Selective age-related loss of calbindin-D28k from basal forebrain cholinergic neurons in the common marmoset (Callithrix jacchus)

Basal forebrain cholinergic system in the dementias: Vulnerability, resilience, and resistance

The basal forebrain cholinergic neurons (BFCN) provide the primary source of cholinergic innervation of the human cerebral cortex. They are involved in the cognitive processes of learning, memory, and attention. These neurons are differentially vulnerable in various neuropathologic entities that cause dementia. This review summarizes the relevance to BFCN of neuropathologic markers associated with dementias, including the plaques and tangles of Alzheimer's disease (AD), the Lewy bodies of diffuse Lewy body disease, the tauopathy of frontotemporal lobar degeneration (FTLD-TAU) and the TDP-43 proteinopathy of FTLD-TDP. Each of these proteinopathies has a different relationship to BFCN and their corticofugal axons. Available evidence points to early and substantial degeneration of the BFCN in AD and diffuse Lewy body disease. In AD, the major neurodegenerative correlate is accumulation of phosphotau in neurofibrillary tangles. However, these neurons are less vulnerable to the tauopathy of FTLD. An intriguing finding is that the intracellular tau of AD causes destruction of the BFCN, whereas that of FTLD does not. This observation has profound implications for exploring the impact of different species of tauopathy on neuronal survival. The proteinopathy of FTLD-TDP shows virtually no abnormal inclusions within the BFCN. Thus, the BFCN are highly vulnerable to the neurodegenerative effects of tauopathy in AD, resilient to the neurodegenerative effect of tauopathy in FTLD and apparently resistant to the emergence of proteinopathy in FTLD-TDP and perhaps also in Pick's disease. Investigations are beginning to shed light on the potential mechanisms of this differential vulnerability and their implications for therapeutic intervention.

Cardiac MRI in common marmosets revealing age-dependency of cardiac function

The aim of this study was to establish a feasible and robust magnetic resonance imaging protocol for the quantitative assessment of cardiac function in marmosets and to present normal values of cardiac function across different ages from young adult, middle-aged, to very old clinically healthy animals. Cardiac MRI of 33 anesthetized marmosets at the age of 2-15 years was performed at 9.4 T using IntraGate-FLASH that operates without any ECG-triggering and breath holding. Normalized to post-mortem heart weight, the left ventricular end-diastolic volume (LV-EDV) was significantly reduced in older marmosets. The LV end-systolic volume (LV-ESV) and the LV stroke volume (LV-SV) showed a similar trend while the LV ejection fraction (LV-EF) and wall thickening remained unchanged. Similar observations were made for the right ventricle. Moreover, the total ventricular myocardial volume was lower in older monkeys while no significant difference in heart weight was found. In conclusion, IntraGate-FLASH allowed for quantification of left ventricular cardiac function but seems to underestimate the volumes of the right ventricle. Although less strong and without significant sex differences, the observed age related changes were similar to previously reported findings in humans supporting marmosets as a model system for age related cardiovascular human diseases.

Obesity, Metabolism, and Aging: A Multiscalar Approach

Obesity contributes to the aging process through the alteration of metabolic pathways evidenced biochemically in the relationship between caloric restriction and longevity. Humans have entered into an era of metabolism and aging entirely unprecedented in their evolution, with a diet that, for many, contains a majority of calories as sugar and yields an expected lifespan of over 80years in industrialized nations. Deeply embedded in the complex issue of obesity are questions of behavior, causality versus correlation, and appropriate models. For example, are primates a better reference than mice for studying metabolic connections between obesity and aging? We consider those issues from the standpoint of life-history theory, especially implications of the interplay of refined sugar and socioeconomic disparities for the future of human health.

