The retina as a window to early dysfunctions of Alzheimer's disease following studies with a 5xFAD mouse model.

Alzheimer's disease (AD) is a progressive neurodegenerative disease leading to neuronal dysfunctions with cognitive impairment. AD can affect visual pathways and visual cortex and result in various visual changes and problems. However, how early the visual dysfunctions occur in AD is still a matter of discussion. Here, we used electrophysiological techniques to show the presence of early anomalies in AD visual system. To this aim, we used a familial AD (FAD) model, the 5xFAD transgenic mouse, characterized by severe progressive amyloid pathology and cognitive deficits. We investigated the retina and primary visual cortex responsivity together with behavioral assessment of the visual acuity. Visual tests and recordings were conducted at different ages in 5xFAD mice, corresponding to different phases of neurodegeneration and beta amyloid accumulation. We showed that the visual system is impaired in 5xFAD mice. In particular, we found that the inner retina impairment precedes neuronal disorders in other brain areas and cognitive deficits. Thus, noninvasive retinal electrophysiology can provide a support for assessing early visual dysfunctions in AD.

Visual Evoked Potentials in Glaucoma and Alzheimer's Disease.

Visual responses to gratings alternating in contrast have been studied in humans and several mammalian species. Previous evidence from human patients and animal models of neurodegeneration has highlighted the importance to record simultaneously the pattern electroretinogram (P-ERG) and visual evoked cortical potentials (VEPs) to investigate retinal and post-retinal sites of neurodegeneration.In view of the increasing importance of research on experimental models of neurodegenerative diseases, we present here the parametric properties of visual evoked responses in animal models of glaucoma and Alzheimer's disease. Glaucoma and Alzheimer's disease (AD) are two distinct multifactorial neurodegenerative and progressive diseases, primarily affecting the elderly.

Generation of a new mouse model of glaucoma characterized by reduced expression of the AP-2ß and AP-2δ proteins.

We generated 6 transgenic lines with insertion of an expression plasmid for the R883/M xanthine dehydrogenase (XDH) mutant protein. Approximately 20% of the animals deriving from one of the transgenic lines show ocular abnormalities and an increase in intra-ocular pressure which are consistent with glaucoma. The observed pathologic phenotype is not due to expression of the transgene, but rather the consequence of the transgene insertion site, which has been defined by genome sequencing. The insertion site maps to chromosome 1qA3 in close proximity to the loci encoding AP-2ß and AP-2δ, two proteins expressed in the eye. The insertion leads to a reduction in AP-2ß and AP-2δ levels. Down-regulation of AP-2ß expression is likely to be responsible for the pathologic phenotype, as conditional deletion of the Tfap2b gene in the neural crest has recently been shown to cause defective development of the eye anterior segment and early-onset glaucoma. In these conditional knock-out and our transgenic mice, the morphological/histological features of the glaucomatous pathology are surprisingly similar. Our transgenic mouse represents a model of angle-closure glaucoma and a useful tool for the study of the pathogenesis and the development of innovative therapeutic strategies.

Synaptic Dysfunction in Alzheimer's Disease and Glaucoma: From Common Degenerative Mechanisms Toward Neuroprotection.

Alzheimer's disease (AD) and glaucoma are two distinct multifactorial neurodegenerative diseases, primarily affecting the elderly. Common pathophysiological mechanisms have been elucidated in the past decades. First of all both diseases are progressive, with AD leading to dementia and glaucoma inducing blindness. Pathologically, they all feature synaptic dysfunction with changes of neuronal circuitry, progressive accumulation of protein aggregates such as the beta amyloid (Aß) and intracellular microtubule inclusions containing hyperphosphorylated tau, which belongs to microtubule associated protein family. During an early phase of degeneration, both diseases are characterized by synaptic dysfunction and changes of mitogen-activated protein kinases (MAPK). Common degenerative mechanisms underlying both diseases are discussed here, along with recent results on the potential use of the visual system as a biomarker for diagnosis and progression of AD. Common neuropathological changes and mechanisms in AD and glaucoma have facilitated the transfer of therapeutic strategies between diseases. In particular, we discuss past and present evidence for neuroprotective effects of brain-derived neurotrophic factor (BDNF).

In vivo study of the role of α6-containing nicotinic acetylcholine receptor in retinal function using subtype-specific RDP-MII(E11R) toxin.

Although α6-contaning (α6*) nicotinic acetylcholine receptors (nAChRs) are densely expressed in the visual system, their role is not well known. We have characterized a family of toxins that are antagonists for α6ß2* receptors and used one of these [RDP-MII(E11R)] to localize α6* nAChRs and investigate their impact on retinal function in adult Long-Evans rats. The α6*nAChRs in retinal tissue were localized using either a fluorescently tagged [RDP-MII(E11R)] or anti-α6-specific antibodies and found to be predominantly at the level of the ganglion cell layer. After intraocular injection of RDP-MII(E11R) in one eye and vehicle or inactive MII in contralateral eyes as controls, we recorded flash electroretinograms (F-ERGs), pattern ERGs (P-ERGs), and cortical visual-evoked potential (VEPs). There was no significant difference in F-ERG between the RDP-MII(E11R)-treated and control eyes. In contrast, P-ERG response amplitude was significantly reduced in the RDP-MII(E11R)-injected eye. Blocking α6* nAChRs at retinal level also decreased the VEP amplitude recorded in the visual cortex contralateral to the injected eye. Because both the cortical and inner retina output were affected by RDP-MII(E11R), whereas photoreceptor output was preserved, we conclude that the reduced visual response was due to an alteration in the function of α6* nAChRs present in the ganglion cell layer.-Barloscio, D., Cerri, E., Domenici, L., Longhi, R., Dallanoce, C., Moretti, M., Vilella, A., Zoli, M., Gotti, C., and Origlia, N. In vivo study of the role of α6-containing nicotinic acetylcholine receptor in retinal function using subtype-specific RDP-MII(E11R) toxin.

Clinical correlates of plasma brain-derived neurotrophic factor in post-traumatic stress disorder spectrum after a natural disaster.

Clinical correlates of plasma Brain-Derived Neurotrophic Factor (BDNF) have been investigated in a clinical population with Post Traumatic Stress Disorder (PTSD) symptoms and healthy control subjects who survived to the L'Aquila 2009 earthquake. Twenty-six outpatients and 14 control subjects were recruited. Assessments included: Structured Clinical Interview for DSM-IV Axis-I disorders Patient Version, Trauma and Loss Spectrum-Self Report (TALS-SR) for post-traumatic spectrum symptoms. Thirteen patients were diagnosed as Full PTSD and 13 as Partial PTSD. The subjects with full-blown PTSD showed lower BDNF level than subjects with partial PTSD and controls. Different relationship patterns of BDNF with post-traumatic stress spectrum symptoms have been reported in the three samples. Our findings add more insight on the mechanisms regulating BDNF levels in response to stress and further proofs of the utility of the distinction of PTSD into full and partial categories.

Olfactory phenotypic expression unveils human aging.

The mechanism of the natural aging of olfaction and its declinein the absence of any overt disease conditions remains unclear. Here, we investigated this mechanism through measurement of one of the parameters of olfactory function, the absolute threshold, in a healthy population from childhood to old age. The absolute olfactory threshold data were collected from an Italian observational study with 622 participants aged 5-105 years. A subjective testing procedure of constant stimuli was used, which was also compared to the 'staircase' method, with the calculation of the reliability. The n-butanol stimulus was used as an ascending series of nine molar concentrations that were monitored using an electronic nose. The data were analyzed using nonparametric statistics because of the multimodal distribution. We show that the age-related variations in the absolute olfactory threshold are not continuous; instead, there are multiple olfactory phenotypes. Three distinct age-related phenotypes were defined, termed as 'juvenile', 'mature' and 'elder'. The frequency of these three phenotypes depends on age. Our data suggest that the sense of smell does not decrease linearly with aging. Our findings provide the basis for further understanding of olfactory loss as an anticipatory sign of aging and neurodegenerative processes.

BDNF prevents amyloid-dependent impairment of LTP in the entorhinal cortex by attenuating p38 MAPK phosphorylation.

