Neuropathology of fragile X-associated tremor/ataxia syndrome (FXTAS).

Fragile X-associated tremor/ataxia syndrome (FXTAS) is an adult-onset neurodegenerative disorder that affects carriers, principally males, of premutation alleles (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene. Clinical features of FXTAS include progressive intention tremor and gait ataxia, accompanied by characteristic white matter abnormalities on MRI. The neuropathological hallmark of FXTAS is an intranuclear inclusion, present in both neurons and astrocytes throughout the CNS. Prior to the current work, the nature of the associations between inclusion loads and molecular measures (e.g. CGG repeat) was not defined. Post-mortem brain and spinal cord tissue has been examined for gross and microscopic pathology in a series of 11 FXTAS cases (males, age 67-87 years at the time of death). Quantitative counts of inclusion numbers were performed in various brain regions in both neurons and astrocytes. Inclusion counts were compared with specific molecular (CGG repeat, FMR1 mRNA level) and clinical (age of onset, age of death) parameters. In the current series, the three most prominent neuropathological characteristics are (i) significant cerebral and cerebellar white matter disease, (ii) associated astrocytic pathology with dramatically enlarged inclusion-bearing astrocytes prominent in cerebral white matter and (iii) the presence of intranuclear inclusions in both brain and spinal cord. The pattern of white matter pathology is distinct from that associated with hypertensive vascular disease and other diseases of white matter. Spongiosis was present in the middle cerebellar peduncles in seven of the eight cases in which those tissues were available for study. There is inclusion formation in cranial nerve nucleus XII and in autonomic neurons of the spinal cord. The most striking finding is the highly significant association between the number of CGG repeats and the numbers of intranuclear inclusions in both neurons and astrocytes, indicating that the CGG repeat is a powerful predictor of neurological involvement in males, both clinically (age of death) and neuropathologically (number of inclusions).

Posthypoxic treatment with MK-801 reduces hypoxic-ischemic damage in the neonatal rat.

We evaluated the neuroprotective effect of MK-801, a noncompetitive, selective N-methyl-D-aspartate receptor antagonist, in a neonatal hypoxic-ischemic animal model. Seven-day-old rats underwent bilateral ligation of the carotid arteries followed by exposure to an 8% oxygen atmosphere for 1 hr. We sacrificed the animals 72 hrs later and assessed the hypoxic-ischemic brain damage histologically. MK-801 (10 mg/kg), administered IP 0.5 hr before the hypoxia, completely prevented hypoxic-ischemic infarction in cerebral cortex, while treatment immediately and 1 hr after the end of the hypoxia resulted in 76% and 52% reduction in the infarcted area, respectively. MK-801, given 0.5 hr before and immediately after the insult, reduced striatal damage and, given 0.5 hr before, attenuated neuronal necrosis in hippocampal regions. These results show that in neonates MK-801 is neuroprotective even when administered up to 1 hr after the end of a hypoxic-ischemic insult.

Posthypoxic treatment with felbamate is neuroprotective in a rat model of hypoxia-ischemia.

Felbamate, a novel dicarbamate anticonvulsant that blocks the glycine site of the N-methyl-D-aspartate receptor and protects the hippocampal slice from hypoxic damage, shows remarkably low toxicity in animals and in humans. Since most treatment of human cerebral ischemia will have to be delivered after the insult, we investigated the neuroprotective potency of post hoc felbamate in rat pups with bilateral carotid ligations exposed to an atmosphere of 6.5% O2 for 1 hour. Brain temperature was unaffected by surgery, hypoxia, or felbamate. Neuroprotection was greatest at 300 mg/kg, less effective at 200 and 400 mg/kg, and ineffective at 100 mg/kg. Post hoc felbamate (300 mg/kg) reduced the volume of infarction from 67% +/- 7% of neocortex in unmedicated rats to 32% +/- 8%, 51% +/- 12%, 38% +/- 19%, and 53% +/- 10% when given 0, 1, 2, and 4 hours after hypoxic exposure, respectively. By 6 hours, post hoc protection was no longer significant. Delayed neuronal necrosis in hippocampal granule cells was reduced from 156 +/- 33 neurons to 12 +/- 7 (0 hours, p < 0.01) and 37 +/- 17 (1 hour, p < 0.05). These effects were obtained at plasma concentrations (60 to 120 mg/ml) that have occasionally been reached without serious toxicity in human anticonvulsant trials. These data suggest that, in this animal model, felbamate given after a hypoxic-ischemic insult is effective in reducing cerebral infarction and extremely effective in preventing delayed neuronal necrosis, but that the window of opportunity for post hoc treatment is only 1 to 4 hours.

