Neuropeptides in Alzheimer type dementia

Bee Pollen and Probiotics May Alter Brain Neuropeptide Levels in a Rodent Model of Autism Spectrum Disorders

Neuropeptides play a major role in maintaining normal brain development in children. Dysfunction of some specific neuropeptides can lead to autism spectrum disorders (ASD) in terms of social interaction and repetitive behavior, but the exact underlying etiological mechanisms are still not clear. In this study, we used an animal model of autism to investigate the role of bee pollen and probiotic in maintaining neuropeptide levels in the brain. We measured the Alpha-melanocyte-stimulating hormone (α-MSH), Beta-endorphin (β-End), neurotensin (NT), and substance P (SP) in brain homogenates of six studied groups of rats. Group I served as control, given only PBS for 30 days; Group II as an autistic model treated with 250 mg PPA/kg BW/day for 3 days after being given PBS for 27 days. Groups III-VI were denoted as intervention groups. G-III was treated with bee pollen (BP) 250 mg/kg body weight/day; G-IV with Lactobacillus paracaseii (LB) (109 CFU/mL) suspended in PBS; G-V with 0.2 g/kg body weight/day Protexin^®, a mixture of probiotics (MPB); and G-VI was transplanted with stool from normal animals (FT) for 27 days prior to the induction of PPA neurotoxicity on the last 3 days of study (days 28–30). The obtained data were analyzed through the use of principal component analysis (PCA), discriminant analysis (DA), hierarchical clustering, and receiver operating characteristic (ROC) curves as excellent statistical tools in the field of biomarkers. The obtained data revealed that brain levels of the four measured neuropeptides were significantly reduced in PPA-treated animals compared to healthy control animals. Moreover, the findings demonstrate the ameliorative effects of bee pollen as a prebiotic and of the pure or mixed probiotics. This study proves the protective effects of pre and probiotics against the neurotoxic effects of PPA presented as impaired levels of α-MSH, β-End, NT, and SP.

Protective Effects of Pituitary Adenylate Cyclase-Activating Polypeptide and Vasoactive Intestinal Peptide Against Cognitive Decline in Neurodegenerative Diseases

Cognitive impairment is one of the major symptoms in most neurodegenerative disorders such as Alzheimer’s (AD), Parkinson (PD), and Huntington diseases (HD), affecting millions of people worldwide. Unfortunately, there is no treatment to cure or prevent the progression of those diseases. Cognitive impairment has been related to neuronal cell death and/or synaptic plasticity alteration in important brain regions, such as the cerebral cortex, substantia nigra, striatum, and hippocampus. Therefore, compounds that can act to protect the neuronal loss and/or to reestablish the synaptic activity are needed to prevent cognitive decline in neurodegenerative diseases. Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two highly related multifunctional neuropeptides widely distributed in the central nervous system (CNS). PACAP and VIP exert their action through two common receptors, VPAC1 and VPAC2, while PACAP has an additional specific receptor, PAC1. In this review article, we first presented evidence showing the therapeutic potential of PACAP and VIP to fight the cognitive decline observed in models of AD, PD, and HD. We also reviewed the main transduction pathways activated by PACAP and VIP receptors to reduce cognitive dysfunction. Furthermore, we identified the therapeutic targets of PACAP and VIP, and finally, we evaluated different novel synthetic PACAP and VIP analogs as promising pharmacological tools.

Neuropeptides Exert Neuroprotective Effects in Alzheimer's Disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by cognitive deficits and neuronal loss. Deposition of beta-amyloid peptide (Aβ) causes neurotoxicity through the formation of plaques in brains of Alzheimer's disease. Numerous studies have indicated that the neuropeptides including ghrelin, neurotensin, pituitary adenylate cyclase-activating polypeptide (PACAP), neuropeptide Y, substance P and orexin are closely related to the pathophysiology of Alzheimer's disease. The levels of neuropeptides and their receptors change in Alzheimer's disease. These neuropeptides exert neuroprotective roles mainly through preventing Aβ accumulation, increasing neuronal glucose transport, increasing the production of neurotrophins, inhibiting endoplasmic reticulum stress and autophagy, modulating potassium channel activity and hippocampal long-term potentiation. Therefore, the neuropeptides may function as potential drug targets in the prevention and cure of Alzheimer's disease.

Cholecystokinin and Alzheimer's disease: a biomarker of metabolic function, neural integrity, and cognitive performance

Cholecystokinin (CCK) is a satiety hormone that is highly expressed in brain regions like the hippocampus. CCK is integral for maintaining or enhancing memory and thus may be a useful marker of cognitive and neural integrity in participants with normal cognition, mild cognitive impairment, and Alzheimer's disease (AD). Cerebrospinal fluid (CSF) CCK levels were examined in 287 subjects from the Alzheimer's Disease Neuroimaging Initiative. Linear or voxelwise regression was used to examine associations between CCK, regional gray matter, CSF AD biomarkers, and cognitive outcomes. Briefly, higher CCK was related to a decreased likelihood of having mild cognitive impairment or AD, better global and memory scores, and more gray matter volume primarily spanning posterior cingulate cortex, parahippocampal gyrus, and medial prefrontal cortex. CSF CCK was also strongly related to higher CSF total tau (R² = 0.342) and p-tau-181 (R² = 0.256) but not Aβ1-42. Tau levels partially mediated CCK and cognition associations. In conclusion, CCK levels may reflect compensatory protection as AD pathology progresses.

Cell-Type-Specific Afferent Innervation of the Nucleus Accumbens Core and Shell

The nucleus accumbens (NAc) is clearly implicated in reward processing and drug addiction, as well as in numerous neurological and psychiatric disorders; nevertheless, the circuit mechanisms underlying the diverse functions of the NAc remain poorly understood. Here, we characterized the whole-brain and monosynaptic inputs to two main projection cell types – D1 dopamine receptor expressing medium spiny neurons (D1R-MSNs) and D2 dopamine receptor expressing medium spiny neurons (D2R-MSNs) – within the NAc core and NAc shell by rabies-mediated trans-synaptic tracing. We discovered that D1R-MSNs and D2R-MSNs in both NAc subregions receive similar inputs from diverse sources. Inputs to the NAc core are broadly scattered, whereas inputs to the NAc shell are relatively concentrated. Furthermore, we identified numerous brain areas providing important contrasting inputs to different NAc subregions. The anterior cortex preferentially innervates the NAc core for both D1R-MSNs and D2R-MSNs, whereas the lateral hypothalamic area (LH) preferentially targets D1R-MSNs in the NAc shell. Characterizing the cell-type-specific connectivity of different NAc subregions lays a foundation for studying how diverse functions of the NAc are mediated by specific pathways.

