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The Properties of Dorseal Spinocerebellar Tract

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The Properties of Dorseal Spinocerebellar Tract PLEASE TYPE THE UNIVERSITY OF NEW SOUTH WALES Thesis/Project Report Sheet Surname or Family name: RAKIC First name: Severin Other name/s: Abbreviation for degree as given in the University calendar: M.Sc school: School of Medical Sciences Faculty: Medicine Title: The Properties of Dorsal Spinocerebellar Tract Neurones and their Role in Signalling Tactile Information from the Skin to the Cerebellum Abstract 350 words maximum: (PLEASE TYPE) The dorsal spinocerebellar tract (DSCT) appears to be the major pathway conveying kinaesthetic and tactile information from the hindlimb to the cerebellum. The aim of the present study was to investigate quantitatively the capacity of dorsal spinocerebellar tract (DSCT) neurones to signal static and dynamic tactile information to the cerebellum. The analysis, conducted in anaesthetised cats, was based on extracellular recording , in Clarke's column and the adjacent dorsal horn of the lumbar spinal cord, from single DSCT neurones activated by tactile inputs from the hairy skin of the ipsilateral hindlimb. Each neurone studied quantitatively was first identified as a DSCT neurone using an antidromic collision procedure and the receptive field carefully mapped. Static tactile stimuli of graded intensities of skin indentation (up to 1500 IJm) , and dynamic tactile stimuli in the form of sinusoidal vibration were delivered to the most sensitive point in the individual neurone's .receptive field. A small minority (<15%) of sampled DSCT neurones displayed a slowly adapting or static tactile sensitivity, and had rather coarsely-graded stimulus-response relations as a function of graded increases in the amplitude of skin indentation. The vast majority of the DSCT neurones sampled (>85% of neurones) was sensitive to just the dynamic components of tactile stimuli. However, their capacity for signalling information about the intensive and frequency parameters of controlled vibrotactile stimuli was limited to a low-frequency bandwidth up to -1OHz. At higher vibration frequencies, responsiveness was confined to the onset of the vibrotactile stimulus train. The study demonstrates that tactile information conveyed by individual DSCT neurones to the cerebellum, for the purpose of regulating movement and posture, appears to be limited in comparison with the detail and precision of tactile information conveyed by neurones of the dorsal column-medial lemniscal pathway to the cerebral cortex, for the purpose of sensation and perceptual experience. Declaration relating to disposition of project report/thesis I am fully a~are of the policy of the University relating to the retention and use of higher degree proje<;t reports and theses, namely that the University retains the copies submitted for exa mination and is free to allow them to be consulted or borrowed. Subject to the provisions of the Copyright Act 1 %8, the University may issue a project report or thesis in whole or in part, in photostat or microfilm or other copying medium. The University recognises that there may be exceptional circumstances r~uiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years must be made in writing to the Registrar. Requests for a longer period of restriction may be considered in exceptional circumstances if accompanied by a letter of support from the Supervisor or Head of School. Such requests must be submitted with the thesis/project re ort. FOR OFFICE USE ONLY Date of completion of requirements for Award: THIS SHEET IS TO BE GLUED TO THE INSIDE FRONT COVER OF THE THESIS N:\FLORENCE\ABSTRACT co .......w ~ 0 The Properties of Dorsal Spinocerebellar Tract N eurones and Their Role in Signalling Tactile Information from the Skin to the Cerebellum Severin Rakic M.D., Grad. Dip. in Med. Submitted for the award of Master of Science School of Medical Sciences Faculty of Medicine The University ofNew South Wales September, 2004. ''l , ... V{ U ~ .. _... ,, t 1 7 AUG 2005 --------'l Declaration of Originality I hereby declare that this submission is my own work and to the best of my lmowledge it contains no materials previously published or written by another person, nor material which has been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due reference is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is aclmowledged. (Signed) ..... ii Table of Contents PUBLICATIONS ....................................................................v Abstracts ............................................................................................. v ABSTRACT ........................................................................ vii 1. INTRODUCTION ..............................................................1 1.1 Role of the dorsal spinocerebellar tract (DSCT) in cerebellar motor control. ......... 2 1.2 Review of the anatomy of the DSCT and other spinocerebellar pathways .............2 1.2.1 Primary afferent fibres that provide input to DSCT neurones of the cat ............ 5 1.2.2 Location of DSCT neurones within the lumbar spinal cord ........................... 7 1.2.3 DSCT and the other spinocerebellar pathways in the spinal cord .................. 10 1.2.4 Tennination of the DSCT and the other spinocerebellar pathways in the cerebellar cortex ........................................................................... 13 1.3 Review of the functional organization of the DSCT ..................................... 18 1.3.1 Peripheral inputs to DSCTneurones .................................................... 19 1.3.2 Functional organization ofthe neurones in Clarke's column nucleus ...............24 1.3.3 Conduction a/peripheral inputs through the DSCT...... .............................29 1.3.4 Distribution of DSCT input infonnation within the cerebellar cortex ............... 30 1.4 Parallel ascending pathways that convey tactile information to non-cerebellar destinations such as the somatosensory cortex ........................................... .32 1.4.1 Structural and functional organization of the dorsal columns (DC) ................. 34 1.4.2 Major anatomical features of the spinocervical tract (SCT) and the processing of tactile infonnation over this sensory pathway ....................................... 37 1.4.3 Organization of the spinothalamic tract (SIT) and its contribution in tactile perception and sensation .................................................................. 39 2. METHODS .................................................................... 42 2.1 Anaesthesia and preparatory surgery ....................................................... 43 2.2 Surgical preparation for electro-physiological recording ............................... .44 2.2.1 Exposure of the recording site in the lumbar spinal cord ............................ .44 2.2.2 Exposure of the caudal cerebellwnfor insertion of antidromic stimulation electrode in the restiform body ............................................................44 2.3 Electro-physiological recording procedure ............................................... .45 2.3.1 Recording from DSCT neurones in the lumbar spinal cord .......................... .45 iii 2. 3. 2 Antidromic identification ofDSCT neurones ... ........................................45 2. 3. 3 Mechanical stimulation ofthe cutaneous receptive field ofindividual DSCT neurones ..................................................................................... 4 7 2.3.4 Recording equipment ....................................................................... 50 2.4 Computer analysis of impulse activity in DSCT neurones in response to controlled mechanical stimulation of the hindlimb skin .............................................. 50 2. 4.1 Computerised data acquisition for analysis .............................................50 2.4.2 Response measurement and stimulus-response relations .............................. 50 2. 4. 3 Analysis oftemporal patterns in the responses ofDSCT neurones .................. 52 2.5 Histological techniques ....................................................................... 56 3. RESULTS ...................................................................... 57 3.1 Identification ofDSCT neurones ............................................................ 58 3.1.1 Antidromic identification ofDSCT neurones ........................................... 58 3.1.2 Location of identified DSCT neurones within the spinal cord.................... .... 61 3.1.3 Trans-synaptic activation ofDSCTneuronesfrom the spinal dorsal columns ..... 61 3.2 Size and distribution of tactile receptive fields ofDSCT neurones .................... 66 3.3 Response ofDSCT neurones to controlled mechanical stimulation of the skin ...... 66 3.3.1 Responsiveness ofDSCTneurones to static indentation ofthe skin ................o.68 3.3.2 Responses ofDSCT neurones to focal cutaneous vibration ........................... 71 3. 3. 3 Responses ofDSCT neurones receiving slowly adapting inputs to focal vibration ...................................................................................... 80 4. D ISCUSSI 0 N .................................................................
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