Environmental enrichment reduces the mnemonic and neural benefits of estrogen

The degree to which memory is enhanced by estrogen replacement in postmenopausal women may depend on environmental factors such as education. The present study utilized an animal model of environmental enrichment to determine whether environmental factors influence the mnemonic and neural response to estrogen. Female mice were raised in standard (SC) or enriched (EC) conditions from weaning until adulthood (7 months). All mice were ovariectomized at 10 weeks, and tested in object recognition and water-escape motivated radial arm maze (WRAM) tasks at 6 months. Each day at the completion of training, mice received injections of 0.1 mg/kg cyclodextrin-encapsulated 17-beta-estradiol (E2), 0.2 mg/kg E2, or cyclodextrin vehicle (VEH). At the completion of behavioral testing, hippocampal levels of the presynaptic protein synaptophysin and of brain-derived neurotrophic factor (BDNF) were measured. Enrichment effects were evident in VEH-treated mice; relative to SC-VEH females, EC-VEH females committed fewer working memory errors in the WRAM and exhibited increased hippocampal synaptophysin levels. Estrogen effects depended on environmental conditions. E2 (0.2 mg/kg) improved object memory only in SC females. The same dose improved working memory in SC females, but somewhat impaired working memory in EC females. Furthermore, both doses reduced hippocampal synaptophysin levels in EC, but not SC, females. In contrast, E2 reduced hippocampal BDNF levels in SC, but not EC, females. This study is the first to compare the effects of estrogen on memory and hippocampal function in enriched and non-enriched female mice. The results suggest that: (1) estrogen benefits object and working memory more in mice raised in non-enriched environments than in those raised in enriched environments, and (2) the changes induced by estrogen and/or enrichment may be associated with alterations in hippocampal synaptic plasticity.     

Spatial reference memory and neocortical neurochemistry vary with the estrous cycle in C57BL/6 mice

Estrous cycle-related variations of spatial reference memory and neurochemistry in intact female mice were examined. Spatial reference memory was tested in cycling females, ovariectomized (OVX) females, and males by using a 1-day water maze protocol. Choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) activities were measured in the hippocampus and neocortex. Estrus females exhibited worse spatial acquisition and 30-min retention than did proestrus and metestrus females, higher neocortical ChAT activity than proestrus females, and higher neocortical GAD activity than OVX females and males. Neocortical, rather than hippocampal, neurochemistry was more sensitive to hormonal modulation, suggesting that hormonal mediation of neocortical function may play a critical role in regulating spatial reference memory in female mice.     

Estrogen replacement improves spatial reference memory and increases hippocampal synaptophysin in aged female mice

Estrogen deficiency during menopause is often associated with memory dysfunction. However, inconsistencies regarding the ability of estrogen to improve memory in menopausal women highlight the need to evaluate, in a controlled animal model, the potential for estrogen to alleviate age-related mnemonic decline. The current study tested whether estrogen could ameliorate spatial reference memory decline in aged female mice. At the conclusion of testing, levels of the presynaptic protein synaptophysin, and activities of the synthetic enzymes for acetylcholine and GABA, were measured in the hippocampus and neocortex. Aged (27-28-month-old) female C57BL/6 mice were given daily subcutaneous injections of 1 microg or 5 microg of beta-estradiol-3-benzoate dissolved in sesame oil. Control mice received daily injections of sesame oil or no injections. Estradiol treatment began 5 days prior to behavioral testing and continued throughout testing. Spatial and non-spatial memory were assessed in the Morris water maze. The 5 microg dose of estradiol significantly improved spatial learning and memory in aged females. The performance of 5 microg females improved significantly more rapidly than that of control females; estradiol-treated females performed at asymptotic levels by session 2. Furthermore, 5 microg females exhibited a more robust spatial bias than controls during probe trials. In contrast, 1 microg of estradiol did not improve spatial task performance. Neither dose affected performance of the non-spatial task. In the hippocampus, synaptophysin was increased in 5 microg females relative to controls. Estrogen did not affect enzyme activities in either brain region.This study is the first to examine the effects of estrogen replacement on spatial reference memory and synaptophysin expression in aged post-estropausal female rodents. The results suggest that: (1) estrogen can profoundly improve spatial reference memory in aged females, and (2) this improvement may be related to increased hippocampal synaptic plasticity, but not modulation of the synthetic enzymes for acetylcholine and GABA.     

