Central actions of corticotropin-releasing hormone (CRH) on behavioral, neuroendocrine, and cardiovascular regulation: brain corticoid receptor involvement

Recruitment of Corticotropin-Releasing Hormone (CRH) Neurons in Categorically Distinct Stress Reactions in the Mouse Brain

Corticotropin-releasing hormone (CRH) neurons in the paraventricular hypothalamic nucleus (PVH) are in the position to integrate stress-related information and initiate adaptive neuroendocrine-, autonomic-, metabolic- and behavioral responses. In addition to hypophyseotropic cells, CRH is widely expressed in the CNS, however its involvement in the organization of the stress response is not fully understood. In these experiments, we took advantage of recently available Crh-IRES-Cre;Ai9 mouse line to study the recruitment of hypothalamic and extrahypothalamic CRH neurons in categorically distinct, acute stress reactions. A total of 95 brain regions in the adult male mouse brain have been identified as containing putative CRH neurons with significant expression of tdTomato marker gene. With comparison of CRH mRNA and tdTomato distribution, we found match and mismatch areas. Reporter mice were then exposed to restraint, ether, high salt, lipopolysaccharide and predator odor stress and neuronal activation was revealed by FOS immunocytochemistry. In addition to a core stress system, stressor-specific areas have been revealed to display activity marker FOS. Finally, activation of CRH neurons was detected by colocalization of FOS in tdTomato expressing cells. All stressors resulted in profound activation of CRH neurons in the hypothalamic paraventricular nucleus; however, a differential activation of pattern was observed in CRH neurons in extrahypothalamic regions. This comprehensive description of stress-related CRH neurons in the mouse brain provides a starting point for a systematic functional analysis of the brain stress system and its relation to stress-induced psychopathologies.

The Steroidogenesis Inhibitor Finasteride Reduces the Response to Both Stressful and Rewarding Stimuli

Finasteride (FIN) is the prototypical inhibitor of steroid 5α-reductase (5αR), the enzyme that catalyzes the rate-limiting step of the conversion of progesterone and testosterone into their main neuroactive metabolites. FIN is clinically approved for the treatment of benign prostatic hyperplasia and male baldness; while often well-tolerated, FIN has also been shown to cause or exacerbate psychological problems in vulnerable subjects. Evidence on the psychological effects of FIN, however, remains controversial, in view of inconsistent clinical reports. Here, we tested the effects of FIN in a battery of tests aimed at capturing complementary aspects of mood regulation and stress reactivity in rats. FIN reduced exploratory, incentive, prosocial, and risk-taking behavior; furthermore, it decreased stress coping, as revealed by increased immobility in the forced-swim test (FST). This last effect was also observed in female and orchiectomized male rats, suggesting that the mechanism of action of FIN does not primarily reflect changes in gonadal steroids. The effects of FIN on FST responses were associated with a dramatic decrease in corticotropin release hormone (CRH) mRNA and adrenocorticotropic hormone (ACTH) levels. These results suggest that FIN impairs stress reactivity and reduces behavioral activation and impulsive behavior by altering the function of the hypothalamus-pituitary-adrenal (HPA) axis.

CRHR2 (Corticotropin-Releasing Hormone Receptor 2) in the Nucleus of the Solitary Tract Contributes to Intermittent Hypoxia-Induced Hypertension

This study tested the hypothesis that CRHRs (corticotropin-releasing hormone receptors) in the nucleus of the solitary tract (NTS) contribute to the hypertension induced by intermittent hypoxia (IH) exposure in rats. Initial studies using in situ hybridization revealed low mRNA level of CRHR1 (CRH type 1 receptor) but high mRNA level of CRHR2 (CRH type 2 receptor) in the NTS. Calcium imaging studies on NTS slice preparations using Fura-2-acetoxymethyl ester demonstrated that CRH induced a transient increase of intracellular calcium level. The CRH-induced calcium response was reproduced in the presence of TTX (tetrodotoxin) but was abolished by depletion of extracellular calcium or by the L-type calcium channel blocker Nifedipine. The CRH-induced calcium influx was attenuated by the CRHR2 antagonist K41498 but not by the CRHR1 antagonist NBI-35 965. Calcium influx can be induced by the CRHR2 agonist Urocortin II but not by the CRHR1 agonist Stressin 1. IH exposure did not affect CRHR1 mRNA level but significantly decreased CRHR2 mRNA level and the CRH-induced calcium influx in the NTS. Further in vivo studies showed that intra-fourth ventricle infusion of K41498 did not affect the basal blood pressure but significantly attenuated the IH-induced hypertension; intra-fourth ventricle infusion of Urocortin II significantly increased basal blood pressure and exacerbated the IH-induced hypertension. Collectively, these results suggest that CRHR2 in the NTS contributes to the IH-induced hypertension; downregulation of CRHR2 and CRHR2-mediated calcium influx in the NTS may serve as an adaptive response to protect against the IH-induced hypertension.

The contribution of total and free iodothyronines to welfare maintenance and management stress coping in Ruminants and Equines: Physiological ranges and reference values

