Expression of the orexinergic system in ischemic cerebral injury and the modulation of the cerebellar fastigial nucleus through electrical stimulation

Abstract

Objective To investigate changes in the expression of prepro-orexin and orexin receptor-1 ( OX1R) following permanent middle cerebral artery occlusion ( MCAO ) with or without preconditioning through electrical stimulation of the cerebellar fastigial nucleus (FNS). Methods Wistar rats were subjected to permanent MCAO and randomly divided into 5 groups: a sham-operated control group (PO), an FNS preconditioning + shamoperated control group (FNS-PO) , an ischemia group, an FNS preconditioning + ischemia group (FNS-PI) and a cerebellar fastigial nucleus injury + FNS preconditioning + ischemia group (FNL-FNS-PI). Each group was divided into 5 subgroups according to the time at which the animals were sacrificed after the MCAO ( 1, 3, 6, 12 and 24 h).RT-PCR was used to detect expression of OX1R mRNA, and ELISA to measure the levels of orexin-A in the hypothalamus and plasma. Results The immunoreactivity of prepro-orexin decreased significantly in the PI groups, with further decreases over time. At the 12th h after MCAO, the immunoreactivity of prepro-orexin reached a minimum.There were significant differences between the rats in the PO and FNS-PO groups. On the contrary, the immunoreactivity of OX1R increased significantly in the PI groups, with further increases continuing over time, peaking at 12 h after the MCAO. There were significant differences between the PO and FNS-PO groups. In the rats with FNS preconditioning (PI-FNS) , the decrease in prepro-orexin and the increase in OX1R were significantly inhibited compared to the PI subgroups at the 6th and 12th hour. There was no significant difference between the FNL-PIFNS group and the PI group. The expression of OX1R mRNA increased significantly in the PI group, with further increases continuing over time, peaking at 24 hours. The plasma levels of orexin-A were not significantly different among the groups, but the levels of orexin-A in the hypothalamus decreased significantly in the PI and FNL-PI-FNS groups, with further decreases continuing over time. At the 12th h after the MCAO the levels were significantly different compared with the PO and PO-FNS groups. While in the rats with FNS preconditioning (PI-FNS) , the decrease in orexin-A level was reversed and there was no significant difference compared with PO and PO-FNS groups. Conclusions The orexinergic system is altered following cerebral ischaemia. FNS preconditioning may be able to regulate these changes. Key words: Orexin; Orexin receptor-1; Ischemia; Cerebellum; Fastigial nucleus; Electrical stimulation