Exercise primes a molecular memory for brain-derived neurotrophic factor protein induction in the rat hippocampus.

Exercise is an important facet of behavior that enhances brain health and function. Increased expression of the plasticity molecule brain-derived neurotrophic factor (BDNF) as a response to exercise may be a central factor in exercise-derived benefits to brain function. In rodents, daily wheel-running exercise increases BDNF gene and protein levels in the hippocampus. However, in humans, exercise patterns are generally less rigorous, and rarely follow a daily consistency. The benefit to the brain of intermittent exercise is unknown, and the duration that exercise benefits endure after exercise has ended is unexplored. In this study, BDNF protein expression was used as an index of the hippocampal response to exercise. Both daily exercise and alternating days of exercise increased BDNF protein, and levels progressively increased with longer running duration, even after 3 months of daily exercise. Exercise on alternating days was as effective as daily exercise, even though exercise took place only on half as many days as in the daily regimen. In addition, BDNF protein remained elevated for several days after exercise ceased. Further, after prior exercise experience, a brief second exercise re-exposure insufficient to cause a BDNF change in naïve animals, rapidly reinduced BDNF protein to levels normally requiring several weeks of exercise for induction. The protein reinduction occurred with an intervening "rest" period as long as 2 weeks. The rapid reinduction of BDNF by an exercise stimulation protocol that is normally subthreshold in naïve animals suggests that exercise primes a molecular memory for BDNF induction. These findings are clinically important because they provide guidelines for optimizing the design of exercise and rehabilitation programs, in order to promote hippocampal function.

Can estrogen play a significant role in the prevention of Alzheimer's disease?

In women the abrupt decline estrogen levels at menopause may be associated with cognitive deficits and increased risk for Alzheimer's disease (AD); estrogen replacement therapy may reduce this risk. Animal studies indicate that estrogen modulates neurotransmitter systems, regulates synaptogenesis, and is neuroprotective. These beneficial effects occur in brain areas critical to cognitive function and involved in AD. Reduced estrogen levels can compromise neuronal function and survival. Estrogen replacement therapy can reverse cognitive deficits associated with low estrogen levels and may reduce the risk of AD. However, clinical trials for estrogen replacement in the treatment of AD have produced ambiguous results. Initial, small, open-label and double blind clinical trials indicated improved cognitive function in women with AD. Recent large trials failed to show a beneficial effect for long-term estrogen replacement for women with AD. There are several variables that could affect these results, such as genetic factors, time between estrogen loss and replacement, extent and types of AD pathology, and other environmental and health factors. Presently large prospective studies are being conducted as the National Institutes of Health in the Women's Health Initiative and the Preventing Postmenopausal Memory Loss and Alzheimer's with Replacement Estrogens studies to provide a better assessment of the role of estrogen for age related health issues, including dementia.

Spatial learning induces neurotrophin receptor and synapsin I in the hippocampus.

We report that rats learning a spatial memory task in the Morris water maze show elevated expression of the signal transduction receptor for BDNF and the synaptic associated protein synapsin I in the hippocampus. Nuclease protection assays showed maximal levels of TrkB and synapsin I mRNAs in the hippocampus by the time that asymptotic learning performance had been reached (Day 6). Increases in synapsin I mRNA were matched by changes in synapsin I protein as revealed by western blot analysis. Synapsin I is a downstream effector for the BDNF tyrosine kinase cascade pathway which has important roles in synaptic remodeling and function. Therefore, parallel changes in TrkB and synapsin I mRNAs suggest a role of the BDNF system in synaptic function or adaptation. Levels of TrkB mRNA in the hippocampus were attenuated after learning acquisition (Day 20), but synapsin I mRNA was still elevated, suggesting that the BDNF system may participate in events secondary to learning, such as strengthening of neural circuits. TrkB and synapsin I mRNAs showed an increasing trend in the cerebellum of learning rats and no changes were observed in the caudal cerebral cortex. The selectivity of the changes in trkB and synapsin I, affecting the hippocampus, is in agreement with the role of this structure in processing of spatial information. Behavioral regulation of neurotrophins may provide a molecular basis for the enhanced cognitive function associated with active lifestyles, and guide development of strategies to promote neural healing after CNS injury or disease.

