Morphological alterations in the amygdala and hippocampus of mice during ageing

Melatonin as an Anti-Aging Therapy for Age-Related Cardiovascular and Neurodegenerative Diseases

The concept of “aging” is defined as the set of gradual and progressive changes in an organism that leads to an increased risk of weakness, disease, and death. This process may occur at the cellular and organ level, as well as in the entire organism of any living being. During aging, there is a decrease in biological functions and in the ability to adapt to metabolic stress. General effects of aging include mitochondrial, cellular, and organic dysfunction, immune impairment or inflammaging, oxidative stress, cognitive and cardiovascular alterations, among others. Therefore, one of the main harmful consequences of aging is the development and progression of multiple diseases related to these processes, especially at the cardiovascular and central nervous system levels. Both cardiovascular and neurodegenerative pathologies are highly disabling and, in many cases, lethal. In this context, melatonin, an endogenous compound naturally synthesized not only by the pineal gland but also by many cell types, may have a key role in the modulation of multiple mechanisms associated with aging. Additionally, this indoleamine is also a therapeutic agent, which may be administered exogenously with a high degree of safety. For this reason, melatonin could become an attractive and low-cost alternative for slowing the processes of aging and its associated diseases, including cardiovascular and neurodegenerative disorders.

Sex-dependent effects of chronic exercise on cognitive flexibility but not hippocampal Bdnf in aging mice

Cognitive impairments associated with advanced age involve alterations in the hippocampus that changes with experience throughout life. The hippocampus is critical for cognitive flexibility involved with extinction and reinstatement of conditioned fear. It is widely accepted that regular exercise can be beneficial for hippocampal function. Therefore, we asked whether chronic voluntary exercise in middle-aged mice can improve extinction and/or reinstatement of conditioned fear compared with standard-housing. Eight-month-old male and female C57Bl/6J mice had access to a running wheel or remained in standard-housing until 11 months of age. Alongside control standard-housed young adult (3-month-old) mice, they received tone-footshock pairings, which were subsequently extinguished with tone-alone presentations the next day. Half of the mice then received a reminder in the form of a single footshock. Male and female 11-month-old mice housed in standard conditions exhibited impaired reinstatement compared with young adult mice. However, for males that had access to a running wheel from 8 months of age, the reminder treatment rescued reinstatement ability. This was not observed in females. Additionally, exercise during middle age in both sexes increased expression of brain-derived neurotrophic factor (Bdnf) mRNA in the hippocampus, specifically exon 4 mRNA. These results show that, at least for males, physical exercise is beneficial for reducing age-related decline in cognitive abilities. Despite not affecting reinstatement, exercise also increased Bdnf gene expression in the female hippocampus, which could potentially benefit other forms of hippocampus-dependent cognition.

A potential biomarker of preclinical Alzheimer's disease: The olfactory dysfunction and its pathogenesis-based neural circuitry impairments

The olfactory dysfunction can signal and act as a potential biomarker of preclinical AD. However, the precise regulatory mechanism of olfactory function on the neural pathogenesis of AD is still unclear. The impairment of neural networks in olfaction system has been shown to be tightly associated with AD. As key brain regions of the olfactory system, the olfactory bulb (OB) and the piriform cortex (PCx) have a profound influence on the olfactory function. Therefore, this review will explore the mechanism of olfactory dysfunction in preclinical AD in the perspective of abnormal neural networks in the OB and PCx and their associated brain regions, especially from two aspects of aberrant oscillations and synaptic plasticity damages, which help better understand the underlying mechanism of olfactory neural network damages related to AD.

Hydrogen Sulfide Reverses Aging-Associated Amygdalar Synaptic Plasticity and Fear Memory Deficits in Rats

As an endogenous neuromodulator, hydrogen sulfide (H₂S) exerts multiple biological effects in the brain. Previous studies have shown that H₂S is involved in the regulation of neural synaptic plasticity and cognition in healthy rodents. It is well known that there is a progressive decline of cognitive function that occurs with increased age. The purpose of this study was to investigate the role of H₂S in aging-associated amygdalar synaptic plasticity and cued fear memory deficits as well as to explore the underlying mechanisms. We found that H₂S levels in the amygdala were significantly lower in aged rats when compared with healthy adult rates, which displayed significant deficits in long-term potentiation (LTP) in the thalamo-lateral amygdala (LA) pathway and amygdala-dependent cued fear memory. Bath application of an H₂S donor, sodium hydrogen sulfide (NaHS), significantly reversed the impaired LTP in brain slices from aged rats, and intra-LA infusion of NaHS restored the cued fear memory in aged rats. Mechanismly, we found that H₂S treatment significantly enhanced NMDAR-mediated synaptic responses in the thalamo-LA pathway of aged rats. Notably, GluN2B-containing NMDARs, but not GluN2A-containing NMDARs, contributed to the effects of H₂S on aging-associated impairments of amygdalar LTP and fear memory, because applying GluN2B antagonist could abolish the beneficial effects of NaHS treatment on amygdalar LTP and cognitive performance in aged rats. Collectively, these results show that H₂S can reverse aging-associated amygdalar synaptic plasticity and fear memory deficits by restoring the function of GluN2B-containing NMDARs, suggesting that supplement of H₂S might be a therapeutic approach for aging-related cognitive disorders.

Safety of the Transcranial Focal Electrical Stimulation via Tripolar Concentric Ring Electrodes for Hippocampal CA3 Subregion Neurons in Rats

Epilepsy is a neurological disorder that affects approximately one percent of the world population. Noninvasive electrical brain stimulation via tripolar concentric ring electrodes has been proposed as an alternative/complementary therapy for seizure control. Previous results suggest its efficacy attenuating acute seizures in penicillin, pilocarpine-induced status epilepticus, and pentylenetetrazole-induced rat seizure models and its safety for the rat scalp, cortical integrity, and memory formation. In this study, neuronal counting was used to assess possible tissue damage in rats (n = 36) due to the single dose or five doses (given every 24 hours) of stimulation on hippocampal CA3 subregion neurons 24 hours, one week, and one month after the last stimulation dose. Full factorial analysis of variance showed no statistically significant difference in the number of neurons between control and stimulation-treated animals (p = 0.71). Moreover, it showed no statistically significant differences due to the number of stimulation doses (p = 0.71) nor due to the delay after the last stimulation dose (p = 0.96). Obtained results suggest that stimulation at current parameters (50 mA, 200 μs, 300 Hz, biphasic, charge-balanced pulses for 2 minutes) does not induce neuronal damage in the hippocampal CA3 subregion of the brain.

