Relation between orexin A and epileptic seizures

One of the unknown mechanisms in epilepsy pathogenesis is the involvement of the hypothalamic neuropeptide orexin. Although the relationship between orexin and sleep has been revealed, its effect in epilepsy has not been fully clarified. In this study, we aimed to show the relationship between orexin A and the seizures that occur during sleep and wakefulness.

This study included 40 patients with drug-resistant focal epilepsy and 37 healthy controls. Night basal orexin (NBO) and morning basal orexin (MBO) levels were measured using enzyme-linked immunosorbent assay in patients and controls. Serum samples were collected from patients after epileptic seizures during sleep and wakefulness.

In both patients and controls, MBO levels (median: 1039 pg/mL, interquartile ranges [IQR] (899-1078)) were higher than NBO levels (median 989 pq/mL, IQR (893-1078) (p = 0.02). Basal orexin levels were lower in patients than in controls (p < 0.001). However, while the duration of seizures was shortened in awake seizures, the level of orexin increased (p = 0.007). Additionally, orexin levels after nocturnal seizure were higher in patients who had an ictal electroencephalography onset in the left hemisphere or a lesion in the left temporal lobe (p = 0.02; p = 0.01, respectively). There was no relationship between postictal somnolence and orexin levels. Although there was no significant difference, the level of post-seizure orexin increased compared to the basal values, especially in seizures during sleep.

The increase in serum orexin levels, especially after seizures, suggests that orexin may be associated with the epileptogenic effect. In further studies, determination of orexin from cerebrospinal fluid (CSF) and correlation of CSF and serum orexin levels may provide more useful information regarding the relationship between orexin and epilepsy.