Area CA1 Of Rat Hippocampus Research Articles

Brain‐Derived Neurotrophic Factor Enhances Bcl‐xL Expression Through Protein Kinase Casein Kinase 2‐Activated and Nuclear Factor Kappa B‐Mediated Pathway in Rat Hippocampus

Brain-derived neurotrophic factor (BDNF) was shown to produce its neuroprotective effect through extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidylinositol-3 kinase (PI3-K) signaling. But whether other pathways also mediate the neuroprotective effect of BDNF is less known. In this study, we found that direct administration of BDNF to rat hippocampal CA1 area dose-dependently increased the mRNA and protein levels of Bcl-xL. BDNF also increased protein kinase casein kinase II (CK2) activity and NF-κB phosphorylation at Ser529 dose-dependently. Further, transfection of the wild-type CK2α DNA to CA1 neurons increased nuclear factor kappa B (NF-κB) phosphorylation and Bcl-xL mRNA expression, whereas transfection of CK2α156A, the catalytically inactive mutant of CK2α, decreased these measures. Moreover, transfection of CK2α small interfering RNA (siRNA) blocked the enhancing effect of BDNF on NF-κB phosphorylation and Bcl-xL expression. These results were further confirmed by treatment of 4,5,6,7-tetrabromobenzotriazole (TBB), a specific CK2 inhibitor. Transfection of NF-κBS529A, the dominant negative mutant of NF-κB, prevented the enhancing effect of BDNF on Bcl-xL expression. More importantly, BDNF activation of CK2 is not affected by co-administration of the ERK1/2 inhibitor, PD98059, and the PI3-K inhibitor, LY294002. These results demonstrate a novel BDNF signaling pathway and provide an alternative therapeutic strategy for the protective effect of BDNF on hippocampal neurons in vivo.

Importance of Cationic Channels for Functioning of the Nuclear Envelope of Neurons as a Calcium Store

The membrane of the endoplasmic reticulum is, in fact, an extension of the nuclear envelope of eukaryotic cells; both these compartments can fulfill the function of intracellular calcium stores. Using a patch-clamp technique, we studied the biophysical properties of the channels expressed in the inner nuclear membrane of pyramidal neurons of the rat hippocampal CA1 area, in particular of large-conductance cationic channels and calcium channels of inositol trisphosphate receptors (the main channels in membranes of this type). As the results of the measurements showed, the activity of channels of both types demonstrates clearly pronounced voltage dependences. The probability of their open state (P o) depends on the voltage inside the nuclear envelope lumen. At positive potentials, the activity of these channels is significantly more intense than at negative potentials. Moreover, channels of both types are reversibly blocked at considerable negative potentials. We believe that this property of ion channels in the nuclear envelope is an important factor responsible for the control of calcium signals in the cell nucleus. We propose a hypothesis on the mechanism underlying termination of Ca2+ release from such intracellular stores, which is based on the specificity of the voltage dependence of ion channels of the above-mentioned types.

Electroacupuncture Protected Pyramidal Cells in Hippocampal CA1 Region of Vascular Dementia Rats by Inhibiting the Expression of P53 and Noxa

Clinically electroacupuncture (EA) is proved an effective therapy for vascular dementia (VD), but their mechanisms remain uncertain. The aim of this study was to determine whether EA protects pyramidal cells from apoptosis in hippocampus of a VD rat model by inhibiting the expression of p53 and Noxa. One month after a VD animal model was established by bilateral occlusion of common carotid arteries, EA treatment was given at "Baihui" (DU20), "Dazhui" (DU14), and "Shenshu" (BL23). The learning and memory ability was assessed by Morris water maze. Neuronal apoptosis in hippocampus was evaluated with hematoxylin-eosin (HE) staining, and the expression of p53 and Noxa was analyzed by confocal laser scanning microscope with immunofluorescence staining. Expressions of p53 and Noxa in the EA group and sham-operated group were less than in the VD model group (P < 0.01), and the expression of p53 was positively correlated to expression of Noxa in hippocampus of VD rats (r = 0.918, P < 0.01). EA treatment could reduce the amount of apoptotic neurons in hippocampal CA1 area of rats with VD. The average latency in the Morris water maze test was significantly shorter, and escape strategies improved from edge and random searches to more linear swim pathway in the EA group compared with the VD model group (P < 0.01). The increasing expressions of p53 and Noxa play important roles in the pathogenesis of VD. EA improves learning and memory ability and protects pyramidal cells from apoptosis by blocking expression of p53 and Noxa in the hippocampal CA1 region of VD rats. These results suggest a novel mechanism of EA treatment to VD.

