Aging attenuates glucocorticoid negative feedback in rat brain

Aging is thought to be a risk factor to develop vulnerability of the neuroendocrine system, including the hypothalamic-pituitary-adrenal (HPA) axis, and dysregulation of this axis characterized by dexamethasone (DEX)-mediated negative feedback resistance is sometimes observed in elderly humans and animals. However, the influence of aging on the feedback system including an involvement of the brain is not fully understood. In the present study, we examined the suppressive effects of DEX by the systemic injection or the intracranial infusion into the prefrontal cortex (PFC), hippocampus, and hypothalamus on circulating corticosterone levels, and compared between young (3-month-old) and aged (24-month-old) rats. Moreover, we examined expression levels of glucocorticoid receptors (GRs) and their translocation from the cytoplasm to the nucleus using immunohistochemical and Western immunoblot techniques in the pituitary in addition to three brain regions. When DEX was injected systemically, the suppressive response was significantly enhanced in aged rats, compared with young rats. When DEX was infused into three brain regions, the suppressive response to DEX was abolished in aged rats. The immunohistochemical analysis revealed that the number of GR positive cells in the PFC, hippocampus, and hypothalamus was decreased, but that in the pituitary was increased, in aged rats, compared with young rats. The Western immunoblot analysis confirmed these results. Thus, basal expression levels of GRs in three brain regions were decreased, but those in the pituitary were increased, in aged rats. After the injection or infusion of DEX, the translocation of GRs in three brain regions was reduced, but that in the pituitary was enhanced, in aged rats. These results suggest that aging in rats enhances the feedback ability at the systemic level, which mainly involves the pituitary, but it attenuates the ability in the brain. These mechanisms may underlie the vulnerable neuroendocrine systems associated with aging.

A molecular chaperone inducer protects neurons from ER stress

The endoplasmic reticulum (ER) stress response is a defense system for dealing with the accumulation of unfolded proteins in the ER lumen. Recent reports have shown that ER stress is involved in the pathology of some neurodegenerative diseases and cerebral ischemia. In a screen for compounds that induce the ER-mediated chaperone BiP (immunoglobulin heavy-chain binding protein)/GRP78 (78 kDa glucose-regulated protein), we identified BiP inducer X (BIX). BIX preferentially induced BiP with slight inductions of GRP94 (94 kDa glucose-regulated protein), calreticulin, and C/EBP homologous protein. The induction of BiP mRNA by BIX was mediated by activation of ER stress response elements upstream of the BiP gene, through the ATF6 (activating transcription factor 6) pathway. Pretreatment of neuroblastoma cells with BIX reduced cell death induced by ER stress. Intracerebroventricular pretreatment with BIX reduced the area of infarction due to focal cerebral ischemia in mice. In the penumbra of BIX-treated mice, ER stress-induced apoptosis was suppressed, leading to a reduction in the number of apoptotic cells. Considering these results together, it appears that BIX induces BiP to prevent neuronal death by ER stress, suggesting that it may be a potential therapeutic agent for cerebral diseases caused by ER stress.

Increased corticospinal excitability during direct observation of self-movement and indirect observation with a mirror box

To explore the effect of mirror box therapy based on the mirror neuron (MN) system of the primary motor cortex (M1), we examined if direct (without a mirror) and indirect (with a mirror) observation of self-movement in healthy subjects induced changes in motor evoked potential (MEP) evoked by transcranial magnetic stimulation (TMS). MEPs were elicited from the first dorsal interosseous (FDI) and the flexor carpi radialis (FCR) muscles. Somatosensory evoked potentials (SEPs) during self-movement observation were also recorded. Both observations of self-movement with and without a mirror increased MEP amplitude. In addition, increase in MEP amplitude was specific to the prime mover muscle involved in the observed movement. The SEPs increased similar to the MEPs during both observations of self-movement with and without a mirror. We conclude that although the MN system can be activated by observing self-movement in a manner similar to that achieved by observing movement of another person, there were no detectable effect on corticospinal excitability that were specific to movements observed with a mirror.

