Cortical somatostatin-like immunoreactivity in cases of Alzheimer's disease and senile dementia of the Alzheimer type

Somatostatin and the pathophysiology of Alzheimer's disease

Among the central features of Alzheimer's disease (AD) progression are altered levels of the neuropeptide somatostatin (SST), and the colocalisation of SST-positive interneurons (SST-INs) with amyloid-β plaques, leading to cell death. In this theoretical review, I propose a molecular model for the pathogenesis of AD based on SST-IN hypofunction and hyperactivity. Namely, hypofunctional and hyperactive SST-INs struggle to control hyperactivity in medial regions in early stages, leading to axonal Aβ production through excessive presynaptic GABAB inhibition, GABAB1a/APP complex downregulation and internalisation. Concomitantly, excessive SST-14 release accumulates near SST-INs in the form of amyloids, which bind to Aβ to form toxic mixed oligomers. This leads to differential SST-IN death through excitotoxicity, further disinhibition, SST deficits, and increased Aβ release, fibrillation and plaque formation. Aβ plaques, hyperactive networks and SST-IN distributions thereby tightly overlap in the brain. Conversely, chronic stimulation of postsynaptic SST2/4 on gulutamatergic neurons by hyperactive SST-INs promotes intense Mitogen-Activated Protein Kinase (MAPK) p38 activity, leading to somatodendritic p-tau staining and apoptosis/neurodegeneration - in agreement with a near complete overlap between p38 and neurofibrillary tangles. This model is suitable to explain some of the principal risk factors and markers of AD progression, including mitochondrial dysfunction, APOE4 genotype, sex-dependent vulnerability, overactive glial cells, dystrophic neurites, synaptic/spine losses, inter alia. Finally, the model can also shed light on qualitative aspects of AD neuropsychology, especially within the domains of spatial and declarative (episodic, semantic) memory, under an overlying pattern of contextual indiscrimination, ensemble instability, interference and generalisation.

Alterations of sleep oscillations in Alzheimer's disease: A potential role for GABAergic neurons in the cortex, hippocampus, and thalamus

Sleep abnormalities are widely reported in patients with Alzheimer's disease (AD) and are linked to cognitive impairments. Sleep abnormalities could be potential biomarkers to detect AD since they are often observed at the preclinical stage. Moreover, sleep could be a target for early intervention to prevent or slow AD progression. Thus, here we review changes in brain oscillations observed during sleep, their connection to AD pathophysiology and the role of specific brain circuits. Slow oscillations (0.1-1 Hz), sleep spindles (8-15 Hz) and their coupling during non-REM sleep are consistently reduced in studies of patients and in AD mouse models although the timing and magnitude of these alterations depends on the pathophysiological changes and the animal model studied. Changes in delta (1-4 Hz) activity are more variable. Animal studies suggest that hippocampal sharp-wave ripples (100-250 Hz) are also affected. Reductions in REM sleep amount and slower oscillations during REM are seen in patients but less consistently in animal models. Thus, changes in a variety of sleep oscillations could impact sleep-dependent memory consolidation or restorative functions of sleep. Recent mechanistic studies suggest that alterations in the activity of GABAergic neurons in the cortex, hippocampus and thalamic reticular nucleus mediate sleep oscillatory changes in AD and represent a potential target for intervention. Longitudinal studies of the timing of AD-related sleep abnormalities with respect to pathology and dysfunction of specific neural networks are needed to identify translationally relevant biomarkers and guide early intervention strategies to prevent or delay AD progression.

GABAergic Inhibitory Interneuron Deficits in Alzheimer's Disease: Implications for Treatment

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized clinically by severe cognitive deficits and pathologically by amyloid plaques, neuronal loss, and neurofibrillary tangles. Abnormal amyloid β-protein (Aβ) deposition in the brain is often thought of as a major initiating factor in AD neuropathology. However, gamma-aminobutyric acid (GABA) inhibitory interneurons are resistant to Aβ deposition, and Aβ decreases synaptic glutamatergic transmission to decrease neural network activity. Furthermore, there is now evidence suggesting that neural network activity is aberrantly increased in AD patients and animal models due to functional deficits in and decreased activity of GABA inhibitory interneurons, contributing to cognitive deficits. Here we describe the roles played by excitatory neurons and GABA inhibitory interneurons in Aβ-induced cognitive deficits and how altered GABA interneurons regulate AD neuropathology. We also comprehensively review recent studies on how GABA interneurons and GABA receptors can be exploited for therapeutic benefit. GABA interneurons are an emerging therapeutic target in AD, with further clinical trials urgently warranted.

Does somatostatin have a role to play in migraine headache?

