Relationship of orexin (hypocretin) system and astrocyte activation in Parkinson's disease with hypersomnolence

Abstract

We studied the relationship of orexin (hypocretin) system and astrocyte activation in hypersomnolence symptom (HS) in Parkinson’s disease (PD). In a total of 30 subjects, including five PD patients with HS, eight PD patients without HS, eight patients with narcolepsy, and nine control subjects, orexin and glial fibrillary acidic protein (GFAP) as well as S100B levels in cerebrospinal fluid (CSF), which are markers of astrocyte activation, were measured and compared. In the comparison of orexin levels among the four groups of subjects, only the narcolepsy group showed significantly lower levels. The levels of CSF orexin in the PD patients with HS tended to be lower compared with those in the control group, although the difference was not statistically significant. The majority of reports have indicated that CSF orexin levels are in the normal range in most PD patients, some PD patients with severe HS showed low orexin levels. Compared with those of the control group, GFAP levels were significantly higher in the group of PD with HS and narcolepsy, but not PD without HS. No groups showed a significant difference in S100B levels. In the whole subjects with PD, narcolepsy, and controls, orexin levels were inversely correlated with GFAP. Therefore, increased GFAP may indicate orexin deficiency both in narcolepsy and PD with HS.