Elsevier

Brain Research

Volume 803, Issues 1–2, 24 August 1998, Pages 178-188
Brain Research

Research report
Sleep–waking discharge patterns of ventrolateral preoptic/anterior hypothalamic neurons in rats

https://doi.org/10.1016/S0006-8993(98)00631-3Get rights and content

Abstract

Numerous lesion, stimulation and recording studies in experimental animals demonstrate the importance of neurons within the preoptic/anterior hypothalamic area (POA) in the regulation of sleep induction and sleep maintenance. Recently, a discrete cluster of cells in the ventrolateral POA (vlPOA) of rats was found to exhibit elevated c-fos gene expression during sleep, indicating that these neurons are strongly activated during nonREM and/or REM sleep stages. We examined neuronal discharge during wakefulness and sleep throughout the dorsal to ventral extent of the lateral POA in rats, using chronic microwire technique. We found that neurons with elevated discharge rates during sleep, compared to waking, were localized to the vlPOA. As a group, vlPOA neurons displayed elevated discharge rates during both nonREM and REM sleep. Discharge of vlPOA neurons reflected the depth of sleep, i.e., discharge rates increased significantly from light to deep nonREM sleep. During recovery sleep following 12–14 h of sleep deprivation, vlPOA neurons displayed increased sleep-related discharge, compared to baseline sleep. Neurons in the vlPOA displaying increased neuronal discharge during sleep were located in the same area where neurons exhibit increased c-fos gene expression during sleep. Such neurons are likely components of a rostral hypothalamic mechanism that regulates sleep onset and sleep maintenance.

Section snippets

Introductions

There is extensive experimental evidence that the rostral hypothalamus is involved in sleep regulation, functioning to promote sleep induction and maintenance. Electrolytic or chemical lesions of the preoptic/anterior hypothalamus (POA) result in persistent insomnia 18, 27, 33, 37. Chemical stimulation of the POA with microinjected benzodiazepines [19], prostaglandin D2[39]and adenosine [38]promote sleep. Local warming of the POA in cats promotes sleep [26]and enhances EEG delta power in the

Subjects and surgical procedures

Subjects were 15 male, Sprague–Dawley rats weighing between 300–350 g at the time of surgery. They were housed individually on a 12:12 light:dark cycle (lights-on at 0700 h) at ambient temperatures of 23±2°C. Food and water were continuously available.

Surgical preparation for chronic sleep-wake and extracellular vlPOA neuronal recordings were performed under anesthesia (Ketamine, 80 mg/kg plus Xylazine, 10 mg/kg, i.p.) using aseptic techniques. Details of the methods are described elsewhere [3]

Distribution of cells with sleep- and wake- related discharge patterns in the lateral preoptic/anterior hypothalamic area

The nonREM/waking discharge ratio was determined for 105 cells recorded from dorsal to ventral microwire passes through the lateral preoptic area of 7 rats. The most frequently encountered cells (27% of the sample) had much higher discharge rates in waking compared to nonREM sleep (ratios between 0.01–0.39) Another large group (24%) had similar rates in waking and nonREM sleep (ratios between 0.80–1.19), and 22% were moderately waking–related (ratios between 0.40–0.79). Seventeen of 105 neurons

Discussion

We found that within the lateral preoptic/anterior hypothalamic area of rats, cells with sleep-related discharge were localized primarily to the vlPOA. A majority of vlPOA sleep-related cells displayed elevated discharge rates in both nonREM and REM sleep, compared to waking. Discharge of vlPOA neurons varied with sleep depth. As EEG delta power increased from the early to late portions of a nonREM sleep episode, discharge rate of vlPOA neurons increased. Following sleep deprivation, increased

Acknowledgements

Supported by the Department of Veterans Affairs Medical Research Service and NIMH MH 474780.

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