Physiology & Behavior

Inbred mouse strains differ in their postoral appetite stimulating response (appetition) to glucose and fructose. For example, C57BL/6J (B6) and FVB strains learn strong preferences for a flavor (CS+, e.g., cherry) paired with intragastric (IG) glucose infusions, but only FVB mice learned to prefer a CS+ paired with IG fructose infusions. Consistent with these findings, "tasteless" B6 knockout (KO) mice missing the taste signaling protein TRPM5 learn strong preferences for a CS+ added to glucose solution as well as for unflavored glucose but weak or no preferences for a fructose-paired CS+ or unflavored fructose. The present experiment reports that "tasteless" P2X2/P2X3 double-knockout (P2X2/3 DKO) mice, unlike TRPM5 KO mice, learned strong preferences for a CS+ mixed with fructose as well as for unflavored fructose. Whether differences in genetic backgrounds or other factors account for the fructose appetition displayed by P2X2/3 DKO mice but not TRPM5 KO mice remains to be determined.

There is evidence that appetites for specific nutrients can guide foraging behaviour and aid in dietary regulation through associative learning processes that link stimuli to nutrient-specific outcomes. However, most, if not all, examples of such behaviour can be interpreted as being stimulus-bound habits, i.e., reflexive responses induced by environmental stimuli. The control of identified goal-directed actions by nutrient-specific appetites has not been directly assessed. To address this question, we trained rats to press a lever for a high protein reward (whey protein shake) and another lever for a high carbohydrate reward (polycose solution). They were then tested under extinction conditions in which both levers were available following the extended exposure to meals that were high in protein or carbohydrate. When otherwise food-deprived rats had been selectively satiated on protein immediately prior to test, they pressed more on the lever they learned had produced polycose, whereas they pressed the lever they learned had produced whey protein more if they had instead been satiated on carbohydrate. Crucially, the same pattern emerged whether the satiety manipulation was achieved using the same nutrient sources that rats had earned during training (i.e., whey or polycose) or with foods high in the relevant nutrients, indicating that these behaviours were under goal-directed control and sensitive to nutritional state. These results show that actions can be motivated by the nutritional relevance of the instrumental outcome to specific appetites, a relationship that may guide natural foraging decisions.

Protein provides essential amino acids critical for survival. Recent research has identified that dietary protein restriction induces physiological and behavioral adaptations and that those adaptations are mediated by liver-produced fibroblast growth factor 21 (FGF21) that acts in the brain. Most of the research on adaptations to dietary protein restriction and the biological factors that mediate those adaptations carries an implicit assumption that the effects of dietary protein restriction are reversible. Rarely is the assumption of reversibility directly examined by varying dietary protein content within animals. Recently collected data on preference for protein versus carbohydrate solutions indicates that when mice are placed on a low (5%) protein diet, preference for protein is rapidly increased. However, when mice are switched from a low to normal (20%) protein diet, relative consumption of protein decreases but preference for protein persists. Re-analysis of published data suggests, similarly, that preference for protein-rich food sources remains elevated following exposure to dietary protein restriction and that calcium influx in the ventral tegmental area of the brain in response to protein consumption also remains persistently elevated following dietary protein restriction. Together, the data suggest that prior protein restriction can exert long-lasting effects on protein preference and on brain activity associated with protein consumption. The finding that the effects of protein restriction do not rapidly reverse implies that protein choice may be a function, not only of current nutritional state, but of historical nutritional conditions. Further, these results suggest that a full understanding of the environmental and biological determinants of protein choice requires studies in which dietary protein intake is varied within subjects.

Changes in motivation have been observed following induction of diet-induced obesity. However, to date, results have been contradictory, some authors reporting an increase in motivation to obtain palatable food, but others observing a decrease. Observed differences might be associated with the length of both the evaluation period and exposure to the diet. Therefore, the aim of this study was to evaluate changes in motivation during 20 weeks of exposure to a hypercaloric diet. Performance of the subjects in a progressive ratio schedule was evaluated before and during the exposure to a high-fat, high-sugar choice diet (HFHSc). A decrease in motivation was observed after 2 weeks of diet exposure, low levels of motivation remained throughout 20 weeks. A comparable decrease in motivation took longer (3 weeks) to develop using chow diet in the control group. Overall, our results suggest that, when changes in motivation are being evaluated, long periods of diet exposure made no further contribution, once motivation decreased, it remained low up to 18 weeks. Exposure to a HFHSc diet is a useful animal model of obesity, since it replicates some pathophysiological and psychological features of human obesity such as an increase in fasting glucose levels, body weight and the weight of adipose tissue.