Migraine is a condition without apparent pathology. Its cardinal symptom is the prolonged excruciating headache. Theories about this pain have posited pathologies which run the gamut from neural to vascular to neurovascular, but no observations have detected a plausible pathology. We believe that no pathology can be found for migraine headache because none exists. Migraine is not driven by pathology - it is driven by neural events produced by triggers - or simply by neural noise- noise that has crossed a critical threshold. If these ideas are true, how does the pain arise? We hypothesise that migraine headache is a consequence of withdrawal of descending pain control, produced by "noise" in the cerebral cortex. Nevertheless, there has to be a neural circuit to transform cortical noise to withdrawal of pain control. In our hypothesis, this neural circuit extends from the cortex, synapses in two brainstem nuclei (the periaqueductal gray matter and the raphe magnus nucleus) and ultimately reaches the first synapse of the trigeminal sensory system. The second stage of this circuit uses serotonin (5HT) as a neurotransmitter, but the neuronal projection from the cortex to the brainstem seems to involve relatively uncommon neurotransmitters. We believe that one of these is somatostatin (SST). Temporal changes in levels of circulating SST mirror the temporal changes in the incidence of migraine, particularly in women. The SST₂ receptor agonist octreotide has been used with some success in migraine and cluster headache. A cortical to PAG/NRM neural projection certainly exists and we briefly review the anatomical and neurophysiological evidence for it and provide preliminary evidence that SST may the critical neurotransmitter in this pathway. We therefore suggest that the withdrawal of descending tone in SST-containing neurons, might create a false pain signal and hence the headache of migraine.

Decrease in somatostatin-positive cell density in the amygdala of females with major depression

BACKGROUND

Somatostatin (SST) is a neuropeptide expressed in a subtype of gamma-aminobutyric acid (GABA) interneurons that target the dendrites of pyramidal neurons. We previously reported reduced levels of SST gene and protein expression in the postmortem amygdala of subjects with major depressive disorder (MDD). This reduction was specific to female subjects with MDD.

METHODS

Here, we used in situ hybridization to examine the regional and cellular patterns of reductions in SST expression in a cohort of female MDD subjects with known SST deficits in the amygdala (N = 10/group).

RESULTS

We report a significant reduction in the density of SST-labeled neurons in the lateral, basolateral, and basomedial nuclei of the amygdala of MDD subjects compared to controls. SST mRNA levels per neuron did not differ between MDD and control subjects in the lateral or basolateral nuclei, but were lower in the basomedial nucleus. There was no difference in cross-sectional density of total cells.

CONCLUSIONS

In summary, we report an MDD-related reduction in the density of detectable SST-positive neurons across several nuclei in the amygdala, with a reduction in SST mRNA per cell restricted to the basomedial nucleus. In the absence of changes in total cell density, these results suggest the possibility of a change in SST cell phenotype rather than cell death in the amygdala of female MDD subjects.

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.

α-Melanocyte stimulating hormone prevents GABAergic neuronal loss and improves cognitive function in Alzheimer's disease

In Alzheimer's disease (AD), appropriate excitatory-inhibitory balance required for memory formation is impaired. Our objective was to elucidate deficits in the inhibitory GABAergic system in the TgCRND8 mouse model of AD to establish a link between GABAergic dysfunction and cognitive function. We sought to determine whether the neuroprotective peptide α-melanocyte stimulating hormone (α-MSH) attenuates GABAergic loss and thus improves cognition. TgCRND8 mice with established β-amyloid peptide pathology and nontransgenic littermates were treated with either α-MSH or vehicle via daily intraperitoneal injections for 28 d. TgCRND8 mice exhibited spatial memory deficits and altered anxiety that were rescued after α-MSH treatment. The expression of GABAergic marker glutamic acid decarboxylase 67 (GAD67) and the number of GABAergic GAD67+ interneurons expressing neuropeptide Y and somatostatin are reduced in the hippocampus in vehicle-treated TgCRND8 mice. In the septohippocampal pathway, GABAergic deficits are observed before cholinergic deficits, suggesting that GABAergic loss may underlie behavior deficits in vehicle-treated TgCRND8 mice. α-MSH preserves GAD67 expression and prevents loss of the somatostatin-expressing subtype of GABAergic GAD67+ inhibitory interneurons. Without decreasing β-amyloid peptide load in the brain, α-MSH improves spatial memory in TgCRND8 mice and prevents alterations in anxiety. α-MSH modulated the excitatory-inhibitory balance in the brain by restoring GABAergic inhibition and, as a result, improved cognition in TgCRND8 mice.

Methylation analysis of SST and SSTR4 promoters in the neocortex of Alzheimer's disease patients

Several observations have pointed to a major pathogenic role of somatostatin depletion with respect to amyloid accumulation, which is often thought to be the crucial event in a cascade leading to Alzheimer's disease (AD). As methylation of CpG islands plays an important role in gene silencing, we studied the methylation status of the CpG islands in the promoters of somatostatin (SST) and in that of its receptor subtype in the cerebral cortex, SSTR4, in tissue samples from the middle temporal (Brodmann area 22) and superior frontal gyrus (Brodmann area 9) of 5 severely affected AD patients aged 72-94 years (Braak stages V-C or VI-C) and 5 non-demented controls aged 50-92 years. Bisulfite sequencing of DNA from cortical gray and infracortical white matter showed that the DNA methylation status at the promoters of SST and SSTR4 did not significantly differ between AD and control samples in any of the regions analyzed. We confirmed these results using deep bisulfite sequencing of PCR products from the SST promoter amplified from DNA from the cortical gray of the superior frontal gyrus of all AD patients and non-demented controls. We observed a trend toward increased DNA methylation with increasing age. In conclusion, deregulated somatostatin signaling in the AD cortices studied cannot be explained by hypermethylation of the SST or SSTR4 promoter CpG islands.

