Despite the increased prevalence of major depressive disorder (MDD) and the continued investment into identifying effective cures, most treatments merely alleviate symptoms rather than addressing causes. Long-term treatments are generally required for this disease and often include many side-effects. The onset of depression is often precipitated by stressful and/or aversive stimuli. Animals, too, are susceptible to the effects of stress. For example, repeated social defeat stress in rodents induces pervasive and long-lasting behavioral changes similar to the symptoms seen in patients with MDD including impaired social interaction, lack of motivation, helplessness and anhedonia. While the behavioral changes associated with depression have been well-studied, there is relatively little knowledge about the accompanying changes in the neural circuitry. Thus, we will anatomically and functionally dissect the distinct neural circuits mediating various stress-induced behaviors in mice to better understand the mechanistic changes in the brain accompanying MDD in human patients, which will help to devise revolutionary circuit-specific and stage-specific diagnosis and treatments. To accomplish this, we will examine the neural circuit mechanism of ventral pallidum (VP), one of the major components of reward circuitry, underlying depressive behaviors elicited by repeated social defeat stress in combination with a variety techniques to address circuit-level mechanisms, including optogenetics, viral mediated tracing, electrophysiology, and real time in vivo fiber photometry. Our preliminary findings showed that different types of neurons in VP project to different target structures which may be involved in different aspects of depressive behaviors. First, we will define the projection specific roles of VP circuity in depressive behaviors induced by repeated social defeat stress using optogenetics and viral tracing methods. Second, using in vivo fiber photometry and newly developed viral tools, we will directly monitor the dynamics of neural activity of VP circuitry in cell-type and projection specific manner in vivo in real time during social interaction before and after the repeated social defeat stress, and their response to anti-depressant treatment. Third, using ex vivo electrophysiology analysis we will examine the circuit-specific electrophysiological and synaptic changes induced by the stress. The accomplishment of the proposed works will be greatly beneficial to both the research and treatment of MDD, and will also provide a fundamental framework for studying mental disorders in circuit-specific manner.

Public Health Relevance

Nearly 5% of adults in the United States are affected by depressive disorder, a neuropsychiatric affliction that comprises a diverse set of symptoms such as the inability to feel pleasure, lack of motivation, changes in appetite and cognitive difficultis. The goal of this application is to take advantage of recent technological advances to dissect and identify specific neural circuitry and neural adaptions that underlie depression, with the ultimate goal of contributing to the treatment of this devastating disorder.

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Research Project (R01)
Project #
5R01MH107742-03
Application #
9260946
Study Section
Special Emphasis Panel (ZMH1)
Program Officer
Simmons, Janine M
Project Start
2015-07-10
Project End
2020-04-30
Budget Start
2017-05-01
Budget End
2018-04-30
Support Year
3
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of California, San Diego
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
804355790
City
La Jolla
State
CA
Country
United States
Zip Code
92093
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Knowland, Daniel; Lim, Byung Kook (2018) Circuit-based frameworks of depressive behaviors: The role of reward circuitry and beyond. Pharmacol Biochem Behav 174:42-52
Knowland, Daniel; Lilascharoen, Varoth; Pacia, Christopher Pham et al. (2017) Distinct Ventral Pallidal Neural Populations Mediate Separate Symptoms of Depression. Cell 170:284-297.e18