Neurobiology Laboratory - Honours projects available in 2009
An Honours project undertaken in this lab would be administered by the Discipline of Physiology.
The Neurobiology laboratory is now concentrating on signal transduction in glial cells, communication between neurons and glial cells, and their applications to neuronal disorders both in central and peripheral nervous systems. Recent studies demonstrate glial cells are active partners in processing information and synaptic integration. However, it is not clear what code signals that glial cells receive from neurons are and how glial cells affect neuronal activity. Furthermore, it is not know if this communication is in normal order, and if not, what changes are in neuronal disorders such as Parkinson's disease.
Recent studies of neuropathic pain states, such as extraterritorial and mirror image pain, have led to new insights concerning a crucial role of aspinal cord astrocytes in creation and maintenance of these pathological painstates. P articularly, in dorsal horn, astrocytes were always dramatically activated in response to diverse axonal lesions that create exaggerated pain. However, it is not know how astrocytes communicate each other and what messengers mediate these communications.
To address the above issues, we examine communications between neuronsand glial cells, and signal transduction among the glial cells in both central nervous system and peripheral nervous system. Multiple techniques are tobe used in these studies, which include tissue culture, brain (spinal cord)slice, calcium imagine, electrophysiology, luciferin-luciferase (ATP) assay,and imunohistochemistry.
- The cellular origins of neuropathic pain: glial cells, macrophages and cytokines
Supervisor + contact details:
- Professor Max Bennett
The fundamental problem in ameliorating neuropathic pain is to block the spontaneous action potential firing, which originates primarily from nociceptor nerve endings in the neuroma formed at the site of nerve lesion. Nociceptors have specific classes of Na+ channels which are modified following a lesion, with tetrodotoxin-sensitive channels up-regulated and insensitive ones down-regulated. The question arises as to what are the mechanisms at the lesion site that engage this transformation in Na+ channel types. There is a proliferation of glial cells (Schwann cells) and macrophages at the neuroma, which are known to release certain species of cytokines, growth factors and transmitter substances. These must engage a retrograde transport system in the injured axons, so as to signal to the nociceptor neuron's nucleus the changes in Na+ channel expression with a concomitant orthograde redistribution of these channels to the site of the neuroma. The capacity to block specific and unique components of these processes lies at the heart of achieving specific oral analgesics without gross side-effects. Of special interest in this regard is the action of lidocaine and of P2x7 receptor antagonists. This project, which is at present the subject of experimentation in our laboratory, involves a comprehensive consideration of these pathways and mechanisms.
- References
- Wall & Malzack (2005) Text Book of Pain, 5th edn, Chapter 58.
I. Nagg & C. Woolf (1996) Pain 64(1): 59-70.
M. Araujo, C. Sinnott et al., (2003) Pain 103(1-2): 21-29.
R. Amir, C. Argoff et al., (2006) Journal of Pain 7 (5 Suppl, 3): S1-S29.
G. Liu, E. Werry & M.R. Bennett (2006) Europ J Neurosci 21(1): 151-160.
G. Liu & M.R. Bennett (2003) NeuroReport 14(16): 2078-2083.
- The cellular origins of migraine pain: astrocyte spreading depression
Supervisor + contact details:
- Professor Max Bennett
Headaches in migraine are thought to be associated with a dilation of cranial blood vessels, particularly those in the dura mater, and an accompanying localized sterile inflammatory response. In many cases the headache phase of migraine is preceded by a condition called aura, in which there is a disturbance of vision, consisting of bright spots and dazzling zigzag lines. This aura is associates with a spreading depression of electrical activity in the cortex. This depression of electrical activity involves a considerable increase in extracellular potassium and a concomitant decrease in extracellular sodium, chloride and calcium. Astrocytes are most likely to be the cell responsible for spreading depression. Calcium waves are propagated by astrocytes, whereas sodium waves (the action potential) are propagated by neurons. Synaptic transmission between astrocytes is mediated by the substance ATP, so that blocking this transmission should block or slow spreading depression. In order to do this, it is first required to identify the mechanism of ATP release and the receptors on which this nucleotide acts.
This project involves an analysis of the mechanism of the spreading depression responsible for both the aura and headache phases of migraine.
- References
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U. Reuter, M. Sanchez del Rio & M. Moskowitz (2000) Functional Neurology 15: Suppl. 3, 9-18.
L. Edvinsson (2001) Pharmacology and Toxicology 89(2); 66-73.
E. Hamel (1999) Canadian Journal of Clinical Pharmacology 6: Suppl. A., 9A-14A
M.R. Bennett, L. Farnell & W.G. Gibson (2005) Biophysical Journal 89(4); 2235-2250.
