Reward loss and the basolateral amygdala: A function in reward comparisons

Frustrative nonreward: Detailed c-Fos expression patterns in the amygdala after consummatory successive negative contrast

The amygdala has been implicated in frustrative nonreward induced by unexpected reward downshifts, using paradigms like consummatory successive negative contrast (cSNC). However, existing evidence comes from experiments involving the central and basolateral nuclei on a broad level. Moreover, whether the amygdala's involvement in reward downshift requires a cSNC effect (i.e., greater suppression in downshifted animals than in unshifted controls) or just consummatory suppression without a cSNC effect, remains unclear. Three groups were exposed to (1) a large reward disparity leading to a cSNC effect (32-to-2% sucrose), (2) a small reward disparity involving consummatory suppression in the absence of a cSNC effect (8-to-2% sucrose), and (3) an unshifted control (2% sucrose). Brains obtained after the first reward downshift session were processed for c-Fos expression, a protein often used as a marker for neural activation. c-Fos-positive cells were counted in the anterior, medial, and posterior portions (A/P axis) of ten regions of the rat basolateral, central, and medial amygdala. c-Fos expression was higher in 32-to-2% sucrose downshift animals than in the other two groups in four regions: the anterior and the medial lateral basal amygdala, the medial capsular central amygdala, and the anterior anterio-ventral medial amygdala. None of the areas exhibited differential c-Fos expression between the 8-to-2% sucrose downshift and the unshifted conditions. Thus, amygdala activation requires exposure to a substantial reward disparity. This approach has identified, for the first time, specific amygdala areas relevant to understand the cSNC effect, suggesting follow-up experiments aimed at testing the function of these regions in reward downshift.

Coping with the experience of frustration throughout life: Sex- and age-specific effects of early life stress on the susceptibility to reward devaluation

Early life stress may lead to lifelong impairments in psychophysiological functions, including emotional and reward systems. Unpredicted decrease in reward magnitude generates a negative emotional state (frustration) that may be involved with susceptibility to psychiatric disorders. We evaluated, in adolescents and adult rats of both sexes, whether maternal separation (MS) alters the ability to cope with an unexpected reduction of reward later in life. Litters of Wistar rats were divided into controls (non handled - NH) or subjected to MS. Animals were trained to find sugary cereal pellets; later the amount was reduced. Increased latency to reach the reward-associated area indicates higher inability to regulate frustration. The dorsal hippocampus (dHC) and basolateral amygdala (BLA) were evaluated for protein levels of NMDA receptor subunits (GluN2A/GluN2B), synaptophysin, PSD95, SNAP-25 and CRF1. We found that adult MS males had greater vulnerability to reward reduction, together with decreased GluN2A and increased GluN2B immunocontent in the dHC. MS females and adolescents did not differ from controls. We concluded that MS enhances the response to frustration in adult males. The change in the ratio of GluN2A and GluN2B subunits in dHC could be related to a stronger, more difficult to update memory of the aversive experience.

Juvenile variable stress modulates, in female but not in male Wistar rats, ethanol intake in adulthood

Early stress can increase vulnerability to psychopathological disorders, including substance use disorders. The effects of stress in the juvenile period of the rat, that extends between weaning and the onset of adolescence (equivalent to late human childhood), have received little attention. This study assessed short and long-term behavioral effects of juvenile stress, with a focus on effects on ethanol intake. Male and female Wistar rats were exposed to variable stress (restraint, elevated platform, forced swimming, and social instability) or to restraint stress only, between postnatal days 26 to 29 (PDs 26-29). During adolescence, patterns of anxiety (PD 31) and depression (PD 33), ethanol intake (PDs 36-45) and behavioral sensitivity to the effects of acute stress (PD 47) were evaluated. In adulthood, alcohol ingestion was assessed through two-bottle ethanol intake tests (PDs 75-85). An additional experiment measured blood ethanol levels after a limited access intake session in adolescence. Exposure to juvenile variable stress exerted very mild effects in adolescence, but reduced ethanol ingestion in adulthood, in females only. Ethanol intake during the limited access session was significantly correlated to blood alcohol levels. The results indicate that a schedule of juvenile variable stress that did not significantly alter anxiety-related behaviors induced, nonetheless, sexually dimorphic effects on ethanol intake in adulthood. Early stress exposure that reduced alcohol intake in Wistar rats has been associated with changes on brain opioid and dopamine receptors. These results highlight the impact of early stress exposure on adult female ethanol consumption and its possible underlying neurobiological changes, involving opioid and dopamine receptors.

