Effects of beacon on the rat pituitary-adrenocortical axis response to stress

Beacon is a peptide expressed in the rat hypothalamus and adrenal cortex, which is involved in the central regulation of feeding and inhibits basal and agonist-stimulated glucocorticoid secretion from adrenocortical cells. In vivo studies on beacon have not yet been carried out, and therefore we investigated the effects of a subcutaneous (sc) injection of beacon on the response of rat hypothalamo-pituitary-adrenal axis to stress. Handling and sc injection per se elicited a moderate increase in the plasma concentrations of ACTH and corticosterone, which was counteracted by beacon. Similarly, beacon dampened ACTH and corticosterone responses to ether stress. In contrast, beacon did not affect ACTH response to cold stress, although it was able to induce a moderate lowering in the corticosterone response. Taken together, these findings allow us to draw the following conclusions: i) beacon inhibits handling/injection- and ether stress-activated, but not cold stress-activated, neural mechanism(s) responsible for stimulation of ACTH secretion and the ensuing increase in corticosterone production; and ii) the beacon-induced dampening in corticosterone response to stress also involves a direct inhibitory effect on the adrenal-cortex secretory activity. The physiological relevance of beacon as endogenous anti-stress agent remains to be evaluated.     

Vagal afferents mediate the feeding response to mercaptoacetate but not to the beta (3) adrenergic receptor agonist CL 316,243

To evaluate the role of subdiaphragmatic vagal afferents in the anorectic response to peripheral administration of the highly selective beta(3)-adrenergic receptor agonist CL 316,243 (CL), we tested the ability of intraperitoneal (IP) injections of CL to inhibit feeding in rats with subdiaphragmatic vagal deafferentation (SDA, n=13) or sham surgeries (SHAM, n=13). Doses of 10, 100 and 1000 ng/kg CL significantly reduced feeding by statistically similar amounts in SHAM and SDA rats. One hour after IP injection, each dose of CL also significantly increased plasma concentrations of free fatty acids and beta-hydroxybutyrate, an indicator of hepatic fatty acid oxidation (FAO), whereas 6h after injection only the two highest CL doses increased plasma beta-hydroxybutyrate. In contrast, peripheral administration of the FAO inhibitor mercaptoacetate (MA, 45.6 mg/kg IP) stimulated feeding in SHAM but not in SDA rats, extending previous data suggesting a necessary role of vagal afferents in the feeding-stimulatory effect of FAO inhibition. We conclude that subdiaphragmatic vagal afferents are essential for the feeding-stimulatory action of MA but not for the anorectic action of peripheral CL and that CL-induced increase in hepatic FAO is not essential for its feeding-inhibitory effect.     

Response to environmental change in rainbow trout selected for divergent stress coping styles

An extensive literature has documented differences in the way individual animals cope with environmental challenges and stressors. Two broad patterns of individual variability in behavioural and physiological stress responses are described as the proactive and reactive stress coping styles. In addition to variability in the stress response, contrasting coping styles may encompass a general difference in behavioural flexibility as opposed to routine formation in response to more subtle environmental changes and non-threatening novelties. In the present study two different manipulations, relocating food from a previously learned location, and introducing a novel object yielded contrasting responses in rainbow trout selected for high (HR) and low (LR) post stress plasma cortisol levels. No difference was seen in the rate of learning the original food location; however, proactive LR fish were markedly slower than reactive HR fish in altering their food seeking behaviour in response to relocated food. In contrast, LR fish largely ignored a novel object which disrupted feeding in HR fish. Hence, it appears that the two lines appraise environmental cues differently. This observation suggests that differences in responsiveness to environmental change are an integral component of heritable stress coping styles, which in this particular case, had opposite effects on foraging efficiency in different situations. Context dependent fitness effects may thus explain the persistence of stable divergence of this evolutionary widespread trait complex.     

Feeding and locomotion responses to centrally injected nociceptin/orphanin FQ in chicks

Nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of the opioid receptor-like receptor or nociceptin receptor (NOP), has been shown to induce feeding, locomotion, anti-stress and anxiolytic effects in rodents after central nervous system injection. In this study, the effect of intracerebroventricular (icv) injection of N/OFQ on feeding and locomotion behavior was evaluated in male broiler-type chickens. The icv injection of N/OFQ caused a moderate but significant increase in feed intake similar to the classical opioid peptides in rats. It also increased feed pecking frequency and feeding time 1 h after injection. Stepping, wing flapping and preening were not affected by N/OFQ. These results suggest that N/OFQ can act within the central nervous system of chickens to increase feed intake.     

