Life-long stability of neurons: a century of research on neurogenesis, neuronal death and neuron quantification in adult CNS

Icariin improves brain function decline in aging rats by enhancing neuronal autophagy through the AMPK/mTOR/ULK1 pathway

CONTEXT

Icariin (ICA) is the main active ingredient of Epimedium brevicornu Maxim (Berberidaceae), which is used in the immune, reproductive, neuroendocrine systems, and anti-aging.

OBJECTIVE

To evaluate the effect of ICA on natural aging rat.

MATERIALS AND METHODS

16-month-old Sprague-Dawley (SD) rats were randomly divided into aging, low and high-dose ICA groups (n = 8); 6-month-old rats were taken as the adult control (n = 8). Rats were fed regular feed (aging and adult control) or feed containing ICA (ICA 2 and 6 mg/kg group) for 4 months. HE and Nissl staining were used to assess pathological changes. Western blot was used to test the expression of autophagy (LC3B, p62, Atg5, Beclin1) and p-AMPK, p-mTOR and p-ULK1 (ser 757). Immunofluorescence was used to detect the co-localization of LC3 and neurons.

RESULTS

ICA improved neuronal degeneration associated with aging and increased the staining of Nissl bodies. Western blot showed that ICA up-regulated autophagy-related proteins LC3B (595%), Beclin1 (73.5%), p-AMPK (464%) protein (p < 0.05 vs. 20 M) in the cortex and hippocampus of aging rats, down-regulated the expression of p62 (56.9%), p-mTOR (53%) and p-ULK1 (ser 757) (65.4%) protein (p < 0.05 vs. 20 M). Immunofluorescence showed that the fluorescence intensity of LC3 decreased in the aging rat brain, but increased and mainly co-localized with neurons after ICA intervention.

CONCLUSIONS

Further research needs to verify the expression changes of AMPK/mTOR/ULK1 and the improvement effect of ICA in elderly. These results will further accelerate the applications of ICA and the treatment for senescence.

Neuroglia in ageing and disease

The proper operation of the mammalian brain requires dynamic interactions between neurones and glial cells. Various types of glial cells are susceptible to morpho-functional changes in a variety of brain pathological states, including toxicity, neurodevelopmental, neurodegenerative and psychiatric disorders. Morphological modifications include a change in the glial cell size and shape; the latter is evident by changes of the appearance and number of peripheral processes. The most blatant morphological change is associated with the alteration of the sheer number of neuroglia cells in the brain. Functionally, glial cells can undergo various metabolic and biochemical changes, the majority of which reflect upon homeostasis of neurotransmitters, in particular that of glutamate, as well as on defence mechanisms provided by neuroglia. Not only glial cells exhibit changes associated with the pathology of the brain but they also change with brain aging.

Age- and calorie restriction-related changes in rat brain mitochondrial DNA and TFAM binding

Aging markedly affects mitochondrial biogenesis and functions particularly in tissues highly dependent on the organelle's bioenergetics capability such as the brain's frontal cortex. Calorie restriction (CR) diet is, so far, the only intervention able to delay or prevent the onset of several age-related alterations in different organisms. We determined the contents of mitochondrial transcription factor A (TFAM), mitochondrial DNA (mtDNA), and the 4.8-kb mtDNA deletion in the frontal cortex from young (6-month-old) and aged (26-month-old), ad libitum-fed (AL) and calorie-restricted (CR), rats. We found a 70 % increase in TFAM amount, a 25 % loss in mtDNA content, and a 35 % increase in the 4.8-kb deletion content in the aged AL animals with respect to the young rats. TFAM-specific binding to six mtDNA regions was analyzed by mtDNA immunoprecipitation and semiquantitative polymerase chain reaction (PCR), showing a marked age-related decrease. Quantitative real-time PCR at two subregions involved in mtDNA replication demonstrated, in aged AL rats, a remarkable decrease (60-70 %) of TFAM-bound mtDNA. The decreased TFAM binding is a novel finding that may explain the mtDNA loss in spite of the compensatory TFAM increased amount. In aged CR rats, TFAM amount increased and mtDNA content decreased with respect to young rats' values, but the extent of the changes was smaller than in aged AL rats. Attenuation of the age-related effects due to the diet in the CR animals was further evidenced by the unchanged content of the 4.8-kb deletion with respect to that of young animals and by the partial prevention of the age-related decrease in TFAM binding to mtDNA.

