Neurones in the median preoptic nucleus (MnPN) and the ventrolateral preoptic area (vlPOA) express immunoreactivity for c-Fos protein following sustained sleep, and display elevated discharge rates during both non-REM and REM sleep compared to waking. We evaluated the hypothesis that MnPN and vlPOA sleep-active neurones are GABAergic by combining staining for c-Fos protein with staining for glutamic acid decarboxylase (GAD). In a group of six rats exhibiting spontaneous total sleep times averaging 82.2 ± 5.1% of the 2 h immediately prior to death, >75% of MnPN neurones that were Fos-immunoreactive (IR) were also GAD-IR. Similar results were obtained in the vlPOA. In a group of 11 rats exhibiting spontaneous sleep times ranging from 20 to 92%, the number of Fos + GAD-IR neurones in MnPN and vlPOA was positively correlated with total sleep time. Compared to control animals, Fos + GAD-IR cell counts in the MnPN were significantly elevated in rats that were sleep deprived for 24 h and permitted 2 h of recovery sleep. These findings demonstrate that a majority of MnPN and vlPOA neurones that express Fos-IR during sustained spontaneous sleep are GABAergic. They also demonstrate that sleep deprivation is associated with increased activation of GABAergic neurones in the MnPN and vlPOA.

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Pathways mediating the generation and/or maintenance of sleep reside within the preoptic/anterior hypothalamus (POAH). Reproduction, water balance, thermoregulation, and neuroendocrine functions are also associated with POAH, but it is not fully understood whether sleep is consolidated with these behavioral and physiological functions, or whether sleep-related circuitry is segregated from other POAH regions. Recent studies indicate that sleep mechanisms may be localized to the ventrolateral preoptic area (VLPO) and that this region sends inhibitory projections to waking/arousal-related neurons in the histaminergic tuberomammillary nucleus (TM), the noradrenergic locus coeruleus (LC), and the serotonergic dorsal raphe (DR). The present study is a quantitative investigation of preoptic area efferents to these monoaminergic groups. The results demonstrate that biotinylated dextran injections in the VLPO region reveal a robust innervation of TM that was as much as five times greater than innervation derived from other POAH subregions. The innervation of TM originated almost exclusively from injection sites in the region of galanin neurons. VLPO projections to the LC were moderately dense and were greater than in other POAH regions except for equivalent input from the medial preoptic area. Projections to the dorsal raphe were equivalent to LC innervation and were generally two to three times greater from VLPO than from other POAH regions, except for projections from the lateral preoptic region, which were similar in magnitude. The rostral and caudal levels projected more to the TM, whereas the midrostral region of VLPO strongly innervated the LC core. These findings, with recent studies demonstrating medial and lateral extensions of the sleep-related VLPO neuronal group, indicate that descending arousal state control may be mediated by this specific galaninergic/gamma-aminobutyric acid (GABA)ergic cell group.

The dentate gyrus (DG) of the adult hippocampus gives rise to progenitor cells, which have the potential to differentiate into neurons. To date it is not known whether sleep or sleep loss has any effect on proliferation of cells in the DG. Male rats were implanted for polysomnographic recording, and divided into treadmill sleep‐deprived (SD), treadmill control (TC) and cage control (CC) groups. SD and TC rats were kept for 96 h on a treadmill that moved either for 3 s on/12 s off (SD group) or for 15 min on/60 min off (TC group) to equate total movement but permit sustained rest periods in TC animals. To label proliferating cells the thymidine analogue 5‐bromo‐2′‐deoxyuridine (BrdU) was injected after the first 48 h of the experimental procedure in all groups (50 mg kg−1, i.p.). The percentage of time awake per day was 93.2 % in the SD group vs. 59.6 % in the TC group and 49.9 % in the CC group (P < 0.001). Stereological analysis showed that the number of BrdU‐positive cells in the DG of the dorsal hippocampus was reduced by 54 % in the SD group in comparison with the TC and by 68 % in comparison with the CC group. These results suggest that sleep deprivation reduces proliferation of cells in the DG of the dorsal hippocampus.

Preoptic area (POA) neuronal activity promotes sleep, but the localization of critical sleep-active neurons is not completely known. Thermal stimulation of the POA also facilitates sleep. This study used the c-Fos protein immunostaining method to localize POA sleep-active neurons at control (22 degrees C) and mildly elevated (31.5 degrees C) ambient temperatures. At 22 degrees C, after sleep, but not after waking, we found increased numbers of c-Fos immunoreactive neurons (IRNs) in both rostral and caudal parts of the median preoptic nucleus (MnPN) and in the ventrolateral preoptic area (VLPO). In animals sleeping at 31.5 degrees C, significantly more Fos IRNs were found in the rostral MnPN compared with animals sleeping at 22 degrees C. In VLPO, Fos IRN counts were no longer increased over waking levels after sleep at the elevated ambient temperature. Sleep-associated Fos IRNs were also found diffusely in the POA, but counts were lower than those made after waking. This study supports a hypothesis that the MnPN, as well as the VLPO, is part of the POA sleep-facilitating system and that the rostral MnPN may facilitate sleep, particularly at elevated ambient temperatures.