Substance P and somatostatin coexist within neuritic plaques: implications for the pathogenesis of Alzheimer's disease

Brain Hydrophobic Peptides Antagonists of Neurotoxic Amyloid β Peptide Monomers/Oligomers-Protein Interactions

Amyloid β (Aβ) oligomers have been linked to Alzheimer's disease (AD) pathogenesis and are the main neurotoxic forms of Aβ. This review focuses on the following: (i) the Aβ(1-42):calmodulin interface as a model for the design of antagonist Aβ peptides and its limitations; (ii) proteolytic degradation as the major source of highly hydrophobic peptides in brain cells; and (iii) brain peptides that have been experimentally demonstrated to bind to Aβ monomers or oligomers, Aβ fibrils, or Aβ plaques. It is highlighted that the hydrophobic amino acid residues of the COOH-terminal segment of Aβ(1-42) play a key role in its interaction with intracellular protein partners linked to its neurotoxicity. The major source of highly hydrophobic endogenous peptides of 8-10 amino acids in neurons is the proteasome activity. Many canonical antigen peptides bound to the major histocompatibility complex class 1 are of this type. These highly hydrophobic peptides bind to Aβ and are likely to be efficient antagonists of the binding of Aβ monomers/oligomers concentrations in the nanomolar range with intracellular proteins. Also, their complexation with Aβ will protect them against endopeptidases, suggesting a putative chaperon-like physiological function for Aβ that has been overlooked until now. Remarkably, the hydrophobic amino acid residues of Aβ responsible for the binding of several neuropeptides partially overlap with those playing a key role in its interaction with intracellular protein partners that mediates its neurotoxicity. Therefore, these latter neuropeptides are also potential candidates to antagonize Aβ peptides binding to target proteins. In conclusion, the analysis performed in this review points out that hydrophobic endogenous brain neuropeptides could be valuable biomarkers to evaluate the risk of the onset of sporadic AD, as well as for the prognosis of AD.

Tachykinin Neuropeptides and Amyloid β (25-35) Assembly: Friend or Foe?

Amyloid β (Aβ) protein is responsible for Alzheimer's disease, and one of its important fragments, Aβ(25-35), is found in the brain and has been shown to be neurotoxic. Tachykinin neuropeptides, including Neuromedin K (NK), Kassinin, and Substance P, have been reported to reduce Aβ(25-35)'s toxicity in cells even though they share similar primary structures with Aβ(25-35). Here, we seek to understand the molecular mechanisms of how these peptides interact with Aβ(25-35) and to shed light on why some peptides with similar primary structures are toxic and others nontoxic. We use both experimental and computational methods, including ion mobility mass spectrometry and enhanced-sampling replica-exchange molecular dynamics simulations, to study the aggregation pathways of Aβ(25-35), NK, Kassinin, Substance P, and mixtures of the latter three with Aβ(25-35). NK and Substance P were observed to remove the higher-order oligomers (i.e., hexamers and dodecamers) of Aβ(25-35), which are related to its toxicity, although Substance P did so more slowly. In contrast, Kassinin was found to promote the formation of these higher-order oligomers. This result conflicts with what is expected and is elaborated on in the text. We also observe that even though they have significant structural homology with Aβ(25-35), NK, Kassinin, and Substance P do not form hexamers with a β-sheet structure like Aβ(25-35). The hexamer structure of Aβ(25-35) has been identified as a cylindrin, and this structure has been strongly correlated to toxic species. The reasons why the three tachykinin peptides behave so differently when mixed with Aβ(25-35) are discussed.

Amyloid β induces interneuron-specific changes in the hippocampus of APPNL-F mice

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline and amyloid-beta (Aβ) depositions generated by the proteolysis of amyloid precursor protein (APP) in the brain. In APPNL-F mice, APP gene was humanized and contains two familial AD mutations, and APP-unlike other mouse models of AD-is driven by the endogenous mouse APP promoter. Similar to people without apparent cognitive dysfunction but with heavy Aβ plaque load, we found no significant decline in the working memory of adult APPNL-F mice, but these mice showed decline in the expression of normal anxiety. Using immunohistochemistry and 3D block-face scanning electron microscopy, we found no changes in GABAA receptor positivity and size of somatic and dendritic synapses of hippocampal interneurons. We did not find alterations in the level of expression of perineuronal nets around parvalbumin (PV) interneurons or in the density of PV- or somatostatin-positive hippocampal interneurons. However, in contrast to other investigated cell types, PV interneuron axons were occasionally mildly dystrophic around Aβ plaques, and the synapses of PV-positive axon initial segment (AIS)-targeting interneurons were significantly enlarged. Our results suggest that PV interneurons are highly resistant to amyloidosis in APPNL-F mice and amyloid-induced increase in hippocampal pyramidal cell excitability may be compensated by PV-positive AIS-targeting cells. Mechanisms that make PV neurons more resilient could therefore be exploited in the treatment of AD for mitigating Aβ-related inflammatory effects on neurons.

The Amygdala as a Locus of Pathologic Misfolding in Neurodegenerative Diseases

Over the course of most common neurodegenerative diseases the amygdala accumulates pathologically misfolded proteins. Misfolding of 1 protein in aged brains often is accompanied by the misfolding of other proteins, suggesting synergistic mechanisms. The multiplicity of pathogenic processes in human amygdalae has potentially important implications for the pathogenesis of Alzheimer disease, Lewy body diseases, chronic traumatic encephalopathy, primary age-related tauopathy, and hippocampal sclerosis, and for the biomarkers used to diagnose those diseases. Converging data indicate that the amygdala may represent a preferential locus for a pivotal transition from a relatively benign clinical condition to a more aggressive disease wherein multiple protein species are misfolded. Thus, understanding of amygdalar pathobiology may yield insights relevant to diagnoses and therapies; it is, however, a complex and imperfectly defined brain region. Here, we review aspects of amygdalar anatomy, connectivity, vasculature, and pathologic involvement in neurodegenerative diseases with supporting data from the University of Kentucky Alzheimer's Disease Center autopsy cohort. Immunohistochemical staining of amygdalae for Aβ, Tau, α-synuclein, and TDP-43 highlight the often-coexisting pathologies. We suggest that the amygdala may represent an "incubator" for misfolded proteins and that it is possible that misfolded amygdalar protein species are yet to be discovered.

Functional Amyloids and their Possible Influence on Alzheimer Disease

Amyloids play critical roles in human diseases but have increasingly been recognized to also exist naturally. Shared physicochemical characteristics of amyloids and of their smaller oligomeric building blocks offer the prospect of molecular interactions and crosstalk amongst these assemblies, including the propensity to mutually influence aggregation. A case in point might be the recent discovery of an interaction between the amyloid β peptide (Aβ) and somatostatin (SST). Whereas Aβ is best known for its role in Alzheimer disease (AD) as the main constituent of amyloid plaques, SST is intermittently stored in amyloid-form in dense core granules before its regulated release into the synaptic cleft. This review was written to introduce to readers a large body of literature that surrounds these two peptides. After introducing general concepts and recent progress related to our understanding of amyloids and their aggregation, the review focuses separately on the biogenesis and interactions of Aβ and SST, before attempting to assess the likelihood of encounters of the two peptides in the brain, and summarizing key observations linking SST to the pathobiology of AD. While the review focuses on Aβ and SST, it is to be anticipated that crosstalk amongst functional and disease-associated amyloids will emerge as a general theme with much broader significance in the etiology of dementias and other amyloidosis.

Interneurons in the human olfactory system in Alzheimer's disease

The principal olfactory structures display Alzheimer's disease (AD) related pathology at early stages of the disease. Consequently, olfactory deficits are among the earliest symptoms. Reliable olfactory tests for accurate clinical diagnosis are rarely made. In addition, neuropathological analysis postmortem of olfactory structures is often not made. Therefore, the relationship between the clinical features and the underlying pathology is poorly defined. Traditionally, research into Alzheimer's disease has focused on the degeneration of cortical temporal projection neurons and cholinergic neurons. Recent evidence has demonstrated the neurodegeneration of interneuron populations in AD. This review provides an updated overview of the pathological involvement of interneuron populations in the human olfactory system in Alzheimer's disease.

Correlation of Alzheimer disease neuropathologic changes with cognitive status: a review of the literature

Clinicopathologic correlation studies are critically important for the field of Alzheimer disease (AD) research. Studies on human subjects with autopsy confirmation entail numerous potential biases that affect both their general applicability and the validity of the correlations. Many sources of data variability can weaken the apparent correlation between cognitive status and AD neuropathologic changes. Indeed, most persons in advanced old age have significant non-AD brain lesions that may alter cognition independently of AD. Worldwide research efforts have evaluated thousands of human subjects to assess the causes of cognitive impairment in the elderly, and these studies have been interpreted in different ways. We review the literature focusing on the correlation of AD neuropathologic changes (i.e. β-amyloid plaques and neurofibrillary tangles) with cognitive impairment. We discuss the various patterns of brain changes that have been observed in elderly individuals to provide a perspective for understanding AD clinicopathologic correlation and conclude that evidence from many independent research centers strongly supports the existence of a specific disease, as defined by the presence of Aβ plaques and neurofibrillary tangles. Although Aβ plaques may play a key role in AD pathogenesis, the severity of cognitive impairment correlates best with the burden of neocortical neurofibrillary tangles.

Age- and disease-related neuroplasticity of chemically identified neuronal circuits: a tribute to Professor Erminio Costa

The following review highlights a small portion of the research ongoing in my laboratory at the Fidia Georgetown Institute of Neuroscience (FGIN) during the years 1989-1994. Specifically, this work focused on the selective vulnerability of neurons in Alzheimer's disease. At the time, it was known that α-amino-3-hydroxy-5-methyl-4-isoaxolepropionate (AMPA) receptors were composed of one or more subunits (GluR1-4). Furthermore, the presence of the GluR2 subunit was known to substantially reduce Ca2+ through AMPA receptors in response to ligand binding. This finding led us to hypothesize that the presence or absence of the GluR2 subunit in the AMPA receptor may have a profound influence on the ability of the cell to gate extracellular Ca2+ and maintain intracellular calcium homeostasis. Furthermore, in Alzheimer's disease we hypothesized that cells at risk for developing AD neuropathology will express certain combinations of glutamate receptor subunits that form channels with increased permeability to Ca2+. In turn, these cells may become more vulnerable to the pathologic consequences of increased intracellular Ca2+ and destabilized intracellular Ca2+ homeostasis. To test this hypothesis we employed anatomical techniques and examined post mortem materials from patients with AD. The results of these studies are summarized in this review. Notably, this review also highlights the valuable collaborations established during my five years at FGIN and pays tribute to the intellectually rich and supportive environment provided by Dr. Costa and colleagues.

Neuropathology and cognitive impairment in Alzheimer disease: a complex but coherent relationship

Amyloid plaques and neurofibrillary tangles (NFTs) are the pathological hallmarks of Alzheimer disease (AD). There is controversy regarding the use of current diagnostic criteria for AD and whether amyloid plaques and NFTs contribute to cognitive impairment. Because AD is specific to humans, rigorous and comprehensiveclinicopathologic studies are necessary to test and refine hypotheses of AD diagnosis and pathogenesis. Neither the clinical nor the pathological aspects of AD evolve in a linear manner, but thepredictable sequence of AD pathology allows for stage-based correlations with cognitive deterioration. We discuss subsets of patients with clinical dementia who lack amyloid plaques and NFTs and, conversely, whether individuals without antemortem cognitive impairment can harbor severe AD-type pathological findings at autopsy. There are many medical, technical, and anatomical challenges to clinicopathologic studies in AD. For example, at least two thirds of persons older than 80 years have non-AD brain diseases that can effect on cognitive function. We argue that existing data strongly support the hypothesis that both amyloid plaques and NFTs contribute to cognitive impairment.

Localization and expression of substance P in transgenic mice overexpressing human APP751 with the London (V717I) and Swedish (K670M/N671L) mutations

Substance P-like immunoreactivity (-LI) is found in neuritic plaques, and is reduced in patients suffering from Alzheimer disease (AD). In this study, we examined the distribution and expression of substance P in transgenic mice overexpressing human amyloid precursor protein (hAPP) APP751 with the London (V717I) and Swedish (K670M/N671L) mutations. Immunohistochemistry was performed to localize substance P- and glial fibrillary acidic protein-LI by confocal microscopy. In hAPP transgenic mice, the number of beta-amyloid plaques significantly increased from 6 to 12 months. About 5% of beta-amyloid plaques were substance P-immunoreactive. In transgenic mice, the morphology of substance P-immunoreactive structures changed by consisting of swollen and dystrophic neurites mostly associated with beta-amyloid plaques. The overall localization and the relative substance P densities were not different between wild type and transgenic mice at 6 and 12 months. At month 12, a dramatic change in the distribution pattern of substance P-LI was observed as it was now expressed in a high number of reactive astrocytes. This expression of substance P in astrocytes was mainly found in the hippocampal formation and thalamic nuclei with a preferential association with beta-amyloid plaques, whereas in cortical regions only faintly substance P-immunoreactive astrocytes were observed. This study indicates that substance P undergoes complex changes in this animal Alzheimer disease model. Future experiments including substance P antagonists are necessary to further explore the interaction between beta-amyloid deposits and substance P.

Neuronal fibrillogenesis: amyloid fibrils from primary neuronal cultures impair long-term memory in the crab Chasmagnathus

Amyloid beta protein (Abeta) fibrillogenesis is considered one of the crucial steps of Alzheimer's disease (AD) pathogenesis. The effect of endogenous neuronal amyloid fibrils on memory processes is unknown. To investigate this issue, we first characterised the Abeta fibrillar aggregates secreted by cerebellar granule cells and then we evaluated the effect of neuronal fibrils on an invertebrate model of memory. An increase of fibril formation, assessed by Thioflavin T (ThT) fluorescence, was observed in the conditioned medium of apoptotic neurons during 48 h of the apoptotic process. Moreover, the depolarisation-stimulated secretion of cerebellar granule cells contains monomers of endogenous Abeta, which undergo cell-free fibrillogenesis over several days of incubation. The pattern of single endogenous fibrils, examined by electron microscopy, was similar to that of synthetic Abeta while a tighter and more complex interfibrillar organization was observed in endogenous fibrils. The biological effect of neuronal fibrils was studied in a long-term memory (LTM) paradigm, namely the context-signal learning of the crab Chasmagnathus. Pre-training injection of neuronal fibril extract (protein concentration, 1 microg/ml) induced amnesia in a dose-dependent manner. On the contrary, no effect on retention was observed with the administration of two orders higher doses (100 microg/ml) of synthetic Abeta1-40. These results indicate that only naturally secreted fibrils, but not synthetic Abeta, clearly interfere with memory process.

Neuropeptide alterations in the hippocampal formation and cortex of transgenic mice overexpressing β-amyloid precursor protein (APP) with the Swedish double mutation (APP23)

The role of neuropeptides and the significance of peptidergic mechanisms in neurodegenerative diseases are still unclear. In the periphery, nerve injury results in dramatic changes in the expression of neuropeptides. An important question regards to what extent similar changes occur, and similar mechanisms operate, after lesions and/or degeneration in the brain. The purpose of this work is, therefore, to study neuropeptides with regard to their presence and distribution in the APP23 mouse (HuAPP(751) K670M/N671L under the murine Thy-1 promoter), a model for Alzheimer's disease, or cerebral amyloidosis, using the immunohistochemical technique. In addition, tyrosine hydroxylase and acetylcholinesterase were analyzed. This study shows marked neuropeptide changes in the hippocampal formation and the ventral cortex, whereas the dorsolateral neocortex was less affected. There was a considerable variation with regard to peptide expression among animals of the same age which was related to the variation in Abeta deposition. Dystrophic and varicose fibers containing galanin, neuropeptide Y, enkephalin, and especially cholecystokinin were commonly seen in close proximity to amyloid plaques. In addition, generalized changes were observed, such as increases of enkephalin and neuropeptide Y in stratum lacunosum moleculare and of neuropeptide Y, enkephalin, and dynorphin in mossy fibers. In contrast, cholecystokinin was decreased in mossy fibers. Comparatively small differences were observed between wild-type and transgenic mice with regard to tyrosine hydroxylase (noradrenergic but also dopaminergic fibers) and acetylcholine esterase (mainly cholinergic fibers). The increase of neuropeptides in dystrophic fibers in this model may represent a response to nerve injury caused by the amyloid accumulation and may reflect attempts to counteract degeneration by initiating protective and/or regenerative processes.

Modulation of somatostatin receptors, somatostatin content and Gi proteins by substance P in the rat frontoparietal cortex and hippocampus

Substance P (SP) and somatostatin (SRIF) are widely spread throughout the CNS where they play a role as neurotransmitters and/or neuromodulators. A colocalization of both neuropeptides has been demonstrated in several rat brain areas and SP receptors have been detected in rat cortical and hippocampal somatostatinergic cells. The present study was thus undertaken to determine whether SP could modulate SRIF signaling pathways in the rat frontoparietal cortex and hippocampus. A single intraperitoneal injection of SP (50, 250 or 500 micro g/kg) induced an increase in the density of SRIF receptors in membranes from the rat frontoparietal cortex at 24 h of its administration, with no change in the hippocampus. The functionality of the SRIF receptors was next investigated. Western blot analysis of Gi proteins demonstrated a significant decrease in Gialpha1 levels in frontoparietal cortical membranes from rats treated acutely (24 h) with 250 micro g/kg of SP, which correlated with a decrease in functional Gi activity, as assessed by use of the non-hydrolyzable GTP analog 5'-guanylylimidodiphosphate. SRIF-mediated inhibition of basal or forskolin-stimulated adenylyl cyclase activity was also significantly lower in the frontoparietal cortex of the SP-treated group, with no alterations in the catalytic subunit of the enzyme. SRIF-like immunoreactivity content was increased in the frontoparietal cortex after acute (24 h) SP administration (250 or 500 micro g/kg) as well as in the hippocampus in response to 7 days of SP (250 micro g/kg) administration. All these SP-mediated effects were prevented by pretreatment with the NK1 receptor antagonist RP-67580. Although the physiologic significance of these results are unknown, the increase in SRIF receptor density together with the desensitization of the SRIF inhibitory signaling pathway might be a mechanism to potentiate the stimulatory pathway of SRIF, inducing a preferential coupling of the receptors to PLC.

Neuropeptides in hippocampus and cortex in transgenic mice overexpressing V717F beta-amyloid precursor protein--initial observations

Immunohistochemistry was used to analyse 18- and 26-month-old transgenic mice overexpressing the human beta-amyloid precursor protein under the platelet-derived growth factor-beta promoter with regard to presence and distribution of neuropeptides. In addition, antisera/antibodies to tyrosine hydroxylase, acetylcholinesterase, amyloid peptide, glial fibrillary acidic protein and microglial marker OX42 were used. These mice have been reported to exhibit extensive amyloid plaques in the hippocampus and cortex [Masliah et al. (1996) J. Neurosci. 16, 5795-5811]. The most pronounced changes were related to neuropeptides, whereas differences between wild-type and transgenic mice were less prominent with regard to tyrosine hydroxylase and acetylcholinesterase. The main findings were of two types; (i) involvement of peptide-containing neurites in amyloid beta-peptide positive plaques, and (ii) more generalized changes in peptide levels in specific layers, neuron populations and/or subregions in the hippocampal formation and ventral cortices. In contrast, the parietal and auditory cortices were comparatively less affected. The peptide immunoreactivities most strongly involved, both in plaques and in the generalized changes, were galanin, neuropeptide Y, cholecystokinin and enkephalin. This study shows that there is considerable variation both with regard to plaque load and peptide expression even among homozygotes of the same age. The most pronounced changes, predominantly increased peptide levels, were observed in two 26-month-old homozygous mice, for example, galanin-, enkephalin- and cholecystokinin-like immunoreactivities in stratum lacunosum moleculare, and galanin, neuropeptide Y, enkephalin and dynorphin in mossy fibers. Many peptides also showed elevated levels in the ventral cortices. However, decreases were also observed. Thus, galanin-like immunoreactivity could not any longer be detected in the diffusely distributed (presumably noradrenergic) fiber network in all hippocampal and cortical layers, and dynorphin-like immunoreactivity was decreased in stratum moleculare, cholecystokinin-like immunoreactivity in mossy fibers and substance P-like immunoreactivity in fibers around granule cells. The significance of generalized peptide changes is at present unclear. For example, the increase in the mainly inhibitory peptides galanin, neuropeptide Y, enkephalin and dynorphin and the decrease in the mainly excitatory peptide cholecystokinin in mossy fibers (and of substance P fibers around granule cells) indicate a shift in balance towards inhibition of the input to the CA3 pyramidal cell layer. Moreover, it may be speculated that the increase in levels of some of the peptides represents a reaction to nerve injury with the aim to counteract, in different ways, the consequences of injury, for example by exerting trophic actions. Further studies will be needed to establish to what extent these changes are typical for Alzheimer mouse models in general or are associated with the V717F mutation and/or the platelet-derived growth factor-beta promoter.

Distribution of glutamate receptor subunit NMDAR1 in the hippocampus of normal elderly and patients with Alzheimer's disease

Immunocytochemical techniques were employed to study the distribution and cytological features of NMDAR1-immunoreactive elements in the human hippocampal formation. Subjects with Alzheimer's disease (AD), presenting with a wide range of neuropathology and classified into six Braak stage (I-VI), and nondemented age-matched controls were examined. In control cases, the most intense NMDAR1 immunoreactivity was observed within the soma and dendrites of granule cells in the dentate gyrus and pyramidal neurons in Ammon's horn. Whereas small variations in the pattern of immunoreactivity were noted in control cases, AD subjects were characterized with intersubject variability which in most instances correlated with neuropathologic severity. For example, AD cases, particularly those with mild/modest pathology (Braak I-III), were indistinguishable from controls in the overall pattern of immunolabeling. In contrast, in those more severe AD cases (Braak IV-VI) the intensity of immunolabeling within the CA fields was greater than observed in controls and those with mild AD pathology. In addition, in pathologically severe cases numerous NMDAR1-positive pyramidal neurons were characterized by unique morphologic features including long and often tortuous apical dendrites. These latter findings were most prevalent in the CA1 region and subiculum. In contrast to the marked increase in immunolabeling in the CA fields, in the dentate gyrus we observed a reduction in NMDAR1 labeling particularly within the outer molecular layer (i.e., termination zone of the perforant pathway). This latter region was also the site of a number of NMDAR1-labeled plaques. Notably, the overall pattern of NMDAR1 immunoreactivity is distinct from that observed with antibodies against AMPA receptor subunits and suggests a differential role of various inotropic glutamate receptors in hippocampal plasticity in AD.

