Increased feeding and food hoarding following food deprivation are associated with activation of dopamine and orexin neurons in male Brandt's voles

Small mammals usually face energetic challenges, such as food shortage, in the field. They have thus evolved species-specific adaptive strategies for survival and reproductive success. In the present study, we examined male Brandt's voles (Lasiopodomys brandtii) for their physiological, behavioral, and neuronal responses to food deprivation (FD) and subsequent re-feeding. Although 48 hr FD induced a decrease in body weight and the resting metabolic rate (RMR), such decreases did not reach statistical significance when compared to the control males that did not experience FD. During the first 2 hr of re-feeding following 48 hr FD, voles showed higher levels of feeding than controls. However, when permitted to hoard food, FD voles showed an increase in food hoarding, rather than feeding, compared to the controls. Further, both feeding and food hoarding induced an increase in neuronal activation, measured by Fos-ir, in a large number of brain areas examined. Interestingly, feeding and food hoarding also induced an increase in the percentage of tyrosine hydroxylase immunoreactive (TH-ir) cells that co-expressed Fos-ir in the ventral tegmental area (VTA), whereas both FD and feeding induced an increase in the percentage of orexin-ir cells that co-expressed Fos-ir in the lateral hypothalamus (LH). Food hoarding also increased orexin-ir/Fos-ir labeling in the LH. Together, our data indicate that food-deprived male Brandt's voles display enhanced feeding or food hoarding dependent upon an environmental setting. In addition, changes in central dopamine and orexin activities in selected brain areas are associated with feeding and hoarding behaviors following FD and subsequent re-feeding.     

Sexual differentiation of motivation: A novel mechanism?

Sex differences in motivation are apparent for the motivation to engage in sexual behavior, the motivation to take drugs of abuse, and the motivation to engage in parental behavior. In both males and females there is an increase in NAcc DA associated with motivated behaviors. Here it proposed that sex differences in the regulation of DA activity in the ascending mesolimbic projections may underlie sex differences in motivation. In particular, sex differences in the neuroendocrine regulation of this brain system play a role in the expression of sex differences in motivated behaviors. Here it is proposed that sexual differentiation of motivation is mediated, at least in part, by a novel mechanism in which ovarian hormones secreted at puberty in the female actively feminize the DA system.     

Pheromones linked to sexual behaviors excite the appetitive phase of feeding behavior of Aplysia fasciata. I. Modulation and excitation of appetitive behaviors

Pheromones presumably secreted by mating conspecifics – as well as homogenates containing tissue that is homologous with the atrial gland – increase the time that Aplysia fasciata spend feeding. This effect is caused by increasing the number of feeding episodes initiated in response to food, whereas the duration of a feeding bout remains unchanged. The increase in the number of feeding episodes is related to increases in head waving and crawling, i.e., appetitive movements that bring the animal into contact with food, as well as an increase in the responsiveness to food after it is contacted. Releasing a homogenate containing atrial gland tissue, or egg laying hormone, in the water near the animal elicited head lifting similar to that seen when animals are food aroused. The data indicate that the facilitation of Aplysia feeding caused by pheromones arises in part by an excitation of appetitive behaviors. These findings suggest that neurons generating appetitive behaviors will be affected by pheromones. Accepted: 28 November 1997     

Vasotocin stimulates appetitive responses to the visual and pheromonal stimuli used by male roughskin newts during courtship

