Pyramidal Cells In CA1 Region Research Articles

Tat-CCT2 Protects the Neurons from Ischemic Damage by Reducing Oxidative Stress and Activating Autophagic Removal of Damaged Protein in the Gerbil Hippocampus.

CCT2 is a eukaryotic chaperonin TCP-1 ring complex subunit that mediates protein folding, autophagosome incorporation, and protein aggregation. In this study, we investigated the effects of CCT on oxidative and ischemic damage using in vitro and in vivo experimental models. The Tat-CCT2 fusion protein was efficiently delivered into HT22 cells in a concentration- and time-dependent manner, and the delivered protein was gradually degraded in HT22 cells. Incubation with Tat-CCT2 significantly ameliorated the 200 µM hydrogen peroxide (H2O2)-induced reduction in cell viability in a concentration-dependent manner, and 8 µM Tat-CCT2 treatment significantly alleviated H2O2-induced DNA fragmentation and reactive oxygen species formation in HT22 cells. In gerbils, CCT2 protein was efficiently delivered into pyramidal cells in CA1 region by intraperitoneally injecting 0.5mg/kg Tat-CCT2, as opposed to control CCT2. In addition, treatment with 0.2 or 0.5mg/kg Tat-CCT2 mitigated ischemia-induced hyperlocomotive activity 1 d after ischemia and confirmed the neuroprotective effects by NeuN immunohistochemistry in the hippocampal CA1 region 4 d after ischemia. Tat-CCT2 treatment significantly reduced the ischemia-induced activation of astrocytes and microglia in the hippocampal CA1 region 4 d after ischemia. Furthermore, treatment with 0.2 or 0.5mg/kg Tat-CCT2 facilitated ischemia-induced autophagic activity and ameliorated ischemia-induced autophagic initiation in the hippocampus 1 d after ischemia based on western blotting for LC3B and Beclin-1, respectively. Levels of p62, an autophagic substrate, significantly increased in the hippocampus following treatment with Tat-CCT2. These results suggested that Tat-CCT2 exerts neuroprotective effects against oxidative stress and ischemic damage by promoting the autophagic removal of damaged proteins or organelles.

Simulations of Learning, Memory, and Forgetting Processes with Model of CA1 Region of the Hippocampus

The aim of this paper is to present a computational model of the CA1 region of the hippocampus, whose properties include (a) attenuation of receptors for external stimuli, (b) delay and decay of postsynaptic potentials, (c) modification of internal weights due to propagation of postsynaptic potentials through the dendrite, and (d) modification of weights for the analog memory of each input due to a pattern of long-term synaptic potentiation (LTP) with regard to its decay. The computer simulations showed that CA1 model performs efficient LTP induction and high rate of sub-millisecond coincidence detection. We also discuss a possibility of hardware implementation of pyramidal cells of CA1 region of the hippocampus.

Neuroprotective effect of minocycline on cognitive impairments induced by transient cerebral ischemia/reperfusion through its anti-inflammatory and anti-oxidant properties in male rat.

Memory deficit is the most visible symptom of cerebral ischemia that is associated with loss of pyramidal cells in CA1 region of the hippocampus. Oxidative stress and inflammation may be involved in the pathogenesis of ischemia/reperfusion (I/R) damage. Minocycline, a semi-synthetic tetracycline derived antibiotic, has anti-inflammatory and antioxidant properties. We evaluated the neuroprotective effect of minocycline on memory deficit induced by cerebral I/R in rat. I/R was induced by occlusion of common carotid arteries for 20min. Minocycline (40mg/kg, i.p.) was administered once daily for 7days after I/R. Learning and memory were assessed using the Morris water maze test. Nissl staining was used to evaluate the viability of CA1 pyramidal cells. The effects of minocycline on the microglial activation was also investigated by Iba1 (Ionized calcium binding adapter molecule 1) immunostaining. The content of malondialdehyde (MDA) and pro-inflammatory cytokines (IL-1β and TNF-α) in the hippocampus were measured by thiobarbituric acid reaction substances method and ELISA, respectively. Minocycline reduced the increase in escape latency time and in swimming path length induced by cerebral I/R. Furthermore, the ischemia-induced reduction in time spent in the target quadrant during the probe trial was increased by treatment with minocycline. Histopathological results indicated that minocycline prevented pyramidal cells death and microglial activation induced by I/R. Minocycline also reduced the levels of MDA and pro-inflammatory cytokines in the hippocampus in rats subjected to I/R. Minocycline has neuroprotective effects on memory deficit induced by cerebral I/R in rat, probably via its anti-inflammatory and antioxidant properties.

