Lateral Hypothalamic Control of the Ventral Tegmental Area: Reward Evaluation and the Driving of Motivated Behavior

Control of sodium appetite by hindbrain aldosterone-sensitive neurons

Mineralocorticoids play a key role in hydromineral balance by regulating sodium retention and potassium wasting. Through favoring sodium, mineralocorticoids can cause hypertension from fluid overload under conditions of hyperaldosteronism, such as aldosterone-secreting tumors. An often-overlooked mechanism by which aldosterone functions to increase sodium is through stimulation of salt appetite. To drive sodium intake, aldosterone targets neurons in the hindbrain which uniquely express 11β-hydroxysteroid dehydrogenase type 2 (HSD2). This enzyme is a necessary precondition for aldosterone-sensing cells as it metabolizes glucocorticoids - preventing their activation of the mineralocorticoid receptor. In this review, we will consider the role of hindbrain HSD2 neurons in regulating sodium appetite by discussing HSD2 expression in the brain, regulation of hindbrain HSD2 neuron activity, and the circuitry mediating the effects of these aldosterone-sensitive neurons. Reducing the activity of hindbrain HSD2 neurons may be a viable strategy to reduce sodium intake and cardiovascular risk, particularly for conditions of hyperaldosteronism.

Acupuncture in the treatment of cocaine addiction: how does it work?

Cocaine is a frequently abused and highly addictive drug that damages brain health and imposes substantial social and economic costs. Acupuncture has been used in the treatment of cocaine addiction and has been shown to improve abnormal mental and motor states. This article mainly focuses on the neurobiological mechanisms involving the central nervous system (CNS) and peripheral nervous system (PNS) that underlie the effects of acupuncture in the treatment of cocaine addiction. The central dopamine system is a key player in acupuncture treatment of cocaine addiction; the ventral tegmental area (VTA)-nucleus accumbens (NAc) signaling pathway, which has a modulatory influence on behavior and psychology after chronic use of cocaine, is a significant target of acupuncture action. Moreover, acupuncture alleviates cocaine-induced seizures or acute psychomotor responses through the paraventricular thalamus and the lateral habenula (LHb)-rostromedial tegmental (RMTg) nucleus circuits. The data suggest that acupuncture can impact various cocaine-induced issues via stimulation of diverse brain areas; nevertheless, the interconnection of these brain regions and the PNS mechanisms involved remain unknown. In this review, we also discuss the effects of specific acupuncture protocols on cocaine addiction and note that variations in needling modalities, current intensities and traditional acupuncture point locations have led to different experimental results. Therefore, standardized acupuncture protocols (with respect to stimulation methods, point locations and number of sessions) may become particularly important in future studies.

Imaging of brain electric field networks

We present a method for direct imaging of the electric field networks in the human brain from electroencephalography (EEG) data with much higher temporal and spatial resolution than functional MRI (fMRI), without the concomitant distortions. The method is validated using simultaneous EEG/fMRI data in healthy subjects, intracranial EEG data in epilepsy patients, and in a direct comparison with standard EEG analysis in a well-established attention paradigm. The method is then demonstrated on a very large cohort of subjects performing a standard gambling task designed to activate the brain's 'reward circuit'. The technique uses the output from standard EEG systems and thus has potential for immediate benefit to a broad range of important basic scientific and clinical questions concerning brain electrical activity, but also provides an inexpensive and portable alternative to function MRI (fMRI).

Changes in taste palatability across the estrous cycle are modulated by hypothalamic estradiol signaling

Food intake varies across the stages of a rat's estrous cycle. It is reasonable to hypothesize that this cyclic fluctuation in consumption reflects an impact of hormones on taste palatability/preference, but evidence for this hypothesis has been mixed, and critical within-subject experiments in which rats sample multiple tastes during each of the four main estrous phases (metestrus, diestrus, proestrus, and estrus) have been scarce. Here, we assayed licking for pleasant (sucrose, NaCl, saccharin) and aversive (quinine-HCl, citric acid) tastes each day for 5-10 days while tracking rats' estrous cycles through vaginal cytology. Initial analyses confirmed the previously-described increased consumption of pleasant stimuli 24-48 hours following the time of high estradiol. A closer look, however, revealed this effect to reflect a general magnification of palatability-higher than normal preferences for pleasant tastes and lower than normal preferences for aversive tastes-during metestrus. We hypothesized that this phenomenon might be related to estradiol processing in the lateral hypothalamus (LH), and tested this hypothesis by inhibiting LH estrogen receptor activity with ICI 182,780 during tasting. Control infusions replicated the metestrus magnification of palatability pattern; ICI infusions blocked this effect as predicted, but failed to render preferences "cycle free," instead delaying the palatability magnification until diestrus. Clearly, estrous phase mediates details of taste palatability in a manner involving hypothalamic actions of estradiol; further work will be needed to explain the lack of a flat response across the cycle with hypothalamic estradiol binding inhibited, a result which perhaps suggests dynamic interplay between brain regions or hormones.

Significance Statement

Consummatory behaviors are impacted by many variables, including naturally circulating hormones. While it is clear that consumption is particularly high during the stages following the high-estradiol stage of the rodent's estrous (and human menstrual) cycle, it is as of yet unclear whether this phenomenon reflects cycle stage-specific palatability (i.e., whether pleasant tastes are particularly delicious, and aversive tastes particularly disgusting, at particular phases). Here we show that palatability is indeed modulated by estrous phase, and that this effect is governed, at least in part, by the action of estradiol within the lateral hypothalamus. These findings shed light on the mechanisms underlying the adverse impact on human welfare due to irregularities observed across the otherwise cyclic menstrual process.

The cognitive (lateral) hypothalamus

Despite the physiological complexity of the hypothalamus, its role is typically restricted to initiation or cessation of innate behaviors. For example, theories of lateral hypothalamus argue that it is a switch to turn feeding 'on' and 'off' as dictated by higher-order structures that render when feeding is appropriate. However, recent data demonstrate that the lateral hypothalamus is critical for learning about food-related cues. Furthermore, the lateral hypothalamus opposes learning about information that is neutral or distal to food. This reveals the lateral hypothalamus as a unique arbitrator of learning capable of shifting behavior toward or away from important events. This has relevance for disorders characterized by changes in this balance, including addiction and schizophrenia. Generally, this suggests that hypothalamic function is more complex than increasing or decreasing innate behaviors.

A hypothalamus-habenula circuit regulates psychomotor responses induced by cocaine

Administration of cocaine increases synaptic dopamine levels by blocking dopamine reuptake and leads to increased locomotor activity and compulsive drug-seeking behaviour. It has been suggested that the lateral hypothalamus (LH) or lateral habenula (LHb) is involved in drug-seeking behaviours. To explore the role of the LH and the LHb in cocaine-induced psychomotor responses, we tested whether modulation of the LH or the LH-LHb circuit affects cocaine-induced locomotion. Cocaine-induced locomotor activity and dopamine release were suppressed by the activation of the LH with 2-[2,6-difluoro-4-[[2-[(phenylsulfonyl)amino]ethyl]thio]phenoxy]acetamide (PEPA), an AMPA receptor agonist. When the LH was inhibited by microinjection of a GABA receptor agonists mixture prior to cocaine injection, the cocaine's effects were enhanced. Furthermore, optogenetic activation of the LH-LHb circuit attenuated the cocaine-induced locomotion, while optogenetic inhibition of the LH-LHb circuit increased it. In vivo extracellular recording found that the LH sent a glutamatergic projection to the LHb. These findings suggest that the LH glutamatergic projection to the LHb plays an active role in the modulation of cocaine-induced psychomotor responses.

