Beyond the Activity-Based Anorexia Model: Reinforcing Values of Exercise and Feeding Examined in Stressed Adolescent Male and Female Mice

Anorexia nervosa (AN), mostly observed in female adolescents, is the most fatal mental illness. Its core is a motivational imbalance between exercise and feeding in favor of the former. The most privileged animal model of AN is the “activity-based anorexia” (ABA) model wherein partly starved rodents housed with running wheels exercise at the expense of feeding. However, the ABA model bears face and construct validity limits, including its inability to specifically assess running motivation and feeding motivation. As infant/adolescent trauma is a precipitating factor in AN, this study first analyzed post-weaning isolation rearing (PWIR) impacts on body weights and wheel-running performances in female mice exposed to an ABA protocol. Next, we studied through operant conditioning protocols i) whether food restriction affects in a sex-dependent manner running motivation before ii) investigating how PWIR and sex affect running and feeding drives under ad libitum fed conditions and food restriction. Besides amplifying ABA-elicited body weight reductions, PWIR stimulated wheel-running activities in anticipation of feeding in female mice, suggesting increased running motivation. To confirm this hypothesis, we used a cued-reward motivated instrumental task wherein wheel-running was conditioned by prior nose poke responses. It was first observed that food restriction increased running motivation in male, but not female, mice. When fed grouped and PWIR mice were tested for their running and palatable feeding drives, all mice, excepted PWIR males, displayed increased nose poke responses for running over feeding. This was true when rewards were proposed alone or within a concurrent test. The increased preference for running over feeding in fed females did not extend to running performances (time, distance) during each rewarded sequence, confirming that motivation for, and performance during, running are independent entities. With food restriction, mice displayed a sex-independent increase in their preference for feeding over running in both group-housed and PWIR conditions. This study shows that the ABA model does not specifically capture running and feeding drives, i.e. components known to be affected in AN

Subcellular specificity of cannabinoid effects in striatonigral circuits

Recent advances in neuroscience have positioned brain circuits as key units in controlling behavior, implying that their positive or negative modulation necessarily leads to specific behavioral outcomes. However, emerging evidence suggests that the activation or inhibition of specific brain circuits can actually produce multimodal behavioral outcomes. This study shows that activation of a receptor at different subcellular locations in the same neuronal circuit can determine distinct behaviors. Pharmacological activation of type 1 cannabinoid (CB1) receptors in the striatonigral circuit elicits both antinociception and catalepsy in mice. The decrease in nociception depends on the activation of plasma membrane-residing CB1 receptors (pmCB1), leading to the inhibition of cytosolic PKA activity and substance P release. By contrast, mitochondrial-associated CB1 receptors (mtCB1) located at the same terminals mediate cannabinoid-induced catalepsy through the decrease in intra-mitochondrial PKA-dependent cellular respiration and synaptic transmission. Thus, subcellular-specific CB1 receptor signaling within striatonigral circuits determines multimodal control of behavior

