Research Overview
Dr. S. John Mihic studies molecular sites of action of drugs of abuse on ligand-gated ion channels.
The rational development of therapies for alcohol and drug abuse requires an understanding, on a molecular level, of how these drugs affect the operation of ion channels in the brain. At present, the molecular targets in the brain responsible for the acute effects of alcohol and inhaled drugs of abuse are not well understood. We also do not understand the molecular mechanisms that underlie drug tolerance and dependence.
Research in the lab is focused on characterizing the molecular mechanisms through which alcohol, inhaled solvents, sedatives and anaesthetics act on ligand-activated ion channels. Our studies focus on the GABAA and glycine receptors, since GABA and glycine are the major inhibitory transmitters in the brain. We also study serotonin3 receptors, since serotonin is a major neuromodulator in the brain. We combine the techniques of chimeragenesis and mutagenesis to produce channels constructed from amino acids whose sequences are slightly altered due to the mutations we introduced. We then evaluate the physiological changes that result from the structural modifications we induced. We do this by injecting the mRNA that codes for the mutated channels into cultured cells or Xenopus oocytes, which then express the mutated channels. The newly expressed channels are studied electrophysiologically to determine which channel properties were changed by the modifications we introduced.
These studies have thus far identified specific amino acids of these receptors responsible for enhancement of the inhibition produced by GABAA and glycine receptors when they bind alcohol or inhaled solvents. Current work in the lab is continuing to characterize alcohol and anaesthetic actions on these receptors and we are also attempting to discover sites of action of these drugs on the serotonin3 receptor. Our long-term goals include the creation of knock-in mice bearing these mutated receptors; these animals will greatly increase our understanding of the relevance of each receptor for the known actions of alcohol, inhalants and sedatives in animals, including ourselves. Other research interests in the lab include the elucidation of the basic mechanisms of ion channel opening and receptor desensitization that occurs after neurotransmitter binding, as well as studies on the molecular mechanisms that regulate the assembly of the subunits from which ion channels are built.
