Experimental animal models are critical for understanding the genetic, environmental and neurobiological underpinnings of alcohol use disorders. Limited studies investigate alcohol-induced effects on behavior using free-choice paradigms. The aims of the present experiment were to study voluntary alcohol intake using a modified intermittent access paradigm, investigate the effects of voluntary alcohol intake on behavioral profiles in water- and alcohol-drinking rats, and select extreme low- and high-drinking animals for a more detailed behavioral characterization. Sixty outbred male Wistar rats were randomized into water and alcohol groups. Behavioral profiles in the multivariate concentric square field™ (MCSF) test were assessed prior to and after voluntary alcohol intake. The animals had intermittent access to 20% alcohol and water for three consecutive days per week for seven weeks. The results revealed increased alcohol intake over time. No major alcohol-induced differences on behavior profiles were found when comparing water- and alcohol-drinking animals. The high-drinking animals displayed an alcohol deprivation effect, which was not found in the low-drinking animals. High-drinking rats had lower risk-taking behavior prior to alcohol access and lower anxiety-like behavior after voluntary alcohol intake compared to low-drinking rats. In conclusion, the modified intermittent access paradigm may be useful for pharmacological manipulation of alcohol intake. With regard to behavior, the present findings highlights the importance of studying subgroup-dependent differences and add to the complexity of individual differences in behavioral traits of relevance to the vulnerability for excessive alcohol intake.
Some personality traits and comorbid psychiatric diseases are linked to a propensity for excessive alcohol drinking. The objective of this study was to investigate the association between individual differences in risk-related behaviors, voluntary alcohol intake and preference. Outbred male Wistar rats were tested in a novel open field, followed by assessment of behavioral profiles using the multivariate concentric square field (MCSF) test. Animals were classified into high risk taking and low risk taking on the basis of open-field behavior and into high risk-assessing (HRA) and low risk-assessing (LRA) on the basis of the MCSF profile. Finally, voluntary alcohol intake was investigated using intermittent access to 20% ethanol and water for 5 weeks. Only minor differences in voluntary alcohol intake were found between high risk taking and low risk taking. Differences between HRA and LRA rats were more evident, with higher intake and increased intake over time in HRA relative to LRA rats. Thus, individual differences in risk-assessment behavior showed greater differences in voluntary alcohol intake than risk taking. The findings may relate to human constructs of decision-making and risk taking associated with a predisposition to rewarding and addictive behaviors. Further studies are needed to clarify the relationship between risk-related behaviors, including risk-assessment behavior, and liability for excessive alcohol intake.
Certain personality types and behavioral traits display high correlations to drug use and an increased level of dopamine in the reward system is a common denominator of all drugs of abuse. Dopamine response to drugs has been suggested to correlate with some of these personality types and to be a key factor influencing the predisposition to addiction. This study investigated if behavioral traits can be related to potassium- and amphetamine-induced dopamine response in the dorsal striatum, an area hypothesized to be involved in the shift from drug use to addiction. The open field and multivariate concentric square field™ tests were used to assess individual behavior in male Wistar rats. Chronoamperometric recordings were then made to study the potassium- and amphetamine-induced dopamine response in vivo. A classification based on risk-taking behavior in the open field was used for further comparisons. Risk-taking behavior was correlated between the behavioral tests and high risk takers displayed a more pronounced response to the dopamine uptake blocking effects of amphetamine. Behavioral parameters from both tests could also predict potassium- and amphetamine-induced dopamine responses showing a correlation between neurochemistry and behavior in risk-assessment and risk-taking parameters. In conclusion, the high risk-taking rats showed a more pronounced reduction of dopamine uptake in the dorsal striatum after amphetamine indicating that this area may contribute to the sensitivity of these animals to psychostimulants and proneness to addiction. Further, inherent dopamine activity was related to risk-assessment behavior, which may be of importance for decision-making and inhibitory control, key components in addiction.
Shift-work is suggested to affect fetal development negatively. In particular, maternal hormonal disturbance arising from sleep deprivation or circadian rhythm changes may disturb fetal growth or lead to complications during pregnancy. Exposure to constant light is an environmental stressor that can affect the circadian system and has been shown to induce neurochemical and behavioral changes when used during the prenatal and/or postnatal period in experimental animals. However, studies investigating long-term effects of constant light in the offspring are sparse.
The cyanobacterial toxin ?-N-methylamino-l-alanine (BMAA) is suggested to play a role in neurodegenerative disease. We have previously shown that although the selective uptake of BMAA in the rodent neonatal striatum does not cause neuronal cell death, exposure during the neonatal development leads to cognitive impairments in adult rats. The aim of the present study was to characterize the changes in the striatal neuropeptide systems of male and female rat pups treated neonatally (postnatal days 9-10) with BMAA (40-460 mg/kg). The label-free quantification of the relative levels of endogenous neuropeptides using mass spectrometry revealed that 25 peptides from 13 neuropeptide precursors were significantly changed in the rat neonatal striatum. The exposure to noncytotoxic doses of BMAA induced a dose-dependent increase of neurosecretory protein VGF-derived peptides, and changes in the relative levels of cholecystokinin, chromogranin, secretogranin, MCH, somatostatin and cortistatin-derived peptides were observed at the highest dose. In addition, the results revealed a sex-dependent increase in the relative level of peptides derived from the proenkephalin-A and protachykinin-1 precursors, including substance P and neurokinin A, in female pups. Because several of these peptides play a critical role in the development and survival of neurons, the observed neuropeptide changes might be possible mediators of BMAA-induced behavioral changes. Moreover, some neuropeptide changes suggest potential sex-related differences in susceptibility toward this neurotoxin. The present study also suggests that neuropeptide profiling might provide a sensitive characterization of the BMAA-induced noncytotoxic effects on the developing brain.
Early-life events can cause long-term neurobiological and behavioural changes with a resultant effect upon reward and addiction processes that enhance risk to develop alcohol use disorders. Maternal separation (MS) is used to study the mediating mechanisms of early-life influences in rodents. In MS studies, the pups are exposed to maternal absence during the first postnatal weeks. The outcome of MS experiments exhibits considerable variation and questions have been raised about the validity of MS models.
Causal links between early-life stress, genes and later psychiatric diagnoses are not possible to fully address in human studies. Animal models therefore provide an important complement in which conditions can be well controlled and are here used to study and distinguish effects of early-life stress and alcohol exposure. The objective of this study was to investigate the impact of rearing conditions on behaviour in young rats and if these changes could be followed over time and to examine interaction effects between early-life environment and adolescent alcohol drinking on behaviour and immunoreactive levels of the opioid peptides dynorphin B, met-enkephalin-Arg(6)Phe(7) and beta-endorphin. We employed a rodent model, maternal separation, to study the impact of rearing conditions on behaviour, voluntary alcohol consumption and alcohol-induced effects. The consequences of short, 15 min (MS 15), and long, 360 min (MS 360), maternal separation in combination with adolescent voluntary alcohol consumption on behaviour and peptides were examined. A difference in the development of risk taking behaviour was found between the MS15 and MS360 while the development of general activity was found to differ between intake groups. Beta-endorphin levels in the pituitary and the periaqueductal gray area was found to be higher in the MS15 than the MS360. Adolescent drinking resulted in higher dynorphin B levels in the hippocampus and higher met-enkephalin-Arg(6)Phe(7) levels in the amygdala. Amygdala and hippocampus are involved in addiction processes and changes in these brain areas after adolescent alcohol drinking may have consequences for cognitive function and drug consumption behaviour in adulthood. The study shows that individual behavioural profiling over time in combination with neurobiological investigations provides means for studies of causality between early-life stress, behaviour and vulnerability to psychiatric disorders.
Hypothalamic AMPK acts as a cell energy sensor and can modulate food intake, glucose homeostasis, and fatty acid biosynthesis. Intrahypothalamic fatty acid injection is known to suppress liver glucose production, mainly by activation of hypothalamic ATP-sensitive potassium (K(ATP)) channels. Since all models employed seem to involve malonyl-CoA biosynthesis, we hypothesized that acetyl-CoA carboxylase can modulate the counter-regulatory response independent of nutrient availability.
The exposure to an increased supply of nutrients before birth may contribute to offspring obesity. Offspring from obese dams that chronically consume a high-fat diet present clinical features of metabolic syndrome, liver lipid accumulation and activation of c-Jun N-terminal kinases (JNK) consistent with the development of nonalcoholic fatty liver disease (NAFLD). However, in spite of the importance of the resistance to insulin for the development of NAFLD, the molecular alterations in the liver of adult offspring of obese dams are yet to be investigated. In this study, we tested the hypothesis that the consumption of excessive saturated fats during pregnancy and lactation contributes to adult hepatic metabolic dysfunction in offspring. Adult male offspring of dams fed a high-fat diet (HN) during pregnancy and lactation exhibited increased fat depot weight; increased serum insulin, tumor necrosis factor ? and interleukin 1?; and reduced serum triglycerides. Liver showed increased JNK and I kappa B kinase phosphorylation and PEPCK expression in the adult. In addition, liver triglyceride content in the offspring 1 week after weaning and in the adult was increased. Moreover, basal ACC phosphorylation and insulin signaling were reduced in the liver from the HN group as compared to offspring of dams fed a standard laboratory chow (NN). Hormone-sensitive lipase phosphorylation (Ser565) was reduced in epididymal adipose tissue from the HN group as compared to the NN group. It is interesting that all changes observed were independent of postweaning diet in 14-week-old offspring. Therefore, these data further reinforce the importance of maternal nutrition to adult offspring health.
Genetic aspects of alcoholism have been modeled using rats selectively bred for extremes of alcohol preference and voluntary alcohol intake. These lines show similar alcohol drinking phenotypes but have different genetic and environmental backgrounds and may therefore display diverse behavioral traits as seen in human alcoholics. The multivariate concentric square field™ (MCSF) test is designed to provoke exploration and behaviors associated with risk assessment, risk taking and shelter seeking in a novel environment. The aim was to use the MCSF to characterize behavioral profiles in rat lines from selective breeding programs in the United States (P/NP, HAD1/LAD1, HAD2/LAD2), Italy (sP/sNP) and Finland (AA/ANA). The open field and elevated plus maze tests were used as reference tests. There were substantial differences within some of the pairs of selectively bred rat lines as well as between all alcohol-preferring rats. The most pronounced differences within the pairs of lines were between AA and ANA rats and between sP and sNP rats followed by intermediate differences between P and NP rats and minor differences comparing HAD and LAD rats. Among all preferring lines, P, HAD1 and HAD2 rats shared similar behavioral profiles, while AA and sP rats were quite different from each other and the others. No single trait appeared to form a common pathway associated with a high alcohol drinking phenotype among all of the alcohol-preferring lines of rats. The marked behavioral differences found in the different alcohol-preferring lines may mimic the heterogeneity observed among human alcoholic subtypes.
Taurine is known to modulate a number of metabolic parameters such as insulin secretion and action and blood cholesterol levels. Recent data have suggested that taurine can also reduce body adiposity in C. elegans and in rodents. Since body adiposity is mostly regulated by insulin-responsive hypothalamic neurons involved in the control of feeding and thermogenesis, we hypothesized that some of the activity of taurine in the control of body fat would be exerted through a direct action in the hypothalamus. Here, we show that the intracerebroventricular injection of an acute dose of taurine reduces food intake and locomotor activity, and activates signal transduction through the Akt/FOXO1, JAK2/STAT3 and mTOR/AMPK/ACC signaling pathways. These effects are accompanied by the modulation of expression of NPY. In addition, taurine can enhance the anorexigenic action of insulin. Thus, the aminoacid, taurine, exerts a potent anorexigenic action in the hypothalamus and enhances the effect of insulin on the control of food intake.
The existence of an "addictive" personality has been extensively debated. The current study investigated personality in male individuals with excessive alcohol consumption (n=100) in comparison to a population-based control group (n=131). The individuals with excessive alcohol consumption were recruited by advertisements in a regional daily newspaper and controls from a population based Swedish Twin Registry. Personality was assessed by the Karolinska Scales of Personality (KSP). Comparisons were made with normative data. Furthermore, by using a multivariate projection-based approach (Principal Component Analysis; PCA), hidden structures of traits and possible relationships among the individuals with excessive consumption and the controls was investigated. The individuals with excessive alcohol consumption as well as the controls had mean values within the normative range in all scales of the KSP. Moreover, the PCA analysis revealed no systematic between-group separation. Taken together, this result demonstrates that male individuals with excessive alcohol consumption do not have a personality different from that of a general population, which supports the notion of no "addictive personality".
We have reported previously that exposure to the cyanobacterial neurotoxin ?-N-methylamino-L-alanine (BMAA) during the neonatal period causes cognitive impairments in adult rats. The aim of this study was to investigate the long-term effects of neonatal BMAA exposure on learning and memory mechanisms and to identify early morphological changes in the neonatal brain. BMAA was injected subcutaneously in rat pups on postnatal days 9-10. BMAA (50 and 200 mg/kg) caused distinct deficits in spatial learning and memory in adult animals but no morphological changes. No impairment of recognition memory was detected, suggesting that neonatal exposure to BMAA preferentially affects neuronal systems that are important for spatial tasks. Histopathological examination revealed early neuronal cell death as determined by TUNEL staining in the hippocampus 24 h after a high dose (600 mg/kg) of BMAA whereas no changes were observed at lower doses (50 and 200 mg/kg). In addition, there was a low degree of neuronal cell death in the retrosplenial and cingulate cortices, areas that are also important for cognitive function. Taken together, these results indicate that BMAA is a developmental neurotoxin inducing long-term changes in cognitive function. The risk posed by BMAA as a potential human neurotoxin merits further consideration, particularly if the proposed biomagnifications in the food chain are confirmed.
