Differential acute influence of medial and lateral preoptic areas on sleep-wakefulness in freely moving rats

Pedunculo-pontine tegmentum cholinergic REM-ON neurons modulate ventral tegmental neurons to modulate rapid eye movement sleep in rats

The interaction among the acetylcholine (ACh)-ergic REM-ON neurons in the pedunculo-pontine area (PPT), noradrenergic REM-OFF neurons in locus coeruleus (LC) and GABA-ergic neurons in the regulation of rapid eye movement sleep (REMS) have been studied in relative details; however, many questions including the role of dopamine (DA) remain unanswered. The ventral tegmental area (VTA) is rich in DA-ergic neurons, which have been implicated with schizophrenia and depression, when REMS is significantly affected. Also, some of the symptoms of REMS and these diseases are common. As the ACh-ergic REM-ON neurons in the PPT project to VTA, we proposed that such inputs might affect REMS, dreams and hallucinations. We recorded sleep-wake-REMS in freely moving, chronically prepared rats under three controlled experimental conditions. In different sets of experiments, either the ACh-ergic inputs to the VTA were blocked by local microinjection of Scopolamine (Scop) alone, or, the PPT neurons were bilaterally stimulated by Glutamate (Glut), or, the PPT neurons were stimulated by Glut in presence of Scop into the VTA. It was observed that Glut into PPT and Scop into the VTA significantly increased and decreased REMS, respectively. Additionally, PPT stimulation induced increased REMS was prevented in the presence of Scop into the VTA. Based on these findings we propose that inputs from ACh-ergic REM-ON neurons to VTA increase REMS and it could be a possible circuitry for expressions of hallucinations and dreams.

Glutamatergic Neurons in the Preoptic Hypothalamus Promote Wakefulness, Destabilize NREM Sleep, Suppress REM Sleep, and Regulate Cortical Dynamics

Clinical and experimental data from the last nine decades indicate that the preoptic area of the hypothalamus is a critical node in a brain network that controls sleep onset and homeostasis. By contrast, we recently reported that a group of glutamatergic neurons in the lateral and medial preoptic area increases wakefulness, challenging the long-standing notion in sleep neurobiology that the preoptic area is exclusively somnogenic.

Clinical and experimental data from the last nine decades indicate that the preoptic area of the hypothalamus is a critical node in a brain network that controls sleep onset and homeostasis. By contrast, we recently reported that a group of glutamatergic neurons in the lateral and medial preoptic area increases wakefulness, challenging the long-standing notion in sleep neurobiology that the preoptic area is exclusively somnogenic. However, the precise role of these subcortical neurons in the control of behavioral state transitions and cortical dynamics remains unknown. Therefore, in this study, we used conditional expression of excitatory hM3Dq receptors in these preoptic glutamatergic (Vglut2⁺) neurons and show that their activation initiates wakefulness, decreases non-rapid eye movement (NREM) sleep, and causes a persistent suppression of rapid eye movement (REM) sleep. We also demonstrate, for the first time, that activation of these preoptic glutamatergic neurons causes a high degree of NREM sleep fragmentation, promotes state instability with frequent arousals from sleep, decreases body temperature, and shifts cortical dynamics (including oscillations, connectivity, and complexity) to a more wake-like state. We conclude that a subset of preoptic glutamatergic neurons can initiate, but not maintain, arousals from sleep, and their inactivation may be required for NREM stability and REM sleep generation. Further, these data provide novel empirical evidence supporting the hypothesis that the preoptic area causally contributes to the regulation of both sleep and wakefulness.

SIGNIFICANCE STATEMENT Historically, the preoptic area of the hypothalamus has been considered a key site for sleep generation. However, emerging modeling and empirical data suggest that this region might play a dual role in sleep-wake control. We demonstrate that chemogenetic stimulation of preoptic glutamatergic neurons produces brief arousals that fragment sleep, persistently suppresses REM sleep, causes hypothermia, and shifts EEG patterns toward a “lighter” NREM sleep state. We propose that preoptic glutamatergic neurons can initiate, but not maintain, arousal from sleep and gate REM sleep generation, possibly to block REM-like intrusions during NREM-to-wake transitions. In contrast to the long-standing notion in sleep neurobiology that the preoptic area is exclusively somnogenic, we provide further evidence that preoptic neurons also generate wakefulness.

Efferent projections of excitatory and inhibitory preBötzinger Complex neurons

The preBötzinger Complex (preBötC), a compact medullary region essential for generating normal breathing rhythm and pattern, is the kernel of the breathing central pattern generator (CPG). Excitatory preBötC neurons in rats project to major breathing-related brainstem regions. Here, we provide a brainstem connectivity map in mice for both excitatory and inhibitory preBötC neurons. Using a genetic strategy to label preBötC neurons, we confirmed extensive projections of preBötC excitatory neurons within the brainstem breathing CPG including the contralateral preBötC, Bötzinger Complex (BötC), ventral respiratory group, nucleus of the solitary tract, parahypoglossal nucleus, parafacial region (RTN/pFRG or alternatively, pF_L /pF_V ), parabrachial and Kölliker-Füse nuclei, as well as major projections to the midbrain periaqueductal gray. Interestingly, preBötC inhibitory projections paralleled the excitatory projections. Moreover, we examined overlapping projections in the pons in detail and found that they targeted the same neurons. We further explored the direct anatomical link between the preBötC and suprapontine brain regions that may govern emotion and other complex behaviors that can affect or be affected by breathing. Forebrain efferent projections were sparse and restricted to specific nuclei within the thalamus and hypothalamus, with processes rarely observed in cortex, basal ganglia, or other limbic regions, e.g., amygdala or hippocampus. We conclude that the preBötC sends direct, presumably inspiratory-modulated, excitatory and inhibitory projections in parallel to distinct targets throughout the brain that generate and modulate breathing pattern and/or coordinate breathing with other behaviors, physiology, cognition, or emotional state.

Sleep-wake and diurnal modulation of nitric oxide in the perifornical-lateral hypothalamic area: real-time detection in freely behaving rats

Nitric oxide (NO) has been implicated in the regulation of sleep. The perifornical-lateral hypothalamic area (PF-LHA) is a key wake-promoting region and contains neurons that are active during behavioral or cortical activation. Recently, we found higher levels of NO metabolites (NOx), an indirect measure of NO levels, in the PF-LHA during prolonged waking (SD). However, NO is highly reactive and diffuses rapidly and the NOx assay is not sensitive enough to detect rapid-changes in NO levels across spontaneous sleep-waking states. We used a novel Nafion®-modified Platinum (NF-PT) electrode for real-time detection of NO levels in the PF-LHA across sleep-wake cycles, dark-light phases, and during SD. Sprague-Dawley male rats were surgically prepared for chronic sleep-wake recording and implantation of NF-PT electrode into the PF-LHA. Electroencephalogram (EEG), electromyogram (EMG), and electrochemical current generated by NF-PT electrode were continuously acquired for 5-7days including one day with 3h of SD. In the PF-LHA, NO levels exhibited a waking>rapid eye movement (REM)>non-rapid eye movement (nonREM) sleep pattern (0.56±0.03μM>0.47±0.02μM>0.42±0.02μM; p<0.01). NO levels were also higher during the dark- as compared to the light-phase (0.53±0.03μM vs. 0.44±0.02μM; p<0.01). NO levels increased during 3h of SD as compared to undisturbed control (0.58±0.04μM vs. 0.47±0.01μM; p<0.05). The findings indicate that in the PF-LHA, NO is produced during behavioral or cortical activation. Since elevated levels of NO inhibits most of the PF-LHA neurons that are active during cortical activation, these findings support a hypothesis that NO produced in conjunction with the activation of PF-LHA neurons during waking/SD, inhibits the same neuronal population to promote sleep.

