Role of orexin receptors in the nucleus accumbens in dopamine-dependent turning behaviour of rats

In vivo microdialysis reveals that blockade of accumbal orexin OX2 but not OX1 receptors enhances dopamine efflux in the nucleus accumbens of freely moving rats

The nucleus accumbens contains orexinergic neural inputs and orexin OX₁ -and OX₂ -receptors. Behavioural studies suggest that accumbal orexin receptors modulate accumbal dopaminergic activity-dependent locomotion in rats. We studied the effects of intra-accumbal injection of orexin receptor ligands on accumbal extracellular dopamine levels in freely moving rats, using in vivo microdialysis, and analysed the roles of OX₁ - and OX₂ -receptors in the regulation of basal accumbal dopamine efflux. The orexin receptor ligands were applied intra-accumbally though a microinjection needle attached with a dialysis probe. Neither the non-selective OX₁ - and OX₂ -receptor agonist orexin-A nor the preferential OX₂ -receptor agonist orexin-B (500.0 pg and 5.0 ng) altered accumbal dopamine levels. The non-selective OX₁ - and OX₂ -receptor antagonist MK-4305 (suvorexant, 500.0 pg, 2.5 and 5.0 ng) enhanced dopamine efflux. A 2-h tetrodotoxin infusion into nucleus accumbens through the probe or co-administration of orexin-A (500.0 pg) strongly inhibited MK-4305 (5.0 ng)-induced accumbal dopamine efflux. The selective OX₂ -receptor antagonist EMPA (90.0 and 900.0 pg, 9.0 ng) increased dopamine efflux. Intra-accumbal infusion of tetrodotoxin abolished EMPA (9.0 ng)-induced dopamine efflux. The selective OX₁ -receptor antagonist SB-334867 (10.0 and 20.0 ng) failed to alter dopamine efflux. Co-administration of orexin-B (500.0 pg) inhibited both EMPA (9.0 ng)- and MK-4305 (5.0 ng)-induced dopamine efflux. Intraperitoneal injection of MK-4305 (10.0 mg/kg) did not affect accumbal dopamine efflux. The present study provides in vivo neuropharmacological evidence that accumbal OX₂ - but not OX₁ -receptors exert inhibitory regulation of basal accumbal dopamine efflux and that blockade of accumbal OX₂ -receptors enhances dopamine efflux in nucleus accumbens of freely moving rats.

OX2 receptors mediate the inhibitory effects of orexin-A on potassium chloride-induced increases in intracellular calcium ion levels in neurons derived from rat dorsal root ganglion in a chronic pain model

AIMS

Orexin-A is known to induce anti-nociceptive effects in animal models of chronic pain. We have found that orexin-A inhibits KCl loading-induced increases in the intracellular calcium ion levels ([Ca²⁺ ]_i ) in C-fiber-like neurons of rats showing inflammatory nociceptive behavior. Here, we examined the effects of orexin-A on the depolarization of C-fiber-like neurons derived from a rat model for another type of chronic pain, namely neuropathic pain. Thus, we analyzed the effects of orexin-A on KCl-induced increases in [Ca²⁺ ]_i in C-fiber-like neurons of rats with sciatic nerve ligation.

METHODS

Paw withdrawal and threshold force in response to tactile stimuli were evaluated using von Frey filaments. Sham-operated rats served as controls. [Ca²⁺ ]_i in neurons were visualized by calcium fluorescent probe. Changes in [Ca²⁺ ]_i were assessed using relative fluorescence intensity.

RESULTS

Seven days after sciatic nerve ligation, paw withdrawal and threshold force for tactile stimuli were increased and reduced, respectively. KCl loading to neurons from either sciatic nerve-ligated or control rats increased relative fluorescence intensity. The KCl-induced increase in relative fluorescence intensity in sciatic nerve-ligated, but not that of control, rats was inhibited by orexin-A. The OX₁ and OX₂ receptor antagonist MK-4305 and OX₂ receptor antagonist EMPA, but not the OX₁ receptor antagonist SB 334867, each counteracted orexin-A-induced inhibition of KCl-provoked increases in relative fluorescence intensity.

CONCLUSION

The present findings constitute neuropharmacological evidence that OX₂ but not OX₁ receptors mediate the inhibitory effects of orexin-A on KCl-induced increases in [Ca²⁺ ]_i in C-fiber-like neurons of rats showing hyperalgesia provoked by sciatic nerve ligation.