Sevoflurane Postconditioning Ameliorates Oxygen–Glucose Deprivation—Reperfusion Injury in the Rat Hippocampus

Sevoflurane is well known to exert a neuroprotective effect through anesthetic preconditioning. However, its effects on postconditioning, a neuroprotective phenomenon following an insult, have not been well studied. In this study, we examined the ability of sevoflurane to induce postconditioning in rat hippocampal slices, in vitro. 2%, 4%, and 6% sevoflurane reduced neurophysiologic and morphologic neuronal injury following oxygen-glucose deprivation (OGD) and reperfusion. The quantity of damaged neurons was significantly reduced on immunofluorescence staining; excitatory amino acids (Asp, Glu) increased and inhibitory amino acids (GABA) decreased significantly. The effect was concentration-dependent. Postconditioning with sevoflurane reduces neuronal damage after OGD-reperfusion injury in the CA1 area of rat hippocampus, in vitro.

A Comparison of the Dynamics of S100B, S100A1, and S100A6 mRNA Expression in Hippocampal CA1 Area of Rats during Long-Term Potentiation and after Low-Frequency Stimulation

The interest in tissue- and cell-specific S100 proteins physiological roles in the brain remains high. However, necessary experimental data for the assessment of their dynamics in one of the most important brain activities, its plasticity, is not sufficient. We studied the expression of S100B, S100A1, and S100A6 mRNA in the subfield CA1 of rat hippocampal slices after tetanic and low-frequency stimulation by real-time PCR. Within 30 min after tetanization, a 2–4 fold increase of the S100B mRNA level was observed as compared to the control (intact slices) or to low-frequency stimulation. Subsequently, the S100B mRNA content gradually returned to baseline. The amount of S100A1 mRNA gradually increased during first hour and maintained at the achieved level in the course of second hour after tetanization. The level of S100A6 mRNA did not change following tetanization or low-frequency stimulation.

Perinatal Nutritional Iron Deficiency Impairs Noradrenergic-Mediated Synaptic Efficacy in the CA1 Area of Rat Hippocampus ,

Many studies have shown that perinatal nutritional iron deficiency (ID) produces learning impairments in children. Research has also shown that catecholamines like epinephrine and norepinephrine play a pivotal role in the consolidation of memories. In this study, we sought to determine if perinatal ID impairs the following: 1) noradrenergic synaptic function in the hippocampus; and 2) several forms of hippocampus-dependent fear learning. Electrophysiological brain slice methods were used to examine noradrenergic-mediated synaptic efficacy in the CA1-hippocampus of rats that were subjected to perinatal ID or control (CN) diets. Rats were fed ID (3 mg Fe/kg) or CN (45 mg Fe/kg) diets on gestational d 14. These diets were maintained until postnatal d (P) 12 after which all rats were switched to the CN diet. Hippocampal slices were prepared between P26 and P30. The noradrenergic agonist isoproterenol (ISO) (1, 2, or 4 μmol) was used to induce modulatory increases in synaptic efficacy in the hippocampal slices. CN slices showed a long-lasting increase in synaptic efficacy as the result of ISO perfusion in the slice bath, whereas ID slices did not show increases in synaptic efficacy as the result of ISO perfusion. ID and CN groups did not differ when ISO was perfused through slices from adult rats (P61). Both young and adult ID rats showed reduced levels of hippocampus-dependent fear learning compared with the young and adult CN rats. Together, these findings suggest that ID may impair early forms of noradrenergic-mediated synaptic plasticity, which may in turn play a role in adult learning deficits.