The effects of aging in the hippocampus and cognitive decline

Aging is a natural process that is associated with cognitive decline as well as functional and social impairments. One structure of particular interest when considering aging and cognitive decline is the hippocampus, a brain region known to play an important role in learning and memory consolidation as well as in affective behaviours and mood regulation, and where both functional and structural plasticity (e.g., neurogenesis) occur well into adulthood. Neurobiological alterations seen in the aging hippocampus including increased oxidative stress and neuroinflammation, altered intracellular signalling and gene expression, as well as reduced neurogenesis and synaptic plasticity, are thought to be associated with age-related cognitive decline. Non-invasive strategies such as caloric restriction, physical exercise, and environmental enrichment have been shown to counteract many of the age-induced alterations in hippocampal signalling, structure, and function. Thus, such approaches may have therapeutic value in counteracting the deleterious effects of aging and protecting the brain against age-associated neurodegenerative processes.

Early-stage reduction of the dendritic complexity in basolateral amygdala of a transgenic mouse model of Alzheimer's disease

Alzheimer's disease is a representative age-related neurodegenerative disease that could result in loss of memory and cognitive deficiency. However, the precise onset time of Alzheimer's disease affecting neuronal circuits and the mechanisms underlying the changes are not clearly known. To address the neuroanatomical changes during the early pathologic developing process, we acquired the neuronal morphological characterization of AD in APP/PS1 double-transgenic mice using the Micro-Optical Sectioning Tomography system. We reconstructed the neurons in 3D datasets with a resolution of 0.32 × 0.32 × 1 μm and used the Sholl method to analyze the anatomical characterization of the dendritic branches. The results showed that, similar to the progressive change in amyloid plaques, the number of dendritic branches were significantly decreased in 9-month-old mice. In addition, a distinct reduction of dendritic complexity occurred in third and fourth-order dendritic branches of 9-month-old mice, while no significant changes were identified in these parameters in 6-month-old mice. At the branch-level, the density distribution of dendritic arbors in the radial direction decreased in the range of 40-90 μm from the neuron soma in 6-month-old mice. These changes in the dendritic complexity suggest that these reductions contribute to the progressive cognitive impairment seen in APP/PS1 mice. This work may yield insights into the early changes in dendritic abnormality and its relevance to dysfunctional mechanisms of learning, memory and emotion in Alzheimer's disease.

White matter hyperintensities are associated with disproportionate progressive hippocampal atrophy

This study investigates relationships between white matter hyperintensity (WMH) volume, cerebrospinal fluid (CSF) Alzheimer's disease (AD) pathology markers, and brain and hippocampal volume loss. Subjects included 198 controls, 345 mild cognitive impairment (MCI), and 154 AD subjects with serial volumetric 1.5‐T MRI. CSF Aβ₄₂ and total tau were measured (n = 353). Brain and hippocampal loss were quantified from serial MRI using the boundary shift integral (BSI). Multiple linear regression models assessed the relationships between WMHs and hippocampal and brain atrophy rates. Models were refitted adjusting for (a) concurrent brain/hippocampal atrophy rates and (b) CSF Aβ₄₂ and tau in subjects with CSF data. WMH burden was positively associated with hippocampal atrophy rate in controls (P = 0.002) and MCI subjects (P = 0.03), and with brain atrophy rate in controls (P = 0.03). The associations with hippocampal atrophy rate remained following adjustment for concurrent brain atrophy rate in controls and MCIs, and for CSF biomarkers in controls (P = 0.007). These novel results suggest that vascular damage alongside AD pathology is associated with disproportionately greater hippocampal atrophy in nondemented older adults. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc.

Regional Gray Matter Atrophy Coexistent with Occipital Periventricular White Matter Hyper Intensities

White matter hyperintensities (WMHs) and brain atrophy often coexist in the elderly. Additionally, WMH is often observed as occipital periventricular hyperintensities (OPVHs) with low-grade periventricular (PV) white matter (WM) lesions and is usually confined within an anatomical structure. However, the effects of OPVHs on gray matter (GM) atrophy remain largely unknown. In this study, we investigated GM atrophy in OPVHs patients and explored the relationship between such atrophy and clinical risk factors. T1-weighted and T2-weighted Magnetic resonance imaging (MRI) were acquired, and voxel-based morphometry (VBM) analysis was applied. The clinical (demographic and cardiovascular) risk factors of the OPVHs patients and healthy controls were then compared. Lastly, scatter plots and correlation analysis were applied to explore the relationship between the MRI results and clinical risk factors in the OPVHs patients. OPVHs patients had significantly reduced GM in the right supramarginal gyrus, right angular gyrus, right middle temporal gyrus, right anterior cingulum and left insula compared to healthy controls. Additionally, OPVHs patients had GM atrophy in the left precentral gyrus and left insula cortex, and such atrophy is associated with a reduction in low-density lipoprotein cholesterol (LDL-C) and apolipoprotein-B (Apo-B).

