癫痫持续状态对发育期大鼠认知功能的影响及cAMP/PKA信号通路所起作用

目的 探讨癫痫持续状态(SE)对发育期大鼠认知功能的影响及环磷酸腺苷/蛋白激酶A(cAMP/PKA)信号转导通路在其中所起的作用.方法 SD大鼠32只按照完全随机数字表法分为SE组、生理盐水(NS)组,每组16只.戊四氮(PTZ)诱导大鼠SE,Morris水迷宫和Y迷宫实验观察大鼠学习记忆功能的改变,放射免疫分析法测定海马组织cAMP的含量,免疫组织化学方法检测海马各区PKA的表达.结果 SE组大鼠在Morris水迷宫中平均逃避潜伏期延长,原平台所在象限的游泳时间缩短,与NS组比较差异有统计学意义(P<0.05).在Y迷宫中达标所需的训练次数增多,24 h记忆保持率下降,与NS组比较差异有统计学意义(P<0.05).NS组大鼠海马cAMP的含量为(280.38±22.66)pmol/g,SE组为(147.25±16.83)pmol/g,差异有统计学意义(P<0.05).SE组CA3区和CA1区PKA的表达较NS组明显减少.结论 SE可以导致发育期大鼠认知功能障碍,其机制可能与cAMP/PKA信号转导通路的功能受损有关.

Abstract：

Objective To observe the influence of status epilepticus (SE) on cognitive function of immature rats and explore the role of hippocampal cAMP/PKA signaling pathway in cognitive function impairment of immature rats. Methods Immature male SD rats were assigned randomly to 2 groups: SE group, induced by intraperitoneal injection of pentylenetetrazole (PTZ, n=16), and normal saline control group (n=16). Learning and memory tests using the Morris water maze and Y-maze were performed 7 d after SE. After testing, alterations of content of cAMP were detected by radioimmunoassay,and the expression of PKA in the hippocampus was examined by immunohistochemistry. Results SE rats exhibited learning and memory deficits in the Morris water maze and Y-maze tests: as compared with those in the controls in Morris water maze, the mean escape latency of searching the platform obviously prolonged and the swimming time in the original platform region significantly shortened in SE rats (P<0.05); as compared with those in the controls in Y maze, the number of standard training times obviously increased and the rate of retention of memory significantly decreased in SE rats (P<0.05). At the same time, the cAMP content in hippocampus of SE rats ([147.25±16.83] pmol/g) was significantly lower as compared with that in controls ([280.38±22.66] pmol/g), and the expression of PKA in the CA3 and CA1 areas within hippocampal area of SE rats was obviously decreased as compared with that in controls (P<0.05). Conclusion SE could result in learning and memory deficits in immature rats, which may be related to the impairment of hippocampal cAMP/PKA signaling pathway.     

Improved spatial learning in aged rats by genetic activation of protein kinase C in small groups of hippocampal neurons

Age-related decline in human cognition is well known, and there are correlative changes in the function of neocortical and hippocampal neurons. Similarly, age-related decline in learning has been observed in rodents, including deficits in a hippocampal-dependent learning paradigm, the Morris water maze. Furthermore, there are correlative deficits in specific signaling pathways, including protein kinase C (PKC) pathways, in cerebellar, hippocampal, or neocortical neurons. PKC pathways are strong candidates for mediating the molecular changes that underlie spatial learning, as they play critical roles in neurotransmitter release and synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), and deletion of specific PKC genes results in deficits in learning. Conversely, genetic activation of PKC pathways in small groups of hippocampal or cortical neurons enhances learning in specific paradigms. In this study, the authors delivered a constitutively active PKC into small groups of hippocampal dentate granule neurons in aged rats (using a herpes simplex virus-1 vector). Aged 2-year-old rats that received the constitutively active PKC displayed improved performance in the Morris water maze relative to controls in three different measures. These results indicate that PKC pathways play an important role in mediating spatial learning in aged rats. Additionally, these results represent a system for studying the neural mechanisms underlying aging-related learning deficits, and potentially developing gene therapies for cognitive and age-related deficits.     

