Selective neuronal death after transient forebrain ischemia in the Mongolian gerbil: a silver impregnation study

Short-term and long-term changes in the postischemic hippocampus

We have demonstrated a far more widespread and selective ischemic cell damage than previously thought. In area CA3, a distinct subpopulation of interneurons, characterized by their spiny dendrites and their calretinin content, was selectively vulnerable in the absence of any other CA3 involvement. In the dentate hilus, four different types of spiny cells were consistently damaged. The common denominator in these two cell groups is the presence of spines on their dendrites and hence the greater density of mossy fiber innervation they receive. A common mechanism of cell death may be the presence of non-NMDA receptor subtypes that are highly permeable to calcium. We speculate that they may constitute an important control mechanism in the CA3 region and the hilus, and impairment of this mechanism may be causal to delayed neuronal death in CA1. We have also shown that neuronal degeneration does not end after delayed cell death of CA1 pyramidal cells. Our results suggest that there is progressive degeneration throughout the life of the animal and degeneration of additional cell populations (e.g. CA1 interneurons and CA3 pyramidal cells) may also occur secondary to the insult.

Use of an amino-cupric-silver technique for the detection of early and semiacute neuronal degeneration caused by neurotoxicants, hypoxia, and physical trauma

A new amino-cupric silver protocol is described for detection of neuronal degeneration. We describe its selectivity in visualizing both early and semiacute degeneration after intracerebral or systemic administration of a variety of neurotoxicants in rats, and after transient ischemic episodes in gerbils. As early as 5 min after physical trauma, or 15 min following either intrastriatal injections of glutamate analogs or exposure to ischemic episodes, neuronal silver staining was evident at primary sites of trauma (i.g. injection sites) and at hodologically related secondary sites. With intoxication by peripheral injections of trimethyltin (IP) or intracerebral injections of Doxorubicin, reproducible patterns of degeneration are demonstrable after 24 h or after 9-13 days, respectively. The amino-cupric silver method permits simultaneous detection of all neuronal compartments against a clear background. Degeneration in the neuronal cell bodies, dendrites, axons and terminals, as well as the recruitment of new structures in a progressive pathologic process, could be accurately followed. The inclusion of new reagents increased the sensitivity vis-à-vis previous versions of the cupric-silver method. The advantages and disadvantages of the current method in comparison with other means of neurotoxic assessment are discussed in detail, with special emphasis on its unique ability to discriminate irreversible degenerative phenomena and degeneration of axonal components in cases where the cell body remains apparently intact. The amino-cupric silver method is an especially useful tool for surveying neuronal damage in basic neuroscience investigations and in neuropathologic and neurotoxic assessment.

Neuronal protection with superoxide dismutase in repetitive forebrain ischemia in gerbils

The underlying mechanism for severe damage with repetitive ischemia is not fully understood. Because of prolonged periods of reperfusions between the brief insults, we speculated that the severe damage may be secondary to excessive generation of oxygen free radicals. In this study we tested the efficacy of peg-superoxide dismutase (SOD) in a model of repeated ischemia in gerbils. Superoxide dismutase (SOD) or vehicle (saline) was delivered through osmotic pumps into the lateral ventricles continuously from the onset of the insult until the gerbils were sacrificed 6 days later. Three doses of SOD were used in the experiments (110, 150, and 190 units per microliter). Damage was assessed using a 0-4 point scoring system and statistical comparisons were done using the Mann-Whitney U-test. There was significant protection in the hippocampus (p < 0.05), striatum (p < 0.001), and substantia nigra reticulata (p < 0.05) in the lowest dose SOD-treated group (110 units per microliter). Animals treated with 150 units showed lesser (but significant) protection in the thalamus, medial geniculate nucleus, and striatum. In the animals treated with the higher dose of SOD (190 units per microliter), the extent of damage was no different than vehicle-treated controls in the cortex, striatum, and hippocampus. Compared to controls, neuronal damage was, however, significantly more severe in the medial geniculate nucleus and the thalamus in the high-dose SOD-treated animals (p < 0.05). Our experiments suggest that the SOD may have a small therapeutic window. Higher doses may either have no neuroprotective effects or may be harmful.

Neuroprotective activity of HU-211, a novel NMDA antagonist, in global ischemia in gerbils

HU-211, a nonpsychotropic cannabinoid and a noncompetitive NMDA antagonist, was tested in a global ischemia model in the Mongolian gerbil. Male Mongolian gerbils underwent a 10-min bilateral common carotid artery occlusion. HU-211, administered i.v. at 4 mg/kg, 30 min postischemia, induced statistically significant neuroprotection of the CA1 subfield of the hippocampus. A dose-response study demonstrated an inverted U curve in which the 4 mg/kg dose induced the best neuroprotection in the CA1 subfield of the hippocampus (p < 0.05 ANOVA followed by Duncan's post-hoc test). The therapeutic window was then investigated, and in another study, HU-211 4 mg/kg were administered i.v. at 30, 60, 120, and 180 min postinsult. A statistically significant neuroprotection was detected at 30 and 60 min administration postinsult.

Effect of graded hypothermia (27 degrees to 34 degrees C) on behavioral function, histopathology, and spinal blood flow after spinal ischemia in rat

BACKGROUND AND PURPOSE

We used a rat model of reversible spinal ischemia to assess the effect of spinal cord temperature on the development of neurological and histopathologic changes after 20 minutes of reversible aortic occlusion. Spinal cord blood flow and CO2 reactivity was tested by using laser Doppler before and 60 minutes after ischemia.

METHODS

In halothane (1%)-anesthetized rats, the spinal cord temperature as assessed by using thermocouple in the paraspinal muscles was lowered to 34 degrees, 31 degrees, or 27 degrees C. After ischemia, spinal cord temperature was raised to 37 degrees C for the next 30 minutes. Animals were maintained in this normothermic condition for 8 hours, after which motor and sensory function were assessed. All animals were then anesthetized and perfused with 10% formalin for light microscopic analysis of spinal cords.

RESULTS

In normothermic animals, 20 minutes of ischemia resulted in a loss of CO2 reactivity and hind limb paraplegia with an attendant allodynia that persisted for the 8 hours of reperfusion. Even mild (34 degrees C) hypothermia resulted in significant improvement of neurological function compared with the normothermic group. In paraplegic animals, lumbosacral interneuronal pools localized primarily in laminae III through VII displayed heavy argyrophilic neurons and areas of localized necrosis. In moderate and deep hypothermic animals preservation of CO2 responsivity and complete recovery of neurological function were seen with no detectable histopathologic changes.

CONCLUSIONS

These results show that a slight decrease in spinal cord temperature in the peri-ischemic period provides significant protection as measured by histopathology and neurological function.

Reduced mortality and brain damage after locomotor activity in gerbil forebrain ischemia

BACKGROUND AND PURPOSE

Preischemic spontaneous locomotor activity was distinguished in this laboratory as a factor influencing outcome after 15 and 20 minutes of forebrain ischemia in gerbils. Histological investigations were carried out to analyze potential relations between postischemic survival and a reduction of cerebral damage by spontaneous locomotor activity.

METHODS

Male Mongolian gerbils were divided into two groups, one with access to running wheels ("runners") and one kept in conventional cages ("nonrunners") for 2 weeks preceding forebrain ischemia of 15 or 20 minutes. A total of 99 gerbils were divided in subgroups and were allowed to recover for 2 weeks for assessment of survival. Other subgroups (n = 7 to 9) were killed at day 4 for quantitative histology of selectively vulnerable areas such as hippocampus, cortex, striatum, and thalamus.

RESULTS

Two weeks after 15-minute ischemia, 44% of non-runners had survived compared with 90% of runners (P < .01). With 20-minute ischemia all runners survived compared with 21% of nonrunners. Quantitative histology (15-minute ischemia) revealed selective nerve cell injury in various cerebral regions in both groups. In runners, however, with the exception of the CA1 sector, damage was attenuated in cortex, striatum, and hippocampus. Furthermore, the extent of thalamic infarction was reduced (P < .05).

CONCLUSIONS

Locomotor activity before global cerebral ischemia is highly efficient in protecting the brain as demonstrated by enhanced survival and a reduction of tissue damage in Mongolian gerbils. The mechanisms underlying this protection are currently unclear. However, further understanding of this intriguing phenomenon should enhance the understanding of ischemia pathophysiology and lead to the development of new treatment strategies.

