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1 Research Service (151A3), Veteran Affairs Greater Los Angeles Healthcare System, Sepulveda, CA, USA
Departments of
2 Psychology
3 Medicine, University of California, Los Angeles, CA, USA
4 Department of Zoology, Patna University, Patna, India
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(Received 7 October 2004;
accepted after revision 17 December 2004;
first published online 21 December 2004)
Corresponding author Md. N. Alam: Research Service (151A3), VAGLAHS, 16111 Plummer Street, Sepulveda, CA 91343, USA. Email: noor{at}ucla.edu
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Introduction |
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-aminobutyric acid (GABA) and glutamate (Bittencourt et al. 1992; Broberger et al. 1998; Peyron et al. 1998; Abrahamson & Moore, 2001; Elias et al. 2001). Both HCRT and MCH neurones are projection neurones and have been implicated in the regulation of food intake, energy homeostasis and sleep–wake regulation (Kilduff & Peyron, 2000; Beuckmann & Yanagisawa, 2002; Forray, 2003; Gerashchenko & Shiromani, 2004; Siegel, 2004). HCRT neurones appear to be active during behavioural arousal and contribute to the promotion and maintenance of waking. For example, HCRT neurones exhibit wake-associated, particularly movement-associated, discharge activity and are quiescent during both non-REM and REM sleep (Lee & Jones, 2004). The intracerebroventricular (I.C.V.) infusion, or local microinjection of the peptide HCRT into its target sites, for example preoptic area (POA), basal forebrain, tuberomammillary nucleus and locus coeruleus, promotes waking and suppresses non-REM and REM sleep (Hagan et al. 1999; Bourgin et al. 2000; Methippara et al. 2000; Espana et al. 2001; Huang et al. 2001; Thakkar et al. 2001). The HCRT level in cerebrospinal fluid is higher during active waking (Kiyashchenko et al. 2002). Human narcoleptics have a dramatically reduced number of HCRT neurones and HCRT-1 is undetectable in cerebrospinal fluid of most human narcoleptics (Peyron et al. 2000; Thannickal et al. 2000; Nishino et al. 2001; Dalal et al. 2002). Many of the symptoms of narcolepsy, including excessive sleepiness, cataplexy and increased REM sleep propensity as well as behavioural state instability, are exhibited by HCRT knockout mice, rats with a targeted destruction of HCRT-receptor expressing neurones in PF-LHA or HCRT/ataxin-3 transgenic mice (Chemelli et al. 1999; Hara et al. 2001; Gerashchenko et al. 2001, 2003; Mochizuki et al. 2004).
Recent evidence suggests that MCH neurones also play a role in the regulation of sleep. MCH-1 receptor-deficient mice become hyperactive (Marsh et al. 2002); I.C.V administration of MCH induces a dose-dependent increase in both non-REM and REM sleep (Verret et al. 2003). MCH neurones exhibit increased c-Fos protein immunoreactivity or expression (Fos-IR), a marker of neuronal activation, in rats during sleep with higher REM sleep rebound subsequent to REM sleep deprivation (Verret et al. 2003).
The PF-LHA contains local GABAergic interneurones and receives GABAergic inputs from other areas including from sleep-promoting GABAergic neurones in the POA region (Abrahamson & Moore, 2001; Gong et al. 2002, 2004). GABAA receptors are present on various PF-LHA neurones including HCRT and MCH neurones and in vitro studies suggest that GABA inhibits those neurones (Li et al. 2002; Eggermann et al. 2003; Moragues et al. 2003; Backberg et al. 2004; van den Pol et al. 2004). Some evidence suggests that the GABAergic system within PF-LHA is involved in the regulation of sleep. GABA release in the posterior hypothalamus is higher during non-REM and REM sleep (Nitz & Siegel, 1996). Local microinjection of muscimol into posterior hypothalamus produces a dose-dependent sedation in cats (Lin et al. 1989) and rats (Nelson et al. 2002).
We hypothesized that increased GABAergic inhibition within PF-LHA contributes to the suppression of wake-promoting systems, including HCRT neurones, during non-REM sleep. We also hypothesized that GABAergic inhibitory tone during sleep is minimal on MCH neurones. We tested these hypotheses by examining effects of bicuculline, a GABAA receptor antagonist, delivered unilaterally into PF-LHA through a microdialysis probe. We examined the effects of bicuculline on Fos-IR in HCRT, MCH and other PF-LHA neurones in the diffusion field of the microdialysis probe and concurrently recorded sleep–wake changes in freely behaving rats during the lights-on period.
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Experiments were performed on 24 Sprague-Dawley male rats, weighing between 250 and 350 g. These rats were maintained on 12–12 h light–dark cycle (lights on at 07.00 h) and with food and water ad libitum. All experiments were conducted in accordance with the National Research Council Guide for the Care and Use of Laboratory Animals and were approved by the Veteran Administration Institutional Animal Research Committee. Under surgical anaesthesia (ketamine/xylazine, 80/10 mg kg–1; I.P.) and aseptic conditions, rats were stereotaxically prepared for chronic recording of electroencephalogram (EEG) and electromyogram (EMG) signals and microdialytic delivery of artificial cerebrospinal fluid (aCSF) or bicuculline, a GABAA receptor antagonist, into PF-LHA. EEG and EMG electrodes were implanted using standard techniques. A microdialysis guide cannula (23G stainless steel tube) was implanted unilaterally such that its tip rested 3 mm above the dorsal aspect of the PF-LHA (A, –2.9 to –3.1; L, 1.4–1.6, H, 4.5–5.5; Paxinos & Watson, 1998) and was blocked with a stylet.
Experiments were started at least 10 days after surgery and after acclimation of the animals to the recording environment. At least 24 h before a recording session, the stylet of the microdialysis guide cannula was replaced by a microdialysis probe (semipermeable membrane tip length, 1 mm; outer diameter, 0.22 mm; molecular cut off size, 50 kDa; Eicom, Japan) fixed with dental acrylic and perfused with aCSF containing (mM): Na+ 145, K+ 2.7, Mg2+ 1.0 , Ca2+ 1.2 , Cl– 1.5 and Na2HPO4 2 (pH 7.2) at a flow rate of 
2 µl min–1.
The experiments were conducted on freely behaving undisturbed animals during lights-on period (between ZT5 and ZT8) when rats spend significantly more time asleep and fewer PF-LHA neurones express Fos-IR (Estabrooke et al. 2001; Espana et al. 2003). The experiments were conducted in pairs; tissues from one experimental and one control animal were processed together for immunostaining using the same batches of reagents. In the control group, rats (n = 7) were allowed to sleep normally for 2 h while the PF-LHA was continuously perfused with aCSF. In the experimental group, rats were allowed to sleep normally, that is they were undisturbed for 2 h while the PF-LHA was perfused with different doses of bicuculline for different time intervals (2 µM for 60 min, n = 2; 20 µM for 60 min, n = 8; 20 µM for 120 min, n = 3). During experiments, EEG and neck muscle EMG were continuously monitored, digitized (Cambridge Electronic Design 1401, UK; supporting software, Spike 2) and stored on a disc for subsequent analyses. Additional experiments were conducted during the lights-off period (between ZT13 and ZT16) during waking to determine whether bicuculline-induced changes in Fos-IR were influenced by the circadian timing and behavioural states. In those rats, aCSF (n = 2) or bicuculline (20 µM for 60 min, n = 2) was perfused while the rats were kept awake. At the end of 2 h, rats were given a lethal dose of pentobarbital (100 mg kg–1) and perfused for immunohistochemical processing for c-Fos protein, HCRT-1 and MCH immunostaining.
Histology and immunohistochemistry
After anaesthetization, rats were injected with heparin (500 U, I.P.), and perfused transcardially with 30–50 ml of 0.1 M phosphate buffer (pH 7.2) followed by 300 ml of 4% paraformaldehyde in phosphate buffer containing 15% saturated picric acid solution, 100 ml of 10% sucrose, and finally 100 ml of 30% sucrose in phosphate buffer. The brains were removed and equilibrated in 30% sucrose. Horizontal sections were freeze-cut at 30 µm thickness. Alternate sections from the series of sections spanning the probe tract were immunostained to reveal c-Fos and HCRT, or c-Fos and MCH proteins.
c-Fos immunostaining. Sections through PF-LHA were first immunostained for c-Fos protein. Free-floating sections were incubated in 0.3% H2O2 in Tris-buffered saline (TBS) at room temperature for 30 min and then rinsed three times for 10 min each in TBS. Then sections were placed in blocking solution (4% goat serum and 0.2% Triton X-100 in TBS) for 2 h. Sections were incubated in rabbit anti-c-Fos (1 : 15 000 Oncogene, CA, USA) in diluent solution containing 4% goat serum and 0.2% Triton X-100 in TBS for 40–48 h at 4°C. After rinsing, sections were incubated in biotinylated goat anti-rabbit secondary antibody (1 : 1000 Vector Laboratories, CA, USA) in diluent solution for 2 h followed by rinsing with TBS. The sections were then incubated in avidin–biotin complex (1 : 500, Vector Laboratories) for 2 h and then developed with nickel-3,3'-diaminobenzidine tetrahydrochloride (DAB, Sigma, USA). Black staining confined to the nucleus indicated Fos-IR. After staining for Fos-IR, alternate sections were processed for HCRT-1 or MCH immunostaining.
HCRT immunostaining. Sections were first washed in TBS followed by incubation in blocking solution for 2 h, followed by a rinse. Sections were then incubated in the primary antibody, rabbit anti-orexin (1 : 1000, Oncogene) for 40–48 h, followed by rinsing in TBS. The sections were then incubated in biotinylated goat anti-rabbit secondary antibody (1 : 500 Vector Laboratories) in diluent solution for 2 h followed by rinsing with TBS. The sections were then incubated in avidin–biotin complex (1 : 250, Vector Laboratories) for 2 h followed by DAB visualization.
MCH immunostaining. Sections were first washed in TBS followed by incubation in blocking solution for 2 h, followed by a rinse. Sections were incubated in the primary antibody, rabbit anti-MCH (1 : 20,000, Phoenix Pharmaceuticals, CA, USA) for 40–48 h, followed by rinsing in TBS. The sections were then incubated in biotinylated goat anti-rabbit secondary antibody (1 : 1000 Vector Laboratories) in diluent solution for 2 h followed by rinsing with TBS. The sections were then incubated in avidin–biotin complex (1 : 500, Vector Laboratories) for 2 h followed by DAB visualization.
Two sections from each brain were treated as above except for the omission of the Fos, HCRT-1 or MCH primary antibody to control for non-specific staining. Finally sections were rinsed in Tris (3 x 10 min) followed by TBS. The sections were mounted on gelatin-coated slides, air-dried, dehydrated and cover-slipped.
Data analysis
Sleep–wake scoring. A single person who was unaware of the experimental conditions scored sleep–waking states in 20-s epochs as active waking, quiet waking, non-REM sleep and REM sleep, according to the method described earlier (Alam & Mallick, 1990). Each behavioural state was further analysed in terms of episode duration or bout lengths to determine the ability of the rats to maintain each state (Franken et al. 1999; Mochizuki et al. 2004). Bouts of each state were subclassified according to increasing bout lengths (20–60 s, 61–120 s and > 120 s) and their frequency were determined.
Cell counting and analyses.
A single person blind to the treatment conditions performed the counting and plotting of the immunoreactive neurones using the Neurolucida computer-aided plotting system (MicroBrightField). All sections were carefully reviewed and four representative sections 120 µm apart and encompassing the maximum number of HCRT-positive (HCRT+) or MCH-positive (MCH+) neurones adjacent to the probe were considered for counting. The identification and counting of different neuronal types; single Fos-positive (Fos+), HCRT+ or MCH+ neurones and double-labelled HCRT+/Fos+ or MCH+/Fos+ neurones were performed manually. Fos-IR was recognized by black stain localized to the nucleus, whereas brown-stained soma and dendrites was indicative of HCRT+ or MCH+ neurones. Neurones having a black nucleus and a brown cytoplasm were identified as HCRT+/Fos+ or MCH+/Fos+ neurones in particular slides.
The effects of bicuculline on Fos-IR in PF-LHA neurones would depend upon its diffusion gradient from the probe. Therefore, a larger area of interest was chosen and a grid system was used for the quantification of Fos-IR. First, a 50-µm area around the perimeter of the microdialysis membrane tract was excluded from analyses because the damaged cells along the wall of the membrane may exhibit abnormal responses to the pharmacological agents. The area of interest (1000 µm each along rostral, caudal, lateral and medial sides) was then marked by four 250-µm wide concentric grids/rectangular boxes of progressively increasing size (grid-1, 0–250 µm; grid-2, 251–500 µm; grid-3, 501–750 µm; and grid-4, 751–1000 µm; Fig. 2). In those cases where the distance between the microdialysis membrane tract and the ventricle (medial side) was less than 1000 µm the number of neurones encountered on the remaining three sides was considered. A comparable area on the contralateral side was also counted, using the same grid system, to determine whether the effect was specific to the perfusion field. The number of HCRT+ or MCH+ neurones in the box adjacent to the probe varied depending upon the anatomical location of the probe. This variation was corrected by calculating the percentage of HCRT+/Fos + or MCH+/Fos+ neurones versus total number of HCRT+ or MCH+ neurones as a function of drug delivery in each animal.
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Results |
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The sleep–wake profiles of rats microdialysed with bicuculline into PF-LHA were compared with those perfused with aCSF during the lights-on period to assess the contribution of endogenous GABAergic tone within PF-LHA to sleep–wake behaviour. Rats with aCSF perfusion into PF-LHA spent a significant portion of the recording time (mean ± S.E.M) in non-REM (58.0 ± 3.8%) and REM sleep (9.5 ± 1.1%) during the 2-h recording period before they were killed (Fig. 1). In contrast, microdialytic delivery of bicuculline into the PF-LHA during the same time period significantly decreased the amount of non-REM and REM sleep and increased total time the animals spent in waking (Fig. 1). In the presence of bicuculline (20 µM for 60 min), non-REM sleep was reduced by 57% and REM sleep was reduced by 80%. As compared to non-REM sleep, the effect on REM suppression also lasted longer (Fig. 1).
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The bicuculline-induced waking resulted from a significant increase in active waking. The bout-length analyses of each of the behavioural states revealed that in the presence of bicuculline into the PF-LHA, rats exhibited a significant increase in the frequency of longer bouts of active waking (Table 1). In contrast, animals fell asleep significantly less frequently and exhibited significant decreases in non-REM and REM sleep bout lengths (Table 1).
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In order to determine the neuronal types that are affected by endogenous GABAergic inhibition during sleep, the effects of different doses of bicuculline versus aCSF perfusion were quantified on Fos-IR in HCRT+, MCH+ and non-HCRT/non-MCH (single Fos+) neurones in rats killed after the above sleep–wake studies.
Effects of bicuculline on Fos-IR in HCRT+ neurones. The effects of aCSF and different doses of bicuculline on Fos-IR in HCRT+ neurones during the lights-on period are shown in Figs 2–4. The number of HCRT+ neurones in aCSF and bicuculline treated rats around the microdialysis probe (370 ± 55 versus 255 ± 47) as well as in comparable regions on the contralateral sides (318 ± 63 versus 427 ± 62) were not significantly different. As reported in earlier studies (Estabrooke et al. 2001; Espana et al. 2003; Baldo et al. 2004), in aCSF-treated rats that were mostly asleep, few HCRT+ neurones expressed Fos-IR on both ipsilateral and contralateral sides, although the percentage of HCRT+/Fos+ neurones around the microdialysis probe was slightly higher (Fig. 4). However, in bicuculline-treated rats the number of HCRT+/Fos+ neurones around the microdialysis probe increased dramatically as compared to aCSF-treated rats. The number of HCRT+/Fos+ neurones in an equivalent region on the contralateral side of bicuculline-treated rats was not different from those found in aCSF-treated rats (Fig. 4).
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The effects of aCSF (n = 2) and bicuculline (n = 2) on Fos-IR in waking animals during the lights-off period were assessed to compare our observations with earlier studies. During the lights-off period when the rats were kept awake, a higher number of HCRT+ neurones expressed Fos-IR on both ipsilateral and contralateral sides during aCSF treatment (Figs 5 and 6). Though the number of subjects was not sufficient for statistical analysis, the bicuculline-treated rats showed a similar trend to that observed during the lights-on period, i.e. the number of HCRT+/Fos+ neurones in bicuculline-treated rats on the ipsilateral side was increased as compared to those found in aCSF-treated animals. However, the effect of bicuculline on Fos-IR during the lights-off period was marginal (HCRT+/Fos+ neurones during aCSF versus bicuculline treatment: 48.5 ± 4.8% versus 59.2 ± 0.4%, n = 2) as compared to that found during the lights-on period (aCSF versus bicuculline treatment: 5.9 ± 2.2% versus 41.1 ± 5.4%, n = 8; Fig. 7).
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Effects of bicuculline on Fos-IR in non-HCRT and non-MCH neurones. The effects of aCSF and different doses of bicuculline perfusion on Fos-IR in non-HCRT/non-MCH neurones are shown in Figs 2, 3 and 8. After aCSF perfusion during the lights-on period, a small number of single Fos+ neurones was found within the standard grid around the microdialysis probe and equivalent region on the contralateral side, although the number of Fos+ neurones ipsilateral to the probe was higher (Fig. 8). In the presence of bicuculline into PF-LHA, the number of Fos+ neurones around the microdialysis probe increased significantly as compared to those found on the ipsilateral side of aCSF-treated rats or a comparable region of the contralateral side. In the presence of bicuculline, the number of Fos+ neurones on the contralateral side also increased, although this effect was not significant.
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Correlation between bicuculline-induced Fos-IR and arousal. Figure 9 shows the correlation between aCSF- and bicuculline-induced changes in Fos-IR in PF-LHA neurones and the amount of active waking during the 2-h recording period before the animals were killed. Bicuculline-induced increase in Fos-IR in HCRT+, MCH+ and other PF-LHA neurones on the ipsilateral side was positively correlated with the amount of active waking. However, changes in the number of HCRT+/Fos +, MCH+/Fos+ and single Fos+ neurones on the contralateral side were not correlated with active waking.
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This is the first study, to our knowledge, that has quantified the effects of focal blockade of GABAergic transmission in PF-LHA on Fos-expression in identified HCRT, MCH and non-HCRT/non-MCH neurones in freely behaving animals. That the increase in Fos-IR in neurones adjacent to the microdialysis probe was induced by the blockade of GABAA receptors and not due to mechanical damage or to non-specific effects of fluid diffusion across the membrane is supported by the following evidence: (1) the bicuculline-induced increase in Fos-IR was significantly higher than that observed after aCSF perfusion; (2) the bicuculline-induced Fos-IR was dose-dependent; (3) bicuculline produced differential effects on HCRT and MCH neurones, the two overlapping neuronal population with differential influences on sleep–wake regulation (Estabrooke et al. 2001; Espana et al. 2003; Verret et al. 2003); (4) the increase in Fos-IR produced in response to bicuculline was positively correlated with the amount of waking; and (5) the magnitude of bicuculline-induced effects on HCRT neurones was different during lights-on and lights-off periods. The method of combined double-label immunohistochemistry adjacent to a microdialysis probe used for drug delivery provides obvious advantages compared to systemic, I.C.V. or microinjection delivery of drugs as well as administration by microdialysis without concomitant study of Fos-induction. However, this method cannot determine whether perfused drugs acted presynaptically on local interneurones, presynaptically on the terminals of distant afferents and/or directly on the receptors located on the dendrites or cell body of the identified neurones.
The PF-LHA neurones play a critical role in the regulation of behavioural arousal (see Introduction). A majority of PF-LHA neurones, including HCRT neurones, exhibit wake-associated discharge activity or Fos-IR (Estabrooke et al. 2001; Alam et al. 2002; Espana et al. 2003; Koyama et al. 2003; Torterolo et al. 2003; Lee & Jones, 2004). That PF-LHA neurones could be under GABAergic influences is supported by earlier studies. The GABAA receptors are present on various PF-LHA neurones including HCRT and MCH neurones (Moragues et al. 2003; Backberg et al. 2004). The GABAA receptor agonist, muscimol, hyperpolarizes HCRT and MCH neurones in in vitro preparations (Li et al. 2002; Eggermann et al. 2003; van den Pol et al. 2004). GABA levels in the posterior hypothalamus are higher during non-REM and REM sleep (Nitz & Siegel, 1996). Muscimol microinjection into posterior hypothalamus including PF-LHA promotes sleep (Lin et al. 1989). In this study bicuculline perfusion into PF-LHA dose-dependently increased waking and suppressed non-REM and REM sleep in freely behaving rats. These findings are in agreement with earlier studies and support a hypothesis that PF-LHA wake-promoting system is subject to increased endogenous GABAergic inhibition during sleep.
Rats exhibiting increased arousal and reduced sleep in response to bicuculline also showed increased number of Fos-IR neurones adjacent to the microdialysis probe. This suggests that the dis-inhibition of the neuronal population around the probe was sufficient to produce bicuculline-induced sleep–wake changes. It is unlikely that the increased number of Fos-IR neurones was indirectly caused by bicuculline-induced changes in waking as Fos-IR produced by waking should be equally expressed both ipsilateral and contralateral to the probe. In contrast, a relatively smaller population of neurones on the contralateral side exhibited Fos-IR. Therefore, it is plausible that bicuculline-induced sleep–wake changes were primarily mediated via the neuronal population around the microdialysis probe that exhibited Fos-IR in response to bicuculline.
