Structural alterations in neurons of aged canine neocortex: a Golgi study

Learning-Dependent Dendritic Spine Plasticity Is Reduced in the Aged Mouse Cortex

Aging is accompanied by a progressive decrease in learning and memory function. Synaptic loss, one of the hallmarks of normal aging, likely plays an important role in age-related cognitive decline. But little is known about the impact of advanced age on synaptic plasticity and neuronal function in vivo. In this study, we examined the structural dynamics of postsynaptic dendritic spines as well as calcium activity of layer 5 pyramidal neurons in the cerebral cortex of young and old mice. Using transcranial two-photon microscopy, we found that in both sensory and motor cortices, the elimination rates of dendritic spines were comparable between young (3-5 months) and mature adults (8-10 months), but seemed higher in old mice (>20 months), contributing to a reduction of total spine number in the old brain. During the process of motor learning, old mice compared to young mice had fewer new spines formed in the primary motor cortex. Motor training-evoked somatic calcium activity in layer 5 pyramidal neurons of the motor cortex was also lower in old than young mice, which was associated with the decline of motor learning ability during aging. Together, these results demonstrate the effects of aging on learning-dependent synapse remodeling and neuronal activity in the living cortex and suggest that synaptic deficits may contribute to age-related learning impairment.

Comparative morphology of gigantopyramidal neurons in primary motor cortex across mammals

Gigantopyramidal neurons, referred to as Betz cells in primates, are characterized by large somata and extensive basilar dendrites. Although there have been morphological descriptions and drawings of gigantopyramidal neurons in a limited number of species, quantitative investigations have typically been limited to measures of soma size. The current study thus employed two separate analytical approaches: a morphological investigation using the Golgi technique to provide qualitative and quantitative somatodendritic measures of gigantopyramidal neurons across 19 mammalian species from 7 orders; and unbiased stereology to compare the soma volume of layer V pyramidal and gigantopyramidal neurons in primary motor cortex between 11 carnivore and 9 primate species. Of the 617 neurons traced in the morphological analysis, 181 were gigantopyramidal neurons, with deep (primarily layer V) pyramidal (n = 203) and superficial (primarily layer III) pyramidal (n = 233) neurons quantified for comparative purposes. Qualitatively, dendritic morphology varied considerably across species, with some (sub)orders (e.g., artiodactyls, perissodactyls, feliforms) exhibiting bifurcating, V-shaped apical dendrites. Basilar dendrites exhibited idiosyncratic geometry across and within taxonomic groups. Quantitatively, most dendritic measures were significantly greater in gigantopyramidal neurons than in superficial and deep pyramidal neurons. Cluster analyses revealed that most taxonomic groups could be discriminated based on somatodendritic morphology for both superficial and gigantopyramidal neurons. Finally, in agreement with Brodmann, gigantopyramidal neurons in both the morphological and stereological analyses were larger in feliforms (especially in the Panthera species) than in other (sub)orders, possibly due to specializations in muscle fiber composition and musculoskeletal systems.

Scanning Ultrasound (SUS) Causes No Changes to Neuronal Excitability and Prevents Age-Related Reductions in Hippocampal CA1 Dendritic Structure in Wild-Type Mice

Scanning ultrasound (SUS) is a noninvasive approach that has recently been shown to ameliorate histopathological changes and restore memory functions in an Alzheimer's disease mouse model. Although no overt neuronal damage was reported, the short- and long-term effects of SUS on neuronal excitability and dendritic tree morphology had not been investigated. To address this, we performed patch-clamp recordings from hippocampal CA1 pyramidal neurons in wild-type mice 2 and 24 hours after a single SUS treatment, and one week and 3 months after six weekly SUS treatments, including sham treatments as controls. In both treatment regimes, no changes in CA1 neuronal excitability were observed in SUS-treated neurons when compared to sham-treated neurons at any time-point. For the multiple treatment groups, we also determined the dendritic morphology and spine densities of the neurons from which we had recorded. The apical trees of sham-treated neurons were reduced at the 3 month time-point when compared to one week; however, surprisingly, no longitudinal change was detected in the apical dendritic trees of SUS-treated neurons. In contrast, the length and complexity of the basal dendritic trees were not affected by SUS treatment at either time-point. The apical dendritic spine densities were reduced, independent of the treatment group, at 3 months compared to one week. Collectively, these data suggest that ultrasound can be employed to prevent an age-associated loss of dendritic structure without impairing neuronal excitability.