Role of the endocannabinoid system in exercise motivation

La sédentarité est un problème majeur de santé publique qui s’explique principalement par un déséquilibre de la balance énergétique. Il résulte (i) d'une prise alimentaire abondante et (ii) d'une absence de motivation pour l’exercice. Malheureusement, les bases neurobiologiques de la motivation pour l’exercice sont encore méconnues. Des travaux du laboratoire avaient montré l’implication du système endocannabinoïde (SEC) dans le contrôle des performances de course chez la souris. Ce contrôle s'effectue via les récepteurs aux cannabinoïdes de type 1 (CB1) localisés sur les terminaisons GABAergiques de l’aire tegmentale ventrale (ATV), cette région cérébrale jouant un rôle clef dans les processus de motivation pour les récompenses. Cependant, les performances de course ne permettent pas de distinguer la motivation pour l’exercice du plaisir de courir. L’objectif de ce travail était d’étudier l’implication des récepteurs CB1 dans la régulation spécifique de la motivation pour l’exercice chez la souris (i) en caractérisant la(les) population(s) de récepteurs participant à celle-ci, puis (ii) en évaluant leur implication dans le choix entre l’exercice et la nourriture palatable, et enfin (iii) en mesurant l’effet de leur stimulation sur la motivation pour l’exercice. Cette étude repose sur l’utilisation du conditionnement opérant (unique moyen d’étude de la motivation chez l’animal) associé à des approches génétiques (mutants des récepteurs CB1) et pharmacologiques (agonistes et antagonistes de ces récepteurs).La première partie de ce travail a permis de développer un protocole de conditionnement opérant permettant de distinguer (i) la motivation pour l’exercice, celle-ci étant corrélée à l’activité des neurones dopaminergiques de l’ATV, (ii) du plaisir de courir. Cette étude a montré que les récepteurs CB1 qui contrôlent la motivation pour l’exercice sont localisées dans l’ATV. Nous avons ensuite démontré le rôle tonique nécessaire et suffisant des récepteurs CB1 des neurones GABAergiques (GABA-CB1) dans la motivation pour l’exercice, mais pas dans le plaisir de courir. Les résultats obtenus ont soulevé la question de la spécificité du contrôle de la motivation pour la course de ces récepteurs. Nous avons alors confirmé l’implication du SEC dans la motivation pour la nourriture palatable avant de montrer que les récepteurs GABA-CB1 n’étaient pas impliqués dans celle-ci.La deuxième partie visait à étudier l’implication du récepteur CB1 dans le choix entre l’exercice et la nourriture palatable lorsque ces deux récompenses sont mises en concurrence. En effet, humains et animaux sont confrontés quotidiennement à plusieurs récompenses simultanées, leur choix étant basé sur leurs motivations respectives pour chacune d'elles. Dans ce but, nous avons développé un protocole de choix en conditionnement opérant permettant d’étudier la préférence de l’animal entre ces deux récompenses. Ainsi, après avoir démontré l’importance du SEC dans le choix entre ces deux récompenses, nous avons montré que la délétion des récepteurs GABA-CB1 a diminué la préférence pour l’exercice au profit de la nourriture palatable. Cette étude identifie donc un potentiel mécanisme neurobiologique participant à la sédentarité.La troisième partie de ce travail avait pour but d’évaluer la possibilité de moduler la motivation pour l’exercice via le SEC. En effet, le contrôle tonique exercé par les récepteurs GABA-CB1 sur la motivation pour courir soulevait la question de l’impact d’une stimulation de ces récepteurs sur cette motivation. Les résultats ont indiqué que la stimulation des récepteurs CB1 par des agonistes directs et indirects de ces récepteurs n’était pas en mesure d'augmenter la motivation pour l’exercice.En conclusion, ce travail démontre le rôle majeur des récepteurs CB1 des neurones GABAergiques dans la motivation pour l'exercice physique.Sedentariness is a major public health issue. It is mainly explained by a lack of exercise motivation, resulting in an energy imbalance in favor of food intake. However, the neurobiological bases of exercise motivation remain poorly described. Previous works in the laboratory have demonstrated the role of the endocannabinoid system (ECS) in the control of running performances in mice. This role is exerted by type-1 cannabinoid receptors (CB1) located on GABAergic terminals in the ventral tegmental area (VTA). This brain region has been shown to play a key role in reward processes. Because the evaluation of running performances does not distinguish between running motivation and pleasure, we aimed at studying the role of CB1 receptors in the regulation of exercise motivation in mice. Using operant conditioning protocols (which allow to specifically study motivation in animals), this work characterized (i) the subpopulation(s) of receptors participating in this regulation, (ii) their potential involvement in the choice between exercise and palatable food, and (iii) the consequences of a selective stimulation of these receptors on exercise motivation. This work combined genetic (mouse mutants for CB1 receptors) and pharmacological (CB1 receptor agonists and antagonists) approaches.The first set of experiments aimed at developing an operant conditioning protocol that allow to distinguish exercise motivation from exercise pleasure, the former but not the latter being positively linked to the activity of VTA dopaminergic neurons. Our results showed that CB1 receptors control exercise motivation through an action in the VTA. Moreover, we demonstrated that CB1 receptors located on GABAergic neurons (GABA-CB1) are necessary and sufficient for the tonic control of exercise motivation. Conversely, exercise pleasure, as assessed by running performance, proved independent from this receptor population. Because previous studies demonstrated the key role exerted by CB1 receptors in motivation for other (than exercise) rewards, we questioned the specificity of the control of running motivation exerted by GABA-CB1 receptors. Indeed, after having confirmed the involvement of the ECS in palatable food motivation, we provided evidence against a role for GABA-CB1 receptors in feeding motivation, hence indicating their reward-specific control.The second set of experiments aimed at evaluating the involvement of CB1 receptors in the choice between exercise and palatable food when both rewards were made concurrent. Indeed, humans and animals are permanently confronted with reward choices, these being dictated by their respective motivation for these alternatives. To this aim, we developed an operant conditioning protocol allowing the study of the animal preference between exercise and palatable food presented simultaneously but being mutually exclusive. By this means, we demonstrated the crucial importance of CB1 receptors in this choice. Moreover, we showed that the lack of GABA-CB1 receptors decreased the mouse preference for exercise in favor of palatable food. This work thus identifies a potential neurobiological mechanism underlying sedentariness.The third set of experiments aimed at evaluating the possibility to stimulate exercise motivation. The tonic control exerted by GABA-CB1 receptors on exercise raises the question of the impact of their stimulation. Indeed, stimulation of CB1 receptors by direct and indirect agonists proved inefficient in altering running motivation.In conclusion, besides providing a paradigm allowing to study exercise motivation in mice, this work provides direct evidence for a specific role of CB1 receptors located on GABAergic neurons on motivation for exercise

