Subthalamic nucleus optogenetic manipulations: a glimpse at deep brain stimulation mechanisms
Although deep brain stimulation (DBS) is now a widely used therapeutic strategy, its precise mechanism remains largely unclear. Since this approach is progressively extended to treat non-motor disorders such as depression, obsessive-compulsive disorders, the comprehension of its effects on motivated behaviors appears of the upmost importance for a possible application for addiction. In intact rats, we used inhibition and high frequency optogenetic activation of subthalamic nucleus (STN) neurons to test whether or not we could reproduce the effects of electric deep brain stimulation on rats motivation for sweet food and cocaine. Rats motivation was assessed using fixed-ratio 5 and progressive ratio schedules of reinforcement for both rewards and illumination was applied during behavioral testing. Efficiency of optogenetic manipulations has been validated using in-vitro electrophysiological recordings. Optogenetic inhibition of STN increased motivation for food and reduced motivation for cocaine. In contrast, optogenetic high frequency stimulation reduced the motivation for food without impacting motivation for cocaine. Optical inhibition mimics the effect of electric deep brain stimulation on food and cocaine motivation, confirming that the effects observed under electric DBS result from a specific inactivation of the STN. In contrast, optogenetic high frequency stimulation induces opposite effects to those of electric one, suggesting a stimulation of the STN that only seems to affect food motivation.