The effects of 5-HT1A and 5-HT2C receptor agonists on behavioral satiety sequence in rats

Aquatic and Terrestrial Invertebrate Welfare

Invertebrates are a diverse group of animals that make up the majority of the animal kingdom and encompass a wide array of species with varying adaptations and characteristics. Invertebrates are found in nearly all of the world's habitats, including aquatic, marine, and terrestrial environments. There are many misconceptions about invertebrate sentience, welfare requirements, the need for environmental enrichment, and overall care and husbandry for this amazing group of animals. This review addresses these topics and more for a select group of invertebrates with biomedical, economical, display, and human companionship importance.

Food-grade titanium dioxide (E171) differentially affects satiation in mice fed a regular or a high fat diet

Food-grade titanium dioxide (E171) is a widely used food additive and the toxicity after oral consumption is still under research, although it has been already banned in some countries. The consumption of this additive occurs mainly through ultra-processed food products which also contain high amounts of fat. High fat diets (HFD) impair the physiological system controlling satiation and satiety, which are responsible for control of food intake and energy status. The impact of E171 on animal behavior has been poorly explored and here we hypothesize that E171 could worsen the effects on feeding behavior induced by HFD. Therefore, we aimed to evaluate the effects of E171 on the feeding pattern and the behavioral satiety sequence (BSS) of mice fed with a regular diet (RD) or a HFD after 1 and 16 weeks of exposure. The results showed that RD + E171 increased food intake and feeding time, but the prototypical structure of the BSS pattern (feeding→ grooming-activity → resting), was preserved. Conversely, food consumption was not altered in HFD + E171, but the BSS pattern was disrupted as the animals prolonged resting time and spent less time being active. Our findings suggest that E171 delayed the onset of satiation in mice fed with RD but induced the opposite effect in mice fed with HFD.

Invertebrate Behavior for the Exotic Pet Practitioner

Invertebrate animals comprise more than 95% of the animal kingdom's species and approximately 40 separate phyla. Yet, invertebrates are an artificial taxon, in which all members simply possess a single negative trait: they lack a vertebral column (backbone). In fact, some invertebrates are more closely related to vertebrates than to their "fellow" invertebrates. For the purpose of this veterinary article, we have elected to review a handful of important groups: Coelenterates, Gastropods, Cephalopods, Chelicerates, Crustaceans, Insects, and Echinoderms. We have primarily included behaviors that may have an impact on clinical case outcome, or be of interest to the veterinary clinician.

Post-feeding behavior in crayfish (Procambarus clarkii): Description of an invertebrate behavioral satiety sequence

Previous studies have demonstrated that food consumption induces the behavioral satiety sequence (BSS) in some animals, a characteristic series of activities which include exploration, grooming, and resting. The BSS, while valuable in assessing the effects of drugs on food intake, has not been widely studied in non-mammalian species. Our experiment examined post-feeding behavior in crayfish using continuous recording of five behaviors: feeding, walking, grooming, leg wave, and quiescence. We found that food intake, but not sham feeding, significantly decreased feeding behavior, increased leg wave, and increased quiescence. Walking and grooming were not significantly altered by food intake. These findings indicate that post-feeding behaviors in crayfish share some characteristics with the mammalian BSS. Detailed descriptions of post-ingestive behavior in invertebrates may contribute to the development of drugs targeting feeding behaviors in medically and economically important species.

Transcranial direct current stimulation (tDCS) modulates biometric and inflammatory parameters and anxiety-like behavior in obese rats

