Conditioned taste aversion as a learning and memory paradigm

Changes in Food Preferences Before and After Intragastric Balloon Placement

BACKGROUNDS

In recent years, numerous studies have tried to decode the way bariatric surgery works toward weight reduction by the use of food preference questionnaires. The intragastric balloon has gained popularity, mainly due to its limited invasiveness, in patients with obesity not fulfilling criteria for bariatric surgery. However, there is no study assessing the changes in food preferences [FP]. We decided to analyze the FP of individuals prior to intragastric balloon insertion and following its removal, on the strict condition that participants must complete the 6-month treatment period and attend at least 4 of the 7 follow-up interviews.

METHODS

Patients were asked to rate the frequency of consumption of 63 food items before balloon insertion, at monthly intervals and after balloon removal. The food categories were protein, carbohydrates, fruit and vegetables, and sweets and fats.

RESULTS

The questionnaires of 320 participants were analyzed. A reduced frequency in consumption of meat and meat products, high-fat, and high-carbohydrate/sugary products and an increase in raw vegetables and fruit was found in all individuals.

CONCLUSION

The intragastric balloon seems to exert analogically similar mechanisms to bariatric surgery for weight loss, both functioning through alterations in FP. These are dictated by the anatomical re-configuration of the stomach, but mainly by counseling of dieticians and the self-education of the patient after experiencing unpleasant postprandial discomfort.

Chemogenetic inhibition of locus coeruleus to rostromedial tegmental nucleus noradrenergic pathway increases light cycle ethanol drinking in male and female mice and blunts ethanol-induced CTA

We recently showed that chemogenetic activation of the locus coeruleus (LC) to the rostromedial tegmental nucleus (RMTg) noradrenergic (NE) pathway significantly blunted binge-like ethanol drinking and induced aversive-like behaviors in mice. The aim of the present study is to determine if silencing this TH + LC → RMTg noradrenergic pathway promotes increased levels of binge-like ethanol intake and reduced ethanol-induced conditioned taste aversion (CTA). To this end, both male and female TH-ires-cre mice on a C57BL/6 J background were cannulated in the RMTg and injected in the LC with rAVV viruses that encode cre-dependent Gi-expressing designer receptor exclusively activated by designer drugs (DREADDs), or its control, to directly control the activity of NE neurons. Inhibition of the LC to RMTg pathway had no effect on the binge-ethanol drinking in a "drinking-in-the-dark" (DID) paradigm. However, when using this paradigm during the light cycle, silencing of this circuit significantly increased ethanol intake without altering sucrose drinking. Moreover, we found that inhibition of this circuit significantly attenuated an ethanol-induced CTA. In addition, when compared to control animals, pairing RMTg-directed Clozapine N-oxide (CNO) with an i.p. injection of 1.5 g/kg ethanol reduced c-Fos activation in the LC, and increased c-Fos expression in the ventral tegmental area (VTA) in Gi-expressing mice. Our data show that inhibition of the TH + LC to the RMTg pathway significantly increased ethanol drinking as well as attenuated ethanol-induced CTA, supporting the involvement of the LC to RMTg noradrenergic circuit as an important protective mechanism against excessive ethanol consumption.

Characterization of taste sensitivities to amino acids and sugars by conditioned taste aversion learning in chickens

Taste plays an essential role in regulating the feeding behaviors of animals. The present study aimed to characterize the taste sensory profiles of amino acids and sugars in chickens. To achieve this, we employed a conditioned taste aversion learning method, which is characterized by a specific pairing of gastrointestinal malaise and taste perception. Our findings revealed that chickens were able to learn to avoid L-Val, L-Lys, and L-His through conditioned taste aversion learning, and exhibited a strong aversion to L-Arg. These results suggest that chickens are primarily sensitive to basic amino acids, including L-Lys, which is a crucial limiting amino acid in feeds. Interstingly, this sensitivity to basic amino acids in chickens contrasts with humans, who are mainly sensitive to acidic amino acids as umami taste. Furthermore, despite the absence of a mammalian sweet taste receptor gene in the chicken genome, we demonstrated that chickens learned to avoid glucose, galactose, sucrose, and maltose by conditioned taste aversion learning. Taken together, the present study provides the idea that chickens possess a gustatory perception toward specific amino acids and sugars for the detection of beneficial nutrients in their feeds.

Effects of food deprivation on conditioned orthonasal olfactory preferences with caloric and non-caloric reinforcers

Three experiments were conducted to investigate Conditioned Olfactory Preferences using orthonasal inhalation, which is a less explored perceptual pathway compared to retronasal inhalation. In these experiments, odors were impregnated onto plastic disks to prevent the subjects from consuming or tasting them. The reinforcers used were a sucrose solution (Caloric groups) and a saccharin solution (Non-Caloric groups). The influence of nutritional deprivation was analyzed, with unrestricted access to food throughout the procedure in Experiment 1, food restriction during the conditioning phase in Experiment 2, and limited access to food during the test phase in Experiment 3. The results revealed conditioned preferences using both sucrose and saccharin as reinforcers. Furthermore, dietary restriction reduced the conditioned preference induced by saccharin, but not the preference induced by sucrose. These findings are discussed in light of the potential differences between orthonasal and retronasal presentation of odors during conditioning.

Back to the future: Progressing memory research in eating disorders

OBJECTIVE

Human behaviors, thoughts, and emotions are guided by memories of the past. Thus, there can be little doubt that memory plays a fundamental role in the behaviors (e.g., binging), thoughts (e.g., body-image concerns), and emotions (e.g., guilt) that characterize eating disorders (EDs). Although a growing body of research has begun to investigate the role of memory in EDs, this literature is limited in numerous ways and has yet to be integrated into an overarching framework.

METHODS

In the present article, we provide an operational framework for characterizing different domains of memory, briefly review existing ED memory research within this framework, and highlight crucial gaps in the literature.

RESULTS

We distinguish between three domains of memory-episodic, procedural, and working-which differ based on functional attributes and underlying neural systems. Most recent ED memory research has focused on procedural memory broadly defined (e.g., reinforcement learning), and findings within all three memory domains are highly mixed. Further, few studies have attempted to assess these different domains simultaneously, though most behavior is achieved through coordination and competition between memory systems. We, therefore, offer recommendations for how to move ED research forward within each domain of memory and how to study the interactions between memory systems, using illustrative examples from other areas of basic and clinical research.

DISCUSSION

A stronger and more integrated understanding of the mechanisms that connect memory of past experiences to present ED behavior may yield more comprehensive theoretical models of EDs that guide novel treatment approaches.

PUBLIC SIGNIFICANCE

Memories of previous eating-related experiences may contribute to the onset and maintenance of eating disorders (EDs). However, research on the role of memory in EDs is limited, and distinct domains of ED memory research are rarely connected. We, therefore, offer a framework for organizing, progressing, and integrating ED memory research, to provide a better foundation for improving ED treatment and intervention going forward.