It is now well established that vasotocin (AVT) and its mammalian homologue vasopressin influence various social behaviors in vertebrates, but less is known about the mechanisms through which these peptides modulate behavior. In male roughskin newts, Taricha granulosa, AVT stimulates a courtship behavior, amplectic clasping. Three general explanations for how AVT affects male courtship behavior have been considered: by enhancing a central state of sexual motivation, by affecting sensorimotor integration mechanisms in individual sensory modalities, or by influencing a nonspecific state of attention, arousal, or anxiety. AVT administration enhanced appetitive responses to visual and olfactory sexual stimuli, as would be expected if AVT affects a state of sexual motivation that affects behavioral responses to sexual stimuli regardless of the sensory modality in which they are processed. However, AVT selectively enhanced responses to female olfactory stimuli (sex pheromones), but similarly enhanced responses to female and food-related visual stimuli (worms), thus questioning the utility of such a motivational mechanism, as responses to female stimuli were not selectively enhanced in all sensory modalities. We therefore propose that exogenous AVT independently influences olfactory processes associated with orientation/attraction toward a female sex pheromone and visual processes associated with orientation/attraction toward a visual feature common to females and worms. In further experiments AVT administration failed to stimulate feeding behavior but did decrease locomotor activity. Thus, AVT does not stimulate courtship behavior in this species by enhancing the animals' general state of attention or by decreasing general anxiety, as responses to nonsexual, attractive stimuli were not uniformly enhanced, nor by stimulating general arousal, as activity levels did not increase. Rather, the data support the conclusion that AVT affects courtship by influencing specific sensorimotor processes associated with behavioral responses to individual releasing stimuli, which suggests a mechanistic framework for understanding socially motivated behavior is this species.     

Activation of Neurons of the Medullary Centers of the Autonomic Nervous System Related to Motivated Operant Movements Realized by Rats

Using the corresponding techniques, we visualized Fos-immunoreactive (Fos-ir) and NADPH diaphorasereactive (NADPH-dr) neurons in the medullary centers of the autonomic nervous system (ANS) of rats, which performed repetitive operant movements (catching of food globules from the manger by the left forelimb under conditions of high food motivation). Animals were trained to perform operant movements in 30 min-long everyday sessions during 12 days. The duration of a single food-procuring movement was about 600 msec. Realization of the operant reflex was accompanied by clearly expressed motivational/affective reactions. The heart rate (HR) in the course of each operant movement sharply dropped (on the 10th day of training, by 12%, on average) with subsequent recovery of this parameter within 3–4 sec. In the course of 30-min-long training sessions, the mean HR gradually decreased (in the examined group, 7%, on average) within an interval from the 5th to the 20th min with subsequent recovery until the end of the training session. The mean numbers of Fos-ir neurons in the medullary nuclei of the ANS (Sol, IRt, CVL, RVL, Amb, 10, and MdD) of rats performing food-procuring movements (n = 4) were significantly (P < 0.05) greater than those in the control, and the intensities of c-fos expression in these structures corresponded to the following succession: Sol > IRt > CVL+RVL/CVL > RVL. Large Fos-ir neurons were observed in the dorsal motor nucleus of the n. vagus (10) and in the Amb/RAmb nuclei. In a considerable proportion of neurons of the Sol and single cells of the 10 and Amb, we observed double labeling (Fos-ir + NADPH-dr). Thus, operant food-procuring movements are accompanied by episodes of bradycardia related to each separate realization; in addition, a long-lasting tonic decrease in the HR developed. These autonomic reactions are mediated by the abovementioned medullary ANS nuclei. It is supposed that the respective weakening of inhibitory sympathetic effects on spindle receptors of the muscles involved in realization of the above operant movements can provide facilitation of generation of proprioceptive impulsation, facilitation of monosynaptic spinal reflexes, and, finally, an increase in the efficacy of targeted limb movements directed toward food procurement.     

When do we eat? Ingestive behavior,survival, and reproductive success

The neuroendocrinology of ingestive behavior is a topic central to human health, particularly in light of the prevalence of obesity, eating disorders, and diabetes. The study of food intake in laboratory rats and mice has yielded some useful hypotheses, but there are still many gaps in our knowledge. Ingestive behavior is more complex than the consummatory act of eating, and decisions about when and how much to eat usually take place in the context of potential mating partners, competitors, predators, and environmental fluctuations that are not present in the laboratory. We emphasize appetitive behaviors, actions that bring animals in contact with a goal object, precede consummatory behaviors, and provide a window into motivation. Appetitive ingestive behaviors are under the control of neural circuits and neuropeptide systems that control appetitive sex behaviors and differ from those that control consummatory ingestive behaviors. Decreases in the availability of oxidizable metabolic fuels enhance the stimulatory effects of peripheral hormones on appetitive ingestive behavior and the inhibitory effects on appetitive sex behavior, putting a new twist on the notion of leptin, insulin, and ghrelin “resistance.” The ratio of hormone concentrations to the availability of oxidizable metabolic fuels may generate a critical signal that schedules conflicting behaviors, e.g., mate searching vs. foraging, food hoarding vs. courtship, and fat accumulation vs. parental care. In species representing every vertebrate taxa and even in some invertebrates, many putative “satiety” or “hunger” hormones function to schedule ingestive behavior in order to optimize reproductive success in environments where energy availability fluctuates.     

