Increased Number of Dorsal Root Ganglion Neurons in Vitamin-E-Deficient Rats

Quantitative and morphometric observations were carried out on neurons of L₃-L₆ dorsal root ganglia (DRGs) in control and vitamin-E-deficient rats at different ages. Controls were fed a standard diet and sacrificed at 1 or at 5 months of age; deficient rats were fed a diet without vitamin E from 1 to 5 months of age and then sacrificed. No significant difference in total number of neurons was found, but an increase in neuron sizes, a decrease in nucleus-cytoplasm ratio, and a more circular neuron shape were found in controls with increasing age (from 1 to 5 months). In L₃-L₆ DRGs of vitamin-E-deficient rats (5 months of age), a higher number of neurons was found than in those of either young or adult controls. Moreover, some morphometric characteristics of neurons in the deficient rats were similar to those of neurons in 1-month-old controls. The findings suggest that vitamin E deficiency can trigger events resulting in appearance of new neurons, possibly anticipating phenomena that normally occur in aging.     

Glial dependent survival of neurons in Drosophila

According to the classical model of insect neurogenesis, neuron fate and survival is determined largely by cell autonomous mechanisms with no requirement for cell-cell interactions to control the total number of neurons. In a recent paper by Booth et al.,(1) however, the central tenet of this model has been called into question. Using a combination of mutations and targeted glial ablation, this paper shows that, contrary to common thinking, neuron survival in the embryonic nervous system of Drosophila is dependent upon normal glial function. This surprising result suggests that insect neurogenesis may have more in common with vertebrate neurogenesis than previously thought.     

Postnatal neurogenesis in the human forebrain: from two migratory streams to dribbles

Subventricular zone neurogenesis occurs throughout life from rodents to primates, but the existence of a rostral migratory stream of immature neurons in postnatal human brains is controversial. A recent report in Nature (Sanai et?al., 2011) identifies two neuronal migratory streams in infant human brains targeting the olfactory bulb and prefrontal cortex.     

Exercise endurance-training alters vitamin E tissue levels and red-blood-cell hemolysis in rodents

Muscle tissue levels of dl--tocopherol (vitamin E) were significantly lower in endurance-trained rats than in sedentary animals, whether the animals were fed on vitamin-E-deficient or control (vitamin-E-sufficient) diets. In vitamin-E-deficient rats, liver tissue levels of vitamin E were significantly lower in those that were endurance-trained than in those that were sedentary; this was not the case in control animals. In addition, for vitamin-E-deficient rats, the onset of red-blood-cell hemolysis in the sedentary animals occurred one week earlier than in the endurance-trained animals. Thus, it appears that training induces a protective effect against hemolysis despite vitamin E deficiency.     

Age-Dependent Neuroplasticity Mechanisms in Alzheimer Tg2576 Mice Following Modulation of Brain Amyloid-β Levels

The objective of this study was to investigate the effects of modulating brain amyloid-β (Aβ) levels at different stages of amyloid pathology on synaptic function, inflammatory cell changes and hippocampal neurogenesis, i.e. processes perturbed in Alzheimer’s disease (AD). Young (4- to 6-month-old) and older (15- to 18-month-old) APP_SWE transgenic (Tg2576) mice were treated with the AD candidate drug (+)-phenserine for 16 consecutive days. We found significant reductions in insoluble Aβ1-42 levels in the cortices of both young and older transgenic mice, while significant reductions in soluble Aβ1-42 levels and insoluble Aβ1-40 levels were only found in animals aged 15–18 months. Autoradiography binding with the amyloid ligand Pittsburgh Compound B (³H-PIB) revealed a trend for reduced fibrillar Aβ deposition in the brains of older phenserine-treated Tg2576 mice. Phenserine treatment increased cortical synaptophysin levels in younger mice, while decreased interleukin-1β and increased monocyte chemoattractant protein-1 and tumor necrosis factor-alpha levels were detected in the cortices of older mice. The reduction in Aβ1-42 levels was associated with an increased number of bromodeoxyuridine-positive proliferating cells in the hippocampi of both young and older Tg2576 mice. To determine whether the increased cell proliferation was accompanied by increased neuronal production, the endogenous early neuronal marker doublecortin (DCX) was examined in the dentate gyrus (DG) using immunohistochemical detection. Although no changes in the total number of DCX⁺-expressing neurons were detected in the DG in Tg2576 mice at either age following (+)-phenserine treatment, dendritic arborization was increased in differentiating neurons in young Tg2576 mice. Collectively, these findings indicate that reducing Aβ1-42 levels in Tg2576 mice at an early pathological stage affects synaptic function by modulating the maturation and plasticity of newborn neurons in the brain. In contrast, lowering Aβ levels in Tg2576 mice when Aβ plaque pathology is prominent mainly alters the levels of proinflammatory cytokines and chemokines.     