Regulation of cathepsin B and caspase-3 in long-term plasticity

It has been previously shown that high-frequency stimulation of Schaffer collaterals (HFS), which induces LTP in the CA1 area of rat hippocampus, under normal conditions results in the activation of caspase-3. In contrast to caspase-3, the activity of cathepsin B weakly decreased in hippocampal slices subjected to HFS (the significance level was p = 0.07). This effect was observed in all slices frozen for subsequent measurements of enzymatic activity in 15 minutes and 3 hours after LTP induction under normal conditions and in the presence of caspase-3 inhibitors. The reciprocal influence of HFS, which was observed in the control slices depending on their initial state (r = 0.59, p < 0.001 in control and r = 0.16, p = 0.46 in slices subjected to HFS), complicated simultaneous measurements of the activity of these enzymes. Though the effect of HFS on cathepsin B activity is not prominent, a significant difference in LTP magnitude in slices with low and high cathepsin B activity.

Effect of midazolam onsynaptic transmission in rat hippocampal CA1 area

：Objective To investigatethe effect of midazolam on synaptic transmission in stratum radiatum of CA1 area of rathippocampus and the underlying mechanism. Methods Thirty-five adult male Wistar ratsweighing 190-220 g were randomly divided into 7 groups ( n = 5 each) . Two types ofstimulation were used: single stimulation and paired pulse stimulation. Four groups undersingle stimulation: control group (group C_1), bicuculline group (group B_1 ), midazolamgroup (group M_1) and bicuculline + midazolam group (group BM). Three groups under pairedpulse stimulation: control group ( group C_2 ), bicuculline group (group B_2 ) andmidazolam group (group M_2 ) . The animals were anesthetized with intraperitoneal (IP)pentobarbital 50 mg/kg. The stimulating and recording electrodes were inserted into thestratum radiatum of CA1 area of the hippocampus. The interval between the 2 pulsestimulation was 30 ms. Excitatory post-synaptic potential (EPSP) was elicited before(baseline) and after IP bicuculline (2 mg/kg) or/and midazolam (3 mg/kg) administration.The EPSP amplitude was recorded during single stimulation. EPSP_2 /EPSP_1 ( E_2 /E_1 )ratio was recorded during paired pulse stimulation. Results Compared with group C, , theEPSP amplitude was significantly decreased in group M, ( P 0.05) . Compared with group C_2 ,E_2 and E_2/E_1, ratio were significantly increased in group B_2 , while E_1 , E_ 2, andE_2/E_1, ratio were significantly decreased in group M2 ( P < 0.05). E_1, E_2 and E_2/E_1, ratio were significantly lower in group M_2 than in group B_2 (P < 0.05) .Conclusion Midazolam can reversibly depress the excitatory synaptic transmission efficacyin the CA1 area of the rat hippocampus through presynaptic inhibitory circuit. CABA_Areceptor is not directly disturbed.

Sodium valproate at the therapeutic concentration inhibits the induction but not the maintenance phase of long-term potentiation in rat hippocampal CA1 area

Sodium valproate (VPA) is currently one of the major antiepileptic drugs and has been reported to impair the induction of long-term potentiation (LTP) in rat hippocampal. However, there are discrepancies when used at therapeutic dose and few researches to study the effects of VPA on the maintenance of LTP. Here we investigated the effects of VPA at therapeutic concentration on two LTP phases: induction and maintenance in CA1 region. We found (1) VPA inhibited field excitatory postsynaptic potentials (fEPSPs) without modifying paired-pulse facilitation (PPF) solely occured presynaptically as a form of synaptic plasticity. (2) Pretreatment with VPA before high-frequency stimulation (HFS) decreased the fEPSPs slope. (3) There were no significant changes in fEPSPs slope with VPA applied in maintenance phase of LTP. These results indicate that VPA inhibited the induction of LTP postsynaptically without modifying presynaptic neurotransmitter release and had no significant influence on the two maintenance phase of LTP.