AbstractProlonged esports play can induce cognitive fatigue by placing sustained demands on executive control, decision-making, and stress regulation. Since the brain relies primarily on glucose as an immediate energy source, we hypothesized that a carbohydrate gel designed to prolong post-ingestion glycaemia stabilizes interstitial glucose, attenuates hunger and cognitive fatigue, and helps preserve performance during extended esports play. Eleven healthy young men completed a randomized, double-blind crossover study with two sessions in which they ingested one of two carbohydrate gels matched for total energy and total carbohydrate but differing in carbohydrate composition (high-fructose corn syrup [HFCS]-dominant vs maltodextrin [MDX]-dominant) before gameplay. Interstitial glucose was monitored continuously, while hunger, salivary cortisol, pupil diameter, executive function, and in-game performance were assessed repeatedly. Compared with the control (HFCS-dominant) condition, the glycaemia-prolonging formulation maintained higher interstitial glucose levels during the later phase of gameplay, blunted the progressive increase in hunger, and attenuated cortisol responses. These physiological and subjective advantages were accompanied by better executive control and more adaptive defensive behaviors in-game, including fewer fouls and more interceptions. In contrast, pupil diameter, an index of global arousal, remained unchanged across conditions, suggesting that benefits were not driven by altered arousal but by improved glycaemic stability and appetite regulation. These findings indicate that a carbohydrate formulation that prolongs glycaemia can reduce hunger-linked cognitive fatigue and support task-relevant behavior during prolonged esports play. This low-burden nutritional strategy may help sustain mental performance during prolonged digital activities that impose high cognitive demands. Highlights- A glycaemia-prolonging gel maintained higher interstitial glucose late in esports play - Hunger and salivary cortisol increased less with the glycaemia-prolonging formulation - Executive control and defensive performance improved (fewer fouls, more interceptions) - Pupil diameter was unchanged, suggesting benefits were not driven by altered arousal - A low-burden, glycaemia-stabilizing strategy may help sustain cognitive stamina

Food is generally hidden in a natural environment and require free-living animals to search for it. Although such food-seeking behaviors involve motivation and exploration, previous studies examined food-seeking simply by measuring the time spent in the food zone or the frequency of pursuing food-cued context. Moreover, after discovering food, animals need to taste and smell it in order to evaluate their nutritional value or possible toxicity. However, researchers could not easily distinguish food-seeking from food-evaluating behaviors because food was visible or accessible throughout each test. Herein, we describe a behavioral protocol that triggers animals to show the behavioral dynamics of food-seeking (e.g., navigation, nose-digging, and paw-digging) and that exclusively elicits food-seeking without provoking any other food-evaluating behaviors. First, we prepared an open-field box with the floor covered with bedding. After we hid foods under the bedding of each corner, the test mice were habituated in this arena for four days (pre-test phase). On the next day (test phase), they were placed under the same conditions, but the foods previously hidden were removed. This process enabled the mice to perceive their surroundings as a food-hidden environment, which induced the animal to exhibit sustained food-seeking. In conclusion, the protocol presented here is a powerful method for provoking multiple forms of food-seeking and quantifies food-seeking independently from other food-related behavioral stages.