Understanding the mechanism of action of ethanol and the neurobiological substrates for alcohol use disorders is challenging. In search of this knowledge, it is imperative to use valid animal experimental models. The Wistar rat is one example of a commonly used strain that also exert foundation stock for several rat lines selectively bred for high and low voluntary ethanol intake. Different studies report varying ethanol intake in Wistar rats posing the question of whether this is because of the methodological differences or the rat strain. The purpose of this study was therefore to compare voluntary ethanol intake in Wistar rats from five different suppliers. Rats from B&K Universal, UK (BK); Charles River, Germany; Harlan Laboratories, IN (Hsd); Harlan Laboratories, The Netherlands (RccHan™); and Taconic, Denmark were exposed to a three-bottle free-choice paradigm with intermittent 24 h access to 5 and 20% ethanol and water three times per week for 6 weeks. A general finding was that the RccHan™ rats differed significantly from the other groups. At the end of the experiment, the RccHan™ group had the highest median ethanol intake of 3.85 g/kg/24 h, whereas the BK rats had the lowest intake of 1.84 g/kg/24 h. The preference for ethanol was also different throughout the experiment. At the end of the experiment, the RccHan™ rats had the highest preference of approximately 80%, whereas the BK rats had the lowest preference around 25%. During the 6-week drinking period, only the Hsd rats increased their ethanol intake, as evidenced by a significant increase of 5% ethanol intake. Although all rats are of Wistar origin, they display profound differences in voluntary ethanol consumption depending on the supplier. The choice of Wistar can therefore have implications for the outcome and make comparisons between studies difficult. The present findings highlight the supplier as an important parameter to consider when planning and performing preclinical animal studies in the field of alcohol research.
The rodent maternal separation (MS) model is frequently used to investigate the impact of early environmental factors on adult neurobiology and behavior. The majority of MS studies assess effects in the offspring and few address the consequences of repeated pup removal in the dam. Such studies are of interest since alterations detected in offspring subjected to MS may, at least in part, be mediated by variations in maternal behavior and the amount of maternal care provided by the dam. The aim of this study was to investigate how daily short (15 min; MS15) and prolonged (360 min; MS360) periods of MS affects the dam by examining postpartum behavioral profiles using the multivariate concentric square field (MCSF) test. The dams were tested on postpartum days 24-25, i.e., just after the end of the separation period and weaning. The results reveal a lower exploratory drive and lower risk-assessment behavior in MS15 dams relative to MS360 or animal facility reared dams. The present results contrast some of the previously reported findings and provide new information about early post-weaning behavioral characteristics in a multivariate setting. Plausible explanations for the results are provided including a discussion how the present results fit into the maternal mediation hypothesis.
In diet-induced obesity, hypothalamic and systemic inflammatory factors trigger intracellular mechanisms that lead to resistance to the main adipostatic hormones, leptin and insulin. Tumor necrosis factor-alpha (TNF-alpha) is one of the main inflammatory factors produced during this process and its mechanistic role as an inducer of leptin and insulin resistance has been widely investigated. Most of TNF-alpha inflammatory signals are delivered by TNF receptor 1 (R1); however, the role played by this receptor in the context of obesity-associated inflammation is not completely known. Here, we show that TNFR1 knock-out (TNFR1 KO) mice are protected from diet-induced obesity due to increased thermogenesis. Under standard rodent chow or a high-fat diet, TNFR1 KO gain significantly less body mass despite increased caloric intake. Visceral adiposity and mean adipocyte diameter are reduced and blood concentrations of insulin and leptin are lower. Protection from hypothalamic leptin resistance is evidenced by increased leptin-induced suppression of food intake and preserved activation of leptin signal transduction through JAK2, STAT3, and FOXO1. Under the high-fat diet, TNFR1 KO mice present a significantly increased expression of the thermogenesis-related neurotransmitter, TRH. Further evidence of increased thermogenesis includes increased O(2) consumption in respirometry measurements, increased expressions of UCP1 and UCP3 in brown adipose tissue and skeletal muscle, respectively, and increased O(2) consumption by isolated skeletal muscle fiber mitochondria. This demonstrates that TNF-alpha signaling through TNFR1 is an important mechanism involved in obesity-associated defective thermogenesis.