The oligomeric form of the amyloid peptide Aß(1-42) is capable of perturbing synaptic plasticity in different brain areas. Here, we evaluated the protective role of brain-derived neurotrophic factor (BDNF) in beta amyloid (Aß)-dependent impairment of long-term potentiation in entorhinal cortex (EC) slices. We found that BDNF (1 ng/mL) supplied by perfusion was able to rescue long-term potentiation in Aß(1-42)-treated slices; BDNF protection was mediated by TrkB receptor as assessed by using the tyrosine kinase inhibitor K252a (200 nM). We also investigated the function of endogenous BDNF using a soluble form of TrkB receptor (TrkB IgG). Incubation of slices with TrkB IgG (1 µg/mL) increased the EC vulnerability to Aß. Finally, we investigated the effect of BDNF on the cell stress-kinase p38 mitogen-activated protein kinase (MAPK) in primary cortical cell cultures exposed to Aß(1-42). We found that Aß induces p38 MAPK phosphorylation, although pretreatment with BDNF prevented Aß-dependent p38 MAPK phosphorylation. This result was confirmed by an immunoassay in tissue extracts from EC slices collected after electrophysiology.

Conjunctivally Applied BDNF Protects Photoreceptors from Light-Induced Damage.

PURPOSE: To test whether the topical eye treatment with BDNF prevents the effects of continuous light exposure (LE) in the albino rat retina. METHODS: Two groups of albino rats were used. The first group of rats received an intraocular injection of BDNF (2 µL, 1 µg/µL) before LE, while the second group was treated with one single drop of BDNF (10 µL, 12 µg/µL) dissolved in different types of solutions (physiological solution, the polysaccharide fraction of Tamarind gum, TSP, and sodium carboxy methyl cellulose), at the level of conjunctival fornix before LE. The level of BDNF in the retina and optic nerve was determined by enzyme-linked immunosorbent assay. We recorded the flash electroretinogram (fERG) in dark adapted rats 1 week after LE. At the end of the recording session, the retinas were removed and labeled so that the number of photoreceptors nuclear rows and thickness of the outer nuclear layer was analyzed. RESULTS: Intravitreal injection of BDNF before LE prevented fERG impairment. Different ophthalmic preparations were used for topical eye application; the TSP resulted the most suitable vehicle to increase BDNF level in the retina and optic nerve. Topical eye application with BDNF/TSP before LE partially preserved both fERG response and photoreceptors. CONCLUSIONS: Topical eye treatment with BDNF represents a suitable, noninvasive tool to increase the retinal content of BDNF up to a level capable of exerting neuroprotection toward photoreceptors injured by prolonged LE. TRANSLATIONAL RELEVANCE: A collyrium containing BDNF may serve as an effective, clinically translational treatment against retinal degeneration.

Volatile organic compounds (VOCs) fingerprint of Alzheimer's disease.

Alzheimer's disease (AD) is a profoundly life changing condition and once diagnosis occurs, this is typically at a relatively late stage into the disease process. Therefore, a shift to earlier diagnosis, which means several decades before the onset of the typical manifestation of the disease, will be an important step forward for the patient. A promising diagnostic and screening tool to answer this purpose is represented by breath and exhaled volatile organic compounds (VOCs) analysis. In fact, human exhaled breath contains several thousand of VOCs that vary in abundance and number in correlation with the physiological status. The exhaled VOCs reflect the metabolism, including the neuronal ones, in healthy and pathological conditions. A growing number of studies clearly demonstrate the effectiveness of VOCs analysis in identifying pathologies, including neurodegenerative diseases. In the present study we recorded, in real time, breath parameters and exhaled VOCs. We were able to demonstrate a significant alteration in breath parameters induced by the pathology of AD. Further, we provide the putative VOCs fingerprint of AD. These vital findings are an important step toward the early diagnosis of AD.

Decreased plasma levels of brain-derived neurotrophic factor (BDNF) during mixed episodes of bipolar disorder.

