Damage In Rat Hippocampus Research Articles

Daily clozapine treatment improves spatial memory deficits produced by hippocampal damage in rats

Glutathione (GSH) is a key component of the cellular defence cascade against injury caused by reactive oxygen species. Kainic acid (KA) is a potent central nervous system excitotoxin. KA-elicited neuronal death may result from the generation of ROS. The present study was undertaken to characterize the role of GSH in KA-induced neurotoxicity. Cultures of cerebellar granule neurons were prepared from 8-day-old rats, and used at 8, 14 and 20 days in vitro (DIV). Granule neurons displayed a developmental increase in their sensitivity to KA injury, as quantified by an ELISA-based assay with the tetrazolium salt MTT. At DIV 14 and 20, a 30-min challenge with KA (500 μM) reduced cell viability by 45% after 24 h, significantly greater (P<0.01) than the 22% cell loss with DIV 8 cultures. Moreover acute (30 min) KA exposure concentration-dependently reduced intracellular GSH and enhanced reactive oxygen species generation (evaluated by 2′,7′-dichlorofluorescein diacetate). In comparison to control, KA (500 μM) lowered GSH levels in DIV 8 granule neurons by 16% (P=0.0388), and by 36% (P=0.0001) in both DIV 14 and DIV 20 neurons, after 30 min. Preincubation of granule neurons with the membrane permeant GSH delivery agent, GSH ethyl ester (5 mM), for 30 min significantly increased intracellular GSH content. Importantly, GSH ethyl ester reduced the toxic effects of KA, becoming significant at 1 mM (P=0.007 vs. KA-treated group), and was maximal at ≥2.5 mM (P<0.0001). GSH ethyl ester displayed a similar dose-dependence in its ability to counteract KA-induced depletion of cellular GSH. The data strengthen the notion that cellular GSH levels have a fundamental role in KA-induced neurotoxicity.

Abnormal Expression of Neuronal Nitric Oxide Synthase Triggers Limbic Seizures and Hippocampal Damage in Rat

Administration of tacrine (5 mg/kg ip), an anticholinesterase agent, in rats pretreated (24 h beforehand) with lithium chloride (LiCl; 12 mEq/kg ip) provides a useful experimental model to study limbic seizures and delayed hippocampal damage. Here we report Western blotting evidence demonstrating that in rat LiCl and tacrine enhance the expression of neuronal nitric oxide synthase (nNOS), but not eNOS, enzyme protein in the hippocampus during the preconvulsive period and this triggers seizures and hippocampal damage. In fact, systemic administration of 7-nitro indazole (7-NI; 50 mg/kg given ip 30 min before tacrine), a selective inhibitor of nNOS, prevented the expression of motor and electrocortical (ECoG) seizures and abolished neuronal cell death in the hippocampus. A lower dose (5 mg/kg ip) of 7-NI was ineffective. In conclusion, the present data support a role for abnormal nNOS expression in the mechanism which triggers limbic seizures and delayed excitotoxic damage in the hippocampus of rat.

Hippocampal damage in rats disrupts decrements in the processing of an intramaze landmark in a spatial task

Using a four-arm plus-shaped maze, rats with neurotoxic lesions in the dorsal hippocampus were trained in a spatial reference memory task in which both the extramaze constellation of stimuli and an intramaze landmark (a piece of sandpaper covering the floor of the goal) indicated the location of the goal arm. After reaching criterion, animals were given two transfer tests in order to investigate how much they had learned about the intra and extramaze cues. Results showed that during the intramaze transfer, based exclusively on the intramaze cue, hippocampal rats produced a performance clearly superior to that of the controls. Importantly, the average percentage of correct responses recorded in the hippocampal group during the extra versus the intramaze transfer test was similar. Thus, no decremental processing of the intramaze cue was detected in the lesioned group. In contrast, control rats showed a decremental processing of the intramaze landmark performing worse during the intramaze transfer as compared with the extramaze transfer. These results support the view that the hippocampus regulates decremental changes in the processing of normally irrelevant stimuli, extending this claim into a spatial domain.

Spatial and associative learning deficits induced by neonatal excitotoxic hippocampal damage in rats: further evaluation of an animal model of schizophrenia.