Outcome of oncology patients in the pediatric intensive care unit.

We evaluated the outcome of oncology patients in the Pediatric Intensive Care Unit (PICU) from a total of 72 consecutive admissions. Severity of illness and quantity of care were measured by the Physiologic Stability Index (PSI) and the Therapeutic Intervention Scoring System (TISS), respectively. The overall mortality was 51% and was especially high in patients admitted for acute organ system failure (OSF)-66%. Acute respiratory failure was the most frequent OSF (73%) and the most common cause for PICU admission. A poor outcome was associated with severe leucopenia (less than 1000 WBC/mm3, 91% mortality), acute renal failure (94% mortality) and central nervous system deterioration (83% mortality). When the outcome was predicted using a quantitative algorithm the observed mortality was significantly higher than the predicted for all admissions with a PSI higher than 5. Improved scoring systems are required to enable characterization of pediatric cancer patients admitted to the PICU.

The pharmacokinetics of isoproterenol in critically ill pediatric patients.

The pharmacokinetics of isoproterenol (ISO) in infants and children have never been reported. The authors studied ISO pharmacokinetics in two disparate groups of pediatric intensive care unit patients: postoperative cardiac patients (POC, n = 10), and reactive airway disease patients (RAD, n = 9). In all, 44 blood samples were taken at steady-state from the 19 patients, whereas from 15 patients samples were also taken just before and after discontinuation of ISO infusion. There were 12 male and 7 female patients in the study, and their ages ranged from 2 days to 14 years. The average ISO dosing rate was 0.30 micrograms/kg/minute for the whole study population, ranging from 0.01 to 5.5 micrograms/kg/minute. The POC patients received a significantly lower dosing rate than the RAD patients (0.029 +/- 0.002 vs 0.50 +/- 0.21 micrograms/kg/minute, P < .0001); the average steady-state plasma concentrations of ISO were also lower in the POC patients (1.3 +/- 0.3 versus 13.9 +/- 4.9 ng/mL, P < .0001). The steady-state plasma concentration, normalized to a dosing rate of .05 micrograms/kg/minute, was 1.9 +/- 0.3 ng/mL for all patients, and the clearance was 42.5 +/- 5.0 mg/kg/minute. Postoperative cardiac patients had a significant higher normalized steady-state plasma concentration and moderately significant lower clearance than did RAD patients (2.1 +/- 0.3 versus 1.7 +/- 0.4 ng/mL, P < .05 and 33.2 +/- 4.9 versus 48.4 +/- 7.3, P < .06, respectively). The average plasma half-life of ISO was 4.2 +/- 1.5 minutes, and the volume of distribution was 216 +/- 57 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Felbamate reduces hypoxic-ischemic brain damage in vivo.

The neuroprotective effects of felbamate were tested in a model of incomplete cerebral ischemia and hypoxia in 7-day-old rat pups. Felbamate pretreatment (300 mg/kg) reduced the surface of infarcted cortex following bilateral carotid ligation, by 42-49% compared to saline and dimethylsulfoxide (DMSO) controls, respectively. The number of necrotic neurons in the dentate gyrus was reduced by 77% over both DMSO controls and saline controls. These results suggest that felbamate deserves further evaluation for its therapeutic potential in hypoxia-ischemia.