NG-Nitro-L-arginine protects against ischaemia-induced increases in nitric oxide and hippocampal neuro-degeneration in the gerbil

To assess the effects of the nitric oxide synthase inhibitor NG-Nitro-L-arginine on behavioural, biochemical and histological changes following global ischaemia, the Mongolian gerbil was used. Ischaemia was induced by bilateral carotid occlusion for 5 min. NG-Nitro-L-arginine was administered i.p. at either 1 or 10 mg/kg 30 min, 6, 24, and 48 h after surgery. 5 min bilateral carotid occluded animals were hyperactive 24, 48 and 72 h after surgery. NG-Nitro-L-arginine caused some attenuation in this hyperactivity. The activity of nitric oxide synthase was increased in the cerebellum, brain stem, striatum, cerebral cortex and hippocampus of 5 min bilateral carotid occluded animals. NG-Nitro-L-arginine reversed the increase in nitric oxide synthase activity in all brain regions. Extensive neuronal death was observed in the CA1 layer of the hippocampus in 5 min bilateral carotid occluded animals 96 h after surgery. NG-Nitro-L-arginine significantly protected against the neuronal death of cells in the CA1 layer.

Alterations in tau immunostaining in the rat hippocampus following transient cerebral ischemia

Previous studies in gerbils have shown that cytoskeletal disruption and a loss of the dendritic microtubule-associated protein, MAP2, may occur after short periods of transient global ischemia. tau, a predominantly axonal microtubule-associated protein, has not been examined following ischemia. We compared neuronal damage with alterations in MAP2, tau, and 72-kD heat shock protein (HSP72) immunostaining at various reperfusion times following 20 min of ischemia in the rat four-vessel occlusion model. tau accumulated in neuronal cell bodies throughout the hippocampal formation 30 min to 2 h after the ischemic insult. Perikaryal tau immunostaining was transient in most regions, but persisted in polymorphic hilar neurons. This was accompanied by a loss of immunostaining in the target of many hilar neurons, the inner molecular layer of the dentate gyrus. The same neuronal populations that exhibited increased tau immunostaining of perikarya later displayed an induction of HSP72 immunoreactivity. In contrast, loss of MAP2 immunostaining was not consistently observed before neuronal death and did not correspond to HSP72 induction. The altered tau immunostaining is not the direct result of excitotoxic insult, as intrahippocampal injection of kainic acid did not cause the somal accumulation of tau, but did cause disruption of MAP2 immunostaining. Taken together, the results suggest that the somal accumulation of tau is an early, sensitive, and selective marker of ischemic insult.

Transient spinal ischemia in rat: characterization of spinal cord blood flow, extracellular amino acid release, and concurrent histopathological damage

Extracellular concentrations of amino acids in halothane-anesthetized rats were measured using a microdialysis fiber inserted transversely through the dorsal spinal cord at the level of the lumbar enlargement in conjunction with HPLC and ultraviolet detection. After a 2-h washout and a 1-h control period, 20 min of reversible spinal cord ischemia was achieved by the inflation of a Fogarty F2 catheter passed through the femoral artery to the descending thoracic aorta. After 2 h of postischemic reperfusion, animals were transcardially perfused with saline followed by 10% formalin or 4% paraformaldehyde. The glutamate concentration in the dialysate was significantly elevated after 10 min of occlusion and returned to near-baseline during the first 30 min of reperfusion. Taurine was elevated significantly 0.5 h postocclusion and continued to increase throughout the 2 h of reperfusion. Glycine concentrations showed a tendency to be slightly above baseline during the reperfusion period. Glutamine concentrations modestly increased following 2 h of reperfusion. No significant changes in aspartate, asparagine, and serine were detected. In control animals no significant changes in any amino acids were detected. To assess the role of complete spinal ischemia on spinal glutamate release, studies were carried out using cardiac arrest. Twenty minutes after induction of cardiac arrest, the glutamate concentration was increased about 350-400%. In a separate group of animals, spinal cord blood flow (SCBF) and its response to decreased CO2 were measured using a laser probe implanted into the epidural space at the level of the L2 vertebral segment. SCBF decreased to 5-6% of the control during aortic occlusion. After reversible ischemia, marked hyperemia was seen for the first 15 min, followed by hypoperfusion at 60 min. Under control-preischemic conditions a decrease in arterial CO2 content caused a decrease in SCBF of about 25%. This autoregulatory response was almost completely absent when assessed 60 min after a 20-min interval of aortic occlusion. Histopathological analysis of spinal cord tissue from these animals demonstrated heavy neuronal argyrophilia affecting small and medium-sized neurons located predominantly in laminae III-V. These changes corresponded to signs of irreversible damage at the ultrastructural level. Occasionally, small areas of focal necrosis, located in the dorsolateral part of the dorsal horn and anterolateral part of the ventral horn, were found. The results are consistent with a role for glutamate in ischemically induced spinal cord damage and suggest that taurine elevation detected during the early reperfusion period may serve as an important indicator of irreversible spinal cord neuronal damage.

Superoxide dismutase, catalase, and U78517F attenuate neuronal damage in gerbils with repeated brief ischemic insults

Repeated ischemic insults at one hour intervals result in more severe neuronal damage than a single similar duration insult. The mechanism for the more severe damage with repetitive ischemia is not fully understood. We hypothesized that the prolonged reperfusion periods between the relatively short ischemic insults may result in a pronounced generation of oxygen free radicals (OFRs). In this study, we tested the protective effects of superoxide dismutase (SOD) and catalase (alone or in combination), and U78517F in a gerbil model of repetitive ischemia. Three episodes (two min each) of bilateral carotid occlusion were used at one hour intervals to produce repetitive ischemia. Superoxide dismutase and catalase were infused via osmotic pumps into the lateral ventricles. Two doses of U78517F were given three times per animal, one half hour prior to each occlusion. Neuronal damage was assessed 7 days later in several brain regions using the silver staining technique. The Mann-Whitney U test was used for statistical comparison. Superoxide dismutase showed significant protection in the hippocampus (CA4), striatum, thalamus and the medial geniculate nucleus (MGN). Catalase showed significant protection in the striatum, hippocampus, thalamus, and MGN and the substantia nigra reticulata. Combination of the two resulted in additional protection in the cerebral cortex. Compared to the controls, there was little protection in a dose of 3 mg/kg of U78517F. There was significant protection with a dose of 10 mg/kg in the hippocampus (CA4), striatum, thalamus, medial geniculate nucleus and the substantia nigra reticulata.(ABSTRACT TRUNCATED AT 250 WORDS)

Postischemic diazepam is neuroprotective in the gerbil hippocampus

In this study, we address the hypothesis that enhancement of gamma-aminobutyric acid (GABA) neurotransmission following an ischemic episode is neuroprotective in the hippocampus. Mongolian gerbils were subjected to transient forebrain ischemia for 5 min by occlusion of the carotid arteries and then administered diazepam (10 mg/kg i.p.) 30 min or 30 and 90 min following ischemia. Diazepam produced a significant decrease in both rectal and brain temperature (4-6 degrees C) in the sham and ischemic gerbils. 1 day following the onset of reperfusion, diazepam substantially reduced the hyperactivity normally induced by the ischemic episode. 7 days later, neuronal viability in the hippocampus was assessed. The single dose of diazepam completely protected the CA1 pyramidal cells of the hippocampus in 62% of the gerbils and the double dose of diazepam completely protected CA1 pyramidal neurons in 67% of the gerbils. There was a significant correlation between the degree of pyramidal cell degeneration in the CA1 area of the hippocampus measured 7 days following ischemia and the degree of hyperactivity measured 1 day following ischemia. Diazepam also prevented the loss of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) binding to GABA-gated chloride channels in the dendritic fields of the CA1 area of the hippocampus. Our findings support the hypothesis that enhancement of GABA neurotransmission following an ischemic event may offset neuronal excitability and prevent neuronal death in specific brain regions. We conclude that GABA-enhancing drugs, such as diazepam, are attractive candidates as neuroprotective agents following ischemic insults.

