Luciana Benedetto

Microinjection of melanin concentrating hormone into the lateral preoptic area promotes non-REM sleep in the rat

The ventrolateral preoptic area (VLPO) has been recognized as one of the key structures responsible for the generation of non-REM (NREM) sleep. The melanin-concentrating hormone (MCH)-containing neurons, which are located in the lateral hypothalamus and incerto-hypothalamic area, project widely throughout the central nervous system and include projections to the VLPO. The MCH has been associated with the central regulation of feeding and energy homeostasis. In addition, recent findings strongly suggest that the MCHergic system promotes sleep. The aim of the present study was to determine if MCH generates sleep by regulating VLPO neuronal activity. To this purpose, we characterized the effect of unilateral and bilateral microinjections of MCH into the VLPO on sleep and wakefulness in the rat. Unilateral administration of MCH into the VLPO and adjacent dorsal preoptic area did not modify sleep. On the contrary, bilateral microinjections of MCH (100 ng) into these areas significantly increased light sleep (LS, 39.2±4.8 vs. 21.6±2.5 min, P<0.05) and total NREM sleep (142.4±23.2 vs. 86.5±10.5 min, P<0.05) compared to control (saline) microinjections. No effect was observed on REM sleep. We conclude that MCH administration into the VLPO and adjacent dorsal lateral preoptic area promotes the generation of NREM sleep.

Melanin-Concentrating Hormone (MCH): Role in REM Sleep and Depression

The melanin-concentrating hormone (MCH) is a peptidergic neuromodulator synthesized by neurons of the lateral sector of the posterior hypothalamus and zona incerta. MCHergic neurons project throughout the central nervous system, including areas such as the dorsal (DR) and median (MR) raphe nuclei, which are involved in the control of sleep and mood. Major Depression (MD) is a prevalent psychiatric disease diagnosed on the basis of symptomatic criteria such as sadness or melancholia, guilt, irritability, and anhedonia. A short REM sleep latency (i.e., the interval between sleep onset and the first REM sleep period), as well as an increase in the duration of REM sleep and the density of rapid-eye movements during this state, are considered important biological markers of depression. The fact that the greatest firing rate of MCHergic neurons occurs during REM sleep and that optogenetic stimulation of these neurons induces sleep, tends to indicate that MCH plays a critical role in the generation and maintenance of sleep, especially REM sleep. In addition, the acute microinjection of MCH into the DR promotes REM sleep, while immunoneutralization of this peptide within the DR decreases the time spent in this state. Moreover, microinjections of MCH into either the DR or MR promote a depressive-like behavior. In the DR, this effect is prevented by the systemic administration of antidepressant drugs (either fluoxetine or nortriptyline) and blocked by the intra-DR microinjection of a specific MCH receptor antagonist. Using electrophysiological and microdialysis techniques we demonstrated also that MCH decreases the activity of serotonergic DR neurons. Therefore, there are substantive experimental data suggesting that the MCHergic system plays a role in the control of REM sleep and, in addition, in the pathophysiology of depression. Consequently, in the present report, we summarize and evaluate the current data and hypotheses related to the role of MCH in REM sleep and MD.

State-dependent pattern of Fos protein expression in regionally-specific sites within the preoptic area of the cat

Clinical and experimental data have shown that the preoptic area of the hypothalamus (POA) is involved in the generation and maintenance of NREM sleep. However, the activity of specific populations of POA neurons during REM sleep, NREM sleep and different waking conditions is still not firmly established. Consequently, we performed a quantitative, regionally-specific analysis of the Fos immunoreactivity of neurons in the POA of the cat during NREM sleep and REM sleep induced by microinjections of carbachol into the nucleus pontis oralis (REMc), as well as during quiet and alert wakefulness. We observed that while the total number of Fos immunoreactive neurons in the POA did not change as a function of these behavioral states, state-specific differences in neuronal activity were detected in restricted regions of the POA. An increase in the number of Fos+ neurons was observed in the rostral tip of the suprachiasmatic nucleus (SCN) during NREM (83.4+/-25.6) compared to quiet wakefulness (5.1+/-1.3, p<0.05) but not with the other behavioral states. In the median preoptic nucleus (MnPN), the number of Fos immunoreactive neurons was greater during NREM sleep (39.5+/-6.1) compared with quiet wakefulness (13.5+/-1.4, p<0.05) and REMc (16.2+/-2.0, p<0.05). State-specific Fos immunoreactive neurons were not observed in the ventro-lateral preoptic nucleus (VLPO). Finally, there was no significant increase in the number of Fos+ neurons during REMc in any of the subregions of the POA. In conclusion, within the POA, a selective neuronal activation during NREM sleep was found only in the MnPN. In addition, our data suggest a potential role of the SCN in NREM sleep. Finally, based on the distribution of Fos+ neurons in the entire POA, we conclude that the neuronal network involved in the regulation of NREM sleep is dispersed and intermingled with waking-related neurons.