Exogenous dehydroisoandrosterone sulfate reverses the dendritic changes of the central neurons in aging male rats

Sex hormones are known to help maintaining the cognitive ability in male and female rats. Hypogonadism results in the reduction of the dendritic spines of central neurons which is believed to undermine memory and cognition and cause fatigue and poor concentration. In our previous studies, we have reported age-related regression in dendrite arbors along with loss of dendritic spines in the primary somatosensory cortical neurons in female rats. Furthermore, castration caused a reduction of dendritic spines in adult male rats. In light of this, it was surmised that dendritic structures might change in normal aging male rats with advancing age. Recently, dehydroepiandrosterone sulfate (DHEAS) has been reported to have memory-enhancing properties in aged rodents. In this study, normal aging male rats, with a reduced plasma testosterone level of 75-80%, were used to explore the changes in behavioral performance of neuronal dendritic arbor and spine density. Aging rats performed poorer in spatial learning memory (Morris water maze). Concomitantly, these rats showed regressed dendritic arbors and spine loss on the primary somatosensory cortical and hippocampal CA1 pyramidal neurons. Exogenous DHEAS and testosterone treatment reversed the behavioral deficits and partially restored the spine loss of cortical neurons in aging male rats but had no effects on the dendritic arbor shrinkage of the affected neurons. It is concluded therefore that DHEAS, has the efficacy as testosterone, and that it can exert its effects on the central neuron level to effectively ameliorate aging symptoms.

Dendritic spine changes associated with normal aging

Given the rapid rate of population aging and the increased incidence of cognitive decline and neurodegenerative diseases with advanced age, it is important to ascertain the determinants that result in cognitive impairment. It is also important to note that much of the aged population exhibit 'successful' cognitive aging, in which cognitive impairment is minimal. One main goal of normal aging studies is to distinguish the neural changes that occur in unsuccessful (functionally impaired) subjects from those of successful (functionally unimpaired) subjects. In this review, we present some of the structural adaptations that neurons and spines undergo throughout normal aging and discuss their likely contributions to electrophysiological properties and cognition. Structural changes of neurons and dendritic spines during aging, and the functional consequences of such changes, remain poorly understood. Elucidating the structural and functional synaptic age-related changes that lead to cognitive impairment may lead to the development of drug treatments that can restore or protect neural circuits and mediate cognition and successful aging.

Age-related alterations of Nestin-immunoreactive neurons in rat basal forebrain with aged memory deficit

Age-related and aged memory deficit changes in Nestin-immunoreactive (Nestin-IR) neurons were studied following recent evidence of distinct Nestin-IR neurons within adult rat basal forebrain. Morris water maze task assessed spatial learning capacity of 3- and 24-month rats (aged-impaired and aged-unimpaired groups). Nestin-IR neuron distributional and morphological features were investigated by immunohistochemistry and positive neuronal number calculation. Nestin-IR neuron number declined with aging, especially aged-impaired. Significant negative correlations existed between average escape latencies and Nestin-IR neuron number in medial septum-diagonal band of Broca (MS-DBB). Correlations of rostral portion [medial septum (MS) and vertical limb diagonal band (vDB)] were higher than caudal portion [horizontal limb diagonal band (hDB)]. Aged-impaired showed reduced complexity of Nestin-IR neuron dendrite arborization and dendritic length. Nestin-IR astrocyte-like cells appeared scattered among Nestin-IR neurons on some aged-impaired slices. In conclusion, aged-impaired rats showed worse cognitive spatial performance and less Nestin-IR neuronal number compared to aged-unimpaired. Nestin-IR neuronal loss and morphological changes are some pathological characteristics of rat aged basal forebrain and may be important in neurobiological mechanisms of brain aging and aged memory deficit.

Changes in the structural complexity of the aged brain

Structural changes of neurons in the brain during aging are complex and not well understood. Neurons have significant homeostatic control of essential brain functions, including synaptic excitability, gene expression, and metabolic regulation. Any deviations from the norm can have severe consequences as seen in aging and injury. In this review, we present some of the structural adaptations that neurons undergo throughout normal and pathological aging and discuss their effects on electrophysiological properties and cognition. During aging, it is evident that neurons undergo morphological changes such as a reduction in the complexity of dendrite arborization and dendritic length. Spine numbers are also decreased, and because spines are the major sites for excitatory synapses, changes in their numbers could reflect a change in synaptic densities. This idea has been supported by studies that demonstrate a decrease in the overall frequency of spontaneous glutamate receptor-mediated excitatory responses, as well as a decrease in the levels of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and N-methyl-d-aspartate receptor expression. Other properties such as gamma-aminobutyric acid A receptor-mediated inhibitory responses and action potential firing rates are both significantly increased with age. These findings suggest that age-related neuronal dysfunction, which must underlie observed decline in cognitive function, probably involves a host of other subtle changes within the cortex that could include alterations in receptors, loss of dendrites, and spines and myelin dystrophy, as well as the alterations in synaptic transmission. Together these multiple alterations in the brain may constitute the substrate for age-related loss of cognitive function.