Obesity is a multifactorial disease associated with metabolic dysfunction and the prevention and treatment of obesity are often unsatisfactory. Transcranial direct-current stimulation (tDCS) is a non-invasive brain stimulation technique that has proven promising in the treatment of eating disorders such as obesity. We investigate the effects of tDCS on locomotor and exploratory activities, anxiety-like and feeding behavior, and levels of brain-derived neurotrophic factor (BDNF), IL (interleukin)-10, IL-1β, and tumor necrosis factor-alpha (TNF-α) in the cerebral cortex of obese rats. A total of 40 adult male Wistar rats were used in our study. Animals were divided into groups of three or four animals per cage and allocated to four treatment groups: standard diet plus sham tDCS treatment (SDS), standard diet plus tDCS treatment (SDT), hypercaloric diet plus sham tDCS treatment (HDS), hypercaloric diet plus tDCS treatment (HDT). After 40 days on a hypercaloric diet and/or standard diet were to assessed the locomotor and exploratory activity and anxiety-like behavior to by the open field (OF) and elevated plus maze (EPM) tests respectively before and after exposure to tDCS treatment. The experimental groups were submitted to active or sham treatment tDCS during eight days. Palatable food consumption test (PFT) was performed 24 h after the last tDCS session under fasting and feeding conditions. Obese animals submitted to tDCS treatment showed a reduction in the Lee index, visceral adipose tissue weight, and food craving. In addition, bicephalic tDCS decreased the cerebral cortex levels of IL-1β and TNF-α in these animals. Exposure to a hypercaloric diet produced an anxiolytic effect, which was reversed by bicephalic tDCS treatment. These results suggest that, in accordance with studies in humans, bicephalic tDCS could modulate biometric and inflammatory parameters, as well as anxiety-like and feeding behavior, of rats subjected to the consumption of a hypercaloric diet.

CB1 receptors in the paraventricular nucleus of the hypothalamus modulate the release of 5-HT and GABA to stimulate food intake in rats

Endocannabinoids and their receptors not only contribute to the control of natural processes of appetite regulation and energy balance but also have an important role in the pathogenesis of obesity. CB1 receptors (CB1R) are expressed in several hypothalamic nuclei, including the paraventricular nucleus (PVN), where induce potent orexigenic responses. Activation of CB1R in the PVN induces hyperphagia by modulating directly or indirectly orexigenic and anorexigenic signals; however, interaction among these mediators has not been clearly defined. CB1R mRNA is expressed in serotonergic neurons that innervate the PVN, and activation of 5-HT receptors in the PVN constitutes an important satiety signal. Some GABAergic terminals are negatively influenced by 5-HT, suggesting that the hyperphagic effect of CB1R activation could involve changes in serotonergic and GABAergic signaling in the PVN. Accordingly, the present study was aimed to characterize the neurochemical mechanisms related to the hyperphagic effects induced by activation of CB1R in the PVN, studying in vitro and in vivo changes induced by direct activation these receptors. Here, we have found that the neurochemical mechanisms activated by stimulation of CB1 receptors in the PVN involve inhibition of 5-HT release, resulting in a decrease of serotonergic activity mediated by 5-HT_1A and 5-HT_1B receptors and inducing disinhibition of GABA release to stimulate food intake. In conclusion, these neurochemical changes in the PVN are determinant to the cannabinoid-induced stimulation of food intake. Our findings provide evidence of a functional connection among CB1R and serotonergic and GABAergic systems on the control of appetite regulation mediated by endocannabinoids.

Dietary Galacto-Oligosaccharides and Resistant Starch Protect Against Altered CB1 and 5-HT1A and 2A Receptor Densities in Rat Brain: Implications for Preventing Cognitive and Appetite Dysfunction During a High-Fat Diet

SCOPE

A high-fat, but low-fiber, diet is associated with obesity and cognitive dysfunction, while dietary fiber supplementation can improve cognition.

METHODS AND RESULTS

This study examines whether dietary fibers, galacto-oligosaccharides (GOS) and resistant starch (RS), could prevent high-fat (HF)-diet-induced alterations in neurotransmitter receptor densities in brain regions associated with cognition and appetite. Rats are fed a HF diet, HF diet with GOS, HF diet with RS, or a low-fat (LF, control) diet for 4 weeks. Cannabinoid CB1 (CB1R) and 5HT_1A (5HT_1A R) and 5-HT_2A (5HT_2A R) receptor binding densities are examined. In the hippocampus and hypothalamus, a HF diet significantly increases CB1R binding, while HF + GOS and HF + RS diets prevented this increase. HF diet also increases hippocampal and hypothalamic 5-HT_1A R binding, while HF + GOS and HF + RS prevented the alterations. Increased 5-HT_2A binding is prevented by HF + GOS and HF + RS in the medial mammillary nucleus.

CONCLUSIONS

These results demonstrate that increased CB1R, 5-HT_1A R and 5-HT_2A R induced by a HF diet can be prevented by GOS and RS supplementation in brain regions involved in cognition and appetite. Therefore, increased fiber intake may have beneficial effects on improving learning and memory, as well as reducing excessive appetite, during the chronic consumption of a HF (standard Western) diet.

Repeated Transcranial Direct Current Stimulation Induces Behavioral, Metabolic and Neurochemical Effects in Rats on High-Calorie Diet

Due to its high prevalence, obesity is considered an epidemic, which stimulated research on non-invasive methods to reduce excess body fat. Transcranial direct current stimulation (tDCS) is a non-invasive technique used to modulate the activity of cerebral cortex, which has already found increasing interest in medicine as a promising methodology. The aim of this study was to analyze the impact of tDCS on feeding behavior, metabolic abnormalities and neurotransmitters in certain brain areas involved in appetite control of obese rats. The male Wistar rats were divided into five subgroups depending on consumed diet effect (lean, obese) and tDCS type (anodal, cathodal, sham, and no stimulation). Two 10-min daily sessions of tDCS for 8 consecutive days of the study were applied. Rats subjected to active tDCS (anodal right or cathodal left of the prefrontal cortex) had reduced appetite and showed lesser body weight gain than the animals subjected to sham procedure or those receiving no stimulation at all. Furthermore, tDCS contributed to reduction of epididymal fat pads and to a decrease in blood concentration of leptin. Neurochemical examination revealed that tDCS modulated serotonin pathways of the reward-related brain areas and contributed to a significant decrease in the density of D2 but not D1 dopamine receptors in the dorsal striatum, recorded 5 h after the last stimulation. No significant effect of tDCS on dopamine and it's metabolites in examined brain regions was observed. It seems that the hypothalamus was not affected by tDCS application as no changes in measured neurotransmitters were detected at any examined time point. However, these results do not exclude the possibility of the delayed response of the monoamines in the examined brain areas to tDCS application. Altogether, these findings imply that repeated tDCS of the prefrontal cortex may change feeding behavior of obese rats. Either right anodal or left cathodal tDCS were sufficient to decrease food intake, to reduce body adiposity and to normalize other metabolic anomalies. These beneficial effects can be at least partially explained by changes in serotoninergic and in lesser extent dopaminergic system activity within some brain areas belonging to reward system.

Contrasting effects of 5-HT3 receptor stimulation of the nucleus accumbens or ventral tegmentum on food intake in the rat

Although serotonin (5-HT) signaling is known to regulate food intake and energy homeostasis, the roles of the 5-HT₃ receptor in feeding processes have been elusive. 5-HT₃ receptors are found throughout mesolimbic circuitry that promote feeding not only in response to hunger, but also to the palatable and rewarding properties of food. These experiments examined if stimulation or blockade of the 5-HT₃ receptor of the nucleus accumbens (NAcc) or ventral tegmentum affected food intake in the rat in response to hunger or the presence of a palatable diet. Rats (N=6-9/group) received bilateral injections of the 5-HT₃ agonist m-chlorophenylbiguanide hydrochloride (mCPBG; at 0.0, 10.0, or 20.0μg/0.5μl/side) or the 5-HT₃ antagonist ondansetron hydrochloride (at 0.0, 1.0, 2.0, or 5.0μg/0.5μl/side) into either the NAcc or the ventral tegmentum. NAcc 5-HT₃ receptor stimulation significantly increased 2-h food intake in food-deprived animals offered rat chow and in a separate group of unrestricted rats offered a sweetened fat diet. In contrast to the feeding increase seen with NAcc treatments, stimulation of 5-HT₃ receptors of the ventral tegmentum significantly reduced food and water intake in food-restricted animals; reductions of intake in non-restricted rats offered the palatable diet did not approach significance. Blockade of the 5-HT₃ receptor had no effect on feeding in either brain region. These data support a functional role for serotonergic signaling in the mesolimbic pathway on motivated behavior, and demonstrate that 5-HT₃ receptors differentially modulate food consumption in a region-dependent manner.

A systematic investigation of the differential roles for ventral tegmentum serotonin 1- and 2-type receptors on food intake in the rat

Central serotonin (5-HT) pathways are known to influence feeding and other ingestive behaviors. Although the ventral tegmentum is important for promoting the seeking and consumption of food and drugs of abuse, the roles of 5-HT receptor subtypes in this region on food intake have yet to be comprehensively examined. In these experiments, food restricted rats were given 2-h access to rat chow; separate groups of non-restricted animals had similar access to a sweetened fat diet. Feeding and locomotor activity were monitored following ventral tegmentum stimulation or blockade of 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2B, or 5-HT2C receptors. 5-HT1A receptor stimulation transiently inhibited rearing behavior and chow intake in food-restricted rats, and had a biphasic effect on non-restricted rats offered the palatable diet. 5-HT1B receptor agonism transiently inhibited feeding in restricted animals, but did not affect intake of non-restricted rats. In contrast, 5-HT1B receptor antagonism decreased palatable feeding. Although stimulation of ventral tegmental 5-HT2B receptors with BW723C86 did not affect hunger-driven food intake, it significantly affected palatable feeding, with a trend for an increasing intake at 2.0µg/side but not at 5.0µg/side. Antagonism of the same receptor modestly but significantly inhibited feeding of the palatable diet at 5.0µg/side ketanserin. Neither stimulation nor blockade of 5-HT2A or 5-HT2C receptors caused prolonged effects on intake or locomotion. These data suggest that serotonin's effects on feeding within the ventral tegmentum depend upon the specific receptor targeted, as well as whether intake is motivated by food restriction or the palatable nature of the offered diet.

Brain signaling systems in the Type 2 diabetes and metabolic syndrome: promising target to treat and prevent these diseases

The changes in the brain signaling systems play an important role in etiology and pathogenesis of Type 2 diabetes mellitus (T2DM) and metabolic syndrome (MS), being a possible cause of these diseases. Therefore, their restoration at the early stages of T2DM and MS can be regarded as a promising way to treat and prevent these diseases and their complications. The data on the functional state of the brain signaling systems regulated by insulin, IGF-1, leptin, dopamine, serotonin, melanocortins and glucagon-like peptide-1, in T2DM and MS, are analyzed. The pharmacological approaches to restoration of these systems and improvement of insulin sensitivity, energy expenditure, lipid metabolism, and to prevent diabetic complications are discussed.

Modulatory Role of Postsynaptic 5-Hydroxytryptamine Type 1A Receptors in (±)-8-Hydroxy-N,N-dipropyl-2-aminotetralin-Induced Hyperphagia in Mice

Brain serotonin (5-HT) is involved in the control of food intake. The ingestive effects of 5-HT are mediated by various receptor subtypes, among others the 5-HT1A receptor. While the involvement of presynaptic 5-HT1A receptors is regarded as certain, the role of postsynaptic 5-HT1A receptors is rather vague. Here, we studied the role of the 5-HT1A receptor on feeding in non-food-deprived and food-deprived (young adult and adult, both sexes) wild-type NMRI mice as well as transgenic NMRI mice, which are characterized by a distinct overexpression of postsynaptic 5-HT1A receptors. The known hyperphagic effect of the 5-HT1A receptor full agonist 8-OH-DPAT ((±)-8-hydroxy-N,N-dipropyl-2-aminotetralin) in non-food-deprived animals was demonstrated in male NMRI wild-type mice and could be antagonized by the selective 5-HT1A receptor antagonist WAY100635. In transgenic mice, this hyperphagic response was induced at lower doses, with an earlier onset and even in females. However, in adult male transgenic mice, the hyperphagic effect did not occur. In food-deprived NMRI wild-type as well as transgenic mice, 8-OH-DPAT first induced a hypophagic and subsequently a hyperphagic effect. Again, in transgenic animals most responses occurred at lower doses and with an earlier onset. The results indicate that postsynaptic 5-HT1A receptors exert a modulatory function in food intake in free-feeding and fasted mice, which for the first time shows an involvement of postsynaptic 5-HT1A receptors in feeding behavior. Understanding the function of pre- and postsynaptic 5-HT1A receptors may help to achieve new insights into the regulation of food intake and foster prospective treatment strategies for eating disorders.

