Use of siRNA in knocking down of dopamine receptors, a possible therapeutic option in neuropsychiatric disorders.

Heightened dopaminergic activity has been shown to be implicated in some major neuropsychiatric disorders such as schizophrenia. Use of dopaminergic antagonists was limited by some serious side effects related to unspecific blocking of dopamine receptors. Thus a target specific dopamine receptor gene silencing method such as using small interfering RNA (siRNA) might be useful. In this study recombinant plasmids expressing siRNA against dopamine receptors (D1-D5DRs) were produced, and their efficiency in knocking down of receptors in were assessed in rat neuroblastoma cell line (B65), using Real-time PCR method. Furthermore, D2DR siRNA expressing plasmid was injected into the rat nucleus accumbens bilaterally to investigate whether it can prevent the hyperactivity induced by apomorphine. Locomotion was measured in 10 min intervals, 50 min before and 60 min after apomorphine injection (0.5 mg/kg, S.C). Our results indicated that the mRNA level of dopamine receptors were reduced between 25 and 75% in B65 cells treated with the plasmids in vitro. In behavioral tests, locomotion was lower at least in the second 10 min after apomorphine injection in rats treated with plasmid expressing D2DR siRNA compare to control group [F (4,24) = 2.77, (P < 0.05)]. The spontaneous activity of treated rats was normal. In conclusion, dopamine receptors can be downregulated by use of siRNA expressing plasmids in nucleus accumbens. Although our work may have some possible clinical applications; the potentially therapeutic application of siRNA in knocking down of dopamine receptors needs further studies.