Neurons in the ventrolateral preoptic nucleus (VLPO) in rats show c-fos activation after sleep and provide GABAergic innervation of the major monoamine arousal systems, suggesting that they may be a necessary part of the brain circuitry that produces sleep. We examined the effects on sleep behavior in rats of cell-specific damage to the VLPO by microinjection of ibotenic acid. Severe lesions of the central cell cluster of the VLPO (ϳ80-90% cell loss bilaterally) caused a 60-70% decrease in delta power and a 50-60% decrease in nonrapid-eyemovement (NREM) sleep time ( p Ͻ 0.001). The number of remaining Fos-immunoreactive neurons in the VLPO cell cluster was linearly related to NREM sleep time (r ϭ 0.77; p Ͻ 0.001) and total electroencephalogram delta power (r ϭ 0.79; p Ͻ 0.001) but not to rapid-eye-movement (REM) sleep (r ϭ 0.35; p Ͼ 0.10). Lesions in the region containing scattered VLPO neurons medial or dorsal to the cell cluster caused smaller changes in NREM sleep time (24.5 or 15%, respectively) but were more closely associated with loss of REM sleep (r ϭ 0.74; p Ͻ 0.01). The insomnia caused by bilateral VLPO lesions persisted for at least 3 weeks. Lesions of the VLPO caused no change in mean body temperature or its circadian variation; after small lesions of the ventromedial preoptic nucleus, body temperature showed normal circadian variation but a wider temperature range, and sleep behavior was not affected. These experiments delineate distinct preoptic sites with primary effects on the regulation of NREM sleep, REM sleep, and body temperature. Key words: preoptic area; hypothalamus; REM sleep; NREM sleep; thermoregulation; circadian rhythmsThe involvement of the preoptic area and adjacent basal forebrain in sleep regulation has been recognized since von Economo (1930) reported that lesions of this region cause prolonged insomnia in humans. Nauta (1946) demonstrated that preopticbasal forebrain lesions cause insomnia in rats, and Sterman and Clemente (1962a,b) demonstrated similar effects in cats. These experimental studies used electrolytic or mechanical lesions that not only destroyed neuronal cell bodies but also damaged fibers of passage. More recent studies using chemical toxins to ablate the neuronal cell bodies in this area in rats and cats have confirmed the production of insomnia (Szymusiak and McGinty, 1986;Sallanon et al., 1989;John and Kumar, 1998). However, these studies used large lesions and hence could not identify a specific neuronal population that was responsible for the deficit in sleep regulation.Recently, Sherin et al. (1996) identified a specific population of neurons in the ventrolateral preoptic nucleus (VLPO) that show Fos immunoreactivity after sleep (sleep-positive neurons). The number of Fos-immunoreactive (-IR) neurons in this region was directly proportional to the number of minutes of sleep during the previous hour (Sherin et al., 1996), in good agreement with electrophysiological studies showing that sleep-active neurons, with firing rates two to three times faster during...

Hypocretins (Hcrts) are recently discovered peptides linked to the human sleep disorder narcolepsy. Humans with narcolepsy have decreased numbers of Hcrt neurons and Hcrt-null mice also have narcoleptic symptoms. Hcrt neurons are located only in the lateral hypothalamus (LH) but neither electrolytic nor pharmacological lesions of this or any other brain region have produced narcoleptic-like sleep, suggesting that specific neurons need to be destroyed. Hcrt neurons express the Hcrt receptor, and to facilitate lesioning these neurons, the endogenous ligand hypocretin-2/orexin B (Hcrt2) was conjugated to the ribosome-inactivating protein saporin (SAP). In vitro binding studies indicated specificity of the Hcrt2-SAP because it preferentially bound to Chinese hamster ovary cells containing the Hcrt/orexin receptor 2 (HcrtR2/OX(2)R) or the Hcrt/orexin receptor 1 (HcrtR1/OX(1)R) but not to Kirsten murine sarcoma virus transformed rat kidney epithelial (KNRK) cells stably transfected with the substance P (neurokinin-1) receptor. Administration of the toxin to the LH, in which the receptor is known to be present, eliminated some neurons (Hcrt, melanin-concentrating hormone, and adenosine deaminase-containing neurons) but not others (a-melanocyte-stimulating hormone), indicating specificity of the toxin in vivo. When the toxin was administered to the LH, rats had increased slow-wave sleep, rapid-eye movement (REM) sleep, and sleep-onset REM sleep periods. These behavioral changes were negatively correlated with the loss of Hcrt-containing neurons but not with the loss of adenosine deaminase-immunoreactive neurons. These findings indicate that damage to the LH that also causes a substantial loss of Hcrt neurons is likely to produce the multiple sleep disturbances that occur in narcolepsy.

No abstract

No abstract