c-Fos expression after neonatal handling in social brain regions: Distinctive profile of RHA-rat schizophrenia model on a social preference test

Neonatal handling (NH) is an environmental manipulation that induces long-lasting changes in behavioural, neuroendocrine, and neuroanatomical processes in rodents. We have previously reported that NH treatment increases social interaction preference in an animal model of schizophrenia-relevant features, the Roman high-avoidance (RHA) rats. The present study was aimed at evaluating whether the increase of social behaviour/preference due to NH treatment in RHA rats is associated with differences in c-Fos expression levels in some of the brain areas that integrate the "social brain". To this aim, we evaluated the performance of adult male rats from both Roman rat strains (RHA vs. RLA -Roman low-avoidance- rats), either untreated (control) or treated with NH (administered during the first 21 days of life) in a social interaction task. For the analyses of c-Fos activation untreated and NH-treated animals were divided into three different experimental conditions: undisturbed home cage controls (HC); rats exposed to the testing set-up context (CTX); and rats exposed to a social interaction (SI) test. It was found that, compared with their RLA counterparts, NH treatment increased social behaviour in RHA rats, and also specifically enhanced c-Fos expression in RHA rats tested for SI in some brain areas related to social behaviour, i.e. the infralimbic cortex (IL) and the medial posterodorsal amygdala (MePD) regions.

Binging from Food to Alcohol: A Sequential Interaction Between Binging Behaviors in Male Wistar Rats

The development of excessive alcohol (ethanol) and/or highly palatable food self-administration is an essential task to elucidate the neurobiological mechanisms that underlie these behaviors. Previous work has highlighted that ethanol self-administration is modulated by both the induction of aversive states (i.e., stress or frustration) and by the concurrent availability of appetitive stimuli (e.g., food). In our protocol, rats are food deprived for three days until they reach 82%-85% of their ad libitum weight. After that, rats are exposed daily for 10 days to a brief binge or control eating experience with highly sugary and palatable food (i.e., the ingestion of 11.66 and 0.97 kcal/3 min, respectively), which is followed by a two-bottle-choice test (ethanol vs. water) in their home cages for 90 min. This model induces robust binge eating, which is followed by a selective increase in ethanol self-administration. Therefore, this protocol allows to study: a) behavioral and neurobiological factors related to binge eating, b) different stages of alcohol use, and c) interactions between the latter and other addictive-like behaviors, like binge eating.

Norepinephrine system at the interface of attention and reward

Reward learning is key to survival for individuals. Attention plays an important role in the rapid recognition of reward cues and establishment of reward memories. Reward history reciprocally guides attention to reward stimuli. However, the neurological processes of the interplay between reward and attention remain largely elusive, due to the diversity of the neural substrates that participate in these two processes. In this review, we delineate the complex and differentiated locus coeruleus norepinephrine (LC-NE) system in relation to different behavioral and cognitive substrates of reward and attention. The LC receives reward related sensory, perceptual, and visceral inputs, releases NE, glutamate, dopamine and various neuropeptides, forms reward memories, drives attentional bias and selects behavioral strategies for reward. Preclinical and clinical studies have found that abnormalities in the LC-NE system are involved in a variety of psychiatric conditions marked by disturbed functions in reward and attention. Therefore, we propose that the LC-NE system is an important hub in the interplay between reward and attention as well as a critical therapeutic target for psychiatric disorders characterized by compromised functions in reward and attention.

Frustrative nonreward and the basal ganglia: Chemogenetic inhibition and excitation of the nucleus accumbens and globus pallidus externus during reward downshift