Culture and regeneration of human neurons after brain surgery.

Cortical human brain tissue was obtained from 11 craniotomies for intractable epilepsy or tumor resection. Neuregen transport medium preserved viability at 4 degrees C during transfer to the culture laboratory. Cells were isolated and cultured by methods previously developed for adult rat neurons (Brewer GJ. Isolation and culture of adult rat hippocampal neurons. J. Neurosci. Meth. 1997:71:143-55). In about 40% of the cases, cultures regenerated with a majority of neuron-like cells that stained for neurofilament and not GFAP. After 3 weeks of culture from a 70 year old meningioma case, synapse-like structures were revealed by electron microscopy. Trophic support from basic human recombinant fibroblast growth factor was synergistically improved with the steroid hormone dehydroepiandrosterone 3-sulfate. Another 40% of the cases resulted in cultures that were predominantly GFAP positive astroglia. The remaining 20% of the cases did not regenerate cells with neuron-like or glial processes. Three postmortem cases did not regenerate neurites. These methods may aid development of human culture models of epilepsy as well as human pharmacology, toxicology and development of improved methods for brain grafts.

Physical activity-antidepressant treatment combination: impact on brain-derived neurotrophic factor and behavior in an animal model.

The mechanism of antidepressant action, at the cellular level, is not clearly understood. It has been reported that chronic antidepressant treatment leads to an up-regulation of brain-derived neurotrophic factor (BDNF) mRNA levels in the hippocampus, and that physical activity (voluntary running) enhances this effect. We wished to investigate whether BDNF expression brought about by these interventions may overcome deficits caused by acute stress, and might impact behavior in an animal model. In this report, we have tested the hypothesis that the combination of the antidepressant, tranylcypromine, and physical exercise could lead to decreased neurotrophin deficits and enhanced swimming time in animals that have been forced to swim in an inescapable water tank. Rats were either treated with tranylcypromine, engaged in voluntary running, or both for one week. After these treatments, the animals underwent a two-day forced swimming procedure. BDNF mRNA levels were significantly depressed in untreated animals subjected to forced swimming. Animals that either underwent prior activity or received antidepressant showed BDNF mRNA levels restored to baseline. Animals receiving the combined intervention showed an increase in hippocampal BDNF mRNA well above baseline. Swimming time during a five-minute test was significantly enhanced in animals receiving the combined intervention over untreated animals. Swimming time was not significantly enhanced over that of animals receiving antidepressant alone, however. Enhanced swimming time correlated with increased levels of BDNF mRNA in one hippocampal sub-region (CA4-hilus). These results suggest that the combination of exercise and antidepressant treatment may have significant neurochemical, and possibly behavioral, effects. In addition, these results support the possibility that the enhancement of BDNF expression may be an important element in the clinical response to antidepressant treatment. The induction of BDNF expression by activity/pharmacological treatment combinations could represent an important intervention for further study, to potentially improve depression treatment and management.

Estrogen and exercise interact to regulate brain-derived neurotrophic factor mRNA and protein expression in the hippocampus.

We investigated the possibility that estrogen and exercise interact in the hippocampus and regulate brain-derived neurotrophic factor (BDNF), a molecule increasingly recognized for its role in plasticity and neuron function. An important aspect of this study is to examine the effect of different time intervals between estrogen loss and estrogen replacement intervention. We demonstrate that in the intact female rat, physical activity increases hippocampal BDNF mRNA and protein levels. However, the exercise effect on BDNF up-regulation is reduced in the absence of estrogen, in a time-dependent manner. In addition, voluntary activity itself is stimulated by the presence of estrogen. In exercising animals, estrogen deprivation reduced voluntary activity levels, while estrogen replacement restored activity to normal levels. In sedentary animals, estrogen deprivation (ovariectomy) decreased baseline BDNF mRNA and protein, which were restored by estrogen replacement. Despite reduced activity levels in the ovariectomized condition, exercise increased BDNF mRNA levels in the hippocampus after short-term (3 weeks) estrogen deprivation. However, long-term estrogen-deprivation blunted the exercise effect. After 7 weeks of estrogen deprivation, exercise alone no longer affected either BDNF mRNA or protein levels. However, exercise in combination with long-term estrogen replacement increased BDNF protein above the effects of estrogen replacement alone. Interestingly, protein levels across all conditions correlated most closely with mRNA levels in the dentate gyrus, suggesting that expression of mRNA in this hippocampal region may be the major contributor to the hippocampal BDNF protein pool. The interaction of estrogen, physical activity and hippocampal BDNF is likely to be an important issue for maintenance of brain health, plasticity and general well-being, particularly in women.

