Neuron atrophy during aging: programmed or sporadic?

Age-dependent changes in the medial prefrontal cortex and medial amygdala structure, and elevated plus-maze performance in the healthy male Wistar rats

Aging affects different parts of the brain structure and function. These changes are associated with several age-related emotional alterations like anxiety that is regulated by the amygdala and medial prefrontal cortex (mPFC). Thus, this study aimed to explore the effects of aging on the morphology changes in these regions. Twenty male Wistar rats were assigned to young and old groups. The anxiety level was evaluated by elevated plus-maze. Then, their brains were removed, fixed, cut, and stained with Cresyl Violet or Golgi-Cox. In addition to the estimation of stereological parameters, dendrite complexity, and spatial distribution of the neurons in the mPFC and amygdala were evaluated. Aging increased the medial amygdala volume and its total number of neurons, but it did not have a significant effect on these parameters in the mPFC. Furthermore, the size of the neurons in the mPFC increased, whereas the total length of the dendrite and its complexity significantly decreased with aging in this structure and increased in the amygdala. Although aging did not significantly change the dendritic spine density in both regions, old rats showed a more mature spine in the mPFC and more anxiety-like behavior. In conclusion, the increase of anxiety in the old individuals could be attributed to structural changes in the morphology of the dendrite and neuron and its spatial distribution in the mPFC and amygdala. The findings of this study partly support this hypothesis.

Neuronal PTEN deletion in adult cortical neurons triggers progressive growth of cell bodies, dendrites, and axons

Deletion of the phosphatase and tensin (PTEN) gene in neonatal mice leads to enlargement of the cell bodies of cortical motoneurons (CMNs) in adulthood (Gutilla et al., 2016). Here, we assessed whether PTEN deletion in adult mice would trigger growth of mature neurons. PTEN was deleted by injecting AAV-Cre into the sensorimotor cortex of adult transgenic mice with a lox-P flanked exon 5 of the PTEN gene and Cre-dependent reporter gene tdTomato. PTEN-deleted CMN's identified by tdT expression and retrograde labeling with fluorogold (FG) were significantly enlarged four months following PTEN deletion, and continued to increase in size through the latest time intervals examined (12-15 months post-deletion). Sholl analyses of tdT-positive pyramidal neurons revealed increases in dendritic branches at 6 months following adult PTEN deletion, and greater increases at 12 months. 12 months after adult PTEN deletion, axons in the medullary pyramids were significantly larger and G-ratios were higher. Mice with PTEN deletion exhibited no overt neurological symptoms and no seizures. Assessment of motor function on the rotarod and cylinder test revealed slight impairment of coordination with unilateral deletion; however, mice with bilateral PTEN deletion in the motor cortex performed better than controls on the rotarod at 8 and 10 months post-deletion. Our findings demonstrate that robust neuronal growth can be induced in fully mature cortical neurons long after the developmental period has ended and that this continuous growth occurs without obvious functional impairments.

Does time heal all wounds? Experimental diffuse traumatic brain injury results in persisting histopathology in the thalamus

BACKGROUND

Thalamic dysfunction has been implicated in overall chronic neurological dysfunction after traumatic brain injury (TBI), however little is known about the underlying histopathology. In experimental diffuse TBI (dTBI), we hypothesize that persisting histopathological changes in the ventral posteromedial (VPM) nucleus of the thalamus is indicative of progressive circuit reorganization. Since circuit reorganization in the VPM impacts the whisker sensory system, the histopathology could explain the development of hypersensitivity to whisker stimulation by 28days post-injury; similar to light and sound hypersensitivity in human TBI survivors.

METHODS

Adult, male Sprague-Dawley rats underwent craniotomy and midline fluid percussion injury (FPI) (moderate severity; 1.8-2.0atm) or sham surgery. At 1d, 7d, and 28days post-FPI (d FPI) separate experiments confirmed the cytoarchitecture (Giemsa stain) and evaluated neuropathology (silver stain), activated astrocytes (GFAP), neuron morphology (Golgi stain) and microglial morphology (Iba-1) in the VPM.

RESULTS

Cytoarchitecture was unchanged throughout the time course, similar to previously published data; however, neuropathology and astrocyte activation were significantly increased at 7d and 28d and activated microglia were present at all time points. Neuron morphology was dynamic over the time course with decreased dendritic complexity (fewer branch points; decreased length of processes) at 7d FPI and return to sham values by 28d FPI.

CONCLUSIONS

These data indicate that dTBI results in persisting thalamic histopathology out to a chronic time point. While these changes can be indicative of either adaptive (recovery) or maladaptive (neurological dysfunction) circuit reorganization, they also provide a potential mechanism by which maladaptive circuit reorganization could contribute to the development of chronic neurological dysfunction. Understanding the processes that mediate circuit reorganization is critical to the development of future therapies for TBI patients.

Cellular senescence and the aging brain

Cellular senescence is a potent anti-cancer mechanism that arrests the proliferation of mitotically competent cells to prevent malignant transformation. Senescent cells accumulate with age in a variety of human and mouse tissues where they express a complex 'senescence-associated secretory phenotype' (SASP). The SASP includes many pro-inflammatory cytokines, chemokines, growth factors and proteases that have the potential to cause or exacerbate age-related pathology, both degenerative and hyperplastic. While cellular senescence in peripheral tissues has recently been linked to a number of age-related pathologies, its involvement in brain aging is just beginning to be explored. Recent data generated by several laboratories suggest that both aging and age-related neurodegenerative diseases are accompanied by an increase in SASP-expressing senescent cells of non-neuronal origin in the brain. Moreover, this increase correlates with neurodegeneration. Senescent cells in the brain could therefore constitute novel therapeutic targets for treating age-related neuropathologies.

Alterations in nitric oxide synthase in the aged CNS

Aging is associated with neuronal loss, gross weight reduction of the brain, and glial proliferation in the cortex, all of which lead to functional changes in the brain. It is known that oxidative stress is a critical factor in the pathogenesis of aging; additionally, growing evidence suggests that excessive nitric oxide (NO) production contributes to the aging process. However, it is still unclear how NO plays a role in the aging process. This paper describes age-related changes in the activity of NADPH-diaphorase (NADPH-d), a marker for neurons containing nitric oxide synthase (NOS), in many CNS regions. Understanding these changes may provide a novel perspective in identifying the aging mechanism.

