Electroconvulsive stimulations prevent stress-induced morphological changes in the hippocampus

Stress can precipitate major depression and other disorders linked to hippocampal shrinkage. It is hypothesized but not established that treatment of these disorders reverses and prevents the hippocampal changes. Dendritic retraction of individual neurons might in concert with other pathophysiological events contribute to the shrinkage phenomenon. Animal studies have shown that various stress paradigms can induce dendritic retraction in the CA3 pyramidal neurons of the hippocampus. Since electroconvulsive treatment is the most effective treatment in humans with major depression, we investigated whether repeated electroconvulsive stimulations (ECSs) could influence such changes in stressed rats. Furthermore, we investigated whether ECSs per se could influence neuronal branching and total length of the CA3 hippocampal neuronal dendritic tree in normal rats. Rats were stressed using the 21-day 6 h daily restraint stress paradigm. The study shows that stress caused remodelling of the pyramidal neurons by significantly reducing the number of dendritic branch points and total length of the apical dendritic tree. Concomitant administration of ECSs prevented these effects. ECSs had no effect on pyramidal neuron dendrites in normal rats.

In vivo cellular uptake of glutamate is impaired in the rat hippocampus during and after transient cerebral ischemia: a microdialysis extraction study

Using microdialysis in CA1 of the rat hippocampus, we studied the effect of transient cerebral ischemia on in vivo uptake and on extracellular levels of glutamate during, and at different time points after ischemia. (3)H-D-aspartate (test substance), and (14)C-mannitol (reference substance), were added to the dialysis perfusate, and the cellular extraction of (3)H-D-aspartate was calculated from scintillation analysis of fractionated dialysate samples. The extraction of (3)H-D-aspartate was studied both in a tracer like condition with a perfusate concentration of 0.2 microM, and in a condition of high saturation level, with 1.0 mM D-aspartate added to the perfusate. In between radioisotope perfusions, dialysate was sampled for analysis of amino acid content by HPLC. During ischemia, extraction of (3)H-D-aspartate (0.2 microM) declined to a maximum reduction of 68%. In the hours after ischemia, extraction of (3)H-D-aspartate (0.2 microM) was decreased by 32%. In the days after ischemia, there was a progressive decline in extraction of (3)H-D-aspartate (1.0 mM), reaching a reduction of 89% on Day 4 after ischemia. Extracellular glutamate remained at control levels at all time points after ischemia. The present study is the first to investigate uptake of glutamate in the intact rat brain in relation to cerebral ischemia. Evidence is provided that uptake of Glu is restrained during ischemia, and that in the hours after ischemia, the extracellular turnover of glutamate is decreased. In the course of the days after ischemia, degeneration of CA1 pyramidal cells occurs concomitantly with a progressive decline in glutamate transport ability, possibly of pathogenetic importance to CA1 pyramidal cell loss.

Intracerebroventricular metformin attenuates salt-induced hypertension in spontaneously hypertensive rats

The aim of this study was to examine the effects of long-term continuous intracerebroventricular (icv) infusion of metformin on blood pressure (BP) in spontaneously hypertensive rats (SHR). To accelerate the development of hypertension, SHR were fed a 8% NaCl diet during the 3-week study period. Metformin was given in the following doses: 0 (isotonic saline; n = 7), 25 (n = 8), 50 (n = 6), 100 (n = 6), and 200 microg/day icv (n = 5). Mean arterial pressure (MAP) and heart rate (HR) were measured by radiotelemetry, and as a measure of the contribution of sympathetic nerve activity to BP, the decrease in MAP in response to ganglionic blockade with hexamethonium, 30 mg/kg iv, was determined once weekly. In vehicle treated rats, MAP increased by 27+/-4 mm Hg, whereas in rats treated with a low dose of metformin (25 microg/day), MAP increased only by 7+/-3 mm Hg (P < .01). The hypotensive response to hexamethonium was attenuated by all doses of metformin suggesting that chronic icv metformin decreased central sympathetic outflow. The highest doses of metformin (100 and 200 microg/day) also prevented development of hypertension, but these doses were highly neurotoxic as demonstrated by histologic evaluation post mortem. Fast-Fourier transformation of MAP revealed increased variability within the 0.15 to 0.6 Hz frequency range in rats treated with neurotoxic doses of metformin, suggesting impaired sympathetic control of BP in these animals. In conclusion, long-term icv infusion with apparently nontoxic doses of metformin attenuates hypertension and decreases the hypotensive responses to ganglionic blockade in SHR, suggesting a centrally elicited sympathoinhibitory action.

Changes in gene expression following induction of ischemic tolerance in rat brain: detection and verification

Tolerance against ischemic insults can be elicited in the CA1 region of rat hippocampus by inducing a short ischemic period 2-3 days prior to the ischemic insult. To detect genes whose expression changes following induction of ischemic tolerance (IT), we applied a differential display technique called restriction fragment differential display-PCR (RFDD-PCR). RFDD-PCR displays the coding region of mRNA and allows detection of differentially expressed mRNA. Double-stranded cDNA generated using a T25V primer is digested by the endonuclease TaqI, and adapters are ligated onto the cDNA fragments. When amplifying the adapter-containing cDNA fragments under high-stringency conditions, reproducible PCR profiles are obtained. By comparing these profiles from naïve and ischemia-tolerant rat brains statistically, significant expression changes of 20 fragments were identified. To verify the observed changes, quantitative PCR and in situ hybridization were performed for three fragments representing proteins with quite different functions (GluR2-flop, SC1, and p68 RNA helicase). Quantitative PCR displayed the same degree of regulation as RFDD-PCR, but in situ hybridization did not display any regulation. As the applied PCR-based techniques detect only polyadenylated mRNA, whereas in situ hybridization detects both nonadenylated and adenylated mRNA, changes in the polyadenylation state of the mRNA, rather than inconsistent changes in the total amount of mRNA, probably explain this discrepancy. Thus, our results show that the expression of genes hitherto not related to IT changes with the induction of IT and that the degree of regulation displayed by RFDD-PCR can be verified by quantitative PCR.

Focal cerebral ischemia induces increased myelin basic protein and growth-associated protein-43 gene transcription in peri-infarct areas in the rat brain

Although oligodendrocytes are vulnerable to focal cerebral ischemia, remyelination of denuded or regenerating axons in the peri-infarct area has been observed in the central nervous system. We studied the expression of myelin basic protein (MBP), a major component of central nervous system myelin, in peri-infarct areas in adult rat brain after transient middle cerebral artery occlusion (MCAO) and correlated it to the expression of the growth-associated protein-43 (GAP-43), a marker for axonal regeneration and sprouting, using non-radioactive in situ hybridization techniques. Within the infarct, MBP messenger RNA (mRNA) had disappeared by 24 h, whereas myelin protein, identified by MBP and myelin oligodendrocyte glycoprotein (MOG) immunohistochemistry, appeared structurally intact until day 3. Peri-infarct oligodendrocytes increased their expression of MBP mRNA from 24 h to maximal levels at day 7, corresponding to the appearance of process-bearing MBP and occasional MOG-immunoreactive oligodendrocytes in parallel sections. Quantitative analysis revealed significant increases in the density of oligodendrocytes (up to 7.6-fold) and in the level of MBP mRNA expressed by individual cells. Parallel sections showed that increased expression of GAP-43 mRNA in neurons was concomitant to MBP mRNA upregulation in oligodendrocytes. While the mechanisms regulating oligodendrocyte survival and myelination signals are not clear at this point, axonal sprouting could putatively serve as a stimulus for the upregulation of oligodendrocyte cell numbers, differentiation state, and/or active myelination in the peri-infarct areas.

Is the AMPA receptor subunit GluR2 mRNA an early indicator of cell fate after ischemia? A quantitative single cell RT-PCR study

After a moderate global cerebral ischemia, two hypothetical populations of pyramidal neurons are present among the hippocampal CA1 pyramidal neurons: one that will die and another one that will survive. Prior analysis of dissected hippocampal CA1 regions has shown a reduction of the GluR1-3 mRNA following ischemia. In order to identify these changes in single neurons, quantitative single cell RT-PCR was used to analyze the expression of GluR1-4 mRNA in rats 24 h after ischemia and also in rats after tolerance inducing ischemia. Control CA1 cells had a median copy-number of 290, 247, 207 and 16 GluR1-4, respectively. The tolerant cells showed small significant up-regulations of GluR1, 3 and 4 mRNA, while the GluR2 mRNA showed a more than 4-fold up-regulation compared to control cells. All the cells from ischemic animals displayed down-regulations of GluR1-3 mRNA. The GluR4 mRNA was not detectable in the ischemic animals. Our results thus show that the CA1 neurons react uniformly 24 h after a moderate ischemia independent of the fate of the neuron: thus two neuron populations with different GluR2 profiles cannot be identified in post-ischemic animals at 24 h. It seems however that an increased level of GluR2 can be used as an indicator of tolerance to ischemia.