Most cyanobacteria (blue-green algae) can produce the neurotoxin beta-N-methylamino-L-alanine (BMAA). Dietary exposure to BMAA has been suggested to be involved in the etiology of the neurodegenerative disease amyotrophic lateral sclerosis/Parkinsonism-dementia complex (ALS/PDC). Little is known about BMAA-induced neurotoxicity following neonatal administration. Our previous studies have revealed an uptake of BMAA in the hippocampus and striatum of neonatal mice. Furthermore, rats treated with BMAA during the neonatal period displayed acute but transient motoric disturbances and failed to show habituation at juvenile age suggesting impairments in learning functions. In the present study, the aim was to investigate long-term behavioral effects of BMAA administration in neonatal rats. BMAA was administered on postnatal days 9-10 (200 or 600 mg/kg; subcutaneous injection). Spatial learning and memory was investigated in adulthood using the radial arm maze test. The results revealed impaired learning but not memory in BMAA-treated animals. The observed impairments were not due to alterations in motoric capacity, general activity, or behavioral profiles, as assessed in the multivariate concentric square field (MCSF) and open field tests. An aversive stimulus in the MCSF test revealed impairments in avoidance learning and/or memory. There was no difference in basal serum corticosterone levels in BMAA-treated animals, indicating that the observed long-term effects were not secondary to an altered basal hypothalamic-pituitary-adrenal axis function. The present data demonstrated long-term learning impairments following neonatal BMAA administration. Further studies on biochemical effects in various brain regions and subsequent behavioral alterations are needed to elucidate the mechanisms of BMAA-induced developmental neurotoxicity.
The present investigation continues previous behavioral profiling studies of selectively bred alcohol-drinking and alcohol non-drinking rats. In this study, alcohol-naïve adult Sardinian alcohol-preferring (sP) and non-preferring (sNP) rats were tested in the multivariate concentric square field (MCSF) test. The MCSF test has an ethoexperimental approach and measures general activity, exploration, risk assessment, risk taking, and shelter seeking in laboratory rodents. The multivariate design enables behavioral profiling in one and the same test situation. Age-matched male Wistar rats were included as a control group. Five weeks after the first MCSF trial, a repeated testing was done to explore differences in acquired experience. The results revealed distinct differences in exploratory strategies and behavioral profiles between sP and sNP rats. The sP rats were characterized by lower activity, lower exploratory drive, higher risk assessment, and lower risk taking behavior than in sNP rats. In the repeated trial, risk-taking behavior was almost abolished in sP rats. When comparing the performance of sP and sNP rats with that of Wistar rats, the principal component analysis revealed that the sP rats were the most divergent group. The vigilant behavior observed in sP rats with low exploratory drive and low risk-taking behavior is interpreted here as high innate anxiety-related behaviors and may be related to their propensity for high voluntary alcohol intake and preference. We suggest that the different lines of alcohol-preferring rats with different behavioral characteristics constitute valuable animal models that mimic the heterogeneity in human alcohol dependence.
Interleukin-10 (IL-10) is an endogenous factor that restrains hepatic insulin resistance in diet-induced steatosis. Reducing IL-10 expression increases proinflammatory activity in the steatotic liver and worsens insulin resistance. As the transcriptional coactivator proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) plays a central role in dysfunctional hepatocytic activity in diet-induced steatosis, we hypothesized that at least part of the action of PGC-1alpha could be mediated by reducing the transcription of the IL-10 gene. Here, we used immunoblotting, real-time polymerase chain reaction, immunocytochemistry, and chromatin immunoprecipitation assay to investigate the role of PGC-1alpha in the control of IL-10 expression in hepatic cells. First, we show that, in the intact steatotic liver, the expressions of IL-10 and PGC-1alpha are increased. Inhibiting PGC-1alpha expression by antisense oligonucleotide increases IL-10 expression and reduces the steatotic phenotype. In cultured hepatocytes, the treatment with saturated and unsaturated fatty acids increased IL-10 expression. This was accompanied by increased association of PGC-1alpha with c-Maf and p50-nuclear factor (NF) kappaB, 2 transcription factors known to modulate IL-10 expression. In addition, after fatty acid treatment, PGC-1alpha, c-Maf, and p50-NFkappaB migrate from the cytosol to the nuclei of hepatocytes and bind to the IL-10 promoter region. Inhibiting NFkappaB activation with salicylate reduces IL-10 expression and the association of PGC-1alpha with p50-NFkappaB. Thus, PGC-1alpha emerges as a potential transcriptional regulator of the inflammatory phenomenon taking place in the steatotic liver.