Rôle du système endocannabinoïde dans la motivation pour l'exercice

Sedentariness is a major public health issue. It is mainly explained by a lack of exercise motivation, resulting in an energy imbalance in favor of food intake. However, the neurobiological bases of exercise motivation remain poorly described. Previous works in the laboratory have demonstrated the role of the endocannabinoid system (ECS) in the control of running performances in mice. This role is exerted by type-1 cannabinoid receptors (CB1) located on GABAergic terminals in the ventral tegmental area (VTA). This brain region has been shown to play a key role in reward processes. Because the evaluation of running performances does not distinguish between running motivation and pleasure, we aimed at studying the role of CB1 receptors in the regulation of exercise motivation in mice. Using operant conditioning protocols (which allow to specifically study motivation in animals), this work characterized (i) the subpopulation(s) of receptors participating in this regulation, (ii) their potential involvement in the choice between exercise and palatable food, and (iii) the consequences of a selective stimulation of these receptors on exercise motivation. This work combined genetic (mouse mutants for CB1 receptors) and pharmacological (CB1 receptor agonists and antagonists) approaches.The first set of experiments aimed at developing an operant conditioning protocol that allow to distinguish exercise motivation from exercise pleasure, the former but not the latter being positively linked to the activity of VTA dopaminergic neurons. Our results showed that CB1 receptors control exercise motivation through an action in the VTA. Moreover, we demonstrated that CB1 receptors located on GABAergic neurons (GABA-CB1) are necessary and sufficient for the tonic control of exercise motivation. Conversely, exercise pleasure, as assessed by running performance, proved independent from this receptor population. Because previous studies demonstrated the key role exerted by CB1 receptors in motivation for other (than exercise) rewards, we questioned the specificity of the control of running motivation exerted by GABA-CB1 receptors. Indeed, after having confirmed the involvement of the ECS in palatable food motivation, we provided evidence against a role for GABA-CB1 receptors in feeding motivation, hence indicating their reward-specific control.The second set of experiments aimed at evaluating the involvement of CB1 receptors in the choice between exercise and palatable food when both rewards were made concurrent. Indeed, humans and animals are permanently confronted with reward choices, these being dictated by their respective motivation for these alternatives. To this aim, we developed an operant conditioning protocol allowing the study of the animal preference between exercise and palatable food presented simultaneously but being mutually exclusive. By this means, we demonstrated the crucial importance of CB1 receptors in this choice. Moreover, we showed that the lack of GABA-CB1 receptors decreased the mouse preference for exercise in favor of palatable food. This work thus identifies a potential neurobiological mechanism underlying sedentariness.The third set of experiments aimed at evaluating the possibility to stimulate exercise motivation. The tonic control exerted by GABA-CB1 receptors on exercise raises the question of the impact of their stimulation. Indeed, stimulation of CB1 receptors by direct and indirect agonists proved inefficient in altering running motivation.In conclusion, besides providing a paradigm allowing to study exercise motivation in mice, this work provides direct evidence for a specific role of CB1 receptors located on GABAergic neurons on motivation for exercise.La sédentarité est un problème majeur de santé publique qui s’explique principalement par un