Transplanted bone marrow mesenchymal stem cells improve memory in rat models of Alzheimer's disease

The present study aims to evaluate the effect of bone marrow mesenchymal stem cells (MSCs) grafts on cognition deficit in chemically and age-induced Alzheimer's models of rats. In the first experiments aged animals (30 months) were tested in Morris water maze (MWM) and divided into two groups: impaired memory and unimpaired memory. Impaired groups were divided into two groups and cannulated bilaterally at the CA1 of the hippocampus for delivery of mesenchymal stem cells (500 × 10(3)/μL) and PBS (phosphate buffer saline). In the second experiment, Ibotenic acid (Ibo) was injected bilaterally into the nucleus basalis magnocellularis (NBM) of young rats (3 months) and animals were tested in MWM. Then, animals with memory impairment received the following treatments: MSCs (500 × 10(3)/μL) and PBS. Two months after the treatments, cognitive recovery was assessed by MWM in relearning paradigm in both experiments. Results showed that MSCs treatment significantly increased learning ability and memory in both age- and Ibo-induced memory impairment. Adult bone marrow mesenchymal stem cells show promise in treating cognitive decline associated with aging and NBM lesions.

Neuron numbers in the hypothalamus of the normal aging rhesus monkey: stability across the adult lifespan and between the sexes

Normal aging is accompanied by changes in hypothalamic functions including autonomic and endocrine functions and circadian rhythms. The rhesus monkey provides an excellent model of normal aging without the potential confounds of incipient Alzheimer's disease inherent in human populations. This study examined the hypothalamus of 51 rhesus monkeys (23 male, 18 female, 6.5-31 years old) using design-based stereology to obtain unbiased estimates of neuron and glia numbers and the Cavalieri method to estimate volumes for eight reference spaces: total unilateral hypothalamus, suprachiasmatic nucleus (SCN), supraoptic nucleus (SON), paraventricular nucleus (PVN), dorsomedial nucleus (DM), ventromedial nucleus (VM), medial mammillary nucleus (MMN), and lateral hypothalamic area (LHA). The results demonstrated no age-related difference in neuron number, glia number, or volume in any area in either sex except the PVN of male monkeys, which showed a significant increase in both neuron and glia numbers with age. Comparison of males and females for sexual dimorphisms revealed no significant differences in neuron number. However, males had more glia overall as well as in the SCN, DM, and LHA and had a larger hypothalamic volume overall and in the SCN, SON, VM, DM, and MMN. These results demonstrate that hypothalamic neuron loss cannot account for age-related deficits in hypothalamic function and provides further evidence of the absence of neurodegeneration and cell death in the normal aging rhesus monkey.

Neurodegeneration in the somatosensory cortex after experimental diffuse brain injury

Disruption and consequent reorganization of central nervous system circuits following traumatic brain injury may manifest as functional deficits and behavioral morbidities. We previously reported axotomy and neuronal atrophy in the ventral basal (VB) complex of the thalamus, without gross degeneration after experimental diffuse brain injury in adult rats. Pathology in VB coincided with the development of late-onset aberrant behavioral responses to whisker stimulation, which lead to the current hypothesis that neurodegeneration after experimental diffuse brain injury includes the primary somatosensory barrel cortex (S1BF), which receives projection of VB neurons and mediates whisker somatosensation. Over 28 days after midline fluid percussion brain injury, argyrophilic reaction product within superficial layers and layer IV barrels at 1 day progresses into the cortex to subcortical white matter by 7 days, and selective inter-barrel septa and subcortical white matter labeling at 28 days. Cellular consequences were determined by stereological estimates of neuronal nuclear volumes and number. In all cortical layers, neuronal nuclear volumes significantly atrophied by 42-49% at 7 days compared to sham, which marginally attenuated by 28 days. Concomitantly, the number of healthy neurons was reduced by 34-45% at 7 days compared to sham, returning to control levels by 28 days. Progressive neurodegeneration, including argyrophilic reaction product and neuronal nuclear atrophy, indicates injury-induced damage and reorganization of the reciprocal thalamocortical projections that mediate whisker somatosensation. The rodent whisker barrel circuit may serve as a discrete model to evaluate the causes and consequences of circuit reorganization after diffuse brain injury.

SCG postnatal remodelling--hypertrophy and neuron number stability--in Spix's yellow-toothed cavies (Galea spixii)

Whilst a fall in neuron numbers seems a common pattern during postnatal development, several authors have nonetheless reported an increase in neuron number, which may be associated with any one of a number of possible processes encapsulating either neurogenesis or late maturation and incomplete differentiation. Recent publications have thus added further fuel to the notion that a postnatal neurogenesis may indeed exist in sympathetic ganglia. In the light of these uncertainties surrounding the effects exerted by postnatal development on the number of superior cervical ganglion (SCG) neurons, we have used state-of-the-art design-based stereology to investigate the quantitative structure of SCG at four distinct timepoints after birth, viz., 1-3 days, 1 month, 12 months and 36 months. The main effects exerted by ageing on the SCG structure were: (i) a 77% increase in ganglion volume; (ii) stability in the total number of the whole population of SCG nerve cells (no change--either increase or decrease) during post-natal development; (iii) a higher proportion of uninucleate neurons to binucleate neurons only in newborn animals; (iv) a 130% increase in the volume of uninucleate cell bodies; and (v) the presence of BrdU positive neurons in animals at all ages. At the time of writing our results support the idea that neurogenesis takes place in the SCG of preás, albeit it warrants confirmation by further markers. We also hypothesise that a portfolio of other mechanisms: cell repair, maturation, differentiation and death may be equally intertwined and implicated in the numerical stability of SCG neurons during postnatal development.

LRRK2 protein levels are determined by kinase function and are crucial for kidney and lung homeostasis in mice

Mutations in leucine-rich repeat kinase 2 (LRRK2) cause late-onset Parkinson's disease (PD), but the underlying pathophysiological mechanisms and the normal function of this large multidomain protein remain speculative. To address the role of this protein in vivo, we generated three different LRRK2 mutant mouse lines. Mice completely lacking the LRRK2 protein (knock-out, KO) showed an early-onset (age 6 weeks) marked increase in number and size of secondary lysosomes in kidney proximal tubule cells and lamellar bodies in lung type II cells. Mice expressing a LRRK2 kinase-dead (KD) mutant from the endogenous locus displayed similar early-onset pathophysiological changes in kidney but not lung. KD mutants had dramatically reduced full-length LRRK2 protein levels in the kidney and this genetic effect was mimicked pharmacologically in wild-type mice treated with a LRRK2-selective kinase inhibitor. Knock-in (KI) mice expressing the G2019S PD-associated mutation that increases LRRK2 kinase activity showed none of the LRRK2 protein level and histopathological changes observed in KD and KO mice. The autophagy marker LC3 remained unchanged but kidney mTOR and TCS2 protein levels decreased in KD and increased in KO and KI mice. Unexpectedly, KO and KI mice suffered from diastolic hypertension opposed to normal blood pressure in KD mice. Our findings demonstrate a role for LRRK2 in kidney and lung physiology and further show that LRRK2 kinase function affects LRRK2 protein steady-state levels thereby altering putative scaffold/GTPase activity. These novel aspects of peripheral LRRK2 biology critically impact ongoing attempts to develop LRRK2 selective kinase inhibitors as therapeutics for PD.

