Hypothalamic contribution to sleep-wake cycle development.
Infant mammals cycle rapidly between sleep and wakefulness and only gradually does a more consolidated sleep pattern develop. The neural substrates responsible for this consolidation are unknown. To establish a reliable measure of sleep-wake cyclicity in infant rats, nuchal muscle tone was measured in 2-, 5-, and 8-day-old rats, as were motor behaviors associated with sleep (i.e. myoclonic twitching) and wakefulness (e.g. kicking, stretching). Sleep-wake cycles of 2-day-old rats were characterized by short periods of muscle atonia followed by equally short periods of high tone. In 8-day-olds, sleep periods lengthened significantly and disproportionately in relation to awake periods. Next, locus coeruleus (LC) lesions in 8-day-olds resulted in rapid sleep-wake cycling similar to that exhibited by 2-day-olds; in addition, LC lesions had no effect on the duration of awake periods. Finally, transections caudal, but not rostral, to the anterior hypothalamus also reinstated rapid cycling in 8-day-olds, again without affecting the duration of awake periods. This last finding implicates neural structures within the anterior hypothalamus (e.g. ventrolateral preoptic area) in the modulation of sleep-wake cyclicity. The temporal coherence of atonia and myoclonic twitching was not disrupted by any of the manipulations. These results suggest the presence of a bistable mesopontine circuit governing rapid sleep-wake cycling that does not include the LC and that comes increasingly under hypothalamic control during the first postnatal week. This circuit may represent a basic building block with which other sleep components become integrated during ontogeny.
Karlsson
K A
KA
Program in Behavioral and Cognitive Neuroscience, Department of Psychology, E11 Seashore Hall, University of Iowa, Iowa City, IA 52242, USA.
Kreider
J C
JC
Blumberg
M S
MS
D000204:Activity Cycles / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D004576:Electromyography; D005260:Female; D007031:Hypothalamus / Q000502:physiology*; D008297:Male; D009129:Muscle Tonus / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012890:Sleep / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology*