Prevention of delayed neuronal death in gerbil hippocampus by ion channel blockers

The inhibitory effect of nilvadipine on calcium channels in retinal ganglion cells in goldfish

PURPOSE

Our aim was to examine the inhibitory effect of nilvadipine on voltage-gated calcium (Ca) channels in solitary ganglion cells.

METHODS

Eyes were excised from goldfish. Ganglion cells were enzymatically dissociated from isolated retina. Whole-cell currents were recorded with the perforated-patch clamp technique.

RESULTS

Depolarizing step pulses to more than -48 mV evoked a slowly inactivating inward Ca current. The current-voltage relation for the nilvadipine-sensitive current was bellshaped, and the peak current reached a maximum at -8 mV in the presence and absence of nilvadipine. Nilvadipine block of voltage-gated Ca current was dose-dependent between 1 and 100 microM. The half-maximum inhibitory dose was 35 microM.

CONCLUSIONS

The inhibitory effect of orally administered nilvadipine on Ca channels had a mild influence in ganglion cells.

Cycloheximide Reduces the Effects of Anoxic Insult In Vivo and In Vitro

In vivo and in vitro techniques were utilized to examine the influence of a protein synthesis blocker, cycloheximide (CHX), on the damaging effects of anoxia in the rat. CHX administered 1 h before transient (30 min) forebrain ischaemia increased the survival of animals, decreased body weight loss and reduced the occurrence of delayed degeneration in the CA1 pyramidal region. The same dose of CHX injected 1 h after ischaemia induced status epilepticus, a decrease in survival rate, and did not reduce weight loss or CA1 damage in any of the surviving rats. Electrophysiological techniques were then used to determine the effects of various periods of anoxia and aglycaemia (AA) on CA1 field excitatory postsynaptic potentials (EPSPs) in hippocampal slices incubated in the presence or absence of CHX. In CHX-treated slices, recuperation of EPSP amplitude (45 +/- 16%) was significantly greater than in control slices (9 +/- 9%) following an AA episode of 3 min 45 s. No difference was seen in the percent recuperation of EPSPs in the control and CHX-treated slices after shorter or longer episodes of AA. From these studies, it appears that CHX protects against the damaging effect of ischaemia in vivo or AA in vitro.

Autoradiographic localization of N-type VGCCs in gerbil hippocampus and failure of omega-conotoxin MVIIA to attenuate neuronal injury after transient cerebral ischemia

In the mammalian central nervous system, transient global ischemia of specific duration causes selective degeneration of CA1 pyramidal neurons in hippocampus. Many of the ischemia-induced pathophysiologic cascades that destroy the neurons are triggered by pre- and postsynaptic calcium entry. Consistent with this, many calcium channel blockers have been shown to be neuroprotective in global models of ischemia. omega-Conotoxin MVIIA, a selective N-type VGCC blocker isolated from the venom of Conus magus, protects CA1 neurons in the rat model of global ischemia, albeit transiently. The mechanism by which this peptide renders neuroprotection is unknown. We performed high-resolution receptor autoradiography with the radiolabeled peptide and observed highest binding in stratum lucidum of CA3 subfield, known to contain inhibitory neurons potentially important in the pathogenesis of delayed neuronal death. This finding suggested that the survival of stratum lucidum inhibitory neurons might be the primary event, leading to CA1 neuroprotection after ischemia. Testing of this hypothesis required the reproduction of its neuroprotective effects in the gerbil model of global ischemia. Surprisingly, we found that omega-MVIIA did not attenuate CA1 hippocampal injury after 5 min of cerebral ischemia in gerbil. Possible reasons are discussed. Lastly, we show that the peptide can be used as a synaptic marker in assessing short and long-term changes that occur in hippocampus after ischemic injury.

Preferential inhibition of L- and N-type calcium channels in the rat hippocampal neurons by cilnidipine

The effect of a dihydropyridine Ca2+ antagonist, cilnidipine, on voltage-dependent Ca2+ channels was studied in acutely dissociated rat CA1 pyramidal neurons using the nystatin-perforated patch recording configuration under voltage-clamp conditions. Cilnidipine had no effect on low-voltage-activated (LVA) Ca2+ channels at the low concentrations under 10(-6) M. On the other hand, cilnidipine inhibited the high-voltage-activated (HVA) Ca2+ current (I(Ca)) in a concentration-dependent manner and the inhibition curve showed a step-wise pattern; cilnidipine selectively reduced only L-type HVA I(Ca) at the low concentrations under 10(-7) and 10(-6) M cilnidipine blocked not only L- but also N-type HVA I(Ca). At the high concentration over 10(-6) M cilnidipine non-selectively blocked the T-type LVA and P/Q- and R-type HVA Ca2+ channels. This is the first report that cilnidipine at lower concentration of 10(-6) M blocks both L-and N-type HVA I(Ca) in the hippocampal neurons.

Ameliorative effects of tamolarizine on place learning impairment induced by transient forebrain ischemia in rats

In the present study we investigated the effect of (+/-)-1-(3, 4-dimethoxyphenyl)-2-(4-diphenylmethylpiperazinyl) ethanol dihydrochloride (tamolarizine), a calcium entry blocker, on place learning impairment in rats with damage selective to the hippocampal CA1 subfield induced by transient forebrain ischemia. Tamolarizine was administered (40 mg/kg) immediately after 15-min brain ischemia. Place learning was tested in a task in which the rat was required to alternatively visit two places located diametrically opposite each other in an open field. The ischemia+saline group showed severe learning impairment in this task; their performance level was significantly inferior to that of the sham-operated group through the test period (30 days). Although the ischemia+tamolarizine group showed slight impairment of place learning during the course of this test, they later reached almost the same performance level as the sham-operated group. Selective neuronal loss in the CA1 subfield was much less in the ischemia+tamolarizine group than in the ischemia+saline group. These results indicate that tamolarizine treatment protects the hippocampus from ischemic brain damage and ameliorates place learning impairment.

Failure of preventive effects of 2-deoxy-D-glucose on ischemia-induced gerbil hippocampal neuronal damage by induced hyperthermia

Post-ischemic administration of 2-deoxy-D-glucose (2-DG), a glucose antimetabolite, markedly reduces the occurrence of ischemia-induced delayed neuronal death (DND) in the gerbil hippocampus. This means that the reduction of energy dependent metabolism after ischemia prevents ischemia-induced damages of hippocampal neurons. In the present study, we demonstrated hyperthermia during ischemia fails to preserve neurons in hippocampal CA1 of 2-DG treated gerbil following transient forebrain ischemia.