A multi-ingredient dietary supplement abolishes large-scale brain cell loss, improves sensory function, and prevents neuronal atrophy in aging mice

Transgenic growth hormone mice (TGM) are a recognized model of accelerated aging with characteristics including chronic oxidative stress, reduced longevity, mitochondrial dysfunction, insulin resistance, muscle wasting, and elevated inflammatory processes. Growth hormone/IGF-1 activate the Target of Rapamycin known to promote aging. TGM particularly express severe cognitive decline. We previously reported that a multi-ingredient dietary supplement (MDS) designed to offset five mechanisms associated with aging extended longevity, ameliorated cognitive deterioration and significantly reduced age-related physical deterioration in both normal mice and TGM. Here we report that TGM lose more than 50% of cells in midbrain regions, including the cerebellum and olfactory bulb. This is comparable to severe Alzheimer's disease and likely explains their striking age-related cognitive impairment. We also demonstrate that the MDS completely abrogates this severe brain cell loss, reverses cognitive decline and augments sensory and motor function in aged mice. Additionally, histological examination of retinal structure revealed markers consistent with higher numbers of photoreceptor cells in aging and supplemented mice. We know of no other treatment with such efficacy, highlighting the potential for prevention or amelioration of human neuropathologies that are similarly associated with oxidative stress, inflammation and cellular dysfunction. Environ. Mol. Mutagen. 57:382-404, 2016. © 2016 Wiley Periodicals, Inc.

Complement C3-Deficient Mice Fail to Display Age-Related Hippocampal Decline

The complement system is part of the innate immune response responsible for removing pathogens and cellular debris, in addition to helping to refine CNS neuronal connections via microglia-mediated pruning of inappropriate synapses during brain development. However, less is known about the role of complement during normal aging. Here, we studied the role of the central complement component, C3, in synaptic health and aging. We examined behavior as well as electrophysiological, synaptic, and neuronal changes in the brains of C3-deficient male mice (C3 KO) compared with age-, strain-, and gender-matched C57BL/6J (wild-type, WT) control mice at postnatal day 30, 4 months, and 16 months of age. We found the following: (1) region-specific and age-dependent synapse loss in aged WT mice that was not observed in C3 KO mice; (2) age-dependent neuron loss in hippocampal CA3 (but not in CA1) that followed synapse loss in aged WT mice, neither of which were observed in aged C3 KO mice; and (3) significantly enhanced LTP and cognition and less anxiety in aged C3 KO mice compared with aged WT mice. Importantly, CA3 synaptic puncta were similar between WT and C3 KO mice at P30. Together, our results suggest a novel and prominent role for complement protein C3 in mediating aged-related and region-specific changes in synaptic function and plasticity in the aging brain. Significance statement: The complement cascade, part of the innate immune response to remove pathogens, also plays a role in synaptic refinement during brain development by the removal of weak synapses. We investigated whether complement C3, a central component, affects synapse loss during aging. Wild-type (WT) and C3 knock-out (C3 KO) mice were examined at different ages. The mice were similar at 1 month of age. However, with aging, WT mice lost synapses in specific brain regions, especially in hippocampus, an area important for memory, whereas C3 KO mice were protected. Aged C3 KO mice also performed better on learning and memory tests than aged WT mice. Our results suggest that complement C3, or its downstream signaling, is detrimental to synapses during aging.

Impact of a deletion of the full-length and short isoform of p75NTR on cholinergic innervation and the population of postmitotic doublecortin positive cells in the dentate gyrus

Analyses of mice carrying a deletion of the pan-neurotrophin receptor p75NTR have allowed identifying p75NTR as an important structural regulator of the hippocampus. Most of the previous analyses were done using p75NTR (ExIII) knockout mice which still express the short isoform of p75NTR. To scrutinize the role of p75NTR in the hippocampus, we analyzed adult and aged p75NTR (ExIV) knockout mice, in which both, the short and the full-length isoform are deleted. Deletion of these isoforms induced morphological alterations in the adult dentate gyrus (DG), leading to an increase in the thickness of the molecular and granular layer. Based on these observations, we next determined the morphological substrates that might contribute to this phenotype. The cholinergic innervation of the molecular and granular layer of the DG was found to be significantly increased in the knockout mice. Furthermore, adult neurogenesis in the DG was found to be significantly altered with increased numbers of doublecortin (DCX) positive cells and reduced numbers of apoptotic cells in p75NTR (ExIV) knockout mice. However, cell proliferation as measured by phosphohiston H3 (PH3) positive cell numbers was not affected. These morphological alterations (number of DCX-positive cells and increased cholinergic fiber densities) as well as reduced cell death in the DG are likely to contribute to the observed thickening of the granular layer in p75NTR (ExIV) knockout mice. In addition, Sholl-analysis of DCX-positive neurons revealed a higher dendritic complexity and could thus be a possible morphological correlate for the increased thickness of the molecular layer in p75NTR deficient animals. Our data clearly demonstrate that deletion of both, the short and the full-length isoform of p75NTR affects DG morphology, due to alterations of the cholinergic system and an imbalance between neurogenesis and programmed cell death within the subgranular zone.

Neurogenesis within the adult hippocampus under physiological conditions and in depression

Adult neurogenesis can only be observed in some specific brain regions. One of these areas is the dentate gyrus of the hippocampal formation. The progenitor cells located in the subgranular layer of the dentate gyrus proliferate, differentiate, and give rise to young neurons that can become integrated into existing neuronal circuits. Under physiological conditions, hippocampal neurogenesis is linked to hippocampal-dependent learning, whereas deficits in adult hippocampal neurogenesis have been shown to correlate with disturbances in spatial learning and memory. This review summarizes the phenomenon of adult hippocampal neurogenesis and the use of suitable markers for the investigation of adult hippocampal neurogenesis. In addition, we focused on the disturbances in neurogenesis that can be seen in depression. Interestingly, several antidepressants have been found to be capable of increasing the rate of hippocampal neurogenesis. Based on that, it can be speculated that factors, which directly or indirectly increase the rate of hippocampal neurogenesis, may be helpful in the treatment of depression.

