Lateral hypothalamic proenkephalin neurons drive threat-induced overeating associated with a negative emotional state.

Psychological stressors, like the nearby presence of a predator, can be strong enough to induce physiological/hormonal alterations, leading to appetite changes. However, little is known about how threats can alter feeding-related hypothalamic circuit functions. Here, we found that proenkephalin (Penk)-expressing lateral hypothalamic (LHPenk) neurons of mice exposed to predator scent stimulus (PSS) show sensitized responses to high-fat diet (HFD) eating, whereas silencing of the same neurons normalizes PSS-induced HFD overconsumption associated with a negative emotional state. Downregulation of endogenous enkephalin peptides in the LH is crucial for inhibiting the neuronal and behavioral changes developed after PSS exposure. Furthermore, elevated corticosterone after PSS contributes to enhance the reactivity of glucocorticoid receptor (GR)-containing LHPenk neurons to HFD, whereas pharmacological inhibition of GR in the LH suppresses PSS-induced maladaptive behavioral responses. We have thus identified the LHPenk neurons as a critical component in the threat-induced neuronal adaptation that leads to emotional overconsumption.

The Role of Dorsal Raphe Serotonin Neurons in the Balance between Reward and Aversion.

BACKGROUND: Reward processing is fundamental for animals to survive and reproduce. Many studies have shown the importance of dorsal raphe nucleus (DRN) serotonin (5-HT) neurons in this process, but the strongly correlative link between the activity of DRN 5-HT neurons and rewarding/aversive potency is under debate. Our primary objective was to reveal this link using two different strategies to transduce DRN 5-HT neurons. METHODS: For transduction of 5-HT neurons in wildtype mice, adeno-associated virus (AAV) bearing the mouse tryptophan hydroxylase 2 (TPH2) gene promoter was used. For transduction in Tph2-tTA transgenic mice, AAVs bearing the tTA-dependent TetO enhancer were used. To manipulate the activity of 5-HT neurons, optogenetic actuators (CheRiff, eArchT) were expressed by AAVs. For measurement of rewarding/aversive potency, we performed a nose-poke self-stimulation test and conditioned place preference (CPP) test. RESULTS: We found that stimulation of DRN 5-HT neurons and their projections to the ventral tegmental area (VTA) increased the number of nose-pokes in self-stimulation test and CPP scores in both targeting methods. Concomitantly, CPP scores were decreased by inhibition of DRN 5-HT neurons and their projections to VTA. CONCLUSION: Our findings indicate that the activity of DRN 5-HT neurons projecting to the VTA is a key modulator of balance between reward and aversion.

c-Fos expression in the ascending arousal system induced by physical exercise in rats: Implication for memory performance.

During exercise, multiple sensory information such as visual outflow, proprioception, and vestibular information promote an increase in arousal state, which may convey positive effects on cognitive abilities such as memory. Nevertheless, which of the components of the ascending arousal system (AAS) are engaged during physical activity and which of them are critical for cognitive enhancement, induced by exercise is still unclear. Two experiments were conducted, to answer these questions: in the first one, the neuronal activity of different components of the AAS was evaluated by c-Fos immunoreactivity (Fos-ir) in running rats exposed to a lock or unlock running wheel. We found a specific Fos-ir increase in the tuberomammillary nucleus (TMN) associated with physical exercise. In the second experiment sedentary and exercised rats were challenged to conduct an object recognition memory task, and the activity of the AAS after learning was evaluated by c-Fos immunoreactivity. The exercised group showed a higher performance in the object recognition memory task which gets correlated with an increase on Fos-ir in the TMN, but not with the other components of the AAS, suggesting that the increase on TMN activity induced by exercise may be the foremost contributor of the AAS to memory enhancement observed in exercised animals.

Sleeve Gastrectomy Rescuing the Altered Functional Connectivity of Lateral but Not Medial Hypothalamus in Subjects with Obesity.