U-92032, a T-type Ca2+ channel blocker and antioxidant, reduces neuronal ischemic injuries

Several diphenylmethylpiperazine derivatives are potential therapeutic agents for prevention of ischemic injuries in the heart and brain, because of their ability to block Ca2+ currents and their antioxidant activity. In this study, the current lead compound, U-92032 ((7-((bis-4-fluorophenyl)methyl)-1-piperazinyl)-2-(2-hydroxyethylamin o)- 4-(1-methylethyl)-2,4,6-cycloheptatrien-1-one), has been compared with flunarizine and nifedipine (well-known T- and L-type Ca2+ channel antagonists, respectively) for their effects on Ca2+ channels in a mouse neuronal cell line, N1E-115 cells, and their ability to preserve the phenomenon of long-term potentiation and to improve neurological symptoms in gerbil ischemic models. U-92032, like flunarizine, blocked transient Ba2+ currents (IBa) through T-type Ca2+ channels with no effect on nifedipine-sensitive non-inactivating currents. Transient IBa was reduced by U-92032 at a constant rate, the magnitude of which depended on the drug concentration, probably because of a time-dependent accumulation of the lipophilic drug in the membrane phase. For instance, the drug at 6 microM reduced IBa by 21% per min and abolished it in less than 5 min, about 3 times faster than flunarizine at the same concentration. Otherwise, U-92032 behaved like flunarizine, showing a use-dependent block without noticeable effects on the current-voltage relationship for transient IBa. Oral administration of U-92032 (1 and 25 mg/kg) or flunarizine (25 mg/kg), but not nifedipine (50 mg/kg), to gerbils 1 h prior to bilateral carotid artery occlusion, preserved long-term potentiation in hippocampal CA1 neurons, which were largely abolished by ischemia without the drug treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient spinal ischemia in the rat: characterization of behavioral and histopathological consequences as a function of the duration of aortic occlusion

To characterize the behavioral and histopathological changes that occur in spinal cord after transient ischemia, reversible occlusion of the descending aorta was achieved in the halothane (1-1.5%)-anesthetized rat by the insertion and subsequent inflation of a 2F Fogarty catheter for 10, 15, 20, or 30 min. Neurological recovery was tested during 8 h of reperfusion. After reflow, animals undergoing 30 min of ischemia displayed an initial flaccidity at 1 h, spasticity at 4 h, and flaccidity at the end of 8 h. Following 20 min of ischemia the initial flaccidity was followed by hindlimb spasticity that persisted for 8 h. Shorter intervals of ischemia had minimal effects on motor function. After reflow, animals developed a prominent allodynea, the incidence of which was dependent on the duration of ischemia. A clear correlation of histopathological changes with the degree of neurological deficit was noted. In spastic animals, small and medium-sized interneurons localized in laminae III to VII were affected. Animals with flaccidity at 8 h additionally displayed a significant incidence of argyrophilic A motoneurons in the ventral horns. Corresponding to the frequent appearance of allodynea, these animals also showed a significant number of damaged neurons in lamina II.

Internucleosomal DNA fragmentation in gerbil hippocampus following forebrain ischemia

Internucleosomal DNA fragmentation, the characteristics feature of programmed cell death, was demonstrated in gerbil hippocampus following 10 min of forebrain ischemia. Quantitative analysis revealed the presence of DNA fragments as early as 12 h after ischemia, reaching a maximum at 48 h. Measurable DNA fragmentation was still present in 3/3 subjects 96 h after the ischemic insult. In situ staining of hippocampus demonstrated pronounced DNA fragmentation that was localized in the CA1 region. The localization of fragmented DNA to the CA1 is consistent with the vulnerability of this layer to ischemic insult, and indicates that DNA fragmentation may be associated with the delayed loss of CA1 neurons in this model of forebrain ischemia.

Differential effects of amphetamine and haloperidol on recovery after global forebrain ischemia

Gerbils subjected to sham surgery or to bilateral occlusion of the carotid arteries were given an injection, during the recovery period, of saline, d-amphetamine, or haloperidol. The animals were subsequently tested once daily for 50 days in an eight-arm radial maze. Global forebrain ischemia had no effect on learning to avoid unbaited arms (reference memory), but greatly increased the number of times animals reentered previously visited arms (working memory errors). Gerbils made ischemic and treated with amphetamine reduced working memory errors more rapidly than did saline-treated ischemic gerbils; conversely, animals made ischemic and treated with haloperidol made more working memory errors than the ischemic controls. Although all ischemic animals were hyperactive, the differential radial maze behaviors of the ischemic groups cannot be explained on the basis of increased activity.

Evidence of nuclear DNA fragmentation following hypoxia-ischemia in the infant rat brain, and transient forebrain ischemia in the adult gerbil

Wistar rats, eight days old, were subjected to permanent bilateral forebrain ischemia, followed by hypoxia for 15 minutes. A cerebral infarct, mainly involving the cerebral neocortex, hippocampus, amygdala, striatum and subcortical white matter was produced. Neurons and glia showing punctate chromatin condensation and karyorrhectic cells were observed 12 hours after hypoxia-ischemia. Their number increased during the first two days and recruitment of cells with degenerating nuclei occurred until day five. In situ labeling of nuclear DNA fragmentation stained many normal-appearing nuclei, as well as punctate chromatin condensations and nuclear fragments in karyorrhectic cells. Delayed neuronal death in the CA1 area of the hippocampus was observed after 20 minutes of transient forebrain ischemia in the adult gerbil. In situ labeling of nuclear DNA fragmentation demonstrated stained punctate chromatin condensation in a few degenerating cells at 48 hours post-ischemia. Substantial labeling of CA1 neurons occurred in the fourth day. Agarose gel electrophoresis of extracted brain DNA from ischemic infant rats and adult gerbils showed a ladder-type pattern which is typical of nuclear DNA fragmentation into oligonucleosomal fragments (internucleosomal cleavage). These findings suggest that endonuclease(s) activation may play a role in cell death induced by different forms of hypoxia-ischemia.

Mortality in gerbils with repetitive ischemia: CGSGS-19755/hypothermia therapy

Repetitive ischemia causes more severe damage than a single insult of comparable duration. Gerbils were followed for 1 month postrepetitive ischemia and 100% mortality was demonstrated in the unprotected ischemia group by 12 days postischemia. Significant protection against mortality due to repetitive ischemia was offered by both CGS-19755 and combination CGS-19755-hypothermia treatments. Current practices of sacrificing repetitive ischemia subjects shortly postischemia may lead to an underestimation of the effects of ischemia and/or an overestimation of the protective effects of experimental treatments.

Dose-related effects of cycloheximide on delayed neuronal death in the gerbil hippocampus after bilateral transitory forebrain ischemia

Degeneration of dendrites followed by punctate chromatin condensation in the CA1 area of the hippocampus is a characteristic of delayed neuronal death following bilateral forebrain ischemia. The effects of the protein synthesis inhibitor cycloheximide on delayed neuronal death following 20 min of bilateral forebrain ischemia were examined in the gerbil hippocampus at the 4th day of reperfusion. Low doses of cycloheximide beginning 10 min after ischemia (1.0 microgram/g body weight in saline followed by 1.0 microgram/g every 24 h) reduced the number of dying cells in the CA1 area, whereas high doses (2.0 micrograms/g, followed by 1.0 microgram/g every 12 h) increased the number of dying cells. No effects were seen when a single dose of cycloheximide was injected 1 h before ischemia. These results indicate that the effects of cycloheximide are dose-dependent, low doses reduce, high doses increase cell death. These findings also indirectly suggest that protein synthesis may play a role in the extent of delayed neuronal death. Some involved proteins could be heat shock proteins, which are induced after ischemia and had been correlated with increased resistance to injury. However, changes of heat shock immunoreactivity in the postischemic hippocampus were not seen in the present study following cycloheximide injection.

Fructose-1,6-bisphosphate fails to ameliorate delayed neuronal death in the CA1 area after transient forebrain ischaemia in gerbils

Fructose-1,6-bisphosphate has been shown to reduce ischaemic-induced brain damage in rabbits and gerbils. In view of these findings, we investigated the effects of fructose-1,6-bisphosphate on delayed neuronal death, following bilateral forebrain ischaemia, in the gerbil hippocampus at the fourth day of reperfusion. We subjected gerbils to bilateral forebrain ischaemia for 20 min. Fructose-1,6-bisphosphate was administered: intraperitoneally at a dose of 1 g/kg in saline in hr before the occlusion or at a dose of 1 g/kg 1 hr before the occlusion and every 24 hr for 3 days; or intraventricularly at a dose of 0.1 g/kg just after the carotid occlusion. No significant differences in the number of dying cells in the CA1 area were found between each group of treated animals when compared with controls. This study suggests that fructose-1,6-bisphosphate, administered according to these three different schedules, fails to ameliorate delayed neuronal death after 20 min of bilateral forebrain ischaemia in the CA1 area of the gerbil hippocampus.

