Hypothermic neuroprotection during reperfusion following exposure to aglycemia in central white matter is mediated by acidification.

Hypoglycemia is a common iatrogenic consequence of type 1 diabetes therapy that can lead to central nervous system injury and even death if untreated. In the absence of clinically effective neuroprotective drugs we sought to quantify the putative neuroprotective effects of imposing hypothermia during the reperfusion phase following aglycemic exposure to central white matter. Mouse optic nerves (MONs), central white matter tracts, were superfused with oxygenated artificial cerebrospinal fluid (aCSF) containing 10 mmol/L glucose at 37°C. The supramaximal compound action potential (CAP) was evoked and axon conduction was assessed as the CAP area. Extracellular lactate was measured using an enzyme biosensor. Exposure to aglycemia, simulated by omitting glucose from the aCSF, resulted in axon injury, quantified by electrophysiological recordings, electron microscopic analysis confirming axon damage, the extent of which was determined by the duration of aglycemia exposure. Hypothermia attenuated injury. Exposing MONs to hypothermia during reperfusion resulted in improved CAP recovery compared with control recovery measured at 37°C, an effect attenuated in alkaline aCSF. Hypothermia decreases pH implying that the hypothermic neuroprotection derives from interstitial acidification. These results have important clinical implications demonstrating that hypothermic intervention during reperfusion can improve recovery in central white matter following aglycemia.

The role of the biochemistry department in the diagnosis of pituitary apoplexy.

A 47-year-old man presented with severe clinical hypoglycaemia. He had long-standing insulin-dependent diabetes with previously good glycaemic control. Intense headaches and vomiting initiated hospitalization. A brain computed tomography (CT) scan was normal, and a lumbar puncture showed elevated cerebrospinal fluid (CSF) protein [0.67 g/L; normal range (NR) 0.15-0.45 g/L], suggesting resolving viral meningitis. Routine thyroid function tests were abnormal (free thyroxine 10.6 pmol/L, NR 9-22.5 pmol/L; thyroid-stimulating hormone 0.16 mU/L, NR 0.35-5 mU/L). In the absence of evident thyroid therapy, the laboratory policy required an urgent cortisol assay to be added; this was very abnormal (42 nmol/L), suggesting hypopituitarism. Later analysis showed that concentrations of gonadotrophins and adrenocorticotrophin were low. An urgent pituitary magnetic resonance imaging scan revealed an unsuspected pituitary tumour with recent haemorrhage (pituitary apoplexy). The patient was given intravenous hydrocortisone and then stabilized on oral hydrocortisone, thyroxine and mesterolone. He made a full recovery and the hypoglycaemia resolved. The normal brain CT scan was falsely reassuring and the CSF protein was not due to viral meningitis but to haemorrhage into the pituitary tumour. If laboratory policy had not required the urgent cortisol assay be added, the diagnosis of hypopituitarism would have been delayed or even missed altogether. This could have led to the death of the patient.

Role of excitatory aminoacids in neonatal hypoglycemia.

BACKGROUND: In many neurological disorders, injury to neurons may be due in part to overstimulation of the receptors for the excitatory amino acids glutamate and aspartate. The same excitotoxic mechanism and high aspartate levels in experimental studies led to this study of the concentrations of glutamate and aspartate and zinc, copper, and magnesium levels in the cerebrospinal fluid (CSF) of hypoglycemic newborns. METHODS: Aspartate and glutamate were determined by high-performance liquid chromatography, and magnesium, zinc and copper by atomic absorption spectrophotometer. RESULTS: The CSF levels of aspartate (3.98 +/- 1.77 mumol/L) and glutamate (1.7 +/- 1.05 mumol/L) in 20 hypoglycemic newborns were significantly higher when compared with the values of aspartate (2.19 +/- 0.6 mumol/L) and glutamate (0.77 +/- 0.34 mumol/L) of 10 control newborns. In the hypoglycemic patients, the concentration of zinc (0.57 +/- 0.13 microgram/mL), but not copper (0.39 +/- 0.40 microgram/mL) was significantly lower when compared with the control values. There was no difference in the magnesium levels between the two groups. CONCLUSIONS: The higher levels of excitatory amino acids found in the CSF of hypoglycemic infants than in controls were consistent with previous animal studies, which may indicate the role of excitatory amino acids in the late biochemical effects of hypoglycemia in newborn brain metabolism.

Adenosine and cerebrovascular hyperemia during insulin-induced hypoglycemia in newborn piglet.

