Increased sensitivity to seizures in repeated exposures to hyperbaric oxygen: role of NOS activation

Nitric oxide is involved in the mechanism of hyperbaric oxygen (HBO(2)) brain toxicity as nitric oxide synthase (NOS) inhibitors delay latent time before the onset of seizures. The purpose of this study was to investigate if seizures affect sensitivity to convulsions during subsequent exposure to HBO(2) and to determine if NOS activity and expression is changed after HBO(2) seizures. Rats were exposed to 5 atm (gauge pressure) 100% O(2) until seizures recorded by electroencephalograph (EEG) and reexposed 1, 2, or 6 days later. Latency to seizures was significantly shorter (P<0.05) in animals reexposed 1 or 2 days after the first exposure. Activity of calcium-dependent NOS activity in cortex was significantly higher 1 and 2 days after seizures compared with controls (P<0.05), while calcium-independent NOS activity was not changed during the 6-day post-seizure interval. The expression of neuronal NOS (nNOS) protein determined by Western blot was higher 1 and 2 days after seizures (P<0.05), while the expression of endothelial (eNOS) and inducible (iNOS) remained unchanged. nNOS upregulation 1 and 2 days after seizures and protection against HBO(2) seizures by nNOS-specific inhibitor 7-nitroindazole (7-NI) suggest possible involvement of NO in the mechanism of increased sensitivity to HBO(2) in reexposures.

Attenuation of brain hyperbaric oxygen toxicity by fasting is not related to ketosis

The effect of 24 h of fasting and changes in blood glucose and beta-hydroxybutyrate (BHB) level on latency to seizures in hyperbaric oxygen (HBO2) was studied. Conscious, unrestrained rats implanted with cortical electroencephalogram electrodes were exposed to 0.5 MPa (gauge pressure) O2 until seizures were observed. Fasting for 24 h significantly (P < 0.01) decreased blood glucose (from 8.6 +/- 0.9 in fed to 6.9 +/- 0.7 mM in the fasted group), increased blood BHB (0.07 +/- 0.02 mM to 0.38 +/- 0.10 mM, respectively), and prolonged the latency to seizures compared with normally fed animals (21.0 +/- 9.8 vs. 34.6 +/- 17.7 min, P < 0.05). Injection of the ketone precursor 1,3-butanediol (BD) to the fed animals increased blood BHB level to 0.72 +/- 0.32; however, seizure latency remained the same as in fed animals. Restoration of blood glucose in fasted animals to the same level as in the fed group did not reverse the protection achieved by fast; instead it increased the latency to seizures. The results indicate that the protection against HBO2 seizures by fasting in short starvation is not related to the increase in circulating ketone bodies or decrease in blood glucose.

Effect of MK-801 on seizures induced by exposure to hyperbaric oxygen: comparison with AP-7

The effect of the noncompetitive N-methyl-d-aspartate (NMDA)-receptor antagonist MK-801 on seizures induced by hyperbaric oxygen in relation to changes in cerebral blood flow (CBF) was investigated. Rats were injected with MK-801 (0.005-8 mg/kg) 30 min before exposure to 100% O2 at 5 atm (gauge pressure). MK-801 administration resulted in a biphasic response in seizure latency. Doses of 0.1-4 mg/kg significantly decreased time to EEG and motor seizures, while 8 mg/kg had no effect on seizure latency. MK-801 had no effect on seizure duration. In a dose range 0.1-8 mg/kg MK-801 increased CBF in awake animals, which might be responsible for the decreased seizure latency. The gradual increase in seizure latency with increasing MK-801 doses suggests involvement of an additional factor probably related to the drug's anticonvulsive effect. Unlike MK-801, a competitive NMDA receptor antagonist, AP-7, at a dose 250 mg/kg had no effect on latency to seizures or CBF.