Manipulating a "cocaine engram" in mice

Experience with drugs of abuse (such as cocaine) produces powerful, long-lasting memories that may be important in the development and persistence of drug addiction. The neural mechanisms that mediate how and where these cocaine memories are encoded, consolidated and stored are unknown. Here we used conditioned place preference in mice to examine the precise neural circuits that support the memory of a cocaine-cue association (the "cocaine memory trace" or "cocaine engram"). We found that a small population of neurons (∼10%) in the lateral nucleus of amygdala (LA) were recruited at the time of cocaine-conditioning to become part of this cocaine engram. Neurons with increased levels of the transcription factor CREB were preferentially recruited or allocated to the cocaine engram. Ablating or silencing neurons overexpressing CREB (but not a similar number of random LA neurons) before testing disrupted the expression of a previously acquired cocaine memory, suggesting that neurons overexpressing CREB become a critical hub in what is likely a larger cocaine memory engram. Consistent with theories that coordinated postencoding reactivation of neurons within an engram or cell assembly is crucial for memory consolidation (Marr, 1971; Buzsáki, 1989; Wilson and McNaughton, 1994; McClelland et al., 1995; Girardeau et al., 2009; Dupret et al., 2010; Carr et al., 2011), we also found that post-training suppression, or nondiscriminate activation, of CREB overexpressing neurons impaired consolidation of the cocaine memory. These findings reveal mechanisms underlying how and where drug memories are encoded and stored in the brain and may also inform the development of treatments for drug addiction.

Post-mortem magnetic resonance microscopy (MRM) of the murine brain at 7 Tesla results in a gain of resolution as compared to in vivo MRM

Small-animal MRI with high field strength allows imaging of the living animal. However, spatial resolution in in vivo brain imaging is limited by the scanning time. Measurements of fixated mouse brains allow longer measurement time, but fixation procedures are time consuming, since the process of fixation may take several weeks. We here present a quick and simple post-mortem approach without fixation that allows high-resolution MRI even at 7 Tesla (T2-weighted MRI). This method was compared to in vivo scans with optimized spatial resolution for the investigation of anesthetized mice (T1-weighted MRI) as well as to ex situ scans of fixed brains (T1- and T2-weighted scans) by using standard MRI-sequences, along with anatomic descriptions of areas observable in the MRI, analysis of tissue shrinkage and post-processing procedures (intensity inhomogeneity correction, PCNN3D brain extract, SPMMouse segmentation, and volumetric measurement). Post-mortem imaging quality was sufficient to determine small brain substructures on the morphological level, provided fast possibilities for volumetric acquisition and for automatized processing without manual correction. Moreover, since no fixation was used, tissue shrinkage due to fixation does not occur as it is, e.g., the case by using ex vivo brains that have been kept in fixatives for several days. Thus, the introduced method is well suited for comparative investigations, since it allows determining small structural alterations in the murine brain at a reasonable high resolution even by MRI performed at 7 Tesla.

Role of oligomeric proanthocyanidins derived from an extract of persimmon fruits in the oxidative stress-related aging process

Many researchers have focused on the oligomeric form of proanthocyanidins with a lower level of polymerization found in foodstuffs such as grape seeds and blackberries. The present study indicated that the oral administration of oligomers isolated from persimmon fruits extended the lifespan of senescence-accelerated mouse prone/8 (SAMP8), a murine model of accelerated senescence. On the other hand, oligomer-treated SAMP8 did not show stereotypical behavior. We also revealed that the oral administration of oligomers improved spatial and object recognition memory in SAMP8. The density of axons in the hippocampal CA1 was significantly increased by oligomer administration. Moreover, the administration of oligomers increased the phosphorylation of vascular endothelial growth factor receptor (VEGFR)-2 in the hippocampal CA3, hypothalamus, and choroid plexus. We speculate that memory improvement accompanied by histological changes may be induced directly in the hippocampus and indirectly in the hypothalamus and choroid plexus through VEGFR-2 signaling. In the present study, we elucidated the protective effect of oligomers against memory impairment with aging. VEGFR-2 signaling may provide a new insight into ways to protect against memory deficit in the aging brain.

Neuronal populations in the basolateral nuclei of the amygdala are differentially increased in humans compared with apes: a stereological study

In human and nonhuman primates, the amygdala is known to play critical roles in emotional and social behavior. Anatomically, individual amygdaloid nuclei are connected with many neural systems that are either differentially expanded or conserved over the course of primate evolution. To address amygdala evolution in humans and our closest living relatives, the apes, we used design-based stereological methods to obtain neuron counts for the amygdala and each of four major amygdaloid nuclei (the lateral, basal, accessory basal, and central nuclei) in humans, all great ape species, lesser apes, and one monkey species. Our goal was to determine whether there were significant differences in the number or percent of neurons distributed to individual nuclei among species. Additionally, regression analyses were performed on independent contrast data to determine whether any individual species deviated from allometric trends. There were two major findings. In humans, the lateral nucleus contained the highest number of neurons in the amygdala, whereas in apes the basal nucleus contained the highest number of neurons. Additionally, the human lateral nucleus contained 59% more neurons than predicted by allometric regressions on nonhuman primate data. Based on the largest sample ever analyzed in a comparative study of the hominoid amygdala, our findings suggest that an emphasis on the lateral nucleus is the main characteristic of amygdala specialization over the course of human evolution.

Response of hippocampal neurons and glial cells to alternating magnetic field in gerbils submitted to global cerebral ischemia

The purpose of this study was to determine whether exposure to an extremely low-frequency magnetic field (ELF-MF, 50 Hz) affects the outcome of postischemic damage in the hippocampus of Mongolian gerbils. After 10-min bilateral carotid occlusion, the gerbils were continuously exposed to ELF-MF (average magnetic induction at the center of the cage was 0.5 mT) for 7 days. The impact of ELF-MF was estimated immediately (the 7th day after reperfusion) and 7 days after cessation of exposure (the 14th day after reperfusion) compared with ischemic gerbils without ELF-MF exposure. Applying stereological methods, histological evaluation of changes in the hippocampus was done for determining its volume, volume densities of degenerating neurons and astrocytes, as well as the number of microglial cells per unit area. ELF-MF per se did not induce any morphological changes, while 10-min global cerebral ischemia led to neuronal death, especially in CA1 region of the hippocampus, as expected. Ischemic gerbils exposed to ELF-MF had significantly a lower degree of cell loss in the examined structure and greater responses of astrocytes and microglial cells than postischemic gerbils without exposure on the seventh day after reperfusion (immediate effect of ELF-MF). Similar response was observed on the 14th day after reperfusion (delayed effect of ELF-MF); however, differences in measured parameters were low and insignificant. Applied ELF-MF has possible neuroprotective function in the hippocampus, as the most sensitive brain structure in the model of global cerebral ischemia, through reduction of neuronal death and activation of astrocytes and microglial cells.