The present study tested the hypothesis that adenosine is involved in mediating the hyperemic response of the newborn brain to hypoglycemia. By use of the cranial window and microdialysis-H2 clearance methodologies, changes in the diameter of pial arterioles (25-50 microns), extracellular adenosine concentrations ([ADO]), and local cerebral blood flow (CBF) were examined in isoflurane-anesthetized piglets subjected to insulin-induced hypoglycemia. Blood glucose concentrations ranged from 10 to 18 mg/dl after insulin administration (25 IU/kg iv). Local CBF in the frontal cortex increased 36 +/- 12% (P = 0.014) at 30 min of hypoglycemia (group 1, n = 12; control = 43 +/- 3 ml.min-1.100 g-1). The mean increase in dialysate [ADO] sampled concurrently from the same cortical area was 59 +/- 29% (P = 0.011; control = 0.11 +/- 0.02 microM). At 30 min of hypoglycemia, pial diameters increased 55 +/- 10% (P = 0.001; group 2, n = 9). The [ADO] in cranial window cerebrospinal fluid (CSF) increased 217 +/- 71% (P = 0.04) in response to hypoglycemia (group 3, n = 8; control = 0.016 +/- 0.006 microM). Local administration of an adenosine antagonist, 10 microM 8-sulfophenyltheophylline, to the cerebral cortex before hypoglycemia caused a 38% reduction (P = 0.011) in the pial arteriolar response at 30 min of hypoglycemia (group 4, n = 9). Similarly, local superfusion of CSF with 3.7 mM glucose attenuated the hypoglycemia-induced pial dilation 33% (P = 0.039; group 5, n = 9). Perfusion of microdialysis probes with 3.7 mM glucose in the CSF abolished the hypoglycemia-induced increase in dialysate [ADO] (group 1).(ABSTRACT TRUNCATED AT 250 WORDS)

Opposite alterations in cerebrospinal fluid uridine after severe cerebral ischemia or intrathecal blood injection.

1. Rats which survived hypoglycemia by insulin, hypoxia by 10% O2, or ischemia by carotid ligation and hypotension to 40 mm Hg, evidenced no changes in cerebrospinal fluid (CSF) uridine. Animals which died soon after the above interventions or as a result of KCl-induced cardiac arrest had elevated CSF uridine concentrations. 2. Injection of whole blood or the soluble contents of lysed blood cells into the lateral ventricle of rats reduced CSF uridine to less than one-half normal at 24 hrs but values returned to normal 3 days later. Changes in hypoxanthine resembled those of uridine, but were less dramatic, whereas xanthine concentrations were largely unaltered. Intraventricular injection of plasma or saline did not alter CSF uridine. 3. It seems most likely that low CSF uridine concentrations previously reported in head injury patients may be secondary to the effects of blood cell contents in the cerebrospinal fluid, rather than responses to altered metabolism in neurons or glia cells.

Cerebrospinal fluid lactate in patients with diabetes mellitus and hypoglycaemic coma.

Cerebrospinal fluid (CSF) lactate and pyruvate concentrations were determined in 20 patients with diabetes mellitus but without disturbance of consciousness and five who recovered from hypoglycaemic coma. CSF lactate was slightly but significantly higher in diabetes mellitus (1.78, SEM 0.04 m mol/l) than that in 15 control subjects (1.40, SEM 0.05 m mol/l). In those who recovered from hypoglycaemic coma, CSF lactate was markedly elevated to 2.45-4.43 m mol/l. CSF glucose concentrations, however, were substantially the same between treated hypoglycaemic and diabetes mellitus groups. These findings indicate that CSF lactate levels increase with glycaemic levels in diabetes mellitus owing to enhanced glucose influx into glycolytic pathway of the brain, and also increases in treated hypoglycaemic coma probably due to mitochondrial dysfunction or damage.

Effects of insulin-induced hypoglycemia on plasma and cerebrospinal fluid levels of ir-beta-endorphins, ACTH, cortisol, norepinephrine, insulin and glucose in the conscious dog.

This study was designed to assess effects of insulin-induced hypoglycemia on plasma and cerebrospinal fluid (CSF) levels of immunoreactive (ir) beta-endorphins, adrenocorticotropin (ACTH), cortisol, norepinephrine, insulin, and glucose in the conscious, overnight fasted dog. Dogs received either an intravenous infusion of saline or insulin (5 mU/kg/min) for 3 h. Infusion of saline alone in conjunction with acute sampling of CSF caused no measurable perturbations of glucose homeostasis. Insulin infusion caused a 60% drop in both plasma and CSF glucose. Plasma levels of ir-beta-endorphins, ACTH and cortisol rose markedly. CSF levels of ir-beta-endorphins and ACTH also increased. While the magnitude of the increase was smaller than that in the plasma, it was greater than would be expected if crossover of the peptides from the plasma were the sole source of the increase. Hypoglycemia also induced elevations in CSF cortisol and insulin. In addition, there was a 45% decrease in CSF norepinephrine in spite of large elevations of norepinephrine in the plasma. We conclude that hypoglycemia is associated with marked changes in central as well as peripheral levels of neuroendocrine factors. The importance of these changes in mediating acute and long-term responses to hypoglycemia remains to be established.