Effect of nilvadipine on the voltage-dependent Ca2+ channels in rat hippocampal CA1 pyramidal neurons

Effects of nilvadipine on the low- and high-voltage activated Ca2+ currents (LVA and HVA ICa, respectively) were compared with other organic Ca2+ antagonists in acutely dissociated rat hippocampal CA1 pyramidal neurons. The inhibitory effects of nilvadipine, amlodipine and flunarizine on LVA ICa were concentration- and use-dependent. The apparent half-maximum inhibitory concentrations (IC50s) at every 1- and 30-s stimulation were 6.3x10-7 M and 1.8x10-6 M for flunarizine, 1.9x10-6 M and 7.6x10-6 M for nilvadipine, and 4.0x10-6 M and 8.0x10-6 M for amlodipine, respectively. Thus, the strength of the use-dependence was in the sequence of nilvadipine>flunarizine>amlodipine. Nilvadipine also inhibited the HVA ICa in a concentration-dependent manner with an IC50 of 1.5x10-7 M. The hippocampal CA1 neurons were observed to have five pharmacologically distinct HVA Ca2+ channel subtypes consisting of L-, N-, P-, Q- and R-types. Nilvadipine selectively inhibited the L-type Ca2+ channel current which comprised 34% of the total HVA ICa. On the other hand, amlodipine non-selectively inhibited the HVA Ca2+ channel subtypes. These results suggest that the inhibitory effect of nilvadipine on the neuronal Ca2+ influx through both LVA and HVA L-type Ca2+ channels, in combination with the cerebral vasodilatory action, may prevent neuronal damage during ischemia.

Neuroprotection by the novel calcium antagonist PCA50938, nimodipine and flunarizine, in gerbil global brain ischemia

Calcium is involved in the physiopathology of cerebral ischemia. Calcium antagonists might prevent the calcium overload and death of cells from ischemically compromised tissue. We compare the neuroprotective effect of various doses (0.2, 0.5 and 1 mg/kg) of two dihydropyridines, nimodipine and the novel 1,4-dihydropyridine derivative PCA50938, and flunarizine in the gerbil model of global ischemia. Improvements in morbidity were observed 2 h after the end of carotid occlusion (McGraw's scale) with 0.5 mg/kg of flunarizine, all doses of PCA50938 and 0.2 mg/kg nimodipine. Neuronal loss in the CA1 sector of the hippocampus was examined. The animals treated with 0.5 mg/kg flunarizine and those treated with 1 mg/kg PCA50938 showed a significant reduction in the percentage of damaged neurons in the hippocampal CA1 area, 72 h after transient ischemia. None of the animals treated with 0.5 mg/kg flunarizine had more than 80% of the evaluated neurons altered. We conclude that PCA50938 and flunarizine may act as neuroprotective drugs with different patterns of dose-response and neuroprotective-morbidity-mortality relationships, in the model of global cerebral ischemia in the gerbil. Flunarizine has a narrow therapeutic range.

Effect of nilvadipine on high-voltage activated Ca2+ channels in rat CNS neurons

The effect of nilvadipine, a dihydropyridine derivative, on high-voltage activated (HVA) Ca2+ channels was investigated in freshly dissociated rat frontal cortical neurons. The cortical neurons were observed to have five pharmacologically distinct HVA Ca2+ channel subtypes consisting of the L-, N-, P-, O- and R-types. Nilvadipine selectively inhibited the L-type Ca2+ channel current which comprised 23% of the total HVA Ca2+ channel current. A reversible inhibitory effect of nilvadipine on the L-type Ca2+ channel current was also observed in a concentration-dependent fashion without affecting the current-voltage relationship. The half-maximum inhibitory concentration was 3 x 10(-8) M. These results suggest that the inhibitory effect of nilvadipine on the neuronal Ca2+ influx, in combination with the cerebral vasodilatory action, may prevent neuronal damage during brain ischemia.

Hyperbaric oxygenation prevents delayed neuronal death following transient ischaemia in the gerbil hippocampus

The mechanism of the neuroprotective effect of hyperbaric oxygenation remains unclear although its clinical benefits have been well recognized for human ischaemic neuronal disease. The preventive effect of hyperbaric oxygenation against delayed neuronal death was investigated in the gerbil following transient forebrain ischaemia. Delayed neuronal death in the gerbil was produced by clips on both the common carotid arteries (10 min). Morphological examination was carried out after several protocols of hyperbaric oxygenation, modified from the protocols for human ischaemic neuronal disease. Neurons in the hippocampal CA1 were well preserved in the gerbils treated with hyperbaric oxygenation, more so than in the gerbils with no hyperbaric oxygenation. Moreover, more neurons were preserved in the CA1 treated with hyperbaric oxygenation within 6 h of the ischaemia, than when the hyperbaric oxygenation was started 24 h after the ischaemia. The induction of heat shock proteins (HSP72 and HSP27) became weaker in the gerbils with hyperbaric oxygenation than in those without hyperbaric oxygenation, as seen immunohistochemically. We also observed an increase in dense bodies, that were shown to be lysosomes and myelinoid structures in the cytoplasm of the neurons ultrastructurally, in the hippocampus with hyperbaric oxygenation. However, no oxygen toxicity to the neurons was detected, up to at least two atmospheres absolute. This experimental system was useful to investigate the preventive mechanism of hyperbaric oxygenation against delayed neuronal death in the gerbil, and to determine the clinical indications and the most effective protocol for hyperbaric oxygenation for ischaemic neuronal damage in the human brain.

