dizocilpine-maleate and Asphyxia-Neonatorum

Birth asphyxia is an important cause of permanent neuro-developmental disability. Asphyxia sets in course a progression of intracellular events which culminates in neuronal death, and this process may take up to 48 h to complete. Entry of calcium into the neurone appears to be the key to the cell death, and it is known that during asphyxia, excessive glutamate is released which stimulates the voltage-dependent N-methyl-D-aspartate (NMDA) receptor to open with an accumulation of excess intracellular calcium. MK-801 is a very effective NMDA receptor antagonist, and it has been shown that this drug prevents or significantly reduces the extent of cortical neurone infarction following experimental asphyxia in 7-day-old rat pups. Unfortunately, MK-801 is toxic to the pup, but newer NMDA receptor antagonists may offer the opportunity for neuroprotection in the human infant who has suffered severe birth asphyxia.

Topics: Amino Acids; Animals; Asphyxia Neonatorum; Brain; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glutamates; Glutamic Acid; Humans; Infant, Newborn; Receptors, N-Methyl-D-Aspartate; Synapses

In vitro experiments have demonstrated that preconditioning primary neuronal cultures by temporary application of NMDA receptor antagonists induces long-term tolerance against lethal insults. In the present study we tested whether similar effects also occur in brain submitted to ischemia in vivo and whether the potential benefit outweighs the danger of enhancing the constitutive apoptosis in the developing brain.. Memantine in pharmacologically relevant doses of 5 mg/kg or (+)MK-801 (3 mg/kg) was administered i.p. 24, 48, 72 and 96 h before 3-min global forebrain ischemia in adult Mongolian gerbils or prior to hypoxia/ischemia in 7-day-old rats. Neuronal loss in the hippocampal CA1 in gerbils or weight deficit of the ischemic hemispheres in the rat pups was evaluated after 14 days. Also, the number of apoptotic neurons in the immature rat brain was evaluated.. In gerbils only the application of (+)MK-801 24 h before ischemia resulted in significant prevention of the loss of pyramidal neurons. In rat pups administration of (+)MK-801 at all studied times before hypoxia-ischemia, or pretreatment with memantine or with hypoxia taken as a positive control 48 to 92 h before the insult, significantly reduced brain damage. Both NMDA receptor antagonists equally reduced the number of apoptotic neurons after hypoxia-ischemia, while (+)MK-801-evoked potentiation of constitutive apoptosis greatly exceeded the effect of memantine.. We ascribe neuroprotection induced in the immature rats by the pretreatment with both NMDA receptor antagonists 48 to 92 h before hypoxia-ischemia to tolerance evoked by preconditioning, while the neuroprotective effect of (+)MK-801 applied 24 h before the insults may be attributed to direct consequences of the inhibition of NMDA receptors. This is the first report demonstrating the phenomenon of inducing tolerance against hypoxia-ischemia in vivo in developing rat brain by preconditioning with NMDA receptor antagonists.

Topics: Animals; Animals, Newborn; Asphyxia Neonatorum; Brain; Brain Ischemia; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Gerbillinae; Immunohistochemistry; Ischemic Preconditioning; Male; Memantine; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

Progesterone modulates gamma-aminobutyric acid and excitatory amino acid neurotransmitter systems and has neuroprotective properties in models of hypoxia-ischemia. This study examined the in vitro effects of allopregnanolone, the active progesterone metabolite, in models of N-methyl-D-aspartate (NMDA)-induced necrosis and apoptosis. Cultured NT2 neurons were exposed to 1 mM NMDA. Lactate dehydrogenase (LDH) release was measured 24 h later. NMDA at a concentration of 1 mM produced a 39 +/- 19% release of total LDH. Exposure to 10 microM allopregnanolone prior to NMDA exposure reduced LDH release by 51% (P = 0.0028). NMDA stimulated apoptotic cell changes defined by terminal dUTP nick-end labeling (TUNEL) and 5,5', 6,6'-tetrachloro-1,1,3,3'-tetra ethlybenzimidazolycarbocyanide iodide staining were reduced to baseline values by both 10 microM allopregnanolone and 100 microM MK-801. Pretreatment with allopregnanolone (0-10 microM) reduced the percentage of TUNEL-positive cells in a dose-dependent manner (EC(50) = 2.7 +/- 0.1 nM). Physiologic concentrations of allopregnanolone provided protection against both necrotic and apoptotic injury induced by NMDA excitotoxicity.

Topics: Apoptosis; Asphyxia Neonatorum; Benzimidazoles; Carbocyanines; Cell Count; Cell Survival; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Fluorescent Dyes; Humans; Hypoxia-Ischemia, Brain; In Situ Nick-End Labeling; Infant, Newborn; L-Lactate Dehydrogenase; Membrane Potentials; Mitochondria; N-Methylaspartate; Neurons; Neuroprotective Agents; Neurotoxins; Pregnancy; Pregnanolone; Progesterone; Tumor Cells, Cultured

Delayed neuronal death following hypoxic ischaemic insult is primarily mediated by the N-methyl D-aspartate (NMDA) receptor. The NMDA receptor antagonist MK 801, has been shown to limit neuronal death following hypoxic ischaemic injury but is too toxic to be used in the human neonate. Magnesium blocks the NMDA channel in a voltage dependent manner. Its administration after a simulated hypoxic ischaemic insult limits neurological damage in several animal models. The efficacy of magnesium in providing neuroprotection in the human neonate, however needs to be established in controlled clinical trials.

Topics: Asphyxia Neonatorum; Cell Death; Dizocilpine Maleate; Humans; Infant, Newborn; Magnesium; Magnesium Sulfate; Neurons; Neuroprotective Agents

This study investigated the influence of temperature or glutamate antagonism on the immediate outcome of perinatal asphyxia. Perinatal asphyxia was produced by water immersion of fetus-containing uterus horns removed by cesarean section from ready to deliver rats. The uterus horns were kept in a water bath for different time periods, before the pups were delivered and stimulated to breathe. After delivery, the pups were assessed for behavior and for systemic glutamate, aspartate, lactate and pyruvate levels measured with in vivo microdialysis, or ex vivo for energy-rich phosphates, including adenosine triphosphate (ATP), in brain, heart and kidney. In a series of experiments, asphyxia was initiated in a water bath at 37 degrees C, before the pup-containing uterus horns were moved for different time intervals to a 15 degrees C bath. In another series of experiments, the mothers were treated with N-methyl-D-aspartate (NMDA) antagonist, dizocilpine (MK-801), or alpha-amino-3-hydroxy-methylisoxazole-4-propionic acid (AMPA) antagonist,2,3-dihydroxy-6-nitro-7-sulfamoyl benzo(f) quinoxalin NBQX) 1 h before hysterectomy and asphyxia at 37 degrees C. The rate of survival rapidly decreased following exposure to more than 16 min of asphyxia, and no survival could be observed after 22 min of asphyxia. An LD50 was estimated to occur at approximately 19 min of asphyxia. The outcome was paralleled by a decrease in ATP in kidney, followed by a decrease in heart and brain. A maximal decrease in ATP was observed after 20 min of asphyxia in all tissues. Systemic microdialysis revealed that glutamate, aspartate and pyruvate levels were increased with a peak after 5 min of asphyxia. In contrast, lactate levels increased along with the length of the insult. Survival was increased when the pup-containing uterus horns were moved from a 37 degrees C to a 15 degrees C bath, at 15 min of asphyxia (the LD50 was thus increased to 30 min). If the shift occurred at 10 or 5 min of asphyxia, the LD50 increased to 80 or 110 min, respectively. The effect of glutamate antagonism was minor compared to hypothermia; the best effect (an increase in the LD50 to approximately 22 min) was observed after combining AMPA and NMDA antagonists.

Topics: Adenosine Triphosphate; Animals; Animals, Newborn; Aspartic Acid; Asphyxia Neonatorum; Behavior, Animal; Brain; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glutamic Acid; Heart; Humans; Hypothermia, Induced; Hypoxia-Ischemia, Brain; Infant, Newborn; Kidney; Lactic Acid; Maternal Behavior; Microdialysis; Pyruvic Acid; Quinoxalines; Rats; Receptors, Glutamate; Survival Rate; Treatment Outcome

The aim was to study the effects of an NMDA receptor antagonist on caspase-3 activation and DNA fragmentation after hypoxia-ischemia (HI) in 7-day-old rats. Animals were treated with vehicle or MK-801 (0.5 mg/kg) directly after HI and sacrificed 8, 24 or 72h later. MK-801 reduced injury (by 53%), cells positive for active caspase-3 (by 39%) and DNA fragmentation (by 79%) in the cerebral cortex. Furthermore, MK-801 significantly decreased caspase-3 activity, and Western blots revealed a tendency towards decreased proteolytic cleavage of the caspase-3 proform. The data imply that NMDA receptors are involved in the activation of apoptotic processes in the immature brain after HI.

Topics: Animals; Animals, Newborn; Apoptosis; Asphyxia Neonatorum; Caspase 3; Caspases; Cerebral Cortex; Dizocilpine Maleate; DNA Fragmentation; Female; Humans; Hypoxia-Ischemia, Brain; Infant, Newborn; Male; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

The present study tests the hypothesis that repeated episodes of asphyxia will lead to alterations in the characteristics of the N-methyl-d-aspartate (NMDA) receptor in the brain cell membrane of newborn piglets and that pre-treatment with allopurinol, a xanthine oxidase inhibitor, will prevent these modifications. Eighteen newborn piglets were studied. Six untreated and six allopurinol treated animals were subjected to eight asphyxial episodes and compared to six normoxic, normocapneic controls. Brain cell membrane Na+,K+-ATPase activity was determined to assess membrane function. Na+,K+-ATPase activity was decreased from control following asphyxia in both the untreated and treated animals (47.7+/-3.2 vs. 43.0+/-2.2 and 41.0+/-5.3 micromol Pi/mg protein/h, p<0.05, respectively). 3H-MK-801 binding studies were performed to measure NMDA receptor binding characteristics. The receptor density (Bmax) in the untreated asphyxia group was decreased compared to control animals (0.80+/-0.11 vs. 1.13+/-0.33, p<0.05); furthermore, the dissociation constant (Kd) was also decreased (3.8+/-0.7 vs. 9.2+/-2.2, p<0.05), indicating an increase in receptor affinity. In contrast, Bmax in the allopurinol treated asphyxia group was similar to control (1. 06+/-0.37); and Kd was higher (lower affinity) than in the untreated group (6.5+/-1.4, p<0.05). The data indicate that recurrent asphyxial episodes lead to alterations in NMDA receptor characteristics; and that despite cell membrane dysfunction as seen by a decrease in Na+,K+-ATPase activity, allopurinol prevents modification of NMDA receptor-ion channel binding characteristics induced by repeated episodes of asphyxia.

Topics: Allopurinol; Animals; Animals, Newborn; Asphyxia Neonatorum; Brain; Dizocilpine Maleate; Energy Metabolism; Enzyme Inhibitors; Humans; Infant, Newborn; Ion Channels; Radioligand Assay; Receptors, N-Methyl-D-Aspartate; Recurrence; Sodium-Potassium-Exchanging ATPase; Swine; Xanthine Oxidase

New insights into the pathophysiology of the hypoxic-ischemic insult have opened the possibility of pharmacologic intervention in neonatal hypoxic-ischemic encephalopathy. It is now known that many neurons survive a hypoxic-ischemic insult but remain dysfunctional for hours, with profound alterations in cell function. A cascade of biochemical alterations occurs as a consequence of cellular ionic shifts, energy depletion, degradation of cell membrane phospholipids, and increased release of neurotransmitters. In addition, there are alterations in the metabolism of arachidonic acid and prostanoids and an excessive production of oxygen free radicals. The new therapeutic modalities are aimed at preventing or arresting the biochemical changes that occur in the period after hypoxia-ischemia. This review details the biochemical alterations associated with neonatal hypoxic-ischemic encephalopathy and discusses the possible use in newborns of pharmacologic agents currently undergoing extensive investigations in experimental animals and adult humans.

Topics: Asphyxia Neonatorum; Brain Ischemia; Calcium Channel Blockers; Dizocilpine Maleate; Free Radical Scavengers; Humans; Hypoxia, Brain; Infant, Newborn; Lipid Peroxides; Pregnatrienes; Reperfusion Injury