The Neuroprotective Effect of Atorvastatin on Apoptosis of Hippocampus Following Transient Global Ischemia/ Reperfusion


 Background: Hippocampus CA1 cells are highly sensitive to ischemia. Because of anti-oxida­tive property, atorvastatin by eliminating free radicals and other constituent due to cell lesions prevents damages or death of intact cells. The aim of this study is to determine neuroprotective effect of atorvastatin on apoptosis of hippocampus CA1 cells in male rats. Material and Meth­ods: In an experimental study 24 male rats –Wistar adult race- were divided into four groups: Ischemic, vehicle, treatment and control. In order to make an ischemic- reperfusion model, common carotid artery was clamped bilaterally for 20 minutes. In treatment group, the first dose of Atorvastatin (10mg/kg) was injected six hours after ischemic- reperfusion and 24, 48 and 72 later intraperitoneally. Four days after ischemic- reperfusion tissue section were obtained and stained using Nissl method. Then intact healthy pyramidal CA1 hippocampus cells were counted. TUKEY and One Way ANOVA were used for analyzing the obtained results. Results: No significant difference was found in numbers of healthy intake pyramidal and apoptotic cells of CA1 hippocampus region between treatment group (10mg/kg Atorvastatin) and controls, whereas a significant reduction of these cells was observed in ischemia and vehicle groups in comparison to controls (P<0.05). Conclusion: Using 10mg/kg atorvastatin following cerebral ischemia- reperfusion has a protective effect on pyramidal cells of CA1 region in hippocampus in male rats leading to reduction of degeneration and apoptosis.[GMJ.2016;5(2):82-89]

Protective effects of low molecular weight chondroitin sulfate on amyloid beta (Aβ)-induced damage in vitro and in vivo

In the present study, we investigated the effects of low molecular weight chondroitin sulfate (LMWCS) on amyloid beta (Aβ)-induced neurotoxicity in vitro and in vivo. The in vitro results showed that LMWCS blocked Aβ25–35-induced cell viability loss and apoptosis, decreased intracellular calcium concentration, reactive oxygen species (ROS) levels, the mitochondrial membrane potential (MMP) depolarization, and the protein expression of Caspase-3. During in vivo experiments, LMWCS improved the cognitive impairment induced by Aβ1–40, increased the level of choline acetyltransferase (ChAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and decreased the level of malondialdehyde (MDA) and acetylcholinesterase (AChE) in the mouse brain. Moreover, LMWCS decreased the density of pyramidal cells of CA1 regions, and suppressed the protein expression of Bax/Bcl-2 and Caspase-3, -9 in the hippocampus of mice. In conclusion, LMWCS possessed neuroprotective properties against toxic effects induced by Aβ peptides both in vitro and in vivo, which might be related to anti-apoptotic activity. LMWCS might be a useful preventive and therapeutic compound for Alzheimer’s disease.

Effect of Cyperus rotundus on ischemia-induced brain damage and memory dysfunction in rats.

Global cerebral ischemia-reperfusion injury causes loss of pyramidal cells in CA1 region of hippocampus. In this study, we investigated the possible neuroprotective effects of the ethanol extract of Cyperus rotundus (EECR) on a model of global transient ischemia in rat, by evaluating the pathophysiology of the hippocampal tissue and spatial memory. Treatment group (EECR, 100 mg/kg/day) was gavaged from 4 days before, to 3 days after ischemia. Morris water maze test was performed 1 week after ischemia for 4 days. Brain tissue was prepared for Nissl staining. Our data showed no statistical difference between the treatment and ischemia groups in water maze task. So, treatment of ischemia with EECR cannot improve spatial learning and memory. On the contrary EECR ameliorated the CA1 pyramidal cell loss due to transient global ischemia/reperfusion injury. These results suggest that EECR cannot reduce the ischemia-induced, cognitive impairments seen after transient, global cerebral ischemia but can prevent pyramidal cell loss in CA1 region of hippocampus.

