Plasticity of the Rat Thalamocortical Auditory System During Development and Following White Noise Exposure PDF Download

Author: Jennifer Lauren Hogsden Robinson
Publisher:
ISBN:
Category :
Languages : en
Pages : 232

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Synaptic plasticity reflects the capacity of synapses to undergo changes in synaptic strength and connectivity, and is highly regulated by age and sensory experience. This thesis focuses on the characterization of synaptic plasticity in the primary auditory cortex (A1) of rats throughout development and following sensory deprivation. Initial experiments revealed an age-dependent decline in plasticity, as indicated by reductions in long-term potentiation (LTP). The enhanced plasticity of juvenile rats appeared to be mediated by NR2B subunits of the N-methyl-d-aspartate receptor (NMDAR), as NR2B antagonist application reduced LTP to adult-like levels in juveniles, yet had no effect in adults. The importance of sensory experience in mediating plasticity was revealed in experiments using white noise exposure, which is a sensory deprivation technique known to arrest cortical development in A1. Notably, adult rats reared in continuous white noise maintained more juvenile-like levels of LTP, which normalized upon subsequent exposure to an unaltered acoustic environment. The white noise-induced LTP enhancements also appeared to be mediated by NR2B subunits, as NR2B antagonists reversed these LTP enhancements in white noise-reared rats. Given the strong influence that sensory experience exerts on plasticity, additional experiments examined the effect of shorter episodes of white noise exposure on LTP in adult rats. Exposure to white noise during early postnatal life appeared to "prime" A1 for subsequent exposure in adulthood, resulting in enhanced LTP. The necessity of early-life exposure was evident, as repeated episodes of white noise in adulthood did not enhance plasticity. In older rats that typically no longer express LTP in A1, pharmacological methods to enhance plasticity were explored. Moderate LTP was observed in older rats with cortical zinc application, which may act through its antagonism of NR2A subunits of the NMDAR. Additionally, current source density and cortical silencing analyses were conducted to characterize the distinct peaks of field postsynaptic potentials recorded in A1, with the earlier and later peaks likely representing thalamocortical and intracortical synapses, respectively. Together, this thesis emphasizes the critical role of sensory experience in determining levels of cortical plasticity, and demonstrates strategies to enhance plasticity in the mature auditory cortex.

Author: Laura Gillian Rosen
Publisher:
ISBN:
Category :
Languages : en
Pages : 152

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Plasticity of synapses is not static across the lifespan. As the brain matures and ages, the ability of neurons to undergo structural and functional change becomes more limited. Further, there are a number of modulatory factors that influence the expression of synaptic plasticity. Here, three approaches were taken to examine and manipulate plasticity in the auditory thalamocortical system of rats. Using an in vivo preparation, long-term potentiation (LTP) and paired pulse (PP) responses were used as measures of long- and short-term plasticity, respectively. First, the effect of intracortical zinc application in the primary auditory cortex (A1) on LTP was examined. Following theta burst stimulation (TBS) of the medial geniculate nucleus (MGN), juvenile and middle-age rats, but not young adults, showed greater levels of LTP with zinc application relative to age-matched control animals. Next, PP responses were examined between rats reared in unaltered acoustic conditions and those reared in continuous white noise (WN) from postnatal day (PD) 5 to PD 50-60 (i.e., subjected to patterned sound deprivation). Rats reared in WN demonstrated less PP depression relative to controls, indicating that WN rearing alters short-term thalamocortical synaptic responses. Furthermore, control males showed no change in PP response following LTP induction, indicating a postsynaptic locus of LTP, whereas increased PP depression following LTP induction was seen in WN animals, suggestive of a presynaptic involvement in LTP. Finally, differences in plasticity between male and female rats were investigated, and the result of early WN exposure on both sexes was examined. Males and females did not show consistent differences in LTP expression; however WN exposure appeared to affect LTP of females less than their male counterparts. PP responses were then compared between WN-reared males and females, and no difference was found. This indicates that short-term plastic properties of auditory thalamocortical synapses between the sexes do not differ, even though plasticity on a longer time scale following sensory deprivation does indicate some difference. Together, the experiments summarized here identify some of the important factors that contribute to the regulation of short- and long-term synaptic plasticity in the central auditory system of the mammalian brain.