Distribution of serotonin 5-HT1A-binding sites in the brainstem and the hypothalamus, and their roles in 5-HT-induced sleep and ingestive behaviors in rock pigeons (Columba livia)

Serotonin 1A receptors (5-HT1ARs), which are widely distributed in the mammalian brain, participate in cognitive and emotional functions. In birds, 5-HT1ARs are expressed in prosencephalic areas involved in visual and cognitive functions. Diverse evidence supports 5-HT1AR-mediated 5-HT-induced ingestive and sleep behaviors in birds. Here, we describe the distribution of 5-HT1ARs in the hypothalamus and brainstem of birds, analyze their potential roles in sleep and ingestive behaviors, and attempt to determine the involvement of auto-/hetero-5-HT1ARs in these behaviors. In 6 pigeons, the anatomical distribution of [(3)H]8-OH-DPAT binding in the rostral brainstem and hypothalamus was examined. Ingestive/sleep behaviors were recorded (1h) in 16 pigeons pretreated with MM77 (a heterosynaptic 5-HT1AR antagonist; 23 or 69 nmol) for 20 min, followed by intracerebroventricular ICV injection of 5-HT (N:8; 150 nmol), 8-OH-DPAT (DPAT, a 5-HT1A,7R agonist, 30 nmol N:8) or vehicle. 5-HT- and DPAT-induced sleep and ingestive behaviors, brainstem 5-HT neuronal density and brain 5-HT content were examined in 12 pigeons, pretreated by ICV with the 5-HT neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) or vehicle (N:6/group). The distribution of brainstem and diencephalic c-Fos immunoreactivity after ICV injection of 5-HT, DPAT or vehicle (N:5/group) into birds provided with or denied access to water is also described. 5-HT1ARs are concentrated in the brainstem 5-HTergic areas and throughout the periventricular hypothalamus, preoptic nuclei and circumventricular organs. 5-HT and DPAT produced a complex c-Fos expression pattern in the 5-HT1AR-enriched preoptic hypothalamus and the circumventricular organs, which are related to drinking and sleep regulation, but modestly affected c-Fos expression in 5-HTergic neurons. The 5-HT-induced ingestivebehaviors and the 5-HT- and DPAT-induced sleep behaviors were reduced by MM77 pretreatment. 5,7-DHT increased sleep per se, decreased tryptophan hydroxylase expression in the raphe nuclei and decreased prosencephalic 5-HT release but failed to affect 5-HT- or DPAT-induced drinking or sleep behavior. 5-HT- and DPAT-induced ingestive and sleep behaviors in pigeons appear to be mediated by heterosynaptic and/or non-somatodendritic presynaptic 5-HT1ARs localized to periventricular diencephalic circuits.

The Effect of Long-Term Intranasal Serotonin Treatment on Metabolic Parameters and Hormonal Signaling in Rats with High-Fat Diet/Low-Dose Streptozotocin-Induced Type 2 Diabetes

In the last years the treatment of type 2 diabetes mellitus (DM2) was carried out using regulators of the brain signaling systems. In DM2 the level of the brain serotonin is reduced. So far, the effect of the increase of the brain serotonin level on DM2-induced metabolic and hormonal abnormalities has been studied scarcely. The present work was undertaken with the aim of filling this gap. DM2 was induced in male rats by 150-day high-fat diet and the treatment with low dose of streptozotocin (25 mg/kg) on the 70th day of experiment. From the 90th day, diabetic rats received for two months intranasal serotonin (IS) at a daily dose of 20 μg/rat. The IS treatment of diabetic rats decreased the body weight, and improved glucose tolerance, insulin-induced glucose utilization, and lipid metabolism. Besides, it restored hormonal regulation of adenylyl cyclase (AC) activity in the hypothalamus and normalized AC stimulation by β-adrenergic agonists in the myocardium. In nondiabetic rats the same treatment induced metabolic and hormonal alterations, some of which were similar to those in DM2 but expressed to a lesser extent. In conclusion, the elevation of the brain serotonin level may be regarded as an effective approach to treat DM2 and its complications.

Serotonin 1A, 1B, and 7 receptors of the rat medial nucleus accumbens differentially regulate feeding, water intake, and locomotor activity

Serotonin (5-HT) signaling has been widely implicated in the regulation of feeding behaviors in both humans and animal models. Recently, we reported that co-stimulation of 5-HT1&7 receptors of the anterior medial nucleus accumbens with the drug 5-CT caused a dose-dependent decrease in food intake, water intake, and locomotion in rats (Pratt et al., 2009). The current experiments sought to determine which of three serotonin receptor subtypes (5-HT1A, 5-HT1B, or 5-HT7) might be responsible for these consummatory and locomotor effects. Food-deprived rats were given 2-h access to rat chow after stimulation of nucleus accumbens 5-HT1A, 5-HT1B, or 5-HT7 receptors, or blockade of the 5-HT1A or 5-HT1B receptors. Stimulation of 5-HT1A receptors with 8-OH-DPAT (at 0.0, 2.0, 4.0, and 8.0 μg/0.5 μl/side) caused a dose-dependent decrease in food and water intake, and reduced rearing behavior but not ambulation. In contrast, rats that received the 5-HT1B agonist CP 93129 (at 0.0, 1.0, 2.0 and 4.0 μg/0.5 μl/side) showed a significant dose-dependent decrease in water intake only; stimulation of 5-HT7 receptors (AS 19; at 0.0, 1.0, and 5.0 μg/0.5 μl/side) decreased ambulatory activity but did not affect food or water consumption. Blockade of 5-HT1A or 5-HT1B receptors had no lasting effects on measures of food consumption. These data suggest that the food intake, water intake, and locomotor effects seen after medial nucleus accumbens injections of 5-CT are due to actions on separate serotonin receptor subtypes, and contribute to growing evidence for selective roles of individual serotonin receptors within the nucleus accumbens on motivated behavior.

Selective serotonin receptor stimulation of the medial nucleus accumbens differentially affects appetitive motivation for food on a progressive ratio schedule of reinforcement

Previously, we reported that stimulation of selective serotonin (5-HT) receptor subtypes in the nucleus accumbens shell differentially affected consumption of freely available food. Specifically, activation of 5-HT(6) receptors caused a dose-dependent increase in food intake, while the stimulation of 5-HT(1/7) receptor subtypes decreased feeding [34]. The current experiments tested whether similar pharmacological activation of nucleus accumbens serotonin receptors would also affect appetitive motivation, as measured by the amount of effort non-deprived rats exerted to earn sugar reinforcement. Rats were trained to lever press for sugar pellets on a progressive ratio 2 schedule of reinforcement. Across multiple treatment days, three separate groups (N=8-10) received bilateral infusions of the 5-HT(6) agonist EMD 386088 (at 0.0, 1.0 and 4.0 μg/0.5 μl/side), the 5-HT(1/7) agonist 5-CT (at 0, 0.5, 1.0, or 4.0 μg/0.5 μl/side), or the 5-HT(2C) agonist RO 60-0175 fumarate (at 0, 2.0, or 5.0 μg/0.5 μl/side) into the anterior medial nucleus accumbens prior to a 1-h progressive ratio session. Stimulation of 5-HT(6) receptors caused a dose-dependent increase in motivation as assessed by break point, reinforcers earned, and total active lever presses. Stimulation of 5-HT(1/7) receptors increased lever pressing at the 0.5 μg dose of 5-CT, but inhibited lever presses and break point at 4.0 μg/side. Injection of the 5-HT(2C) agonist had no effect on motivation within the task. Collectively, these experiments suggest that, in addition to their role in modulating food consumption, nucleus accumbens 5-HT(6) and 5-HT(1/7) receptors also differentially regulate the appetitive components of food-directed motivation.

