Psilocybin restrains activity-based anorexia in female rats by enhancing cognitive flexibility: contributions from 5-HT1A and 5-HT2A receptor mechanisms.

Psilocybin has shown promise for alleviating symptoms of depression and is currently in clinical trials for the treatment of anorexia nervosa (AN), a condition that is characterised by persistent cognitive inflexibility. Considering that enhanced cognitive flexibility after psilocybin treatment is reported to occur in individuals with depression, it is plausible that psilocybin could improve symptoms of AN by breaking down cognitive inflexibility. A mechanistic understanding of the actions of psilocybin is required to tailor the clinical application of psilocybin to individuals most likely to respond with positive outcomes. This can only be achieved using incisive neurobiological approaches in animal models. Here, we use the activity-based anorexia (ABA) rat model and comprehensively assess aspects of reinforcement learning to show that psilocybin (post-acutely) improves body weight maintenance in female rats and facilitates cognitive flexibility, specifically via improved adaptation to the initial reversal of reward contingencies. Further, we reveal the involvement of signalling through the serotonin (5-HT) 1 A and 5-HT2A receptor subtypes in specific aspects of learning, demonstrating that 5-HT1A antagonism negates the cognitive enhancing effects of psilocybin. Moreover, we show that psilocybin elicits a transient increase and decrease in cortical transcription of these receptors (Htr2a and Htr1a, respectively), and a further reduction in the abundance of Htr2a transcripts in rats exposed to the ABA model. Together, these findings support the hypothesis that psilocybin could ameliorate cognitive inflexibility in the context of AN and highlight a need to better understand the therapeutic mechanisms independent of 5-HT2A receptor binding.

Mechanisms underlying the efficacy of a rodent model of vertical sleeve gastrectomy - A focus on energy expenditure.

OBJECTIVE: Bariatric surgery remains the only effective and durable treatment option for morbid obesity. Vertical Sleeve Gastrectomy (VSG) is currently the most widely performed of these surgeries primarily because of its proven efficacy in generating rapid onset weight loss, improved glucose regulation and reduced mortality compared with other invasive procedures. VSG is associated with reduced appetite, however, the relative importance of energy expenditure to VSG-induced weight loss and changes in glucose regulation, particularly that in brown adipose tissue (BAT), remains unclear. The aim of this study was to investigate the role of BAT thermogenesis in the efficacy of VSG in a rodent model. METHODS: Diet-induced obese male Sprague-Dawley rats were either sham-operated, underwent VSG surgery or were pair-fed to the food consumed by the VSG group. Rats were also implanted with biotelemetry devices between the interscapular lobes of BAT to assess local changes in BAT temperature as a surrogate measure of thermogenic activity. Metabolic parameters including food intake, body weight and changes in body composition were assessed. To further elucidate the contribution of energy expenditure via BAT thermogenesis to VSG-induced weight loss, a separate cohort of chow-fed rats underwent complete excision of the interscapular BAT (iBAT lipectomy) or chemical denervation using 6-hydroxydopamine (6-OHDA). To localize glucose uptake in specific tissues, an oral glucose tolerance test was combined with an intraperitoneal injection of 14C-2-deoxy-d-glucose (14C-2DG). Transneuronal viral tracing was used to identify 1) sensory neurons directed to the stomach or small intestine (H129-RFP) or 2) chains of polysynaptically linked neurons directed to BAT (PRV-GFP) in the same animals. RESULTS: Following VSG, there was a rapid reduction in body weight that was associated with reduced food intake, elevated BAT temperature and improved glucose regulation. Rats that underwent VSG had elevated glucose uptake into BAT compared to sham operated animals as well as elevated gene markers related to increased BAT activity (Ucp1, Dio2, Cpt1b, Cox8b, Ppargc) and markers of increased browning of white fat (Ucp1, Dio2, Cited1, Tbx1, Tnfrs9). Both iBAT lipectomy and 6-OHDA treatment significantly attenuated the impact of VSG on changes in body weight and adiposity in chow-fed animals. In addition, surgical excision of iBAT following VSG significantly reversed VSG-mediated improvements in glucose tolerance, an effect that was independent of circulating insulin levels. Viral tracing studies highlighted a patent neural link between the gut and BAT that included groups of premotor BAT-directed neurons in the dorsal raphe and raphe pallidus. CONCLUSIONS: Collectively, these data support a role for BAT in mediating the metabolic sequelae following VSG surgery, particularly the improvement in glucose regulation, and highlight the need to better understand the contribution from this tissue in human patients.