M.R. Bennett, V. Buljan, L. Farnell & W.G. Gibson (2006) Biophysical Journal (EPub)
- The cellular origins of central pain sensitisation I: the astrocyte - microglia network
Supervisor + contact details:
- Professor Max Bennett
The spontaneous action potential firing in nociceptor neurons generated at the site of a neuroma after a lesion causes neuropathic pain. However, after the lesion has healed on-going pain is often still experienced. There is evidence that an astrocyte - microglia cell network in the dorsal horn, at the site of nociceptor synapses, could mediate this process of sensitisation. Nociceptor nerve terminals, firing spontaneous bursts, release both glutamate and substance P which we have shown trigger the release of large amounts of ATP from astrocytes. In addition, microglia migrate to the site of such terminals, where they are in turn triggered to release ATP in response to glutamate release from the terminals. The very large ATP concentrations that ensue are such as to be able to activate P2x7 receptor-forming pores in the microglia, leading to the unregulated release of ATP and cytokines. This ATP/cytokine soup can then activate P2x receptors on the nociceptor terminals to greatly enhance the release of glutamate and ATP under even mild impulse traffic. The resulting positive feedback network ensures an increase in nociceptor transmission in the pain pathway that becomes independent of any elevated action potential firing in the terminals. The experimental and theoretical aspects of this pain sensitisation will be examined in this project.
- References
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M. Tsuda, K, Inoue,& M. Slater (2005) Trends in Neurosciences 28(2): 101-107.
A. Abdipranoto, G. Liu, E. Werry & M.R. Bennett (2003) NeuroReport 14(17): 2177-2181.
G. Liu, A. Kalous, E. Werry & M.R. Bennett (2006) Molecular Pharmacology (Epub).
E. Werry, G. Liu & M.R. Bennett (2006) Journal of Neurochemistry (Epub).
- The cellular origins of central pain sensitisation II: astrocytes, microglia and cytokines
Supervisor + contact details:
- Professor Max Bennett
Cytokines can have a powerful effect onboth transmitter release as well as on the distribution and density of transmitter receptors at synapses. For example, TNFa up-regulates AMPA receptors at glutamatergic synapses and ILib depresses transmitter release. Microglia at synapses are a principal source of both TNFa and ILib and glutamate greatly enhances the release of ILib from these glial cells. In project P3 above, we discussed the role of the astrocyte - microglia network in enhancing glutamate release from nociceptor terminals and of ATP accumulation at the synapses formed by these terminals. Given that microglia migrate to sources of high ATP, these cells can release TNFa in the glutamate -ATP rich environment. This cytokine enhances nociceptor transmission through up-regulating AMPA receptors, greatly increasing the transmission in the pain pathway. The mechanisms involved in the release of both pro-inflammatory and anti-inflammatory cytokines and their actions on nociceptor transmission will be studied in this project with the aim of identifying the appropriate sites of blockade to relieve the sensitising effects of cytokines in pain transmission.
- References
- D. Stellwagen & R. Malenka (2006) Nature 440(2082): 1054-1059.
F. Bianco, N. Solari et al. (2005) Journal of Immunology 174(11): 7268-7277.
D. Taylor et al. (2005) Journal of Neuroscience 25(11): 2952-2964.
- Pain representation in the brain: the astrocytic model for fMRI and the interpretation of images
Supervisor + contact details:
- Professor Max Bennett
Pain of superficial (cutaneous) origin is sharp and restricted, whereas pain of deep origin (muscle and viscera) is dull and diffuse. Using functional magnetic resonance (fMRI), major differences in the regions of the brain 'activated' in these different conditions have been noted by L. Henderson and his colleagues. These include regions associated with the emotions (perigenual cingulate cortex), with stimulus localization and intensity (somatosensory cortex) and motor control (motor cortex and cingulate motor area). However, the identification of regions as 'activated' depends on what fMRI is measuring, which is changes in the blood oxygen level development (BOLD). It is now known that changes in blood flow at the level of capillaries and arterioles is under the control of the endfeet of astrocytes whose processes enfold of the order of 10,000 synapses. Adenosine, nitric oxide and epoxyeicosatrenoic acids (EETs) are the substances released at the interface between astrocyte endfeet and the endothelial cells of blood vessels. These substances have powerful relaxing effects on the smooth muscle of blood vessels, leading to vasodilation and an increase in blood flow.
The question examined in this project is:- what is the mechanism by which activity at synapses is conveyed to blood vessels through astrocytes, and to what extent the resultant BOLD signal changes can be said to reflect "activated" brain regions? Without determination of this mechanism and the factors which perturb it, use of fMRI to investigate pain pathways in the brain must be carried out with some caution.
- References
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L. Henderson et al., (2006) Pain 120: 286-296.
A. Arthurs & S. Boniface (2002) Trends in Neuroscience 25: 27-31.
A. Volterra & J. Meldoles (2005) Nature Reviews Neuroscience 6: 626- .
C. Pepplatt & D. Attwell (2004) Nature 431: 137- .
R. Kochler et al., (2006) Journal of Applied Physiology 100: 302-317.