Role of cerebral blood flow in seizures from hyperbaric oxygen exposure

Hyperbaric O2 exposure causes seizures by an unknown mechanism. Cerebral blood flow (CBF) may affect seizure latency, although no studies have demonstrated a direct relationship. Awake rats (male, Sprague-Dawley, 350-450 g), instrumented for measuring electroencephalographic activity (EEG) and CBF (laser-Doppler flowmetry), were exposed to 100% O2 at 4 or 5 atm (gauge pressure) until EEG seizures. Compression with O2 caused vasoconstriction to about 70% of control flow that was maintained for various times. CBF then suddenly, but transiently, increased at a time that was reliably related to seizure latency (r=0.8, p<0.01). Additional animals were treated with agents that have diverse pharmacology and their effects on CBF and latency were measured. Glutamate receptor antagonists MK-801 (1 or 4 mg/kg) and ketamine (20-100 mg/kg) significantly increased CBF by 60-80% and decreased seizure latency from about 17+/-8 min (+/-S.D.) in controls to 5+/-1 and 6+/-2 min, respectively. In opposite, a nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine (NNA)(25 mg/kg) decreased CBF by about 25% and increased time to seizure to 60+/-16 min. If these effects occur in humans, non-invasive measurement of CBF could potentially improve the safety and reliability of hyperbaric O2 usage in clinical and diving applications. It also appears that the effect of drugs on seizure latency can be explained, at least in part, by their effect on CBF.

The intraischemic and early reperfusion changes of protein synthesis in the rat brain. eIF-2 alpha kinase activity and role of initiation factors eIF-2 alpha and eIF-4E

Rats were subjected to the standard four-vessel occlusion model of transient cerebral ischemia (vertebral and carotid arteries). The effects of normothermic ischemia (37 degrees C) followed or not by 30-minute reperfusion, as well as 30-minute postdecapitative ischemia, on translational rates were examined. Protein synthesis rate, as measured in a cell-free system, was significantly inhibited in ischemic rats, and the extent of inhibition strongly depended on duration and temperature, and less on the model of ischemia used. The ability of reinitiation in vitro (by using aurintricarboxylic acid) decreased after ischemia, suggesting a failure in the synthetic machinery at the initiation level. Eukaryotic initiation factor 2 (eIF-2) presented almost basal activity and levels after 30-minute normothermic ischemia, and the amount of phosphorylated eIF-2 alpha in these samples, as well as in sham-control samples, was undetectable. The decrease in the levels of phosphorylated initiation factor 4E (eIF-4E) after 30-minute ischemia (from 32% to 16%) could explain, at least partially, the impairment of initiation during transient cerebral ischemia. After reperfusion, eIF-4E phosphorylation was almost completely restored to basal levels (29%), whereas the level of phosphorylated eIF-2 alpha was higher (13%) than in controls and ischemic samples (both less than 2%). eIF-2 alpha kinase activity in vitro as measured by phosphorylation of endogenous eIF-2 in the presence of ATP/Mg2+, was higher in ischemic samples (8%) than in controls (4%). It seems probable that the failure of the kinase in phosphorylating eIF-2 in vivo during ischemia is due to the depletion of ATP stores. The levels of the double-stranded activated eIF-2 alpha kinase were slightly higher in ischemic animals than in controls. Our results suggest that the modulation of eIF-4E phosphorylation could be implicated in the regulation of translation during ischemia. On the contrary, phosphorylation of eIF-2 alpha, by an eIF-2 alpha kinase already activated during ischemia, represents a plausible mechanism for explaining the inhibition of translation during reperfusion.

Comparative effects of the N-methyl-D-aspartate antagonist MK-801 and the calcium channel blocker KB-2796 on neurologic and metabolic recovery after spinal cord ischemia

NMDA receptor antagonists have been demonstrated to be neuroprotective in focal cerebral ischemia and are supposed to prevent neurotoxic intracellular calcium increase. Another mechanism of calcium influx during ischemia involves activation of voltage-activated calcium channels, although the efficacy of calcium channel blockers against ischemia-induced damage varies. The purpose of this study was to determine the contributions of the excitotoxic mechanism and of calcium channel activation to metabolic and functional damage to rabbit spinal cord after ischemia induced by occlusion of the abdominal aorta. All metabolic parameters determined (ATP, energy charge, and lactate) completely recovered at 4 days following 20 min of ischemia when NMDA receptor antagonist MK-801 (1 mg/kg given i.v.) or calcium channel blocker KB-2796 (50 mg/kg given i.p.) was administered either prior to or after ischemia. Significant metabolic recovery was also observed after 30 min of ischemia with MK-801 administered before occlusion and KB-2796 given early in recirculation. Similarly, neurologic functions followed by functional performance in the hindlimbs were completely recovered following 20 and 30 min of ischemia and 4 days of recovery. This study demonstrates that although MK-801 or KB-2796 does not prevent paraplegia due to spinal cord ischemia in the rabbit, both drugs can influence the rate of recovery after ischemic injury.

Ischemia-reperfusion injury in the spinal cord of rabbits strongly enhances lipid peroxidation and modifies phospholipid profiles

The effect of spinal cord ischemia (10, 20, and 40 min) and post-ischemic reperfusion (10, 30, and 60 min) on lipid peroxidation and phospholipids was investigated. Spinal cord ischemia was accompanied by lipolytic processes with significant changes in concentration of lipid peroxidation products (LPP). Reestablishment of the blood supply after 10 min ischemia was accompanied by significantly increased levels of thiobarbituric acid reactive substances (TBA-RS) after 10 and 30 min of reperfusion. Following 20 and 40 min ischemia a significant increase was observed at all reperfusion periods. Ischemia itself significantly reduced the concentration of phosphatidyl inositol (IP), phosphatidyl ethanolamine (EP) and ethanolamine plasmalogens (Epls). Significant changes were observed in concentration of phosphatidyl serine (SP) too, but only after 20 and 40 min of ischemia. The concentration of phosphatidic acid (PA) was significantly reduced only after 10 min of ischemia. The onset of reperfusion after ischemia was accompanied by a diverse pattern of changes in PA, IP, Epls and SP, while the concentration of EP remained at the above mentioned ischemic intervals.

Regional lipid peroxidation and protein oxidation in rat brain after hyperbaric oxygen exposure

Reactive oxygen species may participate in development of neurological toxicity resulting from hyperbaric oxygen exposure. To explore the possibility that increased reactive O2 metabolite generation may result in oxidative modification of lipids and proteins, rats were exposed to five atmospheres (gauge pressure) of O2 until development of an electroencephalographic seizure. Lipid peroxidation (as thiobarbituric acid-reactive substances) and protein oxidation (as 2,4-dinitrophenyl-hydrazones) were measured in five brain regions. Oxidized and reduced glutathione were also determined because of their role in regulating lipid peroxidation. Lipid peroxidation was confined to the frontal cortex and hippocampus, while protein oxidation (in both cytoplasmic and membranous fractions) and increased oxidized glutathione was evident throughout the brain. These results support a role for formation of reactive O2 metabolites from hyperbaric O2 exposure and suggest that protein oxidation, especially in soluble proteins, may be one of the most sensitive measures.

Short-term postischemic hypoperfusion improves recovery of protein synthesis in the rat brain cortex

A cell-free system from rat brain cortex was used to follow changes in protein synthesis after ischemia and reperfusion (four-vessel occlusion). The experiment was focused to prevent a violent burst of free oxygen radicals creation during the first period of postischemic reperfusion by short-term hypoperfusion. After 30 min of ischemia, the authors applied hypoperfusion produced by releasing one (right) carotid for the first 5 min of reperfusion lasting from 30 min to 3 d. Results obtained by this procedure show that the activity of protein synthesis machinery from hypoperfused brains is higher than normovolemic ones; the left hemisphere, which is contralateral to direct blood flow during hypoperfusion, shows better results than the right hemisphere.

KB-2796, a calcium channel blocker, ameliorates ischemic spinal cord damage in rabbits

The effect of the calcium channel blocker (KB-2796) on metabolic and functional recovery in rabbit spinal cord after 20, 30, and 40 min ischemia and 4 days of recovery was investigated. The drug was given intraperitoneally in three different doses, 10, 20, or 50 mg/kg pre- or post-ischemia of 20, 30, or 40 min duration. Both higher doses 20 and 30 mg/kg completely recovered energy state and significantly improved neurological functions in the spinal cord following 20 and 30 min ischemia. Partial protection was observed even after 40 min ischemia. The protective effect of KB-2796 exceeds the effect of calcium blockers previously used in experimental spinal cord ischemia.

Effect of propentofylline (HWA 285) on metabolic and functional recovery in the spinal cord after ischemia

The effect of propentofylline on metabolic and functional recovery in the spinal cord after ischemia and reperfusion was investigated. Ischemia was induced by abdominal aorta ligation below the left renal artery for 20 or 30 min. Propentofylline (1, 5, 10 and 20 mg/kg) was administered intravenously, immediately after reperfusion and the animals recovered for 4 days. Propentofylline at a dose of 1 mg/kg and 5 mg/kg had only a slight effect on energy metabolism recovery in the spinal cord and neurological recovery of hindlimbs. However, almost complete recovery of adenine nucleotides, lactate and glucose occurred after 20 min of ischemia in the animals treated with 10 or 20 mg/kg propentofylline. Partial metabolic recovery occurred even after 30 min of ischemia and 20 mg/kg propentofylline. The recovery of energy metabolism correlated closely with the recovery of neurological functions after ischemia and 4 days of survival.