Individual differences in spatial memory among aged rats are related to hippocampal PKCgamma immunoreactivity

We reported previously that the extent of spatial memory impairment among aged rats was correlated positively with levels of protein kinase Cgamma in hippocampal homogenates measured by quantitative Western blotting (Colombo et al., 1997). In the current study, immunocytochemistry was used to test whether the relationship between elevated PKC-gamma and memory impairment among aged rats could be localized further within regions of the hippocampus. Six- and 24-month-old male Long-Evans rats were first trained in the water maze on a standard place-learning task and then trained 2 weeks later on a transfer task designed for rapid acquisition. In comparison with young rats, aged rats with impaired spatial memory had increased PKCgamma-immunoreactivity (PKCgamma-ir) in CA1 of the hippocampus, but not the dentate gyrus. In addition, PKCgamma-ir in CA1 was correlated positively with spatial memory impairment among aged rats on the standard place-learning and the transfer training tasks. The current results are consistent with our previous report of PKCgamma in hippocampal homogenates, and show further that the relationships between PKCgamma-ir and memory impairments among aged rats are most evident in area CA1. Thus age-related impairments of spatial memory, as well as deficits in the flexible use of previously acquired information, may result from dysregulation of PKCgamma.     

Early life seizures cause long-standing impairment of the hippocampal map

Children with seizures are at risk for long-term cognitive deficits. Similarly, recurrent seizures in developing rats are associated with deficits in spatial learning and memory. However, the pathophysiological bases for these deficits are not known. Hippocampal place cells, cells that are activated selectively when an animal moves through a particular location in space, provides the animal with a spatial map. We hypothesized that seizure-induced impairment in spatial learning is a consequence of the rat's inability to form accurate and stable hippocampal maps. To directly address the cellular concomitants of spatial memory impairment, we recorded the activity of place cells from hippocampal subfield CA1 in freely moving rats subjected to 100 brief flurothyl-induced seizures during the first weeks of life and then tested them in the Morris water maze and radial-arm water maze followed by place cell testing. Compared to controls, rats with recurrent seizures had marked impairment in Morris water maze and radial-arm water maze. In parallel, there were substantial deficits in action potential firing characteristics of place cells with two major defects: i) the coherence, information content, center firing rate, and field size were reduced compared to control cells; and ii) the fields were less stable than those in control place cells. These results show that recurrent seizures during early development are associated with significant impairment in spatial learning and that these deficits are paralleled by deficits in the hippocampal map. This study thus provides a cellular correlate for how recurrent seizures during early development lead to cognitive impairment.     

Effects of naloxone on the long-term potentiation of EPSPs from the pathway of Schaffer collateral to CA1 region of hippocampus in aged rats with declined memory

Morris water maze (MWM) was employed to distinguish the aged rats with declined memory to investigate the effect of naloxone on the synaptic plasticity of hippocampus in declined memory aged rats. After administration with naloxone for 7 days, LTP of excitatory post-synaptic potentials (EPSPs) from Schaffer collateral to CA1 region was recorded. The results showed that the maintenance of LTP of EPSPs from Schaffer collateral to CA1 subfield in isolate hippocampal brain slice was prolonged by naloxone with improved Morris water maze performance and reduced threshold of EPSPs. It is suggested that naloxone can improve learning and memory through enhancement of the synaptic plasticity of hippocampus in aged rats with declined memory.     