Alterations induced by gestational stress in brain morphology and behaviour of the offspring.

Retrospective studies in humans suggest that chronic maternal stress during pregnancy, associated with raised plasma levels of CRH, ACTH and cortisol may increase the likelihood of preterm birth, developmental delays and behavioural abnormalities in the children. In adulthood, it may contribute to the significant association between the incidence of schizophrenia, increased left or mixed handedness, reduction in cerebral asymmetry and anomalies in brain morphology. Our studies and others have shown that prenatal stress in rats can mimic these developmental and behavioural alterations. These rats show a reduced propensity for social interaction, increased anxiety in intimidating or novel situations and a reduction in cerebral asymmetry and dopamine turnover, consistent with those in schizophrenic humans. Prenatally-stressed (PS) rats also show behaviour consistent with depression, including a phase-shift in their circadian rhythm for corticosterone, sleep abnormalities, a hedonic deficit and greater acquisition of learned helplessness under appropriate conditions. These behavioural abnormalities are associated with impaired regulation of the hypothalamic-pituitary-adrenal axis response to stress and increased CRH activity. PS males may show demasculinisation and feminisation of their sexual behaviour. The developmental and behavioural abnormalities in PS offspring could occur through sensitisation of the foetal brain by maternal stress hormones to the action of glucocorticoid and CRH and to neurotransmitters affected by them. This may have long-lasting consequences and could explain the precipitation of depressive symptoms or schizophrenia by psychosocial stress in later life. The character of the behavioural abnormalities probably depends on the timing of the maternal stress in relation to development of the particular neuronal systems.     

The orexigenic effect of peripheral ghrelin differs between rats of different age and with different baseline food intake, and it may in part be mediated by the area postrema

Ghrelin is mainly secreted during fasting. While an orexigenic effect of peripherally injected ghrelin has been reported, reproducing this effect has often proven difficult. Here, we hypothesized that ghrelin's effect to increase food intake may depend on the experimental conditions (e.g., age of animals). We therefore investigated the effect of an IP ghrelin injection (100 microg/kg) on food intake in rats of different age and at different times during the light-dark cycle, i.e. with different levels of baseline food intake. Ghrelin injected at dark onset in ad libitum fed young rats (body weight [BW] 92 g) slightly increased feeding while no such effect was observed in 12 h food deprived rats (BW 150 g). In the middle of the light phase, ghrelin significantly increased feeding up to 2 h after injection in ad libitum fed rats (BW 130 g; food intake 1 h after injection: NaCl 0.4 +/- 0.2 g versus ghrelin 1.2 +/- 0.3 g [p < 0.05]). In various subsequent experiments, older rats (BW 300-490 g) tested under the same conditions did not respond to a single ghrelin injection. However repeated ghrelin injection (15 microg/kg/day once daily at light onset) over 10 days significantly increased food intake in rats (BW 400-460 g) starting from day 4 of the experiment (24 h food intake: NaCl approx. 19.5 g, ghrelin 22.5 g). Interestingly, the latter effect was completely abolished in rats lesioned in the area postrema (AP). Cumulative food intake was also increased in SHAM but not in AP-X animals (e.g., after 7 days: SHAM/NaCl 135.1 +/- 5.3 g versus SHAM/ghrelin 149.7 +/- 3.5 g [p < 0.05], AP-X/NaCl 127.2 +/- 16.4 versus AP-X/ghrelin 127.9 +/- 5.3). We conclude that ghrelin's effect to increase food intake can best be demonstrated when basal food intake is low. Ghrelin increases feeding mainly in young, fast growing animals. Ghrelin may therefore link the high energy needs to body growth in young individuals. In older animals, peripheral ghrelin increased feeding when injected repeatedly over several days. At least under these conditions, ghrelin's effect was mediated by the AP/NTS region. Using repeated administration, ghrelin might be an interesting tool to increase feeding in patients suffering from wasting diseases such as cancer anorexia.     

Prostaglandin mediates endotoxaemia-induced hypophagia by activation of pro-opiomelanocortin and corticotrophin-releasing factor neurons in rats

Corticotrophin-releasing factor (CRF) and α-melanocyte-stimulating hormone (α-MSH), both of which are synthesized by hypothalamic neurons, play an essential role in the control of energy homeostasis. Neuroendocrine and behavioural responses induced by lipopolyssacharide (LPS) have been shown to involve prostaglandin-mediated pathways. This study investigated the effects of prostaglandin on CRF and α-MSH neuronal activities in LPS-induced anorexia. Male Wistar rats were pretreated with indomethacin (10 mg kg⁻¹; i.p .) or vehicle; 15 min later they received LPS (500 μg kg⁻¹; i.p .) or saline injection. Food intake, hormone responses and Fos–CRF and Fos–α-MSH immunoreactivity in the paraventricular and arcuate nuclei, respectively, were evaluated. In comparison with saline treatment, LPS administration induced lower food intake and increased plasma ACTH and corticosterone levels, as well as an increase in Fos–CRF and Fos–α-MSH double-labelled neurons in vehicle-pretreated rats. In contrast, indomethacin treatment partly reversed the hypophagic effect, blunted the hormonal increase and blocked the Fos–CRF and Fos–α-MSH hypothalamic double labelling increase in response to the LPS stimulus. These data demonstrate that the activation of pro-opiomelanocortin and CRF hypothalamic neurons following LPS administration is at least partly mediated by the prostaglandin pathway and is likely to be involved in the modulation of feeding behaviour during endotoxaemia.     

Long-term consequences of early maternal deprivation in serotonergic activity and HPA function in adult rat

Increasing body of evidence indicates that early life stressful events may induce permanent alterations in neurodevelopment, which in turn, could lead to the development of psychopathologies in adulthood. In particular, maternal deprivation (MD) for 24 h in rats has been associated with several abnormalities in brain and behaviour during adulthood, relevant to the neurobiological substrate of anxiety disorders. The aim of the present study was to clarify the long-term effects of MD, on hypothalamo–pituitary–adrenal (HPA) axis activity and serotonergic (5-HT) function, in adulthood, subjects that have not been yet thoroughly investigated. For this purpose, Wistar rat pups were deprived from their mothers for a 24-h single period at postnatal day 9 (pnd 9) and were examined when aged 69–90 days. Plasma corticosterone and ACTH levels along with the animal's behaviour in an open field were used as indices of stress. Moreover, serotonergic activity was estimated in hypothalamus and hippocampus, key structures in the coordination of neuroendocrine and behavioural responses to stress. Interestingly, in adulthood, MD rats compared to controls, displayed decreased body weight, increased serotonergic activity and “anxiety” related behaviour, as well as elevated plasma corticosterone and ACTH levels. The findings of this study showed that MD results in long-term modifications in HPA axis and serotonergic activity indicating a clear relationship between early life stressful events and the development of anxiety-like disorders later in adulthood.     

Time course of the effect of maternal deprivation on the hypothalamic-pituitary-adrenal axis in the infant rat.

Prolonged (i.e., 24-hr) maternal deprivation leads to a marked disinhibition of the infant rat's adrenocortical response to stress and/or ACTH. In the following study we examined the time course over which these effects develop. Pups were maternally deprived for varying lengths of time (i.e., 0, 2, 4, 8, & 24 hr); at the end of this period, corticosterone (CORT) secretion in response to stress (novelty or novelty plus saline injection) and ACTH injection was measured. Basal levels of CORT increased progressively over time in 7- and 11- (but not 3-) day-old pups. CORT release in response to stress followed a similar pattern. In contrast, ACTH injection resulted in marked increases in CORT levels regardless of the length of maternal deprivation in 3-day-old animals; at older ages, however, 24 hr of deprivation led to a much larger increase. These findings support the hypothesis that the hypothalamic-pituitary-adrenal axis of the neonatal rat is subject to maternal regulation.     

Temporal differences in the responses of the pituitary adrenocortical axis, the sympathoadrenomedullar axis, heart rate, and behaviour to a daily repeated stressor in domestic pigs.

In this study we examined responses of domestic pigs (Sus scrofa domestica) to a daily repeated stressor. In particular, we focused on differences in temporal changes across treatment repetition between the pituitary adrenocortical axis, the sympathoadrenomedullar axis, heart rate, and behaviour. To induce a stress response, we separated eight castrated male pigs from their group mates visually and auditorily for 1 h on 10 successive days. Overall, enhanced plasma levels of cortisol, ACTH, and adrenaline indicated a clear stress response. Levels of cortisol and ACTH decreased continuously with repetition of exposures to the stressor. In contrast, levels of adrenaline, behavioural activity, and heart rate did not change consistently across repetition of exposures. Interestingly, therefore, hormones of the pituitary adrenocortical axis showed a process of adaptation whereas subjects did not adapt to the stressor with respect to titres of adrenaline, heart rate, and particular behaviours (e.g., grid pressing, vocalisation, locomotion). Instead, they continued to react actively towards the social separation. Our results suggest that different stress systems can differ in temporal pattern of their response towards a repeated stressor. Such temporal differences should be considered when studying the effects of repeated stress.     

