Aging and Alzheimer’s disease (AD) are associated with decreased cognitive function and neural degeneration. The basal forebrain is one of the first areas of the brain to degenerate in AD and depends on the neurotrophin brain-derived neurotrophic factor (BDNF) for survival. Loss of BDNF transport from target neurons may contribute to basal forebrain cholinergic neuron (BFCN) vulnerability in AD and aging. Oxidative stress is associated with cholinergic dysfunction and cognitive decline in aging and AD, and it is possible that oxidative stress may contribute to BDNF transport deficits in BFCNs. BFCNs are grown in microfluidic chambers that allow isolation of BFCN soma and axon terminals so transport of biotinylated and fluorescently labelled BDNF can be quantified. The objective of my research was to determine if oxidative stress induces BDNF retrograde transport deficits in BFCNs, and the mechanism behind this effect. I found that oxidative stress does reduce BDNF retrograde transport in BFCNs. Because it has previously been shown that aged BFCNs have decreased BDNF transport and downregulate the BDNF receptor TrkB, expression of both TrkB and p75NTR receptors was tested following oxidative stress using immunocytochemistry (ICC) and western blotting. This experiment showed that oxidative stress does not affect p75NTR or TrkB receptor levels. A likely alternative is that oxidative stress may lead to alterations in the transport machinery responsible for retrograde BDNF transport. I hypothesized that oxidative stress decreases retrograde axonal transport of BDNF via increased insulin-like growth factor 1 receptor (IGF1R) activity, which decreases the protein expression of the adaptor proteins BICD1 and Hook1 by inhibiting GSK3β activity via the PI3K-Akt pathway. ICC and western blotting showed that oxidative stress has no effect on either BICD1 or Hook1 levels. Future directions of this work involve further studying the involvement of the IGF1R pathway in oxidative stress, and the effect on other proteins involved in BDNF transport, including htt and DISC1. / Thesis / Master of Science (MSc)

Feature binding refers to the fundamental challenge of the brain to integrate sensory information registered by distinct brain regions to form a unified neural representation of a stimulus. While the human cognitive literature has established that attentional processes in a frontoparietal cortical network support feature binding, the neurochemical contributions to this attentional process remain unknown. Using systemic administration of the cholinergic muscarinic receptor antagonist scopolamine and a digging-based rat feature binding task that used both odor and texture stimuli, it was demonstrated that blockade of acetylcholine (ACh) at the muscarinic receptors impaired rats’ ability to feature bind at encoding, and it was proposed that ACh may support the attentional processes necessary for feature binding (Botly & De Rosa, 2007). This series of experiments further investigated a role for ACh and the cholinergic basal forebrain (BF) in feature binding. In Experiment 1, a cross-species experimental design was employed in which rats under the systemic influence of scopolamine and human participants under divided-attention performed comparable feature binding tasks using odor stimuli for rats and coloured-shape visual stimuli for humans. Given the comparable performance impairments demonstrated by both species, Experiment 1 suggested that ACh acting at muscarinic receptors supports the attentional processes necessary for feature binding at encoding. Experiments 2-4 investigated the functional neuroanatomy of feature binding using bilateral quisqualic acid excitotoxic (Experiment 2) and 192 IgG-saporin cholinergic immunotoxic (Experiments 3 and 4) brain lesions that were assessed for completeness using histological and immunohistological analyses. Using the crossmodal digging-based rat feature binding task, Experiment 2 revealed that the nucleus basalis magnocellularis (NBM) of the BF is critically involved in feature binding, and Experiment 3 revealed that cholinergic neurons in the NBM are necessary for feature binding at encoding. Lastly, in Experiment 4, rats performed visual search, the standard test of feature binding in humans, with touchscreen-equipped operant chambers. Here it was also revealed that cholinergic neurons in the NBM of the BF are critical for efficient visual search. Taken together, these behavioural, pharmacological, and brain-lesion findings have provided insights into the neurochemical contributions to the fundamental attentional process of feature binding.

