Spinal sensory processing in the human infant: Development of the flexion withdrawal reflex Laura Louise Cornelissen Thesis submitted for the degree of Doctor of Philosophy University College London 2011 1 Declaration The work in this thesis was conducted in the Department of Neuroscience, Physiology and Pharmacology at University College London, and in the Elizabeth Anderson and Obstetrics Wing at University College Hospital. I, Laura Louise Cornelissen, confirm that the work presented in this thesis is my own. Where other information has been derived from other sources, I confirm that this has been indicated in the thesis. Laura Louise Cornelissen March 2011 2 Abstract Immature spinal sensory reflexes have lower mechanical thresholds and are poorly coordinated and exaggerated compared to adult reflexes. However, little quantitative data is available on how these spinal sensory circuits develop in the human infant. This thesis investigates the development of cutaneous flexion withdrawal reflexes in preterm and full- term human infants following noxious and non-noxious stimulation of the heel, and tests whether flexion withdrawal reflex activity is modulated by the commonly administered analgesic, oral sucrose, in a randomised controlled trial. The studies were undertaken in infants aged 28-45 weeks gestation (GA), in-patients at University College Hospital, London. The noxious stimulus was a clinically required heel lance; non-noxious stimulation was either a light touch of the heel or application of calibrated von Frey hairs to the heel. Flexion withdrawal reflex activity was recorded with surface EMG electrodes placed over the biceps femoris muscle. Video recordings of facial expression were recorded for clinical pain assessment. Noxious heel lance evoked bilateral withdrawal reflex activity across all ages, but the peak amplitude was greater in preterm infants (<37 weeks GA) than full-term infants (>37 weeks GA). Nociceptive reflex activity occurred even when there was no change in facial expression. Non-noxious touch evoked a significantly smaller reflex response than noxious stimulation. The von Frey hair cutaneous mechanical threshold for flexion withdrawal reflex activity increased with gestational age. Repeated stimulation with von Frey hairs at suprathreshold intensities caused greater habituation in full term than preterm infants. Flexion withdrawal reflex properties were not altered by administration of oral sucrose before a heel lance, despite significant reduction in clinical facial expression scores. In conclusion, human spinal sensory circuits undergo significant postnatal development that alters their behavioural responses to touch and pain. The commonly used neonatal analgesic, oral sucrose, does not affect sensory processing at the level of the spinal cord. 3 Acknowledgements Over the course of the last four years I have been fortunate to meet and work with many wonderful people. Completing a doctoral programme and indeed, writing up a thesis is by no means a simple undertaking, however it would be not possible without the personal and practical support of numerous people, of whom I now take pleasure in thanking. First of all I would like to thank my PhD supervisor Maria Fitzgerald for her excellent advice, teaching and encouragement. I have been motivated by her enthusiasm and drive to further understand the development of the nervous system and pain processing throughout my PhD programme and look forward to future research in this area. Secondly, my sincere thanks to my secondary supervisor Stewart Boyd, whom I enjoyed many, many hours of discussion with, and whose gentle encouragement has massively built up my confidence as a scientist. I wish to thank Judith Meek, for enabling the collaboration between UCL and the neonatal unit at UCH, without this it would not have been possible to conduct this work. I would like to thank all the parents and infants who participated in these studies. Many thanks to Rebeccah Slater, who taught me valuable skills in conducting and interpreting electrophysiological recordings on the neonatal unit; along with many hours of discussion and her excellent teaching. I wish to thank Lorenzo Fabrizi, for proving invaluable MatLab code, being a mentor and good friend. Many thanks to Debbie Pattern, Jan Yoxen and Anne Canterella, the neonatal research nurses who meticulously analysed videos for PIPP analysis, and who I have had the pleasure of working alongside on the neonatal unit. Many thanks to Alan Worley, who built the event marking system that enabled the stimuli to be time-locked to the EMG and video recordings, and for his advice on numerous aspects of the recording system set-up and support along the way. To the members of the Fitzgerald and Hunt laboratories, past and present, particularly to Gareth Hathway and Stephanie Koch who provided great advice on the electrophysiological and developmental aspects of this thesis, and to Gemma Williams for numerous discussions and proof-reading this thesis. Also to my science buddy, Katherine Quick, for the useful advice whilst writing up and crucially, for making me laugh. Thank you to the Medical Research Council who financially supported this work. 4 Many thanks to my friends who have always been there: particularly to Melanie Earp, Alexis Hopwood, Laura White, Alison Twelvetrees and Dan Bose for providing a continuous supply of tea, and to my housemates, especially Adrian Barker, Jennifer Fox and Ben Todd who have ensured I have been fed and provided a continuous supply of entertainment. I would like to thank my family for their continual support and encouragement over the years. Finally, I would like to thank Dan Ward for his thorough proof reading, along with his kind support in dealing with ‘those’ moments during writing up of this thesis. Thank you all. 5 Table of Contents Declaration..................................................................................................................2 Abstract.......................................................................................................................3 Acknowledgements....................................................................................................4 Table of Contents.......................................................................................................6 List of Figures...........................................................................................................10 List of Tables ............................................................................................................15 Abbreviations ...........................................................................................................17 Chapter 1: Introduction............................................................................................19 1.1 Sensory processing is vital for survival ...............................................................21 1.1.1 Sensory transduction and peripheral transmission ....................................21 1.1.2 Spinal sensory processing: anatomy and physiology of dorsal and ventral horn circuitry ..............................................................................................27 1.1.3 Anatomy and physiology of sensory and nociceptive pathways in the brainstem and higher-centres ....................................................................31 1.1.4 Spinal sensorimotor output: the flexion withdrawal reflex ..........................35 1.1.5 Other types of physiological activity used as a measure of nociceptive processing..................................................................................................40 1.1.6 Animal models provide information on the development of nociceptive processing… ..............................................................................................42 1.2 The development of nociceptive circuits .............................................................43 1.2.1 Developmental characteristics of flexion withdrawal reflexes ....................43 1.2.2 Developmental neuroanatomy and neurophysiology.................................46 1.3 Pain in the neonatal population...........................................................................54 1.3.1 Pain in the neonatal intensive care unit .....................................................54 1.3.2 Current clinical pain measurement in neonates.........................................54 1.3.3 Management of neonatal pain........................................................................55 1.3.4 Long term effects of tissue injury in the neonatal period............................56 1.4 Aims of the thesis................................................................................................58 Chapter 2: General Methods ...................................................................................59 2.1 Research with human subjects ...........................................................................60 2.2 Participants..........................................................................................................62 2.3 Study design........................................................................................................63 2.4 Stimulus...............................................................................................................64 2.4.1 Noxious stimulus ..........................................................................................64 2.4.2 Non-noxious touch stimulus...........................................................................64