食物成瘾及其神经环路调控机制

食物成瘾是指人们对某些特定食物（高度加工、可口、高热量的食物）的依赖性达到难以控制的程度,并表现出一系列成瘾样的行为学变化,具有强迫性、长期性和反复性的特点。食物成瘾可引起肥胖症,而且是大部分人不能维持减肥效果或坚持限制性饮食以保持健康体重的核心因素。深入理解食物成瘾及其神经生物学机制,将为干预食物成瘾以改善肥胖提供准确的靶点。食物成瘾的诊断标准是耶鲁大学食物成瘾量表,而食物成瘾的动物模型为小鼠食物自我管理模型。外侧下丘脑-腹侧被盖区-伏隔核神经环路、腹侧被盖区-前边缘皮质-伏隔核神经环路和外侧隔核-结节核神经环路是调控食物成瘾的关键神经环路机制。     

Orexins activate histaminergic neurons via the orexin 2 receptor.

Orexins (orexin A and B) are recently identified neuropeptides implicated in the regulation of vigilance states and energy homeostasis. We have shown here the physiological significance of histaminergic neurons in the orexin-induced arousal responses. Immunohistochemical and electron microscopic techniques revealed direct synaptic interaction between orexin-immunoreactive nerve terminals and histidine decarboxylase-immunoreactive neurons in the TMN. Electrophysiological study revealed that orexins dose-dependently activate histaminergic neurons, which were freshly isolated from rats TMN region. To further evaluate, we examined the effect of pyrilamine, an H(1) receptor antagonist, on orexin-induced arousal response in rats. Simultaneously recordings of electroencephalograph and electromyograph showed that intracerebroventricular infusion of orexin A significantly increased the awake state in the light phase. Central application of pyrilamine significantly inhibited this response. These results strongly suggest that activation of histaminergic neurons by orexins might be important for modulation of the arousal.     

Topography of Fos-Immunoreactive and NADPH-d-Reactive Neurons in the Limbic Structures of the Basal Forebrain and in the Hypothalamus during Realization of Motivated Operant Movements in Rats

We estimated in rats the expression of early gene c-fos (marker of neuronal activation) and NADPH-diaphorase activity (NO-synthase marker) in the limbic structures of the basal forebrain and in the hypothalamus. Estimations were performed in the norm, in the state of starvation, and after realization of long-lasting (repeated 4 to 12 times per minute for 30 min) motivated stereotyped food-procuring forelimb movements. In food-deprived animals, a significantly greater (Р < 0.05), as compared with the control, number of Fos-immunoreactive (Fos-ir) and NADPH-diaphorase-reactive (NADPH-dr) neurons was observed in limbic structures, namely in the medial septum (MS), nuclei of the vertical and horizontal branches of the diagonal fascia (VDB and НDB), magnocellular preoptic nucleus (MCPO), complex of the substantia innominata−basal nucleus of Meynert of the pallidum, SI-GP(B), as well as in the laterodorsal tegmental nucleus (LDTg), medial part of the pallidum (MGP), paraventricular and lateral nuclei of the hypothalamus (Pa and LH), and islands of Calleja (ICj and ICjM). In the limbic structures and pontine nuclei of rats of the experimental group (that performed operant movements), greater mean densities of labeled neurons were found in the succession LDTg < SI < MCPO < GP(B) < MS < VDB < HDB. The maximum mean density of Fos-ir neurons (13.8 ± 0.9 labeled nuclei within 200 × 200 μm² area) was found in the HDB. In the hypothalamic nuclei of starving rats, c-fos expression was two times higher than that in the control. After realization of operant movements, the intensity of expression in the LH was somewhat smaller, while in the Ра it was higher. The maximum density of NADPH-dr neurons was observed in the Pa (303.4 ± 18.7 cells), in the ICj and ICjM (287 ± 11.6 and 260 ± 8.7 neurons, respectively), and in the MGP (93 ± 6.7 labeled cells). When analyzing the distribution of labeled neurons in experimental rats, we found high densities of double-labeled cells (Fos + NADPH-d positivity) in the Pa, MGP, ICj, and ICjM. Such specificity of changes in the c-fos expression and NADPH-d reactivity in the hypothalamus correlates, perhaps, with the formation of motivation signals related to a delay in food accessibility and supply of food. Modifications of neuronal activity in limbic structures reflect involvement of the latter in the formation of motor programs for food-procuring movements and their realization. Neirofiziologiya/Neurophysiology, Vol. 41, No. 1, pp. 32–40, January–February, 2009.     