In order to acquire a pattern of thyroid involvement in welfare maintenance in Ruminants and Equines, this review summarizes data concerning the reference values of total and free iodothyronines and their modifications in physiological conditions and in different management conditions (pregnancy, lactation, weaning, growth, isolation, restraint, shearing, confinement and transportation). Thyroidal and extrathyroidal tissues efficiently respond to management practices, giving a differentiated contribution to circulating iodothyronine changes. The hormonal response could be mainly attributed to the intracellular deiodination of T₄ to T_3. Triiodothyronine (T₃) and free iodothyronines (fT₃ and fT₄) result more responsive to management stress, showing different pattern with species and to various conditions, as to environmental conditions in which activities are performed. Intrinsic seasonal changes of iodothyronines and a significant pregnancy effect for T₃ were recorded in mares. Higher, although not significant, T₃ and T₄ concentrations in barren than pregnant mares were observed in donkeys. A positive significant correlation between T₃ and T₄ was described only in pregnant donkeys. Moreover, a significant effect of season on T₃ and fT₃ changes was observed both in pregnant and barren donkeys. A significant lactating effect compared with nonlactating stage for T₃ and T₄ was recorded in mares. In growing foals, body weight (BW) and age were positively correlated with T₃ and negatively correlated with T₄, fT₄ and fT₃. Weaning effects were shown for T₃ and fT₄ concentrations, indicating that weaning represents a severe stress and the presence of conspecific does not reduce psychological stress in this phase. Lambs showed significant decreased T₃ and elevated T₄ concentrations two weeks after weaning, with higher concentrations in both males and females compared to 24 h. Significant positive correlations were observed between BW and T₄, fT₃ and fT₄ concentrations in lambs. A T₃ decrease was detected after isolation, such as induced by confinement and weaning in lambs. Higher T₃ concentration after restraint and shearing than after isolation and significant increases in T₄, fT₃ and fT₄ values after restraint and shearing were recorded. The basal concentrations of fT₃ in both the inexperienced and experienced transported horses were significantly higher than in untransported experienced horses. Moreover, increases of T_3, T₄ and fT₄ after short road transportation, and significant correlations between T₃ and rectal temperature (RT), body weight (BW) and heart rate (HR), confirmed their important role in coping strategy. Thyroid responsiveness to short transport is similar in domestic donkeys and horses, with a preferential release of T₃ in horses. A greatest and constant release of T₃ and T₄, although differentiated, after simulated transportation and after conventional transport of horses confirmed that the degree of stress induced by confinement and additional stressful stimuli associated to road transportation could differently influence the iodothyronine release. Temperamental Limousin young beef bulls showed lower T₄ and fT₄ concentrations after prolonged transportation than calm subjects, and a concomitant decrease of circulating ACTH, cortisol, T₃ and fT₃ concentrations, probably induced by down regulation of HPA axis and cortisol negative feedback. These data reinforce the importance of taking into account the evaluation of iodothyronines, and notably of T₃, as markers of welfare and stress and their role in ensuring energy homeostasis and productive and reproductive performances in Ruminants and Equines.

Possible role of adrenoceptors in the hypothalamic paraventricular nucleus in corticotropin-releasing factor-induced sympatho-adrenomedullary outflow in rats

AIMS

A functional interaction between the corticotropin-releasing factor (CRF) system and noradrenergic neurons in the brain has been suggested. In the present study, we investigated the interrelationship between the central CRF-induced elevation of plasma catecholamines and adrenoceptor activation in the paraventricular nucleus of the hypothalamus (PVN) using urethane-anesthetized rats.

MAIN METHODS

In rats under urethane anesthesia, a femoral venous line was inserted for infusion of saline, and a femoral arterial line was inserted for collecting blood samples. Next, animals were placed in a stereotaxic apparatus for the application of test agents. Catecholamines in the plasma were extracted by alumina absorption and were assayed with high-performance liquid chromatography with electrochemical detection. Quantification of noradrenaline in rat PVN microdialysates was performed with high-performance liquid chromatography with electrochemical detection.

KEY FINDINGS

We showed that centrally administered CRF elevated noradrenaline release in the PVN. Furthermore, we demonstrated that microinjection of phenylephrine into the PVN induced elevation of plasma levels of adrenaline, but not of noradrenaline, whereas microinjection of isoproterenol into the PVN induced elevation of plasma levels of noradrenaline, but not of adrenaline. Bilateral blockade of adrenoceptors in the PVN revealed that phentolamine significantly suppressed the CRF-induced elevation of plasma adrenaline level, while propranolol significantly CRF-induced elevation of plasma noradrenaline level.

SIGNIFICANCE

Our results suggest that centrally administered CRF-induced elevation of plasma levels of adrenaline and noradrenaline can be mediated via activation of α-adrenoceptors and β-adrenoceptors, respectively, in the rat PVN.

Circadian Rhythm and Stress Response in Droppings of Serinus canaria

Serinus canaria is a widespread domestic ornamental songbird, whose limited knowledge of biology make compelling studies aimed to monitor stress. Here, a commercial enzyme immunoassay was adopted to measure immunoreactive corticosterone (CORT) in single Serinus canaria dropping sample, to monitor the daily fecal excretion of CORT in birds bred singly or in-group and to detect the effect promoted by aviary or small transport cage restraint. A robust daily rhythm of CORT was recorded in animals held on short-day light cycle, independent of bred conditions (single or group), which persisted when space availability was modified in single bred animal (transfer in aviary and transport cages). By contrast, a significant change in CORT excretion was recorded when group bred animals are restrained in a smaller cage. The daily rhythm in CORT excretion in response to manipulation showed the greatest response at the beginning of the light period, followed by the absence of the peak usually recorded at the end of the dark phase. These data indicated that EIA could be used as a reliable noninvasive approach to monitor the stress induced by restraint conditions in Serinus canaria.