Evidence of Tau Hyperphosphorylation and Dystrophic Microglia in the Common Marmoset

Common marmosets (Callithrix jacchus) have recently gained popularity in biomedical research as models of aging research. Basically, they confer advantages from other non-human primates due to their shorter lifespan with onset of appearance of aging at 8 years. Old marmosets present some markers linked to neurodegeneration in the brain such as amyloid beta (Aβ)_1-42 and Aβ_1-40. However, there are no studies exploring other cellular markers associated with neurodegenerative diseases in this non-human primate. Using immunohistochemistry, we analyzed brains of male adolescent, adult, old, and aged marmosets. We observed accumulation of Aβ_1-40 and Aβ_1-42 in the cortex of aged subjects. Tau hyperphosphorylation was already detected in the brain of adolescent animals and increased with aging in a more fibrillary form. Microglia activation was also observed in the aging process, while a dystrophic phenotype accumulates in aged subjects. Interestingly, dystrophic microglia contained hyperphosphorylated tau, but active microglia did not. These results support previous findings regarding microglia dysfunctionality in aging and neurodegenerative diseases as Alzheimer's disease. Further studies should explore the functional consequences of these findings to position this non-human primate as animal model of aging and neurodegeneration.

Loss of calbindin-D28K is associated with the full range of tangle pathology within basal forebrain cholinergic neurons in Alzheimer's disease

Basal forebrain cholinergic neurons (BFCN) are selectively vulnerable in Alzheimer's disease (AD). We have shown that most of the BFCN in the human brain contain the calcium-binding protein calbindin-D28K (CB), a large proportion lose their CB in the course of normal aging, and the BFCN which degenerate in AD lack CB. Here, we investigated the relationship between CB in the BFCN and the process of tangle formation in AD using antibodies to tau epitopes that appear early, intermediate or late in the process of tangle formation. Very small percentages (0%-3.7%) of CB-positive BFCN contained pretangles and/or tangles, and very small percentages (0%-5%) of the total BFCN pretangles and/or tangles were in CB-immunoreactive neurons. The number of CB-positive BFCN which contained tau immunoreactivity was highest for the early epitope and lower for intermediate epitopes. A late appearing epitope was absent from CB-positive BFCN. Age-related loss of CB appears to coincide with tangle formation in the BFCN and is associated with the full range of tau pathology, including late appearing epitopes.

Neurocognitive effects of estrogens across the adult lifespan in nonhuman primates: State of knowledge and new perspectives

This article is part of a Special Issue "Estradiol and cognition". This review discusses the unique contribution of nonhuman primate research to our understanding of the neurocognitive effects of estrogens throughout the adult lifespan in females. Mounting evidence indicates that estrogens affect many aspects of hippocampal, prefrontal and cholinergic function in the primate brain and the underlying mechanisms are beginning to be elucidated. In addition, estrogens may also influence cognitive function indirectly, via the modulation of other systems that impact cognition. We will focus on the effects of estrogens on sleep and emphasize the need for primate models to better understand these complex interactions. Continued research with nonhuman primates is essential for the development of therapies that are optimal for the maintenance of women's cognitive health throughout the lifespan.

Neuronal amyloid-β accumulation within cholinergic basal forebrain in ageing and Alzheimer's disease

The mechanisms that contribute to selective vulnerability of the magnocellular basal forebrain cholinergic neurons in neurodegenerative diseases, such as Alzheimer's disease, are not fully understood. Because age is the primary risk factor for Alzheimer's disease, mechanisms of interest must include age-related alterations in protein expression, cell type-specific markers and pathology. The present study explored the extent and characteristics of intraneuronal amyloid-β accumulation, particularly of the fibrillogenic 42-amino acid isoform, within basal forebrain cholinergic neurons in normal young, normal aged and Alzheimer's disease brains as a potential contributor to the selective vulnerability of these neurons using immunohistochemistry and western blot analysis. Amyloid-β1-42 immunoreactivity was observed in the entire cholinergic neuronal population regardless of age or Alzheimer's disease diagnosis. The magnitude of this accumulation as revealed by optical density measures was significantly greater than that in cortical pyramidal neurons, and magnocellular neurons in the globus pallidus did not demonstrate a similar extent of amyloid immunoreactivity. Immunoblot analysis with a panel of amyloid-β antibodies confirmed accumulation of high concentration of amyloid-β in basal forebrain early in adult life. There was no age- or Alzheimer-related alteration in total amyloid-β content within this region. In contrast, an increase in the large molecular weight soluble oligomer species was observed with a highly oligomer-specific antibody in aged and Alzheimer brains when compared with the young. Similarly, intermediate molecular weight oligomeric species displayed an increase in aged and Alzheimer brains when compared with the young using two amyloid-β42 antibodies. Compared to cortical homogenates, small molecular weight oligomeric species were lower and intermediate species were enriched in basal forebrain in ageing and Alzheimer's disease. Regional and age-related differences in accumulation were not the result of alterations in expression of the amyloid precursor protein, as confirmed by both immunostaining and western blot. Our results demonstrate that intraneuronal amyloid-β accumulation is a relatively selective trait of basal forebrain cholinergic neurons early in adult life, and increases in the prevalence of intermediate and large oligomeric assembly states are associated with both ageing and Alzheimer's disease. Selective intraneuronal amyloid-β accumulation in adult life and oligomerization during the ageing process are potential contributors to the degeneration of basal forebrain cholinergic neurons in Alzheimer's disease.