déséquilibre de la balance énergétique. Il résulte (i) d'une prise alimentaire abondante et (ii) d'une absence de motivation pour l’exercice. Malheureusement, les bases neurobiologiques de la motivation pour l’exercice sont encore méconnues. Des travaux du laboratoire avaient montré l’implication du système endocannabinoïde (SEC) dans le contrôle des performances de course chez la souris. Ce contrôle s'effectue via les récepteurs aux cannabinoïdes de type 1 (CB1) localisés sur les terminaisons GABAergiques de l’aire tegmentale ventrale (ATV), cette région cérébrale jouant un rôle clef dans les processus de motivation pour les récompenses. Cependant, les performances de course ne permettent pas de distinguer la motivation pour l’exercice du plaisir de courir. L’objectif de ce travail était d’étudier l’implication des récepteurs CB1 dans la régulation spécifique de la motivation pour l’exercice chez la souris (i) en caractérisant la(les) population(s) de récepteurs participant à celle-ci, puis (ii) en évaluant leur implication dans le choix entre l’exercice et la nourriture palatable, et enfin (iii) en mesurant l’effet de leur stimulation sur la motivation pour l’exercice. Cette étude repose sur l’utilisation du conditionnement opérant (unique moyen d’étude de la motivation chez l’animal) associé à des approches génétiques (mutants des récepteurs CB1) et pharmacologiques (agonistes et antagonistes de ces récepteurs).La première partie de ce travail a permis de développer un protocole de conditionnement opérant permettant de distinguer (i) la motivation pour l’exercice, celle-ci étant corrélée à l’activité des neurones dopaminergiques de l’ATV, (ii) du plaisir de courir. Cette étude a montré que les récepteurs CB1 qui contrôlent la motivation pour l’exercice sont localisées dans l’ATV. Nous avons ensuite démontré le rôle tonique nécessaire et suffisant des récepteurs CB1 des neurones GABAergiques (GABA-CB1) dans la motivation pour l’exercice, mais pas dans le plaisir de courir. Les résultats obtenus ont soulevé la question de la spécificité du contrôle de la motivation pour la course de ces récepteurs. Nous avons alors confirmé l’implication du SEC dans la motivation pour la nourriture palatable avant de montrer que les récepteurs GABA-CB1 n’étaient pas impliqués dans celle-ci.La deuxième partie visait à étudier l’implication du récepteur CB1 dans le choix entre l’exercice et la nourriture palatable lorsque ces deux récompenses sont mises en concurrence. En effet, humains et animaux sont confrontés quotidiennement à plusieurs récompenses simultanées, leur choix étant basé sur leurs motivations respectives pour chacune d'elles. Dans ce but, nous avons développé un protocole de choix en conditionnement opérant permettant d’étudier la préférence de l’animal entre ces deux récompenses. Ainsi, après avoir démontré l’importance du SEC dans le choix entre ces deux récompenses, nous avons montré que la délétion des récepteurs GABA-CB1 a diminué la préférence pour l’exercice au profit de la nourriture palatable. Cette étude identifie donc un potentiel mécanisme neurobiologique participant à la sédentarité.La troisième partie de ce travail avait pour but d’évaluer la possibilité de moduler la motivation pour l’exercice via le SEC. En effet, le contrôle tonique exercé par les récepteurs GABA-CB1 sur la motivation pour courir soulevait la question de l’impact d’une stimulation de ces récepteurs sur cette motivation. Les résultats ont indiqué que la stimulation des récepteurs CB1 par des agonistes directs et indirects de ces récepteurs n’était pas en mesure d'augmenter la motivation pour l’exercice.En conclusion, ce travail démontre le rôle majeur des récepteurs CB1 des neurones GABAergiques dans la motivation pour l'exercice physique

The ergogenic impact of the glucocorticoid prednisolone does not translate into increased running motivation in mice