Effect of mild hypothermia on the expression of acid-sensing ion channels 1a and 2a following global cerebral ischemia-reperfusion in rats

To investigate the effects of mild hypothermia on the expression of ASIC1a and ASIC2a in the rat hippocampus following global cerebral ischemia-reperfusion, so as to speculate the underlying mechanisms of neuroresuscitation. Ninety five male SD rats were randomly divided into five groups (n = 19): sham operation group (I), model group (II), mild hypothermia group (III), PcTX1 group (IV), mild hypothermia combined PcTX1 group (V). Transient (15 min) global cerebral ischemia was induced by the four-vessel occlusion. PcTX1 (500 ng/ml) 6 µl were injected into lateral cerebral ventricle immediately after reperfusion in group IV and V, while the equal volume of normal saline was injected into lateral cerebral ventricle immediately after reperfusion in the other three groups. At the same time, mild hypothermia after reperfusion was performed and lasted for 6 hours in group III and V, the rectal temperature was reduced to 32 - 33°C within 15 min, while it was maintained at 36 - 37°C by lamp in other three groups. Determination the expression of ASIC1a and ASIC2a protein at 6 h and 24 h of reperfusion, and the expression of ASIC1a and ASIC2a mRNA at 24 h of reperfusion. Observe the pathomorphological changes of hippocampal CA1 neurons at 24 h of reperfusion. Detect the brain water content at 72 h of reperfusion. The difference in the expression of ASIC1a mRNA and protein among the groups was not changed significantly (P > 0.05). Compared with group I, the expression of ASIC2a mRNA and ASIC2a protein was up-regulated in other groups (P < 0.05). It was significantly higher in group III and V than in group II and IV (P < 0.05). Compared to 6 h of reperfusion, the expression of ASIC2a protein was higher in group II, III, IV and V respectively after 24 h of reperfusion. Compared to group I, the number of pyramidal cells in CA1 region of hippocampus in group II, III, IV and V were decreased at 24 h of reperfusion (P < 0.01). Compared to group II, the number of pyramidal cells in CA1 region of hippocampus in group III, IV and V were increased at 24 h of reperfusion (P < 0.01); and compared to group III and IV, the number of pyramidal cells at 24 h of reperfusion in group V was significantly higher (P < 0.01). Compared to group I, the content of brain water in II, III and IV group were increased at 72 h of reperfusion (P < 0.01). Compared to group II, the content of brain water in group III, IV and V were decreased at 72 h of reperfusion (P < 0.01). Giving mild hypothermia or PcTX1 could alleviate the damage in CA1 region of hippocampus, with the best effect in group V, which administers PcTX1 combined mild hypothermia. Mild hypothermia attenuates global cerebral ischemia-reperfusion of rat, which may up-regulate the expression of ASIC2a mRNA and protein. Mild hypothermia combined by PcTX1 could induce neuroresuscitation.

Effects of FK506 on Hippocampal CA1 Cells Following Transient Global Ischemia/Reperfusion in Wistar Rat.

Transient global cerebral ischemia causes loss of pyramidal cells in CA1 region of hippocampus. In this study, we investigated the neurotrophic effect of the immunosuppressant agent FK506 in rat after global cerebral ischemia. Both common carotid arteries were occluded for 20 minutes followed by reperfusion. In experimental group 1, FK506 (6 mg/kg) was given as a single dose exactly at the time of reperfusion. In the second group, FK506 was administered at the beginning of reperfusion, followed by its administration intraperitoneally (IP) 6, 24, 48, and 72 hours after reperfusion. FK506 failed to show neurotrophic effects on CA1 region when applied as a single dose of 6 mg/kg. The cell number and size of the CA1 pyramidal cells were increased, also the number of cell death decreased in this region when FK506 was administrated 48 h after reperfusion. This work supports the possible use of FK506 in treatment of ischemic brain damage.