GABAA receptor antisense epilepsy: histological changes following infusion of antisense oligodeoxynucleotide to GABAA receptor gamma 2 subunit into rat hippocampus

A deficiency of neuronal inhibition mediated by gamma-aminobutyric acid (GABA) via the GABAA receptor complex has been hypothesised to be a central factor in epileptogenesis. Intrahippocampal infusion of antisense oligodeoxynucleotide (ODN) to the GABAA receptor gamma 2 subunit in rats leads to electrographic limbic status epilepticus. In this model, epileptic phenomena are accompanied by loss of hippocampal neurones. The purpose of the present study was to investigate the time-course of morphological changes following hippocampal antisense 'knockdown' of the GABAA receptor gamma 2 subunit. gamma 2 subunit antisense ODN was infused continuously into the right hippocampus for periods between 1 and 5 days. After about 4 days of infusion, pronounced neurodegenerative changes were consistently observed within the ipsilateral hippocampus. In general, marked loss of CA3 pyramidal cells was found. The notion that the histological changes induced by the antisense ODN were specific to the applied ODN sequence was supported by the finding that a mismatch control ODN did not induce neurodegenerative changes, except for a small lesion in the immediate vicinity of the infusion site. Extensive ipsilateral hippocampal infiltration with monocytes and macrophages was a feature of antisense ODN infusion, but was considerably less pronounced after the infusion of control ODN. Immunocytochemistry using an antibody labeling glial fibrillary acidic protein (GFAP), revealed marked astroglial hypertrophy/proliferation after 4 days of antisense treatment, i.e., coincident with the development of neurodegeneration, in the ipsilateral hippocampus. At this time GFAP-immunoreactivity was also evident in the contralateral hippocampus, indicating contralateral spread of seizure activity.

Ischemic tolerance affects the adenylation state of GluR2 mRNA

To analyse GluR2 regulations in the rat hippocampal CA1 region following global and tolerance-inducing ischemia in situ hybridization (ISH) and quantitative PCR (Q-PCR) was applied. In addition, cDNA was synthesised from two different primer combinations in order to elucidate possible differences in the adenylation state of GluR2 mRNA. Following global ischemia, ISH and Q-PCR both showed reductions to half of control levels of GluR2 mRNA in consent with previously published results. Following tolerance induction, ISH showed no changes, whereas PCR analysis showed up-regulation to 228% of control value for the general cDNA synthesis, and no change for the specific cDNA synthesis. This indicates that tolerance-inducing ischemia does not increase the amount of GluR2 mRNA; instead polyadenylation of the existing GluR2 mRNA pool takes place.

Is the 5-HT2C receptor a therapeutic target in cerebral ischaemia?

This study examines the effect of a 5-HT2C agonist (RO 60-0175, (s)-2-(chloro-5-fluoro-indol-1-yl)-1-methylethylamine) and a 5-HT2C antagonist (RO 43-0440, benzofuran-2-carboxamidine) for neuroprotective activity in a rat model of global cerebral ischaemia. A mini-osmotic pump implanted subcutaneously delivered 0.25 mg/kg/hr. Seven days after ischaemia the rats were sacrificed and the damage in the CA1 pyramidal cell layer in hippocampus was estimated and the treated groups were compared with vehicle groups. Pretreatment with the 5-HT2C agonist RO 60-0175 significantly increased the damage, whereas the 5-HT2C antagonist RO 43-0440 had no effect on the cell damage. Measurement of the core temperature in a RO 60-0175-treated group of rats revealed no effect compared to a vehicle-treated group. Thus the aggravation of damage in the RO 60-0175-treated group cannot be explained by temperature effect. Our data do not indicate the 5-HT2C receptor as a therapeutic target in cerebral ischaemia.

Ischemia induced changes in expression of the astrocyte glutamate transporter GLT1 in hippocampus of the rat

Changes in cellular uptake of glutamate following transient cerebral ischemia is of possible importance to ischemia induced cell death. In the present study, we employed in situ hybridization and immunohistochemistry to investigate the influence of cerebral ischemia on expression of mRNA and protein of the astrocyte glutamate transporter GLT1, and of glial fibrillary acidic protein. Different subfields of CA1 and CA3 of the rat hippocampus were studied at various time-points after ischemia (days 1, 2, 4, and 21). In CA1, GLT1-mRNA was decreased at all time-points after ischemia except from day 2, whereas in CA3, decreases were seen only on day 1. Expression of GLT1-protein in CA1 was unchanged during the initial days after ischemia, but decreased markedly from day 2 to 4. In CA3, GLT1-protein increased progressively throughout the observation period after ischemia. Following the degeneration of CA1 pyramidal cells, a positive correlation between the number of CA1 pyramidal cells and expression of either GLT1-mRNA or -protein was evident selectively in CA1. Increases in expression of mRNA and protein of glial fibrillary acidic protein were present from day 2, most notable in CA1. The present data provide evidence that expression of GLT1 in CA1 of the hippocampus is not decreased persistently before the degeneration of CA1 pyramidal cells, but is downregulated in response to loss of these neurons. Since the reduction in GLT1 expression evolved concomitantly with the degeneration of CA1 pyramidal cells, it may contribute to the severity of CA1 pyramidal cell loss. A progressive postischemic increase in GLT1 expression in CA3 may be linked to the resistance of CA3 neurons to ischemic cell damage.

GluR2 protein synthesis and metabolism in rat hippocampus following transient ischemia and ischemic tolerance induction

In this study we have determined the metabolic half-life, protein synthesis and expression of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subunit GluR2 in the hippocampus of the living rat. Synthesized proteins were pulse labeled in vivo using intracarotid infusion or intrahippocampal injection of L-[(35)S] labeled amino acids, and the GluR2 protein immunoprecipitated in order to measure the tracer incorporation at different survival time-points. A limited time course study suggested a metabolic half-life of 144 and 108 h in the CA1 region in control animals following carotid artery infusion and intrahippocampal injection, respectively. Twenty-four hours following a moderate ischemic insult, GluR2 protein synthesis was decreased significantly in both the CA1 and DG/CA3 region, whereas the total protein synthesis was decreased significantly only in the CA1 region. Twenty-four hours following ischemic tolerance induction, a significant increase in GluR2 expression was found in the CA1 region using quantitative Western blotting, while no change was found in the dentate gyrus (DG)/CA3 or in expression of GluR1 protein. Data from labeling experiments did not reveal the reason for the increased amount of GluR2 in the CA1 region of the tolerant animals. This study shows that following global ischemia the GluR2 synthesis is decreased both in the CA1 and DG/CA3, which, together with the found GluR2 metabolic half-life, contradict a selective loss of GluR2 protein as a triggering mechanism for the delayed CA1 pyramidal cell death. Twenty-four hours following tolerance induction, we found an increased GluR2 expression in the CA1 region, suggesting that GluR2 plays a role in the acquisition of ischemic tolerance. Our study suggests the ability of neurons to regulate the AMPA receptor subunit expression through changes in protein synthesis and stability.

Neuroprotective effect of 8-OH-DPAT in global cerebral ischemia assessed by stereological cell counting

The neuroprotective effect of the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) was tested in a 2-vessel occlusion model in rats. The post-ischemic core temperature was carefully monitored for 24 h. After 7 days of survival, the viable CA1 neurons were counted in an 8-OH-DPAT (125 microg/kg/h) and vehicle-treated group using the optical fractionator method. The vehicle-treated ischemic rats had a median number of dorsal CA1 neurons of 49,900 whereas the 8-OH-DPAT-treated ischemic rats had a significant lower median number of dorsal CA1 neurons 105,200 (P=0. 018). 8-OH-DPAT significantly lowered the core temperature compared to the vehicle-treated group during the 24-h post-ischemic period. Hypothermia is proposed as a possible explanation of the neuroprotective effect of 8-OH-DPAT.