International audienceGlucocorticoids, such as prednisolone, are considered sport doping agents owing to their ergogenic properties. These are accounted for by peripheral mechanisms associated with energetic and anti-inflammatory processes. However, because glucocorticoids target brain tissues, it is likely that these ergogenic impacts are associated with central effects. One of these might be reward motivation, which relies on glucocorticoid receptor-expressing mesocorticolimbic dopaminergic neurons. In keeping with this possibility, this study has explored in mice whether repeated prednisolone administration (5 or 15 μg/ml of drinking water for 10 days) affected intrinsic motivation for running, a strong reinforcer in rodents. Running motivation was assessed by means of a cued-reward motivated instrumental task wherein wheel-running was conditioned by prior nose poke responses under fixed (FR), and then progressive (PR), ratio reinforcement schedules. Sub-chronic ingestion of prednisolone decreased the running distance covered during each rewarded sequence under FR schedules. This finding did not extend to wheel-running performances in mice provided free (i.e. unconditioned) wheel-running opportunities. Running motivation, as estimated under a PR reinforcement schedule, was found to be decreased (lowest concentration) or to remain unaffected (highest concentration) by prednisolone concentration. Lastly, an inter-individual analysis of the respective effects of prednisolone on muscular endurance (as assessed in the wire grid-hanging test) and on running motivation indicated that the former was not predictive of the latter. This observation suggests that prednisolone ergogenic impacts might occur without any concomitant increase in intrinsic exercise motivation

Cannabis and exercise: Effects of Δ9-tetrahydrocannabinol on preference and motivation for wheel-running in mice

Recent surveys have revealed close links between cannabis and exercise. Specifically, cannabis usage before and/or after exercise is an increasingly common habit primarily aimed at boosting exercise pleasure, motivation, and performance whilst facilitating post-exercise recovery. However, whether these beliefs reflect the true impact of cannabis on these aspects of exercise is unknown. This study has thus examined the effects of cannabis' main psychoactive ingredient, namely ?9-tetrahydrocannabinol (THC), on (i) mouse wheel-running preference and performance and (ii) running motivation and seeking behaviour. Wheel-running preference and performance were investigated using a T-maze with free and locked wheels located at the extremity of either arm. Running motivation and seeking were assessed by a cued-running operant task wherein wheel-running was conditioned by nose poking. Moreover, because THC targets cannabinoid type 1 (CB1) receptors, i.e. receptors previously documented to control running motivation, this study also assessed the role of these receptors in running preference, performance, and craving-like behaviour. Whilst acute blockade or genetic deletion of CB1 receptors decreased running preference and performance in the T-maze, THC proved ineffective on either variable. The failure of THC to affect running variables in the T-maze extended to running motivation, as assessed by cued-running under a progressive ratio (PR) reinforcement schedule. This ineffectiveness of THC was not related to the treatment protocol because it successfully increased motivation for palatable food. Although craving-like behaviour, as indexed by a cue-induced reinstatement of running seeking, was found to depend on CB1 receptors, THC again proved ineffective. Neither running motivation nor running seeking were affected when CB1 receptors were further stimulated by increasing the levels of the endocannabinoid 2-arachidonoylglycerol. These results, which suggest that the drive for running is insensitive to the acute stimulation of CB1 receptors, raise the hypothesis that cannabis is devoid of effect on exercise motivation. Future investigation using chronic administration of THC, with and without other cannabis ingredients (e.g. cannabidiol), is however required before conclusions can be drawn

Deciphering Transcriptional Networks during Human Cardiac Development

Human heart development is governed by transcription factor (TF) networks controlling dynamic and temporal gene expression alterations. Therefore, to comprehensively characterize these transcriptional regulations, day-to-day transcriptomic profiles were generated throughout the directed cardiac differentiation, starting from three distinct human- induced pluripotent stem cell lines from healthy donors (32 days). We applied an expression-based correlation score to the chronological expression profiles of the TF genes, and clustered them into 12 sequential gene expression waves. We then identified a regulatory network of more than 23,000 activation and inhibition links between 216 TFs. Within this network, we observed previously unknown inferred transcriptional activations linking IRX3 and IRX5 TFs to three master cardiac TFs: GATA4, NKX2-5 and TBX5. Luciferase and co-immunoprecipitation assays demonstrated that these five TFs could (1) activate each other’s expression; (2) interact physically as multiprotein complexes; and (3) together, finely regulate the expression of SCN5A, encoding the major cardiac sodium channel. Altogether, these results unveiled thousands of interactions between TFs, generating multiple robust hypotheses governing human cardiac development