Repeated microinjections into the medial prefrontal cortex (mPFC) impair extinction of conditioned place preference in mice

The medial prefrontal cortex (mPFC) is important for extinction of many behaviors including conditioned place preference (CPP). We examined the effects of intra-mPFC inactivation (with bupivacaine) on extinction of ethanol-induced CPP in mice. Injections of both bupivacaine and vehicle impaired extinction whereas no-surgery control mice extinguished normally. Consistent with recently reported effects of mPFC lesions, these data suggest that extinction was impaired by excessive mPFC damage induced by repeated intracranial infusions.

Nitric oxide production in the perifornical-lateral hypothalamic area and its influences on the modulation of perifornical-lateral hypothalamic area neurons

The perifornical-lateral hypothalamic area (PF-LHA) is a major wake-promoting structure. It predominantly contains neurons that are active during behavioral and cortical activation. PF-LHA stimulation produces arousal and PF-LHA lesions produce somnolence. Nitric oxide (NO) is a gaseous neurotransmitter that has been implicated in the regulation of multiple pathological and physiological processes including the regulation of sleep. NO levels are higher in the cortex and in the basal forebrain (BF) during arousal. In this study we determined whether NO levels increase in the PF-LHA during prolonged arousal and whether increased NO modulates the discharge activity of PF-LHA neurons. Experiments were conducted during lights-on phase between 8.00 and 20.00 h (lights-on at 8.00 h). First, we quantified levels of NO metabolites, NO2- and NO3- (collectively called NOx-) in the microdialysis dialysates collected from the PF-LHA during baseline (undisturbed rats), 6 h of sleep deprivation (SD), and recovery after SD. We further determined the effects of a NO donor, NOC-18, on the discharge activity of PF-LHA neurons in urethane-anesthetized rats. Overall, SD significantly affected NOx- production in the PF-LHA (one way repeated measures ANOVA, F=7.827, P=0.004). The levels of NOx- increased progressively in animals that were subjected to prolonged arousal as compared to the undisturbed predominantly sleeping animals and decreased during the recovery period. Local application of NOC-18 significantly suppressed the discharge of PF-LHA neurons including a majority of stimulus-on neurons or neurons exhibiting activation during electroencephalogram (EEG) desynchronization. The findings of this study suggest that in the PF-LHA, NO production is elevated during prolonged waking and that NO exerts predominantly inhibitory effects on PF-LHA neurons, especially on those neurons that are active during cortical activation. These findings are consistent with a hypothesis that NO in the PF-LHA plays a role in sleep regulation by inhibiting its neurons.

Endogenous ouabain-like compounds in locus coeruleus modulate rapid eye movement sleep in rats

Although the detailed mechanism of spontaneous generation and regulation of rapid eye movement sleep (REMS) is yet unknown, it has been reported that noradrenergic REM-OFF neurons in the locus coeruleus (LC) cease firing during REMS and, if they are kept active, REMS is significantly reduced. On the other hand, the activity as well as expression of Na-K ATPase has been shown to increase in the LC following REMS deprivation. Ouabain is a specific inhibitor of Na-K ATPase, and endogenous ouabain-like compounds are present in the brain. These findings led us to propose that a decrease in the level of ouabain-like compounds spontaneously available in and around the LC would stimulate and increase the REM-OFF neuronal activities in this region and thus would reduce REMS. To test this hypothesis, we generated anti-ouabain antibodies and then microinjected it bilaterally into the LC in freely moving chronically prepared rats and recorded electrophysiological signals for evaluation of sleep-wakefulness states; suitable control experiments were also conducted. Injection of anti-ouabain antibodies into the LC, but not into adjacent brain areas, significantly reduced percent REMS (mean +/- SEM) from 7.12 (+/-0.74) to 3.63 (+/-0.65). The decrease in REMS was due to reduction in the mean frequency of REMS episode, which is likely due to increased excitation of the LC REM-OFF neurons. Control microinjections of normal IgG did not elicit this effect. These results support our hypothesis that interactions of naturally available endogenous ouabain-like compounds with the Na-K ATPase in the LC modulate spontaneous REMS.

Role of adenosine A(1) receptor in the perifornical-lateral hypothalamic area in sleep-wake regulation in rats

The perifornical-lateral hypothalamic area (PF-LHA) has been implicated in the regulation of arousal. The PF-LHA contains wake-active neurons that are quiescent during non-REM sleep and in the case of neurons expressing the peptide hypocretin (HCRT), quiescent during both non-REM and REM sleep. Adenosine is an endogenous sleep factor and recent evidence suggests that adenosine via A(1) receptors may act on PF-LHA neurons to promote sleep. We examined the effects of bilateral activation as well as blockade of A(1) receptors in the PF-LHA on sleep-wakefulness in freely behaving rats. The sleep-wake profiles of male Wistar rats were recorded during reverse microdialysis perfusion of artificial cerebrospinal fluid (aCSF) and two doses of adenosine A(1) receptor antagonist, 1,3-dipropyl-8-phenylxanthine (CPDX; 5 microM and 50 microM) or A(1) receptor agonist, N(6)-cyclopentyladenosine (CPA; 5 microM and 50 microM) into the PF-LHA for 2 h followed by 4 h of aCSF perfusion. CPDX perfused into the PF-LHA during lights-on phase produced arousal (F=7.035, p<0.001) and concomitantly decreased both non-REM (F=7.295, p<0.001) and REM sleep (F=3.456, p<0.004). In contrast, CPA perfused into the PF-LHA during lights-off phase significantly suppressed arousal (F=7.891, p<0.001) and increased non-REM (F=8.18, p <0.001) and REM sleep (F=30.036, p<0.001). These results suggest that PF-LHA is one of the sites where adenosine, acting via A(1) receptors, inhibits PF-LHA neurons to promote sleep.

Presence of alpha-1 norepinephrinergic and GABA-A receptors on medial preoptic hypothalamus thermosensitive neurons and their role in integrating brainstem ascending reticular activating system inputs in thermoregulation in rats

Thermal messages are relayed to the medial preoptic O-anterior hypothalamus (mPOAH) via the ascending reticular activating system (ARAS). According to previous findings that norepinephrine (NE)-ergic and GABA (gamma-amino butyric acid)-ergic inputs convey thermal information to the CNS, those neurotransmitters may be responsible for reciprocal correlation between body temperature and mPOAH warm-(WSNs) and cold-(CSNs) sensitive neuronal firing rates for thermoregulation. In this study on Wistar rats, we have characterized in vivo the role of alpha-1 NE-ergic and GABA-A receptors in the possible modulation of ARAS inputs to the thermosensitive neurons in the mPOAH. Nine WSNs, 7 CSNs and 19 thermo-insensitive neurons were recorded from mPOAH and effects of ARAS stimulation and iontophoretic application of prazosin as well as picrotoxin on those neurons were evaluated. The WSNs were excited by ARAS stimulation but inhibited by both prazosin and picrotoxin; whereas the CSNs were inhibited by ARAS stimulation and prazosin, but excited by picrotoxin. The NE excited the WSNs as well as the CSNs, while GABA had opposite effects on them, suggesting that NE and GABA interact in the mPOAH for thermoregulation. The findings unravel an intriguing possibility that in the mPOAH, GABA simultaneously acts on hetero-receptors located at pre-and post-synaptic sites, modulating the release of NE on the WSNs and CSNs for thermoregulation. Further, ARAS stimulation-induced similar excitatory and inhibitory responses of the WSNs and the CSNs support such converging inputs on these neurons for thermoregulation.

Effects of serotonin on perifornical-lateral hypothalamic area neurons in rat

The hypocretin (HCRT) system of the perifornical-lateral hypothalamic area (PF-LHA) has been implicated in the facilitation of behavioral arousal. HCRT neurons receive serotonergic afferents from the dorsal raphe nucleus. Although in-vitro pharmacological studies suggest that serotonin (5-HT) inhibits HCRT neurons, the in-vivo effects of 5-HT on HCRT neurons in the PF-LHA and associated behavioral changes have not been described. We examined the effects of 5-HT delivered locally into the PF-LHA using reverse microdialysis on its neuronal activity and the consequent sleep-wake changes in rats. First, we quantified Fos expression (Fos-IR) in HCRT and other PF-LHA neurons following unilateral 5-HT perfusion in awake rats. Second, we determined the transient effects of 5-HT perfusion on the extracellular activity of the PF-LHA neurons recorded via microwires placed adjacent to the microdialysis probe. Third, we examined the effects of 5-HT perfusion into the PF-LHA on the sleep-wake profiles of the rats during the lights-off period. Unilateral perfusion of 5-HT into the PF-LHA in awake rats dose-dependently decreased the number of HCRT neurons exhibiting Fos-IR. 5-HT also inhibited the discharge activity of four of five responsive wake-related, putative HCRT neurons. However, unilateral perfusion of 5-HT into the PF-LHA did not produce significant behavioral changes during the 2-h recording period. These results confirm the in-vitro findings that 5-HT exerts inhibitory influences on HCRT neurons but further suggest that the inactivation of a limited number of HCRT neurons by unilateral 5-HT microdialysis may not be sufficient to induce behavioral changes.

Role of alpha and beta adrenoceptors in locus coeruleus stimulation-induced reduction in rapid eye movement sleep in freely moving rats

Based on the results of independent studies the involvement of norepinephrine in REM sleep regulation was known. Isolated studies showed that the effect could be mediated through either one or more subtypes of adrenoceptors. Earlier we have reported that REM-OFF neurons continue firing during REM sleep deprivation and mild but continuous stimulation of locus coeruleus (LC) or picrotoxin injection into the LC, that did not allow the REM-OFF neurons in the LC to stop firing, reduced REM sleep. However, the mechanism of action and type of adrenoreceptors involved in REM sleep regulation were unknown. The possible mechanism of action has been investigated in this study. It was proposed that if LC stimulation-induced decrease in REM sleep was due to norepinephrine, adrenergic antagonist must prevent the effect. Therefore, in this study, the effects of alpha1, alpha2 and beta-antagonists, viz. prazosin, yohimbine and propranolol, respectively, and alpha2 agonist, clonidine, on LC stimulation-induced reduction in REM sleep were investigated. The results showed that stimulation of LC inhibited REM sleep by reducing the frequency of generation of REM sleep, although the duration per episode remained unaffected. This decrease in the frequency of REM sleep was blocked by beta-antagonist propranolol while the duration of REM sleep per episode was blocked by alpha1-antagonist, prazosin. Also, a critical level of norepinephrine in the system was required for the generation of REM sleep, however, a higher level may be inhibitory. Based on the results of this study and our earlier studies, an interaction between neurons, containing different neurotransmitters and their subtypes of receptors for LC-mediated regulation of REM sleep has been proposed.

GABA-mediated control of hypocretin- but not melanin-concentrating hormone-immunoreactive neurones during sleep in rats

The perifornical-lateral hypothalamic area (PF-LHA) has been implicated in the regulation of behavioural arousal. The PF-LHA contains several cell types including neurones expressing the peptides, hypocretin (HCRT; also called orexin) and melanin-concentrating hormone (MCH). Evidence suggests that most of the PF-LHA neurones, including HCRT neurones, are active during waking and quiescent during non-rapid eye movement (non-NREM) sleep. The PF-LHA contains local GABAergic interneurones and also receives GABAergic inputs from sleep-promoting regions in the preoptic area of the hypothalamus. We hypothesized that increased GABA-mediated inhibition within PF-LHA contributes to the suppression of neuronal activity during non-REM sleep. EEG and EMG activity of rats were monitored for 2 h during microdialytic delivery of artificial cerebrospinal fluid (aCSF) or bicuculline, a GABAA receptor antagonist, into the PF-LHA in spontaneously sleeping rats during the lights-on period. At the end of aCSF or bicuculline perfusion, rats were killed and c-Fos immunoreactivity (Fos-IR) in HCRT, MCH and other PF-LHA neurones was quantified. In response to bicuculline perfusion into the PF-LHA, rats exhibited a dose-dependent decrease in non-REM and REM sleep time and an increase in time awake. The number of HCRT, MCH and non-HCRT/non-MCH neurones exhibiting Fos-IR adjacent to the microdialysis probe also increased dose-dependently in response to bicuculline. However, significantly fewer MCH neurones exhibited Fos-IR in response to bicuculline as compared to HCRT and other PF-LHA neurones. These results support the hypothesis that PF-LHA neurones, including HCRT neurones, are subject to increased endogenous GABAergic inhibition during sleep. In contrast, MCH neurones appear to be subject to weaker GABAergic control during sleep.

Interleukin-1beta modulates state-dependent discharge activity of preoptic area and basal forebrain neurons: role in sleep regulation

Interleukin-1beta (IL-1) is a pro-inflammatory cytokine that has been implicated in the regulation of nonrapid eye movement (nonREM) sleep. IL-1, IL-1 receptors and the IL-1 receptor antagonist (ra) are present normally in discrete brain regions, including the preoptic area (POA) of the hypothalamus and the adjoining magnocellular basal forebrain (BF). The POA/BF have been implicated in the regulation of sleep-wakefulness. We hypothesized that IL-1 promotes nonREM sleep, in part by altering the state-dependent discharge activity of POA/BF neurons. We recorded the sleep-wake discharge profiles of 83 neurons in the lateral POA/BF and assessed the effects of IL-1, IL-1ra, and IL-ra + IL-1 delivered through a microdialysis probe on state-dependent neuronal discharge activity. IL-1 decreased the discharge rate of POA/BF neurons as a group (n = 55) but wake-related and sleep-related neurons responded differently. IL-1 significantly decreased the discharge rate of wake-related neurons. Of 24 wake-related neurons studied, 19 (79%) neurons exhibited a greater than 20% change in their discharge in the presence of IL-1 during waking. IL-1 suppressed the discharge activity of 18 of 19 responsive neurons. Of 13 sleep-related neurons studied, IL-1 increased the discharge activity of five and suppressed the discharge activity of four neurons. IL-1ra increased the discharge activity of four of nine neurons and significantly attenuated IL-1-induced effects on neuronal activity of POA/BF neurons (n = 19). These results suggest that the sleep-promoting effects of IL-1 may be mediated, in part, via the suppression of wake-related neurons and the activation of a subpopulation of sleep-related neurons in the POA/BF.

The role of the medial preoptic area of the hypothalamus in organizing the paradoxical phase of sleep

Chronic experiments were performed on cats to study the effects of electrical stimulation of the medial preoptic area of the hypothalamus on the latent period, duration, and structure of paradoxical sleep, as well as the dynamics of neuron activity in this structure during the sleep-waking cycle. These investigations showed that low-frequency stimulation of the medial preoptic area during slow-wave sleep led to short-latency development of desynchronization of bioelectrical activity in the neocortex and initiated the development of paradoxical sleep or a similar state. Stimulation of this structure during paradoxical sleep led to a decrease in its duration, to the virtually complete disappearance of the tonic stage of paradoxical sleep, and to an increase in the frequency of rapid eye movements in the phasic stage. Rearrangement of neuron activity in the medial preoptic area during the sleep-waking cycle was similar to that seen in cells of the lower brainstem "executive" centers of paradoxical sleep. It is suggested that neurons in the medial preoptic area of the hypothalamus are actively involved in the mechanisms of paradoxical sleep and, in particular, in the desynchronization of neocortical bioelectrical activity which develops during this stage.

Wake-promoting actions of dopamine D1 and D2 receptor stimulation

Multiple ascending neurotransmitter systems participate in the regulation of behavioral state. For example, noradrenergic, cholinergic, and serotonergic systems increase EEG and, in some cases, behavioral indices of arousal. The extent to which dopaminergic systems exert a similar activating influence on behavioral state remains unclear. The current studies examined the wake-promoting actions of centrally administered D1 and D2 receptor agonists. In these studies, intracerebroventricular infusions of a D1 (SKF-82958; 2.5 and 25 nmol) or D2 (quinpirole; 40 and 140 nmol)-agonist were made into sleeping animals. The effects of these infusions on electroencephalogram/electromyographic indices of sleep-wake state and behavior were examined. D1 agonist administration dose dependently increased time spent awake and suppressed rapid eye movement and slow-wave sleep in the 2 h immediately after infusion. D1 agonist administration also elicited modest increases in measures of locomotion and time spent grooming and eating. D2 agonist administration had similar wake-promoting actions, accompanied by modest effects on drinking and locomotion. Interestingly, D2 agonist administration also significantly increased time spent chewing on inedible material, an arousal/stress-related behavior. Overall, these results demonstrate that dopamine contributes to the alert waking state via actions of D1 and D2 receptors. Additionally or alternatively, these results further suggest a potential involvement of dopamine receptors in the induction of high-arousal states, including stress.

Wakefulness-inducing area in the brainstem excites warm-sensitive and inhibits cold-sensitive neurons in the medial preoptic area in anesthetized rats

Sleep-wakefulness and body temperature are known to influence each other. The body temperature rises during wakefulness and falls during sleep. The midbrain reticular formation is one of the areas in the brainstem that induces wakefulness, while the preoptico-anterior hypothalamic area is the main thermoregulatory center in the brain. In order to understand the neural mechanism for simultaneous regulation of these functions we hypothesized that the wakefulness area in the brainstem is likely to have an opposite influence on warm- and cold-sensitive neurons in the preoptico-anterior hypothalamic area. Hence, first, the wakefulness-inducing area was identified in the brainstem by stimulating the site with high-frequency rectangular wave electrical pulses (100 Hz, 100 microA, 200 microsec for 5-8 sec) in freely behaving chronically prepared experimental rats. Then, single neuronal activity from the medial preoptico-anterior hypothalamic area was recorded and their thermosensitivity was established. Thereafter, the influence of such a confirmed wakefulness-inducing area in the brainstem on the responsiveness of the single neuronal activity of predetermined warm- and cold-sensitive neurons as well as on temperature-insensitive neurons was studied by overlapping stimulus (1 Hz, 500 microA, 200 microsec) bound responses. It was observed that the warm-sensitive neurons were excited and the cold-sensitive neurons were inhibited by stimulation of the wakefulness-inducing area in the brainstem. Most of the temperature-insensitive neurons remained unaffected. The results confirm our hypothesis and help in understanding the mechanism of simultaneous modulation of body temperature in association with changes in wakefulness at the single neuronal level.

Involvement of the dorsomedial striatum in behavioral flexibility: role of muscarinic cholinergic receptors

The present experiments determined whether temporary inactivation or blockade of muscarinic cholinergic receptors in the dorsomedial striatum affects acquisition or reversal learning of a response discrimination. Testing occurred in a modified cross-maze across two consecutive sessions. In the acquisition phase, a rat learned to make a turn to the left or to the right for 10 consecutive correct choices. In the reversal learning phase, a rat learned to turn in the opposite direction as required during acquisition for 10 consecutive correct choices. Experiment 1 investigated the effects of the local anesthetic, 2% bupivacaine, infused into the dorsomedial striatum on acquisition and reversal learning. Experiment 2 examined the effects of the muscarinic cholinergic antagonist, scopolamine injected into the dorsomedial striatum on acquisition and reversal learning. Bupivacaine infusions did not impair acquisition, but did impair reversal learning of the response discrimination. Analysis of the errors indicated that the deficit was not due to perseveration of the previously learned strategy, but to an inability to learn the new strategy. Bilateral injections of scopolamine, 1 or 8 microg/side, did not affect acquisition. Infusions of scopolamine at 8 microg, but not 1 microg, produced a reversal learning deficit. The scopolamine-induced deficit resulted from an inability to learn the new strategy. The results suggest that the dorsomedial striatum is important for behavioral flexibility and that activation of muscarinic cholinergic receptors in this region may facilitate the learning of situationally adaptive response patterns.

Sleep-waking discharge patterns of median preoptic nucleus neurons in rats

Several lines of evidence show that the preoptic area (POA) of the hypothalamus is critically implicated in the regulation of sleep. Functionally heterogeneous cell groups with sleep-related discharge patterns are located both in the medial and lateral POA. Recently a cluster of neurons showing sleep-related c-Fos immunoreactivity was found in the median preoptic nucleus (MnPN). To determine the specificity of the state-related behaviour of MnPN neurons we have undertaken the first study of their discharge patterns across the sleep-waking cycle. Nearly 76 % of recorded cells exhibited elevated discharge rates during sleep. Sleep-related units showed several distinct types of activity changes across sleep stages. Two populations included cells displaying selective activation during either non-rapid eye movement (NREM) sleep (10 %) or REM sleep (8 %). Neurons belonging to the predominant population (58 %) exhibited activation during both phases of sleep compared to wakefulness. Most of these cells showed a gradual increase in their firing rates prior to sleep onset, elevated discharge during NREM sleep and a further increase during REM sleep. This specific sleep-waking discharge profile is opposite to that demonstrated by wake-promoting monoaminergic cell groups and was previously found in cells localized in the ventrolateral preoptic area (vlPOA). We hypothesize that these vlPOA and MnPN neuronal populations act as parts of a GABAergic/galaninergic sleep-promoting ('anti-waking') network which exercises inhibitory control over waking-promoting systems. MnPN neurons that progressively increase activity during sustained waking and decrease activity during sustained sleep states may be involved in homeostatic regulation of sleep.

The effects of dopamine D(1) receptor blockade in the prelimbic-infralimbic areas on behavioral flexibility

This study examined the effects of a dopamine D(1) antagonist, SCH23390, infused into the prelimbic-infralimbic areas on the acquisition of a response and visual-cue discrimination task, as well as a shift from a response to a visual-cue discrimination and vice versa. Each test was carried out in a cross-maze. The response discrimination required learning to always turn in the same direction (right or left) for a cereal reinforcement. The visual-cue discrimination required learning to always enter the arm with the visual cue. In experiment 1, rats were tested on the response discrimination task, followed by the visual-cue discrimination task. In experiment 2, the testing order was reversed. Bilateral infusions of SCH23390 (0.1 or 1 microg/0.5 microL) into the prelimbic-infralimbic areas did not impair acquisition of the response or visual-cue discrimination tasks. SCH23390 injections at 1 microg, but not 0.1 microg impaired performance when shifting from a response to a visual-cue discrimination, and vice versa. Analysis of the errors revealed that the deficit was due to perseveration of the previously learned strategy. These results suggest that activation of dopamine D(1) receptors in the prelimbic-infralimbic areas may be critical for the suppression of a previously relevant strategy and/or generating new strategies.

GABAergic neurons in prepositus hypoglossi regulate REM sleep by its action on locus coeruleus in freely moving rats

GABA in locus coeruleus modulates REM sleep. Apart from the presence of interneurons, locus coeruleus also receives GABAergic inputs from prepositus hypoglossi in the medulla, where the presence of REM-ON-like neurons have been reported. Therefore, it was hypothesized that GABAergic projections from prepositus hypoglossi to locus coeruleus may modulate REM sleep. The experiments were conducted on chronic rats prepared for recording EEG, EOG, and EMG in freely moving conditions. Bipolar stimulating electrodes were implanted in prepositus hypoglossi bilaterally, while chemitrodes were implanted bilaterally in locus coeruleus. The prepositus hypoglossi were bilaterally stimulated (3 Hz, 250 microsec, 100 microA) for 8 h in the presence and absence of picrotoxin (0.25 microg/250 nl) microinjection bilaterally in locus coeruleus, followed by poststimulation recording for 4 h. It was observed that stimulation of prepositus hypoglossi alone significantly increased REM sleep primarily by increasing the REM sleep duration per episode. However, when it was stimulated in the presence of picrotoxin in LC, REM sleep decreased, predominantly due to decreased REM sleep duration per episode. The results of this study suggest that GABAergic inputs from prepositus hypoglossi act on locus coeruleus and regulate REM sleep, possibly by inhibition of REM-OFF neurons.

GABA exerts opposite influence on warm and cold sensitive neurons in medial preoptic area in rats

The preoptic area regulates body temperature. GABA-ergic terminals and receptors are present in this area. Local microinjection studies have shown that GABA, its agonist, and its antagonist in this area may modulate body temperature. However, there are warm and cold sensitive neurons, and they are known to be affected by local and peripheral temperatures. In order to understand the mechanism of action of GABA in temperature regulation at the cellular level it was necessary to study the effect of GABA on individual thermosensitive neurons in in vivo preparations. Hence, in this study the responses of preoptic area thermosensitive and insensitive neurons to microiontophoretic application of picrotoxin, a GABA-A antagonist, were studied in anaesthetized rats. It was observed that a majority of both the thermosensitive and insensitive neurons were affected by microiontophoretic application of picrotoxin. Although almost an equal number of cold and warm sensitive neurons were affected, a majority of the cold sensitive neurons were excited, while a majority of the warm sensitive neurons were inhibited by picrotoxin. The results suggested that in normal conditions GABA acts through GABA-A receptor in modulating the spontaneous activity of thermosensitive neurons in the preoptic area. Furthermore, the results of the present study taken together with other reports suggest that normally GABA exerts a direct inhibitory action on the cold sensitive neurons, while it acts on presynaptic heteroreceptors, possibly on norepinephrinergic afferent input terminals on the warm sensitive neurons, for mediating its action.

GABA-A receptors in mPOAH simultaneously regulate sleep and body temperature in freely moving rats

Sleep-wakefulness and body temperature are two circadian rhythmic biological phenomena. The role of GABAergic inputs in the medial preoptico-anterior hypothalamus (mPOAH) on simultaneous regulation of those phenomena was investigated in freely moving normally behaving rats. The GABA-A receptors were blocked by microinjecting picrotoxin, and the effects on electrophysiological parameters signifying sleep-wakefulness, rectal temperature and brain temperature were recorded simultaneously. The results suggest that, normally, GABA in the medial preoptic area acts through GABA-A receptor that induces sleep and prevents an excessive rise in body temperature. However, the results do not allow us to comment on the cause and effect relationship, if any, between changes in sleep-wakefulness and body temperature. The changes in brain and rectal temperatures showed a positive correlation, however, the former varied within a narrower range than that of the latter.

Interactions between cholinergic and GABAergic neurotransmitters in and around the locus coeruleus for the induction and maintenance of rapid eye movement sleep in rats

The noradrenergic "REM-off" neurons in the locus coeruleus cease firing, whereas some cholinergic and non-cholinergic "REM-on" neurons increase firing during rapid eye movement sleep. A reciprocal interaction between these neurons was proposed. However, acetylcholine did not inhibit neurons in the locus coeruleus. Nevertheless, since GABA levels increase during rapid eye movement sleep and picrotoxin injections into the locus coeruleus reduced rapid eye movement sleep, it was hypothesized that GABA in the locus coeruleus might play an intermediary inhibitory role for rapid eye movement sleep regulation. Therefore, the effects of GABA or carbachol (a mixed cholinergic agonist receptor) alone, as well as an agonist of one in presence of an antagonist of the other, in the locus coeruleus were investigated on sleep-wakefulness and rapid eye movement sleep. The cholinergic agonist carbachol increased, while the muscarinic antagonist receptor scopolamine decreased, the frequency of induction of rapid eye movement sleep per hour. In contrast, GABA and picrotoxin increased and decreased, respectively, the duration of rapid eye movement sleep per episode. However, when carbachol was injected in the presence of picrotoxin or GABA was injected in the presence of scopolamine, the effect of GABA or picrotoxin was dominant. Microinjection of both scopolamine and picrotoxin in combination reduced both the frequency of initiation as well as the duration per episode of rapid eye movement sleep. From these results we suggest that in the locus coeruleus cholinergic input modulates the frequency of induction of rapid eye movement sleep and this action is mediated through GABA interneurons, whereas the length of rapid eye movement sleep per episode is maintained by the presence of an optimum level of GABA. A model of neural connections for initiation and maintenance of rapid eye movement sleep is proposed and discussed.

Differential sensitivity to the wake-promoting actions of norepinephrine within the medial preoptic area and the substantia innominata

Mapping studies were conducted to delineate the site(s) of action for the arousal-enhancing actions of norepinephrine (NE) within the basal forebrain region encompassing the medial preoptic area (MPOA) and the substantia innominata (SI). Varying doses of NE, the beta-agonist, isoproterenol, or the alpha1-agonist, phenylephrine, were infused into the MPOA or SI in the resting rat. Infusions of NE (4 nmol, 16 nmo/150 nl), isoproterenol (15 nmol/150 nl), and phenylephrine (40 nmol/250 nl) into the MPOA elicited robust increases in waking. In contrast, neither isoproterenol or phenylephrine infusions into the SI altered behavioral state. NE infusions into the SI increased waking only at the highest dose, and at this dose there was an anatomical gradient for NE-induced waking, with infusions placed farther from the MPOA, producing smaller increases in waking. Thus, in contrast to the MPOA, the SI is relatively insensitive to the wake-promoting actions of NE.

