Assessment of Sleep, K-Complexes, and Sleep Spindles in a T21 Light-Dark Cycle

Abstract

Circadian rhythm misalignment has a deleterious impact on the brain and the body. In rats, exposure to a 21-hour day length impairs hippocampal dependent memory. Sleep, and particularly K-complexes and sleep spindles in the cortex, have been hypothesized to be involved in memory consolidation. Altered K-complexes, sleep spindles, or interaction between the cortex and hippocampus could be a mechanism for the memory consolidation failure but has yet to be assessed in any circadian misalignment paradigm. In the current study, continuous local field potential recordings from five rats were used to assess the changes in aspects of behavior and sleep, including wheel running activity, quiet wakefulness, motionless sleep, slow wave sleep, REM sleep, K-complexes and sleep spindles, in rats exposed to six consecutive days of a T21 light-dark cycle (L9:D12). Except for a temporal redistribution of sleep and activity during the T21, there were no changes in period, or total amount for any aspect of sleep or activity. These data suggest that the memory impairment elicited from 6 days of T21 exposure is likely not due to changes in sleep architecture. It remains possible that hippocampal plasticity is affected by experiencing light when subjective circadian phase is calling for dark. However, if there is a reduction in hippocampal plasticity, changes in sleep appear not to be driving this effect.

Impaired Morris water task retention following T21 light dark cycle exposure is not due to reduced hippocampal c-FOS expression

“…In terms of activity rhythms, a lack of a change in period during T21 exposure suggests that the rats were not able to entrain and instead freeran. Freerunning in a short T-cycle has been documented in rodents before (Stephan, 1983;Campuzano, 1998;Cambras et al, 2004Cambras et al, , 2007Vivanco et al, 2010;Casiraghi et al, 2012;Deibel et al, 2020). A delayed phase in the last 6-day block of assessment may indicate that the rats were still not quite entrained to the phase of the finishing light dark cycle.…”

“…During this type of schedule animals are eating, sleeping, and are active at the same circadian time, but a different zeitgeber time each day. Thus, there is a phase mismatch between the rat’s circadian system and that of the T21 ( Deibel et al, 2020 ).…”

“…Yet we do not know exactly how hippocampal clock genes are modulated. We have ruled out some possibilities such as an increased stress response ( Deibel et al, 2014 ) and sleep disruption ( Deibel et al, 2020 ). Circadian rhythm disruption induced changes in neuromodulators such as corticosterone, melatonin, dopamine, gamma-aminobutyric have been discussed as likely candidates ( Ruby et al, 2008 ; Cain et al, 2017 ; Iggena, 2017 ).…”

Roles of Neuropeptide S in Anesthesia, Analgesia, and Sleep

“…Conversely, NREM sleep is characterized by high-amplitude, low-frequency EEG pattern (synchronous EEG), low skeletal muscle tone, and minimum psychological activity. The synchronous EEG includes sleep spindles, slow-wave, and k-complexes [ 57 ]. In humans, NREM sleep is divided into four subgroups (stage 1, 2, 3, and 4) based on the EEG pattern [ 58 ].…”