Novel mutation of the Notch3 gene in a Japanese patient with CADASIL

We report a novel missense mutation of the Notch3 gene in a Japanese family with CADASIL. The Cys49Gly mutation in this family is located in exon 2 of the Notch3 gene. Most of the documented Notch3 gene mutations occur in exons 3 or 4. On the other hand, there are few reports around the world of mutations in exon 2 of the Notch3 gene, and this is the first report of a mutation in exon 2 of the gene in a Japanese family. In general, CADASIL mutations involve a cysteine residue. Such mutations may influence the tertiary structure of the Notch3 protein, resulting in protein dysfunction. Thus, the CADASIL in the present case may be a consequence of the mutation in exon 2 causing a structural change in the Notch3 protein.

The pathogenesis of CADASIL: an update

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) appears to be the most common form of hereditary stroke disorder. CADASIL is associated with arterial smooth muscle degeneration linked to mutations in the Notch3 gene, whose product is a transmembrane receptor that functions in cell-cell communication. The pathogenesis of CADASIL remains unclear. Current research efforts are directed towards the elucidation of various features of the disorder including investigations on CADASIL-like disorders, early cognitive changes, specificity of neuroimaging for diagnosis, discovery of de novo mutations, the development of Notch3 transgenic mouse models and molecular cellular studies in Notch3 signaling. The genetics of cerebrovascular disorders (CVD) was virtually unknown until recently. Genetic associations may have been evaded because of widely variable phenotypes, even within monogenic disorders such as CADASIL. Several investigators have attempted genotype-phenotype correlation in CADASIL cases but the relationship between genetic alterations and overt manifestation of phenotype remains elusive. However, the elucidation of the genetics and pathogenesis of CADASIL have been important in further understanding of the primary vascular mechanisms that lead to ischemic blood flow and its consequences on neuronal survival. This report summarizes some of the highlights of the satellite symposium on CADASIL at Vas-Cog 2003.

Chronic stress attenuates glucocorticoid negative feedback: involvement of the prefrontal cortex and hippocampus

Disruption of the glucocorticoid negative feedback system is observed in approximate one half of human depressives, and a similar condition is induced in animals by chronic stress. This disruption is thought to involve down-regulation of glucocorticoid receptors (GRs) in the feedback sites of the brain. However, the responsible site of the brain has not been well elucidated. Here we examined the effects of chronic stress induced by water immersion and restraint (2 h/day) for 4 weeks followed by recovery for 10 days on the GR levels in the prefrontal cortex (PFC), hippocampus, and hypothalamus of rats using a Western immunoblot technique. In the PFC, the cytosolic GR levels were decreased, but the nuclear GR levels were not changed. In the hippocampus, the levels of cytosolic and nuclear GRs were increased. However, there were no marked changes in the GR levels in the hypothalamus. The changes in the cytosolic GR levels were confirmed at the mRNA level by an in situ hybridization technique. We next examined the suppressive effects of dexamethasone (DEX) infusions into these regions on the circulating corticosterone levels. When DEX was infused into the PFC or hippocampus of the chronically stressed rats, the suppressive response to DEX was abolished, but the response was normal in the hypothalamus. In addition, when DEX was injected systemically to the chronically stressed rats, the suppressive response to DEX was significantly attenuated. These results suggest that the abnormal changes in GRs in the higher centers of the hypothalamo-pituitary-adrenal axis are involved in the chronic stress-induced attenuation of the feedback. Since dysfunction of the PFC or hippocampus is implicated in the pathogenesis of depression, the present findings would help to understand the mechanisms underlying the disrupted feedback system and its relation to brain dysfunction in depression.

Significance of intracellular Abeta42 accumulation in Alzheimer's disease

Abeta plays a pivotal role in the pathogenesis of Alzheimer's disease (AD), but it is still obscure how it causes AD. We have established transgenic mice carrying wild-type or familial Alzheimer's disease (FAD) mutant-type presenilin 1 (PS1). In these mice, the number of cortical and hippocampal neurons decreased along with age in mutant mice. In addition, the old mutant mice showed a significant increase of dark neurons by silver staining and the number of neurons with intracellular Abeta42 by immunohistochemistry. Our extended study also showed a significant increase of intracellular Abeta42-positive neurons in isolated cases of AD as well as in PS1 mutant FAD cases. These neurons frequently showed apoptotic staining. However, coincidence of apoptotic markers and intraneuronal neurofibrillary tangles (NFT) was insignificant. Notably intraneuronal Abeta42-labeling was frequently seen in a case of AD showing cotton-wool type senile plaques with a few NFT positive neurons and dystrophic neurites. These results indicate that intraneuronal deposition of Abeta42 is important in the pathogenesis of AD.