Time course of increased vulnerability of cholinergic neurotransmission following traumatic brain injury in the rat

We have previously shown that spatial memory changes following experimental traumatic brain injury (TBI) include long-term changes that are (1) ‘overt’: detected by routine behavioral assessments, or (2) ‘covert’: undetected in the absence of a secondary pharmacological challenge, such as by the cholinergic antagonist, scopolamine. Our objective in this study was to extend this finding by characterizing the time course of recovery of overt and covert spatial memory performance following two magnitudes of experimental TBI. The Morris water maze was used to assess cognitive performance. Rats received either moderate magnitude (6 m/s, 1.7 mm deformation) or low magnitude (6 m/s, 1 mm deformation) impacts through a lateral craniectomy under isoflurane anesthesia. Sham rats underwent identical surgical procedures but were not injured. To avoid motor deficits, water maze testing started two weeks post-injury. Rats were given four trials per day for seven consecutive days. For each trial, latency to find a hidden platform was timed. On the sixth, rats were injected (i.p.) with scopolamine (1 mg/kg) 15 min prior to maze testing. The next day, rats were retested. This testing regimen was repeated, beginning 4, 6, and 10 weeks post-TBI. Results showed that, while the low-magnitude injury produced no overt spatial memory deficits, the moderate-magnitude group exhibited overt deficits during the first test regimen. Also, while both injury magnitudes produced an enhanced sensitivity to spatial memory impairment by scopolamine at two weeks post-TBI, this covert deficit persisted only in the severe group at 4, 6, and 10 weeks post-TBI. Qualitative light microscopy showed that both injury groups had graded cortical necrosis. However, underlying subcortical structures such as the hippocampus appeared intact, with no overt cellular or parenchymal damage to the neuropil. These data suggest three distinct stages of functional recovery: (1) the initial period when overt deficits are present, (2) a period following recovery from overt deficits within which covert deficits can be reinstated by a pharmacological challenge, and (3) a period following recovery from both overt and covert deficits. Covert deficits can persist long after the recovery of overt deficits and, like other neurological deficits, the rate of recovery is dependent on the magnitude of TBI. Finally, spatial memory deficits can occur in the absence of light microscopic evidence of cell death in the hippocampus.     

Experience on the Barnes Spatial Maze Influences PKCγ Levels in the Hippocampus

In order to examine hippocampal plasticity following spatial learning, expression of the γ isoform of protein kinase C (PKCγ) was analyzed in mice, following experience and training on the Barnes spatial maze. Both context-exposed (animals familiarized with the maze but not trained) and trained animals (animals trained to escape the maze using spatial cues) showed increased immunoreactivity to PKCγ in the CA1 region in comparison to naive, home-caged animals. However, there were no quantitative differences in PKCγ immunoreactivity between context-exposed and trained animals. These changes suggest that spatial experience and training result in altered activation of PKCγ, consistent with the idea that PKCγ activation in the CA1 region participates in postsynaptic plasticity associated with spatial experiences and learning.     

Exposure to chronic psychosocial stress and corticosterone in the rat: Effects on spatial discrimination learning and hippocampal protein kinase Cγ immunoreactivity

Previous reports have demonstrated a striking increase of the immunoreactivity of the γ-isoform of protein kinase C (PKCγ-ir) in Ammon's horn and dentate gyrus (DG) of rodent hippocampus after training in a spatial orientation task. In the present study, we investigated how 8 days of psychosocial stress affects spatial discrimination learning in a hole board and influences PKCγ-ir in the hippocampal formation. The acquisition of both reference memory and working memory was significantly delayed in the stressed animals during the entire training period. With respect to cellular plasticity, the training experience in both nonstressed and stressed groups yielded enhanced PKCγ-ir in the CA1 and CA3 regions of the posterior hippocampus but not in subfields of the anterior hippocampus. Stress enhanced PKCγ-ir in the DG and CA3 pyramidal cells of the anterior hippocampus. In stressed animals that were subsequently trained, the PKCγ-ir was increased in the posterior CA1 region to the same level as that found in nonstressed trained animals. Stress apparently abrogated the PKCγ-ir training response in the CA3 region. In a second experiment, the elevation of plasma corticosterone levels to values that are found during stress did not significantly influence reference memory scores but slightly and temporarily affected working memory. The training-induced enhancement of PKCγ-ir in the CA1 region was similar in trained and corticosterone-treated trained animals, but the learning-induced PKCγ-ir response in the posterior CA3 area was absent after corticosterone pretreatment. These results reveal that prolonged psychosocial stress causes spatial learning deficits, whereas artificial elevation of corticosterone levels to the levels that occur during stress only mildly affects spatial memory performance. The spatial learning deficits following stress are reflected only in part in the redistribution of hippocampal PKCγ-ir following training. Hippocampus 7:427–436, 1997. © 1997 Wiley-Liss, Inc.     