Apical vulnerability to dendritic retraction in prefrontal neurones of ageing SAMP10 mouse: a model of cerebral degeneration

The SAMP10 mouse is a model of accelerated ageing in which senescence is characterized by age-related atrophy of the cerebral cortex and limbic structures, poor learning and memory task performance with depressive behaviour and cholinergic and dopaminergic alterations. Here we studied age-related changes in the dendritic arbors and spine density of pyramidal cells in the medial prefrontal cortex of SAMP10 mice using a quantitative Golgi method. Dendrites of prefrontal neurones gradually retracted with ageing towards the soma with the relative preservation of overall complexity. Apical dendrites were much more severely affected than basal dendrites. The combined length of the apical dendrites and spine density were decreased by 45% and 55%, respectively, in mice at 12 months, compared with mice at 3 months of age. Immunohistochemical and immunoblot analyses indicated that expression of microtubule-associated protein (MAP) 2, a marker of dendrites, decreased in an age-related manner not only in the anterior cortex but also in the posterior cortex and olfactory structures in SAMP10 mice. Decreased expression of MAP2 mRNA caused the decrease in MAP2 protein expression. These results suggest that retraction of apical, but not of basal dendrites, with a loss of spines in prefrontal neurones, appears to be responsible for poor learning and memory performance in aged SAMP10 mice. It is also suggested that age-related dendritic retraction occurs in a wide area including the entire cerebral cortex and olfactory structures.

Changes in the axonal conduction velocity of pyramidal tract neurons in the aged cat

The present study was undertaken to determine whether age-dependent changes in axonal conduction velocity occur in pyramidal tract neurons. A total of 260 and 254 pyramidal tract neurons were recorded extracellularly in the motor cortex of adult control and aged cats, respectively. These cells were activated antidromically by electrical stimulation of the medullary pyramidal tract. Fast- and slow-conducting neurons were identified according to their axonal conduction velocity in both control and aged cats. While 51% of pyramidal tract neurons recorded in the control cats were fast conducting (conduction velocity greater than 20 m/s), only 26% of pyramidal tract neurons in the aged cats were fast conducting. There was a 43% decrease in the median conduction velocity for the entire population of pyramidal tract neurons in aged cats when compared with that of pyramidal tract neurons in the control cats (P < 0.001, Mann-Whitney U-test). A linear relationship between the spike duration of pyramidal tract neurons and their antidromic latency was present in both control and aged cats. However, the regression slope was significantly reduced in aged cats. This reduction was due to the appearance of a group of pyramidal tract neurons with relatively shorter spike durations but slower axonal conduction velocities in the aged cat. Sample intracellular data confirmed the above results. These observations form the basis for the following conclusions: (i) there is a decrease in median conduction velocity of pyramidal tract neurons in aged cats; (ii) the reduction in the axonal conduction velocity of pyramidal tract neurons in aged cats is due, in part, to fibers that previously belonged to the fast-conducting group and now conduct at slower velocity.

Physical Activity, Age, and Cognitive-Neuropsychological Function

Findings from three research paradigms that employed aerobic exercise as an independent variable were used to test the hypothesis that aerobic exercise improves cognitive-neuropsychological functioning. The research paradigms were animal intervention studies, cross-sectional human studies, and human intervention studies. Results from studies of animals, usually rodents, provide consistent evidence that aerobic fitness is associated with improved neurobiological and behavioral functioning. Cross-sectional studies with humans indicate a strong positive association between physical activity level and cognitive-neuropsychological performance. However, results from these studies must be interpreted cautiously, as individuals who elect to exercise or not exercise may differ on other variables that could influence cognitive-neuropsychological performance. To date, human intervention studies have not consistently demonstrated cognitive-neuropsychological improvements following exercise training. To satisfactorily test the exercise/cognition hypothesis with humans, carefully controlled intervention studies that last longer than those previously employed are needed.

Aging reverts to juvenile conditions the synaptic connectivity of cerebral cortical pyramidal shafts

Quantitative analysis of the total number and distribution of dendritic spines along the apical shafts of layer V cerebral cortical pyramids has been performed on aging rats (90-120 to 1,135 days old) and on rats during the period of early and late development (10-80 days). As expected from previous work, present results show that the total number of dendritic spines along the shafts increase from 10 to 80 days, after which it starts to gradually decrease until the last age studied (1,135 days). The quantitative analysis of the effect of aging on the relative decrease of dendritic spines shows that this decrease starts being homogeneous along the whole length of the apical shafts and that from a certain age onwards, estimated according to present results in 400 days, this effect is significantly more pronounced in layers IV and III-II than in deep layers. Furthermore, the comparison made between the distribution of dendritic spines along the apical shafts of pyramidal neurons of old and young animals has shown that aging produces a regression of this distribution to juvenile conditions.

Exogenous nerve growth factor reverses age-related structural changes in neocortical neurons in the aging rat. A quantitative Golgi study

The role of chronic exogenous intracerebroventricular administration of nerve growth factor (NGF) on the morphology of layer V pyramidal cell dendrites in aging rats was quantified using Golgi impregnations. Both dendritic branching and dendritic spines from the basilar tree of randomly selected pyramidal neurons of the frontal cortex were evaluated in young control (4-month-old) Fischer 344 rats, in old controls (24-month-old), and in 24-month-old rats administered NGF for 4 weeks. Sholl analysis of basilar dendritic trees showed that neuronal branching in older rats was significantly greater than that in young rats (probably due to compensatory dendritic hypertrophy). The extent of dendritic material in aged rats receiving NGF, however, was identical to that in young rats, that is, the dendritic tree had regressed in size. Dendritic spine response to NGF treatment depended on the region of the dendritic tree sampled. Normal aging resulted in spine loss. However, NGF treatment restored dendritic spine densities to those seen in young controls on terminal tip segments ("plastic" regions). Internal branch segments ("nonplastic" regions) showed no response to NGF. As dendritic spines are thought to represent the neuroanatomic basis of learning and memory, results suggest that NGF can influence the morphology of cortical neurons (probably indirectly via the basal forebrain projections) and therefore may play an efficacious role in the treatment of geriatric cognitive dysfunction and even perhaps in Alzheimer's disease.