Melanin-concentrating hormone in the medial preoptic area reduces active components of maternal behavior in rats.

Melanin-concentrating hormone (MCH) is an inhibitory neuropeptide mainly synthesized in neurons of the lateral hypothalamus and incerto-hypothalamic area of mammals that has been implicated in behavioral functions related to motivation. During lactation, this neuropeptide is also expressed in the medial preoptic area (mPOA), a key region of the maternal behavior circuitry. Notably, whereas MCH expression in the mPOA progressively increases during lactation, maternal behavior naturally declines, suggesting that elevated MCHergic activity in the mPOA inhibit maternal behavior in the late postpartum period. To explore this idea, we assessed the maternal behavior of early postpartum females following bilateral microinfusions of either MCH (50 and 100 ng/0.2 μl/side) or the same volume of vehicle into the mPOA. As expected, females receiving 100 ng MCH into the mPOA exhibited significant deficits in the active components of maternal behavior, including retrieving and nest building. In contrast, nursing, as well as other behaviors, including locomotor activity, exploration, and anxiety-like behavior, were not affected by intra-mPOA MCH infusion. The present results, together with previous findings showing elevated expression of this neuropeptide toward the end of the postpartum period, suggest that modulation of mPOA function by MCH may contribute to the weaning of maternal responsiveness characteristic of the late postpartum period.

GABAergic processes within the median preoptic nucleus promote NREM sleep

GABAergic mechanisms in the preoptic region of the hypothalamus (POA) have been implicated in the generation and maintenance of NREM (quiet) sleep. We recently reported that neurons in the median peptic nucleus (MnPN) in the POA of the cat are selectively activated during NREM sleep. In the present study, we explored the hypothesis that NREM sleep is controlled by GABAergic mechanisms within the MnPN. Consequently, adult cats were utilized to determine GABA immunorreactivity within the MnPN and to examine the effects on sleep of the microinjection of a GABA(A) agonist (muscimol) and a GABA(A) antagonist (bicuculline) into this area. GABAergic neurons were present throughout the MnPN. Compared with control microinjections, after the application of muscimol, the time spent in NREM sleep (59.8±7.5 min) and REM sleep (6.9±4.7 min) decreased compared with control microinjections (103.8±5.2 and 20.2±4.3 min, respectively; P<0.005). In contrast, bicuculline microinjections increased only NREM sleep time (103.0±23.0 vs 77.7±23.7 min; P<0.05). These results demonstrate that GABAergic processes within the MnPN are involved in the generation and maintenance of sleep, especially NREM sleep.

Hypocretinergic system in the medial preoptic area promotes maternal behavior in lactating rats

Hypocretin-1 and 2 (HCRT-1 and HCRT-2, respectively) are neuropeptides synthesized by neurons located in the postero-lateral hypothalamus, whose projections are widely distributed throughout the brain. The hypocretinergic (HCRTergic) system has been associated with the generation and maintenance of wakefulness, as well as with the promotion of motivated behaviors. In lactating rats, intra-cerebroventricular HCRT-1 administration stimulates maternal behavior, whilst lactation per se increases the expression of HCRT type 1 receptor (HCRT-R1). Due to the fact that HCRTergic receptors are expressed in the medial preoptic area (mPOA), a region critically involved in maternal behavior, we hypothesize that HCRT-1 promotes maternal behavior acting on this region. In order to evaluate this hypothesis, we assessed the maternal behavior of lactating rats following microinjections of HCRT-1 (10 or 100μM) and the selective HCRT-R1 antagonist SB-334867 (250μM) into the mPOA, during the first and second postpartum weeks. While intra-mPOA microinjections of HCRT-1 (100μM) increased corporal pup licking during the second postpartum week, the blockade of HCRT-R1 significantly decreased active components of maternal behavior, such as retrievals, corporal and ano-genital lickings, and increased the time spent in nursing postures in both postpartum periods. We conclude that HCRTergic system in the mPOA may stimulate maternal behavior, suggesting that endogenous HCRT-1 is necessary for the natural display of this behavior.

