Our research focuses on understanding the biological bases of addiction. We use a combination of models that are associated with increased addiction liability, such as that associated with age (i.e. adolescence), naturally-occurring within outbred populations (i.e. inter-individual differences), or induced by exposure to drugs and to stress. Throughout our studies, we use a systems-approach, combining complementary levels of analysis, which include molecular (protein expression), cellular (neuronal activity and synaptic transmission using in vivo and ex vivo electrophysiology), anatomical (optogenetics and functional neuroanatomy), and behavioral studies (self-administration). By combining these levels of analysis, it is possible to answer questions of behavioral relevance at multiple levels, in the hope of gaining more insight on the mechanisms and treatment strategies for addiction.