Reduced [3H]IP3 binding but unchanged IP3 receptor levels in the rat hippocampus CA1 region following transient global ischemia and tolerance induction

Changes in inositol (1,4,5)-trisphosphate (IP3) binding properties and the protein level of the IP3 receptor have been reported in different pathological conditions in the brain, e.g. cerebral ischemia, Alzheimer's disease, and Huntingtons disease. We used the 4-vessel occlusion model in rat brain to investigate the effect of transient ischemia insults on the IP3 receptor mRNA level, the IP3 receptor protein level and [3H]IP3 binding. Recirculation periods were limited (1-72 h) to avoid the development of delayed neuronal death. We found that the IP3 receptor mRNA levels were decreased after damage-inducing ischemia (9 min) in the hippocampus CA1 and CA3 regions. The mRNA levels were unaltered after tolerance-inducing ischemia (3 min). However, [3H]IP3 binding was significantly reduced after both damage- and tolerance-inducing ischemia in the hippocampus CA1 region. Furthermore, all investigated brain areas showed a decreased [3H]IP3 binding when tolerance-inducing ischemia was followed by a second ischemic insult (3 + 8.5 min ischemia). The IP3 receptor protein levels remained constant in all investigated brain areas. These results indicate that a reduced [3H]IP3 binding capability in the particularly vulnerable areas occurs as an early consequence of cerebral ischemia, before IP3 receptor protein levels are reduced in these areas. Structural or conformational changes altering IP3 binding may be of necessity on the pathway leading to down-regulation of IP3 receptor protein levels, as observed by others.

Quantitative PCR analysis of AMPA receptor composition in two paradigms of global ischemia

Quantitative PCR was used to analyse the expression of GluR1, GluR2, GluR2 flip, GluR2 flop and GluR3 mRNA in animals after ischemia and tolerance-inducing ischemia. The ischemic animals showed a decrease in the GluRs to approximately 30%, except for GluR2-flip, which decreased to 75%. The tolerance animals displayed regulation of GluR1 to 75%, GluR2 and GluR2-flop to 283% and 265% respectively. We did not find a correlation between GluR2 regulation and cell loss in the ischemic group. The selective upregulation of GluR2/GluR2 flop in tolerant animals indicates a possible mechanism for enhanced AMPA receptor desensitisation leading to tolerance to ischemia.

Secretory phospholipase A2 potentiates glutamate-induced rat striatal neuronal cell death in vivo

The secretory phospholipases A2 (sPLA2) OS2 (10, 20 and 50 pmol) or OS1, (50 pmol) purified from taipan snake Oxyuranus scutellatus scutellatus venom, and the excitatory amino acid glutamate (Glu) (2.5 and 5.0 micromol) were injected into the right striatum of male Wistar rats. Injection of 10 and 20 pmol OS2 caused no neurological abnormalities or tissue damage. OS2 (50 pmol) caused apathy and circling towards the injection side. Histology revealed an infarct at the injection site. Injection of 50 pmol OS1 showed very little or no signs of neurotoxicity. Injection of 2.5 micromol Glu caused no tissue damage or neurological abnormality. After injection of 5.0 micromol Glu, the animals initially circled towards the side of injection, and gradually developed generalized clonic convulsions. These animals showed a well demarcated striatal infarct. When non-toxic concentrations of 20 pmol OS2 and 2.5 micromol Glu were co-injected, a synergistic neurotoxicity was observed. Extensive histological damage occurred in the entire right hemisphere, and in several rats comprising part of the contralateral hemisphere. These animals were apathetic in the immediate hours following injection, with circling towards the side of injection in the following days. Thus, OS2 greatly potentiates glutamate excitoxicity in vivo.

Double-tracer autoradiographic study of protein synthesis and glucose consumption in rats with focal cerebral ischemia

A double-tracer autoradiographic method for simultaneous measurement of regional glucose utilization (rCMRglc) and regional protein synthesis (PS) in consecutive brain sections is described and applied to study the metabolism of the ischemic penumbra 2 h after occlusion of the middle cerebral artery (MCAO) in rats. In halothane anesthesia, the left middle cerebral artery was permanently occluded. Two hours after MCAO an i.v. bolus injection of 14C-deoxyglucose and 3H-leucine was given and circulated for 45 min. Two sets of brain sections were processed for quantitative autoradiography. Neighboring brain sections exposed an X-ray film (3H-insensitive), and a 3H-sensitive for determination of rCMRglc and PS, respectively. Sections for PS determination were washed in trichloroacetic acid (TCA) prior to film exposure in order to remove 14C-deoxyglucose and unincorporated 3H-leucine. Regional rates of PS and glucose utilization were measured by densitometric image analysis. Normal rates of metabolism were defined as mean +/- 2 SD of values in the non-ischemic cortex. The volumes of ischemic cortex displaying normal rates of PS and glucose utilization, respectively, were measured. The cortical volume with normal PS was significantly less than that of normal rCMRglc: 142 (127-147) mm3 vs. 203 (184-206) mm3. Treatment with the glutamate antagonists MK-801 (1 mg kg-1) and NBQX (30 mg kg-1 x 2) did not significantly change this, although MK-801 tended to reduce the size of the metabolic penumbra calculated as the difference between ischemic cortex with reduced PS and ischemic cortex with reduced rCMRglc.

Characterization of a new AMPA receptor radioligand, [3H]2-amino-3-(3-carboxy-5-methyl-4-isoxazolyl)propionic acid

(RS)-2-Amino-3-(3-carboxy-5-methyl-4-isoxazolyl)propionic acid (ACPA), which is a potent and selective agonist at (RS)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptors, has previously been shown to desensitize AMPA receptors to a much lower degree than AMPA itself. We now report the synthesis of [3H]ACPA (32.5 Ci/mmol), the neurochemical and pharmacological characterization of [3H]ACPA binding, and a comparison of the distribution of [3H]ACPA, [3H]AMPA, and [3H](S)-5-fluorowillardiine binding sites in rat brain. Under equilibrium conditions, [3H]ACPA was shown to bind to a single population of receptor sites on rat brain membranes. [3H]ACPA was shown to bind with single and similar affinities (15-45 nM) to cloned AMPA receptor subunits (GluR1-4), expressed in insect cells, whereas a K(D) value of 330 nM was determined for the binding of [3H]ACPA to cloned kainic acid preferring GluR5 subunits. Whereas Bmax and K(D) values for [3H]ACPA binding, determined using filtration techniques, were different from such obtained in centrifugation assays, Bmax and K(D) values as well as association and dissociation constants were not significantly affected by the addition of the chaotropic agent KSCN. K(D) values, determined under equilibrium conditions, were, however, markedly different from K(D) values derived from kinetic data. Furthermore, the results of analyses of these kinetic data were consistent with the existence of two different populations of [3H]ACPA binding sites. The pharmacology of [3H]ACPA binding sites was characterized using a series of AMPA receptor agonists and antagonists. Whereas addition of KSCN had little effect on the affinities of AMPA receptor agonists for [3H]ACPA binding, this chaotropic agent reduced the affinities of AMPA receptor antagonists structurally related to AMPA. Based on these and previously reported data, the AMPA receptor agonists, ACPA, AMPA and (S)-5-fluorowillardiine, seem to bind to and activate AMPA receptors in a nonidentical fashion, and these three agonists together may be useful tools for studies of AMPA receptor mechanisms.

Equilibrium binding characteristics of [3H]thiomuscimol

The equilibrium binding characteristics of the tritiated GABAA agonist, 5-aminomethyl-3-isothiazolol (thiomuscimol) are described. Using the filtration technique to separate bound- from free-ligand, [3H]thiomuscimol was shown to bind to the GABA(A) receptor site(s) in a saturable manner with a Kd value of 28+/-6.0 nM and a Bmax value of 50+/-4.0 fmol/mg original tissue. In parallel binding experiments, the Kd and Bmax values for [3H]muscimol were determined to be 5.4+/-2.8 nM and 82+/-11 fmol/mg original tissue, respectively. In binding assays using the centrifugation technique, Kd and Bmax values for [3H]thiomuscimol were found to be 116+/-22 nM and 154 13 fmol/mg original tissue, respectively, whereas a Kd value of 16+/-1.8 nM and a Bmax value of 155+/-8.0 fmol/mg original tissue were determined for [3H]muscimol. In comparative inhibition studies using the GABA(A) antagonist SR 95531 and a series of specific GABAA agonists, the binding sites for [3H]thiomuscimol and [3H]muscimol were shown to exhibit similar pharmacological profiles. Autoradiographic studies disclosed similar regional distribution of [3H]thiomuscimol and [3H]muscimol binding sites in rat brain. Highest densities of binding sites were detected in cortex, hippocampus, and cerebellum, whereas low densities were measured in the midbrain structures of rat cortex. In conclusion, the equilibrium GABA(A) receptor binding characteristics of [3H]thiomuscimol are very similar to those of [3H]muscimol.