Diphenyl diselenide diet intake improves spatial learning and memory deficits in hypothyroid female rats

Cognitive deficits have been observed in different animal models of adult-onset hypothyroidism. Thus, this study was delineated to evaluate whether diphenyl diselenide, an organoselenium compound with neuroprotective and antioxidant properties, could afford protection against the detrimental effects of hypothyroidism on behavioral parameters. Hypothyroidism condition was induced in female rats by continuous exposure to methimazole (MTZ) at 20 mg/100 ml in the drinking water, during 3 months. MTZ-induced hypothyroid rats were fed with either standard or a diet containing 5 ppm of diphenyl diselenide for 3 months. Behavioral assessments were performed monthly, in the following order: elevated plus maze, open field and Morris water maze. The levels of thyroid hormones in the animals exposed to MTZ were lower than control until the end of experimental period. The rats exposed to MTZ had a significant weight loss from the first month, which was not modified by diphenyl diselenide supplementation. In elevated plus maze test, MTZ exposure caused a reduction on the number of entries of animals in closed arms, which was avoided by diphenyl diselenide supplementation. In Morris water maze, the parameters latency to reach the platform and distance performed to find the escape platform in the test session were significantly greater in MTZ group when compared to control. These cognitive deficits observed in MTZ-induced hypothyroid rats were restored by dietary diphenyl diselenide. The group fed with diphenyl diselenide alone exhibited a better spatial learning and memory capability in some parameters of Morris water maze when compared to the control group. In summary, our data provide evidence of the effectiveness of dietary diphenyl diselenide in improving the performance of control and hypothyroid rats in the water maze test.     

Expression changes of growth-associated protein-43 (GAP-43) and mitogen-activated protein kinase phosphatase-1 (MKP-1) and in hippocampus of streptozotocin-induced diabetic cognitive impairment rats

Diabetes mellitus (DM) may give rise to cognitive impairment, but the pathological mechanism involved was still unknown. We employed streptozotocin (STZ)-induced diabetic rats and test their capacity for learning and memory by three-arm radial maze. We determined the expression level of growth-associated protein-43 (GAP-43) and mitogen activated protein kinase phosphatase-1 (MKP-1) in the hippocampus by immunohistochemistry. MKP-1 mRNA level in the CA1 and dentate gyrus (DG) Hippocampal area is further determined by RT-PCR method. We also observed the ultrastructures of Hippocampal neurons by transmission electron microscopy (TEM). All data were analyzed by the independent samples t-test. Four weeks after STZ induction, the diabetic rats showed decreased capacity for learning and memory as indicated by the increase in the error number and reaction time in three-arm radial maze test. TEM results showed the ultrastructures of diabetic hippocampus, including area CA1 and DG, neurons were characterized by swollen mitochondria, increased heterochromatin accumulation and reduced synaptic contacts. The optical density as well as the positive neuron number for GAP-43 and MKP-1 decreased significantly in the CA1 and DG Hippocampal area in diabetic rats (P<0.01). RT-PCR results also showed MKP-1 mRNA in the CA1 and DG Hippocampal area was decreased in the diabetic rats. These results indicated that DM could down-regulate GAP-43 and MKP-1 expression in Hippocampal area that is in charge of memory and cognition. As indicated by our study, the changes in GAP-43 and MKP-1 expression in hippocampus may play a role in the pathogenesis of diabetic dementia.     