Centrally administered isoproterenol induces sympathetic outflow via brain prostaglandin E2-mediated mechanisms in rats

Brain β-adrenoceptor stimulation can induce elevations of plasma levels of noradrenaline. However, there have been no detailed studies related to signaling pathways downstream of β-adrenoceptors responsible for central sympathetic outflow. In the present study, we pharmacologically examined the possibility that centrally administered isoproterenol can induce elevations of plasma noradrenaline levels in a brain prostaglandin-dependent manner. In addition, we also examined whether or not intracerebroventricular administration of isoproterenol could release endogenously synthesized prostaglandin (PG) E2 in the hypothalamic paraventricular nucleus (PVN) by using the brain microdialysis technique combined with liquid chromatography-ion trap tandem mass spectrometry (LC-ITMS(n)). Under urethane anesthesia, a femoral venous line was inserted for infusion of saline and a femoral arterial line was inserted for collecting blood samples. Next, animals were placed in a stereotaxic apparatus for application of test agents. Catecholamines in the plasma were extracted by alumina absorption and were assayed by high-performance liquid chromatography with electrochemical detection. Quantification of PGE2 in rat PVN microdialysates was performed by the LC-ITMS(n) method. We demonstrated that centrally administered isoproterenol-induced elevations of plasma noradrenaline could be mediated via activation of β-adrenoceptors and the downstream phospholipase A2-cyclooxygenase pathway. Furthermore, PGE2 in the PVN and the PGE2 receptor EP3 subtype appear to play an important role in the process. Our results suggest that central isoproterenol-induced sympathetic outflow is mediated via brain PGE2 in a PGE2 receptor EP3 subtype-dependent manner.

Validation of an enzyme immunoassay for the measurement of faecal glucocorticoid metabolites in spotted hyenas (Crocuta crocuta)

The use of enzyme immunoassays (EIAs) to measure faecal glucocorticoid metabolites (fGCM) is a useful non-invasive technique to monitor adrenocortical activity in vertebrates. The first objective of this study was to validate an 'in-house' EIA (cortisol-3-CMO) for the measurement of fGCM concentrations in spotted hyenas. High-performance liquid chromatography (HPLC) was used to characterise fGCM in samples from a captive hyena that received an i.v. injection of [(3)H] cortisol. All HPLC fractions were analysed with the EIA for the presence and quantities of radiolabelled fGCM. Radiolabelled fGCM consisted of substances with a higher polarity than cortisol and substances of lower polarity that eluted between cortisol and corticosterone. Authentic radiolabelled cortisol was not detected. The EIA measured substantial amounts of immunoreactivity corresponding to the radioactive peaks. It also detected a significant increase in fGCMs after an adrenocorticotropic hormone (ACTH) challenge in two other captive animals and a significant increase in fGCMs in a fourth captive animal after anaesthesia. The second objective was to investigate an age effect on fGCM: we conducted pairwise comparisons of fGCM concentrations in individual free-ranging juvenile spotted hyenas when less than 6 months of age and when between 6 and 24 months of age. We expected juveniles to experience a more unpredictable and therefore more stressful environment when younger than when older. When younger, juveniles had significantly higher fGCM concentrations than when they were older. Our results demonstrate that our assay can be used to assess adrenocortical activity in spotted hyenas.

Behavioral and physiological responses of young horses to different weaning protocols: a pilot study

In this study, effects of weaning on behavioral and physiological stress parameters in young horses (foals) were determined. Foals were weaned either simultaneously without the presence of adult horses (group A, n = 6), or in the presence of two adult females familiar but unrelated to the foals (group B, n = 5), or weaned consecutively by removing two mother horses per day (group C, n = 6). Behavior, locomotion, salivary cortisol concentration, beat-to-beat (RR) interval, heart rate variability (HRV) and weight were determined. Group A foals lost weight for 2 days (mean ± SEM) - 8.3 ± 1.6 kg, p < 0.05. Weaning was followed by increased vocalization which was least pronounced in foals of group B (p < 0.05). Locomotion was most pronounced on weaning day in foals of group A and lowest in group B (p < 0.05). Weaning increased salivary cortisol concentration on the day of weaning in groups A and B and for 2 days in group C (p < 0.05). The RR interval decreased most pronouncedly in group A foals (p < 0.05). There were no consistent changes in HRV. Based on cortisol release and behavior, weaning is associated with stress but this was least pronounced in foals weaned in the presence of two familiar but unrelated adult female horses.

Anorexia nervosa: a unified neurological perspective

The roles of corticotrophin-releasing factor (CRF), opioid peptides, leptin and ghrelin in anorexia nervosa (AN) were discussed in this paper. CRF is the key mediator of the hypothalamo-pituitary-adrenal (HPA) axis and also acts at various other parts of the brain, such as the limbic system and the peripheral nervous system. CRF action is mediated through the CRF1 and CRF2 receptors, with both HPA axis-dependent and HPA axis-independent actions, where the latter shows nil involvement of the autonomic nervous system. CRF1 receptors mediate both the HPA axis-dependent and independent pathways through CRF, while the CRF2 receptors exclusively mediate the HPA axis-independent pathways through urocortin. Opioid peptides are involved in the adaptation and regulation of energy intake and utilization through reward-related behavior. Opioids play a role in the addictive component of AN, as described by the "auto-addiction opioids theory". Their interactions have demonstrated the psychological aspect of AN and have shown to prevent the functioning of the physiological homeostasis. Important opioids involved are β-lipotropin, β-endorphin and dynorphin, which interact with both µ and κ opioids receptors to regulate reward-mediated behavior and describe the higher incidence of AN seen in females. Moreover, ghrelin is known as the "hunger" hormone and helps stimulate growth hormone (GH) and hepatic insulin-like-growth-factor-1(IGF-1), maintaining anabolism and preserving a lean body mass. In AN, high levels of GH due to GH resistance along with low levels of IGF-1 are observed. Leptin plays a role in suppressing appetite through the inhibition of neuropeptide Y gene. Moreover, the CRF, opioid, leptin and ghrelin mechanisms operate collectively at the HPA axis and express the physiological and psychological components of AN. Fear conditioning is an intricate learning process occurring at the level of the hippocampus, amygdala, lateral septum and the dorsal raphe by involving three distinct pathways, the HPA axis-independent pathway, hypercortisolemia and ghrelin. Opioids mediate CRF through noradrenergic stimulation in association with the locus coeruleus. Furthermore, CRF's inhibitory effect on gonadotropin releasing hormone can be further explained by the direct relationship seen between CRF and opioids. Low levels of gonadotropin have been demonstrated in AN where only estrogen has shown to mediate energy intake. In addition, estrogen is involved in regulating µ receptor concentrations, but in turn both CRF and opioids regulate estrogen. Moreover, opioids and leptin are both an effect of AN, while many studies have demonstrated a causal relationship between CRF and anorexic behavior. Moreover, leptin, estrogen and ghrelin play a role as predictors of survival in starvation. Since both leptin and estrogen are associated with higher levels of bone marrow fat they represent a longer survival than those who favor the ghrelin pathway. Future studies should consider cohort studies involving prepubertal males and females with high CRF. This would help prevent the extrapolation of results from studies on mice and draw more meaningful conclusions in humans. Studies should also consider these mechanisms in post-AN patients, as well as look into what predisposes certain individuals to develop AN. Finally, due to its complex pathogenesis the treatment of AN should focus on both the pharmacological and behavioral perspectives.