Role of nitric oxide in the rat hippocampal CA1 in morphine antinociception

In the present study, the effects of intra-hippocampal CA1 injections of l-arginine, a nitric oxide (NO) precursor and N G-nitro- l-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, on morphine-induced antinociception in rat formalin test were investigated. To induce inflammation pain, formalin (50 μl at 2.5%) was injected into the right hind-paw of male Wistar rats prior to testing. Morphine (3–9 mg/kg) was injected intraperitoneally (i.p.) 10 min before injection of formalin. The present study shows that administration of l-arginine (0.08, 0.15, 0.3, 1.0 and 3.0 μg/rat), but not L-NAME (0.15, 0.3 and 1.0 μg/rat), 5 min before formalin injection reversed morphine-induced antinociception at the early phase of formalin test. However, both drugs blocked morphine antinociception at the late phase of the test, but none of these drugs elicited any response by themselves at the tonic phase when injected alone. Moreover, the response to l-arginine was potentiated by L-NAME pre-treatment. It should be noted that a single injection of both l-arginine and L-NAME showed nociceptive effect at the early phase of the test. The present study reveals an expression of NADPH-diaphorase in the rat brain samples administered by l-arginine. Expression of NADPH-d is decreased in the samples which were pre-injected with L-NAME. This study suggests NO participation in the rat hippocampal CA1 area in morphine-induced antinociception.

A Neural Circuit Mechanism Integrating Motivational State with Memory Expression in Drosophila

Behavioral expression of food-associated memory in fruit flies is constrained by satiety and promoted by hunger, suggesting an influence of motivational state. Here, we identify a neural mechanism that integrates the internal state of hunger and appetitive memory. We show that stimulation of neurons that express neuropeptide F (dNPF), an ortholog of mammalian NPY, mimics food deprivation and promotes memory performance in satiated flies. Robust appetitive memory performance requires the dNPF receptor in six dopaminergic neurons that innervate a distinct region of the mushroom bodies. Blocking these dopaminergic neurons releases memory performance in satiated flies, whereas stimulation suppresses memory performance in hungry flies. Therefore, dNPF and dopamine provide a motivational switch in the mushroom body that controls the output of appetitive memory.

Lateralized learning and memory effects of vasoactive intestinal peptide infused into the rat hippocampal CA1 area

The effects of VIP microinjected unilaterally (left or right) and bilaterally (left and right) at a dose of 50 ng into hippocampal CA1 area of male Wistar rats on learning and memory (shuttle-box) were studied. Bilateral VIP microinjections impaired learning and memory, i.e., decreased the number of avoidances during the second training day and memory tests, compared to the respective controls. When infused into the left CA1 area, VIP exerted a marked inhibitory effect. Right-side VIP microinjections did not change the number of avoidances during the learning and memory tests. Compared to the right-side, left-side VIP infusions provoked a threefold decrease of the number of avoidances on the second training day and on the memory tests (24 h after the 2nd training day and on 7th day). These findings reveal lateralized inhibitory effects of VIP on cognitive processes in hippocampus.

Opioid withdrawal for 4 days prevents synaptic depression induced by low dose of morphine or naloxone in rat hippocampal CA1 area in vivo

The formation of memory is believed to depend on experience- or activity-dependent synaptic plasticity, which is exquisitely sensitive to psychological stress since inescapable stress impairs long-term potentiation (LTP) but facilitates long-term depression (LTD). Our recent studies demonstrated that 4 days of opioid withdrawal enables maximal extents of both hippocampal LTP and drug-reinforced behavior; while elevated-platform stress enables these phenomena at 18 h of opioid withdrawal. Here, we examined the effects of low dose of morphine (0.5 mg kg(-1), i.p.) or the opioid receptor antagonist naloxone (1 mg kg(-1), i.p.) on synaptic efficacy in the hippocampal CA1 region of anesthetized rats. A form of synaptic depression was induced by low dose of morphine or naloxone in rats after 18 h but not 4 days of opioid withdrawal. This synaptic depression was dependent on both N-methyl-D-aspartate receptor and synaptic activity, similar to the hippocampal long-term depression induced by low frequency stimulation. Elevated-platform stress given 2 h before experiment prevented the synaptic depression at 18 h of opioid withdrawal; in contrast, the glucocorticoid receptor (GR) antagonist RU38486 treatment (20 mg kg(-1), s.c., twice per day for first 3 days of withdrawal), or a high dose of morphine reexposure (15 mg kg(-1), s.c., 12 h before experiment), enabled the synaptic depression on 4 days of opioid withdrawal. This temporal shift of synaptic depression by stress or GR blockade supplements our previous findings of potentially correlated temporal shifts of LTP induction and drug-reinforced behavior during opioid withdrawal. Our results therefore support the idea that stress experience during opioid withdrawal may modify hippocampal synaptic plasticity and play important roles in drug-associated memory. (c) 2009 Wiley-Liss, Inc.