Membrane lipid degradation during ischemia and impact on the monolayer surface pressure area diagram (SPAD)

This article briefly reviews the importance and relevance of membrane lipid degradation to the pathogenesis of ischemic brain damage ranging from the liberation and accumulation of free fatty acids (FFA) to their consequences on the biophysical characteristics of membrane lipids. The rapid accumulation of brain FFA during cerebral ischemia is a hallmark of the evolution and pathogenesis of ischemic brain damage: It signals the degradation of membrane lipids; it generates the precursors to the metabolically and physiologically potent eicosanoids; and it promotes the generation of lipid oxidizing free radicals, which could propagate the destruction of membrane lipids. The impact of ischemia-induced changes in cerebral membrane lipid composition on membrane function is difficult to assess in vivo. Some estimate of the impact of the changes, however, can be obtained by evaluating the changes induced in the surface pressure-area diagrams (SPAD) of membrane lipid monolayers at the air-water interface. Lipid monolayers are used as model membranes to study the effects of lipid composition on the biophysical behavior of membrane lipids and their interaction. Regional brain lipids were quantitated at different times during ischemia, and their impact on their surface pressure area diagrams was assessed and their potential impact on membrane function discussed.

[Protective effect of propentophylline (HWA 285) in ischemic spinal cord injury]

The effect of propentophylline (HWA 285) on the course of the functional regeneration of the hind extremities and on the regeneration of the energetic metabolism in the spinal cord after ischaemia produced by ligating the abdominal aorta for 20 or 30 mins was investigated. Administration of 20 mg/kg i.v. propentophylline after the induction of ischaemia produced marked regeneration of these parameters in comparison with ischaemia without administration of the drug in the course of four days. The protective effect of propentophylline administered prior to ischaemia was markedly weaker.

Effect of stobadine on lipid peroxidation and phospholipids in rabbit spinal cord after ischaemia

Stobadine, a drug with the pyridoindol structure, was compared with thiopental and pentobarbital for its ability to inhibit stimulated peroxidation in homogenates of spinal cord in vitro. The antioxidative capacity of the drug exceeded that of barbiturates more than 100-fold. Stobadine was also shown to inhibit the increase in formation of TBA-RS in homogenates of rabbit spinal cord, subjected to 20 min ischaemia, to the level comparable with controls. Administration of the drug (6 mg kg-1) to animals 5 min before 20 min ischaemia had no effect on level of lipid peroxidation products in the spinal cord; however, it slowed down stimulated Fe(2+)-dependent peroxidation after in vitro incubation of the homogenates and increased the concentration of phosphatidylserine and ethanolamine plasmalogens, as compared with non-treated animals. Application of stobadine 2 min before the release of an aortic occlusion increased the antiradical capacity in homogenates of spinal cord and revealed an ameliorating effect on the composition of phospholipids.

Regional lipid composition in the rat brain

The lipid composition of the brain is of great importance to its metabolism and function. Although much research has been done on regional brain lipid composition, studies usually suffer from limited brain regions or from limited lipids analyzed. We modified a previously described method for the separation of brain phospholipids and glycolipids, improving the separation and sensitivity of the method. Using this modified method, we measured the lipid composition of the frontal and entorhinal cortices, the hippocampus, basal ganglia, cerebellum, and medulla oblongata of five rats under nitrous oxide analgesia. Total lipid content was highest (p < 0.05) in the medulla oblongata (111.0 +/- 6.0 mg/g wet brain, X +/- SD) followed by the hippocampus (72.6 +/- 2.8), cerebellum (62.7 +/- 4.6), basal ganglia (62.6 +/- 1.5), frontal cortex (57.7 +/- 2.1), and entorhinal cortex (53.3 +/- 1.9). The areas with higher total lipid content (p < 0.05) also had higher percentages of cerebrosides (18.6 +/- 2.2 in the medulla oblongata vs 8.3 +/- 1.2 in the frontal cortex) and 40 to 50% lower levels of phosphatidylcholine and phosphatidylinositol. The relation between the ratio of cerebrosides plus sulfatides to phosphatidylcholine and the total lipid content indicates that differences in brain lipid composition between regions are attributable to their relative gray/white matter content.