Cortisol release, heart rate, and heart rate variability in transport-naive horses during repeated road transport

Domestic animals are often repeatedly exposed to the same anthropogenic stressors. Based on cortisol secretion and heart rate, it has been demonstrated that transport is stressful for horses, but so far, changes in this stress response with repeated road transport have not been reported. We determined salivary cortisol concentrations, fecal cortisol metabolites, cardiac beat-to-beat (RR) interval, and heart rate variability (HRV) in transport-naive horses (N = 8) transported 4 times over a standardized course of 200 km. Immunoreactive salivary cortisol concentrations always increased in response to transport (P < 0.001), but cortisol release decreased stepwise with each transport (P < 0.05). Concentrations of fecal cortisol metabolites increased from 55.1 +/- 4.6 ng/g before the first transport to 161 +/- 17 ng/g the morning after (P < 0.001). Subsequent transport did not cause further increases in fecal cortisol metabolites. In response to the first transport, mean RR interval decreased with loading of the horses and further with the onset of transport (1551 +/- 23, 1304 +/- 166, and 1101 +/- 123 msec 1 d before, immediately preceding, and after 60-90 min of transport, respectively; P < 0.05). Decreases in RR interval during subsequent transports became less pronounced (P < 0.001). Transport was associated with a short rise in the HRV variable standard deviation 2 (P < 0.001 except transport 1), indicating sympathetic activation. No consistent changes were found for other HRV variables. In conclusion, a transport-induced stress response in horses decreased with repeated transport, indicating that animals habituated to the situation, but an increased cortisol secretion remained detectable.

Cortisol release and heart rate variability in horses during road transport

Based on plasma cortisol concentrations it is widely accepted that transport is stressful to horses. So far, cortisol release during transport has not been evaluated in depth by non-invasive techniques such as analysis of salivary cortisol and faecal cortisol metabolites. Transport also causes changes in heart rate and heart rate variability (HRV). In this study, salivary cortisol, faecal cortisol metabolites, heart rate and HRV in horses transported by road for short (one and 3.5 h) and medium duration (8 h) were determined. With the onset of transport, salivary cortisol increased immediately but highest concentrations were measured towards the end of transport (4.1+/-1.6, 4.5+/-2.6, 6.5+/-1.8 ng/ml in horses transported for one, 3.5 and 8 h, respectively). Faecal cortisol metabolite concentrations did not change during transport, but 1 day after transport for 3.5 and 8 h had increased significantly (p<0.01), reflecting intestinal passage time. Compared to salivary cortisol, changes in faecal cortisol metabolites were less pronounced. Heart rate increased and beat-to-beat (RR) interval decreased (p<0.05) with the onset of transport. Standard deviation of heart rate increased while root mean square of successive RR differences (RMSSD) decreased in horses transported for 3.5 (from 74+/-5 to 45+/-6 ms) and 8 h (from 89.7+/-7 to 59+/-7 ms), indicating a reduction in vagal tone. In conclusion, transport of horses over short and medium distances leads to increased cortisol release and changes in heart rate and HRV indicative of stress. The degree of these changes is related to the duration of transport. Salivary cortisol is a sensitive parameter to detect transient changes in cortisol release.

Fluoxetine inhibits corticotropin-releasing factor (CRF)-induced behavioural responses in rats

Corticotropin-releasing factor (CRF) is a potent neuromodulator of stress-related behaviour but the neural mechanisms underlying these effects are not clear. Studies were designed to test the hypothesis that CRF-induced behavioural arousal involves interactions with brainstem serotonergic systems. To examine interactions between CRF and serotonergic systems in the regulation of behaviour, CRF (1 microg, intracerebroventricular (i.c.v.)) or vehicle was infused in the presence or absence of the selective serotonin re-uptake inhibitor fluoxetine (0, 0.1, 1 or 10 mg/kg, intravenous (i.v.)). Fluoxetine was used at these doses because it is known to decrease serotonin cell firing rates while increasing extracellular serotonin concentrations in select forebrain regions. We then measured behavioural, neurochemical and endocrine responses. CRF increased locomotion and spontaneous non-ambulatory motor activity (SNAMA) in the home cages. Fluoxetine decreased tissue 5-hydroxyindoleacetic acid concentrations, a measure of serotonin metabolism, in specific limbic brain regions of CRF-treated rats (nucleus accumbens shell region, entorhinal cortex, central nucleus of the amygdala). Furthermore, fluoxetine inhibited CRF-induced SNAMA. CRF and fluoxetine independently increased plasma corticosterone concentrations, but the responses had distinct temporal profiles. Overall, these data are consistent with the hypothesis that CRF-induced facilitation of behavioural activity is dependent on brainstem serotonergic systems. Therefore, fluoxetine may attenuate or alleviate some behavioural responses to stress by interfering with CRF-induced responses.