Extracellular GABA in the medial hypothalamus is increased following hypocretin-1 administration

AIM: Hypocretin 1 is an hypothalamic neuropeptide that induces an increase in food intake when administered into the cerebral lateral ventricle. As it is well known that the medial hypothalamus (MH) is involved in the feeding behaviour also through GABAergic circuits, the aim of this experiment was to investigate the effect of an hypocretin 1 intracerebroventricular (icv) injection on the extracellular levels of GABA in the MH. METHODS: GABA levels in the MH were evaluated in six rats by microdialysis and high performance liquid chromatography-electrochemical detection 30 min before and every 30 min for an over all period of 6 h after an icv injection of hypocretin 1. The same procedure was used in another group of six rats but saline was injected into the lateral ventricle as control. RESULTS: The results show that extracellular GABA increases in the MH after the injection of hypocretin 1 at 60 min and at 3 h after the injection. CONCLUSION: This finding suggests a possible mechanism by which hypocretin 1 should induce hyperphagia in the first hour after injection. As it is already known that the inhibition of the MH by injection of GABA causes an increase of food intake, it is possible that hypocretin 1 causes an increase in food intake by increasing the GABA release in the MH. The lack of an increase in the GABA level after the fourth hour is consistent with the lack of an increase in food intake at this time, as we observed in previous experiments. The finding of a biphasic increase in the GABA level, at 60 min and at 3 h, was unexpected and should be further investigated.     

ACTH response induced in capsaicin-desensitized rats by intravenous injection of interleukin-1 or prostaglandin E.

1. We investigated whether afferent nerves are involved in the development of adrenocorticotrophic hormone (ACTH) responses induced either by systemic administration of interleukin-1 beta (IL-1 beta) and prostaglandin E2, or by psychological stress. The capsaicin desensitization method was used to impair afferent C fibres and we compared the ACTH responses between capsaicin desensitized and vehicle pretreated control rats. 2. The present results showed that the capsaicin desensitized rats had significantly smaller increases in plasma ACTH than the control rats in response to intravenous injection of IL-1 beta or prostaglandin E2. 3. There were no significant differences between the capsaicin desensitized and control rats in the ACTH responses induced by cage switch stress. 4. The capsaicin desensitized rats responded to intravenous injection of corticotrophin releasing factor (CRF) with a greater increase in the plasma level of ACTH than the control rats, indicating that capsaicin pretreatment resulted in augmentation of pituitary gland sensitivity to CRF. 5. These results suggest that afferent neurons play an important role in the ACTH responses induced by systemic injection of IL-1 beta or prostaglandin E2.     

Effect of selection for behavior on pituitary-adrenal axis and proopiomelanocortin gene expression in silver foxes (Vulpes vulpes)

Silver foxes from a commercial population (farm bred or unselected for behavior control) and from populations selected for tame behavior and enhanced aggressiveness towards man have been investigated. Plasma cortisol and adrenocorticotropic hormone (ACTH) levels, pituitary ACTH levels, POMC gene expression in the anterior pituitary, and corticotropin-releasing factor (CRF) gene expression in the hypothalamus were assessed. The results indicate that the males from the tame-behavior group have lower plasma cortisol and ACTH levels and POMC gene expression in the anterior pituitary in response to capture and handling in comparison with unselected ones. Foxes from the aggressive behavior group also have lower POMC expression, although plasma cortisol and ACTH levels remain the same as in unselected ones. The three groups of animals show no significant changes in the ACTH level in the pituitary and CRF expression in the hypothalamus.     