Impairment of long-term depression induced by chronic brain inflammation in rats

Although deficits in synaptic plasticity have been identified in aged or neuroinflamed animals with memory impairments, few studies have examined the cellular basis of plasticity in such animals. Here, we examined whether chronic neuroinflammation altered long-term depression (LTD) and studied the underlying mechanism of LTD impairment by neuroinflammation. Chronic neuroinflammation was induced by administration of lipopolysaccharide (LPS) to the fourth ventricle. Excitatory postsynaptic potentials were recorded extracellularly in the rat hippocampal CA1 area to examine alterations in synaptic plasticity. Chronic administration of LPS induced remarkable memory impairment in the Morris water maze test. N-methyl-d-aspartate receptor (NMDAR)-dependent LTD was almost absent in LPS-infused animals. The AMPA receptor (AMPAR)-mediated synaptic response was reduced in the LPS-infused group. These results suggest that reduction in NMDAR-dependent LTD might arise because of alterations in postsynaptic AMPARs as well as NMDARs and that such changes may be present in mild and early forms of Alzheimer-type dementia.

Chronic brain inflammation impairs two forms of long-term potentiation in the rat hippocampal CA1 area

Neuroinflammation plays an important role in the progression of Alzheimer's disease (AD) and is characterized by the presence of activated microglia. We investigated whether chronic neuroinflammation affects the induction of N-methyl- d-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) and NMDAR-independent LTP which is expressed by voltage-dependent calcium channel (VDCC). Chronic neuroinflammation was induced by administration of lipopolysaccharide (LPS) (28 days, 0.35 μg/h) to the fourth ventricle. The Morris water maze test was conducted to measure the memory impairment and then excitatory postsynaptic potentials were recorded extracelluarly from stratum radiatum in the rat hippocampal CA1 area to examine the changes in synaptic plasticity induced by LPS infusion. Chronic administration of LPS induced remarkable memory impairment. The field recording experiments revealed that the induction of both NMDAR-dependent LTP and NMDAR-independent LTP were impaired in the hippocampal Schaffer collateral-CA1 synapse in animals chronically infused with LPS. The present results show that chronic neuroinflammation can lead to the impaired spatial memory and attenuation of VDCC-dependent LTP as well as NMDAR-dependent LTP. The attenuation of synaptic plasticity may be caused by the impairment of both NMDAR and L-type Ca 2+ via elevated levels of inflammatory proteins, which may underlie aspects of dementia.

Protein kinase C mediates amyloid β-protein fragment 31–35-induced suppression of hippocampal late-phase long-term potentiation in vivo

Amyloid β-protein (Aβ) in the brain of Alzheimer’s disease (AD) plays a detrimental role in synaptic plasticity and cognitive function. The effects of Aβ on the early-phase long-term potentiation (E-LTP) have been reported widely. However, whether the late-phase long-term potentiation (L-LTP), which differs from E-LTP mechanistically, is also affected by Aβ is still an open question. The present study examined the effects of intracerebraventricular injection of Aβ fragments 25–35 and 31–35 on the L-LTP in the CA1 area of rat hippocampus in vivo, and further investigated its possible underlying mechanism. Our results showed that: (1) Aβ25–35 (6.25–25 nmol) did not affect the baseline field excitatory postsynaptic potentials, but dose-dependently suppressed multiple high-frequency stimuli-induced L-LTP; (2) Aβ31–35, a shorter Aβ fragment than Aβ25–35, also significantly suppressed L-LTP, with the same suppressive effects as Aβ25–35; (3) pretreatment with PMA (6 nmol/5 μl), a membrane permeable PKC agonist, effectively prevented Aβ31–35-induced deficits in the early and the late components of L-LTP; (4) co-application of Aβ31–35 and chelerythrine (12 nmol/5 μl), a PKC antagonist, caused no additive suppression of L-LTP. These results indicate that both Aβ25–35 and Aβ31–35 can impair hippocampal synaptic plasticity in vivo by suppressing the maintenance of L-LTP, and PKC probably mediates the Aβ-induced suppression of hippocampal L-LTP. In addition, the similar efficacy of Aβ31–35 and Aβ25–35 in L-LTP suppression supports the hypothesis we suggested previously that the sequence 31–35 in Aβ might be the shortest active sequence responsible for the neuronal toxicity induced by full length of Aβ molecules.