The inhibition of experimentally induced visceral hyperalgesia by nifedipine - a voltage-gated Ca(2+) channels blocker (VGCCs) in sheep

Present study examined the effect of VGCC L-type blocker - nifedipine given i.c.v. (0.25, 0.5, 1 and/or 2mg in toto) on the development of nociceptive behavior, clinical symptoms, plasma catecholamin concentration and reticulo-rumen motility following 5 min lasting mechanical duodenal distension (DD) in sheep. After 24h of fasting, all animals received i.m. ketamine analgesia (20 mg kg(-1)B.W) and anesthetized with pentobarbital (20 mg kg(-1)B.W., i.v. infusion) The permanent stainless steel cannula 29 mm in length and 2mm in diameter was inserted into the lateral cerebral ventricle (controlled by cerebro-spinal efflux) 10mm above the bregma and 5mm laterally from the midline sutures using stereotaxic method. Under the same general anesthesia/analgesia a T-shaped silicon cannula (inside diameter of 21 mm), was inserted into the duodenum (12 cm from pylorus). Second identical cannule was inserted into the dorsal sac of the rumen, a previously described. After surgery each animal was kept in individual boxes for 10 days prior to experiment and was treated i.m. with benzyl procaine penicillin 30,000 I.U kg(-1)B.W.)+dihydrostreptomycine sulfate (10 g kg(-1)B.W.)+prednisolone acetate (1.2 mg kg(-1)B.W.) combination and i.m. ketamine (20 mg kg(-1)B.W.) every day by seven consecutive days. Experimental DD was conducted by insertion and then distension of rubber balloon (containing 40 ml of warm water) inserted into sheep duodenum. Duodenal distension produced a significant increase in behavioral pain manifestations, tachycardia, hyperventilation, inhibition of reticulo-ruminal contractions rate (from 87.2 to 38.0% during 15-20 min), an increase of plasma catecholamine concentration (over 6.4-fold increase of epinephrine during 2h following DD, 2-times norepinephrine and 84% increase of dopamine). Nifedipine infusion administered 10 min prior to DD decreased intensity of visceral pain manifestations such as: behavioral changes, hyperventilation, reticulo-rumen motility and efficiently prevent appearance of catecholamine release. These data demonstrated that the development and persistence of duodenal hyperalgesia depends on the activation of Ca(2+) ion flux leading to neurotransmitters release and modulation of membrane excitability. It seems that nifedipine given i.c.v. 10 min prior to DD (as a source of visceral pain), inhibited specific receptors 1 subunits of VGCCs in target tissues, prevented depolarization of cell membranes and release of neurotransmitters responsible for pain sensitivity in sheep. The observed antinociceptive action of VGCCs type L blockers suggest that these channels play a crucial role in the modulation of acute visceral hyperalgesia in sheep.

Differential blockade of CRF-evoked behaviors by depletion of norepinephrine and serotonin in rats

RATIONALE

Central administration of corticotropin-releasing factor (CRF) elicits a specific pattern of behavioral responses resembling a stress-like state and is anxiogenic in rodent models of anxiety.

OBJECTIVES

Specific behaviors evoked by the administration of CRF were measured. The roles of CRF receptor subtypes and that of serotonergic and noradrenergic systems in mediating these responses were studied.

MATERIALS AND METHODS

Burying, grooming, and head shakes were quantified in rats following intracerebroventricular administration of CRF and urocortin II and after pretreatment with antagonists. The role of forebrain norepinephrine in the behavioral responses to CRF (0.3 microg) was examined following pretreatment with the neurotoxin DSP-4 and that of serotonin after depletion using systemic administration of para-chlorophenylalanine (p-CPA).

RESULTS

CRF at 0.3 and 3.0 microg caused robust increases in burying, grooming, and head shakes, but urocortin II was ineffective. Pretreatment with either antalarmin or propranolol significantly attenuated the CRF-evoked behaviors. Destruction of forebrain norepinephrine pathways blocked spontaneous burying behavior elicited by CRF and conditioned burying directed towards an electrified shock probe. In contrast, depletion of 5-HT selectively attenuated CRF-evoked grooming.

CONCLUSIONS

Overt behavioral responses produced by CRF, burying, grooming, and head shakes appeared to be mediated through the CRF(1) receptor. Spontaneous burying behavior evoked by CRF or conditioned burying directed towards a shock probe was disrupted by lesion of the dorsal noradrenergic bundle and may represent anxiety-like behavior caused by CRF activation of the locus ceruleus. In contrast, CRF-evoked increases in grooming were dependent on serotonin.

Role of brain adrenoceptors in the corticortopin-releasing factor-induced central activation of sympatho-adrenomedullary outflow in rats

We investigated the role played by catecholamine-dependent pathways in modulating the ability of centrally administered corticotropin releasing factor (CRF) to activate sympatho-adrenomedullay outflow, using urethane-anesthetized rats. The CRF (1.5 nmol/animal, i.c.v.)-induced elevations of both plasma noradrenaline and adrenaline were attenuated by phentolamine (a non-selective alpha adrenoceptor antagonist) [125 and 250 microg (0.33 and 0.66 micromol)/animal], Heat (a selective alpha(1) adrenoceptor antagonist) [10 and 30 microg (30 and 90 nmol)/animal, i.c.v.] and clonidine (a selective alpha(2) adrenoceptor agonist) [100 microg (0.375 micromol)/animal, i.c.v.]. On the other hand, the CRF (1.5 nmol/animal, i.c.v.)-induced elevation of both catecholamines was not influenced by RS 79948 (a selective alpha(2) adrenoceptor antagonist) [10 and 30 microg (7.2 and 72 nmol)/animal, i.c.v.]. Furthermore, the CRF (1.5 nmol/animal, i.c.v.)-induced elevation of noradrenaline was attenuated by sotalol (a non-selective beta adrenoceptor antagonist) [125 and 250 microg (0.4 and 0.8 micromol)/animal, i.c.v.], while that of adrenaline was not influenced by sotalol. These results suggest that centrally administered CRF-induced elevation of plasma noradrenaline is mediated by an activation of alpha(1) and beta adrenoceptors in the brain, and that of plasma adrenaline is mediated by an activation of alpha(1) adrenoceptors in the brain. Furthermore, central alpha(2) adrenoceptors are involved in modulating the CRF-induced elevation of both plasma catecholamines.