Cerebellar Prediction and Feeding Behaviour

Given the importance of the cerebellum in controlling movements, it might be expected that its main role in eating would be the control of motor elements such as chewing and swallowing. Whilst such functions are clearly important, there is more to eating than these actions, and more to the cerebellum than motor control. This review will present evidence that the cerebellum contributes to homeostatic, motor, rewarding and affective aspects of food consumption.Prediction and feedback underlie many elements of eating, as food consumption is influenced by expectation. For example, circadian clocks cause hunger in anticipation of a meal, and food consumption causes feedback signals which induce satiety. Similarly, the sight and smell of food generate an expectation of what that food will taste like, and its actual taste will generate an internal reward value which will be compared to that expectation. Cerebellar learning is widely thought to involve feed-forward predictions to compare expected outcomes to sensory feedback. We therefore propose that the overarching role of the cerebellum in eating is to respond to prediction errors arising across the homeostatic, motor, cognitive, and affective domains.

The Validation and Psychometric Properties of the Gaming Instinctual Motivation Scale

Being able to quantify gaming motivation in a valid, systematic way has important implications for game designers and gaming user experience researchers. In the present study, we aimed to develop and validate a 30-item Gaming Instinctual Motivation Scale (GIMS) based on Dillon's 6-11 Framework on instinctual gaming motivation and Lazzaro's gaming experience model. To validate the scale, we recruited 194 regular gamers (Mage = 22.70 years old, SD = 4.38) to complete the GIMS based on their general gaming experience and their experience playing role-laying games (RPGs), first-person shooters (FPSs), real-time strategy, puzzle, and action games. We used a cross-validation approach and performed exploratory factor analysis and confirmatory factor analysis to test the structure of the scale and the reliability and validity of the scale, respectively. The final version of the GIMS had a one-dimensional structure with 15 items. It also had good construct validity, χ2 (N = 117, df = 86) = 126.28, p = 0.003, CFI = 0.93, TLI = 0.92, and RMSEA = 0.064 (90% CI [0.04, 0.09]), and reliability (CR = 0.89), and an acceptable convergent validity (AVE = 0.35). The one-dimensional structure was generalizable to RPG and FPS games, demonstrating the applicability of the scale to these two gaming genres. Higher scores on the GIMS were also associated with a greater intention to play games.

Restoring the firing activity of ventral tegmental area neurons by lateral hypothalamic deep brain stimulation following morphine administration in rats: LH DBS and the spiking activity of VTA neurons

We have previously shown that high-frequency deep brain stimulation (DBS) of the lateral hypothalamus (LH) compromises morphine-induced addiction-like behavior in rats. The exact mechanism underlying this effect is not known. Here, we investigated the assumption that DBS in the LH influences the firing activity of neurons in the ventral tegmental area (VTA). To that end, male Wistar rats received morphine (5 mg/kg; s.c.) for three days and underwent extracellular single unit recording under general anesthesia one day later. During the recording, the rats received an intraoperative injection of morphine (5 mg/kg; s.c.) plus DBS in the LH (130 Hz pulse frequency, 150 μA amplitude, and 100 μs pulse width). One group of animals also received preoperative DBS after each morphine injection before the recording. The spiking frequency of VTA neurons was measured at three successive phases: (1) baseline (5-15 min); (2) DBS-on (morphine + DBS for 30 min); and (3) After-DBS (over 30 min after termination of DBS). Results showed that morphine suppressed the firing activity of a large population of non-DA neurons, whereas it activated most DA neurons. Intraoperative DBS reversed morphine suppression of non-DA firing, but did not alter the excitatory effect of morphine on DA neurons firing. With repeated preoperative application of DBS, non-DA neurons returned to the morphine-induced suppressive state, but DA neurons released from the excitatory effect of morphine. It is concluded that the development of morphine reward is associated with a hypoactivity of VTA non-DA neurons and a hyperactivity of DA neurons, and that DBS modulation of the spiking activity may contribute to the blockade of morphine addiction-like behavior.

Rewarding-unrewarding prediction signals under a bivalent context in the primate lateral hypothalamus

Animals can expect rewards under equivocal situations. The lateral hypothalamus (LH) is thought to process motivational information by producing valence signals of reward and punishment. Despite rich studies using rodents and non-human primates, these signals have been assessed separately in appetitive and aversive contexts; therefore, it remains unclear what information the LH encodes in equivocal situations. To address this issue, macaque monkeys were conditioned under a bivalent context in which reward and punishment were probabilistically delivered, in addition to appetitive and aversive contexts. The monkeys increased approaching behavior similarly in the bivalent and appetitive contexts as the reward probability increased. They increased avoiding behavior under the bivalent and aversive contexts as the punishment probability increased, but the mean frequency was lower under the bivalent context than under the aversive context. The population activity correlated with these mean behaviors. Moreover, the LH produced fine prediction signals of reward expectation, uncertainty, and predictability consistently in the bivalent and appetitive contexts by recruiting context-independent and context-dependent subpopulations of neurons, while it less produced punishment signals in the aversive and bivalent contexts. Further, neural ensembles encoded context information and "rewarding-unrewarding" and "reward-punishment" valence. These signals may motivate individuals robustly in equivocal environments.

Net gain and loss: influence of natural rewards and drugs of abuse on perineuronal nets

Overindulgence, excessive consumption, and a pattern of compulsive use of natural rewards, such as certain foods or drugs of abuse, may result in the development of obesity or substance use disorder, respectively. Natural rewards and drugs of abuse can trigger similar changes in the neurobiological substrates that drive food- and drug-seeking behaviors. This review examines the impact natural rewards and drugs of abuse have on perineuronal nets (PNNs). PNNs are specialized extracellular matrix structures that ensheathe certain neurons during development over the critical period to provide synaptic stabilization and a protective microenvironment for the cells they surround. This review also analyzes how natural rewards and drugs of abuse impact the density and maturation of PNNs within reward-associated circuitry of the brain, which may contribute to maladaptive food- and drug-seeking behaviors. Finally, we evaluate the relatively few studies that have degraded PNNs to perturb reward-seeking behaviors. Taken together, this review sheds light on the complex way PNNs are regulated by natural rewards and drugs and highlights a need for future studies to delineate the molecular mechanisms that underlie the modification and maintenance of PNNs following exposure to rewarding stimuli.

Sleep-mediated regulation of reward circuits: implications in substance use disorders

Our modern society suffers from both pervasive sleep loss and substance abuse-what may be the indications for sleep on substance use disorders (SUDs), and could sleep contribute to the individual variations in SUDs? Decades of research in sleep as well as in motivated behaviors have laid the foundation for us to begin to answer these questions. This review is intended to critically summarize the circuit, cellular, and molecular mechanisms by which sleep influences reward function, and to reveal critical challenges for future studies. The review also suggests that improving sleep quality may serve as complementary therapeutics for treating SUDs, and that formulating sleep metrics may be useful for predicting individual susceptibility to SUDs and other reward-associated psychiatric diseases.

Rapid Eye Movement Sleep Engages Melanin-Concentrating Hormone Neurons to Reduce Cocaine Seeking

BACKGROUND

Persistent sleep disruptions following withdrawal from abused drugs may hold keys to battle drug relapse. It is posited that there may be sleep signatures that predict relapse propensity, identifying which may open new avenues for treating substance use disorders.

METHODS

We trained male rats (approximately postnatal day 56) to self-administer cocaine. After long-term drug withdrawal (approximately postnatal day 100), we examined the correlations between the intensity of cocaine seeking and key sleep features. To test for causal relationships, we then used behavioral, chemogenetic, or optogenetic methods to selectively increase rapid eye movement sleep (REMS) and measured behavioral and electrophysiological outcomes to probe for cellular and circuit mechanisms underlying REMS-mediated regulation of cocaine seeking.

RESULTS

A selective set of REMS features was preferentially associated with the intensity of cue-induced cocaine seeking after drug withdrawal. Moreover, selectively increasing REMS time and continuity by environmental warming attenuated a withdrawal time-dependent intensification of cocaine seeking, or incubation of cocaine craving, suggesting that REMS may benefit withdrawal. Warming increased the activity of lateral hypothalamic melanin-concentrating hormone (MCH) neurons selectively during prolonged REMS episodes and counteracted cocaine-induced synaptic accumulation of calcium-permeable AMPA receptors in the nucleus accumbens-a critical substrate for incubation. Finally, the warming effects were partly mimicked by chemogenetic or optogenetic stimulations of MCH neurons during sleep, or intra-accumbens infusions of MCH peptide during the rat's inactive phase.