Ischemia and lesion induced imbalances in cortical function

Cortical structures are often critically affected by ischemic and traumatic lesions which may cause transient or permanent functional disturbances. These disorders consist of changes in the membrane properties of single cells and alterations in synaptic network interactions within and between cortical areas including large-scale reorganizations in the representation of the peripheral input. Prominent functional modifications consisting of massive membrane depolarizations, suppression of intracortical inhibitory synaptic mechanisms and enhancement of excitatory synaptic transmission can be observed within a few minutes following the onset of cortical hypoxia or ischemia and probably represent the trigger signals for the induction of neuronal hyperexcitability, irreversible cellular dysfunction and cell death. Pharmacological manipulation of these early events may therefore be the most effective approach to control ischemia and lesion induced disturbances and to attenuate long-term neurological deficits. The complexity of secondary structural and functional alterations in cortical and subcortical structures demands an early and powerful intervention before neuronal damage expands to intact regions. The unsatisfactory clinical experience with calcium and N-methyl-D-aspartate antagonists suggests that this result might be achieved with compounds that show a broad spectrum of actions at different ligand-activated receptors, voltage-dependent channels and that also act at the vascular system. Whether the same therapy strategies developed for the treatment of ischemic injury in the adult brain may be applied for the immature cortex is questionable, since young cortical networks with a high degree of synaptic plasticity reveal a different response pattern to hypoxic and ischemic insults. Age-dependent molecular biological, morphological and physiological parameters contribute to an enhanced susceptibility of the immature brain to these noxae during early ontogenesis and have to be investigated in more detail for the development of adequate clinical therapy.

Biochemical changes associated with selective neuronal death following short-term cerebral ischaemia

A brief interruption of blood flow to the brain results in the selective loss of specific subpopulations of neurons. Important advances have been made in recent years in defining the biochemical changes associated with cerebral ischaemia and reperfusion and in identifying physical and chemical interventions capable of modifying the extent of neuronal loss. Neuronal death is not irreversibly determined by the ischaemic period but develops during recirculation over a period of hours or even days in different susceptible neuronal populations. The onset of ischaemia produces a rapid decline in ATP production and an associated major redistribution of ions across the plasma membrane including a large intracellular accumulation of Ca2+ in many neurons. Alterations subsequently develop in many other metabolites. These include a marked and progressive release of neurotransmitters and a rapid accumulation of free fatty acids. Most of these alterations are reversed within the first 20 min to 1 hr of recirculation. The changes essential for initiating damage in neurons destined to die have not been definitively identified although there is some evidence suggesting roles for the intracellular Ca2+ accumulation, the release of the neurotransmitter glutamate and a brief burst of free radical production which occurs during early recirculation. During further recirculation, there are reductions in oxidative glucose metabolism and protein synthesis in many brain regions. Few changes have been detected which distinguish tissue containing ischaemia-susceptible neurons from ischaemia-resistant regions until the development of advanced degeneration and neuronal loss. Subtle changes in cytoplasmic Ca2+ content and a decrease in the respiratory capacity of mitochondria are two changes apparently selectively affecting ischaemia-susceptible regions which could contribute to neuronal loss. The mitochondrial change may be one indicator of a slowly developing post-ischaemic increase in susceptibility to oxidative damage in some cells.

Physiological results of monkey brain ischemia, and protection by a calcium blocker

Physiological and histological investigation was undertaken to examine dynamic and metabolic changes due to transient ischemic insult of the monkey brain with and without postischemic treatment by the calcium entry blocker, NC-1100 (1 mg/kg, IV). Monkeys were subjected to temporary occlusion of the eight major arteries: bilateral common carotid, internal and external carotid, and vertebral arteries. Blood flow was restored after 5-, 10-, 13-, and 15-min ischemia in different monkeys. The amplitudes of extradural, cortical, and hippocampal electroencephalograms decreased severely within 1-6 min after beginning occlusion. Complete recovery of these electroencephalograms required more than 1 h. During ischemia, significant change was obvious in arterial glucose, and systolic, diastolic, and mean blood pressure, all of which increased. There were no significant physiological differences between the untreated and NC-1100-treated groups, except decreased diastolic blood pressure and slightly lower postischemic heart rate in the treated group. These small differences might be accounted for by the effect of the calcium blocker. Ten to 15 minutes ischemia caused cell changes, including cell death, which were confined almost exclusively to the CA1 subfield of untreated hippocampi examined the fifth day after occlusion. However, no ischemia-induced cell change was observed in the CA1 subfield of hippocampi subjected to 10 to 15 min ischemia in the NC-1100-treated group. It was concluded that a calcium entry blocker can protect neurons from mild ischemia-induced injury and might ameliorate morphological damage and functional impairment of the brain due to ischemia in patients who suffer transient anoxic or hypoxic injury. The present physiological data should contribute to their clinical treatment.

N-methyl-D-aspartate receptor-mediated, prolonged afterdischarges of CA1 pyramidal cells following transient cerebral ischemia in the rat hippocampus in vivo

We previously reported the post-ischemic potentiation (PIP) of synaptic efficacy in hippocampal Schaffer collateral/CA1 responses of the rat beginning at 6-8 h following 12 min transient cerebral ischemia in vivo. The present study demonstrated that repetitive stimulation with a relatively low frequency (5 Hz, 6 s), which produced short-lasting afterdischarges (ADs; duration, 4.49 +/- 4.26 s; n = 7) in sham-controls, resulted in prolonged ADs (duration, 26.33 +/- 12.63 s; n = 6; P < 0.001) at the same period after ischemia. The PIP was not affected by 2-amino-5-phosphonovalerate (APV) administered via microdialysis at 7 h post-ischemia. The prolonged ADs in response to repetitive stimulation were, however, reversed to short-lasting ADs (duration, 7.13 +/- 1.44 s; n = 4; P < 0.02) by the same procedure, leaving the response to single stimulation unaffected. These findings suggest that, during the reperfusion period, Ca2+ influx into the CA1 pyramidal cells can be greatly increased through N-methyl-D-aspartate (NMDA) receptor-coupled ion channels if appropriately timed multiple synaptic inputs bombard these cells. Such Ca2+ influx may contribute to delayed death of CA1 pyramidal cells after transient cerebral ischemia if synaptic activity is maintained at relatively high levels during the reperfusion period.

Protective effects of kamikihi-to, a traditional Chinese medicine, against cerebral ischemia, hypoxia and anoxia in mice and gerbils

The protective effects of Kamikihi-To (KMK), a traditional Chinese medicine, against cerebral ischemia, hypoxia and anoxia were investigated with various experimental models in mice and gerbils. KMK (2.0 g/kg/day, p.o. for 5 days) significantly prolonged the survival time of mice subjected to bilateral common carotid artery occlusion. KMK (0.5 and 2.0 g/kg/day, p.o. for 5 days) also prolonged the survival time of mice injected with N-methyl-D-aspartic acid (NMDA: 80 mg/kg, i.v.). Furthermore, KMK (in a diet containing 8% KMK given orally for 34 days) showed protective effects against delayed neuronal death in CA1 pyramidal cells in the gerbil hippocampus after transient forebrain ischemia. On the other hand, we failed to show any protective effects of KMK (0.5-2.0 g/kg/day, p.o. for 5 days) against normobaric hypoxia and KCN-induced cytotoxic anoxia in mice. These results suggest that KMK may have protective effects against cerebral ischemic disorders, but not against severe hypoxic and anoxic disorders.