Changes in the basal dendrites of cortical pyramidal cells from alcoholic patients--a quantitative Golgi study

Although a variety of pathological changes have been described in the brains of chronic alcoholic patients, there have been no studies which have addressed the question of alterations in cortical neuronal dendritic arborisation. Loss of neurons from the superior frontal gyrus and shrinkage of neurons from both the superior frontal gyrus and motor cortex has been documented in chronic alcoholic patients; these areas were chosen for this study. Using a modified rapid Golgi technique the basal dendritic arborisation of layer III pyramidal neurons was compared in 15 male alcoholic patients and 15 age-matched male controls. All parameters measuring basal dendritic arborisation were significantly less in the alcoholic cases for both the superior frontal and motor cortices. Changes in the arbor are in the terminal branches, which is consistent with other models of dendritic plasticity. Such changes may explain both permanent and reversible functional deficits in chronic alcoholic patients.

Distribution of calcium-activated protease calpain in the rat brain

Calpain is a calcium-activated neutral protease that degrades a number of cytoskeletal proteins. It may participate in the maintenance of the cytoskeleton and in the rapid turnover of structural proteins associated with synaptic plasticity. Calpain may also be involved in the neurodegeneration that accompanies aging and age-related diseases. To aid in the interpretation of disease-related alterations in staining patterns, the present study examined calpain's normal distribution in the mammalian brain and spinal cord. A monoclonal antibody was employed with the avidin-biotin-peroxidase immunocytochemical technique on samples of rat tissue. Glia (astrocytes, microglia) and virtually all neurons were immunopositive, although neuronal processes exhibited varying staining patterns. The axonal staining pattern depended upon either the origin or destination of the process: those axons remaining within the brain (e.g., corpus callosum) were only lightly immunoreactive, whereas spinal cord and peripheral axons (trigeminal nerve) were more darkly labeled. The architecture of the dendritic tree determined the dendritic staining pattern: neurons with prominent apical and basal dendritic trees (e.g., pyramidal cells) were immunolabeled along their entire extent; labeling of multipolar cells (e.g., hilar cells of dentate gyrus) was limited to the proximal dendrites. The ubiquitous distribution of calpain argues against a primary role for the enzyme in the regional pattern of neuronal death seen in Alzheimer's disease. An alteration in the concentration, localization, or inhibition of the enzyme could, however, lead to the abnormal accumulations of cytoskeletal elements seen with the disease.

Dietary restriction suppresses age-related changes in dendritic spines

The effects of dietary restriction by every-other-day (EOD) feeding on dendritic spines in the aging rat neocortex were evaluated in Golgi preparations. After weaning, male Wistar rats were offered a 24% protein diet either ad lib (AL) or EOD. AL-fed groups were sacrificed at 6 and 24-25 months of age. EOD-fed groups were sacrificed at 6, 24, and 30 months. To assess the effects of EOD feeding late in life, another group was fed AL for 19 months, then EOD for 5 months and sacrificed when 24 months old. Spine density and configuration were quantified along 20 microns terminal tip segments from the basilar tree of layer V pyramidal cells of the parietal cortex. Evaluation of spine densities from the 6 and 24 months AL-fed groups showed that there was a significant loss of spines with normal aging (-38%). In EOD-fed rats, spine density did not differ significantly from AL age-matched controls at either 6 or 24 months of age. However, spine densities in 24-month-old rats diet restricted late in life and EOD-fed 30-month-old rats were the same as 6-month-old AL-fed controls and EOD 6-month-old rats, an observation suggesting protection of dendritic spines from age-related loss. Spines were categorized as either L-type (lollipop-shaped), which are more prevalent in young adults, or N-type (nubbin). With normal aging (comparing 6- and 24-month-old AL-fed groups) there was a significant decrease in L-type spines. However, all dietarily restricted groups showed retention of L-type spines.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of aging on body systems of the dog

A common property of all aging systems is that of progressive and irreversible change, which may be hastened by the effects of disease, stress, nutrition, exercise, genetics, and environment. Current knowledge and technology provide increasing opportunity to effect change and improvement in the pursuit of health, longevity, and enhanced quality of animal life. Older animals seldom have a single disease, but rather each one represents a unique combination of varying levels of loss of function at both the cellular and systems level. Veterinarians should not accept that poor health and old age are inevitable companions. Knowledge of the common pathologic changes associated with age and their effect on function allows the clinician to plan more effectively and manage health care programs.