Hormones,neuroblasts and the adult insect

Insect neurogenesis has been subjected to extensive study and as a result is regarded as being well understood. It is, therefore, all the more surprising when a fundamentally novel aspects of the process is uncovered. Until recently it was thought that the production of central neurons ceased before the emergence of the adult. Recently, however, Cayre et al. have shown that neurogenesis also occurs in the adult brain. Their studies also show that the rate at which adult neuroblasts divide is controlled by hormones, suggesting that hormones may play a more important role in regulating neurogenesis than previously suspected.     

The pentylenetetrazole-kindling model of epilepsy in SAMP8 mice: glial-neuronal metabolic interactions

Recently, a new experimental model of epilepsy was introduced by the authors [Neurochem. Int. 40 (2002) 413]. This model combines pentylenetetrazole (PTZ)-kindling in senescence-accelerated mice P8 (SAMP8), a genetic model of aging. Since imbalance of glutamate and GABA is a major cause of seizures, the study of glial–neuronal interactions is of primary importance. Nuclear magnetic resonance spectroscopy (NMRS) is an excellent tool for metabolic studies. Thus, we examined whether NMRS when combined with administration of [1-¹³C]glucose and [1,2-¹³C]acetate might give valuable insights into neurotransmitter metabolism in this new model of epilepsy and aging. The 2- and 8-month-old SAMP8 were kindled with PTZ alone, received PTZ and phenobarbital (PB), or served as controls. In older animals, PTZ-kindling decreased labeling in glutamate C-4 from [1-¹³C]glucose, whereas, in the younger mice, labeling in glutamine C-4 was decreased both from [1-¹³C]glucose and [1,2-¹³C]acetate. It could be concluded that PTZ-kindling affected astrocytes in younger and glutamatergic neurons in older animals. In the presence of PTZ, phenobarbital decreased labeling of most metabolites in all cell types, except GABAergic neurons, from both labeled precursors in the younger animals. However, in older animals only GABAergic neurons were affected by phenobarbital as indicated by an increase in GABA labeling.     

Neurogenesis in the aged and neurodegenerative brain

It has been well established that adult neurogenesis occurs throughout life in the subventricular (SVZ) and subgranular (SGZ) zones. However, the exact role of this type of brain plasticity is not yet clear. Many studies have shown that neurogenesis is involved in learning and memory. This has led to a hypothesis which suggests that impairment in memory during aging and neurodegenerative diseases such as Alzheimer’s disease (AD) may involve abnormal neurogenesis. Indeed, during aging, there is an age-related decline in adult neurogenesis. This decline is mostly related to decreased proliferation, associated to decreased stimulation to proliferate in an aging brain. In AD, there is also evidence for decreased neurogenesis, that accompanies the neuronal loss characteristic of the disease. Interestingly in AD, there is increased proliferation, that may be caused by increasing amounts of soluble amyloid ß42-protein (Aβ₄₂). However, most of these new neurons die, and fibrillar Aβ₄₂ seems to be involved in generating an inappropriate environment for these neurons to mature. These findings open prospects for new strategies that can increase neurogenesis in normal or pathological processes in the aging brain, and by that decrease memory deficits.     

Facts and fictions regarding post-natal neurogenesis in the developing human cerebral cortex.

In a recent paper (Shankle et al., 1998a), post-natal neurogenesis in the human cerebral cortex was discussed. Based on re-calculations of morphometric data from the literature, the authors concluded an average 1.1% monthly increase in post-natal cortical neuron number between post-natal months 15-72. The present paper makes clear by discussing four main assumptions done by Shankle et al., i.e. shrinkage of the tissue, morphometric features of the neurons under study, conversion of cell densities per area to number per unit volume and estimation of coefficients of variation, that their final conclusion about an increase in neuron number is unsound. Furthermore, five points are discussed here that Shankle et al. had mentioned in order to demonstrate that the pulse thymidine labeling method is less reliable than some have assumed. The present paper refute these assumptions point by point. Thus, the Shankle et al. paper does not provide scientifically valid evidence of a post-natal neurogenesis in the developing human cerebral cortex.     