Reduced brain somatostatin in mood disorders: a common pathophysiological substrate and drug target?

Our knowledge of the pathophysiology of affect dysregulation has progressively increased, but the pharmacological treatments remain inadequate. Here, we summarize the current literature on deficits in somatostatin, an inhibitory modulatory neuropeptide, in major depression and other neurological disorders that also include mood disturbances. We focus on direct evidence in the human postmortem brain, and review rodent genetic and pharmacological studies probing the role of the somatostatin system in relation to mood. We also briefly go over pharmacological developments targeting the somatostatin system in peripheral organs and discuss the challenges of targeting the brain somatostatin system. Finally, the fact that somatostatin deficits are frequently observed across neurological disorders suggests a selective cellular vulnerability of somatostatin-expressing neurons. Potential cell intrinsic factors mediating those changes are discussed, including nitric oxide induced oxidative stress, mitochondrial dysfunction, high inflammatory response, high demand for neurotrophic environment, and overall aging processes. Together, based on the co-localization of somatostatin with gamma-aminobutyric acid (GABA), its presence in dendritic-targeting GABA neuron subtypes, and its temporal-specific function, we discuss the possibility that deficits in somatostatin play a central role in cortical local inhibitory circuit deficits leading to abnormal corticolimbic network activity and clinical mood symptoms across neurological disorders.

Lipid peroxidation and neurodegenerative disease

Lipid peroxidation is a complex process involving the interaction of oxygen-derived free radicals with polyunsaturated fatty acids, resulting in a variety of highly reactive electrophilic aldehydes. Since 1975, lipid peroxidation has been extensively studied in a variety of organisms. As neurodegenerative diseases became better understood, research establishing a link between this form of oxidative damage, neurodegeneration, and disease has provided a wealth of knowledge to the scientific community. With the advent of proteomics in 1995, the identification of biomarkers for neurodegenerative disorders became of paramount importance to better understand disease pathogenesis and develop potential therapeutic strategies. This review focuses on the relationship between lipid peroxidation and neurodegenerative diseases. It also demonstrates how findings in current research support the common themes of altered energy metabolism and mitochondrial dysfunction in neurodegenerative disorders.

Roles of 3-nitrotyrosine- and 4-hydroxynonenal-modified brain proteins in the progression and pathogenesis of Alzheimer's disease

Proteins play an important role in normal structure and function of the cells. Oxidative modification of proteins may greatly alter the structure and may subsequently lead to loss of normal physiological cell functions and may lead to abnormal function of cell and eventually to cell death. These modifications may be reversible or irreversible. Reversible protein modifications, such as phosphorylation, can be overcome by specific enzymes that cause a protein to 'revert' back to its original protein structure, while irreversible protein modifications cannot. Several important irreversible protein modifications include protein nitration and HNE modification, both which have been extensively investigated in research on the progression of Alzheimer's disease (AD). From the earliest stage of AD throughout the advancement of the disorder there is evidence of increased protein nitration and HNE modification. These protein modifications lead to decreased enzymatic activity, which correlates directly to protein efficacy and provides support for several common themes in AD pathology, namely altered energy metabolism, mitochondrial dysfunction and reduced cholinergic neurotransmission. The current review summarized some of the findings on protein oxidation related to different stages of Alzheimer's disease (AD) that will be helpful in understanding the role of protein oxidation in the progression and pathogenesis of AD.

Mice knock out for the histone acetyltransferase p300/CREB binding protein-associated factor develop a resistance to amyloid toxicity

p300/CREB binding protein-associated factor (PCAF) regulates gene expression by acting through histone acetylation and as a transcription coactivator. Although histone acetyltransferases were involved in the toxicity induced by amyloid-beta (Abeta) peptides, nothing is known about PCAF. We here analyzed the sensitivity of PCAF knockout (KO) mice to the toxic effects induced by i.c.v. injection of Abeta(25-35) peptide, a nontransgenic model of Alzheimer's disease. PCAF wild-type (WT) and KO mice received Abeta(25-35) (1, 3 or 9 nmol) or scrambled Abeta(25-35) (9 nmol) as control. After 7 days, Abeta(25-35) toxicity was measured in the hippocampus of WT mice by a decrease in CA1 pyramidal cells and increases in oxidative stress, endoplasmic reticulum stress and induction of apoptosis. Memory deficits were observed using spontaneous alternation, water-maze learning and passive avoidance. Non-treated PCAF KO mice showed a decrease in CA1 cells and learning alterations. However, Abeta(25-35) injection failed to induce toxicity or worsen the deficits. This resistance to Abeta(25-35) toxicity did not involve changes in glutamate or acetylcholine systems. Examination of enzymes involved in Abeta generation or degradation revealed changes in transcription of presenilins, activity of neprilysin (NEP) and an absence of Abeta(25-35)-induced regulation of NEP activity in PCAF KO mice, partly due to an altered expression of somatostatin (SRIH). We conclude that PCAF regulates the expression of proteins involved in Abeta generation and degradation, thus rendering PCAF KO insensitive to amyloid toxicity. Modulating acetyltransferase activity may offer a new way to develop anti-amyloid therapies.

Redox proteomic identification of 4-hydroxy-2-nonenal-modified brain proteins in amnestic mild cognitive impairment: insight into the role of lipid peroxidation in the progression and pathogenesis of Alzheimer's disease

Numerous investigations point to the importance of oxidative imbalance in mediating AD pathogenesis. Accumulated evidence indicates that lipid peroxidation is an early event during the evolution of the disease and occurs in patients with mild cognitive impairment (MCI). Because MCI represents a condition of increased risk for Alzheimer's disease (AD), early detection of disease markers is under investigation. Previously we showed that HNE-modified proteins, markers of lipid peroxidation, are elevated in MCI hippocampus and inferior parietal lobule compared to controls. Using a redox proteomic approach, we now report the identity of 11 HNE-modified proteins that had significantly elevated HNE levels in MCI patients compared with controls that span both brain regions: Neuropolypeptide h3, carbonyl reductase (NADPH), alpha-enolase, lactate dehydrogenase B, phosphoglycerate kinase, heat shock protein 70, ATP synthase alpha chain, pyruvate kinase, actin, elongation factor Tu, and translation initiation factor alpha. The enzyme activities of lactate dehydrogenase, ATP synthase, and pyruvate kinase were decreased in MCI subjects compared with controls, suggesting a direct correlation between oxidative damage and impaired enzyme activity. We suggest that impairment of target proteins through the production of HNE adducts leads to protein dysfunction and eventually neuronal death, thus contributing to the biological events that may lead MCI patients to progress to AD.

The dentate gyrus in Alzheimer's disease

As part of the hippocampus, the dentate gyrus is considered to play a crucial role in associative memory. The reviewed data suggest that the dentate gyrus withstands the formation of plaques, tangles and neuronal death until late stages of Alzheimer's disease (AD). However, changes related to a disconnecting process, and more subtle intrinsic alterations, may contribute to disturbances in memory and learning observed in early stages of AD.

Specificity and timing of neocortical transcriptome changes in response to BDNF gene ablation during embryogenesis or adulthood

Brain-derived neurotrophic factor (BDNF) has been reported to be critical for the development of cortical inhibitory neurons. However, the effect of BDNF on the expression of transcripts whose protein products are involved in gamma amino butric acid (GABA) neurotransmission has not been assessed. In this study, gene expression profiling using oligonucleotide microarrays was performed in prefrontal cortical tissue from mice with inducible deletions of BDNF. Both embryonic and adulthood ablation of BDNF gave rise to many shared transcriptome changes. BDNF appeared to be required to maintain gene expression in the SST-NPY-TAC1 subclass of GABA neurons, although the absence of BDNF did not alter their general phenotype as inhibitory neurons. Furthermore, we observed expression alterations in genes encoding early-immediate genes (ARC, EGR1, EGR2, FOS, DUSP1, DUSP6) and critical cellular signaling systems (CDKN1c, CCND2, CAMK1g, RGS4). These BDNF-dependent gene expression changes may illuminate the biological basis for transcriptome changes observed in certain human brain disorders.

Somatostatin presynaptically inhibits both GABA and glutamate release onto rat basal forebrain cholinergic neurons

A whole cell patch-clamp study was carried out in slices obtained from young rat brain to elucidate the roles of somatostatin in the modulation of synaptic transmission onto cholinergic neurons in the basal forebrain (BF), a region that contains cholinergic and GABAergic corticopetal neurons and somatostatin (SS)-containing local circuit neurons. Cholinergic neurons within the BF were identified by in vivo prelabeling with Cy3 IgG. Because in many cases SS is contained in GABAergic neurons in the CNS, we investigated whether exogenously applied SS can influence GABAergic transmission onto cholinergic neurons. Bath application of somatostatin (1 muM) reduced the amplitude of the evoked GABAergic inhibitory presynaptic currents (IPSCs) in cholinergic neurons. SS also reduced the frequency of miniature IPSCs (mIPSCs) without affecting their amplitude distribution. SS-induced effect on the mIPSC frequency was significantly larger in the solution containing 7.2 mM Ca(2+) than in the standard (2.4 mM Ca(2+)) external solution. Similar effects were observed in the case of non-NMDA glutamatergic excitatory postsynaptic currents (EPSCs). SS inhibited the amplitude of evoked EPSCs and reduced the frequency of miniature EPSCs dependent on the external Ca(2+) concentration with no effect on their amplitude distribution. Pharmacological analyses using SS-receptor subtype-specific drugs suggest that SS-induced action of the IPSCs is mediated mostly by the sst(2) subtype, whereas sst subtypes mediating SS-induced inhibition of EPSCs are mainly sst(1) or sst(4). These findings suggest that SS presynaptically inhibits both GABA and glutamate release onto BF cholinergic neurons in a Ca(2+)-dependent way, and that SS-induced effect on IPSCs and EPSCs are mediated by different sst subtypes.