Cerebral aging: a quantitative study of gliosis in old nude mice

Morphometric glial fibrillary acidic protein (GFAP) studies of the brains of 11 old (18-29 months) female, outbred athymic mice demonstrated astrocytic gliosis (increase in GFAP-positive astrocytes; GFAP-PA) in all mice with a consistent distribution pattern. Specific areas such as the central white matter, hippocampus, diencephalon, gray matter at the floor of the 4th ventricle, and posterior colliculi showed the change most conspicuously, revealing GFAP-PA both interstitially and perivascularly. There was no apparent demyelination in the affected white matter. In addition, there was an increase in GFAP-PA in the external limiting membrane surrounding the diencephalon and base of brain stem, but only to a minor degree over the cerebral hemispheres. The cerebral and cerebellar cortices and hypothalamus showed no significant increase. In contrast, all of the 2-month-old control animals showed only minor amounts of GFAP-PA, seen in the external limiting membrane and a trace in the cerebral white matter. The present data suggest that astroglial sclerotic change in various regions of the brain is an important morphological expression of cerebral aging. In view of the lack of other demonstrable histological changes (i.e., silver and amyloid stains were negative) or significant atrophy, the cause of the observed gliosis in BALB/c mice might represent a genuine aging change. As an incidental finding, aggregates of PAS-positive granules were noted in the Ammon's horn of most old animals, while none were seen in the young controls.

Effects of chronic choline and lecithin on mouse hippocampal dendritic spine density

Dendritic spines, which project from the dendrites of central neurons, are thought to contribute to the amount of contact area available for synaptic connections. The density of these spines has been found to correlate with learning and memory function, and there is a progressive decrease in dendritic spine density with aging. In addition, experimental animals given a choline-enriched diet have an increase in neocortical spine density compared to controls. In this study, the dendritic spine density of hippocampal pyramidal cells was examined in aged mice which had received life-long choline enriched, choline deficient or lecithin enriched diets. These treatments had no effect on hippocampal dendritic spine density compared to control. The results indicate that dietary supplementation may have different effects in different brain areas and that the relative increase in learning and memory function in aged animals given a choline or lecithin enriched diet is not due to an increase in hippocampal dendritic spine density.

Dendritic spine loss in hippocampus of aged rats. Effect of brain phosphatidylserine administration

Dendritic spine density of pyramidal cells in region CA1 of the hippocampus has been evaluated in young (3 months), old (27 months) and old phosphatidylserine (BC-PS)-treated rats. BC-PS (50 mg/kg, suspended in tap water) was administered daily, starting at the age of 3 months until 27 months. Spine density was analyzed on Golgi-stained pyramidal neurons by a computerized analysis system. In 27-month-old rats, spine density showed with respect to 3-month-old animals, a significant decrease in both basal and apical dendrites (p less than 0.01; one-way ANOVA), with a mean loss of 12.11% in the basal dendrites and of 10.64% in the apical ones. In 27-month-old rats treated with BC-PS, values of spine density were not statistically different when compared to those of 3-month-old animals. The mechanisms underlying the beneficial effect of BC-PS treatment on neuronal connectivity might be explained on the basis of its pharmacological actions on neuronal membranes [9], neurotransmission [43] and/or interaction with NGF [7].

Dendritic extent in human dentate gyrus granule cells in normal aging and senile dementia

Granule cells of the hippocampal dentate gyrus of 22 human brains obtained at autopsy were studied in Golgi-Cox stained tissue. Seventeen cases were cognitively normal and ranged from 43 to 95 years of age. Five cases had a progressive, dementing disease consistent with the diagnosis of senile dementia (SD) of the Alzheimer's type. Dendritic extent of granule cells was found to increase in normal aging between middle age (fifties) and early old age (seventies). However, dendritic regression was found in the oldest old (nineties). This finding of dendritic regression following growth is in contrast to previous quantitative reports of continued dendritic growth in parahippocampal gyrus of normal aging human brain and suggests that changes in dendritic extent in normal aging are region and age specific. In cases with SD, dendritic extent was greatly reduced when compared with the normal cases of the same age (seventies) and slightly reduced when compared with middle-aged cases. The very old normal and SD cases were similar in dendritic extent, suggesting that the functional and memory deficits characteristic of SD cannot be explained solely on the basis of the static status of dendritic extent of single neurons.

Dendritic changes in the basal nucleus of Meynert and in the diagonal band nucleus in Alzheimer's disease--a quantitative Golgi investigation

Golgi-impregnated reticular neurons and multipolar giant neurons, the two main classes of neurons in the basal nucleus of Meynert and in the diagonal band nucleus, were investigated morphometrically in five cases of Alzheimer's disease, and compared to controls. Both degenerative as well as regenerative neuronal changes were observed in cases of Alzheimer's disease. Degenerative changes such as irregular swellings and the fragmentation of dendrites are most pronounced on reticular neurons but can also be detected to a lesser extent on multipolar giant neurons. Regenerative changes are restricted to reticular neurons. They are characterized by the appearance of perisomatic filopodia, by an increase in the size of cell soma, by an increase in the degree of dendritic arborization and spatial extension of the dendritic tree. These regenerative changes are probably signs of a compensatory mechanism which might be induced by degeneration in this area.