Synaptic plasticity modulation by circulating peptides and metaplasticity: Involvement in Alzheimer's disease

Synaptic plasticity is a cellular process involved in learning and memory whose alteration in its two main forms (Long Term Depression (LTD) and Long Term Potentiation (LTP)), is observed in most brain pathologies, including neurodegenerative disorders such as Alzheimer's disease (AD). In humans, AD is associated at the cellular level with neuropathological lesions composed of extracellular deposits of β-amyloid (Aβ) protein aggregates and intracellular neurofibrillary tangles, cellular loss, neuroinflammation and a general brain homeostasis dysregulation. Thus, a dramatic synaptic environment perturbation is observed in AD patients, involving changes in brain neuropeptides, cytokines, growth factors or chemokines concentration and diffusion. Studies performed in animal models demonstrate that these circulating peptides strongly affect synaptic functions and in particular synaptic plasticity. Besides this neuromodulatory action of circulating peptides, other synaptic plasticity regulation mechanisms such as metaplasticity are altered in AD animal models. Here, we will review new insights into the study of synaptic plasticity regulatory/modulatory mechanisms which could influence the process of synaptic plasticity in the context of AD with a particular attention to the role of metaplasticity and peptide dependent neuromodulation.

Neurochemical Markers in the Mammalian Brain: Structure, Roles in Synaptic Communication, and Pharmacological Relevance

BACKGROUND

Knowledge of molecular marker (typically protein or mRNA) expression in neural systems can provide insight to the chemical blueprint of signal processing and transmission, assist in tracking developmental or pathological progressions, and yield key information regarding potential medicinal targets. These markers are particularly relevant in the mammalian brain in the light of its unsurpassed cellular diversity. Accordingly, molecular expression profiling is rapidly becoming a major approach to classify neuron types. Despite a profusion of research, however, the biological functions of molecular markers commonly used to distinguish neuron types remain incompletely understood. Furthermore, most molecular markers of mammalian neuron types are also present in other organs, therefore complicating considerations of their potential pharmacological interactions.

OBJECTIVE

Here, we survey 15 prominent neurochemical markers from five categories, namely membrane transporters, calcium-binding proteins, neuropeptides, receptors, and extracellular matrix proteins, explaining their relation and relevance to synaptic communication.

METHOD

For each marker, we summarize fundamental structural features, cellular functionality, distributions within and outside the brain, as well as known drug effectors and mechanisms of action.

CONCLUSION

This essential primer thus links together the cellular complexity of the brain, the chemical properties of key molecular players in neurotransmission, and possible biomedical opportunities.

Alzheimer's disease: clinical, neuropathologic, neuropsychologic, and brain metabolic findings

Approximately four million individuals over 65 years ofage sufferfrom some form of dementia. A majority of these people sufferfrom an Alzheimer's-type dementia. Brain alterations associated with this disease process include neurofibrillary tangles and senile plaques and reductions in concentrations of chemical messengers. Alzheimer's-type dementia is typified by a slow decline in intellect andpersonality. It is usually diagnosed after other possibilities have been excluded, and can be correctly diagnosed only upon autopsy. Over 12 of these chemical messenger systems have been examined in Alzheimer's disease. Brain tissue of autopsied Alzheimer's patients has revealed reductions in chemical messenger systems such as the cholinergic, noradrenergic, dopaminergic, serotoninergic, and recently, somatostatin and corticotropin. Treatment strategies based on the deficits of these chemical systems has been unremarkable to date. The only treatment that has yielded positive results thus far has been with a drug of the cholinergic system, physostigmine. However, side effects limit its use. A new brain scanning methodology called Positron Emission Tomography has revealed brain metabolic deficits in the parietal and temporal lobes of the brain in patients with mild to moderate Alzheimer's disease. Patients with severe Alzheimer's disease have brain metabolic deficits throughout their brain. Effective study ofAlzheimer's disease must encompass clinicalandpost-mortem studies that include brain chemical evaluations in addition to PET scanning. A combined approach willyield a better understanding of what Alzheimer's-type dementia is, how it progresses, and how it might better be treated.

Dissecting the role of sortilin receptor signaling in neurodegeneration induced by NGF deprivation

Sortilin is a member of the family of vacuolar protein sorting 10 protein domain receptors which has emerged as a co-receptor in cell death and neurodegeneration processes mediated by proneurotrophins.

Here we tested the possibility that sortilin deficiency interferes with behavioral and neuropathological endpoints in a chronic Nerve Growth factor (NGF)-deprivation model of Alzheimer’s disease (AD), the AD10 anti-NGF mouse. AD10 mice show cholinergic deficit, increased APP processing and tau hyper-phosphorylation, resulting in behavioral deficits in learning and memory paradigms assessed by novel object recognition and Morris water maze tests. Sort1^−/− mice were crossed with AD10 anti-NGF mice and the neurodegenerative phenotype was studied. We found that the loss of sortilin partially protected AD10 anti-NGF mice from neurodegeneration. A protective effect was observed on non-spatial memory as assessed by novel object recognition, and histopathologically at the level of Aβ and BFCNs, while the phosphotau increase was unaltered by knocking out sortilin. We suggest that sortilin might be involved in different aspects of neurodegeneration in a complex way, supporting the view that sortilin functions in the CNS are broader than being a co-receptor in proneurotrophin and neurotrophin signaling.

Overexpression of the human β-amyloid precursor protein downregulates cortistatin mRNA in PDAPP mice

We measured preprocortistatin mRNA expression in young and aged transgenic (Tg) mice overexpressing the human beta-amyloid precursor protein (hbetaAPP) under the platelet-derived growth factor-beta promoter. Our findings suggest that the significant increase in hippocampal cortistatin mRNA expression during normal aging is significantly attenuated in Tg mice at an age known to exhibit beta-amyloid protein (Abeta) deposition. These deficits in cortistatin expression may play a role in the deficits in hippocampal-dependent spatial learning and sleep/wake states previously demonstrated in aged Tg mice.

Effect of memantine on the levels of glial cells, neuropeptides, and peptide-degrading enzymes in rat brain regions of ibotenic acid-treated alzheimer's disease model

It has been implicated that glia activation plays a critical role in the progression of Alzheimer's disease (AD). However, the precise mechanism of glia activation is not clearly understood yet. In our present studies, we confirmed our previous results where change the levels of neuropeptides and peptidases in ibotenic acid (IBO) infusion into the rat nucleus basalis magnocellularis, an animal model of AD. Furthermore, we extended our study to investigate a possible protection effect of co-administration on the changes of neuropeptides, and neuronal and glial cells in IBO-infused rat brain by memantine treatment. The levels of substance P and somatostatin were decreased in the striatum and frontal cortex 1 week after IBO infusion, and recovered to the control level by memantine treatment, indicating the involvement of neuropeptides in AD pathology. Furthermore, the immunohistochemical and enzymatic studies of GFAP and CD 11b, and peptidylarginine deiminase, markers of glia, in the striatum and frontal cortex showed the increase in IBO-treated rat brain as compared with controls, while co-administration of memantine and IBO no increase of astrocytes and microglia activation was observed. The present biochemical and immunohistochemical results suggest that glia activation might play an important role to the pathology of AD, and correlate with the changes of neuropeptide levels in AD brain that is recovered by memantine treatment.

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.

S 17092: a prolyl endopeptidase inhibitor as a potential therapeutic drug for memory impairment. Preclinical and clinical studies

Any treatment that could positively modulate central neuropeptides levels would provide a promising therapeutic approach to the treatment of cognitive deficits associated with aging and/or neurodegenerative diseases. Therefore, based on the activity in rodents, S 17092 (2S,3aS,7aS)-1][(R,R)-2-phenylcyclopropyl]carbonyl]-2-[(thiazolidin-3-yl)carbonyl]octahydro-1H-indole) has been selected as a potent inhibitor of cerebral prolyl-endopeptidase (PEP). By retarding the degradation of neuroactive peptides, S 17092 was successfully used in a variety of memory tasks. These tasks explored short-term, long-term, reference and working memory in aged mice, as well as in rodents and monkeys with chemically induced amnesia or spontaneous memory deficits. S 17092 has also been safely administered to humans, and showed a clear peripheral expression of its mechanism of action through its inhibitory effect upon PEP activity in plasma. S 17092 exhibited central effects, as evidenced by EEG recording in healthy volunteers, and could improve a delayed verbal memory task. Collectively, the preclinical and clinical effects of S 17092 have suggested a promising role for this compound as an agent for the treatment of cognitive disorders associated with cerebral aging.

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.

Further evidence for a dissociation between different forms of mnemonic expressions in a mouse model of age-related cognitive decline: effects of tacrine and S 17092, a novel prolyl endopeptidase inhibitor

It has been demonstrated previously on the radial maze that the emergence of an age-related mnemonic impairment is critically dependent on the form which the discrimination problems took. Hence, when the arms were presented one by one (i.e., successive go-no-go discrimination), both adult and aged mice learned to distinguish between positive (baited) and negative (unbaited) arms readily, as evidenced by their increased readiness to enter positive relative to negative arms (i.e., by a differential in arm-entry latencies). A selective impairment in the aged mice was seen when these arms were presented subsequently as pairs, such that the mice were confronted with an explicit choice (i.e., simultaneous 2-choice discrimination). When discriminative performance was measured by the differential run speed between positive and negative arms, aged mice were also impaired. This was particularly pronounced in the 2-choice discrimination condition. We examined the effects of tacrine (3mg/kg, subcutaneously) or S 17092 (10mg/kg, orally) in aged mice on the three behavioral indices of this 2-stage spatial discrimination paradigm. The results indicated that: (1) Tacrine, but not S 17092, enhanced the acquisition of go-no-go discrimination as reflected in arm-entry latencies; (2) both drugs improved choice accuracy in simultaneous discrimination, although the effect of tacrine was less striking and, in particular, far from statistical significance in the very first 2-choice responses; and (3) neither drugs significantly affected run-speed performance. We conclude further that the specific patterns of drug effects on the three indices of discriminative performance might suggest that each index is associated with a distinct form of mnemonic expression relying on separate neural systems.

Determination of extracellular release of neurotensin in discrete rat brain regions utilizing in vivo microdialysis/electrospray mass spectrometry

In vivo microdialysis was used together with structure-specific high sensitivity nano-flow capillary liquid chromatography/micro-electrospray mass spectrometry to quantify and compare extracellular neurotensin from discrete regions of the rat brain. Microdialysis probes were implanted in the hypothalamus or globus pallidus/ventral pallidum in unanesthetized freely moving animals. Utilizing this specific methodology, recovered basal levels of neurotensin were detectable in hypothalamus and globus pallidus/ventral pallidum. The basal level of neurotensin in these regions were slightly higher in hypothalamus (101+/-11 amol/10 microl, n=6) compared to those in the globus pallidus/ventral pallidum region (74+/-12 amol/10 microl, n=8) in samples collected for 30 min at a flow-rate of 0.4 microl/min 150-180 min after the microdialysis probe implantation. After a pulse of 1.0 microl of 100 mM KCl-containing artificial cerebrospinal fluid during the next 30-min sampling period (180-210 min), the recovered neurotensin increased in hypothalamus and globus pallidus/ventral pallidum by 544% (548+/-90 amol/10 microl) and 674% (499+/-99 amol/10 microl), respectively. The basal levels of endogenously released neurotensin in the hypothalamus and globus pallidus/ventral pallidum were lower in the present study compared to those previously reported in the rat brain using in vivo microdialysis and radioimmunoassays. Our data demonstrate the effectiveness of combining in vivo microdialysis and structure-specific micro-electrospray mass spectrometry for the quantitation of basal and stimulated in vivo levels of endogenous neurotensin (NT) in different brain areas.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on spatial memory and on cholinergic and peptidergic neurons in rats with ibotenate-induced lesions of the nucleus basalis magnocellularis

We conducted behavioral and neurochemical studies of a novel prolyl endopeptidase inhibitor, (S)2-[[(S)-2-(hydroxyacetyl)-1pyrrolidinyl]carbonyl]-N-(phenylmeth yl)-1-pyrrolidine-carboxamide (JTP-4819), in rats with lesions of the nucleus basalis magnocellularis (NBM-lesioned rats) induced by ibotenate. Administration of JTP-4819 (1 and 3 mg/kg, p.o.), on and after the 8th day, significantly shortened the escape latency in the Morris water maze as compared to the vehicle-treated group. JTP-4819 also significantly increased the path length in the quadrant with the platform removed in the spatial probe trial. Neurochemical studies of brains removed after the Morris water maze task showed that choline acetyltransferase activity in the cerebral cortex, but not the hippocampus, was significantly reduced by NBM lesioning, while there were no changes of muscarinic M1 receptor binding activity detected using [3H]pirenzepine. JTP-4819 had almost no effect on these cholinergic parameters in NBM-lesioned rats. Substance P-like immunoreactivity (LI), thyrotropin-releasing hormone (TRH)-LI, and arginine-vasopressin-LI were not significantly changed in the cerebral cortex and hippocampus of NBM-lesioned rats as compared to sham-operated rats. However, these neuropeptide levels were significantly increased in both brain regions by repeated administration of JTP-4819 (1, 3 and/or 10 mg/kg, p.o.). These results suggest that JTP-4819 ameliorated memory impairment due to NBM lesioning by potentiating SP, TRH and AVPergic neurons secondary to PEP inhibition.

Age and species-dependent differences in the neurokinin B system in rat and human brain

Neurokinin B and its cognate neurokinin-3 receptor are expressed more in the forebrain than in brain stem structures but little is known about the primary function of this peptide system in the central processing of information. In general, few studies have specifically addressed age-related changes of tachykinins, notably the changes in number and/or distribution of the neurokinin B-expressing and neurokinin-3 receptor-bearing neurons. Data on functions and changes of neurokinins in physiological aging are limited and apply mainly to the substance P/neurokinin-1 receptor system. In the present study, we analyzed neurokinin B/neurokinin-3 receptor system in young (5 months) versus middle aged (15 months) and old rats (23-25 months) and also in aging human brains. For the majority of the immunohistochemically examined regions of the rat brain, there was no statistically significant change in neuronal number and size of the neurokinin B and neurokinin-3 receptor staining. In the adult human brain, there was no age-associated change of the number or size of neurokinin-B-positive neurons. However, we found a major decline in number of neurokinin-3 receptor-expressing neurons between young/middle aged (30 years to 69 years) versus old (70 years and older) adults. Interestingly, numbers of neurokinin-3 receptor-positive microglia increased whereas the neurokinin-3 receptor-positive astrocytes remained unchanged in both aging rat and human brains. Finally, in addition to assessing the morphological and quantitative changes of the neurokinin B/neurokinin-3 receptor system in the rat and human brain, we discuss functional implications of the observed interspecies differences.

Transgenic mouse models of Alzheimer's disease and amyotrophic lateral sclerosis

Over the past several years, there has been enormous progress in generating transgenic mice that model aspects of human neurodegenerative diseases. These studies build upon the efforts of molecular geneticists who have identified a number of genes that, when mutated, cause familial forms of these diseases. In this review, we focus on the mutations that cause familial forms of Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), and transgenic mouse models that develop clinical and pathological abnormalities resembling those occurring in the human diseases.

A novel prolyl endopeptidase inhibitor, JTP-4819--its behavioral and neurochemical properties for the treatment of Alzheimer's disease

Formation of beta-amyloid and neurofibrillary tangles in the brain due to genetic or other factors is the most frequent cause of Alzheimer's disease. In addition, marked reduction of certain brain neuropeptide levels is a consistent finding in patients with Alzheimer's disease, together with the deterioration of cholinergic neurons. Currently, there is great demand for the development of new drugs to improve memory deficits or to delay the neurodegenerative process in conditions such as Alzheimer's disease. In this report, the pharmacological actions of JTP-4819, a novel specific prolyl endopeptidase (PEP) inhibitor devised for the treatment of Alzheimer's disease, are reviewed with respect to its effects on PEP activity, neuropeptidergic and cholinergic neurons, and memory-related behavior in rats. We also discuss the possible beneficial effect of JTP-4819 on beta-amyloid metabolism and its potential neuroprotective properties.

Postnatal development of somatostatin- and neuropeptide Y-immunoreactive neurons in rat cerebral cortex: a double-labeling immunohistochemical study

The postnatal development of somatostatin (SOM)- and neuropeptide Y (NPY)-immunoreactive (ir) neurons was examined in rat cerebral cortex, while considering their coexistence in cortical neurons. Using double immunohistochemical staining for SOM and NPY with diaminobenzidine and benzidine dihydrochloride as chromogens, we subdivided immunoreactive cells into double-labeled SOM/NPY-, SOM only-, and NPY only-ir neurons. SOM/NPY- and SOM only-ir neurons were detectable even at the day of birth, in contrast on NPY only-ir cells which first appeared in most cortices from week two. The morphological features of double-labeled SOM/NPY neurons differed with those of SOM only- and NPY only-ir neurons. No apparent changes in the shape and size of single-labeled neurons occurred with age; throughout their postnatal life they were round and ovoid, had a thin rim of perinuclear cytoplasm, and short processes. However, the features of SOM/NPY-ir neurons were not consistent according to postnatal age; by day P7, these neurons showed immature features and they began to show more advanced neuronal characteristics by week P2, when they had a larger and more intensely-stain cytoplasm. In addition, their processes were longer, thicker and more complex than at earlier ages. At this age, SOM/NPY-ir somata were close to their near maximum size. From week P4, they became smaller and were lightly labeled. SOM/NPY-ir somata were larger than SOM only- and NYP only-ir somata at and after two weeks of age. The present results, showing different postnatal maturation patterns such as time of appearance and morphological features, raise the possibilities that double-labeled SOM/NPY and single-labeled immunoreactive neurons may be different populations regulated by different mechanisms in their development, and with different functional properties during development.

Alterations of peptide metabolism and neuropeptidase activity in senile dementia of the Alzheimer's type

Work in our laboratory has shown that in addition to previously characterized changes in the level of neuropeptides in SDAT brain, the activity of degradative enzymes responsible for peptide metabolism is also affected. In addition to other reported alterations in peptide metabolism, we have observed that SS-28 degradation is increased in Brodmann area 22 whereas substance P degradation is increased in temporal cortex. Changes in the degradation of these neuropeptides known to be affected in SDAT correlate well with alterations in the activity of specific neuropeptidases. Trypsin-like serine protease activity is increased in SDAT Brodmann area 22 which parallels the increased degradation of SS-28. The activity of MEP 24.15 is decreased in temporal cortex which corresponds to the decreased degradation of substance P. Changes in the activity of these degradative enzymes in SDAT brain can potentially affect the action of other neuropeptide substrates because the neuropeptidases discussed here terminate the action of several neuropeptides. As more neuropeptide and degradative peptidase alterations are discovered in SDAT, greater emphasis may be placed on the role that peptides and neuropeptidases play in the progression of SDAT.

Age-related changes of VIP, NPY and somatostatin-immunoreactive neurons in the cerebral cortex of aged rats

Recent studies have explored certain changes with aging of neurons containing neuropeptides. The degree of loss of vasoactive intestinal polypeptide (VIP)-, neuropeptide Y (NPY)- and somatostatin-containing neurons in the aged CNS has not yet been established with certainty however, and available data is often contradictory. Changes with aging of VIP- and NPY-containing neurons were demonstrated by immunocytochemistry in this study. A major loss of VIP-immunoreactive (ir) neurons in aged rat brain was observed in the frontal cortex area 3, parietal cortex area 1, hindlimb area, temporal cortex area 1 and 2, monocular part of occipital cortex area 1, occipital cortex area 2, and retrosplenial cortex. VIP-ir cells in the frontal cortex areas 1 and 2, parietal cortex area 2, forelimb area, binocular part of the occipital cortex area 1, and the dentate gyrus were moderately decreased. The axis of VIP neurons in the aged group showed an irregular orientation tendency, especially in layers II and III. Major loss of NPY-ir neurons in aged rat brain were observed in the retrosplenial cortex, frontal cortex areas 1 and 2, parietal cortex areas 1 and 2, occipital cortex areas 1 and 2, the temporal cortex, hippocampus proper and cingulate cortex. Loss of NPY-ir neurons was observed mostly in layers V and VI. The number and length of dendritic branches also appeared to have decreased and shortened in the aged group. There were only slight decreases of somatostatin-ir cell numbers in the parietal and occipital cortex of the aged group. These results indicate the involvement of VIP and NPY-ir neurons in the aging process of cerebral cortex, and provide the morphological evidence for the decreased number of VIP and NPY neurons by immunocytochemistry in each area of cerebral cortex of aged rats.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on spatial memory and central cholinergic neurons in aged rats

The effects of a novel prolyl endopeptidase inhibitor (PEP), (S)-2-[[(S)-2-(hydroxyacetyl)-1-pyrrolidinyl]carbonyl]-N-(phenylmethyl)- 1-pyrrolidinecar-boxamide (JTP-4819), on performance of the Morris water maze task and on central cholinergic function were investigated in aged rats. Spatial memory (escape latency, path length, and swimming speed to the platform) was impaired in aged rats performing the Morris water maze task when compared to young rats. Administration of JTP-4819 (1 mg/kg, p.o.) for 14 days improved this memory deficit in aged rats, as shown by the decrease in escape latency and path length. In addition, when JTP-4819 (at doses of 1 and 3 mg/kg, p.o.) was administered for 3 wk, it reversed the age-related increase of ChAT activity in the cerebral cortex and the decrease of 3H-choline uptake in the hippocampus. These data suggest that JTP-4819 ameliorates age-related impairment of spatial memory and partly reverses central cholinergic dysfunction, possibly due to the enhancement of neuropeptide function by inhibition of PEP mediated degradation of substance P, arginine-vasopressin, and thyrotropin-releasing hormone.

A novel prolyl endopeptidase inhibitor, JTP-4819, with potential for treating Alzheimer's disease

The pharmacological actions of JTP-4819, a new prolyl endopeptidase (PEP) inhibitor targeted for the treatment of Alzheimer's disease, are reviewed with respect to its effects on PEP activity, brain neurotransmitters, and memory-related behaviour in rats. JTP-4819 was shown to be a very potent and specific inhibitor of PEP. At nanomolar concentration, JTP-4819 inhibited the degradation of substance P, arginine-vasopressin, and thyrotropin-releasing hormone by PEP in supernatants of the rat cerebral cortex and hippocampus. Repeated administration of JTP-4819 reversed the aging-induced decrease in brain substance P-like and thyrotropin-releasing hormone-like immunoreactivity, suggesting that this drug may be able to improve the imbalance of peptidergic neuronal systems that develops with senescense by inhibiting PEP activity. JTP-4819 increased acetylcholine release from the frontal cortex and hippocampus, regions closely associated with memory, in both young and aged rats. In addition, it improved performance in several memory and learning-related tests (e.g., the Morris water maze task in aged or MCA-occluded rats and the passive avoidance test). This memory-enhancing effect of JTP-4819 may result from prevention of the metabolic degradation of brain neuropeptides by PEP as well as from the enhancement of acetylcholine release. Taken together, these unique and potent pharmacological actions of JTP-4819 suggest that it may have the potential to be used for treating Alzheimer's disease.

Ceruletide improves event-related potential indicators of cognitive processing in young but not in elderly humans

The effect of intravenously administered ceruletide, a cholecystokinin (CCK) analogue, on neurophysiologic signs of stimulus processing was tested in 16 young (19-28 years) and 16 aged (70-86 years) healthy subjects. Placebo or 2.5 micrograms ceruletide was infused within 30 minutes according to a double-blind within-subject crossover design. Thereafter, auditory event-related brain potential (AERP) responses to stimuli of an "oddball" task (including the random presentation of frequent standard tones and rare target tones) were recorded. Amplitudes of the P2, P3, and SW components of the AERP were reduced in aged subjects (p < 0.05, p < 0.001, and p < 0.01, respectively), and latencies (from stimulus onset) of the N2 and P3 components were prolonged (p < 0.05 and p < 0.01, respectively). Together, these changes indicate impaired cognitive processing capabilities in aged compared with young subjects. Ceruletide enhanced P3 and also the subsequent slow-wave (SW) component that occurs 500 to 700 ms poststimulus in young subjects (p < 0.05 and p < 0.001, respectively). The peptide did not at all affect AERPs in the elderly subjects. Results demonstrate the capability of ceruletide after systemic administration to enhance central nervous system indicators of cognitive processing such as P3 and SW in young subjects. However, despite the clear effect of the CCK analogue in young subjects, it remained ineffective in the group of aged subjects and, thus, failed to compensate for the decline in AERP signs of working memory functioning in the elderly subjects.

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.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on neuropeptide metabolism in the rat brain

The effect of a novel prolyl endopeptidase (PEP) inhibitor, (S)-2-[[(S)-2-(hydroxyacetyl)-1-pyrrolidinyl] carbonyl]-N-(phenylmethyl)-1-pyrrolidine-carboxamide (JTP-4819), on neuropeptide metabolism was investigated in the rat brain. JTP-4819 exhibited a strong in vitro inhibitory effect on cortical and hippocampal PEP activity, with the IC50 values being approximately 0.58 +/- 0.02 and 0.61 +/- 0.06 nM, respectively. JTP-4819 also inhibited the in vitro degradation of substance P (SP), arginine-vasopressin (AVP), and thyrotropin-releasing hormone (TRH) by rat brain supernatants, with the IC50 values being respectively 3.4, 2.1, and 1.4 nM in the cerebral cortex and 3.3, 2.8, and 1.9 nM in the hippocampus. Oral administration of JTP-4819 at doses of 1 and 3 mg/kg increased SP-like immunoreactivity (LI) and AVP-LI in the cerebral cortex. JTP-4819 also increased hippocampal SP-LI and AVP-LI at doses of 1 and 3 mg/kg, as well as hippocampal TRH-LI at a dose of 3 mg/kg. These findings suggest that JTP-4819 inhibited the degradation of SP, AVP, and TRH in the rat brain secondary to the inhibition of PEP, and thus increased cortical and hippocampal SP-LI and AVP-LI as well as hippocampal TRH-LI.