Synaptic loss reflected by secretoneurin-like immunoreactivity in the human hippocampus in Alzheimer's disease

Secretoneurin is a recently described peptide derived by endoproteolytic processing from secretogranin II, previously named chromogranin C. In this study, we have investigated the distribution of secretoneurin-like immunoreactivity in the human hippocampus in controls and in Alzheimer's disease patients, and compared the staining pattern to that of calretinin. Secretoneurin-like immunoreactivity is present throughout the hippocampal formation. At the border of the dentate molecular layer and the granule cell layer, a band of dense secretoneurin immunostaining appeared. In this part, as in the area of the CA2 sector, the high density of secretoneurin-immunoreactivity coincided with calretinin-like immunoreactivity. The mossy fibre system displayed a moderate density of secretoneurin-immunoreactivity. In the entorhinal cortex, a particularly high density of secretoneurin-immunoreactivity was observed. The density of secretoneurin-like immunoreactivity was significantly reduced in the innermost part of the molecular layer and in the outer molecular layer of the dentate gyrus in Alzheimer's disease. For calretinin-like immunoreactivity, a less pronounced decrease was found in the innermost part of the molecular layer. About 40-60% of neuritic plaques were secretoneurin-immunopositive. This study shows that secretoneurin is distinctly distributed in the human hippocampus and that significant changes of secretoneurin-like immunoreactivity occur in Alzheimer's disease, reflecting synaptic loss.

Somatostatin and brain-derived neurotrophic factor mRNA expression in the primate brain: decreased levels of mRNAs during aging

The expression of the genes for somatostatin (SRIF) and brain-derived neurotrophic factor (BDNF) was investigated in the central nervous system (CNS) of the macaque monkey (Macaca fuscata fuscata). Using Northern blot analysis, one SRIF mRNA transcript, 0.65 kb, and two BDNF mRNA transcripts, 1.6 and 4.0 kb in length, were detected in the monkey brain tissues. During the aging process (2 years, 10 years, and > 30 years), the ratio of SRIF mRNA/glyceraldehyde-3 phosphate dehydrogenase (G3PDH) mRNA significantly decreased (60-70%) in the hippocampus and in several cerebral subdivisions such as frontal cortex, temporal cortex, motor cortex, somatosensory cortex and visual cortex. BDNF mRNA was expressed in the various cerebral subdivisions and in the hippocampus. During the aging process, the gene expression of BDNF declined (20-50% for the 4.0 kb transcript, and 40-70% for the 1.6 kb transcript) in the various cerebral subdivisions. In the hippocampus, the level of the 1.6 kb mRNA at > 30 years old declined to 60% of the level at 2 years old, while the 4.0 kb mRNA did not change significantly during the aging process. Recent studies have shown that BDNF enhances the expression of SRIF mRNA in the rodent cerebral cortex (Nawa, H. et al., J. Neurochem., 60 (1993) 772-775; Nawa, H. et al., J. Neurosci., 14 (1994) 3751-3765). These studies and our present results suggest that the decrease in gene expression for a neurotrophic molecule, such as BDNF, might cause the levels of SRIF mRNA to decline in the primate brain during the aging process.

Expression and distribution of the dentatorubral-pallidoluysian atrophy gene product (atrophin-1/drplap) in neuronal and non-neuronal tissues

Utilizing an affinity-purified antiserum directed against the carboxyl terminal region of atrophin-1/drplap (residues 1170-1185), we have examined the expression and distribution of the protein in a variety of neuronal and non-neuronal tissues. Immunohistochemical analyses of gelatin-embedded sections of monkey brain demonstrated a wide-spread distribution of the protein throughout the cerebrum and cerebellum. Labeling was primarily cytoplasmic within neuronal cell bodies and dendrites. Prominently staining regions included layers II, III, V, and VI of cerebral cortex, CA1-4 of the hippocampus, caudate nucleus, putamen, globus pallidus, amygdala, thalamus, red nucleus, pons, Purkinje cells, and deep cerebellar nuclei. Immunoblot analysis of extracts of frontal cortex from a wide variety of mammalian species (human, monkey, rabbit, rat, mouse, and bovine) detected a 190 kDa band in each extract. No cross-reactive material of similar molecular weight was detected in an extract of avian (chicken) central nervous system (CNS) tissue. Furthermore, in the rat, expression of the protein was predominantly neuronal in origin as immunoblot analyses of non-neuronal tissue extracts detected little or no 190 kDa protein. Collectively these investigations suggest a ubiquitous expression of atrophin-1/drplap in mammalian CNS tissue and provide initial immunochemical data for the study of the neuroanatomic and perhaps, phylogenetic relationships between mammalian and non-mammalian forms of the protein.

Tachykinins, neurotrophism and neurodegenerative diseases: a critical review on the possible role of tachykinins in the aetiology of CNS diseases

The tachykinins are a family of undecapeptides that are widely distributed throughout the body, including the central nervous system (CNS). They have several well defined roles in non-CNS sites as well as in the dorsal horn, where they are involved in the transmission of nociceptive information. However their function(s) in other CNS sites is unclear, but there is some evidence that they function as neuromodulators rather than neurotransmitters. This neuromodulation includes a possible role in maintaining the integrity of neuronal populations, analogous to the functions of neurotrophic factors. This review critically evaluates the role of tachykinins as neurotrophic factors, with particular reference to the common neurodegenerative diseases of the CNS.

Identification and characterization of a B-cell determinant within the amphipathic domain (residues 178-238) of the myelin proteolipid protein

Pooled polyclonal rabbit anti-rat myelin and mouse anti-human proteolipid protein (PLP) antisera were screened against a panel of PLP synthetic peptides spanning residues 178-238 of the protein. Cross-reactivity against one determinant defined by PLP(200-219) was particularly prominent in both the anti-myelin and anti-PLP antisera and was chosen for further study. Competitive inhibition studies, utilizing a panel of overlapping synthetic peptides, demonstrated that the C-terminal portion of PLP(200-219), specifically residues comprising PLP(200-217), was important for antibody recognition of this region. Immunohistochemical analyses with an affinity-purified rabbit anti-PLP(200-219) antiserum demonstrated antibody cross-reactivity with PLP in both paraffin- and gelatin-embedded brain sections and immunocytochemical staining of mouse oligodendrocyte-enriched cultures demonstrated antibody binding with native PLP in situ. Staining of living non-permeabilized cells localized binding to the extracellular face of the myelin membrane. Collectively, these data argue for the presence of an immunodominant B-cell determinant defined by PLP residues 200-219. Furthermore, the structural conformation of this determinant in native PLP can be mimicked by the synthetic peptide, resulting in the generation of an antibody reagent that has considerable utility for immunohistochemical and immunocytochemical investigations of PLP expression and localization within the central nervous system myelin membrane.

Neuropeptide changes in cortical and deep gray structures in Alzheimer's disease

The alteration of certain neuropeptide levels is a dramatic and consistent finding in the brains of AD patients. Levels of SS, which is normally present in high concentrations in cerebral cortex /75/, are consistently decreased in the neocortex, hippocampus and CSF of AD patients. In addition, decreased levels of SS correlate regionally with the distribution of neurofibrillary tangles in AD /47/. Most available evidence suggests that the subset of SS-containing neurons which lack NADPH diaphorase may be relatively vulnerable to degeneration in AD. CRF is another neuropeptide with frequently observed changes in AD. Levels of CRF, which is normally present in low concentrations in cortical structures /75/, are decreased in the neocortex and hippocampus of AD patients. However, levels of CRF in the CSF of AD patients are not consistently reduced, but this is likely a reflection of the relatively low levels of CRF normally present in cerebral cortex. Studies of deep gray structures in AD brains reveal elevated levels of GAL in the nucleus basalis. The ability of GAL to inhibit cholinergic neurotransmission has generated considerable interest, since degeneration of cholinergic neurons in the basal forebrain consistently occurs in AD. In addition, the presence of NADPH diaphorase in GAL-containing neurons may underlie the relative resistance of these neurons to degeneration. From the aforementioned studies, it appears that the neurons which are relatively resistant to neurodegeneration in AD contain NADPH diaphorase. It is hypothesized that the presence of NADPH diaphorase protects these neurons from neurotoxicity mediated by glutamate or nitric oxide. Although one recent study /147/ has reported an elevation of the microtubule-associated protein tau in the CSF of AD patients (and this could become a useful antemortem diagnostic tool for AD), no similar CSF abnormality has been found for any of the neuropeptides. Thus, the measurement of CSF neuropeptide levels presently remains unhelpful in the diagnosis and treatment of AD. Future research on neuropeptides and their potential roles in the pathogenesis, diagnosis, and treatment of AD will likely involve further development of pharmacological modulators of neuropeptide systems, together with the further study of brain neuropeptidases.