Aging, Neurodegenerative Disease and the Brain

L'eorganisation anatomique et chimique du cerveau humain subit de nombreux changements au cours du vieillissement. Certains neurons meurent, d'autres s'atrophient et ily a une réduction marquée du nombre de synapses dans des régions spécifiques du cerveau. Des diminutions du métabolisme du glucose et des effets pré- et post-synaptiques des neurotransmetteurs ont aussi été rapportées. À l'exception de certaines structures sous-corticales, il existe cependant une controverse quant à la sévérité des changements dans l'ensemble du cerveau. De plus, les effets du vieillissement sont très variables d'une région du cerveau à l'autre ainsi que d'un individu à l'autre. Certains phénomènes observès dans le vieillissement normal, tels la perte des neurones dopaminergique de la substance noire et celle des neurones cholinergiques du prosencé;phale basal, apparaissent sous une forme grandement exacerbées dans diverses pathologies neurodégénératives comme les maladies de Parkinson et d'Alzeimer. Les faibles altérations qui surviennent au niveau de ces systémes lors du vieillissement normal pourraient étre responsables des troubles d'équilibre, de la pauvreté de mouvement et des pertes de mémoires que l'on observent chez les gens âgés. Cependant, l'inflammation chronique du cerveau semble être une caractéristique typique des individus atteints de maladies neurodégénératives. L'hypothèse voulant que cette inflammation puisse être ralentie par un traitement avec des agents anti-inflammatoires a été supportée par les résultats de 19 études épidémiologiques ainsi que par un essai clinique de moindre envergure. Cependant, d'Autres études cliniques devront ètre réalisées et une attention particulière devra être portée aux effets secondaires de la thérapie anti-inflammatoire conventionnelle afin d'en arriver à une conclusion définitive.

Age-related synaptic loss of the medial olivocochlear efferent innervation

Age-related functional decline of the nervous system is consistently observed, though cellular and molecular events responsible for this decline remain largely unknown. One of the most prevalent age-related functional declines is age-related hearing loss (presbycusis), a major cause of which is the loss of outer hair cells (OHCs) and spiral ganglion neurons. Previous studies have also identified an age-related functional decline in the medial olivocochlear (MOC) efferent system prior to age-related loss of OHCs. The present study evaluated the hypothesis that this functional decline of the MOC efferent system is due to age-related synaptic loss of the efferent innervation of the OHCs. To this end, we used a recently-identified transgenic mouse line in which the expression of yellow fluorescent protein (YFP), under the control of neuron-specific elements from the thy1 gene, permits the visualization of the synaptic connections between MOC efferent fibers and OHCs. In this model, there was a dramatic synaptic loss between the MOC efferent fibers and the OHCs in older mice. However, age-related loss of efferent synapses was independent of OHC status. These data demonstrate for the first time that age-related loss of efferent synapses may contribute to the functional decline of the MOC efferent system and that this synaptic loss is not necessary for age-related loss of OHCs.

Probing the biology of Alzheimer's disease in mice

Alzheimer's disease (AD), the most common cause of dementia among the elderly, may either represent the far end of a continuum that begins with age-related memory decline or a distinct pathobiological process. Although mice that faithfully model all aspects of AD do not yet exist, current mouse models have provided valuable insights into specific aspects of AD pathogenesis. We will argue that transgenic mice expressing amyloid precursor protein should be considered models of accelerated brain aging or asymptomatic AD, and the results of interventional studies in these mice should be considered in the context of primary prevention. Studies in mice have pointed to the roles of soluble beta-amyloid (Abeta) oligomers and soluble tau in disease pathogenesis and support a model in which soluble Abeta oligomers trigger synaptic dysfunction, but formation of abnormal tau species leads to neuron death and cognitive decline severe enough to warrant a dementia diagnosis.

Age and Parkinson's disease-related neuronal death in the substantia nigra pars compacta

During aging, decline in memory and cognitive abilities as well as motor weakening is of great concern. The dopaminergic system mediates some aspects of manual dexterity, in addition to cognition and emotion, and may be especially vulnerable to aging. A common neurodegenerative disorder of this system, Parkinson's disease, is characterized by a selective, progressive loss of dopaminergic neurons in the substantia nigra pars compacta. This review includes studies quantifying age and Parkinson's-related changes of the substantia nigra, with emphasis on stereological studies performed in the substantia nigra pars compacta.

Age-related changes in vagal afferents innervating the gastrointestinal tract

Recent progress in understanding visceral afferents, some of it reviewed in the present issue, serves to underscore how little is known about the aging of the visceral afferents in the gastrointestinal (GI) tract. In spite of the clinical importance of the issue-with age, GI function often becomes severely compromised-only a few initial observations on age-related structural changes of visceral afferents are available. Primary afferent cell bodies in both the nodose ganglia and dorsal root ganglia lose Nissl material and accumulate lipofucsin, inclusions, aggregates, and tangles. Additionally, in changes that we focus on in the present review, vagal visceral afferent terminals in both the muscle wall and the mucosa of the GI tract exhibit age-related structural changes. In aged animals, both of the vagal terminal types examined, namely intraganglionic laminar endings and villus afferents, exhibit dystrophic or regressive morphological changes. These neuropathies are associated with age-related changes in the structural integrity of the target organs of the affected afferents, suggesting that local changes in trophic environment may give rise to the aging of GI innervation. Given the clinical relevance of GI tract aging, a more complete understanding both of how aging alters the innervation of the gut and of how such changes might be mitigated should be made research priorities.

The septo-hippocampal system, learning and recovery of function

We understand this review as an attempt to summarize recent advances in the understanding of cholinergic function in cognition. Such a role has been highlighted in the 1970s by the discovery that dementia patients have greatly reduced cholinergic activity in cortex and hippocampus. A brief anatomical description of the major cholinergic pathways focuses on the basal forebrain and its projections to cortex and hippocampus. From this distinction, compelling evidence suggests that the basal forebrain --> cortex projection regulates the excitability of principal cortical neurons and is thereby critically involved in attention, stimulus detection and memory function, although the biological conditions for these functions are still debated. Similar uncertainties remain for the septo-hippocampal cholinergic system. Although initial lesions of the septum caused memory deficits reminiscent of hippocampal ablations, recent and more refined neurotoxic lesion studies which spared non-cholinergic cells of the basal forebrain failed to confirm these memory impairments in experimental animals despite a near total loss of cholinergic labeling. Yet, a decline in cholinergic markers in aging and dementia still stands as the most central piece of evidence for a link between the cholinergic system and cognition and appear to provide valuable targets for therapeutic approaches.