Absence of neurogenesis of adult rat dorsal root ganglion cells

Recently, an age-related increase in the number of dorsal root ganglion (DRG) cells was reported in adult rats. This suggests neurogenesis of adult primary afferent neurons, which would be an extremely important phenomenon if it occurred. Other evidence is not compatible with this idea, however, so the issue is not settled. The primary point of contention concerns the counts of DRG cells in relation to age. In our opinion, these disagreements arise, at least in part, because different counting methods give different results for the same material. Thus, any method for determining DRG cell numbers should be calibrated. We previously calibrated some of the common methods used to count DRG cells and found that an empirical method gave accurate cell counts. In the present study, we have used this method and asked whether an age-related increase in the number of lumbar DRG cells can be demonstrated in adult rats. Our data indicate that DRG cell numbers remain essentially constant from 3 to 22 months of age. Most ancillary evidence is consistent with the hypothesis that mammalian DRG cell numbers do not change during adult life. Thus, we feel that the evidence does not support the hypothesis that there is neurogenesis of adult rat primary afferent neurons.     

Altered expression of P2X3 in vagal and spinal afferents following esophagitis in rats

Purinergic P2X₃ receptors are predominantly expressed in small diameter primary afferent neurons and activation of these receptors by adenosine triphosphate is reported to play an important role in nociceptive signaling. The objective of this study was to investigate the expression of P2X₃ receptors in spinal and vagal sensory neurons and esophageal tissues following esophagitis in rats. Two groups of rats were used including 7 days fundus-ligated (7D-ligated) esophagitis and sham-operated controls. Esophagitis was produced by ligating the fundus and partial obstruction of pylorus that initiated reflux of gastric contents. The sham-operated rats underwent midline incision without surgical manipulation of the stomach. Expressions of P2X₃ receptors in thoracic dorsal root ganglia (DRGs), nodose ganglia (NGs), and esophageal tissues were evaluated by RT–PCR, western blot and immunohistochemistry. Esophageal neurons were identified by retrograde transport of Fast Blue from the esophagus. There were no significant differences in P2X₃ mRNA expressions in DRGs (T1–T3) and NGs between 7D-ligated and sham-operated rats. However, there was an upregulation of P2X₃ mRNA in DRGs (T6–T12) and in the esophageal muscle. At protein level, P2X₃ exhibited significant upregulation both in DRGs and in NGs of rats having chronic esophagitis. Immunohistochemical analysis exhibited a significant increase in P2X₃ and TRPV1 co-expression in DRGs and NGs in 7D-ligated rats compared to sham-operated rats. The present findings suggest that chronic esophagitis results in upregulation of P2X₃ and its co-localization with TRPV1 receptor in vagal and spinal afferents. Changes in P2X₃ expression in vagal and spinal sensory neurons may contribute to esophageal hypersensitivity following acid reflux-induced esophagitis.     

Amitriptyline reduces olfactory neuron adenylyl cyclase activity

Adenylyl cyclase plays an important role in olfactory signaltransduction. Recently, a novel type III adenylyl cyclase hasbeen localized in olfactory neurons (Pfeuffer et al., 1989;Bakalyar and Reed, 1990). Because amitriptyline (AMI), a tricyclicantidepressant, appears to have an inhibitory effect on adenylylcyclase activity in other in other neuronal tissue (Yamaokaet al., 1988; Wong et al., 1991), we measured the effect ofAMI on forskolin-stimulated adenylyl cyclase activity in membranepreparations of olfactory mucosa from adult rats. In the presenceof 5'-guanylyl-imidodiphosphate, AMI (0.5–8.0 µM)inhibited forskolin-stimulated adenylyl cyclase activity ina dose-dependent manner. To determine whether this effect wasspecific for olfactory neurons, as opposed to other cells inthe olfactory epithelium, rats were unilaterally bulbectomizedin order to reduce selectively the number of olfactory neuronson the side ipsilateral to the bulbectomy. In membrane preparationsfrom unilaterally bulbectomized animals we saw significantlylower adenylyl cyclase activity in ipsilateral olfactory mucosa,compared with adenylyl cyclase activity from non-bulbectomizedmucosa. These results indicate that AMI inhibition of adenylylcyclase activity is primariy localized in olfactory neurons.     