Age-related impairments in memory and in CREB and pCREB expression in hippocampus and amygdala following inhibitory avoidance training

This experiment examined whether age-related changes in CREB and pCREB contribute to the rapid forgetting seen in aged animals. Young (3-month-old) and aged (24-month-old) Fischer-344 rats received inhibitory avoidance training with a low (0.2 mA, 0.4 s) or moderate (0.5 mA, 0.5 s) foot shock; memory was measured 7 days later. Other rats were euthanized 30 min after training, and CREB and pCREB expression levels were examined in the hippocampus, amygdala, and piriform cortex using immunohistochemistry. CREB levels decreased with age in the hippocampus and amygdala. After training with either shock level, young rats exhibited good memory and increases in pCREB levels in the hippocampus and amygdala. Aged rats exhibited good memory for the moderate but not the low shock but did not show increases in pCREB levels after either shock intensity. These results suggest that decreases in total CREB and in pCREB activation in the hippocampus and amygdala may contribute to rapid forgetting in aged rats. After moderate foot shock, the stable memory in old rats together with absence of CREB activation suggests either that CREB was phosphorylated in a spatiotemporal pattern other than analyzed here or that the stronger training conditions engaged alternate mechanisms that promote long-lasting memory.

Effect of growth hormone and melatonin on the brain: from molecular mechanisms to structural changes

Aging of the brain causes important reductions in quality of life and has wide socio-economic consequences. An increase in oxidative stress, and the associated inflammation and apoptosis, could be responsible for the pathogenesis of aging associated brain lesions. Melatonin has neuroprotective effects, by limiting the negative effects of oxygen and nitrogen free radicals. Growth hormone (GH) might exert additional neuro-protective and or neurogenic effects on the brain. The molecular mechanisms of the protective effects of GH and melatonin on the aging brain have been investigated in young and old Wistar rats. A reduction in the total number of neurons in the hilus of the dentate gyrus was evident at 24 months of age and was associated with a significant increase in inflammation markers as well as in pro-apoptotic parameters, confirming the role of apoptosis in its reduction. Melatonin treatment was able to enhance neurogenesis in old rats without modification of the total number of neurons, whereas GH treatment increased the total number of neurons without enhancing neurogenesis. Both GH and melatonin were able to reduce inflammation and apoptosis in the hippocampus. In conclusion, neuroprotective effects demonstrated by GH and melatonin in the hippocampus were exerted by decreasing inflammation and apoptosis.

Microglia in the normally aged hippocampus

The hippocampus plays important roles in the regulation and combination of short and long term memory and spatial navigation with other brain centers. Aging is accompanied by a functional decline of the hippocampus and degenerative disease. Microglia are major immune cells in the central nervous system and response to degenerative changes in the aged brain. In this respect, functional and morphological changes of the hippocampus have been closely related to microglial changes during normal aging with or without disease. Therefore, in this review, we discuss morphological and functional changes of the hippocampus and microglia in the aging brain.

Different fear states engage distinct networks within the intercalated cell clusters of the amygdala

Although extinction-based therapies are among the most effective treatments for anxiety disorders, the neural bases of fear extinction remain still essentially unclear. Recent evidence suggests that the intercalated cell masses of the amygdala (ITCs) are critical structures for fear extinction. However, the neuronal organization of ITCs and how distinct clusters contribute to different fear states are still entirely unknown. Here, by combining whole-cell patch-clamp recordings and biocytin labeling with full anatomical reconstruction of the filled neurons and ultrastructural analysis of their synaptic contacts, we have elucidated the cellular organization and efferent connections of one of the main ITC clusters in mice. Our data showed an unexpected heterogeneity in the axonal pattern of medial paracapsular ITC (Imp) neurons and the presence of three distinct neuronal subtypes. Functionally, we observed that the Imp was preferentially activated during fear expression, whereas extinction training and extinction retrieval activated the main ITC nucleus (IN), as measured by quantifying Zif268 expression. This can be explained by the IPSPs evoked in the IN after Imp stimulation, most likely through the GABAergic monosynaptic innervation of IN neurons by one subtype of Imp cells, namely the medial capsular-projecting (MCp)-Imp neurons. MCp-Imp neurons also target large ITC cells that surround ITC clusters and express the metabotropic glutamate receptor 1α. These findings reveal a distinctive participation of ITC clusters to different fear states and the underlying anatomical circuitries, hence shedding new light on ITC networks and providing a novel framework to elucidate their role in fear expression and extinction.

Involvement of BDNF in age-dependent alterations in the hippocampus

It is known since a long time that the hippocampus is sensitive to aging. Thus, there is a reduction in the hippocampal volume during aging. This age-related volume reduction is paralleled by behavioral and functional deficits in hippocampus-dependent learning and memory tasks. This age-related volume reduction of the hippocampus is not a consequence of an age-related loss of hippocampal neurons. The morphological changes associated with aging include reductions in the branching pattern of dendrites, as well as reductions in spine densities, reductions in the densities of fibers projecting into the hippocampus as well as declines in the rate of neurogenesis. It is very unlikely that a single factor or a single class of molecules is responsible for all these age-related morphological changes in the hippocampus. Nevertheless, it would be of advantage to identify possible neuromodulators or neuropeptides that may contribute to these age-related changes. In this context, growth factors may play an important role in the maintenance of the postnatal hippocampal architecture. In this review it is hypothesized that brain-derived neurotrophic factor (BDNF) is a factor critically involved in the regulation of age-related processes in the hippocampus. Moreover, evidences suggest that disturbances in the BDNF-system also affect hippocampal dysfunctions, as e.g. seen in major depression or in Alzheimer disease.

Aging of cerebellar Purkinje cells

Cerebellar Purkinje cells (PCs), the sole output neurons in the cerebellar cortex, play an important role in the cerebellar circuit. PCs appear to be rather sensitive to aging, exhibiting significant changes in both morphology and function during senescence. This article reviews such changes during the normal aging process, including a decrease in the quantity of cells, atrophy in the soma, retraction in the dendritic arborizations, degeneration in the subcellular organelles, a decline in synapse density, disorder in the neurotransmitter system, and alterations in electrophysiological properties. Although these deteriorative changes occur during aging, compensatory mechanisms exist to counteract the impairments in the aging PCs. The possible neural mechanisms underlying these changes and potential preventive treatments are discussed.

Expression of leucine-rich-repeat-kinase 2 (LRRK2) during embryonic development

The LRRK2 gene was recently found to have multiple mutations that are causative for the most common inherited form of late onset Parkinson's disease. In the adult brain, LRRK2 mRNA is broadly expressed, also in regions other than the nigrostriatal system. In order to establish a basis for assessing more detailed functional implications of LRRK2 in development, we provide here an in-depth analysis of its mRNA expression patterns in neural and extra-neural tissues with a focus on murine embryonic development. LRRK2 mRNA is detectable at E8.5 in non-neural and at E10.5 in neural tissues. From E12.5 to E16.5, LRRK2 mRNA is prominently expressed throughout the neocortex and subsequently highly concentrated in ventricular and subventricular zones and cortical plate. In addition, developing cerebellar granule and Purkinje neurons and spinal cord neurons display robust LRRK2 expression. In non-neural tissues LRRK2 was highly expressed in limb interdigital zones, developing kidney glomeruli, and spermatogenetic cells. Together, our results suggest roles for LRRK2 in controlling proliferation, migration, and differentiation of neural cells as well as in morphogenesis of extra-neural tissues.

Oligomeric proanthocyanidins improve memory and enhance phosphorylation of vascular endothelial growth factor receptor-2 in senescence-accelerated mouse prone/8

Senescence-accelerated mouse prone/8 (SAMP8), a murine model of accelerated senescence, shows age-related deficits in learning and memory. We investigated the effect of oligomeric proanthocyanidins (oligomers) on memory impairment using the SAMP8 model involving the oral administration of oligomers for 5 weeks. To analyse memory improvement in SAMP8, we performed Morris water maze, object location and object recognition tests. The oral administration of oligomers improved spatial and object recognition impairment in SAMP8. Expressions of phosphorylated neurofilament-H (P-NF-H, axon marker), microtubule-associated proteins (MAP) 2a and 2b (MAP2; dendrite marker) and synaptophysin were increased in the brains of SAMP8-administered oligomers. In particular, the expression of P-NF-H was significantly elevated in the hippocampal CA1. This indicates that oligomers result in an increase in the densities of axons, dendrites and synapses. To investigate the protective mechanisms of oligomers against brain dysfunction with ageing, we carried out a receptor tyrosine kinase phosphorylation antibody array, and clarified that the administration of oligomers led to an increase in the phosphorylation of vascular endothelial growth factor receptor (VEGFR)-2, suggesting the neuroprotective role of oligomers. The phosphorylation of VEGFR-2 was more greatly increased in the hypothalamus and choroid plexus than in other brain regions of SAMP8. Memory in oligomer-treated mice was impaired by SU1498, a VEGFR-2-specific antagonist. Elucidating the relationship between memory impairment with ageing and VEGFR-2 signalling may provide new suggestions for protection against memory deficit in the ageing brain.

Structure and function of dendritic spines within the hippocampus

Most excitatory input in the hippocampus impinges on dendritic spines. Therefore, the dendritic spines are likely to be of major importance for neural processing. The morphology of dendritic spines is very diverse and changes in spine size as well as in their density are thought to reflect changes in the strength of synaptic transmission. Thus, alterations in dendritic spine densities or shape are suspected to be morphological manifestations of psychopathological, pathophysiological, physiological and/or behavioural changes. However, in spite of a long history of research, the specific function of dendritic spines within the hippocampal formation is still not well understood. This review will shed light on the hippocampal dendritic spines, their ultrastructure and morphology, as well as their supposed roles in neuronal plasticity and in certain mental illnesses.

Localized delivery of fibroblast growth factor-2 and brain-derived neurotrophic factor reduces spontaneous seizures in an epilepsy model

A loss of neurons is observed in the hippocampus of many patients with epilepsies of temporal lobe origin. It has been hypothesized that damage limitation or repair, for example using neurotrophic factors (NTFs), may prevent the transformation of a normal tissue into epileptic (epileptogenesis). Here, we used viral vectors to locally supplement two NTFs, fibroblast growth factor-2 (FGF-2) and brain-derived neurotrophic factor (BDNF), when epileptogenic damage was already in place. These vectors were first characterized in vitro, where they increased proliferation of neural progenitors and favored their differentiation into neurons, and they were then tested in a model of status epilepticus-induced neurodegeneration and epileptogenesis. When injected in a lesioned hippocampus, FGF-2/BDNF expressing vectors increased neuronogenesis, embanked neuronal damage, and reduced epileptogenesis. It is concluded that reduction of damage reduces epileptogenesis and that supplementing specific NTFs in lesion areas represents a new approach to the therapy of neuronal damage and of its consequences.