Frustrative nonreward contributes to anxiety disorders and addiction, and is included in the Research Domain Criteria initiative as a relevant endophenotype. These experiments explored the role of the basal ganglia in consummatory reward downshift (cRD) using inhibitory and excitatory DREADDs (designer receptors exclusively activated by designer drugs) infused in either the nucleus accumbens (NAc) or one of its downstream targets, the globus pallidus externus (GPe). NAc inhibition did not disrupt consummatory suppression during a 32-to-2% (Experiment 1) or 8-to-2% sucrose downshift (Experiment 2). However, NAc excitation enhanced consummatory suppression during a 32-to-2% sucrose downshift (Experiment 1). GPe inhibition caused a trend toward increased consummatory suppression after a 32-to-2% sucrose downshift, whereas GPe excitation eliminated consummatory suppression after an 8-to-2% sucrose downshift (Experiment 3). Chemogenetic manipulations of NAc and GPe had no detectable effects on open field activity. The effects of DREADD activation via clozapine N-oxide (CNO) administration were compared to controls that carried the DREADDs, but received vehicle injections. There was no evidence that CNO or vehicle injections in virus vector control (VVC) animals affected cRD or OF activity after either CNO or vehicle injections. NAc and GPe excitation led to opposite results in the cRD task, providing evidence that the basal ganglia circuit has a function in frustrative nonreward in the absence of detectable motor effects.

Under or Absent Reporting of Light Stimuli in Testing of Anxiety-Like Behaviors in Rodents: The Need for Standardization

Behavioral neuroscience tests such as the Light/Dark Test, the Open Field Test, the Elevated Plus Maze Test, and the Three Chamber Social Interaction Test have become both essential and widely used behavioral tests for transgenic and pre-clinical models for drug screening and testing. However, as fast as the field has evolved and the contemporaneous involvement of technology, little assessment of the literature has been done to ensure that these behavioral neuroscience tests that are crucial to pre-clinical testing have well-controlled ethological motivation by the use of lighting (i.e., Lux). In the present review paper, N = 420 manuscripts were examined from 2015 to 2019 as a sample set (i.e., n = ~20–22 publications per year) and it was found that only a meager n = 50 publications (i.e., 11.9% of the publications sampled) met the criteria for proper anxiogenic and anxiolytic Lux reported. These findings illustrate a serious concern that behavioral neuroscience papers are not being vetted properly at the journal review level and are being released into the literature and public domain making it difficult to assess the quality of the science being reported. This creates a real need for standardizing the use of Lux in all publications on behavioral neuroscience techniques within the field to ensure that contributions are meaningful, avoid unnecessary duplication, and ultimately would serve to create a more efficient process within the pre-clinical screening/testing for drugs that serve as anxiolytic compounds that would prove more useful than what prior decades of work have produced. It is suggested that improving the standardization of the use and reporting of Lux in behavioral neuroscience tests and the standardization of peer-review processes overseeing the proper documentation of these methodological approaches in manuscripts could serve to advance pre-clinical testing for effective anxiolytic drugs. This report serves to highlight this concern and proposes strategies to proactively remedy them as the field moves forward for decades to come.

Evidence of successive negative contrast in terrestrial toads (Rhinella arenarum): central or peripheral effect?

Prior research with terrestrial toads (Rhinella arenarum) in a water-reinforced instrumental situation indicated a direct relationship between acquisition rate and reward magnitude. However, a reward downshift produced a gradual adjustment of instrumental performance and a rapid adjustment of consummatory performance, rather than the abrupt and transient deterioration of behavior typical of a successive negative contrast effect. In Experiment 1, using a two-chamber box, a downshift from deionized water (which supports maximal rehydration) to 250-mM sodium chloride solution (which supports a lower rehydration), also yielded a gradual adjustment of instrumental behavior. In this experiment, animals received one trial per day and were allowed 300 s of access to the reward in the goal box. Experiment 2 used the same procedure, except that animals were allowed access to the solution in the goal box for 600 s. Under these conditions, reward downshift led to longer latencies (instrumental) and lower rehydration levels (consummatory) than those of unshifted controls, providing evidence for successive negative contrast. Unlike in similar experiments with mammals, the effect was not transient, but persisted relatively unmodified over twelve daily postshift trials. In this case, the possibility of adaptation of the peripheral mechanisms for water uptake is considered. The comparative relevance of these results is discussed in terms of habit formation versus expectancy-guided behavior in vertebrate learning.