Author: Maryse Thomas
Publisher:
ISBN:
Category :
Languages : en
Pages :

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"The ability of the brain to change in response to its external environment is known as experience-dependent plasticity. Robust experience-dependent plasticity is typically restricted to early stages of life, when developing neural circuits are readily shaped by passive sensory experience. In the auditory system, for example, exposing juvenile but not adult rats to pure tones produces a functional over-representation of the tone frequency in the cortical tonotopic map. Recent studies have revealed the continued potential for passive experience to induce robust plasticity in the adult brain, however. In particular, chronic exposures to uninformative or disruptive sounds, such as white noise, have been shown to alter experience-dependent plasticity in the adult auditory cortex, returning the brain to a more plastic and juvenile state. This phenomenon provides an opportunity to study unprecedented cortical plasticity late in life, yet also reveals the brain’s vulnerability to abnormal sensory environments. Tackling both issues, the present thesis uses white noise as a tool to probe experience-dependent plasticity in the adult rat auditory cortex in three studies. In the first study, passive exposures to non-traumatic white noise of varying amplitude modulation depths are used to show the importance of salient temporal inputs for mature auditory function. Exposure to unmodulated but not modulated noise induces juvenile-like plasticity and frequency over-representation in response to a second exposure to pure tones, demonstrating that white noise triggers plasticity by masking temporal inputs from the environment. Since greater functional representation is generally thought to improve perceptual discrimination, the hypothesis that noise-induced plasticity could be used to improve adult perceptual learning is tested in the second study. Contrary to our expectations, sound-exposed animals were worse at discriminating the over-represented frequency, demonstrating that increased functional representation is not sufficient to improve discrimination. Finally, the third study investigates the possibility that changes in neural activity induced by noise exposure could be indicative of maladaptive plasticity leading to aberrant or unwanted perceptual consequences. Common neural and behavioral correlates of the auditory disorders tinnitus and hyperacusis were assessed in noise-exposed animals. Evidence of hyperacusis in exposed rats suggests that noise exposure opens windows of plasticity that may be understood as windows of vulnerability to maladaptive plastic changes. The results presented in this thesis help to elucidate the mechanisms and perceptual consequences of noise-induced plasticity in the adult rat auditory cortex. They describe the profound impact of noise on brain structure and function, advance our present understanding of experience-dependent plasticity in sensory circuits, and demonstrate how sensory environments may powerfully influence the brain throughout life"--

Author: Theodore M. Moallem
Publisher:
ISBN:
Category :
Languages : en
Pages : 110

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 140

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Neocortical architecture is established by both intrinsic, genetic factors and experience- dependent factors. Postnatal sensory experience plays a significant role in the maturation and refinement of cortical sensory fields, such as the primary auditory cortex (A1). In this thesis, I investigated the effects of manipulating postnatal acoustic experience on the functional and morphological properties of neurons in the thalamocortical auditory pathway of adult rats. In Experiment 1, I used two converging electrophysiological techniques to determine the effects of patterned acoustic deprivation (through exposure to continuous, moderate-level white noise; cWN) on the functional properties of neurons in the central auditory system. In Experiment 2, I used Golgi-Cox staining to visualize morphological correlates of experience-dependent changes in neuron functioning. Long- and short-term plasticity mediate synaptic strengthening in sensory cortices in response to postnatal sensory experience. I assessed levels of long-term plasticity (using long- term potentiation; LTP) and short-term plasticity (using paired-pulse facilitation/depression; PPF/PPD) in vivo (under deep urethane anesthesia) in the A1 of normally reared rats and rats reared in the absence of patterned acoustic input through cWN exposure. Rats reared under cWN showed significantly greater LTP of field postsynaptic potentials (fPSPs) for thalamocortical, but not intracortical synapses in A1 compared to age-matched controls, indicative of immature, more plastic synaptic connectivity. Both groups showed similar, moderate levels of PPD (across interstimulus intervals ranging from 25 to 1000 ms) prior to LTP induction. Across groups, PPD was significantly enhanced after LTP induction, indicative of a presynaptic component of thalamocortical LTP in A1. I also assessed the morphology of layer II/III pyramidal neurons in A1 using Golgi-Cox staining and two-dimensional neuron reconstruction. Morphological features, including dendritic length, arbor complexity, and spine density, did not differ significantly between rats reared under cWN and age-matched controls. Rats reared under cWN showed a significantly greater proportion of filopodia to mature spines on apical dendrites compared to age-matched controls. Together, these data indicate that patterned acoustic experience results in a reduction of plasticity in A1, indicative of more mature, hard-wired synaptic connectivity. Furthermore, LTP in A1 in vivo is mediated in part by presynaptic mechanisms, such as increases in transmitter release probability at thalamocortical synapses.

Author: Laurence O. Trussell
Publisher: Springer Science & Business Media
ISBN: 144199517X
Category : Science
Languages : en
Pages : 242

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Book Description
Synaptic Mechanisms in the Auditory System will provide a basic reference for students, clinicians, and researchers on how synapses in the auditory system function to encode acoustic signals. These mechanisms are the groundwork for all auditory processing, and understanding them requires knowledge of the microphysiology of synapses, cellular biophysics, receptor pharmacology, and an appreciation for what these synapses must do for a living, what unique jobs they carry out.

