The central mechanism of risperidone-induced hyperprolactinemia

- The level of NPY mRNA increased in the Arc after administration of risperidone.
- TH co-expressed with NPY-Y1 receptor in the PVN.
- Risperidone inhibited dopamine synthesis in the PVN due to decrease of TH.
- Reduced dopamine may cause overexpression of prolactin in the pituitary gland.

Risperidone is known to increase prolactin secretion in treating mental illness patients. This side-effect is thought to be mediated via central signaling pathway. However, the exact pathway involved between risperidone and hyperprolactinemia are still unknown. Therefore, we have treated mice with risperidone and investigated the central mechanisms. The present study showed that in risperidone treated group, the level of the serum prolactin significantly increased, which was consistent with increased positive prolactin staining in pituitary gland. Elevated c-fos expression was observed in the arcuate hypothalamic nucleus (Arc) where we found 65% c-fos positive neurons co-localised with neuropeptide Y (NPY) in mice treated with risperidone. In addition, the results from in situ hybridization showed that the NPY mRNA in the Arc was significantly increased, whereas the tyrosine hydroxylase (TH) mRNA dramatically decreased compared with control group in the paraventricular hypothalamic nucleus (PVN). These findings revealed that risperidone may mediate the transcriptional regulation of Arc NPY and TH in the PVN. Furthermore, risperidone induced a decreased dopamine synthesis in the PVN and thus reduced the dopamine-induced inhibition of prolactin release, ultimately lead to hyperprolactinemia. Therefore, insights into these neuronal mechanisms open up potential new ways to treat schizophrenia patients in order to ameliorate hyperprolactinemia.