Functional Neural Alterations in Pathological Internet Use: A Meta-Analysis of Neuroimaging Studies

Previous resting-state functional MRI (fMRI) studies found spontaneous neural activity in the brains of Pathological Internet Use (PIU) subjects. However, the findings were inconsistent in studies using different neuroimaging analyses. This meta-analytic study aimed to identify a common pattern of altered brain activity from different studies. Resting-state fMRI studies, based on whole-brain analysis methods published before July 1, 2021, were searched in multiple databases (PubMed, EMBASE, MEDLINE, and Web of Science). A voxel-based signed differential mapping (SDM) method was used to clarify brain regions, which showed anomalous activity in PIU subjects compared with healthy controls (HCs). Ten eligible publications consisting of 306 PIU subjects and 314 HCs were included in the SDM meta-analysis. Compared with HCs, subjects with PIU showed increased spontaneous neural functional activity in the left temporal pole of the superior temporal cortex, left amygdala, bilateral median cingulate cortex, and right insula. Meanwhile, a decreased spontaneous neural activity was identified in the left dorsolateral superior frontal gyrus and right middle frontal gyrus in the subjects with PIU. These abnormal brain regions are associated with cognitive executive control and emotional regulation. The consistent changes under different functional brain imaging indicators found in our study may provide important targets for the future diagnosis and intervention of PIU.

Systematic Review Registration:www.crd.york.ac.uk/PROSPERO, identifier: CRD42021258119.

Frustrative nonreward and cannabinoid receptors: Chronic (but not acute) WIN 55,212-2 treatment increased resistance to change in two reward downshift tasks

Assessing the role of cannabinoid (CB) receptors in behavior is relevant given the trend toward the legalization of medicinal and recreational marijuana. The present research aims at bridging a gap in our understanding of CB-receptor function in animal models of frustrative nonreward. These experiments were designed to (1) determine the effects of chronic administration of the nonselective CB1-receptor agonist WIN 55,212-2 (WIN) on reward downshift in rats and (2) determine whether the effects of chronic WIN were reducible to acute effects. In Experiment 1, chronic WIN (7 daily injections, 10 mg/kg, ip) accelerated the recovery of consummatory behavior after a 32-to-4% sucrose downshift relative to vehicle controls. In addition, chronic WIN eliminated the preference for an unshifted lever when the other lever was subject to a 12-to-2 pellet downshift in free-choice trials, but only in animals with previous experience with a sucrose downshift. In Experiment 2, acute WIN (1 mg/kg, ip) reduced consummatory behavior, but did not affect recovery from a 32-to-4% sucrose downshift. The antagonist SR 141716A (3 mg/kg, ip) also failed to interfere with recovery after the sucrose downshift. In Experiment 3, acute WIN administration (1 mg/kg, ip) did not affect free-choice behavior after a pellet downshift, although it reduced lever pressing and increased magazine entries relative to vehicle controls. The effects of chronic WIN on frustrative nonreward were not reducible to acute effects of the drug. Chronic WIN treatment in rats, like chronic marijuana use in humans, seems to increase resistance to the effects of frustrative nonreward.

Converging vulnerability factors for compulsive food and drug use

Highly palatable foods and substance of abuse have intersecting neurobiological, metabolic and behavioral effects relevant for understanding vulnerability to conditions related to food (e.g., obesity, binge eating disorder) and drug (e.g., substance use disorder) misuse. Here, we review data from animal models, clinical populations and epidemiological evidence in behavioral, genetic, pathophysiologic and therapeutic domains. Results suggest that consumption of highly palatable food and drugs of abuse both impact and conversely are regulated by metabolic hormones and metabolic status. Palatable foods high in fat and/or sugar can elicit adaptation in brain reward and withdrawal circuitry akin to substances of abuse. Intake of or withdrawal from palatable food can impact behavioral sensitivity to drugs of abuse and vice versa. A robust literature suggests common substrates and roles for negative reinforcement, negative affect, negative urgency, and impulse control deficits, with both highly palatable foods and substances of abuse. Candidate genetic risk loci shared by obesity and alcohol use disorders have been identified in molecules classically associated with both metabolic and motivational functions. Finally, certain drugs may have overlapping therapeutic potential to treat obesity, diabetes, binge-related eating disorders and substance use disorders. Taken together, data are consistent with the hypotheses that compulsive food and substance use share overlapping, interacting substrates at neurobiological and metabolic levels and that motivated behavior associated with feeding or substance use might constitute vulnerability factors for one another. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.