Hypocretins: The Timing of Sleep and Waking

The appropriate time and place for sleep and waking are important factors for survival. Sleep and waking, rest and activity, flight and fight, feeding, and reproduction are all organized in relation to the day and night. A biological clock, the suprachiasmatic nucleus (SCN), synchronized by photic influences and other environmental cues, provides an endogenous timing signal that entrains circadian body rhythms and is complemented by a homeostatic sleep pressure factor. Cholinergic, catecholaminergic, serotonergic, and histaminergic nuclei control wakefulness and mutually interact with the SCN as well as sleep- and wake-promoting neurons in the hypothalamus to form a bistable switch that controlls the timing of behavioral state transitions. Hypocretin neurons integrate circadian-photic and nutritional-metabolic influences and act as a conductor in the aminergic orchestra. Their loss causes narcolepsy, a disease conferring the inability to separate sleep and waking. Their role in appetitive behavior, stress, and memory functions is important to our understanding of addiction and compulsion.     

Hypocretins: the timing of sleep and waking

The appropriate time and place for sleep and waking are important factors for survival. Sleep and waking, rest and activity, flight and fight, feeding, and reproduction are all organized in relation to the day and night. A biological clock, the suprachiasmatic nucleus (SCN), synchronized by photic influences and other environmental cues, provides an endogenous timing signal that entrains circadian body rhythms and is complemented by a homeostatic sleep pressure factor. Cholinergic, catecholaminergic, serotonergic, and histaminergic nuclei control wakefulness and mutually interact with the SCN as well as sleep- and wake-promoting neurons in the hypothalamus to form a bistable switch that controls the timing of behavioral state transitions. Hypocretin neurons integrate circadian-photic and nutritional-metabolic influences and act as a conductor in the aminergic orchestra. Their loss causes narcolepsy, a disease conferring the inability to separate sleep and waking. Their role in appetitive behavior, stress, and memory functions is important to our understanding of addiction and compulsion.     

Comparative studies of the ingestive behaviors produced by microinjections of muscimol into the midbrain raphe nuclei of the ventral tegmental area of the rat

Microinjection of the GABA-A agonist muscimol into the median (MR) or dorsal (DR) raphe nuclei or the ventral tegmental area (VTA) of non-deprived rats induced intense feeding and drinking in a dose-dependent and site-specific manner. Lower doses of muscimol were required to increase food intake, spillage and water intake with injections into the MR than with injections into the other two sites. These data demonstrate that the MR is a more sensitive site for the elicitation of ingestive behavior than either the DR or the VTA.     