Power and coherence of cortical High Frequency Oscillations during wakefulness and sleep

Recently, a novel type of fast cortical oscillatory activity that occurs between 110 and 160 Hz (high‐frequency oscillations (HFO)) was described. HFO are modulated by the theta rhythm in hippocampus and neocortex during active wakefulness and REM sleep. As theta‐HFO coupling increases during REM, a role for HFO in memory consolidation has been proposed. However, global properties such as the cortex‐wide topographic distribution and the cortico‐cortical coherence remain unknown. In this study, we recorded the electroencephalogram during sleep and wakefulness in the rat and analyzed the spatial extent of the HFO band power and coherence. We confirmed that the HFO amplitude is phase‐locked to theta oscillations and is modified by behavioral states. During active wakefulness, HFO power was relatively higher in the neocortex and olfactory bulb compared to sleep. HFO power decreased during non‐REM and had an intermediate level during REM sleep. Furthermore, coherence was larger during active wakefulness than non‐REM, while REM showed a complex pattern in which coherence increased only in intra and decreased in inter‐hemispheric combination of electrodes. This coherence pattern is different from gamma (30–100 Hz) coherence, which is reduced during REM sleep. This data show an important HFO cortico‐cortical dialog during active wakefulness even when the level of theta comodulation is lower than in REM. In contrast, during REM, this dialog is highly modulated by theta and restricted to intra‐hemispheric medial‐posterior cortical regions. Further studies combining behavior, electrophysiology and new analytical tools are needed to plunge deeper into the functional significance of the HFO.

Microinjection of the dopamine D2-receptor antagonist Raclopride into the medial preoptic area reduces REM sleep in lactating rats

The medial preoptic area (mPOA) is a brain structure classically related to both non-REM (NREM) sleep and maternal behavior. Although the dopaminergic system is known to play a role in the control of the states of sleep and wakefulness, its effects within the mPOA on sleep are still not clear. Microinjection of the dopamine D2 receptor antagonist Raclopride into the mPOA has been shown to promote nursing postures in lactating dams with no effects on active maternal behavior. We hypothesized that the facilitation of nursing postures may be also associated with the promotion of NREM sleep. In order to test the hypothesis, Raclopride was microinjected into the mPOA and maternal behavior and sleep were assessed in lactating rats. The changes observed included a reduction of the latency to start nursing and an increase of the time to reunite the entire litter. Contrary to our hypothesis, NREM sleep was not affected by Raclopride. On the other hand, REM sleep and its transitional stage from NREM sleep, were significantly reduced by this pharmacological agent. These data suggest that dopamine D2 receptors within the mPOA are involved in the transition from NREM to REM sleep.

Functional Interactions Between MCHergic and Dopaminergic Neurons: Role in the Control of Wakefulness and Sleep

Dopamine (DA) plays an important role in emotional arousal. In addition, recent studies have demonstrated that there is an increase in DAergic activity both in the nucleus accumbens and prefrontal cortex during rapid-eye-movement (REM) sleep; this DAergic activity has been involved in the generation of dreams. The melanin-concentrating hormone (MCH) is a peptide with neuromodulatory functions synthesized by neurons located in the postero-lateral hypothalamus and incerto-hypothalamic area. MCHergic neurons project throughout the central nervous system, including the substantia nigra pars compacta and ventral tegmental area, where DAergic neurons are located. MCH controls energy homeostasis, with a main role in energy conservation. In agreement with the energy-conserving function of sleep, MCH promotes sleep. In comparison to wakefulness (W), MCHergic neurons increase their firing rate during non-REM (NREM) sleep and reach their maximal rate during REM sleep. Although there is almost no direct information regarding the interaction between MCHergic and DAergic neurons in the control of W and sleep, indirect evidence strongly suggests an important interaction between both systems in the control of these behavioral states. MCHergic fibers and receptors are present in the DAergic mesocorticolimbic system, a key center for activation and motivation. Furthermore, the absence of MCH leads to an increase in DA release and the up-regulation of DA receptors that is known to facilitate the generation of W. On the other hand, DA decreases the release of MCH; this fact would also promote W. While both systems seem to have opposite effects in the generation of W, they appear to have complementary roles in the regulation of different aspects of REM sleep. In conclusion, although more experimental data is needed, available evidence tends to indicate that functional interactions between the MCHergic and DAergic systems play an important role in the control of behavioral states.

Melanin-Concentrating Hormone in Medical Conditions

In the last decade, there was an impressive advance in the knowledge of the anatomy and physiology of the melanin-concentrating hormone (MCH) neuronal system. However, its role in pathology is still not clear. MCH is a peptidergic neuromodulator synthesized by neurons whose somas are mainly located in the posterolateral hypothalamus and incerto-hypothalamic area. The MCHergic neurons project throughout the central nervous system innervating areas involved in several physiological functions. MCH exerts its biological effects acting through two metabotropic receptors. There are substantive experimental data suggesting that the MCHergic system is involved in the control of energy homeostasis, mood, and sleep. In the present study, we summarize data related to the role of MCH in these functions, as well as preclinical and clinical evidences showing that dysfunction of the MCHergic system might be involved in several medical disorders including obesity, central hypersomnia, mood disorders, and ciliopathies.