BACKGROUND: Lateral and medial hypothalamus (LH and MH) play important roles in energy balance. Changed hypothalamic function has been found in subjects with obesity. However, the effect of bariatric surgery on the function of the two sub-regions has been poorly investigated. METHODS: Thirty-eight subjects with obesity and 34 age- and sex-matched normal-weight controls were included. Seventeen of the 38 subjects underwent laparoscopic sleeve gastrectomy. Functional magnetic resonance imaging data and metabolic parameters were collected to investigate functional connectivity networks of the two hypothalamic sub-regions as well as the influence of sleeve gastrectomy on the two networks in subjects with obesity. RESULTS: Compared to normal-weight controls, pre-surgical subjects had increased functional connectivity (FC) in the reward region (putamen) within the LH network, and increased FC in somatosensory cortical area (insula), as well as decreased FC in the cognitive control regions (prefrontal regions) within the MH network. After the surgery, post-surgical FC of the putamen within the LH network changed towards the patterns found in the control group. Furthermore, the changes in fasting glucose before and after the surgery were associated with the changes in FC of the putamen within the LH network. CONCLUSIONS: The FC within the LH and MH networks were changed in subjects with obesity. Part of these altered FC was rescued after the surgery.

Ghrelin and electrical stimulating the lateral hypothalamus area regulated the discharges of gastric distention neurons via the dorsal vagal complex in cisplatin-treated rats.

OBJECTIVE: Cisplatin is an important antineoplastic drug and has side effects such as nausea, vomiting, and dyspepsia. The detailed mechanisms for its side effects are yet not well be illustrated. Our purpose was to investigate the discharges of gastric distention (GD) sensitive neurons regulated by ghrelin and electrical stimulation of the lateral hypothalamus area (LHA) via the dorsal vagal complex (DVC) in cisplatin-treated rats. MATERIALS AND METHODS: Extracellular discharge recording was performed to observe the effects of ghrelin and electrical stimulation of the LHA on discharges of GD neurons in the DVC. RESULTS: GD neurons were recorded in DVC in saline-treated and cisplatin-treated rats and identified as GD-excitatory (GD-E) neurons, which are excited by gastric distension, and GD-inhibitory (GE-I) neurons, which are inhibited by gastric distension. Microinjection of ghrelin into the DVC increased the firing frequency of most GD neurons, while the ratios of excited GD-E and GD-I neurons in cisplatin-treated rats were significantly lower than those in saline-treated rats. The excitatory effect of ghrelin was eliminated completely by DVC pretreatment with ghrelin receptor antagonist [D-Lys-3]-GHRP-6. After electrical stimulation of the LHA, the firing frequency of these neurons significantly increased. This excitatory effect was weaker in cisplatin-treated rats than in saline-treated rats and could be partly blocked by DVC pretreatment with [D-Lys-3]-GHRP-6. CONCLUSION: GD neurons in the DVC could be excited by microinjecting ghrelin into the DVC and electrical stimulation of the LHA, respectively. The excitatory effect was attenuated by cisplatin injected intraperitoneally.

Cocaine- and amphetamine-regulated transcript peptide (CART) induced reward behavior is mediated via Gi/o dependent phosphorylation of PKA/ERK/CREB pathway.

Although the role of cocaine- and amphetamine-regulated transcript peptide (CART) in modulating the mesolimbic reward pathway has been suggested, underlying cellular mechanisms have not been elucidated. Herein, we investigate the involvement of Gi/o dependent protein kinase A (PKA)/extracellular signal-regulated kinase (ERK)/cAMP response element binding protein (CREB) signaling in CART induced reward behavior. The rat was implanted with a stimulating electrode targeted at the lateral hypothalamus (LH)-medial forebrain bundle (MFB) and conditioned to intracranial self-stimulation (ICSS) in an operant chamber. Intracerebroventricular (icv) administration of CART (55-102) dose-dependently lowered ICSS threshold suggesting reward promoting action, however, pretreatment with subeffective doses of Gi/o inhibitor (pertussis toxin, PTX) or PKA inhibitor (Rp-cAMPS) or ERK inhibitor (U0126) via icv route, attenuated CART mediated reward experience. Operant conditioned rats showed increased pCREB levels in the nucleus accumbens shell (AcbSh), ventral tegmental area (VTA) and hypothalamic paraventricular nucleus (PVN). Infusion of CART (icv) in the conditioned rats augmented the population of pCREB positive cells in the AcbSh, VTA and PVN areas, but not in the arcuate nucleus (ARC). Pretreatment with U0126 significantly decreased CART induced pCREB activation in the AcbSh and VTA, but not in PVN and ARC. ICSS or CART induced CREB mRNA expression in Acb and VTA was attenuated by U0126. We suggest that recruitment of Gi/o dependent PKA/ERK/CREB phosphorylation signaling in Acb and VTA might play an important role in CART induced reward behavior.