A Motivational and Neuropeptidergic Hub: Anatomical and Functional Diversity within the Nucleus Accumbens Shell

The mesocorticolimbic pathway is canonically known as the "reward pathway." Embedded within the center of this circuit is the striatum, a massive and complex network hub that synthesizes motivation, affect, learning, cognition, stress, and sensorimotor information. Although striatal subregions collectively share many anatomical and functional similarities, it has become increasingly clear that it is an extraordinarily heterogeneous region. In particular, the nucleus accumbens (NAc) medial shell has repeatedly demonstrated that the rules dictated by more dorsal aspects of the striatum do not apply or are even reversed in functional logic. These discrepancies are perhaps most easily captured when isolating the functions of various neuromodulatory peptide systems within the striatum. Endogenous peptides are thought to play a critical role in modulating striatal signals to either amplify or dampen evoked behaviors. Here we describe the anatomical-functional backdrop upon which several neuropeptides act within the NAc to modulate behavior, with a specific emphasis on nucleus accumbens medial shell and stress responsivity. Additionally, we propose that, as the field continues to dissect fast neurotransmitter systems within the NAc, we must also provide considerable contextual weight to the roles local peptides play in modulating these circuits to more comprehensively understand how this important subregion gates motivated behaviors.

Nucleus Accumbens Shell Orexin-1 Receptors Are Critical Mediators of Binge Intake in Excessive-Drinking Individuals

Excessive, binge alcohol drinking is a potent and pernicious obstacle to treating alcohol use disorder (AUD), and heavy-drinking humans are responsible for much of the substantial costs and harms of AUD. Thus, identifying key mechanisms that drive intake in higher-drinking individuals may provide important, translationally useful therapeutic interventions. Orexin-1-receptors (Ox1Rs) promote states of high motivation, and studies with systemic Ox1R inhibition suggest a particular role in individuals with higher intake levels. However, little has been known about circuits where Ox1Rs promote pathological intake, especially excessive alcohol consumption. We previously discovered that binge alcohol drinking requires Ox1Rs in medial nucleus accumbens shell (Shell), using two-bottle-choice Drinking-in-the-Dark (2bc-DID) in adult, male C57BL/6 mice. Here, we show that Shell Ox1Rs promoted intake during intermittent-access alcohol drinking as well as 2bc-DID, and that Shell inhibition with muscimol/baclofen also suppressed 2bc-DID intake. Importantly, with this large data set, we were able to demonstrate that Shell Ox1Rs and overall activity were particularly important for driving alcohol consumption in higher-drinking individuals, with little overall impact in moderate drinkers. Shell inhibition results were compared with control data combined from drug treatments that did not reduce intake, including NMDAR or PKC inhibition in Shell, Ox1R inhibition in accumbens core, and systemic inhibition of dopamine-1 receptors; these were used to understand whether more specific Shell Ox1R contributions in higher drinkers might simply result from intrinsic variability in mouse drinking. Ineffectiveness of Shell inhibition in moderate-drinkers was not due to a floor effect, since systemic baclofen reduced alcohol drinking regardless of basal intake levels, without altering concurrent water intake or saccharin consumption. Finally, alcohol intake in the first exposure predicted consumption levels weeks later, suggesting that intake level may be a stable trait in each individual. Together, our studies indicate that Shell Ox1Rs are critical mediators of binge alcohol intake in higher-drinking individuals, with little net contribution to alcohol drinking in more moderate bingers, and that targeting Ox1Rs may substantially reduce AUD-related harms.

Role of the orexin receptors within the nucleus accumbens in the drug priming-induced reinstatement of morphine seeking in the food deprived rats

Orexin plays a key role in mediating stress-induced drug relapse. However, the role of different types of orexinergic receptors that modulate stress-induced drug seeking remains unknown. The nucleus accumbens (NAc) has an important role in the reward system and receives orexinergic projections of the lateral hypothalamus. In addition, orexin interacts with other receptors that are involved in drug reinstatement. Therefore, in the present study, the role of orexin receptors in the NAc in morphine priming- induced reinstatement and the effect of food deprivation (FD) on drug reinstatement were examined. The extinguished morphine preference rats were tested for reinstatement following the 24-h FD condition after conditioning was induced. In the other groups, the animals were given intra-accumbal administration of SB334867 (01, 1 and 10 nM/0.5 μl DMSO) as an orexin-1 receptor antagonist and TCSOX229 (1, 5 and 25 nM/0.5 μl DMSO), as an orexin-2 receptor antagonist. The results showed that the blockade of two types of orexin receptors in the NAc remarkably attenuated the effect of FD on the drug reinstatement; however, they were more effective in FD condition. These findings indicate that the NAc is a brain area within which orexin has a fundamental role in the effect of stress on morphine-induced reinstatement and the effect of food deprivation- on the reinstatement of morphine.