Neuroendocrine mechanisms underlying bariatric surgery: Insights from human studies and animal models.

Obesity has reached epidemic proportions and, to date, bariatric surgery remains the only effective treatment for morbid obesity in terms of its capacity to achieve durable weight loss. Bariatric surgery procedures, including Roux-en-Y gastric bypass (RYGB), adjustable gastric banding (AGB) and sleeve gastrectomy (SG), have been the primary procedures conducted over the past decade, with SG increasing in popularity over the past 5 years at the expense of both RYGB and AGB. Although these procedures were initially proposed to function via restrictive or malabsorptive mechanisms, it is now clear that profound physiological changes underlie the metabolic improvements in patients who undergo bariatric surgery. Data generated in human patients and animal models highlight the rapid and sustained changes in gut hormones that coincide with these procedures. Furthermore, recent studies highlight the involvement of the nervous system, specifically the vagus nerve, in mediating the reduction in appetite and food intake following bariatric surgery. What is unclear is where these pathways converge and interact within the gut-brain axis and whether vagally-mediated circuits are sufficient to drive the metabolic sequalae following bariatric surgery.

A focus on reward in anorexia nervosa through the lens of the activity-based anorexia rodent model.

Patients suffering anorexia nervosa (AN) become anhedonic, unable or unwilling to derive normal pleasures and tend to avoid rewarding outcomes, most profoundly in food intake. The activity-based anorexia model recapitulates many of the pathophysiological and behavioural hallmarks of the human condition, including a reduction in food intake, excessive exercise, dramatic weight loss, loss of reproductive cycles, hypothermia and anhedonia, and therefore it allows investigation into the underlying neurobiology of anorexia nervosa. The use of this model has directed attention to disruptions in central reward neurocircuitry, which may contribute to disease susceptibility. The purpose of this review is to demonstrate the utility of this unique model to provide insight into the mechanisms of reward relevant to feeding and weight loss, which may ultimately help to unravel the neurobiology of anorexia nervosa and, in a broader sense, the foundation of reward-based feeding.

Identification of CNS neurons with polysynaptic connections to both the sympathetic and parasympathetic innervation of the submandibular gland.

Coordinated modulation of sympathetic and parasympathetic nervous activity is required for physiological regulation of tissue function. Anatomically, whilst the peripheral sympathetic and parasympathetic pathways are separate, the distribution of premotor neurons in higher brain regions often overlaps. This co-distribution would enable coordinated regulation and might suggest individual premotor neurons could project to both sympathetic and parasympathetic outflows. To investigate this one submandibular gland was sympathectomized. One of two isogenic strains of the pseudorabies virus, expressing different fluorophores, was injected into the cut sympathetic nerve and the other into the submandibular gland. Independent labeling of the peripheral sympathetic and parasympathetic pathways was observed. Dual-labeled neurons were observed in many CNS regions known to be involved in regulating salivary function. We propose these observations highlight a common pattern of organization of the CNS, providing the anatomical framework for the fine control of organ function required for homeostatic regulation and the coordination of organ responses to enable complex behaviors.

Hypothalamic control of adipose tissue.

A detailed appreciation of the control of adipose tissue whether it be white, brown or brite/beige has never been more important to the development of a framework on which to build therapeutic strategies to combat obesity. This is because 1) the rate of fatty acid release into the circulation from lipolysis in white adipose tissue (WAT) is integrally important to the development of obesity, 2) brown adipose tissue (BAT) has now moved back to center stage with the realization that it is present in adult humans and, in its activated form, is inversely proportional to levels of obesity and 3) the identification and characterization of "brown-like" or brite/beige fat is likely to be one of the most exciting developments in adipose tissue biology in the last decade. Central to all of these developments is the role of the CNS in the control of different fat cell functions and central to CNS control is the integrative capacity of the hypothalamus. In this chapter we will attempt to detail key issues relevant to the structure and function of hypothalamic and downstream control of WAT and BAT and highlight the importance of developing an understanding of the neural input to brite/beige fat cells as a precursor to its recruitment as therapeutic target.