Contrasting effects of noradrenergic beta-receptor blockade within the medial septal area on forebrain electroencephalographic and behavioral activity state in anesthetized and unanesthetized rat

The locus coeruleus-noradrenergic system participates in the modulation of behavioral state. Previous studies demonstrated that beta-receptors located within the general region encompassing the medial septum/vertical limb of the diagonal band of Broca (medial septal area) exert arousal-enhancing actions in both anesthetized and unanesthetized animals. These studies also demonstrated that, under conditions of limited locus coeruleus discharge rates, blockade of beta-receptors within this region decreased forebrain electroencephalographic indices of arousal. The current studies assess the extent to which medial septal area beta-receptors contribute to the maintenance of electroencephalographic and/or behavioral indices of arousal, under conditions associated with elevated locus coeruleus discharge rates. In the halothane-anesthetized rat, bilateral, but not unilateral, blockade of beta-receptors within this area prevented forebrain (cortical and hippocampal) electroencephalographic activation elicited by activation of locus coeruleus neurons. Placement of beta-antagonist immediately adjacent to the medial septal area had no effect on locus coeruleus-dependent cortical and hippocampal electroencephalographic activation. In contrast, in unanesthetized rat, bilateral pretreatment of the medial septal area did not alter either electroencephalographic or behavioral measures in animals tested in an arousal-enhancing, brightly-lit novel environment, which has been demonstrated to elicit an activation of the locus coeruleus-noradrenergic system. The results obtained in anesthetized animals are consistent with previous studies demonstrating potent modulatory actions of noradrenergic systems on actions of general anesthetics, and suggest that beta-receptors may be an appropriate target for pharmacological adjuncts to general anesthetics. In contrast to that observed in anesthetized animals, medial septal beta-receptors alone do not contribute significantly to the maintenance of an activated forebrain in unanesthetized animals. It is presumed that actions of other noradrenergic receptors and/or other neurotransmitter systems located within or outside the medial septal area make the arousal-modulating actions of medial septal area beta-receptors redundant, in the unanesthetized, alert animal.

A sleep inducing factor from common Indian toad (Bufo melanostictus, Schneider) skin extract

Bufo melanostictus (common Indian toad) acquire different bioactive substances in their skin during their life-time in wide ecological habitat. Earlier investigation from this laboratory revealed that toad (B. melanostictus) skin extract (TSE) posses different bioactive compounds of different diversity (Das, M., Auddy, B. and Gomes, A., 1996. Pharmacological study of the toad skin extract on experimental animals. Indian J. Pharmacol. 28, 72-76). Among these sleep induction and sleep potentiation indicated the possibility of sleep inducing factor(s) in TSE. One such sleep inducing factor (SIF) was isolated and purified by neutral alumina column chromatography followed by HPLC. Spectroscopy (UV, IR, FAB-MASS) study indicated that the sleep inducing factor was a 880 Dalton conjugated aromatic compound with a hydroxyl and carbonyl functional group. Biological study showed that SIF produced no lethality in male albino mice upto the dose of 8 mg/kg, i.v. Cyproheptadine antagonised SIF induced contraction of isolated smooth muscle indicating histamine/serotonin receptor mediated action of SIF. EEG studies showed that SIF increased sleep and decreased awakening condition of freely moving rats. Biochemical studies showed that SIF produced significant alteration of brain biogenic amine levels, monoamine oxidase (MAO) and tryptophan hydroxylase (TH) activity. This may be the reason of SIF induced sleep, although the SIF induced sleep mechanism needs further detail investigation.

Amphetamine acts within the medial basal forebrain to initiate and maintain alert waking

Amphetamine-like stimulants exert well-known arousal-enhancing actions. Surprisingly, little is known concerning the neuroanatomical substrates through which these drugs enhance arousal. Previous work implicates a number of basal forebrain structures in the regulation of behavioral state. The current studies examined the effects of amphetamine infusions made directly within basal forebrain sites on behavioral, electroencephalographic, and electromyographic indices of arousal in anesthetized and unanesthetized rat. In the anesthetized rat, amphetamine elicited prolonged epochs of bilateral electroencephalographic activation when infused unilaterally (3.75 microg/150 nl) into an extended region of the medial basal forebrain, demarcated anteriorally by the anterior portion of the medial septal area (which includes posterior accumbens shell) and posteriorally by the posterior aspect of the preoptic area of the hypothalamus. In the unanesthetized (undisturbed, resting) rat, amphetamine infusions into this region elicited prolonged epochs of alert waking, which at the lowest dose (3.75 microg), qualitatively resembled normal waking. Infusions placed lateral (including within the substantia innominata), anterior (including within the core subregion of the nucleus accumbens), posterior, or dorsal to these structures, as well as directly within the lateral ventricles did not alter electroencephalographic or behavioral measures. These results indicate that a region of the medial basal forebrain, extending from the anterior medial septum/accumbens shell to the posterior preoptic area, is a site within which amphetamine-like stimulants act to enhance behavioral and electroencephalographic measures of arousal.

Role of GABA-A receptor in the preoptic area in the regulation of sleep-wakefulness and rapid eye movement sleep

The role of GABA in medial preoptico-anterior hypothalamic area in the regulation of spontaneous sleep-wakefulness and rapid eye movement sleep was investigated in this study. Local microinjection of picrotoxin, a GABA-A antagonist, into this area increased quiet wakefulness but significantly reduced deep sleep and rapid eye movement sleep. Both the frequency of generation and duration per episode of the latter were significantly reduced. It is concluded that GABA-ergic neurotransmission in the medial preoptic area is spontaneously active in modulating the hypnogenic function including rapid eye movement sleep and the action is mediated by GABA-A receptor.

Diurnal rhythm in cyclic GMP/nitric oxide efflux in the medial preoptic area of male rats

Since nitric oxide (NO) is implicated in the neuroendocrine control of luteinizing hormone-releasing hormone (LHRH) secretion and sexual behavior which show diurnal variations, we monitored cGMP levels (an index of NO activity) in the extracellular compartment of the medial preoptic area (MPOA) using microdialysis. It was observed that MPOA cGMP levels rose significantly in the afternoon in both castrated and intact male rats, thereby suggesting the existence of a diurnal rhythm in MPOA cGMP/NO efflux which may participate in eliciting the well-known diurnal variations in LHRH neuronal activity and male sexual behavior.

Adrenergic and cholinergic inputs in preoptic area of rats interact for sleep-wake thermoregulation

Isolated studies have shown that both norepinephrine and acetylcholine into the medial preoptico-anterior hypothalamic area tonically regulate sleep-wake and body temperature. A possible interaction between these neurotransmitters for the regulation of such functions has been investigated in this study. To study this interaction a combination of either prazosin and carbachol or, scopolamine and methoxamine was injected into the medial preoptico-anterior hypothalamic area and the effect on sleep, wake, and rectal temperature recorded simultaneously. The combination of chemicals were selected based on our previous studies where it was observed that each of the chemicals in a combination had opposite effects. It was observed that injection of the combination expressed a resultant summated effects of individual component chemicals when injected in isolation (observed in previous studies). Because effect of neither of the chemicals in the combination was dominant, the results suggest an interaction and integration of the adrenergic and cholinergic inputs in the medial preoptico-anterior hypothalamic area for the regulation of sleep-wakefulness and body temperature.