BACKGROUND: Brain-derived neurotrophic factor (BDNF) is a neurotrophin involved in neurogenesis and neuroplasticity. Decreased blood levels of BDNF have been found during acute manic and depressive states. BDNF has been proposed as a biomarker in illness phases of mood disorders. No information is available regarding BDNF levels during the mixed states of bipolar disorder (BD). The aim of this study was to evaluate BDNF levels during mixed episodes of BD patients and compare them with those of healthy subjects and depressed patients. METHODS: Plasma BDNF levels were measured by an ELISA assay in 18 patients with major depressive episode (MDE), 19 patients with mixed episode (ME) and 15 healthy subjects (HS). RESULTS: BDNF levels were significantly higher in HS, as compared with patients׳ samples (HS vs. MDE patients: p<001; HS vs. ME patients: p=.022). No significant differences were found between BDNF levels of ME and MDE patients. The severity of illness as assessed by CGI-S was significantly higher in ME than in MDE patients (p=.01). LIMITATIONS: The small sample size may have weakened the power of statistical analyses. All patients received mood-stabilizing and antidepressant treatments which have been reported to influence peripheral BDNF levels. CONCLUSIONS: Our results are consistent with previous studies showing reduced BDNF during both manic and depressive episodes. This finding supports the role of BDNF as a state-marker of mood episodes, and may represent a contribution to a unitary approach model between unipolar and BDs, as well as to the manic-depressive spectrum model.

Rescue of retinal function by BDNF in a mouse model of glaucoma.

Vision loss in glaucoma is caused by progressive dysfunction of retinal ganglion cells (RGCs) and optic nerve atrophy. Here, we investigated the effectiveness of BDNF treatment to preserve vision in a glaucoma experimental model. As an established experimental model, we used the DBA/2J mouse, which develops chronic intraocular pressure (IOP) elevation that mimics primary open-angle glaucoma (POAG). IOP was measured at different ages in DBA/2J mice. Visual function was monitored using the steady-state Pattern Electroretinogram (P-ERG) and visual cortical evoked potentials (VEP). RGC alterations were assessed using Brn3 immunolabeling, and confocal microscope analysis. Human recombinant BDNF was dissolved in physiological solution (0.9% NaCl); the effects of repeated intravitreal injections and topical eye BDNF applications were independently evaluated in DBA/2J mice with ocular hypertension. BDNF level was measured in retinal homogenate by ELISA and western blot. We found a progressive decline of P-ERG and VEP responses in DBA/2J mice between 4 and 7 months of age, in relationship with the development of ocular hypertension and the reduction of Brn3 immunopositive RGCs. Conversely, repeated intravitreal injections (BDNF concentration = 2 µg/µl, volume = 1 µl, for each injection; 1 injection every four days, three injections over two weeks) and topical eye application of BDNF eye-drops (12 µg/µl, 5 µl eye-drop every 48 h for two weeks) were able to rescue visual responses in 7 month DBA/2J mice. In particular, BDNF topical eye treatment recovered P-ERG and VEP impairment increasing the number of Brn3 immunopositive RGCs. We showed that BDNF effects were independent of IOP reduction. Thus, topical eye treatment with BDNF represents a promisingly safe and feasible strategy to preserve visual function and diminish RGC vulnerability to ocular hypertension.

Insulin induces phosphorylation of the AMPA receptor subunit GluR1, reversed by ZIP, and over-expression of Protein Kinase M zeta, reversed by amyloid beta.

Insulin receptor (IR) in the brain plays a role in synaptic plasticity and cognitive functions. Phosphorylation of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors GluR1 subunit at Serine 831 is regulated by calcium-calmodulin-dependent protein kinase II and protein kinase C that underlie long-term potentiation and learning/memory. Recent studies have shown that the novel Protein Kinase M zeta (PKMζ) underlies synaptic plasticity and may regulate AMPAr. In this study, we show that insulin induces phosphorylation of Serine 831 GluR1 subunit of AMPAr and induces over-expression of PKMζ; pre-treatment with either the IR inhibitor 3-Bromo-5-t-butyl-4-hydroxy-benzylidenemalonitrile (AG1024) or PKMζ inhibitor protein kinase C zeta pseudo-substrate inhibitor returned the phosphorylation value of GluR1 to control level. Amyloid beta (Aß) peptide in the form of oligomers interferes with IR signaling. Pre-treating neuronal cultures with Aß following incubation with insulin, we found a reduction of insulin-dependent PKMζ over-expression and MAPK/Erk (1/2) phosphorylation, i.e., signaling pathways involved in synaptic plasticity and learning/memory. These results indicate a new intracellular insulin signaling pathway, and, additionally, that insulin resistance in Alzheimer's disease is a response to the production and accumulation of Aß.

