Seizures induce phase shifts of rat circadian rhythms.
BACKGROUND
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 likewise induce phase shifts.


METHODS
We monitored the circadian rhythm of temperature (CRT) with intraperitoneal radiotelemetry in rats (n=21) isolated 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 cycle).


RESULTS
Phase shifts (individual responses=57) differed across the circadian cycle. Rather than forming a clear phase-response curve, phase shifts were especially variable between 00:00 and 06:00 h.


CONCLUSIONS
This study demonstrates that electrically-induced seizures induce advances and delays in CRT in a phase-dependent fashion but in a pattern different from typical light-induced phase shifts. Disorders of circadian regulation may contribute to some of the altered endogenous cycles associated with epilepsy.
Quigg
M
M
Comprehensive Epilepsy Program, Department of Neurology, University of Virginia, Box 394, Health Sciences Center, Charlottesville, VA 22908, USA. quigg@virginia.edu
Straume
M
M
Smith
T
T
Menaker
M
M
Bertram
E H
EH
D000818:Animals; D001833:Body Temperature Regulation / Q000502:physiology*; D001921:Brain / Q000473:pathology / Q000503:physiopathology*; D021081:Chronobiology Disorders / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D002940:Circadian Rhythm / Q000502:physiology*; D004558:Electric Stimulation / Q000009:adverse effects; D004827:Epilepsy / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D007696:Kindling, Neurologic / Q000502:physiology*; D008297:Male; D010775:Photic Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley