Effect of unilateral decortication on choline acetyltransferase activity in the nucleus basalis and other areas of the rat brain

Acetyl-coenzyme A: choline O-acetyltransferase (EC 2.3.1.6) (ChAT) enzyme activity was measured in the nucleus basalis and other microscopically identified brain areas at various times after unilateral cortical lesions were made in the rat. Initially, a significant decrease in ChAT activity was detected in the nucleus basalis ipsilateral to the lesion. However, after 120 days ChAT activity had apparently recovered, as levels of the enzyme at that time were not significantly different from control values. No changes in ChAT activity could be detected in any of the other brain areas similarly studied. The significance of these findings and their relationship to the morphological changes seen in neurones of the nucleus basalis after cortical lesions are discussed.

Substance P immunoreactive neurons following neonatal administration of capsaicin

Neonatal administration of capsaicin on the days 2, 10 or 20 leads to a long-lasting loss of substance P immunoreactive material in fibers of primary sensory neurons in the spinal cord and medulla oblongata. The degree of depletion examined 6 months after treatment was related to the day of injection. Injections on the second day produced dramatic losses of substance P in fibers of the substantia gelatinosa and the marginal layer of the spinal cord and the spinal nucleus of the trigeminal nerve, although these losses were never complete. The observed depletion of substance P immunoreactive material was homogenous throughout the superficial layers of the dorsal horn and the spinal nucleus of the trigeminal nerve. No changes were observed for the immunoreactivity of Leu-enkephalin in the substantia gelatinosa and the marginal layer of the spinal cord in consecutive sections from the same treated animals. In the medulla oblongata a reduction of substance P immunofluorescent fibers was found in the nucleus tractus solitarii and the spinal nucleus of the trigeminal nerve. Other areas of the central nervous system with a rich innervation of substance P immunoreactive fibers were not affected by capsaicin treatment.

Identification of serotonergic neurons in human brain by a monoclonal antibody binding to all three aromatic amino acid hydroxylases

A monoclonal antibody, PH8, has been isolated and shown by immunocytochemistry to bind to serotonergic and catecholaminergic neurons in sections of the rat and human brain. In human brain, obtained at autopsy, particular fixation and embedding conditions eliminate the labelling of catecholaminergic neurons while leaving intact the labelling of serotonergic neurons. This property makes the antibody of potential use for structural studies of serotonergic neurons in the normal and diseased human brain. PH8 was raised to pure monkey phenylalanine hydroxylase and has been shown to bind to the 50,000 mol. wt. phenylalanine hydroxylase polypeptide. Immunocytochemical and immunochemical evidence is presented in support of the hypothesis that the labelling of serotonergic and catecholaminergic neurons results from the binding of PH8 to tryptophan and tyrosine hydroxylase, respectively.

Revisiting the Cholinergic Hypothesis in Alzheimer's Disease: Emerging Evidence from Translational and Clinical Research

Scientific evidence collected over the past 4 decades suggests that a loss of cholinergic innervation in the cerebral cortex of patients with Alzheimer's disease is an early pathogenic event correlated with cognitive impairment. This evidence led to the formulation of the "Cholinergic Hypothesis of AD" and the development of cholinesterase inhibitor therapies. Although approved only as symptomatic therapies, recent studies suggest that long-term use of these drugs may also have disease-modifying benefits. A Cholinergic System Workgroup reassessed the role of the cholinergic system on AD pathogenesis in light of recent data, including neuroimaging data charting the progression of neurodegeneration in the cholinergic system and suggesting that cholinergic therapy may slow brain atrophy. Other pathways that contribute to cholinergic synaptic loss and their effect on cognitive impairment in AD were also reviewed. These studies indicate that the cholinergic system as one of several interacting systems failures that contribute to AD pathogenesis.

Intracellular Aβ pathology and early cognitive impairments in a transgenic rat overexpressing human amyloid precursor protein: a multidimensional study

Numerous studies have implicated the abnormal accumulation of intraneuronal amyloid-β (Aβ) as an important contributor to Alzheimer's disease (AD) pathology, capable of triggering neuroinflammation, tau hyperphosphorylation and cognitive deficits. However, the occurrence and pathological relevance of intracellular Aβ remain a matter of controversial debate. In this study, we have used a multidimensional approach including high-magnification and super-resolution microscopy, cerebro-spinal fluid (CSF) mass spectrometry analysis and ELISA to investigate the Aβ pathology and its associated cognitive impairments, in a novel transgenic rat model overexpressing human APP. Our microscopy studies with quantitative co-localization analysis revealed the presence of intraneuronal Aβ in transgenic rats, with an immunological signal that was clearly distinguished from that of the amyloid precursor protein (APP) and its C-terminal fragments (CTFs). The early intraneuronal pathology was accompanied by a significant elevation of soluble Aβ42 peptides that paralleled the presence and progression of early cognitive deficits, several months prior to amyloid plaque deposition. Aβ38, Aβ39, Aβ40 and Aβ42 peptides were detected in the rat CSF by MALDI-MS analysis even at the plaque-free stages; suggesting that a combination of intracellular and soluble extracellular Aβ may be responsible for impairing cognition at early time points. Taken together, our results demonstrate that the intraneuronal development of AD-like amyloid pathology includes a mixture of molecular species (Aβ, APP and CTFs) of which a considerable component is Aβ; and that the early presence of these species within neurons has deleterious effects in the CNS, even before the development of full-blown AD-like pathology.

Immunocytochemical localization of substance P in the spinal trigeminal nucleus of the rat: a light and electron microscopic study

The neuropeptide substance P is a transmitter candidate for certain primary afferent fibers which terminate in the substantia gelatinosa. In this study the light and electron microscopic localization of substance P in the substantia gelatinosa of the spinal trigeminal nucleus of the rat has been studied using immunocytochemical procedures. Substance P immunoreactive fibers were observed mainly in lamina I and outer lamina II. Ultrastructural analysis revealed immunoreactivity in unmyelinated fibers and in axon terminals which contained agranular spherical vesicles and large dense-cored vesicles and which made predominantly simple asymmetric axodendritic synaptic contacts. Immunoreactive terminals only rarely formed the central terminal of synaptic glomeruli and in only one example was a stained terminal possibly postsynaptic to an unstained terminal. The majority of synapses were onto small dendrites in outer lamina II and in some cases these dendrites were themselves presynaptic to other dendrites. Immunoreactive terminals also synapsed with the soma and proximal dendrites of large neurons on the border of laminae I and II. The results show that there are at least two distinct targets for substance P immunoreactive terminals in the substantia gelatinosa, namely the large lamina I neurons and lamina II probable interneurons. Some of the former may be projection neurons while some of the latter may correspond to the inhibitory islet cells described by Gobel and colleagues in the cat. In addition the results indicate that few substance P immunoreactive terminals receive axoaxonic synapses and emphasize instead the role of postsynaptic interactions. In particular the results suggest several sites at which substance P might interact postsynaptically with the neuropeptide enkephalin.

eIF2α controls memory consolidation via excitatory and somatostatin neurons

An important tenet of learning and memory is the notion of a molecular switch that promotes the formation of long-term memory1-4. The regulation of proteostasis is a critical and rate-limiting step in the consolidation of new memories5-10. One of the most effective and prevalent ways to enhance memory is by regulating the synthesis of proteins controlled by the translation initiation factor eIF211. Phosphorylation of the α-subunit of eIF2 (p-eIF2α), the central component of the integrated stress response (ISR), impairs long-term memory formation in rodents and birds11-13. By contrast, inhibiting the ISR by mutating the eIF2α phosphorylation site, genetically11 and pharmacologically inhibiting the ISR kinases14-17, or mimicking reduced p-eIF2α with the ISR inhibitor ISRIB11, enhances long-term memory in health and disease18. Here we used molecular genetics to dissect the neuronal circuits by which the ISR gates cognitive processing. We found that learning reduces eIF2α phosphorylation in hippocampal excitatory neurons and a subset of hippocampal inhibitory neurons (those that express somatostatin, but not parvalbumin). Moreover, ablation of p-eIF2α in either excitatory or somatostatin-expressing (but not parvalbumin-expressing) inhibitory neurons increased general mRNA translation, bolstered synaptic plasticity and enhanced long-term memory. Thus, eIF2α-dependent mRNA translation controls memory consolidation via autonomous mechanisms in excitatory and somatostatin-expressing inhibitory neurons.

5-Hydroxytryptamine, substance P, and thyrotropin-releasing hormone in the adult cat spinal cord segment L7: immunohistochemical and chemical studies

The terminal projections of the descending 5-hydroxytryptamine (5-HT) bulbospinal pathway and the coexistence among 5-HT-, substance P (SP)-, and thyrotropin-releasing hormone (TRH)-like immunoreactivities (LI) in fibers innervating the L7 segment in the cat spinal cord were studied quantitatively and semiquantitatively by use of the indirect double-staining immunofluorescence technique. The content of 5-HT, SP, and TRH in different parts of the spinal cord was determined by use of radioimmunoassay (RIA) (SP and TRH) and high-performance liquid chromatography with electrochemical detection (HPLC-ECD) (5-HT). For all three substances studied, immunoreactive (IR) axon terminals were found in all parts of the gray matter, but with clear regional variation in the density of innervation. Thus, all three substances showed a dense innervation in the motor nucleus, particularly in the ventral part of the nucleus, while the superficial dorsal horn was very densely innervated by SP-IR fibers (laminae I and II) and TRH-IR fibers (laminae II and III). In the motor nucleus, the studied substances coexisted to a very high degree, but some 5-HT-IR fibers (about 10%) lacked peptide-LI and some SP-IR fibers (about 10%) lacked 5-HT-LI while virtually all TRH-IR fibers also contained 5-HT-LI. In the superficial dorsal horn (laminae I-III), no coexistence was detected, while other parts of the gray matter displayed various degrees of coexistence in between those found in the motor nucleus and laminae I-III. The quantitative analysis of IR varicosities in the motor nucleus suggested that the unilateral L7 motor nucleus is innervated by about 55-110 x 10(6) 5-HT-IR nerve terminals, which may indicate as many as 4,000 boutons per descending 5-HT cell body in the brain stem only with this restricted projection. When combing these results with the biochemical data, it could be calculated that the concentration of 5-HT in IR varicosities is about 3-6 x 10(-3) M, while the corresponding figures for SP and TRH was 0.3-0.5 x 10(-3) M and 0.1-0.2 x 10(-3) M, respectively. In cats subjected to spinal cord transection at the lower thoracic level, all 5-HT-IR fibers in the L7 segment had disappeared 44 days after the lesion, indicating a strict suprasegmental origin of 5-HT-IR fibers in this segment.(ABSTRACT TRUNCATED AT 400 WORDS)

A TrkA-selective, fast internalizing nerve growth factor-antibody complex induces trophic but not neuritogenic signals

Nerve growth factor (NGF) is a neurotrophin that induces neuritogenic and trophic signals by binding to TrkA and/or p75 receptors. We report a comparative study of the binding, internalization, and biological activity of NGF versus that of NGF in association with an anti-NGF monoclonal antibody (mAb NGF30), directed against the C termini of NGF. NGF.mAb complexes do not bind p75 effectively but bind TrkA with high affinity. After binding, NGF. mAb complexes stimulate internalization faster and to a larger degree than NGF. NGF.mAb-induced activation of TrkA, Shc, and MAPK is transient compared with NGF-induced activation; yet NGF and NGF. mAb afford identical trophic responses. In contrast, NGF induces Suc-1-associated neurotrophic activating protein phosphorylation and neuritogenic differentiation, but NGF.mAb does not. Thus, an absolute separation of trophic and neuritogenic function is seen for NGF.mAb, suggesting that biological response modifiers of neurotrophins can afford ligands with selected activities.

Engagement of the PFC in consolidation and recall of recent spatial memory

The standard model of system consolidation proposes that memories are initially hippocampus dependent and become hippocampus independent over time. Previous studies have demonstrated the involvement of the medial prefrontal cortex (mPFC) in the retrieval of remote memories. The transformations required to make a memory undergo system's consolidation are thought to require synaptic plasticity. In this study, we investigated the participation of the mitogen-activated protein kinase (MAPK)/ERK pathway in acquisition, memory consolidation, and recent memory recall of the Morris water maze (MWM) task using a 1-d training protocol. To this end, bilateral injections of the MEK inhibitor U0126 into the rat mPFC were performed. The injection of the MEK inhibitor in the mPFC did not affect the acquisition of the MWM. However, MEK inhibitor resulted in impairments on recent memory retrieval either when applied at the end of the learning phase (memory consolidation) or prior to the retention test. The results strongly support the concept that recently acquired and consolidated spatial memories require the mPFC, and that local activation of the MAPK/ERK pathway in the mPFC is necessary for the consolidation and recall of recent memories.

Long-lasting rescue of age-associated deficits in cognition and the CNS cholinergic phenotype by a partial agonist peptidomimetic ligand of TrkA

Previously, we developed a proteolytically stable small molecule peptidomimetic termed D3 as a selective ligand of the extracellular domain of the TrkA receptor for the NGF. Ex vivo D3 was defined as a selective, partial TrkA agonist. Here, the in vivo efficacy of D3 as a potential therapeutic for cholinergic neurons was tested in cognitively impaired aged rats, and we compared the consequence of partial TrkA activation (D3) versus full TrkA/p75 activation (NGF). We show that in vivo D3 binds to TrkA receptors and affords a significant and long-lived phenotypic rescue of the cholinergic phenotype both in the cortex and in the nucleus basalis. The cholinergic rescue was selective and correlates with a significant improvement of memory/learning in cognitively impaired aged rats. The effects of the synthetic ligand D3 and the natural ligand NGF were comparable. Small, proteolytically stable ligands with selective agonistic activity at a growth factor receptor may have therapeutic potential for neurodegenerative disorders.

The Brain NGF Metabolic Pathway in Health and in Alzheimer's Pathology

Emerging research has re-emphasized the role of the cortical cholinergic system in the symptomology and progression of Alzheimer's disease (AD). Basal forebrain (BF) cholinergic nuclei depend on target-derived NGF for survival during development and for the maintenance of a classical cholinergic phenotype during adulthood. In AD, BF cholinergic neurons lose their cholinergic phenotype and function, suggesting an impairment in NGF-mediated trophic support. We propose that alterations to the enzymatic pathway that controls the maturation of proNGF to mature NGF and the latter's ulterior degradation underlie this pathological process. Indeed, the NGF metabolic pathway has been demonstrated to be impaired in AD and other amyloid pathologies, and pharmacological manipulation of NGF metabolism has consequences in vivo for both levels of proNGF/NGF and the phenotype of BF cholinergic neurons. The NGF pathway may also have potential as a biomarker of cognitive decline in AD, as its changes can predict future cognitive decline in patients with Down syndrome as they develop preclinical Alzheimer's pathology. New evidence suggests that the cholinergic system, and by extension NGF, may have a greater role in the progression of AD than previously realized, as changes to the BF precede and predict changes to the entorhinal cortex, as anticholinergic drugs increase odds of developing AD, and as the use of donepezil can reduce rates of hippocampal and cortical thinning. These findings suggest that new, more sophisticated cholinergic therapies should be capable of preserving the basal forebrain thus having profound positive effects as treatments for AD.

Purkinje cells of adult rat cerebellum express nerve growth factor receptor immunoreactivity: light microscopic observations

Adult rat cerebellum was examined for the presence of nerve growth factor receptor (NGFr) immunoreactivity (IR) using the monoclonal antibody 192-IgG. In normal animals, light NGFr-IR was observed consistently in Purkinje cells and molecular layer throughout the flocculonodular lobe. However, animals treated with intracerebroventricular colchicine 7-72 h prior to analysis displayed a graded increase of IR in Purkinje cells of all regions with progressively longer survival times. These findings demonstrate the usefulness of colchicine in revealing accumulation of NGFr in adult CNS neurons where previously not visualized and suggest responsiveness of a non-cholinergic neuronal population to nerve growth factor (NGF).

Altered mitogen-activated protein kinase signaling, tau hyperphosphorylation and mild spatial learning dysfunction in transgenic rats expressing the β-amyloid peptide intracellularly in hippocampal and cortical neurons

The pathological significance of intracellular Abeta accumulation in vivo is not yet fully understood. To address this, we have studied transgenic rats expressing Alzheimer's-related transgenes that accumulate Abeta intraneuronally in the cerebral and hippocampal cortices but do not develop extracellular amyloid plaques. In these rats, the presence of intraneuronal Abeta is sufficient to provoke up-regulation of the phosphorylated form of extracellular-regulated kinase (ERK) 2 and its enzymatic activity in the hippocampus while no changes were observed in the activity or phosphorylation status of other putative tau kinases such as p38, glycogen synthase kinase 3, and cycline-dependent kinase 5. The increase in active phospho-ERK2 was accompanied by increased levels of tau phosphorylation at S396 and S404 ERK2 sites and a decrease in the phosphorylation of the CREB kinase p90RSK. In a water maze paradigm, male transgenic rats displayed a mild spatial learning deficit relative to control littermates. Our results suggest that in the absence of plaques, intraneuronal accumulation of Abeta peptide correlates with the initial steps in the tau-phosphorylation cascade, alterations in ERK2 signaling and impairment of higher CNS functions in male rats.

Substance P: a carotid body peptide

Immunofluorescent studies have shown that substance P or substance P-like material is present in the cat carotid body, being located in some of the glomus cells and also in nerve axons. About 20% of the glomus cells were substance P positive. Substance P may be stored in glomus cells containing monoamine(s), but further studies are needed to investigate this aspect and also to determine what role, if any, substance P plays in the process of chemoreception.

The impact of Aβ-plaques on cortical cholinergic and non-cholinergic presynaptic boutons in alzheimer's disease-like transgenic mice

A previous study in our laboratory, involving early stage, amyloid pathology in 8-month-old transgenic mice, demonstrated a selective loss of cholinergic terminals in the cerebral and hippocampal cortices of doubly transgenic (APP(K670N,M671L)+PSl(M146L)) mice, an up-regulation in the single mutant APP(K670N,M671L) mice and no detectable change in the PSl(M146L) transgenics [J Neurosci 19 (1999) 2706]. The present study investigates the impact of amyloid plaques on synaptophysin and vesicular acetylcholine transporter (VAChT) immunoreactive bouton numbers in the frontal cortex of the three transgenic mouse models previously described. When compared as a whole, the frontal cortices of transgenic and control mice show no observable differences in the densities of synaptophysin-immunoreactive boutons. An individual comparison of layer V of the frontal cortex, however, shows a significant increase in density in transgenic models. Analysis of the cholinergic system alone shows significant alterations in the VAChT-immunoreactive bouton densities as evidenced by an increased density in the single (APP(K670N,M671L)) transgenics and a decreased density in the doubly transgenics (APP(K670N,M671L)+PSl(M146L)). In investigating the impact of plaque proximity on bouton density at early stages of the amyloid pathology in our doubly (APP(K670N,M671L)+PSl(M146L)) transgenic mouse line, we observed that plaque proximity reduced cholinergic pre-synaptic bouton density by 40%, and yet increased synaptophysin-immunoreactive pre-synaptic bouton density by 9.5%. Distance from plaques (up to 60 microm) seemed to have no effect on bouton density; however a significant inverse relationship was visible between plaque size and cholinergic pre-synaptic bouton density. Finally, the number of cholinergic dystrophic neurites surrounding the truly amyloid, Thioflavin-S(+) plaque core, was disproportionately large with respect to the incidence of cholinergic boutons within the total pre-synaptic bouton population. Confocal and electron microscopic observations confirmed the preferential infiltration of dystrophic cholinergic boutons into fibrillar amyloid aggregates. We therefore hypothesize that extracellular Abeta aggregation preferentially affects cholinergic terminations prior to progression onto other neurotransmitter systems. This is supported by the observable presence of non-cholinergic sprouting, which may be representative of impending neuritic degeneration.

An inflammatory and trophic disconnect biomarker profile revealed in Down syndrome plasma: Relation to cognitive decline and longitudinal evaluation

INTRODUCTION

Given that Alzheimer's pathology develops silently over decades in Down syndrome (DS), prognostic biomarkers of dementia are a major need.

METHODS

We investigated the plasma levels of Aβ, proNGF, tPA, neuroserpin, metallo-proteases and inflammatory molecules in 31 individuals with DS (with and without dementia) and in 31 healthy controls. We examined associations between biomarkers and cognitive decline.

RESULTS

Aβ40 and Aβ42 were elevated in DS plasma compared to controls, even in DS individuals without dementia. Plasma Aβ correlated with the rate of cognitive decline across 2 years. ProNGF, MMP-1, MMP-3, MMP-9 activity, TNF-α, IL-6, and IL-10 were higher in DS plasma, even at AD-asymptomatic stages. Declining plasma Aβ42 and increasing proNGF levels correlated with cognitive decline. A combined measure of Aβ and inflammatory molecules was a strong predictor of prospective cognitive deterioration.

CONCLUSIONS

Our findings support the combination of plasma and cognitive assessments for the identification of DS individuals at risk of dementia.

Potentiation of nerve growth factor-induced alterations in cholinergic fibre length and presynaptic terminal size in cortex of lesioned rats by the monosialoganglioside GM1

The effect of monosialoganglioside GM1 and/or nerve growth factor treatment on the cholinergic innervation of the rat cortex was studied using both light- and electron-microscopic techniques assisted by image analysis. Adult male Wistar rats were unilaterally decorticated and received continuous infusions, via minipump, of vehicle, GM1 (1.5 mg/day) and/or nerve growth factor (12 micrograms/day) into the cerebroventricular space. Treatments were initiated immediately post-lesion and ended after seven days. Thirty days post-lesion (i.e. 23 days after the end of drug administration) brains were processed for choline acetyltransferase immunocytochemistry for either light- or electron-microscopic analysis. At this time-point choline acetyltransferase-immunoreactive neurons in the ipsilateral nucleus basalis magnocellularis were significantly reduced in size especially in the mid portion of this nucleus, in lesion vehicle-treated rats. Moreover, decreases in choline acetyltransferase immunoreactive fibre length (ranging from 31 to 50%) and varicosity number (ranging from 26 to 39%) occurred in all cortical layers within a portion of the remaining cortex of these animals. Monosialoganglioside GM1 or nerve growth factor treatment equally attenuated deficits in nucleus basalis magnocellularis cell size and cortical choline acetyltransferase immunoreactive fibre length. However, nerve growth factor, but not monosialoganglioside GM1 treatment also increased choline acetyltransferase-immunoreactive varicosity number above control levels. In lesioned rats which received both nerve growth factor and the monosialoganglioside GM1, the mean cross-sectional area of nucleus basalis magnocellularis cholinergic neurons did not differ significantly from control values. By contrast, cortical choline acetyltransferase-immunoreactive fibre length and varicosity number were significantly increased above control values and that induced by nerve growth factor treatment alone. Quantitative electron-microscopic analysis showed that cholinergic boutons in cortical layer V were considerably shrunken in lesioned vehicle-treated rats and that GM1 treatment failed to significantly attenuate this deficit. However, exogenous nerve growth factor provoked a significant increase (35% above control values) in cortical cholinergic presynaptic terminal size which was even further augmented by concurrent GM1 treatment (69% above control values). This trophic factor-induced increase in bouton size was confirmed using serial electron microscopy and computer-assisted three-dimensional reconstruction of the cholinergic varicosities. The number of synaptic contacts in cortical layer V was also found to be significantly reduced (45% of control values) in lesioned vehicle-treated rats but was maintained at control levels by exogenous GM1 treatment. In addition, a significant increase (95% above control levels) in the number of choline acetyltransferase-immunoreactive boutons with synaptic differentiations was noted in lesioned nerve growth factor-treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Evolution of neuroinflammation across the lifespan of individuals with Down syndrome

Epidemiological and experimental studies suggest that a disease-aggravating neuroinflammatory process is present at preclinical stages of Alzheimer's disease. Given that individuals with Down syndrome are at increased genetic risk of Alzheimer's disease and therefore develop the spectrum of Alzheimer's neuropathology in a uniform manner, they constitute an important population to study the evolution of neuroinflammation across the Alzheimer's continuum. Therefore, in this cross-sectional study, we characterized the brain inflammatory profile across the lifespan of individuals with Down syndrome. Microglial morphology and inflammatory cytokine expression were analysed by immunohistochemistry and electrochemiluminescent-based immunoassays in the frontal cortex from foetuses to adults with Down syndrome and control subjects (16 gestational weeks to 64 years), totalling 127 cases. Cytokine expression in mixed foetal primary cultures and hippocampus of adults with Down syndrome, as well as the effects of sex on cytokine expression were also analysed. A higher microglial soma size-to-process length ratio was observed in the frontal cortex of children and young adults with Down syndrome before the development of full-blown Alzheimer's pathology. Moreover, young adults with Down syndrome also displayed increased numbers of rod-like microglia. Increased levels of interleukin-8 and interleukin-10 were observed in children with Down syndrome (1-10 years; Down syndrome n = 5, controls n = 10) and higher levels of interleukin-1β, interleukin-1α, interleukin-6, interleukin-8, interleukin-10, interleukin-15, eotaxin-3, interferon gamma-induced protein 10, macrophage-derived chemokine, and macrophage inflammatory protein-beta, were found in young adults with Down syndrome compared to euploid cases (13-25 years, Down syndrome n = 6, controls n = 24). Increased cytokine expression was also found in the conditioned media of mixed cortical primary cultures from second trimester foetuses with Down syndrome (Down syndrome n = 7, controls n = 7). Older adults with Down syndrome (39-68 years, Down syndrome n = 22, controls n = 16) displayed reduced levels of interleukin-10, interleukin-12p40, interferon-gamma and tumour necrosis factor-alpha. Microglia displayed larger somas and shorter processes. Moreover, an increase in dystrophic microglia and rod-like microglia aligning to neurons harbouring tau pathology were also observed. Sex stratification analyses revealed that females with Down syndrome had increased interleukin-6 and interleukin-8 levels compared to males with Down syndrome. Finally, multivariate projection methods identified specific cytokine patterns among individuals with Down syndrome. Our findings indicate the presence of an early and evolving neuroinflammatory phenotype across the lifespan in Down syndrome, a knowledge that is relevant for the discovery of stage-specific targets and for the design of possible anti-inflammatory trials against Alzheimer's disease in this population.

Transmitter expression and morphological development of embryonic medullary and mesencephalic raphé neurones after transplantation to the adult rat central nervous system. I. Grafts to the spinal cord

Suspensions of cells derived from the mesencephalic raphé or medullary raphé regions of the 13-14 day old embryonic rat brain were injected into the spinal cord of adult rats which had been previously denervated with 5,7-dihydroxytryptamine. At periods of up to 12 months after grafting, the spinal cords were taken for immunohistochemical analysis of 5-hydroxytryptamine (5HT), substance P (SP) and thyrotropin releasing hormone (TRH). In nearly all cases, surviving transplants were found. The grafts derived from mesencephalic raphé cells contained neurones which were immunoreactive to 5HT, or SP, but not both together. On average 4% of the total possible number of the available embryonic mesencephalic serotoninergic cells were found. A very dense outgrowth of 5HT positive fibres from the transplant was observed, extending up to 1.5 cm in both the caudal and rostral directions from the graft locus. Some SP immunoreactive fibres were also apparent near the implant. The grafts derived from the medullary transplant also contained 5HT-immunoreactive cells, comprising on average 25% of the total 5HT neurones available from the embryonic medullary primordium. In addition, neurones co-localizing 5HT together with SP and TRH were visible, closely reflecting the situation found in the medullary raphé in situ. Dense plexi of fibres containing 5HT-LI extended both caudally and rostrally up to 12-15 mm from the transplant. Outgrowth of SP and TRH varicose fibres was also demonstrable, although to a lesser degree than for 5HT. It was also possible to find many motoneurones surrounded by varicose fibres containing both 5HT and SP, in contrast to the situation with the mesencephalic grafts, where no such patterns of innervation were seen. The experiments indicate that the milieu of the spinal cord may compromise the survival of mesencephalic raphé 5HT neurones far more than of medullary serotonin cells. However, despite this effect on cell survival, the outgrowth of fibres from the remaining mesencephalic 5HT neurones was apparently unaffected by their ectopic position. Similarly, the transmitter content of both classes of raphé cells was largely unaltered, either by the transplantation process or by the environment into which they were placed. It is concluded that although the adult denervated spinal cord can selectively affect neuronal survival, it is incapable either of inducing in other serotoninergic cells placed within it the transmitter phenotype typical of medullary raphé neurones, or of causing those ectopically located 5HT cells to form connections appropriate to the descending serotonin fibres.

Immunohistochemical indications of gastrin releasing peptide--bombesin-like immunoreactivity in the nervous system of the rat. Codistribution with substance P-like immunoreactive nerve terminal systems and coexistence with substance P-like immunoreactivity in dorsal root ganglion cell bodies

Weak to strong gastrin releasing peptide--bombesin (GRP-Bn)-like immunoreactivity was found in fine varicose nerve terminal systems of low to high densities in several parts of the CNS. The highest densities of strongly immunoreactive terminals were found in the marginal layer and in the substantia gelatinosa of the spinal cord, and in parts of the nuc. tractus spinalis nervi trigemini. Morphometrical analysis in the spinal cord demonstrates that GRP-BN-like-immunoreactive and substance P (SP), but not somatostatin (SS)-immunoreactive nerve terminals strikingly codistribute. Coexistence of SP and GRP-BN-like immunoreactivities was demonstrated in trigeminal and spinal ganglion nerve cells. Thus, GRP-BN-like immunoreactivity may coexist with SP in certain SP-immunoreactive nerve terminal systems.

