Seizures induce phase shifts of rat circadian rhythms

Rationale: Epileptic seizures may alter neuroendocrinological cycles. Light pulses induce phase shifts in circadian rhythms. Using hippocampal-kindled rats to ensure maximal clinical expression, we determined if seizures like wise induce phase shifts. Methods: We monitored the circadian rhythm of tem perature (CRT) with intraperitoneal radiotelemetry in rats (n = 21) isolate d from time cues and light for 3-week trials. Seizures were triggered with hippocampal electrical stimulation at different circadian phases. Optimized , least-error phase shifts were calculated from preictal and postictal CRTs . Induced seizures were referenced to CRT (t(max)=00:00, 24-h circadian cyc le). Results: Phase shifts (individual responses=57) differed across the ci rcadian cycle. Rather than forming a clear phase-response curve, phase shif ts were especially variable between 00:00 and 06:00 h. Conclusions: This st udy demonstrates that electrically-induced seizures induce advances and del ays in CRT in a phase-dependent fashion but in a pattern different from typ ical light-induced phase shifts. Disorders of circadian regulation may cont ribute to some of the altered endogenous cycles associated with epilepsy. ( C) 2001 Elsevier Science B.V. All rights reserved.