Morphological manifestations of compensatory-adaptive processes in the liver during aging

Light and electron microscopy and morphometry revealed an age-related increase in the average size of hepatocytes and their nuclei in 24- and 30-month-old rats compared to 8-month-old animals, the density of hepatocytes distribution per area unit being decreased. In 24-month-old rats the number of binuclear hepatocytes increased with a subsequent decrease in their number in 30-month-old animals, which accounted for the shift in regeneration processes during ageing to predominantly intracellular one. The number of sinusoidal cells per area unit in three age groups was statistically similar. The results of morphometry and electron microscopy suggest that the compensatory-adaptive processes during hepatocyte ageing were mediated by intracellular regeneration, which led to cellular and nuclear hypertrophy similar to that observed in cells of static population (neurons, cardiomyocytes).     

Does senile impairment of cholinergic system in rats concern only disturbances in cholinergic phenotype or the progressive degeneration of neuronal cell bodies?

The trophic effect of continuous intraventricular infusion of nerve growth factor (NGF) on morphology of the basal forebrain (BF) cholinergic neurons was tested in 4- and 28-month-old male Wistar rats. All studies were conducted using behaviorally uncharacterized animals from the same breeding colony. Immunohistochemical procedure for choline acetyltransferase (ChAT) and p75NTR receptor has been applied to identify cholinergic cells in the structures of basal forebrain (BF). Using a quantitative image analyzer, morphometric and densitometric parameters of ChAT- and p75NTR-positive cells were measured immediately after cessation of NGF infusion. In 28-month-old non-treated rats the number of intensively ChAT-positive cells in all forebrain structures was reduced by 50-70% as compared with young animals. The remaining ChAT-positive cells appeared shrunken and the neuropil staining was NTR markedly reduced. In contrast, the same neurons when stained for p75 were numerous and distinctly visible with perfect morphology. Analysis of Nissl stained sections also showed that 28-month-old rats did not display significant losses of neuronal cell bodies. NGF restored the number of intensely stained ChAT-positive cells to about 90% of that for young controls and caused a significant increase in size of those cells in 28-month-old rats as compared with the control, age-matched group. NGF did not influence the morphology of p75NTR-positive neurons, which were well labeled, irrespective of treatment and age of the rats. In 4-month-old rats, NGF infusion decreased the intensity of both ChAT and p75NTR immunostaining. These data provide some evidence for preservation of BF cholinergic neurons from atrophy during aging and indicate that senile impairment of the cholinergic system in rats concerns decrease in ChAT-protein expression rather than an acute degeneration of neuronal cell bodies. Treatment with NGF resulted in restoration of cholinergic phenotype in the BF neurons of aged rats. However, the present study also rises issue of possible detrimental effects of NGF in young normal animals.     

Circadian control of neurogenesis

The life-long addition of new neurons has been documented in many regions of the vertebrate and invertebrate brain, including the hippocampus of mammals (Altman and Das, 1965; Eriksson et al., 1998; Jacobs et al., 2000), song control nuclei of birds (Alvarez-Buylla et al., 1990), and olfactory pathway of rodents (Lois and Alvarez-Buylla, 1994), insects (Cayre et al., 1996) and crustaceans (Harzsch and Dawirs, 1996; Sandeman et al., 1998; Harzsch et al., 1999; Schmidt, 2001). The possibility of persistent neurogenesis in the neocortex of primates is also being widely discussed (Gould et al., 1999; Kornack and Rakic, 2001). In these systems, an effort is underway to understand the regulatory mechanisms that control the timing and rate of neurogenesis. Hormonal cycles (Rasika et al., 1994; Harrison et al., 2001), serotonin (Gould, 1999; Brezun and Daszuta, 2000; Beltz et al., 2001), physical activity (Van Praag et al., 1999) and living conditions (Kemperman and Gage, 1999; Sandeman and Sandeman, 2000) influence the rate of neuronal proliferation and survival in a variety of organisms, suggesting that mechanisms controlling life-long neurogenesis are conserved across a range of vertebrate and invertebrate species. The present article extends these findings by demonstrating circadian control of neurogenesis. Data show a diurnal rhythm of neurogenesis among the olfactory projection neurons in the crustacean brain, with peak proliferation during the hours surrounding dusk, the most active period for lobsters. These data raise the possibility that light-controlled rhythms are a primary regulator of neuronal proliferation, and that previously-demonstrated hormonal and activity-driven influences over neurogenesis may be secondary events in a complex circadian control pathway.     