Exposure to food rich in fat and sugar (High Fat and Sugar Diet, HFSD) is believed to induce behavioral and neurobiological changes that would produce addiction-like behavior and increase the risks of obesity and overweight. Studies in rodents have led to conflicting results suggesting that several factors such as sex and age of exposure contribute to the development of maladaptive behavior towards food. In addition, it is not clear whether the effects of exposure to HFSD persist after its discontinuation which would indicate long-term risk to develop addiction-like behavior. In this study, we investigated the persistent effects of an intermittent 8-week exposure to HFSD in male and female rats as a function of age of exposure (adult and adolescent). We found that intermittent exposure to HFSD did not alter body weight, but it affected consumption of standard food during the time of exposure in all groups. In addition, in adults, HFSD produced a decrease in the initial baseline responding in FR1 schedules that persisted for 4 weeks in males but not in female rats. However, we found that exposure to HFSD did not affect resistance to punishment measured by progressive shock strength (PSS) break points or motivation for food measured by progressive-ratio break points regardless of sex or age of exposure. Altogether, these results do not provide support to the hypothesis that intermittent exposure to HFSD produce persistent increases in the vulnerability to develop addiction-like behaviors towards palatable food.

Vagus nerve signals from the gut to brain carry information about nutrients and drive food reward. Such signals are disrupted by consuming large amounts of high-calorie foods, necessitating greater food intake to elicit a similar neural response. Non-invasive vagus nerve stimulation (nVNS) via a branch innervating the ear is a candidate treatment for obesity in humans. There is disagreement on the optimal location of nVNS in the ear for experimental and clinical studies. There are also no studies comparing nVNS in hungry and full states. We aimed to compare ear position(s) for nVNS and explore the effects of nVNS during hungry and full states on proxies for autonomic outflow (heart-rate variability) and efferent metabolism (gastric frequency and resting energy expenditure). In a within-subject design, 14 participants (10 women, on average 29.4 +/- 6.7 years old) received nVNS in four different locations (cymba conchae, tragus, earlobe, or tragus AND cymba conchae) on separate days. In each session, participants were asked to consume a palatable chocolate flavored milk. With electrography on the abdomen and indirect calorimetry in a canopy, we measured electro-cardiogram, electro-gastrogram and resting energy expenditure for 15 minutes before and at least 35 minutes after consumption of the palatable drink. We also collected ratings of the palatable drink and internal and other states. Pre-drink consumption (in a hungry state) we observed no differences in the effect of location of acute nVNS on resting energy expenditure and gastric frequency. However, nVNS in cymba conchae decreases heart-rate variability and ratings of how much participants want to consume the drink. After drink consumption and with continued nVNS, gastric frequency is unchanged, and resting energy expenditure increases regardless of stimulation location. Heart-rate variability decreases in all locations, except cymba conchae. We also observe a trend for an increase in gastric frequency in late post-drink consumption time-points in cymba conchae. These results suggest that nVNS in the cymba conchae in a hungry state has a similar acute effect on vagal tone as food consumption: to decrease heart rate variability. This effect then negates the usual postprandial effects of a decrease in heart rate variability as seen in the other nVNS locations. This suggests that nVNS in cymba conchae may act primarily on vagal afferent autonomic (and only modestly on metabolic output) in a similar way as food consumption does. HighlightsO_LIWe measured autonomic outflow and efferent metabolism before and after consumption C_LIO_LIWe manipulated the location of nVNS stimulation in the outer ear C_LIO_LIThe different locations were earlobe, cymba conchae, tragus, cymba conchae+tragus C_LIO_LInVNS in cymba conchae decreases pre-consumption heart-rate variability and wanting C_LIO_LInVNS in other locations decreases post-consumption heart-rate variabilty C_LI

Stress-related disorders encompass diverse behavioral alterations, including impaired social functioning. The zebrafish (Danio rerio) is a valuable model for studying these phenomena, particularly because of its robust and ethologically conserved social behaviors. Unpredictable chronic stress (UCS) produces behavioral, physiological, and molecular changes in zebrafish that parallel core features of human anxiety and depressive disorders; however, its impact on social outcomes remains unclear. Here, we examined whether a 14-day UCS protocol alters social behavior in adult zebrafish using two complementary assays: the social preference test and the shoal cohesion test. Across two independent experiments, UCS did not elicit detectable changes in individual social approach or group-level cohesion. In contrast, UCS induced clear anxiety-like behavior in the novel tank test, validating the stress manipulation, with stressed fish displaying reduced vertical exploration and decreased time in the upper zone. Shoal cohesion measures showed a time-dependent decrease in both groups, consistent with habituation to the testing environment rather than a stress-specific effect. Together, these results suggest that social behavior in adult zebrafish is relatively resilient to UCS under the conditions tested, whereas anxiety-like responses are markedly affected. Future work should investigate whether factors such as stressor intensity, developmental stage, sex composition, or social hierarchy modulate the sensitivity of social behavior to chronic stress.