CONCLUSIONS

REMS may encode individual vulnerability to relapse, and MCH neuron activities can be selectively targeted during REMS to reduce drug relapse.

Distinct Encoding of Reward and Aversion by Peptidergic BNST Inputs to the VTA

Neuropeptides play an important role in modulating mesolimbic system function. However, while synaptic inputs to the ventral tegmental area (VTA) have been extensively mapped, the sources of many neuropeptides are not well resolved. Here, we mapped the anatomical locations of three neuropeptide inputs to the VTA: neurotensin (NTS), corticotrophin releasing factor (CRF), and neurokinin B (NkB). Among numerous labeled inputs we identified the bed nucleus of the stria terminalis (BNST) as a major source of all three peptides, containing similar numbers of NTS, CRF, and NkB VTA projection neurons. Approximately 50% of BNST to VTA inputs co-expressed two or more of the peptides examined. Consistent with this expression pattern, analysis of calcium dynamics in the terminals of these inputs in the VTA revealed both common and distinct patterns of activation during appetitive and aversive conditioning. These data demonstrate additional diversification of the mesolimbic dopamine system through partially overlapping neuropeptidergic inputs.

Inactivation of the Lateral Hypothalamus Attenuates Methamphetamine-Induced Conditioned Place Preference through Regulation of Kcnq3 Expression

Repeated administration of methylamphetamine (MA) induces MA addiction, which is featured by awfully unpleasant physical and emotional experiences after drug use is terminated. Neurophysiological studies show that the lateral hypothalamus (LH) is involved in reward development and addictive behaviors. Here, we show that repeated administration of MA activates the expression of c-Fos in LH neurons responding to conditioned place preference (CPP). Chemogenetic inhibition of the LH can disrupt the addiction behavior, demonstrating that the LH plays an important role in MA-induced reward processing. Critically, MA remodels the neurons of LH synaptic plasticity, increases intracellular calcium level, and enhances spontaneous current and evoked potentials of neurons compared to the saline group. Furthermore, overexpression of the potassium voltage-gated channel subfamily Q member 3 (Kcnq3) expression can reverse the CPP score and alleviate the occurrence of addictive behaviors. Together, these results unravel a new neurobiological mechanism underlying the MA-induced addiction in the lateral hypothalamus, which could pave the way toward new and effective interventions for this addiction disease.

Racing and Pacing in the Reward System: A Multi-Clock Circadian Control Over Dopaminergic Signalling

Level of motivation, responsiveness to rewards and punishment, invigoration of exploratory behaviours, and motor performance are subject to daily fluctuations that emerge from circadian rhythms in neuronal activity of the midbrain’s dopaminergic system. While endogenous circadian rhythms are weak in the ventral tegmental area and substantia nigra pars compacta, daily changes in expression of core clock genes, ion channels, neurotransmitter receptors, dopamine-synthesising enzymes, and dopamine transporters, accompanied by changes in electrical activity, are readily observed in these nuclei. These processes cause dopamine levels released in structures innervated by midbrain dopaminergic neurons (e.g., the striatum) to oscillate in a circadian fashion. Additionally, growing evidence show that the master circadian clock located in the suprachiasmatic nucleus of the hypothalamus (SCN) rhythmically influences the activity of the dopaminergic system through various intermediate targets. Thus, circadian changes in the activity of the dopaminergic system and concomitant dopamine release observed on a daily scale are likely to be generated both intrinsically and entrained by the master clock. Previous studies have shown that the information about the value and salience of stimuli perceived by the animal is encoded in the neuronal activity of brain structures innervating midbrain dopaminergic centres. Some of these structures themselves are relatively autonomous oscillators, while others exhibit a weak endogenous circadian rhythm synchronised by the SCN. Here, we place the dopaminergic system as a hub in the extensive network of extra-SCN circadian oscillators and discuss the possible consequences of its daily entrainment for animal physiology and behaviour.

Anatomy and Function of Ventral Tegmental Area Glutamate Neurons

The ventral tegmental area (VTA) is well known for regulating reward consumption, learning, memory, and addiction behaviors through mediating dopamine (DA) release in downstream regions. Other than DA neurons, the VTA is known to be heterogeneous and contains other types of neurons, including glutamate neurons. In contrast to the well-studied and established functions of DA neurons, the role of VTA glutamate neurons is understudied, presumably due to their relatively small quantity and a lack of effective means to study them. Yet, emerging studies have begun to reveal the importance of glutamate release from VTA neurons in regulating diverse behavioral repertoire through a complex intra-VTA and long-range neuronal network. In this review, we summarize the features of VTA glutamate neurons from three perspectives, namely, cellular properties, neural connections, and behavioral functions. Delineation of VTA glutamatergic pathways and their interactions with VTA DA neurons in regulating behaviors may reveal previously unappreciated functions of the VTA in other physiological processes.

Utility of an experimental medicine model to evaluate efficacy, side-effects and mechanism of action of novel treatments for obesity and binge-eating disorder

Obesity and Binge Eating Disorder (BED) are prevalent conditions that are associated with increased risk of morbidity and mortality. There is evidence that the use of pharmacotherapy alongside behavioural treatments can improve quality of life and reduce disease risk for patients with these disorders. However, there are few approved drug therapies for obesity, and these are limited by poor efficacy and/or side effects and only one drug has been approved for the treatment of BED. There is considerable potential to use experimental medicine models to identify new drug treatments for obesity and BED, with greater efficacy and an improved side effect profile, at an early stage of development. Here, we present a model developed in our laboratory that incorporates both behavioural and neuroimaging measures which can be used to facilitate drug development for obesity and BED. The results from validation studies conducted to date using our model suggest that it is sensitive to the effects of agents with behavioural, neurophysiological and neuropharmacological mechanisms of action known to be associated with weight loss and reductions in binge eating. Future studies using the model will be valuable to evaluate the potential efficacy and side-effects of new candidate drugs at an early stage in the development pipeline for both obesity and BED.

The physiological control of eating: signals, neurons, and networks

During the past 30 yr, investigating the physiology of eating behaviors has generated a truly vast literature. This is fueled in part by a dramatic increase in obesity and its comorbidities that has coincided with an ever increasing sophistication of genetically based manipulations. These techniques have produced results with a remarkable degree of cell specificity, particularly at the cell signaling level, and have played a lead role in advancing the field. However, putting these findings into a brain-wide context that connects physiological signals and neurons to behavior and somatic physiology requires a thorough consideration of neuronal connections: a field that has also seen an extraordinary technological revolution. Our goal is to present a comprehensive and balanced assessment of how physiological signals associated with energy homeostasis interact at many brain levels to control eating behaviors. A major theme is that these signals engage sets of interacting neural networks throughout the brain that are defined by specific neural connections. We begin by discussing some fundamental concepts, including ones that still engender vigorous debate, that provide the necessary frameworks for understanding how the brain controls meal initiation and termination. These include key word definitions, ATP availability as the pivotal regulated variable in energy homeostasis, neuropeptide signaling, homeostatic and hedonic eating, and meal structure. Within this context, we discuss network models of how key regions in the endbrain (or telencephalon), hypothalamus, hindbrain, medulla, vagus nerve, and spinal cord work together with the gastrointestinal tract to enable the complex motor events that permit animals to eat in diverse situations.

Closed-loop Modulation of the Self-regulating Brain: A Review on Approaches, Emerging Paradigms, and Experimental Designs

Closed-loop approaches, setups, and experimental designs have been applied within the field of neuroscience to enhance the understanding of basic neurophysiology principles (closed-loop neuroscience; CLNS) and to develop improved procedures for modulating brain circuits and networks for clinical purposes (closed-loop neuromodulation; CLNM). The contents of this review are thus arranged into the following sections. First, we describe basic research findings that have been made using CLNS. Next, we provide an overview of the application, rationale, and therapeutic aspects of CLNM for clinical purposes. Finally, we summarize methodological concerns and critics in clinical practice of neurofeedback and novel applications of closed-loop perspective and techniques to improve and optimize its experiments. Moreover, we outline the theoretical explanations and experimental ideas to test animal models of neurofeedback and discuss technical issues and challenges associated with implementing closed-loop systems. We hope this review is helpful for both basic neuroscientists and clinical/ translationally-oriented scientists interested in applying closed-loop methods to improve mental health and well-being.