The developing and restructuring superior cervical ganglion of guinea pigs (Cavia porcellus var. albina)

Post-natal development comprises both maturation (from newborn to adult) and ageing (from adult to senility) and, during this phase, several adaptive mechanisms occur in sympathetic ganglia, albeit they are not fully understood. Therefore, the present study aimed at detecting whether post-natal development would exert any effect on the size and number of a guinea pig's superior cervical ganglion (SCG) neurons. Twenty right SCGs from male subjects were used at four ages, i.e. newborn (7 days), young (30 days), adult (7 months) and old animals (50 months). Using design-based stereological methods the volume of ganglion and the total number of mononucleate and binucleate neurons were estimated. Furthermore, the mean perikaryal volume of mononucleate and binucleate neurons was estimated using the vertical nucleator. The main findings of this study were a combination of post-natal-dependent increases and decreases in some variables: (i) 27% increase in ganglion volume, (ii) 24% and 43% decreases in the total number of mono and binucleate neurons, respectively, and (iii) 27.5% and 40% decreases in the mean perikaryal volume of mono and binucleate neurons, respectively. Despite the fall in neuron numbers found here, post-natal development is not only associated with neuron loss, but also embraces other structural adaptive mechanisms, which are discussed in this paper.

Asymmetric post-natal development of superior cervical ganglion of paca (Agouti paca)

Functional asymmetry has been reported in sympathetic ganglia. Although there are few studies reporting on body side-related morphoquantitative changes in sympathetic ganglion neurons, none of them have used design-based stereological methods to address this issue during post-natal development. We therefore aimed at detecting possible asymmetry-related effects on the quantitative structure of the superior cervical ganglion (SCG) from pacas during ageing, using very precise design-based stereological methods. Forty (twenty left and twenty right) SCG from twenty male pacas were studied at four different ages, i.e. newborn, young, adult and aged animals. By using design-based stereological methods the total volume of ganglion and the total number of mononucleate and binucleate neurons were estimated. Furthermore, the mean perikaryal volume of mononucleate and binucleate neurons was estimated, using the vertical nucleator. The main findings of this study were: (1) the right SCG from aged pacas has more mononucleate and binucleate neurons than the left SCG in all other combinations of body side and animal age, showing the effect of the interaction between asymmetry (right side) and animal age, and (2) right SCG neurons (mono and binucleate) are bigger than the left SCG neurons (mono and binucleate), irrespective of the animal age. This shows, therefore, the exclusive effect of asymmetry (right side). At the time of writing there is still no conclusive explanation for some SCG quantitative changes exclusively assigned to asymmetry (right side) and those assigned to the interaction between asymmetry (right side) and senescence in pacas. We therefore suggest that forthcoming studies should focus on the functional consequences of SCG structural asymmetry during post-natal development. Another interesting investigation would be to examine the interaction between ganglia and their innervation targets using anterograde and retrograde neurotracers. Would differences in the size of target organs explain ganglia structural asymmetry?

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.

Morphometry of the human substantia nigra in ageing and Parkinson's disease

To investigate the relation between the loss of substantia nigra (SN) neurons in normal ageing and Parkinson's disease (PD), we measured the total number and the cell body volume of pigmented (neuromelanin) neurons in the SN. We examined young (n = 7, mean age: 19.9), middle-aged (n = 9, mean age: 50.1), and older controls from the Baltimore Longitudinal Study of Aging (n = 7, mean age: 87.6), as well as PD cases (n = 8, mean age: 74.8). On random-systematically selected paraffin Nissl-stained sections, we used the Optical Fractionator to estimate the total number of neurons on one side of the SN. Using the Nucleator probe, we measured the volume of these neurons. In young and older controls, we also estimated the total number and volume of tyrosine hydroxylase (TH) positive (+) nigral neurons. We observed a significant loss of pigmented (-28.3%, P < 0.01) and TH (+) (-36.2%, P < 0.001) neurons in older controls compared with younger subjects. Analysis of the size distribution of pigmented and TH (+) neurons showed a significant hypertrophy in older controls compared to young controls (P < 0.01). In contrast, in PD we observed a significant atrophy of pigmented neurons compared to all control groups (P < 0.01). These data suggest that neuronal hypertrophy represents a compensatory mechanism within individual SN neurons that allows for normal motor function despite the loss of neurons in normal ageing. Presumably, this compensatory mechanism breaks down or is overwhelmed by the pathological events of PD leading to the onset of the characteristic motor disturbances.

Amyloid precursor protein increases cortical neuron size in transgenic mice

The amyloid precursor protein (APP) is the source of beta-amyloid, a pivotal peptide in the pathogenesis of Alzheimer's disease (AD). This study examines the possible effect of APP transgene expression on neuronal size by measuring the volumes of cortical neurons (microm(3)) in transgenic mouse models with familial AD Swedish mutation (APPswe), with or without mutated presenilin1 (PS1dE9), as well as in mice carrying wild-type APP (APPwt). Overexpression of APPswe and APPwt protein, but not of PS1dE9 alone, resulted in a greater percentage of medium-sized neurons and a proportionate decrease in the percentage of small-sized neurons. Our observations indicate that the overexpression of mutant (APPswe) or wild-type APP in transgenic mice is necessary and sufficient for hypertrophy of cortical neurons. This is highly suggestive of a neurotrophic effect and also raises the possibility that the lack of neuronal loss in transgenic mouse models of AD may be attributed to overexpression of APP.

Macro- and Microstructure of the Superior Cervical Ganglion in Dogs, Cats and Horses during Maturation