Neuropeptide deficits in schizophrenia vs. Alzheimer's disease cerebral cortex

Neuropeptide concentrations were determined in the postmortem cerebral cortex from 19 cognitive-impaired schizophrenics, 4 normal elderly subjects, 4 multi-infarct dementia (MID) cases, and 13 Alzheimer's disease (AD) patients. Only AD patients met criteria for AD. The normal elderly and MID cases were combined into one control group. Somatostatin concentrations were reduced in both schizophrenia and AD. Neuropeptide Y concentrations were reduced only in schizophrenia, and corticotropin-releasing hormone concentrations were primarily reduced in AD. Concentrations of vasoactive intestinal polypeptide and cholecystokinin also were reduced in schizophrenia, although not as profoundly as somatostatin or neuropeptide Y. In AD, cholecystokinin and vasoactive intestinal peptide were unchanged. Neuropeptide deficits in schizophrenics were more pronounced in the temporal and frontal lobes than in the occipital lobe. The mechanisms underlying these deficits in schizophrenia and AD are likely distinct. In schizophrenia, a common neural element, perhaps the cerebral cortical gaba-aminobutyric acid (GABA)-containing neuron, may underlie these deficits.

The neurochemistry of Alzheimer type, vascular type and mixed type dementias compared

We present the results of a meta-analysis of neurochemical changes in human post mortem brains of Alzheimer type (AD), vascular type (VD) and mixed type (MF) dementias, and matched controls based on 275 articles published between January 1980 and February 1994. Severity of degeneration between the different neurochemical systems is as follows, although ranking is difficult with regard to limited numbers of investigations in some neurochemical systems: Cholinergic system > serotonergic system > excitatory amino acids > GABAergic system > energy metabolism > NA > oxidative stress parameters > neuropeptides > DA. But, within a neurochemical system, degeneration is not evenly distributed. Spared parameters, e.g. muscarinic receptors and MAO-B, allow to make some suggestions for future therapeutic strategies.

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.

Age related change in the vasoactive intestinal polypeptide-immunoreactive neurons in the cerebral cortex of aged rats

Recent studies have explored certain changes in neurons containing neuropeptides with aging. However, until now, the degree of vasoactive intestinal polypeptide (VIP)-containing neuronal cell loss in the aged CNS has not yet been established with certainty, and available data are often contradictory. Changes in the VIP-containing neurons with aging were demonstrated by immunocytochemisty. Major loss of VIP-immunoreactive neurons in the aged rat brain were observed in frontal cortex area 3, parietal cortex area 1, hindlimb area, temporal cortex area 1 and 2, monocular part of occipital cortex area 1, occipital cortex area 2, and retrosplenial cortex. Frontal cortex area 1 and 2, parietal cortex area 2, forelimb area, binocular part of the occipital cortex area 1, and the dentate gyrus were moderately decreased. The axis of the VIP neurons in the aged group showed an irregular orientation tendency, especially in layers II and III. These results indicate the involvement of a neuronal system containing VIP in the aging brain, and provide the first morphological evidence for the loss of VIP neurons in the cerebral cortex of the aged rat.

Changes in neuropeptide levels after brain damage in rats

The physiological and pathophysiological roles of neuropeptides are still not clear. The aim of our study was to detect long lasting changes of vasoactive-intestinal peptide (VIP), somatostatin (SOM) and substance P (SP) contents in the rat cerebral cortex and hippocampus after brain lesion. The experiments were performed on groups of adult male Wistar rats. The first group consisted of animals with unilateral ablation of the sensorimotor cortex performed at the age of 60 days. The second group was a control one (rats of the same age but with an intact brain). Both groups of animals were sacrificed at the age of 90-105 days and radioimmunoassay was used to determine amounts of VIP, SOM and SP. The mean values of VIP levels were decreased significantly only in contralateral cortical areas, while there was an increase of SP in lesioned animals. Our results suggest that descrete changes in neuropeptide levels occur during restorative processes after brain lesion.

Trophic-factor modulation of cortical acetylcholinesterase reappearance following transection of the medial cholinergic pathway in the adult rat

Laminar patterns of cortical acetylcholinesterase (AChE) activity are reestablished in the adult, pharmacologically unmanipulated rat following axotomy of the medial cholinergic pathway. The extent to which trophic and/or growth promoting or inhibiting agents modulate AChE fiber reappearance is not fully understood. Such studies, however, would further clarify possible roles for these agents in neuronal plasticity in response to injury, as well as in plastic processes associated with normative functions. In the present experiments, we explored trophic modulation by intracortically infusing nerve growth factor (NGF) or somatostatin into cingulate cortex at a site distal to transection of the medial cholinergic pathway. Comparisons were made with sham-operated or noninfused transected controls, as well as with transected animals infused with renin or antibodies against NGF. Administration began 2 days after axotomy and continued at successive 3-day intervals for 4 weeks. It was found that, proximal to the lesion site, NGF increased and somatostatin decreased optical density of AChE; the number of AChE-containing fibers was unaltered compared to controls. Distal to the knife cut, both NGF and somatostatin increased number of AChE fibers but did not alter overall AChE optical density. Nonetheless, NGF produced an increase in the number of intensely staining puncta both proximal and distal to the cut. Neither renin nor anti-NGF antibodies produced statistically significant effects on optical density or number of fibers at any cortical locus studied. We conclude that NGF and somatostatin have opposite effects on the expression of AChE: whereas NGF increases AChE levels, somatostatin inhibits AChE accumulation in proximal fibers, perhaps by actions on synthesis or transport. Fiber proliferation, which only occurred distally, was affected positively by both NGF and somatostatin, indicating that neurite-promoting effects produced by both agents are confined to tissue regions where neurite extension is stimulated by axotomy. Increases in AChE-positive puncta produced by NGF, however, were not confined to regions of fiber proliferation.