Transcriptome Analysis of the Hippocampal CA1 Pyramidal Cell Region after Kainic Acid-Induced Status Epilepticus in Juvenile Rats

Molecular mechanisms involved in epileptogenesis in the developing brain remain poorly understood. The gene array approach could reveal some of the factors involved by allowing the identification of a broad scale of genes altered by seizures. In this study we used microarray analysis to reveal the gene expression profile of the laser microdissected hippocampal CA1 subregion one week after kainic acid (KA)-induced status epilepticus (SE) in 21-day-old rats, which are developmentally roughly comparable to juvenile children. The gene expression analysis with the Chipster software generated a total of 1592 differently expressed genes in the CA1 subregion of KA-treated rats compared to control rats. The KEGG database revealed that the identified genes were involved in pathways such as oxidative phosporylation (26 genes changed), and long-term potentiation (LTP; 18 genes changed). Also genes involved in Ca2+ homeostasis, gliosis, inflammation, and GABAergic transmission were altered. To validate the microarray results we further examined the protein expression for a subset of selected genes, glial fibrillary protein (GFAP), apolipoprotein E (apo E), cannabinoid type 1 receptor (CB1), Purkinje cell protein 4 (PEP-19), and interleukin 8 receptor (CXCR1), with immunohistochemistry, which confirmed the transcriptome results. Our results showed that SE resulted in no obvious CA1 neuronal loss, and alterations in the expression pattern of several genes during the early epileptogenic phase were comparable to previous gene expression studies of the adult hippocampus of both experimental epileptic animals and patients with temporal lobe epilepsy (TLE). However, some changes seem to occur after SE specifically in the juvenile rat hippocampus. Insight of the SE-induced alterations in gene expression and their related pathways could give us hints for the development of new target-specific antiepileptic drugs that interfere with the progression of the disease in the juvenile age group.

Neuroprotective effects of lactation against kainic acid treatment in the dorsal hippocampus of the rat

Marked hippocampal changes in response to excitatory amino acid agonists occur during pregnancy (e.g. decreased frequency in spontaneous recurrent seizures in rats with KA lesions of the hippocampus) and lactation (e.g. reduced c-Fos expression in response to N-methyl- d, l-aspartic acid but not to kainic acid). In this study, the possibility that lactation protects against the excitotoxic damage induced by KA in hippocampal areas was explored. We compared cell damage induced 24 h after a single systemic administration of KA (5 or 7.5 mg/kg bw) in regions CA1, CA3, and CA4 of the dorsal hippocampus of rats in the final week of lactation to that in diestrus phase. To determine cellular damage in a rostro-caudal segment of the dorsal hippocampus, we used NISSL and Fluorojade staining, immunohistochemistry for active caspase-3 and TUNEL, and we observed that the KA treatment provoked a significant loss of neurons in diestrus rats, principally in the pyramidal cells of CA1 region. In contrast, in lactating rats, pyramidal neurons from CA1, CA3, and CA4 in the dorsal hippocampus were significantly protected against KA-induced neuronal damage, indicating that lactation may be a natural model of neuroprotection.

Ethanol Exposure and Withdrawal Sensitizes the Rat Hippocampal CA1 Pyramidal Cell Region to ??-Amyloid (25-35)-Induced Cytotoxicity: NMDA Receptor Involvement

Millions of Americans suffer from Alzheimer's Disease (AD), which is characterized by significant neurological impairment and an accumulation in brain tissue of senile plaques consisting of beta amyloid (Abeta) peptide. The hippocampus, a region primarily responsible for learning and memory, appears to be particularly susceptible to AD-related injury and chronic alcohol abuse. Although certain risk factors for AD are known, it is unclear if alcohol abuse or dependence may contribute to neuropathology in AD. Recent research suggests that low-to-moderate consumption of alcohol may protect against development of AD, while alcohol dependence may increase risk of developing AD. Therefore, the current studies aimed to investigate the effects of exposure to 50 or 100 mM ethanol (EtOH) and withdrawal on hippocampal injury induced by Abeta peptide treatment. The present studies exposed organotypic hippocampal slice cultures to 50 or 100 mM ethanol (EtOH) for 10 days, after which the slices underwent ethanol withdrawal (EWD) in the presence of varying concentrations of Abeta 25-35 (0.1, 1, 10 microM), or 35-25 (200 microM), a negative control reverse sequence peptide. Cellular injury, as evidenced by uptake of propidium iodide (PI), was assessed for each subregion of the hippocampal complex (CA1, CA3, and dentate gyrus). Cellular injury in the CA1 pyramidal cell layer was significantly increased during withdrawal from exposure to 100 mM, but not 50 mM, EtOH. Exposure to Abeta in ethanol-naïve cultures did not produce significant cytotoxicity. However, exposure to Abeta during EWD from 100 mM produced marked increases in CA1 pyramidal cell region cytotoxicity, effects reversed by cotreatment with a nontoxic concentration of the NMDA receptor channel blocker MK-801 (20 microM). These data suggest that withdrawal from exposure to a high concentration of EtOH produces marked cellular injury in the hippocampus, particularly the CA1 subregion. Further, this EtOH exposure and withdrawal regimen sensitizes the hippocampus to the toxic effects of Abeta treatment in a manner reflecting over activity of NMDA receptor function.