The behavior of mossy cells of the rat dentate gyrus during theta oscillations in vivo

Intracellular current clamp recordings were obtained from mossy cells (n = 6, identified by intracellular injection of biocytin) of the dorsal dentate gyrus from rats under ketamine-xylazine anesthesia. During electroencephalographic theta rhythm (4-6 Hz), recorded with a macroelectrode placed in the contralateral dorsal hippocampus near the fissure, mossy cells displayed intracellular membrane potential oscillations at low frequencies (4-6 Hz) which appeared to be phase locked to the electroencephalographic theta rhythm. The frequency of the intracellular theta rhythm was independent of the membrane potential. However, the phase difference between the intracellular and the electroencephalographic theta rhythms as well as the amplitude of the intracellular theta oscillations were voltage-dependent. These findings are consistent with the hypothesis that rhythmic GABAA receptor-mediated inhibitory postsynaptic potentials contribute to the genesis of the intracellular theta rhythm. Indeed, mossy cells displayed an early, fast inhibitory postsynaptic potential in response to electrical stimulation of the entorhinal cortex, which most likely represents a GABAA receptor-mediated event, indicating that mossy cells possess functional GABAA receptors. At the resting membrane potential, mossy cells did not fire at each cycle of the electroencephalographic theta rhythm but fired only rarely (< 1 Hz). However, when they did fire they did so preferentially in phase with the peak positivity of the electroencephalographic theta rhythm. Reconstruction of two mossy cells with axonal projections to the inner molecular layer showed that the spatial extent of the influence such weakly discharging mossy cells may have on other dentate gyrus neurons during theta oscillations can be several millimeters in the septotemporal direction. In conclusion, these findings show that mossy cells of the rat hilus during ketamine-xylazine anesthesia participate in theta oscillations of the hippocampal formation, during which their low-frequency firing may contribute to the phase-locking of a large number of spatially distributed postsynaptic neurons with postsynaptic sites in the inner molecular layer of the dentate gyrus.

Four modified silver methods for thick sections of formaldehyde-fixed mammalian central nervous tissue: 'dark' neurons, perikarya of all neurons, microglial cells and capillaries

Four reliable silver methods for the visualization of acute or advanced phases of neuronal damage have been modified so that they can be performed with good results on materials freshly fixed with transcardial perfusion of buffered formaldehyde for other silver methods and immunocytochemical techniques. The four modified methods respectively stain: (1) the somata and dendrites of 'dark' (impaired) neurons, (2) the perikarya of all neurons, (3) microglial cells, and (4) capillaries. Without the present modifications the 'dark' neuron method is only effective with glutaraldehyde fixation while the other three methods predominantly stain myelin in freshly fixed mammalian nervous tissue.

CGS-19755 is neuroprotective during repetitive ischemia: this effect is significantly enhanced when combined with hypothermia

In small animals the damaging effects of repetitive ischemia are more severe than a single insult of similar duration. Prolonged release of glutamate may correlate with the degree of damage. We report the protective effects of CGS-19755 (an N-methyl-D-aspartate receptor blocker), hypothermia or CGS-19755 in combination with mild hypothermia, in a gerbil model of repetitive ischemia. We used 3 min of forebrain ischemia and repeated it for a total of three times as 1-h intervals. Damage was assessed seven days after the insult. In the group where only CGS-19755 was used, significant neuronal protection was evident in the hippocampus (CA1 and CA3), striatum, and medial geniculate nucleus. With hypothermia significantly less damage was seen in the cerebral cortex, hippocampus (CA1 and CA4), and substantia nigra reticulata. When CGS-19755 was combined with mild hypothermia the effects of repetitive ischemia were completely abolished in all but one gerbil. Compared to hypothermia alone, significant protection was seen in the cerebral cortex, hippocampus (sibiculum, CA1 and CA4), striatum, medial geniculate nucleus, thalamus, and substantia nigra reticulata. The use of N-methyl-D-aspartate receptor blockers may protect the brain in repetitive ischemia. Combination with hypothermia may further enhance this protection.

Early degeneration of calretinin-containing neurons in the rat hippocampus after ischemia

The mechanism of delayed death of pyramidal cells in the hippocampal CA1 region and the acute death of various types of hilar neurons after ischemia is still unknown. Excitotoxicity may play a role in ischemic cell death, a prerequisite of which is the development of increased excitability or an enhanced excitatory transmission in the selectively vulnerable subfields of the hippocampus. Such changes may take place upon the loss or malfunction of local inhibitory neurons in the early postischemic period. In the present study we examined the vulnerability of non-pyramidal neurons containing a recently discovered calcium binding protein, calretinin, in the rat hippocampus following 15 min ischemia induced by four-vessel occlusion. Immunostaining for calretinin enabled us to visualize a new type of spiny non-pyramidal cell in the hippocampus specifically associated with the mossy fiber system. This cell type is present exclusively in regions where mossy fiber terminals occur, i.e. in the hilus of the dentate gyrus and in stratum lucidum of the CA3 subfield. A selective loss of immunoreactivity in these neurons was already observed at 12-24 h after ischemia, when the pyramidal cells in the CA1 region showed no signs of damage. At a survival time of two to three days, most if not all spiny calretinin-immunoreactive cells had disappeared from the hippocampus. Other types of calretinin-containing GABAergic neurons were also reduced in number, but only at a time when CA1 pyramidal cells also started to degenerate, i.e. two to three days after ischemia. We speculate that the early loss of spiny calretinin-containing cells, together with other non-pyramidal cells associated with the mossy fiber system (somatostatin-containing neurons and mossy cells of the hilus), may result in pathological network activity in the hippocampus, which may ultimately lead to an increased excitatory transmission and delayed pyramidal cell death in the CA1 region.

Rapid decline of GABAA receptor subunit mRNA expression in hippocampus following transient cerebral ischemia in the gerbil

Inhibitory neurotransmission may play an important role in neuronal degeneration following transient cerebral ischemia. We studied the effect of transient forebrain ischemia on the GABAA receptor system in the gerbil hippocampus. Gerbils were subjected to 5 minutes of bilateral carotid occlusion and were sacrificed at various times over 4 days following reperfusion. There was a substantial loss of pyramidal cells in the CA1 area of the hippocampus 4 days following ischemia. No cell loss was detected in CA3 pyramidal cells of the hippocampus, granule cell layer of the dentate gyrus, and ventroposterior medial and ventroposterior lateral nuclei of the thalamus at any time following ischemia. Examination of brain slices by in situ hybridization histochemistry revealed that a change in expression of the GABAA receptor alpha 1 and beta 2 subunit mRNAs occurred in two phases following onset of reperfusion. The early phase (rapid) occurred within the first 4 hours following reperfusion. The expression of mRNAs significantly decreased (up to 25%) within 1 hour after occlusion in CA1 and CA3 pyramidal cell layers of the hippocampus and in the granule cell layer of the dentate gyrus. The expression of the mRNAs in these regions continued to decrease for 4 hours (up to 43%). In the second phase, which began between 4 and 12 hours following reperfusion, mRNA expression started to return to control levels in CA3 hippocampus and in the dentate. However, expression of both mRNAs continued to decline slowly in the CA1 pyramidal cell layer (up to 85%) over the next 3 days, concomitantly with degeneration of the CA1 pyramidal cells. Expression of mRNAs in the ventroposterior medial or ventroposterior lateral nuclei of the thalamus was similar to control values. To determine if a change in GABAA receptor distribution paralleled changes in receptor subunit mRNA expression, we also measured the binding of [35S]t-butylbicyclophosphorothionate to GABAA receptor chloride channels. The t-butylbicyclophosphorothionate [35S] binding decreased between 1 and 4 days after reperfusion in the dendritic fields of CA1 pyramidal cells (strata oriens, radiatum, and lacunosum-moleculare) but not in the pyramidal cell body layer. These results indicate that expression of GABAA receptor subunit mRNAs decrease well before CA1 pyramidal cell degeneration and loss of GABAA receptors. At present, it is not clear if an early loss of mRNA expression after an ischemic insult leads to a functional defect in GABAA receptors. If so, a loss of GABA neurotransmission may contribute to the development of neuronal degeneration following cerebral ischemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Long-term observations in gerbil brain following transient cerebral ischemia: autoradiographic and histological study

We investigated the long-term changes that occur in the gerbil brain following transient cerebral ischemia using histology and receptor autoradiography. Transient ischemia was induced for 3 and 10 min, and animals were allowed to survive for 8 months. A histological study showed that 3-min ischemia caused neuronal damage and mild atrophy only in the hippocampal CA1 sector, and that 10-min ischemia produced severe neuronal damage and marked shrinkage in the hippocampal CA1 and CA3 sectors. Furthermore, severe neuronal damage was seen in the striatum after 10-min ischemia. Autoradiography study revealed that 3-min ischemia caused a significant reduction in [3H] naloxone binding in the frontal cortex, striatum, dentate gyrus, and thalamus, whereas [3H]SCH 23390 and [3H] forskolin binding was not significantly altered in all regions. In contrast, 10-min ischemia produced marked alteration in these binding sites in the striatum, hippocampus, thalamus, and substantia nigra. The alteration was especially notable in the hippocampal region and substantia nigra. These results indicate that hippocampal damage after transient ischemia, compared with that in other regions, is not static, but particularly progressive. Furthermore, they demonstrate a reduction in adenylate cyclase system in the striatum and substantia nigra after transient ischemia. Moreover, our results suggest that long-term survival after ischemia may induce synaptic modification of neurotransmitter and adenylate cyclase system in the hippocampus.