IntroductionTaste is a key sensory modulator of eating behaviour and thus energy intake. The effects of acute exercise has recently been confirmed especially regarding sweet and salty tastes. Physical activity is a safe and effective countermeasure to certain types of chemosensory losses, especially in older populations. Knowing that taste can be impaired with increased adiposity, it is unknown if the adoption of an active lifestyle on a regular basis can mitigate such impairments. MethodsData were extracted from NHANES 2013-2014 database. Perception of salt and bitter tastes for Tongue Tip Test and Whole Mouth Test, physical activity levels over an 8-9-day period and adiposity were analyzed. Moderation analyses were used to study the impact of adiposity on taste perceptions, with physical activity level as the moderator. ResultsThe 197 participants (130 males) included in this project had a mean{+/-}standard deviation age of 49.1{+/-}5.2 years, a mean body fat percentage of 31.7{+/-}7.6% and mean daily physical activity levels of 11 084{+/-}3531 Monitor-Independent Movement Summary unit (MIMS). The positive association between adiposity and both bitter Tongue Tip Test and overall result (salt+bitter) of Tongue Tip Test were moderated by the adoption of an active lifestyle, with better taste scores observed in individuals achieving higher physical activity levels. When moderation analysis were stratified by gender, the effect of physical activity was no longer significant. PerspectivesThis study is the first to evaluate the influence of an active lifestyle on the preservation of some taste perceptions across a wide range of adiposity levels. While differences in taste can be observed regarding body fat percentage, physical activity moderates that relation only when men and women are analysed together.

Non-human primates (NHP) provide an important model for studying biological mechanisms that underlie behavior and cognition, and are crucial for supplying translational knowledge that can aid the development of new clinical approaches. At the same time, the importance of the 3Rs to minimize suffering during experiments encouraged the development of environmental enrichment programs. Among them, tools for feeding and foraging are central. However, it remains unclear whether the behavioral enrichment tools are used by the animals only for feeding and to satisfy hunger (and hence for survival), or whether these feeding tools serve also as behavioral enrichment in itself (namely, the animals enjoy it per-se). To answer this, we designed a novel dispenser method - that requires significant yet reasonable energetic effort to obtain food - and tested food consumption via the dispenser compared to free-access, namely that did not require any effort on the animal side. We found that primates consumed food from both the dispenser and when presented in free-access, and importantly, that the consumption via the dispenser was in correlation with the consumption in free-access. This was similar across different subjects, different times during the day, and different types of food. We suggest that monkeys can benefit from using the dispenser for food consumption, but also benefit from it for play (i.e. as behavioral enrichment in itself). Such an approach allows non-human-primates to preserve their natural food procurement activities.

Measures of rodent drinking (lick) patterns are used to test how various manipulations affect fluid intake. Decades of research indicate that manipulating the satiating potency of a stimulus affects the number of licking bursts whereas manipulating the hedonic value of the solution affects the size of the licking bursts or rate of licking. This type of analysis has been largely applied to manipulations that modulate drinking that is already occurring (i.e., indirect controls or modulators of intake), but there is a dearth of studies with detailed measures of licking in response to stimuli that are primary drivers of intake (i.e., direct controls). A better understanding of licking behavior in response to direct controls of fluid intake could provide insight into how drinking is stimulated. Accordingly, we analyzed lick patterns after varying doses of primary drivers (direct controls) of intake, angiotensin II, hypertonic saline, or carbochol, in male and female rats. As expected, all treatments dose-dependently increased licks for water. Analysis of licking patterns revealed dose-related increases in burst number after treatment with all stimuli, but dose did not predict burst size or lick rate. Together with previous work on licking patterns these data suggest that direct controls of water intake are more related to processes associated with satiety than to changes in hedonic value of the consumed substance.

