A reversible type of neuronal injury following ischemia in the gerbil hippocampus

Brain damage in a new hemorrhagic shock model in the rat using long-term recovery

A new shock model in the rat using hemorrhagic hypotension for production of brain damage is described. Hemorrhagic shock was induced by lowering arterial blood pressure with bleeding. The MABP was maintained at approximately 25 mm Hg, accompanied by isoelectric EEG, and then shed blood was retransfused. At 1 week of recovery, morphological and 45Ca autoradiographic changes were examined. No brain damage was observed in rats after 1 min of isoelectric EEG. Mild neuronal damage in the hippocampal CA1 subfield was seen in some animals after 2 min of isoelectric EEG. Severe and consistent neuronal loss in the hippocampal CA1 subfield was recognized after 3 min of isoelectric EEG. Additional damage was also seen in the dentate hilus and the thalamus in some animals. This model can be used to study the pathophysiology of postshock brain damage and to assess new therapies following shock.

Vinconate prevents ischemic neuronal damage in the rat hippocampus

The neuroprotective effect of vinconate, a novel vinca alkaloid derivative, was examined in a rat model of forebrain ischemia induced by 4-vessel occlusion. Hippocampal cell loss was quantified histologically 3 days after 10 or 15 min of ischemia. Intraperitoneal application of vinconate (25 and 50 mg/kg) 10 min before and immediately after 10 min of ischemia significantly reduced the neuronal cell loss in the CA1 sector of the hippocampus. Protective effect of vinconate against 15 min of ischemia was reduced, but there was still significant protection at the higher dose. Autoradiography using 14C-vinconate showed that the drug easily penetrates the blood-brain barrier and distributes in the hippocampus. The result suggests that vinconate prevents ischemic neuronal damage by direct action on the hippocampal CA1 neurons.

Regional impairment of protein synthesis following brief cerebral ischemia in the gerbil

Regional cerebral protein synthesis following brief ischemia was investigated in the Mongolian gerbil, utilizing L-[methyl-14C]methionine autoradiography. Transient ischemia was induced for 1, 2 or 3 min. At various recirculation periods up to 48 h, animals received a single dose of L-[methyl-14C]methionine and then were terminated 35 min later. Sham-operated animals showed a normal pattern of amino acid incorporation into the proteins of the brain. Following 1-min ischemia, the pattern of protein synthesis was similar to that in the sham-operated gerbils. Ischemia for 2 min, however, caused marked inhibition of protein synthesis in the neocortex, striatum, hippocampal CA1 sector and the thalamus at 1 h of recirculation. Extensive recovery of protein synthesis was found in the neocortex, the striatum, the hippocampal CA1 sector and the thalamus at 5-24 h of recirculation, but, a slight inhibition was detectable in the hippocampal CA1 sector in one of six animals. This inhibition had fully recovered at 48 h of recirculation. Following 3-min ischemia, severe impairment of protein synthesis was found in the neocortex, striatum, the whole hippocampus and the thalamus. After 5-24 h of recirculation, the protein synthesis in these regions had gradually recovered, except that complete lack of amino acid incorporation was seen in the hippocampal CA1 subfield. This impairment of protein synthesis in the hippocampal CA1 sector was not recovered at 48 h of recirculation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a brief hypoxic/hypotensive episode on the in vivo release of cerebral cortical gamma-aminobutyric acid and glycine

gamma-Aminobutyric acid (GABA) and glycine levels in rat cerebral cortical superfusates rose during a 10-min period to reach stable concentrations of approximately 0.55 microM and approximately 12.3 microM, respectively. In cerebrospinal fluid withdrawn from the fourth ventricle, the GABA concentration was 0.1 microM, and that of glycine, 10.55 microM. GABA, and to a lesser extent glycine, concentrations increased in the cortical superfusates during and immediately following exposure of the rats to a 5-min period of 5% oxygen in nitrogen inhalation.