Taste Responses and Ingestive Behaviors to Ingredients of Fermented Milk in Mice

Fermented milk is consumed worldwide because of its nutritious and healthful qualities. Although it is somewhat sour, causing some to dislike it, few studies have examined taste aspects of its ingredients. Wild-type mice and T1R3-GFP-KO mice lacking sweet/umami receptors were tested with various taste components (sucrose, galactose, lactose, galacto-oligosaccharides, fructo-oligosaccharides, l- and d-lactic acid) using 48 h two-bottle tests and short-term lick tests. d-lactic acid levels were measured after the ingestion of d- or; l-lactic acid or water to evaluate d-lactic acidosis. In wild-type mice, for the sweet ingredients the number of licks increased in a concentration-dependent manner, but avoidance was observed at higher concentrations in 48 h two-bottle tests; the sour ingredients d- and l-lactic acid showed concentration-dependent decreases in preference in both short- and long-term tests. In 48 h two-bottle tests comparing d- and l-lactic acid, wild-type but not T1R3-GFP-KO mice showed higher drinking rates for l-lactic acid. d-lactic acidosis did not occur and thus did not contribute to this preference. These results suggest that intake in short-term lick tests varied by preference for each ingredient, whereas intake variation in long-term lick tests reflects postingestive effects. l-lactic acid may have some palatable taste in addition to sour taste.

Taste aversion learning in the snail Cornu aspersum

The present study was conducted to provide evidence of conditioned taste aversion learning (CTA) in the snail Cornu aspersum, using quinidine as the aversive stimulus in a procedure of Pavlovian Conditioning of Tentacle Lowering. Subjects were split into two groups: paired and unpaired. During the devaluation phase, subjects from the "paired group" received the US followed by the quinidine exposure, while subjects from the "unpaired group" received the quinidine and, 30 min later, the US. Subjects which had received the US paired with the quinidine showed a decrease of the conditioned response (CR), in contrast to subjects which had received the quinidine and the US unpaired. These results provide a useful CTA procedure in terrestrial snails. The implication of the results for learning and the physiological correlates is discussed.

Uncovering novel regulators of memory using C. elegans genetic and genomic analysis

How organisms learn and encode memory is an outstanding question in neuroscience research. Specifically, how memories are acquired and consolidated at the level of molecular and gene pathways remains unclear. In addition, memory is disrupted in a wide variety of neurological disorders; therefore, discovering molecular regulators of memory may reveal therapeutic targets for these disorders. C. elegans are an excellent model to uncover molecular and genetic regulators of memory. Indeed, the nematode's invariant neuronal lineage, fully mapped genome, and conserved associative behaviors have allowed the development of a breadth of genetic and genomic tools to examine learning and memory. In this mini-review, we discuss novel and exciting genetic and genomic techniques used to examine molecular and genetic underpinnings of memory from the level of the whole-worm to tissue-specific and cell-type specific approaches with high spatiotemporal resolution.

Novel approaches to the study of viscosity discrimination in rodents

Texture has enormous effects on food preferences. The materials used to study texture discrimination also have tastes that experimental animal can detect; therefore, such studies must be designed to exclude taste differences. In this study, to minimize the effects of material tastes, we utilized high- and low-viscosity forms of carboxymethyl cellulose (CMC-H and CMC-L, respectively) at the same concentrations (0.1-3%) for viscosity discrimination tests in rats. In two-bottle preference tests of water and CMC, rats avoided CMC-H solutions above 1% (63 mPa·s) but did not avoid less viscous CMC-L solutions with equivalent taste magnitudes, suggesting that rats spontaneously avoided high viscosity. To evaluate low-viscosity discrimination, we performed conditioned aversion tests to 0.1% CMC, which initially showed a comparable preference ratio to water in the two-bottle preference tests. Conditioning with 0.1% CMC-L (1.5 mPa·s) did not induce aversion to 0.1% CMC-L or CMC-H. However, rats acquired a conditioned aversion to 0.1% CMC-H (3.6 mPa·s) even after latent inhibition to CMC taste by pre-exposure to 0.1% CMC-L. These results suggest that rats can discriminate considerably low viscosity independent of CMC taste. This novel approach for viscosity discrimination can be used to investigate the mechanisms of texture perception in mammals.

Using Postmeal Measures and Manipulations to Investigate Hippocampal Mnemonic Control of Eating Behavior

Episodic meal-related memories provide the brain with a powerful mechanism for tracking and controlling eating behavior because they contain a detailed record of recent energy intake that likely outlasts the physiological signals generated by feeding bouts. This review briefly summarizes evidence from human participants showing that episodic meal-related memory limits later eating behavior and then describes our research aimed at investigating whether hippocampal neurons mediate the inhibitory effects of meal-related memory on subsequent feeding. Our approach has been inspired by pioneering work conducted by Ivan Izquierdo and others who used posttraining manipulations to investigate memory consolidation. This review describes the rationale and value of posttraining manipulations, how Izquierdo used them to demonstrate that dorsal hippocampal (dHC) neurons are critical for memory consolidation, and how we have adapted this strategy to investigate whether dHC neurons are necessary for mnemonic control of energy intake. I describe our evidence showing that ingestion activates the molecular processes necessary for synaptic plasticity and memory during the early postprandial period, when the memory of the meal would be undergoing consolidation, and then summarize our findings showing that neural activity in dHC neurons is critical during the early postprandial period for limiting future intake. Collectively, our evidence supports the hypothesis that dHC neurons mediate the inhibitory effects of ingestion-related memory on future intake and demonstrates that post-experience memory modulation is not confined to artificial laboratory memory tasks.

Learning, fast and slow

Animals can learn efficiently from a single experience and change their future behavior in response. However, in other instances, animals learn very slowly, requiring thousands of experiences. Here, I survey tasks involving fast and slow learning and consider some hypotheses for what differentiates the underlying neural mechanisms. It has been proposed that fast learning relies on neural representations that favor efficient Hebbian modification of synapses. These efficient representations may be encoded in the genome, resulting in a repertoire of fast learning that differs across species. Alternatively, the required neural representations may be acquired from experience through a slow process of unsupervised learning from the environment.

Temporal dynamics of fMRI signal changes during conditioned interoceptive pain-related fear and safety acquisition and extinction

Associative learning and memory mechanisms drive interoceptive signaling along the gut-brain axis, thus shaping affective-emotional reactions and behavior. Specifically, learning to predict potentially harmful, visceral pain is assumed to succeed within very few trials. However, the temporal dynamics of cerebellar and cerebral fMRI signal changes underlying early acquisition and extinction of learned fear signals and the concomitant evolvement of safety learning remain incompletely understood. 3T fMRI data of healthy individuals from three studies were uniformly processed across the whole brain and the cerebellum including an advanced normalizing method of the cerebellum. All studies employed differential delay conditioning (N=94) with one visual cue (CS⁺) being repeatedly paired with visceral pain as unconditioned stimulus (US) while a second cue remained unpaired (CS^-). During subsequent extinction (N=51), all CS were presented without US. Behavioral results revealed increased CS⁺-aversiveness and CS^--pleasantness after conditioning and diminished valence ratings for both CS following extinction. During early acquisition, the CS^- induced linearly increasing neural activation in the insula, midcingulate cortex, hippocampus, precuneus as well as cerebral and cerebellar somatomotor regions. The comparison between acquisition and extinction phases yielded a CS^--induced linear increase in the posterior cingulate cortex and precuneus during early acquisition, while there was no evidence for linear fMRI signal changes for the CS⁺ during acquisition and for both CS during extinction. Based on theoretical accounts of discrimination and temporal difference learning, these results suggest a gradual evolvement of learned safety cues that engage emotional arousal, memory, and cortical modulatory networks. As safety signals are presumably more difficult to learn and to discriminate from learned threat cues, the underlying temporal dynamics may reflect enhanced salience and prediction processing as well as increasing demands for attentional resources and the integration of multisensory information. Maladaptive responses to learned safety signals are a clinically relevant phenotype in multiple conditions, including chronic visceral pain, and can be exceptionally resistant to modification or extinction. Through sustained hypervigilance, safety seeking constitutes one key component in pain and stress-related avoidance behavior, calling for future studies targeting the mechanisms of safety learning and extinction to advance current cognitive-behavioral treatment approaches.