Antisense oligonucleotide to GABA(A) receptor gamma2 subunit induces limbic status epilepticus

Gamma-Aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the brain. A deficiency of GABAergic inhibition mediated via the GABAA receptor complex has for a long time been suspected to be a central factor in epileptogenesis. Status epilepticus is a condition of sustained and prolonged excitation of neuronal circuits, as detected by epileptiform discharges in the electroencephalogram (EEG). Reduction of GABAA receptor-mediated hippocampal inhibition has been implicated in the development of status epilepticus. The present study provides direct evidence of a link between the GABAA receptor and epilepsy. We show that selective inhibition of the expression of the GABAA receptor gamma2 subunit in the rat hippocampus by means of antisense oligonucleotides leads to spontaneous electrographic seizures that evolve into profound limbic status epilepticus, ultimately resulting in severe neurodegenerative changes. Concurrent treatment with diazepam prevents the development of status epilepticus and markedly reduces neuronal cell loss. These findings strongly support the hypothesis that the GABAA receptor is critically involved in the pathogenesis of seizures and status epilepticus.

Microglia and macrophages are major sources of locally produced transforming growth factor-beta1 after transient middle cerebral artery occlusion in rats

The potentially neurotrophic cytokine transforming growth factor-beta1 (TGF-beta1) is locally expressed following human stroke and experimental ischemic lesions, but the cellular source(s) and profile of induction have so far not been established in experimental focal cerebral ischemia. This study presents the time course and a cellular localization of TGF-beta1 mRNA, visualized by in situ hybridization combined with immunohistochemical staining for microglia, macrophages, or astrocytes, on brain sections from adult spontaneously hypertensive rats subjected to transient proximal occlusion of their middle cerebral artery. Six hours after ischemia, an early and transient neuronal and microglial expression of TGF-beta1 mRNA was observed in the extraischemic cingulate and frontal cortices. Both early and protracted expression of TGF-beta1 mRNA in the caudate-putamen and neocortical infarcts and in the caudate-putamen penumbra colocalized with OX42/ED1-immunoreactive microglia and macrophages, whereas TGF-beta1 mRNA in the neocortical penumbra colocalized with OX42/ED1-immunoreactive cells of a microglial morphology. No astrocytes were double-labeled. The number of TGF-beta1 mRNA-expressing microglia and macrophages increased strongly during the first week. Thereafter, TGF-beta1 mRNA became increasingly restricted to the neocortical penumbra (3 weeks), and after 3 months it was confined to activated microglia in the anterior commissure. Our data establish activated microglia and macrophages as the major source of TGF-beta1 mRNA following experimental focal cerebral ischemia. Consequently, TGF-beta1-mediated functions may be exerted by microglia both in the early degenerative phase, and later in combination with blood-borne macrophages, in the remodeling and healing phase after focal cerebral ischemia.

Microglial and macrophage reactions mark progressive changes and define the penumbra in the rat neocortex and striatum after transient middle cerebral artery occlusion

Transient middle cerebral artery occlusion in rats leads to infarction of the lateral part of the striatum and adjacent neocortex, with selective neuronal necrosis in the bordering penumbral zones. Administration of glutamate, cytokine, and leukocyte antagonists have rescued mainly neocortical neurons, indicating differences in the degenerative processes. The aim of this study was, therefore, to describe the microglial/macrophage activation and polymorphonuclear leukocyte recruitment patterns and to correlate these with the ischemia-induced degenerative processes. The analysis showed significant differences in the characteristics and timing of the microglial/macrophage responses between the caudate putamen and neocortical infarct zones, the infarct zones and their associated penumbral zones, as well as between the striatal and the neocortical penumbral zone. Infiltrations with polymorphonuclear leukocytes into the infarct zones were limited and shortlasting and confined to the acutely degenerating striatum and piriform cortex. A delayed, massive infiltration with lipid phagocytes into the caudate putamen infarct markedly contrasted an early recruitment and activation of microglia/macrophages in the adjacent penumbra. Within the neocortex, a later onset of degeneration along the insular-parietal axis was marked by neuronal expression of heat shock protein and a progressive microglial activation with induction of the full repertoire of microglial activation markers, including a widespread microglial major histocompatibility complex (MHC) class II antigen expression. We interpret the present results as delineating two differentially progressing penumbral zones, which are likely to reflect differences in the underlying degenerative processes. Differences in the microglial/macrophage activation pattern attract special attention, as these cells may constitute specific targets for therapeutic intervention.

Serotonin1A receptor autoradiography during alcohol-withdrawal kindling

A series of autoradiography experiments were conducted in order to test the theory that the serotonin (5-HT) receptor subtype 5-HT(1a) is involved in alcohol-withdrawal kindled convulsive behaviour. Alcohol-withdrawal kindling was performed by subjecting male Wistar rats to multiple episodes consisting of 2 days of alcohol intoxication and 5 days of alcohol withdrawal. In the first episode alcohol intoxication led to focal downregulation of [3H]-8-hydroxy-2-(di-n-propylamino)tetralin ([3H]-8-OH-DPAT) binding sites in septum and subregions of frontal cortex, hippocampus, and entorhinal cortex. This alcohol-induced response was blunted in both alcohol-withdrawal kindled animals and in animals exposed to repeated alcohol dependence in which the previous withdrawal reactions were blocked by diazepam administration. A paradoxical upregulation of [3H]-8-OH-DPAT binding sites was found in septum and subregions of frontal cortex, hippocampus, and entorhinal cortex in control animals which were fed isocalorically with the alcohol-withdrawal kindled animals and subsequently exposed to 2 days of alcohol intoxication. It was concluded that the alterations in the alcohol induced 5-HT(1a) receptor regulation after multiple episodes of alcohol dependence were not caused by alcohol-withdrawal kindling processes per se, but were due to both alcohol specific and alcohol non-specific effects.

Ischemia changes the coexpression of somatostatin and neuropeptide Y in hippocampal interneurons

Transient cerebral ischemia causes extensive cell death in hippocampal CA1 pyramidal cells and selective loss of interneurons in the dentate hilus. Many hippocampal interneurons can be classified by their contents of somatostatin (SS) and/or neuropeptide Y (NPY). Following ischemia in the rat, most of the NPY immunoreactivity is permanently lost in hippocampus. Furthermore, SS interneurons in the dentate hilus die, whereas CA1 interneurons survive and their expression of SS mRNA and peptide returns to preischemic levels within 16 days after ischemia. We have addressed the following questions: (1) Does the loss of NPY involve a specific downregulation in surviving CA1 interneurons that pre-ischemically expressed both SS and NPY? (2) Can the subpopulation of dying interneurons in hilus be identified from their preischemic coexpression of SS and NPY? We investigated the coexpression of SS mRNA and NPY peptide using combined in situ hybridization and immunocytochemistry. Cells containing one or both markers were counted in control sections and sections taken 2-16 days after ischemia from the hippocampal formation. In CA1, a decrease in the number of neurons containing NPY alone as well as a decrease in the number of neurons coexpressing NPY and SS was observed, whereas the number of neurons containing SS alone increased 16 days after ischemia. We conclude that neurons coexpressing SS and NPY before ischemia added to the number of neurons containing SS alone after ischemia, because NPY expression was selectively down regulated in the coexpressing population. In hilus, we demonstrated both survival and ischemic cell death of neurons expressing either SS, NPY or both, indicating that hilar interneurons dying from ischemia cannot unequivocally be identified from their preischemic colocalization of SS and NPY.

