Sleep changes during chronic cold exposure showed that the homeostatic requirement of sleep is reduced in the medial preoptic area lesioned rats.
The effects of chronic exposure to a mildly cold ambient temperature (T(a)) of 18 degrees C on sleep wakefulness (S-W) and brain temperature (T(br)) were studied in the medial preoptic area (mPOA) lesioned male Wistar rats. Electroencephalogram (EEG), electrooculogram (EOG) and electromyogram (EMG) electrodes were chronically implanted to assess S-W, and a thermocouple above the dura to record the T(br). After three recordings (24 h each) of S-W and T(br) at 24 degrees C, N-methyl D-aspartic acid (NMDA) was intracerebrally injected to produce bilateral destruction of neurons in the mPOA. There was decreased sleep and increased T(br) even four weeks after the mPOA lesion. T(a) of the environmental chamber was then reduced to 18 degrees C, and the S-W and T(br) were again recorded for 24 h each on the 1st, 7th, 14th, 21st, and on 28th days of continuous exposure to the mild cold T(a). Exposure to the cold produced further decrease in sleep and increase in the T(br). However, sleep came back to the pre-exposure level by the 14th day. An increase in the duration of sleep episodes was responsible for the restoration of sleep during chronic cold exposure. The study showed that the requirement of sleep was reset at a lower level in the mPOA lesioned rats. The mPOA lesion affected the sleep maintenance and sleep initiation, though the latter became evident only during chronic cold exposure. The magnitude of the acute changes in T(br) and S-W were less in the lesioned rats, as compared to those observed in the normal rats exposed to similar cold T(a). On the basis of these observations, it could be proposed that the mPOA plays some role in cold induced changes in thermoregulation and sleep regulation. The T(br) remained elevated throughout the period of cold exposure. Resetting of the T(br), at a higher level may be part of the homeostatic readjustment to restore sleep.
Prasad
Ambika
A
Department of Physiology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi--110 029.
Mahapatra
K
K
Mallick
Hruda Nanda
HN
Kumar
Velayudhan Mohan
VM
D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D003080:Cold Temperature; D004569:Electroencephalography; D004576:Electromyography; D004585:Electrooculography; D018690:Excitatory Amino Acid Agonists / Q000008:administration & dosage / Q000494:pharmacology; D006706:Homeostasis / Q000502:physiology*; D008297:Male; D016202:N-Methylaspartate / Q000008:administration & dosage / Q000494:pharmacology; D017286:Polysomnography / Q000187:drug effects; D011301:Preoptic Area / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012890:Sleep / Q000502:physiology*
D018690:Excitatory Amino Acid Agonists; D016202:N-Methylaspartate