Melanin concentrating hormone induces hippocampal acetylcholine release via the medial septum in rats

Melanin-Concentrating Hormone Is Associated With Delayed Neurocognitive Recovery in Older Adult Patients With Preoperative Sleep Disorders Undergoing Spinal Anesthesia

BACKGROUND

Aging and preoperative sleep disorders are the main risk factors affecting postoperative cognitive outcomes. However, the pathogenesis of delayed neurocognitive recovery after surgery remains ambiguous, and there is still a lack of potential biomarkers for delayed neurocognitive recovery in older adult patients with preoperative sleep disorders. Our study aimed to explore the relationship between melanin-concentrating hormone (MCH) and delayed neurocognitive recovery early after surgery in older adult patients with preoperative sleep disorders.

METHODS

In this monocentric prospective observational study, 156 older adult patients (aged 65 years or older) with preoperative sleep disorders undergoing elective total hip arthroplasty (THA) or total knee arthroplasty (TKA) were included at an academic medical center in Inner Mongolia, China, from October 2021 to November 2022, and all patients underwent spinal anesthesia. The Pittsburgh Sleep Quality Index (PSQI) was applied to assess the preoperative sleep quality of all patients, and preoperative sleep disorders were defined as a score of PSQI >5. We measured the levels of cerebrospinal fluid (CSF) MCH and plasma MCH of all patients. The primary outcome was delayed neurocognitive recovery early after surgery. All patients received cognitive function assessment through the Montreal Cognitive Assessment (MoCA) 1 day before and 7 days after surgery (postoperative day 7 [POD7]). Delayed neurocognitive recovery was defined as a score of POD7 MoCA <26. The potential confounders included variables with P < .2 in the univariate logistic analysis, as well as the important risk factors of delayed neurocognitive recovery reported in the literature. Multivariable logistic regression model based on the Enter method assessed the association of MCH and delayed neurocognitive recovery in older adult patients with preoperative sleep disorders.

RESULTS

Fifty-nine (37.8%) older adult patients with preoperative sleep disorders experienced delayed neurocognitive recovery at POD7. Increase in CSF MCH levels (odds ratio [OR] for an increase of 1 pg/mL = 1.16, 95% confidence interval [CI], 1.09-1.23, P < .001) and decrease in plasma MCH levels (OR for an increase of 1 pg/mL = 0.92, 95% CI, 0.86-0.98, P = .003) were associated with delayed neurocognitive recovery, after adjusting for age, sex, education, baseline MoCA scores, American Society of Anesthesiologists (ASA) grade, and coronary heart disease (CHD).

CONCLUSIONS

In older adult patients with preoperative sleep disorders, MCH is associated with the occurrence of delayed neurocognitive recovery after surgery. Preoperative testing of CSF MCH or plasma MCH may increase the likelihood of identifying the high-risk population for delayed neurocognitive recovery in older adult patients with preoperative sleep disorders.

Projections from LIM homeobox 6 (Lhx6) + zona incerta neurons to the cholinergic or monoaminergic nuclei of the rat

A recent report suggested that LIM homeobox 6 (Lhx6) + GABA-releasing neurons of the ventral zona incerta (VZI) promote sleep, particularly paradoxical sleep (PS). While their potential involvement in sleep still needs to be firmly confirmed, little is known about their specific input/output connections with widespread brain regions, including those involved in sleep. Thus, the present study was designed to examine whether Lhx6-expressing neurons (in parallel to intermingled MCH-expressing ones) may send efferent projections to cholinergic and/or monoaminergic nuclei from basal forebrain (BF) to brainstem (BS). Based on the present observations, the proportions of Lhx6+ neuronal projection to the BF and BS cholinergic nuclei over the total number of Lhx6+ VZI cells were approximately 5.9% and 6.9%, respectively. Likewise, the proportions of Lhx6+ neuronal projection to the dorsal raphe and locus coeruleus over the total number of Lhx6+ VZI cells were about 4.3% and 3.9%, respectively. In addition, Lhx6+ cells projecting to the cholinergic or monoaminergic nuclei were scattered along the entire dorsal-to-ventral extent of the VZI. Based on the present as well as our previous observations, it is suggested that Lhx6+ VZI neurons might play an important role in the regulation of PS, partly via the neural network involving the cholinergic as well as monoaminergic nuclei of the rat.

The melanin-concentrating hormone system as a target for the treatment of sleep disorders

Given the widespread prevalence of sleep disorders and their impacts on health, it is critical that researchers continue to identify and evaluate novel avenues of treatment. Recently the melanin-concentrating hormone (MCH) system has attracted commercial and scientific interest as a potential target of pharmacotherapy for sleep disorders. This interest emerges from basic scientific research demonstrating a role for MCH in regulating sleep, and particularly REM sleep. In addition to this role in sleep regulation, the MCH system and the MCH receptor 1 (MCHR1) have been implicated in a wide variety of other physiological functions and behaviors, including feeding/metabolism, reward, anxiety, depression, and learning. The basic research literature on sleep and the MCH system, and the history of MCH drug development, provide cause for both skepticism and cautious optimism about the prospects of MCH-targeting drugs in sleep disorders. Extensive efforts have focused on developing MCHR1 antagonists for use in obesity, however, few of these drugs have advanced to clinical trials, and none have gained regulatory approval. Additional basic research will be needed to fully characterize the MCH system’s role in sleep regulation, for example, to fully differentiate between MCH-neuron and peptide/receptor-mediated functions. Additionally, a number of issues relating to drug design will continue to pose a practical challenge for novel pharmacotherapies targeting the MCH system.

The prediction-error hypothesis of schizophrenia: new data point to circuit-specific changes in dopamine activity

Schizophrenia is a severe psychiatric disorder affecting 21 million people worldwide. People with schizophrenia suffer from symptoms including psychosis and delusions, apathy, anhedonia, and cognitive deficits. Strikingly, schizophrenia is characterised by a learning paradox involving difficulties learning from rewarding events, whilst simultaneously 'overlearning' about irrelevant or neutral information. While dysfunction in dopaminergic signalling has long been linked to the pathophysiology of schizophrenia, a cohesive framework that accounts for this learning paradox remains elusive. Recently, there has been an explosion of new research investigating how dopamine contributes to reinforcement learning, which illustrates that midbrain dopamine contributes in complex ways to reinforcement learning, not previously envisioned. This new data brings new possibilities for how dopamine signalling contributes to the symptomatology of schizophrenia. Building on recent work, we present a new neural framework for how we might envision specific dopamine circuits contributing to this learning paradox in schizophrenia in the context of models of reinforcement learning. Further, we discuss avenues of preclinical research with the use of cutting-edge neuroscience techniques where aspects of this model may be tested. Ultimately, it is hoped that this review will spur to action more research utilising specific reinforcement learning paradigms in preclinical models of schizophrenia, to reconcile seemingly disparate symptomatology and develop more efficient therapeutics.

In vivo uptake of a fluorescent conjugate of melanin-concentrating hormone in the rat brain

Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide synthesized by posterior hypothalamic and incerto-hypothalamic neurons that project throughout the central nervous system. The MCHergic system modulates several important functions such as feeding behavior, mood and sleep. MCH exerts its biological functions through interaction with the MCHR-1 receptor, the only functional receptor present in rodents. The internalization process of MCHR-1 triggered by MCH binding was described in vitro in non-neuronal heterologous systems with over-expression of MCHR-1. Reports of in vivo MCHR-1 internalization dynamics are scarce, however, this is an important process to explore based on the critical functions of the MCHergic system. We had previously determined that 60 min after intracerebroventricular (i.c.v.) microinjections of MCH conjugated with fluorophore rhodamine (R-MCH), the dorsal and median raphe nucleus presented R-MCH positive labeled neurons. In the present work, we further studied the in vivo uptake process focusing on the distribution and time-dependent pattern of R-MCH positive cells 10, 20 and 60 min (T10, T20 and T60, respectively) after i.c.v. microinjection of R-MCH. We also explored this uptake process to see whether it was receptor- and clathrin-dependent and examined the phenotype of R-MCH positive cells and their proximity to MCHergic fibers. We found a great number of R-MCH positive cells with high fluorescence intensity in the lateral septum, nucleus accumbens and hippocampus at T20 and T60 (but not at T10), while a lower number with low intensity was observed in the dorsal raphe nucleus. At T20, in rats pre-treated with a MCHR-1 antagonist (ATC-0175) or with phenylarsine oxide (PAO), a clathrin endocytosis inhibitor, a robust decrease (> 50 %) of R-MCH uptake occurred in these structures. The R-MCH positive cells were identified as neurons (NeuN positive, GFAP negative) and some MCHergic fibers run in the vicinities of them. We concluded that neurons localized at structures that were close to the ventricular surfaces could uptake R-MCH in vivo through a receptor-dependent and clathrin-mediated process. Our results support volume transmission of MCH through the cerebrospinal fluid to reach distant targets. Finally, we propose that R-MCH would be an effective tool to study MCH-uptake in vivo.

Neuropeptide glutamic acid-isoleucine (NEI)-induced paradoxical sleep in rats

Neuropeptideglutamic acid-isoleucine (NEI) as well as melanin concentrating hormone (MCH) is cleaved from the 165 amino acid protein, prepro-melanin concentrating hormone (prepro-MCH). Among many physiological roles of MCH, we demonstrated that intracerebroventricular (icv) injection of MCH induced increases in REM sleep episodes as well as in non REM sleep episodes. However, there are no studies on the effect of NEI on the sleep-wake cycle. As for the sites of action of MCH for induction of REM sleep, the ventrolateral periaqueductal gray (vlPAG) has been reported to be one of its site of action. Although MCH neurons contain NEI, GABA, MCH, and other neuropeptides, we do not know which transmitter(s) might induce REM sleep by acting on the vlPAG. Thus, we first examined the effect of icv injection of NEI on the sleep-wake cycle, and investigated how microinjection of either NEI, MCH, or GABA into the vlPAG affected REM sleep in rats. Icv injection of NEI (0.61μg/5μl: n=7) significantly increased the time spent in REM episodes compared to control (saline: 5μl; n=6). Microinjection of either NEI (61ng/0.2μl: n=7), MCH (100ng/0.2μl: n=6) or GABA (250mM/0.2μl: n=7) into the vlPAG significantly increased the time spent in REM episodes and the AUC. Precise hourly analysis of REM sleep also revealed that after those microinjections, NEI and MCH increased REM episodes at the latter phase, compared to GABA which increased REM episodes at the earlier phase. This result suggests that NEI and MCH may induce sustained REM sleep, while GABA may initiate REM sleep. In conclusion, our findings demonstrate that NEI, a cleaved peptide from the same precursor, prepro-MCH, as MCH, induce REM sleep at least in part through acting on the vlPAG.

Awake dynamics and brain-wide direct inputs of hypothalamic MCH and orexin networks

The lateral hypothalamus (LH) controls energy balance. LH melanin-concentrating-hormone (MCH) and orexin/hypocretin (OH) neurons mediate energy accumulation and expenditure, respectively. MCH cells promote memory and appropriate stimulus-reward associations; their inactivation disrupts energy-optimal behaviour and causes weight loss. However, MCH cell dynamics during wakefulness are unknown, leaving it unclear if they differentially participate in brain activity during sensory processing. By fiberoptic recordings from molecularly defined populations of LH neurons in awake freely moving mice, we show that MCH neurons generate conditional population bursts. This MCH cell activity correlates with novelty exploration, is inhibited by stress and is inversely predicted by OH cell activity. Furthermore, we obtain brain-wide maps of monosynaptic inputs to MCH and OH cells, and demonstrate optogenetically that VGAT neurons in the amygdala and bed nucleus of stria terminalis inhibit MCH cells. These data reveal cell-type-specific LH dynamics during sensory integration, and identify direct neural controllers of MCH neurons.

Hypothalamic neurons expressing melanin-concentrating-hormone (MCH) maintain body weight by orchestrating behaviour and metabolism, but little is known about their intrinsic regulation. Here, Gonzalez and colleagues reveal their behaviour-related dynamics during wakefulness, and map their brain-wide neural inputs.

Predictive models of glucose control: roles for glucose-sensing neurones

The brain can be viewed as a sophisticated control module for stabilizing blood glucose. A review of classical behavioural evidence indicates that central circuits add predictive (feedforward/anticipatory) control to the reactive (feedback/compensatory) control by peripheral organs. The brain/cephalic control is constructed and engaged, via associative learning, by sensory cues predicting energy intake or expenditure (e.g. sight, smell, taste, sound). This allows rapidly measurable sensory information (rather than slowly generated internal feedback signals, e.g. digested nutrients) to control food selection, glucose supply for fight-or-flight responses or preparedness for digestion/absorption. Predictive control is therefore useful for preventing large glucose fluctuations. We review emerging roles in predictive control of two classes of widely projecting hypothalamic neurones, orexin/hypocretin (ORX) and melanin-concentrating hormone (MCH) cells. Evidence is cited that ORX neurones (i) are activated by sensory cues (e.g. taste, sound), (ii) drive hepatic production, and muscle uptake, of glucose, via sympathetic nerves, (iii) stimulate wakefulness and exploration via global brain projections and (iv) are glucose-inhibited. MCH neurones are (i) glucose-excited, (ii) innervate learning and reward centres to promote synaptic plasticity, learning and memory and (iii) are critical for learning associations useful for predictive control (e.g. using taste to predict nutrient value of food). This evidence is unified into a model for predictive glucose control. During associative learning, inputs from some glucose-excited neurones may promote connections between the 'fast' senses and reward circuits, constructing neural shortcuts for efficient action selection. In turn, glucose-inhibited neurones may engage locomotion/exploration and coordinate the required fuel supply. Feedback inhibition of the latter neurones by glucose would ensure that glucose fluxes they stimulate (from liver, into muscle) are balanced. Estimating nutrient challenges from indirect sensory cues may become more difficult when the cues become complex and variable (e.g. like human foods today). Consequent errors of predictive glucose control may contribute to obesity and diabetes.