Excitatory amino acid and calcium content of subarachnoid spinal fluid during hypoglycemia in the rat.

The concentrations of amino acids and calcium were measured in the subarachnoid cerebrospinal fluid (CSF) of rats prior to, and following, profound hypoglycemia. Calcium concentrations fell and amino acid changes were non-specific following hypoglycemia. In particular, elevations in excitatory amino acids did not occur, even though typical neuropathologic changes were found. These data do not support a role for excitatory amino acids or calcium as a 'CSF-borne toxin' in hypoglycemic brain injury. Moreover, the histopathological patterns of cell loss in the dentate gyrus often could not be reconciled with the concept of a CSF-borne toxin.

[Transfer of conditioned reflex hypoglycemia in dogs]. / Perenos uslovnoreflektornoi gipoglikemii u sobak.

Conditioned hypoglycemia was induced by intravenous injection of a 20% glucose solution to donor dogs. In control tests the dogs were injected the same volume of 0.9% saline. Then 0.5 ml of cerebrospinal fluid from donor animals was injected into suboccipital cisterna of recipient dogs. 24 hours later the recipient animals were exposed to the conditioned signal and injected physiological saline. It has been demonstrated that hypoglycemic response in recipient and donor dogs was identical, the reactions retained in the recipient dogs for 5-7 days after the liquor administration.

Effect of hypoglycemic stress on plasma and cerebrospinal fluid immunoreactive beta-endorphin in conscious sheep.

The effect of insulin-induced hypoglycemic stress on the concentrations of immunoreactive beta-endorphin (ir beta-EP) in plasma and cerebrospinal fluid (CSF) was examined in conscious non-pregnant ewes in which the cisterna magna and a jugular vein had been previously catheterized. In control experiments, no significant changes were observed in plasma cortisol or ir beta-EP and CSF ir beta-EP concentrations. During hypoglycemia induced by intravenous injection of 20 units of insulin, plasma cortisol concentrations rose significantly, reaching a peak 1.5 h after injection. The changes in plasma ir beta-EP concentration were significantly different between hypoglycemic and normoglycemic sheep (analysis of variance, P = 0.0089). Following insulin injection, mean plasma ir beta-EP rose by 100% within 0.75 h, continued to rise six-fold over initial concentrations by 2.25 h, and remained elevated for 3.75 h. The CSF ir beta-EP concentrations following insulin injection were not significantly different from those observed in controls. These results suggest that if beta-endorphin mediated hypoglycemic stress-induced analgesia, its actions may be peripheral, not central.

The distribution of hypoglycemic brain damage.

Rats were exposed to insulin-induced hypoglycemia resulting in periods of cerebral isoelectricity ranging from 10 to 60 min. After recovery with glucose, they were allowed to wake up and survive for 1 week. Control rats were recovered at the stage of EEG slowing. After sub-serial sectioning, the number and distribution of dying neurons was assessed in each brain region. Acid fuchsin was found to stain moribund neurons a brilliant red. Brains from control rats showed no dying neurons. From 10 to 60 min of cerebral isoelectricity, the number of dying neurons per brain correlated positively with the number of minutes of cerebral isoelectricity up to the maximum examined period of 60 min. Neuronal necrosis was found in the major brain regions vulnerable to several different insults. However, within each region the damage was not distributed as observed in ischemia. A superficial to deep gradient in the density of neuronal necrosis was seen in the cerebral cortex. More severe damage revealed a gradient in relation to the subjacent white matter as well. The caudatoputamen was involved more heavily near the white matter, and in more severely affected animals near the angle of the lateral ventricle. The hippocampus showed dense neuronal necrosis at the crest of the dentate gyrus and a gradient of increasing selective neuronal necrosis medially in CA1. The CA3 zone, while relatively resistant, showed neuronal necrosis in relation to the lateral ventricle in animals with hydrocephalus. Sharp demarcations between normal and damaged neuropil were found in the hippocampus. The periventricular amygdaloid nuclei showed damage closest to the lateral ventricles. The cerebellum was affected first near the foramina of Luschka, with damage occurring over the hemispheres in more severely affected animals. Purkinje cells were affected first, but basket cells were damaged as well. Rare necrotic neurons were seen in brain stem nuclei. The spinal cord showed necrosis of neurons in all areas of the gray matter. Infarction was not seen in this study. The possibility is discussed that a neurotoxic substance borne in the tissue fluid and cerebrospinal fluid (CSF) contributes to the pathogenesis of neuronal necrosis in hypoglycemic brain damage.