Amelioration of ischemic spinal cord damage by postischemic treatment with propentofylline (HWA 285)

The effect of the xanthine derivative propentofylline (HWA 285) on metabolic and functional recovery in rabbit spinal cord after 20 and 30 min ischemia and 4 days of reperfusion was investigated. Pre-treatment with 20 mg/kg significantly improved recovery of the energy state in the spinal cord, however, without significant functional recovery of hindlimbs. In contrary, post-treatment with HWA 285 recovered the energy state to pre-ischemic value and also significantly improved functional recovery. These findings suggest that the neuroprotective mechanism of HWA 285 in the spinal cord is not associated with inhibition of glutamate release as supposed to operate in the gerbil brain.

Regional differences in rat brain lipids during global ischemia

BACKGROUND AND PURPOSE

Membrane lipid degradation plays an important role in the pathogenesis of ischemic brain damage, but there is little information on changes in cerebrosides, sulfatides, and sphingomyelin. We studied regional changes in the quantities of these lipids during complete global brain ischemia in rats.

METHODS

Nitrous oxide-anesthetized rats were subjected to ischemia by a high-pressure neck cuff and arterial hypotension for 0 (control), 3, 10, or 30 minutes (n = 5 at each time). Brain temperature was allowed to fall spontaneously during ischemia, and the brain was frozen in situ with liquid N2 without recirculation. The frontal cortex, hippocampus, and basal ganglia were dissected at -15 degrees C. The lipids were separated by column and high-performance thin-layer chromatography and quantified by charring and densitometry.

RESULTS

Total lipid content was higher (p less than 0.01) in the hippocampus (72.6 +/- 2.8 mg/g wet wt, mean +/- SD) than in the frontal cortex and basal ganglia (57.7 +/- 2.1 and 62.6 +/- 1.5 mg/g wet wt, respectively). Ischemic changes occurred only in the frontal cortex, where total lipid content fell (p less than 0.01) by 11% after 30 minutes of ischemia because sulfatide and cerebroside contents fell by 44% and 38%, respectively.

CONCLUSIONS

Despite a marked accumulation of free fatty acids during complete global brain ischemia in rats, the only detectable changes in brain lipids were in the amounts of cerebrosides and sulfatides in the frontal cortex.

[Neurotransplantation, critical analysis and perspectives]

Basic morphological and functional properties of basal ganglia are described and their role in the development of Parkinson's disease is discussed in detail. Based on recent experimental data, the problem of human autologous adrenal medulla transplants as well as human dopaminergic neurons is analyzed and prospective approaches to successful therapeutic interventions are considered mainly from the molecular and immunobiological point of view. The relative limitations of the regenerative capacity and transplantability of the nervous tissue are assessed and compared with the critical developmental periods of human neurogenesis (Fig. 6, Ref. 47.).

Blood flow and electrolytes in spinal cord ischemia

The contribution of reoxygenation-reperfusion injury to ischemic brain damage has been clearly demonstrated but not in the spinal cord. To evaluate this phenomenon in spinal cord ischemia, we measured spinal cord blood flow (SCBF) by [14C]iodoantipyrine and electrolytes in rabbits after 10 or 40 min ischemia followed by 30 min or 4 days recirculation. Ischemia for 10 or 40 min reduced blood flow in the lower lumbar segments L5-L7 (30 ml/100 g/min) to 5 and 10% of control. After 30 min of recirculation moderate hyperemia (25-40% above control) was observed in segments L5-L7 which was not related to the degree of functional impairment. Na+, water, and Ca2+ increased and K+ decreased after 40 min ischemia, but were unchanged after 10 min ischemia. Recirculation for 30 min after 40 min of ischemia resulted in a progressive rise in Ca2+ which correlated with irreversible spinal cord injury.

Postischemic hypoxia improves metabolic and functional recovery of the spinal cord

We studied the effect of graded postischemic reoxygenation on the tissue concentrations of adenylates, glucose, and lactate in the rabbit lumbar spinal cord after 10, 20, and 30 minutes of ischemia. In comparison with recirculation without manipulated PaO2, a decrease of PaO2 to 40 to 45 mm Hg upon reestablishment of blood circulation after ischemia led to an amelioration of the energy metabolism in the spinal cord tissue as determined by measuring the ATP concentration and energy charge. The protective effect of postischemic hypoxia was also reflected by the improvement of neurologic functions in animals after 10 and 20 minutes of ischemia.