Early association of reactive astrocytes with senile plaques in Alzheimer's disease

The fibrillar beta-amyloid protein (A beta) plaques of Alzheimer's disease (AD) are associated with reactive astrocytes and dystrophic neurites and have been suggested to contribute to neurodegenerative events in the disease. We recently reported parallel in vitro and in situ findings, suggesting that the adoption of a reactive phenotype and the colocalization of astrocytes with plaques in AD may be mediated in large part by aggregated A beta. Thus, A beta-mediated effects on astrocytes may directly affect disease progression by modifying the degenerative plaque environment. Alternatively, plaque-associated reactive astrocytosis may primarily represent a glial response to the neural injury associated with plaques and not significantly contribute to AD pathology. To investigate the validity of these two positions, we examined the differential colocalization of reactive astrocytes and dystrophic neurites with plaques. Hippocampal sections from AD brains--ranging in neuropathology from mild to severe--were triple-labeled with antibodies recognizing A beta protein, reactive astrocytes, and dystrophic neurites. We observed not only plaques containing both or neither cell type, but also plaques containing (1) reactive astrocytes but not dystrophic neurites and (2) dystrophic neurites but not reactive astrocytes. The relative proportion of plaques colocalized with reactive astrocytes in the absence of dystrophic neurites is relatively high in mild AD but significantly decreases over the course of the disease, suggesting that plaque-associated astrocytosis may be an early and perhaps contributory event in AD pathology rather than merely a response to neuronal injury. These data underscore the potentially significant contributions of reactive astrocytosis in modifying the plaque environment in particular and disease progression in general.

The morphologic and neurochemical basis of dementia: aging, hierarchical patterns of lesion distribution and vulnerable neuronal phenotype

Alzheimer's disease is the most common form of dementia in elderly individuals. Approximately 11% of the population older than 65, and up to 50% of individuals over 85 qualify as having "probable Alzheimer's disease" on the basis of clinical evaluation. Since the early description of the clinical symptoms and neuropathologic features of Alzheimer's disease, there has been an extraordinary growth in the knowledge of the morphologic and molecular characteristics of Alzheimer's disease. Although the pathogenetic events that lead to dementia are not yet fully understood, several hypotheses regarding the formation of the hallmark pathologic structures of Alzheimer's disease have been proposed. In this context, the use of specific histochemical techniques in the primate brain has greatly expanded our understanding of neuron typology, connectivity and circuit distribution in relation to neurochemical identity. In this respect, very specific subsets of cortical neurons and cortical afferents can be identified by their particular content of certain neurotransmitters and structural proteins. In this article, we discuss the possible relationships between the distribution of pathologic changes in aging, Alzheimer's disease, and possibly related dementing conditions, in the context of the specific elements of the cortical circuitry that are affected by these alterations. Also, evidence for links between the neurochemical phenotype of a given neuron and its relative vulnerability or resistance to the degenerative process are presented in order to correlate the distribution of cellular pathologic changes, neurochemical characteristics related to vulnerability, and affected cortical circuits.

Cortical and subcortical neuropeptides in Alzheimer's disease

Given the clinical features of AD, the severe atrophy of cerebral cortex that accompanies the disease, and the predominant cortical location of plaques and tangles, it is not surprising to find the most consistent changes in neuropeptides in this disease occurring in the cerebral cortex. The neuropeptide changes that have been reproducibly demonstrated in AD are reduced hippocampal and neocortical SS and CRF concentrations and a reduced CSF level of SS. In cerebral cortex, SS and CRF are found in GABAergic local circuit neurons in layers II, III, and VI. The function of these neurons is not well established, although these cells may act to integrate the flow of incoming and outgoing information in cerebral cortex. If this is true, then dysfunction of this integration could produce widespread failure of cerebrocortical function, resulting in the various neurobehavioral deficits seen in AD. The interpretation of neuropeptide changes in subcortical brain regions, either those that project to cortex, or those that are the efferent targets of cortical projections, is also uncertain. The observed neuropeptide abnormalities in these brain regions in AD are less consistent than are those seen in cerebral cortex. Perhaps the most intriguing result in these regions is the increases in galanin-immunoreactive terminals seen in the nucleus basalis of AD brains. Galanin has been shown to inhibit acetylcholine release and to impair memory function in rats (46,113).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of neurokinin substance P with morphine in effects on food-reinforced operant behavior and feeding

In the present study, substance P (SP) was injected intraperitoneally (IP), and its effects on operant behavior were assessed in rats, which had been trained to bar press for food reward on a fixed-ratio (FR) 20 schedule. These effects were compared with IP injection of morphine sulfate, which had previously been shown to strongly suppress operant responding on FR schedules. The IP injection of SP resulted in a dose-related decrement in response rates. SP in a dose range of 250-500 micrograms/kg decreased operant responding, whereas SP in a dose range of 5-50 micrograms/kg did not influence response rates. The IP injection of morphine (10 mg/kg) markedly suppressed operant responding. However, in contrast to the rate-decreasing effects of SP, this suppression was not selective for the reinforced lever as responding on the nonreinforced lever, used as a control, was also decreased. Furthermore, both injection of 10 mg/kg morphine and SP in a dose range of 250-500 micrograms/kg was found to reduce food intake when the animals had free access to food subsequent to the operant conditioning session. The present results provide the first evidence that systemically administered neurokinin SP can affect operant responding for food reward. The suppressive effects on operant behavior and feeding obtained with systemic SP or morphine are discussed with respect to recent findings showing that both drugs can modulate mesolimbic dopamine activity after systemic drug injection.

Immunocytochemical distribution of peptidergic and cholinergic fibers in the human amygdala: their depletion in Alzheimer's disease and morphologic alteration in non-demented elderly with numerous senile plaques

As part of an ongoing investigation devoted to understanding the pathogenesis of senile plaques, we employed histochemical and immunocytochemical techniques to examine the distribution and cytologic features of acetylcholinesterase (AChE), choline acetyltransferase (ChAT), somatostatin (SOM), neurotensin (NT) and substance P (SP) containing fibers and neurons within the amygdala of: (1) patients with Alzheimer's disease (AD); (2) age-matched non-demented controls (NC); and (3) a group of non-demented cases, who upon postmortem neuropathologic examination exhibited sufficient numbers of senile plaques to be classified as AD. This latter group was referred to as high plaque non-demented (HPND). For every case, the distribution of immunolabeled fibers and neurons were determined for each transmitter throughout the various subnuclei of the amygdala. In addition, in the AD and HPND cases the topographic distribution of senile plaques was determined throughout the amygdala using thioflavine-S and Bielschowsky silver methods. In the amygdala, the distribution and density of senile plaques were not bound by conventional cytoarchitectural groupings but rather were most dense in the ventromedial regions of the amygdala with decreasing density in dorsal and lateral directions. Importantly, the density and distribution of senile plaques failed to correlate with the normal topography and/or density of the various peptidergic or cholinergic fibers within the amygdala. The finding that plaques do not correlate with the topographic distribution of any specific transmitter system suggests that plaques likely do not arise from the degeneration of a single neurotransmitter system (i.e., the cholinergic system). However, the finding that in AD a transmitter is most markedly depleted in regions of greatest plaque density, suggests certain constituents of the plaque (e.g. beta-amyloid) may be contributing to the degeneration of local fibers. The extent to which a transmitter was depleted in AD patients varied considerably among those four investigated with the cholinergic and NT systems displaying the most dramatic reductions, followed by SP and SOM. Despite these differential reductions in fiber density, all four neurotransmitters were found localized within dystrophic neurites and in most instances these dystrophic neurites were associated with thioflavine-positive senile plaques. In contrast to the AD cases, the HPND cases were characterized by no significant reductions in immunolabeled fibers, although immunostained dystrophic neurites were very prevalent in the HPND cases. These data suggest that dystrophic neurites occur very early in the disease process and likely precede the actual loss of fibers when or if it occurs.(ABSTRACT TRUNCATED AT 400 WORDS)