Pro-apoptotic effect of presenilin 2 (PS2) overexpression is associated with down-regulation of Bcl-2 in cultured neurons

Presenilin 2 (PS2) is a polytopic membrane protein that is mutated in some cases of familial Alzheimer's disease (AD). The normal functions of PS2 and its pathogenic role in AD remain unclear. We investigated the biological role of this protein in neurons, using adenovirus-mediated transduction of the PS2 gene into rat primary cortical neurons. Immunocytochemical analyses demonstrated increased PS2 immunoreactivity in most neurons infected with recombinant adenoviruses expressing PS2. Neurons infected with wild-type or mutant (N141I) PS2-expressing adenoviruses showed a significant increase in basal cell death, compared with those infected with control beta-galactosidase-expressing adenovirus. Moreover, PS2 overexpression markedly increased neuronal susceptibility to staurosporine-induced apoptosis. Mutant PS2 was more effective in enhancing apoptosis than its wild-type counterpart. Staurosporine-induced death was significantly inhibited by a specific caspase 3 inhibitor. Western analyses revealed that Bcl-2 protein expression was specifically down-regulated in neurons overexpressing PS2, which temporally corresponded to the accumulation of C- and N-terminal fragments of PS2. Additionally, expression of mutant, but not wild-type PS2, increased the production of beta-amyloid protein (Abeta) 42. These data collectively suggest that the pro-apoptotic effect of PS2 is mediated by down-regulation of Bcl-2. PS2 mutations may increase the susceptibility of neurons to apoptotic stimuli by perturbing the regulation of cell death.

Motoneuron pool excitability of hemiplegic patients: assessing recovery stages by using H-reflex and M response

OBJECTIVES

To compare the excitability of the motoneuron pools of both the spastic and the unimpaired sides of patients with hemiplegia with a new method by using H-reflexes and M responses. The method determines the ratio of the developmental slope of the H-reflex (Hslp) to the slope of the M response (Mslp). We also examined the relation between the Brunnstrom stages and the Hslp/Mslp.

DESIGN

Experiment.

SETTING

Electrophysiologic experimental laboratory in a Japanese medical school.

PATIENTS

Fifteen hemiplegic patients (9 men, 6 women; age range, 48-71yr; mean, 60yr) with spasticity caused by a stroke.

INTERVENTIONS

The subject was instructed to relax while seated in a reclining chair with his foot fixed on an immobile pedal. After the soleus H-reflex and M responses on one side were recorded, the same experimental procedures were carried out on the other side.

MAIN OUTCOME MEASURES

Hslp/Mslp Brunnstrom stages.

RESULTS

Hslp/Mslp had better predictive value than conventional indicators of motoneuron pool excitability. Hslp/Mslp appeared to be a better match for the bell-shaped pattern of the Brunnstrom stages.

CONCLUSION

Hslp/Mslp is the preferred index for evaluating the motoneuron pool excitability of the spastic side of hemiplegic patients.

Genetic analysis in patients with familial and sporadic frontotemporal dementia: two tau mutations in only familial cases and no association with apolipoprotein epsilon4

We screened for tau gene mutations among 24 Japanese (6 familial and 18 sporadic cases) and 4 Polish patients with frontotemporal dementia (FTD) using PCR-SSCP analysis followed by DNA sequencing. We identified 2 missense mutations in exon 10: N279K and P301L in 2 Japanese patients with familial FTD. Additionally 3 DNA polymorphisms: 2 known (3' exon 3 + 9, A --> G and exon 7, codon 176, G --> A) and 1 new (exon 8, codon 185, T --> C) were identified in 1 Polish patient. Tau mutations were not found in subjects with a negative family history suggesting that tau mutations do not account for most sporadic cases of FTD. We also found no association of apolipoprotein E4 allele with FTD.

Decreased expression of MAP-2 and GAD in the brain of cats infected with feline immunodeficiency virus

HIV-1 infection is often complicated by the dysfunction of central nervous system (CNS). Degenerative neuronal changes as well as neuronal loss have been documented in individuals with acquired immunodeficiency syndrome. Feline immunodeficiency virus (FIV) causes similar CNS manifestation and FIV infected cats provide an animal model for human immunodeficiency virus infection in humans. In this study, we examined the brain of FIV-infected cats and controls with immunohistochemical techniques using antibodies to microtubule-associated protein 2 (MAP-2) and glutamic acid decarboxylase (GAD). We found a significant decrease in expression of MAP-2 and GAD in neurons of infected animals compared to controls. In contrast, the expression of neurofilaments and glial fibrillary acidic protein was rather increased. The changes observed in the brain were similar to those seen in humans undergoing the normal aging process as well as those suffering from neurological diseases like Alzheimer's disease and other dementing disorders. These changes in the feline brain give insight into the deleterious effects of FIV on the CNS.

