Dr. Hitoshi Morikawa
Office: PAT 402
Lab: PAT 415
phone: (512) 232-9299
lab: 232-9485
fax: 232-2525
email:
Hitoshi Morikawa earned his M.D. at Kyoto University in Japan in 1990. After completing his clinical training as an anesthesiologist at Kyoto University Hospital and Ohtsu Municipal Hospital in Japan, Dr. Morikawa started his graduate work in 1994 and received his Ph.D. in Medical Science (Anesthesiology) from Kyoto University in 1999. He was appointed as an Instructor in the Department of Anesthesiology at Kyoto University in 1997, and then moved to Vollum Institute at Oregon Health & Science University as a research fellow in 1999. Dr. Morikawa joined the faculty at the University of Texas at Austin in 2002.
Research Interests
People start to take addictive drugs to experience elevation or alteration in mood (‘highs’). However, after repeated use of drugs, the drug-seeking and drug-taking behaviors get out of control and become compulsive, which is the defining feature of drug addiction. My lab studies the brain circuits involved in the acute actions of drugs and the plastic changes in the circuits that are responsible for the development of addiction.
This lab specifically focuses on the dopaminergic neurons in the ventral midbrain. They are activated by the perception and expectation of rewards. Therefore, the dopaminergic projections from the midbrain to the limbic structures constitute an endogenous reward circuit. Behaviors that lead to the enhancement of dopamine release in this brain reward circuit tend to be repeated (reinforced). Addictive drugs induce stronger stimulation of dopaminergic transmission than almost any natural reinforcers (food, sex, etc). Thus, drugs are repeatedly used (abused) in vulnerable individuals, which will lead to plastic changes in the reward circuit.
The amount and temporal profile of dopamine release is controlled by the firing pattern of dopamine neurons, which is determined by the interaction of their intrinsic membrane properties and the afferent inputs they receive from other neurons. Accordingly, we make detailed analyses of the influence of addictive drugs on membrane ionic conductances and neurotransmitter inputs of dopamine neurons, and investigate the resulting alteration in the firing pattern. We use brain slices because they retain intact synaptic connections that are necessary for these studies. Brain slices are obtained from drug-naïve animals and animals that are chronically treated with drugs to elucidate the plastic changes induced by repeated exposure to drugs in vivo. Technically, we perform patch clamp electrophysiological recordings combined with confocal fluorescent imaging of intracellular ions. These methods will allow us to delineate the cellular events that determine the excitability of neurons with a preciseness that could not be attained by other conventional techniques. Therefore, this lab offers an ideal system to link the behavior of a certain type of central neurons to that of a whole organism.