The synaptic organization of the neocortex in Alzheimer's disease

Alzheimer's disease (AD) is characterized by a progressive deterioration of cognitive functions. Recent studies have shown that, in addition to the classically described lesions (plaques and tangles) found in AD, this neurodegenerative disorder is characterized by neuronal and synaptic loss and by synapto-axonal pathology. Stepwise regression analysis has shown that the major correlate of cognitive deficiency is the synapse loss in the prefrontal cortex, contributing about 70% of the strength of the correlation with global psychometric tests. We review evidence that supports the theory that most of the synaptic loss in the neocortex is derived from loss of cortico-cortical associational input into the modules. This hypothesis also predicts that neuritic plaque formation in the neocortical modules could represent an aberrant sprouting reaction of associational fibers responding to abnormal growth stimuli or to local damage. On these bases, it is also proposed that the cellular substrate of AD pathology is synapto-axonal, while in certain other forms of dementia such as Creutzfeldt-Jacob disease (CJD) and HIV encephalitis (HIVE) it is primarily dendritic.

Morphologic alterations of choline acetyltransferase-positive neurons in the basal forebrain of aged behaviorally characterized Fisher 344 rats

We examined Fisher 344 female rats aged 6, 27, and 33 months old. Prior to sacrifice and morphometric analyses of forebrain cholinergic neurons all rats underwent behavioral characterization in a spatial learning task using the Morris water maze. Performance on the spatial task permitted subsequent grouping of the 27- and 33-month-old animals into impaired or nonimpaired groups. Importantly, the percentage of animals that displayed spatial impairments increased sharply with advancing age. Quantitative assessment of the size and density of choline acetyltransferase (ChAT)-positive neurons throughout the basal forebrain revealed a significant enlargement of forebrain cholinergic neurons within 27-month-old nonimpaired rats compared to 6-month-old rats and 27- and 33-month-old impaired animals. This increase in size was most noted in the medial septum and nucleus of the diagonal band. Significant decreases in the density of ChAT-positive neurons was observed only in the nucleus of the diagonal band of 27-month-old impaired rats compared to 6-month-old controls. Although the significance of enlarged forebrain cholinergic neurons is unclear, we discuss the possibility that within aged rodents neuronal swelling is an active event and represents an early manifestation of the aging process and may constitute a restorative and/or compensatory event in that these rats are relatively asymptomatic with respect to their behavioral deficits. In addition, we discuss in some detail various technical and life effect issues which may vary the outcome of investigations of aged rodents.

Differential incorporation of processes derived from different classes of neurons into senile plaques in Alzheimer's disease

The incorporation of neurites into amyloid deposits is an important step in the formation of senile plaques in Alzheimer's disease. It is unknown whether all neuronal types contribute neurites equally to plaques, or whether the processes of certain types are preferentially incorporated. We addressed this question by comparing the incorporation into neocortical plaques of neurites containing the widely distributed neuronal markers chromogranin A (CgA), parvalbumin (PV) and calbindin D-28K (CaBP) in relation to the number of neuronal perikarya expressing each of these substances in the neocortex. We found a consistent, statistically significant ranking, so that CgA-immunoreactive (ir) neurites were preferentially incorporated into plaques in comparison with PV-ir, and PV-ir were favoured over CaBP-ir neurites.

Parvalbumin-immunoreactive dystrophic neurites and aberrant sprouts in the cerebral cortex of patients with Alzheimer's disease

Parvalbumin-immunoreactive dystrophic neurites and aberrant terminal sprouts associated with senile plaques, together with preserved density of parvalbumin-immunoreactive neurons, were found in the cerebral cortex of two patients with Alzheimer's disease, one of them familiar, in which a biopsy of the left frontal lobe was carried out for diagnostic and counselling purposes. These findings suggest that, although parvalbumin-immunoreactive cells are relatively resistant to degeneration in Alzheimer's disease, parvalbumin-immunoreactive neuronal processes can degenerate in some cases of Alzheimer's disease.

Evidence that transmitter-containing dystrophic neurites precede those containing paired helical filaments within senile plaques in the entorhinal cortex of nondemented elderly and Alzheimer's disease patients

Within the amygdala of elderly subjects and patients with Alzheimer's disease (AD), we recently found evidence suggesting amyloid beta-protein (A beta P) deposition occurs before the appearance of dystrophic neurites. Moreover, these data suggested dystrophic neurites initially lack evidence of cytoskeletal pathology although with time and further maturation, the dystrophic neurites display an altered cytoskeleton as evidenced by their immunoreactivity to Alz-50 and paired-helical filaments (PHF). These findings are of particular relevance to our understanding of the sequence of pathologic events in AD and thus it has become important to determine whether these events are unique to the amygdala or are representative of a more general pattern which can be found throughout the brain. Using a battery of antibodies to markers that are characteristic of AD pathology (i.e., A beta P, PHF, and Alz-50), three peptidergic neurotransmitters (neurotensin, somatostatin, and substance P), and one neurotransmitter biosynthetic enzyme (choline acetyltransferase), we examined the entorhinal cortex (EC) of three groups of subjects (AD, normal elderly, and a group of nondemented elderly with numerous senile plaques). The EC was studied, in part, because it is well recognized as a brain region displaying severe and, most importantly, early pathologic changes. Like the amygdala, we found evidence that amyloid beta-protein immunoreactive (A beta P-IR) and thioflavine-S-positive senile plaques occur within the EC prior to the appearance of transmitter-, Alz-50-, or PHF-immunoreactive dystrophic neurites. We also observed transmitter-immunoreactive dystrophic neurites in the absence of Alz-50 or PHF-immunolabeled dystrophic neurites and transmitter- and Alz-50-IR dystrophic neurites in the absence of those containing PHF. Collectively, these findings were similar to those seen within the amygdala and thus reinforced the concept that A beta P deposition is the primary event in plaque pathology, and this deposition is subsequently followed by the appearance of dystrophic neurites which retain their transmitter phenotype yet lack an altered cytoskeleton. With time, these dystrophic neurites develop cytoskeletal alterations and become immunoreactive to Alz-50 and PHF.