Neuron and glia numbers in the basolateral nucleus of the amygdala from preweaning through old age in male and female rats: a stereological study

The rat basolateral nucleus of the amygdala continues to develop connectivity with the frontal cortex through the periadolescent period and even into young adulthood. Although neuronal loss in the prefrontal cortex has been found during the periadolescent period, prior literature has not examined whether neuron number in the basolateral amygdala is stable through this period. In addition, aging of the rat basolateral nucleus is accompanied by significant increases in the dendritic tree of its principal neurons, but whether this occurs in the context of neuronal death has not been previously explored. In the present study, a stereological examination of neuron and glia numbers in the rat basolateral amygdalar nucleus was undertaken in male and female hooded rats at four ages across the lifespan. Our findings indicate 1) a significant decrease in the number of neurons and glia in the basolateral nucleus between adolescence and adulthood; and 2) the number of glia, as well as the volume of the basolateral nucleus, increases between adulthood and old age, whereas neuron number remains stable. These findings provide an important cellular context for interpretation of the neurochemical and other alterations documented in developmental and age-related literature on the rat basolateral amygdala, and underline the substantial development of this brain area during adolescence, as well as its comparative preservation during aging.

Age-related dendritic hypertrophy and sexual dimorphism in rat basolateral amygdala

Little research has examined the influence of aging or sex on anatomical measures in the basolateral amygdala. We quantified spine density and dendritic material in Golgi-Cox stained tissue of the basolateral nucleus in young adult (3-5 months) and aged (20-24 months) male and female Long-Evans rats. Dendritic branching and spine density were measured in principal neurons. Age, but not sex, influenced the dendritic tree, with aged animals displaying significantly more dendritic material. Previous findings from our laboratory in the same set of subjects indicate an opposite effect of aging on dendritic material in the medial prefrontal cortex and hippocampus. We also report here a sex difference across ages in dendritic spine density, favoring males.

The food-conditioned place preference task in adolescent, adult and aged rats of both sexes

The rat basolateral amygdala shows neuroanatomical sex differences, continuing development after puberty and aging-related alterations. Implications for amygdala-dependent memory processes were explored here by testing male and female hooded rats in adolescence, adulthood and old age on the food-conditioned place preference task. While aged rats were unimpaired, adolescents failed to learn the task. This finding may be related to ongoing development of the basolateral amygdala and related memory systems during the adolescent period.

Folate deficiency induces neurodegeneration and brain dysfunction in mice lacking uracil DNA glycosylase

Folate deficiency and resultant increased homocysteine levels have been linked experimentally and epidemiologically with neurodegenerative conditions like stroke and dementia. Moreover, folate deficiency has been implicated in the pathogenesis of psychiatric disorders, most notably depression. We hypothesized that the pathogenic mechanisms include uracil misincorporation and, therefore, analyzed the effects of folate deficiency in mice lacking uracil DNA glycosylase (Ung-/-) versus wild-type controls. Folate depletion increased nuclear mutation rates in Ung-/- embryonic fibroblasts, and conferred death of cultured Ung-/- hippocampal neurons. Feeding animals a folate-deficient diet (FD) for 3 months induced degeneration of CA3 pyramidal neurons in Ung-/- but not Ung+/+ mice along with decreased hippocampal expression of brain-derived neurotrophic factor protein and decreased brain levels of antioxidant glutathione. Furthermore, FD induced cognitive deficits and mood alterations such as anxious and despair-like behaviors that were aggravated in Ung-/- mice. Independent of Ung genotype, FD increased plasma homocysteine levels, altered brain monoamine metabolism, and inhibited adult hippocampal neurogenesis. These results indicate that impaired uracil repair is involved in neurodegeneration and neuropsychiatric dysfunction induced by experimental folate deficiency.

TrkB but not trkC receptors are necessary for postnatal maintenance of hippocampal spines

Dendritic spines are major sites of excitatory synaptic transmission and changes in their densities have been linked to alterations in learning and memory. The neurotrophins brain-derived neurotrophic factor and neurotrophin-3 and their receptors, trkB and trkC, are thought to be involved in learning, memory and long-term potentiation (LTP). LTP is known to induce trkB and trkC gene expression as well as spinogenesis in the hippocampus. In the aging hippocampus, declines in trkB and trkC mRNA levels may underlie, at least in part, impairments in spatial memory and reductions in spine densities. To determine the significance of trkB and trkC for the maintenance of dendritic spines, we have analyzed Golgi-impregnated hippocampi of adult and aged mice heterozygous for trkB, trkC, or both along with respective wildtype littermates. Deletion of one allele of trkB, but not trkC, significantly reduces spine densities of CA1 pyramidal neurons in both adult and aged mice, as compared to age-matched controls. This indicates that trkB, but not trkC, receptors are necessary for the maintenance of hippocampal spines during postnatal life.

WITHDRAWN: Bcl-2 Upregulation is Significantly Enhanced in the Hippocampus of Normal Aging Mice After an Acute Challenge Elicited by Pro-inflammatory Cytokines Circulating in the Cerebrospinal Fluid

Ahead of Print article withdrawn by publisher

Distribution of TRPC4 in developing and adult murine brain

The transient receptor potential (TRP) superfamily comprises of a group of non-selective cation channels that have been implicated in both receptor and store-operated channel functions. The family of classical TRPs (TRPCs) consists of seven members (TRPC1-7), with TRPC4 possibly playing a role in neuronal signaling. We have examined the distribution pattern of TRPC4 mRNA and protein in the developing and postnatal murine brain by using in situ hybridization, Western blotting, and immunocytochemistry. Expression of TRPC4 mRNA starts at embryonic day 14.5 (E14.5) in the developing septal area and cerebellar anlagen. At E16.5, prominent expression is additionally seen in the hippocampal formation and cortical plate. High densities of cells expressing TRPC4 mRNA occur in the adult olfactory bulb and hippocampus, whereas the cortex and septum display lower densities of cells positive for TRPC4 mRNA. Analysis of the adult hippocampal formation has revealed TRPC4 immunoreactivity in hippocampal areas CA1 to CA3 and in the dentate gyrus. Functions consistent with this spatially restricted pattern of expression remain to be revealed.