A self-training device to teach conservation-working dogs to avoid poison baits

Abstract Context Accidental poisoning of domestic dogs is a potential risk when using baits to control invasive animals. We developed and trialled an electrical device attached to a non-toxic bait to assess whether we could induce a learned aversion towards baits in conservation-working dogs. Aims We tested the device on conservation-working dogs licenced to enter conservation estate as part of feral pig control, and consequently are potentially exposed to lethal baits for controlling red foxes. Methods Over 1 year (up to seven separate training sessions per dog), 27 dogs were sequentially presented with electrified and non-electrified non-toxic baits and their behavioural responses were recorded. On-farm training (Days 0, 1, 7, Months 1, 12) comprised dogs being called by their owner standing nearby the electrified bait. If the dog touched the bait and demonstrated aversive behaviour (we assume that it received an electric shock or ‘correction’), it was then presented with a non-electrified bait. If they ate either bait, they were shown another electrified bait (up to three electrified baits per session). Key results Seventeen dogs (17/27) touched the bait and received a correction. Eleven dogs required only a single correction and did not touch another bait, three dogs needed two corrections, and two dogs needed three or four corrections. These 17 dogs showed increasing avoidance to the bait over successive training sessions (χ212 = 67.96, P < 0.001), including avoiding looking at the bait, refusing to come within 5–10 m of the bait and their owner, or leaving the training vicinity. All these dogs (17/17) avoided baits encountered in a working environment (1/17 touched but did not consume a bait) and bait-aversion was still detected up to 1-year post-initial training. Nine dogs (9/27) did not appear to receive a correction or show any change in bait-aversion behaviour. One dog (1/27) showed no aversion to the stimulus and continued to eat baits. Conclusions Here we present a proof of concept for a deterrent device and associated experimental protocol to produce learned aversion behaviour in conservation-working dogs. Implications We demonstrated that it is possible to induce a learned aversion to baits in conservation-working dogs, thereby reducing the risk of accidental poisoning.

Behavior and Fos activation reveal that male and female rats differentially assess affective valence during CTA learning and expression

Females are more affected by psychiatric illnesses including eating disorders, depression, and post-traumatic stress disorder than males. However, the neural mechanisms mediating these sex differences are poorly understood. Animal models can be useful in exploring such neural mechanisms. Conditioned taste aversion (CTA) is a behavioral task that assesses how animals process the competition between associated reinforcing and aversive stimuli in subsequent task performance, a process critical to healthy behavior in many domains. The purpose of the present study was to identify sex differences in this behavior and associated neural responses. We hypothesized that females would value the rewarding stimulus (Boost®) relative to the aversive stimulus (LiCl) more than males in performing CTA. We evaluated behavior (Boost® intake, LiCl-induced behaviors, ultrasonic vocalizations (USVs), CTA performance) and Fos activation in relevant brain regions after the acute stimuli [acute Boost® (AB), acute LiCl (AL)] and the context-only task control (COT), Boost® only task (BOT) and Boost®-LiCl task (BLT). Acutely, females drank more Boost® than males but showed similar aversive behaviors after LiCl. Females and males performed CTA similarly. Both sexes produced 55 kHz USVs anticipating BOT and inhibited these calls in the BLT. However, more females emitted both 22 kHz and 55 kHz USVs in the BLT than males: the latter correlated with less CTA. Estrous cycle stage also influenced 55 kHz USVs. Fos responses were similar in males and females after AB or AL. Females engaged the gustatory cortex and ventral tegmental area (VTA) more than males during the BOT and males engaged the amygdala more than females in both the BOT and BLT. Network analysis of correlated Fos responses across brain regions identified two unique networks characterizing the BOT and BLT, in both of which the VTA played a central role. In situ hybridization with RNAscope identified a population of D1-receptor expressing cells in the CeA that responded to Boost® and D2 receptor-expressing cells that responded to LiCl. The present study suggests that males and females differentially process the affective valence of a stimulus to produce the same goal-directed behavior.

Increasing dietary choline attenuates spatial memory deficits resulting from exposure to the chemotherapeutic agents cyclophosphamide and doxorubicin

BACKGROUND

Choline supplementation (+Ch) improves cognitive function in impaired animals and humans. Chemotherapy-related cognitive deficits (CRCDs) occur in cancer patients, and these deficits persist following treatment, adversely impacting quality of life. To date, there are no approved treatments for this condition.

AIM

Because +Ch improves impaired memory, it was of interest to determine whether +Ch can attenuate spatial memory deficits induced by the chemotherapeutic agents doxorubicin (DOX) and cyclophosphamide (CYP).

METHODS

Female BALB/C mice, 64 days of age, were trained in the Morris water maze and baseline performance determined on day 15. Following baseline assessment, mice were placed on +Ch diet (2.0% Ch) or remained on standard diet (0.12% Ch). Mice received intravenous injections of DOX (2.5 mg/kg) and CYP (25 mg/kg), or equivalent volumes of saline (0.9% NaCl), on days 16, 23, 30, and 37, and spatial memory was assessed weekly from day 22 to 71.

RESULTS

DOX and CYP produced a prolonged impairment in spatial memory as indicated by an increased latency to the correct zone (p < 0.05), and a decrease in time in the correct zone (p < 0.05), % of total swim distance in the correct zone (p < 0.05) and % entries to the correct zone (p < 0.05). These effects were attenuated by +Ch.

CONCLUSION

Although it remains to be determined whether this effect extends to other cognitive domains and whether +Ch is prophylactic or therapeutic, these findings suggest that +Ch may be an effective intervention for CRCDs.

Role of NMDA Receptors and Protein Synthesis in the Conditioned Aversion Learning in Young Chicks

The brain mechanisms underlying conditioned aversion learning in birds were studied using experimental model in young chicks. The learning consisted of a conditioning stimulus presentation followed by a delayed sickness-inducing treatment reinforcement. Intraventricular administration of an NMDA receptor antagonist MK-801, a protein synthesis inhibitor anisomycin, or an inhibitor of glycoprotein fucosylation 2-deoxygalactose just before presentation of the conditioning stimulus prevented aversion learning. Injections of the same chemicals before reinforcement did not affect learning. The obtained results show that the investigated mechanisms underlying aversion learning were critical at the early stage of memory formation. Later processes of association of the conditioning stimulus with the reinforcement appear to be independent of the NMDA receptors and protein synthesis/glycosylation, or alternatively to be located in other brain areas.

Homeostatic synaptic scaling establishes the specificity of an associative memory

Correlation-based (Hebbian) forms of synaptic plasticity are crucial for the initial encoding of associative memories but likely insufficient to enable the stable storage of multiple specific memories within neural circuits. Theoretical studies have suggested that homeostatic synaptic normalization rules provide an essential countervailing force that can stabilize and expand memory storage capacity. Although such homeostatic mechanisms have been identified and studied for decades, experimental evidence that they play an important role in associative memory is lacking. Here, we show that synaptic scaling, a widely studied form of homeostatic synaptic plasticity that globally renormalizes synaptic strengths, is dispensable for initial associative memory formation but crucial for the establishment of memory specificity. We used conditioned taste aversion (CTA) learning, a form of associative learning that relies on Hebbian mechanisms within gustatory cortex (GC), to show that animals conditioned to avoid saccharin initially generalized this aversion to other novel tastants. Specificity of the aversion to saccharin emerged slowly over a time course of many hours and was associated with synaptic scaling down of excitatory synapses onto conditioning-active neuronal ensembles within gustatory cortex. Blocking synaptic scaling down in the gustatory cortex enhanced the persistence of synaptic strength increases induced by conditioning and prolonged the duration of memory generalization. Taken together, these findings demonstrate that synaptic scaling is crucial for sculpting the specificity of an associative memory and suggest that the relative strengths of Hebbian and homeostatic plasticity can modulate the balance between stable memory formation and memory generalization.