Contrasting effects of systemic and central sibutramine administration on the intake of a palatable diet in the rat

Sibutramine hydrochloride monohydrate is the only centrally active weight-modifying agent currently approved by the FDA for long-term use in the treatment of obesity. Systemic sibutramine treatment has been shown to reduce food intake in humans and rodent models in a manner that is consistent with the enhancement of satiety mechanisms. Although it is generally assumed that the hypophagic effects of the drug are mediated by actions within the brain, the locus or loci of these effects remains unclear. These experiments compared the effects of systemic and intracranial injections of sibutramine on the intake of a palatable diet in non-deprived animals. Consistent with prior reports, systemic injections of sibutramine hydrochloride (at 0, 0.5, 1.0, or 3.0mg/kg sibutramine i.p.) dose-dependently reduced feeding on a high fat/high sucrose diet across a 2-h feeding session, but did not alter water intake or locomotor activity. In contrast, bilateral injections of sibutramine (at 0.0, 2.0, 4.0 and 10.0μg/0.5μl/side) into either the paraventricular nucleus of the hypothalamus (PVN) or the medial nucleus accumbens shell (ACb) significantly and dose-dependently increased food intake of the sweetened fat diet. ACb treatment also modestly inhibited locomotor behavior; intracranial injections had no effect on water consumption. These experiments are the first to suggest that sibutramine treatment may have distinct actions upon separate neural circuits that modulate food intake behavior in the rat.

Effects of the increase in neuronal fatty acids availability on food intake and satiety in mice

RATIONALE

Neurons detect free fatty acids (FFAs) availability and use this nutritional status to modulate feeding and control body weight.

OBJECTIVES

The work is designed to characterize the impact on feeding behavior of either oleic acid (OA) administration (experiment 1) or the inhibition (experiment 2) of the enzyme carnitine palmitoyltransferase-1 (CPT-1). The structure of feeding behavior and satiation time course were examined through the behavioral satiety sequence (BSS) paradigm.

METHODS

Adult male mice were initially habituated to a palatable diet, then subjected to intracerebroventricular (i.c.v.) infusion of different doses of OA or the CPT-1 inhibitor ST1326. Food intake at different time points, duration, and frequencies of feeding and non-feeding-related behaviors were continuously monitored over 40 min and satiety development profiled according to BSS.

RESULTS

Intra-i.c.v. infusion of oleic acid (300 nM) and ST1326 (50 and 75 pM) suppressed food intake. As indicated by the earlier leftward shifting of the normal transition from eating to resting, both strategies similarly accelerated the onset of satiety. The premature onset of satiety resulted in a dose-related fashion with 50 pM of ST1326 producing a marked premature onset than the lower dose. However, at the highest dose injected, the inhibition of CPT-1 disrupted the BSS profile.

CONCLUSIONS

The increased neuronal availability of FFAs mediates a significant anorectic response which is mirrored by an early occurrence of satiety onset. Besides supporting the role of central nutrient sensing in feeding, the present data demonstrate that the modulation of satiety enhancement can produce appetite suppressant effects within narrow range of neuronal FFAs availability.

The effects of antipsychotic drugs administration on 5-HT1A receptor expression in the limbic system of the rat brain

Increasing evidence suggests that 5-HT1A receptors are involved in the pathophysiology and treatment of schizophrenia. This paper investigated 5-HT1A receptor mRNA expression and binding density in female rats treated with aripiprazole (2.25 mg/kg/day), olanzapine (1.5 mg/kg/day), haloperidol (0.3 mg/kg/day) or vehicle (control) orally three times/day for 1 or 12 weeks. Animals were sacrificed 48 h after the last administration. Aripiprazole significantly increased 5-HT1A receptor binding density by 33% in the CA1 region of the hippocampus and by 21% in the medial posterodorsal nuclei of posterior amygdala (MeP) compared to the control group after 1 week of treatment. Olanzapine significantly decreased 5-HT1A receptor binding density by 17-22% in Layers I-IV of the cingulate cortex after 1 week of treatment. Neither of these antipsychotic drugs affected 5-HT1A receptor binding density after 12 weeks drug treatment. As expected, haloperidol treatment did not have any significant effect on 5-HT1A binding density after 1 or 12 weeks of treatment. 5-HT1A receptor mRNA expression was not altered by antipsychotic treatment in any brain region. The results indicate that aripiprazole and olanzapine have differential effects on 5-HT1A receptor expression, which may contribute to their distinct profiles in improving negative symptoms and cognitive deficits in schizophrenia. Aripiprazole and olanzapine may produce adaptation and desensitization of 5-HT1A receptor expression after long term treatment.