Comparison of the effects of glycerol, mannitol, and urea on ischemic hippocampal damage in gerbils

The effects of glycerol and mannitol, as well as urea, on delayed neuronal death (DND) in the gerbil hippocampus were investigated. 20% solution of glycerol, mannitol and urea were prepared, and 6.5 ml/kg of each agent, or saline, was administered to male Mongolian gerbils intraperitoneally 30 min before ischemia. The animals were subjected to transient forebrain ischemia for 5 min. Seven days after the ischemic insult, the brains were fixed and stained for histopathological analysis. The number of normal neurons (neuronal density, ND) in a 1 mm linear length of hippocampal CA1 region was counted. ND of sham-operated group (n = 6) was 275.3 +/- 16.7 (mean +/- SD). ND in the saline-treated group (n = 6) was 14.8 +/- 5.0. ND of groups treated with glycerol (n = 6), mannitol (n = 6) and urea (n = 4) was 68.2 +/- 56.7 (p < 0.01), 52.8 +/- 54.4 (p < 0.01) and 12.0 +/- 2.5 (NS), respectively. The present study demonstrates that glycerol and mannitol have some protective effects against DND in the gerbil hippocampus, whereas urea has no effect.

An immunohistochemical study of copper/zinc superoxide dismutase and manganese superoxide dismutase in rat hippocampus after transient cerebral ischemia

We investigated the changes of copper/zinc superoxide dismutase (CuZn-SOD) and manganese superoxide dismutase (Mn-SOD) in the rat hippocampus after 10 min of cerebral ischemia induced by 4-vessel occlusion. The rats were allowed to survive for 4 h, 1 day, 3 days, and 7 days after ischemia. The distribution of SODs were determined by immunohistochemical staining with antibodies against rat CuZn-SOD and Mn-SOD. CA1 pyramidal neurons and granule cells of the dentate gyrus showed intense CuZn-SOD immunoreactivity, whereas CA3 and CA4 neurons showed weaker immunostaining than CA1 neurons in normal animals. The immunoreactivity was reduced by 4 h after ischemia in CA1, CA3, and CA4 neurons when no histological damage was observed. Mn-SOD immunostaining revealed more intense immunoreactivity in CA3 pyramidal neurons than in CA1 neurons in normal animals. Interneurons in the CA1 and CA3 regions and the dentate hilus also showed high Mn-SOD immunostaining. Although CA1 neurons lost Mn-SOD immunoreactivity by 1 day after ischemia, CA3 neurons and interneurons retained the immunoreactivity and preserved intact cell contour after ischemia. In addition, reactive glial cells, which were differentiated by immunocytochemical staining against glial fibrillary acidic protein for reactive astrocytes and histochemical staining for reactive microglial cells, were intensely stained for CuZn-SOD and Mn-SOD after ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of KB-2796, a new diphenylpiperazine Ca2+ antagonist, on voltage-dependent Ca2+ currents and oxidative metabolism in dissociated mammalian CNS neurons

The effects of KB-2796, 1-[bis(4-fluorophenyl)methyl]-4-(2,3,4- trimethoxybenzyl)piperazine-2HCl, on the low- and high-voltage activated Ca2+ currents (LVA and HVA ICa, respectively) and on oxidative metabolism were studied in neurons freshly dissociated from rat brain. KB-2796 reduced the peak amplitude of LVA ICa in a concentration-dependent manner with a threshold concentration of 10(-7) M when the LVA ICa was elicited every 30 s in the external solution with 10 mM Ca2+. The concentration for half-maximum inhibition (IC50) was 1.9 x 10(-6) M. At 10(-5) M or more of KB-2796, a complete suppression of the LVA ICa was observed in the majority of neurons tested. There was no apparent effect on the current-voltage (I-V) relationship and the current kinetics. KB-2796 delayed the reactivation and enhanced the inactivation of the Ca2+ channel for LVA ICa voltage- and time-dependently, suggesting that KB-2796 preferentially binds to the inactivated Ca2+ channel. KB-2796 at a concentration of 3.0 x 10(-6) M also decreased the peak amplitude of the HVA ICa without shifting the I-V relationship. In addition, KB-2796 reduced the oxidative metabolism (the formation of reactive oxygen species) of the neuron in a concentration-dependent manner with a threshold concentration of 3 x 10(-6) M. It is suggested that the inhibitory action of KB-2796 on the neuronal Ca2+ influx and the oxidative metabolism, in combination with a cerebral vasodilatory action, may reduce ischemic brain damage.

The NMDA receptor contributes to anoxic aglycemic induced irreversible inhibition of synaptic transmission

Percent recovery of CA1 field EPSP amplitude following various anoxic aglycemic (AA) periods was examined in rat hippocampal slices superfused with MK-801 (0.1 microM, 1 microM, 10 microM) or Mg(2+)-free artificial cerebrospinal fluid. Slices treated with 0.1 microM MK-801 showed greater percent recuperation of EPSP amplitude following 3 min 30 s of AA (36 +/- 12% vs 6 +/- 4% in controls). Higher concentrations of MK-801 resulted in a greater recovery of EPSP amplitudes in more than one time period of AA, with 10 microM MK-801 providing protection in up to 4 min 30 s AA. Percent recuperation of EPSP amplitude was smaller in Mg(2+)-free slices following 2 min (34 +/- 15% vs 81 +/- 11% in controls) and 2 min 30 (25 +/- 14% vs 77 +/- 10% in controls) of AA. These results suggest that the activation of the N-methyl-D-aspartate (NMDA) receptor channel may contribute to irreversible AA induced synaptic failure in CA1.

A new type of Ca2+ channel blocker, NC-1100, inhibits the low- and high-threshold Ca2+ currents in the rat CNS neurons

The effect of a new type of organic Ca2+ channel blocker, NC-1100 [(+/-)-1-(3,4-dimethoxyphenyl)-2-(4-diphenylmethylpiperazinyl)etha nol dihydrochloride], on both low- and high-threshold Ca2+ currents was studied in the whole-cell mode of the pyramidal neurons freshly dissociated from rat hippocampal CA1 region under voltage-clamp condition. The NC-1100 reversibly reduced the high-threshold Ca2+ current (HVA ICa) in a concentration-dependent manner without affecting the current-voltage relationship. The values of half-inhibition (IC50) were 1.3 x 10(-5) and 9.1 x 10(-6) M in external solution containing 10 and 2.5 mM Ca2+, respectively. The NC-1100 also decreased the low-threshold Ca2+ current (LVA ICa) in a concentration-dependent manner. The inhibitory potency was augmented by increasing the stimulation frequency and/or decreasing the extracellular Ca2+ concentration to a physiological range (2.5 mM). The IC50 value decreased to 7.7 x 10(-7) M in external solution containing 2.5 mM Ca2+ at a stimulation frequency of 1 Hz. The NC-1100 delayed the reactivation of LVA Ca2+ channel and enhanced voltage-dependently the steady-state inactivation, suggesting that this drug bound not only the resting LVA Ca2+ channel but also the inactivated one.

Attenuation of ischemic and postischemic damage to brain metabolism and circulation by a novel Ca2+ channel antagonist, NC-1100, in spontaneously hypertensive rats

We investigated the effect of a newly synthesized Ca2+ channel antagonist, NC-1100, on cerebral blood flow (CBF) and metabolism in spontaneously hypertensive rats. The rats received a bolus injection of 0.2 or 1.0 mg/kg NC-1100 i.v. and 1-h cerebral ischemia was then induced by bilateral carotid artery occlusion (group 1). The rats in group 2 were continuously infused with NC-1100 0.03 or 0.1 mg/kg per min, starting immediately after bilateral carotid artery occlusion, for the 1 h of ischemia and following 3-h recirculation. Group 1: during ischemia, CBF in all rats decreased to 6-8% of the resting values. At 1 h cerebral ischemia, brain tissue lactate increased 11.5-, 10.1- and 9.8-fold of the normal control given vehicle or NC-1100, 0.2 and 1.0 mg/kg, respectively. The ATP levels were better preserved by NC-1100 administration; 0.61 +/- 0.04 (mean +/- S.E.M.), 0.80 +/- 0.09 and 0.97 +/- 0.14 mmol/kg (P < 0.05 vs. vehicle), respectively. Group 2: during recirculation, CBF in NC-1100-treated rats returned to 83-90% of the resting values, but to only 65% in the vehicle group. Postischemic brain lactate at 3 h was less well preserved and ATP was dose dependently better preserved in NC-1100- than vehicle-treated rats. It is considered that pre- as well as postischemic administration of a Ca2+ channel antagonist, NC-1100, is beneficial to attenuate and also ameliorate the metabolic and circulatory derangement in the ischemic brain.

Cellular alterations produced by the experimental increase in intracellular calcium and the nature of protective effects from pretreatment with nimodipine

The immortalized septal cell line, SN56 B5 G4, generated by the fusion of mouse septal area cells and neuroblastoma cells, was used to determine if nimodipine, an antagonist of voltage sensitive calcium 'L' channels, might act in a neuroprotective fashion when intracellular calcium levels were raised by incubation in ouabain and monensin. Fluorescent indicator dyes and the automated spectrofluorometer, the CytoFluor 2300, were used to analyze specific cellular targets and functions affected by ouabain and monensin and possible protection by prior incubation with nimodipine. Ouabain and monensin were used together to create a time- and dose-dependent toxic episode. Increases in the emission intensity of Fluo3-AM demonstrated that the concentration of intracellular calcium was monotonically increased by increasing levels of ouabain-monensin. The calcein-AM fluorescent probe indicated that there were no changes in plasma membrane permeability during the toxic episode. Lysosomal integrity decreased as indicated by decreases in neutral red retention. The concentration of free radicals increased as shown by the increase in emission intensity of 2',7'-dichlorfluorescein. Nimodipine pretreatment of the cells incubated with ouabain and monensin resulted in apparent protection of lysosomes and a reduction in the level of free radicals. While nimodipine, by itself, produced a small decrease in intracellular calcium, it actually augmented the ouabain-monensin induced increase in intracellular calcium. The data suggest that in immortalized septal cells, (a) nimodipine offers protection to certain of the responses induced by ouabain-monensin, (b) the protection offered by nimodipine may be independent of antagonism of voltage sensitive calcium channels, and (c) that the protective changes can occur at the same time that intracellular calcium is increasing. These latter observations question the hypothesis that the protection against cell death and dysfunction offered by nimodipine is due solely to maintaining calcium homeostasis.

Enhanced calcium uptake by CA1 pyramidal cell dendrites in the postischemic phase despite subnormal evoked field potentials: excitatory amino acid receptor dependency and relationship to neuronal damage

After 6-12 h of recovery from transient cerebral ischemia, the pyramidal cells of the hippocampal CA1 region take up excessive amounts of calcium upon electrical stimulation, which has been suggested to be important for the development of delayed neuronal death. The aim of this study was to further characterize this enhanced calcium uptake with respect to time-course of development, relationship to neuronal damage, and amplitude of evoked field potentials as well as the dependency on N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Adult Wistar rats were used and calcium-sensitive microelectrodes were placed in the stratum radiatum of the CA1 hippocampus for recording of the extracellular calcium concentration ([Ca2+]ec) during 20 min of ischemia and for 6 h of reflow. High-frequency stimulation of the perforant pathway elicited burst firing in CA1 and a transient decrease in [Ca2+]ec which reflects neuronal uptake. Shifts in [Ca2+]ec could not be evoked 0-1 h after ischemia. However, from 1-2 h burst firing could be evoked and the accompanying shift in [Ca2+]ec increased thereafter in amplitude with prolonged reflow, exceeded preischemic levels after 4 h, and reached 250 +/- 116% (mean +/- SD) of control after 6 h of reflow (p less than 0.05). The extracellular reference potential shift during electrical stimulation and the amplitude of evoked field potentials were still subnormal after 6 h [85 +/- 25% and 83 +/- 25%, respectively (mean +/- SD)]. There was a significant correlation between the degree of stimulated calcium uptake at 6 h postischemia and the extent of CA1 damage evaluated 7 days after the ischemic insult (r = 0.849; p less than 0.001). The shifts in [Ca2+]ec were reduced by the NMDA antagonist MK-801 (0.5-2 mg/kg, i.v.) to approximately 50% of the initial level during both control and postischemic conditions (p less than 0.01). The non-NMDA antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo[F]quinoxaline (NBQX) (42 +/- 13 mg/kg, i.p.; mean +/- SD) decreased the amplitude of the evoked field potentials (to 30 +/- 28% of control, p less than 0.05) and completely abolished the evoked shifts in [Ca2+]ec. In conclusion, the uptake of calcium into CA1 pyramidal cells during electrical stimulation was enhanced already 4 h after ischemia in spite of the fact that other measures of excitability were subnormal. This calcium uptake correlated to the extent of CA1 pyramidal cell damage and was dependent on both NMDA and non-NMDA receptor activation.

