Individual Differences in Rhythms of Behavioral Sleep and Its Neural Substrates in Nile Grass Rats

Abstract

Laboratory populations of grass rats (Arvicanthis niloticus) housed with a running wheel show considerable variation in patterns of locomotor activity. At the extremes are "day-active" (DA) animals with a monophasic distribution of running throughout the light phase and "night-active" (NA) animals exhibiting a biphasic pattern with an extended peak at the beginning of the dark phase and a brief peak shortly before lights-on. Here, the authors use this intraspecific variation to explore interactions between circadian and homeostatic influences on sleep and the effects of these interactions on the activity of brain regions involved in sleep regulation. Male animals were singly housed with running wheels in a 12:12 LD cycle, videotaped for 24 h, and perfused at ZT 4 or 16. Behavioral sleep was scored from the videotapes, and brains were processed for cFos immunoreactivity (cFos-ir). Sleep duration within the light and dark phases was higher in NA and DA animals, respectively, but these groups did not differ with respect to total sleep. In both groups, sleep bouts were shortest in the light phase and longest between ZT 20 and ZT 23. In the ventrolateral preoptic area (VLPO), cFos-ir was higher at ZT 16 than at ZT 4 in DA but not NA grass rats, and it was correlated with behavioral sleep at ZT 16 but not ZT 4. In OXA neurons, cFos-ir was high at ZT 4 in DA grass rats and at ZT 16 in NA grass rats, and it was correlated with behavioral sleep at both times. In the lower subparaventricular zone (LSPV), cFos-ir was higher at ZT 16 in both DA and NA animals, and it was unrelated to behavioral sleep. Thus, patterns of cFos-ir in the LSPV and OXA neurons were most tightly linked to time and sleep, respectively, whereas cFos-ir in the VLPO was influenced by an interaction between these 2 variables.

Dysfunctions in circadian behavior and physiology in mouse models of Huntington's disease

“…We scored a mouse as being asleep only when its eyes were closed as it lay on its side, or if it was curled up with its head tucked into its body, or if the mouse did not make any movements other than brief transitional changes in posture for durations of at least 40 sec. We and others have previously employed this method to determine the basic temporal distribution of behavioral sleep across a 24-h period (Loh, et al, 2010, Pack, et al, 2007, Schwartz and Smale, 2005). Sleep/wake behavior was scored visually in 5 min intervals, which were summed and averaged to determine day and night percentages of time spent in sleep.…”

Functional Analysis of Circadian Pacemaker Neurons inDrosophila melanogaster

“…Clearly, a multitude of phase relationships between the molecular rhythm and behavior are possible. Brain regions outside the pacemaker center may be responsible for these different phases as was shown recently for mammals (Nixon and Smale, 2004;Schwartz et al, 2004;Saper et al, 2005;Schwartz and Smale, 2005). It appears that the same is true within the circadian system of the fly.…”

Circadian organization of the diurnal Caviomorph rodent,Octodon degus

“…This appears to be the case for the degu, which, despite clear field behavior and physiological adaptations for a classification as a ''diurnal'' species, can show diurnal, crepuscular, or nocturnal activity patterns depending on laboratory conditions (Kas & Edgar 1999). This laboratory-induced deviation from rigid day-activity presents two excellent opportunities for researchers: (1) it may represent an exaggeration of the unimodal and bimodal activity patterns observed in the wild during different seasons (Fulk 1976), and thus could facilitate the study of seasonal activity changes, and (2) it may allow for within-species examination of the neural and behavioral correlates of circadian activity phase preference (e.g., Arvicanthus niloticus, Smale et al 2001;Nixon & Smale 2004;Schwartz & Smale 2005). It must be cautioned, however, that the neural underpinnings for this artificial variation in phase preference may not be the same as those that produce the difference in phase preference between diurnal and nocturnal species.…”