Effect of partial ischemia on phospholipids and postischemic lipid peroxidation in rabbit spinal cord

Rabbit spinal cord, subjected to severe partial ischemia induced by abdominal aorta ligation tightly below the renal arteries, was analyzed for phospholipid composition and levels of lipid peroxidation products after 10, 20, and 40 min of the insult. Under conditions when spinal cord blood flow was decreased below 5% of control, concentrations of inositol and ethanolamine phospholipids were decreased by 30% and 10%, respectively. Phosphatidic acid concentration was also altered during ischemia. No accumulation of thiobarbituric acid reactive substances (TBA-RS), conjugated dienes and fluorescent lipid soluble material was found throughout the ischemic period. Pattern of TBA-RS, conjugated diene, and fluorophore formation during postischemic in vitro incubation without and with a peroxidation couple (Fe2+, ascorbic acid) showed increased susceptibility to postischemic lipid peroxidation in tissues after 20 and 40 min of ischemia.

[Levels of homovanillic acid and 5-hydroxyindoleacetic acid in the cerebrospinal fluid in patients with focal cerebral ischemia]

The investigated group comprised 35 patients where clinical examination revealed focal cerebral ischaemia in the area of the a. cerebri media. In the group of elderly patients above 60 years, as compared with controls, the homovanillic acid (HVA) and 5-hydroxyindolacetic acid (5-HIAA) concentration in cerebrospinal fluid was elevated. In the group of patients under 60 years no changes in the concentration of these metabolites were found. In older patients the increased level of metabolites in cerebrospinal fluid persisted also after three days following the attack, while in younger patients the elevated HVA and 5-HIAA levels were found only in specimens collected up to three days.

Improvement of energy state and basic modifications of neuropathological damage in rabbits as a result of graded postischemic spinal cord reoxygenation

The role of graded postischemic reoxygenation applied at the end of 20 min of spinal cord ischemia was studied with respect to the intraspinal pO2 tension, energy state, and histopathological sequelae. Graded postischemic reoxygenation can induce a positive shift in the intraspinal pO2 tension, but normal postischemic reoxygenation with normotensive pO2 blood tension inevitably causes the postischemic intraspinal pO2 overshoot. Graded postischemic reoxygenation significantly improves the energy state expressed by higher adenosine triphosphate (ATP), phosphocreatine (PCr) and glucose levels. Using the Nauta impregnating degenerating method, clear histopathological differences were found in the L3-S3 segments after 20 min of ischemia. Apparently divergent damage was observed when normal reoxygenation or graded postischemic reoxygenation was used. Diametrically different histopathological outcomes were obtained with normal reoxygenation and graded postischemic reoxygenation 2 and 4 days postoperatively.

Effect of spinal cord ischemia on axonal transport of cholinergic enzymes in rabbit sciatic nerve

The fast axonal transport of acetylcholinesterase (AChE) and the slow transport of choline acetyltransferase (ChAT) were measured by the stop-flow ligation technique in the sciatic nerve of rabbits 6 and 24 h after ischemia performed by the occlusion of the abdominal aorta which lasted 40 min. Activities of these enzymes were also measured in punched samples of the spinal cord (L5-6). Results were correlated with those obtained from the sham-operated control group. Six h after ischemia, its only apparent effect was a different distribution of accumulated enzymes in the central nerve segments. Twenty-four h after ischemia, the transport of AChE was markedly depressed; proximodistal accumulation decreased by 68%, whereas enzyme activity in the intact contralateral nerve and in the ventral horns of the spinal cord was preserved. No effect of ischemia on the retrograde axonal transport of AChE was observed in this experimental model. Cytoplasmic ChAT is much more susceptible to necrotic degeneration than membrane-bound AChE; 24 h after ischemia its activity decreased significantly in all investigated parts of the sciatic motoneurones but the rate of slow axonal transport did not seem to be affected.

Axoplasmic transport of monoamine oxidase after ischemia

Rabbit spinal cords were subjected to 40 min of ischemia by abdominal aorta occlusion followed by 1 or 4 days of recirculation. Axoplasmic transport of mitochondria was investigated by monitoring the accumulation of monoamine oxidase activity (MAO, EC 1.4.3.4) at the proximal and distal ligatures placed on sciatic nerves. Within 1 day following ischemia, MAO accumulation was reduced to 45% and 34% at the proximal and distal ties, respectively. Within 4 days after ischemia, MAO accumulation was depressed still further to 22% in either direction. The substantial decrease in transport velocity appears to be the immediate cause for the observed decrease in MAO accumulation in sciatic nerve.