Increased number of neurons in the cervical spinal cord of aged female rats

In the brain, specific signaling pathways localized in highly organized regions called niches allow the persistence of a pool of stem and progenitor cells that generate new neurons in adulthood. Much less is known about the spinal cord where a sustained adult neurogenesis is not observed. Moreover, there is scarce information concerning cell proliferation in the adult mammalian spinal cord and virtually none in aging animals or humans. We performed a comparative morphometric and immunofluorescence study of the entire cervical region (C1-C8) in young (5 mo.) and aged (30 mo.) female rats. Serum prolactin (PRL), a neurogenic hormone, was also measured. Gross anatomy showed a significant age-related increase in size of all of the cervical segments. Morphometric analysis of cresyl violet stained segments also showed a significant increase in the area occupied by the gray matter of some cervical segments of aged rats. The most interesting finding was that both the total area occupied by neurons and the number of neurons increased significantly with age, the latter increase ranging from 16% (C6) to 34% (C2). Taking the total number of cervical neurons the age-related increase ranged from 19% (C6) to 51% (C3), C3 being the segment that grew most in length in the aged animals. Some bromodeoxyuridine positive-neuron specific enolase negative (BrdU(+)-NSE(-)) cells were observed and, occasionally, double positive (BrdU(+)-NSE(+)) cells were detected in some cervical segments of both young and aged rats groups. As expected, serum PRL increased markedly with age. We propose that in the cervical spinal cord of female rats, both maturation of pre-existing neuroblasts and/or possible neurogenesis occur during the entire life span, in a process in which PRL may play a role.     

Diabetic neuropathy: inhibitory G protein dysfunction involves PKC-dependent phosphorylation of Goalpha

We examined the hypothesis that decreased inhibitory G protein function in diabetic neuropathy is associated with increased protein kinase C (PKC)-dependent phosphorylation of the Goalpha subunit. Streptozotocin-induced diabetic rats were studied between 4 and 8 weeks after onset of diabetes and compared with aged-matched healthy animals as controls. Opioid-mediated inhibition of forskolin-stimulated cyclic AMP was significantly less in dorsal root ganglia (DRGs) from diabetic rats compared with controls. Activation of PKC in DRGs from control rats was associated with a significant decrease in opioid-mediated inhibition of forskolin-stimulated cyclic AMP that was similar to the decrease in inhibition observed in DRGs from diabetic rats. Both basal and PKC-mediated labeling of Goalpha with 32Pi was significantly less in DRGs from diabetic rats, supporting increased endogenous PKC-dependent phosphorylation of Goalpha. Probing of immunoprecipitated Goalpha with an anti-phospho-serine/threonine specific antibody revealed a significant increase in baseline phosphorylation in diabetic DRGs. Activation of PKC produced a significant increase in phosphorylation in control DRGs but no significant increase in Goalpha in diabetic DRGs. Phosphorylation of PKC-alpha was increased, PKC-betaII was unchanged and PKC-delta decreased in diabetic DRGs. These results suggest that diminished inhibitory G protein function observed in DRGs neurons from diabetic rats involves an isoform-specific PKC-dependent pathway.     

Neurogenesis and aging: FGF-2 and HB-EGF restore neurogenesis in hippocampus and subventricular zone of aged mice