Complex and region-specific changes in astroglial markers in the aging brain

Morphological aging of astrocytes was investigated in entorhinal cortex (EC), dentate gyrus (DG), and cornu ammonis 1 (CA1) regions of hippocampus of male SV129/C57BL6 mice of different age groups (3, 9, 18, and 24 months). Astroglial profiles were visualized by immunohistochemistry by using glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), and s100β staining; these profiles were imaged using confocal or light microscopy for subsequent morphometric analysis. GFAP-positive profiles in the DG and the CA1 of the hippocampus showed progressive age-dependent hypertrophy, as indicated by an increase in surface, volume, and somata volume at 24 months of age compared with 3-month-old mice. In contrast with the hippocampal regions, aging induced a decrease in GFAP-positive astroglial profiles in the EC: the surface, volume, and cell body volume of astroglial cells at 24 months of age were decreased significantly compared with the 3-month group. The GS-positive astrocytes displayed smaller cellular surface areas at 24 months compared with 3-month-old animals in both areas of hippocampus, whereas GS-positive profiles remained unchanged in the EC of old mice. The morphometry of s100β-immunoreactive profiles revealed substantial increase in the EC, more moderate increase in the DG, and no changes in the CA1 area. Based on the morphological analysis of 3 astroglial markers, we conclude that astrocytes undergo a complex age-dependent remodeling in a brain region-specific manner.

Cognitive and tactile factors affecting human haptic performance in later life

BACKGROUND

Vision and haptics are the key modalities by which humans perceive objects and interact with their environment in a target-oriented manner. Both modalities share higher-order neural resources and the mechanisms required for object exploration. Compared to vision, the understanding of haptic information processing is still rudimentary. Although it is known that haptic performance, similar to many other skills, decreases in old age, the underlying mechanisms are not clear. It is yet to be determined to what extent this decrease is related to the age-related loss of tactile acuity or cognitive capacity.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated the haptic performance of 81 older adults by means of a cross-modal object recognition test. Additionally, we assessed the subjects' tactile acuity with an apparatus-based two-point discrimination paradigm, and their cognitive performance by means of the non-verbal Raven-Standard-Progressive matrices test. As expected, there was a significant age-related decline in performance on all 3 tests. With the exception of tactile acuity, this decline was found to be more distinct in female subjects. Correlation analyses revealed a strong relationship between haptic and cognitive performance for all subjects. Tactile performance, on the contrary, was only significantly correlated with male subjects' haptic performance.

CONCLUSIONS

Haptic object recognition is a demanding task in old age, especially when it comes to the exploration of complex, unfamiliar objects. Our data support a disproportionately higher impact of cognition on haptic performance as compared to the impact of tactile acuity. Our findings are in agreement with studies reporting an increase in co-variation between individual sensory performance and general cognitive functioning in old age.

Metabolic and functional differences between brain and spinal cord mitochondria underlie different predisposition to pathology

Mitochondrial dysfunctions contribute to neurodegeneration, the locations of which vary among neurodegenerative diseases. To begin to understand what mechanisms may underlie higher vulnerability of the spinal cord motor neurons in amyotrophic lateral sclerosis, compared with brain mitochondria, we studied three major functions of rat brain mitochondria (BM) and spinal cord mitochondria (SCM) mitochondria: oxidative phosphorylation, Ca(2+) sequestration, and production of reactive oxygen species (ROS), using a new metabolic paradigm (Panov et al., J. Biol. Chem. 284: 14448-14456, 2009). We present data that SCM share some unique metabolic properties of the BM. However, SCM also have several distinctions from the BM: 1) With the exception of succinate, SCM show significantly lower rates of respiration with all substrates studied; 2) immunoblotting analysis showed that this may be due to 30-40% lower contents of respiratory enzymes and porin; 3) compared with BM, SCM sequestered 40-50% less Ca(2+), and the total tissue calcium content was 8 times higher in the spinal cord; 4) normalization for mitochondria from 1 g of tissue showed that BM can sequester several times more Ca(2+) than was available in the brain tissue, whereas SCM had the capacity to sequester only 10-20% of the total tissue Ca(2+); and 5) with succinate and succinate-containing substrate mixtures, SCM showed significantly higher state 4 respiration than BM and generated more ROS associated with the reverse electron transport. We conclude that SCM have an intrinsically higher risk of oxidative damage and overload with calcium than BM, and thus spinal cord may be more vulnerable under some pathologic conditions. (250).

