ABSTRACT
Corticosteroids (CORT) have been widely used in anti-inflammatory medication. Chronic CORT treatment can cause mesocorticolimbic system dysfunctions, which are known to play a key role for the development of psychiatric disorders. The VTA is a critical site in the mesocorticolimbic pathway and is responsible for motivation and reward-seeking behaviors. However, the mechanism by which chronic CORT alters VTA dopamine neuronal activity is largely unknown. We treated periadolescent male mice with vehicle, 1 d, or 7 d CORT in the drinking water, examined behavioral impacts with light/dark box, elevated plus maze, operant chamber, and open field tests, measured the effects of CORT on VTA dopamine neuronal activity using patch-clamp electrophysiology and dopamine concentration using fast-scan cyclic voltammetry, and tested the effects of dopamine D2 receptor (D2R) blockade by intra-VTA infusion of a D2R antagonist. CORT treatment induced anxiety-like behavior as well as decreased food-seeking behaviors. We show that chronic CORT treatment decreased excitability and excitatory synaptic transmission onto VTA dopamine neurons. Furthermore, chronic CORT increased somatodendritic dopamine concentration. The D2R antagonist sulpiride restored decreased excitatory transmission and excitability of VTA dopamine neurons. Furthermore, sulpiride decreased anxiety-like behavior and rescued food-seeking behavior in mice with chronic CORT exposure. Together, 7 d CORT treatment induces anxiety-like behavior and impairs food-seeking in a mildly aversive environment. D2R signaling in the VTA might be a potential target to ameliorate chronic CORT-induced anxiety and reward-seeking deficits.SIGNIFICANCE STATEMENT With widespread anti-inflammatory effects throughout the body, corticosteroids (CORT) have been used in a variety of therapeutic conditions. However, long-term CORT treatment causes cognitive impairments and neuropsychiatric disorders. The impact of chronic CORT on the mesolimbic system has not been elucidated. Here, we demonstrate that 7 d CORT treatment increases anxiety-like behavior and attenuates food-seeking behavior in a mildly aversive environment. By elevating local dopamine concentration in the VTA, a region important for driving motivated behavior, CORT treatment suppresses excitability and synaptic transmission onto VTA dopamine neurons. Intriguingly, blockade of D2 receptor signaling in the VTA restores neuronal excitability and food-seeking and alleviates anxiety-like behaviors. Our findings provide a potential therapeutic target for CORT-induced reward deficits.