Royal Jelly Ameliorates Behavioral Deficits, Cholinergic System Deficiency, and Autonomic Nervous Dysfunction in Ovariectomized Cholesterol-Fed Rabbits

Estrogen deficiency after menopause is associated with autonomic nervous changes, leading to memory impairment and increased susceptibility to Alzheimer's disease (AD). Royal jelly (RJ) from honeybees (Apis mellifera) has estrogenic activity. Here, we investigated whether RJ can improve behavior, cholinergic and autonomic nervous function in ovariectomized (OVX) cholesterol-fed rabbits. OVX rabbits on high-cholesterol diet were administered with RJ for 12 weeks. The results showed that RJ could significantly improve the behavioral deficits of OVX cholesterol-fed rabbits and image structure of the brain. RJ reduced body weight, blood lipid, as well as the levels of amyloid-beta (Aβ), acetylcholinesterase (AchE), and malonaldehyde (MDA) in the brain. Moreover, RJ also increased the activities of choline acetyltransferase (ChAT) and superoxide dismutase (SOD) in the brain, and enhanced heart rate variability (HRV) and Baroreflex sensitivity (BRS) in OVX cholesterol-fed rabbits. Furthermore, RJ was also shown to reduce the content of Evans blue and the expression levels of Aβ, beta-site APP cleaving enzyme 1(BACE1), and receptor for advanced glycation end products (RAGE), and increase the expression level of LDL(low density lipoprotein) receptor-related protein 1 (LRP-1) in the brain. Our findings suggested that RJ has beneficial effects in neurological disorders of postmenopausal women, which were associated with reducing cholesterol and Aβ deposition, enhancing the estrogen levels and the activities of cholinergic and antioxidant systems, and ameliorating the blood⁻brain barrier (BBB) permeability and restoring autonomic nervous system.

Emotional Reactivity to Incentive Downshift in Adult Rats Exposed to Binge-Like Ethanol Exposure During Adolescence

Alcohol use in adolescents is often characterized by binge-like ethanol consumption pattern, which is associated with long-term health consequences and even with important harms to his developing brain. Among this, ethanol exposure induces long-lasting alterations in anxiety-related neurobiological systems such as corticotropin releasing factor (CRF) or melanocortin system (MC). Recently, it has been demonstrated that adult rats exposed to adolescent intermittent ethanol (AIE) exposure exhibited anxiogenic-like behavior. Given that it has been demonstrated that negative affective state is relevant to development of addictive behavior, it is tempting to suggest that increased risk of adult abusive alcohol use exhibited in rats exposed to ethanol during adolescence may be related with differences in anxiety-related behavior. We conducted a study investigating the emotional reactivity after a reward devaluation (12-to-1 pellet or 32-to-4% sucrose downshift) in adult rats exposed to binge-like ethanol exposure during adolescence. For this aim, adolescent Sprague-Dawley rats were treated with ethanol (2.5 g/kg ip; AIE) or saline (AIS) for 2 consecutive days at 48-h intervals over a 14-day period (PND30-PND43). Following 25 free-ethanol days, adult rats were trained in consummatory and instrumental successive negative contrast task (cSNC and iSNC). Our data shows that both AIE and AIS groups exhibited suppression of the consummatory and instrumental behavior after reward devaluation relative to unshifthed control. Also, adult rats exposed to alcohol during adolescence exhibited a particularly strong negative affective state (lower sucrose consumption) with regards to the AIS group in the cSNC. This data demonstrated that adolescent binge-like ethanol exposure might trigger a greater emotional reactivity following incentive downshift, which might be linked to higher vulnerability to substance use disorder.

Reward devaluation disrupts latent inhibition in fear conditioning

Three experiments explored the link between reward shifts and latent inhibition (LI). Using consummatory procedures, rewards were either downshifted from 32% to 4% sucrose (Experiments 1-2), or upshifted from 4% to 32% sucrose (Experiment 3). In both cases, appropriate unshifted controls were also included. LI was implemented in terms of fear conditioning involving a single tone-shock pairing after extensive tone-only preexposure. Nonpreexposed controls were also included. Experiment 1 demonstrated a typical LI effect (i.e., disruption of fear conditioning after preexposure to the tone) in animals previously exposed only to 4% sucrose. However, the LI effect was eliminated by preexposure to a 32%-to-4% sucrose devaluation. Experiment 2 replicated this effect when the LI protocol was administered immediately after the reward devaluation event. However, LI was restored when preexposure was administered after a 60-min retention interval. Finally, Experiment 3 showed that a reward upshift did not affect LI. These results point to a significant role of negative emotion related to reward devaluation in the enhancement of stimulus processing despite extensive nonreinforced preexposure experience.