Opioid signal transduction regulates the dendritic morphology of somatostatin and parvalbumin interneurons in the medial prefrontal cortex.

The endogenous opioid system is of great importance to normal brain functions. Opiate acts on GABAergic cells in both the ventral tegmental area and the nucleus accumbens to exert psychological effects. However, the effects of opioid signal transduction on the morphology of GABAergic interneurons (INs) of the medial prefrontal cortex (mPFC), a brain region critical for motivational and addictive behaviors, are unclear. By fluorescent dye injection and morphological reconstruction, we found that the total dendrite length and dendritic complexity of both parvalbumin (PV) INs and somatostatin (SST) INs in mPFC were significantly increased after chronic morphine administration, and such changes lasted 7 days after morphine abstinence. We then downregulated the endogenous μ-opioid and δ-opioid receptors (ORs) in the mPFC by adeno-associated virus-mediated shRNA expression. Results showed that downregulating either μ-OR or δ-OR decreased the total dendrite length and dendritic complexity of SST-INs, whereas downregulating neither μ-OR nor δ-OR affected the morphology of PV-INs. Furthermore, δ-OR but not μ-OR knockdown impaired the dendritic structure of SST-INs in the mice upon single morphine administration. Our findings indicate the differential roles of endogenous ORs in the dendritic remodeling of SST-INs and PV-INs in mPFC.