Expression of metabotropic glutamate receptor 5 is increased in astrocytes after kainate-induced epileptic seizures.

In the CNS there is a differential distribution of the metabotropic glutamate receptor 5 (mGluR5) in neurons and glia. Hippocampal nerve cells contain large amounts of the receptor transcript and protein that are expressed at very low levels in astrocytes. This is unexpected, as mGluR-induced phosphoinositide hydrolysis is substantial in cultured astrocytes and is mediated only by mGluR5 in these cells. In order to detect mGluR5 in astrocytes in vivo, we destroyed in a circumscribed part of the hippocampus nerve cells that have high level of receptor expression. Unilateral injection of kainate into the right amygdala produced epileptic seizures, as well as selective degeneration of nerve cells restricted to the ipsilateral CA3 and CA4 regions of the hippocampus, followed by the development of gliosis. In the affected fields only, mGluR5 immunoreactivity was severely reduced 3 days after kainate injection, followed by a progressive reappearance and lasting presence of the receptor protein. Receptor mRNA virtually disappeared from the pyramidal cell layer of the lesioned CA3/4 region. On the other hand, the message level increased persistently in the CA3 stratum lucidum and radiatum, the site of massive astrogliosis. In these sites, mGluR5 mRNA became detectable in double labeling studies in glial fibrillary acidic protein-positive astrocytes. We showed previously that growth factors induce a pronounced elevation of mGluR5 expression in cultured astrocytes (Miller et al. J Neurosci 15:-6109, 1995). The well-documented increase in the level of growth factors in the damaged brain may underlie the induction of the receptor expression in astrocytes in vivo, which may also be involved in repair processes in the injured nervous tissue.

Learning upregulates brain-derived neurotrophic factor messenger ribonucleic acid: a mechanism to facilitate encoding and circuit maintenance?

Brain-derived neurotrophic factor (BDNF) promotes neuron survival, enhances sprouting, protects neurons against insult, and may be involved in several aspects of learning and memory. In this study, rats trained to locate a submerged platform in a water maze had elevated levels of BDNF messenger ribonucleic acid (mRNA) in the hippocampus (p < .05), a structure associated with spatial memory. BDNF mRNA expression increased after 3 and 6 days but not after 1 day of training in the water maze. A yoked control group that swam without the platform present, to control for physical activity, showed a trend for elevated BDNF mRNA at an intermediate level between the learning and sedentary groups. Other cortical and subcortical areas did not show a significant increase in BDNF mRNA after learning or activity (p > .05). These findings suggest that learning can impact BDNF mRNA expression localized to the brain areas involved in the processing of spatial information. Furthermore, behaviors such as physical activity and learning may help maintain and protect neurons at risk in aging and neurodegenerative disease via increased BDNF expression.

Spatial learning and physical activity contribute to the induction of fibroblast growth factor: neural substrates for increased cognition associated with exercise.