Upward spirals of positive emotions counter downward spirals of negativity: insights from the broaden-and-build theory and affective neuroscience on the treatment of emotion dysfunctions and deficits in psychopathology

This review integrates Fredrickson's broaden-and-build theory of positive emotions with advances in affective neuroscience regarding plasticity in the neural circuitry of emotions to inform the treatment of emotion deficits within psychopathology. We first present a body of research showing that positive emotions broaden cognition and behavioral repertoires, and in so doing, build durable biopsychosocial resources that support coping and flourishing mental health. Next, by explicating the processes through which momentary experiences of emotions may accrue into self-perpetuating emotional systems, the current review proposes an underlying architecture of state-trait interactions that engenders lasting affective dispositions. This theoretical framework is then used to elucidate the cognitive-emotional mechanisms underpinning three disorders of affect regulation: depression, anxiety, and schizophrenia. In turn, two mind training interventions, mindfulness and loving-kindness meditation, are highlighted as means of generating positive emotions that may counter the negative affective processes implicated in these disorders. We conclude with the proposition that positive emotions may exert a countervailing force on the dysphoric, fearful, or anhedonic states characteristic of psychopathologies typified by emotional dysfunctions.

Aging-related changes in astrocytes in the rat retina: imbalance between cell proliferation and cell death reduces astrocyte availability

The aim of this study was to investigate changes in astrocyte density, morphology, proliferation and apoptosis occurring in the central nervous system during physiological aging. Astrocytes in retinal whole-mount preparations from Wistar rats aged 3 (young adult) to 25 months (aged) were investigated qualitatively and quantitatively following immunofluorohistochemistry. Glial fibrillary acidic protein (GFAP), S100 and Pax2 were used to identify astrocytes, and blood vessels were localized using Griffonia simplicifolia isolectin B4. Cell proliferation was assessed by bromodeoxyuridine incorporation and cell death by TUNEL-labelling and immunolocalization of the apoptosis markers active caspase 3 and endonuclease G. The density and total number of parenchymal astrocytes in the retina increased between 3 and 9 months of age but decreased markedly between 9 and 12 months. Proliferation of astrocytes was detected at 3 months but virtually ceased beyond that age, whereas the proportion of astrocytes that were TUNEL positive and relative expression of active caspase 3 and endonuclease G increased progressively with aging. In addition, in aged retinas astrocytes exhibited gliosis-like morphology and loss of Pax2 reactivity. A small population of Pax2(+)/GFAP(-) cells was detected in both young adult and aged retinas. The reduction in the availability of astrocytes in aged retinas and other aging-related changes reported here may have a significant impact on the ability of astrocytes to maintain homeostasis and support neuronal function in old age.

The aging brain: Accumulation of DNA damage or neuron loss?

Age-related molecular and cellular alterations in the central nervous system are known to show selectivity for certain cell types and brain regions. Among them age-related accumulation of nuclear (n) DNA damage can lead to irreversible loss of genetic information content. In the present study on the aging mouse brain, we observed a substantial increase in the amount of nDNA single-strand breaks in hippocampal pyramidal and granule cells as well as in cerebellar granule cells but not in cerebellar Purkinje cells. The reverse pattern was found for age-related reductions in total numbers of neurons. Only the total number of cerebellar Purkinje cells was significantly reduced during aging whereas the total numbers of hippocampal pyramidal and granule cells as well as of cerebellar granule cells were not. This formerly unknown inverse relation between age-related accumulation of nDNA damage and age-related loss of neurons may reflect a fundamental process of aging in the central nervous system.