Effects of parenterally administered triazolam on sleep in rats with lesions of the preoptic area

In previous work we have reported that microinjections of triazolam or pentobarbital into the medial preoptic area of the anterior hypothalamus produce a hypnotic effect. This finding raised the possibility that the sleep-enhancing actions after systemic administration of these compounds might be mediated by hypnogenic mechanisms in the preoptic area. The current study examined whether sleep enhancement by triazolam requires the anatomic integrity of the preoptic area. Nine rats with histologically confirmed lesions of the preoptic area induced by ibotenic acid (2.5 microg/microl in 0.4 microl), and 10 rats that had undergone a sham lesion procedure, had 2-h sleep studies that confirmed that by day 5 measures of total sleep time and sleep latency had returned to preintervention values. Rats were then given triazolam 0.8 mg/kg or vehicle intraperitoneally in counterbalanced order, on days 7 and 9 postlesion, in an environment with an ambient temperature of 25 degrees C. Following injections at 1000 h, in conditions in which lights were on from 0800-2000 h, 2-h sleep studies were performed. In the lesioned rats, triazolam significantly decreased sleep latency and increased total sleep time, primarily by increasing NREM sleep, whereas injections of vehicle did not. In summary, parenterally administered triazolam was found to have hypnotic effects in rats who were 1 week post-preoptic area lesion. These data are interpreted in light of previous evidence of redundancy of sleep-regulating mechanisms in the nervous system.

GABAergic and cholinergic basal forebrain and preoptic-anterior hypothalamic projections to the mediodorsal nucleus of the thalamus in the cat

The present study examined projections of GABAergic and cholinergic neurons from the basal forebrain and preoptic-anterior hypothalamus to the "intermediate" part of the mediodorsal nucleus of the thalamus. Retrograde transport from this region of the mediodorsal nucleus was investigated using horseradish peroxidase-conjugated wheatgerm agglutinin in combination with peroxidase-antiperoxidase immunohistochemical staining for glutamic acid decarboxylase and choline acetyltransferase. A relatively large number of retrogradely-labelled glutamic acid decarboxylase-positive neurons are located in the basal forebrain, amounting to more than 7% of the total population of glutamic acid decarboxylase-positive cells in this region. Moreover, retrogradely-labelled choline acetyltransferase-positive cells are interspersed among glutamic acid decarboxylase-positive neurons, accounting for about 6% of the total choline acetyltransferase-positive cell population in the basal forebrain. The glutamic acid decarboxylase-positive and choline acetyltransferase-positive retrogradely-labelled neurons are distributed throughout several regions of the basal forebrain, including the medial septum, the diagonal band of Broca, the magnocellular preoptic nucleus, the substantia innominata pars anterior, the substantia innominata pars posterior, and the globus pallidus where only a few retrogradely-labelled neurons were seen. The choline acetyltransferase-positive mediodorsal-projecting neurons are morphologically different from the choline acetyltransferase-positive neurons in the basal forebrain, suggesting that those projecting to the mediodorsal nucleus are a small proportion of the cholinergic neuronal population in the basal forebrain. In the preoptic-anterior hypothalamus, many retrogradely-labelled glutamic acid decarboxylase-positive cells were found, amounting to more than 7% of the total population of glutamic acid decarboxylase-positive cells in this region. These retrogradely-labelled glutamic acid decarboxylase-positive neurons are distributed throughout the preoptic-anterior hypothalamus in a continuous line with those in the basal forebrain, including the lateral preoptic area, the medial preoptic area, the bed nucleus of the stria terminalis, and the anterior and dorsal hypothalamic areas. The highest percentage of mediodorsal-projecting GABAergic neurons is in the anterior lateral hypothalamus where more than 25% of the total population of glutamic acid decarboxylase-positive cells project to the mediodorsal nucleus of the thalamus. Overall, of the large population of retrogradely-labelled neurons in the basal forebrain and preoptic-anterior hypothalamus, a significant proportion are glutamic acid decarboxylase-positive neurons (> 60% in the basal forebrain and > 30% in the preoptic-anterior hypothalamus), while the choline acetyltransferase-positive neurons amount to a smaller percentage of the neurons projecting to the mediodorsal nucleus (< 13% in the basal forebrain and < 2% in the preoptic-anterior hypothalamus). These results provide anatomical evidence of direct GABAergic projections from the basal forebrain and preoptic-anterior hypothalamic regions to the "intermediate" part of the mediodorsal nucleus in the cat. This GABAergic projection field could be the direct pathway by which the basal forebrain directly modulates thalamic excitability and may also be involved in mechanisms modulating electroencephalographic synchronization and sleep through the "intermediate" mediodorsal nucleus.

Thermosensitive neurons of the diagonal band in rats: relation to wakefulness and non-rapid eye movement sleep

The thermosensitivity of the neurons in the diagonal band of Broca (DBB) was studied in 12 freely moving rats by determining responses to local cooling or warming with a water perfused thermode. Of 151 neurons studied, 37 (25%) neurons met the criterion for thermosensitivity including 17 warm-sensitive (WSNs) and 20 cold-sensitive neurons (CSNs). The spontaneous discharge rates of WSNs and CSNs were recorded through 1-3 sleep-waking cycles. The discharge of WSNs and CSNs during waking and non-rapid eye movement (NREM) sleep were different. Of 17 WSNs, 10 exhibited increased discharge rates during NREM sleep as compared with waking (NREM/Wake discharge ratio, > 1.2). Of 20 CSNs, 14 discharged more slowly during NREM sleep as compared with waking (NREM/Wake discharge ratio, < 0.8). In both WSNs and CSNs, changes in discharge rate preceded EEG changes at the waking-NREM transition. These results support a hypothesis that the activation of sleep-related WSNs and the deactivation of wake-related CSNs play a role in the onset and regulation of NREM sleep.

Role of cholinergic inputs to the medial preoptic area in regulation of sleep-wakefulness and body temperature in freely moving rats

The medial preoptico-anterior hypothalamic area receives adrenergic as well as cholinergic inputs. Independent studies showed that both these inputs influence sleep, wakefulness and body temperature. The role of the adrenergic inputs was studied earlier. The role of cholinergic inputs is reported here. The cholinergic agonist, carbachol, and antagonist, scopolamine, were injected into this area during the day and the night in freely moving rats and the effects on sleep-wakefulness and body temperature studied. It was observed that carbachol induced wakefulness accompanied by a fall in body temperature while scopolamine induced an opposite effect, i.e. sleep accompanied by an increase in body temperature. This suggested that the cholinergic input into the medial preoptic area is spontaneously active in regulating sleep-wakefulness and body temperature and this regulation is mediated through muscarinic receptors present in this area. The results also suggest that, contrary to the action of adrenergic inputs (which have a dissociated effect on sleep-wakefulness and body temperature), the cholinergic input is unlikely to have a dissociated effect on those functions.

Mild electrical stimulation of pontine tegmentum around locus coeruleus reduces rapid eye movement sleep in rats

The norepinephrinergic neurons in the locus coeruleus (LC) cease firing during REM sleep (REMS) and increase firing during REMS deprivation. Most of the earlier studies used lesion and transection techniques which could not confirm the role of LC in REMS generation and/or its maintenance, if at all. Hence, in this study it was hypothesized that if the LC REM-off neurons must cease firing before the onset of REMS, its continuous activation should eliminate or at least reduce REMS. Electrophysiological parameters characterizing sleep-wakefulness-REMS were recorded in freely moving male albino rats. In an attempt not to allow the REM-off LC neurons to cease firing, low intensity (200 microA), low frequency (2 Hz) rectangular (300 microseconds) pulses were continuously delivered to the LC bilaterally through chronically implanted electrodes, and the effects on sleep-wakefulness-REMS were investigated. Although the stimulation did not affect sleep state of the animals, it reduced REMS significantly. The effect on REMS was similar to that of REMS deprivation. Total duration of REMS was significantly reduced during stimulation and showed a rebound increase during the post stimulation period. This reduction in REMS duration was primarily due to a significant reduction in the REMS frequency/h while the mean REMS duration/episode was not affected. Thus, the results of this study suggest that the stimulated area (LC) affects REMS, most likely by suppression of REMS generation process.