New evidence indicates that neural activity regulates the expression of trophic factors in the brain but regulation of these molecules by select aspects of behaviour remains solely a fascinating possibility. We report that following training in the Morris water maze, a spatial memory task, the hippocampus and cerebellum of learning rats exhibited an increase in basic fibroblast growth factor messenger RNA. Basic fibroblast growth factor messenger RNA levels were higher during the learning of the task and decreased once asymptotic performance was reached, suggesting an involvement of basic fibroblast growth factor in learning/memory. An active control group, which exercised for the same time as the learning group but the spatial learning component of the task was minimized, exhibited a minor increase in basic fibroblast growth factor messenger RNA. The intensification of the physical activity component of the task by massed or intensive training resulted in greater increases in basic fibroblast growth factor messenger RNA for both learning and yoked groups, but levels of basic fibroblast growth factor messenger RNA in the learning group remained higher than yoked only in the cerebellum. Changes in basic fibroblast growth factor were accompanied by an increase in astrocyte density in the hippocampus in agreement with described roles of basic fibroblast growth factor in astrocyte proliferation/reactivity. Results suggest that learning potentiates the effects of physical activity on trophic factor induction in select brain regions. Trophic factor involvement in behaviour may provide a molecular basis for the enhanced cognitive function associated with active lifestyles, and guide development of strategies to improve rehabilitation and successful ageing.

Life-long dietary restriction attenuates age-related increases in hippocampal glial fibrillary acidic protein mRNA.

The expression of astrocyte-specific glial fibrillary acidic protein increases after experimental lesions and is elevated throughout the brain in aged rodents and primates. Clusterin (ApoJ) expression increases in astrocytes and microglia after lesions, but changes during aging have not been reported. Dietary restriction (DR) delays the onset and progression of many age-related physiological deficits in rodents. This study showed that the age-related increase in glial fibrillary acidic protein mRNA in the hippocampus was attenuated in 24-month-old male Fischer 344 rats subjected to a 50% DR beginning at 6 weeks of age. ApoJ mRNA expression in astrocytes was unchanged by DR. These results demonstrate that DR can delay neurodegeneration in aged rats as assessed by a marker of reactive astrogliosis.

Memory training for individuals with Alzheimer's disease improves name recall.

Alzheimer's disease is clinically characterized by a variety of progressive cognitive deficits, most notably an impaired ability to acquire new information, such as name recall. Eleven demented patients and 11 controls participated in a 4 week memory program that included training in name-face recall. Individuals were taught strategies for name-face rehearsal, and administered task specific and standardized tests to assess the intervention efficacy. During the memory training patients improved recall of names and faces (p < 0.05), while controls remained stable. Patients also improved on the weekly standardized measures, including the Kendrick Digit Copy and Geriatric Depression Scale (p < 0.05). Thus, the memory training can be beneficial for improving name recall and some aspects of behavior. This can provide a framework for development of programs to enhance cognitive function in patients with dementia and may tap biological mechanisms that promote neural plasticity to compensate for the degenerative condition.

Roles of metabotropic glutamate receptors in brain plasticity and pathology.

In summary, the mGluRs are a large family of receptor subtypes with diverse properties in terms of transduction coupling, pharmacology, and anatomical distribution. Many divergent studies have demonstrated that activation of these receptors can result in either neuroprotection or neuropathology. We hypothesized that the mGluRs of astrocytes may have a role in determining the response following administration of mGluR agonists in vivo, and we have defined a suitable in vitro model for the study of these receptors. The experimental plasticity demonstrated in the astrocyte culture model may represent a more general principle that conditions in the microenvironment may differentially alter mGluR subtype expression as part of development, functional specialization, or pathology. This astrocyte model of receptor regulation provides a system suitable for studying the effects of specific growth factors, neurotrophins, cytokines, and other substances released by neurons and glia that may act in both autocrine and paracrine fashions. Alteration in the ratios of receptors by such variables could then modify future signaling properties and neuroglial interactions, a form of conditioning of the astrocytic response that would alter the physiological output following glutamate release. One measure of the value of this model will be its usefulness in stimulating the generation of hypotheses that can be tested in vivo. For example, the morphology of the astrocytes when cultured in the defined medium has similarities to the morphology of astrocytes undergoing reactive gliosis in pathological states. It is also interesting to note that treatments that have been reported to increase excitatory amino acid-stimulated PI hydrolysis in ex vivo brain slices (lesions, ischemia, and kindling) are accompanied by reactive gliosis. Those findings combined with the present in vitro results lead us to speculate that mGluR5 expression may also be altered in vivo during reactive gliosis. If so, it will be important to examine the functional consequences of such a change with regard to the astrocytic response to injury and maintaining the balance between excitatory transmission and excitotoxicity.