Neuropeptide Y immunoreactive neurons in murine trisomy 16 cortical cultures. Plasticity of expression and differentiation

Neuropeptide Y (NPY)-containing neurons are depleted in the cortices of individuals with Alzheimer disease (AD), yet spared in the striatum of patients with Huntington chorea. It is unknown whether this neuronal phenotype is inherently susceptible to the neurodegenerative processes that are a hallmark of AD. To study this question, the murine trisomy 16 model of Down syndrome and Alzheimer disease was investigated. Since trisomic fetuses die in utero, studies were carried out on primary cultures of dissociated cortical neurons. These were prepared from 15-d gestational trisomy 16 fetuses and their littermate euploid controls, and examined by immunocytochemical staining for neuropeptide Y at 7 and 12 d in vitro. Trisomy 16 neurons were also grown on euploid glial carpets, whereas euploid neurons were grown on trisomic glia. The results demonstrate a significant increase in the number of NPY neurons and a stunting in the dendritic arbor of these neurons in trisomic vs euploid cortex. Both of these parameters could be normalized by direct contact with euploid glia. When euploid cortex was plated on trisomic glia, the number of NPY neurons and their morphology were altered so that they began to resemble trisomic NPY cortical neurons. These results indicate a dysregulation of NPY neuronal expression and differentiation in trisomy 16 cortex that are modifiable by interaction with euploid glia and imply an abnormal trophic (glial) environment in trisomic cortex.

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)

Nerve growth factor and Alzheimer's disease

Nerve growth factor (NGF) is a well-characterized protein that exerts pharmacological effects on a group of cholinergic neurons known to atrophy in Alzheimer's disease (AD). Considerable evidence from animal studies suggests that NGF may be useful in reversing, halting, or at least slowing the progression of AD-related cholinergic basal forebrain atrophy, perhaps even attenuating the cognitive deficit associated with the disorder. However, many questions remain concerning the role of NGF in AD. Levels of the low-affinity receptor for NGF appear to be at least stable in AD basal forebrain, and the recent finding of AD-related increases in cortical NGF brings into question whether endogenous NGF levels are related to the observed cholinergic atrophy and whether additional NGF will be useful in treating this disorder. Evidence regarding the localization of NGF within the central nervous system and its presumed role in maintaining basal forebrain cholinergic neurons is summarized, followed by a synopsis of the relevant aspects of AD neuropathology. The available data regarding levels of NGF and its receptor in the AD brain, as well as potential roles for NGF in the pathogenesis and treatment of AD, are also reviewed. NGF and its low affinity receptor are abundantly present within the AD brain, although this does not rule out an NGF-related mechanism in the degeneration of basal forebrain neurons, nor does it eliminate the possibility that exogenous NGF may be successfully used to treat AD. Further studies of the degree and distribution of NGF within the human brain in normal aging and in AD, and of the possible relationship between target NGF levels and the status of basal forebrain neurons in vivo, are necessary before engaging in clinical trials.

Induction of beta (A4)-amyloid in primates by injection of Alzheimer's disease brain homogenate. Comparison with transmission of spongiform encephalopathy

Amyloid plaques, associated with argyrophilic dystrophic neurites, and cerebral amyloid angiopathy (CAA), but no neurofibrillary tangles, were found in the brains of three middle-aged marmoset monkeys that had been injected intracerebrally (ic) 6-7 yr earlier with brain tissue from a patient with early-onset Alzheimer's disease. Such changes were not found in the brains of three age-matched control marmosets. Immunochemically the amyloid plaques and CAA stained with antibody to beta (A4)-protein. The plaques and CAA displayed dichroic birefringence when stained with Congo red and viewed under polarized light. beta (A4)-amyloid plaques and CAA were also found in the brain of one of two marmosets injected ic 6 yr previously with brain tissue from a patient with prion disease with concomitant beta (A4)-amyloid plaques and CAA. An occasional beta (A4)-amyloid plaque was found in the brains of two of four marmosets injected ic > 4.5 yr previously with brain tissue from three elderly patients, two of whom had suspected (but untransmitted) CJD. No beta (A4)-amyloid plaques or CAA were found in six marmosets who were older than the injected animals, in four marmosets that had not developed spongiform encephalopathy (SE) having been injected several years previously with human brain tissue from three younger patients with suspected or atypical prion disease, or in 10 younger marmosets who had undergone various neurosurgical procedures. Seventeen marmosets injected in the same way with brain tissue from patients or animals with SE developed SE 17-49 mo after injection. These results suggest that beta (A4)-amyloidosis is a transmissible process comparable to the transmissibility of SE.

Widespread deficits in somatostatin but not neuropeptide Y concentrations in Alzheimer's disease cerebral cortex

Somatostatin-like immunoreactivity (SLI) and neuropeptide Y-like immunoreactivity (NPYLI) were measured in the cerebral cortex of 49 patients with Alzheimer's disease (AD), and 9 elderly controls. Concentrations of SLI were lower in AD patients relative to controls in 9 of 10 cortical regions. In contrast, no significant differences in NPYLI concentrations between the two groups were observed in any of 10 regions. These studies suggest a dissociation between SLI deficits and NPYLI concentrations in the postmortem cerebral cortex of AD patients. The apparent sparing of NPYLI-containing neurons suggests that neuropeptide Y may be located within a separate group of neurons compared to somatostatin.

Peptide histidine methionine in cerebrospinal fluid of patients with senile dementia of the Alzheimer type

Immunoreactivities (IRs) of peptide histidine methionine (PHM) as well as somatostatin and vasoactive intestinal peptide (VIP) in the cerebrospinal fluid (CSF) were measured in patients with senile dementia of the Alzheimer type (SDAT) and age-matched control subjects. We found statistically significant reductions in the PHM-IR and somatostatin-IR levels in the CSF from patients with SDAT, as compared with those of the controls. However, the VIP-IR level in the CSF from SDAT was not different from that of the controls. These results suggest that selective degeneration of neurons containing somatostatin and PHM or the alteration in metabolism of PHM in the CSF might occur in SDAT.

The role of cortical connectivity in Alzheimer's disease pathogenesis: a review and model system

Here we review current evidence in support of the cortical disconnection/cortical connectivity model of Alzheimer disease (AD) pathogenesis, a model which predicts that one of the first events in AD is damage to the entorhinal cortex and/or subiculum resulting in the disconnection of the hippocampal formation and neocortex, and the subsequent progression of the disease in a stepwise fashion along cortico-cortical connections. Much of the evidence for this model has been obtained from studies involving the limbic system where investigators have demonstrated a precise correspondence between established patterns of connectivity and the degenerative changes associated with AD. In addition, some studies of the distribution of neuritic plaques (NP) and neuro-fibrillary tangles (NFT) in the neocortex and subcortical structures have yielded corroborative data. The validity of the cortical disconnection/connectivity model in the neocortex remains to be established or refuted. We propose that testing of this model can be accomplished with systematic studies of the laminar and regional distribution of NP and NFT in a series of sequentially interconnected cytoarchitectural regions that also form part of two functional hierarchies--the paralimbic and occipitotemporal visual systems. To adequately control for variation between brains affected by AD, it is imperative that such studies be conducted in a large but varied population of AD cases exhibiting differences in several variables, including clinical and/or neuropathological severity of the disease, temporal duration of the disease, and clinical/neuropsychological profile. We believe that further understanding of the relationship between characteristic AD pathology and intrinsic anatomico-functional circuits will contribute not only to our comprehension of AD pathogenesis but also to our general knowledge of the human brain.