Anti-obesity effects of the combined administration of CB1 receptor antagonist rimonabant and melanin-concentrating hormone antagonist SNAP-94847 in diet-induced obese mice.

OBJECTIVE: Current anti-obesity monotherapies have proven only marginally effective and are often accompanied by adverse side effects. The cannabinoid 1 (CB1) receptor antagonist rimonabant, while effective at producing weight loss, has been discontinued from clinical use owing to increased incidence of depression. This study investigates the interaction between the cannabinoid and melanin-concentrating hormone (MCH) systems in food intake, body weight control, and mood. DESIGN: Lean male C57BL/6 mice were injected i.p. with rimonabant (0.0, 0.03, 0.3 and 3.0 mg kg(-1)) or the MCH1-R antagonist SNAP-94847 (0.0, 1.0, 5.0 and 10.0 mg kg(-1)) to establish dose response parameters for each drug. Diet-induced obese (DIO) mice were given either vehicle, sub-threshold dose of rimonabant and SNAP-94847 alone or in combination. Impact on behavioral outcomes, food intake, body weight, plasma metabolites and expression of key metabolic proteins in the brown adipose tissue (BAT) and white adipose tissue (WAT) were measured. RESULTS: The high doses of rimonabant and SNAP-94847 produced a reduction in food intake after 2 and 24 h. Combining sub-threshold doses of rimonabant and SNAP-94847 produced a significantly greater loss of body weight in DIO mice compared with vehicle and monotherapies. In addition, combining sub effective doses of these drugs led to a shift in markers of thermogenesis in BAT and lipid metabolism in WAT consistent with increased energy expenditure and lipolysis. Furthermore, co-administration of rimonabant and SNAP-94847 produced a transient reduction in food intake, and significantly reduced fat mass and adipocyte size. Importantly, SNAP-94847 significantly attenuated the ability of rimonabant to reduced immobility time in the forced swim test. CONCLUSION: These results provide proof of principle that combination of rimonabant and a MCH1 receptor antagonist is highly effective in reducing body weight below that achieved by rimonabant and SNAP-94847 monotherapies. In addition, the combination therapy normalizes the rimonabant-induced behavioral changes seen in the forced swim test.

Neural and humoral changes associated with the adjustable gastric band: insights from a rodent model.

BACKGROUND: Bariatric surgical procedures, including the laparoscopic adjustable gastric band (LAGB), are currently the only effective treatments for morbid obesity, however, there is no clear understanding of the mechanisms underpinning the efficacy of LAGB. The aim of this study is to examine changes in activation of the sensory neuronal pathways and levels of circulating gut hormones associated with inflation of an AGB. DESIGN AND RESULTS: The trajectory within the central nervous system of polysynaptic projections of sensory neurons innervating the stomach was determined using the transsynaptically transported herpes simplex virus (HSV). Populations of HSV-infected neurons were present in the brainstem, hypothalamus and cortical regions associated with energy balance. An elevation of Fos protein was present within the nucleus of the solitary tract, a region of the brainstem involved in the control of food intake, following acute and chronic band inflation. Two approaches were used to test (1) the impact of inflation of the band alone (on a standard caloric background) or (2) the impact of a standard caloric meal (on the background of the inflated band) on circulating gut hormones. Importantly, there was a significant elevation of glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) following oral gavage of a liquid meal in animals with pre-inflated bands. There was no impact of inflation of the band alone on circulating GLP-1, PYY or ghrelin in animals on a standard caloric background. CONCLUSION: These data are consistent with the notion that the LAGB exerts its effects on satiety, reduced food intake and reduced body weight by the modulation of both neural and hormonal responses with the latter involving an elevation of meal-related levels of GLP-1 and PYY. These data are contrary to the view that the surgery is purely 'restrictive'.