Nucleus Accumbens Shell and mPFC but Not Insula Orexin-1 Receptors Promote Excessive Alcohol Drinking

Addiction to alcohol remains a major social and economic problem, in part because of the high motivation for alcohol that humans exhibit and the hazardous binge intake this promotes. Orexin-1-type receptors (OX1Rs) promote reward intake under conditions of strong drives for reward, including excessive alcohol intake. While systemic modulation of OX1Rs can alter alcohol drinking, the brain regions that mediate this OX1R enhancement of excessive drinking remain unknown. Given the importance of the nucleus accumbens (NAc) and anterior insular cortex (aINS) in driving many addictive behaviors, including OX1Rs within these regions, we examined the importance of OX1Rs in these regions on excessive alcohol drinking in C57BL/6 mice during limited-access alcohol drinking in the dark cycle. Inhibition of OX1Rs with the widely used SB-334867 within the medial NAc Shell (mNAsh) significantly reduced drinking of alcohol, with no effect on saccharin intake, and no effect on alcohol consumption when infused above the mNAsh. In contrast, intra-mNAsh infusion of the orexin-2 receptor TCS-OX2-29 had no impact on alcohol drinking. In addition, OX1R inhibition within the aINS had no effect on excessive drinking, which was surprising given the importance of aINS-NAc circuits in promoting alcohol consumption and the role for aINS OX1Rs in driving nicotine intake. However, OX1R inhibition within the mPFC did reduce alcohol drinking, indicating cortical OXR involvement in promoting intake. Also, in support of the critical role for mNAsh OX1Rs, SB within the mNAsh also significantly reduced operant alcohol self-administration in rats. Finally, orexin ex vivo enhanced firing in mNAsh neurons from alcohol-drinking mice, with no effect on evoked EPSCs or input resistance; a similar orexin increase in firing without a change in input resistance was observed in alcohol-naïve mice. Taken together, our results suggest that OX1Rs within the mNAsh and mPFC, but not the aINS, play a central role in driving excessive alcohol drinking.

Evidence for a Role of Orexin/Hypocretin System in Vestibular Lesion-Induced Locomotor Abnormalities in Rats

Vestibular damage can induce locomotor abnormalities in both animals and humans. Rodents with bilateral vestibular loss showed vestibular deficits syndrome such as circling, opisthotonus as well as locomotor and exploratory hyperactivity. Previous studies have investigated the changes in the dopamine system after vestibular loss, but the results are inconsistent and inconclusive. Numerous evidences indicate that the orexin system is implicated in central motor control. We hypothesized that orexin may be potentially involved in vestibular loss-induced motor disorders. In this study, we examined the effects of arsanilate- or 3,3′-iminodipropionitrile (IDPN)-induced vestibular lesion (AVL or IVL) on the orexin-A (OXA) labeling in rat hypothalamus using immunohistochemistry. The vestibular lesion-induced locomotor abnormalities were recorded and verified using a histamine H4 receptor antagonist JNJ7777120 (20 mg/kg, i.p.). The effects of the orexin receptor type 1 antagonist SB334867 (16 μg, i.c.v.) on these behavior responses were also investigated. At 72 h post-AVL and IVL, animals exhibited vestibular deficit syndrome and locomotor hyperactivity in the home cages. These responses were significantly alleviated by JNJ7777120 which also eliminated AVL-induced increases in exploratory behavior in an open field. The numbers of OXA-labeled neurons in the hypothalamus were significantly increased in the AVL animals at 72 h post-AVL and in the IVL animals at 24, 48, and 72 h post-IVL. SB334867 significantly attenuated the vestibular deficit syndrome and locomotor hyperactivity at 72 h post-AVL and IVL. It also decreased exploratory behavior in the AVL animals. These results suggested that the alteration of OXA expression might contribute to locomotor abnormalities after acute vestibular lesion. The orexin receptors might be the potential therapeutic targets for vestibular disorders.