Characteristics of spontaneous and evoked EPSPs recorded from dentate spiny hilar cells in rat hippocampal slices

1. Excitation of the spiny subtype of hilar neurons in the fascia dentata was characterized by intracellular recording from hilar cells in hippocampal slices. Stimulation of the outer molecular layer was used to activate the perforant path. Evoked responses were examined, as well as the large spontaneous excitatory potentials that are a distinctive characteristic of spiny hilar cells. 2. Excitatory potentials that occurred spontaneously, as well as those that occurred in response to outer molecular layer stimulation, were similar among the cells that were sampled, regardless of morphological variations such as the presence or absence of thorny excrescences. Spontaneous and evoked excitatory postsynaptic potentials (EPSPs) were complex depolarizations that often had several discrete peaks. Spontaneous EPSPs increased in amplitude slightly with hyperpolarization, and evoked EPSPs clearly increased with hyperpolarization. 3. Applications of selective antagonists of excitatory amino acid receptors were used to determine which excitatory amino acid receptor mediates EPSPs of these cells. 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) was used to block the receptor subtype selective for the agonists alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainic acid (the "AMPA/kainate" receptor). 2-amino-5-phosphonovaleric acid (APV) was used to block receptors specific for the agonist N-methyl-D-aspartate (NMDA; the "NMDA" receptor). Perfusion with CNQX (5-25 microM) completely blocked all spontaneous and evoked excitation, even when activity was examined at relatively depolarized membrane potentials and a low concentration of extracellular magnesium (0.5 mM) was used. Under these conditions, APV (25-50 microM) had no detectable effect on spontaneous activity but did increase the stimulus strength required to elicit responses to outer molecular layer stimulation. 4. When extracellular magnesium was lowered to 0 mM (nominally), there was strong evidence for a contribution of NMDA receptors to spontaneous and evoked EPSPs. Thus, when cells were perfused with 0 mM extracellular magnesium and 5 microM CNQX, spontaneous depolarizations were present and EPSPs could be triggered by stimulation of the outer molecular layer. Both the spontaneous and evoked EPSPs were blocked by 25 microM APV. 5. Because gamma-aminobutyric acid (GABA)A receptors can cause depolarizations in hippocampal neurons, the GABAA receptor antagonist bicuculline was used to determine whether some of the EPSPs were mediated by GABAergic neurons that are normally activated by spontaneous release of excitatory amino acids. Bicuculline (5-25 microM) had no effect on spontaneous depolarizations, and led to an enhancement of evoked depolarizations. Therefore it does not appear that GABAA receptor-mediated depolarizations contribute to hilar cell depolarizations.(ABSTRACT TRUNCATED AT 400 WORDS)

Forebrain ischemia in the gerbil increases lambda opiate binding in hippocampal mossy fibers

Transient forebrain ischemia was produced in gerbils by short-term occlusion of the common carotid arteries under halothane anesthesia. Histological analysis of brains 7 days post-ischemia demonstrated characteristic destruction of CA1 pyramidal cells. lambda Opiate binding (measured with [3H]naloxone in the presence of 300 nM diprenorphine) at 7 days post-ischemia was significantly increased in the stratum lucidum of the hippocampus (the mossy fiber layer), but not in any other region measured, including other hippocampal regions, cortex, amygdala, caudate putamen, thalamus, and hypothalamus. The increase in mossy fiber lambda binding was slow to develop (no increase detected up to 48 h post-ischemia), and long-lasting (binding remained elevated at 32 days post-ischemia). While MK-801 significantly inhibited CA1 pyramidal cell destruction when administered 20 min prior to ischemia, the increase in mossy fiber lambda binding was still evident. None of seven different opioid agonists and antagonists examined had an effect on either the pyramidal cell damage or increased mossy fiber lambda binding seen 7 days after ischemia.

Parvalbumin immunoreactivity in the hippocampus of the gerbil after transient forebrain ischaemia: a qualitative and quantitative sequential study

Parvalbumin immunoreactivity is examined in the hippocampus of the Mongolian gerbil (Meriones unguiculatus) in controls and in animals subjected to 20 min of forebrain ischaemia produced by bilateral clipping of the carotids. In comparison with other species, the hippocampus of the gerbil is characterized by strong immunoreactivity of the (presumably excitatory) perforant pathway, and weak immunoreactivity (low numbers of neurons and scarce dendritic arbors) in nonpyramidal nerve cells (inhibitory neurons) of the CA1 area. These properties may play some role in the development and maintenance of seizures in this susceptible species. Parvalbumin immunoreactivity is rapidly and ephemerally increased in the hippocampus 15 min after reperfusion. Later on, there is a transitory decrease of parvalbumin immunoreactivity which is followed by an increase 6 h later in the stratum granulare hilus and CA3 area, and not until the first and second days in the CA1 area. This increase significantly surpasses the number of immunoreactive neurons in control animals in CA1 and CA3 from 48 h after reperfusion onwards. The effect is similar using different anaesthetics and does not occur in sham-operated animals. In contrast with these findings, the number of parvalbumin-immunoreactive neurons in the somatosensory cortex is not affected in our model of forebrain ischaemia. On the other hand, GABA-immunoreactive neurons in CA1 are preserved during the first week after reperfusion, although an increase in the number of these cells occurs at the end of this period. Delayed neuronal death occurs in the CA1 area 48 h after ischaemia, and marked reduction in the number of CA1 neurons is found by the end of the first week. Eighty per cent of the remaining cells in CA1 at day 7, and 83% at day 15, are parvalbumin-immunoreactive nonpyramidal neurons in contrast to 3% parvalbumin-immunoreactive cells in control animals. These findings indicate that GABAergic neurons in CA1 are preserved after forebrain ischaemia, and that parvalbumin in CA1 neurons is associated with survival.

Activation of dentate hilar neurons by stimulation of the fimbria in rat hippocampal slices

It is has been shown that the major afferent input to the dentate gyrus, the perforant path, excites dentate hilar neurons. However, little is known about the other inputs to hilar cells. Therefore, we examined the responses of hilar neurons to stimulation of the fimbria. We positioned our stimulating electrodes so that granule cells were not excited antidromically by fimbria stimulation, although action potentials were easily triggered in area CA3b and CA3c pyramidal cells by such stimulation. In these experiments, fimbria stimulation evoked responses from every hilar cell tested, including examples of both of the major cell types, the spiny hilar 'mossy' cells (n = 15) and the relatively aspiny, 'fast-spiking' cells (putative interneurons, n = 5). Hilar cell responses consisted primarily of EPSPs that could trigger action potentials, but small IPSPs were also evoked in some cases, particularly in the fast-spiking cells. Excitation was blocked by an antagonist of the AMPA/kainate receptor subtype of excitatory amino acid receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 5 microM, n = 5), whereas the cholinergic antagonist atropine (10 microM) had no effect (n = 4). When sequential intracellular recordings were made from hilar cells and area CA3 pyramidal cells in the same slice, hilar cell EPSPs began after action potentials of CA3b pyramidal cells, and stimulus strengths required to evoke hilar cell EPSPs were above threshold for area CA3b pyramidal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroprotective activity of dimer of 16,16'-dimethyl-15-dehydroprostaglandin B1 (di-Calciphor) in cerebral ischemia

Post-ischemic treatment of di-Calciphor (16,16'-dimethyl-15- dehydroprostaglandin B1) significantly improves animal survival and prevents ischemia-induced neurodegeneration of vulnerable forebrain regions assessed with histochemical and biochemical techniques in gerbils. Neuronal degeneration seen by Cresyl violet staining and silver impregnation in the CA1 sector of the hippocampus and the dorso-lateral sector of the striatum was significantly reduced in animals treated with di-Calciphor. In addition, the early onset of selective degradation of calpain I substrates spectrin and microtubule-associated protein (MAP2) in these same vulnerable regions was prevented. The lack of adverse side effects may facilitate the potential therapeutic use of this drug in preventing neuronal damage caused by stroke.