Effect of prenatal exposure to an anti-inflammatory drug on neuron number in cornu ammonis and dentate gyrus of the rat hippocampus: A stereological study

Prenatal exposed to an anti-inflammatory drug is a major problem for the developing central nervous system. It is not well known the effect of prenatal exposed to a non-steroidal anti-inflammatory drug on the hippocampus. Total neuron number in one side of the cornu ammonis (CA) and gyrus dentatus (GD) of the hippocampal formation in control and drug-treated (diclofenac sodium, DS) groups of male rats was estimated using the optical fractionator technique. Each main group has also two subgroups that are 4 weeks old (4W-old) and 20 weeks old (20W-old). In CA, no significant difference between 4W-old DS-treated and their control was found, but a significant difference was observed between 20W-old DS-treated and their controls. A decreasing of neuron number was 12% for 20W-old DS-treated group. In GD, a decreasing of the granule cell number in 4W-old of DS-treated group was seen but an increasing of granule cell number was found in the 20W-old drug-treated rats in comparison to its control group, 7% and 9%, respectively. Although an increasing of neuron number in CA at the control group was seen with age, from 4th week to 20th week (10%), age-dependent substantial granule cell decline (17%) was observed in GD. No age effect on the total cell numbers of CA and GD of the drug-treated groups was seen in comparison to 4W-old week and 20W-old. A pronounced neuron loss observed in the drug-treated group may be attributed to the neurotoxicity of diclofenac sodium (DS) on the developing hippocampal formation. Age-dependent neuron increase in the CA of 20W-old and neuron decline in GD of 20W-old control groups may be a result of a dual effect of saline injection during the fetal life, since these animals were exposed to a stress of 15-day-period of saline injection, prenatal stress. The reason of no age effect on CA and GD cell number in the drug-treated groups may be attributed to the depletion of the progenitor cells due to neurotoxicity of DS in the fetal life of these animals.

Opioid systems in the dentate gyrus

Opiate drugs alter cognitive performance and influence hippocampal excitability, including long-term potentiation (LTP) and seizure activity. The dentate gyrus (DG) contains two major opioid peptides, enkephalins and dynorphins, which have opposing effects on excitability. Enkephalins preferentially bind to delta- and mu-opioid receptors (DORs and MORs) while dynorphins preferentially bind to kappa-opioid receptors (KORs). Opioid receptors can also be activated by exogenous opiate drugs such as the MOR agonist morphine. Enkephalins are contained in the mossy fiber pathway, in the lateral perforant path (PP) and in scattered GABAergic interneurons. MORs and DORs are predominantly in distinct subpopulations of GABAergic interneurons known to inhibit granule cells, and are present at low levels within granule cells. MOR and DOR agonists increase excitability and facilitate LTP in the molecular layer. Anatomical and physiological evidence is consistent with somatodendritic and axon terminal targeting of both MORs and DORs. Dynorphins are in the granule cells, most abundantly in mossy fibers but also in dendrites. KORs have been localized to granule cell mossy fibers, supramammillary afferents to granule cells, and PP terminals. KOR agonists, including endogenous dynorphins, diminish the induction of LTP. Recent evidence indicates that opiates and opioids also modulate other processes in the hippocampal formation, including adult neurogenesis, the actions of gonadal hormones, and development of neonatal transmitter systems.

Effects of formaldehyde exposure on granule cell number and volume of dentate gyrus: A histopathological and stereological study

The hippocampal formation is a complex region of the brain related to memory and learning. The purpose of the present study was to determine whether exposure of neonatal rats to formaldehyde (FA) had either early or delayed effects on the numbers of granule cells in the dentate gyrus (DG). After birth, the neonatal male Wistar rats were exposed throughout a 30-day period to various concentrations of FA: 0 (control group), 6 ppm (low concentration group) and 12 ppm (high concentration group). This was done by placing them for 6 h/day and 5 days per week in a glass chamber containing FA vapor. Then, five animals from each group were anesthetized and decapitated on postnatal day (PND) 30, and the remaining five animals were sacrificed on PND 90 by intracardiac perfusion using 10% neutral buffered FA solution. The Cavalieri principle of stereological approaches was used to determine the volume of the DG in these sections. The optical fractionator counting method was used to estimate the total number of granule cells in the DG. The appearance of granule cells was normal under light microscopy in all PND 30 and PND 90 groups. There were significant age-related reductions in the volume of the DG at PND 90 irrespective of which group was examined. Significant age-related neuron loss was also determined at PND 90 compared to that at PND 30. Rats treated with a high concentration FA were found to have fewer granule cells than either the animals treated with a low concentration FA or the control group (p<0.01 and p<0.01, respectively) at PND 90 but not at PND 30. These findings clearly indicate that granule cells in the DG may be vulnerable to stress and the concentration of FA to which they are exposed during early postnatal life, and also that a neurotoxic effect of high dose FA on cell number is only seen after a long time period. These results may explain why some disorders do not appear until later life.