RAGE inhibition in microglia prevents ischemia-dependent synaptic dysfunction in an amyloid-enriched environment.

Ischemia is known to increase the deleterious effect of ß-amyloid (Aß), contributing to early cognitive impairment in Alzheimer's disease. Here, we investigated whether transient ischemia may function as a trigger for Aß-dependent synaptic impairment in the entorhinal cortex (EC), acting through specific cellular signaling. We found that synaptic depression induced by oxygen glucose deprivation (OGD) was enhanced in EC slices either in presence of synthetic oligomeric Aß or in slices from mutant human amyloid precursor protein transgenic mice (mhAPP J20). OGD-induced synaptic depression was ameliorated by functional suppression of RAGE. In particular, overexpression of the dominant-negative form of RAGE targeted to microglia (DNMSR) protects against OGD-induced synaptic impairment in an amyloid-enriched environment, reducing the activation of stress-related kinases (p38MAPK and JNK) and the release of IL-1ß. Our results demonstrate a prominent role for the RAGE-dependent neuroinflammatory pathway in the synaptic failure induced by Aß and triggered by transient ischemia.

Plasma amyloid-ß levels in drug-resistant bipolar depressed patients receiving electroconvulsive therapy.

AIMS: Alterations of plasma amyloid-ß (Aß) peptides have been related to a high risk for cognitive impairment and dementia. The present study aimed to measure plasma Aß peptides (Aß40, Aß42) and the Aß40/Aß42 ratio in a sample of drug-resistant bipolar depressed patients, as well as to explore the possible correlation between biological parameters and clinical changes along an electroconvulsive therapy (ECT) course. METHODS: Aß40 and Aß42 were measured by means of an ELISA assay in 25 drug-resistant bipolar depressed patients before (T0) and 1 week after (T1) the end of ECT. The patients were clinically evaluated by means of the Hamilton Rating Scale for Depression, 21-item (HRSD-21), the Mini-Mental State Examination, and the Clinical Global Impressions-Severity of Illness Scale. RESULTS: Plasma Aß levels and the Aß40/Aß42 ratio were similar at T0 and T1. The Aß40/Aß42 ratio correlated positively with the HRSD total score at both T0 and T1. At T0, a negative correlation was found between the Aß40/Aß42 ratio and the improvement of depressive and cognitive symptoms. Moreover, remitters (n = 9; HRSD ≤10) showed a significantly lower Aß40/Aß42 ratio at T0 than nonremitters. CONCLUSION: The present data suggest that a low Aß40/Aß42 ratio might characterize a subgroup of depressed patients who respond to ECT, while higher values of this parameter seem to be typical of more severe cases of patients with cognitive impairment.

Neurodegeneration, ß-amyloid and mood disorders: state of the art and future perspectives.

OBJECTIVE: Depression may increase the risk of developing Alzheimer's disease (AD). Recent studies have shown modifications in blood beta-amyloid (Aß) levels in depressed patients. This literature review examines the potential relationship between Aß-mediated neurotoxicity and pathophysiology of mood disorders. DESIGN: We conducted a review of the literature focusing on recent studies reporting alterations of plasma and serum Aß peptides levels in patients suffering from mood disorders. RESULTS: Different data suggest that patients with mood disorders are at great risk of developing cognitive impairment and dementia. In particular, low plasma levels of Aß42 peptide and a high Aß40/Aß42 ratio have been found in depressed patients. In addition, changes in Aß protein levels in patients with mood disorders have been associated with the severity of cognitive impairment and correlated positively with the number of episodes and severity of illness course. CONCLUSIONS: Given the intriguing association between change in plasma level of Aß, depression and cognitive impairment, future work should focus on the relationship between Aß peripheral level(s), biomarkers of neurodegeneration and development of dementia in patients affected by mood disorders.

Cancer and non-cancer brain and eye effects of chronic low-dose ionizing radiation exposure.