Aβ-degrading enzymes: modulators of Alzheimer's disease pathogenesis and targets for therapeutic intervention

The accumulation of Aβ (amyloid β-protein) peptides in the brain is a pathological hallmark of all forms of AD (Alzheimer's disease) and reducing Aβ levels can prevent or reverse cognitive deficits in mouse models of the disease. Aβ is produced continuously and its concentration is determined in part by the activities ofseveral degradative enzymes, including NEP (neprilysin), IDE (insulin-degrading enzyme), ECE-1 (endothelinconverting enzyme 1) and ECE-2, and probably plasmin. Decreased activity of any of these enzymes due to genetic mutation, or age- or disease-related alterations in gene expression or proteolytic activity, may increase the risk for AD. Conversely, increased expression of these enzymes may confer a protective effect. Increasing Aβ degradation through gene therapy, transcriptional activation or even pharmacological activation of the Aβ-degrading enzymes represents a novel therapeutic strategy for the treatment of AD that is currently being evaluated in cell-culture and animal models. In this paper, we will review the roles of NEP, IDE, ECE and plasmin in determining endogenous Aβ concentration, highlighting recent results concerning the regulation of these enzymes and their potential as therapeutic targets.

Somatostatin and Alzheimer's disease

One of the most consistent neurochemical deficits in Alzheimer's disease is a reduction in cortical somatostatin concentrations. The probability of a predominant regulatory change is heightened by the finding that 90% of somatostatin positive nonpyramidal neurons are also positive for NADPH, and NADPH neurons are 'protected' in Alzheimer's disease and do not appear to be lost. The first evidence that somatostatin influences learning and memory processes in experimental animals was published more than a decade ago. These reports of somatostatin effects on cognitive functions in rats were later confirmed by several other studies. The somatostatin depleting substance cysteamine inhibited the learning and memory performance of rats in active and passive avoidance behavior tests. Post-mortem human studies suggest that although somatostatin concentration is reduced, the somatostatin receptors are less affected in the brain in Alzheimer's disease. These findings may be of importance for possible therapeutic approaches using somatostatin-receptor-influencing compounds.

Realistic expectations for the management of Alzheimer's disease

Alzheimer's disease (AD) is a chronic and progressive neurodegenerative disorder characterized clinically by cognitive and functional deficits and behavioural disturbances. Over the past two decades, the devastating nature of AD has captured the attention of the general and medical communities alike. This is due partly to the increased prevalence of AD and the expansion of the aged population. Furthermore, and perhaps inappropriately, the media have encouraged speculation concerning a 'cure' for AD. Such treatment strategies are in the early stages of pre-clinical investigation and well-designed clinical trials are awaited. Nevertheless, other strategies, aimed at reducing the progression or effects through pharmacological symptomatic therapies and psychosocial interventions have demonstrated some clinical benefit and are now available and practicable. This paper critically evaluates the merits of both currently available and potential future therapeutic strategies according to primary, secondary and tertiary levels of preventative treatment.

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.

Patterns of synaptic and nerve cell pathology in Alzheimer's disease

Recent neuropathological evidence suggests that synapse pathology is the major correlate of cognitive decline in Alzheimer's disease (AD) patients, but also in other dementia syndromes. We suggest that synapse loss in AD-patients mainly reflects neuronal destruction in other iso- and allocortical areas as well as in brain stem nuclei. In addition an impaired compensatory synaptogenesis may contribute to the reduction in synaptic connectivity. The patterns of cell death in AD-brains determined by analysis of DNA-fragmentation in situ revealed significantly higher numbers of dying cells (neurons as well as glia cells) in AD-brains compared to controls. Amyloid deposition as well as neurofibrillary pathology apparently do not induce cell death directly, but may increase the risk of cells to die in response to additional minor metabolic insults. We propose that multiple pathogenetic factors are involved in the reduction of synaptic connectivity in AD-brains, which finally is reflected in the decline of cognitive functions.

Somatostatin-like immunoreactivity, its molecular forms and monoaminergic metabolites in aged and demented patients with Parkinson's disease--effect of L-Dopa

There is some evidence that Parkinson's disease (PD) seems to be a heterogenous and generalized brain disorder reflecting a degeneration of multiple neuronal networks, including somatostatinergic neurons. Somatostatin-like immunoreactivity (SLI) and its molecular forms, high molecular weight form (HMV-SST), somatostatin-14 (SST-14), somatostatin-25/28 (SST-25/28) and Des-ala-somatostatin (Des-ala-SST), as well as homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were estimated using HPLC and radioimmunoassay in the cerebrospinal fluid (CSF) of 35 aged parkinsonian patients with different stages of intellectual deterioration. The influence of L-dopa-treatment on these neurochemical parameters was evaluated. Without a correlation with dementia scores (p = 0.11), SLI was significantly reduced in PD in comparison to the control group (p < 0.05). The reduction was related to the progression of the disease. Correlations between SLI, HVA and 5-HIAA indicate a heterogenous brain disorder in PD with alterations of several transmitter systems and functions. Complex qualitative and quantitative changes in the molecular pattern of SLI are compatible with a dysregulated synthesis and/or posttranslational processing. L-dopa-treatment was associated with a significant increase of HVA (p < 0.05) and HMV-SST (p < 0.05) and a slight, but insignificant increase of SLI (p = 0.11).