Metaplastic regulation of neocortical long-term depression in vivo is sensitive to distinct phases of conditioned taste aversion

Metaplasticity refers to the persistent modification, by previous activity, in the ability to induce synaptic plasticity. Accumulated evidence has proposed that metaplasticity contributes to network function and cognitive processes such as learning and memory. In this regard, it has been observed that training in several behavioral tasks modifies the possibility to induce subsequent synaptic plasticity, such as long-term potentiation (LTP) and long-term depression (LTD). For instance, our previous studies have shown that conditioned taste aversion (CTA) training prevents the induction of in vivo LTP in the projection from the basolateral nucleus of the amygdala to the insular cortex (BLA-IC). Likewise, we reported that extinction of CTA allows induction but not maintenance of LTP in the same pathway. Besides, we showed that it is possible to express in vivo low-frequency stimulation LTD in the BLA-IC projection and that its induction prior to CTA training facilitates the extinction of this task. However, until now, little is known about the participation of LTD on metaplastic processes. The present study aimed to analyze whether CTA training modifies the expression of in vivo LTD in the BLA-IC projection. To do so, animals received low-frequency stimulation to induce IC-LTD 48 h after CTA training. Our results show that CTA training occludes the subsequent induction of LTD in the BLA-IC pathway in a retrieval-dependent manner. These findings reveal that CTA elicits a metaplastic regulation of long-lasting changes in the IC synaptic strength, as well as that specific phases of learning differentially take part in adjusting the expression of synaptic plasticity in neocortical regions.

Adolescent intermittent ethanol exposure does not alter responsiveness to ifenprodil or expression of vesicular GABA and glutamate transporters

Adolescent intermittent ethanol (AIE) exposure in the rat results in a retention of adolescent-like responsiveness to ethanol into adulthood characterized by enhanced sensitivity to socially facilitating and decreased sensitivity to socially suppressing and aversive effects. Similar pattern of responsiveness to social and aversive effects of the selective glutamate NMDA NR2B receptor antagonist ifenprodil is evident in adolescent rats, suggesting that AIE would also retain this pattern of ifenprodil sensitivity into adulthood. Social (Experiment 1) and aversive (measured via conditioned taste aversion; Experiment 2) effects of ifenprodil were assessed in adult male and female rats following AIE exposure. Sensitivity to the social and aversive effects of ifenprodil was not affected by AIE exposure. Experiment 3 assessed protein expression of vesicular transporters of GABA (vGAT) and glutamate (vGlut2) within the prelimbic cortex and nucleus accumbens in adolescents versus adults and in AIE adults versus controls. vGlut2 expression was higher in adolescents relative to adults within the PrL, but lower in the NAc. AIE adults did not retain these adolescent-typical ratios. These findings suggest that AIE is not associated with the retention of adolescent-typical sensitivity to NR2B receptor antagonism, along with no AIE-induced shift in vGlut2 to vGAT ratios.

Gut microbiome and multiple sclerosis: New insights and perspective

The human gastrointestinal microbiota, also known as the gut microbiota living in the human gastrointestinal tract, has been shown to have a significant impact on several human disorders including rheumatoid arthritis, diabetes, obesity, and multiple sclerosis (MS). MS is an inflammatory disease characterized by the destruction of the spinal cord and nerve cells in the brain due to an attack of immune cells, causing a wide range of harmful symptoms related to inflammation in the central nervous system (CNS). Despite extensive studies on MS that have shown that many external and genetic factors are involved in its pathogenesis, the exact role of external factors in the pathophysiology of MS is still unclear. Recent studies on MS and experimental autoimmune encephalomyelitis (EAE), an animal model of encephalitis, have shown that intestinal microbiota may play a key role in the pathogenesis of MS. Therefore, modification of the intestinal microbiome could be a promising strategy for the future treatment of MS. In this study, the characteristics of intestinal microbiota, the relationship between intestine and brain despite the blood-brain barrier, various factors involved in intestinal microbiota modification, changes in intestinal microbial composition in MS, intestinal microbiome modification strategies, and possible use of intestinal microbiome and factors affecting it have been discussed.

Behavioral Conditioning, the Placebo Effect, and Emergency Department Pain Management

Animals and humans can be readily conditioned to associate a novel stimulus (often a unique taste) by pairing it with the effects of a drug or other agent. When later presented with the stimulus alone, their body's systems respond as if the drug or agent were given. The earliest clinical applications demonstrated both conditioned suppression and enhancement of immune processes. Unique benign stimuli, paired with chemotherapy, come to elicit T-cell suppression when administered alone. The beneficial immune responses to an antigen can be conditioned in the same manner. Further study of what came to be called "psychoneuroimmunology" led to the understanding that the familiar placebo effect, previously attributed to suggestion and expectation, is at least equally dependent on the same sorts of behavioral conditioning. The demonstrated ability to manipulate the immune system by a conditioned taste stimulus is, by definition, a placebo: a therapeutic effect caused by an inactive agent. The purpose of this analysis was to stimulate research in, and the application of, placebo-response conditioning to emergency medicine. Clinical and experimental studies confirm the usefulness of conditioned placebos in analgesia and in placebo-controlled dose reduction. Such conditioning paradigms demonstrate "one-trial learning," making them potentially useful in pain and addiction management within a single emergency department encounter.

Fasting- and ghrelin-induced food intake is regulated by NAMPT in the hypothalamus

AIM

Neurons in the arcuate nucleus of the hypothalamus are involved in regulation of food intake and energy expenditure, and dysregulation of signalling in these neurons promotes development of obesity. The role of the rate-limiting enzyme in the NAD⁺ salvage pathway, nicotinamide phosphoribosyltransferase (NAMPT), for regulation energy homeostasis by the hypothalamus has not been extensively studied.

METHODS

We determined whether Nampt mRNA or protein levels in the hypothalamus of mice were affected by diet-induced obesity, by fasting and re-feeding, and by leptin and ghrelin treatment. Primary hypothalamic neurons were treated with FK866, a selective inhibitor of NAMPT, or rAAV carrying shRNA directed against Nampt, and levels of reactive oxygen species (ROS) and mitochondrial respiration were assessed. Fasting and ghrelin-induced food intake was measured in mice in metabolic cages after intracerebroventricular (ICV)-mediated FK866 administration.

RESULTS

NAMPT levels in the hypothalamus were elevated by administration of ghrelin and leptin. In diet-induced obese mice, both protein and mRNA levels of NAMPT decreased in the hypothalamus. NAMPT inhibition in primary hypothalamic neurons significantly reduced levels of NAD⁺ , increased levels of ROS, and affected the expression of Agrp, Pomc and genes related to mitochondrial function. Finally, ICV-induced NAMPT inhibition by FK866 did not cause malaise or anhedonia, but completely ablated fasting- and ghrelin-induced increases in food intake.