Differential expression of molecular markers of synaptic plasticity in the hippocampus, prefrontal cortex, and amygdala in response to spatial learning, predator exposure, and stress-induced amnesia

We have studied the effects of spatial learning and predator stress-induced amnesia on the expression of calcium/calmodulin-dependent protein kinase II (CaMKII), brain-derived neurotrophic factor (BDNF) and calcineurin in the hippocampus, basolateral amygdala (BLA), and medial prefrontal cortex (mPFC). Adult male rats were given a single training session in the radial-arm water maze (RAWM) composed of 12 trials followed by a 30-min delay period, during which rats were either returned to their home cages or given inescapable exposure to a cat. Immediately following the 30-min delay period, the rats were given a single test trial in the RAWM to assess their memory for the hidden platform location. Under control (no stress) conditions, rats exhibited intact spatial memory and an increase in phosphorylated CaMKII (p-CaMKII), total CaMKII, and BDNF in dorsal CA1. Under stress conditions, rats exhibited impaired spatial memory and a suppression of all measured markers of molecular plasticity in dorsal CA1. The molecular profiles observed in the BLA, mPFC, and ventral CA1 were markedly different from those observed in dorsal CA1. Stress exposure increased p-CaMKII in the BLA, decreased p-CaMKII in the mPFC, and had no effect on any of the markers of molecular plasticity in ventral CA1. These findings provide novel observations regarding rapidly induced changes in the expression of molecular plasticity in response to spatial learning, predator exposure, and stress-induced amnesia in brainregions involved in different aspects of memory processing.     

Activation pattern of the limbic system following spatial learning under stress

Anatomical evidence suggests an interplay between the dorsal CA1 of the hippocampus (CA1), the basolateral amygdala (BLA) and the entorhinal cortex (EC), but their specific interactions in the context of emotional memory remain obscure. Here, we sought to elucidate the activation pattern in these areas following spatial learning under different stress conditions in the Morris water maze, using cAMP response element-binding protein (CREB) activation as a marker. Stress levels were manipulated by maintaining the water maze at one of two different temperatures: lower stress (warm water) or higher stress (cold water). Three groups of animals were tested under each condition: a Learning group, trained in the water maze with a hidden escape platform; a No-Platform group, subjected to the maze without an escape platform; and a Naïve group. To evaluate the quality of the spatial memory formed, we also tested long-term memory retention of the initial location of the platform following an interference procedure (reversal training). In the CA1 and EC, we found different CREB activation patterns for the lower- and higher-stress groups. By contrast, in the BLA a similar pattern of activation was detected under both stress levels. The data reveal a difference in the sensitivity of the memory to interference, with reversal training interference affecting the memory of the initial platform location only under the higher-stress condition. The results suggest that stress-dependent alterations in limbic system activation patterns underlie differences in the quality of the memory formed.     

Isoflurane exerts neuroprotective actions at or near the time of severe traumatic brain injury

Isoflurane improves outcome vs. fentanyl anesthesia, in experimental traumatic brain injury (TBI). We assessed the temporal profile of isoflurane neuroprotection and tested whether isoflurane confers benefit at the time of TBI. Adult, male rats were randomized to isoflurane (1%) or fentanyl (10 mcg/kg iv bolus then 50 mcg/kg/h) for 30 min pre-TBI. Anesthesia was discontinued, rats recovered to tail pinch, and TBI was delivered by controlled cortical impact. Immediately post-TBI, rats were randomized to 1 h of isoflurane, fentanyl, or no additional anesthesia, creating 6 anesthetic groups (isoflurane:isoflurane, isoflurane:fentanyl, isoflurane:none, fentanyl:isoflurane, fentanyl:fentanyl, fentanyl:none). Beam balance, beam walking, and Morris water maze (MWM) performances were assessed over post-trauma d1-20. Contusion volume and hippocampal survival were assessed on d21. Rats receiving isoflurane pre- and post-TBI exhibited better beam walking and MWM performances than rats treated with fentanyl pre- and any treatment post-TBI. All rats pretreated with isoflurane had better CA3 neuronal survival than rats receiving fentanyl pre- and post-TBI. In rats pretreated with fentanyl, post-traumatic isoflurane failed to affect function but improved CA3 neuronal survival vs. rats given fentanyl pre- and post-TBI. Post-traumatic isoflurane did not alter histopathological outcomes in rats pretreated with isoflurane. Rats receiving fentanyl pre- and post-TBI had the worst CA1 neuronal survival of all groups. Our data support isoflurane neuroprotection, even when used at the lowest feasible level before TBI (i.e., when discontinued with recovery to tail pinch immediately before injury). Investigators using isoflurane must consider its beneficial effects in the design and interpretation of experimental TBI research.     