Brown adipose tissue thermogenesis heats brain and body as part of the brain-coordinated ultradian basic rest-activity cycle.

Brown adipose tissue (BAT), body and brain temperatures, as well as behavioral activity, arterial pressure and heart rate, increase episodically during the waking (dark) phase of the circadian cycle in rats. Phase-linking of combinations of these ultradian (<24 h) events has previously been noted, but no synthesis of their overall interrelationships has emerged. We hypothesized that they are coordinated by brain central command, and that BAT thermogenesis, itself controlled by the brain, contributes to increases in brain and body temperature. We used chronically implanted instruments to measure combinations of bat, brain and body temperatures, behavioral activity, tail artery blood flow, and arterial pressure and heart rate, in conscious freely moving Sprague-Dawley rats during the 12-h dark active period. Ambient temperature was kept constant for any particular 24-h day, varying between 22 and 27 degrees C on different days. Increases in BAT temperature (> or = 0.5 degrees C) occurred in an irregular episodic manner every 94+/-43 min (mean+/-SD). Varying the temperature over a wider range (18-30 degrees C) on different days did not change the periodicity, and neither body nor brain temperature fell before BAT temperature episodic increases. These increases are thus unlikely to reflect thermoregulatory homeostasis. Episodic BAT thermogenesis still occurred in food-deprived rats. Behavioral activity, arterial pressure (18+/-5 mmHg every 98+/-49 min) and heart rate (86+/-31 beats/min) increased approximately 3 min before each increase in BAT temperature. Increases in BAT temperature (1.1+/-0.4 degrees C) were larger than corresponding increases in brain (0.8+/-0.4 degrees C) and body (0.6+/-0.3 degrees C) temperature and the BAT episodes commenced 2-3 min before body and brain episodes, suggesting that BAT thermogenesis warms body and brain. Hippocampal 5-8 Hz theta rhythm, indicating active engagement with the environment, increased before the behavioral and autonomic events, suggesting coordination by brain central command as part of the 1-2 h ultradian basic rest-activity cycle (BRAC) proposed by Kleitman.

Projections of RFamide-related peptide-3 neurones in the ovine hypothalamus, with special reference to regions regulating energy balance and reproduction.

RFamide-related peptide-3 (RFRP-3) is a neuropeptide produced in cells of the paraventricular nucleus and dorsomedial nucleus of the ovine hypothalamus. In the present study, we show that these cells project to cells in regions of the hypothalamus involved in energy balance and reproduction. A retrograde tracer (FluoroGold) was injected into either the arcuate nucleus, the lateral hypothalamic area or the ventromedial nucleus. The distribution and number of retrogradely-labelled RFRP-3 neurones was determined. RFRP-3 neurones projected to the lateral hypothalamic area and, to a lesser degree, to the ventromedial nucleus and the arcuate nucleus. Double-label immunohistochemistry was employed to identify cells receiving putative RFRP-3 input to cells in these target regions. RFRP-3 cells were seen to project to neuropeptide Y and pro-opiomelanocortin neurones in the arcuate nucleus, orexin and melanin-concentrating hormone neurones in the lateral hypothalamic area, as well as orexin cells in the dorsomedial nucleus and corticotrophin-releasing hormone and oxytocin cells in the paraventricular nucleus. Neurones expressing gonadotrophin-releasing hormone in the preoptic area were also seen to receive input from RFRP-3 projections. We conclude that RFRP-3 neurones project to hypothalamic regions and cells involved in regulation of energy balance and reproduction in the ovine brain.

Characterization of the projections to the hypothalamic paraventricular and periventricular nuclei in the female sheep brain, using retrograde tracing and immunohistochemistry.