Quantitative morphology of medium-sized caudate spiny neurons in aged cats

These studies were designed to assess some of the morphological alterations that occur in medium-sized spiny neurons of the caudate nucleus in aged cats. Computer assistance was used to quantify in three dimensions the extent of the dendritic trees of 164 neurons from 11 cats (5 1-3 years and 6 over 10 years of age) stained by the rapid Golgi technique. In all animals beyond 10 years of age there was a decrease in the density of spines on distal dendritic segments. This decrease was moderate (16%) in 13 year old cats and reached about 50% in 15 and 18 year old animals. In addition, there was an increase in the frequency of occurrence of spines with enlarged heads in all aged cats. In cats over 13 years there was a marked loss of portions of distal dendritic segments. All measures of dendrite length displayed statistically significant decreases of 30-40% in cats 15 and 18 years of age. There were no significant age-related alterations in numbers of dendrites, number of branches per dendrite or soma diameter. These morphological results indicate that there is a sequence of age-related changes that occurs in caudate medium-sized spiny neurons and provides a basis from which to assess functional alterations.

Age-related dendritic growth in dentate gyrus of human brain is followed by regression in the 'oldest old'

Dendritic extent in dentate gyrus granule cells of normal aging human brain was found to increase between middle age (fifties) and early old age (seventies). However, dendritic regression was found in the oldest old (nineties). This finding of dendritic regression following growth is in contrast to previous quantitative reports of continued dendritic growth in parahippocampal gyrus of aging human brain. This new result reinforces the concept of age and region specificity in changes in dendritic extent.

Morphologic and functional abnormalities that develop in kitten Purkinje neurons during maintenance for months after maturation in organotypic cultures

The morphologic and functional properties of the Purkinje cells (P-cells) grown for 10-11 weeks in organotypic cultures from newborn kitten cerebella were studied and compared to cultures which had been grown for 4-5 weeks under the same standard conditions. Electrophysiological and morphological data were obtained from HRP iontophoretically labeled neurons and were quantified by means of computerized techniques. Extracellular recordings of spontaneous activity showed that the 10-11-week-old P-cells had a pacemaker-like firing rate whereas the P-cells aged 4-5 weeks in vitro displayed a bursting activity. The qualitative morphological data evidenced abnormal swellings both on dendritic and axonal processes of the 10-11-week-old P-cells which were not present on the 4-5-week-old P-cells. The quantitative data revealed a significant decrease in the overall size of the dendritic network of the 10-11-week-old P-cells mainly due to a reduction in the total dendritic length and in the total number of dendritic segments, whereas the individual segment lengths remained almost unchanged. Dendritic spine counts showed no decrease in the dendritic density of these older P-cells. Such data suggest that the changes observed in 10-11-week-old cultured P-cells may be compared to the age-related changes occurring in vivo and that such in vitro models could be useful tools in the study of the pathology of aging. However, alternative factors other than senescence are discussed since they may account for some degenerative changes observed in the older cultured P-cells.

Age-related changes in the subiculum of Macaca mulatta: dendritic branching pattern

The dendritic branching pattern was studied in the subiculum of nine Macaca mulatta from 7 to 28 years of age. Morphometric analysis of pyramidal neurons revealed significant age-related differences at various designated branch orders in both the centrifugal and centripetal ordering methods. There was continued branching and growth of the apical dendrites in adulthood. Basal dendrites did not show any added complexity, but rather showed continued growth of existing terminal branches. The three oldest animals showed a preferential loss of whole terminal branches on the apical portion of the dendritic tree, whereas shortening of existing terminal branches was the characteristic feature of the basal dendrites. Data obtained from the subiculum provide quantitative evidence indicating the considerable potential for dendritic plasticity beyond the early developmental stages and eventual loss of dendritic complexity in the old M. mulatta.

Age-related changes of pyramidal cell basal dendrites in layers III and V of human motor cortex: a quantitative Golgi study

Age-related changes of pyramidal cell basal dendrites in layers III and V of human motor cortex (area 4) were analyzed quantitatively in Golgi-impregnated sections by Sholl's method of concentric circles (Sholl 1953). The present data suggested that basal dendrites of the pyramidal cells were decreased in number with advancing age, and that the decrease was more prominent in basal dendrites of layer V pyramidal cells than in those of layer III pyramidal cells.

