Steven F. Glotzbach

Changes in the thermal characteristics of hypothalamic neurons during sleep and wakefulness.

The characteristics of the mammalian thermoregulatory system are dependent upon arousal state. During NREM sleep thermoregulatory mechanisms are intact but body temperature is regulated at a lower level than during wakefulness. In REM sleep thermoregulatory effector mechanisms are inhibited and thermal homeostasis is severely disrupted. Thermosensitivity of neurons in the preoptic/anterior hypothalamus (POAH) was determined for behaving kangaroo rats (Dipodomys deserti) during electrophysiologically defined wakefulness, NREM sleep and REM sleep to elucidate possible neural mechanisms for previous findings of state-dependent changes in thermoregulation. Thirty cells were tested during at least two arousal states. During wakefulness, 70% of the recorded cells were sensitive to changes in local temperature, with the number of warm-sensitive (W) cells outnumbering cold-sensitive (C) cells by 1.6:1. In NREM sleep, 43% of the cells were thermally sensitive, with the ratio of W:C remaining the same as in wakefulness. In REM sleep only two cells were thermosensitive (both W). The decrease in neuronal thermosensitivity of POAH cells during REM sleep parallels findings of inhibition of thermoregulatory effector responses during REM, although further work is necessary to determine the source and nature of the inhibition.

Activity of suprachiasmatic and hypothalamic neurons during sleep and wakefulness in the rat

Single unit activity was recorded from the suprachiasmatic nucleus (SCN) and preoptic/anterior hypothalamus (POAH) of unrestrained Wistar rats during sleep and wakefulness. Regularly firing cells, which are abundant in in vitro SCN preparations and have been considered the basis of a central neuronal oscillator, were conspicuously absent in this preparation and in other in vivo studies. Most of the 55 cells recorded in the SCN and POAH were characterized by spontaneous firing rates below 12 Hz and with heterogeneous patterns of changes in frequency with arousal states. In vivo neurophysiological studies of the SCN in which the anesthetic agent urethane is used should consider the effect of different levels of arousal, as indicated by the cortical EEG, in evaluating the relationship between sensory stimulation and single unit activity.

Sleep-Dependent Changes in the Thermoregulatory System

the thermoregulatory system is particularly convenient and interesting for studies of the influence of arousal state on homeostatic processes. State-related changes in thermoregulatory functions are substantial and are a general phenomenon in mammals and birds. The sleep phase of the daily rest/activity cycle is associated with decreases in metabolic rate and body temperature. In addition, the onset of sleep at any time of day tends to result in declines in metabolic rate and body temperature. Sleep is not a unitary phenomenon but consists of specific states definable by electroencephalographic (EEG), electromyographic (EMG), and electrooculographic (EOG) criteria. At a minimum, two sleep states, rapid-eye-movement (REM) and non-REM (NREM) sleep, are distinguished with these electrographic parameters. Changes in thermoregulatory functions in comparison to wakefulness are qualitatively different in these two sleep states. During periods of NREM sleep, adjustments are made in thermoregulatory responses that decrease heat production and/or increase heat loss in comparison to contiguous periods of wakefulness. During REM sleep there is a cessation of ongoing thermoregulatory responses (for reviews, see refs. 11 and 13).

Periodic breathing cycle duration in preterm infants.

ABSTRACT: Periodic breathing cycle duration (PCD), the time interval from the beginning of one respiratory pause to the beginning of the next pause within an episode of periodic breathing (PB), was measured by examination of 24-h impedance pneumograms in 51 preterm infants. Calculations of the SD of PCD within a given PB episode (~3 s) and comparison of PCD values between two PB episodes in each infant (r=0.68) revealed considerable variability in PCD. This variability was not related to the number of cycles in the PB episode or to the amount of PB in the recording. Contrary to the decrease in PCD from 15.0 s at 1 wk to 12.4 s at 12 wk in term infants reported previously, PCD did not vary as a function of postconceptional, gestational, or postnatal age in our preterm population. PCD has limited value as an indicator of chemoreceptor maturation in the preterm infant, and most likely reflects transient adjustments in respiratory system control.

The influence of ambient temperature on sleep characteristics in the aged cat.

Sleep characteristics were compared in young adult and aged cats over a range of environmental temperatures from 5 to 35 degrees C. Although both groups exhibited sleep disruptions as ambient temperatures decreased, transient arousals were increased at temperature extremes in the aged group compared to young adults. Declining efficiency of thermoregulatory control and increased sensitivity to environmental temperature in the elderly may contribute to the changes in sleep quality which occur during the aging process.

Absence of a circadian rhythm of protein synthesis in the rat suprachiasmatic nucleus

Male Wistar rats chronically catheterized in the jugular vein were entrained to a 12 L:12 D (lights on at 07.00 h) photoperiod. [1-14C]Leucine was administered in behaving rats at either 10.00 (day) or 22.00 (night) h. After 45 min of incubation animals were sacrificed, brains frozen, sectioned, and autoradiographed. The relative amount of label in the hypothalamic suprachiasmatic nucleus (SCN) was measured as the ratio of the optical density (OD) of the image of the SCN on the autoradiograph to the OD of white matter. The relative incorporation of labelled leucine into protein did not differ in the SCN of day vs night animals. This finding is in contrast to the prominent circadian rhythm of glucose utilization which has been seen in the rat SCN at identical points in the circadian cycle.

INTERRELATION BETWEEN SLEEP AND TEMPERATURE REGULATION

Publisher Summary This chapter focuses on the interrelation between sleep and temperature regulation. The possibility of interaction between the thermoregulatory system and arousal state controlling systems requires a new look at studies on the involvement of the hypothalamus on the control of arousal states. The effects of hypothalamic lesions and electrical stimulation have led to the postulation that the preoptic nuclei and anterior hypothalamus (POAH) are involved in producing cortical synchrony and sleep whereas the posterior hypothalamic areas are involved in producing cortical desynchrony and arousal. One criticism of the lesion and stimulation studies of putative hypothalamic sleep centers is that the effects may be a cause of disruption or stimulation of fibers of passage rather than to hypothalamic nuclei. For example, the lateral hypothalamus includes the medial forebrain bundle that includes descending pathways from septal and olfactory nuclei plus olfactory, hippocampal, and orbitofrontal cortices to the midbrain and possibly lower brainstem. Ascending fibers in the median forebrain bundle include those from several brainstem nuclei. The medial forebrain bundle also contains axons from various hypothalamic nuclei.