Cocaine- and amphetamine-regulated transcript peptide- and dopamine-containing systems interact in the ventral tegmental area of the zebra finch, Taeniopygia guttata, during dynamic changes in energy status

The mesolimbic dopamine (DA)-pathway regulates food-reward, feeding-related behaviour and energy balance. Evidence underscores the importance of feeding-related neuropeptides in modulating activity of these DA neurons. The neuropeptide, CART, a crucial regulator of energy balance, modulates DA-release, and influences the activity of ventral tegmental area (VTA) DAergic neurons in the mammalian brain. Whether CART- and DA-containing systems interact at the level of VTA to regulate energy balance, however, is poorly understood. We explored the interaction between CART- and DA-containing systems in midbrain of the zebra finch, Taeniopygia guttata, an interesting model to study dynamic changes in energy balance due to higher BMR/daytime body temperature, and rapid responsiveness of the feeding-related neuropeptides to changes in energy state. Further, its midbrain DA-neurons share similarities with those in mammals. In the midbrain, tyrosine hydroxylase-immunoreactive (TH-i) neurons were seen in the substantia nigra (SN) and VTA [anterior (VTAa), mid (VTAm) and caudal (VTAc)]; those in VTA were smaller. In the VTA, CART-immunoreactive (CART-i)-fibers densely innervated TH-i neurons, and both CART-immunoreactivity (CART-ir) and TH-immunoreactivity (TH-ir) responded to energy status-dependent changes. Compared to fed and fasted birds, refeeding dramatically enhanced TH-ir and the percentage of TH-i neurons co-expressing FOS in the VTA. Increased prepro-CART-mRNA, CART-ir and a transient appearance of CART-i neurons was observed in VTAa of fasted, but not fed birds. To test the functional interaction between CART- and DA-containing systems, ex-vivo superfused midbrain-slices were treated with CART-peptide and changes in TH-ir analysed. Compared to control tissues, CART-treatment increased TH-ir in VTA but not SN. We propose that CART is a potential regulator of VTA DA-neurons and energy balance in T. guttata.

Role of the Neuropeptide S System in Emotionality, Stress Responsiveness and Addiction-Like Behaviours in Rodents: Relevance to Stress-Related Disorders

The neuropeptide S (NPS) and its receptor (NPSR1) have been extensively studied over the last two decades for their roles in locomotion, arousal/wakefulness and anxiety-related and fear-related behaviours in rodents. However, the possible implications of the NPS/NPSR1 system, especially those of the single nucleotide polymorphism (SNP) rs324981, in stress-related disorders and substance abuse in humans remain unclear. This is possibly due to the fact that preclinical and clinical research studies have remained separated, and a comprehensive description of the role of the NPS/NPSR1 system in stress-relevant and reward-relevant endpoints in humans and rodents is lacking. In this review, we describe the role of the NPS/NPSR1 system in emotionality, stress responsiveness and addiction-like behaviour in rodents. We also summarize the alterations in the NPS/NPSR1 system in individuals with stress-related disorders, as well as the impact of the SNP rs324981 on emotion, stress responses and neural activation in healthy individuals. Moreover, we discuss the therapeutic potential and possible caveats of targeting the NPS/NPSR1 system for the treatment of stress-related disorders. The primary goal of this review is to highlight the importance of studying some rodent behavioural readouts modulated by the NPS/NPSR1 system and relevant to stress-related disorders.

Characterization of basal forebrain glutamate neurons suggests a role in control of arousal and avoidance behavior

The basal forebrain (BF) is involved in arousal, attention, and reward processing but the role of individual BF neuronal subtypes is still being uncovered. Glutamatergic neurons are the least well-understood of the three main BF neurotransmitter phenotypes. Here we analyzed the distribution, size, calcium-binding protein content and projections of the major group of BF glutamatergic neurons expressing the vesicular glutamate transporter subtype 2 (vGluT2) and tested the functional effect of activating them. Mice expressing Cre recombinase under the control of the vGluT2 promoter were crossed with a reporter strain expressing the red fluorescent protein, tdTomato, to generate vGluT2-cre-tdTomato mice. Immunohistochemical staining for choline acetyltransferase and a cross with mice expressing green fluorescent protein selectively in GABAergic neurons confirmed that cholinergic, GABAergic and vGluT2+ neurons represent distinct BF subpopulations. Subsets of BF vGluT2+ neurons expressed the calcium-binding proteins calbindin or calretinin, suggesting that multiple subtypes of BF vGluT2+ neurons exist. Anterograde tracing using adeno-associated viral vectors expressing channelrhodopsin2-enhanced yellow fluorescent fusion proteins revealed major projections of BF vGluT2+ neurons to neighboring BF cholinergic and parvalbumin neurons, as well as to extra-BF areas involved in the control of arousal or aversive/rewarding behavior such as the lateral habenula and ventral tegmental area. Optogenetic activation of BF vGluT2+ neurons elicited a striking avoidance of the area where stimulation was given, whereas stimulation of BF parvalbumin or cholinergic neurons did not. Together with previous optogenetic findings suggesting an arousal-promoting role, our findings suggest that BF vGluT2 neurons play a dual role in promoting wakefulness and avoidance behavior.

Role of Lateral Hypothalamus in Acupuncture Inhibition of Cocaine Psychomotor Activity

Acupuncture modulates the mesolimbic dopamine (DA) system; an area implicated in drug abuse. However, the mechanism by which peripheral sensory afferents, during acupuncture stimulation, modulate this system needs further investigation. The lateral hypothalamus (LH) has been implicated in reward processing and addictive behaviors. To investigate the role of the LH in mediating acupuncture effects, we evaluated the role of LH and spinohypothalamic neurons on cocaine-induced psychomotor activity and NAc DA release. Systemic injection of cocaine increased locomotor activity and 50 kHz ultrasonic vocalizations (USVs), which were attenuated by mechanical stimulation of needles inserted into HT7 but neither ST36 nor LI5. The acupuncture effects were blocked by chemical lesions of the LH or mimicked by activation of LH neurons. Single-unit extracellular recordings showed excitation of LH and spinohypothalamic neurons following acupuncture. Our results suggest that acupuncture recruits the LH to suppress the mesolimbic DA system and psychomotor responses following cocaine injection.

Activation State of the Supramammillary Nucleus Regulates Body Composition and Peripheral Fuel Metabolism

Whole body fuel metabolism and energy balance are controlled by an interactive brain neuronal circuitry involving multiple brain centers regulating cognition, circadian rhythms, reward, feeding and peripheral biochemical metabolism. The hypothalamic supramammillary nucleus (SuMN) comprises an integral node having connections with these metabolically relevant centers, and thus could be a key central coordination center for regulating peripheral energy balance. This study investigated the effect of chronically diminishing or increasing SuMN neuronal activity on body composition and peripheral fuel metabolism. The influence of neuronal activity level at the SuMN area on peripheral metabolism was investigated via chronic (2-4 week) direct SuMN treatment with agents that inhibit neuronal activity (GABAa receptor agonist [Muscimol] and AMPA plus NMDA glutamate receptor antagonists [CNQX plus dAP5, respectively]) in high fat fed animals refractory to the obesogenic effects of high fat diet. Such treatment reduced SuMN neuronal activity and induced metabolic syndrome, and likewise did so in animals fed low fat diet including inducement of glucose intolerance, insulin resistance, hyperinsulinemia, hyperleptinemia, and increased body weight gain and fat mass coupled with both increased food consumption and feed efficiency. Consistent with these results, circadian-timed activation of neuronal activity at the SuMN area with daily local infusion of glutamate receptor agonists, AMPA or NMDA at the natural daily peak of SuMN neuronal activity improved insulin resistance and obesity in high fat diet-induced insulin resistant animals. These studies are the first of their kind to identify the SuMN area as a novel brain locus that regulates peripheral fuel metabolism.

Reward motivation and cognitive flexibility in tau null-mutation mice

The reduction of tau or hyperphosphorylated tau (p-tau) has been proposed as a therapeutic strategy for Alzheimer's disease (AD) and frontotemporal dementia (FTD). Cognitive decline and sleep-wake dysregulation seen in AD and FTD patients are mimicked in transgenic and null-mutation mouse models of tauopathy. Alterations in the reward system are additional symptoms of AD and FTD. However, the role of tau in reward processes is not well understood. The present study aimed to examine reward and reward-motivated cognitive processes in male and female tau knockout (tau-/-) and wild-type mice using progressive ratio and reversal learning tasks. Tau-/- mice were heavier, ate more in the home cage, and reached criterion in operant lever training faster than wild-type mice. Tau-/- mice had a higher breakpoint in progressive ratio but were unimpaired in reversal learning or reward sensitivity. These data indicate that tau loss of function alters reward processing. This may help to explain aberrant reward-related behaviors in tauopathy patients and highlights a potentially important area for consideration in the development of anti-tau therapies.

LSD1-BDNF activity in lateral hypothalamus-medial forebrain bundle area is essential for reward seeking behavior

Reward induces activity-dependant gene expression and synaptic plasticity-related changes. Lysine-specific histone demethylase 1 (LSD1), a key enzyme driving histone modifications, regulates transcription in neural circuits of memory and emotional behavior. Herein, we focus on the role of LSD1 in modulating the expression of brain derived neurotrophic factor (BDNF), the master regulator of synaptic plasticity, in the lateral hypothalamus-medial forebrain bundle (LH-MFB) circuit during positive reinforcement. Rats, trained for intracranial self-stimulation (ICSS) via an electrode-cannula assembly in the LH-MFB area, were assayed for lever press activity, epigenetic parameters and dendritic sprouting. LSD1 expression and markers of synaptic plasticity like BDNF and dendritic arborization in the LH, showed distinct increase in conditioned animals. H3K4me2 levels at Bdnf IV and Bdnf IX promoters were increased in ICSS-conditioned rats, but H3K9me2 was decreased. While intra LH-MFB treatment with pan Lsd1 siRNA inhibited lever press activity, analyses of LH tissue showed reduction in BDNF expression and levels of H3K4me2 and H3K9me2. However, co-administration of BDNF peptide restored lever press activity mitigated by Lsd1 siRNA. BDNF expression in LH, driven by LSD1 via histone demethylation, may play an important role in reshaping the reward pathway and hold the key to decode the molecular basis of addiction.

A new GABAergic somatostatin projection from the BNST onto accumbal parvalbumin neurons controls anxiety

The prevailing view is that parvalbumin (PV) interneurons play modulatory roles in emotional response through local medium spiny projection neurons (MSNs). Here, we show that PV activity within the nucleus accumbens shell (sNAc) is required for producing anxiety-like avoidance when mice are under anxiogenic situations. Firing rates of sNAc^PV neurons were negatively correlated to exploration time in open arms (threatening environment). In addition, sNAc^PV neurons exhibited high excitability in a chronic stress mouse model, which generated excessive maladaptive avoidance behavior in an anxiogenic context. We also discovered a novel GABAergic pathway from the anterior dorsal bed nuclei of stria terminalis (adBNST) to sNAc^PV neurons. Optogenetic activation of these afferent terminals in sNAc produced an anxiolytic effect via GABA transmission. Next, we further demonstrated that chronic stressors attenuated the inhibitory synaptic transmission at adBNST^GABA → sNAc^PV synapses, which in turn explains the hyperexcitability of sNAc PV neurons on stressed models. Therefore, activation of these GABAergic afferents in sNAc rescued the excessive avoidance behavior related to an anxious state. Finally, we identified that the majority GABAergic input neurons, which innervate sNAc^PV cells, were expressing somatostatin (SOM), and also revealed that coordination between SOM- and PV- cells functioning in the BNST → NAc circuit has an inhibitory influence on anxiety-like responses. Our findings provide a potentially neurobiological basis for therapeutic interventions in pathological anxiety.

The lateral hypothalamus and orexinergic transmission in the paraventricular thalamus promote the attribution of incentive salience to reward-associated cues

RATIONALE

Prior research suggests that the neural pathway from the lateral hypothalamic area (LHA) to the paraventricular nucleus of the thalamus (PVT) mediates the attribution of incentive salience to Pavlovian reward cues. However, a causal role for the LHA and the neurotransmitters involved have not been demonstrated in this regard.

OBJECTIVES

To examine (1) the role of LHA in the acquisition of Pavlovian conditioned approach (PavCA) behaviors, and (2) the role of PVT orexin 1 receptors (OX1r) and orexin 2 receptors (OX2r) in the expression of PavCA behaviors and conditioned reinforcement.

METHODS

Rats received excitotoxic lesions of the LHA prior to Pavlovian training. A separate cohort of rats characterized as sign-trackers (STs) or goal-trackers (GTs) received the OX1r antagonist SB-334867, or the OX2r antagonist TCS-OX2-29, into the PVT, to assess their effects on the expression of PavCA behavior and on the conditioned reinforcing properties of a Pavlovian reward cue.

RESULTS

LHA lesions attenuated the development of sign-tracking behavior. Administration of either the OX1r or OX2r antagonist into the PVT reduced sign-tracking behavior in STs. Further, OX2r antagonism reduced the conditioned reinforcing properties of a Pavlovian reward cue in STs.

CONCLUSIONS

The LHA is necessary for the development of sign-tracking behavior; and blockade of orexin signaling in the PVT attenuates the expression of sign-tracking behavior and the conditioned reinforcing properties of a Pavlovian reward cue. Together, these data suggest that LHA orexin inputs to the PVT are a key component of the circuitry that encodes the incentive motivational value of reward cues.

The dynamic regulation of appetitive behavior through lateral hypothalamic orexin and melanin concentrating hormone expressing cells

The lateral hypothalamic area (LHA) is a heterogeneous brain structure extensively studied for its potent role in regulating energy balance. The anatomical and molecular diversity of the LHA permits the orchestration of responses to energy sensing cues from the brain and periphery. Two of the primary cell populations within the LHA associated with integration of this information are Orexin (ORX) and Melanin Concentrating Hormone (MCH). While both of these non-overlapping populations exhibit orexigenic properties, the activities of these two systems support feeding behavior through contrasting mechanisms. We describe the anatomical and functional properties as well as interaction with other neuropeptides and brain reward and hedonic systems. Specific outputs relating to arousal, food seeking, feeding, and metabolism are coordinated through these mechanisms. We then discuss how both the ORX and MCH systems harmonize in a divergent yet overall cooperative manner to orchestrate feeding behavior through transitions between various appetitive states, and thus offer novel insights into LHA allostatic control of appetite.

Bidirectional gut-brain communication: A role for orexin-A

It is increasingly evident that bidirectional gut-brain signaling provides a communication pathway that uses neural, hormonal, and immunological routes to regulate homeostatic mechanisms such as hunger/satiety as well as emotions and inflammation. Hence, disruption of the gut-brain axis can cause numerous pathophysiologies, including obesity and intestinal inflammatory diseases. One chemical mediator in the gut-brain axis is orexin-A, given that hypothalamic orexin-A affects gastrointestinal motility and secretion, and peripheral orexin in the intestinal mucosa can modulate brain functions, making possible an orexinergic gut-brain network. It has been proposed that orexin-A acts on this axis to regulate nutritional processes, such as short-term intake, gastric acid secretion, and motor activity associated with the cephalic phase of feeding. Orexin-A has also been related to stress systems and stress responses via the hypothalamic-pituitary-adrenal axis. Recent studies on the relationship of orexin with immune system-brain communications in an animal model of colitis suggested an immunomodulatory role for orexin-A in signaling and responding to infection by reducing the production of pro-inflammatory cytokines (e.g., tumor necrosis factor α, interleukin-6, and monocyte chemoattractant protein-1). These studies suggested that orexin administration might be of potential therapeutic value in irritable bowel syndrome or chronic intestinal inflammatory diseases, in which gastrointestinal symptoms frequently coexist with behavioral disorders, including loss of appetite, anxiety, depression, and sleeping disorders. Interventions in the orexinergic system have been proposed as a therapeutic approach to these diseases and for the treatment of chemotherapeutic drug-related hyperalgesia and fatigue in cancer patients.

Neural and Hormonal Control of Sexual Behavior

Gonadal hormones contribute to the sexual differentiation of brain and behavior throughout the lifespan, from initial neural patterning to "activation" of adult circuits. Sexual behavior is an ideal system in which to investigate the mechanisms underlying hormonal activation of neural circuits. Sexual behavior is a hormonally regulated, innate social behavior found across species. Although both sexes seek out and engage in sexual behavior, the specific actions involved in mating are sexually dimorphic. Thus, the neural circuits mediating sexual motivation and behavior in males and females are overlapping yet distinct. Furthermore, sexual behavior is strongly dependent on circulating gonadal hormones in both sexes. There has been significant recent progress on elucidating how gonadal hormones modulate physiological properties within sexual behavior circuits with consequences for behavior. Therefore, in this mini-review we review the neural circuits of male and female sexual motivation and behavior, from initial sensory detection of pheromones to the extended amygdala and on to medial hypothalamic nuclei and reward systems. We also discuss how gonadal hormones impact the physiology and functioning of each node within these circuits. By better understanding the myriad of ways in which gonadal hormones impact sexual behavior circuits, we can gain a richer and more complete appreciation for the neural substrates of complex behavior.

Cell-type specific knockout of peptidylglycine α-amidating monooxygenase reveals specific behavioral roles in excitatory forebrain neurons and cardiomyocytes

Neuropeptides and peptide hormones play a crucial role in integrating the many factors that affect physiologic and cognitive processes. The potency of many of these peptides requires an amidated amino acid at the C-terminus; a single enzyme, peptidylglycine α-amidating monooxygenase (PAM), catalyzes this modification. Anxiety-like behavior is known to be altered in mice with a single functional Pam allele (Pam^+/- ) and in mice unable to express Pam in excitatory forebrain neurons (Pam^Emx1-cKO/cKO ) or in cardiomyocytes (Pam^Myh6-cKO/cKO ). Examination of PAM-positive and glutamic acid decarboxylase 67 (GAD)-positive cells in the amygdala of Pam^Emx1-cKO/cKO mice demonstrated the absence of PAM in pyramidal neurons and its continued presence in GAD-positive interneurons, suggestive of altered excitatory/inhibitory balance. Additional behavioral tests were used to search for functional alterations in these cell-type specific knockout mice. Pam^Emx1-cKO/cKO mice exhibited a less focused search pattern for the Barnes Maze escape hole than control or Pam^Myh6-cKO/cKO mice. While wildtype mice favor interacting with novel objects as opposed to familiar objects, both Pam^Emx1-cKO/cKO and Pam^Myh6-cKO/cKO mice exhibited significantly less interest in the novel object. Since PAM levels in the central nervous system of Pam^Myh6-cKO/cKO mice are unaltered, the behavioral effect observed in these mice may reflect their inability to produce atrial granules and the resulting reduction in serum levels of atrial natriuretic peptide. In the sociability test, male mice of all three genotypes spent more time with same-sex stranger mice; while control females showed no preference for stranger mice, female Pam^Emx1-cKO/cKO mice showed preference for same-sex stranger mice in all trials.

Melanin-concentrating hormone in rat nucleus accumbens or lateral hypothalamus differentially impacts morphine and food seeking behaviors

BACKGROUND

Identifying neural substrates that are differentially affected by drugs of abuse and natural rewards is key to finding a target for an efficacious treatment for substance abuse. Melanin-concentrating hormone is a polypeptide with an inhibitory effect on the mesolimbic dopamine system. Here we test the hypothesis that melanin-concentrating hormone in the lateral hypothalamus and nucleus accumbens shell is differentially involved in the regulation of morphine and food-rewarded behaviors.

METHODS

Male Sprague-Dawley rats were trained with morphine (5.0 mg/kg, subcutaneously) or food pellets (standard chow, 10-14 g) to induce a conditioned place preference, immediately followed by extinction training. Melanin-concentrating hormone (1.0 µg/side) or saline was infused into the nucleus accumbens shell or lateral hypothalamus before the reinstatement primed by morphine or food, and locomotor activity was simultaneously monitored. As the comparison, melanin-concentrating hormone was also microinjected into the nucleus accumbens shell or lateral hypothalamus before the expression of food or morphine-induced conditioned place preference.

RESULTS

Microinfusion of melanin-concentrating hormone into the nucleus accumbens shell (but not into the lateral hypothalamus) prevented the reinstatement of morphine conditioned place preference but had no effect on the reinstatement of food conditioned place preference. In contrast, microinfusion of melanin-concentrating hormone into the lateral hypothalamus (but not in the nucleus accumbens shell) inhibited the reinstatement of food conditioned place preference but had no effect on the reinstatement of morphine conditioned place preference.

CONCLUSIONS

These results suggest a clear double dissociation of melanin-concentrating hormone in morphine/food rewarding behaviors and melanin-concentrating hormone in the nucleus accumbens shell. Melanin-concentrating hormone could be a potential target for therapeutic intervention for morphine abuse without affecting natural rewards.

Synergy of Distinct Dopamine Projection Populations in Behavioral Reinforcement

Dopamine neurons of the ventral tegmental area (VTA) regulate reward association and motivation. It remains unclear whether there are distinct dopamine populations to mediate these functions. Using mouse genetics, we isolated two populations of dopamine-producing VTA neurons with divergent projections to the nucleus accumbens (NAc) core and shell. Inhibition of VTA-core-projecting neurons disrupted Pavlovian reward learning, and activation of these cells promoted the acquisition of an instrumental response. VTA-shell-projecting neurons did not regulate Pavlovian reward learning and could not facilitate acquisition of an instrumental response, but their activation could drive robust responding in a previously learned instrumental task. Both populations are activated simultaneously by cues, actions, and rewards, and this co-activation is required for robust reinforcement of behavior. Thus, there are functionally distinct dopamine populations in the VTA for promoting motivation and reward association, which operate on the same timescale to optimize behavioral reinforcement.

The Lateral Hypothalamus: An Uncharted Territory for Processing Peripheral Neurogenic Inflammation

The roles of the hypothalamus and particularly the lateral hypothalamus (LH) in the regulation of inflammation and pain have been widely studied. The LH consists of a parasympathetic area that has connections with all the major parts of the brain. It controls the autonomic nervous system (ANS), regulates feeding behavior and wakeful cycles, and is a part of the reward system. In addition, it contains different types of neurons, most importantly the orexin neurons. These neurons, though few in number, perform critical functions such as inhibiting pain transmission and interfering with the reward system, feeding behavior and the hypothalamic pituitary axis (HPA). Recent evidence has identified a new role for orexin neurons in the modulation of pain transmission associated with several inflammatory diseases, including rheumatoid arthritis and ulcerative colitis. Here, we review recent findings on the various physiological functions of the LH with special emphasis on the orexin/receptor system and its role in mediating inflammatory pain.

Neurotensin in reward processes

Neurotensin (NTS) is a neuropeptide neurotransmitter expressed in the central and peripheral nervous systems. Many studies over the years have revealed a number of roles for this neuropeptide in body temperature regulation, feeding, analgesia, ethanol sensitivity, psychosis, substance use, and pain. This review provides a general survey of the role of neurotensin with a focus on modalities that we believe to be particularly relevant to the study of reward. We focus on NTS signaling in the ventral tegmental area, nucleus accumbens, lateral hypothalamus, bed nucleus of the stria terminalis, and central amygdala. Studies on the role of NTS outside of the ventral tegmental area are still in their relative infancy, yet they reveal a complex role for neurotensinergic signaling in reward-related behaviors that merits further study. This article is part of the special issue on 'Neuropeptides'.

Blunted leptin sensitivity during hedonic overeating can be reinstated by activating galanin 2 receptors (Gal2R) in the lateral hypothalamus

AIM

Since foods with high hedonic value are often consumed in excess of energetic needs, this study was designed to identify the mechanisms that may counter anorexigenic signalling in the presence of hedonic foods in lean animals.

METHODS

Mice, in different states of satiety (fed/fasted, or fed/fasted and treated with ghrelin or leptin, respectively), were allowed to choose between high-fat/high-sucrose and standard foods. Intake of each food type and the activity of hypothalamic neuropetidergic neurons that regulate appetite were monitored. In some cases, food choice was monitored in leptin-injected fasted mice that received microinjections of galanin receptor agonists into the lateral hypothalamus.

RESULTS

Appetite-stimulating orexin neurons in the lateral hypothalamus are rapidly activated when lean, satiated mice consume a highly palatable food (PF); such activation (upregulated c-Fos expression) occurred even after administration of the anorexigenic hormone leptin and despite intact leptin signalling in the hypothalamus. The ability of leptin to restrain PF eating is restored when a galanin receptor 2 (Gal2R) agonist is injected into the lateral hypothalamus.

CONCLUSION

Hedonically-loaded foods interrupt the inhibitory actions of leptin on orexin neurons and interfere with the homeostatic control of feeding. Overeating of palatable foods can be curtailed in lean animals by activating Gal2R in the lateral hypothalamus.

Increased Hypothalamic Projections to the Lateral Hypothalamus and Responses to Leptin in Rat Neonates From High Fat Fed Mothers

The lateral hypothalamus (LHA) is a central hub in the regulation of food intake and metabolism, as it integrates homeostatic and hedonic circuits. During early development, maturing input to and output from the LHA might be particularly sensitive to environmental dietary changes. We examined the effects of a maternal high fat diet (HFD, 60% Kcal in fat) on the density of hypothalamic projections to the orexin (ORX-A) field of the LHA in 10 day-old (PND10) rat pups using retrograde labeling with fluorescent microspheres. We also compared responsiveness of phenotypically identified LHA neurons to leptin administration (3 mg/kg, bw) between pups from control (CD) or high fat (HFD) fed mothers on PND10 and 15-16, at the onset of independent feeding. HFD pups exhibited a higher density of LHA projections (p = 0.05) from the ventromedial hypothalamus (VMH) compared to CD pups and these originated from both SF-1 and BDNF-positive neurons in the VMH. Increased circulating leptin levels in HFD pups, particularly on PND15-16 was consistent with enhanced pSTAT3 responses to leptin in the orexin (ORX-A) field of the LHA, with some of the activated neurons expressing a GABA, but not CART phenotype. ORX-A neurons colocalizing with pERK were significantly higher in PND15-16 HFD pups compared to CD pups, and leptin-induced increase in pERK signaling was only observed in CD pups. There was no significant effect of leptin on pERK in HFD pups. These results suggest that perinatal maternal high fat feeding increases hypothalamic projections to the ORX-A field of the LHA, increases basal activation of ORX-A neurons and direct responsiveness of LHA neurons to leptin. Since these various LHA neuronal populations project quite heavily to Dopamine (DA) neurons in the ventral tegmental area, they might participate in the early dietary programming of mesocorticolimbic reward circuits and food intake.

The Lateral Preoptic Area: A Novel Regulator of Reward Seeking and Neuronal Activity in the Ventral Tegmental Area

The lateral preoptic area (LPO) is a hypothalamic region whose function has been largely unexplored. Its direct and indirect projections to the ventral tegmental area (VTA) suggest that the LPO could modulate the activity of the VTA and the reward-related behaviors that the VTA underlies. We examined the role of the LPO on reward taking and seeking using operant self-administration of cocaine or sucrose. Rats were trained to self-administer cocaine or sucrose and then subjected to extinction, whereby responding was no longer reinforced. We tested if stimulating the LPO pharmacologically with bicuculline or chemogenetically with Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) modifies self-administration and/or seeking. In another set of experiments, we tested if manipulating the LPO influences cocaine self-administration during and after punishment. To examine the functional connectivity between the LPO and VTA, we used in vivo electrophysiology recordings in anesthetized rats. We tested if stimulating the LPO modifies the activity of GABA and dopamine neurons of the VTA. We found that stimulating the LPO reinstated cocaine and sucrose seeking behavior but had no effect on reward intake. Furthermore, both stimulating and inhibiting the LPO prevented the sustained reduction in cocaine intake seen after punishment. Finally, stimulating the LPO inhibited the activity of VTA GABA neurons while enhancing that of VTA dopamine neurons. These findings indicate that the LPO has the capacity to drive reward seeking, modulate sustained reductions in self-administration following punishment, and regulate the activity of VTA neurons. Taken together, these findings implicate the LPO as a previously overlooked member of the reward circuit.

Assessment of sleep and obesity in adults and children: Observational study

The sleep allows many psychological processes, such as immune system activity, body metabolism and hormonal balance, emotional and mental health, learning, mnemonic processes. The lack of sleep could undermine mental and physical purposes, causing an alteration in cognitive functions or metabolic disorders. In our study, we have examined the irregular sleep effects with the overweight and obesity risk in children and adults.The sample was composed of 199 subjects, of which 71 adults, (29 males and 42 females), and 128 children (73 males and 55 females). We have measured the weight and height with standard techniques; we also have measured the body mass index dividing the weight in kg with the height square expressed in meters (kg/m). Subjects were divided into underweight, normal weight, overweight, and obese. Were administered some questionnaires to measure the quantity and quality of sleep, and eating habits and individual consumption of food.Analysis of demographic variables not showed significant differences between male and female groups but highlighted a significant trend differences in normal-weight score. The clinical condition has a substantial impact on body mass index score and sleep hours were significant predictor on this.Quantity and quality sleep can also represent a risk factor of overweight and obesity, so sufficient sleep is a factor that influence a normal weight. Adults and children that sleep less, have an increase in obesity and overweight risk with dysfunctional eating behaviors, decreased physical activity, and metabolic changes.

Identifying roles for peptidergic signaling in mice

Despite accumulating evidence demonstrating the essential roles played by neuropeptides, it has proven challenging to use this information to develop therapeutic strategies. Peptidergic signaling can involve juxtacrine, paracrine, endocrine, and neuronal signaling, making it difficult to define physiologically important pathways. One of the final steps in the biosynthesis of many neuropeptides requires a single enzyme, peptidylglycine α-amidating monooxygenase (PAM), and lack of amidation renders most of these peptides biologically inert. PAM, an ancient integral membrane enzyme that traverses the biosynthetic and endocytic pathways, also affects cytoskeletal organization and gene expression. While mice, zebrafish, and flies lacking Pam (Pam^KO/KO ) are not viable, we reasoned that cell type-specific elimination of Pam expression would generate mice that could be screened for physiologically important and tissue-specific deficits. Conditional Pam^cKO/cKO mice, with loxP sites flanking the 2 exons deleted in the global Pam^KO/KO mouse, were indistinguishable from wild-type mice. Eliminating Pam expression in excitatory forebrain neurons reduced anxiety-like behavior, increased locomotor responsiveness to cocaine, and improved thermoregulation in the cold. A number of amidated peptides play essential roles in each of these behaviors. Although atrial natriuretic peptide (ANP) is not amidated, Pam expression in the atrium exceeds levels in any other tissue. Eliminating Pam expression in cardiomyocytes increased anxiety-like behavior and improved thermoregulation. Atrial and serum levels of ANP fell sharply in PAM myosin heavy chain 6 conditional knockout mice, and RNA sequencing analysis identified changes in gene expression in pathways related to cardiac function. Use of this screening platform should facilitate the development of therapeutic approaches targeted to peptidergic pathways.