Morphological changes in the suprachiasmatic nucleus of aging female marmosets (Callithrix jacchus)

The suprachiasmatic nuclei (SCN) are pointed to as the mammals central circadian pacemaker. Aged animals show internal time disruption possibly caused by morphological and neurochemical changes in SCN components. Some studies reported changes of neuronal cells and neuroglia in the SCN of rats and nonhuman primates during aging. The effects of senescence on morphological aspects in SCN are important for understanding some alterations in biological rhythms expression. Therefore, our aim was to perform a comparative study of the morphological aspects of SCN in adult and aged female marmoset. Morphometric analysis of SCN was performed using Nissl staining, NeuN-IR, GFAP-IR, and CB-IR. A significant decrease in the SCN cells staining with Nissl, NeuN, and CB were observed in aged female marmosets compared to adults, while a significant increase in glial cells was found in aged marmosets, thus suggesting compensatory process due to neuronal loss evoked by aging.

Co-localization of L-type voltage dependent calcium channel alpha 1D subunit (Ca(v)1.3) and calbindin (CB) in the mouse central nervous system

Previous study has shown that the co-localization of calbindin (CB) with L-type voltage dependent Ca(2+) channel (VDCC) alpha 1C subunit (Ca(v)1.2) in the rat insulinoma 1046-38 (RIN) beta cells may play an important regulatory role in Ca(2+) influx and exocytosis of insulin granules. In the present study, L-type voltage dependent Ca(2+) channel (VDCC) and calbindin (CB) were demonstrated in different regions of the mouse central nervous system (CNS). Double labeling immunofluorescence staining showed a co-localization of Ca(v)1.3 and CB. The co-localization of Ca(v)1.3 and CB in certain brain regions such as the hippocampus suggests their important roles in neuroplasticity. The relative high percentages of co-localization of Ca(v)1.3 with CB in the laminae II of the dorsal horn of the spinal cord indicate that the regulation mechanism of nociceptive transmission may be related with both VDCC and Ca(2+) binding protein.

Alterations of Ca²⁺-responsive proteins within cholinergic neurons in aging and Alzheimer's disease

The molecular basis of selective neuronal vulnerability in Alzheimer's disease (AD) remains poorly understood. Using basal forebrain cholinergic neurons (BFCNs) as a model and immunohistochemistry, we have demonstrated significant age-related loss of the calcium-binding protein calbindin-D(28K) (CB) from BFCN, which was associated with tangle formation and degeneration in AD. Here, we determined alterations in RNA and protein for CB and the Ca(2+)-responsive proteins Ca(2+)/calmodulin-dependent protein kinase I (CaMKI), growth-associated protein-43 (GAP43), and calpain in the BF. We observed progressive downregulation of CB and CaMKI RNA in laser-captured BFCN in the normal-aged-AD continuum. We also detected progressive loss of CB, CaMKIδ, and GAP43 proteins in BF homogenates in aging and AD. Activated μ-calpain, a calcium-sensitive protease that degrades CaMKI and GAP43, was significantly increased in the normal aged BF and was 10 times higher in AD BF. Overactivation of μ-calpain was confirmed using proteolytic fragments of its substrate spectrin. Substantial age- and AD-related alterations in Ca(2+)-sensing proteins most likely contribute to selective vulnerability of BFCN to degeneration in AD.

Distribution of secretagogin-containing neurons in the basal forebrain of mice, with special reference to the cholinergic corticopetal system

Cholinergic and GABAergic corticopetal neurons in the basal forebrain play important roles in cortical activation, sensory processing, and attention. Cholinergic neurons are intermingled with peptidergic, and various calcium binding protein-containing cells, however, the functional role of these neurons is not well understood. In this study we examined the expression pattern of secretagogin (Scgn), a newly described calcium-binding protein, in neurons of the basal forebrain. We also assessed some of the corticopetal projections of Scgn neurons and their co-localization with choline acetyltransferase (ChAT), neuropeptide-Y, and other calcium-binding proteins (i.e., calbindin, calretinin, and parvalbumin). Scgn is expressed in cell bodies of the medial and lateral septum, vertical and horizontal diagonal band nuclei, and of the extension of the amygdala but it is almost absent in the ventral pallidum. Scgn is co-localized with ChAT in neurons of the bed nucleus of the stria terminalis, extension of the amygdala, and interstitial nucleus of the posterior limb of the anterior commissure. Scgn was co-localized with calretinin in the accumbens nucleus, medial division of the bed nucleus of stria terminalis, the extension of the amygdala, and interstitial nucleus of the posterior limb of the anterior commissure. We have not found co-expression of Scgn with parvalbumin, calbindin, or neuropeptide-Y. Retrograde tracing studies using Fluoro Gold in combination with Scgn-specific immunohistochemistry revealed that Scgn neurons situated in the nucleus of the horizontal limb of the diagonal band project to retrosplenial and cingulate cortical areas.

In vivo AAV-mediated expression of calbindin-D₂₈k in rat basal forebrain cholinergic neurons

The cholinergic neurons of the basal forebrain (BFCNs) in human and non-human primates are rich in the calcium binding protein calbindin-D(28k) (CB). We have shown a selective loss of CB from BFCNs in the course of normal aging, which appears to predispose these neurons to tangle formation and degeneration in Alzheimer's disease. Our previous preliminary investigation demonstrated that rodent BFCNs are devoid of CB. Here we confirm that rat choline acetyltransferase-rich BFCNs are devoid of CB immunoreactivity. We then describe a method for adeno-associated viral vector (AAV) induced expression of CB in rat BFCNs in vivo. We constructed AAV vectors bearing the CB gene under the control of the CMV promoter, or neuron-specific enolase (NSE) promoter, to bias expression in neurons. Both vectors resulted in CB expression in mouse neuronal cultures, and in rat brain following injections. AAV-NSE-CB resulted in more robust expression in neurons. Injections of 10 μl of AAV-NSE-CB in the BFCNs component located within the internal segment of globus pallidus and internal capsule resulted in expression of CB in 84% of BFCNs. Expression was optimum at 14 days. Injections of AAV-NSE-LacZ resulted in robust β-galactosidase expression, but no CB immunoreactivity. Our results show that use of NSE promoter leads to high expression of genes in neurons and that the BFCNs can be targeted for expression of genes that are differentially expressed in the rodent and primate brains. These findings have important implications for gene replacement therapy in human BFCNs.

Age-related loss of calcium buffering and selective neuronal vulnerability in Alzheimer's disease

The reasons for the selective vulnerability of distinct neuronal populations in neurodegenerative disorders are unknown. The cholinergic neurons of the basal forebrain are vulnerable to pathology and loss early in Alzheimer's disease and in a number of other neurodegenerative disorders of the elderly. In the primate, including man, these neurons are rich in the calcium buffer calbindin-D(28K). Here, we confirm that these neurons undergo a substantial loss of calbindin in the course of normal aging and report a further loss of calbindin in Alzheimer's disease both at the level of RNA and protein. Significantly, cholinergic neurons that had lost their calbindin in the course of normal aging were those that selectively degenerated in Alzheimer's disease. Furthermore, calbindin-containing neurons were virtually resistant to the process of tangle formation, a hallmark of the disease. We conclude that the loss of calcium buffering capacity in these neurons and the resultant pathological increase in intracellular calcium are permissive to tangle formation and degeneration.