Effects of the AMPA-receptor antagonist, NBQX, on neuron loss in dentate hilus of the hippocampal formation after 8, 10, or 12 min of cerebral ischemia in the rat

The alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA) receptor antagonist, 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX), offers protection to hippocampal CA1 pyramidal cells after short episodes of transient cerebral ischemia. Besides CA1 pyramidal cells, neurons containing somatostatin (SS) and located in the dentate hilus of the hippocampal formation are lost after cerebral ischemia. We studied the protective effects of NBQX on SS neurons in the hilus and on hippocampal CA1 pyramidal cells following 8, 10, or 12 min of four-vessel occlusion ischemia during systemic hypotension. NBQX was administered 3 x 30 mg/kg at 0, 10, and 25 after induction of ischemia or sham, and all rats survived for 7 days. NBQX given to control rats without ischemia had no influence on number or morphology of hilar SS neurons and CA1 pyramidal cells. After 8 min of ischemia, NBQX prevented loss of hilar SS neurons. After 10 and 12 min of ischemia, NBQX had no significant effects on loss of SS neurons in the dentate hilus. However, in all ischemic groups, NBQX significantly reduced loss of CA1 pyramidal cells as compared to control rats. This neuroprotective effect decreased gradually and significantly as the time of ischemia increased. Our results support the observation that SS neurons in hilus are among the most ischemia-vulnerable neurons in the brain. We found that administration of NBQX in generally accepted dosages can protect the rapidly dying SS neurons in hilus from only brief episodes of ischemia.

Evidence for increased cellular uptake of glutamate and aspartate in the rat hippocampus during kainic acid seizures. A microdialysis study using the "indicator diffusion' method

Using a newly developed technique, based on microdialysis, which allows cellular uptake of glutamate and aspartate to be studied in awake animals, we investigated uptake of glutamate and aspartate in the hippocampal formation of rats during limbic seizures induced by systemical administration of kainic acid (KA). With [14C]mannitol as an extracellular reference substance, the cellular extraction of the test substance [3H]D-aspartate was measured at different stages of seizure-activity. The results were compared to those obtained in a sham operated control group. During severe generalized clonic seizures, the extraction of [3H]D-aspartate was increased by 17%. The increase in uptake of [3H]D-aspartate was accompanied by a 24% increase in the extracellular level of aspartate, as obtained by conventional microdialysis. No significant changes were observed in the extracellular level of glutamate. The results indicate that during KA-induced seizures, uptake of glutamate and aspartate is increased, possibly aimed at maintaining the extracellular homeostasis of these two excitatory amino acids.

Effects of phenylsuccinate on potassium-stimulated taurine release in cultured neurons and astrocytes and in rat hippocampus in vivo

Swelling-induced release of taurine was investigated in vivo in hippocampus by microdialysis or in vitro in cultured neocortical neurons or astrocytes. Swelling was induced either by increasing the extracellular K+ concentration or by exposing the cells to hyposmotic conditions. It was found that the drug phenylsuccinate, which inhibits the mitochondrial dicarboxylate carrier as well as biosynthesis of neurotransmitter glutamate, inhibits swelling-induced taurine release both in vivo and in cultured cells. Thus, phenylsuccinate may be used to investigate the mechanism involved in taurine release associated with regulatory volume decrease in cells.

Glutamate and benzodiazepine receptor autoradiography in rat brain after repetition of alcohol dependence

During repeated alcohol withdrawal, convulsive withdrawal behavior has been shown to be increased in a kindling-like manner in both clinical and experimental studies. In the present experiment, quantitative autoradiography was used to investigate binding of tritiated ligands to glutamate receptor subtypes and the benzodiazepine/GABA (BZ/GABA) receptor complex in rats exposed to 14 episodes of alcohol withdrawal. Seizures were detected in 25% of the animals during withdrawal episode 10-13. Repeated alcohol withdrawal resulted in a decrease in the number of [3H]-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ([3H]-AMPA) binding sites in striatum and sub-regions of the entorhinal cortex, the cerebellum and the hippocampus, while the [3H]-flunitrazepam binding was down-regulated in the frontal cortex. There was no differences between the controls and the multiple withdrawal animals regarding the [3H]-dizocilpine ([3H]-MK801) binding and the [3H]-kainic acid binding. However, within the latter group, those animals in which withdrawal seizures were observed had increased [3H]-MK801 binding sites in focal regions of entorhinal cortex and hippocampus, compared to those in which seizures were not observed. The decreased AMPA binding suggested impaired glutamate neurotransmission. As such, this receptor probably did not contribute to alcohol withdrawal kindling, but rather was involved in seizure protective mechanisms during this process.

Exercise-induced changes in local cerebral glucose utilization in the rat

In exercise, little is known about local cerebral glucose utilization (LCGU), which is an index of functional neurogenic activity. We measured LCGU in resting and running (approximately 85% of maximum O2 uptake) rats (n = 7 in both groups) previously equipped with a tail artery catheter. LCGU was measured quantitatively from 2-deoxy-D-[1-14C]glucose autoradiographs. During exercise, total cerebral glucose utilization (TCGU) increased by 38% (p < 0.005). LCGU increased (p < 0.05) in areas involved in motor function (motor cortex 39%, cerebellum approximately 110%, basal ganglia approximately 30%, substantia nigra approximately 37%, and in the following nuclei: subthalamic 47%, posterior hypothalamic 74%, red 61%, ambiguous 43%, pontine 61%), areas involved in sensory function (somatosensory 27%, auditory 32%, and visual cortex 42%, thalamus approximately 75%, and in the following nuclei: Darkschewitsch 22%, cochlear 51%, vestibular 30%, superior olive 23%, cuneate 115%), areas involved in autonomic function (dorsal raphe nucleus 30%, and areas in the hypothalamus approximately 35%, amygdala approximately 35%, and hippocampus 29%), and in white matter of the corpus callosum (36%) and cerebellum (52%). LCGU did not change with exercise in prefrontal and frontal cortex, cingulum, inferior olive, nucleus of solitary tract and median raphe, lateral septal and interpenduncular nuclei, or in areas of the hippocampus, amygdala, and hypothalamus. Glucose utilization did not decrease during exercise in any of the studied cerebral regions. In summary, heavy dynamic exercise increases TCGU and evokes marked differential changes in LCGU. The findings provide clues to the cerebral areas that participate in the large motor, sensory, and autonomic adaptation occurring in exercise.

Differential effect of NMDA and AMPA receptor blockade on protein synthesis in the rat infarct borderzone

We investigated whether the known neuroprotective effects of two selective glutamate receptor antagonists, the NMDA antagonist MK-801 and the AMPA antagonist NBQX, are reflected in the regional cerebral protein synthesis rates (CPSR) in rats with middle cerebral artery occlusion (MCAO). Rats treated with either saline, MK-801 (5 mg/kg i.p.) or NBQX (30 mg/kg i.p. x 3) were subjected to permanent MCAO. Regional CPSR and volumes of gray matter structures displaying normal CPSR were measured in coronal cryosections of the brain by quantitative autoradiography following an i.v. bolus injection of 35S-labelled L-methionine 2 h after occlusion. MCAO completely inhibited protein synthesis in the lateral part of striatum and part of the adjacent frontoparietal cortex corresponding to the ischemic focus. Surrounding this, a metabolic penumbra with approximately 50% reductions in CPSR was present. Treatment with MK-801 significantly increased the volume of tissue with normal CPSR in the ischemic hemisphere compared to controls, whereas this was not seen with NBQX treatment. The results suggest that MK-801 and NBQX have different effects on peri-infarct protein synthesis after MCAO. Since both compounds reduce infarct size, it is questionable that acute inhibition of protein synthesis in focal ischemia is of significant importance to the final outcome of a stroke lesion.

Extended studies on the effect of glutamate antagonists on ischemic CA-1 damage

Glutamate receptors are numerous on the ischemia vulnerable CA-1 pyramidal cells. Postischemic use of the AMPA antagonist NBQX has shown up to 80% protection against cell death. Three aspects of this were studied: In the first study, male Wistar rats were given NBQX (30 mg/kg x 3) either 20 hours or immediately (0 h) before 12 min of 4-vessel occlusion with hypotension. After six days of reperfusion comparison with an untreated group showed almost full protection in the 0 h group (4% cell loss, p < 0.001) but only slight protection in the 20 h group (62% cell loss, p < 0.05). After 12 min of ischemia in the present model, eosinophilic CA-1 cells are seen from day 2 on. Since there could be a late, deleterious calcium influx via NMDA receptors, one group of ischemic rats was given MK-801 (5 mg/kg i.p.) 24 hours after ischemia. However, quantitation 6 days later of remaining CA-1 cells showed no protection. In the third study referred here, two groups of ischemic rats were given NBQX (30 mg/kg x 3) immediately after ischemia. The groups survive for six and 21 days, respectively. Counting of CA-1 pyramidal cells showed an equal, significant protection in both groups (approx 20% cell loss).

