The lab is interested in determining the neural basis of normal motivated behaviors including feeding and drinking as well as maladaptive behaviors such as drug-taking and the over-consumption associated with obesity. The nucleus accumbens and the neurotransmitter dopamine are critical brain substrates involved in motivated behavior including feeding and drug-taking. Since the nucleus accumbens accesses motor-related structures, it is well suited to modulate behavior based on changes in motivational state and learned associations. Our research seeks to determine how signaling in the nucleus accumbens is altered in response to changes in motivated state and learned associations. To accomplish this, we employ two state-of-the-art recording techniques combined with detailed behavioral analyses. Electrophysiological recordings of many single neurons and electrochemical (fast-scan cyclic voltammetry) recordings of dopamine release in the nucleus accumbens are made in real-time during behavior. These two recording techniques are performed while rats taste rewarding and aversive stimuli or are working to obtain food or drug rewards. Learned associations are manipulated by pairing a rewarding taste with illness thereby rendering it aversive in the future. Motivational state is altered by food or water restriction or by the delivery of hormones or neuropeptides to mimic need-states or satiety. Finally, we are interested in whether the propensity to take drugs, such as cocaine, can be altered through the delivery of hormones or neuropeptides that affect food intake. This program of research will shed considerable light on human disorders of motivation such as obesity and drug-addiction.
Encoding of reward and aversion
We use the intra-oral delivery of taste solutions to explore how phasic dopamine release and phasic changes in the firing rate of nucleus accumbens neurons ecode both rewarding and aversive stimuli. Intra-oral delivery puts stimulus control in the hands of the experimenter and thus neural responses to reward and aversion transduced via the same sensory modality can be directly compared.
Motivational state tunes mesolimbic circuitry
States of need and satiety modulate our motivated behavior. How these states modulate motivationally-relevant circuitry is another major focus of the lab. We manipulate the physiological state of our subjects or deliver peptides/hormones that are increased under specific physiological conditions (e.g. hunger, satiety) while rats engage in feeding or drug seeking while measuring phasic mesolimbic activity.
Revisiting mechanisms of drug action
Psychostimulants are thought to increase dopamine concentration in the nucleus accumbens primarily through action at dopamine terminals (e.g. reuptake blockade, vesicular depletion/reverse transport). As drugs of abuse increase the frequency of phasic dopamine release events, we are interested in effects of drugs of abuse on dopamine cell excitability. Most recently in our lab, this is approached through the use of transgenic rats and opto- and chemogenetics.