Ethanol antagonizes kainate receptor-mediated inhibition of evoked GABA(A) inhibitory postsynaptic currents in the rat hippocampal CA1 region.

Many studies have demonstrated that ethanol reduces glutamatergic synaptic transmission primarily by inhibiting the N-methyl-D-aspartate subtype of glutamate receptor. In contrast, the other two subtypes of ionotropic glutamate receptor (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and kainate) have generally been shown to be insensitive to intoxicating concentrations of ethanol. However, we have previously identified a population of kainate receptors that mediate slow excitatory postsynaptic currents in the rat hippocampal CA3 pyramidal cell region that is potently inhibited by low concentrations of ethanol. In this study, we examined the effect of ethanol on kainate receptor-mediated inhibition of evoked GABA(A) inhibitory postsynaptic currents (IPSCs) in the rat hippocampal CA1 pyramidal cell region. Under our recording conditions, bath application of 1 microM kainate significantly inhibited GABA(A) IPSCs. This inhibition seemed to be mediated by the activation of somatodendritic kainate receptors on GABAergic interneurons and the subsequent activation of metabotropic GABA(B) receptors, because the kainate inhibition was largely blocked by pretreating slices with a GABA(B) receptor antagonist. Ethanol pretreatment significantly antagonized the inhibitory effect of kainate on GABA(A) IPSCs, at concentrations as low as 20 mM. In contrast, ethanol did not block the direct inhibitory effect of a GABA(B) receptor agonist on GABA(A) IPSCs. The results of this study suggest that modest concentrations of ethanol may antagonize presynaptic, as well as postsynaptic, kainate receptor function in the rat hippocampus.

Sevoflurane improves electrophysiological recovery of rat hippocampal slice CA1 pyramidal neurons after hypoxia.

Sevoflurane is a volatile anesthetic agent that reduces cerebral metabolism and thereby may reduce neuronal damage during energy deprivation. We have examined the effect of sevoflurane on hypoxic neuronal damage in rat hippocampal slices. Slices were subjected to 0%, 2%, or 4% sevoflurane 10 minutes before, during, and 10 minutes after hypoxia. The Schaffer collateral pathway was stimulated every 10 seconds and the evoked population spike recorded in the CA1 pyramidal cell region throughout the experiment. During hypoxia, the postsynaptic evoked response was blocked. The time until the blockade of this response in the 0% sevoflurane group was 158 seconds. Sevoflurane (4%) significantly delayed the loss of the evoked response during hypoxia (242 seconds). The percent recovery of the postsynaptic population spike was calculated by dividing the size of the response 120 minutes after hypoxia by its prehypoxic, presevoflurane amplitude. There was no recovery of the population spike in the 0% sevoflurane group 120 minutes after the end of 5 minutes of hypoxia (6 +/- 6%); there was significantly better recovery after 5 minutes of hypoxia in the sevoflurane (4%) treated group (40 +/- 9%). A lower concentration of sevoflurane (2%) delayed the loss of evoked response during hypoxia (191 seconds), but it did not significantly affect recovery of the population spike after hypoxia (7 +/- 7%). Hypoxia irreversibly damages electrophysiologic activity. A high, but clinically usable, concentration of sevoflurane increases the time during hypoxia until the postsynaptic evoked response is blocked and improves recovery of this response after 5 minutes of hypoxia.

Low external NaCl concentration and low osmolarity enhance voltage-gated Ca currents but depress K currents in freshly isolated rat hippocampal neurons