The superior cervical ganglion (SCG) provides sympathetic input to the head and neck, its relation with mandible, submandibular glands, eyes (second and third order control) and pineal gland being demonstrated in laboratory animals. In addition, the SCG's role in some neuropathies can be clearly seen in Horner's syndrome. In spite of several studies published involving rats and mice, there is little morphological descriptive and comparative data of SCG from large mammals. Thus, we investigated the SCG's macro- and microstructural organization in medium (dogs and cats) and large animals (horses) during a very specific period of the post-natal development, namely maturation (from young to adults). The SCG of dogs, cats and horses were spindle shaped and located deeply into the bifurcation of the common carotid artery, close to the distal vagus ganglion and more related to the internal carotid artery in dogs and horses, and to the occipital artery in cats. As to macromorphometrical data, that is ganglion length, there was a 23.6% increase from young to adult dogs, a 1.8% increase from young to adult cats and finally a 34% increase from young to adult horses. Histologically, the SCG's microstructure was quite similar between young and adult animals and among the 3 species. The SCG was divided into distinct compartments (ganglion units) by capsular septa of connective tissue. Inside each ganglion unit the most prominent cellular elements were ganglion neurons, glial cells and small intensely fluorescent cells, comprising the ganglion's morphological triad. Given this morphological arrangement, that is a summation of all ganglion units, SCG from dogs, cats and horses are better characterized as a ganglion complex rather than following the classical ganglion concept. During maturation (from young to adults) there was a 32.7% increase in the SCG's connective capsule in dogs, a 25.8% increase in cats and a 33.2% increase in horses. There was an age-related increase in the neuronal profile size in the SCG from young to adult animals, that is a 1.6-fold, 1.9-fold and 1.6-fold increase in dogs, cats and horses, respectively. On the other hand, there was an age-related decrease in the nuclear profile size of SCG neurons from young to adult animals (0.9-fold, 0.7-fold and 0.8-fold in dogs, cats and horses, respectively). Ganglion connective capsule is composed of 2 or 3 layers of collagen fibres in juxtaposition and, as observed in light microscopy and independently of the animal's age, ganglion neurons were organised in ganglionic units containing the same morphological triad seen in light microscopy.

Potent Nonpeptide Antagonists of the Bradykinin B1 Receptor: Structure−Activity Relationship Studies with Novel Diaminochroman Carboxamides

The bradykinin B1 receptor is induced following tissue injury and/or inflammation. Antagonists of this receptor have been studied as promising candidates for treatment of chronic pain. We have identified aryl sulfonamides containing a chiral chroman diamine moiety that are potent antagonists of the human B1 receptor. Our previously communicated lead, compound 2, served as a proof-of-concept molecule, but suffered from poor pharmacokinetic properties. With guidance from metabolic profiling, we performed structure-activity relationship studies and have identified potent analogs of 2. Variation of the sulfonamide moiety revealed a preference for 3- and 3,4-disubstituted aryl sulfonamides, while bulky secondary and tertiary amines were preferred at the benzylic amine position for potency at the B1 receptor. Modifying the beta-amino acid core of the molecule lead to the discovery of highly potent compounds with improved in vitro pharmacokinetic properties. The most potent analog at the human receptor, compound 38, was also active in a rabbit B1 receptor cellular assay. Furthermore, compound 38 displayed in vivo activity in two rabbit models, a pharmacodynamic model with a blood pressure readout and an efficacy model of inflammatory pain.

Perisomatic Thalamic Axotomy After Diffuse Traumatic Brain Injury Is Associated With Atrophy Rather Than Cell Death

Morbidity and mortality associated with traumatic brain injury (TBI) stem from diffuse axonal injury (DAI) throughout subcortical and brainstem white matter and subcortical nuclei. After midline fluid percussion brain injury, DAI in the thalamus includes perisomatic axotomy and resembles human post-traumatic pathology where the degree of morbidity correlates with thalamic damage. After axotomy, acute somatic perturbations resolve and appear compatible with cell survival; however, the long-term fate of neurons in an area with perisomatic axotomy is unknown. From brain-injured and uninjured rats at 1, 7 and 28 days after injury (injury, n = 5/group; sham, n = 4), alternate sections were immunostained for amyloid precursor protein (APP) to detect perisomatic axotomy or Giemsa stained for quantification of neuronal number, neuronal density, regional volume, and neuronal nuclear volume using design-based stereology. One day postinjury, APP-immunoreactive axons were identified consistently within the perisomatic domains of thalamic neurons of the ventral basal complex. Bilateral systematic-random quantification of the ventral basal complex indicated a significant reduction in neuronal density (number per mm, but not number alone) at 1 week after injury, compared with sham and 1 day postinjury. Furthermore, by 1 day and persisting through 1 week after injury, the mean neuronal nuclear volume was atrophied significantly compared with sham. Therefore, diffuse TBI results in early perisomatic axonal injury followed by neuronal atrophy in the ventral basal complex, without gross degeneration. Enduring atrophy in thalamic relays could underlie circuit disruption responsible for post-traumatic morbidity.

Efficient solid-phase synthesis of a library of imidazo[1,2-a]pyridine-8-carboxamides

A versatile method for the solid-phase synthesis of imidazo[1,2-a]pyridine-based derivatives, imidazo[1,2-a]pyridine-8-carboxamides, has been developed. They were obtained by treatment of the amino group of the polymer-bound 2-aminonicotinate with different alpha-haloketones, followed by halogenation at the 3-position of the polymer-bound imidazo[1,2-a]pyridine. The derived polymer-bound imidazo[1,2-a]pyridines 5, 6, and 7 were finally cleaved from the solid-support with an excess of primary or secondary amines. The final crude products were purified from excess amines by solid-supported liquid-liquid extraction (SLE).

Cholinergic system, rearing environment and trajectory learning during aging in mice

Three, 12- and 20-month-old C57BL6/J mice, reared in standard conditions or in enriched environments, were administered subcutaneously either scopolamine hydrobromide, 0.6 or 1.2 mg kg(-1), or physiological saline (control mice) 15 min before testing their abilities to find an invisible platform in a modified version of the Morris water maze, the starting point being kept unchanged throughout the experiment to allow the aged animals to solve the task. The results demonstrated that: 1) All control mice, whatever their age, were able to learn the platform location, but the number of trials needed to reach the learning criterion (3 consecutive trials in less than 8 s) increased with age; 2) All the scopolamine-treated mice, whatever their age, were also able to learn the platform location. However, compared to age-matched controls, the number of trials needed to reach the learning criterion was greater; 3) Rearing the animals in an enriched environment antagonized the effect of scopolamine, but only in the youngest (3 month-old) mice. All control and scopolamine-treated mice, whatever their age and their rearing environment, remembered, 7 days later, the platform location.

Identification of the Critical Residues of Bradykinin Receptor B1 for Interaction with the Kinins Guided by Site-Directed Mutagenesis and Molecular Modeling

We report the critical residues for the interaction of the kinins with human bradykinin receptor 1 (B1) using site-directed mutagenesis in conjunction with molecular modeling of the binding modes of the kinins in the homology model of the B1 receptor. Mutation of Lys118 in transmembrane (TM) helix 3, Ala270 in TM6, and Leu294 in TM7 causes a significant decrease in the affinity for the peptide agonists des-Arg10kallidin (KD) and des-Arg9BK but not the peptide antagonist des-Arg10Leu9KD. In contrast, mutations in TM2, TM3, TM6, and TM7 cause a significant decrease in the affinity for both the peptide agonists and the antagonist. These data indicate that the B1 bradykinin binding pocket for agonists and antagonists is similar, but the manners in which they interact with the receptor do not completely overlap. Therefore, there is a potential to influence the receptor's ligand selectivity.