Assessing chronic brain damage by quantification of regional volumes in postischemic rat brains

The present study provides data on fresh volumes of 39 anatomically defined brain regions after a 10 min transient forebrain ischemia in the rat. Ischemia was induced by occlusion of the carotid arteries and simultaneous hypotension. After a survival period of 3 months the rats were transcardially perfusion-fixed with Bodian's solution, and the brains processed for paraffin embedding and serially sectioned. The sections were Nissl-stained for delineation of the brain regions. The volume of a brain region was calculated from 8-10 equidistant sections, using the Cavalieri method and corrected for shrinkage of the brain. Fresh volumes were reduced by 27-50% in the layers of the hippocampal CA1 sector, by 40-46% in the substantia nigra, by 19% in the caudate nucleus, by 13% in the subiculum and the cingulate areas 1-3, by 12-14% in the retrosplenial and temporal areas. The results show that determination of fresh volumes is a sensitive method for quantification and localization of ischemic brain damage in the whole brain.

Acidic fibroblast growth factor infusion reduces ischemic CA1 hippocampal damage in the gerbil

Occlusion of the carotid arteries for 5 minutes in the Mongolian gerbil results in selective necrosis of CA1 pyramidal neurons. In the present experiments we studied whether intraventricular infusion of acidic fibroblast growth factor (aFGF) could attenuate this damage. Intraventricular infusions of bovine serum albumin (BSA-10 ng/h) or aFGF (1, 10 or 100 ng/h) were started 2 days prior to 5 minutes of bilateral carotid occlusion and continued for 5 days post-ischemia. The brains were perfused and fixed at 5 days post-ischemia and histological assessment of CA1 damage was made. Animals receiving intraventricular infusions of 10 or 100 ng/h aFGF showed a significant reduction of CA1 neuronal damage in comparison to no treatment ischemic controls (no treatment-8 +/- 1; aFGF 10 ng/h-147 +/- 28; aFGF 100 ng/h-168 +/- 35 cells/mm CA1; P < 0.05 for both aFGF groups). The results indicate that aFGF infusion can attenuate the severity of ischemic neuronal necrosis in the gerbil hippocampus.

Prediction of specific damage or infarction from the measurement of tissue impedance following repetitive brain ischaemia in the rat

The development of irreversible brain damage during repetitive periods of hypoxia and normoxia was studied in anaesthetized rats with unilateral occlusion of the carotid artery (modified Levine model). Rats were exposed to 10 min hypoxia and normoxia until severe damage developed. As indices of damage, whole striatal tissue impedance (reflecting cellular water uptake), sodium/potassium contents (due to exchange with blood). Evans Blue staining (blood-brain barrier [BBB] integrity) and silver staining (increased in irreversibly damaged neurons) were used. A substantial decrease in blood pressure was observed during the hypoxic periods possibly producing severe ischaemia. Irreversibly increased impedance, massive changes in silver staining, accumulation of whole tissue Na and loss of K occurred only after a minimum of two periods of hypoxia, but there was no disruption of the BBB. Microscopic examination of tissue sections revealed that cell death was selective with reversible impedance changes, but became massive and non-specific after irreversible increase of the impedance. The development of brain infarcts could, however, not be predicted from measurements of physiological parameters in the blood. We suggest that the development of cerebral infarction during repetitive periods of hypoxia may serve as a model for the development of brain damage in a variety of clinical conditions. Furthermore, the present model allows the screening of potential therapeutic measuring of the prevention and treatment of both infarction and selective cell death.

Ischemia as an excitotoxic lesion: protection against hippocampal nerve cell loss by denervation

There are several indications for an involvement of neuroexcitatory mechanisms in ischemic neuron damage. Since we forwarded the hypothesis in 1982 that the transmitter glutamate is playing a key role, several lines of evidence have substantiated this: there is a pronounced transmitter release induced by ischemia and there is uptake of Ca++ via NMDA-operated calcium channels. Under certain circumstances postischemic neuron death can be impaired by administration of either NMDA-antagonists or calcium blockers. Further proof for the induction of harmful excitatory mechanisms by ischemia has been obtained by preischemic denervation of the vulnerable nerve cells. After transient cerebral ischemia in rats or gerbils, there are signs of irreversible damage (eosinophilia) of neurons in the dentate hilus (somatostatin-positive cells) after 2-3 hours and of hippocampal pyramidal neurons after 2-3 days (delayed neuron death). In the first case, removal of the (main) input to hilus cells by degranulation (colchicine selectively eliminates granule cells) protects these. In the case of pyramidal neurons removal of Schaffer collaterals/commisurals or input from the entorhinal cortex have a protective effect. Recently, we have measured glutamate and calcium in CA1 of denervated rats during 10 min of ischemia, and it turns out that there is almost no extracellular glutamate release or lowering of calcium in contrast to ischemic animals with intact innervation. Also in the postischemic period there are indications of a continuation of the damaging processes induced by ischemia. Besides the well known postischemic hypoperfusion, a prolonged release of glutamate has been reported, as well as burst firing in some models.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrogen peroxide production by monoamine oxidase during ischemia-reperfusion in the rat brain

Monoamine oxidase (MAO) as a source of hydrogen peroxide (H2O2) was evaluated during ischemia-reperfusion in vivo in the rat brain. H2O2 production was assessed with and without inhibition of MAO during and after 15 min of ischemia. Metabolism of H2O2 by catalase during ischemia and reperfusion was measured in forebrain homogenates using aminotriazole (ATZ), an irreversible H2O2-dependent inhibitor of catalase. Catecholamine and glutathione concentrations in forebrain were measured with and without MAO inhibitors. During ischemia, forebrain blood flow was reduced to 8% of baseline and H2O2 production decreased as measured at the microperoxisome. During reperfusion, a rapid increase in H2O2 generation occurred within 5 min as measured by a threefold increase in oxidized glutathione (GSSG). The H2O2-dependent rates of ATZ inactivation of catalase between control and ischemia-reperfusion were similar, indicating that H2O2 was more available to glutathione peroxidase than to catalase in this model. MAO inhibitors eliminated the biochemical indications of increased H2O2 production and increased the catecholamine concentrations. Mortality was 67% at 48 h after ischemia-reperfusion, and there was no improvement in survival after inhibition of MAO. We conclude that MAO is an important source of H2O2 generation early in brain reperfusion, but inhibition of the enzyme does not improve survival in this model despite ablating H2O2 production.

Production of limbic motor seizures and brain damage by systemic and intracerebral injections of paraquat in rats

The behavioural and neuropathological effects of both systemic and intrahippocampal injections of paraquat dichloride (1,1'-dimethyl 4,4'-bipyridinium dichloride) were studied in rats. Paraquat (0.1-1.0 mumol) injected into the dorsal hippocampus, produced limbic motor seizures within a few minutes of injection followed by neuronal damage in the CA1 and CA3 pyramidal cell layers, pyriform cortex, dentate granule cell layer and in the hilus fascia dentata at 24 hr (n = 9 rats). A smaller dose of paraquat (10 nmol) was ineffective. The effects of intrahippocampal injections of paraquat (1 mumol) were prevented by administering it together with atropine (50 nmol; n = 6 rats) or by giving it 60 min. after MK 801 (0.3 mg.kg-1 intraperitoneally). Systemic injections of paraquat (20-100 mg.kg-1) also produced forelimb clonus and rearing in 10 out of 15 animals. Neuronal cell death was found 24 hr later in 9 of these rats and was restricted to the pyriform cortex, the brain region with the highest concentrations of paraquat. Atropine (150 mg.kg-1 intraperitoneally given 60 min. previously) completely prevented the motor seizures but cell death still occurred in 2 of the 6 animals tested. In conclusion, both systemic and intrahippocampal injections of paraquat produced behavioural excitation accompanied 24 hr later by brain damage and antagonist studies suggested involvement of muscarinic and NMDA receptors in the neurotoxic mechanism.