In previous experiments, reducing bath osmolarity ( π o) or external NaCl concentration ([NaCl] o) caused an increase in synaptic currents recorded in whole-cell configuration from pyramidal cells of CA1 region of hippocampal slices. Slow inward current surges, assumed to be calcium currents, were also enhanced. This contrasted with the strong, reversible, generalized depression of voltage-dependent ion currents in isolated neurons, caused by sudden, brief exposure to very low π o. I have now recorded voltage-dependent whole-cell Na-, K- and Ca-currents from freshly isolated hippocampal CA1 pyramidal neurons during more gradual lowering of π o or [NaCl] o. Changes in cell size were determined from image areas and changes in intracellular Ca 2+ activity were measured as the ratio of the fluorescences of fluo-3/fura-red by confocal microscopy. Iso-osmotic substitution of 40 or 60 mM NaCl by mannitol or sucrose for 5–7 min, or reducing π o by deleting NaCl from the bath (osmolarity decreased by 69 or 108 mosM/kg) depressed K currents. Na currents were also strongly depressed, but this is in part attributable to reduced driving potential and ionic conductance. The depression of I K varied widely and it was inversely correlated with the degree of hypotonic swelling, suggesting that reduced ion channel conductance also reduces permeability to water. Reducing [NaCl] o by 60 mM, or π o by 105 mosM/kg consistently and reversibly increased Ca currents. Intracellular Ca 2+ level also increased, but the changes of [Ca 2+] i and I Ca were not correlated. Facilitation of the Ca influx into presynaptic terminals could explain the increase of synaptic currents. Depression of outward currents could also contribute to the irritability of the central nervous system typical of clinical hyponatremia.

Effect of small changes in temperature on CA1 pyramidal cells from rat hippocampal slices during hypoxia: implications about the mechanism of hypothermic protection against neuronal damage

Small reductions in temperature have been shown to improve neurologic recovery after ischemia. We have examined the effect of temperature on biochemical and physiological changes during hypoxia using rat hippocampal slices as a model system. The postsynaptic population spike recorded from the CA1 pyramidal cell region of slices subjected to 7 min of hypoxia with hypothermia (34°C) recovered to 73% of its prehypoxic level; slices subjected to the same period of hypoxia at 37°C did not recover. After 7 min of hypoxia ATP fell to 48% of its prehypoxic concentration at 34°C and 30% at 37°C. Potassium fell to 86% during 7 min of hypoxia with hypothermia, this compares to a fall to 58% at 37°C. The increase in sodium after 7 min of hypoxia was also attenuated by hypothermia (133% vs. 163% of its prehypoxic concentration). When the hypoxic period was shortened to 3 min (37°C) the population spike recovered to 94%. If the temperature was increased to 40°C there was only 7% recovery of the population spike after 3 min of hypoxia. With hyperthermia (40°C), ATP fell to 33% after 3 min of hypoxia, this compares to 81% at normothermia. Potassium fell to 76% after 3 min of hypoxia with hyperthermia, this compares to 91% at 37°C. Sodium concentrations increased with hyperthermia before hypoxia, at 3 min of hypoxia there was no significant difference between the hyperthermic and normothermic tissue; there was a large increase in sodium with hyperthermia after 5 min of hypoxia (209% vs. 146%). We conclude that the improved recovery after hypothermic hypoxia is at least in part due to the attenuated changes in ATP, potassium and sodium during hypoxia and that the worsened recovery with hyperthermia is due to an exacerbation of the change in ATP, potassium and sodium concentrations during hypoxia.

Normal perfusion pressure breakthrough: the role of capillaries.

Excision of human cerebral arteriovenous malformations (AVMs) can be complicated by postoperative edema and hemorrhage in adjacent brain tissue, despite the complete excision of the malformation. Various theories have purported to explain the hemodynamic basis for this predisposition, including disordered autoregulation causing "normal perfusion pressure breakthrough" and obstruction of venous drainage leading to "occlusive hyperemia." This study did not evaluate the arterial or venous circulations in this scenario, but rather examined the capillaries in adjacent brain parenchyma for any structural deficiencies that would predispose the brain to the postoperative formation of edema and hemorrhage. Arteriovenous fistulas (AVFs) were created surgically in the necks of 10 male Sprague-Dawley rats, which caused chronic cerebral hypoperfusion with a reduction in cerebral blood flow of between 25% and 50%. Ten age-matched animals were used as controls. Twenty-six weeks after AVF formation the animals were killed and perfusion fixed. Their brain tissue was prepared for light microscopic studies by staining for glial fibrillary acidic protein or for transmission electron microscopy. In the CA1 pyramidal cell region of the hippocampus, it was found that in the animals with AVFs there was increased capillary density and absent astrocytic foot processes in some of these vessels. It was concluded that these vessels had developed as a result of neovascularization in response to chronic cerebral ischemia and that their anatomical configuration made them prone to mechanical weakness and instability following the increase in perfusion pressure that occurs in adjacent brain parenchyma after AVM excision. The authors believe that this study pinpoints a structural accompaniment to the hemodynamic changes that occur in brain tissue in the vicinity of cerebral AVMs that predispose these areas to the formation of edema and hemorrhage after AVM excision.