Size and number of binucleate and mononucleate superior cervical ganglion neurons in young capybaras

The total number of neurons in the superior cervical ganglion (SCG) of adult capybaras is known from a previous study, where a marked occurrence of binucleate neurons (13%) was also noted. Here, distribution, number and fate of binucleate neurons were examined in younger, developing capybaras, aged 3 months. The mean neuronal cross-sectional area was 575.2 microm2 for mononucleate neurons and 806.8 microm2 in binucleate neurons. Frequency of binucleate neurons was about 36%. The mean ganglion volume was about 190 mm3 in young capybaras and the mean neuronal density was about 9,517 neurons/mm3. The total number of neurons per ganglion was about 1.81 mill. Neuronal cell bodies constituted 22.5% of the ganglion volume and the average neuronal volume was 23,600 microm3. By comparing the present data with those previously published the conclusion is drawn that the maturation period was characterized by the following points: a 26% remarkable decrease in neuronal density which was significant (P < 0.05) and a significant 16% (P < 0.05) decrease in the total number of SCG neurons accompanied by a 23% decrease in the total number of SCG binucleate neurons.

Combining 4D Pharmacophore Generation and Multidimensional QSAR: Modeling Ligand Binding to the Bradykinin B2 Receptor

We recently reported the development of two receptor-modeling concepts (software Quasar and Raptor) based on multidimensional quantitative structure-activity relationships (QSAR) and allowing for the explicit simulation of induced fit. As the identification of the bioactive configuration of ligand molecules in such studies is all but unambiguous, each compound may be represented by an ensemble of different conformations, orientations, stereoisomers, and protonation states, leading to a 4D data set. In this account, we present a novel technology (software Symposar) allowed to automatically generate a 4D pharmacophore as input for multidimensional QSAR. Symposar aligns ligands utilizing fuzzylike 2D-subfeature mapping and, subsequently, a Monte Carlo search on a 3D similarity grid. The two-step concept (4D pharmacophore generation and quantification of ligand binding by multidimensional QSAR) was applied to 186 compounds binding to the bradykinin B2 receptor. The prediction of their binding affinity by means of the Quasar and Raptor technologies allowed for consensus scoring and generated topologically and quantitatively consistent receptor models. These converged at a cross-validated r2 of 0.752 and 0.815 and yielded a predictive r2 of 0.784 and 0.853 for a test set (for Quasar and Raptor, respectively).

Transforming growth factor-beta1 is a negative modulator of adult neurogenesis

Transforming growth factor (TGF)-beta1 has multiple functions in the adult central nervous system (CNS). It modulates inflammatory responses in the CNS and controls proliferation of microglia and astrocytes. In the diseased brain, TGF-beta1 expression is upregulated and, depending on the cellular context, its activity can be beneficial or detrimental regarding regeneration. We focus on the role of TGF-beta1 in adult neural stem cell biology and neurogenesis. In adult neural stem and progenitor cell cultures and after intracerebroventricular infusion, TGF-beta1 induced a long-lasting inhibition of neural stem and progenitor cell proliferation and a reduction in neurogenesis. In vitro, although TGF-beta1 specifically arrested neural stem and progenitor cells in the G0/1 phase of the cell cycle, it did not affect the self-renewal capacity and the differentiation fate of these cells. Also, in vivo, TGF-beta1 did not influence the differentiation fate of newly generated cells as shown by bromo-deoxyuridine incorporation experiments. Based on these data, we suggest that TGF-beta1 is an important signaling molecule involved in the control of neural stem and progenitor cell proliferation in the CNS. This might have potential implications for neurogenesis in a variety of TGF-beta1-associated CNS diseases and pathologic conditions.

Cognitive aging as an extension of brain development: A model linking learning, brain plasticity, and neurodegeneration

Differences in cognitive aging rates among mammals suggest that the pace of brain aging is genetically determined. In this work, we investigate the possibility that brain aging is an extension of brain development. It is possible that a subset of developmental mechanisms are extreme cases of antagonistic pleiotropy in that they are necessary for reaching adulthood and yet later cause age-related diseases. We derive a model linking development and brain aging in which childhood events essential for brain development later result in neurodegeneration. The hypothesis presented herein involves brain plasticity in which the same mechanisms that shape the adult phenotype continue at later ages contributing to cognitive dysfunction and eventually dementia. The same genetic program that decreases brain plasticity at early ages to focus our mind to the surrounding environment may continue in adulthood resulting in cognitive aging. Experimental implications for understanding neurodegeneration in this context are also discussed.

Reversible age impairments in neurite outgrowth by manipulations of astrocytic GFAP

Aging is associated with neuron atrophy and impaired sprouting after lesions. In contrast during normal aging without neurodegenerative diseases, astrocytes display increasing activation, with progressive increases of glial fibrillary acidic protein (GFAP) beginning before midlife. Because many neuronal functions depend on astrocytic support, we developed a heterochronic co-culture system to study influences of aging astrocytes on neurons. Neurite outgrowth by embryonic neurons (E18) was markedly less when co-cultured with confluent astrocytes derived from old (24 mo) versus young (3 mo) cortex. These impairments were reversible. Diminishing the GFAP levels of old astrocytes by RNAi restored neurite outgrowth, whereas overexpression of GFAP in young astrocytes modeled these effects of aging by reducing neurite outgrowth. Quantitative relationships were found such that neurites were co-localized with high intensity laminin, which both varied inversely with GFAP. These results implicate increased astrocytic GFAP expression as a proximal cause of neuron atrophy during normal aging.

Postnatal-related changes in the size and total number of neurons in the caudal mesenteric ganglion of dogs: Total number of neurons can be predicted from body weight and ganglion volume

Aging is mostly characterized by a progressive decline of neuronal function that involves both the central and the peripheral nervous system. The aging process is accompanied by changes in either the number or the size of neurons. However, these data are controversial and not very well known in the sympathetic ganglia of large mammals. Hence, the present investigation aimed to study the dog's caudal mesenteric ganglion (CMG) in three different periods of postnatal development, searching for qualitative and quantitative alterations. The CMG is responsible for the large intestine, internal anal sphincter, and partially the urogenital system innervations. Nine dead male dogs from the Veterinary Hospital of the College of Veterinary Medicine at University of São Paulo were divided into three well-defined age groups (1-2 months old, 1-2 years old, and 5-10 years old). The stereological study was pursued using the physical disector method combined to the Cavalieri principle. The postnatal development was accompanied by an increase in the nonneuronal tissue amount and in ganglion volume. Additionally, the total number of neurons also increased during aging (from 70,140 to 1,204,516), although the neuronal density showed an opposite trend (from 29,911 to 11,500 mm(-3)). Due to the interrelation between either body weight or ganglion volume and aging in the dogs investigated in this study, it was possible to predict the total number of neurons in CMG using both body weight and ganglion volume in an attempt to verify whether or not size and total number of neurons are both allometrically and aging ruled, i.e., if either the animal's body weight and ganglion volume or aging influence these parameters. The prediction of the total number of neurons was very close to the initially estimated values.