Functional changes in neuropeptide Y- and somatostatin-containing neurons induced by limbic seizures in the rat

The influence of sustained epileptic seizures evoked by intraperitoneal injection of kainic acid on the gene expression of the neuropeptides somatostatin and neuropeptide Y and on the damage of neurons containing these peptides was studied in the rat brain. Injection of kainic acid induced an extensive loss of somatostatin and, though less pronounced, of neuropeptide Y neurons in the inner part of the hilus of the dentate gyrus. Neuropeptide Y-immunoreactive neurons located in the subgranular layer of the hilus, presumably pyramidal-shaped basket cells, were spared by the treatment. Although neuropeptide Y messenger RNA was not detected in granule cells of control rats, it was found there after kainic acid seizures at all time intervals investigated (12 h to 90 days after injection of kainic acid). High concentrations of neuropeptide Y messenger RNA were especially observed 24 h after injection of kainic acid. At this time neuropeptide Y messenger RNA was also transiently observed in CA1 pyramidal cells. Neuropeptide Y synthesis in granule cells in turn gave rise to an intense immunoreactivity of the peptide in the terminal field of mossy fibers which persisted for the entire time period (90 days) investigated. In addition, neuropeptide Y messenger RNA concentrations were also drastically elevated in presumptive basket cells located at the inner surface of the granule cell layer, especially at the "late" time intervals investigated (30-90 days after kainic acid). These data support the concept that extensive activation of granule cells by limbic seizures contributes to the observed neuronal cell death in CA3 pyramidal neurons and interneurons of the hilus. Consecutively, basket cells containing neuropeptide Y and presumably GABA might be activated and participate in recurrent inhibition of granule cells. Neuropeptide Y-immunoreactive fibers observed in the inner molecular layer at "late" time intervals after kainic acid may result either from collateral sprouting of mossy fibers or from basket cells extensively expressing the peptide. It is speculated that neuropeptide Y synthesized and released at a high rate from granule cells and basket cells may exert a protective action against seizures.

Long-term changes in gerbil brain neurotransmitter receptors following transient cerebral ischaemia

1. Receptor autoradiographic and histological techniques were used to investigate long-term changes in the gerbil brain following transient cerebral ischaemia. 2. Transient ischaemia was induced for 3 min and 10 min, and the animals were allowed to survive for 8 months. 3. Histological examination revealed that 3 min ischaemia caused neuronal damage and mild shrinkage only in the hippocampal CA1 sector. Ten minutes of ischaemia produced severe neuronal damage in the striatum and the hippocampal CA1 and CA3 sectors. Considerable shrinkage was seen in the hippocampus; the dentate gyrus, however, was not damaged. 4. Three minutes of ischaemia produced changes in the binding of [3H]-quinuclidinylbenzilate ([3H]-QNB), [3H]-muscimol, and [3H]-MK-801 in various brain regions, as determined autoradiographically. In contrast, [3H]-cyclohexladenosine ([3H]-CHA) and [3H]-PN200-110 ([3H]-isradipine) binding in the brain was unaltered. 5. Ten minutes of ischaemia resulted in a major loss of neurotransmitter receptors, especially in the hippocampus. The substantia nigra showed a significant reduction in [3H]-CHA binding, whereas the striatum, which was morphologically damaged, showed no significant changes in any of the neurotransmitter receptors examined. 6. The results demonstrated that long-term survival after transient cerebral ischaemia produced alterations in neurotransmitter receptors, especially in the hippocampal formation, where considerable shrinkage was noted. These results also suggest that the hippocampal damage was not static, but progressive.

Gamma-vinyl GABA prevents hippocampal and substantia nigra reticulata damage in repetitive transient forebrain ischemia

GABAergic inhibitory mechanisms may offer protection to neurons after global ischemia. We tested the effects of gamma-vinyl GABA, a GABA-transaminase inhibitor, via continuous infusion in the third ventricle (Alza pumps) in a gerbil model of repetitive forebrain ischemia. We used two episodes of 3 min duration with a 'reperfusion' interval of 1 h between the insults. Histological analysis was done with silver staining 5 days after the insult. Our results show that there is significant protection of the hippocampus CA1 region and substantia nigra reticulata in treated animals compared to controls. An increase in GABA levels, decrease in glutamate, or mild hypothermia, may be potential mechanisms for this protection. GABAergic agents may prove useful agents in repetitive ischemia.

Blockade of excitation reveals inhibition of dentate spiny hilar neurons recorded in rat hippocampal slices

1. Extracellular and intracellular recordings in rat hippocampal slices were used to compare the synaptic responses to perforant path stimulation of granule cells of the dentate gyrus, spiny "mossy" cells of the hilus, and area CA3c pyramidal cells of hippocampus. Specifically, we asked whether aspects of the local circuitry could explain the relative vulnerability of spiny hilar neurons to various insults to the hippocampus. 2. Spiny hilar cells demonstrated a surprising lack of inhibition after perforant path activation, despite robust paired-pulse inhibition and inhibitory postsynaptic potentials (IPSPs) in adjacent granule cells and area CA3c pyramidal cells in response to the same stimulus in the same slice. However, when the slice was perfused with excitatory amino acid antagonists [6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), or CNQX with 2-amino-5-phosphonovaleric acid (APV)], IPSPs could be observed in spiny hilar cells in response to perforant path stimulation. 3. The IPSPs evoked in spiny hilar cells in the presence of CNQX were similar in their reversal potentials and bicuculline sensitivity to IPSPs recorded in dentate granule cells or hippocampal pyramidal cells in the absence of CNQX. 4. These results demonstrate that, at least in slices, perforant path stimulation of spiny hilar cells is primarily excitatory and, when excitation is blocked, underlying inhibition can be revealed. This contrasts to the situation for dentate and hippocampal principal cells, which are ordinarily dominated by inhibition, and only when inhibition is compromised can the full extent of excitation be appreciated.(ABSTRACT TRUNCATED AT 250 WORDS)

Silver impregnability of ischemia-sensitive neocortical neurons after 15 minutes of cardiac arrest in the dog

The development of postischemic neuronal argyrophilia and the subsequent fate of argyrophilic neurons were studied in dogs after 15 min of complete cerebral ischemia and survival varying from 1 h to 7 days. Histopathological examination of the vulnerable neocortical region was performed using the Nauta degeneration method, and the time course of cellular changes was described. Clear-cut neuronal argyrophilia was found to precede cell body shrinkage and gradual disintegration corresponding to selective neuronal death. To clarify this initial stage of neuronal impregnability, the samples from the animals surviving 8 h postarrest were stained with toluidine blue or processed for electron microscopy, and the distribution of argyrophilic cells was confirmed to be identical with that of hyperchromatic or electron-dense cells. On the other hand, infrequently observed "tissue infarctions" exhibited no silver affinity in spite of apparent cellular damage. These findings indicate that enhanced impregnability is related to cytochemical processes incidental to the phenomenon of "selective neuronal death", which can be readily detected by the Nauta method.

Mapping of second messenger and rolipram receptors in mammalian brain

Autoradiographic localizations of major second messengers and a selective cyclic adenosine monophosphate (cyclic-AMP) phosphodiesterase in the brain were visualized in the gerbil and the rat using receptor autoradiography. [3H]Phorbol 12,13-dibutyrate (PDBu), [3H]inositol 1,4,5-trisphosphate (IP3), [3H]forskolin, [3H]cyclic-AMP, and [3H]rolipram were used to label protein kinase C, IP3 receptor, adenylate cyclase, cyclic-AMP-dependent protein kinase (cyclic-AMP-DPK), and Ca2+/calmodulin-independent cyclic-AMP phosphodiesterase (PDE), respectively. Most second messengers and rolipram binding activities were especially found in the limbic system, basal ganglia, and cerebellum. Marked differences were noted in the hippocampus, where cyclic-AMP and rolipram binding activities were very low in gerbils but high in rats. In contrast, regional localization in the binding sites of PDBu, IP3, and forskolin in gerbil brain was relatively similar to that in rat brain. Further, alteration of the cyclic-AMP and rolipram binding sites was studied in the gerbil hippocampus 7 days after 10-min cerebral ischemia. The results suggest that the gerbil differs from the rat with respect to the characteristic neurons or interneurons, especially in the hippocampal formation. This finding may help further elucidate the relationship or difference between gerbils and rats for brain function and behavioral pharmacology. Furthermore, our results suggest that cyclic-AMP and rolipram binding sites are predominantly distributed on the pyramidal cell layer of the hippocampal CA1 sector and that transient cerebral ischemia can cause marked reduction in these binding sites in the hippocampus.