NLRP3-dependent synaptic plasticity deficit in an Alzheimer's disease amyloidosis model in vivo

Pro-inflammatory mechanisms have recently emerged as an important component of early Alzheimer's disease (AD) pathogenesis. A particularly attractive therapeutic strategy is to selectively prevent the disruptive effects of activation of the innate immune system in the brain at an early transitional stage by reducing the production or directly neutralizing pro-inflammatory cytokines, in particular IL-1β and TNF-α. Here we tested their in vivo effects on synaptic plasticity deficits, which provide sensitive and robust measures of synaptic failure, in a rat model of AD amyloidosis. Using electrophysiological techniques we longitudinally studied the effects of the NLRP3 inflammasome inhibitor Mcc950, the IL-1 receptor antagonist (anakinra) and an anti-TNF-α agent (etanercept) in awake freely moving transgenic rats overexpressing AD associated β-amyloid precursor protein at a pre-plaque stage of amyloidosis. Repeated treatment with Mcc950 reversibly abrogated the inhibition of long-term potentiation. The IL-1 receptor antagonist and etanercept also had a similar beneficial effect on the deficit in synaptic plasticity. Our findings support the clinical development of Mcc950 and clinically available IL-1- and TNF-α-neutralizing agents in early AD.

Nerve growth factor metabolic dysfunction in Down's syndrome brains

Basal forebrain cholinergic neurons play a key role in cognition. This neuronal system is highly dependent on NGF for its synaptic integrity and the phenotypic maintenance of its cell bodies. Basal forebrain cholinergic neurons progressively degenerate in Alzheimer's disease and Down's syndrome, and their atrophy contributes to the manifestation of dementia. Paradoxically, in Alzheimer's disease brains, the synthesis of NGF is not affected and there is abundance of the NGF precursor, proNGF. We have shown that this phenomenon is the result of a deficit in NGF's extracellular metabolism that compromises proNGF maturation and exacerbates its subsequent degradation. We hypothesized that a similar imbalance should be present in Down's syndrome. Using a combination of quantitative reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting and zymography, we investigated signs of NGF metabolic dysfunction in post-mortem brains from the temporal (n = 14), frontal (n = 34) and parietal (n = 20) cortex obtained from subjects with Down's syndrome and age-matched controls (age range 31-68 years). We further examined primary cultures of human foetal Down's syndrome cortex (17-21 gestational age weeks) and brains from Ts65Dn mice (12-22 months), a widely used animal model of Down's syndrome. We report a significant increase in proNGF levels in human and mouse Down's syndrome brains, with a concomitant reduction in the levels of plasminogen and tissue plasminogen activator messenger RNA as well as an increment in neuroserpin expression; enzymes that partake in proNGF maturation. Human Down's syndrome brains also exhibited elevated zymogenic activity of MMP9, the major NGF-degrading protease. Our results indicate a failure in NGF precursor maturation in Down's syndrome brains and a likely enhanced proteolytic degradation of NGF, changes which can compromise the trophic support of basal forebrain cholinergic neurons. The alterations in proNGF and MMP9 were also present in cultures of Down's syndrome foetal cortex; suggesting that this trophic compromise may be amenable to rescue, before frank dementia onset. Our study thus provides a novel paradigm for cholinergic neuroprotection in Alzheimer's disease and Down's syndrome.

Intracellular A-beta amyloid, a sign for worse things to come?

In this review the authors discuss the possible neuropathological role of intracellular amyloid-beta accumulation in Alzheimer's disease (AD) pathology. There is abundant evidence that at early stages of the disease, prior to A-beta amyloid plaque formation, A-beta peptides accumulate intraneuronally in the cerebral cortex and the hippocampus. The experimental evidence would indicate that intracellular amyloid-beta could originate both by intracellular biosynthesis and also from the uptake of amyloidogenic peptides from the extracellular milieu. Herein the aspects of the possible impact of intracellular amyloid-beta in human AD pathology are discussed, as well as recent observations from a rat transgenic model with a phenotype of intracellular accumulation of A-beta fragments in neurons of the hippocampus and cortex, without plaque formation. In this model, the intracellular amyloid-beta phenotype is accompanied by increased MAPK/ERK activity and tau hyperphosphorylation. Finally, the authors discuss the hypothesis that, prior to plaque formation, intracellular A-beta accumulation induces biochemical and pathological changes in the brain at the cellular level priming neurons to further cytotoxic attack of extracellular amyloidogenic peptides.