Species- and tissue-specific relationships between mitochondrial permeability transition and generation of ROS in brain and liver mitochondria of rats and mice

In animal models of neurodegenerative diseases pathological changes vary with the type of organ and species of the animals. We studied differences in the mitochondrial permeability transition (mPT) and reactive oxygen species (ROS) generation in the liver (LM) and brain (BM) of Sprague-Dawley rats and C57Bl mice. In the presence of ADP mouse LM and rat LM required three times less Ca(2+) to initiate mPT than the corresponding BM. Mouse LM and BM sequestered 70% and 50% more Ca(2+) phosphate than the rat LM and BM. MBM generated 50% more ROS with glutamate than the RBM, but not with succinate. With the NAD substrates, generation of ROS do not depend on the energy state of the BM. Organization of the respiratory complexes into the respirasome is a possible mechanism to prevent ROS generation in the BM. With BM oxidizing succinate, 80% of ROS generation was energy dependent. Induction of mPT does not affect ROS generation with NAD substrates and inhibit with succinate as a substrate. The relative insensitivity of the liver to systemic insults is associated with its high regenerative capacity. Neuronal cells with low regenerative capacity and a long life span protect themselves by minimizing ROS generation and by the ability to withstand very large Ca(2+) insults. We suggest that additional factors, such as oxidative stress, are required to initiate neurodegeneration. Thus the observed differences in the Ca(2+)-induced mPT and ROS generation may underlie both the organ-specific and species-specific variability in the animal models of neurodegenerative diseases.

Chronically increased transforming growth factor-beta1 strongly inhibits hippocampal neurogenesis in aged mice

There is increasing evidence that hippocampal learning correlates strongly with neurogenesis in the adult brain. Increases in neurogenesis after brain injury also correlate with improved outcomes. With aging the capacity to generate new neurons decreases dramatically, both under normal conditions and after injury. How this decrease occurs is not fully understood, but we hypothesized that transforming growth factor (TGF)-beta1, a cell cycle regulator that rapidly increases after injury and with age, might play a role. We found that chronic overproduction of TGF-beta1 from astrocytes almost completely blocked the generation of new neurons in aged transgenic mice. Even young adult TGF-beta1 mice had 60% fewer immature, doublecortin-positive, hippocampal neurons than wild-type littermate controls. Bromodeoxyuridine labeling of dividing cells in 2-month-old TGF-beta1 mice confirmed this decrease in neuro-genesis and revealed a similar decrease in astrogenesis. Treatment of early neural progenitor cells with TGF-beta1 inhibited their proliferation. This strongly suggests that TGF-beta1 directly affects these cells before their differentiation into neurons and astrocytes. Together, these data show that TGF-beta1 is a potent inhibitor of hippocampal neural progenitor cell proliferation in adult mice and suggest that it plays a key role in limiting injury and age-related neurogenesis.

Reactive oxygen species, dietary restriction and neurotrophic factors in age-related loss of myenteric neurons

We have studied the mechanisms underlying nonpathological age-related neuronal cell death. Fifty per cent of neurons in the rat enteric nervous system are lost between 12 and 18 months of age in ad libitum (AL) fed rats. Caloric restriction (CR) protects almost entirely against this neuron loss. Using the ROS-sensitive dyes, dihydrorhodamine (DHR) and 2-[6-(4'-hydroxy)phenoxy-3H-xanthen-3-on-9-yl]benzoic acid (HPF) in vitro, we show that the onset of cell death is linked with elevated intraneuronal levels of reactive oxygen species (ROS). Treatment with the neurotrophic factors NT3 and GDNF enhances neuronal antioxidant defence in CR rats at 12-15 months and 24 months but not in adult or aged AL-fed animals. To examine the link between elevated ROS and neuronal cell death, we assessed apoptotic cell death following in vitro treatment with the redox-cycling drug, menadione. Menadione fails to increase apoptosis in 6-month neurons. However, in 12-15mAL fed rats, when age-related cell death begins, menadione induces a 7- to 15-fold increase in the proportion of apoptotic neurons. CR protects age-matched neurons against ROS-induced apoptosis. Treatment with neurotrophic factors, in particular GDNF, rescues neurons from menadione-induced cell death, but only in 12-15mCR animals. We hypothesize that CR enhances antioxidant defence through neurotrophic factor signalling, thereby reducing age-related increases in neuronal ROS levels and in ROS-induced cell death.