Neurogenesis, which may contribute to the ability of the adult brain to function normally and adapt to disease, nevertheless declines with advancing age. Adult neurogenesis can be enhanced by administration of growth factors, but whether the aged brain remains responsive to these factors is unknown. We compared the effects of intracerebroventricular fibroblast growth factor (FGF)-2 and heparin-binding epidermal growth factor-like growth factor (HB-EGF) on neurogenesis in the hippocampal dentate subgranular zone (SGZ) and the subventricular zone (SVZ) of young adult (3-month) and aged (20-month) mice. Neurogenesis, measured by labelling with bromodeoxyuridine (BrdU) and by expression of doublecortin, was reduced by approximately 90% in SGZ and by approximately 50% in SVZ of aged mice. HB-EGF increased BrdU labelling in SGZ at 3 months by approximately 60% and at 20 months by approximately 450%, which increased the number of BrdU-labelled cells in SGZ of aged mice to approximately 25% of that in young adults. FGF-2 also stimulated BrdU labelling in SGZ, by approximately 25% at 3 months and by approximately 250% at 20 months, increasing the number of newborn neurones in older mice to approximately 20% of that in younger mice. In SVZ, HB-EGF and FGF-2 increased BrdU incorporation by approximately 140% at 3 months and approximately 170% at 20 months, so the number of BrdU-labelled cells was comparable in untreated 3-month-old and growth factor-treated 20-month-old mice. These results demonstrate that the aged brain retains the capacity to respond to exogenous growth factors with increased neurogenesis, which may have implications for the therapeutic potential of neurogenesis enhancement in age-associated neurological disorders.     

Notch1 signaling modulates neuronal progenitor activity in the subventricular zone in response to aging and focal ischemia

Neurogenesis diminishes with aging and ischemia‐induced neurogenesis also occurs, but reduced in aged brain. Currently, the cellular and molecular pathways mediating these effects remain largely unknown. Our previous study has shown that Notch1 signaling regulates neurogenesis in subventricular zone (SVZ) of young adult brain after focal ischemia, but whether a similar effect occurs in aged normal and ischemic animals is unknown. Here, we used normal and ischemic aged rat brains to investigate whether Notch1 signaling was involved in the reduction of neurogenesis in response to aging and modulates neurogenesis in aged brains after focal ischemia. By Western blot, we found that Notch1 and Jagged1 expression in the SVZ of aged brain was significantly reduced compared with young adult brain. Consistently, the activated form of Notch1 (Notch intracellular domain; NICD) expression was also declined. Immunohistochemistry confirmed that expression and activation of Notch1 signaling in the SVZ of aged brain were reduced. Double or triple immunostaining showed that that Notch1 was mainly expressed in doublecortin (DCX)‐positive cells, whereas Jagged1 was predominantly expressed in astroglial cells in the SVZ of normal aged rat brain. In addition, disruption or activation of Notch1 signaling altered the number of proliferating cells labeled by bromodeoxyuridine (BrdU) and DCX in the SVZ of aged brain. Moreover, ischemia‐induced cell proliferation in the SVZ of aged brain was enhanced by activating the Notch1 pathway and was suppressed by inhibiting the Notch1 signaling. Reduced infarct volume and improved motor deficits were also observed in Notch1 activator–treated aged ischemic rats. Our data suggest that Notch1 signaling modulates the SVZ neurogenesis in aged brain in normal and ischemic conditions.     

Hippocampal neurogenesis is associated with migratory behaviour in adult but not juvenile sparrows (Zonotrichia leucophrys ssp.)

It has been hypothesized that individuals who have higher demands for spatially based behaviours should show increases in hippocampal attributes. Some avian species have been shown to use a spatially based representation of their environment during migration. Further, differences in hippocampal attributes have been shown between migratory and non-migratory subspecies as well as between individuals with and without migratory experience (juveniles versus adults). We tested whether migratory behaviour might also be associated with increased hippocampal neurogenesis, and whether potential differences track previously reported differences in hippocampal attributes between a migratory (Zonotrichia leucophrys gambelii) and non-migratory subspecies (Z. l. nuttalli) of white-crowned sparrows. We found that non-migratory adults had relatively fewer numbers of immature hippocampal neurons than adult migratory birds, while adult non-migrants had a lower density of new hippocampal neurons than adult and juvenile migratory birds and juvenile non-migratory birds. Our results suggest that neurogenesis decreases with age, as juveniles, regardless of migratory status, exhibit similar and higher levels of neurogenesis than non-migratory adults. However, our results also suggest that adult migrants may either seasonally increase or maintain neurogenesis levels comparable to those found in juveniles. Our results thus suggest that migratory behaviour in adults is associated with maintained or increased neurogenesis and the differential production of new neurons may be the mechanism underpinning changes in the hippocampal architecture between adult migratory and non-migratory birds.