Alterations in MAP2 immunostainability after prolonged complete brain ischaemia in the rat

Immediate loss of MAP2 immunostainability after very short ischaemic periods (3-5 min) has been reported in the gerbil. With longer periods of ishaemia this loss of immunoreactivity becomes identical with the pattern of ischaemia-induced selective neuronal injury. In contrast, in the four-vessel occlusion rat model, no such changes were observed during the early recirculation period. As no studies have focused on immediate changes due to complete brain ischaemia, we studied MAP2 immunoreactivity in the rat after cardiac arrest for up to 30 min. We observed a moderate decrease in stainability but the changes did not resemble those of selective vulnerability. We conclude that prolonged complete brain ischaemia without recirculation in the rat does not cause selective loss of MAP2 immunostainability in the vulnerable regions.

Unchanged balance between levels of mRNA encoding AMPA glutamate receptor subtypes following global cerebral ischemia in the rat

Transient global ischemia leads to glutamate mediated delayed neuronal death in the CA1 but not in the CA3 region of the rat hippocampus, and changes in AMPA receptor subunit composition has been proposed to cause a difference in excitatory input to the CA1 and CA3 regions. In situ hybridization with riboprobes for AMPA receptor subtype GluR1-4 mRNA was performed on sections from the brain of sham operated and ischemic rats in two models (neck cuff and 4-vessel occlusion combined with hypotension) with identical results: the content of the GluR1-3 mRNA species was down regulated in the hippocampal regions CA1 and CA3 but only weak changes were observed in the dentate gyrus. The down regulation observed in CA1 was non-selective among GluR1-3, i.e. all GluR mRNA species showed approximately the same degree of down regulation. A change in calcium permeability of the AMPA channels mediated by a shift in channel sub-unit composition and corroborating an increased calcium influx is thus not supported by these findings.

Long-term decrease in the hippocampal [3H]inositoltriphosphate binding following repeated electroshock in the rat

A quantitative autoradiographic study was made on the binding of the phosphatidylinositol system ligand [3H]inositol(1,4,5)-triphosphate (IP3) to forebrain sections from electroconvulsive shock (ECS)-treated rats. One group of rats was sacrificed 1 day and 1 month, respectively, after 12 ECSs administered three times weekly for 4 weeks. SHAM-stimulated rats served as controls. A single ECS did not change the [3H]IP3 binding in any of the brain regions examined. One day after the last of 12 ECSs, a decrease in [3H]IP3 binding (21%) was found within the CA1 region of the hippocampus and the piriform cortex (39%). In rats sacrificed 1 month after the last of 12 ECSs, the [3H]IP3 binding in piriform cortex had returned to control level. In the CA1 region of the hippocampus, the binding was still decreased (24%). It is possible that changes in the phosphatidylinositol system may play a part in the neurobiological events responsible for the therapeutic effect of electroconvulsive therapy.

Microdialysis as a tool for in vivo investigation of glutamate transport capacity in rat brain

The role of glutamate as a possible mediator of neurodegeneration is well described, and the homeostasis of extracellular glutamate is considered of major importance when addressing the pathogenesis of excitatory neurodegeneration. Applying the 'indicator diffusion' method to the microdialysis technique, we present a method that is suitable for the in vivo investigation of the capacity of cellular uptake of glutamate. Using 14C-mannitol as reference, we measured the cellular extraction and the cell membrane permeability of the test substance 3H-D-aspartate in the corpus striatum of the rat brain. The cellular extraction fraction of 3H-D-aspartate was 0.29, and the cell membrane permeability 2.24 x 10(-4) cm/s. In the presence of the glutamate-uptake blocker DL-threo-beta-hydroxyaspartate (THA) the extraction of 3H-D-aspartate was completely abolished, indicating that extraction of 3H-D-aspartate was due to cellular uptake by glutamate transporters. The cell membrane permeability towards 3H-D-aspartate was reduced by approximately 98% due to THA, indicating that the cell membranes per se are highly resistant to diffusion of 3H-D-aspartate. It is concluded that the present method can be used in studying the capacity of the glutamate transporters in vivo.

Kainic acid-induced seizures and brain damage in the rat: role of calcium homeostasis

Seizure activity induced by kainic acid (KA) and subsequent neuronal death are thought to be associated with an increase in cytoplasmic free calcium ([Ca2+]i) and can be prevented by N-methyl-D-aspartate (NMDA) antagonists. In addition to influx through receptor operated Ca2+ channels the increase in [Ca2+]i may be the result of an increased influx through voltage-operated calcium channels and/or release from intracellular deposits. It was therefore investigated whether compounds other than NMDA antagonists with known actions on the intracellular Ca2+ homeostasis had any protective effect against KA-induced neuronal death. Voltage-operated calcium channels in the cell membrane were blocked with the L-type ion channel antagonist, Nimodipine (1.0 mg/kg), and release of Ca2+ from internal stores was prevented with Dantrolene (10 mg/kg). Animals from two control groups injected with kainate (8 mg/kg) exhibited a survival rate of 67 and 53%, respectively. Countings of neurons in dorsal hippocampus showed subtotal or total loss in the CA1 and CA3 subregions. There were no significant differences concerning seizure and survival rates in the groups injected with kainate and treated with Dantrolene or Nimodipine and the control groups. The group treated with Dantrolene showed no neuropathological changes in the hippocampal CA3 region and only slight changes in the Ca1 region, while the neuron loss in the Nimodipine group did not differ from that of its control group. The results emphasize the importance of Dantrolene-sensitive Ca2+ release from intracellular stores for the development of seizure-induced neuronal death.

Co-localization of somatostatin mRNA and parvalbumin in the dorsal rat hippocampus after cerebral ischemia

Following transient global ischemia most of the neurons containing somatostatin in the fascia dentata of the dorsal hippocampal formation die, while somatostatinergic neurons in the CA1 region survive. The neurons react to ischemia with a transiently reduced expression of somatostatin mRNA and peptide. We have tested the hypothesis that this selective vulnerability is solely related to those somatostatinergic neurons which do not express the calcium-binding protein parvalbumin. Postischemic changes were studied in rat dorsal hippocampus at 2 and 16 days after 10 min of global cerebral ischemia using a four-vessel occlusion model. We performed a double-staining visualizing the mRNA coding for somatostatin by non-radioactive in situ hybridization and parvalbumin protein by immunocytochemistry. Only 5% of the somatostatinergic cells in the fascia dentata contained parvalbumin. The number of somatostatinergic cells was permanently reduced following ischemia. Among surviving neurons we found cells with and without parvalbumin expression. Thus, expression of parvalbumin is not predictive for survival of somatostatinergic cells in the fascia dentata. In contrast, in CA1, 37% of the somatostatinergic cells contained parvalbumin. These cells were unaffected by the transient ischemic period. The somatostatinergic cells lacking parvalbumin showed transiently reduced mRNA levels at day 2, but recovered to control values at the 16th postischemic day. Thus, expression of the calcium-buffering protein parvalbumin coincides with resistance of somatostatinergic neurons in CA1 to transient effects of ischemia. We conclude that the calcium-buffering capacity of parvalbumin may partially contribute to the protection of somatostatinergic neurons from ischemia in the dorsal hippocampus. However, the survival of somatostatinergic cells without parvalbumin indicates the importance of other factors as well.