Neonatal ventral hippocampal lesions in the rat result in post-pubertal onset of behavioural abnormalities, modelling some aspects of schizophrenia. We further assessed the behavioural effects of neonatal lesions in rats in a variety of cognitive tasks and in the prepulse inhibition (PPI) of startle response paradigm. Prepubescent, lesioned rats exhibited startle responses and PPI similar to controls whereas, at adulthood, they showed a deficit in PPI. Lesioned rats acquired both passive and active avoidance responses. However, compared to controls, they showed a deficit in passive avoidance retention and in acquisition of active avoidance responses. In a cued Morris water-maze task, lesioned rats demonstrated adequate sensorimotor functions and appropriate motivation to escape from water. However, they were impaired in place learning and in remembering the location of a submerged platform. In conclusion, neonatal ventral hippocampal lesions result in the post-pubertal emergence of long-lasting deficits in sensorimotor gating and in the capacity to acquire and retain information in tests of spatial and avoidance learning. Therefore, this neurodevelopmental model of schizophrenia seems to exhibit an interesting degree of validity in possibly simulating some cognitive impairments and sensorimotor gating deficits frequently observed in psychotic patients.

Protective effects of C-phycocyanin against kainic acid-induced neuronal damage in rat hippocampus

The neuroprotective role of C-phycocyanin was examined in kainate-injured brains of rats. The effect of three different treatments with C-phycocyanin was studied. The incidence of neurobehavioral changes was significantly lower in animals receiving C-phycocyanin. These animals also gained significantly more weight than the animals only receiving kainic acid, whereas their weight gain did not differed significantly from controls. Equivalent results were found when the neuronal damage in the hippocampus was evaluated through changes in peripheral benzodiazepine receptors (microglial marker) and heat shock protein 27kD expression (astroglial marker). Our results are consistent with the oxygen radical scavenging properties of C-phycocyanin described elsewhere. Our findings and the virtual lack of toxicity of C-phycocyanin suggest this drug could be used to treat oxidative stress-induced neuronal injury in neurodegenerative diseases, such as Alzheimer's and Parkinson's.

Temporally Graded Retrograde Amnesia of Contextual Fear after Hippocampal Damage in Rats: Within-Subjects Examination

We have shown previously that electrolytic lesions of the dorsal hippocampus (DH) produce a severe deficit in contextual fear if made 1 d, but not 28 d, after fear conditioning (). As such, the hippocampus seems to play a time-limited role in the consolidation of contextual fear conditioning. Here, we examine retrograde amnesia of contextual fear produced by DH lesions in a within-subjects design. Unlike our previous reports, rats had both a remote and recent memory at the time of the lesion. Rats were given 10 tone-shock pairings in one context (remote memory) and 10 tone-shock pairings in a distinct context (with a different tone) 50 d later (recent memory), followed by DH or sham lesions 1 d later. Relative to controls, DH-lesioned rats exhibited no deficit in remote contextual fear, but recent contextual fear memory was severely impaired. They also did not exhibit deficits in tone freezing. This highly specific deficit in recent contextual memory demonstrated in a within-subjects design favors mnemonic over performance accounts of hippocampal involvement in fear. These findings also provide further support for a time-limited role of the hippocampus in memory storage.

Hyperthermia delayed by 24 hours aggravates neuronal damage in rat hippocampus following global ischemia.

We investigated whether moderate, transient whole-body hyperthermia (approximately 39.6 degrees C), if imposed 1 day following a brief episode of forebrain ischemia, would affect the neuropathologic outcome. Forty-two Wistar rats were subjected to either a 5- or 7-minute period of bilateral common carotid artery occlusion plus hypotension (50 mm Hg), or to the equivalent sham procedure. Twenty-four hours later, rats of one subgroup were placed into a hyperthermic chamber containing high-intensity lamps designed to elevate rectal temperature to 39 to 40 degrees C for 3 hours. Normothermic subgroups received the same procedures, but the heating lamps were turned off. Eight days after brain ischemia or the sham procedure, brains were perfusion-fixed, and numbers of ischemic-appearing CA1 pyramidal neurons were counted. In rats with 7-minute forebrain ischemia, delayed hyperthermia increased mean numbers of ischemic neurons by 2.6- to 2.7-fold in all subsectors of area CA1 (p < 0.05, ANOVA). Delayed hyperthermia in 5-minute ischemic rats also tended to increase mean numbers of ischemic neurons (by 11-fold in lateral, 6-fold in middle, and 5-fold in medial CA1 subsectors), but these differences were not statistically significant. We conclude that moderate, transient hyperthermia, even if occurring 1 day after a 7-minute global ischemic insult, exacerbates the extent of ischemic neuronal injury.

Neonatal hippocampal damage in rats: long-term spatial memory deficits and associations with magnitude of hippocampal damage.