Cyanobacteria are extensively distributed in terrestrial and aquatic environments all over the world. Most cyanobacteria can produce the neurotoxin beta-N-methylamino-L-alanine (BMAA), which has been detected in several water systems and could accumulate in food chains. The aim of the study was to investigate the transfer of BMAA to fetal and neonatal brains and the effects of BMAA on the development of behavioral characteristics during the brain growth spurt (BGS) in rodents. Pregnant and neonatal mice were given an injection of (3)H-BMAA on gestational day 14 and postnatal day (PND) 10, respectively, and processed for tape-section autoradiography. The study revealed transplacental transfer of (3)H-BMAA and a significant uptake in fetal mouse brain. The radioactivity was specifically located in the hippocampus, striatum, brainstem, spinal cord and cerebellum of 10-day-old mice. The effect of repeated BMAA treatment (200 or 600 mg/kg s.c.) during BGS on rat behavior was also studied. BMAA treatment on PND 9-10 induced acute alterations, such as impaired locomotor ability and hyperactivity, in the behavior of neonatal rats. Furthermore, rats given the high dose of BMAA failed to habituate to the test environment when tested at juvenile age. In conclusion, the results demonstrated that BMAA was transferred to the neonatal brain and induced significant changes in the behavior of neonatal rats following administration during BGS. The observed behavioral changes suggest possible cognitive impairment. Increased information on the long-term effects of BMAA on cognitive function following fetal and neonatal exposure is required for assessment of the risk to childrens health.
Consumption of dietary fats is amongst the most important environmental factors leading to obesity. In rodents, the consumption of fat-rich diets blunts leptin and insulin anorexigenic signaling in the hypothalamus by a mechanism dependent on the in situ activation of inflammation. Since inflammatory signal transduction can lead to the activation of apoptotic signaling pathways, we evaluated the effect of high-fat feeding on the induction of apoptosis of hypothalamic cells. Here, we show that consumption of dietary fats induce apoptosis of neurons and a reduction of synaptic inputs in the arcuate nucleus and lateral hypothalamus. This effect is dependent upon diet composition, and not on caloric intake, since pair-feeding is not sufficient to reduce the expression of apoptotic markers. The presence of an intact TLR4 receptor, protects cells from further apoptotic signals. In diet-induced inflammation of the hypothalamus, TLR4 exerts a dual function, on one side activating pro-inflammatory pathways that play a central role in the development of resistance to leptin and insulin, and on the other side restraining further damage by controlling the apoptotic activity.
Central leptin action requires PI3K activity to modulate glucose homeostasis and peripheral metabolism. However, the mechanism behind this phenomenon is not clearly understood. We hypothesize that hypothalamic PI3K activity is important for the modulation of the AMP-activated protein kinase (AMPK)/acetyl-CoA carboxylase (ACC) pathway, PGC1 alpha, and AKT in skeletal muscle (SM). To address this issue, we injected leptin into the lateral ventricle of rats. Hypothalamic JAK2 and AKT were activated by intracerebroventricular (ICV) injection of leptin in a time-dependent manner. Central leptin improved tolerance to glucose (GTT), increased PGC1 alpha expression, and AKT, AMPK, ACC and JAK2 phosphorylation in the soleus muscle. Previous ICV administration of either LY294002 or propranolol (IP) blocked these effects. We concluded that the activation of the hypothalamic PI3K pathway is important for leptin-induced AKT phosphorylation, as well as for active catabolic pathway through AMPK and PGC1 alpha in SM. Thus, a defective leptin signalling PI3K pathway in the hypothalamus may contribute to peripheral resistance to insulin associated to diet-induced obesity.
A major challenge in neuroscience is to resolve the connection between gene functionality, neuronal circuits, and behavior. Most, if not all, neuronal circuits of the adult brain contain a glutamatergic component, the nature of which has been difficult to assess because of the vast cellular abundance of glutamate. In this study, we wanted to determine the role of a restricted subpopulation of glutamatergic neurons within the forebrain, the Vglut2-expressing neurons, in neuronal circuitry of higher brain function. Vglut2 expression was selectively deleted in the cortex, hippocampus, and amygdala of preadolescent mice, which resulted in increased locomotor activity, altered social dominance and risk assessment, decreased sensorimotor gating, and impaired long-term spatial memory. Presynaptic VGLUT2-positive terminals were lost in the cortex, striatum, nucleus accumbens, and hippocampus, and a downstream effect on dopamine binding site availability in the striatum was evident. A connection between the induced late-onset, chronic reduction of glutamatergic neurotransmission and dopamine signaling within the circuitry was further substantiated by a partial attenuation of the deficits in sensorimotor gating by the dopamine-stabilizing antipsychotic drug aripiprazole and an increased sensitivity to amphetamine. Somewhat surprisingly, given the restricted expression of Vglut2 in regions responsible for higher brain function, our analyses show that VGLUT2-mediated neurotransmission is required for certain aspects of cognitive, emotional, and social behavior. The present study provides support for the existence of a neurocircuitry that connects changes in VGLUT2-mediated neurotransmission to alterations in the dopaminergic system with schizophrenia-like behavioral deficits as a major outcome.