Cytokines in cerebral ischemia: expression of transforming growth factor beta-1 (TGF-beta 1) mRNA in the postischemic adult rat hippocampus

Transient global cerebral ischemia induces selective neuronal degeneration in the adult rat hippocampus, which is both preceded and accompanied by activation of microglia and astrocytes. Altered expression patterns of cytokines and growth factors might influence the postischemic neuron-glial interactions as well as the degenerative neuronal processes. Northern blotting of hippocampal tissue from ischemic animals revealed elevated levels of transforming growth factor beta-1 (TGF-beta 1) mRNA, and in the present in situ hybridization study we examine the endogenous expression and cellular localization of TGF-beta 1 mRNA in the adult rat hippocampus at various intervals following 10 min of global cerebral ischemia. Six hours after ischemia, a diffuse expression of TGF-beta 1 mRNA was found throughout the brain, which further intensified until Day 2 and thereafter subsided. In parallel, a massive increase of signal was observed in the hilus fascia dentata from Day 1 and in area CA1 from Day 2 to 4, both areas displaying selective neuronal degeneration. Peak levels of TGF-beta 1 mRNA were found in the hilus around Day 4, whereas expression in the CA1 area persisted through Day 21, the latest time point examined. A similar biphasic response, consisting of a transient, generalized reaction and a persistent lesion-associated activation in areas undergoing selective neuronal degeneration, was previously described for microglia and is reconfirmed in the present study. Cells of the microglial/macrophage lineage thus include the potent modulatory cytokine TGF-beta 1 in their potential repertoire of responses to both CNS activation and lesioning.

Evidence for formation of hydroxyl radicals during reperfusion after global cerebral ischaemia in rats using salicylate trapping and microdialysis

Systemic administration of salicylate (SA) to rats (100 mg kg-1 i.p. ) was used as an in vivo trap of hydroxyl radicals (.OH). In the brain SA reacts with hydroxyl radicals to form the stable adducts 2, 3- and 2,5 dihydroxybenzoic acid (DHBAs) which can thus be taken as an index of .OH formation. The DHBAs were recovered by intracerebral microdialysis in hippocampus or striatum and quantified by high pressure liquid chromatography (HPLC) with electrochemical detection. There were no peaks corresponding to 2,5-DHBA or 2,3-DHBA in the chromatograms from rats not receiving SA. A basal level of 2,5-DHBA was seen in the dialysates from all animals given SA whereas 2, 3-DHBA was not detected. In one group of rats generation of free oxygen radicals was induced in the striatum by adding Fe2+ and ascorbate to the perfusion fluid to test the sensitivity of the system. Addition of Fe2+ ascorbate to the perfusion fluid induced a significant 7-fold increase in 2,5-DHBA that gradually returned to baseline after removal of Fe2+/ascorbate. In two other groups the microdialysis probes were implanted in either the striatum or the hippocampus and the animals were subjected to 20 min of four-vessel occlusion + hypotension (4-VOH). Significant reductions in 2,5-DHBA were detected during ischaemia followed by significant increases of 5-fold and 3-fold in the striatum and hippocampus, respectively, beginning immediately upon reperfusion and lasting for the remainder of the observation period (160 min).

Changes in metabotropic glutamate receptor mRNA levels following global ischemia: increase of a putative presynaptic subtype (mGluR4) in highly vulnerable rat brain areas

Metabotropic glutamate receptors mediate their intracellular response by coupling to G proteins and may be divided into three subfamilies: mGluR1 and mGluR5, which stimulate phosphatidylinositol hydrolysis; mGluR2 and mGluR3, which are negatively coupled to cyclic AMP formation; and mGluR4 and mGluR6, which also inhibit forskolin-stimulated cyclic AMP formation. The mGluR4 subtypes may represent L-2-amino-4-phosphonobutyrate-sensitive presynaptic autoreceptors, and two alternatively spliced variants of the mGluR4 coding for two receptors with different C termini have been identified. Using in situ hybridization, we measured the levels of mGluR1-mGluR5 mRNA in regions of the rat brain 24 h after transient global ischemia, a time point when no neuronal damage can yet be observed morphologically. In the hippocampus, the mRNA levels for mGluR1, mGluR2, and mGluR5 were decreased, mGluR3 mRNA levels were unchanged, and the mGluR4 mRNA levels were strongly increased. The strongest increase appeared to be in the mRNA encoding mGluR4b. The mGluR4 mRNA was also increased in the parietal cortex, whereas the ventral posteromedial thalamic nucleus showed a small decrease in its mRNA content. These results suggest that vulnerable neurons react to an increased extracellular glutamate concentration by differential regulation of the mRNA for pre- and postsynaptically located metabotropic glutamate receptors.

The susceptibility of CA1 pyramidal cells to cerebral ischemia is maintained after neonatal, lesion-induced reorganization of the hippocampal circuitry

Acute lesions of hippocampal pathways have been shown previously to ameliorate CA1 pyramidal cell loss after subsequent transient cerebral ischemia. In this study, we examined the effect of chronic neonatal lesion with reorganization of hippocampal circuitry on adult postischemic neuron loss in the hippocampus. Newborn rats were subjected to unilateral knife-cut lesions at various positions along the trisynaptic entorhino-dentato-hippocampal pathway. Seven months later, the rats were subjected to transient cerebral ischemia using the four-vessel occlusion technique. At the time of killing 4 days later, a Nissl stain was used to demonstrate neuronal degeneration, while connective reorganization resulting from the neonatal lesions was monitored by Timm staining. In one group of rats, neonatal lesions had caused severe depletion of entorhinal projections to the septodorsal fascia dentata and hippocampus (CA1 and CA3), without any direct damage to the dorsal hippocampus itself. Another group had extensive damage of the dorsal CA3, with removal of the Schaffer collaterals from these levels to CA1, and variable damage to the entorhinal afferents. In both groups, the extent and pattern of ischemia-induced degeneration of CA1 pyramidal cells were the same on the lesioned and nonlesioned sides of the brain, demonstrating that neonatal lesions and the subsequent connective reorganization did not have a sparing effect. Seen in relationship to previous observations in adult rats of the neuroprotective actions of acute, preischemic lesions of the trisynaptic hippocampal pathway, it is concluded that CA1 pyramidal cell loss requires the presence of intact excitatory afferents rather than an intact hippocampal circuitry.

Changes in mRNA for metabotropic glutamate receptors after transient cerebral ischaemia

Using a rat 4-vessel occlusion model of cerebral ischaemia we studied the changes in the mRNA level for the metabotropic receptor subtypes mGluR1 alpha, mGluR1 beta, mGluR2, mGluR3, mGluR4, and mGluR5 by means of in situ hybridization with oligonucleotides. After 24 hours of reperfusion the mRNA levels were significantly increased for mGluR2 and mGluR4 while it was significantly decreased for mGluR5. These results suggest that vulnerable neurones react to an increased extracellular glutamate concentration by differential regulation of the mRNA for metabotropic glutamate receptor subtypes which perhaps reflects the different pre- or postsynaptic location and different involvement in ischaemic neurodegeneration.

Hypoxia-ischemia in the neonatal rat brain: histopathology after post-treatment with NMDA and non-NMDA receptor antagonists

In a model of perinatal hypoxic-ischemic brain damage, we examined the neuroprotective efficacy of posttreatment with the NMDA receptor antagonist MK-801 and the AMPA receptor antagonist NBQX. Unilateral brain damage developed in 95% of rat pups subjected to hypoxia-ischemia with a 27.8 +/- 1.2% weight deficit of the damaged hemisphere. MK-801 in doses of 0.3 and 0.5 mg/kg i.p. reduced the brain damage by 61% (p < 0.001) and 43% (p < 0.001), respectively. A higher dose of MK-801 (0.75 mg/kg) did not offer neuroprotection. Treatment with NBQX (40 mg/kg) reduced the hemispheric lesion by 28% (p < 0.05). In conclusion, posttreatment with both NBQX and low doses of MK-801 reduced perinatal brain damage. The NMDA receptor antagonist offered stronger neuroprotection which is in agreement with a proposed NMDA receptor hyperactivity around postnatal day 7 in rats.

A paradox after systemic kainate injection in rats: lesser damage of hippocampal CA1 neurons after higher doses

The pyramidal neuron loss in dorsal rat hippocampus was determined 4 days after i.p. administration of 10 or 20 mg/kg kainic acid (KA). Histological examination revealed that subtotal-to-total loss of the pyramidal neurons in both the CA3 and CA1 regions of hippocampus was produced after 10 mg/kg KA. At the higher dose, severe damage was evident in the CA3 region while no or only sporadic damage was observed in the CA1 region. These findings suggest that the high KA dose damaged the CA3 pyramidal neurons before excitatory input through the Schaffer collaterals produced irreversible damage to the CA1 pyramidal neurons.