This study investigated the effects of neonatal hippocampal ablation on the development of spatial learning and memory abilities in rats. Newborn rats sustained bilateral electrolytic lesions of the hippocampus or were sham-operated on postnatal day 1 (PN1). At PN20-25, PN50-55, or PN90-95, separate groups of rats were tested in a Morris water maze on a visible "cue" condition (visible platform in a fixed location of the maze), a spatial "place" condition (submerged platform in a fixed location), or a no-contingency "random" condition (submerged platform in a random location). Rats were tested for 6 consecutive days, with 12 acquisition trials and 1 retention (probe) trial per day. During acquisition trials, the rat's latency to escape the maze was recorded. During retention trials (last trial for each day, no escape platform available), the total time the rat spent in the probe quadrant was recorded. Data from rats with hippocampal lesions tested as infants (PN20-25) or as adults (PN50-55 and PN90-95) converged across measures to reveal that 1) spatial (place) memory deficits were evident throughout developmental testing, suggesting that the deficits in spatial memory were long-lasting, if not permanent, and 2) behavioral performance measures under the spatial (place) condition were significantly correlated with total volume of hippocampal tissue damage, and with volume of damage to the right and anterior hippocampal regions. These results support the hypothesis that hippocampal integrity is important for the normal development of spatial learning and memory functions, and show that other brain structures do not assume hippocampal-spatial memory functions when the hippocampus is damaged during the neonatal period (even when testing is not begun until adulthood). Thus, neonatal hippocampal damage in rats may serve as a rodent model for assessing treatment strategies (e.g., pharmacological) relevant to human perinatal brain injury and developmental disabilities within the learning and memory realm.

Effect of CNTF on ischaemic cell damage in rat hippocampus.

The neuroprotective effect of neurotrophic factors has been demonstrated in experimental cerebral ischaemia recently. These include nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), and basic fibroblast growth factor (basic FGF). The neuroprotective effect of ciliary neurotrophic factor (CNTF), however, has not been studied so far. We have examined the neuroprotective effect of recombinant rat CNTF in a rat forebrain ischaemia model. A continuous infusion of CNTF was started 1 week before the induction of ischaemia and continued until 1 week after the ischaemia. Reversible forebrain ischaemia was induced by 7 minutes of bilateral carotid occlusion with hypotension. Neuronal cell death in the hippocampal CA1 sector was evaluated 1 week after the ischaemia. For the control group artificial CSF (cerebrospinal fluid) was infused instead of CNTF. Per cent neuronal cell death was 83.4 +/- 5.9% (mean +/- SEM, n = 5) in the control group, and 71.1 +/- 10.0% (mean +/- SEM, n = 5) in the CNTF group. Although percentage of neuronal cell death was lower in the CNTF group, the difference was not statistically significant. This result suggests that the protective effect of CNTF in the rat forebrain ischaemia model may be limited compared with other neurotrophic factors. It is considered that the number of neurons protected by CNTF may be small.

Neonatal excitotoxic hippocampal damage in rats causes post-pubertal changes in prepulse inhibition of startle and its disruption by apomorphine.

Neonatal excitotoxic hippocampal damage in the rat results in postpubertal onset of a variety of abnormal behaviors related to excessive dopaminergic transmission in the mesolimbic/nigrostriatal system, and thus may be considered an animal model of some aspects of schizophrenia. Because sensorimotor gating is impaired in adult patients with schizophrenia and in rats with experimentally induced mesolimbic dopamine hyperactivity, the present experiments investigated the effects of neonatal (postnatal day 7, PD7) ibotenic acid (3 micrograms) lesions of the ventral hippocampus (VH) on the amplitude and prepulse inhibition (PPI) of acoustic startle in prepubertal (PD35) and postpubertal (PD56) rats. Startle was elicited using 105 and 118-dB pulses alone or preceded by 4, 8, or 16 dB above-background prepulses in rats treated with vehicle or apomorphine (APO; 0.025 or 0.1 mg/kg SC). At PD35, PPI in VH-lesioned rats did not differ significantly from these measures in sham operated rats. Apomorphine significantly increased startle amplitude and reduced PPI in both sham operated and VH-lesioned rats at PD35. At PD56, startle amplitude in VH-lesioned rats was not significantly different from controls, but PPI was reduced significantly compared to controls. Ventral hippocampus lesioned rats also exhibited an exaggerated reduction in PPI after treatment with APO. These findings provide further evidence of postpubertal impairments that may be related to increased mesolimbic dopamine transmission and receptor sensitivity in rats with neonatal hippocampal damage, and provide further support for the fidelity of this animal model of schizophrenia.