Mechanism of detection of acute cerebral ischemia in rats by diffusion-weighted magnetic resonance microscopy

BACKGROUND AND PURPOSE

The aim of this study was to measure apparent diffusion coefficients in rat brain tissue exposed to ouabain, glutamate, and N-methyl-D-aspartate and to compare them with apparent diffusion coefficients found in acute cerebral ischemia.

METHODS

The apparent diffusion coefficient was measured using magnetic resonance microscopy in four groups of Sprague-Dawley rats after occlusion of the right middle cerebral artery and ipsilateral common carotid artery (n = 7), after ouabain exposure (n = 6), during glutamate exposure (n = 7), or during N-methyl-D-aspartate exposure (n = 3). Ouabain, glutamate, and N-methyl-D-aspartate were applied via an intracerebrally implanted microdialysis membrane.

RESULTS

Three hours after the induction of focal cerebral ischemia, a 33% reduction in the apparent diffusion coefficient was observed in the right dorsolateral corpus striatum and olfactory cortex. After ouabain exposure, reductions in the apparent diffusion coefficient were observed within a 1,500-microns radius of the microdialysis membrane. Quantitative analysis revealed that apparent diffusion coefficient values in ischemic and ouabain-exposed tissue fell within the same range. Glutamate and N-methyl-D-aspartate reduced the brain tissue apparent diffusion coefficient by 35% and 40%, respectively.

CONCLUSIONS

On the basis of these findings, we conclude that ischemia-induced apparent diffusion coefficient reductions are likely caused by a shift of extracellular to intracellular water.

Emphasized selective vulnerability after repeated nonlethal cerebral ischemic insults in rats

BACKGROUND AND PURPOSE

We examined the density and distribution of brain damage after repeated periods of nonlethal ischemic insult in rats in comparison with damage after single lethal periods of ischemic insult.

METHODS

Transient cerebral ischemia was induced by four-vessel occlusion for 3, 10, 20, and 30 minutes, and 3-minute periods of ischemia were repeated two, three, or five times at 1-hour intervals, followed by 7 days of survival.

RESULTS

Three minutes of ischemia produced no brain damage, but 10-30 minutes of ischemia produced neuronal damage, depending on the length of ischemia, to the selectively vulnerable forebrain regions such as hippocampal CA1 and CA4 subfields, neocortex, striatum, and ventral thalamus, as well as to the brain stem structures (medial geniculate body, substantia nigra, and inferior colliculus) and cerebellar Purkinje cells. Two 3-minute periods of ischemic insult produced neuronal damage to the hippocampal CA1 subfield. Three and five 3-minute insults produced neuronal damage extensively to the selectively vulnerable forebrain areas. An intense cumulative effect of damage was observed in the ventral thalamus, whereas the substantia nigra and the inferior colliculus were resistant to repeated ischemic insults.

CONCLUSIONS

Our data indicate that the density and distribution of neuronal damage after repeated ischemic insults are altered as compared with after single ischemia.

Pattern of neuronal death in the rat hippocampus after status epilepticus. Relationship to calcium binding protein content and ischemic vulnerability

The pattern of hippocampal cell death has been studied following hippocampal seizure activity and status epilepticus induced by 110-min stimulation of the perforant pathway in awake rats. The order of vulnerability of principal cells in the different hippocampal subfields--as determined by silver impregnation--was found to be very similar to the pattern found in ischemia; i.e., dentate hilus greater than CA1, subiculum greater than CA3c greater than CA3a,b greater than dentate granule cells. The hilar somatostatin-containing cells were the most vulnerable cell type, whereas all other subpopulations of nonprincipal neurons--visualized by immunocytochemistry for the calcium binding proteins parvalbumin and calbindin--were remarkably resistant. Pyramidal cells in the CA3 region containing neither of the examined calcium binding proteins were more resistant to overexcitation than CA1 pyramidal cells, most of which do contain calbindin. This indicates that no simple relationship exists between vulnerability in status epilepticus and neuronal calcium binding protein content, and that local and/or systemic hypoxia during status epilepticus may be responsible for the ischemic pattern of cell death.

Post-ischemic regional changes in acetylcholine synthesis following transient forebrain ischemia in gerbils

The synthesis rate of brain acetylcholine (ACh) was estimated 30 min and 5 days following transient forebrain ischemia performed by 10 min bilateral carotid occlusion in gerbils. ACh synthesis was evaluated from the conversion of radiolabeled choline (Ch) into ACh after an i.v. administration of [methyl-3H]Ch. Endogenous and labeled Ch and ACh were quantified by HPLC. The synthesis rate of Ach was significantly decreased following 30 min of recirculation. The reductions reached 55.4% in the hippocampus, 51.2% in the cerebral cortex and 44.4% in the striatum. Five days after ischemia, the values returned to normal in the cerebral cortex and in the striatum, while ACh synthesis remained selectively lowered (-30.4%, p less than 0.01) in the hippocampus. These cholinergic alterations may account for both early and delayed post-ischemic behavioral and mnesic deficits.

Time course and distribution of neuronal degeneration in the dentate gyrus of rat after adrenalectomy: a silver impregnation study

Recently, Sloviter et al. reported that adrenalectomy (ADX) of young adult rats after 3 months led to a selective loss of granule neurons in the dentate gyrus (DG) and that this loss could be prevented by low doses of corticosterone. In the present study, the ADX-induced neuronal degeneration was investigated in Wistar rats, using a silver impregnation method for degenerating neurons. To examine the time course and distribution of the ADX-induced degeneration, young adult male rats were allowed to survive 2, 3, and 5 days and 1, 2, and 3 weeks after ADX. Argyrophilic neurons were present in the dentate granule cell layer on the second day following ADX. Three days after ADX, the number of argyrophilic granule neurons was much more abundant, and it increased gradually with longer post-ADX survival times. Argyrophilia was specifically confined to dentate granule cells and was accompanied by the occurrence of pyknotic nuclei as observed in adjacent cresyl violet-stained sections. There were significant differences between individual rats in quantity of argyrophilia. About one fifth of the ADX rats showed sporadic or no argyrophilia, in spite of plasma corticosterone levels below the detection limit (10 ng/mL). Sham-operated rats and ADX rats receiving corticosterone (10 mg/L) or dexamethasone (15 mg/L) in their drinking water did not display any argyrophilic neurons in the dentate gyrus. The distribution of the argyrophilia within the DG was highly characteristic with the highest number of degenerating cells in the hidden blade of the middle and the temporal thirds of the DG.(ABSTRACT TRUNCATED AT 250 WORDS)

Repetitive transient forebrain ischemia in gerbils: delayed neuronal damage in the substantia nigra reticulata

Repetitive cerebral ischemia results in severe neuronal damage in multiple regions of the brain including the hippocampus, striatum, thalamus, medial geniculate nucleus and the substantia nigra reticulata (SNr). We postulated that the damage in the SNr was delayed, resulting from a loss of striatal inhibitory input. We used the gerbil model of repetitive ischemia (3 min times 2 and 3 min times 3) to evaluate the extent of neuronal damage at 2, 3, 5 and 7 days after the ischemic insult. Silver degeneration stain was used for histological evaluation. Our results indicate that damage in the SNr begins after 48 h and is maximum at 7 days. This delay in onset of damage offers a window for pharmacological protection.

Time- and temperature-dependent forebrain ischemic damage in Mongolian gerbils

The influence of transient bilateral carotid artery occlusion time, core body temperature regulation and post-operative survival time was examined on delayed neuronal death in the hippocampal subregions of Mongolian gerbils. A simple and rapid histologically based scoring system was used. A carotid artery occlusion time of 5 min with stabile core body temperature at 37.5-38.0 degrees C and a post-operative survival time of 4 days was sufficient to induce a reproducible and almost total neuronal damage in the hippocampal subfields. Furthermore, the use of gerbils with ages varying from 50 to 100 days did not markedly influence the development of the neuronal damage although the variation in the severity of the damage seemed to decrease with age. The addition of a drop of room tempered (21-22 degrees C) isotonic water, to avoid adherence between the clips and the carotid artery, reduced neuronal damage in some animals.