Influences of feeding and drinking on circadian rhythms of opioid peptides in plasma, hypothalamus and pituitary gland in rats

Changes of plasma, hypothalamic and pituitary immunoreactive beta-endorphin (IR-beta-end), methionine-enkephalin (IR-Met-enk) and ACTH (IR-ACTH) were studied under various conditions of feeding and watering in rats. When rats were fed from 17:00 to 09:00 hr and water was given ad lib, plasma IR-beta-end and IR-ACTH had parallel circadian rhythms with a peak before feeding and drinking. In the hypothalamus, IR-beta-end and IR-Met-enk showed parallel circadian rhythms with a decrease before these behaviors. When rats were fed from 09:00 to 17:00 hr, the peaks of plasma IR-beta-end and IR-ACTH shifted to one hour before the onset of feeding and drinking. When feeding and watering were restricted to 17:00-09:00 hr and 09:00-12:00 hr respectively, plasma IR-beta-end and IR-ACTH exhibited parallel circadian rhythms with two separate peaks at one hour before drinking and feeding, respectively. In the hypothalamus, IR-beta-end, IR-Met-enk and IR-ACTH showed parallel circadian rhythms with a decrease before feeding but not before drinking. When rats were fed from 17:00 to 20:00 hr, plasma IR-beta-end increased and neurohypophysial IR-beta-end and IR-Met-enk decreased at 16:00 hr, one hour before feeding. It was observed that locomotor activities increased at the time of transition from light to dark and at one hour before the onset of feeding and drinking. The present results suggest that endogenous opioid peptides may have some physiological roles in feeding and drinking behaviors.     

Physiological and biomechanical analysis of treadmill walking up various gradients in men and women

This investigation was undertaken to examine the physiological and biomechanical responses during treadmill walking up various gradients in men and women. Groups of 11 men and 11 women took part in four experiments consisting of 8 min treadmill walks at 1.3 m·s^–1 up gradients of 0%, 5%, 10% and 15%. The subjects also underwent an anthropometric assessment during which their height, body mass (BM), percentage (%) body fat, lean body mass (LBM), and waist-to-hip ratio (WHR) were obtained. During exercise, each subject was videotaped during three walking cycles so that sagittal kinematics including stride length (SL) and frequency (SF) and ranges of motion achieved at the shoulder, hip and knee during a walking cycle could be determined using a motion analysis system. The motion capture was followed by a measurement of steady-state oxygen uptake (VO₂) and heart rate (HR) using indirect calorimetry and a HR monitor. Compared to men, women were higher in % body fat, but lower in height, BM, LBM, and WHR. The VO₂ in millilitres per kilogram per minute and HR were similar between men and women at 0% and 5%, but greater in women than men at 10% and 15%. The SL and SF were greater and smaller, respectively, in men than women up all gradients. Shoulder extension was greater up gradients of 10% and 15% in women than men, whereas no sex difference in shoulder flexion was noted. Hip extension and flexion as well as knee flexion remained the same between men and women up all gradients. An inverse relationship was observed between VO₂ in millilitres per kilogram per minute and BM, LBM, and WHR when men and women were combined. In conclusion, the mass-specific metabolic cost of treadmill walking up high gradients is greater in women than men. Such an increase in relative metabolic cost may be attributable to the fact that women are smaller in size, and/or have relatively more BM distributed peripherally. This sex difference may also be due to a greater movement of the upper limbs in women during walking uphill, although direct evidence is needed to support this contention. Electronic Publication     

Levels of 17-hydroxycorticosteroids in blood plasma of rhesus monkeys and hamadry as baboons and changes caused by neuro-emotional action

Summary Experiments were made by Porter and Silber's method in N. A. Yudaev and Yu. A. Pankov's modification to establish the normal level of 17-hydroxycorticosteroids in the blood plasma of monkeys. The concentration of 17-hydroxycorticosteroids in male rhesus macaques was on the average 34±1.3 mg %, in females –44±1.2 mg %; in male and female hamadryads –41±1.5 mg % and 52±1.5 mg % respectively.Variable reaction of the adrenal cortex to intravenous injection of ACTH was found in different species of monkeys, in rhesus macaques the maximum increase in the amount of 17-hydroxycorticosteroids was registered one hour after the injection of the preparation, in hamadryads-in two hours.Nembutal anesthesis presents the development of the stress condition. It was found that the neuro-emotional strain in monkeys brings about a marked increase in the hormonal function of the adrenal cortex.Presented by Member of the Academy of the Medical Sciences of the USSR V. V. Zakusov Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 61, No. 5, pp. 54–57, May, 1966     

Central and peripheral doses of cholecystokinin that inhibit feeding in pigs also stimulate vasopressin and cortisol release

The effects on vasopressin and cortisol secretion of centrally and peripherally administered cholecystokinin octapeptide (CCK) were investigated in conscious prepubertal pigs. Injection of 1.3 micrograms CCK into the lateral cerebral ventricle resulted in a sustained increase in plasma vasopressin after a latency of 5 min but no change in cortisol concentrations. Intravenous injection of 0.7 and 1.3 micrograms/kg CCK initiated a rapid surge (within 2 min) in plasma vasopressin and a later increase in cortisol secretion. The time course of the vasopressin response to the central injection of CCK was found to be similar to the period of behavioural inhibition induced when an equivalent dose of the peptide was given by the same route in an earlier feeding experiment. An analogous situation was also observed when CCK was given peripherally and, in this case, the threshold dose at which the behavioural and endocrine responses were induced was found to be the same.     

