Reduction In Voluntary Food Intake Research Articles

Adolescent activity-based anorexia has a substantial and prolonged impact on social behavior in young adult female rats

Activity-based anorexia (ABA) is a rodent model of anorexia nervosa (AN) that induces several key components of AN, including voluntary reduction in food intake, reduced body weight, hyperactivity, and alterations to the hypothalamic-pituitary-adrenal (HPA) axis. Previous research has demonstrated persistently increased anxiety-like behavior in the elevated plus maze (EPM), a test measuring avoidance of novel and open areas in adult female rats that experienced ABA during adolescence and are weight-restored in adulthood. Whether the same behavioral effects of two bouts of adolescent ABA emerge in response to different anxiety-provoking stimuli, however, has not been explored. We used the social partition (SP), novelty suppressed feeding (NSF), marble burying, and EPM tests to explore whether two bouts of adolescent ABA have persistent effects on anxiety-like behavior in weight restored young adult female rats. One-way ANOVA analyses revealed that female rats that experienced two bouts of ABA during adolescence had increased anxiety-like behavior in the EPM and SP tests in young adulthood following weight restoration compared with controls. These data demonstrate that the enduring behavioral effects of two bouts of adolescent ABA are specific to particular anxiety-provoking stimuli and suggest that adolescent ABA has enduring effects on social relationships.

Reduction in voluntary food intake, but not fasting, stimulates hypothalamic gonadotropin-inhibitory hormone precursor mRNA expression in chicks under heat stress

Heat stress is an issue of rising concern across the globe. Recently, we found that mRNA expression of gonadotropin-inhibitory hormone (GnIH), an orexigenic neuropeptide, was increased in the heat-exposed chick brain when food intake was reduced. The aim of the current study was to examine mRNA expression of GnIH and of the glucocorticoid receptors (GRs) in the hypothalamus as well as the plasma corticosterone (CORT) and metabolites in 14-d-old chicks exposed to a high ambient temperature (HT; 40 ± 1 °C for 1 or 5 h) or a control thermoneutral temperature (CT; 30 ± 1 °C), either with free access to food or fasted. Heat stress caused a voluntary reduction of food intake and reduced plasma triacylglycerol concentration, but increased rectal temperature and plasma CORT and glucose concentrations (P < 0.05). Heat stress also increased (P < 0.05) the expression of diencephalic GnIH mRNA in chicks when they reduced food intake voluntarily, but did not do so under fasting conditions. Although the expression of GR mRNA was not altered as a result of heat stress, its expression was decreased (P < 0.05) in fasted chicks at 5 h in comparison with fed chicks. In addition, the rectal temperature of fasted chicks was lower than that of fed chicks under both CT and HT. In conclusion, voluntary reduction of food intake caused an increase in brain GnIH mRNA expression, plasma CORT, and body temperature in chicks under heat stress. Interestingly, brain GnIH mRNA expression was not induced by heat stress in fasted chicks and was not accompanied by a decrease in rectal temperature. These results suggest that the increased expression of brain GnIH mRNA in chicks under heat stress could be a consequence of a mechanism mediated by the voluntary reduction of food intake, but that it is not a consequence of fasting.

Assessing Activity-based Anorexia in Mice.

Rodents develop activity-based anorexia (ABA) when exposed to a restricted feeding schedule and allowed free access to a running wheel. These conditions lead to a life-threatening reduction in body weight. However, rodents exposed to only one of these conditions ultimately adapt to re-establish normal body weight. Although increased running coupled with reduction in voluntary food intake appear paradoxical under ABA conditions, ABA behavior is observed across numerous mammalian species. The ABA paradigm provides an animal model for anorexia nervosa (AN), an eating disorder with severe dysregulation of appetite-behavior. Subjects are singly housed with free access to a running wheel. Each day, the subject is offered food for a limited amount of time. During the course of the experiment, a subject's body weight decreases from high activity and low caloric intake. The duration of the study varies based on how long food is offered daily, the type of food offered, the strain of mouse, if drugs are being tested, and environmental factors. A lack of effective pharmacological treatments for AN patients, their low quality of life, high cost of treatment, and their high mortality rate indicate the urgency to further research AN. We provide a basic outline for performing ABA experiments with mice, offering a method to investigate AN-like behavior in order to develop novel therapies. This protocol is optimized for use in Balb/cJ mice, but can easily be manipulated for other strains, providing great flexibility in working with different questions, especially related to genetic factors of ABA.

