RESEARCH SUMMARY

My laboratory is focused on understanding the structure and function of recombinant and native gamma aminobutyric acid (GABA) type A (GABAA) receptor channels, and the basic mechanisms of epilepsy and anticonvulsant drugs. GABAA receptor channels are the major inhibitory neurotransmitter receptors in the brain. Reduction of GABAA receptor function produces seizures and epilepsy in animals and man, and enhancement of GABAA receptor function has been used to treat seizures. At least four forms of human epilepsy have been linked to mutations in the alpha1 and gamma2 GABAA receptor subunits. The mechanisms for neurotransmitter activation, regulation of the opening and closing (gating), desensitization and intracellular trafficking of these channels are unknown.

We study recombinant and native GABAA receptor channels using single channel and whole cell patch clamp recording and ultra rapid drug application techniques. Single channel and whole cell recordings of native neurotransmitter receptor channels are made from acute hippocampal slices to study their physiological and biophysical properties and regulation by drugs and phosphorylation. Recombinant receptors and channels are studied using acute transfection of mammalian cells with expression vectors containing receptor subunit cDNAs followed by whole cell or single channel recording. Site-directed mutagenesis and construction of receptor chimeric cDNAs are used to determine binding and kinase phosphorylation sites, and to characterize receptor channel gating and desensitization. Human mutations are made in relevant receptor channel subunits to determine the basic mechanism underlying these genetic human epilepsies. Receptor trafficking is studied using flow cytometry, confocal microscopy and biotinylation and Western blotting of receptors.

SELECTED RECENT PUBLICATIONS

1. Dibbens LM, Hua-Jun Feng H-J, Richards MC, Harkin LA, Hodgson BL, Scott D, Jenkins M, Petrou S, Sutherland GR, Scheffer IE, Berkovic SF, Macdonald RL, Mulley JC: GABRD encoding a protein for extra-synaptic GABAA receptors is a susceptibility locus for Generalized Epilepsies. Human Molecular Genetics, 13:1315-1319 2004.

2. Gallagher MJ, Song L, Macdonald RL: An autosomal dominant juvenile myoclonic epilepsy GABAA receptor alpha1 subunit mutation produces asymmetrical, subunit position-dependent reduction of heterozygous receptor currents. J Neurosci., 24:5570-5578, 2004.

3. Feng H-J, Macdonald RL: Proton modulation of alpha1beta3gamma GABAA receptor channel gating and desensitization. J Neurophysiol 92:1577-1585, 2004.

4. Feng H-J, Bianchi MT, Macdonald RL: Pentobarbital differentially modulates alpha1beta3gamma and alpha1beta3gamma2L GABAA receptor currents. Mol Pharm, 66:988-1003, 2004.

5. Macdonald RL, Gallagher MJ, Feng H-J, Kang J: GABAA receptor epilepsy mutations. Biochem Pharm, 68:1497-1506, 2004.

6. Kang J, Macdonald RL: The GABAA receptor gamma2 subunit R43Q mutation linked to childhood absence epilepsy and febrile seizures causes retention of alpha1beta2gamma2 receptors in the endoplasmic reticulum. J Neurosci, 24:8672-8677, 2004.

7. Feng H-J, Macdonald RL: The differential actions of propofol on delta and gamma2L subunit-containing GABAA receptors. Mol Pharm, 66:1517-1524, 2004.

8. Jones-Davis DM, Song L, Macdonald RL: Structural determinants of benzodiazepine allosteric regulation of GABAA receptor currents. J Neurosci, 25: 8056-8065, 2005.

9. Gallagher MJ, Song L, Shen W, Macdonald RL: Endoplasmic reticulum retention and associated degradation of a GABAA receptor epilepsy mutation that inserts an aspartate in the M3 transmembrane segment of the alpha1 subunit. J Biol Chem, 280: 37995-38004, 2005.

10. Feng H-J, Kang J-Q, Song L and Macdonald RL: The delta subunit susceptibility variants E177A and R220H associated with complex epilepsy alter channel gating and cause endoplasmic reticulum retention of alpha4beta2gamma GABAA receptors. J Neurosci, 26: 1499-1506, 2006.

11. Kang J-Q, Shen W, Macdonald RL: Why does fever trigger seizures?: GABAA receptor gamma2 subunit mutations associated with idiopathic generalized epilepsies have temperature-dependent trafficking deficiencies. J Neurosci, 26:2590-2597, 2006.

12. Audenaert D, Schwartz E, Claeys KG, Claes L, Deprez L, Suls A, Van Dyck T, Lagae L, Van Broeckhoven C, Macdonald RL, De Jonghe P: The GABRG2 gene and febrile seizures: extension of the mutational spectrum. Neurology, 67:687-90, 2006.

13. Macdonald RL, Kang J, Gallagher MJ, Feng H-J: GABAA receptor mutations epilepsy associated with generalized epilepsies. Adv Pharmacol, 54:147-169, 2006.

14. Lagrange AH, Botzolakis EJ,, Macdonald RL: Enhanced macroscopic desensitization shapes the response of alpha4 subtype-containing GABAA receptors to synaptic and extrasynaptic GABA. J Physiol, 578.3:655-676, 2007.


     
 
     

Faculty>
Robert L. Macdonald, M.D., Ph.D., Professor and Chairman of Neurology

BIOGRAPHICAL SKETCH

Robert L. Macdonald is professor and chair of Neurology, as well as professor of Pharmacology and Professor of Molecular Physiology & Biophysics.

Dr. Macdonald earned an S.B. degree in Electrical Engineering in 1966 from the Massachusetts Institute of Technology. He attended two years of medical school at Case Western Reserve University, and then transferred to the University of Virginia, where he earned a Ph.D. in Neurophysiology in 1969. Dr. Macdonald stayed at the University of Virginia for an NIMH-supported postdoctoral fellowship in Physiology (1969-70), and in 1970 he joined the faculty as assistant professor of Physiology. Two years later, he enrolled in medical school there and earned his M.D. in 1973. He stayed at UVa for an internship in Medicine and a residency in Neurology, following which he also served as research assistant professor of Neurology and as a research associate in the Laboratory of Developmental Neurobiology at the NICHHD.

In 1978, Dr. Macdonald joined the faculty at the University of Michigan as an associate professor of Neurology. He was made professor of Neurology in 1981, professor of Physiology in 1982, and in 1995 was named the Russell N. DeJong Professor of Neurology. He stayed at Michigan until 2001, when he moved to Vanderbilt to assume chairmanship of Vanderbilt’s department of Neurology. He has been professor of Neurology, Pharmacology, and Molecular Physiology & Biophysics since that time.

Dr. Macdonald has been the recipient of numerous awards and honors, including the Cotzias Award and Lecture of the American Academy of Neurology in 1996, the Milken Basic Neurosciences Award Epilepsy of the American Epilepsy Society in 1997, the Foundation of Michigan Lifetime Achievement Award in 2000 and the Clinical Teaching Award in Neurology at Vanderbilt in 2002.

An accomplished lecturer, Dr. Macdonald is a frequently invited speaker at universities and meetings around the country and around the world. He has served on a variety of review boards and committees, has participated in a number of study sections, and has served as a consultant in establishing epilepsy programs at Duke University and the Mayo Clinic.

Dr. Macdonald is licensed to practice medicine in Tennessee, and has been a member of the American Board of Psychiatry and Neurology since 1979.




Printer friendly format

 

 

 

 

 

      
   
   
Vanderbilt University is committed to principles of equal opportunity and affirmative action.