Prevention of ischemic neuronal damage by alpha 1-adrenoceptor agonist (methoxamine)

The effect of methoxamine, an alpha 1-adrenoceptor agonist, on ischemic neuronal damage was studied in the gerbil. The animals were subjected to 5 min of ischemia by bilateral common carotid arteries occlusion. Morphological changes and calcium accumulation were evaluated in the CA1 sector of the hippocampus after 7 days of survival. The degree of ischemic neuronal damage and calcium accumulation in the methoxamine-treated groups were significantly attenuated compared with the saline-treated ischemic group. The results suggest that alpha 1-adrenoceptor stimulation prevents ischemic neuronal damage.

Effects of a new calcium channel blocker, KB-2796, on protein synthesis of the CA1 pyramidal cell and delayed neuronal death following transient forebrain ischemia

The effects of a new calcium channel blocker, 1-[bis(4-fluorophenyl)methyl]-4-(2,3,4-trimethoxybenzyl)-piperazine dihydrochloride (KB-2796), on delayed neuronal death (DND) in the hippocampus were examined in gerbils in comparison with those of pentobarbital and flunarizine. The neuronal density in the hippocampal CA1 subfield was counted on the seventh day of recirculation following 5 min of bilateral carotid occlusion, and protein biosynthesis in the brain was also determined at 1, 2, 4, 24, and 72 h following occlusion. The drugs were intraperitoneally administered after recirculation. KB-2796 (10 mg/kg) significantly prevented DND in the CA1 subfield. Pentobarbital (40 mg/kg), but not flunarizine (3 and 10 mg/kg), inhibited DND. Protein synthetic activity in the CA1 subfield was reduced by ischemia and the reduction was not restored even at 72 h after recirculation. KB-2796 did not ameliorate the reduction of protein synthesis in the CA1 subfield by 24 h after recirculation, but in one of three animals restoration of protein synthesis was observed at 72 h of recirculation. Pentobarbital also restored the reduced protein synthesis in two of three animals at 72 h. These results suggest that calcium influx into neurons participates in the pathogenesis of DND, and also that KB-2796 might prevent both morphological and functional cell damage in CA1 neurons induced by transient ischemia.

A method for examining turnover and synthesis of palmitate-containing brain lipids in vivo

1. A theoretical three compartment model is presented which gives the rate of incorporation of plasma palmitate into brain, Jpalm, in terms of turnover and synthesis of palmitate-containing lipids, de novo synthesis of palmitate from acetate, and recycling of palmitate within lipids. 2. Jpalm equals 4 h brain radioactivity following intravenous injection of [U-14C]-palmitate (determined with quantitative autoradiography), divided by integrated plasma specific activity of palmitate. Jpalm follows the time course of brain lipid synthesis during development of the rat, but is age-invariant in the adult. 3. At 1-7 days after 5 min of bilateral carotid occlusion in the awake gerbil, intravascular [14C]-palmitate incorporation is reduced in the CA1 pyramidal layer of the hippocampus, consistent with delayed neuronal death, but is elevated in the CA3 and CA4 pyramidal layers and dentate gyrus, suggesting synthesis of new membrane during recovery from the ischaemic insult. 4. Several weeks after unilateral destruction of the cochlea in 11 day old rats, incorporation of [14C]-palmitate from plasma into appropriate central auditory regions is reduced, corresponding to reduced cell size and altered morphology. 5. [14C]-palmitate incorporation into the left hypoglossal nucleus is increased during and following axonal regeneration (up to 23% compared with control side) following transection of the left hypoglossal nerve in Fischer-344 rats, whereas incorporation is decreased 6-7% when regeneration is prevented. Time courses of incorporation in both cases correspond to histological changes. 6. The results show that the palmitate method can be used to examine regional turnover and synthesis of brain lipids following injury, sensory deprivation, development, regeneration and ageing.