Anxiety has been implicated in obesity and in the overconsumption of highly palatable foods such as those high in fat, sugar, or both. Also, the novelty-seeking trait has been associated with failure in weight-loss programs. The aim of this study was to investigate the associations of experimental anxiety and the self-administration of sucrose and high fat pellets in non-food deprived rats across different operant schedules. Male Wistar rats were subjected to the elevated plus-maze test (EPM) of anxiety-like behavior. The rats were tested for fixed ratio 5 (FR5) and progressive ratio (PR) operant responding for 50% sucrose, 95% sucrose, and high-fat pellets. PR active lever press response for 95% sucrose, but not the other pellet types, was correlated to % time spent on open arms (P=0.019) in the EPM. On the FR5 schedule, activity (closed arm entries) was correlated to the self-administration of 50% sucrose (P=0.027) and high-fat (P=0.002). This indicates an association of novelty-induced activity and self-administration of palatable food in sated rats, as well as a specific association of PR lever press response for 95% sucrose and low anxiety-like behavior. It has been argued that such active lever press response on PR may be interpreted as craving for the reinforcer; thus, our findings indicate an inverse relationship of experimental anxiety and craving for sucrose. This connection may have implications for human situations, since anxiety and novelty-seeking have been associated with obesity and failure in weight-loss programs.
The defensive withdrawal test (DWT) is used to model anxiety-like behaviour in rats. The aim of this study was to investigate whether an aversive stimulus, bright light, affects the behaviour in this test. Additionally, the effect of habituation to the apparatus was studied. Both male and female Wistar rats were used to study whether sex differences exist in the DWT, as reported for other tests of anxiety. On day 1 half of the rats were tested under low light and half under bright light. Two to seven days after trial one the same rats were repeatedly tested under the same light condition for five consecutive days. The male rats showed a higher degree of anxiety-like behaviour when tested under bright light than under low light. In contrast, the behaviour of the female rats was not affected by changes in illumination. Male rats also exhibited elevated anxiety-like behaviour compared to female rats under bright light, whereas under low light conditions no sex difference was seen. Males in low light habituated much faster than males tested under bright light, whereas in females there was little difference in habituation between low and bright light. In summary, we found that bright light is aversive for male but not female Wistar rats in the DWT. Whether this is due to sex differences in light sensitivity or if females respond with a different behavioural strategy in response to bright light, which could not be detected in the DWT, remains to be elucidated.
The cyanobacterial toxin ?-N-methylamino-L-alanine (BMAA) has been proposed to contribute to neurodegenerative disease. We have previously reported a selective uptake of BMAA in the mouse neonatal hippocampus and that exposure during the neonatal period causes learning and memory impairments in adult rats. The aim of this study was to characterize effects in the brain of 6-month-old rats treated neonatally (postnatal days 9-10) with the glutamatergic BMAA. Protein changes were examined using the novel technique Matrix-Assisted Laser Desorption Ionization (MALDI) imaging mass spectrometry (IMS) for direct imaging of proteins in brain cryosections, and histological changes were examined using immunohistochemistry and histopathology. The results showed long-term changes including a decreased expression of proteins involved in energy metabolism and intracellular signaling in the adult hippocampus at a dose (150 mg/kg) that gave no histopathological lesions in this brain region. Developmental exposure to a higher dose (460 mg/kg) also induced changes in the expression of S100?, histones, calcium- and calmodulin-binding proteins, and guanine nucleotide-binding proteins. At this dose, severe lesions in the adult hippocampus including neuronal degeneration, cell loss, calcium deposits, and astrogliosis were evident. The data demonstrate subtle, sometimes dose-dependent, but permanent effects of a lower neonatal dose of BMAA in the adult hippocampus suggesting that BMAA could potentially disturb many processes during the development. The detection of BMAA in seafood stresses the importance of evaluating the magnitude of human exposure to this neurotoxin.
The brain is constantly exposed to external and internal input and to function in an ever-changing environment we are dependent on processes that enable the brain to adapt to new stimuli. Exposure to postnatal environmental stimuli can interfere with vital adaption processes and cause long-term changes in physiological function and behavior. Early-life alterations in brain function may result in impaired ability to adapt to new situations, in altered sensitivity to challenges later in life and thereby mediate risk or protection for psychopathology such as alcohol use disorders (AUD). In clinical research the studies of mechanisms, mediators, and causal relation between early environmental factors and vulnerability to AUD are restricted and attempts are made to find valid animal models for studies of the early-life influence on the brain. This review focuses on rodent models and the effects of adverse and naturalistic conditions on peptide networks within the brain and pituitary gland. Importantly, the consequences of alcohol addiction are not discussed but rather neurobiological alterations that can cause risk consumption and vulnerability to addiction. The article reviews earlier results and includes new data and multivariate data analysis with emphasis on endogenous opioid peptides but also oxytocin and vasopressin. These peptides are vital for developmental processes and it is hypothesized that early-life changes in peptide networks may interfere with neuronal processes and thereby contribute the individual vulnerability for AUD. The summarized results indicate a link between early-life rearing conditions, opioids, and ethanol consumption and that the ethanol-induced effects and the treatment with opioid antagonists later in life are dependent on early-life experiences. Endogenous opioids are therefore of interest to further study in the early-life impact on individual differences in vulnerability to AUD and treatment outcome.