Anatomical organization of MCH connections with the pallidum and dorsal striatum in the rat

Neurons producing the melanin-concentrating hormone (MCH) are distributed in the posterior hypothalamus, but project massively throughout the forebrain. Many aspects regarding the anatomical organization of these projections are still obscure. The present study has two goals: first to characterize the topographical organization of neurons projecting into the cholinergic basal forebrain (globus pallidus, medial septal complex), and second to verify if MCH neurons may indirectly influence the dorsal striatum (caudoputamen) by innervating afferent sources to this structure. In the first series of experiments, the retrograde tracer fluorogold was injected into multiple sites in the pallidal and medial septal regions and the distribution of retrogradely labeled neurons were analyzed in the posterior lateral hypothalamus. In the second series of experiments, fluorogold was injected into the caudoputamen, and the innervation by MCH axons of retrogradely labeled cells was analyzed. Our results revealed that the MCH system is able to interact with the basal nuclei in several different ways. First, MCH neurons provide topographic inputs to the globus pallidus, medial septal complex, and substantia innominata. Second, striatal projecting neurons in the cortex, thalamus, and substantia nigra presumably receive only sparse inputs from MCH neurons. Third, the subthalamic nucleus is heavily innervated by MCH projections, thus, presumably serves as one important intermediate station to mediate MCH influence on other parts of the basal nuclei.

Different distributions of preproMCH and hypocretin/orexin in the forebrain of the pig (Sus scrofa domesticus)

Neurons producing melanin-concentrating hormone (MCH) or hypocretin/orexin (Hcrt) have been implicated in the sleep/wake cycle and feeding behavior. Sleep and feeding habits vary greatly among mammalian species, depending in part of the prey/predatory status of animals. However, the distribution of both peptides has been described in only a limited number of species. In this work, we describe the distribution of MCH neurons in the brain of the domestic pig. Using in situ hybridization and immunohistochemistry, their cell bodies are shown to be located in the posterior lateral hypothalamic area (LHA), as expected. They form a dense cluster ventro-lateral to the fornix while only scattered cells are present dorsal to this tract. By comparison, Hcrt cell bodies are located mainly dorsal to the fornix. Therefore, the two populations of neurons display complementary distributions in the posterior LHA. MCH projections are, as indicated by MCH-positive axons, very abundant in all cortical fields ventral to the rhinal sulcus, as well as in the lateral, basolateral and basomedial amygdala. In contrast, most of the isocortex is sparsely innervated. To conclude, the distribution of MCH cell bodies and projections shows some very specific features in the pig brain, that are clearly different of that described in the rat, mouse or human. In contrast, the Hcrt pattern seems more similar to that in these species, i.e. more conserved. These results suggest that the LHA anatomic organization shows some very significant interspecies differences, which may be related to the different behavioral repertoires of animals with regard to feeding and sleep/wake cycles.

Optogenetic identification of a rapid eye movement sleep modulatory circuit in the hypothalamus

Rapid-Eye Movement (REM) sleep correlates with neuronal activity in the brainstem, basal forebrain and lateral hypothalamus (LH). LH melanin-concentrating hormone (MCH)-expressing neurons are active during sleep, however, their action on REM sleep remains unclear. Using optogenetic tools in newly-generated Tg(Pmch-Cre) mice, we found that acute activation of MCH neurons (ChETA, SSFO) at the onset of REM sleep extended the duration of REM, but not non-REM sleep episode. In contrast, their acute silencing (eNpHR3.0, ArchT) reduced the frequency and amplitude of hippocampal theta rhythm, without affecting REM sleep duration. In vitro activation of MCH neuron terminals induced GABA_A-mediated inhibitory post-synaptic currents (IPSCs) in wake-promoting histaminergic neurons of the tuberomammillary nucleus (TMN), while in vivo activation of MCH neuron terminals in TMN or medial septum also prolonged REM sleep episodes. Collectively, these results suggest that activation of MCH neurons maintains REM sleep, possibly through inhibition of arousal circuits in the mammalian brain.