Author: Jeffery A. Winer
Publisher: Springer Science & Business Media
ISBN: 1441900748
Category : Science
Languages : en
Pages : 711

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Book Description
There has been substantial progress in understanding the contributions of the auditory forebrain to hearing, sound localization, communication, emotive behavior, and cognition. The Auditory Cortex covers the latest knowledge about the auditory forebrain, including the auditory cortex as well as the medial geniculate body in the thalamus. This book will cover all important aspects of the auditory forebrain organization and function, integrating the auditory thalamus and cortex into a smooth, coherent whole. Volume One covers basic auditory neuroscience. It complements The Auditory Cortex, Volume 2: Integrative Neuroscience, which takes a more applied/clinical perspective.

Author: J. A. Winer
Publisher: Springer
ISBN: 9783540132547
Category : Medical
Languages : en
Pages : 100

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In the operation of reasoning, the mind does nothing but run over its objects, as they are supposed to stand in reality, without adding any thing to them or diminishing any thing from them. If I examine the Ptolomaic and Copernican systems, I endeavour only, by my inquiries, to know the real situation of the planets; that is, in other words, I endeavour to give them, in my conception, the same relation that they bear towards each other in the heavens. To this operation of the mind, therefore, there seems to be always a real, though often unknown standard, in the nature of things; nor is truth or falsehood variable by the various apprehensions of mankind. D. Hume, The sceptic. In: Essays. Moral Political and Literary. Oxford University Press, Oxford, 1963, p. 166. Contents 1 Introduction 1 2 Materials and Methods 2 3 Observations . . . . 4 3. 1 Topography of the Medial Geniculate Body 4 3. 2 Cytoarchitectonic Subdivisions of the Medial Geniculate Body 4 3. 3 Neuronal Architecture of the Ventral Division 7 3. 4 Structure ofAxons in the Ventral Division 21 3. 5 Cortical Connections of the Ventral Division 27 3. 6 Neuronal Architecture of the Dorsal Division 27 3. 7 Structure of Axons in the Dorsal Nuclei 39 3. 8 Neuronal and Axonal Architecture of the Suprageniculate Nucleus and the Posterior Limitans Nucleus . . . . . . 43 3. 9 Cortical Connections of the Dorsal Division . . . . . . 49 3. 10 Neuronal and Axonal Architecture of the Medial Division 56 4 Discussion . . . . . . . . . . . . . . . . . . .

Author: Christopher Cederroth
Publisher: Frontiers Media SA
ISBN: 2889458962
Category :
Languages : en
Pages : 832

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Tinnitus is the perception of a sound when no external sound is present. The severity of tinnitus varies but it can be debilitating for many patients. With more than 100 million people with chronic tinnitus worldwide, tinnitus is a disorder of high prevalence. The increased knowledge in the neuroscience of tinnitus has led to the emergence of promising treatment approaches, but no uniformly effective treatment for tinnitus has been identified. The large patient heterogeneity is considered to be the major obstacle for the development of effective treatment strategies against tinnitus. This eBook provides an inter- and multi-disciplinary collection of tinnitus research with the aim to better understand tinnitus heterogeneity and improve therapeutic outcomes.

Author: Charlotte Hurtley
Publisher: WHO Regional Office Europe
ISBN: 9289041730
Category : Health & Fitness
Languages : en
Pages : 183

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Book Description
The WHO Regional Office for Europe set up a working group of experts to provide scientific advice to the Member States for the development of future legislation and policy action in the area of assessment and control of night noise exposure. The working group reviewed available scientific evidence on the health effects of night noise, and derived health-based guideline values. In December 2006, the working group and stakeholders from industry, government and nongovernmental organizations reviewed and reached general agreement on the guideline values and key texts for the final document of the "Night noise guidelines for Europe". Considering the scientific evidence on the thresholds of night noise exposure indicated by "Lnight,outside" [L suffix night,outside] as defined in the Environmental Noise Directive (2002/49/EC), an Lnight, outside of 40 dB should be the target of the night noise guideline (NNG) to protect the public, including the most vulnerable groups such as children, the chronically ill and the elderly. "Lnight,outside" value of 55 dB is recommended as an interim target for the countries where the NNG cannot be achieved in the short term for various reasons, and where policy-makers choose to adopt a stepwise approach. These guidelines are applicable to the Member States of the European Region, and may be considered as an extension to, as well as an update of, the previous WHO "Guidelines for community noise" (1999). [Ed.]