Dendritic caliber and the 3/2 power relationship of dentate granule cells

A quantitative examination of granule cell dendritic caliber and knowledge of dendritic lengths allows assessment of the distribution of dendritic membrane and the 3/2 power relationship at branch points. This paper presents caliber data of Golgi-impregnated rat dentate gyrus. We used camera lucida drawings of the dendritic trees of 15 dorsal leaf and 15 ventral leaf granule cells to quantify mean dendritic caliber, dendritic taper, the 3/2 power relationship of parent and sibling dendritic diameters at branch points, and surface area. First-order dendrites vary substantially in diameter. However, the mean caliber of all other dendrites is uniform across the proximal two-thirds of the molecular layer for the dorsal and ventral leaves. The average diameter here is 1 micron. More distally, only mean ventral leaf dendritic caliber declines. Granule cell dendritic taper is due primarily to caliber decreases at branch points and not to a gradual decline in diameter across the length of a dendritic segment. Comparing the parent segment diameter raised to the 3/2 power with the sum of the 3/2 powers of the two sibling segment diameters reveals, for the dendritic tree located within the distal two-thirds of the molecular layer, the desired 3/2 power relationship for the dorsal and ventral leaves. More proximally, where first-, second-, and third-order dendrites branch sequentially across a 60-100-micron extent, a 3/2 power relationship is not obtained. For the average dorsal leaf granule cell, dendritic surface area (without spines) is 11,984 micron2. The ratio of dendritic to somatic surface area is 28:1. Discussion of these data includes their implications for electrotonic modeling of the dentate granule cell.

Aging of dendrites in the cerebral cortex of the mouse

Quantitative analysis of the dendritic branchings of pyramidal cells in layers V and III of the visual cortex was performed in aging mice (540 and 720 days) and compared to adult mice (180 days). The number of spines on apical dendrites of the same cells was also counted. Between 180 and 720 days of age, the decrease in dendritic branchings around the perikaryon was dramatic (30-40%) and that in dendritic spines was even more so (about 50%). However, most of the decrease in both dendritic branchings and spines has already occurred at 540 days, and the difference between 540 and 720 days was not statistically significant. This suggests a real loss in cortical connections with aging, taking place prior to the final months of the lifespan of the mouse.

Recovery of function after brain damage: differences in aged rats?

Age at the time of brain injury is generally considered an important determinant in recovery of function. The implication is that older individuals show less recovery. Existing data challenge this common notion, but suggest differential effects of brain damage in aged subjects. To assess these differences old rats were trained on a two-choice brightness discrimination, subjected to visual decortication, and retrained with nonreversed or reversed reinforcement contingencies. A significant reversal impairment established that sparing of function in aged rats was similar to that in adult rats. However, a significant reversal X brightness interaction suggested that the progress of recovery of function in aged rats is influenced not only by what is spared but also by whether the expression of what is spared is consistent with or antagonistic to competing innate response biases.

Neuritic plaques in senile dementia of Alzheimer type: a Golgi analysis in the hippocampal region

Tissue sections from the hippocampal region of patients with senile dementia of Alzheimer type were examined in 75-100 microns thick vibratome sections impregnated by the Golgi-Cox method and counterstained with cresyl violet. The morphology of dendrites and axons with neuritic plaques was frequently abnormal. Abnormalities included pleomorphic outpouchings of terminal and preterminal dendritic and axonal segments, many of which contained filiform processes occurring singly and in tufts. The axon collaterals of some hippocampal neurons appeared to branch richly as they entered plaques. Impregnated neurites could occasionally be traced from a neuritic plaque to adjacent pyramidal and local circuit neurons. The findings confirm that local neurons of different types contribute dendrites and axons to plaques and that these processes may proliferate within the confines of the plaques.

Regional cerebral metabolic rate for glucose in beagle dogs of different ages

Regional cerebral metabolic rates for glucose (rCMRglc) were studied in unanesthetized Beagle dogs in five age groups. Significant age-related differences did not occur in the cingulate, pyriform or visual cortices, cerebellar flocculus, corpus callosum, or cerebellar white matter. However, age-related decrements were apparent in 15 of the 22 brain regions examined. The apparent time course of age effect on rCMRglc varied among the brain regions. Most regions had significantly lower rCMRglc at 6 years than at 1 year. Decrements of more than 25% were seen in the mammillary bodies, pons, hippocampus, superior colliculus, basis of the midbrain, temporal cortex, geniculate bodies, caudate nucleus, and superior frontal gyrus. There were no age differences in rCMRglc at 10-12 years compared with 6 years. Senescence-associated decrements (after 6 years) were noted in only 5 regions: the frontal and temporal cortices, mammillary bodies, and areas involved in sensory functions. The results indicate that rCMRglc in the adult Beagle brain declines by midlife, and continues to decline in some brain regions through senescence.

Chronic exposure to caffeine during early development increases dendritic spine and branch formation in midbrain optic tectum

Sibling juvenile jewel fish were chronically exposed to caffeine solution (14 mg/l) between 50 and 100 days after fertilization. Some experimental animals were sacrificed at this time, together with control siblings reared without drugs; others were allowed to recover in the absence of caffeine for 18 months. Golgi-stained preparations showed increased formation of dendritic spines on apical stem dendrites of pyriform tectal neurons in juveniles exposed to caffeine. Adults showed minimal effects on the stem dendrite, but caffeine adults formed more primary dendritic branches and more spines on branches than controls did. This study demonstrates the facilitation of neuronal growth and complexity by chronic administration of a chemical agent commonly present during early development in humans.