Functional genomics of brain aging and Alzheimer's disease: focus on selective neuronal vulnerability

Pivotal brain functions, such as neurotransmission, cognition, and memory, decline with advancing age and, especially, in neurodegenerative conditions associated with aging, such as Alzheimer’s disease (AD). Yet, deterioration in structure and function of the nervous system during aging or in AD is not uniform throughout the brain. Selective neuronal vulnerability (SNV) is a general but sometimes overlooked characteristic of brain aging and AD. There is little known at the molecular level to account for the phenomenon of SNV. Functional genomic analyses, through unbiased whole genome expression studies, could lead to new insights into a complex process such as SNV. Genomic data generated using both human brain tissue and brains from animal models of aging and AD were analyzed in this review. Convergent trends that have emerged from these data sets were considered in identifying possible molecular and cellular pathways involved in SNV. It appears that during normal brain aging and in AD, neurons vulnerable to injury or cell death are characterized by significant decreases in the expression of genes related to mitochondrial metabolism and energy production. In AD, vulnerable neurons also exhibit down-regulation of genes related to synaptic neurotransmission and vesicular transport, cytoskeletal structure and function, and neurotrophic factor activity. A prominent category of genes that are up-regulated in AD are those related to inflammatory response and some components of calcium signaling. These genomic differences between sensitive and resistant neurons can now be used to explore the molecular underpinnings of previously suggested mechanisms of cell injury in aging and AD.

The marmoset as a model of aging and age-related diseases

The common marmoset (Callithrix jacchus) is poised to become a standard nonhuman primate aging model. With an average lifespan of 5 to 7 years and a maximum lifespan of 16½ years, marmosets are the shortest-lived anthropoid primates. They display age-related changes in pathologies that mirror those seen in humans, such as cancer, amyloidosis, diabetes, and chronic renal disease. They also display predictable age-related differences in lean mass, calf circumference, circulating albumin, hemoglobin, and hematocrit. Features of spontaneous sensory and neurodegenerative change--for example, reduced neurogenesis, ß-amyloid deposition in the cerebral cortex, loss of calbindin D(28k) binding, and evidence of presbycusis--appear between the ages of 7 and 10 years. Variation among colonies in the age at which neurodegenerative change occurs suggests the interesting possibility that marmosets could be specifically managed to produce earlier versus later occurrence of degenerative conditions associated with differing rates of damage accumulation. In addition to the established value of the marmoset as a model of age-related neurodegenerative change, this primate can serve as a model of the integrated effects of aging and obesity on metabolic dysfunction, as it displays evidence of such dysfunction associated with high body weight as early as 6 to 8 years of age.

Susceptibility to Calcium Dysregulation during Brain Aging

Calcium (Ca(2+)) is a highly versatile intracellular signaling molecule that is essential for regulating a variety of cellular and physiological processes ranging from fertilization to programmed cell death. Research has provided ample evidence that brain aging is associated with altered Ca(2+) homeostasis. Much of the work has focused on the hippocampus, a brain region critically involved in learning and memory, which is particularly susceptible to dysfunction during senescence. The current review takes a broader perspective, assessing age-related changes in Ca(2+) sources, Ca(2+) sequestration, and Ca(2+) binding proteins throughout the nervous system. The nature of altered Ca(2+) homeostasis is cell specific and may represent a deficit or a compensatory mechanism, producing complex patterns of impaired cellular function. Incorporating the knowledge of the complexity of age-related alterations in Ca(2+) homeostasis will positively shape the development of highly effective therapeutics to treat brain disorders.

Calcium alters monoamine oxidase-A parameters in human cerebellar and rat glial C6 cell extracts: possible influence by distinct signalling pathways

AIMS

Calcium (Ca(2+)) is known to augment monoamine oxidase-A (MAO-A) activity in cell cultures as well as in brain extracts from several species. This association between Ca(2+) and MAO-A could contribute to their respective roles in cytotoxicity. However, the effect of Ca(2+) on MAO-A function in human brain has as yet to be examined as does the contribution of specific signalling cascades.

MAIN METHODS

We examined the effects of Ca(2+) on MAO-A activity and on [(3)H]Ro 41-1049 binding to MAO-A in human cerebellar extracts, and compared this to its effects on MAO-A activity in glial C6 cells following the targeting of signalling pathways using specific chemical inhibitors.