Neuropeptide abnormalities in anorexia nervosa

Starvation-induced alterations of neuropeptide activity probably contribute to neuroendocrine dysfunctions in anorexia nervosa. For example, CRH alterations contribute to hypercortisolemia and NPY alterations may contribute to amenorrhea. Alterations of these peptides as well as opioids, vasopressin, and oxytocin activity could contribute to other characteristic psychophysiological disturbances, such as reduced feeding, in acutely ill anorexics. Such neuropeptide disturbances could contribute to the vicious cycle that has been hypothesized to occur in anorexia nervosa. That is, the consequences of malnutrition perpetuate pathological behavior.

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.

Differential correlation between neurochemical deficits, neuropathology, and cognitive status in Alzheimer's disease

The relationships between neurofibrillary tangles (NFT), senile plaques (SP), and the deficits in somatostatin (SRIH) and choline acetyltransferase (ChAT) levels were determined in Brodmann area 9, 40, 22, and 17/18 in 12 women whose Blessed test score (BTS) ranged from 27 to 1. NFT density correlated with the cognitive decline in areas 9, 40, and 22 and with SP number in area 22 and 17/18. ChAT levels were linked to the BTS in area 9, 40, and 22 and SRIH levels in area 9 only. ChAT, but not SRIH, did correlate with SP (area 22) and NFT (area 40 and 22). Decreases in ChAT and SRIH were correlated in areas 9 and 22. These results indicate that the somatostatinergic deficit in Alzheimer's disease is more regionally restricted than the cholinergic one. The correlation between SRIH and ChAT as observed in area 9 and 22 may indicate that somatostatin- and acetylcholine-containing elements in the frontal and temporal lobes are particularly relevant to the cognitive decline as observed in Alzheimer's disease.

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.

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.

A long-term follow-up study of cerebrospinal fluid somatostatin in delirium

Cerebrospinal fluid somatostatin-like immunoreactivity (CSF SLI) was determined for elderly delirious patients during the acute stage and after 1- and 4-year follow-up periods, and the SLI levels were compared with age-equivalent controls. As a whole group, and also when the group was subdivided according to the severity of cognitive decline at the acute stage, type of delirium or the central nervous system disease, delirious patients showed significant reduction of SLI as compared with the controls. In the follow-up, we observed a further reduction of CSF SLI together with significant correlations in the second, third and fourth samples between SLI levels and Mini-Mental State Examination scores. Our results suggest a role for somatostatinergic dysfunction in the genesis of some symptoms of delirium, and this dysfunction may be linked to the long-term prognosis of delirious patients.

Cerebrospinal fluid TRH immunoreactivity in anorexia nervosa

Central nervous system (CNS) thyrotropin-releasing hormone (TRH) activity is of interest in patients with anorexia nervosa. First, anorexics have peripheral thyroid abnormalities that appear to be related to weight and nutritional status. Second, CNS TRH activity may effect many other physiologic systems that are known to be disturbed in patients with anorexia nervosa. We found that anorexic patients, when both underweight and studied after attaining goal weight, had significantly reduced CSF TRH concentrations in comparison to controls. These data suggest that weight gain or increased caloric intake, in contrast to its large effect on peripheral thyroid function, has relatively little effect on CNS TRH activity. The reason for reduced CSF TRH in goal weight anorexics is not known but could be trait related, a persistent defect slow to normalize after weight gain, or related to these patients still being at a weight lower than controls. Finally, in terms of CSF TRH concentrations, this study suggests that anorexia nervosa has a different pathophysiology than major depressive disorder.

Cultured GABA-immunoreactive neurons are resistant to toxicity induced by beta-amyloid

Neurodegeneration in Alzheimer's disease is characterized by a selective loss of particular cell populations. Several recent lines of evidence suggest that beta-amyloid protein directly contributes to the disease's progression and is likely responsible for the observed pattern of neuronal death. We have previously demonstrated that aggregated beta-amyloid peptides are neurotoxic to cultured neurons. We now report that a neuronal population exhibiting GABA-immunoreactivity is resistant to beta-amyloid-induced toxicity in vitro, a finding consistent with observations in the Alzheimer brain. Determination of the intrinsic neuronal characteristics responsible for resistance to beta-amyloid may prove beneficial in both understanding the mechanism(s) of beta-amyloid neurotoxicity and halting the disease's progressive neuronal degeneration.