Ageing of the enteric nervous system

The intrinsic neurones of the enteric nervous system (ENS) play a fundamental role in the regulation of gastrointestinal functions. Although much remains to be learnt about the changes that take place in intestinal nerves during ageing, evidence suggests that selective neurodegeneration may occur in the ageing ENS. Age-associated changes in intestinal innervation may contribute to the gastrointestinal disorders that increase in incidence in the elderly, such as dysphagia, gastrointestinal reflux and constipation. A number of other factors, such as immobility, co-morbidity, and side effects of therapeutic medication for other disorders however, are also likely to contribute to the aetiology of these conditions. An important finding in rodents is that the neuronal losses that take place in the ENS during ageing may be prevented by calorie restriction; an indication that diet may influence gastrointestinal ageing. Thus, it is of importance to understand not only how the ENS changes during 'normal' ageing, but also how external factors contribute to these changes. Here, current knowledge of how intestinal innervation is affected during normal ageing and how these changes may impact upon gastrointestinal physiology are reviewed.

The helix-loop-helix inhibitor of differentiation (ID) proteins induce post-mitotic terminally differentiated Sertoli cells to re-enter the cell cycle and proliferate

Prior to puberty the Sertoli cells undergo active cell proliferation, and at the onset of puberty they become a terminally differentiated postmitotic cell population that support spermatogenesis. The molecular mechanisms involved in the postmitotic block of pubertal and adult Sertoli cells are unknown. The four known helix-loop-helix ID proteins (i.e., Id1, Id2, Id3, and Id4) are considered dominant negative regulators of cellular differentiation pathways and act as positive regulators of cellular proliferation. ID proteins are expressed at low levels by postpubertal Sertoli cells and are transiently induced by serum. The hypothesis tested was that ID proteins can induce a terminally differentiated postmitotic Sertoli cell to reenter the cell cycle if they are constitutively expressed. To test this hypothesis, ID1 and ID2 were stably integrated and individually overexpressed in postmitotic rat Sertoli cells. Overexpression of ID1 or ID2 allowed postmitotic Sertoli cells to reenter the cell cycle and undergo mitosis. The cells continued to proliferate even after 300 cell doublings. The functional markers of Sertoli cell differentiation such as transferrin, inhibin alpha, Sert1, and androgen binding protein (ABP) continued to be expressed by the proliferating Sertoli cells, but at lower levels. FSH receptor expression was lost in the proliferating Sertoli cell-Id lines. Some Sertoli cell genes, such as cyclic protein 2 (cathepsin L) and Sry-related HMG box protein-11 (Sox11) increase in expression. At no stage of proliferation did the cells exhibit senescence. The expression profile as determined with a microarray protocol of the Sertoli cell-Id lines suggested an overall increase in cell cycle genes and a decrease in growth inhibitory genes. These results demonstrate that overexpression of ID1 and ID2 genes in a postmitotic, terminally differentiated cell type have the capacity to induce reentry into the cell cycle. The observations are discussed in regards to potential future applications in model systems of terminally differentiated cell types such as neurons or myocytes.

Age-associated synapse elimination in mouse parasympathetic ganglia

Little is known about the effects of aging on synapses in the mammalian nervous system. We examined the innervation of individual mouse submandibular ganglion (SMG) neurons for evidence of age-related changes in synapse efficacy and number. For approximately 85% of adult life expectancy (30 months) the efficacy of synaptic transmission, as determined by excitatory postsynaptic potential (EPSP) amplitudes, remains constant. Similarly, the number of synapses contacting individual SMG neurons is also unchanged. After 30 months of age, however, some neurons (23%) dramatically lose synaptic input exhibiting both smaller EPSP amplitude and fewer synaptic boutons. Attenuation of both the amplitude and frequency of miniature EPSPs was also observed in neurons from aged animals. Electron micrographs revealed that, although there were many vesicle-laden preganglionic axonal processes in the vicinity of the postsynaptic membrane, the number of synaptic contacts was significantly lower in old animals. These results demonstrate primary, age-associated synapse elimination with functional consequences that cannot be explained by pre- or postsynaptic cell death.