Caliban's heritance and the genetics of neuronal aging

Although current research on brain aging is dominated by Alzheimer's disease (AD), many other brain changes arise during middle age in humans and in rodent models that are independent of AD-like neurodegeneration. Differences and continuities between normal and pathological aspects of neuronal aging reveal the relative contributions and interactions of genetic and environmental factors. Apolipoprotein E alleles might be prototypes for genetic polymorphisms associated with functional changes that arise during middle age. Mice are valuable models for these aspects of aging because most genotypes show little neurodegeneration, and none accumulate beta-amyloid unless human transgenes are introduced. As further human genes are found to modify normal and pathological neuronal aging, this zoo of aging-animal variants will facilitate analysis both of pathways of age-related neuronal dysfunction and of environmental influences on these pathways.

Aging and subcellular localization of m2 muscarinic autoreceptor in basalocortical neurons in vivo

By using immunohistochemical approaches at the light and electron microscopic levels, we have shown that aging modifies the subcellular distribution of the m2 muscarinic autoreceptor (m2R) differentially at somato-dendritic postsynaptic sites and at axonal presynaptic sites in cholinergic basalocortical neurons, in vivo. In cholinergic perikarya and dendrites of the nucleus basalis magnocellularis (NBM), aging is associated with a decrease of the density of m2R at the plasma membrane and in the cytoplasm, suggesting a decrease of the total number of m2R in the somato-dendritic field. In contrast, the number of substance P receptors per somato-dendritic surface was not affected. In the frontal cortex (FC), we have shown a decrease of cytoplasmic m2R density also leading to a decrease of the number of m2R per surface of varicosities but with no change of the density of m2R at the membrane. Our results suggest that the decrease of m2R in the somato-dendritic field of the NBM, but not a modification of the number of presynaptic m2 autoreceptors at the plasma membrane in the FC, could contribute to the decrease of the efficacy of cholinergic transmission observed with aging in the rat.

Raptor: Combining Dual-Shell Representation, Induced-Fit Simulation, and Hydrophobicity Scoring in Receptor Modeling: Application toward the Simulation of Structurally Diverse Ligand Sets

We present a novel receptor-modeling approach (software Raptor) based on multidimensional quantitative structure-activity relationships (QSARs). To accurately predict relative free energies of ligand binding, it is of utmost importance to simulate induced fit. In Raptor, we explicitly and anisotropically allow for this phenomenon by a dual-shell representation of the receptor surrogate. In our concept, induced fit is not limited to steric aspects but includes the variation of the physicochemical fields along with it. The underlying scoring function for evaluating ligand-receptor interactions includes directional terms for hydrogen bonding and hydrophobicity and thereby treats solvation effects implicitly. This makes the approach independent from a partial-charge model and, as a consequence, allows one to smoothly model ligand molecules binding to the receptor with different net charges. We have applied the new concept toward the estimation of ligand-binding energies associated with the chemokine receptor-3 (50 ligands: r(2) = 0.965; p(2) = 0.932), the bradykinin B(2) receptor (52 ligands: r(2) = 0.949; p(2) = 0.859), and the estrogen receptor (116 ligands: r(2) = 0.908; p(2) = 0.907), respectively.

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.

Histological changes of the dopaminergic nigrostriatal system in aging

Although the maximum human lifespan has not increased in recent history, average life expectancy has risen dramatically since the beginning of the last century. Lengthening of lifespan has little merit if the quality of life is not preserved. In the elderly, the decline in memory and cognitive abilities is of great concern, as is motor weakening, which increases with age. The dopaminergic system mediates some aspects of manual dexterity, in addition to cognition and emotion, and may be especially vulnerable to aging. Therefore, the aging of this system has both clinical and vocational aspects. This review includes studies quantitating age-related changes of the nigrostriatal system, with emphasis on the use of stereological methods, and provides tables of stereological studies performed in the nigrostriatal system.

A New Class of Nonpeptide Bradykinin B2 Receptor Ligand, Incorporating a 4-Aminoquinoline Framework. Identification of a Key Pharmacophore To Determine Species Difference and Agonist/Antagonist Profile

Introduction of various aliphatic amino groups at the 4-position of the quinoline moiety of our nonpeptide bradykinin (BK) B(2) receptor antagonists afforded highly potent ligands for human B(2) receptor with various affinities for guinea pig B(2) receptor, indicating remarkable species difference. A representative 4-dimethyamino derivative 40a exhibited subnanomolar and nanomolar binding affinities for human and guinea pig B(2) receptors, respectively, and significantly inhibited BK-induced bronchoconstriction in guinea pigs at 10 microg/kg by intravenous administration. Further chemical modification led us to discover unique partial agonists for the human B(2) receptor that increase inositol phosphates (IPs) production by themselves in Chinese hamster ovary (CHO) cells expressing the cloned human B(2) receptor. Although their potency and efficacy were much lower than those of BK, we identified them as screening leads for nonpeptide B(2) agonists. In these studies it was revealed the 4-substituent of the quinoline moiety is the key pharmacophore to determine species difference and agonist/antagonist profiles.

A New Series of Highly Potent Non-Peptide Bradykinin B2 Receptor Antagonists Incorporating the 4-Heteroarylquinoline Framework. Improvement of Aqueous Solubility and New Insights into Species Difference

Introduction of nitrogen-containing heteroaromatic groups at the 4-position of the quinoline moiety of our non-peptide B(2) receptor antagonists resulted in enhancing binding affinities for the human B(2) receptor and reducing binding affinities for the guinea pig one, providing new structural insights into species difference. A CoMFA study focused on the diversity of the quinoline moiety afforded correlative and predictive QSAR models of binding for the human B(2) receptor but not for the guinea pig one. A series of 4-(1-imidazolyl)quinoline derivatives could be dissolved in a 5% aqueous solution of citric acid up to a concentration of 10 mg/mL. A representative compound 48a inhibited the specific binding of [(3)H]BK to the cloned human B(2) receptor expressed in Chinese hamster ovary cells with an IC(50) value of 0.26 nM and significantly inhibited BK-induced bronchoconstriction in guinea pigs even at 1 microg/kg by intravenous administration.