Fructose consumption causes insulin resistance and favors hepatic gluconeogenesis through mechanisms that are not completely understood. Recent studies demonstrated that the activation of hypothalamic 5-AMP-activated protein kinase (AMPK) controls dynamic fluctuations in hepatic glucose production. Thus, the present study was designed to investigate whether hypothalamic AMPK activation by fructose would mediate increased gluconeogenesis. Both ip and intracerebroventricular (icv) fructose treatment stimulated hypothalamic AMPK and acetyl-CoA carboxylase phosphorylation, in parallel with increased hepatic phosphoenolpyruvate carboxy kinase (PEPCK) and gluconeogenesis. An increase in AMPK phosphorylation by icv fructose was observed in the lateral hypothalamus as well as in the paraventricular nucleus and the arcuate nucleus. These effects were mimicked by icv 5-amino-imidazole-4-carboxamide-1-?-d-ribofuranoside treatment. Hypothalamic AMPK inhibition with icv injection of compound C or with injection of a small interfering RNA targeted to AMPK?2 in the mediobasal hypothalamus (MBH) suppressed the hepatic effects of ip fructose. We also found that fructose increased corticosterone levels through a mechanism that is dependent on hypothalamic AMPK activation. Concomitantly, fructose-stimulated gluconeogenesis, hepatic PEPCK expression, and glucocorticoid receptor binding to the PEPCK gene were suppressed by pharmacological glucocorticoid receptor blockage. Altogether the data presented herein support the hypothesis that fructose-induced hypothalamic AMPK activation stimulates hepatic gluconeogenesis by increasing corticosterone levels.
One major cause for discrepancies in results from animal experimental studies is the use of different animal strains and suppliers. We have previously reported that Wistar rats from five different suppliers display profound differences in ethanol intake and behavior. One of the neurobiological processes that could be underlying these differences is the endogenous opioid system, which has been implicated in the rewarding and reinforcing effects of alcohol. We therefore hypothesized that the differences between the supplier groups would also be evident in the endogenous opioid system. Radioimmunoassay was used to determine the levels of the opioid peptides Met-enkephalin-Arg(6)Phe(7) and dynorphin B in several brain areas of ethanol-drinking and ethanol naïve Wistar rats from five different suppliers. In the ethanol naïve animals, differences between the supplier groups were found in the pituitary gland, hypothalamus, frontal cortex, dorsal striatum and hippocampus. In the ethanol-drinking rats, differences were found in the same structures, with the addition of medial prefrontal cortex and substantia nigra. Correlations between ethanol intake and peptide levels were also found in several of the areas examined. The structures in which differences were found have all been implicated in the transition from drug use to addiction and these differences may lead to different propensities and vulnerability to this transition. Because the endogenous opioids have been suggested to be involved in a number of neurobiological disorders the results do not only have implications for research on alcohol or drug addiction, but many other fields as well.
Defective liver gluconeogenesis is the main mechanism leading to fasting hyperglycemia in type 2 diabetes, and, in concert with steatosis, it is the hallmark of hepatic insulin resistance. Experimental obesity results, at least in part, from hypothalamic inflammation, which leads to leptin resistance and defective regulation of energy homeostasis. Pharmacological or genetic disruption of hypothalamic inflammation restores leptin sensitivity and reduces adiposity. Here, we evaluate the effect of a hypothalamic anti-inflammatory approach to regulating hepatic responsiveness to insulin. Obese rodents were treated by intracerebroventricular injections, with immunoneutralizing antibodies against Toll-like receptor (TLR)4 or tumor necrosis factor (TNF)?, and insulin signal transduction, hepatic steatosis, and gluconeogenesis were evaluated. The inhibition of either TLR4 or TNF? reduced hypothalamic inflammation, which was accompanied by the reduction of hypothalamic resistance to leptin and improved insulin signal transduction in the liver. This was accompanied by reduced liver steatosis and reduced hepatic expression of markers of steatosis. Furthermore, the inhibition of hypothalamic inflammation restored defective liver glucose production. All these beneficial effects were abrogated by vagotomy. Thus, the inhibition of hypothalamic inflammation in obesity results in improved hepatic insulin signal transduction, leading to reduced steatosis and reduced gluconeogenesis. All these effects are mediated by parasympathetic signals delivered by the vagus nerve.
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