Anorexia Reduces GFAP+ Cell Density in the Rat Hippocampus.

Anorexia nervosa is an eating disorder observed primarily in young women. The neurobiology of the disorder is unknown but recently magnetic resonance imaging showed a volume reduction of the hippocampus in anorexic patients. Dehydration-induced anorexia (DIA) is a murine model that mimics core features of this disorder, including severe weight loss due to voluntary reduction in food intake. The energy supply to the brain is mediated by astrocytes, but whether their density is compromised by anorexia is unknown. Thus, the aim of this study was to estimate GFAP+ cell density in the main regions of the hippocampus (CA1, CA2, CA3, and dentate gyrus) in the DIA model. Our results showed that GFAP+ cell density was significantly reduced (~20%) in all regions of the hippocampus, except in CA1. Interestingly, DIA significantly reduced the GFAP+ cells/nuclei ratio in CA2 (−23%) and dentate gyrus (−48%). The reduction of GFAP+ cell density was in agreement with a lower expression of GFAP protein. Additionally, anorexia increased the expression of the intermediate filaments vimentin and nestin. Accordingly, anorexia increased the number of reactive astrocytes in CA2 and dentate gyrus more than twofold. We conclude that anorexia reduces the hippocampal GFAP+ cell density and increases vimentin and nestin expression.

Hypothalamic Agouti-Related Peptide mRNA is Elevated During Natural and Stress-Induced Anorexia.

As part of their natural lives, animals can undergo periods of voluntarily reduced food intake and body weight (i.e. animal anorexias) that are beneficial for survival or breeding, such as during territorial behaviour, hibernation, migration and incubation of eggs. For incubation, a change in the defended level of body weight or ‘sliding set point’ appears to be involved, although the neural mechanisms reponsible for this are unknown. We investigated how neuropeptide gene expression in the arcuate nucleus of the domestic chicken responded to a 60–70% voluntary reduction in food intake measured both after incubation and after an environmental stressor involving transfer to unfamiliar housing. We hypothesised that gene expression would not change in these circumstances because the reduced food intake and body weight represented a defended level in birds with free access to food. Unexpectedly, we observed increased gene expression of the orexigenic peptide agouti‐related peptide (AgRP) in both incubating and transferred animals compared to controls. Also pro‐opiomelanocortin (POMC) mRNA was higher in incubating hens and significantly increased 6 days after exposure to the stressor. Conversely expression of neuropeptide Y and cocaine‐ and amphetamine‐regulated transcript gene was unchanged in both experimental situations. We conclude that AgRP expression remains sensitive to the level of energy stores during natural anorexias, which is of adaptive advantage, although its normal orexigenic effects are over‐ridden by inhibitory signals. In the case of stress‐induced anorexia, increased POMC may contribute to this inhibitory role, whereas, for incubation, reduced feeding may also be associated with increased expression in the hypothalamus of the anorexigenic peptide vasoactive intestinal peptide.

Dehydration-Induced Anorexia Reduces Astrocyte Density in the Rat Corpus Callosum.

Anorexia nervosa is an eating disorder associated with severe weight loss as a consequence of voluntary food intake avoidance. Animal models such as dehydration-induced anorexia (DIA) mimic core features of the disorder, including voluntary reduction in food intake, which compromises the supply of energy to the brain. Glial cells, the major population of nerve cells in the central nervous system, play a crucial role in supplying energy to the neurons. The corpus callosum (CC) is the largest white matter tract in mammals, and more than 99% of the cell somata correspond to glial cells in rodents. Whether glial cell density is altered in anorexia is unknown. Thus, the aim of this study was to estimate glial cell density in the three main regions of the CC (genu, body, and splenium) in a murine model of DIA. The astrocyte density was significantly reduced (~34%) for the DIA group in the body of the CC, whereas in the genu and the splenium no significant changes were observed. DIA and forced food restriction (FFR) also reduced the ratio of astrocytes to glial cells by 57.5% and 22%, respectively, in the body of CC. Thus, we conclude that DIA reduces astrocyte density only in the body of the rat CC.

Pathogen-induced anorexia: a herbivore strategy or an unavoidable consequence of infection?

A reduction in voluntary food intake is a common feature of infection with pathogens and is frequently referred to as pathogen-induced anorexia. Anorexia has been previously viewed either as an unavoidable consequence of infection or as an animal strategy that enables them to cope with the consequences of infection. Both approaches lead to certain expectations as far as the characteristics of anorexia are concerned. By linking anorexia to host immune response one should be able to make predictions about when and for how long anorexia would occur. By appreciating what an infected animal is trying to achieve through its feeding behaviour, one would be able to make predictions about the extent of anorexia on different quality foods. The thesis of the paper is that these approaches should no longer be viewed as mutually exclusive, but, by combining them, one should be able to make pathogen-induced anorexia more predictable. This is done in the development of a model that aims to predict the food intake of grazing sheep exposed to an abomasal parasite. The predictions of the model are consistent with the features and consequences of parasite-induced anorexia of sheep given access to moderate and high quality foods. However, there is a degree of uncertainty about the validity of predictions made by the model on anorexia seen on poor quality foods of low energy content. This is not a deficiency of the model developed but can be attributed to the lack of appropriate experiments against which model predictions can be tested.

P039 NUTRITIONAL STATUS OF NURSING HOME RESIDENTS

Rationale: Limited information exists on the efficacy of high energy density (>2 kcal/ml) oral nutritional supplements (ONS). This pilot study investigated elderly patients’ compliance with a novel, low volume, energy dense (2.4 kcal/ml) ONS and its effects on food and total energy intakes, appetite and anthropometry. Methods: Thirty one community-based patients identified at risk of malnutrition (using “MUST”, www.bapen.org.uk) were recruited (mean age: 82±12years, mean body mass index (BMI) 20.3±2.4 kg/m2, 52% medium risk, 48% high risk). Patients were offered two 125ml, 2.4 kcal/ml oral nutritional supplements (Fortisip Compact, Nutricia; total provision 600 kcal, 24 g protein in 250ml) daily in addition to the diet for 4 weeks. Compliance, palatability and tolerance of the supplement and its effects on food and total energy intake, hunger (100mm visual analogue scale) and anthropometry (body weight, mid upper arm circumference, MUAC) were assessed. Results are presented as mean±SD. Results: Compliance with supplementation was 97% with mean wastage per bottle of 4ml (3% of bottle volume). There were no significant gastro-intestinal side effects with supplementation and > 80% of patients rated the supplement pleasant and convenient. Patients’ mean total daily energy intake significantly increased (from 1430±599 kcal to 1965±596 kcal, p = 0.0001) with supplementation, with no significant reduction in voluntary food intake and a significant increase in hunger score (from 24±24mm to 36±24mm, p = 0.018). A small but significant increase in body weight (+0.9 kg, p = 0.009) and mid upper arm circumference (+0.3 cm, p = 0.025) were observed. Conclusion: This pilot study in community patients shows that compliance with a high energy density (2.4 kcal/ml), low volume supplement is excellent, leading to significant improvements in total energy intakes and anthropometry. Further controlled study is required to ascertain the clinical benefits of using such an energy dense supplement in the management of patients with malnutrition.

The effects of pathogen challenges on the performance of naïve and immune animals: the problem of prediction

Predictive frameworks for performance under both physical and social stressors are available, but no general framework yet exists for predicting the performance of animals exposed to pathogens. The aim of this paper was to identify the key problems that would need to be solved to achieve this. Challenges of a range of hosts by a range of pathogens were reviewed to consider reductions in growth beyond those associated with reductions in voluntary food intake (VFI). Pair-feeding and marginal response studies identified the extent and mechanisms of how further reductions in growth occur beyond those caused by reduced VFI. Further reductions in growth depended on the pathogen, the host and the dose and were time dependent. In some instances the reduction in VFI fully explained the reduction in growth. Marginal response experiments showed increased maintenance requirements during exposure to pathogens, but these were different for specific amino acids. There were no clear effects on marginal efficiency. Innate immune functions, repair of damaged tissue and expression of acquired immunity caused significant but variable increases in protein (amino acid) requirements. More resistant genotypes had greater requirements for mounting immune responses. The partitioning of protein (amino acids) was found to be different during pathogen challenges. Prediction of the requirements and partitioning of amino acids between growth and immune functions appears to be a crucial problem to solve in order to predict performance during pathogen challenges of different kinds and doses. The problems of accounting for reductions in performance during pathogen challenges that are described here provide a useful starting point for future modelling and experimental solutions.

Responses in production and body composition traits in ad libitum fed pigs from lines selected for high and low growth rate on a fixed ration

Large White pigs from lines which had been divergently selected over 4 years for high and for low post-weaning daily gain on a fixed but restricted ration of approximately 80% of ad libitum, were sampled for growth testing on ad libitum individual feeding during a 6-week period starting at 50 kg. Genetic parameters and breeding values for performance and carcass composition traits were estimated on 758 pigs with pedigrees comprising a total of 5324 animals, using restricted maximum likelihood (REML) and best linear unbiased prediction (BLUP) methods applied to a multiple trait animal model. Selection resulted in significant differences between the lines. Average breeding values (± S.E.) for the high and low growth lines respectively were 24.3 and − 13.4 g/day (4.1) for test daily gain (TDG), − 0.29 and 0.50 mm (0.09) for ultrasonic P2 fat depth (UBF), − 15 and 22 g/day (5.3) for daily food intake during test (TFI), − 0.11 and 0.10 (0.01) for food conversion ratio during test (TFC), 7.2 and − 4.3 g/day (2.4) for lifetime daily gain (LDG), 5.9 and − 3.2 g/day (1.8) for carcass weight daily gain (CDG), − 0.90 and 1.25 mm (0.21) for carcass fat (CFT). Phenotypic differences between the lines were similar to these breeding value differences. Compared with low growth selection, the correlated genetic responses to high growth selection on restricted feeding measured in these ad libitum fed pigs were economically desirable for both performance and carcass composition traits. The increase in growth and decrease in fatness, associated with a reduction in voluntary food intake in the high line pigs, suggested a reduced energy cost of the gain relative to the low growth line. It is concluded that selection for high growth rate on restricted feeding will produce pigs which perform more profitably on ad libitum individual feeding.

Amino Acids Stimulate Muscle Protein Synthesis In The Elderly More Effectively Than Intact Protein

PURPOSE To combat the debilitating progression of sarcopenia, a nutritional supplement should provide a calorically efficient anabolic stimulus that does not result in a compensatory reduction in voluntary food intake. We sought to quantify net muscle protein synthesis in healthy elderly individuals following bolus oral ingestion of an intact whey protein supplement (whey: n=5, 70 ± 6 yr) and an essential amino acid supplement (EAA: n= 7, 67 ± 2 yr). METHODS Femoral arterio-venous blood samples and vastus lateralis muscle biopsy samples were obtained during a primed, constant infusion of L-[ring-2H5]phenylalanine. Muscle protein kinetics and mixed muscle fractional synthetic rate (FSR) were calculated during the post-absorptive period and for 3 h following ingestion of 15g EAA or 15g whey. RESULTS EAA ingestion stimulated net phenylalanine uptake and FSR more than whey protein. Postabsorptive FSR values were 0.056 ± 0.004 %.hr−1 (EAA) and 0.053 ± 0.004 %.hr−1 (whey), p > 0.05), while postprandial FSR values increased to 0.088 ± 0.011 %.hr−1 (EAA) and 0.072 ± 0.04 %.hr−1 (whey), (p < 0.05). CONCLUSIONS Compared to an equivalent quantity of intact protein, EAAs may provide a more effective and energetically efficient anabolic nutritional supplement for elderly individuals.

The effect of concurrent corticosteroid induced immuno-suppression and infection with the intestinal parasite Trichostrongylus colubriformis on food intake and utilization in both immunologically naïve and competent sheep

AbstractThe nutritional cost of both the acquisition and maintenance of immunity to gastro-intestinal nematodes was investigated using immunologically naïve 5-month-old lambs and immunologically competent 17-month-old ewes. Within each age cohort, animals were either infected with the equivalent of 80 L3Trichostrongylus colubriformislarvae per kg live weight (LW) per day (IF), similarly infected and concurrently immuno-suppressed with weekly injections of 1·3 mg/kg LW of the glucocorticoid methylprednisolone acetate (ISIF), immuno-suppressed only (IS) or remained as controls (C). Body composition of all animals was estimated using X-ray computer tomography on days -14 and 76 relative to the start of infection. Body weight and faecal nematode egg counts (FEC; eggs per gram of fresh faeces (e.p.g.)) were taken weekly and blood samples for serum proteins and antibodies were obtained every 2 weeks. FEC in IF lambs peaked at 1250 e.p.g. before a typical decline as immunity developed to less than 100 e.p.g. by day 75. FEC of less than 100 e.p.g. in IF ewes indicated immunity was maintained. Successful immuno-suppression in ISIF lambs and ewes was indicated by FEC of 4000 e.p.g. on day 75 and was confirmed by comparative worm burdens and serum antibody titres. The typical reduction in voluntary food intake (VFI) as a consequence of infection was observed in IF lambs (proportionately 0·30,P&lt; 0·001) but not in IF ewes, ISIF lambs or ISIF ewes. Gross efficiency of use of metabolizable energy for net energy deposition was reduced by proportionately 0·20 in lambs during acquisition of immunity and by 0·16 in ewes maintaining an established immunity. Infection in immuno-suppressed animals reduced efficiency by 0·05 and 0·15 for lambs and ewes, respectively. These findings allowed the hypothesis that the reduction in VFI and loss in performance in young parasitised sheep is caused by physiological signalling associated with the acquisition phase of the host immune response to infection, rather than simply the damage caused by the parasiteper se.

Y2 Receptor-Selective Agonist Delays the Estrogen-Induced Luteinizing Hormone Surge in Ovariectomized Ewes, but Y1-Receptor-Selective Agonist Stimulates Voluntary Food Intake

Neuropeptide Y (NPY) plays a major role in the regulation of food intake, regulation of homeostasis, and neuroendocrine function. We have previously shown that third ventricular infusion of this peptide delays the estradiol benzoate-induced surge in LH secretion in ovariectomized ewes. To determine the receptor subtype that transmits this effect, we have now used the same model to infuse a Y1 receptor agonist [NPY Leu31 Pro34], a Y2 receptor agonist (PYY3-36), and a Y4 receptor agonist (pancreatic polypeptide). We monitored the surges in animals given these agonists or artificial cerebrospinal fluid by measuring plasma LH levels, and we also measured daily voluntary food intake (VFI). A low (7 microg/h) dose of Y2 agonist delayed the surge but did not affect VFI, whereas a higher dose (14 microg/h) stimulated VFI. A dose of 18 microg/h of the Y1 agonist did not affect surge generation but also stimulated VFI. A dose of 24 microg/h of Y4 agonist affected neither surge generation nor VFI. These specificities are different from those reported for the rat and human (in which a Y2 agonist causes reduction in VFI). We conclude that, in sheep, the negative regulation of the reproductive axis by NPY and Y-receptor agonists is effected via the Y2 receptors, whereas the orexigenic effects are most likely effected via the Y1 receptors.

Keeping Obesity and Metabolic Syndrome at Bay with Central Leptin and Cytokine Gene Therapy

The incidence of obesity and metabolic syndrome along with the annual cost of treating obesity and related metabolic disorders are rising steeply world wide. In this article, the potential of gene therapy application directly into the hypothalamus, a CNS site involved in integration of energy homeostasis, as a therapeutic modality is reviewed. We engineered a non-immunogenic, non-pathogenic recombinant adeno-associated virus vector to encode leptin, leptin receptor, or the cytokines, leukemia inhibitory factor and ciliary neurotrophic factor. A single injection of virus vectors encoding any of these genes either intraventricularly or into selected hypothalamic sites of wild type or genetically obese rodents curtailed the gradual age-related and rapid high fat diet-induced obesity for long periods. Parameters of metabolic syndrome, hyperleptinemia, hyperinsulinemia and hyperlipidemia were normalized along with fat depletion and increased non-shivering thermogenic energy expenditure either alone or in association with voluntary reduction in food intake. Operation of hypothalamic appetite and energy regulating network was correspondingly modified to conform with the anorectic and obesity suppressing effects of central leptin and cytokine gene therapy. These results advocate central gene therapy as a viable alternative to curb the rising tide of obesity and associated metabolic diseases with or without a voluntary reduction in food intake. Keywords: gene therapy, cytokines, leptin, viral vectors, adeno-associated virus, hypothalamus, adiposity, metabolic syndrome, hyperinsulinemia, type 2 diabetes

Obesity and metabolic syndrome: long-term benefits of central leptin gene therapy.

The recent rapid rise in the incidence of obesity has prompted investigations into understanding the hormonal and neuronal pathways involved in body weight homeostasis in order to devise novel therapeutic strategies. The early enthusiasm for the adipocyte hormone leptin as a regulator of fat mass was largely discarded because of the apparent development of leptin resistance, as seen in obese subjects with elevated blood leptin levels. We postulated that this leptin ineffectiveness may be caused by a lack of leptin availability at target sites in the hypothalamus. To test this hypothesis, we used viral vectors to introduce the leptin gene into the brain for a sustained supply of leptin in the hypothalamus. A single injection of recombinant adeno-associated virus encoding the leptin gene (rAAV-lep) into the third cerebroventricle prevented the aging-associated gradual increase in body weight and adiposity in adult rats for 6 months of the experiment. When administered to prepubertal rats, significantly lower body weight gain and adiposity were maintained for up to 10 months of the experiment. In addition, obesity was prevented in rats introduced to a high-fat diet and also reversed in obese-prone rats maintained on a high-fat diet. Body weight homeostasis and loss of adiposity by leptin gene therapy was achieved by an increase in energy expenditure, and when the rAAV-lep titer was increased, there was also a voluntary reduction in food intake. Importantly, this therapy reduced blood levels of insulin, triglycerides and free fatty acids, the pathophysiologic correlates of the metabolic syndrome. Thus, the long-term beneficial effects of central leptin gene therapy may herald the development of newer therapeutic strategies to control the epidemic of obesity and related metabolic disorders.

Modelling the effect of high, constant temperature on food intake in young growing pigs

AbstractPerformance in pigs is greatly reduced during periods of heat stress through a reduction in voluntary food intake (VFI). However, little information is available as to what extent growth in piglets is affected by high temperature. The objective of this study was therefore to quantify the change in VFI as affected by environmental temperature. Piglets, initially 15·5 (s.e. 1·9) kg body weight (BW), were individually housed and exposed over a period of 17 days to either 19, 21, 23, 25, 27, 29, 31, 33, or 35ºC. Animals had ad libitum access to a starter diet and water. VFI was measured daily whereas BW was determined twice weekly. Over the 17 days, daily VFI and BW gain were proportionately 0·48 and 0·51 lower at 35ºC than at 19ºC. Due to the reduced VFI at high temperatures, the average BW during the experiment was greater at low temperatures than at high temperatures. Consequently, part of the difference in VFI is directly due to temperature and part may be explained by cascading, indirect effects (i.e. the increased BW). To account for this, VFI was expressed as a power function of BW (VFI = aBWb). It was assumed that environmental temperature affected the scalar (a) through a quadratic or a ‘plateau-linear decline’ function of temperature. The VFI appeared relatively constant between 19 and 25ºC (0·096 (kg/day)/(kg BW0·83)) and decreased thereafter. Between 25 and 35ºC, VFI decreased on average by proportionately 0·28 in a 20-kg pig.

Food bulk: Its measurements and their relationship to the voluntary food intake of pigs

When a highly digestible food is progressively diluted with one of greater ‘bulk’ the prevailing view is that the rate of food intake will initially increase at such a rate such that DE intake remains constant and, that beyond a critical point, intake of food and DE will fall as the dilution proceeds further. The critical point has been assumed to reflect the capacity of the pig for ‘bulk’. Current models which attempt to predict the voluntary food intake (VFI) of pigs use either food dry matter (DM) as a measure of bulk (eg Whittemore, 1983) or the undigested organic matter (eg Roan, 1991), or ignore the problem (ARC, 1981). It has long been known however, that such views are likely to be inadequate across the complete range of foods (eg the significant reduction in VFI of pigs on foods based on sugar beet pulp, compared to that on other more undigestible materials).The experiment described here was designed (i) to try to identify the property of ‘bulky’ foods which might be responsible for limiting their VFI and (ii) to see the extent to which the capacity for a ‘bulky’ food might be modified by prior experience.

