Dopamine in the median raphe region
Tiago Chaves1, Bibiána Török1, 2, Csilla Fazekas1, 2, Pedro Correia1, 2, Eszter Sipos1, Dóra Zelena1, 3
According to previous studies the median raphe region (MRR) is known to contribute significantly to social behavior. Apart from serotonin, there are some dopaminergic neurons in this region. Dopamine is connected to the reward system and locomotion, but very little is known about its role in the MRR. This experiment was designed to clarify this question. We used pharmacogenetic technology in mice containing Cre enzyme under the promoter of the dopamine transporter. With the help of adenoassociated virus, artificial receptors (DREADD, stimulatory, inhibitory as well as control mCherry) were injected into the MRR. Few weeks later the animals were injected with the artificial ligand (clozapine-N-oxide) 30 min before the following experiments: locomotion (open field/OF), anxiety (elevated plus maze/EPM), social behavior (sociability; resident-intruder/RI/SI), short-term memory (y-maze), reward seeking (operant conditioning) and prolactin secretion (with and without 15 min restraint). Stimulation of the dopaminergic cells of the MRR induced no difference in locomotion, but anxiolytic-like behaviour on EPM, less aggressive behaviour in RI and better discrimination abilities in sociability; while inhibition of the same cells worsened the memory in y-maze. In operant conditioning stimulated animals showed higher reward seeking reflected by enhanced total responses at the beginning of testing, but the preference for baited hole did not increased with time. Inhibition of the dopaminergic cells of MRR lead to enhanced prolactin release, but the stimulation did not influence the restrain-induced changes.