychological effects of cannabis: the current status of research

Evidence for the residual neuropsychological effects of cannabis must first be separated from evidence regarding (i) the acute effects of the drug, (ii) attributes of heavy cannabis users, and (iii) actual psychiatric disorders caused or exacerbated by cannabis. The remaining evidence must then be subdivided into (a) data supporting a 'drug residue' effect during the 12-24 h period immediately after acute intoxication and (b) data suggesting a more lasting toxic effect on the central nervous system which persists even after all drug residue has left the system. We reviewed the literature, comparing both 'drug-administration' studies in which known amounts of cannabis were administered to volunteers, and 'naturalistic studies' in which heavy marijuana users were tested after some period of abstinence. The data support a 'drug residue' effect on attention, psychomotor tasks, and short-term memory during the 12-24 h period immediately after cannabis use, but evidence is as yet insufficient to support or refute either a more prolonged 'drug residue' effect, or a toxic effect on the central nervous system that persists even after drug residues have left the body. We describe possible study designs to address these latter questions.

MR and cognitive testing of patients undergoing osmotic blood-brain barrier disruption with intraarterial chemotherapy

PURPOSE

To determine whether osmotic blood-brain barrier disruption is associated with MR abnormalities or cognitive deterioration and, if so, whether the MR findings correlate with cognitive test results.

METHODS

Fifteen brain tumor patients who had a complete tumor response (nine central nervous system lymphoma, three germ cell and two astrocytoma, and one primitive neuroectodermal tumor) treated with blood-brain barrier disruption procedures (318 total procedures) with intraarterial chemotherapy were included. MR images were evaluated for the development of white matter hyperintensity, vascular lesions, or atrophy. Cognitive testing was performed to assess deterioration caused by this therapy.

RESULTS

In two patients white matter hyperintensity developed, in two small vascular lesions developed, and in one mild atrophy developed. One infarct was asymptomatic and the second one resulted in mild dysesthesia in one upper extremity. No patient showed diminished cognitive function on the posttherapy evaluation.

CONCLUSION

In patients undergoing blood-brain barrier disruption with intraarterial chemotherapy, new abnormalities on MR imaging may develop. These patients maintain the same level of cognitive and neurologic function and MR findings do not correlate with the results of cognitive testing.

Lack of involvement of nitric oxide in the mechanisms of seizures and hippocampal damage produced by kainate and ouabain in rats

The gross behavioural, electrocortical and neuropathological effects of kainate (10 mg/kg i.p,) and ouabain (1 micrograms, given into one dorsal hippocampus) were studied in rats. The effects of these treatments on nitric oxide synthase (NOS) activity in homogenates of hippocampus and cortex were also studied. Administration of kainate or ouabain produced motor and electrocortical seizures similar for latency to onset (approximately 15 min) and intensity (in all instances 80-100% of the treated rats showed behavioural and electrographic seizures). These effects were accompanied at 24 h by severe damage to all subsectors of the hippocampal formation and this concerned a similar proportion of the treated rats (n = 4-8 per treatment). No significant changes in nitric oxide synthase (NOS) activity were noted in the cerebral cortex and hippocampus of rats receiving injections of kainate and ouabain. In addition, pretreatment with N omega-Nitro-L-arginine methyl ester (300 micrograms, given into one lateral cerebral ventricle 15 min previously) was ineffective in preventing the effects of kainate and ouabain. In conclusion, present data suggest that excessive production of NO is not involved in the mechanisms triggering seizures and neurodegeneration produced by kainate or ouabain.

Differential brain area vulnerability to long-term subcortical excitotoxic lesions

To investigate the long-term effects of excitatory amino acid microinjections into the basal forebrain and its correlation with a possible Ca2+ imbalance associated with the excitotoxic process, ibotenic acid, mainly an N-methyl-D-aspartate receptor agonist, and quisqualic acid, an agonist of non-N-methyl-D-aspartate receptors, were injected into two regions rich in cholinergic neurons, namely the medial septal nucleus and the ventral globus pallidus. Within the globus pallidus but not within the medial septal nucleus, 13 days and one year postlesion, nerve cell death was associated with the appearance of calcium deposits within the large putative GABAergic pallidal neurons, being more pronounced in ibotenic acid than quisqualic acid-lesioned rats. An intermediate two month post-lesion study with alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and ibotenic acid microinjections in globus pallidus demonstrated that the AMPA subtype of glutamate receptor may also be involved in this Ca2+ imbalance, together with the N-methyl-D-aspartate and metabotropic subtype receptors. Quisqualic acid lesions in globus pallidus and medial septum were associated with a substantial disappearance of cholinergic cell bodies and their nerve terminal networks within the cerebral cortex and hippocampal formation respectively, as assessed by choline acetyltransferase and acetylcholine esterase immunocytochemistry. Ibotenic acid lesions resulted in a lower reduction of cholinergic markers. One year after septal lesions induced either by ibotenic or quisqualic acid, a marked atrophy of the entire dorsolateral septal nucleus was observed. Our results support the hypothesis that brief and intense glutamate exposure can induce long-term neurodegenerative processes and give evidence that long-term excitotoxic lesions of the two areas studied result in marked differences in neuronal damage, including intracellular calcium deposits which do not correlate with the cholinergic deficits produced by multiple glutamate receptor subtypes.