Amygdala and Hypothalamus: Historical Overview With Focus on Aggression

Aggressiveness has a high prevalence in psychiatric patients and is a major health problem. Two brain areas involved in the neural network of aggressive behavior are the amygdala and the hypothalamus. While pharmacological treatments are effective in most patients, some do not properly respond to conventional therapies and are considered medically refractory. In this population, surgical procedures (ie, stereotactic lesions and deep brain stimulation) have been performed in an attempt to improve symptomatology and quality of life. Clinical results obtained after surgery are difficult to interpret, and the mechanisms responsible for postoperative reductions in aggressive behavior are unknown. We review the rationale and neurobiological characteristics that may help to explain why functional neurosurgery has been proposed to control aggressive behavior.

Vagal Interoceptive Modulation of Motivated Behavior

In addition to regulating the ingestion and digestion of food, sensory feedback from gut to brain modifies emotional state and motivated behavior by subconsciously shaping cognitive and affective responses to events that bias behavioral choice. This focused review highlights evidence that gut-derived signals impact motivated behavior by engaging vagal afferents and central neural circuits that generally serve to limit or terminate goal-directed approach behaviors, and to initiate or maintain behavioral avoidance.

To eat or to sleep: That is a lateral hypothalamic question

The lateral hypothalamus (LH) is a functionally and anatomically complex brain region that is involved in the regulation of many behavioral and physiological processes including feeding, arousal, energy balance, stress, reward and motivated behaviors, pain perception, body temperature regulation, digestive functions and blood pressure. Despite noteworthy experimental efforts over the past decades, the circuit, cellular and synaptic bases by which these different processes are regulated by the LH remains incompletely understood. This knowledge gap links in large part to the high cellular heterogeneity of the LH. Fortunately, the rapid evolution of newer genetic and electrophysiological tools is now permitting the selective manipulation, typically genetically-driven, of discrete LH cell populations. This, in turn, permits not only assignment of function to discrete cell groups, but also reveals that considerable synergistic and antagonistic interactions exist between key LH cell populations that regulate feeding and arousal. For example, we now know that while LH melanin-concentrating hormone (MCH) and orexin/hypocretin neurons both function as sensors of the internal metabolic environment, their roles regulating sleep and arousal are actually opposing. Additional studies have uncovered similarly important roles for subpopulations of LH GABAergic cells in the regulation of both feeding and arousal. Herein we review the role of LH MCH, orexin/hypocretin and GABAergic cell populations in the regulation of energy homeostasis (including feeding) and sleep-wake and discuss how these three cell populations, and their subpopulations, may interact to optimize and coordinate metabolism, sleep and arousal. This article is part of the Special Issue entitled 'Hypothalamic Control of Homeostasis'.

Updates on the neurobiology of food reward and their relation to the obesogenic environment

PURPOSE OF REVIEW

To summarize recent findings about the neurobiological control of food reward and discuss their relevance for hedonic food intake and obesity in our current obesogenic environment.

RECENT FINDINGS

Recent data show new roles for circuits involving neuronal subpopulations within the central amyglada (CeA) and lateral hypothalamus in the regulation of feeding and reward in rodents under free and operant conditions and also in restrain from reward consumption. Recent work also shows that the orbitofrontal cortex (OFC) codes for subjective perception of food features during reward assessment of individual foods and that activity in the nucleus accumbens (NAc) codes for anticipation for reward, which can be blocked by time-locked neurostimulation of NAc.

SUMMARY

New data illustrates that different aspects of hedonic intake and food reward are coded in a distributed brain network. In particular, as our obesogenic environment facilitates access to palatable food and promotes cue-induced feeding, neuronal circuits related to control of impulsivity, food valuation and duration of hedonic intake episodes might have a significant role in our ability to control food intake and development of obesity by excess intake.

Daily Fluctuation of Orexin Neuron Activity and Wiring: The Challenge of "Chronoconnectivity"

In the heterogeneous hub represented by the lateral hypothalamus, neurons containing the orexin/hypocretin peptides play a key role in vigilance state transitions and wakefulness stability, energy homeostasis, and other functions relevant for motivated behaviors. Orexin neurons, which project widely to the neuraxis, are innervated by multiple extra- and intra-hypothalamic sources. A key property of the adaptive capacity of orexin neurons is represented by daily variations of activity, which is highest in the period of the animal’s activity and wakefulness. These sets of data are here reviewed. They concern the discharge profile during the sleep/wake cycle, spontaneous Fos induction, peptide synthesis and release reflected by immunostaining intensity and peptide levels in the cerebrospinal fluid as well as postsynaptic effects. At the synaptic level, adaptive capacity of orexin neurons subserved by remodeling of excitatory and inhibitory inputs has been shown in response to changes in the nutritional status and prolonged wakefulness. The present review wishes to highlight that synaptic plasticity in the wiring of orexin neurons also occurs in unperturbed conditions and could account for diurnal variations of orexin neuron activity. Data in zebrafish larvae have shown rhythmic changes in the density of inhibitory innervation of orexin dendrites in relation to vigilance states. Recent findings in mice have indicated a diurnal reorganization of the excitatory/inhibitory balance in the perisomatic innervation of orexin neurons. Taken together these sets of data point to “chronoconnectivity,” i.e., a synaptic rearrangement of inputs to orexin neurons over the course of the day in relation to sleep and wake states. This opens questions on the underlying circadian and homeostatic regulation and on the involved players at synaptic level, which could implicate dual transmitters, cytoskeletal rearrangements, hormonal regulation, as well as surrounding glial cells and extracellular matrix. Furthermore, the question arises of a “chronoconnectivity” in the wiring of other neuronal cell groups of the sleep-wake-regulatory network, many of which are characterized by variations of their firing rate during vigilance states.

Hypocretin as a Hub for Arousal and Motivation

The lateral hypothalamus is comprised of a heterogeneous mix of neurons that serve to integrate and regulate sleep, feeding, stress, energy balance, reward, and motivated behavior. Within these populations, the hypocretin/orexin neurons are among the most well studied. Here, we provide an overview on how these neurons act as a central hub integrating sensory and physiological information to tune arousal and motivated behavior accordingly. We give special attention to their role in sleep-wake states and conditions of hyper-arousal, as is the case with stress-induced anxiety. We further discuss their roles in feeding, drug-seeking, and sexual behavior, which are all dependent on the motivational state of the animal. We further emphasize the application of powerful techniques, such as optogenetics, chemogenetics, and fiber photometry, to delineate the role these neurons play in lateral hypothalamic functions.

Lateral Hypothalamus as a Motivation-Cognition Interface in the Control of Feeding Behavior

Converging evidence for an essential function of the lateral hypothalamus (LHA) in the control of feeding behavior has been accumulating since the classic work conducted almost 80 years ago. The LHA is also important in reward and reinforcement processes and behavioral state control. A unifying function for the LHA across these processes has not been fully established. Nonetheless, it is considered to integrate motivation with behavior. More recent work has demonstrated that the LHA is also required when cognitive processes, such as associative learning and memory control feeding behavior, suggesting it may serve as a motivation-cognition interface. Structurally, the LHA is well positioned within the cerebral hemisphere, with its extensive connectional network across the forebrain-brainstem axis, to link motivational and behavioral systems with cognitive processes. Studies that examined how learned cues control food seeking and consumption have implicated the LHA, but due to methodological limitations could not determine whether it underlies motivation, learning, or the integration of these processes. Furthermore, the identification of specific substrates has been limited by the LHA's extraordinary complexity and heterogeneity. Recent methodological advancements with chemo-and opto-genetic approaches have enabled unprecedented specificity in interrogations of distinct neurons and their pathways in behaving animals, including manipulations during temporally distinct events. These approaches have revealed novel insights about the LHA structure and function. Recent findings that the GABA LHA neurons control feeding and food-reward learning and memory will be reviewed together with past work within the context of the LHA function as an interface between cognition and motivation.