The hypocretins/orexins: integrators of multiple physiological functions

The hypocretins (Hcrts), also known as orexins, are two peptides derived from a single precursor produced in the posterior lateral hypothalamus. Over the past decade, the orexin system has been associated with numerous physiological functions, including sleep/arousal, energy homeostasis, endocrine, visceral functions and pathological states, such as narcolepsy and drug abuse. Here, we review the discovery of Hcrt/orexins and their receptors and propose a hypothesis as to how the orexin system orchestrates these multifaceted physiological functions.

Blockade of orexin-1 receptors in the ventral tegmental area could attenuate the lateral hypothalamic stimulation-induced potentiation of rewarding properties of morphine

The orexins (hypocretins) are lateral hypothalamic (LH) neuropeptides that have been implicated in a variety of behaviors ranging from feeding to sleep and arousal. Evidence from animal models suggests a role for orexins in reward processing and drug addiction. In the present study, we investigated the direct effect of an orexin antagonist in the ventral tegmental area (VTA) on acquisition and expression of morphine conditioned place preference (CPP) induced by concurrent stimulation of the LH. Eighty-one adult male Wistar rats weighing 220-280 g were unilaterally implanted by two separate cannulae into the LH and VTA. The CPP paradigm was done; conditioning score and locomotor activity were recorded by Ethovision software. The animals received SB334867 as a selective orexin-1 receptor antagonist (0.1, 1 and 10 nmol/0.3 μl DMSO) in the VTA, just 5 min prior to intra-LH administration of ineffective dose of carbachol as a cholinergic agonist (62.5 nmol/0.5 μl saline) that stimulates orexin neurons in the LH and ineffective dose of morphine (1 mg/kg, subcutaneously) concurrently during conditioning phase (acquisition experiments) or post-conditioning phase (expression experiments). Data showed that the blockade of orexin-1 receptors in the VTA could inhibit the acquisition (development) but not expression of LH stimulation-induced morphine CPP in the rats. Our findings suggest that the orexinergic projections from the LH to the VTA are involved in the development of the LH stimulation-induced potentiation of morphine rewarding properties and orexin-1 receptors in the VTA have a substantial role in this phenomenon.

Orexin receptors within the nucleus accumbens shell mediate the stress but not drug priming-induced reinstatement of morphine conditioned place preference

Orexins are found to participate in mediating stress-induced drug relapse. However, the neuroanatomical basis that orexin transmission modulates stress-induced drug seeking remains unknown. The nucleus accumbens shell (NAcSh), best known for its role in appetitive and negative motivation via dopamine receptors, is likely to be the potential important brain area where the orexin system mediates stress-induced drug relapse since the function of dopamine system in the NAcSh can be regulated by orexin transmission. In the present study, a morphine conditioned place preference (CPP) model was used to determine whether the two types of orexin receptors would be involved into footshock-induced and/or drug priming-induced CPP reinstatement differentially. The results showed that blockade of orexin-1 or orexin-2 receptor in the NAcSh significantly attenuated stress-induced morphine CPP reinstatement, but neither of the orexin antagonists had any effect on morphine priming-induced reinstatement. These findings indicate that the NAcSh is a brain area through which orexins participate in stress but not drug priming-induced relapse of opioid seeking.

Central orexin (hypocretin) 2 receptor antagonism reduces ethanol self-administration, but not cue-conditioned ethanol-seeking, in ethanol-preferring rats