Identification of preoptic sleep neurons using retrograde labelling and gene profiling.

In humans and other mammalian species, lesions in the preoptic area of the hypothalamus cause profound sleep impairment, indicating a crucial role of the preoptic area in sleep generation. However, the underlying circuit mechanism remains poorly understood. Electrophysiological recordings and c-Fos immunohistochemistry have shown the existence of sleep-active neurons in the preoptic area, especially in the ventrolateral preoptic area and median preoptic nucleus. Pharmacogenetic activation of c-Fos-labelled sleep-active neurons has been shown to induce sleep. However, the sleep-active neurons are spatially intermingled with wake-active neurons, making it difficult to target the sleep neurons specifically for circuit analysis. Here we identify a population of preoptic area sleep neurons on the basis of their projection target and discover their molecular markers. Using a lentivirus expressing channelrhodopsin-2 or a light-activated chloride channel for retrograde labelling, bidirectional optogenetic manipulation, and optrode recording, we show that the preoptic area GABAergic neurons projecting to the tuberomammillary nucleus are both sleep active and sleep promoting. Furthermore, translating ribosome affinity purification and single-cell RNA sequencing identify candidate markers for these neurons, and optogenetic and pharmacogenetic manipulations demonstrate that several peptide markers (cholecystokinin, corticotropin-releasing hormone, and tachykinin 1) label sleep-promoting neurons. Together, these findings provide easy genetic access to sleep-promoting preoptic area neurons and a valuable entry point for dissecting the sleep control circuit.

Galanin-Expressing GABA Neurons in the Lateral Hypothalamus Modulate Food Reward and Noncompulsive Locomotion.

The lateral hypothalamus (LHA) integrates reward and appetitive behavior and is composed of many overlapping neuronal populations. Recent studies associated LHA GABAergic neurons (LHA GABA ), which densely innervate the ventral tegmental area (VTA), with modulation of food reward and consumption; yet, LHA GABA projections to the VTA exclusively modulated food consumption, not reward. We identified a subpopulation of LHA GABA neurons that coexpress the neuropeptide galanin (LHA Gal ). These LHA Gal neurons also modulate food reward, but lack direct VTA innervation. We hypothesized that LHA Gal neurons may represent a subpopulation of LHA GABA neurons that mediates food reward independent of direct VTA innervation. We used chemogenetic activation of LHA Gal or LHA GABA neurons in mice to compare their role in feeding behavior. We further analyzed locomotor behavior to understand how differential VTA connectivity and transmitter release in these LHA neurons influences this behavior. LHA Gal or LHA GABA neuronal activation both increased operant food-seeking behavior, but only activation of LHA GABA neurons increased overall chow consumption. Additionally, LHA Gal or LHA GABA neuronal activation similarly induced locomotor activity, but with striking differences in modality. Activation of LHA GABA neurons induced compulsive-like locomotor behavior; while LHA Gal neurons induced locomotor activity without compulsivity. Thus, LHA Gal neurons define a subpopulation of LHA GABA neurons without direct VTA innervation that mediate noncompulsive food-seeking behavior. We speculate that the striking difference in compulsive-like locomotor behavior is also based on differential VTA innervation. The downstream neural network responsible for this behavior and a potential role for galanin as neuromodulator remains to be identified.SIGNIFICANCE STATEMENT The lateral hypothalamus (LHA) regulates motivated feeding behavior via GABAergic LHA neurons. The molecular identity of LHA GABA neurons is heterogeneous and largely undefined. Here we introduce LHA Gal neurons as a subset of LHA GABA neurons that lack direct innervation of the ventral tegmental area (VTA). LHA Gal neurons are sufficient to drive motivated feeding and locomotor activity similar to LHA GABA neurons, but without inducing compulsive-like behaviors, which we propose to require direct VTA innervation. Our study integrates galanin-expressing LHA neurons into our current understanding of the neuronal circuits and molecular mechanisms of the LHA that contribute to motivated feeding behaviors.