Habenulo-interpeduncular descending pathways and their relationship to enkephalin- and somatostatin-immunoreactive neurons in the interpeduncular nucleus of human fetuses

The interpeduncular nucleus of six human fetuses aged 15 (one specimen), 26 (one specimen), 38 (one specimen) and 40 (three specimens) gestation weeks was studied by immunohistochemistry for enkephalin and somatostatin localization and immunohistochemistry coupled with silver staining. Enkephalin-positive and somatostatin-positive cells were detected, the former initially at 15 weeks gestation and the latter at 26 weeks gestation. They appeared to receive long afferents from the habenular region and projected short efferents to adjacent cells devoid of enkephalin and somatostatin positivity. We postulate that these enkephalin- and somatostatin-positive neurons function as modulatory interneurons in the habenulo-interpeduncular and related pathways.

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.

Regional distribution of neuropeptide somatostatin gene expression in the human brain

The regional distribution of mRNA coding for the neuropeptide somatostatin has been studied in the human brain by in situ hybridization histochemistry using 32P-labeled oligonucleotides. We show that somatostatin mRNA-containing neurons are widely distributed in a number of nuclei and grey areas of the human brain, including neocortex, putamen, nucleus caudatus, nucleus accumbens, amygdala, midbrain, medulla oblongata, hippocampal formation, reticular nucleus of the thalamus, and posterior nucleus of the hypothalamus. No significant hybridization signal was observed in the substantia nigra, claustrum, globus pallidus, thalamus, and cerebellum. The topographic localization of neurons containing SOM mRNA in the human brain is in agreement with previous studies using immunocytochemical or radioimmunoassay techniques. These results show that in situ hybridization histochemistry with oligonucleotide probes can be used to map the distribution of neurons expressing SOM mRNA in human postmortem materials.

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.

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.

Effects of scopolamine on visual evoked potentials in aging and dementia

The unusual combination of a normal pattern reversal VEP and a delayed flash VEP has been reported in patients with dementia of Alzheimer's type (DAT). Hyoscine hydrobromide has been reported to produce a similar VEP abnormality in young, healthy subjects. In the present study, we assessed the relative sensitivity of DAT patients and healthy young, middle-aged and elderly subjects to temporary cholinergic blockade. We report VEP latency values following 3 doses of scopolamine and after a peripheral anticholinergic agent. Flash P2 latency was not significantly slower in DAT patients than in the healthy elderly. Scopolamine increased P2 latency in the young controls but did not affect any other group. The pattern reversal P100 was normal in DAT, and a significant increase in latency occurred following scopolamine administration in both the control and patient groups.

Neurotransmitters in neocortex of aged rhesus monkeys

The effects of aging on levels of neurotransmitters were determined in two regions of the cerebral cortex in rhesus monkeys (Macaca mulatta). Choline acetyltransferase (ChAT) activity as well as somatostatin, neuropeptide Y, and substance P immunoreactivities were analyzed in the right caudal cingulate gyrus and in the left and right inferior occipital poles in five age groups: 4-6 years; 8-11 years; 20-25 years; 26-29 years; and 31-34 years. Neuroactive amino acids and markers for monoamine transmitters were analyzed only in the youngest (4-6 years) and oldest (31-34 years) animals. Across the five age groups studied. ChAT activity as well as somatostatin and neuropeptide Y immunoreactivities were significantly decreased bilaterally in occipital poles of the 31- to 34-year-old group. There were no significant age-related differences in substance P immunoreactivity. In 4-6-year-old vs. 31-34-year-old monkeys, levels of amino acid neurotransmitters were unchanged. However, there were significant reductions in norepinephrine, serotonin and its metabolites, kynurenine, and 4-hydroxyphenyllactic acid in occipital poles of the 31- to 34-year-old monkeys. No significant neurochemical changes were detected in the cingulate cortex. These findings demonstrate that aged nonhuman primates show reductions in cortical markers for a variety of neurotransmitters, including acetylcholine, somatostatin, neuropeptide Y, norepinephrine, and serotonin but that these changes do not occur uniformly in the neocortex.

Distribution of GABA and neuropeptides in the human cerebral cortex. A light and electron microscopic study

Antibodies were used to identify neurons in human frontal and temporal cortex that were immuno-positive to gamma-aminobutyric acid (GABA) and the neuropeptides vasoactive intestinal polypeptide (VIP), substance P (SP) and somatostatin (SOM). Specimens were taken at surgical biopsy and fixed immediately after removal. The results described for both light and electron microscopy were obtained when relatively high concentrations of glutaraldehyde (2.5-3%) were present in the fixative. Specimens were examined from three adults and an infant aged 5 months. GABAergic neurons were present in all cortical layers, with fewest in layers I, deep III and V, and were mainly small, and round or oval. No labelled pyramidal neurons were detected. GABAergic puncta were common in the neuropil, probably representing axonal profiles. VIP-neurons were also found in all layers, including layer I, and were approximately twice as numerous as GABA-cells. SP-positive cells were found throughout the layers, but were sparse in layers I and VI. They were about three times commoner than GABAergic neurons. SOM-reactivity was demonstrated in about the same number of cells as that for SP. Again, this involved all layers, but layer I least. Peptidergic neurons were larger, on the average, than GABAergic cells, and were frequently pyramidal in character. In the infant, the distribution, size and frequency of immunoreactive neurons were similar to those in the adult. However, GABAergic puncta were commoner.