Determination of serum and brain concentrations of neuroprotective and non-neuroprotective doses of MK-801.

We developed a sensitive and reliable gas chromatographic (GC) technique for the quantitative analysis of MK-801 in brain and serum and applied the technique to investigate tissue concentrations of neuroprotective and non-neuroprotective doses of MK-801 in a neonatal rat model of hypoxic-ischemia. Brain concentrations of MK-801 were a linear function of dose over 4 orders of magnitude. After administration of a neuroprotective dose of MK-801 (29.6 mumol/kg) to control rats, both serum and brain concentrations rose rapidly to approximately 300 nM and approximately 2000 nM, respectively, within 30 min. Approximately 60% of serum and 90% of brain MK-801 were bound leaving the free concentrations in both blood and brain at approximately 100-200 nM. After hypoxic-ischemia, serum MK-801 concentrations were not different from controls but brain concentrations were lowered by 32%. Free brain concentrations of MK-801 after hypoxic-ischemic were 124 nM after 29.6 mumol/kg while after 8.9 mumol/kg (the non-neuroprotective dose) they were 39 nM. In view of the slow kinetics of MK-801 channel blockade, which never reaches equilibrium during the current experiment, this difference in concentration would be expected to result in an 80-fold (or greater) difference in the current flux through NMDA receptor-operated ion-channels as the rate of NMDA receptor-operated ion-channel blockade is concentration dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac arrest and resuscitation alters the pharmacokinetics of MK-801 in the rat.

We investigated the effects of cardiac arrest and resuscitation on (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine meleate (MK-801) pharmacokinetics. The clearance of MK-801 in control animals was 108 +/- 9 mL.kg.min while its apparent volume of distribution was 12.6 +/- 0.7 L/kg. The half-life of the distribution phase was 4.9 +/- 1.2 min while that of the elimination phase was 87 +/- 8 min. Transient circulatory arrest decreased the overall clearance of MK-801 by 38% with no effect on the apparent volume of distribution. The distribution half-life was not affected although the initial distribution was increased 46%; the half-life of elimination was increased by 58%. Serum levels of transaminases in arrested animals were significantly elevated (258-322%) while blood urea nitrogen, creatinine, and creatine kinase were minimally affected, suggesting that the reduced clearance of MK-801 might be secondary to hepatic ischemic damage. Post-ischemic alterations in hemodynamics resulting in lowering and/or redistribution of cardiac output may also be responsible for the reduced clearance of MK-801 as the hemodynamic response to MK-801 in the post-ischemic animals was quite different from that in the controls. We conclude that transient cardiac arrest significantly alters the pharmacokinetics of MK-801 and that this must be taken into consideration when using this or other drugs to treat ischemic injury.

The pharmacokinetics of dobutamine in pediatric intensive care unit patients.

Dobutamine is used for hemodynamic support in critically ill patients; however, due to the relative insensitivity of most available assays, there is little detailed information about its pharmacokinetics. We studied the pharmacokinetics of dobutamine in 27 children and infants using a high-sensitivity HPLC technique. The patients' ages ranged from 0.13 to 16.6 years; 17 received dobutamine for treatment of shock while 10 received it for treatment of post-cardiac surgery. Blood samples were collected before (N = 27) and after (N = 10, 9 time points each) the cessation of dobutamine infusion. The duration of dobutamine infusion before sampling was 1.87 +/- 0.29 days (range: 0.2-5.5; median: 1). The steady-state plasma concentration of dobutamine (infusion rate corrected to 5.0 micrograms/kg/min) was 105 +/- 19 ng/ml (range: 3.79-400; median: 76). The clearance rate was 151.1 +/- 47.5 ml/kg/min (range: 12.5-1319; median: 66). Most post-infusion time-concentration data were best fit to a biexponential function suggestive of a two-compartment model. The t1/2 alpha was 1.65 +/- 0.20 min (range: 0.64-3.01; median: 1.52) while the t1/2 beta was 25.8 +/- 11.5 min (range: 4.6-68.6; median: 16.9). Neither age, weight, sex, disease state, duration of infusion, nor blood measures of renal or hepatic dysfunction were found to be covariates of the above parameters. It was found, however, that the concomitant administration of dopamine altered dobutamine's pharmacokinetics, indicating the possible presence of a competitive component in dobutamine's disposition.