Cue-induced food seeking after punishment is associated with increased Fos expression in the lateral hypothalamus and basolateral and medial amygdala.

In humans, relapse to unhealthy eating habits following dieting is a significant impediment to obesity treatment. Food-associated cues are one of the main triggers of relapse to unhealthy eating during self-imposed abstinence. Here we report a behavioral method examining cue-induced relapse to food seeking following punishment-induced suppression of food taking. We trained male rats to lever press for food pellets that were delivered after a 10-s conditional stimulus (CS) (appetitive). Following training, 25% of reinforced lever presses resulted in the presentation of a compound stimulus consisting of a novel CS (aversive) and the appetitive CS followed by a pellet and footshock. After punishment-imposed abstinence, we tested the rats in an extinction test where lever pressing resulted in the presentation of either the appetitive or aversive CS. We then compared activity of lateral hypothalamus (LH) and associated extrahypothalamic regions following this test. We also assessed Fos expression in LH orexin and GABA neurons. We found that cue-induced relapse of food seeking on test was higher in rats tested with the appetitive CS compared to the aversive CS. Relapse induced by the appetitive CS was associated with increased Fos expression in LH, caudal basolateral amygdala (BLA), and medial amygdala (MeA). This relapse was also associated with increased Fos expression in LH orexin and VGAT-expressing neurons. These data show that relapse to food seeking can be induced by food-associated cues after punishment-imposed abstinence, and this relapse is associated with increased activity in LH, caudal BLA, and MeA. (PsycINFO Database Record

Stimulation of the Pontine Parabrachial Nucleus Promotes Wakefulness via Extra-thalamic Forebrain Circuit Nodes.

Human and animal studies have identified an especially critical role for the brainstem parabrachial (PB) complex in regulating electrocortical (electroencephalogram [EEG]) and behavioral arousal: lesions of the PB complex produce a monotonous high-voltage, slow-wave EEG and eliminate spontaneous behaviors. We report here that targeted chemogenetic activation of the PB complex produces sustained EEG and behavioral arousal in the rat. We further establish, using viral-mediated retrograde activation, that PB projections to the preoptic-basal forebrain and lateral hypothalamus, but not to the thalamus, mediate PB-driven wakefulness. We exploited this novel and noninvasive model of induced wakefulness to explore the EEG and metabolic consequences of extended wakefulness. Repeated (daily) chemogenetic activation of the PB was highly effective in extending wakefulness over 4 days, although subsequent PB activation produced progressively lesser wake amounts. Curiously, no EEG or behavioral sleep rebound was observed, even after 4 days of induced wakefulness. Following the last of the four daily induced wake bouts, we examined the brains and observed a chimeric pattern of c-Fos expression, with c-Fos expressed in subsets of both arousal- and sleep-promoting nuclei. From a metabolic standpoint, induced extended wakefulness significantly reduced body weight and leptin but was without significant effect on cholesterol, triglyceride, or insulin levels, suggesting that high sleep pressure or sleep debt per se does not, as previously implicated, result in a deleterious metabolic phenotype.

The Proinflammatory Cytokine Interleukin 18 Regulates Feeding by Acting on the Bed Nucleus of the Stria Terminalis.