Recovery after chronic stress within spatial reference and working memory domains: correspondence with hippocampal morphology

Chronic stress results in reversible spatial learning impairments in the Morris water maze that correspond with hippocampal CA3 dendritic retraction in male rats. Whether chronic stress impacts different types of memory domains, and whether these can similarly recover, is unknown. This study assessed the effects of chronic stress with and without a post-stress delay to evaluate learning and memory deficits within two memory domains, reference and working memory, in the radial arm water maze (RAWM). Three groups of 5-month-old male Sprague-Dawley rats were either not stressed [control (CON)], or restrained (6 h/day for 21 days) and then tested on the RAWM either on the next day [stress immediate (STR-IMM)] or following a 21-day delay [stress delay (STR-DEL)]. Although the groups learned the RAWM task similarly, groups differed in their 24-h retention trial assessment. Specifically, the STR-IMM group made more errors within both the spatial reference and working memory domains, and these deficits corresponded with a reduction in apical branch points and length of hippocampal CA3 dendrites. In contrast, the STR-DEL group showed significantly fewer errors in both the reference and working memory domains than the STR-IMM group. Moreover, the STR-DEL group showed better RAWM performance in the reference memory domain than did the CON group, and this corresponded with restored CA3 dendritic complexity, revealing long-term enhancing actions of chronic stress. These results indicate that chronic stress-induced spatial working and reference memory impairments, and CA3 dendritic retraction, are reversible, with chronic stress having lasting effects that can benefit spatial reference memory, but with these lasting beneficial effects being independent of CA3 dendritic complexity.     

Hippocampal kindled seizures impair spatial cognition in the Morris water maze

We investigated the effects of hippocampally kindled seizures on spatial performance of rats in the Morris water maze (MWM). Seizures were elicited with stimulation of field CA1 of dorsal hippocampus 25-45 min prior to daily testing in the water maze. One group of rats was naive to the MWM (acquisition groups), while another group received pretraining in the MWM (retention groups). These groups were further subdivided into rats that experienced non-convulsive seizures prior to daily testing and rats that experienced fully generalized convulsive seizures prior to daily testing. We found that CA1 seizures significantly disrupted water maze performance during both acquisition and retention, and the effects were similar when either non-convulsive or fully generalized convulsive seizures were evoked. Our findings are consistent with previous reports suggesting that epileptiform activity in the hippocampus acutely impairs performance in tasks sensitive to spatial learning and memory deficits and suggest that both new learning and demonstration of an established place response are susceptible to such disruption.     

化学点燃癫痫大鼠在水迷宫中学习记忆能力的测定

目的 观察印防己毒（Picrotoxin,PTX)化学点燃癫痫大鼠在水迷宫中学习记忆能力与发作频率及类型的关系。为进一步研究癫痫患者记忆损害的治疗提供线索。方法 34只雄性SD大鼠随机分为点燃组和对照组。分别用PTX和生理盐水腹腔注射，根据点燃情况点燃组再分为全面发作（A），频繁发作（B）和部分发作（C）组，对照组即为迷宫训练（D）组。然后进行水迷宫行为测试，评价其学习记忆能力。结果 癫痫大鼠在水迷宫测定中，除B组第1天的成绩较对照组差外，其余各组及B组在第2，3，4、5天中寻找平台的潜伏期时间与对照组相比没有显著性差异。点燃各组对平台空间位置的记忆能力较对照组要差。差异有显著性。结论 首次用化学点燃模型研究癫痫大鼠在水迷宫中的学习记忆能力后发现。PTX化学点燃癫痫大鼠在水迷宫中学习记忆能力下降。发作频繁者学习记忆受损明显，但与发作的严重程度无关。     