CONCLUSION

Our findings indicate that regulation of NAMPT levels in hypothalamic neurons is important for the control of fasting- and ghrelin-induced food intake.

DNA damage and synaptic and behavioural disorders in glucose-6-phosphate dehydrogenase-deficient mice

Mice deficient in glucose-6-phosphate dehydrogenase (G6PD) cannot replenish the cellular antioxidant glutathione, which detoxifies neurodegenerative reactive oxygen species (ROS). To determine the functional consequences of G6PD deficiency, young and aging G6PD-deficient mice were evaluated for brain G6PD activity, DNA damage (comets, γH2AX), Purkinje cell loss, brain function (electrophysiology, behaviour) and lifespan. DNA comet formation was increased and Purkinje cell counts were decreased in a G6pd gene dose-dependent fashion. γH2AX formation varied by age, sex and brain region, with increased levels in G6PD-deficient young and aging females, and in aging males. Aging male G6PD-deficient mice exhibited synaptic dysfunction in hippocampal slices. G6PD-deficient young and aging females exhibited deficits in executive function, and young deficient mice exhibited deficits in social dominance. Conversely, median lifespan in G6PD-deficient females and males was enhanced. Enhanced ROS-initiated brain damage in G6PD deficiency has functional consequences, suggesting that G6PD protects against ROS-mediated neurodegenerative disorders.

Excitatory/inhibitory balance across ontogeny contributes to age-specific behavioral outcomes of ethanol-like challenge in conditioned taste aversion

Adolescent-typical sensitivities to ethanol (EtOH) are characterized in part by reduced sensitivity to EtOH's aversive effects. Rodent studies have shown that adolescents are less sensitive than adults to aversive properties of EtOH in a conditioned taste aversion (CTA) paradigm. To the extent that EtOH exerts antagonist-like actions upon glutamate receptors and/or agonist-like actions upon γ-aminobutyric acid (GABA) receptors, age differences in excitatory/inhibitory balance may regulate age-specific EtOH sensitivities, such as attenuated sensitivity of adolescents to EtOH aversion. In our experiments, adolescent and adult Sprague-Dawley rats were tested for CTA following challenge with one of the following pharmacological agents: glutamatergic AMPA1 receptor antagonist NBQX, glutamatergic N-methyl-d-aspartate NR2B receptor antagonist ifenprodil, and extrasynaptic GABAA receptor agonist THIP to determine whether these induced age-specific aversive sensitivities like those seen with EtOH. NBQX administration did not induce CTA. The highest dose of extrasynaptic GABAA agonist THIP induced CTA in adolescents but not adults, an opposite ontogenetic profile as seen following EtOH. Ifenprodil exerted an age-specific pattern of CTA similar to that seen with EtOH in males, with adolescents being insensitive to ifenprodil's aversive effects relative to adults. Thus, only antagonism of NR2B receptors in male rats mimicked age-specific sensitivities to the aversive effects of EtOH.

Retronasal Odor Perception Requires Taste Cortex, but Orthonasal Does Not

Smells can arise from a source external to the body and stimulate the olfactory epithelium upon inhalation through the nares (orthonasal olfaction). Alternatively, smells may arise from inside the mouth during consumption, stimulating the epithelium upon exhalation (retronasal olfaction). Both ortho- and retronasal olfaction produce highly salient percepts, but the two percepts have very different behavioral implications. Here, we use optogenetic manipulation in the context of a flavor preference learning paradigm to investigate differences in the neural circuits that process information in these two submodalities of olfaction. Our findings support a view in which retronasal, but not orthonasal, odors share processing circuitry commonly associated with taste. First, our behavioral results reveal that retronasal odors induce rapid preference learning and have a potentiating effect on orthonasal preference learning. Second, we demonstrate that inactivation of the insular gustatory cortex selectively impairs expression of retronasal preferences. Thus, orally sourced (retronasal) olfactory input is processed by a brain region responsible for taste processing, whereas externally sourced (orthonasal) olfactory input is not.

Food Intake and Eating Behavior After Bariatric Surgery

Obesity is an escalating global chronic disease. Bariatric surgery is a very efficacious treatment for obesity and its comorbidities. Alterations to gastrointestinal anatomy during bariatric surgery result in neurological and physiological changes affecting hypothalamic signaling, gut hormones, bile acids, and gut microbiota, which coalesce to exert a profound influence on eating behavior. A thorough understanding of the mechanisms underlying eating behavior is essential in the management of patients after bariatric surgery. Studies investigating candidate mechanisms have expanded dramatically in the last decade. Herein we review the proposed mechanisms governing changes in eating behavior, food intake, and body weight after bariatric surgery. Additive or synergistic effects of both conditioned and unconditioned factors likely account for the complete picture of changes in eating behavior. Considered application of strategies designed to support the underlying principles governing changes in eating behavior holds promise as a means of optimizing responses to surgery and long-term outcomes.

Difference in Subjective Accessibility of On Demand Recall of Visual, Taste, and Olfactory Memories

We present here significant difference in the evocation capability between sensory memories (visual, taste, and olfactory) throughout certain categories of the population. As object for this memory recall we selected French fries that are simple and generally known. From daily life we may intuitively feel that there is much better recall of the visual and auditory memory compared to the taste and olfactory ones. Our results in young (age 12-21 years) mostly females and some males show low capacity for smell and taste memory recall compared to far greater visual memory recall. This situation raises question whether we could train smell and taste memory recall so that it could become similar to visual or auditory ones. In our article we design technique of the volunteers training that could potentially lead to an increase in the capacity of their taste and olfactory memory recollection.

Diet, Gut Microbiota, and Vitamins D + A in Multiple Sclerosis

Central to the understanding of the relationships between diet, gut microbiota, and vitamins D and A in multiple sclerosis is low-grade inflammation, which is involved in all chronic inflammatory diseases and is influenced by each of the above effectors. We show that food components have either proinflammatory or anti-inflammatory effects and influence both the human metabolism (the "metabolome") and the composition of gut microbiota. Hypercaloric, high-animal-fat Western diets favor anabolism and change gut microbiota composition towards dysbiosis. Subsequent intestinal inflammation leads to leakage of the gut barrier, disruption of the blood-brain barrier, and neuroinflammation. Conversely, a vegetarian diet, rich in fiber, is coherent with gut eubiosis and a healthy condition. Vitamin D levels, mainly insufficient in a persistent low-grade inflammatory status, can be restored to optimal values only by administration of high amounts of cholecalciferol. At its optimal values (>30 ng/ml), vitamin D requires vitamin A for the binding to the vitamin D receptor and exert its anti-inflammatory action. Both vitamins must be supplied to the subjects lacking vitamin D. We conclude that nutrients, including the nondigestible dietary fibers, have a leading role in tackling the low-grade inflammation associated with chronic inflammatory diseases. Their action is mediated by gut microbiota and any microbial change induced by diet modifies host-microbe interactions in a consequent way, to improve the disease or worsen it.

Gustatory processing and taste memory in Drosophila

Taste allows animals to discriminate the value and potential toxicity of food prior to ingestion. Many tastants elicit an innate attractive or avoidance response that is modifiable with nutritional state and prior experience. A powerful genetic tool kit, well-characterized gustatory system, and standardized behavioral assays make the fruit fly, Drosophila melanogaster, an excellent system for investigating taste processing and memory. Recent studies have used this system to identify the neural basis for acquired taste preference. These studies have revealed a role for dopamine-mediated plasticity of the mushroom bodies that modulate the threshold of response to appetitive tastants. The identification of neural circuitry regulating taste memory provides a system to study the genetic and physiological processes that govern plasticity within a defined memory circuit.