Effects of age and sex on volumes of the thalamus, pons, and cortex

Volumes of thalamus, pons, cortical gray matter, and white matter were derived from MR brain images of healthy men and women spanning the adult age range in order to delineate patterns of aging and to compare age and sex effects in thalamus and pons with such effects in cortical gray and white matter volumes. Men had larger intracranial volume (ICV) than women, but ICV did not correlate with age in either sex. Thalamic, pontine, and cortical white matter volumes did not differ between men and women once ICV differences were taken into account, but men had more cortical gray matter than women even after accounting for ICV. Volumes of pons and thalamus were associated, independent of ICV, in women but not in men. Thalamic volume declined linearly with age at a similar rate in both men and women, whereas cortical gray matter volume declined more steeply with age in men than women. Both pontine and cortical white matter volumes remained stable across the age span in both men and women.

Cerebellar Purkinje cell loss in aging Hu-Bcl-2 transgenic mice

The number of cerebellar Purkinje cells is increased by over 40% in young transgenic mice that overexpress a human Bcl-2 transgene (Hu-Bcl-2). To determine whether the Bcl-2-mediated rescue of Purkinje cells persists through life, the numbers of Purkinje cells were estimated in 6-, 12-, 18-, and 24-month-old Hu-Bcl-2 transgenic mice and age-matched controls. In addition, the expression of four markers for Purkinje cell differentiation, calbindin (CaBP), the 67-kDa isoform of glutamic acid decarboxylase (GAD67), gamma-aminobutyric acid transaminase (GABA-T), and the NMDA-R1 receptor subtype (NMDA-NR1) was analyzed in 6-month-old Hu-Bcl-2 transgenics and controls to determine whether overexpression of Bcl-2 and rescue from naturally occurring cell death affects the normal differentiation of Purkinje cells. The estimates of Purkinje cell numbers showed that the number of Purkinje cells in the Hu-Bcl-2 transgenics declines after 6 months to approach wild-type values by 18 months. Although the exogenous human BCL-2 is still expressed in Purkinje cells at 24 months, the expression levels of human BCL-2 appear to decline significantly after 6 months, suggesting that survival of the supernumary Purkinje cells depends on the sustained overexpression of Bcl-2. All the Purkinje cells in the Hu-Bcl-2 transgenic mice appeared to express normal levels of the differentiation markers analyzed so there was no evidence for a class of Purkinje cells that do not differentiate normally when rescued from naturally occurring cell death.

Search for a common mechanism of mood stabilizers

Manic-depression, or bipolar affective disorder, is a prevalent mental disorder with a global impact. Mood stabilizers have acute and long-term effects and at a minimum are prophylactic for manic or depressive poles without detriment to the other. Lithium has significant effects on mania and depression, but may be augmented or substituted by some antiepileptic drugs. The biochemical basis for mood stabilizer therapies or the molecular origins of bipolar disorder is unknown. One approach to this problem is to seek a common target of all mood stabilizers. Lithium directly inhibits two evolutionarily conserved signal transduction pathways. It both suppresses inositol signaling through depletion of intracellular inositol and inhibits glycogen synthase kinase-3 (GSK-3), a multifunctional protein kinase. A number of GSK-3 substrates are involved in neuronal function and organization, and therefore present plausible targets for therapy. Valproic acid (VPA) is an antiepileptic drug with mood-stabilizing properties. It may indirectly reduce GSK-3 activity, and can up-regulate gene expression through inhibition of histone deacetylase. These effects, however, are not conserved between different cell types. VPA also inhibits inositol signaling through an inositol-depletion mechanism. There is no evidence for GSK-3 inhibition by carbamazepine, a second antiepileptic mood stabilizer. In contrast, this drug alters neuronal morphology through an inositol-depletion mechanism as seen with lithium and VPA. Studies on the enzyme prolyl oligopeptidase and the sodium myo-inositol transporter support an inositol-depletion mechanism for mood stabilizer action. Despite these intriguing observations, it remains unclear how changes in inositol signaling underlie the origins of bipolar disorder.