Bicuculline-induced waking was accompanied by an insignificant increase in the number of HCRT+/Fos+ or single Fos-IR neurones on the contralateral side. This could be due to the fact that only sustained periods of waking accompanied by behavioural arousal or nocturnal spontaneous waking activates Fos-IR in HCRT and other PF-LHA neurones (Estabrooke et al. 2001; Espana et al. 2003). It is likely that bicuculline-induced arousal was neither sufficient in duration nor intense enough to evoke significant Fos-IR contralateral to the probe during the lights-on period. This interpretation is supported by our findings in rats that were kept awake during the lights-off period. In those rats a larger population of PF-LHA neurones, including HCRT neurones, were found to exhibit Fos-IR on the contralateral side. Our results are similar to the findings in a recent study where microdialytic perfusion of muscimol into the POA suppressed non-REM and REM sleep and increased Fos-IR in HCRT neurones located ipsilateral to the perfusion site while producing no effects on HCRT neurones located on the contralateral side (Satoh et al. 2004).
We found that a majority of neurones encountered in a 750 µm radius from the microdialysis probe that exhibited Fos-IR in response to bicuculline were of non-HCRT/non-MCH types. HCRT and MCH neurones constituted only 19 ± 2% and 8 ± 1%, respectively, of the responsive neurones. This suggests that the majority of PF-LHA neurones activated during waking contain neurotransmitters/neuromodulators other than HCRT or MCH. Evidence suggests that local glutamatergic neurones in PF-LHA regulate the excitability of HCRT and other PF-LHA neurones (Li et al. 2002; Baldo et al. 2004) and it is possible that some of the non-HCRT/non-MCH neurones that exhibited Fos-IR in response to bicuculline are wake-active glutamatergic neurones. Evidence suggests that GABA receptors are present on glia (Lin & Bergles, 2004). Although the role of glia in GABA-mediated neuronal signalling leading to sleep–wake changes is yet to be established, it is possible that some of the Fos-IR observed in the presence of bicuculline may be in the glial cells.
A significantly larger number of HCRT neurones, as compared to MCH neurones, exhibited Fos-IR in response to bicuculline (41 ± 5% versus 8 ± 1%) during the lights-on period, although during aCSF perfusion, when the animals were predominantly sleeping, fewer HCRT and MCH neurones exhibited Fos-IR. However, during the lights-off period when rats were kept awake, the number of HCRT neurones exhibiting Fos-IR increased substantially while the number of MCH neurones exhibiting Fos-IR remained very low. These findings are consistent with our hypothesis that HCRT neurones are under stronger GABAergic inhibition during sleep as compared to MCH neurones. MCH neurones exert potent inhibitory influences on the synaptic activity of the PF-LHA neurones and have been implicated in the facilitation of sleep (Gao & van den Pol, 2001; Verret et al. 2003). The minimal GABAergic influence on MCH neurones found in this study is consistent with the sleep-associated role of MCH neurones.
Recent evidence from our laboratory suggests that most of the sleep-active neurones within median preoptic nucleus (MnPN) of the POA region are GABAergic and MnPN constitutes a significant source of afferents to PF-LHA (Gong et al. 2002, 2004). Recently we found that MnPN electrical stimulation suppressed the discharge activity in the majority of PF-LHA neurones suggesting that at least a subset of PF-LHA neurones are under direct MnPN inhibitory control during sleep (Suntsova et al. 2003). Although the present study cannot determine whether bicuculline-induced increase in Fos-IR in PF-LHA neurones was due to the blockade of GABAergic inputs from MnPN sleep-active neurones or the local interneurones, it is reasonable to believe that both GABAergic sources may have been involved.
In conclusion, the present study suggests that focal blockade of GABAergic transmission in PF-LHA activates HCRT, MCH and other PF-LHA neurones leading to the suppression of non-REM and REM sleep and induction of arousal. Given the well-documented role of HCRT and other PF-LHA neurones in behavioural arousal and wakefulness, these results support the hypothesis that the wake-promoting PF-LHA system is subject to increased endogenous GABAergic inhibition during sleep. However, bicuculline caused minimal changes in the number of MCH neurones expressing Fos-IR suggesting that, as compared to other PF-LHA neurones, MCH neurones are under weaker GABAergic control during sleep.
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) versus percentage active wake time during the 2-h recording period before the rats were killed. The bicuculline-induced Fos-IR in a different neuronal population ipsilateral to the microdialysis probe was positively correlated with the amount of active waking. No significant correlation was found for neurones on the contralateral side. The active–wake and Fos-IR data were pooled from all rats used in this study for aCSF and bicuculline treatments.