Noradrenaline inhibits preoptic sleep-active neurons through alpha 2-receptors in the rat

Effects of noradrenaline (NA) on the activity of sleep-related neurons in the preoptic area (POA) and the neighboring basal forebrain were examined in the rat. Of 36 sleep-active neurons tested, 19 were inhibited and the other 17 were unaffected by NA applied through a multibarrel pipette. The alpha 2-agonist clonidine inhibited 11 of 14 sleep-active neurons and did not affect the other 3 neurons, whereas the alpha 1-agonist methoxamine (n = 13) and the beta-agonist isoproterenol (n = 11) had no effect on any of the sleep-active neurons tested. Thus, alpha 2-receptors mediated the NA-induced inhibition. Of 22 waking-active neurons tested, NA excited 10, inhibited 1, and had no effect on the remaining 11. Methoxamine excited 4 of 13 waking-active neurons tested, whereas isoproterenol (n = 9) and clonidine (n = 4) were without effect on any of the waking-active neurons tested. Accordingly, alpha 1-receptors probably mediated the NA-induced excitation. Seventy-seven state-indifferent neurons, which lacked activity related to the sleep-waking state, and 20 paradoxical sleep-active neurons were mostly (65%-70%) insensitive to NA. These results suggest that NA promotes wakefulness by inhibiting sleep-active neurons and by exciting waking-active neurons.

Immediate-early genes in spontaneous wakefulness and sleep: expression of c-fos and NGFI-A mRNA and protein

We have recently shown that the expression of two immediate-early genes, c-fos and NGFI-A, is strongly affected by sleep deprivation, In this work, we investigated c-fos and NGFI-A expression after periods of spontaneous wakefulness or sleep. We used in situ hybridization and immunocytochemistry to detect the corresponding mRNA and protein levels, respectively. A first group of rats (S-L) was sacrificed during the light hours at the end of a long period of sleep. A second group (W-L) was sacrificed under similar conditions, except that during the last half hour the animals had been spontaneously awake. A third group (W-D) was sacrificed during the dark hours after a long period of continuous wakefulness. We found that c-fos and NGFI-A expression in several brain areas was increased in W-L and W-D rats with respect to S-L rats. Some of these areas, including the cerebral cortex, basal ganglia, and colliculi, may have been activated by the increased sensory and motor activity associated with waking. The activation of other areas, such as the medial preoptic area of the hypothalamus and some brainstem nuclei, may be more directly related to sleep regulation. These results indicate that many regions showing an increased expression of immediate early genes after wakefulness induced by sleep deprivation are also activated by periods of spontaneous wakefulness.

Role of lateral preoptic area alpha-1 and alpha-2 adrenoceptors in sleep-wakefulness and body temperature regulation

The preoptic area is anatomically divided into medial and lateral portions and both are involved in the regulation of sleep-wakefulness and body temperature. We have recently reported the specific role of the adrenoceptors, present in the medial preoptic area, in the regulation of those functions. In this study an attempt was made to investigate the specific participation and contribution of the lateral preoptic area alpha-1 and alpha-2 adrenoceptors in the regulation of sleep-wakefulness and body temperature. Sleep-wakefulness and rectal temperature were simultaneously recorded in freely moving rats, both during day and night, under normal condition and after bilateral local microinjection of either agonist or antagonist of alpha-1 and alpha-2 adrenoceptors into the lateral preoptic area. The results suggest that the lateral preoptic area alpha-2 adrenoceptors are predominantly involved in the regulation of sleep-wakefulness whereas alpha-1 adrenoceptors are more effective in thermoregulation.

Sleep-inducing function of noradrenergic fibers in the medial preoptic area

The aim of the investigation was to find out the role of noradrenergic (NE) terminals of the medial preoptic area (mPOA), in the regulation of sleep-wakefulness. Studies were conducted on free-moving adult male rats with chronically implanted cannulae in the mPOA. Sleep-wakefulness was assessed on the basis of EEG, EMG, and EOG recordings along with behavioral observations. Lesioning of catecholamine terminals (with 6-hydroxydopamine) in the mPOA produced an increase in quiet wakefulness. Prevention of NE fiber destruction, by pretreating the rats with imipramine, prevented this effect. This demonstrated that the increased quiet wakefulness produced by 6-OHDA was the result of NE fiber destruction. Changes in sleep-wakefulness were also assessed after microinjection of NE into the mPOA, in normal and ventral noradrenergic bundle (VNA)-lesioned rats. NE administration induced sleep in VNA-lesioned rats, and arousal in normal rats. The findings suggest that the NE terminals in the mPOA, projecting via VNA, play a role in the induction of sleep.

Different types of norepinephrinergic receptors are involved in preoptic area mediated independent modulation of sleep-wakefulness and body temperature

The preoptic area is known to regulate sleep-wakefulness and body temperature. It was suggested earlier that though sleep-wakefulness and body temperature may affect each other, the preoptic area mediated influence on those two physiological phenomena is likely to be independent of alteration in each other. Since intrapreoptic area norepinephrine could modulate both those functions, study of that system was undertaken. It was hypothesized that since the preoptic area has different types of norepinephrinergic receptors (viz. alpha 1, alpha 2 and beta), independent modulation of those two functions was probably due to activation or inactivation of separate receptors. Hence, the effects of different agonist and antagonist of those receptors individually as well as in combination into the preoptic area were studied on those two functions in freely moving rats. The results suggest that norepinephrine induced preoptic area mediated influence on the body temperature is primarily regulated by the alpha 1 receptors while the sleep and wakefulness are regulated by alpha 2 and beta receptors, respectively. The finding should help in explaining several poorly understood observations reported earlier and it suggests that similar phenomena may possibly exist in other system involving other neurotransmitters as well.

Differential influence of medial and lateral preoptic areas on body temperature in conscious and unconscious rats

Since temperature sensitive neurons are unevenly distributed in the medial and the lateral preoptic areas, it was hypothesized that the two areas possibly would influence body temperature to a different extent. As alteration in sleep-wakefulness and body movement may affect the body temperature, experiments were conducted by reversible inactivation of those two areas, in freely moving (conscious) rats as well as in rats where changes in EEG and movement were restricted (unconscious). Results showed that the medial preoptic area is more effective in body temperature regulation. The study also revealed that the preoptic area mediated effect on body temperature regulation is not necessarily linked to simultaneous changes in sleep-wakefulness and alteration in the latter probably helps in maintaining the former within limit.

Medial preoptic area affects sleep-wakefulness independent of associated body temperature change in free moving rats

Sleep-wakefulness and body temperature may modulate each other. Though both the functions are influenced by the medial preoptic area, the mechanism of action was not clear. This study was aimed at finding out whether the tonic influence of the medial preoptic area on sleep-wakefulness was independent of or secondary to simultaneous change in body temperature. The effects of inactivation of the area by a long acting local anaesthetic, marcain, on those physiological functions were investigated during the night and the day in freely moving rats. Though medial preoptic area influenced sleep-wakefulness and body temperature simultaneously, the effect on the latter was prolonged. The results suggest that the influence on sleep-wakefulness is unlikely to be associated with simultaneously changing body temperature. However, this study fails to differentiate whether the observed effects were due to inactivation of the cell body or the fibers passing through the area.