Disruption of Perceptual Learning by a Brief Practice Break

Some forms of associative learning require only a single experience to create a lasting memory [1, 2]. In contrast, perceptual learning often requires extensive practice within a day for performance to improve across days [3, 4]. This suggests that the requisite practice for durable perceptual learning is integrated throughout each day. If the total amount of daily practice is the only important variable, then a practice break within a day should not disrupt across-day improvement. To test this idea, we trained human listeners on an auditory frequency-discrimination task over multiple days and compared the performance of those who engaged in a single continuous practice session each day [4] with those who were given a 30-min break halfway through each practice session. Continuous practice yielded significant perceptual learning [4]. In contrast, practice with a rest break led to no improvement, indicating that the integration process had decayed within 30 min. In a separate experiment, a 30-min practice break also disrupted durable learning on a non-native phonetic classification task. These results suggest that practice trials are integrated up to a learning threshold within a transient memory store before they are sent en masse into a memory that lasts across days. Thus, the oft cited benefits of distributed over massed training [5, 6] may arise from different mechanisms depending on whether the breaks occur before or after a learning threshold has been reached. Trial integration could serve as an early gatekeeper to plasticity, helping to ensure that longer-lasting changes are only made when deemed worthwhile.

A standardized Hippophae extract (SBL-1) counters neuronal tissue injuries and changes in neurotransmitters: implications in radiation protection

CONTEXT

Effects of a radioprotective, standardized leaf extract (code SBL-1) from traditional medicinal plant, sea buckthorn [Hippophae rhamnoides L. (Elaeagnaceae)], on neurotransmitters and brain injuries in rats showing radiation-induced conditioned taste aversion (CTA), are not known. Understanding CTA in rats is important because its process is considered parallel to nausea and vomiting in humans.

OBJECTIVE

This study investigated the levels of neurotransmitters, antioxidant defences and histological changes in rats showing radiation CTA, and their modification by SBL-1.

MATERIALS AND METHODS

The inbred male Sprague-Dawley rats (age 65 days, weighing 190 ± 10 g) were used. Saccharin-preferring rats were selected using standard procedure and divided into groups. Group I (untreated control) was administered sterile water, group II was 60Co-γ-irradiated (2 Gy), and group III was administered SBL-1 before irradiation. Observations were recorded up to day 5.

RESULTS

Irradiation (2 Gy) caused (i) non-recoverable CTA (≥ 64.7 ± 5.0%); (ii) degenerative changes in cerebral cortex, amygdala and hippocampus; (iii) increases in brain dopamine (DA, 63.4%), norepinephrine (NE, 157%), epinephrine (E, 233%), plasma NE (103%) and E (160%); and (iv) decreases in brain superoxide dismutase (67%), catalase (60%) and glutathione (51%). SBL-1 treatment (12 mg/kg body weight) 30 min before irradiation (i) countered brain injuries, (ii) reduced CTA (38.7 ± 3.0%, day 1) and (iii) normalized brain DA, NE, E, superoxide dismutase, catalase and CTA from day 3 onwards.

DISCUSSION AND CONCLUSION

Radiation CTA was coupled with brain injuries, disturbances in neurotransmitters and antioxidant defences. SBL-1 pretreatment countered these disturbances, indicating neuroprotective action.

Acquisition and retention of conditioned aversions to context and taste in laboratory mice

We compared the rate of acquisition and strength of retention of conditioned context aversion (CCA) with conditioned taste aversion (CTA) using pigmented, genetically heterogeneous mice (derived from Large and Small strains). Extending previous findings, in Experiment 1, mice accustomed to drinking from large glass bottles in the colony room learned to avoid graduated tubes after a single conditioning trial when drinking from these novel tubes was paired with injections of LiCl. The results also showed that CCA could be developed even when there was a 30-minute delay between conditioned stimulus and unconditioned stimulus. Retention of the aversion lasted for 4 weeks in both Immediate and Delay groups. Studies of conditioned saccharin aversion were conducted in Experiment 2. CTA acquisition was very similar to that observed in CCA and duration of aversion retention was similar in the CCA and CTA Delay groups, although at least 2 weeks longer in the Immediate group. Thus, CCA acquisition and retention characteristics are closer to those seen for CTA than has previously been reported. In Experiment 3, we examined whether albino mice (which are known to have weaker visual abilities compared to pigmented mice) would develop CCA comparable to those of pigmented mice. The development of conditioned aversion and its duration of retention was similar in albinos and pigmented mice. Nonspecific aversion emerged as an important contributor to strength of aversion during retention trials in both CCA and CTA paradigms with pigmented (but not albino) mice and deserves additional scrutiny in this field of inquiry.

Shifts in Food Preferences After Bariatric Surgery: Observational Reports and Proposed Mechanisms

PURPOSE OF REVIEW

Bariatric surgery is currently the most effective treatment for obesity. Roux-en-Y gastric bypass (RYGB) is the most commonly performed bariatric procedure and results in long-term weight loss. Alterations in food preference and choices may contribute to the long-term benefits of RYGB. This manuscript reviews the available literature documenting changes in food preference in both humans and experimental animals after RYGB and discusses the current theory on the underlying mechanisms involved.

RECENT FINDINGS

Obesity is associated with an increased preference for sweet and high-fat foods, and the most consistent evidence has been the shift away from these calorie-dense foods in both animal and human studies after RYGB. Self-reporting is the most common method used to record food preferences in humans, while more direct approaches have been used in animal work. This methodological heterogeneity may give rise to inconsistent findings. Future studies in humans should focus on direct measures to permit corroboration of mechanistic insights gained from animal studies.

The evolution of the host microbiome as an ecosystem on a leash

The human body carries vast communities of microbes that provide many benefits. Our microbiome is complex and challenging to understand, but evolutionary theory provides a universal framework with which to analyse its biology and health impacts. Here we argue that to understand a given microbiome feature, such as colonization resistance, host nutrition or immune development, we must consider how hosts and symbionts evolve. Symbionts commonly evolve to compete within the host ecosystem, while hosts evolve to keep the ecosystem on a leash. We suggest that the health benefits of the microbiome should be understood, and studied, as an interplay between microbial competition and host control.

Involvement of the prelimbic cortex in contextual fear conditioning with temporal and spatial discontinuity

Time plays an important role in conditioning, it is not only possible to associate stimuli with events that overlap, as in delay fear conditioning, but it is also possible to associate stimuli that are discontinuous in time, as shown in trace conditioning for a discrete stimuli. The environment itself can be a powerful conditioned stimulus (CS) and be associated to unconditioned stimulus (US). Thus, the aim of the present study was to determine the parameters in which contextual fear conditioning occurs by the maintenance of a contextual representation over short and long time intervals. The results showed that a contextual representation can be maintained and associated after 5s, even in the absence of a 15s re-exposure to the training context before US delivery. The same effect was not observed with a 24h interval of discontinuity. Furthermore, optimal conditioned response with a 5s interval is produced only when the contexts (of pre-exposure and shock) match. As the pre-limbic cortex (PL) is necessary for the maintenance of a continuous representation of a stimulus, the involvement of the PL in this temporal and contextual processing was investigated. The reversible inactivation of the PL by muscimol infusion impaired the acquisition of contextual fear conditioning with a 5s interval, but not with a 24h interval, and did not impair delay fear conditioning. The data provided evidence that short and long intervals of discontinuity have different mechanisms, thus contributing to a better understanding of PL involvement in contextual fear conditioning and providing a model that considers both temporal and contextual factors in fear conditioning.