Distinct regulation of brain-derived neurotrophic factor and noradrenaline in S100B knockout mice

The mainly glia-derived protein S100B has been shown to be involved in the pathophysiology of diseases such as neurodegenerative diseases, schizophrenia or depression. These diseases go along with distinct changes of cerebral neurotransmitters and neurotrophic factors. Few and partly inconsistent data exist on the influence of cerebral S100B protein levels on different neurotransmitters. Therefore we investigated levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA), noradrenaline (NA), dopamine (DA), brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the hippocampus, frontal cortex and residual neocortex in S100B knock out (S100B KO) mice compared to wildtype controls. There was a significant increase of hippocampal BDNF (+53%) and a decrease of hippocampal (-12%) and residual neocortical (-15%) NA in 10-month-old S100B KO mice compared to wildtype mice whereas the other mediators investigated did not show genotype-dependent changes. The increased hippocampal BDNF may represent an endogenous attempt to compensate trophic effects of S100B protein especially on serotonergic neurons, which have been shown to be unaffected in S100B KO mice previously. As referred to changes in NA levels functional studies are warranted to elucidate the link between S100B protein and the noradrenergic metabolism.     

Age-related deficits as working memory load increases: relationships with growth factors

Young and aged female rats were tested on a water radial-arm maze designed to measure performance as working memory load increased, followed by brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), and neurotrophin 3 (NT3) protein assessments in hippocampus and frontal cortex. Aged rats showed deficiencies in both working and reference memory. There were also profound age-related working memory load effects. Aged rats made more errors as working memory load increased and showed learning only during early trials when memory load was low, while young rats exhibited learning over all trials. Neurotrophin assessment showed that frontal cortex NGF and BDNF levels were positively, and hippocampal NT3 negatively, correlated with number of errors made during specific trials in aged animals. Comparison to untested rats showed that testing increased NT3, but not BDNF or NGF, protein levels in both age groups. Findings suggest that young rats learn to handle a higher working memory load as testing progresses, while aged rats do not, and that frontal cortex and hippocampal neurotrophin levels may relate to working memory proficiency in aged female rats.     

Regional alterations in amyloid precursor protein and nerve growth factor across age in a mouse model of Down's syndrome

Individuals with Down's syndrome (DS) develop the pathological hallmarks of Alzheimer's (AD) disease at an early age, subsequently followed by memory decline and dementia. We have utilized an animal model for DS, mice with segmental trisomy of chromosome 16 (Ts65Dn), to study biological events linked to memory loss. Previous studies demonstrated a cognitive decline and loss of cholinergic markers after 6-8 months of age. In the current study, we found increased levels of amyloid precursor protein (APP) in the striatum by 6-8 months of age, and in the hippocampus and parietal cortex by 13-16 months of age in Ts65Dn but not in normosomic mice. Additionally, Ts65Dn mice exhibited alterations in nerve growth factor (NGF) levels in the basal forebrain and hippocampus. Ts65Dn mice demonstrated a significant decline in NGF levels in the basal forebrain with age, as well as a reduction in hippocampal NGF by 13-16 months of age. These findings demonstrate that elevated APP and decreased NGF levels in limbic areas correlate with the progressive memory decline and cholinergic degeneration seen in middle-aged trisomic mice.     

Cellular hybridization for BDNF. trkB, and NGF mRNAs and BDNF-immunoreactivity in rat forebrain after pilocarpine-induced status epilepticus

The messenger RNAs (mRNAs) for the neurotrophins, brain-derived neurotrophic factor (BDNF), and nerve growth factor (NGF), are upregulated during epileptic seizure activity, as visualized by in situ hybridization techniques. Neurotrophins might be protective against excitotoxic cell stress, and the upregulation during seizures might provide such cell protection. In this study, a high dose of pilocarpine (300 mg/kg) was used to induce long-lasting, limbic motor status epilepticus and a selective pattern of brain damage. The regulation of BDNF, trkB, and NGF mRNA was studied by in situ hybridization at 1, 3, 6, and 24 h after induction of limbic motor status epilepticus. BDNF immunoreactivity was examined with an anti-peptide antibody and the neuropathological process studied in parallel. BDNF mRNA increased in hippocampus, neocortex, piriform cortex, striatum, and thalamus with a maximum at 3–6 h. Hybridization levels increased earlier in the resistant granule and CA1 cells as compared to the vulnerable CA3 neurons. BDNF immunoreactivity was elevated in dentate gyrus at 3–6 h. trKB mRNA increased in the entire hippocampus. NGF mRNA in hippocampus appeared in dentate gyrus at 3–6 h and declined in hilar neurons at 6–24 h. Cell damage was found in the CA3 area, entire basal cortex, and layers II/III of neocortex. Endogenous neurotrophins are upregulated during status epilepticus caused by pilocarpine, which is related to the coupling between neuronal excitation and trophic factor expression. This upregulation of neurotrophic factors may serve endogenous protective effects; however, the excessive levels of neuronal hyperexcitation resulting from pilocarpine seizures lead to cell damage which cannot be prevented by endogenous neurotrophins.     

EGF培养条件下NGF与BDNF对大鼠海马神经干细胞向神经元分化的差异

目的探讨在表皮生长因子(EGF)培养条件下,相同浓度神经生长因子(NGF)与脑源性神经生长因子(BDNF)对成年大鼠海马神经干细胞向神经元分化比例的差异。方法用含碱性成纤维生长因子(bFGF)、EGF、B27的无血清细胞培养技术体外培养成年大鼠海马神经干细胞,单细胞克隆后行Nestin免疫细胞化学染色,诱导分化1周,行GFAP和NSE免疫细胞化学染色;根据培养液中所加营养因子的不同将单细胞克隆传代细胞分为5组培养:EGF组、NGF组、BDNF组、EGF+NGF组、EGF+BDNF组,此5组细胞培养1周,进行NSE免疫细胞化学染色,计数阳性细胞比例后进行统计学分析。结果:单细胞克隆培养后克隆球细胞表达Nestin,诱导分化1周,细胞表达NSE、GFAP;与EGF组、NGF组、BDNF组相比,EGF+NGF组和EGF+BDNF组细胞分化为神经元的比例较高(P<0.05),其中EGF+BDNF组细胞的比例最高。结论在EGF培养条件下,BDNF促进成年大鼠海马神经干细胞向神经元分化的能力高于NGF。     

BDNF对慢性应激性大鼠海马神经元损伤的保护作用

目的研究脑源性神经营养因子(BDNF)对大鼠海马神经元的保护作用。方法40只成年Wistar大鼠随机分为对照组、应激组、BDNF低剂量组和高剂量组,每组10只。用电击足底结合噪声建立慢性应激大鼠模型,Morris水迷宫观察动物的空间学习和记忆能力,Nissl染色观察和计数海马神经元数量,Fara-2荧光法测海马突触体内游离钙浓度。结果在双海马注射BDNF后,对于因慢性应激引起的空间学习和记忆能力下降,海马神经元数量减少,海马突触体内游离钙浓度增高有明显保护作用。结论BDNF对应激海马损伤有保护作用,其机制可能是通过调节海马细胞内的钙浓度,防止海马神经细胞丢失有关。     

Brain-derived neurotrophic factor

Since the purification of BDNF in 1982, a great deal of evidence has mounted for its central roles in brain development, physiology, and pathology. Aside from its importance in neural development and cell survival, BDNF appears essential to molecular mechanisms of synaptic plasticity. Basic activity-related changes in the central nervous system are thought to depend on BDNF modification of synaptic transmission, especially in the hippocampus and neocortex. Pathologic levels of BDNF-dependent synaptic plasticity may contribute to conditions such as epilepsy and chronic pain sensitization, whereas application of the trophic properties of BDNF may lead to novel therapeutic options in neurodegenerative diseases and perhaps even in neuropsychiatric disorders.     

Environmental enrichment: effects on stereotyped behavior and neurotrophin levels

The present study evaluated whether environmental enrichment-related effects on the development of stereotyped behavior in deer mice were associated with alterations in neurotrophin levels. Deer mice were reared in enriched or standard cage conditions for 60 days. The mice were then tested in automated photocell detectors and classified as either stereotypic or nonstereotypic. This testing paradigm yielded four behaviorally distinct groups: enriched stereotypic, enriched nonstereotypic, standard cage stereotypic, and standard cage nonstereotypic. The motor cortex, striatum, and hippocampus were dissected, and the levels of brain-derived neurotrophin factor (BDNF) and nerve growth factor (NGF) in each brain region were analyzed using Promega ELISA kits. There were no differences in either NGF or BDNF in either the motor cortex or the hippocampus. In the striatum, the enriched nonstereotypic mice exhibited significantly more BDNF than the enriched stereotypic, the standard cage nonstereotypic, or the standard cage stereotypic mice. There were no differences in NGF in the striatum. These results provide evidence that the enrichment-related prevention of stereotyped behavior in deer mice is associated with increased BDNF in the striatum.     

Changes in cognition induced by social isolation in the mouse are restored by electro-acupuncture

Social isolation by individual housing the mice eliminates social interaction and induces pathophysiological changes including decreased learning capabilities. Acupuncture with the manipulation of the needles according to traditional Chinese medicine or with the electrical stimulation applied on needles inserted into the acupoints (referred as electro-acupuncture, EA) may modulate stress response, mood, learning and memory process. We investigated whether or not EA could reverse memory impairments induced in the male mouse by social isolation. We also studied any changes due to EA or social isolation in neurotrophic factors as nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF) known to have a role in regulating memory and learning processes. We found that 30 min daily session of EA for a period of 4 days at the acupoint Zusanli (low burst frequency of 2 Hz, each pulse was a square electric wave and had a duration of 180, length of 0.1, and internal burst frequency of 80 Hz; intensity 1.0-1.5 mA) reverses the changes in the passive avoidance responses of isolated mice. These findings were associated with decreased NGF and BDNF in the hippocampus and decreased NGF in the striatum of isolated mice exposed to EA. In conclusion the present data in the mouse show that EA may modulate cognition in mice subjected to social isolation.     

Time course of the expression of genes of brain-derived neurotrophic factor and nerve growth factor in the hippocampus and frontal cortex induced by semax in rats

Semax is a synthetic peptide consisting of the ACTH fragment (4–7) and the C-terminal Pro-Gly-Pro peptide. It promotes neuron survival during hypoxia and increases selcective attention and memory consolidation. It has been shown that semax influences the expression of some genes, particularly nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). In the present study, we performed an analysis of the time course of the expression of NGF and BDNF genes in the hippocampus and frontal cortex in rats after a single intranasal administration of semax at a dose of 50 μg/kg. We found that semax administration resulted in a rapid long-term activation of the NGF and BDNF genes expression, which was specific for different rat brain structures investigated.     

Estrous cycle regulates activation of hippocampal Akt, LIM kinase, and neurotrophin receptors in C57BL/6 mice

Estradiol modulates dendritic spine morphology and synaptic protein expression in the rodent hippocampus, as well as hippocampal-dependent learning and memory. In the rat, these effects may be mediated through nongenomic steroid signaling such as estradiol activation of the Akt and LIM kinase (LIMK) pathways, in addition to genomic signaling involving estradiol upregulation of brain-derived neurotrophic factor expression (BDNF). Due to the many species differences between mice and rats, including differences in the hippocampal response to estradiol, it is unclear whether estradiol modulates these pathways in the mouse hippocampus. Therefore, we investigated whether endogenous fluctuations of gonadal steroids modulate hippocampal activation of the Akt, LIMK, and the BDNF receptor TrkB in conjunction with spatial memory in female C57BL/6 mice. We found that Akt, LIMK, and TrkB were activated throughout the dorsal hippocampal formation during the high-estradiol phase, proestrus. Cycle phase also modulated expression of the pre- and post-synaptic markers synaptophysin and post-synaptic density 95. However, cycle phase did not influence performance on an object placement test of spatial memory, although this task is known to be sensitive to the complete absence of ovarian hormones. The findings suggest that endogenous estradiol and progesterone produced by the ovaries modulate specific signaling pathways governing actin remodeling, cell excitability, and synapse formation.     

Lamotrigine attenuates deficits in synaptic plasticity and accumulation of amyloid plaques in APP/PS1 transgenic mice

Hyperactivity and its compensatory mechanisms may causally contribute to synaptic and cognitive deficits in Alzheimer's disease (AD). Blocking the overexcitation of the neural network, with levetiracetam (LEV), a sodium channel blocker applied in the treatment of epilepsy, prevented synaptic and cognitive deficits in human amyloid precursor protein (APP) transgenic mice. This study has brought the potential use of antiepileptic drugs (AEDs) in AD therapy. We showed that the chronic treatment with lamotrigine (LTG), a broad-spectrum AED, suppressed abnormal spike activity, prevented the loss of spines, synaptophysin immunoreactivity, and neurons, and thus attenuated the deficits in synaptic plasticity and learning and memory in APP and presenilin 1 (PS1) mice, which express human mutant APP and PS1. In contrast with LEV, which failed to reduce the generation of amyloid β, the chronic LTG treatment reduced the cleavage of APP by β-secretase and thus the numbers and the size of amyloid plaques in the brains of APP and PS1 mice. Moreover, the levels of brain-derived neurotrophic growth factor (BDNF) and nerve growth factor (NGF) were enhanced in the brains of APP and PS1 mice by the chronic LTG treatment. Therefore, these observations demonstrate that LTG attenuates AD pathology through multiple mechanisms, including modulation of abnormal network activity, reduction of the generation of amyloid beta and upregulation of BDNF and NGF.     

Object recognition memory and BDNF expression are reduced in young TgCRND8 mice

The TgCRND8 mouse model of Alzheimer's disease exhibits progressive cortical and hippocampal β-amyloid accumulation, resulting in plaque pathology and spatial memory impairment by 3 months of age. We tested whether TgCRND8 cognitive function is disrupted prior to the appearance of macroscopic plaques in an object recognition task. We found profound deficits in 8-week-old mice. Animals this age were not impaired on the Morris water maze task. TgCRND8 and littermate controls did not differ in their duration of object exploration or optokinetic responses. Thus, visual and motor dysfunction did not confound the phenotype. Object memory deficits point to the frontal cortex and hippocampus as early targets of functional disruption. Indeed, we observed altered levels of brain-derived neurotrophic factor (BDNF) messenger ribonucleic acid (mRNA) in these brain regions of preplaque TgCRND8 mice. Our findings suggest that object recognition provides an early index of cognitive impairment associated with amyloid exposure and reduced brain-derived neurotrophic factor expression in the TgCRND8 mouse.     

BDNF upregulation rescues synaptic plasticity in middle-aged ovariectomized rats

Brain-derived neurotrophic factor (BDNF) has emerged as a possible broad-spectrum treatment for the plasticity losses found in rodent models of human conditions associated with memory and cognitive deficits. We have tested this strategy in the particular case of ovariectomy. The actin polymerization in spines normally found after patterned afferent stimulation was greatly reduced, along with the stabilization of long-term potentiation, in hippocampal slices prepared from middle-aged ovariectomized rats. Both effects were fully restored by a 60-minute infusion of 2 nM BDNF. Comparable rescue results were obtained after elevating endogenous BDNF protein levels in hippocampus with 4 daily injections of a short half-life ampakine (positive modulator of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate [AMPA]-type glutamate receptors). These results provide the first evidence that minimally invasive, mechanism-based drug treatments can ameliorate defects in spine plasticity caused by depressed estrogen levels.     