Effect of chronic stress on cholinergic transmission in rat hippocampus

We previously demonstrated that chronic stress impaired prefrontal cortex-sensitive working memory, but not reference memory. Since the hippocampal cholinergic system is also involved in these memories, we examined the effects of chronic stress on cholinergic transmission in the rat hippocampus. A microdialysis study revealed that the stress did not affect the basal acetylcholine release, but enhanced the KCl-evoked response. These results suggest that cholinergic transmission in the chronically stressed hippocampus does not contribute to working memory impairment, but it may be involved in maintenance of reference memory.

Changes in brain morphology in Alzheimer disease and normal aging: is Alzheimer disease an exaggerated aging process?

BACKGROUND AND PURPOSE

Whether Alzheimer disease (AD) represents exaggerated aging rather than a disease is controversial. Data about the effects of normal aging on the human brain are essential for clarifying this issue; however, whether coherent common patterns of regional morphologic brain changes emerge in the normal aged brain is unclear. Clarification of regional morphologic changes in the brain associated with normal aging and AD was sought using MR imaging.

METHODS

Ninety-two healthy volunteers and 26 mildly to moderately impaired patients with AD participated. Images were anatomically normalized, and voxel-by-voxel analyses were done.

RESULTS

In healthy volunteers, an age-related decline in the volume of the prefrontal cortex, insula, anterior cingulate gyrus, superior temporal gyrus, inferior parietal lobule, and precuneus was found. These decreases might contribute to the cognitive changes during normal aging. In patients with AD, a significant reduction of gray matter volume in the hippocampal formation and entorhinal cortex bilaterally was noted.

CONCLUSION

Morphologic changes associated with normal aging are clearly different from those seen with AD.

CXCR4 is the primary receptor for feline immunodeficiency virus in astrocytes

Feline astrocytes were productively infected with the Crandell feline kidney (CrFK) cell-adapted feline immunodeficiency virus (FIV) Petaluma strain in a primary culture. They expressed mRNA of CXCR4, and the FIV infection was blocked by stromal cell-derived factor 1alpha (SDF-1alpha), SDF-1beta, or the bicyclam AMD3100 in a dose-dependent manner. These observations suggest that, like FIV infection in CrFK cells and lymphocytes, the virus uses CXCR4 as a primary receptor for infecting astrocytes and this can be a possible natural model for AIDS dementia complex.

Three novel alternatively spliced isoforms of the human beta-site amyloid precursor protein cleaving enzyme (BACE) and their effect on amyloid beta-peptide production

Three novel alternatively spliced transcripts of the beta-site amyloid precursor protein cleaving enzyme (BACE) were cloned from human brain. Alternative splicing of the RNA occurs at an internal donor in exon 3 and/or an internal acceptor in exon 4. The splicing events lead to a deletion of 25 (BACE-I-476), 44 (BACE-I-457) and 69 (BACE-I-432) amino acids and the latter two caused the loss of two of four N-linked glycosylation sites. Although the mature form of BACE-501 was resistant to endoglycosidase H treatment, glycosylated forms of BACE-I-457 and BACE-I-476 were sensitive. This result suggests that BACE-I-457 and BACE-I-476 underwent different post-translational modifications. Moreover, the beta-secretase activity of BACE-I-457 and BACE-I-476 was significantly weaker than that of BACE-501. Thus, these isoforms may contribute to a physiological function of BACE.