The paraventricular nucleus (PVN) and the periventricular nucleus (Pe) are important neuroendocrine centers, but the neuronal input to these regions is poorly defined in nonrodent species. We utilized the retrograde transport of injected tracers to determine the neural input to these two nuclei in the ovine brain. Adult Corriedale ewes were studied following FluoroGold injection into either the PVN (n = 5) or the Pe (n = 3). Both the PVN and the Pe were found to receive neuronal input from a number of hypothalamic nuclei. Projections to the PVN from the lateral hypothalamic area were from neurons that produce melanin-concentrating hormone or orexins and a subset of those from the arcuate nucleus were immunopositive for neuropeptide Y and gamma-melanocyte stimulating hormone. This pathway was verified by staining of terminals in the PVN. Input to the PVN from the brain stem was seen to originate from the catecholaminergic and serotoninergic neurons. The projections to the PVN and Pe from hypothalamic and brain stem regions in the sheep brain are generally similar to those in the rat, with some minor differences. These studies highlight the differences in the afferent input to these two closely related nuclei in the ovine brain.

A rodent model of adjustable gastric band surgery-implications for the understanding of underlying mechanisms.

BACKGROUND: Bariatric surgery is currently the only anti-obesity therapy that can deliver weight loss of up to 20-30% of body weight. Laparoscopic adjustable gastric banding (LAGB) and Roux-en-y gastric bypass are the most commonly performed of these surgeries. The mechanisms by which LAGB initiates an increase in satiety remain completely unknown. The aim of this study is to establish a rodent model of adjustable gastric banding (AGB) that will enable investigation of these mechanisms. METHODS: Sprague-Dawley rats were implanted with adjustable gastric bands immediately below the gastro-esophageal junction around the glandular stomach. This band, as in humans, can be inflated via an exteriorized port resulting in an incremental impact on the stomach. RESULTS: Rats with an incremental inflation of the AGB showed a clear stepwise reduction in food intake and body weight. Normal food intake and body weight gain were restored with band deflation. Barium-assisted X-ray of the stomach showed the formation of a small gastric pouch proximal to the inflated band in a manner analogous to the human LAGB. CONCLUSIONS: This is the first animal model of the AGB that allows incremental inflation for optimal tightening of the band in the conscious animal with corresponding effects on food intake and body weight. This model will allow measurement of acute and chronic neural and hormonal changes following activation of the band in the conscious animal and will provide the potential to inform and improve surgical approaches that are at the forefront of obesity treatments.

Neural connectivity in the mediobasal hypothalamus of the sheep brain.

The ventromedial nucleus of the hypothalamus (VMN) and the arcuate nucleus (ARC) are two centres regulating energy balance and food intake, but inter-connectivity of these nuclei is not well defined in non-rodent species. In this study, we performed retrograde tracing and immunohistochemistry in the ovine brain with ewes receiving FluoroGold (FG) injections into either ARC or VMN for the mapping of retrogradely labelled cells. Strong reciprocal connections were found between the two regions. The distribution of the FG labelled neurons in other regions of the hypothalamus and brain stem was also mapped. Some of the cells projecting from ARC to VMN were immunopositive for neuropeptide Y, galanin, adrenocorticotropin (marker of pro-opiomelanocortin cells) or tyrosine hydroxylase (marker of dopaminergic cells). Melanin-concentrating hormone and orexin neurons in the lateral hypothalamic area were also found to provide input to the VMN and ARC. This observed interconnectivity between regions important for metabolic regulation and other neuroendocrine functions presumably allows coordinated functions. Input to both the ARC and VMN from other brain regions, such as brain stem cell groups, provides a further level of regulation. These data provide a substrate upon which further understanding of appetite regulation and neuroendocrine function can be derived in this species.

Lateral hypothalamic 'command neurons' with axonal projections to regions involved in both feeding and thermogenesis.

The concept of 'command neurons', whereby single neurons mediate complex and complementary motor functions to generate a stereotyped behaviour, is well developed in invertebrate physiology. The term has also been adopted more recently to explain the neural basis of 'fight or flight'. In this study we have investigated the possibility that single lateral hypothalamic neurons have the necessary neuroanatomical connections to coordinate two complementary limbs of body weight control, feeding and thermogenesis, thereby acting as 'command neurons'. The transynaptic retrograde transport of pseudorabies virus (Bartha) from a thermogenic endpoint in the brown adipose tissue of rats has been used in conjunction with other neuronal tracers, introduced into putative CNS feeding centres, to assess the potential for the involvement of command neurons in coordinating these processes. In discrete regions of the lateral hypothalamus, neurons have been identified which have the necessary complement of orexigenic peptides and collateral branching axons to both putative feeding sites and thermogenic sites in brown fat to qualify as candidate central command neurons controlling body weight.