Apoptotic proteins in the course of aging of central nervous system in the rat

Studies were performed on the level of cells with damaged DNA (TUNEL), the level of protein engaged in DNA repair (PARP) and the level of proteins indicating the extent of apoptosis (Bax:Bcl-2) (Western blot). The studies were performed on cerebral cortex (GM), white matter (WM), medulla oblongata (MO), cerebellum (C) of rats, 3.0-3.5-, 12-, 24-months of age. The highest levels of DNA injury in GM of 1-year-old rats and in MO of 2-year-old rats were accompanied by peak levels of PARP. In the remaining structures (WM, C) levels of DNA injury showed no correspondence with levels of PARP. Levels of Bax proteins exceeded levels of Blc-2 protein in all cerebral structures of young rats. In old animals, Bax protein continued to exceed Blc-2 levels both in GM and in MO, in which most pronounced fragmentation of DNA was observed. The data indicated that in spite of high level of TUNEL positive cells in aged brain PARP and Bcl-2 are probably engaged in protection of the cells against death.

The glial cell response to a viral vector in the aged brain

The normal aged brain undergoes pro-inflammatory changes. We investigated the effect of injecting a potential inflammatory stimulus, an adenoviral vector, on the response of microglia and astroglia in the aged brain. Groups of young (4 months) and old (31 months) male C57BL/Icrfat mice received a unilateral injection into the striatum of adenoviral vector encoding the LacZ gene. After 48 h, the mice were killed and the brains analysed for numbers of activated microglia and macrophages using the biotinylated lectin Griffonia simplicifolia as a marker; astroglia were identified by immunohistochemistry for glial fibrillary acidic protein (GFAP). The cell counts were analysed using two-way analysis of variance (anova). Transgene expression was assessed by beta-galactosidase histochemistry. The numbers of activated microglia in the striatum increased in response to the adenovirus in both young [contralateral 19.5 (3.7), ipsilateral 36 (3.0)] and old [contralateral 23.1 (9.6), ipsilateral 40.8 (6.9)] mice (two-way anova; P < 0.0001), but there was no significant difference between the two age groups. There was a significant age-related increase in the number of GFAP-positive astroglia in the uninjected, contralateral striatum [4 months, 2.5 (1.4); 31 months, 29.7 (9.3)] (two-way anova; P < 0.0001). However, there was no difference in response to the adenovirus in both young [contralateral 2.5 (1.4), ipsilateral 3.2 (1.2)] and old [contralateral 29.7 (9.3), ipsilateral 28.9 (8.2)] mice. We conclude that even though it has been argued that the aged brain is in a pro-inflammatory state, under the experimental conditions used in this study, there was no difference in the nature of the immune response between young and old mice of this strain to an adenoviral load.

Effects of aging on neurons and glial cells from the superficial layers of the superior colliculus in rats

The aim of this study was to investigate the effect of aging on glial cells and neurons from the superficial layers of the superior colliculus in rats. We used stereological methods to estimate the volume of the superficial layers, neuron size, and the number of neurons and glial cells in Wistar male rats aged 3, 24, 26, and 28 months. A 32.6% volume increase was found in the stratum griseum superficiale between the ages of 3 and 26 months, while in the 28-month-old animals a 19% decrease was observed. The stratum opticum did not show any changes in volume with age. Also, our analysis revealed a process of somatic and nuclear atrophy in the neurons of the superficial layers in animals aged 26 and 28 months. On the other hand, no statistically significant differences were found in the numbers of neurons. The number of glial cells in the stratum griseum superficiale showed an increase between the 3rd and 26th month, while the stratum opticum suffered no change.

Survival of fetal hippocampal CA3 cell grafts in the middle-aged and aged hippocampus: effect of host age and deafferentation

The potential application of neural transplantation to many neurodegenerative disorders at early stages of disease progression would involve middle-aged and aged persons. Hence, it is important to examine critically the extent of graft cell survival in both intact and partially deafferented middle-aged and aged brain. We investigated the degree of survival of 5'-bromodeoxyuridine (BrdU)-labeled fetal hippocampal CA3 cells after grafting into both intact hippocampus and partially deafferented hippocampus (i.e., hippocampus contralateral to intracerebroventricular administration of kainic acid) of middle-aged and aged Fischer 344 rats. Absolute cell survival within these grafts was rigorously analyzed using BrdU immunostaining of serial sections and the optical fractionator cell counting method. In the intact hippocampus, graft cell survival was 23% of injected cells for middle-aged rats and 18% for aged rats, which is consistent with the survival of fetal hippocampal cells in the intact young adult hippocampus reported earlier (Shetty and Turner [1995] Neuroscience 67:561-582). A partial deafferentation at the time of grafting significantly enhanced the degree of graft cell survival to 35% of injected cells in the middle-aged hippocampus and 27% in the aged hippocampus. However, the overall graft cell survival after deafferentation was significantly (30%) greater in the middle-aged hippocampus compared with the aged hippocampus. These results reveal that 1) the degree of survival of fetal neural cells in the intact mature brain remains constant with aging and 2) a partial deafferentation of the mature host brain at the time of grafting enhances survival of grafted fetal cells, regardless of the host age. However, the overall extent of graft cell survival after deafferentation depends on the age of the mature brain at the time of deafferentation.

Intraneuronal amyloid precursor protein (APP) and appearance of extracellular beta-amyloid peptide (abeta) in the brain of aging kokanee salmon

Antibodies to human amyloid precursor protein (APP(695)) and beta-amyloid peptide (A beta(1-42)) were used to determine timing of amyloidosis in the brain of kokanee salmon (Oncorhynchus nerka kennerlyi) in one of four reproductive stages: immature (IM), maturing (MA), sexually mature (SM), and spawning (SP), representing a range of aging from somatically mature but sexually immature to spawning and somatic senescence. In IM fish, immunoreactive (ir) intracellular APP occurred in 18 of 23 brain regions. During sexual maturation and aging, the number of neurons expressing APP increased in 11 of these APP-ir regions. A beta-ir was absent in IM fish, present in seven regions in MA fish, moderately abundant in 15 regions in SM fish, and was most abundant in all brain regions of SP fish exhibiting A beta-ir. Intracellular APP-ir was observed in brain regions involved in sensory integration, olfaction, vision, stress responses, reproduction, and coordination. Intra- and extracellular A beta(1-42) immunoreactivity (A beta-ir) was present in all APP-ir regions except the nucleus lateralis tuberis (hypothalamus) and Purkinje cells (cerebellum). APP-ir and A beta deposition increase during aging. APP-ir is present in IM fish; A beta-ir usually appears first in MA or SM fish and increases in SM fish as does APP-ir. Extracellular A beta deposition dramatically increases between SM and SP stages (1-2 weeks) in all fish, indicating an extremely rapid and synchronized process. Rapid senescence observed in pacific salmon could make them a useful model to investigate timing of amyloidosis and neurodegeneration during brain aging.