Dopamine D2L Receptor Deficiency Causes Stress Vulnerability through 5-HT1A Receptor Dysfunction in Serotonergic Neurons

Mental disorders are caused by genetic and environmental factors. We here show that deficiency of an isoform of dopamine D2 receptor (D2R), D2LR, causes psychosocial stress vulnerability in mouse. This occurs through dysfunction of type 1A serotonin (5-hydroxytryptamine, 5-HT) receptor (5-HT1AR) on serotonergic neurons in the mouse brain. Exposure to forced swim stress significantly increased anxiety- and depressive-like behaviors in D2LR knockout (D2LR-KO) male mice as compared with wild-type mice. Treatment with 8-OH-DPAT, a 5-HT1AR agonist, failed to alleviate the stress-induced behaviors in D2LR-KO mice. In forced swim-stressed D2LR-KO mice, 5-HT release in the medial prefrontal cortex was elevated and the expression of genes related to 5-HT levels was up-regulated by the transcription factor PET1 in the dorsal raphe nucleus. Notably, D2LR formed a heteromer with 5-HT1AR in serotonergic neurons, thereby suppressing 5-HT1AR–activated G-protein–activated inwardly rectifying potassium (GIRK) conductance in D2LR-KO serotonergic neurons. Finally, D2LR overexpression in serotonergic neurons in the dorsal raphe nucleus alleviated stress vulnerability observed in D2LR-KO mice. Taken together, we conclude that disruption of the negative feedback regulation by the D2LR/5-HT1A heteromer causes stress vulnerability. To identify differentially expressed genes following forced swim stress (FS), we compared three FS-stressed mouse groups (WT, D2R-KO, and D2LR-KO) with non-stressed control WT group. The mice were submitted to 6-min FS stress on four consecutive days, and the dorsal raphe nucleus (DRN) was dissected 12 h after the last FS stress exposure and gene expression analyzed. n = 5 mice per group per pool.