Effect of central administration of QRFP(26) peptide on energy balance and characterization of a second QRFP receptor in rat.

The recently identified neuropeptide QRFP(26) is predominantly expressed in the hypothalamus and was suggested to play a role in the regulation of food intake following the observation of an acute orexigenic effect after central administration in mice. QRFP(26) exerts its effect via GPR103 and a newly identified receptor in mouse. The aim of our study was (a) to investigate the distribution of QRFP(26) and a newly discovered QRFP receptor mRNA in rat and (b) to further characterize the effects of central administration of QRFP(26) on energy balance in rats. QRFP(26) mRNA was detected in the retrochiasmatic nucleus, periventricular nucleus, arcuate nucleus and restricted areas of the lateral nucleus of the hypothalamus. We found an additional receptor with high homology for GPR103 in rat. This receptor increases inositol triphosphate production in transfected cells in presence of QRFP(26) and its mRNA was particularly enriched in ventral and posterior thalamic groups, anterior hypothalamus and medulla. When QRFP(26) (10 microg and 50 microg) was administered centrally before the start of the light phase both doses increased food intake for 2 h after injection without reaching statistical significance. QRFP(26) caused no changes in locomotor activity or energy expenditure. In summary, central QRFP(26) injection causes slight and transient hyperphagia in rats without changing any other energy balance parameters after 24 h. We conclude that QRFP(26) has limited impact on the central regulation of energy balance in rats and that its essential function remains to be clarified.

Physiological and pathophysiological influences on thirst.

Thirst motivates animals to seek fluid and drink it. It is regulated by the central nervous system and arises from neural and chemical signals from the periphery interacting in the brain to stimulate a drive to drink. Our research has focussed on the lamina terminalis and the manner in which osmotic and hormonal stimuli from the circulation are detected by neurons in this region and how that information is integrated with other neural signals to generate thirst. Our studies of osmoregulatory drinking in the sheep and rat have produced evidence that osmoreceptors for thirst exist in the dorsal cap of the organum vasculosum of the lamina terminalis (OVLT) and in the periphery of the subfornical organ, and possibly also in the median preoptic nucleus. In the rat, the hormones angiotensin II and relaxin act on neurons in the periphery of the subfornical organ to stimulate drinking. Studies of human thirst using functional magnetic resonance imaging (fMRI) techniques show that systemic hypertonicity activates the lamina terminalis and the anterior cingulate cortex, but the neural circuitry that connects sensors in the lamina terminalis to cortical regions subserving thirst remains to be determined. Regarding pathophysiological influences on thirst mechanisms, both excessive (polydipsia) and inadequate (hypodisia) water intake may have dire consequences. One of the most common primary polydipsias is that observed in some cases of schizophrenia. The neural mechanisms causing the excessive water intake in this disorder are unknown, so too are the factors that result in impaired thirst and inadequate fluid intake in some elderly humans.

Vasopressin secretion: osmotic and hormonal regulation by the lamina terminalis.

The lamina terminalis, located in the anterior wall of the third ventricle, is comprised of the subfornical organ, median preoptic nucleus (MnPO) and organum vasculosum of the lamina terminalis (OVLT). The subfornical organ and OVLT are two of the brain's circumventricular organs that lack the blood-brain barrier, and are therefore exposed to the ionic and hormonal environment of the systemic circulation. Previous investigations in sheep and rats show that this region of the brain has a crucial role in osmoregulatory vasopressin secretion and thirst. The effects of lesions of the lamina terminalis, studies of immediate-early gene expression and electrophysiological data show that all three regions of the lamina terminalis are involved in osmoregulation. There is considerable evidence that physiological osmoreceptors subserving vasopressin release are located in the dorsal cap region of the OVLT and possibly also around the periphery of the subfornical organ and in the MnPO. The circulating peptide hormones angiotensin II and relaxin also have access to peptide specific receptors (AT(1) and LGR7 receptors, respectively) in the subfornical organ and OVLT, and both angiotensin II and relaxin act on the subfornical organ to stimulate water drinking in the rat. Studies that combined neuroanatomical tracing and detection of c-fos expression in response to angiotensin II or relaxin suggest that both of these circulating peptides act on neurones within the dorsal cap of the OVLT and the periphery of the subfornical organ to stimulate vasopressin release.