Pharmacokinetics of exogenous epinephrine in critically ill children.

OBJECTIVES: This study was designed to determine the steady-state plasma concentrations and clearance rates of epinephrine in critically ill children, to examine if epinephrine pharmacokinetics conform to a linear model, and to compare epinephrine clearance rates with clearance rates of dopamine and dobutamine. DESIGN: This study was prospective, without intervention or control groups. SETTING: The pediatric ICUs of two tertiary care teaching hospitals. PATIENTS: All patients who were hemodynamically stable while requiring continuous epinephrine infusions were eligible for the study. INTERVENTIONS: Blood samples were taken at steady state and analyzed for epinephrine concentrations, as well as dopamine and dobutamine concentrations, if present, by high-pressure liquid chromatography with electrochemical detection. RESULTS: Plasma epinephrine concentrations during steady-state infusions of 0.03 to 0.2 micrograms/kg/min ranged from 670 to 9430 pg/mL (3660 to 51,490 pmol/L), with a mean of 4360 +/- 3090 pg/mL (23,810 +/- 16,870 pmol/L) and were linearly related to dose. Epinephrine clearance rates ranged from 15.6 to 79.2 mL/kg/min (mean 29.3 +/- 16.1) and were not dependent on steady-state plasma concentrations. Epinephrine clearance rate was in the same range as the clearance rates of dopamine (34.1 +/- 16.6) and dobutamine (35.9 +/- 27.8) and was linearly related to them (p < .005). CONCLUSIONS: Epinephrine infusions produce pharmacologic plasma concentrations of epinephrine in critically ill children. The plasma concentration of epinephrine correlates with the infusion rate, suggesting linear pharmacokinetics. Epinephrine clearance rates in critically ill children appear to be lower than the reported clearance rates in healthy adults. The clearance rates of two other inotropic catecholamines, dopamine and dobutamine, are significantly correlated with the clearance rate of epinephrine.

Investigation of an animal model of a Reye-like syndrome caused by Margosa oil.

Following reports of a Reye-like syndrome in children resulting from Margosa oil (MO) ingestion, we administered MO to laboratory rats in an attempt to produce an animal model of Reye's syndrome. Male rats were injected intraperitoneally with either MO or corn oil and observed for clinical signs of a toxic response. After 15 h the animals were administered a second dose and the MO-treated animals developed florid neurological symptoms. The animals were then sacrificed and blood samples were analyzed for glucose, ammonia, aspartate aminotransferase, and alanine aminotransferase. Sections of liver, kidney, and brain were examined by light microscopy after Sudan black B, hematoxylin and eosin, and periodic acid-Schiff staining. Liver was additionally examined by electron microscopy. Liver samples were analyzed for hepatic enzyme levels and brain samples were analyzed for water content. There were greatly increased levels of ammonia, aspartate aminotransferase, and alanine aminotransferase and decreased glucose levels in the blood of MO-treated animals. Light microscopy of MO-treated livers revealed fatty infiltration, granularity of the cytoplasm with normal nuclei, and glycogen depletion; electron microscopy revealed mitochondrial pathology in the livers of MO-treated animals. There were no significant morphological changes in brain or kidney specimens although the kidneys did show some fatty infiltration. Hepatic mitochondrial enzyme levels were unchanged and there was no increase in brain water content in the MO-treated animals. Thus, many of the abnormalities seen in Reye's syndrome were seen in this model; however, there were no hepatic enzyme changes despite altered mitochondrial morphology and no evidence of cerebral edema despite a florid encephalopathy. Nonetheless, this model may have important implications for the understanding of the pathogenetic mechanisms of this Reye-like syndrome and, perhaps, Reye's syndrome.