Corticotropin releasing factor induces anxiogenic locomotion in trout and alters serotonergic and dopaminergic activity

Corticotropin releasing factor (CRF) and serotonin (5-HT) are strongly linked to stress and anxiety in vertebrates. As a neuromodulator in the brain, CRF has anxiogenic properties often characterized by increased locomotion and stereotyped behavior in familiar environments. We hypothesized that expression of anxiogenic behavior in response to CRF will also be exhibited in a teleost fish. Rainbow trout were treated with intracerebroventricular (icv) injections of artificial cerebrospinal fluid (aCSF), 500 or 2000 ng ovine CRF, or not injected. Treatment with either dose of CRF elicited greater locomotion and pronounced head shaking behavior but did not influence water column position. Locomotor and head shaking behaviors may be analogous to the increased stereotypy evoked by icv CRF in rats and may reflect the expression of stress/anxiety behavior. Injection with either aCSF or CRF produced significant increases in plasma cortisol. The absence of behavioral changes in aCSF-injected fish suggests that the behavioral responses following CRF were not due to cortisol. Treatment with 2000 ng CRF significantly increased serotonin, 5-HIAA and dopamine concentrations in the subpallium and raphé and increased 5-HIAA in the preoptic hypothalamus (POA). Concurrent effects of CRF on central monoamines, locomotion and head shaking in trout suggest that anxiogenic properties of CRF are evolutionarily conserved. In addition, positive linear correlations between locomotion and serotonergic and dopaminergic function in the subpallium, POA and raphé nuclei suggest a locomotory function for these monoamines.

Influence of enclosure size and animal density on fecal cortisol concentration and aggression in Père David's deer stags

We investigated the impact of enclosure size and animal density on behavior and adrenocortical secretion in Père David's deer in Dafeng Nature Reserve, China. From February 15 to April 16 in 2004, we conducted two experiments. First, we studied maintenance behavior and conflict behavior of Père David's deer stags in a large enclosure (200 ha) with low animal density (0.66 deer/ha) and a small display pen (0.75 ha) with high animal density (25.33 deer/ha). The maintenance behavior we recorded included standing, locomotion, foraging and rest. During the behavioral observations, we collected fresh voided fecal samples from the stags periodically, and analyzed the fecal cortisol concentrations in those samples using radioimmunoassay technique. Second, we monitored the fecal cortisol concentrations of one group of stags (12 deer lived in an enclosure of 100 ha) before and after transferred into a small pen (0.5 ha). We found that in the first experiment: (1) there were significant differences in standing and rest whereas no significant differences of locomotion and foraging between the free-ranging group and the display group; (2) frequency of conflict behavior in the display group was significantly higher than those in the free-ranging group; and (3) fecal cortisol concentration of the display group (326.17+/-16.98 ng/g dry feces) was significantly higher than that of the free-ranging group (268.98+/-15.21 ng/g dry feces). In the second experiment, there was no significant difference of the fecal cortisol concentrations among sampling days, but the mean fecal cortisol concentration of the day after transferring (337.46+/-17.88 ng/g dry feces) was significantly higher than that of the day before transferring (248.44+/-7.99 ng/g dry feces). Comparison with published findings, our results indicated that enclosure size and animal density affect not only behaviors, but also adrenocortical secretion in Père David's deer. Small living space with high animal density may impose physiological stress to captive Père David's deer. Moreover, long-term physiological stress and increase of conflict behavior may subsequently affect survival and reproduction of the deer.

Intracerebroventricular administration of corticotrophin-releasing hormone receptor antagonists produces different effects on hypothalamic pituitary adrenal responses to novel restraint depending on the stress history of the animal

Corticotrophin-releasing hormone (CRH) regulates acute stress-induced changes in neuroendocrine function and behaviour. However, little is known about CRH functions in animals that have prior experience with repeated stress. Repeatedly-stressed rats exhibit a habituated hypothalamic-pituitary-adrenal (HPA) response to a familiar, homotypic stressor but exhibit maintained or enhanced HPA responses to a novel, heterotypic stressor. We examined the effects of intracerebroventricular (i.c.v.) administration of two different nonselective CRH receptor antagonists, alpha-helical CRH(9-41) (ahCRH) or D-Phe CRH(12-41) (D-PheCRH), on HPA responses to acute restraint in rats previously exposed to repeated cold stress (i.e. facilitated responses). Antagonists were administered as single i.c.v. injections prior to restraint to provide a general index of CRH function in control versus repeatedly-stressed rats. CRH receptor blockade with either ahCRH or D-PheCRH produced different effects on HPA responses to novel restraint depending on whether the animal had been previously cold stressed or not. Interestingly, some agonist-type effects were observed but only in repeatedly-stressed rats. In summary, these results indicate that manipulations of the CRH receptor have different effects on HPA activity depending on the stress history of the animal.