Pharmacological Inhibition of c-Jun N-terminal Kinase Reduces Food Intake and Sensitizes Leptin's Anorectic Signaling Actions

The role for c-Jun N-terminal Kinase (JNK) in the control of feeding and energy balance is not well understood. Here, by use of novel and highly selective JNK inhibitors, we investigated the actions of JNK in the control of feeding and body weight homeostasis. In lean mice, intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) administration of SR-3306, a brain-penetrant and selective pan-JNK (JNK1/2/3) inhibitor, reduced food intake and body weight. Moreover, i.p. and i.c.v. administrations of SR11935, a brain-penetrant and JNK2/3 isoform-selective inhibitor, exerted similar anorectic effects as SR3306, which suggests JNK2 or JNK3 mediates aspect of the anorectic effect by pan-JNK inhibition. Furthermore, daily i.p. injection of SR3306 (7 days) prevented the increases in food intake and weight gain in lean mice upon high-fat diet feeding, and this injection paradigm reduced high-fat intake and obesity in diet-induced obese (DIO) mice. In the DIO mice, JNK inhibition sensitized leptin’s anorectic effect, and enhanced leptin-induced STAT3 activation in the hypothalamus. The underlying mechanisms likely involve the downregulation of SOCS3 by JNK inhibition. Collectively, our data suggest that JNK activity promotes positive energy balance, and the therapeutic intervention inhibiting JNK activities represents a promising approach to ameliorate diet-induced obesity and leptin resistance.

Calcium/calmodulin-dependent serine protein kinase (CASK), a protein implicated in mental retardation and autism-spectrum disorders, interacts with T-Brain-1 (TBR1) to control extinction of associative memory in male mice

BACKGROUND

Human genetic studies have indicated that mutations in calcium/calmodulin-dependent serine protein kinase (CASK) result in X-linked mental retardation and autism-spectrum disorders. We aimed to establish a mouse model to study how Cask regulates mental ability.

METHODS

Because Cask encodes a multidomain scaffold protein, a possible strategy to dissect how CASK regulates mental ability and cognition is to disrupt specific protein-protein interactions of CASK in vivo and then investigate the impact of individual specific protein interactions. Previous in vitro analyses indicated that a rat CASK T724A mutation reduces the interaction between CASK and T-brain-1 (TBR1) in transfected COS cells. Because TBR1 is critical for glutamate receptor, ionotropic, N-methyl-D-aspartate receptor subunit 2B (Grin2b) expression and is a causative gene for autism and intellectual disability, we then generated CASK T740A (corresponding to rat CASK T724A) mutant mice using a gene-targeting approach. Immunoblotting, coimmunoprecipitation, histological methods and behavioural assays (including home cage, open field, auditory and contextual fear conditioning and conditioned taste aversion) were applied to investigate expression of CASK and its related proteins, the protein-protein interactions of CASK, and anatomic and behavioural features of CASK T740A mice.

RESULTS

The CASK T740A mutation attenuated the interaction between CASK and TBR1 in the brain. However, CASK T740A mice were generally healthy, without obvious defects in brain morphology. The most dramatic defect among the mutant mice was in extinction of associative memory, though acquisition was normal.

LIMITATIONS

The functions of other CASK protein interactions cannot be addressed using CASK T740A mice.

CONCLUSION

Disruption of the CASK and TBR1 interaction impairs extinction, suggesting the involvement of CASK in cognitive flexibility.

Forebrain neurone-specific deletion of insulin-regulated aminopeptidase causes age related deficits in memory

Central infusion of Insulin-Regulated Aminopeptidase (IRAP) inhibitors improves memory in both normal rodents and in models of memory deficit. However, in contrast, the global IRAP knockout mice (KO) demonstrate age-accelerated spatial memory deficits and no improvements in performance in any memory tasks. Potentially, the observed memory deficit could be due to the absence of IRAP in the developing brain. We therefore generated a postnatal forebrain neuron-specific IRAP knockout mouse line (CamKIIalphaCre; IRAPlox/lox). Unexpectedly, we demonstrated that postnatal deletion of IRAP in the brain results in significant deficits in both spatial reference and object recognition memory at three months of age, although spatial working memory remained intact. These results indicate a significant role for IRAP in postnatal brain development and normal function of the hippocampus in adulthood.

Predator recognition learning in rainbow darters Etheostoma caeruleum: specific learning and neophobia

This study investigated whether rainbow darters Etheostoma caeruleum can learn to recognize unfamiliar predators through the process of classical conditioning. Etheostoma caeruleum were conditioned by exposing them simultaneously to their chemical alarm cues (a known fright stimulus) and either chemical cues from larval ringed salamanders Ambystoma annulatum (unfamiliar predator) or to a blank water cue (control). Conditioning could result in either specific learning of the A. annulatum cue or increased wariness in response to any novel cue (neophobia). To distinguish between these possibilities, E. caeruleum in both groups were exposed to either A. annulatum cues alone or to chemical cues from western rat snakes Pantherophis obsoletus (novel cue) 2 days after conditioning. Treatment (A. annulatum-conditioned) E. caeruleum, but not control E. caeruleum, showed a fright response when they were exposed to both the conditioned (A. annulatum) and novel (P. obsoletus) cues, indicating increased sensitivity to new stimuli. When E. caeruleum were retested after an additional 32 days, however, the fright response occurred only following exposure to the conditioned (A. annulatum) stimulus, indicating that specific learning of the A. annulatum cue had been retained whereas the neophobia to novel stimuli was temporary.

What Is the Effect of Basic Emotions on Directed Forgetting? Investigating the Role of Basic Emotions in Memory

Studies presenting memory-facilitating effect of emotions typically focused on affective dimensions of arousal and valence. Little is known, however, about the extent to which stimulus-driven basic emotions could have distinct effects on memory. In the present paper we sought to examine the modulatory effect of disgust, fear, and sadness on intentional remembering and forgetting using widely used item-method directed forgetting (DF) paradigm. Eighteen women underwent fMRI scanning during encoding phase in which they were asked either to remember (R) or to forget (F) pictures. In the test phase all previously used stimuli were re-presented together with the same number of new pictures and participants had to categorize them as old or new, irrespective of the F/R instruction. On the behavioral level we found a typical DF effect, i.e., higher recognition rates for to-be-remembered (TBR) items than to-be-forgotten (TBF) ones for both neutral and emotional categories. Emotional stimuli had higher recognition rate than neutral ones, while among emotional those eliciting disgust produced highest recognition, but at the same time induced more false alarms. Therefore, when false alarm corrected recognition was examined the DF effect was equally strong irrespective of emotion. Additionally, even though subjects rated disgusting pictures as more arousing and negative than other picture categories, logistic regression on the item level showed that the effect of disgust on recognition memory was stronger than the effect of arousal or valence. On the neural level, ROI analyses (with valence and arousal covariates) revealed that correctly recognized disgusting stimuli evoked the highest activity in the left amygdala compared to all other categories. This structure was also more activated for remembered vs. forgotten stimuli, but only in case of disgust or fear eliciting pictures. Our findings, despite several limitations, suggest that disgust have a special salience in memory relative to other negative emotions, which cannot be put down to differences in arousal or valence. The current results thereby support the suggestion that a purely dimensional model of emotional influences on cognition might not be adequate to account for observed effects.

