Presentation on theme: "Restorative therapies for motor function after stroke (cerebral ischemia) Dr Lawrence Moon Please take two minutes to fill in the quick questionnaire During."— Presentation transcript:
Restorative therapies for motor function after stroke (cerebral ischemia) Dr Lawrence Moon Please take two minutes to fill in the quick questionnaire During the lecture, do interrupt with questions if you have any
After this lecture and appropriate reading you should be able to 1.Describe the anatomy of cortical efferents. 2.Describe a focal animal model of stroke. You should be able to highlight the patterns of midbrain and spinal denervation that occur after stroke and identify spared cortical efferents that could be exploited by pro-plasticity therapies. 3. Describe possible mechanisms contributing to loss of function. 4. Define compensation, collateral sprouting and plasticity. 5. Explain mechanisms preventing spared axons growing in the adult CNS. 6. Describe experiments enhancing growth of spared axons after stroke.
1.Anatomy of human cortical efferents 2.How do rats reach for food (?!) 3.Anatomy of rat cortical efferents 4.What is lost after unilateral stroke? 5.What is spared after unilateral stroke? 6.Why is there little spontaneous recovery? 7.How have scientists attempted to restore lost function? Overview / structure
decussation & lateralised CST n.b. species differ radically n.b. other cortical efferents
Anatomy of human corticospinal tract Thus the right hemisphere largely supplies the left spinal cord (“decussation to contralateral side”) and vice versa. Some minor projections to the same (“ipsilateral”) side. In the spinal cord, the cortical efferents run in the lateral columns.
Unilateral cerebral ischemia causes... Loss of oxygen and nutrients to neurons and glia on one side of brain Cell death (primary, secondary) Loss of cortical axons (projections / efferents) to regions including ipsilateral (same side) striatum ipsilateral red nucleus ipsilateral pons contralateral spinal cord hence hemiplegia on opposite side of body to stroke Damage to the human CST is devastating to fine and gross motor control. Animal models allow us to model this and test therapies...
How do rats reach for food? Excellent precision in their motor control.
How do rats control their forelimbs? Two tracts are vital in rats: The corticospinal tract Piecharka et al., 2005 Brain Research Bulletin 66:203-211. The cortico-rubro-spinal tract Whishaw et al,. 1998 Behavioural Brain Research 93:167-183.
Anatomy of rat corticospinal tract Injection of anterograde tracer (here in the right cortex) show that the rat CST anatomy is similar to the human but the cortical efferents run in the dorsal columns. There is also a minor dorsolateral component. The ipsilateral component runs ventrally. Brosamle & Schwab (1997). Interruption of the rat CST leads only to minor deficits in motor function.
Anatomy of rat and human cortico- rubro-spinal tract n.b. Rubro- = red Cortico-rubral tract runs ipsilaterally. Rubro-spinal tract decussates and runs contralaterally. Hence the cortex influences the contralateral side of the body directly via the corticospinal tract and indirectly via the rubrospinal relay.
Unilateral cerebral ischemia in rat Stroke kills cortical neurons. Descending axons (efferents) degenerate. Loss of input to contralateral spinal cord. Loss of input to ipsilateral red nucleus, striatum and pons. Hence denervated zones. But there is a spared cortex. with spared efferents to one side of the spinal cord and to one red nucleus & pons reparative
What if intact axons could be induced to sprout to denervated zones? Would the spared circuitries learn to restore the lost function?
Novel area of research: new therapies? There are spared axons. These do not, however, spontaneously grow into zones of denervation e.g. contralateral red nucleus e.g. ipsilateral spinal cord If we can understand why not, it may be possible to exploit spared axons to cause repair. Possible new therapies!
Why little spontaneous recovery? Very few new neurons are born (neurogenesis) Limited endogenous repair (adult vs neonate) Insufficient compensatory plasticity Poor intrinsic axon growth Pro-growth molecules down-regulated Anti-growth pathways switched on Inhospitable extrinsic environment Growth-inhibitory molecules (intact & injured) Lack of growth factors, permissive substrates
Many growth inhibitory molecules have been discovered in the nervous system (read reviews; Sandvig et al., 2004; Schwab, 2004). White matter is particularly growth inhibitory (Caroni & Schwab, 1989). Biochemical fractions of myelin contain molecules including Nogo-A, MAG, OMgp. These are all inhibitory to axon growth. Nogo-A is a component of myelin synthesised by oligodendrocytes. Growth inhibitory molecules
Neuronal growth is inhibited because neurons express a receptor complex for Nogo-A comprised of Nogo receptor (NgR) p75 / NGF receptor LINGO This receptor complex cause axon growth failure by signalling to the cytoskeleton via RhoA Rho kinase (ROCK) Neuronal receptors for inhibitors Schwab 2004
Do antibodies against Nogo-A provide a an effective therapy for stroke? Schwab 2004
MCAO mouse IN-1 antibodies from cells no delay to treat forepaw reaching test
Papadopolous et al., 2002 (continued). -- TRACER Spared cortico-rubral axons sprouted across the midline
Improved antibody Extra animal model and different reaching test Assessment of corticospinal sprouting (c.f. rubrospinal in previous) Data presented poorly. Is it persuasive? (e.g. Fig 6E). Is axon sprouting effect big enough to explain behaviour?