The role of the adrenal medulla in cardiovascular responses to hypertonic saline in haemorrhaged conscious rats

The aim of this study was to determine if the adrenal medulla plays a role in mediating haemodynamic effects of hypertonic saline (HTS) resuscitation during haemorrhagic hypotension in conscious rats. Wistar-Kyoto rats were either adrenomedullectomized (ADMX, n = 11) or sham-operated (SHAM, n = 10) and implanted with intravascular catheters. Pre-haemorrhage resting mean arterial pressure (MAP) was lower in the ADMX than in the SHAM group. Haemorrhage was performed by withdrawal of blood through the venous catheter, and a MAP of 50 mmHg was maintained for 1 h by further withdrawal when necessary. Both groups responded to haemorrhage with marked bradycardia. Plasma adrenaline (A) rose 10-fold in response to hypotension in the SHAM group, while remaining at pre-haemorrhage levels in the ADMX group, indicating successful adrenal demedullation. Infusion of 2.0 ml kg^-1 HTS (NaCl 8.0 mg ml^-1 i.v.) produced an immediate increase in MAP and heart rate (HR) in both groups, to pre-haemorrhage values or higher. Plasma noradrenaline (NA) increased in both groups after HTS, while the high levels of A in the SHAM group slowly returned toward baseline. Plasma glucose and rate of haemodilution was higher in the SHAM group during and after hypotension. The maintenance of MAP above 60 mmHg was less effective in the SHAM group during the first 2 h after HTS, but after 24 h, pre-haemorrhage MAP was established in both groups. In conclusion, the adrenal medulla does not play a major role in the response to HTS resuscitation.     

Consistent boldness behaviour in early emerging fry of domesticated Atlantic salmon (Salmo salar): Decoupling of behavioural and physiological traits of the proactive stress coping style

Individual variation in the way animals cope with stressors has been documented in a number of animal groups. In general, two distinct sets of behavioural and physiological responses to stress have been described: the proactive and the reactive coping styles. Some characteristics of stress coping style seem to be coupled to the time to emerge of fry from spawning redds in natural populations of salmonid fishes. In the present study, behavioural and physiological traits of stress coping styles were compared two and five months after emergence in farmed Atlantic salmon (Salmo salar), using individuals with an early or late time to emerge. Initially, compared to late emerging individuals, early emerging individuals showed a shorter time to resume feeding after transfer to rearing in isolation. Resumption of feeding after isolation was suggested to be related to boldness behaviour, rather than hunger, in the present study. This observation was repeated five months after emergence, demonstrating behavioural consistency over time in this trait. However, in other traits of proactive and reactive stress coping styles, such as social status, resting metabolism or post stress cortisol concentrations, early and late emerging individuals did not differ. Therefore, this study demonstrates that boldness in a novel environment is uncoupled from other traits of the proactive and reactive stress coping styles in farmed salmonids. It is possible that this decoupling is caused by the low competitive environment in which fish were reared. In natural populations of salmonids, however, the higher selection pressure at emergence could select for early emerging individuals with a proactive coping style.     

Behavioral effects of intracerebroventricular injection of oxytocin in birds

In addition to playing a role as a hormone, oxytocin (OT) can act as a neurotransmitter. In birds, mesotocin (MT) replaces OT. There is both direct and indirect evidence for behavioral effects of OT in rats and humans, but there have been no such studies performed in birds. The purpose of this study was to define the effect of intracerebroventricular (i.c.v.) injection of OT (0-10 microg) on locomotion and feeding behaviors of broiler cockerels. Stepping and wing flapping were increased dose-dependently, but OT decreased preening. The i.c.v. injection of OT also caused a dose-dependent decrease in feed intake, feeding time and pecking frequency. These results suggest that OT might play a unique role in inducing a state of arousal in chickens that resembles fear/anxiety and also in reducing feed intake by acting on MT and/or vasotocin receptors.