A comparison of dendritic spine number and type on pyramidal neurons of the visual cortex of old adult rats from social or isolated environments

The present study determined the effect of the housing condition experienced by old adult male rats on the appearance and number of dendritic spines. Specifically, 20-month-old rats were killed following 6 months of living in either a social environment (three to a cage) or living alone. The total number of dendritic spines per unit length was examined along segments of oblique, basal, and apical dendritic branches of pyramidal cells from layers II, III, Va, and Vb of the visual cortex. In addition to determining the total spine number, the spines were differentiated into two topographical categories: those with a lollipop configuration (type L) and those with a nubbin configuration (type N). Our results show that neither the total spine density nor the type L spine density were generally influenced by the two housing conditions. However, the density of type N spines was almost always greater on neurons from rats which had been living alone irrespective of the cortical layer or the dendritic segment counted. Some differences in total spine density and type L spine density were noted when neurons from the same environment but different cortical layers were compared, and these findings are discussed. However, the major focus of this paper was to extend our previous report of a selective increase in type N spines with age. We now show that in addition to increasing with age, type N spine density is also selectively increased by the condition of social deprivation.

Early development of spiny neurons in fish and mouse: morphometric measures of dendritic spine formation pattern

Positions of spines on apical dendrites were evaluated using 4 pattern analysis techniques: spine counts, variance/mean ratio, Lloyd's patchiness index, and nearest neighbor distance matrix. Spiny tectal interneurons from jewel fish (100, 130, 160 and 1550 days old), and layer V pyramidal cells in layer IV auditory cortex of CBA/J mice (100 and 450 days old) were studied. Fish's spines became more numerous and more clumped on distal dendritic strata during development, while mice lost dendritic spines with age. Both species developed a significantly regular spacing pattern between neighboring spines during development. These changes are explained in the context of spine function and a biophysical model of dendritic spine patterns.

Brain metabolism and blood flow during development and aging of the Fischer-344 rat

In cerebral cortical regions of the conscious Fischer-344 rat, regional cerebral blood flow (rCBF) as measured with 14C-indoantipyrine, and the cerebral metabolic rate for O2(CMRO2) do not decline after 3 months of age. On the other hand, the regional cerebral metabolic rate for glucose (rCMRglc) as measured with 14C-2-deoxy-D-glucose, falls significantly in some but not all cerebral cortical regions after 3 months. More generally, rCBF and rCMRglc do not follow identical courses during development and aging of the rat brain, although they remain stoichiometrically coupled among specific regions at any given age. Between 1 and 3 months, both increase in most brain regions, but after 3 months of age rCMRglc tends to fall throughout the brain, whereas rCBF tends to rise or remain unchanged in cerebral cortical regions, and falls after 12 months in posterior brain regions. The courses of rCBF, rCMRglc and CMRO2 during development and aging of the rat brain indicate that (a) stoichiometric coupling between flow and metabolism is maintained between 1 and 34 months of age, (b) the calculated coupling relation between rCBF and rCMRglc changes with age, possibly because rCBF increasingly sensitive to metabolism or because "constants" are employed to calculate rCMRglc or rCBF change with aging, and (c) cerebral cortical oxidative metabolism does not generally decline after 1 year of age. This constantly suggests that plasticity responses in the cerebral cortex of the rat compensate for senescence-associated morphological and neurochemical defects so as to preserve resting cortical functional activity.

Quantitative evidence for selective dendritic growth in normal human aging but not in senile dementia

Parahippocampal gyrus was sampled from human brains at autopsy to form three groups: adult (n = 5, mean age 51.2 years), normal aged (n = 5, mean age 79.6), and senile dementia (SD) (n = 5, mean age 76.0). Classification as normal aged or senile demented was based on both behavioral and neuropathological criteria. Tissue was processed for Golgi-Cox, cresyl violet, hematoxylin and eosin and Bodian silver stains. Both atrophied and normal dendritic trees were seen in all cases. Dendrites of layer II pyramidal neurons were quantified with a computer-microscope system. Quantitative data showed that normal aged individuals had longer and more branched dendrites than either adult or SD individuals. There was a slight tendency for SD individuals to have shorter, less-branched dendrites than adults. Differences among groups were greater in apical than in basal portions of the dendritic tree. These differences were largely accounted for by the lengthening and branching (apical dendrites) or lengthening only (basal dendrites) of terminal dendritic segments. These data suggest a model in which aging cortex contains both regressing, dying neurons and surviving, growing neurons. In normal aging it is the latter group that predominates. This is the first demonstration of plasticity in the adult human brain.

Dendritic growth in the aged human brain and failure of growth in senile dementia

Golgi-stained dendrites of single randomly chosen layer-II pyramidal neurons in the human parahippocampal gyrus were quantified with a computer-microscope system. In nondemented aged cases (average age, 79.6 years), dendritic trees were more extensive than in adult cases (average age, 51.2), with most of the difference resulting from increases in the number and average length of terminal segments of the dendritic tree. These results provide morphological evidence for plasticity in the mature and aged human brain. In senile dementia (average age, 76.0), dendritic trees were less extensive than in adult brains, largely because their terminal segments were fewer and shorter. Cells with shrunken dendritic trees were found in all brains. These data suggest a model of aging in the central nervous system in which one population of neurons dies and regresses and the other survives and grows. The latter appears to be the dominant population in aging without dementia.