Deciphering transcriptional networks during human cardiac development

Abstract Human heart development is governed by transcription factor (TF) networks controlling dynamic and temporal gene expression alterations. Therefore, to comprehensively characterize these transcriptional regulations, day-to-day transcriptomic profiles were generated throughout the directed cardiac differentiation, starting from three distinct human induced pluripotent stem cell lines from healthy donors (32 days). We applied an expression-based correlation score to the chronological expression profiles of the TF genes, and clustered them into 12 sequential gene expression waves. We then identified a regulatory network of more than 23 000 activation and inhibition links between 216 TFs. Within this network, we observed previously unknown inferred transcriptional activations linking IRX3 and IRX5 TFs to three master cardiac TFs: GATA4, NKX2-5 and TBX5. Luciferase and co-immunoprecipitation assays demonstrated that these 5 TFs could (1) activate each other’s expression, (2) interact physically as multiprotein complexes and (3) together, finely regulate the expression of SCN5A , encoding the major cardiac sodium channel. Altogether, these results unveiled thousands of interactions between TFs, generating multiple robust hypotheses governing human cardiac development

Exercise craving potentiates excitatory inputs to ventral tegmental area dopaminergic neurons

International audiencePhysical exercise, which can be addictogenic on its own, is considered a therapeutic alternative for drug craving. Exercise might thus share with drugs the ability to strengthen excitatory synapses onto ventral tegmental area (VTA) dopaminergic neurones, as assessed by the ratio of AMPA receptor (AMPAR)‐mediated excitatory postsynaptic currents (EPSCs) to NMDA receptor (NMDAR)‐mediated EPSCs. As did acute cocaine, amphetamine, or Δ9‐tetrahydrocannabinol (THC) pretreatments, an acute 1‐h wheel‐running session increased the AMPAR/NMDAR ratio in VTA dopaminergic neurones. To dissect the respective influences of wheel‐running seeking and performance, mice went through an operant protocol wherein wheel‐running was conditioned by nose poking under fixed ratio schedules of reinforcement. Conditioned wheel‐running increased the AMPAR/NMDAR ratio to a higher extent than free wheel‐running, doing so although running performance was lower in the former paradigm than in the latter. Thus, the cue‐reward association, rather than reward consumption, played a major role in this increase. The AMPAR/NMDAR ratio returned to baseline levels in mice that had extinguished the cued‐running motivated task, but it increased after a cue‐induced reinstatement session. The amplitude of this increase correlated with the intensity of exercise craving, as assessed by individual nose poke scores. Finally, cue‐induced reinstatement of running seeking proved insensitive to acute cocaine or THC pretreatments. Our study reveals for the first time that the drive for exercise bears synaptic influences on VTA dopaminergic neurones which are reminiscent of drug actions. Whether these influences play a role in the therapeutic effects of exercise in human drug craving remains to be established

The motivation for exercise over palatable food is dictated by cannabinoid type-1 receptors

International audienceThe lack of intrinsic motivation to engage in, and adhere to, physical exercise has major health consequences. However, the neurobiological bases of exercise motivation are still unknown. This study aimed at examining whether the endocannabinoid system (ECS) is involved in this process. To do so, we developed an operant conditioning paradigm wherein mice unlocked a running wheel with nose pokes. Using pharmacological tools and conditional mutants for cannabinoid type-1 (CB1) receptors, we provide evidence that CB1 receptors located on GABAergic neurons are both necessary and sufficient to positively control running motivation. Conversely, this receptor population proved dispensable for the modulation of running duration per rewarded sequence. Although the ECS mediated the motivation for another reward, namely palatable food, such a regulation was independent from CB1 receptors on GABAergic neurons. In addition, we report that the lack of CB1 receptors on GABAergic neurons decreases the preference for running over palatable food when mice were proposed an exclusive choice between the two rewards. Beyond providing a paradigm that enables motivation processes for exercise to be dissected either singly or in concurrence, this study is the first to our knowledge to identify a neurobiological mechanism that might contribute to sedentary behavio