Regulation of behavioral responses by corticotropin-releasing factor

In the wild, animals survive by responding to perceived threats with adaptive and appropriate changes in their behaviors and physiological states. The exact nature of these responses depends on species-specific factors plus the external context and internal physiological states associated with the stressful condition. The neuroendocrine mechanisms that control context-dependent stress responses are poorly understood for most animals, but some progress has been made recently. Corticotropin-releasing factor (CRF) plays an important role in mediating neuroendocrine, autonomic, and behavioral responses to stress. Across many vertebrate taxa, CRF not only stimulates the HPA axis by increasing the secretion of ACTH and glucocorticoid hormones, but also acts centrally by modifying neurotransmitter systems and behaviors. CRF or one of several CRF-related neuropeptides acts to stimulate locomotor activity during periods of acute stress. This behavioral activation consists of anxiety-related non-ambulatory motor activity, ambulatory locomotion, or swimming depending on the species and context. CRF-related neuropeptides increase swimming behaviors in amphibians and fish, apparently by activating brainstem serotonergic systems because the administration of fluoxetine (a selective serotonin re-uptake inhibitor) greatly enhances CRF-induced locomotor activity. Thus, our working model is that CRF, in part via interactions with brainstem serotonergic systems, modulates context-dependent behavioral responses to perceived threats, including both anxiety-related risk assessment behaviors and fight-or-flight locomotor responses.

Time- and dose-dependent effects of corticotropin releasing factor on cerebral glucose metabolism in rats

The time course and the relation to dose of locomotor activity and of the regional cerebral metabolic rates for glucose (rCMRglc) were measured in freely moving Sprague-Dawley rats after intracerebroventricular administration of ovine corticotropin releasing factor (oCRF). Motor activity was determined using a familiar photocage cell. rCMRglc was measured, using the quantitative autoradiographic [(14)C]2-deoxyglucose procedure, in 73 brain regions at 10, 30, 90 and 180 min after administration of oCRF 10 microg and at 90 min after oCRF 0.1, 1 and 100 microg. oCRF 10 microg increased motor activity in a sustained fashion and increased rCMRglc with different time courses throughout brain regions. In cerebellar regions rCMRglc increases peaked at 90 min and were sustained up to 180 min. In non-cerebellar regions rCMRglc increases peaked at 90 min but declined thereafter. At lower doses (0.1 and 1 microg) oCRF increased rCMRglc in fewer brain regions (1 and 5 regions affected, average increases 1% and 7%) including cerebellar areas and brainstem sensory nuclei and decreased rCMRglc in medial prefrontal cortex. At the highest dose (100 microg) oCRF induced large and widespread rCMRglc increases in cerebellar, brainstem, hypothalamic, limbic and neocortical areas (40 brain regions affected, average increase 32%). The findings indicate that cerebellar areas and brainstem nuclei are highly sensitive to oCRF and may mediate oCRF autonomic and behavioral effects.

Cardiovascular effects of long-term central and peripheral administration of urocortin, corticotropin-releasing factor, and adrenocorticotropin in sheep

The neuroendocrine hormones ACTH and corticotropin- releasing factor (CRF), which are involved in the stress response, have acute effects on arterial pressure. New evidence indicates that urocortin (UCN), the putative agonist for the CRF type 2 receptor, has selective cardiovascular actions. The responses to long-term infusions of these hormones, both peripherally and centrally, in conscious animals have not been studied. Knowledge of the long-term effects is important because they may differ considerably from their acute actions, and stress is frequently a chronic stimulus. The present experiments investigated the cardiovascular effects of CRF, UCN, and ACTH in conscious sheep. Infusions were made either into the lateral cerebral ventricles (i.c.v.) or i.v. over 4 d at 5 microg/h. UCN infused i.c.v. or i.v. caused a prolonged increase in heart rate (HR) (P < 0.01) and a small increase in mean arterial pressure (MAP) (P < 0.05). CRF infused i.c.v. or i.v. progressively increased MAP (P < 0.05) but had no effect on HR. Central administration of ACTH had no effect, whereas systemic infusion increased MAP and HR (P < 0.001). In conclusion, long-term administration of these three peptides associated with the stress response had prolonged, selective cardiovascular actions. The striking finding was the large and sustained increase in HR with i.c.v. and i.v. infusions of UCN. These responses are probably mediated by CRF type 2 receptors because they were not reproduced by infusions of CRF.

Receptor-Independent Activation of GABAergic Neurotransmission and Receptor-Dependent Nontranscriptional Activation of Phosphatidylinositol 3-kinase/Protein Kinase Akt Pathway in Short-Term Cardiovascular Actions of Dexamethasone at the Nucleus Tractus Solitarii of the Rat

Whereas glucocorticoids are important blood pressure regulators via an action on peripheral circulation, their roles in central cardiovascular regulation are less known. This study evaluated the short-term cardiovascular effect of glucocorticoid in the nucleus tractus solitarii (NTS) and delineated the underlying molecular mechanisms. In Sprague-Dawley rats maintained under propofol anesthesia, microinjection bilaterally into the NTS of a synthetic glucocorticoid, dexamethasone (Dex; 12.5, 25, 50, or 100 pmol), elicited hypertensive and tachycardiac responses. The initial cardiovascular responses, which lasted 15 to 30 min, were blunted by coadministration of a selective GABA(A) or GABA(B) receptor antagonist, bicuculline (15 pmol) or 2-hydroxy saclofen (150 pmol). The delayed responses, which endured at least 90 min and entailed maintained hypertension and tachycardia, were reversed by selective glucocorticoid type II receptor (GR) antagonist mifepristone (100 or 200 pmol), phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one] (20 nmol), or nitric-oxide synthase inhibitor N(G)-monomethyl-l-arginine acetate (5 nmol), but not by the RNA synthesis inhibitor actinomycin D (20 nmol). Moreover, Dex induced an association of GR with the regulatory subunit of PI3K, p85alpha, in a ligand-dependent manner and promoted serine/threonine kinase Akt phosphorylation that was blocked by coadministration of mifepristone or LY294002. These cardiovascular and molecular responses occurred when translocation of activated GR into the nucleus was minimal. Our results indicate that Dex acts on the NTS to elicit hypertension and tachycardia via both a GR-independent interaction with GABA(A) and GABA(B) receptors and a GR-dependent but nontranscriptional mechanism that involves activation of PI3K/Akt pathway.