Post-training cocaine exposure facilitates spatial memory consolidation in C57BL/6 mice

In this study, we examined the ability of post-training injections of cocaine to facilitate spatial memory performance using the Morris water maze (MWM). We also investigated the role that hippocampal protein kinase A (PKA) and extracellular signal-regulated kinase 1/2 (ERK) signaling may play in cocaine-mediated spatial memory consolidation processes. Male and female C57BL/6 mice were first trained in a MWM task (eight consecutive trials) then injected with cocaine (0, 1.25, 2.5, 5, or 20 mg/kg), and memory for the platform location was retested after a 24 h delay. Cocaine had a dose-dependent effect on spatial memory performance because only the mice receiving 2.5 mg/kg cocaine displayed a significant reduction in latency to locate the platform. No sex differences in MWM performance were observed; however, females showed higher hippocampal levels of PKA when compared with males. A second experiment demonstrated that 2.5 mg/kg cocaine enhanced MWM performance only when administered within 2, but not 4 h after spatial training. We also found that cocaine (2.5 mg/kg) increased ERK2 phosphorylation within the hippocampus and one of its downstream targets (ribosomal S6 kinase), a mechanism that may be responsible, at least in part, for the enhanced cocaine-mediated spatial memory performance. Overall, these data demonstrate that a low dose of cocaine (2.5 mg/kg) administered within 2 h after training facilitates MWM spatial memory performance in C57BL/6 mice.     

Systemic and developmental exposure to lead causes spatial memory deficits and a reduction in COX-2 immunoreactivity in the hippocampus of male rats

Chronic lead exposure during development is known to produce learning deficits. In the present study, we investigated the effects of developmental exposure to lead on spatial memory, as shown in the Morris water maze, and on expression of inducible cyclooxygenase-2 protein in the hippocampi of male rats. Rats were separated into four groups according to which concentration of lead acetate at which developmental stage they were exposed. One group was exposed maternally to lead acetate at a concentration of 250 parts per million (ppm), one group was exposed continuously to 250 ppm lead, one group was exposed maternally to 750 ppm lead, and one group was exposed continuously to 750 ppm lead. Increases were observed in both average escape latency and traveled distance of the rats in the maternally and continuously 750 ppm lead-exposed groups, indicating significant impairment of spatial memory. Quantitative immunostaining analysis by optical density measurement of brain sections from rats in all lead-exposed groups revealed a significant reduction (P < 0.001) in the intensity of cyclooxygenase-2 immunoreactivity in the Ammon's horn region 1 (CA1) and the dentate gyrus areas of the hippocampus. This reduction was concentration-dependent, with the maximum reduction observed in rats exposed to 750 ppm lead. Taken together, these findings suggest that exposure to lead causes spatial memory deficits in male rats and a significant reduction in cyclooxygenase-2 immunoreactivity in the CA1 and dentate gyrus areas.     

缺血后处理对脑缺血大鼠学习记忆能力的影响

目的研究缺血后处理(IP)对大鼠脑缺血再灌注损伤后的学习和记忆能力的影响,探讨各组大鼠脑缺血再灌注后海马CA1区β淀粉样蛋白前体(APP)表达。方法将48只雄性SD大鼠随机分为3组:假手术组、对照组和缺血后处理组(IP组),每组16只大鼠。术后用Morris水迷宫方法测定大鼠认知记忆能力变化。3组大鼠脑组织切片行HE染色和APP染色,并行统计学分析。结果 Morris水迷宫试验显示,对照组大鼠训练第1~4天逃避潜伏期长于IP组(P 0. 01);跨越原平台次数IP组明显多于对照组(P 0. 05)。HE染色结果显示,对照组大鼠海马CA1区神经元细胞脱失明显,而IP可减轻这种形态学改变。免疫组化结果显示,在脑缺血再灌注144 h后对照组中APP表达明显高于假手术组(P 0. 01); IP组海马CA1区APP表达较对照组减少(P 0. 05)。结论缺血后处理可通过抑制APP的表达改善缺血再灌注后大鼠的记忆减退。