UNLABELLED: The proinflammatory cytokine IL-18 has central anorexigenic effects and was proposed to contribute to loss of appetite observed during sickness. Here we tested in the mouse the hypothesis that IL-18 can decrease food intake by acting on neurons of the bed nucleus of the stria terminalis (BST), a component of extended amygdala recently shown to influence feeding via its projections to the lateral hypothalamus (LH). We found that both subunits of the heterodimeric IL-18 receptor are highly expressed in the BST and that local injection of recombinant IL-18 (50 ng/ml) significantly reduced c-fos activation and food intake for at least 6 h. Electrophysiological experiments performed in BST brain slices demonstrated that IL-18 strongly reduces the excitatory input on BST neurons through a presynaptic mechanism. The effects of IL-18 are cell-specific and were observed in Type III but not in Type I/II neurons. Interestingly, IL-18-sensitve Type III neurons were recorded in the juxtacapsular BST, a region that contains BST-LH projecting neurons. Reducing the excitatory input on Type III GABAergic neurons, IL-18 can increase the firing of glutamatergic LH neurons through a disinhibitory mechanism. Imbalance between excitatory and inhibitory activity in the LH can induce changes in food intake. Effects of IL-18 were mediated by the IL-18R because they were absent in neurons from animals null for IL-18Rα (Il18ra(-/-)), which lack functional IL-18 receptors. In conclusion, our data show that IL-18 may inhibit feeding by inhibiting the activity of BST Type III GABAergic neurons. SIGNIFICANCE STATEMENT: Loss of appetite during sickness is a common and often debilitating phenomenon. Although proinflammatory cytokines are recognized as mediators of these anorexigenic effects, their mechanism and sites of action remain poorly understood. Here we show that interleukin 18, an anorexigenic cytokine, can act on neurons of the bed nucleus of the stria terminalis to reduce food intake via the IL-18 receptor. The findings identify a site and a mode of action that indicate targets for the treatment of cachexia or other eating disorders.

The Histaminergic Tuberomamillary Nucleus Is Involved in Appetite for Sex, Water and Amphetamine.

The histaminergic system is one component of the ascending arousal system which is involved in wakefulness, neuroendocrine control, cognition, psychiatric disorders and motivation. During the appetitive phase of motivated behaviors the arousal state rises to an optimal level, thus giving proper intensity to the behavior. Previous studies have demonstrated that the histaminergic neurons show an earlier activation during the appetitive phase of feeding, compared to other ascending arousal system nuclei, paralleled with a high increase in arousal state. Lesions restricted to the histaminergic neurons in rats reduced their motivation to get food even after 24 h of food deprivation, compared with intact or sham lesioned rats. Taken together, these findings indicate that the histaminergic system is important for appetitive behavior related to feeding. However, its role in other goal-directed behaviors remains unexplored. In the present work, male rats rendered motivated to obtain water, sex, or amphetamine showed an increase in Fos-ir of histaminergic neurons in appetitive behaviors directed to get those reinforcers. However, during appetitive tests to obtain sex, or drug in amphetamine-conditioned rats, Fos expression increased in most other ascending arousal system nuclei, including the orexin neurons in the lateral hypothalamus, dorsal raphe, locus coeruleus and laterodorsal tegmental neurons, but not in the ventral tegmental area, which showed no Fos-ir increase in any of the 3 conditions. Importantly, all these appetitive behaviors were drastically reduced after histaminergic cell-specific lesion, suggesting a critical contribution of histamine on the intensity component of several appetitive behaviors.

Different Hypothalamic Nicotinic α7 Receptor Expression and Response to Low Nicotine Dose in Alcohol-Preferring and Alcohol-Avoiding Rats.