Feature binding refers to the fundamental challenge of the brain to integrate sensory information registered by distinct brain regions to form a unified neural representation of a stimulus. While the human cognitive literature has established that attentional processes in a frontoparietal cortical network support feature binding, the neurochemical contributions to this attentional process remain unknown. Using systemic administration of the cholinergic muscarinic receptor antagonist scopolamine and a digging-based rat feature binding task that used both odor and texture stimuli, it was demonstrated that blockade of acetylcholine (ACh) at the muscarinic receptors impaired rats’ ability to feature bind at encoding, and it was proposed that ACh may support the attentional processes necessary for feature binding (Botly & De Rosa, 2007). This series of experiments further investigated a role for ACh and the cholinergic basal forebrain (BF) in feature binding. In Experiment 1, a cross-species experimental design was employed in which rats under the systemic influence of scopolamine and human participants under divided-attention performed comparable feature binding tasks using odor stimuli for rats and coloured-shape visual stimuli for humans. Given the comparable performance impairments demonstrated by both species, Experiment 1 suggested that ACh acting at muscarinic receptors supports the attentional processes necessary for feature binding at encoding. Experiments 2-4 investigated the functional neuroanatomy of feature binding using bilateral quisqualic acid excitotoxic (Experiment 2) and 192 IgG-saporin cholinergic immunotoxic (Experiments 3 and 4) brain lesions that were assessed for completeness using histological and immunohistological analyses. Using the crossmodal digging-based rat feature binding task, Experiment 2 revealed that the nucleus basalis magnocellularis (NBM) of the BF is critically involved in feature binding, and Experiment 3 revealed that cholinergic neurons in the NBM are necessary for feature binding at encoding. Lastly, in Experiment 4, rats performed visual search, the standard test of feature binding in humans, with touchscreen-equipped operant chambers. Here it was also revealed that cholinergic neurons in the NBM of the BF are critical for efficient visual search. Taken together, these behavioural, pharmacological, and brain-lesion findings have provided insights into the neurochemical contributions to the fundamental attentional process of feature binding.

<p>Auditory sensations can arise from objects in our environment or from our own actions, such as when we speak or make music. We must able to distinguish such sources of sounds, as well as form new associations between our actions and the sounds they produce. The brain is thought to accomplish this by conveying copies of the motor command, termed corollary discharge signals, to auditory processing brain regions, where they can suppress the auditory consequences of our own actions. Despite the importance of such transformations in health and disease, little is known about the mechanisms underlying corollary discharge in the mammalian auditory system. Using a range of techniques to identify, monitor, and manipulate neuronal circuits, I characterized a synaptic and circuit basis for corollary discharge in the mouse auditory cortex. The major contribution of my studies was to identify and characterize a long-range projection from motor cortex that is responsible for suppressing auditory cortical output during movements by activating local inhibitory interneurons. I used similar techniques to understand how this circuit is embedded within a broader neuromodulatory brain network important for learning and plasticity. These findings characterize the synaptic and circuit mechanisms underlying corollary discharge in mammalian auditory cortex, as well as uncover a broad network interaction potentially used to pattern neural associations between our actions and the sounds they produce.</p> / Dissertation

No description available.

No / A neurological disorder is any disorder or abnormality in the nervous system. Among different neurological disorders, Alzheimer’s disease (AD) is recognized as the sixth leading cause of death globally. Considerable research has been conducted to find pioneer treatments for this devastating disorder among which cell therapy has attracted remarkable attentions over the last decade. Up to now, targeted differentiation into specific desirable cell types has remained a major obstacle to clinical application of cell therapy. Also, potential risks including uncontrolled growth of stem cells could be disastrous. In our novel protocol, we used basal forebrain cholinergic progenitor cells (BFCN) derived from human chorion-derived mesenchymal stem cells (hC-MSCs) which made it possible to obtain high-quality population of cholinergic neurons and in vivo in much shorter time period than previous established methods. Remarkably, the transplanted progenitors fully differentiated to cholinergic neurons which in turn integrated in higher cortical networks of host brains, resulting in significant improvement in cognitive assessments. This method may have profound implications in cell therapies for any other neurodegenerative disorders. / This work was carried outwithin the framework of a collaborative project (Project Grant No. 94-02-30-25922) by the School of Medicine, Iran University of Medical Sciences, (Project Grant No. REP209) council for stem cell sciences and technologies (Presidency of the Islamic Republic of Iran, vice-presidency for science and technology), and Iran National Science Foundation (INSF).

Neuromodulatory systems, such as the cholinergic basal forebrain (CBF), are promising targets of behavioral neuroscientific research because of the clear role(s) they play in fundamental neural and behavioral plasticity processes. Previous research suggests that the CBF is a promising target for augmenting post-stroke behavioral rehabilitation. Several studies were conducted to establish a novel paradigm for investigating and ameliorating post-stroke related motor deficits in a rodent model. The first two studies describe the invention and validation of a novel apparatus for conducting individualized rodent research in an environmentally and socially enriched context. The second study specifically investigated how this approach yields novel insights into post-stroke motor deficits. The third study describes how electrical stimulation of the CBF may improve poststroke motor rehabilitation. Together, these studies are expected to improve current stroke models, our understanding of how the CBF supports fundamental learning processes, and how to best manipulate the CBF to improve recovery from neurological injury.