Restricted feeding with scheduled sucrose access results in an upregulation of the rat dopamine transporter

Recent studies suggest that the mesoaccumbens dopamine system undergoes neurochemical alterations as a result of restricted feeding conditions with access to sugars. This effect appears to be similar to the neuroadaptation resulting from drugs of abuse and may underlay some pathological feeding behaviors. To further investigate the cellular mechanisms of these alterations, the present study used quantitative autoradiography and in situ hybridization to assess dopamine membrane transporter (DAT) protein density and mRNA expression in restricted-fed and free-fed adult male rats. The restricted feeding regimen consisted of daily limited access to either a normally preferred sucrose solution (0.3 M) or a less preferred chow in a scheduled (i.e., contingent) fashion for 7 days. Restricted-fed rats with the contingent sucrose access lost less body weight, ate more total food, and drank more fluid than free-fed, contingent food, or noncontingent controls. In addition, these animals had selectively higher DAT binding in the nucleus accumbens and ventral tegmental area. This increase in protein binding also was accompanied by an increase in DAT mRNA levels in the ventral tegmental area. In contrast to the restricted-fed groups, no differential effect in DAT regulation was observed across free-fed groups. The observed alteration in behavior and DAT regulation suggest that neuroadaptation in the mesoaccumbens dopamine system develops in response to repeated feeding on palatable foods under dietary constraints. This supports the notion that similar cellular changes may be involved in restrictive eating disorders and bingeing.     

c-Fos expression in hypothalamic nuclei of food-entrained rats

The present study aimed to identify the hypothalamic nuclei involved with food entrainment by using c-Fos-like immunoreactivity (c-Fos-IR) as a marker of functional activation. We studied rats entrained 3 wk to restricted feeding schedules (RF), their ad libitum (AL) controls, and the persistence of c-Fos-IR temporal patterns in entrained-fasted rats. In addition, we included 22-h fasting and 22-h fasting-refeeding groups as controls of fasting and refeeding acute effects. Diurnal patterns of c-Fos-IR were observed in the tuberomammilar nucleus (TM) and suprachiasmatic nucleus (SCN) in AL rats. In all nuclei, except the SCN and ventromedial nucleus (VMH), restricted feeding schedules imposed a temporal pattern of increased c-Fos-IR around mealtime. An increase in c-Fos-IR before and after meal time was observed in dorsomedial nucleus (DMH), lateral nucleus (LH), perifornical area (PeF), and TM, and a marked increase was observed in the paraventricular nucleus (PVN) after feeding. Food-entrained c-Fos-IR patterns persisted after 3 days in fasting in DMH, LH, and PeF. Present data suggest that FEO might not rely on a single nucleus and rather may be a distributed system constituted of interacting nuclei in which the PVN is mainly involved with the response to signals elicited by food ingestion and, therefore, with the entraining pathway. We can suggest that the PeF and TM may be involved with the arousal state during food anticipation and the DMH and LH with the time-keeping mechanism of FEO or its output.     

Conjunctive processing of locomotor signals by the ventral tegmental area neuronal population

The ventral tegmental area (VTA) plays an essential role in reward and motivation. How the dopamine (DA) and non-DA neurons in the VTA engage in motivation-based locomotor behaviors is not well understood. We recorded activity of putative DA and non-DA neurons simultaneously in the VTA of awake mice engaged in motivated voluntary movements such as wheel running. Our results revealed that VTA non-DA neurons exhibited significant rhythmic activity that was correlated with the animal's running rhythms. Activity of putative DA neurons also correlated with the movement behavior, but to a lesser degree. More importantly, putative DA neurons exhibited significant burst activation at both onset and offset of voluntary movements. These findings suggest that VTA DA and non-DA neurons conjunctively process locomotor-related motivational signals that are associated with movement initiation, maintenance and termination.     

Leptin receptor signaling in midbrain dopamine neurons regulates feeding

The leptin hormone is critical for normal food intake and metabolism. While leptin receptor (Lepr) function has been well studied in the hypothalamus, the functional relevance of Lepr expression in the ventral tegmental area (VTA) has not been investigated. The VTA contains dopamine neurons that are important in modulating motivated behavior, addiction, and reward. Here, we show that VTA dopamine neurons express Lepr mRNA and respond to leptin with activation of an intracellular JAK-STAT pathway and a reduction in firing rate. Direct administration of leptin to the VTA caused decreased food intake while long-term RNAi-mediated knockdown of Lepr in the VTA led to increased food intake, locomotor activity, and sensitivity to highly palatable food. These data support a critical role for VTA Lepr in regulating feeding behavior and provide functional evidence for direct action of a peripheral metabolic signal on VTA dopamine neurons.     

Neural integration of reward, arousal, and feeding: Recruitment of VTA, lateral hypothalamus, and ventral striatal neurons

The ability to control neuronal activity using light pulses and optogenetic tools has revealed new properties of neural circuits and established causal relationships between activation of a single genetically defined population of neurons and complex behaviors. Here, we briefly review the causal effect of activity of six genetically defined neural circuits on behavior, including the dopaminergic neurons DA in the ventral tegmental area (VTA); the two main populations of medium-sized spiny neurons (D1- and D2-positive) in the striatum; the giant Cholinergic interneurons in the ventral striatum; and the hypocretin- and MCH- expressing neurons in the lateral hypothalamus. We argue that selective spatiotemporal recruitment and coordinated spiking activity among these cell type-specific neural circuits may underlie the neural integration of reward, learning, arousal and feeding.     

Identification of a histaminergic circuit in the caudal hypothalamus: An evidence for functional heterogeneity of histaminergic neurons

It is well established that histaminergic neurons in the posterior hypothalamus make connections with whole brain areas and regulate several functions. Recent evidence indicates that histaminergic neurons are heterogeneous cell group and organized into distinct circuits. However, functional circuits of histaminergic neurons have not been fully mapped so far. To address this issue, we have investigated antihistamine-sensitive neuronal activation in the hypothalamus to determine the hypothalamic region primarily innervated by histaminergic neurons. Here we review our recent findings showing the existence of the heterogeneous subpopulations of histaminergic neurons in the TMN that innervated distinct regions to regulate particular functions. We have identified the caudal part of the arcuate nucleus of hypothalamus (cARC) as a target region of histaminergic neurons in food-restricted rats by assessing suppression of c-Fos expression by pretreatment with antihistamines. Histaminergic neurons in the tuberomammillary nucleus (TMN) are morphologically subdivided into five groups (E1–E5). Among the subdivisions, the E3 group was found to be activated corresponding to the activation of cARC neurons. Our findings suggest that this subpopulation selectively innervate cARC neurons. Accumulating reports have also described c-Fos expression in other TMN subpopulations. Various stress challenge induced c-Fos expression primarily in E4 and E5 subpopulations. Motivation- and drug-induced arousal elicited in common activation of ventrolateral part of the TMN containing E1 and E2 subdivisions, which receive projections from wake-active orexin neurons and sleep-active GABA neurons. These lines of evidence support the hypothesis that there are heterogeneous subpopulations in the TMN that innervated distinct regions to regulate particular functions.     

Key roles of the histaminergic system in sleep-wake regulation

Histamine plays an important role in mediating wakefulness in mammals. Based on the findings from gene-manipulated mice, we provide several lines of evidence showing the roles of the histaminergic system in the somnogenic effects of prostaglandin (PG) D2 and adenosine, and in the arousal effects of PGE2 and orexin. PGD2 activates DP1 receptors (R) to promote sleep by stimulating them to release adenosine. The released adenosine activates adenosine A2AR and subsequently excites the ventrolateral preoptic area (VLPO), one of the sleep centers in the anterior hypothalamus. VLPO neurons then send inhibitory signals to downregulate the histaminergic tuberomammillary nucleus (TMN), which contributes to arousal. A1R is expressed in histaminergic neurons of the rat TMN. Adenosine in the TMN inhibits the histaminergic system via A1R and promotes non–rapid eye movement sleep. Conversely, both endogenous PGE2 and orexin activate the histaminergic system through EP4R and OX-2R, respectively, to promote wakefulness via histamine H1R. Furthermore, the arousal effect of ciproxifan, H3R antagonist, depends on the activation of histaminergic systems. These findings indicate that VLPO and TMN regulate sleep and wakefulness by means of a “flip-flop” mechanism operating in an anti-coincident manner during sleep–wake state transitions.