Axospinous synaptic subtype‐specific differences in structure, size, ionotropic receptor expression, and connectivity in apical dendritic regions of rat hippocampal CA1 pyramidal neurons

The morphology of axospinous synapses and their parent spines varies widely. Additionally, many of these synapses are contacted by multiple synapse boutons (MSBs) and show substantial variability in receptor expression. The two major axospinous synaptic subtypes are perforated and nonperforated, but there are several subcategories within these two classes. The present study used serial section electron microscopy to determine whether perforated and nonperforated synaptic subtypes differed with regard to their distribution, size, receptor expression, and connectivity to MSBs in three apical dendritic regions of rat hippocampal area CA1: the proximal and distal thirds of stratum radiatum, and the stratum lacunosum-moleculare. All synaptic subtypes were present throughout the apical dendritic regions, but there were several subclass-specific differences. First, segmented, completely partitioned synapses changed in number, proportion, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor expression with distance from the soma beyond that found within other perforated synaptic subtypes. Second, atypically large, nonperforated synapses showed N-methyl-D-aspartate (NMDA) receptor immunoreactivity identical to that of perforated synapses, levels of AMPA receptor expression intermediate to that of nonperforated and perforated synapses, and perforated synapse-like changes in structure with distance from the soma. Finally, MSB connectivity was highest in the proximal stratum radiatum, but only for those MSBs composed of nonperforated synapses. The immunogold data suggest that most MSBs would not generate simultaneous depolarizations in multiple neurons or spines, however, because the vast majority of MSBs are comprised of two synapses with abnormally low levels of receptor expression, or involve one synapse with a high level of receptor expression and another with only a low level.

Expression of Ref-1 in hippocampus CA1 area of rats with Alzheimer's disease

To investigate the expression of Redox factor-1(Ref-1) in rats with Alzheimer's disease (AD). AD rat model was established by a single injection of beta-amyloid peptide (Abeta25-35) into the lateral cerebral ventricle of rats. Y-shape maze task was conducted to check the ethology. At 4th, 7th and 14th day after injection, Ref-1 expression in hippocampus CA1 area was detected by immunohistochemistry. The numbers of repeated learning and error and the total reaction time in AD group were significantly higher than those in control group at 7th and 14th day after injection of Abeta25-35 (P<0.05). At 4th day after injection of Abeta25-35, the Ref-1 expression was increased with time prolongation in AD group(P<0.01). Injection of Abeta25-35 in lateral cerebral ventricle can decrease the learning and memory abilities of rats, and results also indicate that Ref-1 expression in hippocampus may be involved in the development of AD.

Effects of ginkgolide B on neuronal discharges in rat hippocampal CA1 area

Effects of ginkgolide B on neuronal discharges in rat hippocampal CA1 area

Diazepam attenuates the post-traumatic hyperactivity of excitatory synapses in rat hippocampal CA1 neurons

The effect of diazepam, a benzodiazepine derivative, on the post-traumatic hyperactivity of excitatory synaptic transmission was examined in rat hippocampal CA1 area. Optical recordings showed that the activity of hippocampal neurons was enhanced in rats treated with fluid percussion injury (FPI) as compared with that of sham-operated rats. The optical response was characterized by fast and slow components. FPI did not affect the fast component that reflects presynaptic action potentials, but enhanced the slow component that reflects excitatory synaptic responses. Intracellular recordings showed that the amplitude and duration of the excitatory postsynaptic potential (EPSP) were increased after FPI. However, FPI did not affect the resting membrane potential and action potentials of hippocampal neurons. Intraperitoneal (i.p.) administration of diazepam (30 and 90 min after FPI) attenuated the post-traumatic hyperactivity of the slow optical response. The slope of input-to-output relation of excitatory synapses was decreased by acute administration of diazepam to FPI rats, but not by delayed administration of diazepam (4 and 5 h after FPI). The fast optical responses were not affected by either FPI or i.p. administration of diazepam. These results suggest that administration of diazepam at early post-traumatic period prevents the FPI-induced delayed enhancement of excitatory synaptic transmission in rat hippocampal CA1 neurons.