Investigating the properties and mechanisms of coordination among neurons plays an important role in understanding how the brain encodes information and performs in thalamocortical processing in the auditory system. Whether the coordinated neuronal spikes in the auditory thalamus enhance the thalamocortical communications in the auditory cortex (AC) is the main concern in this project. Researchers are mostly focusing on the investigation of the V1 and V2 in visual system and corticortical circuits in auditory system using neuronal pairwise correlations as the method. However, what we explored in this project is the coordination among neurons in thalamocortical circuits. we applied the Jensen-Shannon divergence method to measure the similarity between two distributions and analyze the coordination in thalamus neurons and different parts of AC in ascending pathway and descending pathway of auditory system respectively. At the same time, we designed an algorithm to calculated spiking coordination. The result shows that the coordination pattern differs in separate pathway when keeping sound stimulation and basal forebrain (BF) stimulation on or off. In ascending pathway, the coordination in thalamus neurons precedes information to AC when the brain is silent, keeping sound and BF stimulation off. In descending pathway, the coordination mainly in the superficial area of AC precedes information to thalamus. The coordination is lower in the case of keeping sound on. In the future, more data on rats can be verified using our method and algorithm to investigate the coordinated spikes in auditory system. / Att undersöka egenskaperna och mekanismerna för koordination mellan neuroner spelar en viktig roll för att förstå hur hjärnan kodar information och fungerar i talamokortikal bearbetning i hörselsystemet. Huruvida de koordinerade neuronala spikarna i den auditiva thalamus förstärker den talamokortikala kommunikationen i den auditiva cortex (AC) är huvudproblemet i detta projekt. Forskare fokuserar mestadels på undersökningen av V1 och V2 i visuella system och kortikokortikala kretsar i hörselsystemet med hjälp av neuronala parvisa korrelationer som metod. Men vad vi utforskade i detta projekt är koordinationen mellan neuroner i talamokortikala kretsar. vi tillämpade Jensen-Shannon-divergensmetoden för att mäta likheten mellan två distributioner och analysera koordinationen i thalamusneuroner och olika delar av AC i stigande bana respektive fallande bana i hörselsystemet. Samtidigt designade vi en algoritm för att beräkna spikkoordination. Resultatet visar att koordinationsmönstret skiljer sig åt i separata vägar när ljudstimulering och basal framhjärnsstimulering (BF) hålls på eller av. I stigande väg föregår koordinationen i talamusneuroner information till AC när hjärnan är tyst, vilket håller ljud och BF-stimulering borta. I fallande väg föregår koordinationen huvudsakligen i det ytliga området av AC information till thalamus. Koordinationen är lägre när det gäller att hålla ljud på. I framtiden kan mer data om råttor verifieras med vår metod och algoritm för att undersöka de samordnade spikarna i hörselsystemet.

