Division of Neurology

Michel P. Rathbone

MD, CHB, PhD, FRCPC

Professor, Division of Neurology, Department of Medicine

 

 

Research Program

The overall Objective of the laboratory is to study the methods of reducing neural damage after various metabolic or physical insults and to enhance function after such events. Specifically, our major projects include:

  1. Investigation of the trophic effects of extracellular purines, particularly non-adenine based purines and
  2. Determination of the ability of glia from the enteric nervous system to enhance regeneration in the central nervous system, particularly the spinal cord.

A. The trophic effects of extracellular purines, particularly non-adenine based purines

My laboratory was the first to report the neurotrophic effects of non-adenine based purines. We have shown that these compounds affect a variety of cell types, including astrocytes, microglia, endothelial cells and neurons. Non-adenine based purines, we have reported, stimulate cell differentiation and enhance the production of protein neurotrophic factors and cytokines by various cell types.

The research has led to the development of a compound currently in phase IIB trials for Alzheimer's disease. Dr. Rathbone holds several patents on this agent and on related processes.

We have determined that the non-adenine based purines have a neuroprotective role in acute neurological insults such as stroke and neurotrauma. They are released from cells in high concentrations under physiological, and particularly, pathological conditions. Indeed their extracellular concentrations exceed those of adenosine by up to 5 fold. Certain non-adenine based purines are now known additionally to possess anticonvulsant and sedative activities.

We have shown that, unlike adenosine, the non-adenine based purines do not induce apoptosis. During the course of these studies we have demonstrated that adenosine causes apoptosis in 2 ways - intracellularly by altering the ratio of S-adenosyl methionine to S-adenosyl homocysteine and at the cell surface through activation of a P2X7 receptor was required for induction of apoptosis by low concentrations of adenosine and the receptor was only synthesized under certain cellular conditions.

Most recently the stimulatory effects of non-adenine based purines on growth of axons in the central nervous system has been demonstrated. We are currently using this remarkable activity to enhance recovery of function after spinal cord injury in association with transplantation of enteric glia into the spinal cord.

Meanwhile, these studies have led to the development of an automated computer-based assay for determination of neurite outgrowth in cultured cell lines and neuronal precursor cells.

B. Glia from the enteric nervous system to enhance regeneration in the central nervous system, particularly the spinal cord

We have developed a simple procedure for isolation of pure cultures of enteric glia from rat small intestine. There are 2 morphologically distinct types of enteric glia. One of these is a mature form which supports outgrowth of nerve processes in culture. We have demonstrated that these cells can be inter converted using various trophic factors and non adenine-based purines.

We transplanted these cells into the spinal cord of rats. The enteric glia survived for prolonged periods of several months. They are vascularized. The capillaries that enter the grafts develop characteristics of the blood-brain barrier, demonstrating that these cells possess certain properties similar to astrocytes which can also induce formation of a blood-brain barrier in capillaries.

The enteric glia can be induced to migrate in the spinal cord after implantation.

Transected dorsal root axons normally do not regenerate through CNS myelin in spinal cord. We tested whether enteric glia could promote regeneration in this paradigm. The lower thoracic spinal cord of adult Wistar rats was exposed and one T12 dorsal root completely transected at the cord entry point. The root stump was micro surgically anastomosed to the cord and a suspension of Phaseolus vulgaris Leucoagglutinin (PHAL) - prelabeled enteric glia was injected into the corresponding dorsal root entry zone. Three weeks after transplantation, numerous regenerating dorsal root axons reentered the spinal cord. Ingrowth of dorsal root axons in the region of the migrating enteric glia was observed using Dil and antibodies against PHAL. Primary sensory afferents invaded laminae 1, 2, and 3, grew through laminae 4 and 5, and reached the dorsal gray commissure. No axonal ingrowth was observed in control animals, indicating transplanted enteric glia enabled regeneration of injured dorsal root axons into the adult spinal cord. These data indicate that enteric glia may be of value as stimulators of axonal growth after CNS injuries. We are currently investigating the combination of non-adenine based purines and enteric glia in stimulating axonal regeneration in spinal cord.

Dr. Rathbone's work has been recognized internationally. He was the invited Chairman of a special session devoted to non adenine-based purines at the World Congress on Purines in Madrid in 2000. He has been awarded the honor of Supremi Magistri by the University of Chietl. He was invited guest speaker at "Settimana del Cervello 2001" organized by the Societa Italiana di Neuroscience and DANA Alliance for the Brain.