Dopamine’ functions in the central nervous system are of great interest, since they regulate many neuronal activities such as synaptic plasticity and novelty acquisition, locomotion and addiction, and are involved in the pathogenesis of various neurological and psychiatric disorders. The major dopamine (DA) source in the midbrain is the ventral tegmental area (VTA) and substantia nigra (SN). We injected an AAV virus encoding FLEXed channelrhodopsin-2 (ChR2) and a fluorescent protein into the midbrain of DA active transporter (DAT)-Cre mice and obtained fluorescently labeled DA projections in acute brain slices. Consistent with previous observations, the distribution and density of endogenous DA-containing fibers varied between different forebrain regions, being high in striatum and low in hippocampus. In the striatum, endogenous DA has been detected by fast scan cyclic voltammetry (FSCV) in vitro and in vivo. By contrast, equivalent results are lacking in the hippocampus. To exclusively examine the dopamine signal, we combined FSCV with optogenetics in acute slices. Under these conditions we could measure dopamine in the olfactory tubercle (OT), which is part of the ventral striatum. We are currently optimizing the hippocampal DA signal considering frequency of photostimulation and developmental factors to corroborate pharmacological results (effects of DA agonists) by endogenous DA.