Prevention of delayed neuronal death in gerbil hippocampus by a novel vinca alkaloid derivative (vinconate)

We investigated the effect of vinconate, a novel vinca alkaloid derivative, on delayed neuronal death using Mongolian gerbils. The animals were allowed to survive for 7 d after 3 or 5 min of forebrain ischemia induced by bilateral occlusion of the common carotid arteries. Morphological changes and calcium (45Ca) accumulation were evaluated in the CA1 sector of the hippocampus after ischemia. Vinconate (50, 100, and 300 mg/kg) showed protective effects against neuronal death in a dose-dependent manner when administered intraperitoneally (ip) 10 min before 5 min of ischemia. However, the administration of vinconate (100 and 300 mg/kg, ip) immediately after 5 min of ischemia showed no therapeutic effect, whereas a marked therapeutic effect of vinconate (50 and 100 mg/kg, ip) was observed when administered immediately after 3 min of ischemia. An anesthetic dose of pentobarbital (40 mg/kg, ip) also produced significant protection against neuronal death. Furthermore, a 45Ca autoradiographic study indicated that a marked calcium accumulation was found in the Ca1 sector at 7 d after 5 min of ischemia, which was consistent with the extent of histological neuronal damage. When vinconate (100 and 300 mg/kg, ip) was administered 10 min before 5 min of ischemia, the abnormal calcium accumulation was not detected in the CA1 sector. These data indicate that suppression of abnormal neuronal activity may be owing to the antagonistic action of vinconate on calcium accumulation.

Neuronal damage in the rat hippocampus in a new model of repeated reversible transient cerebral ischemia

The influence of the interval of the repeated reversible transient cerebral ischemia on the neuronal damage in the hippocampal CA1 sector was investigated in the rats using a 4-vessel occlusion (4-VO) model. A single 3-min 4-VO did not produce any significant neuronal damage in the hippocampal CA1 sector, whereas the rats subjected to three 3-min 4-VO at 1-h intervals revealed a very severe neuronal damage which was much more severe than that in the rats subjected to a single 9-min 4-VO. In contrast, the rats subjected to three 3-min 4-VO at 6-h intervals revealed only a mild neuronal damage. The degree of the neuronal damage in the rats subjected to three 3-min 4-VO at 5-min intervals was similar to that in the rats subjected to a single 9-min 4-VO. The present study indicates that even such a brief, non-lethal ischemia as 3-min 4-VO can produce a severe neuronal damage if it occurs repeatedly at 1-h intervals.

Phenytoin protects against ischemia-produced neuronal cell death

Brief bilateral carotid occlusion in the gerbil produces forebrain ischemia that results in almost complete neuronal destruction in the CA1 sector of the hippocampus. Treatment with phenytoin (200 mg/kg) blocked the ischemia-induced neuronal death. The average density of CA1 pyramidal neurons (cells/mm CA1) was 253.6 +/- 4.4 in the sham surgery group, 12.3 +/- 3.4 in the ischemia group, and 119.5 +/- 16.6 in the group treated with phenytoin before ischemia. Thus, phenytoin reduced ischemia-produced neuronal loss in hippocampal CA1 by 44.4% (P less than 0.001). The plasma levels of phenytoin that produced this effect ranged from 28.1 to 45.0 mg per liter, with a mean phenytoin level of 34.7 +/- 1.7 mg/l (n = 10). The results suggest that phenytoin may be a clinically useful cerebroprotective agent.

A role for gamma-aminobutyric acid (GABA) in the evolution of delayed neuronal death following ischemia

A series of putative neuroprotective agents was tested to determine their efficacy in preventing the loss of the CA 1 neurons of the hippocampus at 4 days following 5 min of bilateral ischemia in the gerbil. Agents associated with the GABAergic system were determined to be the most effective, but only when given prior to the ischemic episode, suggesting that there was a gamma-aminobutyric acid (GABA)-related event during ischemia which triggers the delayed neuronal death of these cells. In this report, the unidirectional release of GABA and glutamate from gerbil hippocampal slices was determined under conditions mimicking anoxia and/or ischemia. Pentobarbital, the most effective of the GABAergic agents, had little or no effect on the time-dependent release of glutamate. In contrast, pentobarbital reduced in release of GABA in both anoxia and ischemia, but only after 25 to 30 min of incubation.