BACKGROUND: According to a fundamental law of radiobiology ("Law of Bergonié and Tribondeau", 1906), the brain is a paradigm of a highly differentiated organ with low mitotic activity, and is thus radio-resistant. This assumption has been challenged by recent evidence discussed in the present review. RESULTS: Ionizing radiation is an established environmental cause of brain cancer. Although direct evidence is lacking in contemporary fluoroscopy due to obvious sample size limitation, limited follow-up time and lack of focused research, anecdotal reports of clusters have appeared in the literature, raising the suspicion that brain cancer may be a professional disease of interventional cardiologists. In addition, although terminally differentiated neurons have reduced or mild proliferative capacity, and are therefore not regarded as critical radiation targets, adult neurogenesis occurs in the dentate gyrus of the hippocampus and the olfactory bulb, and is important for mood, learning/memory and normal olfactory function, whose impairment is a recognized early biomarker of neurodegenerative diseases. The head doses involved in radiotherapy are high, usually above 2 Sv, whereas the low-dose range of professional exposure typically involves lifetime cumulative whole-body exposure in the low-dose range of < 200 mSv, but with head exposure which may (in absence of protection) arrive at a head equivalent dose of 1 to 3 Sv after a professional lifetime (corresponding to a brain equivalent dose around 500 mSv). CONCLUSIONS: At this point, a systematic assessment of brain (cancer and non-cancer) effects of chronic low-dose radiation exposure in interventional cardiologists and staff is needed.

Plasma ß-amyloid peptides levels: a pilot study in bipolar depressed patients.

BACKGROUND: Patients with mood disorders present a great risk for dementia and generally for cognitive decline. Low levels of ß-amyloid peptide 1-42 (Aß42) and high Aß40/Aß42 ratio have been associated with this risk and have been reported also in geriatric patients suffering from depression. The aim of the present study was to compare the plasma levels of Aß40 and Aß42 in patients with bipolar depression and healthy subjects, and to correlate them with the characteristics of clinical course. METHODS: Levels of Aß40 and Aß42 were measured by using specific ELISA kits in 16 patients with bipolar depression and in 16 control subjects with a negative history for somatic, psychiatric, neurological and substance abuse disorders. RESULTS: Patients presented significantly lower plasma Aß42 levels and higher Aß40/Aß42 ratio, as compared with control subjects. Moreover, a significant negative correlation was found between Aß42 plasma levels and the duration of the illness, while a positive correlation was detected between the Aß40/Aß42 ratio and the number of affective episodes. LIMITATIONS: The major limitations of the study are the small sample size, the scanty characterization of the illness episodes and the fact that all the patients were under psychopharmacological treatment. CONCLUSION: Although further research is necessary to establish firm conclusions, the present data would suggest that changes in plasma levels of different Aß peptides might represent a useful tool to identify the risk for cognitive decline in bipolar patients.

Visual acuity is reduced in alpha 7 nicotinic receptor knockout mice.

PURPOSE: Nicotinic receptors (nAChRs) are part of a heterogeneous family of pentameric ligand-gated ion channels that are widely expressed in the visual system. The impact of α7 homomeric nAChRs on visual function was investigated using mutant mice lacking the α7 nicotinic receptor subunit. METHODS: The spatial resolution limit was measured in α7 knockout (α7 KO) and age-matched control mice using three independent methods: an operant behavioral visual task (Prusky maze), cortical visual evoked potentials (VEPs), and the pattern electroretinogram (PERG) evoked by alternating gratings of different spatial frequencies and contrasts. RESULTS: Visual acuity measured by means of the visual water maze task was significantly decreased in the α7 KO mice and, concordantly, there was a reduction of the cortical spatial resolution limit measured by VEPs. However, the PERG was normal in α7 KO mice, compared with control mice. The use of fluorescently tagged cholera toxin showed that projections from the retina segregate normally in α7 KO mice and, in line with this, the visual cortical responses elicited by stimulating either eye were normally balanced in both visual cortices and showed no retinotopic anomalies. CONCLUSIONS: These findings indicate that the absence of the α7 nicotinic subunit reduces visual acuity. Because the cortical output has an abnormal spatial resolution but retinal output is preserved, it can be concluded that the low visual acuity was due to a deficit specifically present in the visual cortex.