BACKGROUND: The aim of this study was to examine possible differences in nicotinic acetylcholine receptors and responses in rats with genetic preference or avoidance for alcohol. This was done by using 2 rat lines with high alcohol preference (Alko Alcohol [AA]) or alcohol avoidance (Alko Non-Alcohol [ANA]). METHODS: Locomotor activity was measured following nicotine and histamine H3 receptor (H3R) antagonist treatment. In situ hybridization and receptor ligand binding experiments were used in drug-naïve animals to examine the expression of different α nicotinic receptor subunits. RESULTS: The AA rats were found to be more sensitive to the stimulatory effect of a low dose of nicotine than ANA rats, which were not significantly activated. Combination of histamine H3R antagonist, JNJ-39220675, and nicotine resulted to similar locomotor activation as nicotine alone. To further understand the mechanism underlying the difference in nicotine response in AA and ANA rats, we studied the expression of α5, α6, and α7 nicotinic receptor subunits in specific brain areas of AA and ANA rats. We found no differences in the expression of α5 nicotinic receptor subunits in the medial habenula and hippocampus or in α6 subunit in the ventral tegmental area and substantia nigra. However, the level of α7 nicotinic receptor subunit mRNA was significantly lower in the tuberomamillary nucleus of posterior hypothalamus of alcohol-preferring AA rats than in alcohol-avoiding ANA rats. Also the hypothalamic [125I-α-bungarotoxin binding was lower in AA rats indicating lower levels of α7 nicotinic receptors. CONCLUSIONS: The lower expression and receptor binding of α7 nicotinic receptors in the tuberomamillary nucleus of AA rats suggest a difference in the regulation of brain histamine neurons between the rat lines since the α7 nicotinic receptors are located in histaminergic neurons. Stronger nicotine-induced locomotor response, mediated partially via α7 receptors, and previously described high alcohol consumption in AA rats could be explained by the found difference in tuberomamillary α7 receptor levels.

Increase in c-Fos and Arc protein in retrosplenial cortex after memory-improving lateral hypothalamic electrical stimulation treatment.

Post-training Intracranial self-stimulation (ICSS) of the lateral hypothalamus (LH), a kind of rewarding deep-brain stimulation, potentiates learning and memory and increases c-Fos protein expression in specific memory-related brain regions. In a previous study, Aldavert-Vera et al. (2013) reported that post-acquisition LH-ICSS improved 48 h retention of a delay two-way active avoidance conditioning (TWAA) and induced c-Fos expression increase in CA3 at 90 min after administration. Nevertheless, this c-Fos induction was only observed after the acquisition session and not after the retention test at 48 h, when the ICSS improving effect was observed on memory. This current study aims to examine the hypothesis that post-training ICSS treatment may stimulate c-Fos expression at the time of the TWAA retention test in retrosplenial cortex (RSC), a hippocampus-related brain region more closely related with long-lasting memory storage. Effects of ICSS on Arc protein, a marker of memory-associated synaptic plasticity, were also measured by immunohistochemistry in granular and agranular RSC. The most innovative results are that the ICSS treatment potentiates the c-Fos induction across TWAA conditions (no conditioning, acquisition and retention), specifically in layer V of the granular RSC, along with increases of Arc protein levels in the granular but not in agranular areas of RSC ipsilaterally few hours after ICSS. This leads us to suggest that plasticity-related protein activation in the granular RSC could be involved in the positive modulatory effects of ICSS on TWAA memory consolidation, opening a new approach for future research in ICSS memory facilitation.

Reduction in 50-kHz call-numbers and suppression of tickling-associated positive affective behaviour after lesioning of the lateral hypothalamic parvafox nucleus in rats.

The parvafox nucleus is located ventrolaterally in the lateral hypothalamic area (LHA). Its core and shell are composed of neurons expressing the calcium-binding protein parvalbumin (PV) and the transcription factor Foxb1, respectively. Given the known functions of the LHA and that the parvafox nucleus receives afferents from the lateral orbitofrontal cortex and projects to the periaqueductal gray matter, a functional role of this entity in the expression of positive emotions has been postulated. The purpose of the present study was to ascertain whether the deletion of neurons in the parvafox nucleus influenced the tickling-induced 50-kHz calls, which are thought to reflect positive affective states, in rats. To this end, tickling of the animals (heterospecific play) was combined with intracerebral injections of the excitotoxin kainic acid into the parvafox nucleus. The most pronounced surgery-associated reduction in 50-kHz call-numbers was observed in the group of rats in which, on the basis of PV-immunoreactive-cell counts in the parvafox nucleus, bilateral lesions had been successfully produced. Two other parameters that were implemented to quantify positive affective behaviour, namely, an approach towards and a following of the hand of the tickling experimenter, were likewise most markedly suppressed in the group of rats with bilaterally successful lesions. Furthermore, positive correlations were found between each of the investigated parameters. Our data afford evidence that the parvafox nucleus plays a role in the production of 50-kHz calls in rats, and, more generally, in the expression of positive emotions.

The ventrolateral hypothalamic area and the parvafox nucleus: Role in the expression of (positive) emotions?

The lateral hypothalamus has been long suspected of triggering the expression of positive emotions, because stimulations of its tuberal portion provoke bursts of laughter. Electrophysiological studies in various species have indeed confirmed that the lateral hypothalamus contributes to reward mechanisms. However, only the rudiments of the neural circuit underlying the expression of positive emotions are known. The prefrontal cortex, the lateral hypothalamus, and the periaqueductal gray matter (PAG) are involved in these circuits; so, too, are the brainstem nuclei that control the laryngeal muscles and subserve mimicry, as well as the cardiovascular and respiratory systems. The implicated populations of hypothalamic neurons have not been defined either anatomically or molecularly. One promising candidate is the novel parvafox nucleus, which we recently described, in the murine medial forebrain bundle (mfb), which specifically expresses parvalbumin and Foxb1. With the molecularly defined parvafox nucleus as a centerpiece, the inputs from the prefrontal cortex and the projections to the PAG and brainstem can be studied with precision. By drawing on genetic approaches, it will be possible to manipulate the circuitry selectively with spatial and temporal exactitude and to evaluate the concomitant autonomic changes. These data will serve as a basis for imaging studies in humans using various paradigms to provoke the expression of positive emotions. In conclusion, studies of the hypothalamic parvafox nucleus will reveal whether this entity represents the fulcrum for positive emotions, as is the amygdala for fear and the insula for disgust.

dcc Haploinsufficiency results in blunted sensitivity to cocaine enhancement of reward seeking.

Mesocortical dopamine connectivity continues to mature during adolescence. This protracted development confers increased vulnerability for environmental and genetic factors to disrupt mesocortical wiring and subsequently influence responses to drugs of abuse in adulthood. The netrin-1 receptor, DCC, orchestrates medial prefrontal cortex dopamine input during adolescence and dictates the functional organization of local circuitry. Haploinsufficiency of dcc results in increased dopamine innervation to the medial prefrontal cortex, which in turn leads to resilience against the behavioral activating effects of stimulant drugs. However, whether sensitivity to the rewarding effects of drugs of abuse is also altered in dcc haploinsufficiency remains to be resolved. Here, we used the curve-shift method to measure cocaine-induced facilitation of intracranial self-stimulation (ICSS) in adult dcc haploinsufficient mice and wild-type littermates. We found that dcc haploinsufficient mice acquire ICSS behavior at comparable stimulation parameters to wild-type controls. However, cocaine-induced potentiation of ICSS is significantly blunted in dcc haploinsufficient mice. These results are consistent with decreased sensitivity to the rewarding effects of cocaine and/or decreased proclivity to invest effort in the pursuit of reward in dcc haploinsufficient mice. Moreover, these findings suggest that DCC signaling determines adult susceptibility to drug abuse most likely by controlling prefrontal cortex development in adolescence.

Role of the lateral hypothalamus in submandibular salivary secretion during feeding in rats.