Effect of dihydroergotoxine mesylate (Hydergine) on delayed neuronal death in the gerbil hippocampus

The CA 1 neurons in the gerbil hippocampus exhibiting necrosis with delayed onset following 5 min ischemia were reduced markedly by the systemic administration of dihydroergotoxine mesylate (Hydergine; HYG). Immediately after 5 min of forebrain ischemia, the animals were injected intraperitoneally with HYG. Seven days after ischemia, perfusion-fixed brains were processed by conventional histology. The number of neurons per millimeter in the CA 1 pyramidal cell layer were calculated and they were labelled neuronal density. In the control group, the neuronal density was 66.03 +/- 7.37 (mean +/- SEM), in the vehicle group, it was 11.25 +/- 4.93. The neuronal density in the HYG group was 69.19 +/- 6.49. The difference in the neuronal density between the HYG group and the control group was not statistically significant. These data indicate that HYG protects on the CA 1 neurons, and this suggest that the suppression of adrenoceptors by this drugs may be the main mechanism of action. This morphologic outcome may explain the functional amelioration of mental impairment by HYG.

Metabolic alterations in fiber layers of the CA 1 region of the gerbil hippocampus following short-term ischemia: high-energy phosphates, glucose-related metabolites, and amino acids

The CA 1 neurons of the gerbil hippocampus die at 4 days following 5 min of bilateral ischemia. The fiber and somal layers of the CA 1 region of the gerbil hippocampus were analyzed for high-energy phosphates, glucose-related metabolites, and amino acids from 0.75 hr to 4 days of postischemia. The results were compared to those from two layers of the CA 3 region and the cerebral cortex. The metabolite changes in the fiber layers of the CA 1 region were qualitatively similar to those in the somal layer. The energy status of the tissues taken from the CA 1 region was never compromised for up to 2 days of recirculation, after which the ATP and P-creatine in the somal layer decreased to 43 and 56% of the control, respectively, whereas the average decreases in the CA 1 fiber layers were only 71 and 88% of the control, respectively. Thus, the high-energy phosphate response of the neuronal elements in the fiber layers was temporally similar to that found in the somal layer of the CA 1 region. The biphasic increases in glycogen, glucose, glucose-6-phosphate, and high-energy phosphates to values greater than the control indicated that the metabolic restoration following transient ischemia is a dynamic process which persists for up to 2 days of recirculation, even in resistant tissues. A similar pattern of delayed changes was observed in glutamate, gamma-aminobutyric acid (GABA), and glutamine, but the change in each amino acid appeared to be independent of the others despite their close metabolic relationship. The delayed decreases in GABA would favor a loss of inhibition to the CA 1 neurons and may be related to the phenomenon of delayed neuronal death.

MK-801 is neuroprotective in gerbils when administered during the post-ischaemic period

The neuroprotective effects of the non-competitive N-methyl-D-aspartate receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) have been evaluated in the gerbil hippocampus when the drug was administered i.p. at various times during and after a 5 min period of transient forebrain ischaemia, induced by bilateral common carotid artery occlusion. A single dose of 1, 3 or 10 mg/kg of MK-801 gave significant protection of hippocampal CA1 and CA2 pyramidal neurons when administered during the occlusion and up to 24 h following the period of ischaemia. A dose of 0.3 mg/kg was effective when administered during the occlusion period but gave no protection at 30 min or 2 h post-ischaemia. Experiments in which MK-801 was administered in repeated doses indicated that significant protection was achieved with 1 mg/kg of MK-801 repeated post-ischaemically and with 1 mg/kg MK-801 supplemented with repeated doses of 0.3 mg/kg of MK-801. However 0.3 mg/kg of MK-801 followed by repeated doses of 0.03 mg/kg administered post-ischaemically was not neuroprotective. These results indicate that MK-801 can protect hippocampal neurons from ischaemia-induced neuronal degeneration when it is administered up to 24 h after the insult. These data provide further evidence that therapeutic intervention in the post-ischaemic period can successfully prevent neurodegenerative events, and that the delayed degeneration of hippocampal neurons following an ischaemic insult occurs by an N-methyl-D-aspartate receptor-mediated process.