Identification of a seasonal elevation in daytime melatonin levels associated with the rut in fallow bucks (Dama dama): The effect of day length and exogenous melatonin

The timing of the seasonal reduction in voluntary food intake and hormonal changes associated with the rut were investigated in mature fallow bucks subjected to artificial long-day exposure with and without superimposed melatonin-releasing implants. Circulating testosterone profiles and the period of inappetence, signalling the onset of the period of reproductive activity in untreated bucks under natural photoperiod, were phase-advanced in both treatment groups. In the long-day treated group, these profiles were phase-advanced by 1 week, while in the long-day + melatonin group, the phase advance was 6 weeks compared to the controls. Circulating daytime melatonin, elevated in all three groups, corresponds with seasonal changes in circulating testosterone levels associated with the rut. Prolactin profiles followed ambient photoperiod, being high during natural or artificial long days and low during natural short days. Exogenous melatonin administered during long-day exposure initiated a rapid and reversible decrease in circulating prolactin levels. The elevation in plasma melatonin could not be separated temporally from the seasonal testosterone peak by exposure to long days or to exogenous melatonin. However, this daytime melatonin profile was abolished by the ablation of circulating testosterone following immunization against luteinizing hormone releasing hormone (LHRH). The presence of this endogenous melatonin during daylight was observed only during the rut, as measured in two radioimmunoassays and confirmed by mass spectrometry. It is likely that both testosterone and melatonin influence the onset of the seasonal rut in fallow bucks.

Effects of chronic long-acting bromocriptine treatment on liveweight, voluntary food intake, coat growth and breeding season in non-pregnant red deer hinds.

Seventeen red deer hinds were housed in individual pens and from 28 February until 11 November were injected each week with vehicle (group A; n = 6) or 5 (group B; n = 6) or 12.5 mg (group C; n = 5) of a long-acting formulation of bromocriptine. Liveweight and voluntary food intake (VFI) were recorded for each hind, and blood was collected for determination of progesterone, prolactin, tri-iodothyronine (T3) and cortisol concentrations by radioimmunoassay. Treatment with the high dose of bromocriptine was associated with a significant (P less than 0.05) reduction in VFI, with the effect being greatest between March and July. There was no treatment effect on liveweight, but there was a significant (P less than 0.01) interaction between time and treatment due to the faster rate of weight gain in control animals at the beginning of the experiment. Changes in liveweight could be explained by changes in VFI rather than by changes in the efficiency of utilization of intake. Termination of the breeding season was significantly (P less than 0.01) delayed by 54 days in group C hinds. Growth of the summer coat and subsequent winter coats was delayed by 1 and 3 months respectively in group C hinds, and in groups B and C the duration that animals were in summer coat was increased by about 1 month. The seasonal increase in prolactin concentrations was seen in all groups, but levels were significantly (P less than 0.05) lower in group C hinds. Concentrations of T3 and cortisol were not affected by bromocriptine.

Reduced synthetic activity as a contributing factor to weight-loss in the circannüal cycle of Richardson's ground squirrels

1. 1. Glycogen concentrations in Richardson's ground squirrels of the weight-loss phase were 1/4-1/2 those in animals of the weight-gain phase. White adipose lipid content was similar in animals in the two phases when total body weight was similar. 2. 2. Specific activity of 14C in muscle glycogen of fed, starved and refed ground squirrels in the weight-loss phase was similar to that in starved weight-gain phase animals. Activity in adipose lipids of fed, starved, and refed ground squirrels in the weight-gain phase was 5–8 times greater than that in the same nutritional states in weight-loss phase animals. 3. 3. In addition to a voluntary reduction in food intake, a depressed synthetic activity in lipids and glycogen may account in part for the rapid decrease in body weight during the weight-loss phase of the circannual cycle.