The sensory circumventricular organs of the mammalian brain.

The brain's three sensory circumventricular organs, the subfornical organ, organum vasculosum of the lamina terminalis and the area postrema lack a blood brain barrier and are the only regions in the brain in which neurons are exposed to the chemical environment of the systemic circulation. Therefore they are ideally placed to monitor the changes in osmotic, ionic and hormonal composition of the blood. This book describes their. General structure and relationship to the cerebral ventricles Regional subdivisions Vasculature and barrier properties Neurons, glia and ependymal cells Receptors, neurotransmitters, neuropeptides and enzymes Neuroanatomical connections Functions.

The effect of urocortin on ingestive behaviours and brain Fos immunoreactivity in mice.

The influence of urocortin (UCN) on ingestive behaviours and brain neural activity, as measured immunohistochemically by the presence of Fos protein, was determined in mice. Rat UCN was administered by continuous intracerebroventricular (ICV) or subcutaneous (SC) infusion. ICV infusion of UCN (100 ng/h, 14 days) transiently reduced daily food and water intakes (days 1-4) but body weight was reduced from day 2 into the post-infusion period. Sodium intake was reduced from day 3 to the end of infusion. SC infusion of UCN caused similar but smaller reductions in food and water intakes and body weight, without change in sodium intake. In separate experiments, Fos immunoreactivity was increased in several brain nuclei known to be involved in the control of body fluid and energy homeostasis, e.g. central nucleus of the amygdala, median preoptic nucleus, bed nucleus of the stria terminalis and arcuate nucleus. Increased Fos expression was similar for ICV and SC infusions when measured on days 2-3 or 6-7 of infusion. In conclusion, increases of brain activity by UCN may be associated with stimulation of adrenocorticotrophic hormone release and sympathetic nervous activity, but increases may also indicate suppression of ingestive behaviours by stimulating central inhibitory mechanisms located in areas known to control body fluid and energy homeostasis.

Circulating angiotensin II activates neurones in circumventricular organs of the lamina terminalis that project to the bed nucleus of the stria terminalis.

The aim of this study was to determine, in conscious rats, whether elevated concentrations of circulating angiotensin II activate neurones in both the subfornical organ and organum vasculosum of the lamina terminalis (OVLT) that project to the bed nucleus of the stria terminalis (BNST). The strategy employed was to colocalize retrogradely transported cholera toxin B subunit (CTB) from the BNST, with elevated levels of Fos protein in response to angiotensin II. Circulating angiotensin II concentrations were increased by either intravenous infusion of angiotensin II or subcutaneous injection of isoproterenol. Neurones exhibiting Fos in response to angiotensin II were present in the subfornical organ, predominantly in its central core but with some also seen in its peripheral aspect, the dorsal and lateral margins of the OVLT, the supraoptic nucleus and the parvo- and magnocellular divisions of the paraventricular nucleus. Fos-labelling was not apparent in control rats infused with isotonic saline intravenously or injected with either CTB or CTB conjugated to gold particles (CTB-gold) only. Of the neurones in the subfornical organ that were shown by retrograde labelling to project to BNST, approximately 50% expressed Fos in response to isoproterenol. This stimulus also increased Fos in 33% of neurones in the OVLT that project to BNST. Double-labelled neurones were concentrated in the central core of the subfornical organ and lateral margins of the OVLT in response to increased circulating angiotensin II resulting from isoproterenol treatment. These data support a role for circulating angiotensin II acting either directly or indirectly on neurones in subfornical organ and OVLT that project to the BNST and provide further evidence of functional regionalization within the subfornical organ and the OVLT. The function of these pathways is yet to be determined; however, a role in body fluid homeostasis is possible.