KEY FINDINGS

Ca(2+) enhances MAO-A activity as well as the association of [(3)H]Ro 41-1049 to MAO-A in human cerebellar extracts. The screening of neuronal and glial cell cultures reveals that MAO-A activity does not always correlate with the expression of either mao-A mRNA or MAO-A protein. Inhibition of the individual PI3K/Akt, ERK and p38(MAPK) signalling pathways in glial C6 cells all augment basal MAO-A activity. Inhibition of the p38(MAPK) pathway also augments Ca(2+)-sensitive MAO-A activity. We also observe the inverse relation between p38(MAPK) activation and MAO-A function in C6 cultures grown to full confluence.

SIGNIFICANCE

The Ca(2+)-sensitive component to MAO-A activity is present in human brain and in vitro studies link it to the p38(MAPK) pathway. This means of influencing MAO-A function could explain its role in pathologies as diverse as neurodegeneration and cancers.

Cholinergic neuronal and axonal abnormalities are present early in aging and in Alzheimer disease

A large body of evidence indicates that basal forebrain cholinergic neurons are selectively vulnerable to degeneration early in Alzheimer disease (AD). Recent studies, however, demonstrate reductions in cortical activity of the cholinergic enzyme choline acetyltransferase only in late stages of AD. To address this apparent contradiction, we compared abnormalities in magnocellular basal forebrain cholinergic neurons and their axons in nondemented young (<65 years; n = 6), nondemented old (>65 years; n = 7), pathologically mild (n = 5), and pathologically severe (n = 5) AD cases. Cholinergic axon abnormalities (i.e. thickened fibers and ballooned terminals) were evident in nondemented middle-aged cases, increased in nondemented old cases, and reduced in density in severe AD. This suggests that loss of cortical cholinergic axons in AD occurs preferentially in fibers with these abnormalities. Paired helical filament 1-immunoreactive pretangles and tangles were observed as early as the third decade prior to their appearance in entorhinal/perirhinal cortex; they were increased in mild and severe AD. These results indicate that basal forebrain cholinergic neuron abnormalities are present very early in aging and in the course of AD. Therefore, despite the morphologic alterations, choline acetyltransferase activity, but not necessarily normal neuron functions, may be preserved.

Calcium-sensitive regulation of monoamine oxidase-A contributes to the production of peroxyradicals in hippocampal cultures: implications for Alzheimer disease-related pathology

Background

Calcium (Ca²⁺) has recently been shown to selectively increase the activity of monoamine oxidase-A (MAO-A), a mitochondria-bound enzyme that generates peroxyradicals as a natural by-product of the deamination of neurotransmitters such as serotonin. It has also been suggested that increased intracellular free Ca²⁺ levels as well as MAO-A may be contributing to the oxidative stress associated with Alzheimer disease (AD).

Results

Incubation with Ca²⁺ selectively increases MAO-A enzymatic activity in protein extracts from mouse hippocampal HT-22 cell cultures. Treatment of HT-22 cultures with the Ca²⁺ ionophore A23187 also increases MAO-A activity, whereas overexpression of calbindin-D28K (CB-28K), a Ca²⁺-binding protein in brain that is greatly reduced in AD, decreases MAO-A activity. The effects of A23187 and CB-28K are both independent of any change in MAO-A protein or gene expression. The toxicity (via production of peroxyradicals and/or chromatin condensation) associated with either A23187 or the AD-related β-amyloid peptide, which also increases free intracellular Ca²⁺, is attenuated by MAO-A inhibition in HT-22 cells as well as in primary hippocampal cultures.

Conclusion

These data suggest that increases in intracellular Ca²⁺ availability could contribute to a MAO-A-mediated mechanism with a role in AD-related oxidative stress.

Postnatal development of GABA and calbindin cells and fibers in the prefrontal cortex and basolateral amygdala of gerbils (Meriones unguiculatus)