Hunger and satiety are interoceptions involved in the control of food intake. How they change across the day and from one day to the next, as well as their relationships with physiological parameters, remain poorly understood. In a five-day laboratory study, 20 healthy male participants (24.2 {+/-} 3.3 years) were given 3 meals per day (breakfast, lunch, dinner), at times based on each individuals internal time. Subjects had a 8-h sleep opportunity at night recorded by polysomnography, during which time they were exposed to 4 different light intensities (0, 3, 8, or 20 lux). Hunger and satiety were assessed before and after each meal. Heart rate was measured continuously and glucose levels were sampled every 15 minutes. We found that: 1) hunger and satiety varied dynamically with the lowest levels at breakfast and the highest at lunch and dinner (p < 0.001); 2) Hunger and satiety were subject-dependent, and keep stable across the five experimental days; 3) heart rate was higher after than before meals (p < 0.0001), and higher around breakfast than dinner; 4) Glycemia before and after meals was respectively stable throughout the day and over the five-day study; 5) interoception was correlated with fluctuations in heart rate, glucose levels and sleep duration. Overall, our results reveal that hunger and satiety perception are individual characteristics. To better understand the role of interoception in food intake control, both hunger and satiety should be measured, but separately in their respective states.

BackgroundExercise is well known to generally improve health status in humans and seems to be beneficial not only for physical, but also learning processes. The evidence for the impact of general physical activity on emotional learning, is however scarce. Here, we test the pre-registered hypothesis that the individual physical activity level of the past seven days is positively associated with observational threat learning, indicated by the differentiation between threat and safety cues. MethodsWe conducted a two day online study. 90 healthy participants (mean age = 27.82 years) engaged by completing questionnaires (State-Trait Anxiety Inventory (STAI-S/STAI-T and International Physical Activity Questionnaire (IPAQ)) on day one, followed by an observational learning task. Participants were asked to rate their discomfort, fear, and physiological response towards the CS+ and CS-both before and after the learning phase using a visual analogue scale. On day two (approximately 24 hours after day one), participants completed the STAI-S again, followed by a direct generalization task. Similar to before, participants were asked to report their discomfort, fear, and physiological response both before and after the generalization task. To quantify the level of physical activity (PA) of the past seven days a sum score of the IPAQ was calculated. The pre-registered primary endpoint was to test for apositive association between PA and the ability to discriminate the conditioned stimuli. ResultsPearsons correlation analyses revealed no significant correlations between the combined total physical activity (PA) score and differential ratings of subjective discomfort (r = 0.11, pcorr = 0.150), fear (r = 0.203, pcorr = 0.081) or physiological responses (r = 0.145, pcorr = 0.17) on day 1. The same analysis revealed no significant correlations on day 2, either (differential ratings of subjective discomfort, r = 0.053, pcorr = 0.93, fear, r = -0.068, pcorr = 0.99, and physiological responses, r = -0.072, pcorr = 0.751 on day 2). However, we also found no sufficient evidence supporting the null hypothesis (i.e. no correlation) for the association between differential learning and PA on day 1, when applying bayesian statistics. Instead, we found a covariation between the ratings of discomfort and physical activity, as well as between ratings of fear and physical activity on day 1 and 2 within a repeated measurement ANOVA. This was supported by bayesian statistics. ConclusionOur results provided no convincing evidence for a correlation between differential observational threat learning and physical activity (as measured by the IPAQ). Future studies that provide a better control for individual physical activity are warranted.

Identifying behavioral and physiological responses to rewarding stimuli is essential for understanding positive emotional states in animals and for investigating their neural basis. Ultrasonic vocalizations (USVs) in rats are modulated by various behavioral contexts and are thought to represent affective-like states. However, their diversity during palatable food consumption remains underexplored. In this study, we investigated acoustic features of USVs in male rats consuming chocolate, a highly palatable food. Using a machine-learning-assisted logistic regression model trained on spectrogram features, we identified a distinct USV subtype--the 40-kHz inverted-U type--that was selectively emitted during chocolate consumption. The emission of this subtype was tightly time-locked to chocolate feeding behavior. Systemic administration of naloxone, an opioid receptor antagonist, significantly reduced the emission of the 40-kHz inverted-U USVs during chocolate intake. These findings suggest that these USVs may reflect internal states associated with palatable feeding and are under modulation by the endogenous opioid system. Moreover, our data demonstrate the utility of machine learning for high-throughput, objective classification of USV subtypes. This framework provides a promising approach for decoding emotion-related vocal expressions in rats and highlights the potential of specific USVs as behavioral readouts for studying the neurobiology of positive emotions. Significance StatementUltrasonic vocalizations (USVs) are high-frequency calls produced by rats known to correlated with emotional and motivational states, yet their diversity and functional relevance remain underexplored. In this study, we identified a novel 40-kHz inverted-U USV subtype associated with chocolate consumption. These calls were closely tied to feeding behavior and were selectively suppressed by an opioid receptor antagonist, suggesting modulation by the brains reward system. Using machine learning-assisted classification, we established a robust method to detect these vocalizations. Our findings highlight the potential of specific USVs as non-invasive, real-time behavioral indicators of internal states, offering new tools for studying affect, reward, and communication in animal models.