Pharmacokinetics of dopamine in infants and children.

OBJECTIVE: We studied the pharmacokinetics of dopamine in hemodynamically stable children. DESIGN: Prospective clinical trial. SETTING: Pediatric ICU. PATIENTS: Children (age 3 months to 13 yrs) recovering from cardiac surgery or shock. INTERVENTION: Plasma dopamine concentrations were measured at the steady state or at termination of infusion using high-performance liquid chromatography. RESULTS: The half-lives of distribution and elimination were 1.8 +/- 1.1 and 26 +/- 14 (SD) mins, respectively. The apparent volume of distribution was 2952 +/- 2332 mL/kg. The clearance rate was 454 +/- 900 mL/kg.min. Dopamine clearance was linearly related to dose only in patients who were also receiving dobutamine (r2 = .76, p less than .05). Hepatic and renal dysfunction did not affect the pharmacokinetics of dopamine. CONCLUSIONS: A relationship between dopamine and dobutamine that affects the disposition of these two drugs may exist. The pharmacokinetics of dopamine are variable even in hemodynamically stable children. Hepatic or renal function does not adversely affect the pharmacokinetics of dopamine.

A rat model of severe neonatal hypoxic-ischemic brain injury.

BACKGROUND AND PURPOSE: Perinatal hypoxic-ischemic brain injury is a common problem with severe neurological sequelae. In this report we describe in detail a simple model of hypoxia-ischemia in the neonatal rat that gives rise to severe neocortical infarction and to selective hippocampal neuronal necrosis. METHODS: Seven-day-old Simonsen Wistar rat pups underwent bilateral carotid artery ligation under methoxyflurane anesthesia and, after a 4 to 6-hour recovery, were exposed to 60 minutes of hypoxia (6.5% O2); they were perfusion-fixed 3 days later for histological study. Brain temperature was monitored throughout this treatment. RESULTS: We found that 64 +/- 3% of neocortex above the rhinal sulcus was infarcted; this infarction was evenly distributed through the cerebral hemispheres. In the hippocampus, neuronal necrosis was selective for the internal (hilar) layers of granule cells of the dentate gyrus, with relative sparing of CA1 pyramidal cells. In addition, brain temperature was tightly controlled throughout the experimental manipulations. CONCLUSIONS: The present model is easy and sensitive and provides an infarct of sufficient severity and homogeneity to make it well suited for pharmacological and biochemical studies directed toward therapeutic amelioration and mechanisms of hypoxic-ischemic brain damage, respectively. In addition, the pattern of damage in the hippocampus is quite different from that seen in the adult brain, which should be helpful in studying the ontogeny of selective vulnerability.

Novel rat cardiac arrest model of posthypoxic myoclonus.

We describe the time course of and pharmacology associated with auditory-induced muscle jerks following cardiac arrest in rats. The data indicate that several key features of this model mimic those of human posthypoxic myoclonus. Similar to the human form, the muscle jerks appear in the rats following an acute hypoxic episode (cardiac arrest). Initially, it is known that both spontaneous and auditory-induced myoclonus are present in these animals; some cardiac-arrested rats also exhibit seizures. Over the first few days after the arrest, episodes of both the seizure activity and spontaneous myoclonus disappear. The auditory-induced myoclonus continues to worsen, reaches a peak about 2 weeks after the arrest, then declines over time to subnormal levels. The auditory-induced muscle jerks exhibited by the cardiac arrested animals are attenuated by the typical antimyoclonic drugs 5-hydroxytryptophan, valproic acid, and clonazepam. In addition, the novel anticonvulsant felbamate was found to have antimyoclonic properties. The data suggest that this rat cardiac arrest model may be a valuable tool for investigating the pathophysiologic mechanisms of posthypoxic myoclonus and for developing new therapeutic strategies for treating the disorder.