The postnatal maturation of immunohistochemically stained gamma-amino-butyric acid (GABA) and calbindin (CB) cells and fibers were quantitatively examined in the prefrontal cortex (PFC) and the basolateral amygdala (BLA) of the Mongolian gerbil (Meriones unguiculatus). Animals of different ages, ranging from juvenile (postnatal day (PD)14, PD20, PD30), to adolescent (PD70), adult (PD180, PD540) and aged (PD720) were analyzed. Results reveal an increase in GABAergic fiber densities between PD14-20 in the PFC and the BLA with a concomitant decrease in cell density. After PD70 GABA fiber density slightly decreases again in the BLA, while there is a further slow but significant increase in the PFC between PD70 and PD540. Fibers immunoreactive for the calcium binding-protein CB, which is predominantly localized in particular GABAergic subpopulations, also accumulate between PD14 and PD20 in the PFC and BLA, while a concomitant decrease in cell density is only seen in the BLA. Both areas reveal a decrease of CB cells between PD30 and PD70, which parallels with a decrease of CB fibers in the PFC. However, there is no particular 'aging-effect' in the fiber or cell densities of GABA or CB in any of the investigated areas in old animals. In conclusion, we here demonstrate long-term dynamics in cell and fiber densities of the GABAergic system until late in development which might correspond to the prolonged maturation of other neuroanatomical and functional systems.

Acceleration of amyloid beta-peptide aggregation by physiological concentrations of calcium

Alzheimer disease is characterized by the accumulation of aggregated amyloid beta-peptide (Abeta) in the brain. The physiological mechanisms and factors that predispose to Abeta aggregation and deposition are not well understood. In this report, we show that calcium can predispose to Abeta aggregation and fibril formation. Calcium increased the aggregation of early forming protofibrillar structures and markedly increased conversion of protofibrils to mature amyloid fibrils. This occurred at levels 20-fold below the calcium concentration in the extracellular space of the brain, the site at which amyloid plaque deposition occurs. In the absence of calcium, protofibrils can remain stable in vitro for several days. Using this approach, we directly compared the neurotoxicity of protofibrils and mature amyloid fibrils and demonstrate that both species are inherently toxic to neurons in culture. Thus, calcium may be an important predisposing factor for Abeta aggregation and toxicity. The high extracellular concentration of calcium in the brain, together with impaired intraneuronal calcium regulation in the aging brain and Alzheimer disease, may play an important role in the onset of amyloid-related pathology.

Simultaneous glutamate and GABA(A) receptor agonist administration increases calbindin levels and prevents hippocampal damage induced by either agent alone in a model of perinatal brain injury

Perinatal brain injury is associated with the release of amino acids, principally glutamate and GABA, resulting in massive increases in intracellular calcium and eventual cell death. We have previously demonstrated that independent administration of kainic acid (KA), an AMPA/kainate receptor agonist, or muscimol, a GABA(A) receptor agonist, to newborn rats results in hippocampal damage [Hilton, G.D., Ndubuizu, A., and McCarthy, M.M., 2004. Neuroprotective effects of estradiol in newborn female rat hippocampus. Dev. Brain Res. 150, 191-198; Hilton, G. D., Nunez, J.L. and McCarthy, M.M., 2003. Sex differences in response to kainic acid and estradiol in the hippocampus of newborn rats. Neuroscience. 116, 383-391; Nunez, J.L. and McCarthy, M.M., 2003. Estradiol exacerbates hippocampal damage in a model of preterm infant brain injury. Endocrinology. 144, 2350-2359; Nunez, J.L., Alt, J.J. and McCarthy, M.M., 2003. A new model for prenatal brain damage. I. GABA(A) receptor activation induces cell death in developing rat hippocampus. Exp. Neurol. 181, 258-269]. We now report that KA or muscimol alone administered to immature hippocampal neurons in culture induces significant cell death as evidenced by TUNEL assay. Surprisingly, simultaneous administration of equimolar quantities of these two agonists blocks the effect of either one alone. Moreover, treatment of newborn pups results in less damage compared to either muscimol or KA alone. We further observed that immunoreactivity for the calcium-binding protein, calbindin D(28K), is increased in the brains of pups simultaneously administered KA and muscimol as compared to either alone.