Changes in brain cholinergic markers and spatial learning in old galanin-overexpressing mice

The cholinergic forebrain system is involved in learning and memory, and its age-dependent decline correlates with a decrease in cognitive performance. Since the neuropeptide galanin participates in cholinergic neuron regulation, we have studied 19- to 23-month-old male mice overexpressing galanin under the platelet-derived growth factor B promoter (GalOE) and wild-type (WT) littermates by monitoring behavioral, neurochemical and morphological/histochemical parameters. In the Morris water maze test, old transgenic animals showed a significant impairment in escape latency in the hidden platform test compared to age-matched WT animals. The morphological/histochemical studies revealed that cholinergic neurons in the basal forebrain display a slight, age- but not genotype-related, alteration in choline acetyltransferase- (ChAT) immunoreactivity. The neurochemical studies showed an age-related decline in ChAT activity in the cerebral cortex of all mice, whereas in the hippocampal formation this effect was seen in GalOE but not WT animals. Expression of BDNF mRNA in the hippocampal formation, as evaluated by RT-PCR, was reduced in old animals; no age- or genotype-induced variations in NGF mRNA expression were observed. These data suggest that galanin overexpression further accentuates the age-related decline of the cholinergic system activity in male mice, resulting in impairment of water maze performance in old animals.

Nitric oxide synthase-containing neurons in the amygdaloid nuclear complex of the rat

The nitric oxide-producing neurons in the rat amygdala (Am) were studied, using reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry. Almost all nuclei of the Am contained NADPHd-positive neurons and fibers, but the somatodendritic morphology and the intensity of staining of different subpopulations varied. The strongly stained neurons displayed labeling of the perikaryon and the dendritic tree with Golgi impregnation-like quality, whilst the dendrites of the lightly stained neurons were less successfully followed. Many strongly positive neurons were located in the external capsule and within the intraamygdaloid fiber bundles. A large number of small, strongly stained cells was present in the amygdalostriatal transition area. In the Am proper, a condensation of deeply stained cells occurred in the lateral amygdaloid nucleus. In the basolateral nucleus, the strongly NADPHd-positive neurons were few, and were located mainly along the lateral border of the nucleus. These cells clearly differed from the large, pyramidal, and efferent cells. The basomedial nucleus contained numerous positive cells but most of them were only lightly labeled. A moderate number of strongly stained neurons appeared in the medial division of the central nucleus, and a larger accumulation of strongly positive cells was present in the lateral and the capsular divisions. The medial amygdaloid nucleus contained numerous moderately stained neurons and displayed the strongest diffuse neuropil staining in Am. In the nucleus of the lateral olfactory tract, the first layer contained only NADPHd-stained axons, in the second layer, there were numerous moderately stained cells, and in the third layer, a few but deeply stained neurons. From the cortical nuclei, the most appreciable number of stained neurons was seen in the anterior cortical nucleus. The anterior amygdaloid area contained numerous NADPHd-positive neurons; in its dorsal part the majority of cells were only moderately stained, whereas in the ventral part the neurons were very strongly stained. The intercalated amygdaloid nucleus lacked NADPHd-positive neurons but an appreciable plexus of fine, tortuous axons was present. In the intra-amygdaloid part of the bed nucleus of the stria terminalis (st) some lightly stained cells were seen but along the entire course of st strongly stained neurons were observed. Some Am nuclei, and especially the central lateral nucleus and the intercalated nucleus, display considerable species differences when compared with the primate Am. The age-related changes of the nitrergic Am neurons, as well as their involvement in neurodegenerative diseases is discussed.

Bcl-2 over-expression fails to prevent age-related loss of calretinin positive neurons in the mouse dentate gyrus

BACKGROUND

Cognitive performance declines with increasing age. Possible cellular mechanisms underlying this age-related functional decline remain incompletely understood. Early studies attributed this functional decline to age-related neuronal loss. Subsequent studies using unbiased stereological techniques found little or no neuronal loss during aging. However, studies using specific cellular markers found age-related loss of specific neuronal types. To test whether there is age-related loss of specific neuronal populations in the hippocampus, and subsequently, whether over-expression of the B-cell lymphoma protein-2 (Bcl-2) in these neurons could delay possible age-related neuronal loss, we examined calretinin (CR) positive neurons in the mouse dentate gyrus during aging.

RESULT

In normal mice, there was an age-related loss of CR positive cells in the dentate gyrus. At the same region, there was no significant decrease of total numbers of neurons, which suggested that age-related loss of CR positive cells was due to the decrease of CR expression in these cells instead of cell death. In the transgenic mouse line over-expressing Bcl-2 in neurons, there was an age-related loss of CR positive cells. Interestingly, there was also an age-related neuronal loss in this transgenic mouse line.

CONCLUSION

These data suggest an age-related loss of CR positive neurons but not total neuronal loss in normal mice and this age-related neuronal change is not prevented by Bcl-2 over-expression.

In vivo MRI and histological evaluation of brain atrophy in APP/PS1 transgenic mice

Regional cerebral atrophy was evaluated in APP/PS1 mice harboring mutated transgenes linked to familial Alzheimer's disease, using complementary methods. In vivo high resolution MRI was selected for measurements of brain atrophy and associated cerebrospinal fluid dilation; histological analysis was performed to reveal localized atrophies and to evaluate amyloid burden. Young APP/PS1 mice examined at a pre-amyloid stage (10 weeks) showed disruption in development (reduced intracranial and brain volumes). Comparison of young and old (24 months) mice, indicated that both APP/PS1 and control brains endure growth during adulthood. Aged APP/PS1 animals showed a moderate although significant global brain atrophy and a dilation of CSF space in posterior brain regions. The locus of this atrophy was identified in the midbrain area and not, as expected, at isocortical/hippocampal levels. Atrophy was also detected in fiber tracts. The severity of brain atrophy in old APP/PS1 mice was not correlated with the extent of cerebral amyloidosis. The relevance of current transgenic mouse models for the study of brain atrophy related to Alzheimer's disease is discussed.