Chronic stress differentially regulates glucocorticoid negative feedback response in rats

Exposure to chronic stress is thought to play an important role in the etiology of depression. In this disorder, a disrupted negative feedback response to exogenous glucocorticoids on cortisol secretion has been indicated. However, the regulation of glucocorticoid negative feedback by chronic stress is not fully understood. In the present study, we investigated the effects of chronic stress administered by water immersion and restraint (2 h/day) for four weeks on the glucocorticoid feedback in rats. In the acutely (one-time) stressed rats, the basal plasma corticosterone (CORT) level was markedly elevated, remained at high levels for 5 h after the termination of stress, and then decreased. In the chronically stressed rats, the CORT level was initially elevated similarly, but rapidly decreased at 2 h. In the dexamethasone (DEX) suppression test, the peak CORT level in response to stress was not suppressed by DEX in the acutely stressed rats, but was significantly suppressed in the chronically stressed rats. In contrast, the suppressive effects of DEX on the basal CORT secretion in naive rats were attenuated in the chronically stressed rats. In the chronically stressed hippocampus, which plays an important role in the regulation of the glucocorticoid feedback response, the binding of [3H]DEX was decreased and the increased response of activator protein-1 induced by acute stress was abolished. These results suggest that chronic stress induces a hypersuppressive state for induced CORT secretion in response to acute stress, which is caused by partial habituation, coping, and adaptation to the stressor, whereas it induces a hyposuppressive state for the basal CORT secretion, which is caused by glucocorticoid receptor downregulation. These mechanisms may be involved in the stress-induced neural abnormalities observed in depression.

Familial frontotemporal dementia and parkinsonism with a novel mutation at an intron 10+11-splice site in the tau gene

We report a case of familial frontotemporal dementia and parkinsonism characterized by early onset with mental retardation. The patient died at the age of 54; neuronal loss was severe in the frontal and temporal cortices, globus pallidus, substantia nigra, red nucleus and dentate nucleus. Anti-tau-positive fibrillary changes were observed in neurons and glia in these regions. Although the patient had 2 novel point mutations of the tau gene, P301P (CCG to CCA) and an intron 10+11-splice site (T to C), exon trapping analysis indicated that the latter was pathogenic.

Mutations of the notch3 gene in non-caucasian patients with suspected CADASIL syndrome

The Notch3 gene has been recently identified as a causative gene for cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). To investigate the genetic contribution of Notch mutations in familial cases with vascular leukoencephalopathy, we screened 13 patients from 11 unrelated families, which were selected on the basis of magnetic resonance imaging findings and positive family history. We identified three different missense mutations in 5 patients from 4 families. Two (Arg90Cys and Arg133Cys) are the same as previously reported in Caucasian patients, the other (Cys174Phe) is a novel mutation causing a loss of a cysteine in epidermal-growth-factor-like repeats of Notch3. These data indicate that the CADASIL Notch3 mutations were found in approximately 35% of familial cases with leukoencephalopathy, suggesting genetic heterogeneity of the disease.

Apoptotic neurons in Alzheimer's disease frequently show intracellular Abeta42 labeling

It is widely accepted that Abeta plays a pivotal role in the pathogenesis of Alzheimer's disease (AD) [27]. Attention has been focused mainly on how extracellular Abeta exerts its effects on neuronal cells [7,11,16,32]. However, neuronal degeneration from an accumulation of intracellular Abetax-42 (iAbeta42) occurs in presenilin 1 (PS1) mutant mice without extracellular Abeta deposits [5]. In the present study, intracellular deposits of iAbeta42 are correlated with apoptotic cell death in AD and PS-1 familial AD (PS1 FAD) brains by means of triple staining with antibodies to Abeta, TUNEL, and staining with Hoechst 33342. Neurons simultaneously positive for iAbeta42 and the TUNEL assay were significantly more abundant in AD brains than in controls. The number of apoptotic neurons with intracellular neurofibrillary tangles (iNFTs) was insignificant. Our results indicate that intraneuronal deposition of a neurotoxic form of Abeta seems to be an early event in the neurodegeneration of AD.

Overexpression of presenilin-2 enhances apoptotic death of cultured cortical neurons

Presenilin-2 (PS2) is a gene of unknown function linked with some forms of familial Alzheimer's disease. To investigate the biological role of PS2 in neurons, we overexpressed PS2 in primary cortical neurons using recombinant adenoviral vectors. Western blot and immunohistochemical analyses showed enhanced expression of PS2 proteins in infected neurons after infection of recombinant adenoviruses containing the human wild-type or mutant PS2 gene. Neuronal survival was decreased by approximately 30% in cultures infected with adenovirus expressing either wild-type or mutant PS2, as compared with those infected with adenovirus expressing the LacZ gene. Fragmented nuclei were frequently observed in dying neurons. These data suggest that apoptotic death of cultured cortical neurons is enhanced by PS2 overexpression.