Maternal nutrition before conception is recognised as a determinant of offspring development; however, the behavioural and neuroendocrine consequences of preconception calorie restriction (CR) remain poorly understood. This study isolated the preconception window to examine how different CR patterns, stable (25% reduction; CR-25%), unpredictable deprivation (CR-A), and variable (25-75% fluctuation; CR-V), affect adult offspring outcomes. Male and female progeny from preconception CR female Wistar rats were assessed across domains sensitive to early-life programming, including anxiety- and depression-like behaviour, coping style, socio-sexual behaviour, and hypothalamic-pituitary-gonadal (HPG) axis activity. Preconception CR produced sex- and diet-specific effects. Females exhibited transient reductions in exploratory behaviour and more active coping styles, particularly CR-25% and CR-V animals. In males, all CR regimens enhanced copulatory behaviour and reduced aggression toward females. Endocrine profiling revealed divergent HPG responses: CR-A males showed elevated basal faecal testosterone metabolites (fTM) but reduced basal serum testosterone, whereas CR-V males exhibited blunted androgenic reactivity post-social provocation. These findings demonstrate that maternal preconception CR can program male offspring toward a prosocial, sexually motivated phenotype and female offspring toward an enhanced coping style, underscoring this period as a sensitive window for shaping behavioural and endocrine trajectories.

Food intake varies across the stages of a rats estrous cycle. It is reasonable to hypothesize that this cyclic fluctuation in consumption reflects an impact of hormones on taste palatability/preference, but evidence for this hypothesis has been mixed, and critical within-subject experiments in which rats sample multiple tastes during each of the four main estrous phases (metestrus, diestrus, proestrus, and estrus) have been scarce. Here, we assayed licking for pleasant (sucrose, NaCl, saccharin) and aversive (quinine-HCl, citric acid) tastes each day for 5-10 days while tracking rats estrous cycles through vaginal cytology. Initial analyses confirmed the previously-described increased consumption of pleasant stimuli 24-48 hours following the time of high estradiol. A closer look, however, revealed this effect to reflect a general magnification of palatability--higher than normal preferences for pleasant tastes and lower than normal preferences for aversive tastes--during metestrus. We hypothesized that this phenomenon might be related to estradiol processing in the lateral hypothalamus (LH), and tested this hypothesis by inhibiting LH estrogen receptor activity with ICI182,780 during tasting. Control infusions replicated the metestrus magnification of palatability pattern; ICI infusions blocked this effect as predicted, but failed to render preferences "cycle free," instead delaying the palatability magnification until diestrus. Clearly, estrous phase mediates details of taste palatability in a manner involving hypothalamic actions of estradiol; further work will be needed to explain the lack of a flat response across the cycle with hypothalamic estradiol binding inhibited, a result which perhaps suggests dynamic interplay between brain regions or hormones. Significance StatementConsummatory behaviors are impacted by many variables, including naturally circulating hormones. While it is clear that consumption is particularly high during the stages following the high-estradiol stage of the rodents estrous (and human menstrual) cycle, it is as of yet unclear whether this phenomenon reflects cycle stage-specific palatability (i.e., whether pleasant tastes are particularly delicious, and aversive tastes particularly disgusting, at particular phases). Here we show that palatability is indeed modulated by estrous phase, and that this effect is governed, at least in part, by the action of estradiol within the lateral hypothalamus. These findings shed light on the mechanisms underlying the adverse impact on human welfare due to irregularities observed across the otherwise cyclic menstrual process.