Kainic acid-induced seizures and brain damage in the rat: different effects of NMDA- and AMPA receptor antagonists

We have studied the effect of two glutamate receptor antagonists on seizures and hippocampal neurone loss in the rat after systemic kainic acid administration. Intraperitoneal injection of the novel AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolproprionic acid) receptor antagonist NBQX (6-nitro-7-sulphamoylbenzo(f)quinoxaline-2,3-dione) (30 mg/kg x 3 and 15 mg/kg x 3) administered 30 and 15 min. before and simultaneously with injection of kainic acid (5 mg/kg) intraperitoneally, dramatically enhanced the toxicity of kainic acid leading to death of all animals. When the NBQX dose was reduced to 8 mg/kg x 3, all animals survived and neurone damage in the hippocampus did not differ from control animals. When NBQX (30 mg/kg x 3) was administered 30- or 60 min after injection of kainic acid (8 mg/kg) intraperitoneally, no changes were observed concerning survival rates, seizure generation and neurone loss. Post-kainic acid treatment with the non-competitive NMDA receptor antagonist MK-801 (0.5 mg/kg and 1.0 mg/kg), 30 and 60 min. after intraperitoneally injection of kainic acid 8 mg/kg, abolished seizures in all animals and the neurone damage in the hippocampus was completely prevented. The results emphasize the importance of the NMDA-receptor activation for seizure generation and subsequent brain damage after intraperitoneally kainic acid. The paradoxical, unexpected effects of NBQX contrast to the protective effect of this compound after cerebral ischaemia and hypoglycaemia, conditions which are also characterized by glutamate-mediated damage. One possible explanation of the lowered seizure threshold to kainic acid after NBQX could be that NBQX is blocking AMPA receptors on interneurones more efficiently than on pyramidal cells.

The effect of an AMPA antagonist (NBQX) on postischemic neuron loss and protein synthesis in the rat brain

Two groups of rats were subjected to 12 min of global cerebral ischemia and 6 days recirculation using the four-vessel occlusion model with hypotension and then treated with the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) antagonist NBQX [2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo (F) quinoxalinedione (Honoré et al. 1988]. One group was used for routine and quantitative histology and immunostaining for glial fibrillary acidic protein (GFAP). The second group was subjected to autoradiographic studies of regional cerebral protein synthesis, with special emphasis on the hippocampus, the frontal cortex, and the thalamus. It was found that neuroprotective treatment with NBQX normalized cerebral protein synthesis rate (CPSR) in all investigated regions 6 days after ischemia. In untreated ischemic animals CPSR was normalized in all regions except for the CA3 and thalamus, where it had increased by 29% and 41%, respectively. Treatment of controls with NBQX had no effect on CPSR after 6 days. The histological investigations revealed that NBQX did not protect vulnerable cells in the dentate hilus and the reticular thalamic nucleus (RTN). In these regions reactive astrocytosis visualized by GFAP immunostaining was equally pronounced in both ischemic and NBQX-treated animals, and most neurons in the RTN were eosinophilic. The 80-100% pyramidal neuron loss in CA1 was accompanied by a high degree of reactive astrocytosis, whereas the NBQX-treated animals showed no signs of astrocytosis in this region. The ischemic CA1 pyramidal layer was also massively invaded by microglia.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of infarct volume by thrombolysis with rt-PA in an embolic rat stroke model

Thrombolytic therapy with recombinant tissue plasminogen activator was tested in an embolic stroke model. In rats the internal carotid territory was embolized through the internal carotid artery with 50 microliters thrombin-rich (n = 18), 50 microliters thrombin-poor (n = 17) and 20 microliters thrombin poor (n = 13) suspension of arterial-like microthrombi formed under pressure. Hemispheric cerebral blood flow before and after embolization was measured by intra-arterial 133Xe injection method. Fifteen minutes after embolization 19 animals were treated with tissue plasminogen activator 20 mg kg-1, and 22 animals with saline. Carotid angiography displayed the degree of occlusion of the cerebral arterial supply before and after treatment. Brains were evaluated neuropathologically and infarct volume measured. Cerebral blood flow was reduced 72% after embolization with 50 microliters emboli suspension and 32% after embolization with 20 microliters suspension. The comparison of pre- and post-treatment angiography showed some recanalization in the treated animals, control animals had no recanalization. Thrombolytic therapy reduced the infarct volume from 72.8% to 20.9% of embolized hemisphere volume (p = 0.0037) in the 50-microliters thrombin rich-embolized group, from 22.9 to 9.0 (NS) in the 50-microliters-thrombin-poor-embolized group and from 6.6 to 0.0 (NS) in the 20-microliters-embolized group. One third of treated animals recanalized completely and developed smaller (p = 0.03) infarcts than the non-recanalized. No hemorrhagic complications were observed. Early thrombolytic therapy reduced infarct volume after embolic stroke in this model, this effect was dependent upon recanalization.

Impairment of Fos protein formation in the rat infarct borderzone by MK-801, but not by NBQX

In the present immunocytochemical study, we investigated the mechanism of Fos protein induction and the regional distribution of the Fos protein in brains of spontaneously hypertensive rats subjected to 2 h of permanent middle cerebral artery occlusion (MCAO). Rats were administered either saline or a glutamate receptor antagonist; the non-competitive NMDA receptor antagonist MK-801 or the AMPA receptor antagonist NBQX which are known to be able to reduce infarct size in MCA occluded rats. The saline treated rats showed presence of Fos protein in nerve cell nuclei throughout the cortical and striatal infarct borderzone, but no staining in the infarct core or contralateral hemisphere. MK-801 almost totally abolished this expression of Fos protein whereas NBQX had no significant effect on Fos protein expression. It is suggested that the Fos protein induction is due to repeated spreading depressions mediated by NMDA receptors in the infarct borderzone, and that Fos protein due to its persistence in the tissue can be used as a histochemical marker of borderzone tissue at risk for eventually becoming recruited in the infarct.

Microglial and astroglial reactions to ischemic and kainic acid-induced lesions of the adult rat hippocampus

The aim of this study was to characterize the microglial and astroglial reactions to degeneration of (a) hippocampal CA1 pyramidal cells and dentate hilar neurons induced by cerebral ischemia and (b) CA3 pyramidal cells and dentate hilar neurons induced by intraventricular injections of kainic acid (KA). The microglial reactions to ischemia, as monitored by histochemical staining for the enzyme nucleoside diphosphatase (NDPase) and immunohistochemical staining for the complement type 3 receptor (CR3), could be divided into (1) initial and generalized, but transient, reactions which also included areas devoid of subsequent neural degeneration and (2) protracted, degeneration-specific reactions in the areas with neural degeneration. Due to more widespread hippocampal involvement a similar distinction was not possible after KA lesions. After both ischemia and KA application the protracted degeneration-specific reactions were characterized by increased NDPase/CR3 reactivity and prominent morphological changes. In the dentate hilus, reactive microglial cells clustered around the degenerating hilar neurons. In stratum radiatum of CA1, reactive microglial cells transformed into either (1) "rod cells," aligned along the postischemic, degenerating pyramidal cell dendrites, followed by subsequent transformation into ameboid-like cells, or (2) "bushy" cells, in response to degeneration of Schaffer collaterals induced by KA lesioning of CA3 pyramidal cells. Within stratum radiatum of the KA-lesioned CA3, where both dendrites and axons were degenerating, the microglial cells developed into stellate cells with thickened, retracted processes and plump cell bodies. These cells were supplemented by rounded macrophage-like cells. Astroglial reactions, monitored by immunohistochemical staining for the intermediate filament proteins glial fibrillary acidic protein (GFAP) and vimentin (VIM), and the normal plasma constituent immunoglobulin G (IgG), showed an initial and generalized astroglial immunoreactivity for IgG, which paralleled the initial and transient microglial reactions, while the reactive changes in GFAP and VIM immunohistochemistry paralleled the protracted, degeneration-specific reactions with regard to timing, strength, and distribution. In the KA-lesioned CA3, the most prominent finding was a prompt loss of astroglial GFAP immunoreactivity corresponding to the degenerating pyramidal cell layer and the adjacent mossy fiber layer. The results strongly indicate that stimuli other than neural degeneration initiated the activation of both microglial and astroglial cells, which then upon further activation by actual neuronal damage and degeneration adjust according to which neuronal structures were undergoing degeneration.