Evidence that transmitter-containing dystrophic neurites precede paired helical filament and Alz-50 formation within senile plaques in the amygdala of nondemented elderly and patients with Alzheimer's disease

Immunocytochemical techniques were employed to examine the temporal ordering whereby amyloid beta-protein (A beta P) and neuronal elements collectively come together to form senile plaques in Alzheimer's disease (AD). Specifically, we addressed three questions: (1) whether A beta P deposition precedes or follows neuritic changes; (2) whether paired helical filament (PHF) formation is an early or late event in the genesis of the dystrophic neurites which participate in plaque formation; and (3) whether the density of senile plaques displays any relationship with the prevalence of PHF or Alz-50 containing neurons. To address these questions we studied the amygdala from a group of patients with AD, a group of nondemented age-matched individuals exhibiting a sufficient number of senile plaques to be classified by neuropathological criteria as AD, and a group of age-matched controls without AD pathology. Amyloid-bearing plaques were demonstrated by A beta P immunolabeling and thioflavine-S staining. Neuritic changes in the form of dystrophic neurites were observed with the aid of antibodies against PHF, Alz-50, as well as antibodies against several neuropeptides (i.e., substance P, somatostatin, and neurotensin) and the acetylcholine biosynthetic enzyme, choline acetyltransferase. By using a graded range of pathologic changes both within and across the patient population to provide us with a means of evaluating plaque deposition from its earliest to most advanced stages of development, we observed in patients and/or regions of the amygdala displaying a mild degree of pathologic change A beta P deposition in the absence of any neuritic changes. With increasing density of A beta P, however, we began to observe dystrophic neurites within plaques. In regions of relatively few plaques, the dystrophic neurites were immunolabeled only with antibodies against the various neurotransmitters and they lacked evidence of cytoskeletal pathology (i.e., Alz-50 or PHF). Only as the density of A beta P increased further within a region, were dystrophic neurites observed that exhibited Alz-50 or PHF. In no instance did we observe a relationship between the density of A beta P deposition and the density of Alz-50 or PHF-immunoreactive neurons. Collectively, our data suggest that the deposition of A beta P is an early pathologic event in senile plaque formation. Thereafter, swollen neurites can be seen in the vicinity of A beta P. This early neuritic response, which can first be visualized by immunolabeling for one or another transmitter substance, is followed by alterations in the cytoskeleton as recognized initially by antibodies to Alz-50 and subsequently by the presence of PHF.

Cholecystokinin-, enkephalin-, and substance P-like immunoreactivity in the dentate area, hippocampus, and subiculum of the domestic pig

The distribution of cholecystokinin-like, enkephalin-like, and substance P-like immunoreactivities is described in the dentate area, hippocampus, and subiculum of the domestic pig (Sus scrofa domesticus) as a baseline for future experimental studies. The distributions in the pig are compared with previous observations in other species. Cholecystokinin-like immunoreactive nerve cell bodies were intensely stained and present in large numbers in all subfields studied. Cholecystokinin-like immunoreactive terminals appeared as stained puncta, whereas fibers were only rarely encountered. The puncta were mainly seen in the dentate molecular layer and dentate granule cell layer, the pyramidal cell layer of the hippocampal regio inferior, stratum moleculare of the hippocampal regio superior, and in the subiculum. Enkephalin-like immunoreactive nerve cell bodies were faintly stained and generally present in very small numbers, except for some pyramidal cells in the subicular cell layer. Enkephalin-like immunoreactive fibers were few in number, whereas stained puncta appeared with variable densities. Puncta of particularly high densities were found in the dentate molecular layer, whereas they appeared of moderate density in the dentate hilus, stratum moleculare of the hippocampal regio superior, and in the subiculum. Substance P-like immunoreactive nerve cell bodies were few and very faintly stained. They primarily occurred in the dentate hilus, stratum oriens of the hippocampus, and in the subicular cell layer. Stained fibers were few in number, whereas stained puncta were present in abundant numbers corresponding to the mossy fiber projection in the dentate hilus and the layer of mossy fibers of the hippocampal regio inferior, and in moderate numbers in stratum moleculare of the hippocampal regio superior and in the subiculum. For all three neuropeptides there were consistent and very characteristic variations in the distribution of immunoreactivity along the septotemporal axis of the hippocampus. When viewed in a comparative perspective the distribution of enkephalin-like and substance P-like terminals in the domestic pig displayed striking differences from the basic pattern observed in other species. This contrasted with the distribution of cholecystokinin-like neurons and terminals, which resembled more closely these species.

Alzheimer's disease-like dystrophic neurites characteristically associated with senile plaques are not found within other neurodegenerative diseases unless amyloid beta-protein deposition is present

Swollen, bulbous-shaped (dystrophic) neurites are a common pathologic feature of Alzheimer's disease (AD) and represent one of the most abundant neuritic abnormalities within the brains of patients with this disease. In the present study, we sought to determine whether the dystrophic neurites which are observed in association with senile plaques are unique to AD or whether they are characteristic of a more generalized process of neuritic and/or neuronal degeneration which can be observed in other neurodegenerative diseases. To accomplish this, we examined post-mortem brain material from patients with AD, Parkinson's disease (PD), Parkinson's disease with associated AD, Parkinson's disease with dementia yet without AD pathology, Huntington's disease (HD), Pick's disease and normal age-matched controls (NC). Using a battery of antibodies to amyloid beta-protein (A beta P), paired-helical filaments (PHF), tyrosine hydroxylase, substance P, neurotensin, and somatostatin we found that immunolabeled dystrophic neurites of the type characteristically observed in AD, were seen only in cases and in brain regions where A beta P deposition was present. More specifically, brain areas known to display severe afferent and/or local degenerative changes such as the caudate and putamen in all three PD groups, the caudate in the HD cases, and the temporal cortex in the HD and Pick's cases were conspicuously free of these swollen neurites unless A beta P deposition was also present.(ABSTRACT TRUNCATED AT 250 WORDS)

Facilitation of tunnel maze performance by systemic injection of the neurokinin substance P

The effect of peripheral injections of substance P (SP) on performance in two different configurations of an automated tunnel maze was examined in three experiments. In two experiments, the effect of pretrial SP injections (10-1000 micrograms/kg) on performance in the hexagonal and radial maze configuration of an automated tunnel maze was investigated. In the hexagonal maze, which measures activity, exploratory efficiency, habituation, and perimeter walking, injection of SP affected perimeter walking only. In the radial maze, SP produced a facilitation of measures of efficiency and long-term and short-term memory without affecting activity. In the third experiment, the effect of pre- and posttrial injections of SP (50 or 500 micrograms/kg) on performance in the radial maze configuration was tested. Again, pretrial injections of 500 micrograms of SP facilitated performance with respect to measures of efficiency and short- and long-term memory; 50 micrograms produced a weaker effect. Virtually no effect was seen with posttrial injections.

Morphological evidence for a substance P projection from medial septum to hippocampus

The medial septal nucleus provides one of the major afferents to the hippocampal formation. The two major types of neurons present in the medial septum are cholinergic and GABAergic, but other types of neurons are also present. A small population of substance P-containing neurons is present along the border between the medial and lateral septum, but it is unclear whether these project to the hippocampus. The present study, by employing both anterograde and retrograde tracing techniques, combined with immunocytochemistry for substance P, provides direct morphological evidence for a substance P projection from the lateral region of medial septum to a portion of CA2/3a, which is restricted to the mid-septotemporal portion of the hippocampus.

Distribution of neurotensin immunoreactivity within the human amygdaloid complex: a comparison with acetylcholinesterase- and Nissl-stained tissue sections

In a previous study, we reported marked depletion of neurotensin-immunoreactivity (NT-IR) within selected regions of the amygdala of patients with Alzheimer's disease. The significance of these observations was partly obscured largely because we lacked a thorough understanding of the innervation pattern of neurotensin in the normal human amygdala. Accordingly, in the present study, we used a polyclonal antibody against neurotensin to characterize the distribution and morphology of neurotensin-immunoreactive neuronal elements within the human amygdaloid complex. NT-IR occurred in a topographic manner that respected the cytoarchitectural boundaries of the amygdaloid subregions as defined by Nissl staining and acetylcholinesterase histochemistry. Most NT-IR in the amygdala was contained within beaded fibers and dot-like puncta. Within the subnuclei of the amygdala, immunoreactive neuritic elements were most dense within the central nucleus followed by the medial nucleus and intercalated nuclei. The anterior amygdaloid area, basal complex, paralaminar nucleus, cortical nucleus, cortical-amygdaloid transition area, and amygdalohippocampal area contained moderate densities of immunoreactivity. The accessory basal and lateral nuclei exhibited scant NT-IR. Immunoreactive neurons were found only within the anterior amygdaloid area and the central, medial, intercalated, and lateral capsular nuclei. The distribution of NT-immunoreactive processes and cell bodies within selected regions of the amygdala provides an anatomical substrate that may explain, in part, the neuromodulatory actions of neurotensin upon autonomic, endocrine, and memory systems.