Basal forebrain cholinergic neurons (BFCNs) are critical for learning and memory. Profound and early BFCN degeneration is a hallmark of aging and Alzheimer’s disease (AD). BFCNs depend for their survival on the retrograde axonal transport of neurotrophins, proteins critical for neuronal function. Neurotrophins like brain derived neurotrophic factor (BDNF) and pro-nerve growth factor (proNGF) are retrogradely transported to BFCNs from their synaptic targets. In AD, neurotrophin levels are increased within BFCN target areas and reduced in the basal forebrain, implicating dysfunctional neurotrophin transport in AD pathogenesis. However, neurotrophin transport within this highly susceptible neuronal population is currently poorly understood. We began by establishing protocols for the accurate quantification of axonal transport in BFCNs using microfluidic culture. We then determined the effect of age on neurotrophin transport. BFCNs were left in culture for up to 3 weeks to model aging in vitro. BFCNs initially displayed robust neurotrophin transport, which diminished with in vitro age. We observed that the levels of proNGF receptor tropomyosin-related kinase-A (TrkA) were reduced in aged neurons. Additionally, neurotrophin transport in BFCNs derived from 3xTg-AD mice, an AD model, was also impaired. Next, we sought to determine a mechanism for these transport deficits. First, we determined that proNGF transport was solely contingent upon the levels of TrkA. We then found that elevation of oxidative stress, an established AD contributor, significantly reduced both TrkA levels and proNGF retrograde transport. TrkA levels are partially regulated by protein tyrosine phosphatase-1B (PTP1B), an enzyme whose activity is reduced by oxidation. PTP1B antagonism significantly reduced TrkA levels and proNGF retrograde transport in BFCNs. Treatment of BFCNs with PTP1B-activating antioxidants rescued TrkA levels, proNGF transport, and proNGF-mediated axonal degeneration. Our results suggest that oxidative stress contributes to BFCN degeneration in aging and AD by impairing retrograde neurotrophin transport via oxidative PTP1B-mediated TrkA loss. / Thesis / Doctor of Philosophy (PhD) / During aging and Alzheimer’s disease (AD), the connections between neurons, a type of brain cell, break down, causing memory loss. This breakdown begins in a brain area called the basal forebrain. Basal forebrain neurons rely upon the transport of nutrients along their connections with other neurons, called axons, for proper function. This transport process becomes impaired in AD. Our goal was to understand why this happens. First, we determined that axonal transport was impaired with age and in basal forebrain neurons of mice genetically predisposed to develop AD. We recreated these impairments by increasing the levels of harmful molecules called reactive oxidative species (ROS). ROS levels increase with age and become abnormally high during AD. We found that increased ROS impair axonal transport and contribute to the breakdown of basal forebrain neurons. Our work suggests that reducing ROS will help prevent the breakdown of basal forebrain neurons in AD.

Le système cholinergique est impliqué dans les phénomènes d’attention, de mémoire et d’apprentissage et les récepteurs cholinergiques régulent de multiples fonctions du système nerveux central. Néanmoins, leur rôle au niveau de la modulation des propriétés du cortex visuel reste à être établi. L’un des objectifs de cette thèse était d’étudier le rôle des récepteurs muscariniques impliqués dans le fonctionnement normal du cortex visuel. Nous avons pu déterminer que les récepteurs muscariniques sont impliqués dans l’établissement de nombreuses propriétés visuelles telles la taille des champs récepteurs, la sensibilité au contraste, la sélectivité à la fréquence spatiale et la finesse de la connectivité corticale. L’autre objectif était d’identifier les récepteurs cholinergiques impliqués dans la potentiation des capacités visuelles. Nous avons amélioré le traitement cognitif de l’information visuelle par stimulation électrique du télencéphale basal (noyau où sont localisés les corps cellulaires cholinergiques) et par la stimulation cholinergique par le donépézil, un inhibiteur de l’acétylcholinestérase. La combinaison répétée d’une stimulation visuelle et cholinergique (qu’elle soit électrique ou pharmacologique) améliore similairement l’activité corticale visuelle. Toutefois, les récepteurs impliqués ne sont pas les mêmes. Suite à la stimulation pharmacologique, ce sont principalement les récepteurs muscariniques qui influencent l’acuité visuelle de manière tardive et cette modulation est plus précoce lors de la stimulation électrique. Ces résultats démontrent que le couplage répétitif d’une stimulation cholinergique et d’une stimulation visuelle est en mesure d’améliorer l’activité corticale visuelle. Le fait de connaître les récepteurs cholinergiques impliqués permettra dans un futur proche de les cibler directement pour améliorer la fonction corticale. / The cholinergic system is involved in attention, learning and memory and cholinergic receptors regulate multiple functions of the central nervous system. Nevertheless, their role in modulating the properties of the visual cortex remains to be established. One of the objectives of this thesis was to study the role of muscarinic receptors involved in the normal function of the visual cortex. We have been able to determine that the muscarinic receptors are involved in the establishment of many visual properties such as the size of the receptor fields, contrast sensitivity, spatial frequency selectivity and accuracy of the cortical connectivity. The other objective was to identify the cholinergic receptors involved in the potentiation of visual abilities. We improved the cognitive processing of visual information by electrical stimulation of the basal forebrain (the nucleus where the cholinergic cell bodies are located) and by cholinergic stimulation using donepezil, an acetylcholinesterase inhibitor. The repeated combination of visual and cholinergic stimulations (whether electrical or pharmacological) similarly enhances visual cortical activity. However, the receptors involved are not the same. Following the pharmacological stimulation, it is mainly the muscarinic receptors that influence visual acuity with a delay in the receptors expression and this modulation is earlier for the electrical stimulation. These results demonstrate that repetitive coupling of cholinergic stimulation and visual stimulation can enhance visual cortical activity. Knowing the cholinergic receptors involved will allow in a near future to target them directly to improve cortical function.