Calcium entry blocker ameliorates ischemic neuronal damage in monkey hippocampus

Effects of treatment with (+/-)-1-(3,4-dimethoxyphenyl)-2-(4- diphenylmethylpiperazinyl)ethanol dihydrochloride (NC-1100), a calcium entry blocker, on ischemic neuronal damage were investigated. Monkeys were subjected to temporary occlusion of eight (bilateral common carotid, internal and external carotid, and vertebral arteries) major arteries. Blood flow was restored after 5, 10, 13, and 15 min occlusion, and NC-1100 (1 mg/kg) was then immediately infused intravenously. Monkeys were killed by perfusion fixation 5 days after occlusion. All brain regions were then histologically investigated for ischemic neuronal changes. Physiological data of NC-1100-treated subjects were not significantly different than those of untreated subjects. Heart rate tended to decrease after ischemia in treated subjects. Occlusion of 8 arteries for 10 to 15 min produced ischemic neuronal damage confined exclusively to the CA1 subfield of the hippocampus. Treatment with NC-1100 markedly reduced ischemic neuronal damage in the CA1 subfield of the hippocampus. It is suggested that postischemic treatment with the calcium entry blocker, NC-1100, might protect the brain from the ischemic damage produced in patients suffering from transient ischemia.

Recombinant human superoxide dismutase can attenuate ischemic neuronal damage in gerbils

The effects of recombinant human superoxide dismutase (r-hSOD) on ischemic neuronal injury were examined. Cerebral ischemia was produced in Mongolian gerbils by occluding bilateral common carotid arteries for 5 min. Preischemic treatment with r-hSOD clearly reduced hippocampal neuronal damages while postischemic treatment did not. This result suggests that oxygen free radicals play an important role in selective vulnerability to ischemia and r-hSOD has a potential clinical usefulness against cerebral ischemia.

Therapeutic window of halothane anesthesia for reversal of delayed neuronal injury in gerbils: relationship to postischemic motor hyperactivity

The effect of postischemic halothane anesthesia on locomotor activity and delayed neuronal injury in the hippocampal CA1 sector was examined in gerbils subjected to 5-min forebrain ischemia. Locomotor activity was assessed for 48 h after ischemia using an animal activity monitor, and CA1 injury was evaluated by counting the number of surviving neurons following 7 days of recirculation. Sham-treated animals exhibited a slight decrease of motor activity for about 1 day after surgery. Gerbils subjected to ischemia without postischemic halothane anesthesia developed significant motor hyperactivity (18 times higher than control activity) between 1.7 h and 6.7 h of recirculation. Surviving CA1 neurons in this group amounted to only 17% of those in the control animals. Postischemic halothane anesthesia during the initial 1.7 h of recirculation abolished subsequent motor hyperactivity and protected 84% of all CA1 neurons. Postischemic halothane anesthesia during 1.7 h-3.3 h of recirculation and 3.3-5 h of recirculation did not abolish motor hyperactivity except during the period of anesthesia, and did not protect hippocampal CA1 neurons (only 24% and 10% neuronal survival, respectively). These results demonstrate that the therapeutic window of halothane anesthesia for protection of hippocampal injury precedes the phase of locomotor hyperactivity, and that the appearance of the latter predicts delayed neuronal death.

Current concepts of hypoxic-ischemic cerebral injury in the term newborn

Acute perinatal hypoxic-ischemic cerebral injury in the term newborn is a major cause of long-term neurologic abnormalities in childhood. Earlier diagnosis and more precise localization of hypoxic-ischemic cerebral injury has been made possible by optimal timing and the use of new imaging modalities (e.g., magnetic resonance imaging, spectroscopy, computed tomography, cerebral perfusion techniques). Recent concepts on pathogenesis of such injury involves metabolic factors, regional distribution of excitatory (glutamate) synapses, and factors related to active myelination in specific areas at the time of insult. Consideration of these aspects of pathogenesis permit a rational approach to the management of this major neurologic problem in the newborn.

Blockade of intracellular actions of calcium may protect against ischaemic damage to the gerbil brain

1. The brain cytoprotective effects of a putative calcium-associated protein kinase inhibitor, HA1077, as well as a calcium entry blocker nicardipine were evaluated in models of cerebral ischaemia in Mongolian gerbils. Morphological changes characterizing delayed neuronal death of selectively vulnerable CA1 pyramidal neurones in the hippocampus of the Mongolian gerbil brain occurred 7 days after transient bilateral occlusion of the common carotid arteries. 2. A single injection of HA1077 (1 and 3 mg kg-1, i.p.) 5 min after the occlusion led to a dose-dependent protection of the CA1 neurones. Repeated administrations of HA1077 (1 and 3 mg kg-1, i.p., twice daily for 7 days post-ischaemia) revealed an increase in the number of normal cells, compared to findings with a single administration. 3. In contrast to HA1077, nicardipine (0.3 and 1 mg kg-1, i.p.) did not reduce neuronal degeneration. 4. HA1077 did not interact with the ion channel within which MK-801 binds, as determined by receptor binding. 5. The calcium ionophore, A23187, caused a tonic contraction in canine cerebral arterial strips. HA1077, but not nicardipine, relaxed the A23187-induced contraction, concentration-dependently. 6. These results suggest that blockade of the intracellular actions of calcium may provide protection against ischaemic damage in the brain.