Astroglia in Alzheimer's disease

Amyloid deposits are characteristic of Alzheimer's Disease (AD) and there is growing evidence that amyloid may play an important role in the genesis of this neurodegenerative disease. This review discusses data which suggests that reactive astrocytes and microglia may be a necessary concomitant with amyloid to produce the neuropathology which manifests as AD. Several hypotheses and supporting data for mechanisms by which reactive astrocytes may mediate this neuropathology are presented. These include the possibility that amyloid induces excitotoxicity by interferring with astrocytic glutamate uptake, the possibility that amyloid has this effect via an action on a tachykinin-related receptor and the possibility that proteoglycans released by astrocytes may facilitate the deposition of amyloid plaques. Both symptomatic treatment to enhance cognitive function and treatment to stop the progression of AD are needed. It is hoped that answers to some of the unique questions raised here may provide new insight into the etiology and treatment of AD.

Synaptic pathology in Alzheimer's disease: immunological data for markers of synaptic and large dense-core vesicles

We have analysed several markers for small synaptic vesicles (synaptin-synaptophysin, p65 and SV2) and large dense-core vesicles (chromogranin A, secretogranin II/chromogranin C) in the brains of patients with Alzheimer's disease, and normal controls by immunoblotting and immunohistochemistry. In comparison to age-matched controls the levels of all three synaptic vesicle markers were decreased in temporal cortex of Alzheimer patients. On the other hand, the levels of chromogranin A were increased, and those of secretogranin II lowered. This resulted in a significant increase of the ratios of chromogranin A to synaptophysin, p65 or SV2 and of that for chromogranin A to secretogranin II. These increases were significantly correlated to clinical severity of dementia and extent of neuropathological changes. By immunohistochemistry a high percentage of senile plaques was found to contain chromogranin A-reactive dystrophic neurites, whereas synaptophysin reactivity within plaques was rare. These results indicate that the number of synaptic vesicles is lowered in Alzheimer's disease, and that one component of large dense-core vesicles, i.e. chromogranin A, is elevated. We, thus, suggest that in Alzheimer's brain distinct changes occur for both types of synaptic organelles.

Parvalbumin immunoreactive neurons in normal human temporal neocortex and in patients with Alzheimer's disease

Parvalbumin-immunoreactive (PARV-ir) neurons were studied in the temporal neocortex of 4 normal subjects and in 7 patients with Alzheimer's disease (AD) whose brains were removed from the skull between 1 and 4 h after death and immediately fixed by perfusion through the carotid arteries to minimize pitfalls related to delayed tissue processing. Freezing microtome sections were immunostained free-floating for PARV using a well characterized monoclonal antibody diluted at 1:5000 and the peroxidase-antiperoxidase method. PARV-ir cells predominated in layers III, IV and V and were classified as bitufted cells and small, medium and large multipolar neurons according to their dendritic arbors. Immunoreactive cell processes surrounding the soma of neighbouring cells and immunoreactive vertical strings of buttons were consistent, respectively, with terminal axons of basket cells and chandelier neurons. The number of PARV-ir cells in the superior (T1), middle (T2) and inferior (T3) temporal gyri was variable from one case to another in both normal and pathological cases. Only 1 of 7 patients with AD had significantly reduced numbers of PARV-ir neurons, thus suggesting that PARV-ir cells in the neocortex are relatively resistant to degeneration in Alzheimer's disease.

Non-endocrine applications of somatostatin and octreotide acetate: facts and flights of fancy

Somatostatin, originally detected by Krulich and ultimately isolated by Brazeau, was initially described as a growth hormone release-inhibiting factor. Subsequent investigation into the use of native somatostatin and the development of long-acting somatostatin analogues, especially octreotide acetate, have fostered increasing uses of these compounds. Though the clinical and investigational uses of somatostatin and its analogues are varied, one central theme remains constant: the ability of these agents to suppress circulating peptide levels. This article, a review of the current non-endocrine applications of somatostatin and its analogues, covers a wide range of potential applications for somatostatin-like compounds. These include use in cirrhosis and variceal bleeding, peptic ulcer disease, pancreatic fistulas, acute and chronic pancreatitis, dumping syndrome, cancer therapy, small bowel fistulas, psoriasis, pain control, and autonomic hypotension. Somatostatin may also play a role in the development and potential treatment of neurologic disease and may have profound found influence on behavior.

Substance P and neurodegenerative disorders. A speculative review

The causes of the neurodegenerative disorders of Parkinson's disease (PD), Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS) are unknown. It is proposed that all these disorders result primarily from a loss of trophic peptidergic neurotransmitter, possibly Substance P (SP). This loss in turn produces the classical neuronal degeneration seen in each of these diseases and occurs due to a combination of natural aging and chronic autoimmune destruction following a viral infection of the CNS, early in life. The loss is therefore slow and by the time of clinical presentation the inflammatory process is disappearing as the antigenic stimulus lessens with its removal. The implications of the theory in terms of future research and therapy are briefly discussed.

Pathology of Parkinson's disease. Changes other than the nigrostriatal pathway

In Parkinson's disease (PD), in addition to degeneration of the nigrostriatal dopaminergic pathway, a variety of neuronal systems are involved, causing multiple neuromediator dysfunctions that account for the complex patterns of functional deficits. Degeneration affects the dopaminergic mesocorticolimbic system, the noradrenergic locus ceruleus (oral parts) and motor vagal nucleus, the serotonergic raphe nuclei, the cholinergic nucleus basalis of Meynert, pedunculopontine nucleus pars compacta, Westphal-Edinger nucleus, and many peptidergic brainstem nuclei. Cell losses in subcortical projection nuclei range from 30 to 90% of controls; they are more severe in depressed and demented PD patients. Most of the lesions are region-specific, affecting not all neurons containing a specific transmitter or harboring Lewy bodies. In contrast to Alzheimer's disease (AD), subcortical system lesions in Parkinson's disease appear not to be related to cortical pathology, suggesting independent or concomitant degeneration. The pathogenesis of multiple-system changes contributing to chemical pathology and clinical course of Parkinson's disease are unknown.

Reduction of neurotensin immunoreactivity in the amygdala in Alzheimer's disease

The density of neurotensin immunoreactivity (NT-IR) was dramatically decreased in 6 of 12 amygdaloid nuclear subregions in patients with Alzheimer's disease (AD) compared to age-matched normals. Diminution of NT-IR was most pronounced in amygdaloid regions containing the greatest number of senile plaques. This contrasts to our previous findings of little, if any, loss of substance P or somatostatin immunoreactivity within these same regions. The present findings corroborate biochemical reports of a decrease in NT-IR in the AD amygdala and suggest that this peptide may be selectively affected relative to other neuropeptides.

A high ratio of chromogranin A to synaptin/synaptophysin is a common feature of brains in Alzheimer and Pick disease

Chromogranin A and synaptin/synaptophysin were characterized by immunological methods in human autopsy brain tissue from patients with Alzheimer's and Pick's disease. In immunoblots there was no qualitative difference between the antigens in control and diseased brain, but significant quantitative differences were found. In all Alzheimer cases there was a significantly lower level of synaptin/synaptophysin, whereas chromogranin A was higher in 4 out of 5 cases and in all cases relative to synaptin/synaptophysin. An analogous finding was obtained for Pick's disease. Immunohistologically a consistent staining of neuritic plaques for chromogranin A, but not for secretogranin II was found in Alzheimer cases. In Pick's disease the characteristic Pick bodies showed an analogous specific immunostaining.