Orexins are hypothalamic neuropeptides which bind to two G-protein-coupled receptors, orexin-1 (OX(1)R) and orexin-2 (OX(2)R) receptor. While a role for OX(1)R has been established in both ethanol reinforcement and ethanol-seeking behaviour, the role of OX(2)R in these behaviours is relatively less-studied. The aim of this study was to determine the role of central OX(2)R in ethanol-taking and ethanol-seeking behaviour. Indiana ethanol-preferring rats were trained to self-administer ethanol (10% w/v) or sucrose (0.7–1% w/v) in the presence of reward-associated cues before being implanted with indwelling guide cannulae. The selective OX(2)R antagonist TCS-OX2-29 was administered i.c.v. to assess its effect on operant self-administration and cue-induced reinstatement following extinction. Following i.c.v. injection TCS-OX2-29 reduced self-administration of ethanol, but not sucrose. Despite reducing ethanol self-administration, TCS-OX2-29 had no impact on cue-induced reinstatement of ethanol seeking. To determine where in the brain OX(2)R were acting to modulate ethanol self-administration, TCS-OX2-29 was microinjected into either the shell or core of the nucleus accumbens (NAc). Intra-NAc core, but not shell, infusions of TCS-OX2-29 decreased responding for ethanol. Importantly, the doses of TCS-OX2-029 used were non-sedating. Collectively, these findings implicate OX(2)R in the NAc in mediating the reinforcing effects of ethanol. This effect appears to be drug-specific as antagonism of central OX(2)R had no impact on sucrose self-administration. Thus, OX(2)R in addition to OX(1)R may represent a potential therapeutic target for the treatment of ethanol-use disorders. However, unlike OX(1)R, no impact of OX(2)R antagonism was observed on cue-induced reinstatement, suggesting a more prominent role for OX(2)R in ethanol self-administration compared to cue-conditioned ethanol-seeking.

Local hypocretin-1 modulates terminal dopamine concentration in the nucleus accumbens shell

Hypocretins (hcrt), also known as orexins, play a critical role in reward-seeking behavior for natural rewards and drugs of abuse. The mesolimbic dopamine pathway that projects from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) is critically involved in the neural mechanisms underlying reward-seeking and motivation. Hcrt immunopositive fibers densely project to the shell of the nucleus accumbens (NAcSh), suggesting that the NAcSh might be a site for the interaction between hcrt and dopaminergic modulation of reward-seeking behavior. While it is known that hcrt action in the VTA can increase dopamine in the NAc, it has not been determined if hcrt released locally at dopaminergic terminals in the NAcSh can modulate dopamine concentration. Here, we use fast scan cyclic voltammetry (FSCV) in forebrain slices containing the NAcSh to determine whether hcrt can alter evoked dopamine concentration. We found bath application of hcrt-1 increases phasically evoked dopamine release, without altering reuptake at dopamine terminals in the NAcSh. Hcrt-1-induced potentiation of dopamine concentration was inhibited by SB334867, a hcrt receptor 1 antagonist, as well as ionotropic glutamate receptor antagonists, AP-5, CNQX and DNQX. Taken together, these results suggest that local hcrt-1 can modulate dopamine in the NAcSh and may play a role in reward-seeking and appetitive behaviors.

Modulation of LPS-stimulated neuroinflammation in BV-2 microglia by Gastrodia elata: 4-hydroxybenzyl alcohol is the bioactive candidate

ETHNOPHARMACOLOGICAL RELEVANCE

Gastrodia elata Blume (Orchidaceae, GE) a traditional plant in Oriental countries is known for its enormous benefits to treat headaches, dizziness, vertigo and convulsive illnesses. In the present study, the ethnopharmacological role of GE in neuroinflammation mediated by activated microglia and the mechanisms underlying were reported.

MATERIALS AND METHODS

BV-2 microglia activated by lipopolysaccharide (LPS) was employed and the effects of GE on corresponding neuroinflammatory parameters were assessed.

RESULTS

GE extract inhibited LPS-stimulated production of inflammatory cytokines and down regulated the c-Jun NH(2)-Terminal Kinase (JNK) and nuclear factor-kappa B (NF-κB) signaling pathways, which are known to be involved in neuroinflammation. Further, inhibition of NO and iNOS by 4-hydroxybenzyl alcohol (4-HBA), one of the active constituent of GE in LPS-stimulated BV-2 cells suggest that 4-HBA might be the bioactive candidate.

CONCLUSION

GE extract and its active constituent 4-HBA could be further exploited to mitigate microglial activation and may be developed as a new therapeutic remedy in treating various neuroinflammatory diseases.