Relationship between brain damage and memory impairment in rats exposed to transient forebrain ischemia

The relationship between changes in learning behavior and neurological damage following transient forebrain ischemia was studied in rats. The transient forebrain ischemia was induced by 4-vessel occlusion, and behavioral experiments were started 4 weeks later when histological damage to the brain seemed to have stabilized. Histological evaluation of brain damage was conducted after completion of the behavioral studies. The rats showed marked learning impairment in a radial maze task done from 4 to 10 weeks after ischemia. In particular, there was an increase in the number of working memory errors according to the duration of forebrain ischemia. However, the same rats showed good avoidance responses in a passive avoidance task done 12 weeks after ischemia. The rats also showed good acquisition of escape response in a water maze task carried out 13 weeks after ischemia, but showed slight impairment of spatial navigation in the transfer test. Marked neuronal degeneration was observed in the hippocampal pyramidal cells of the rats exposed to ischemia. This neuronal damage was closely related to memory impairment in the radial maze task, as demonstrated by a significant negative correlation (r = -0.609 or -0.709) between the number of surviving neurons and the number of reference or working memory errors. These results suggest that rats exposed to transient forebrain ischemia show marked impairment of both reference and working memories as a result of postischemic hippocampal damage.

Regional neuroprotective effects of pentobarbital on ischemia-induced brain damage

We investigated the neuroprotective effect of pentobarbital, a GABAA receptor-effector, on ischemic neuronal damage in the gerbils. The animals were allowed to survive for 7 days after 10-min ischemia induced by bilateral occlusion of the common carotid arteries. Morphological changes and abnormal calcium accumulation were evaluated in selectively vulnerable areas after ischemia. Pentobarbital (40 mg/kg, IP), administered 30 min prior to ischemia, significantly reduced neuronal cell loss in the neocortex, the striatum, and the hippocampal CA3 sector. However, pentobarbital failed to prevent the damage to the hippocampal CA1 sector and the thalamus. 45Ca autoradiographic study also revealed that a marked calcium accumulation was found in the selectively vulnerable regions after ischemia, which was consistent with the extent of histological neuronal damage. The abnormal calcium accumulation was reduced in the sites corresponding to most of the regions in which the protective effect of pentobarbital was found. The results suggest that ischemia-induced neuronal damage may be partly caused by an imbalance between excitatory and inhibitory input.

Comparative neuroprotective effects of pentobarbital, vinpocetine, flunarizine and ifenprodil on ischemic neuronal damage in the gerbil hippocampus

We studied the protective effects of pentobarbital, vinpocetine, flunarizine, and ifenprodil on delayed neuronal death using Mongolian gerbils. The animals were allowed to survive for 7 days after 5 min of cerebral ischemia induced by bilateral occlusion of the common carotid arteries. Hippocampal cell loss was quantified histologically 7 days following ischemia. Intraperitoneal application of pentobarbital (40 mg/kg) 30 min and vinpocetine (50 and 100 mg/kg) 10 min before ischemia significantly reduced neuronal cell loss in the CA1 sector. However, the intraperitoneal administration of flunarizine (10 and 30 mg/kg) and ifenprodil (10 and 30 mg/kg) 15 min before ischemia was not protective. The results suggest that pentobarbital and vinpocetine prevent ischemic neuronal damage, but not flunarizine and ifenprodil. These findings are of interest in relation to the mechanism of delayed neuronal death.

Therapeutic window of CA1 neuronal damage defined by an ultrashort-acting barbiturate after brain ischemia in gerbils

Previous therapeutic studies on the prevention of selective vulnerability of neurons in the hippocampus have suggested that the critical period for induction of delayed neuronal injury occurs early during recirculation. To determine the onset and duration of this period, an ultrashort-acting barbiturate (methohexital) was infused into the left carotid artery of 47 gerbils after various times of recirculation following 10 minutes of bilateral forebrain ischemia. Neuronal density in the left CA1 sector was determined 7 days later by counting the number of surviving neurons per millimeter of pyramidal cell layer. In 16 saline-treated gerbils, less than 10% of the CA1 neurons survived the 10 minutes of ischemia. Postischemic carotid infusion of methohexital improved neuronal survival, the degree of improvement depending on the timing and duration of the methohexital infusion. When carried out during the initial 40 minutes of recirculation, methohexital infusion for 10 minutes increased the number of surviving neurons to approximately 60% of that in five sham-operated control gerbils. This increase was significant for infusions carried out between the 10th and 20th minutes (n = 6, p less than 0.05) and between the 30th and 40th minutes (n = 6, p less than 0.05) of recirculation. Methohexital infusion for 20 minutes increased neuronal survival to 95% and 73% of that in the controls when carried out between the 0th and 20th minutes (n = 5, p less than 0.005) and between the 20th and 40th minutes (n = 5, p less than 0.005) of recirculation, respectively. Protection was nonsignificant for 10- or 20-minute methohexital infusions carried out after the 40th minute of recirculation. Our results demonstrate that the pathologic processes leading to delayed neuronal injury in the CA1 sector are induced during the initial 40 minutes of recirculation and that barbiturates are able to reverse these processes only if given during this period.

'Ischemic tolerance' phenomenon found in the brain

We investigated the possibility that neuronal cells given a mild ischemic treatment sufficient to perturb the cellular metabolism acquired tolerance to a subsequent, and what would be lethal, ischemic stress in vivo. Cerebral ischemia was produced in the gerbils by occlusion of both common carotids for 5 min, which consistently resulted in delayed neuronal death in the CA1 region of the hippocampus. Minor 2-min ischemia in this model depletes high-energy phosphate compounds and perturbs the protein synthesis, but never causes neuronal necrosis, and therefore was chosen as mild ischemic treatment. Single 2-min ischemia 1 day or 2 days before 5 min ischemia exhibited only partial protective effects against delayed neuronal death. However, two 2-min ischemic treatments at 1 day intervals 2 days before 5 min ischemia exhibited drastically complete protection against neuronal death. The duration and intervals of ischemic treatment, enough to perturb cellular metabolism and cause protein synthesis, were needed respectively, because neither 1-min ischemia nor 2-min ischemia received twice at short intervals exhibited protective effects. This 'ischemic tolerance' phenomenon induced by ischemic stress--which is unquestionably important--and frequent stress in clinical medicine, is intriguing and may open a new approach to investigate the pathophysiology of ischemic neuronal damage.