Vulnerability of the hippocampus to kainate excitotoxicity in the aged, mature and young adult rat.

Sensitivity to excitotoxic damage was assessed in young adult, mature and aged male Sprague-Dawley rats. Kainic acid was injected into the hippocampus and the size of the hippocampal lesion rated. Intrahippocampal injection of kainic acid produced lesions in aged animals that were significantly smaller than lesions in the young rats (P < 0.05), while lesion size in mature rats was intermediate. Excitotoxic damage was localized primarily to the CA3 region of the hippocampus in the aged rats. Young adult rats had more damage to the hippocampus with involvement of CA1 pyramidal and dentate granule cells. These results suggest that increased age may reduce susceptibility to excitotoxic damage.

Magnetic resonance imaging of the aging brain in Down syndrome.

MRI studies to date have confirmed and expanded upon findings of morphologic differences between the brains of subjects with DS and those of the general population found by CT and post-mortem examination. [table; see text] Hippocam pal and neocortical structures are smaller in DS while unexpectedly the parahippocampal gyrus was found to be larger. MRI has demonstrated that subjects with DS develop signs associated with [table; see text] brain aging at an earlier age. These findings include increased rate of dilatation of ventricles, increased peripheral atrophy, and increased deep white matter lesions. In addition, changes that are associated with AD occur earlier in the DS population. Functional studies reveal decreasing cerebral perfusion with age in adults with DS, a pattern similar to non-DS subjects with clinically progressive dementia, and provide evidence for altered blood-brain barrier permeability. Dynamic MRI studies have also shown adults with DS to have fluctuating cortical CSF volumes, similar to some elderly non-DS subjects and subjects with shunted hydrocephalus. This is a new finding in brain aging that suggests a relationship between aging in DS and edematous states of the brain.

Decreased levels of C1q in cerebrospinal fluid of living Alzheimer patients correlate with disease state.

Recent reports that complement proteins comprising the classical pathway are associated with senile plaques suggest that activation of the classical complement cascade in Alzheimer's disease tissue results in bystander cell lysis and may contribute to AD neuropathology. Analysis of cerebrospinal fluid may prove to be a useful means of detecting changes in immunological activity in the brain. We use an enzyme-linked immunosorbent assay to measure levels of C1q, a subunit of the classical complement cascade, in the CSF of patients clinically diagnosed with possible or probable AD. Significantly lower levels of C1q were detected in the CSF of the Alzheimer group as compared to control CSF [AD: mu = 268 ng/ml, SD = 84; non-AD: mu = 340 ng/ml, SD = 76; F(1, 44) = 5.84, p = 0.02]. Diminished performance on global measures of mental status such as the Mini-Mental State Exam (R = 0.45; p = 0.0072) and Blessed's Information, Memory, and Concentration test (R = 0.42; p = 0.0138) showed high correlations with decreased C1q levels. More specific measures of cognitive function, such as word recall (R = 0.42; p = 0.012), word recognition (R = 0.52; p = 0.0017) and delayed recall (R = 0.45; p = 0.0062) memory tasks also correlated strongly with decreased C1q levels.

Magnetic resonance imaging analysis of age-related changes in the brains of individuals with Down's syndrome.

Neuroanatomic characteristics of the brains of individuals with Down's syndrome (DS) are typically characterized at autopsy. Apparent anatomic differences in brain between DS and normal individuals are observable upon gross inspection of MRIs. Area measurements from coronal MRIs are used in this study to determine quantitative structural differences that may occur in DS and during aging. In DS individuals, a significantly larger parahippocampal gyrus, and smaller hippocampus and neocortex, are reported relative to age-matched controls. We also examine two DS individuals with a clinical diagnosis of dementia who exhibit atrophy similar to that typically observed in Alzheimer's disease. MRI appears to be a useful tool for quantitative anatomic analysis and may be beneficial for determining baseline anatomic measures that can be useful in the diagnosis of changes associated with dementia.

Analysis of brain injury following intrahippocampal administration of beta-amyloid in streptozotocin-treated rats.