Prolonged effects of intracerebroventricular angiotensin II on drinking, eating and locomotor behavior in mice

The effects of centrally administered Angiotensin II (Ang II) on water and food intake in rodent models are well known. However, most studies have focused on the acute effects of intracranial Ang II. In the current study, we evaluated the effects of intracerebroventricular Ang II on food and water intake as well as locomotor activity over the entire dark phase of the murine diurnal cycle. Consistent with the previous reports, centrally administered Ang II rapidly stimulated water intake over the initial 1-hour period following treatment. However, this acute increase was immediately followed by a marked reduction in water intake resulting in decreased cumulative water intake approximately 7h after Ang II treatment. Pretreating animals with an Ang II type 1 receptor blocker, Losartan, completely antagonized the acute effect of Ang II and abolished initial water intake. In contrast, application of an Ang II type 2 receptor blocker, PD123319, abrogated the prolonged inhibitory effect of Ang II on drinking behavior and partially suppressed the initial increases in water intake. The suppressive effects of Ang II on cumulative food intake and spontaneous physical activity were also evident throughout the entire dark phase of diurnal cycle. These experiments are the first to suggest that the stimulatory effect of central Ang II treatment on water consumption is very temporary and that it causes a sustained suppressive effect on voluntary locomotion and food intake behavior in mice.

Electrophysiological effects of orexin-B and dopamine on rat nucleus accumbens shell neurons in vitro

Orexin (ORX) plays a critical role in reward-seeking behavior for natural rewards and drugs of abuse. The mesolimbic dopamine (DA) pathway that projects into the nucleus accumbens (NAc) from the ventral tegmental area is deeply involved in the neural mechanisms underlying reward, drug abuse and motivation. A recent study demonstrated that ORX-immunopositive fibers densely project into the shell of the NAc (NAcSh), suggesting that the NAcSh might be a site of the interaction between the ORXergic and DAergic systems for reward-seeking behavior. Therefore, the electrophysiological effects of ORX-B and DA on NAcSh neurons were examined extracellularly in rat brain slice preparations. ORX-B excited approximately 78% of neurons tested and inhibited 4%, whereas DA excited 50% and inhibited 22% of NAcSh neurons. These excitations and inhibitions persisted during synaptic blockade in a low-Ca(2+)/high-Mg(2+) solution. DA-induced excitation was attenuated by SCH23390 or sulpiride, whereas DA-induced inhibition was suppressed by sulpiride. Of the neurons that were excited by ORX-B, 71% and 18% were excited and inhibited by DA, respectively. In 63% of neurons that were excited by ORX-B, the simultaneous application of ORX-B and DA increased the firing rate to two times greater than ORX-B alone, whereas, the simultaneous application significantly decreased the neuronal firing rate by 73% in the remaining 37% compared to ORX-B. These results suggest that an interaction between the ORXergic and DAergic systems occurs in the NAcSh and that the NAcSh is involved in the neural mechanisms in which ORX participates in the regulation of reward-seeking behavior.

Electrophysiological effects of orexin/hypocretin on nucleus accumbens shell neurons in rats: an in vitro study

Orexin-A (ORX-A) and orexin-B (ORX-B) play critical roles in the regulation of sleep-wakefulness, energy homeostasis, neuroendocrine system and autonomic functions. Although ORXs are also implicated in the reward process, their electrophysiological effects on neurons in the shell of nucleus accumbems (NAcSh) have not been described thoroughly. Therefore we examined the electrophysiological effects of ORXs on rat NAcSh neurons. Whole cell patch clamp recording in vitro revealed that ORX-A and ORX-B depolarize NAcSh neurons in normal and/or tetrodotoxin (TTX)-containing artificial cerebrospinal fluid (ACSF). The depolarization accompanied by a decrease of membrane resistance was concentration-dependent, and there was no significant difference between the two dose-response curves obtained by ORX-A and ORX-B. The ORX-B-induced depolarization was reduced in low-Na(+), flufenamic acid-containing, and high-K(+) TTX ACSFs, and completely abolished in low-Na(+)/high-K(+) TTX ACSF. An inhibitor of the Na(+)/Ca(2+) exchanger had no effect on the depolarization. The reversal potential obtained from I-V relationships before and during the ORX-B-induced depolarization in low-Na(+) TTX ACSF was about -84mV, and that obtained in TTX ACSF using patch pipettes with Cs(+)-containing internal solution was about -38mV. These results suggest that ORXs directly depolarize NAcSh neurons via OX(2) receptors and via a dual ionic mechanism including an increase of nonselective cationic conductance and a decrease of K(+) conductance, and that NAcSh neurons are involved in the cellular mechanisms through which ORXs participate in the regulation of the reward process as well as feeding and arousal.