Effects of experimental cerebral malaria in memory, brain-derived neurotrophic factor and acetylcholinesterase acitivity in the hippocampus of survivor mice

Malaria is the most important human parasitic disease and cerebral malaria (CM), its main neurological complication, is characterized by neurological and cognitive damage in both human and animal survivors. The brain-derived neurotrophic factor (BDNF) appears to be involved with activity-dependent synaptic plasticity. There is great interest regarding its role in learning and memory as well as acetylcholinesterase activity (AChE) that is implicated in many cognitive functions and probably plays important roles in neurodegenerative disorders. In the present work, we evaluated BDNF protein levels and AChE activity in the hippocampus and habituation in an animal model of CM using C57BL/6 mice after fifteen days of the induction. The results demonstrated that there was a decrease in BDNF levels in the hippocampus of C57BL/6 mice infected with PbA when compared with C57BL/6 non-infected mice and C57BL/6 non-infected mice that received treatment with chloroquine. However, no difference was observed in AChE activity in the hippocampus. When habituation was evaluated there was memory impairment in the C57BL/6 mice infected with Plasmodium berghei ANKA (PbA). In conclusion, we believe that the decreased BDNF levels in the hippocampus may be related with memory impairment without alterations on AChE activity.     

Septal cholinergic afferents regulate expression of brain-derived neurotrophic factor andβ-nerve growth factor mRNA in rat hippocampus

Summary In situ hybridization was used to study the expression of members of the nerve growth factor family of trophic factors in rat hippocampus following stimulation of afferent cholinergic and glutamatergic pathways with quisqualate. A transient increase in brain-derived neurotrophic factor (BDNF) and-nerve growth factor (NGF) mRNA expression in the hippocampus was seen 4 h after a quisqualate injection into the medial septal nucleus. Both BDNF and NGF mRNA levels increased more than 4-fold in the granule layer of the dentate gyrus and for BDNF mRNA also in the pyramidal cells of CA1, while the levels of BDNF mRNA in CA3 increased 2-fold. The increase in BDNF and NGF mRNA levels were completely prevented by pretreatment with systemic injections of either scopolamine or diazepam. A quisqualate injection into the entorhinal cortex, containing glutamatergic afferents to the hippocampus, resulted in a 15-, 5- and 17-fold increase in the expression of BDNF mRNA in the ipsilateral granule cells, CA3 and CA1 pyramidal cells, respectively. Similar increases were also seen in the hippocampus contralateral to the injections. In contrast, the level of NGF mRNA did not increase significantly in any of the subfields in the hippocampus. The increase in BDNF mRNA after cortex injections was attenuated by diazepam but not by scopolamine. These findings imply that increased activity in afferent cholinergic and glutamatergic pathways to the hippocampus differentially regulate expression of the NGF family of neurotrophic factors in the hippocampus.     

The multi-herbal medicine Gongjin-dan enhances memory and learning tasks via NGF regulation

Nerve growth factor (NGF) decreases degeneration of cholinergic neurons, improves memory loss, and increases long-term potentiation and learning tasks. Therefore, NGF mimetics or NGF inducers may be important targets for the treatment of various neurodegenerative disorders. Traditionally, Gongjin-dan (GJD) has been used clinically for the treatment of central nervous system disorders. In this study, we examined the effects of GJD on NGF mimetic activity in PC12 cells and the induction of NGF secretion in primary astrocytes. Moreover, we also measured neuron survival by MAP-2 staining in an immobilization stress rat model and induction of long-term potentiation by the MEA system in rat hippocampus slices treated with dexamethasone. The behavioral syndrome by novel object test was also performed in mice. GJD increased neurite outgrowth in PC12 cells and NGF secretion in primary astrocytes. Also, it reduced neuronal cell death and increased long-term potentiation in the rat hippocampus. Moreover, the number of entries, the time spent and the distance moved in the center area of the test region by the mice was increased by oral administration of GJD in comparison with the distance moved over the total area. These data suggest that administration of GJD may improve memory and learning tasks via NGF regulation, and that it may have a potential for multiple function neuroprotection via NGF regulation.