Silver staining of native and denatured eucaryotic DNA in agarose gels

A modified method of silver staining for native and denatured eucaryotic DNA in 1% agarose gel is described. This method is at least fivefold more sensitive than ethidium bromide staining, with a detection limit of 2.5 ng for total DNA. The calibration curve is linear within the range 5-30 ng of single-stranded and double-stranded DNA. This method is especially advantageous for electrophoretic assessment of DNA molecular weights.

Effects of incomplete ischemia and subsequent recirculation on free palmitate, stearate, oleate and arachidonate levels in lumbar and cervical spinal cord of rabbit

The effect of severe incomplete ischemia, induced by abdominal aorta ligation for 40 minutes, and subsequent recirculation for one and four days on accumulation of free fatty acids was studies in the lumbar and cervical part of rabbit spinal cord. Changes in free fatty acid levels were determined separately in gracile fascicle (Fg), dorsal part (Dp, without Fg) and ventral part (Vp) of both spinal cord regions. In lumbar spinal cord increases in free fatty acid levels, especially that of arachidonate, were observed in Fg, Dp and Vp a the end of the ischemic period. During recirculation all values were similar to nonischemic controls. In cervical spinal cord a slight increase in free fatty acid levels was found in Fg after four days of recirculation, and in Dp arachidonate and stearate levels were most markedly elevated after one day of recirculation. No changes at any interval were found in Vp of cervical spinal cord. The present results indicate that the experimental insult induced typical ischemic injury to spinal cord tissue demonstrated by fatty acid liberation from membrane lipids. This injury may affect neurotransmission and other processes and free fatty acids themselves impair tissue metabolism (inhibition of oxidative phosphorylation, edema precipitation, synthesis of eicosanoids) and thus restrict the possibilities to enhance recovery in the recirculation period.

Adenine nucleotide levels and regional distribution of ATP in rabbit spinal cord after ischemia and recirculation

Rabbit spinal cords were subjected to 10 to 40 minutes of ischemia with and without 4 days of recirculation and L-4 segment was analyzed for adenylates and ATP-induced bioluminiscence. ATP level and energy charge was progressively reduced by increasing durations of ischemia. Regional evaluation of ATP-induced bioluminiscence after 10 and 20 minutes of ischemia revealed ATP depletion mainly in the gray matter of spinal cord. Forty minutes of ischemia resulted in complete reduction of ATP bioluminiscence in both gray and white matter. Within 4 days of recirculation following all periods of ischemia studied, only partial metabolic recovery occurred. Restitution of ATP-induced bioluminiscence was regionally heterogeneous, reduced predominantly in the anterior horns of gray matter.

The arrangement of endoplasmic reticulum and proteosynthesis in spinal ganglia neurons of dog after ischemia

The authors studied ultrastructural and biochemical changes in spinal ganglia neurons of dogs after ischemia. Partial spinal cord ischemia was induced by occlusion of the abdominal aorta just below the renal arteries and the arterial blood pressure was registered above and below the occlusion. - In the course of 2-4 hours' ischemia the amount of free ribosomes increased. In some cases the formation of filamentous material or tubular structures inside the cisterns of endoplasmic reticulum was apparent. The proteosynthesis declined. Incorporation of 14C - leucine into the spinal ganglion was 50% as compared to the control animals. The morphological and biochemical changes were more pronounced after 4 h ischemia.

Molecular mechanisms of ischemic damage of spinal cord

Incomplete ischemia of the spinal cord of rabbits was produced by a 40-min occlusion of the abdominal aorta followed by 1 and 4 days of recirculation. Regional evaluation of ATP-induced bioluminescence after 20 min of ischemia revealed ATP depletion mainly in the gray matter of the spinal cord. After 40 min of ischemia, ATP-induced bioluminescence was too faint to expose the photographic film. Within 1 and 4 days of recovery following 40 min of ischemia, restitution of ATP was regionally heterogeneous, reduced predominantly in the anterior horns of gray matter. Polysome profiles remained unaltered during the ischemic period, but a marked disaggregation of polyribosomes occurred after 10 min of recirculation. Protein synthesis in a cell-free system was inhibited by the addition of a postischemic cytosol or protein fraction isolated from cytosols on a DEAE column. The inhibition can be overcome by the addition of each initiation factor 2 (eIF-2), GTP and GDP exchange factor (GEF). Occlusion of abdominal aorta for 40 min results in decrease in monoamine oxidase accumulation in both proximal and distal ligature placed on sciatic nerve. Within 4 days of recovery the transport was progressively depressed to 22 and 21% in the proximal and distal direction, respectively.