Effects of prenatal cocaine exposure on the developing hippocampus: intrinsic and synaptic physiology.

A variety of neurological complications has been reported in infants exposed to cocaine during gestation. In the present study, intrinsic cell properties of hippocampal neurons from CA1, CA3, and dentate gyrus regions were measured and compared in tissue from neonatal rats exposed to saline or cocaine in utero. Synaptic properties of the CA1 pyramidal cell region were analyzed at postnatal day (P) 20 with the use of extracellular and intracellular recording techniques. In vitro intracellular recordings (n = 223) obtained at P10, P15 and P20 in tissue from cocaine- and saline-exposed animals revealed no differences in standard cell properties such as resting membrane potential, input resistance, time constant, and action potential amplitude or duration. Hippocampal slices from cocaine-exposed animals exhibited a marked reduction of spike frequency adaptation for all three types of principal hippocampal neurons (e.g., CA1, CA3, and granule cells). The amplitudes of afterhyperpolarizations following a spike train were also decreased in CA1 and CA3 cells in tissue from cocaine-exposed animals. Extracellular and intracellular recordings in the CA1 pyramidal cell region at P20 were obtained to assess and compare synaptic function in tissue from cocaine- and saline-exposed animals. In hippocampal slices from cocaine-exposed animals, synaptic responses in the CA1 region were characterized by multiple population spike activity and reduced inhibitory postsynaptic potentials. The reduction in fast inhibitory postsynaptic potential conductance was not associated with a change in reversal potential. These results suggest that gestational cocaine exposure induces significant changes in intrinsic and synaptic electrophysiological properties of hippocampal neurons in the developing animal. The cell and synaptic features are consistent with an increase in hippocampal excitability, which may contribute to the neurobehavioral deficits and epileptogenic predisposition reported in this infant population. As such, this in utero drug exposure model may provide a useful system in which to elucidate and study the basic cellular mechanisms underlying neurological complications associated with maternal cocaine abuse.

Imaging NMDA- and kainate-induced intrinsic optical signals from the hippocampal slice.

1. Brain ischemia causes excess release and accumulation of glutamate that binds to postsynaptic receptors. This opens ionotropic channels that mediate neuronal depolarization and ionic fluxes that can lead to neuronal death. 2. The CA1 pyramidal cell region of the hippocampus is particularly susceptible to this neurotoxic process. Brain cell swelling is considered an early excitotoxic event, but remains poorly under stood and documented. As cells swell, light transmittance (LT) increases through brain tissue, so we hypothesized that brief exposure to glutamate agonists would elicit cell swelling that could be imaged in real time in the hippocampal slice. 3. A 1-min bath application of 100 microM N-methyl-D-aspartate (NMDA) or 100 microM kainate at 22 degrees C greatly increased LT, particularly in the dendritic regions of CA1. The response peaked by 2-3 min and slowly reversed over the subsequent 20 min following exposure. Peak LT increases were > 50% in CA1 stratum radiatum and > 20% in both CA1 stratum oriens and the dendritic region of the dentate gyrus, all areas with a high concentration of NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors. The CA3 stratum radiatum, which contains fewer of these receptors, showed a comparatively small LT increase. 4. The NMDA receptor antagonist 2-amino-5-phosphonovalerate (AP-5) [but not 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)] blocked the CA1 response to NMDA, whereas the non-NMDA receptor antagonist CNQX (but not AP-5) blocked the response to kainate. The relative tissue resistance measured across CA1 stratum radiatum increased after NMDA or kainate exposure with a time course similar to the LT change described above. The increase in relative tissue resistance was blocked by kynurenate, a nonspecific glutamate antagonist. Increases in both LT and tissue resistance provide two independent lines of evidence that cell swelling rapidly developed in CA1 dendritic areas after activation of NMDA or AMPA receptors. 5. This swelling at 22 degrees C was accompanied by a temporary loss of the evoked CA1 field potential. However, at 37 degrees C the dendritic swelling rapidly progressed to an irreversible LT increase (swelling) of the CA1 cell bodies accompanied by a permanent loss of the evoked field. 6. We propose that dendritic swelling mediated by NMDA and AMPA receptors is an early excitotoxic event that can herald permanent damage to CA1 neurons, those cells most vulnerable to ischemic insult.