Monoamine neurotransmitters and their metabolites in brain regions in Alzheimer's disease: a postmortem study

1. Concentrations of the neurotransmitter amines noradrenaline (NA), dopamine (DA), and 5-hydroxytryptamine (5-HT) and the acid metabolites homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in four regions of postmortem brains of demented patients with or without Alzheimer's disease (AD). 2. NA was deficient in the temporal cortex (BA 21) of AD, but not of non-AD, patients. 3. Caudate, in particular, had an impaired dopaminergic system in AD patients, with low HVA levels. 4. In all regions investigated [amygdala, caudate, putamen, temporal cortex (BA 21)] 5-HT was significantly depleted in AD patients, and 5-HIAA was also depleted in amygdala and caudate. 5. These results indicate that neurotransmitter systems other than cholinergic systems are also widely affected in AD and suggest that these deficits may also play an important role in determining the symptomatology of AD.

Amygdala cell loss and atrophy in Alzheimer's disease

The amygdala and its subnuclei undergo severe volumetric atrophy in Alzheimer's disease (AD). To determine whether this atrophy is due to loss of neuropil, specific neuronal populations, or both, we evaluated the number, size, and packing density of neurons and glia in the cortical and magnocellular basal amygdaloid subregions. The neuropil fraction did not change with AD in either region. Despite a mean 35% increase in cell packing density in the AD amygdala, total numbers of neurons and glia within tissue sections were reduced significantly; medium and large neurons were preferentially affected. The total number of small neurons was stable in the AD sample despite sharp reductions in nuclear size, suggesting that AD also results in pronounced amygdaloid neuronal shrinkage. Differences in the degree of cell loss between the two nuclei as well as changes in glial cell numbers are discussed in relation to characteristic AD neuropathology and relevant anatomical connectivity.

Effect of various neurotransmitters and neuropeptides on the release of corticotropin-releasing hormone from the rat cortex in vitro

Corticotropin-releasing hormone (CRH), in addition to its neuroendocrine role, may act as a central neurotransmitter. Cerebral cortical CRH may have an important role in behavioral and neurodegenerative disorders. To gain an understanding of factors that may influence cortical CRH, we investigated the effect of several neurotransmitters and neuropeptides on the release of immunoreactive CRH (iCRH) from various cerebral cortical regions [frontal (FC), parietal (PC), temporal (TC), and occipital (OC)] in vitro. The hypothalamic release of iCRH was also evaluated under the same experimental conditions. Basal release of iCRH was approximately 2-fold, and KCl-stimulated iCRH release was approximately 4-fold higher in the hypothalamus than in any of the cortical regions. Cortical iCRH release was stimulated by 10 nM somatostatin (SRIF) in PC and 1 nM neuropeptide Y (NPY) in TC. Cortical iCRH release was inhibited by 1 and 10 nM acetylcholine (ACh), 0.1 microM glutamate, and 10 nM NPY. These effects were confined to the FC and/or PC. Hypothalamic iCRH release was stimulated by 1 and 10 nM ACh, 10 microM GABA, and 1 and 10 nM serotonin but was inhibited by 10 nM SRIF and 1 microM GABA. Growth hormone-releasing hormone did not affect cortical or hypothalamic iCRH release. These results demonstrate that CRH release from the cerebral cortex and the hypothalamus are under different regulatory mechanism(s). Furthermore, they indicate that the release of CRH in various cortical regions may be regulated differentially by the same neurotransmitter.

Growth hormone secretion in Alzheimer's disease: 24-hour profile of basal levels and response to stimulation and suppression studies

The 24-h growth hormone secretory pattern and GH response to growth hormone releasing hormone, the alpha 2-adrenoceptor agonist clonidine and the somatostatin-analogue SMS 201-995 were evaluated in 9 patients with Alzheimer's disease and 9 age- and body body-matched control subjects. The secretory profile did not differentiate between patients and controls. Both secreted the largest amount of GH during the early nighthours between 22.00-02.00, whereas the majority of daytime GH levels were below the assay's detection limit (0.4 ng/ml). No difference was found in GH response to GHRH between patients and controls. All subjects showed significantly enhanced GH secretion after GHRH. Dividing the patients into two groups according to age-of-onset (less than 60 years greater than), there was a trend toward larger GH responses to GHRH for the early-onset group. No other parameter differentiated the groups. GH levels after clonidine were blunted in all subjects but one AD patient, probably due to an age-dependent attenuation frequently observed in subjects over 45 years of age. Finally, the administration of the somatostatin-analogue did not render conclusive results, since spontaneous decline of GH concentration was already beginning 2 hours before the drug was given and continued steadily throughout the observation period. In conclusion, patients with only mild to moderate degree of Alzheimer's disease have no prominent changes in GH regulation.

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.

Neuropeptide modulation of muscarinic receptors and function in cerebral cortex of young and senescent rats

The possible influence of several neuropeptides on muscarinic receptor binding and function in fronto-parietal cortex of young and senescent Fischer 344 rats was examined. Low concentrations (100 nM) of cholecystokinin, neurotensin and vasoactive intestinal polypeptide (VIP), added in vitro, enhanced carbachol-stimulated phosphoinositide metabolism in cortical miniprisms from both young and senescent rats, while somatostatin was ineffective. Interestingly, the VIP receptor antagonist [d-parachloro-Phe6,Leu17[VIP shifted the dose-response curve for carbachol significantly to the right, indicating inhibition of phosphoinositide hydrolysis. No direct actions of neuropeptides on the number or affinity of [3H]l-quinuclidinyl benzilate binding sites nor on agonist conformation states of the muscarinic receptor were noted in cortex from young animals. The neuropeptide modulation of phosphoinositide metabolism was selective for muscarinic systems, as norepinephrine-stimulated phosphoinositide hydrolysis was not altered. Pretreatment with hemicholinium-3, an inhibitor of high-affinity choline uptake, did not prevent the neuropeptide effects, indicating the interaction was probably postsynaptic. It is possible that pharmacologic manipulation of peptidergic processes could improve cholinergic neurotransmission in brain.