Cerebrospinal fluid markers of disturbed brain cell metabolism.

Reversibly and irreversibly disturbed brain cell metabolism may be monitored in an indirect way by the analyses of enzymes in the CSF according to the hypothesis of cell swelling induced by energy shortage. Adenylate kinase fulfils the criteria for an ideal CSF marker with the exception that it is not organspecific, which necessitates precautions to avoid influence of AK in erythrocytes and serum. When taking such limitating factors into account, AK determinations may be diagnostically useful in combination with radiological and clinical observations. Besides, it is possible that a combination of AK analyses and clinical signs are useful in the prognostication in individual patients suffering from global cerebral ischemia and cerebral infarction.

The effect of severe hypoglycemia upon cerebrospinal fluid formation, ventricular iodide clearance, and brain electrolytes in rabbits.

Severe insulin-induced hypoglycemia in rabbits reduces cerebrospinal fluid (CSF) formation, but not ventricular iodide clearance as measured by ventriculocisternal perfusion. This indicates that CSF production is ultimately glucose-dependent but that ventricular iodide clearance is not. The data suggest that severe hypoglycemia results in intracellular potassium loss within the brain and show that extracellular sodium replaces lost intracellular potassium. Hypoglycemia probably results in cellular adenosine triphosphate (ATP) reduction which affects membrane Na/K ATPase and the ability of the brain cell to maintain a potassium gradient. Potassium levels in the CSF also rise consequent to hypoglycemia. Homeostatic mechanisms that maintain a constant CSF potassium, therefore, are also affected by hypoglycemia.

The significance of the cerebrospinal fluid examination in the management of chlorpropamide-induced hypoglycemia.

Chlorpropamide-induced hypoglycemia is often overlooked, misdiagnosed, and mistreated, because of the atypical, insidious, and intermittent clinical picture and because of the normal serum glucose level in some of the patients when arriving at the hospital. These facts are demonstrated in three case reports. Since the correction of low glucose levels in the cerebrospinal fluid occurs hours after its correction in the serum, examining and at times following the cerebrospinal fluid glucose levels in patients with chlorpropamide-induced neuroglycopenia will enable physicians to diagnose and cure more patients. A high index of suspicion should exist in the presence of any atypical encephalopathy, mainly in the elderly diabetic patient treated with chlorpropamide and suffering from impaired cerebral, hepatic, or renal function. By suspecting and identifying neuroglycopenia, disabling residual deficits and even death could eventually be prevented.

Removal of 14-C-palmitate during ventriculocisternal perfusion in conscious dogs in insulin-induced hypoglycemia.

A detailed description of a method is presented allowing continous ventriculocisternal perfusion of metabolites in the conscious dog. Using this preparation, the loss of the infused albuminbound 14-C-aplmitate, was studied in 14 conscious dogs during ventriculocisternal perfusion with artificial cerebrospinal fluid (CSF). Forty-five percent of the infused 14-C-palmitate was recovered from the cisternal effluent under equilibrium conditions after 60 min of perfusion. The effect of the injection of 2.0 U insulin/kg was also investigated in seven dogs. Plasma glucose concentration decreased to 40--50 mg% and the amount of 14-C-palmitate recovered was significantly higher one hour after insulin compared to the controls receiving saline injections. No significant changes in cerebral arteriovenous differences of glucose or oxygen or in venous 14-C-palmitate concentration were observed during the same time. It is concluded that the combined use of ventriculocisternal perfusion and the analysis of cerebral arteriovenous differences are useful in studying brain metabolism in the consciuos dog.

Hypoglycorrhachia in pediatric patients.

Hypoglycorrhachia (abnormally low cerebro spinal fluid glucose content) eludes exact numerical definition, largely because of the dynamic equilibrium between blood and CSF glucose. A group of 181 pediatric patients with a CSF glucose less than 50 mg/100 ml or a CSF/blood glucose ratio less than 0.50 were studied. Hypoglycorrhachia was present in patients with bacterial meningitis, aseptic meningitis, meningeal carcinomatosis, subarachnoid hemmorrhage, and hypoglycemia. Markedly diminished CSF glucose values were seen primarily in patients with bacterial meningitis. Higher CSF/blood glucose ratios predominated in those with hypoglycemia and neonates with low-normal blood sugars. Following bacterial meningitis and hypoglycemia, aseptic meningitis (including five children with documented enterovirus meningitis and one with documented mumps meningitis) was the third most common cause of hypoglycorrhachia in children. When readily available, positive CSF viral cultures may allow early cessation of antibiotic therapy in two types of patients with meningitis and hypoglycorrhachia: (1) those receiving previous recent antibiotic therapy, and (2) those with CSF findings more typical of a bacterial meningitis.