Neurochemical aspects on aging and diseases with cognitive impairment

The concentrations of monoamines and cholineacetyl transferase (CAT) are reduced in brains from patients with normal aging. According to findings about the dopamine (DA) system, the age-sensitive decrease has its onset in the 60s and after that has a continuous progress. In patients with Alzheimer's disease (AD/SDAT), multiple changes indicate disturbed metabolism in the acetylcholine (ACh), DA, noradrenaline (NA), and 5-hydroxytryptamine (5-HT) systems. The activity of monoamine oxidase B (MAO-B) increases significantly with age and a further increase has been reported to occur in Alzheimer-afflicted brains. In the platelets, too, there is increased MAO-B activity in AD/SDAT patients. Increased enzyme activity is considered a marker of gliosis in the brain and a marker of macrocytosis in platelets. Gangliosides are reduced in several areas of the brain in AD/SDAT patients, which indicates a reduction of nerve terminals. Significantly reduced concentrations of myelin components have also been recorded in brains from patients with AD/SDAT, which is in agreement with histopathological findings. The neurochemical changes recorded in brains from normally aged individuals are very similar to those found in AD/SDAT brains, although the latter changes are more severe. Thus, it has been suggested that the pathological process in AD/SDAT may be an exacerbation of the process taking place in normal aging. The multiple neurochemical changes recorded in grey, as well as in white matter must still be considered changes of secondary nature. At the present level of knowledge, it is not possible to single out any one of these changes as of special etiological importance.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatostatin in neurodegenerative illnesses

Somatostatin may play a role in several neurodegenerative diseases. Somatostatin concentrations are depleted in cerebral cortex in both Alzheimer's disease and in the dementia that accompanies Parkinson's disease. Somatostatin neurons in both illnesses are markedly dystrophic and may be reduced in number. In Huntington's disease, somatostatin concentrations are increased in the basal ganglia, as is the density of somatostatin neurons. The precise role of somatostatin changes in the pathophysiology of these illnesses requires further study.

Endocrine responses to growth hormone releasing hormone and corticotropin releasing hormone in early-onset Alzheimer's disease

In a study of the hypothalamic-pituitary-somatotropic (HPS) and the hypothalamic-pituitary-adrenal (HPA) systems in early-onset Alzheimer's disease (AD), 10 drug-naive patients and matched controls were given 50 micrograms growth hormone releasing hormone (GHRH) at 9 a.m. and 100 micrograms corticotropin releasing hormone (CRH) at 6 p.m. as an i.v. bolus dose. Compared with controls, patients with AD showed attenuated GHRH-induced growth hormone (GH) responses and decreased adrenocorticotropic hormone (ACTH) but normal cortisol secretion following CRH. GH responses to GHRH were negatively correlated with the plasma insulin-like growth factor (IGF-I) concentrations and the severity of dementia. A positive correlation was found between GHRH-evoked GH release and ACTH responses to CRH. The results suggest a pathological process at the level of the pituitary or the hypothalamus, possibly involving a cholinergic, monoaminergic, or peptidergic imbalance in AD, and support the view that altered HPS and HPA secretory dynamics in AD are related to the underlying brain dysfunction.

Neuropeptides and Alzheimer's disease

Because of their putative roles as neurotransmitters, neuromodulators, and neuroregulators in the central nervous system, neuropeptides have been the focus of considerable research over the past two decades. There is evidence that alterations in the synaptic availability of particular neuropeptides occur in certain neuropsychiatric disorders, such as schizophrenia and affective disorders. Alzheimer's disease is the most common neurodegenerative disorder, affecting a sizable proportion of our aging population. Alzheimer's disease is characterized by the presence of neurofibrillary tangles and senile plaques in the central nervous system. Postmortem studies have provided evidence that several neuropeptide-containing neurons are pathologically altered in this disorder. The purpose of this article is to describe recent advances in neuropeptide biology with a focus on the role of neuropeptides in the pathogenesis of Alzheimer's disease.

Cerebrospinal fluid somatostatin in delirium. II. Changes at the acute stage and at one year follow-up

Cerebrospinal fluid somatostatin-like immunoreactivity (CSF SLI) was determined for elderly delirious patients during the acute stage and after one-year follow-up. The SLI levels were compared with age-equivalent controls. For the group as a whole, and also when the group was subdivided according to the severity of cognitive decline at the acute stage, type of delirium, or the central nervous system disease, delirious patients showed significant reduction of SLI as compared with the controls. In the follow-up, we observed a further reduction of CSF SLI together with significant correlations in the second and third samples between SLI levels and Mini-Mental State Examination score. Our results suggest a role for somatostatinergic dysfunction in the genesis of some symptoms of delirium. This dysfunction may be a common phenomenon in various forms of delirium and dementia.