To evaluate the role of the lateral hypothalamic area (LH) in the masticatory-salivary reflex, we investigated submandibular salivary secretion and the electromyographic (EMG) activity of the jaw-closer masseter muscle in sham-operated rats and rats with unilateral LH lesions. One week prior to surgery and recording, the rats were given daily experience of eating pellets; powder; or hard, medium or soft mash, all of which were composed of laboratory chow. Salivary secretion was induced during eating and grooming behavior. During eating, the powdered food induced the highest salivary flow rate, and the soft (wet) mash induced the lowest salivary flow rate. Conversely, the amount of food consumed (dry weight) was greatest when soft mash was provided and lowest when the powder or pellets (a dry diet) were provided. The EMG activity of the masseter muscle during eating was greatest during consumption of the pellets and weakest during consumption of the powder. LH lesions that were ipsilateral to the examined submandibular gland reduced salivary secretion to about 20-30% of the control value, whereas contralateral LH lesions reduced it to about 40-50% of the control value. Neither masseter muscle EMG activity nor food consumption was markedly affected by the presence of an LH lesion. These results suggest that the texture of food, especially its water content, affects the flow rate of saliva and that the LH is heavily involved in the masticatory-salivary reflex.

Delta-like 1 homologue (DLK1) protein in neurons of the arcuate nucleus that control weight homeostasis and effect of fasting on hypothalamic DLK1 mRNA.

Delta-like 1 homologue (DLK1; also called preadipocyte factor 1) is an epidermal growth factor repeat-containing transmembrane protein that is cleaved by tumor necrosis factor-α-converting enzyme to generate a biologically active soluble form. DLK1 is involved in the differentiation of several cell types, including adipocytes. Lack of the dlk1 gene results in adiposity, and polymorphism within the gene encoding DLK1 is associated with human obesity. The dlk1 gene is expressed in restricted areas of the adult brain, with an enrichment of cell bodies expressing DLK1 mRNA in the hypothalamus. Antibodies to DLK1 were used to study the cellular localization and chemical identity of DLK1-immunoreactive neuronal cell bodies in rat hypothalamus. DLK1 immunoreactivity was demonstrated in the cell soma and dendrites of cell bodies in the suprachiasmatic, supraoptic, paraventricular, dorsomedial, arcuate nuclei and in the perifornical/lateral hypothalamic area. In the arcuate nucleus (Arc), DLK1 immunoreactivity was mainly seen in many neurons of the ventromedial and to a lesser extent in its ventrolateral division. Double labeling showed that 93.7% of orexigenic agouti-related peptide (AgRP) and 94.1% of neuropeptide Y (NPY) neurons located in the ventromedial part of the Arc were DLK1 positive, whereas 36.1% of anorexigenic pro-opiomelanocortin and 34.6% of cocaine- and amphetamine-regulated transcript neurons of the Arc contained DLK1 immunoreactivity. DLK1 mRNA was downregulated in the hypothalamus of fasted animals. Presence of DLK1 in the majority of orexigenic Arc NPY/AgRP neurons and regulation of DLK1 mRNA by nutritional challenge suggest that DLK1 has a role in hypothalamic regulation of body weight control. © 2014 S. Karger AG, Basel.

Activation of lateral hypothalamus-projecting parabrachial neurons by intraorally delivered gustatory stimuli.

The present study investigated a subpopulation of neurons in the mouse parabrachial nucleus (PbN), a gustatory and visceral relay area in the brainstem, that project to the lateral hypothalamus (LH). We made injections of the retrograde tracer Fluorogold (FG) into LH, resulting in fluorescent labeling of neurons located in different regions of the PbN. Mice were stimulated through an intraoral cannula with one of seven different taste stimuli, and PbN sections were processed for immunohistochemical detection of the immediate early gene c-Fos, which labels activated neurons. LH projection neurons were found in all PbN subnuclei, but in greater concentration in lateral subnuclei, including the dorsal lateral subnucleus (dl). Fos-like immunoreactivity (FLI) was observed in the PbN in a stimulus-dependent pattern, with the greatest differentiation between intraoral stimulation with sweet (0.5 M sucrose) and bitter (0.003 M quinine) compounds. In particular, sweet and umami-tasting stimuli evoked robust FLI in cells in the dl, whereas quinine evoked almost no FLI in cells in this subnucleus. Double-labeled cells were also found in the greatest quantity in the dl. Overall, these results support the hypothesis that the dl contains direct a projection to the LH that is activated preferentially by appetitive compounds; this projection may be mediated by taste and/or postingestive mechanisms.