Approximately 14% of U.S. households are estimated to be food insecure. The neurocognitive and metabolic impacts of unpredictable food access during early-life periods of development are poorly understood. To address these gaps we devised a novel rat model of food insecurity to control the timing, type, and quantity of accessible food using programmable feeders. Male rats were divided into 3 groups: Secure-chow (SC), a control group given 100% of daily caloric needs, distributed evenly across 4 daily meals of standard chow at set mealtimes; Secure-mixed (SM), a 2nd control group identical to the SC group except that the food type predictably alternated daily between chow and a high-fat, high-sugar diet (HFHS); and Insecure-mixed (IM), the experimental group given randomly alternating daily access to either chow or HFHS at either 85% or 115% of daily caloric needs, distributed evenly across 3 daily meals with unpredictable mealtimes. These feeding schedules were implemented from postnatal days (PNs) 26-45, after which all groups received chow ad libitum. Metabolic assessments performed in adulthood revealed no group differences in caloric intake, body weight, or body composition when maintained on either chow (PN46-149) or a cafeteria diet (PN150-174). Behavioral measures (PN66-126) revealed no group differences in anxiety-like, exploratory, or impulsive behavior (zero maze, open field, differential reinforcement of low rates of responding procedures). However, the IM group exhibited hippocampus-dependent memory impairments compared to both control groups in the novel location recognition test. These findings suggest that early-life food insecurity may contribute to long-term impairments in memory function.

The transition to motherhood has been shown to result in significant changes in the structure and function of the brain, with particular emphasis on the enhancement of cognitive abilities that are essential for survival. Specifically, in murine models, spatial learning and cognitive flexibility have been identified as critical components of mothering. These abilities facilitate efficient navigation of the environment, resource acquisition, and responsiveness to offsprings needs. While cognitive enhancements during the postpartum period have been observed in various experimental setups, research using long-term data collection with automated monitoring in home cage setup is completely lacking even though it provides a more reliable approach than other experimental procedures. This study aims to address this knowledge gap by systematically examining spatial learning and cognitive flexibility in female mice during the reproductive stages using IntelliCage, with the objective of offering a more comprehensive understanding of maternal cognitive adaptations. Utilising the IntelliCage system, we observed that female mice in the postpartum phase outperformed pregnant and nulliparous females in place learning, reversal learning, and fixed schedule drinking tasks, demonstrating faster adaptation and superior retention of information. These paradigms mirror real-world challenges faced by mothers, such as navigating resources and balancing caregiving with self-maintenance. The enhanced performance demonstrated by the mothers could be attributed to their heightened motivation and cognitive abilities, potentially influenced by substantial hormonal shifts, which have been known to modify neuroplasticity in critical brain regions. The identification of these improvements in maternal behaviour may offer novel insights into the impact of reproductive experiences on brain function, with implications for maternal health and broader cognitive research.

Sexual motivation is a complex concept involving both the initial drive to begin mating and the motivation to sustain copulation. Disruptions in sexual motivation are often observed in psychiatric disorders. This study proposes that sexual motivation can be divided into two distinct components: sexual incentive motivation and the drive to sustain copulation. To investigate this, we utilized the Motivation to Continue Copulation (MCC) test, which measures effort (nose pokes) to gain access to a sexual reward, and compared it with the Sexual Incentive Motivation (SIM) test and standard copulation tests. Male and female rats were trained on a fixed ratio (FR) 1 schedule using cheese rewards before transitioning to sexual rewards. After six FR1 sessions, the effort required increased to FR5 and progressive ratio (PR) schedules. Results revealed that sexual incentive motivation, measured by the SIM test, was higher in males after sexual experience, while females maintained consistent levels. In the MCC test, both males and females exhibited increased motivation to continue copulation with experience, but the motivation declined in the 2nd ejaculatory series. These findings demonstrate that sexual motivation comprises distinct components. The MCC test effectively measures the drive to sustain copulation, while the SIM test assesses incentive motivation. This distinction is crucial for advancing behavioral neuroscience and understanding sexual dysfunction in psychiatric conditions.