Issues to critically evaluate while reading Do the animal models of stroke adequately model human strokes? Am I persuaded that antibodies to Nogo-A restore function after stroke? Critically evaluate Wiessner et al., 2003 in particular. If I had a stroke, would I be prepared to be the first recipient of these antibodies? What extra data might I want? What would need to be done to prove that the sprouting axons actually restore the lost function? If not persuaded, why not? What remains to be shown?
Future targets? Read more and critically question what you read. What other inhibitors are there in the midbrain and spinal cord? What are their receptors? Would interfering with these promote recovery of function after stroke? How might we interfere with these interactions? Sandvig et al,. 2004 Critically evaluate the mechanism of action of other experimental therapies inosine amphetamine rehabilitation Do we know if they work? Do we know how they work?
Tips on answering exam questions! Answer the question, not just the part you revised! Show evidence of additional reading and critical thought. e.g. use references to support EACH claim you make (Bob et al., 2008)
Anatomy of cortical efferents 1.Kandel, Schwartz & Jessell, Principles of Neural Science 2.Fig.1; Brosamle & Schwab, 1997 J Comparative Neurology 386:293-303. Why don’t spared axons grow spontaneously after stroke? 1.Schwab, 2004. Nogo and axon regeneration. Curr Opin Neurobiol. 14:118-24 2.Sandvig et al,. 2004. Myelin-, reactive glia-, and scar-derived CNS axon growth inhibitors: expression, receptor signaling, and correlation with axon regeneration. Glia 46:225-51 How might we exploit spared circuits after stroke? a) Nogo-A antibodies 1.Seymour et al., 2005 Delayed treatment with monoclonal antibody IN-1 1 week after stroke results in recovery of function and corticorubral plasticity in adult rats. J Cerebral Blood Flow & Metabolism 25, 1366–1375 2.Papadopolous et al., 2005 Functional recovery and neuroanatomical plasticity following middle cerebral artery occlusion and IN-1 antibody treatment in the adult rat. Ann Neurol. 51:433-41. 3.Markus et al., 2005 Recovery and brain reorganization after stroke in adult and aged rats. Ann Neurol. 2005 58(6):950-3. 4.Wiessner et al., 2003 Anti-Nogo-A antibody infusion 24 hours after experimental stroke improved behavioral outcome and corticospinal plasticity in... rats J Cerebral Blood Flow & Metabolism. 23:154-165. Reading list
How might we exploit spared circuits after stroke? b) D-amphetamine 1. Ramic et al., 2006. Axonal plasticity is associated with motor recovery following amphetamine treatment combined with rehabilitation after brain injury in the adult rat. Brain Res. 1111:176- 186. 2.Platz et al,. 2007. Amphetamine fails to facilitate motor performance and to enhance motor recovery among stroke patients with mild arm paresis: interim analysis and termination of a double blind, randomised, placebo-controlled trial. Restor Neurol Neurosci. 23:271-80 c) inosine 1. Chen et al., 2002 Inosine induces axonal rewiring and improves behavioral outcome after stroke. Proc Natl Acad Sci U S A. 99:9031-6. d) locomotor rehabilitation / cognitive / social enrichment 1.Boake et al., 2007 Constraint-Induced Movement Therapy During Early Stroke Rehabilitation. Neurorehabil Neural Repair 21:14-24 2.Biernaskie & Corbett, 2001. Enriched rehabilitative training promotes improved forelimb motor function and enhanced dendritic growth after focal ischemic injury. J Neurosci. 21:5272-80. 3.Johansson, 2004. Functional and cellular effects of environmental enrichment after experimental brain infarcts. Restor Neurol Neurosci. 22:163-74 Reading list
Plasticity Nudo, 2006 Plasticity. NeuroRx 3:420-7 Which neurons have receptors for growth inhibitors? Barrette et al., 2007. Expression profile of receptors for myelin-associated inhibitors of axonal regeneration in the intact and injured mouse central nervous system. Molecular and Cellular Neuroscience (Epub ahead of print). Reading list Powerpoint and pdfs can be downloaded from http://www.lawrencemoon.co.uk/resources/stroke.asp