Apoptotic signals within the basal forebrain cholinergic neurons in Alzheimer's disease

A relatively early and substantial loss of basal forebrain cholinergic neurons is a constant feature of Alzheimer's disease (AD). However, the mechanisms that contribute to the selective vulnerability of these neurons are not fully delineated. In the present series of experiments, we determined the possible contribution of apoptotic processes and other pathologic cascades to the degeneration of the cholinergic neurons of the nucleus basalis of Meynert (NBM) in AD. In contrast to neurons in the frontal cortex which showed prominent DNA fragmentation as detected by the TUNEL method, no DNA fragmentation was observed within the NBM in any of the AD or normal brains. Similarly, immunoreactivity for the apoptotic signals Fas, Fas-ligand, Bax, Bcl-x, caspase-8, caspase-9 and caspase-3 was absent from the NBM of AD and control brains. In contrast, a substantial subpopulation of cholinergic neurons within the NBM in AD displayed prominent immunoreactivity for the apoptotic signal Fas-associated death domain (FADD) in the form of tangles. FADD immunoreactivity was also present in dystrophic neurites. FADD-positive tangle-like structures were localized in neurons which contained immunoreactivity for the cholinergic marker choline acetyltransferase (ChAT) and the low affinity neurotrophin receptor p75NTR. While many of the NBM cholinergic neurons in control brains contained immunoreactivity for the calcium binding protein calbindin-D28K (CB), the NBM neurons in AD displayed a substantial loss of CB immunoreactivity. Importantly, most of FADD-immunoreactive cholinergic neurons were devoid of CB immunoreactivity, and, conversely, most CB-positive cholinergic neurons had no FADD immunoreactivity. FADD immunoreactivity within the basal forebrain was colocalized with phosphorylated tau immunoreactive tangles and dystrophic neurites. In contrast, FADD immunoreactivity did not appear to be related to the primarily diffuse amyloid-beta deposits intermingled between cholinergic neurons in AD NBM. Finally, many CD68-positive microglia were observed surrounding the NBM cholinergic neurons in AD. In conclusion, the findings of the present study indicate that, while the FADD apoptotic signaling pathway may be triggered within the basal forebrain cholinergic neurons in AD, the apoptotic cascade is most likely aborted as no DNA fragmentation was detected and the executioner caspase-3 was not up-regulated within these neurons. The findings also suggest possible relationships between loss of CB, FADD expression and phosphorylation of tau within the basal forebrain cholinergic neurons in AD.

Detection of nitric oxide synthase (NOS) immunoreactive neurons in the human septal area: a matter of method?

There is a remarkable discrepancy between biochemical and cell morphological findings with regard to the presence of NADPH diaphorase/neuronal nitric oxide synthase (NOS) in the primate septal area. Whereas considerable concentrations of neuronal nitric oxide synthase and high enzyme activities have been measured in postmortem human septal nuclei, histochemical studies were either unable to detect any nitric oxide synthase immunoreactivity in primate septal neurons, or found only a very few nitrergic neurons in this region. This study aimed to investigate the possible presence of nitrergic neurons in human the septal region in greater detail. After having studied a total of 16 postmortem human brains we conclude that the immunohistochemical demonstration of nitric oxide synthase in human septal neurons is largely dependent on the mode of tissue handling: in brain specimens which were fixed en-bloc with paraffin and embedded in paraplast, nitric oxide synthase immunoreactivity is barely detectable, whereas a satisfying immunostaining is obtained on free-floating frozen sections after an immersion-fixation with 4% paraformaldehyde and 0.5% glutaraldehyde, followed by sucrose protection of the specimens. We show herein that there are indeed nitric oxide synthase-containing neurons in the human septum, thus supporting results from previous biochemical studies.

Loss of calbindin-D28K from aging human cholinergic basal forebrain: relation to plaques and tangles

Reports from our laboratory have indicated a substantial and specific loss of the calcium binding protein calbindin-D28K (CB) from the human basal forebrain cholinergic neurons (BFCN) in the course of normal aging. In the present set of experiments we determined the relationship between the age-related loss of CB and the presence and density of plaques and tangles in the brains of normal elderly. In 23 cases ranging in age from 20 to 93 years of age we observed plaques and tangles in the BFCN region and the cerebral cortex in a subset of cases. Plaques were seen in the basal forebrain in very few cases above 65 years. Plaque density in the basal forebrain and cortex displayed a significant negative correlation with the proportion of the BFCN, which contained CB immunoreactivity. However, the brains of 2 elderly cases that displayed a substantial loss of CB from the BFCN did not contain any plaques. Tangles were observed in the BFCN as early as 26 years of age. Only tangles in the entorhinal cortex showed a significant negative correlation with the loss of CB from the BFCN. It is likely that loss of CB from the BFCN and formation of plaques and tangles are part of general age-related processes that occur in parallel rather than being causally related.