Night and day: diurnal differences in the behavioural satiety sequence in male rats

The behavioural satiety sequence (BSS) is an important method for assessing the selectivity of treatment (physiological, pharmacological and/or genetic) effects on food intake in rodents. The concept describes the natural progression from feeding to resting, with the transition between the two a useful biomarker of behavioural satiety. Although treatments can accelerate (anorexigenics) or delay (orexigenics) this transition without disrupting behavioural structure, the detection of such changes depends upon the timing of the transition under control conditions. Fasting and presatiation are known to affect this timing. However, recent observations in our laboratory have suggested that phase of testing (light or dark) might also be an important consideration. The present study therefore directly compared food intake and the BSS in thoroughly habituated male rats maintained either on a normal light cycle and tested during the light phase or on a reversed light cycle and tested during the dark phase. The results show that phase of testing had relatively little impact on food intake or diverse measures of ingestive and non-ingestive behaviour. Although modest differences were detected in locomotion, grooming and scratching (higher in dark phase), by far the largest difference concerned resting behaviour which had both a later onset and a much lower peak level during dark phase testing. Importantly, these behavioural differences delayed the transition between eating and resting. The potential contribution of diurnal differences in rate of eating is discussed as are the implications of these findings for future studies on the neurobiology of feeding behaviour.

The effects of metergoline and 8-OH-DPAT injections into arcuate nucleus and lateral hypothalamic area on feeding in female rats during the estrous cycle

The present study examined the effects of local injections of metergoline (MET, an antagonist of 5-HT1/2 receptors, 2 and 20 nmol) and 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT, selective 5-HT1A receptor agonist, 0.6 and 6 nmol) into the arcuate nucleus (ARC) and the lateral hypothalamus (LH), on ingestive and non-ingestive behaviors of female rats. These effects were examined during the diurnal periods of diestrus and estrus in rats adapted to eat a wet mash diet (enriched with 10% sucrose) during 1h for 3 consecutive days at the recording chamber. The results showed that 8-OH-DPAT injected into the LH significantly reduced food intake at all doses and both cycle stages, while in the ARC these treatments evoked hypophagia only at the highest 8-OH-DPAT dose and only at the estrous phase. MET administered into the ARC (at all doses) failed to affect food intake during both estrous stages. On the other hand, food intake decreased after injection of both doses of MET into the LH of rats during estrous and diestrus phases. In estrus stage, injections of the higher dose of 8-OH-DPAT into the ARC and into the LH decreased the duration of feeding. Latency to start feeding, drinking, and non-ingestive behaviors were not affected by 8-OH-DPAT or MET treatments in the ARC or the LH in both cycle phases. These results indicated that 5-HT1A receptors participate in the serotonergic control of feeding-related mechanisms located at the ARC and the LH. These feeding-related serotonergic circuits in both areas are possibly affected by ovarian hormones that could increase sensitivity of ARC neurons to the hypophagic effects of 8-OH-DPAT or increase the efficacy of satiety signals that terminate feeding. In addition, the present data indicated that serotonergic inputs do not exert a tonic inhibitory activity on the ARC and the LH feeding-related circuits.

Imprinted genes and neuroendocrine function

Imprinted genes are monoallelically expressed in a parent-of-origin dependent manner. Whilst the full functional repertoire of these genes remains obscure, they are generally highly expressed in the brain and are often involved in fundamental neural processes. Besides influencing brain neurochemistry, imprinted genes are important in the development and function of the hypothalamus and pituitary gland, key sites of neuroendocrine regulation. Moreover, imprinted genes may directly modulate hormone-dependent signalling cascades, both in the brain and elsewhere. Much of our knowledge about imprinted gene function has come from studying knockout mice and human disorders of imprinting. One such disorder is Prader-Willi syndrome, a neuroendocrine disorder characterised by hypothalamic abnormalities and aberrant feeding behaviour. Through examining the role of imprinted genes in neuroendocrine function, it may be possible to shed light on the neurobiological basis of feeding and aspects of social behaviour and underlying cognition, and to provide insights into disorders where these functions go awry.