It has been suggested that the vulnerability of the aged brain to Alzheimer's disease (AD) pathogenesis depends on a number of risk factors, including abnormal glycolytic metabolism and beta-amyloid accumulation. Intrahippocampal injections of beta-amyloid and related peptides were administered to chronically hyperglycemic rats to examine beta-amyloid toxicity and the interaction with imbalances of glucose metabolism. Chronic hyperglycemia was induced by systemic injection of streptozotocin (STZ) which selectively destroys pancreatic beta-islet cells. Ten days after intrahippocampal injection of synthetic beta-amyloid peptides (beta 1-42, beta 25-35, scrambled beta 25-35), lesion volume, blood glucose, and plasma corticosterone concentrations, beta 1-42 immunoreactivity and gliosis were assessed to determine peptide toxicity in the normoglycemic and hyperglycemic conditions. Glucose levels correlated with plasma corticosterone concentrations (r = 0.85) and increased lesion volume size (r = 0.36). Intrahippocampal peptide injections in normoglycemic subjects did not induce significant damage as compared to control injections of vehicle alone. STZ-treated groups demonstrated a trend for increased lesion volume size following injection of either vehicle, beta 1-42, or beta 25-35. The combination of the beta 1-42 peptide and streptozotocin-induced hyperglycemia was toxic and induced significantly larger lesions (p < 0.01) of the dorsal blade of the dentate gyrus as compared to injections of beta 1-42 into normoglycemic subjects.

Lesions of the rat postsubiculum impair performance on spatial tasks.

Previous studies have identified a population of neurons in the postsubiculum that discharge as a function of the rat's head direction in the horizontal plane (Taube, Muller, & Ranck, 1990a). To assess the contribution of these cells in spatial learning, Long-Evans rats were tested in a variety of spatial and nonspatial tasks following bilateral electrolytic or neurotoxic lesions of the postsubiculum. Compared to unlesioned control animals, lesioned animals were impaired on two spatial tasks, a radial eight-arm maze task and a Morris water task, although the performance scores of both lesion groups improved over the course of behavioral testing. In contrast, lesioned animals were unimpaired on two nonspatial tasks, a cued version of the water maze task and a conditioned taste-aversion paradigm. In addition, lesioned animals showed transient hyperactivity in an open-field activity test. These results support the concept that neurons in the postsubiculum are part of a neural network involved in the processing of spatial information.

Transplantation of fetal cholinergic neurons into the hippocampus attenuates the cognitive and neurochemical deficits induced by AF64A.

The present experiments examined whether transplanted fetal cholinergic neurons would attenuate the behavioral and neurochemical deficits induced by the cholinotoxin AF64A (ethylcholine aziridinium ion). Bilateral injections of AF64A (3 nmol) into the lateral ventricles produced significant learning and memory impairments together with decreases in hippocampal high-affinity choline uptake (HAChU). AF64A-treated rats were impaired on both a standard radial arm maze (RAM) task and a working memory version in which a one-hour delay was imposed between the fourth and fifth arm choices. Transplantation of embryonic day E-17 septal/diagonal band tissue into the hippocampus (HPC) promoted recovery of performance on the standard version of the RAM task. However, this recovery was not observed when the animals were tested on the more difficult delay version of the task. Neurochemical analysis indicated that AF64A produced a significant (31%) decrease in hippocampal HAChU that was attenuated (14%) by transplantation of fetal cholinergic neurons. Histological analysis revealed that the transplants survived and innervated the HPC. There was no apparent relationship between fiber ingrowth into the HPC and behavioral recovery. These data indicate that transplant-induced behavioral recovery may be related to and limited by the cognitive demands of the testing situation. Generalized increases in cholinergic activity, transplant-mediated release of trophic factors, or a combination of both may underlie the behavioral recovery observed in the present studies.

Olfactory function in chronic alcoholics.

8 patients participating in an outpatient program for chronic alcohol abuse and 8 age-matched controls were tested for olfactory function. There was a significant difference between the two groups on a match-to-sample test using uncommon odors but not on a smell identification test using common odors. Ability to detect and identify common odors does not appear to be impaired by chronic alcohol abuse. Deficits on the odor-matching task may be related to difficulty in encoding olfactory information rather than a primary olfactory deficit.