Neuroprotective effects of NBQX on hypoxia-induced neuronal damage in rat hippocampus.

Models of cerebral ischaemia were used for analysis of mechanism of neuronal cell death and/or damage. Ischaemia is caused dominantly by severe hypoxia and hypoglycaemia: in the present study, we examined the influence of severe in vivo hypoxia (5% O2/95% N2 for 30 min at 22 degrees C). After hypoxia, neuronal damage was observed in the CA3 and dentate gyrus (DG) after 3 and 21 days of survival, but not in the CA1.2,3-Dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (NBQX), an antagonist for AMPA/kainate receptors, showed neuroprotective effects in the CA3 and DG. These results suggest that hypoxia may induce neuronal damage in the CA3 and DG through activation of AMPA/kainate receptors.

Genetic variation in vulnerability to the behavioral effects of neonatal hippocampal damage in rats.

We explored how two independent variables, one genetic (i.e., specific rat strains) and another environmental (i.e., a developmental excitotoxic hippocampal lesion), contribute to phenotypic variation. Sprague-Dawley (SD), Fischer 344 (F344), and Lewis rats underwent two grades of neonatal excitotoxic damage: small and large ventral hippocampal (SVH and LVH) lesions. Locomotion was tested before puberty [postnatal day 35 (P35)] and after puberty (P56) following exposure to a novel environment or administration of amphetamine. The behavioral effects were strain- and lesion-specific. As shown previously, SD rats with LVH lesions displayed enhanced spontaneous and amphetamine-induced locomotion as compared with controls at P56, but not at P35. SVH lesions in SD rats had no effect at any age. In F344 rats with LVH lesions, enhanced spontaneous and amphetamine-induced locomotion appeared early (P35) and was exaggerated at P56. SVH lesions in F344 rats resulted in a pattern of effects analogous to LVH lesions in SD rats--i.e., postpubertal onset of hyperlocomotion (P56). In Lewis rats, LVH lesions had no significant effect on novelty- or amphetamine-induced locomotion at any age. These data show that the degree of genetic predisposition and the extent of early induced hippocampal defect contribute to the particular pattern of behavioral outcome. These results may have implications for modeling interactions of genetic and environmental factors involved in schizophrenia, a disorder characterized by phenotypic heterogeneity, genetic predisposition, a developmental hippocampal abnormality, and vulnerability to environmental stress.

Dendrotoxin-K produces seizures and hippocampal damage in rats via N-methyl-D-aspartate (NMDA) receptor mediated mechanisms

Dendrotoxin-K produces seizures and hippocampal damage in rats via N-methyl-D-aspartate (NMDA) receptor mediated mechanisms

Neuroprotective effect of free radical scavengers on [formula omitted] (BOAA)-induced neuronal damage in rat hippocampus

The neurotoxin β-N- oxalylamino- l-alanine (BOAA), found in Lathyrus sativus seeds, is thought to be the causative agent of neurolathyrism. We have investigated the neuroprotective effects of free radical scavengers on BOAA-induced toxicity following focal injection (1 μl) of BOAA and comparing the pathological outcome with the effects of injections of α-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA), kainate (KA) or N- methyl- d-aspartate (NMDA) into the dorsal hippocampus of male Wistar rats. Cellular damage was assessed histologically. BOAA (50 nmol) induced a highly selective pattern of hippocampal damage identical with that seen with AMPA (1 nmol). BOAA-induced neurotoxicity, but not AMPA, KA (0.5 nmol) or NMDA (25 nmol)-induced neurotoxicity, was prevented in a dose-dependent manner by focal co-injection of four potential free radical scavengers; dimethyl sulphoxide (DMSO) (1750–7000 nmol), dimethylthiourea (DMTU) (8000 nmol), dimethylformamide (DMF) (7000 nmol) and mannitol (1000 nmol). These findings suggest that hippocampal damage induced by BOAA involves an interaction between AMPA receptors and free radicals.

Propidium iodide in vivo: an early marker of neuronal damage in rat hippocampus

We have investigated the use of the fluorescent exclusion dye propidium iodide as a marker for acutely degenerating cells in vivo, and report here that combined injection of kainic acid and propidium iodide into the lateral cerebral ventricle results in labelling of CA3 pyramidal cells 1 and 6 h after injection. Alternate sections stained with thionin at these early times revealed little evidence of histologically detectable cell damage.

Brain-derived neurotrophic factor protects against ischemic cell damage in rat hippocampus.