Influence of blood sera from dogs subjected to ischemia and recirculation on incorporation of 14C-amino acids in vitro

Incomplete ischemia of the spinal cord was produced in dogs by 40 min occlusion of the abdominal aorta that was followed by 5-40 min of recirculation. Amino acid incorporation into ribosomes in vitro in the presence of venous blood sera was estimated. The most significant reduction in incorporation was produced by sera of the dogs following a short recirculation period (5-10 min). No significant changes were observed at the end of the ischemic period nor at longer periods of recirculation. The decrease in incorporation might be the consequence of inactivation or absence of a substance stimulating polypeptide synthesis in vitro, normally present in blood sera of intact dogs, that temporarily loses its activity during recirculation.

Rapid determination of adenine nucleotides in brain tissue by ion-paired reversed-phase column liquid chromatography under isocratic conditions

A rapid method for analysis of adenine nucleotides (AMP, ADP and ATP) in nervous tissue based on ion-paired reversed-phase column liquid chromatography under isocratic conditions is described. An optimal composition of elution buffer was 25 mM potassium phosphate and 4% triethylamine adjusted to pH 6.5 with phosphoric acid. Typical separation time did not exceed 10 min with a 10-cm long compact glass cartridge packed with 5-microns silica C18. The method was employed to determine ATP, ADP and AMP concentrations in rat brain extracts and values thus obtained were compared with those published elsewhere.

Free amino acids in the spinal cord, ganglia and ischiadic nerve of the dog after ligature of the abdominal aorta

The effect of occlusion of the abdominal aorta for 10, 20 and 40 minutes on the concentration of aspartic and glutamic acids, glutamine, glycine, alanine and gamma-amino butyric acid in the anterior and posterior horns of the lumbosacral spinal cord was studied in the dog, further, concentration of amino acids (except GABA) in lumbosacral spinal ganglia and in the ischiadic nerve following 40 minutes of occlusion. The changes were most marked after 40 minutes of occlusion with a rise in concentration of alanine, glutamine and glutamic acid in the dorsal part of grey matter. Striking was also the simultaneous elevated concentration of Glu and Gln in spinal ganglia. The significance of these changes is discussed from the aspect of metabolism and function of nerve cells. Under physiological conditions the free amino acid pool in the central nervous system remains essentially constant. Under pathological conditions, however, like ischemic-hypoxic states, various changes occur.

The dynamics of choline acetyltransferase and acetylcholinesterase changes in dog spinal cord during ischemia

Activities of choline acetyltransferase (CAT) and acetylcholinesterase (AChE) were measured in several regions of the spinal cord, spinal ganglia and the sciatic nerve following ligation of the abdominal aorta just below the renal arteries for 20; 40; 80 and 120 min. Aortic ligation for 40 min produced a significant increase in the activities of both enzymes in the lumbar spinal cord. After ligation lasting 80 min the activity of CAT dropped under the control level and that of AChE remained elevated and returned to the control level in animals sacrificed 120 after the ligation. Similar but smaller AChE elevation was also found in the lower thoracic and the sacral spinal cord, respectively. In ischemic spinal ganglia and the sciatic nerve a decrease in AChE activity was found.

Effect of ischemia on the activity of DNA-dependent RNA polymerase and DNA polymerase

Ischemia, anoxia, and hypoxia of the brain have been shown to inhibit protein synthesis in the central nervous system. To obtain data on the changes in DNA-dependent RNA and DNA polymerase as they pertain specifically to neurons and glia, nuclear enriched neuronal and glial fractions were prepared, by sucrose-gradient centrifugation, from spinal cords of adult dogs that had been subjected to prolonged ischemia. The isolated fractions were assayed for enzyme activity by a radiochemical technique. RNA polymerase was affected more than DNA polymerase, activity being reduced considerably in both neurons and glia. Possible causes of the difference in sensitivity to ischemia are discussed.