Increases in striatal and hippocampal impedance and extracellular levels of amino acids by cardiac arrest in freely moving rats

The time course of changes in the tissue impedance and the levels of extracellular transmitter and non-transmitter amino acids was studied in the striatum and hippocampus of the unanesthetized rat after cardiac arrest. Electrodes were implanted for the continuous measurement of tissue impedance so that a measure of the volume of extracellular space was provided. Alternatively, bilateral dialysis probes were used for monitoring levels of extracellular amino acids in subsequent 30-s samples using an automated precolumn derivatization technique for reversed-phase HPLC analysis and fluorimetric detection. The impedance started to rise approximately 1.2 min following cardiac arrest, increased rapidly during the first 5 min, and increased almost linearly thereafter. After 15 min, a decrease of approximately 50% in the extracellular space was calculated. The impedance rose more steeply in the striatum than in the hippocampus. The extracellular levels of taurine, which increased greater than 300% within 5 min after cardiac arrest, most closely resembled the time course of the change in impedance. Glutamate and aspartate levels did not increase until 5 min after circulatory arrest, and at 15 min they had risen to a level of 465 and 265% for the striatum and 298 and 140% for the hippocampus of the resting release, respectively. The release of gamma-aminobutyric acid (GABA) was multiphasic and did not resemble that of any of the other--putative--transmitter amino acids. Fifteen minutes after cardiac arrest, the levels of GABA were 617 and 774% of the resting release in the striatum and hippocampus, respectively. Glycine and alanine efflux substantially increased (232 and 151% in striatum and 141 and 154% in hippocampus, respectively) 15 min postmortem, whereas the glutamine level was slightly increased and levels of asparagine, histidine, threonine, ethanolamine, serine, arginine, and tyrosine were inconsistently higher in the two brain regions. At this time, the extracellular levels of glutamate, GABA, and aspartate were only slightly lower, as expected from the tissue levels and from levels of the other amino acids, an observation indicating that all the amino acids may diffuse through postmortem brain tissue to a nearly similar extent.(ABSTRACT TRUNCATED AT 400 WORDS)

S-adenosyl-L-methionine protects the hippocampal CA1 neurons from the ischemic neuronal death in rat

We investigated the effect of S-adenosyl-L-methionine (SAMe) on the prevention of the delayed neuronal death in rats subjected to transient and brief forebrain ischemia. As the results, SAMe dose-dependently protected the hippocampal CA1 neurons from degeneration and necrosis, whose effect was suppressed by simultaneous administration of S-adenosyl-L-homocysteine, a potent inhibitor in transmethylation. No protective effect was observed in CDP-choline, phosphatidylcholine and L-methionine. Therefore, it is necessary for the prevention of the delayed neuronal death to enhance cerebral SAMe level and to activate transmethylation using SAMe as a methyl donor in postischemic brain.

Involvement of platelet-activating factor (PAF) in cerebral post-ischemic phase in Mongolian gerbils

Platelet-activating factor (PAF) is a potent mediator of anaphylaxis and shock. In addition, evidence for PAF participation in gastric, intestinal and heart post-ischemic phase has been recently demonstrated. Ginkgo biloba extracts improve cerebral metabolism and protect brain against hypoxic damage in various models of cerebral ischemia. Potent and specific antagonists of PAF have been found in Ginkgo biloba and termed Ginkgolides: BN 52020, BN 52021, BN 52022, BN 52024. We therefore undertook the investigation of the role of Ginkgolides in cerebral ischemia obtained by bilateral ligature of the common carotid for 10 min and 6 h of recirculation in male Mongolian adult gerbils. Given preventively (one week treatment 10 mg/kg/day orally) or at the time of clamping, BN 52021 and related Ginkgolides dose-dependently antagonize morbidity assessed by the stroke-index. Similarly the mitochondrial respiration evaluated by the respiratory control ratio is significantly improved. In both determinations, the range of activity: BN 52021 greater than, BN 52020 greater than BN 52022 greater than BN 52024 shows that the effect of Ginkgolides in cerebral ischemia are correlated with their PAF antagonistic properties. Given curatively, 1 h after declamping, BN 52021 is able to reverse the cerebral impairment trend. Kadsurenone and brotizolam, two other chemically unrelated PAF antagonists led to similar recovery. Therefore PAF appears to play an important role in the post-ischemic phase after bilateral carotid ligation in Mongolian gerbils.