Amphetamine and morphine may produce acute-withdrawal related hypoactivity by initially activating a common dopamine pathway

Rats given drugs of abuse such as amphetamine or morphine show longer-term effects, that is, signs of acute withdrawal, including hypoactivity, hypophagia, and blunted affect, sometime between 12 and 24h after treatment. This research explores the possibility that signs of acute withdrawal produced by different drugs of abuse are instigated by overlapping mechanisms. The specific objectives of the research were to see if amphetamine and morphine produced longer-term hypoactivity, and to see if any longer-term hypoactivity elicited by the drugs could be blocked by SCH23390, a dopamine D1 antagonist. Six groups of rats, with eight rats in each group, were exposed to a series of five-day tests. Near light onset of Test Day 1, each animal was given control administrations, consisting of a saline treatment (1.0ml/kg) followed 30m later by a saline posttreatment, and locomotor activity was monitored for the next 24h. On Test Day 3, each animal was given experimental administrations, and locomotor activity was again monitored for 24h. Each group received only one combination of experimental administrations across tests. Experimental administrations consisted of saline, amphetamine (2.0mg/kg), or morphine (5.0mg/kg), followed by saline or SCH23390 (0.05mg/kg). All administrations were subcutaneous. Amphetamine and morphine produced longer-term hypoactivity, having similar time courses and magnitudes. SCH23390 blocked the longer-term hypoactivity produced by both drugs. Saline and SCH23390 produced no changes in longer-term activity in their own right. The time course of amphetamine-elicited longer-term hypoactivity resembled that of amphetamine-elicited longer-term hypophagia observed in a prior study. Approximately 1/4 of the animals given amphetamine or morphine did not show longer-term hypoactivity ("low withdrawal" rats). Amphetamine and morphine may initiate the cascade of events resulting in signs of acute withdrawal by producing activation in a common pathway that uses dopamine as a neurotransmitter. Different signs of acute withdrawal (hypoactivity and hypophagia) may involve the short-term activation of the same common pathway. Low withdrawal rats may have a different vulnerability to amphetamine and may show differences in drug assessment outcomes relative to animals that manifest distinct signs of acute withdrawal.

Role for the Rostromedial Tegmental Nucleus in Signaling the Aversive Properties of Alcohol

BACKGROUND

While the rewarding effects of alcohol contribute significantly to its addictive potential, it is becoming increasingly appreciated that alcohol's aversive properties also play an important role in the propensity to drink. Despite this, the neurobiological mechanism for alcohol's aversive actions is not well understood. The rostromedial tegmental nucleus (RMTg) was recently characterized for its involvement in aversive signaling and has been shown to encode the aversive properties of cocaine, yet its involvement in alcohol's aversive actions have not been elucidated.

METHODS

Adult male and female Long-Evans rats underwent conditioned taste aversion (CTA) procedures where exposure to a novel saccharin solution was paired with intraperitoneal administration of saline, lithium chloride (LiCl), or ethanol (EtOH). Control rats underwent the same paradigm except that drug and saccharin exposure were explicitly unpaired. Saccharin consumption was measured on test day in the absence of drug administration, and rats were sacrificed 90 to 105 minutes following access to saccharin. Brains were subsequently harvested and processed for cFos immunohistochemistry. The number of cFos-labeled neurons was counted in the RMTg and the lateral habenula (LHb)-a region that sends prominent glutamatergic input to the RMTg.

RESULTS

In rats that received paired drug and saccharin exposure, EtOH and LiCl induced significant CTA compared to saline to a similar degree in males and females. Both EtOH- and LiCl-induced CTA significantly enhanced cFos expression in the RMTg and LHb but not the hippocampus. Similar to behavioral measures, no significant effect of sex on CTA-induced cFos expression was observed. cFos expression in both the RMTg and LHb was significantly correlated with CTA magnitude with greater cFos being associated with more pronounced CTA. In addition, cFos expression in the RMTg was positively correlated with LHb cFos.

CONCLUSIONS

These data suggest that the RMTg and LHb are involved in the expression of CTA and are consistent with previous work implicating the RMTg in aversive signaling. Furthermore, increased cFos expression in the RMTg following EtOH-induced CTA suggests that this region plays a role in signaling alcohol's aversive properties.

The incretin system ABCs in obesity and diabetes - novel therapeutic strategies for weight loss and beyond

Incretins are gastrointestinal-derived hormones released in response to a meal playing a key role in the regulation of postprandial secretion of insulin (incretin effect) and glucagon by the pancreas. Both incretins, glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 (GLP-1), have several other actions by peripheral and central mechanisms. GLP-1 regulates body weight by inhibiting appetite and delaying gastric, emptying actions that are dependent on central nervous system GLP-1 receptor activation. Several other hormones and gut peptides, including leptin and ghrelin, interact with GLP-1 to modulate appetite. GLP-1 is rapidly degraded by the multifunctional enzyme dipeptidyl peptidase-4 (DPP-4). DPP-4 is involved in adipose tissue inflammation, which is associated with insulin resistance and diabetes progression, being a common pathophysiological mechanism in obesity-related complications. Furthermore, the incretin system appears to provide the basis for understanding the high weight loss efficacy of bariatric surgery, a widely used treatment for obesity, often in association with diabetes. The present review brings together new insights into obesity pathogenesis, integrating GLP-1 and DPP-4 in the complex interplay between obesity and inflammation, namely, in diabetic patients. This in turn will provide the basis for novel incretin-based therapeutic strategies for obesity and diabetes with promising benefits in addition to weight loss. © 2016 World Obesity.

Olfactory Stimuli Increase Presence in Virtual Environments

BACKGROUND

Exposure therapy (EXP) is the most empirically supported treatment for anxiety and trauma-related disorders. EXP consists of repeated exposure to a feared object or situation in the absence of the feared outcome in order to extinguish associated anxiety. Key to the success of EXP is the need to present the feared object/event/situation in as much detail and utilizing as many sensory modalities as possible, in order to augment the sense of presence during exposure sessions. Various technologies used to augment the exposure therapy process by presenting multi-sensory cues (e.g., sights, smells, sounds). Studies have shown that scents can elicit emotionally charged memories, but no prior research has examined the effect of olfactory stimuli upon the patient's sense of presence during simulated exposure tasks.

METHODS

60 adult participants navigated a mildly anxiety-producing virtual environment (VE) similar to those used in the treatment of anxiety disorders. Participants had no autobiographical memory associated with the VE. State anxiety, Presence ratings, and electrodermal (EDA) activity were collected throughout the experiment.

RESULTS

Utilizing a Bonferroni corrected Linear Mixed Model, our results showed statistically significant relationships between olfactory stimuli and presence as assessed by both the Igroup Presence Questionnaire (IPQ: R2 = 0.85, (F(3,52) = 6.625, p = 0.0007) and a single item visual-analogue scale (R2 = 0.85, (F(3,52) = 5.382, p = 0.0027). State anxiety was unaffected by the presence or absence of olfactory cues. EDA was unaffected by experimental condition.

CONCLUSION

Olfactory stimuli increase presence in virtual environments that approximate those typical in exposure therapy, but did not increase EDA. Additionally, once administered, the removal of scents resulted in a disproportionate decrease in presence. Implications for incorporating the use of scents to increase the efficacy of exposure therapy is discussed.