Androgens modulate glucocorticoid receptor mRNA, but not mineralocorticoid receptor mRNA levels, in the rat hippocampus.

Androgen, mineralocorticoid and glucocorticoid receptors (AR, MR and GR, respectively) are ligand-activated transcription factors that alter gene expression and have a wide variety of effects in the central nervous system. High levels of AR, MR and GR mRNA have been found in the CA1 pyramidal cell region of the rat hippocampus and all 3 of these proteins bind to a similar hormone response element in DNA suggesting the possibility of common receptor function or cross-talk between these receptors at the level of transcription. To begin to investigate this hypothesis, we examined the regulation of AR, MR and GR mRNA expression in the rat hippocampus following treatment with androgens in combination with gonadectomy and/or adrenalectomy. Three-month-old male Sprague-Dawley rats were either castrated for 3 weeks, castrated and immediately implanted with 2 Silastic capsules filled with the non-aromatizable androgen, dihydrotestosterone, or left gonadally intact. Four days prior to sacrifice, these animals were either adrenalectomized or sham operated. GR, MR and AR mRNA were measured in the hippocampal subfields using in situ hybridization. In the CA1 region, dihydrotestosterone treatment of castrates decreased GR mRNA levels to 69 percent of levels found in gonadally intact rats and prevented the adrenalectomy-induced increases in GR mRNA observed in the gonadally intact and castrated animals. No changes in GR mRNA were observed in the CA3 region or dentate gyrus, where AR expression is low or absent. There was no effect of androgen treatment on MR mRNA levels nor did gonadectomy or androgen replacement alter the increases in MR mRNA following adrenalectomy. AR mRNA levels in the CA1 region were unchanged across all treatment groups. In vitro binding studies revealed almost complete nuclear occupancy of hippocampal AR in dihydrotestosterone-treated castrates. No appreciable in vitro binding of dihydrotestosterone to hippocampal MR or GR (Ki approximately 1500 nM) was observed which suggests that androgen regulation of GR mRNA in the hippocampus is occurring through AR binding. These data demonstrate a functional similarity of androgens and glucocorticoids in the regulation of GR mRNA levels in an area where AR and GR are colocalized. Androgen-mediated downregulation of GR expression may prove to be an important event in the adaptive responses of CA1 pyramidal cells to hormonal stimuli.

Electrophysiology of CA1 pyramidal neurons in an animal model of neuronal migration disorders: prenatal methylazoxymethanol treatment.

Prenatal methylazoxymethanol acetate (MAMac) injection disrupts cell migration in developing rats. We investigated the electrophysiological characteristics of hippocampal CA1 pyramidal neurons from young MAMac-treated animals (postnatal days 25-35). In vitro intracellular recordings from CA1 cells in MAMac-treated tissue revealed resting membrane potential (mean, -61.5 +/- 1.5 mV), action potential amplitude (mean, 69 +/- 3.1 mV), action potential duration (mean, 2.1 +/- 0.2 ms), input resistance (mean, 51.5 +/- 3.6 M omega) and time constant (mean, 33.2 +/- 1.2 ms) similar to those of CA1 cells from control tissue. However, MAMac-treated tissue could be distinguished as having a higher percentage of cells (62% vs. 10%) which fire a burst of action potentials in response to suprathreshold current injection. The synaptic responses of CA1 cells in MAMac-treated and control tissue were comparable. The CA1 field response to stimulation was also comparable at all stimulus intensities tested (50-1500 microA). Elevation of extracellular potassium concentration ([K+]o) from 3 mM to 6 mM resulted in epileptiform discharge activity in response to stratum radiatum stimulation in all MAMac-treated slices (10/10) but in only one-third of controls (3/9). Spontaneous epileptiform discharges were also observed in the majority (8/13) of MAMac-treated slices bathed in 6 mM KCl but in no controls. These data suggest that MAMac treatment during fetal development not only disrupts normal anatomical organization but also leads to alterations in electrophysiological features of the hippocampal CA1 pyramidal cell region. As such, the MAMac model may provide insights into early onset seizure syndromes associated with developmental abnormalities.