Senior Principal Research Fellow, NeuRA
Professor of Integrative Physiology, School of Medicine, Western Sydney University
Vaughan Macefield completed his PhD in respiratory neurophysiology under Dr Bruce Nail at UNSW in 1986 and then spent four years with Prof David Burke and Prof Simon Gandevia at Prince Henry Hospital, learning microneurography and other human neurophysiological techniques. In 1990, he received an NHMRC CJ Martin Fellowship to study with Prof Roland Johansson, Prof Gunnar Wallin and Prof Ake Vallbo in Sweden and then spent a year with Prof Bigland-Ritchie at Yale University. Vaughan has been at Neuroscience Research Australia – supported by an NHMRC RD Wright Fellow, NHMRC Research Fellow and Senior Research Fellow – since 1994, before moving to Western Sydney University in 2006. Vaughan maintains an active laboratory at NeuRA, and performs concurrent microneurography and fMRI at the Clinical Imaging Facility.
Parkinson's disease (PD) is a degenerative neurological condition, associated with cardiovascular dysfunction. Many studies have utilised heart rate variability (HRV) to assess the autonomic nervous system in PD, but blood pressure variability (BPV) has received less attention. The purpose of the present study was to compare HRV and BPV between participants with established PD, extrapyramidal motor slowing (EPMS) (not reaching clinical criteria for PD), older healthy controls (OHC), and young healthy controls (YHC), in order to ascertain whether either of these measures can be used as an early marker of non-motor symptoms in PD.
Conditioned pain modulation is a powerful analgesic mechanism, occurring when a painful stimulus is inhibited by a second painful stimulus delivered at a different body location. Reduced conditioned pain modulation capacity is associated with the development of some chronic pain conditions and the effectiveness of some analgesic medications. Human lesion studies show that the circuitry responsible for conditioned pain modulation lies within the caudal brainstem, although the precise nuclei in humans remain unknown. We employed brain imaging to determine brainstem sites responsible for conditioned pain modulation in 54 healthy individuals. In all subjects, 8 noxious heat stimuli (test stimuli) were applied to the right side of the mouth and brain activity measured using functional magnetic resonance imaging. This paradigm was then repeated. However, following the fourth noxious stimulus, a separate noxious stimulus, consisting of an intramuscular injection of hypertonic saline into the leg, was delivered (conditioning stimulus). During this test and conditioning stimulus period, 23 subjects displayed conditioned pain modulation analgesia whereas 31 subjects did not. An individual's analgesic ability was not influenced by gender, pain intensity levels of the test or conditioning stimuli or by psychological variables such as pain catastrophizing or fear of pain. Brain images were processed using SPM8 and the brainstem isolated using the SUIT toolbox. Significant increases in signal intensity were determined during each test stimulus and compared between subjects that did and did not display CPM analgesia (p<0.05, small volume correction). The expression of analgesia was associated with reduction in signal intensity increases during each test stimulus in the presence of the conditioning stimulus in three brainstem regions: the caudalis subdivision of the spinal trigeminal nucleus, i.e., the primary synapse, the region of the subnucleus reticularis dorsalis and in the dorsolateral pons in the region of the parabrachial nucleus. Furthermore, the magnitudes of these signal reductions in all three brainstem regions were significantly correlated to analgesia magnitude. Defining conditioned pain modulation circuitry provides a framework for the future investigations into the neural mechanisms responsible for the maintenance of persistent pain conditions thought to involve altered analgesic circuitry.
Low-frequency sinusoidal linear acceleration (0.08 Hz, ±4 mG) modulates skin sympathetic nerve activity (SSNA) in seated subjects (head vertical), suggesting that activation of the utricle in the peripheral vestibular labyrinth modulates SSNA. The aim of the current study was to determine whether SSNA is also modulated by input from the saccule. Tungsten microelectrodes were inserted into the common peroneal nerve to record oligounitary SSNA in 8 subjects laying supine on a motorized platform with the head aligned with the longitudinal axis of the body. Slow sinusoidal (0.08 Hz, 100 cycles) linear acceleration-decelerations (peak ±4 mG) were applied rostrocaudally to predominately activate the saccules, or mediolaterally to predominately activate the utricles. Cross-correlation histograms were constructed between the negative-going sympathetic spikes and the positive peaks of the sinusoidal stimuli. Sinusoidal linear acceleration along the rostrocaudal axis or mediolateral axis both resulted in sinusoidal modulation of SSNA (Median, IQR 27.0, 22-33% and 24.8, 17-39%, respectively). This suggests that both otolith organs act on sympathetic outflow to skin and muscle in a similar manner during supine displacements.