Staurosporine, a novel protein kinase C inhibitor, prevents postischemic neuronal damage in the gerbil and rat

The protective effects of protein kinase inhibitors and a calmodulin kinase inhibitor (W-7) against ischemic neuronal damage were examined in the CA1 subfield of the hippocampus. Staurosporine, KT5720, and KT5822 were used as inhibitors of protein kinase C (PKC), cyclic AMP-dependent protein kinase, and cyclic GMP-dependent protein kinase, respectively. All test compounds were injected topically into the CA1 subfield of the hippocampus. In the gerbil ischemia model, staurosporine (0.1-10 ng) administered 30 min before ischemia prevented neuronal damage in a dose-dependent manner. However, KT5720, KT5822, and W-7 were ineffective, even at a dose of 10 ng. In the rat ischemia model, staurosporine (10 ng) also prevented neuronal damage when administered before ischemic insult, although staurosporine administered 10 or 180 min after recirculation was ineffective. These results suggest the involvement of PKC in CA1 pyramidal cell death after ischemia and that the fate of vulnerable CA1 pyramidal cells through PKC-mediated processes could be determined during the early recirculation period.

Prevention of postischemic hyperthermia prevents ischemic injury of CA1 neurons in gerbils

Halothane-anesthetized Mongolian gerbils were submitted to 5-min bilateral carotid artery occlusion. After ischemia, halothane anesthesia was continued for various periods of up to 85 min, and the degree of CA1 neuronal injury was estimated 7 days later by counting the number of surviving pyramidal cells. During ischemia and postischemic halothane anesthesia, rectal and cranial temperature was kept at control level (37.7 and 37.0 degrees C, respectively) using a feedback-controlled heating system. When anesthesia was discontinued after ischemia, transient hyperthermia occurred. In animals with 0- and 15-min postischemic halothane anesthesia, both cranial and rectal temperature rose by approximately 1.5 degrees C, and the number of surviving CA1 neurons amounted to less than 25% of control. After 45- or 85-min postischemic anesthesia, hyperthermia was significantly reduced and the number of surviving neurons increased to 65 and 89%, respectively. The protective effect of postischemic anesthesia was lost when anesthetized animals were submitted to the same hyperthermic profile as nonanesthetized ones, using a feedback-controlled heating system (16% surviving neurons in hyperthermia vs. 89% in normothermia, respectively). These observations demonstrate that postischemic anesthesia with 1% halothane protects against delayed neuronal death by preventing postischemic hyperthermia and not by its anesthetic effects.

Role of the excitotoxic mechanism in the development of neuronal damage following repeated brief cerebral ischemia in the gerbil: protective effects of MK-801 and pentobarbital

Pretreatment with MK-801 (an NMDA antagonist) or pentobarbital (a GABAA receptor-effector) ameliorated histopathological neuronal damage to the hippocampal CA1 subfield and to the thalamus following three 2-min forebrain ischemia at 1-h intervals in the gerbil. Flunarizine, a calcium antagonist, failed to prevent the neuronal damage. The results suggest that the excitotoxic mechanism plays a role in the neuronal damage following repeated ischemia.

Neuronal damage following non-lethal but repeated cerebral ischemia in the gerbil

Brief, non-lethal transient forebrain ischemia in the gerbil can injure selectively vulnerable neurons when such ischemia is induced repeatedly. The influence of the number and interval of the ischemic insults on neuronal damage, as well as the time course of damage, following repeated 2-min forebrain ischemia were examined. A single 2-min ischemic insult caused no morphological neuronal damage. A moderate number of hippocampal CA1 neurons were destroyed following two ischemic insults with a 1-h interval, and destruction of almost all CA1 neurons resulted from three or five insults at 1-h intervals. Three and five insults also resulted in moderate to severe damage to the striatum and thalamus, depending on the number of episodes. Although three ischemic insults at 1-h intervals caused severe neuronal damage, this number of insults at 5-min and 4-h intervals caused destruction of relatively few neurons, and no neurons were destroyed at 12-h intervals. Following three ischemic insults at 1-h intervals, damage to the striatum, neocortex, hippocampal CA4 subfield and thalamus was observed at 6-24 h of survival, whereas damage to the hippocampal CA1 subfield appeared at 2-4 days. The results indicate that even a brief non-lethal ischemic insult can produce severe neuronal damage in selectively vulnerable regions when it is induced repeatedly at a certain interval. The severity of neuronal damage was dependent on the number and interval of ischemic episodes.

Free radical generation during brief period of cerebral ischemia may trigger delayed neuronal death

We investigated the pathogenic role of free radical formation in ischemic neuronal death using radical scavenger, superoxide dismutase. Cerebral ischemia was produced in the gerbil by bilateral common carotid occlusion for 5 min, which consistently resulted in delayed neuronal death in the CA1 region of the hippocampus. The effects of free superoxide dismutase and a derivatized superoxide dismutase, pyran copolymer conjugated superoxide dismutase, on early ischemic damages, detected sensitively by the immunohistochemical reaction for microtubule associated protein 2, and a subsequent delayed neuronal death after restoration of blood flow were investigated. Preischemic treatment by pyran conjugated superoxide dismutase showed clear protective effects against both the neuronal damages detected by immunohistochemistry after 5 min ischemia and the delayed neuronal necrosis after one week of recovery, although no clear beneficial effects were observed when this drug was administered just before the recirculation or free superoxide dismutase was used. These results strongly suggest that free radical generation during brief period of ischemia plays a pivotal role in triggering the ischemic neuronal damages causing delayed neuronal death at the selectively vulnerable areas of the brain.

Selective neuronal vulnerability following transient cerebral ischemia in the gerbil: distribution and time course

An important feature of ischemic brain damage is the selective vulnerability of specific neuronal populations. We studied the distribution and time course of neuronal damage following transient cerebral ischemia in the gerbil, using light microscopy and 45Ca autoradiography. Following 5 min of ischemia, selective neuronal damage determined by abnormal 45Ca accumulation was recognized only in the hippocampal CA1 subfield and part of the inferior colliculus. Ischemia for 10 to 15 min caused extensive neuronal injury in the 3rd and 5th layers of neocortex, the striatum, the septum, the whole hippocampus, the thalamus, the medial geniculate body, the substantia nigra, and the inferior colliculus. Progression of the damage was rapid in the medial geniculate body and the inferior colliculus, moderate in the neocortex, striatum, septum, thalamus, and the substantia nigra, and was delayed in the hippocampal CA1 sector. However, the delayed damage of the hippocampus occurred earlier when the ischemia period was prolonged. Histological observation revealed neuronal loss in the identical sites of the 45Ca accumulation. This study revealed that the distribution and time course of selective neuronal damage by ischemia proceeded with different order of susceptibility and different speed of progression.

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.

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.

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.