The neuroprotective action of brain-derived neurotrophic factor (BDNF) was evaluated in a rat model of transient forebrain ischemia. A continuous intraventricular infusion of BDNF for 7 days starting immediately before the onset of ischemia significantly increased the number of pyramidal cells in the vulnerable CA1 sector of the hippocampus. In situ hybridization experiments suggest the neuroprotection to be mediated via trkB-receptors in the hippocampus. The data indicate a therapeutic potential for the treatment of cerebral ischemia.

Genetic differences in behavioral response to neonatal hippocampal damage in rats

Genetic differences in behavioral response to neonatal hippocampal damage in rats

Electrolytic lesions of the locus coeruleus or 6-hydroxydopamine lesions of the medial forebrain bundle protect against excitotoxic damage in rat hippocampus

Unilateral lesioning of the rat locus coeruleus by an electric current (0.3 mA/10 s) reduces the ipsilateral hippocampal tissue content of dopamine (DA) and noradrenaline (NA) by 80% and 60% respectively, and protects against the excitotoxic action of bilateral kainate injections (1.1 nmol/μl) in the hippocampus. On the ipsilateral side hippocampal CA1, CA2 and DG cells were protected; lesser protection of CA1 cells was seen on the contralateral side. The unilateral injection of 6-hydroxydopamine (8.8 μg/2 μl/5 min) into the medial forebrain bundle abolishes the increase in extracellular NA concentration induced by in the ipsilateral hippocampus without altering the low extracellular DA levels. This medial forebrain bundle lesion protects (on the ipsilateral side) against kainate toxicity (500 μM through the probe for 20 min) in the hippocampus (CA1, CA2 and DG cells). The noradrenergic innervation of the hippocampus apparently potentiates the excitotoxic effect of focal injection of kainate.

Protective Effect of Nimodipine against Ischemic Neuronal Damage in Rat Hippocampus without Changing Postischemic Cerebral Blood Flow

The purpose of the present study was to investigate the neuroprotective action of nimodipine. Furthermore, the influence of nimodipine on postischemic local CBF (LCBF) was examined. Forebrain ischemia of the rat was performed for 10 min by bilateral carotid clamping, administration of trimethaphan, and blood withdrawal to obtain an MABP of 40 mm Hg. LCBF was measured after 10 min of postischemic recirculation by injecting [14C]iodoantipyrine in saline solution. Nimodipine (0.1, 0.3, and 1.0 mg/kg) was suspended in miglyol oil and applied orally 60 min prior to ischemia. Histological evaluation was performed 7 days after ischemia. Hippocampal neuronal damage was determined as the percentage of necrotic neurons. After preischemic application of nimodipine, neuronal damage was significantly reduced in the hippocampal CA1 subfield. Postischemic LCBF was not affected by treatment with nimodipine. These findings show that nimodipine is able to protect neurons against ischemic damage. The neuroprotective effect of nimodipine was not mediated by a postischemic cerebral vasodilation, but by a direct action on the neurons.

Immunohistochemical study of glial reaction and serum-protein extravasation in relation to neuronal damage in rat hippocampus after ischemia

Transient forebrain ischemia of 30 min duration was produced in anaesthetized rats by four-vessel occlusion. After survival periods of 3 h to three days brains were perfusion-fixed and sections through the mid-dorsal hippocampus were processed for conventional staining and immunohistochemical analysis. Neuronal damage in the hilus was manifested 3–8 h after ischemia; neurons in the CA1 and CA2 sector suffered delayed neuronal death after 48–72 h whereas the dentate gyrus and the CA3 sector were normal. Vasogenic edema formation was visualized using antibodies against rat serum-proteins, serum albumin and immunoglobulins. By 3 h after ischemia, only faint and diffuse serum-staining was detected. At 8 h survival, weak astrocytic-staining was present. After 24–72 h CA1–CA2 exhibited massive serum extravasation. The molecular layer of the dentate gyrus showed edema formation in the absence of granule cell damage. The glial reaction was studied using antibodies against glial fibrillary acidic protein, vimentin and S-100 protein, Glial fibrillary acidic protein and S-100 protein-staining increased in areas with either edema or neuronal damage. In contrast, changes in vimentin were only detected in areas with neuronal necrosis. The observations demonstrate that following 30 min of ischemia neuronal damage is accompanied by changes in blood-brain barrier function and reactive glial alterations. The dissociation between neuronal necrosis and astroglial hypertrophy and hyperplasia reflects differences in cellular responsiveness which constitute inherent features of postischemic hippocampal injury.