Validation of a minimally invasive blood-sampling technique for the analysis of hormones in domestic rabbits, Oryctolagus cuniculus (Lagomorpha)

Previous studies in small mammals showed that blood-sucking bugs (Reduviidae, Heteroptera) can be used to obtain blood from veins difficult to access by human experimenters. In the present study, we validated the use of reduviid bugs for endocrinological studies in endotherms using domestic rabbits as a model organism. Two processes could alter the hormone concentrations in the blood ingested by the bug: (1) Mixing of ingested blood with saliva, gut fluid, or hemolymph and (2) digestive processes. We compared concentrations of progesterone, testosterone, and hydrocortisone in blood samples that were acquired from domestic rabbits (Oryctolagus cuniculus) by bugs (Dipetalogaster maxima) with hormone concentrations in blood obtained from the same individual rabbits with a conventional method, i.e., syringe. We found no significant differences in hormone concentrations between the two methods. Thus, the mixing effect is negligible immediately after the blood meal. In addition, we also could not find significant changes in concentrations of progesterone and hydrocortisone for up to 8h after the blood meal. Whereas levels of hydrocortisone remained unchanged for even 24h, progesterone levels significantly increased between eight and 24h. Thus, the bugs' excretory apparatus did not fractionate between water and hormones. Thirdly, we hypothesized that reduviid bugs impose less stress on the rabbits than the conventional method. We showed that deviations in hydrocortisone concentrations between the two blood sampling routines were lower when the bug method was used first and higher when the conventional method was used first. Thus, bugs imposed less stress on the study animals than the conventional method. Overall, we conclude that reduviid bugs present a minimally invasive method for obtaining blood from endotherm animals for endocrinological studies.

Visceromotor and spinal neuronal responses to colorectal distension in rats with aldosterone onto the amygdala

Stereotaxic delivery of corticosterone onto the amygdala produces colorectal hypersensitivity through activation of lumbosacral spinal neurons. Since corticosterone activates both the mineralocorticoid (MR) and glucocorticoid (GR) receptors, the aim of this study was to determine the importance of MRs in the regulation of colorectal hypersensitivity through the use of aldosterone that preferentially binds to MRs. Fischer-344 rats received either aldosterone (n = 18)- or cholesterol (control, n = 18)-containing micropellets bilaterally placed stereotaxically on the dorsal margin of the amygdala. After 1 wk, colorectal sensitivity to distension (30 mmHg) was measured in a subgroup of rats (n = 8/group). In other rats (n = 10/group), extracellular potentials of single L6-S1 spinal neurons in response to colorectal distension (CRD; 10-80 mmHg) were recorded. In aldosterone-implanted rats, CRD produced a greater visceromotor behavioral response compared with cholesterol controls (19 +/- 0.5 vs. 11.5 +/- 2.7; P < 0.01). A total of 68/182 (37%) and 56/167 (34%) of spinal neurons responded to noxious CRD in aldosterone-implanted and control groups, respectively. A total of 36/42 (86%) neurons excited by CRD had spontaneous activity in aldosterone-implanted groups compared with control (19/33, 58%, P < 0.01). Neurons with low thresholds for excitatory responses to CRD were seen more frequently in aldosterone-implanted rats than those in the control group (35/39 vs. 18/31, P < 0.05). Maximal excitatory responses of neurons to CRD in aldosterone-implanted rats were significantly greater (23.9 +/- 2.2 vs. 16.4 +/- 2.0 imp/s, P < 0.05), and the durations were longer (34.3 +/- 2.7 vs. 24.9 +/- 1.4 s, P < 0.05) than those in control group. Finally, a greater number of neurons had wide dynamic range responses to somatic stimulation in aldosterone-treated rats compared with cholesterol controls. Our findings suggest that, in the amygdala, MR receptor-mediated mechanisms are likely involved in descending pathways onto lumbosacral spinal neurons that induce colorectal hypersensitivity to luminal distension.

Effect of chronic administration of selective glucocorticoid receptor antagonists on the rat hypothalamic-pituitary-adrenocortical axis

The effects of the selective glucocorticoid receptor (GR) antagonists ORG 34850, ORG 34116, and ORG 34517 on the rat hypothalamic-pituitary-adrenocortical (HPA) system were investigated. To assess the potency of the compounds to occupy GR in the brain and pituitary, we applied a single acute subcutaneous (s.c.) injection (10 mg/kg). ORG 34517 was most potent to occupy GR in the anterior pituitary and distinct brain areas, whereas all compounds were unable to occupy mineralocorticoid receptor (MR). Chronic administration of ORG 34850, ORG 34116, and ORG 34517 (20 mg/kg/day) for 1, 3, and 5 weeks resulted only in minor changes in brain GR levels. However, profound increases of hippocampal MR were observed virtually at all time points. Treatment with ORG 34850 and ORG 34116 elicited episodic increases in HPA axis activity, whereas ORG 34517 did not cause any changes in HPA activity. Thus, the GR antagonists exert distinct effects on the HPA axis, which may be pertinent for the proposed antidepressant activity of these compounds.

Neuroendocrine pharmacology of stress

Exposure to hostile conditions initiates responses organized to enhance the probability of survival. These coordinated responses, known as stress responses, are composed of alterations in behavior, autonomic function and the secretion of multiple hormones. The activation of the renin-angiotensin system and the hypothalamic-pituitary-adrenocortical axis plays a pivotal role in the stress response. Neuroendocrine components activated by stressors include the increased secretion of epinephrine and norepinephrine from the sympathetic nervous system and adrenal medulla, the release of corticotropin-releasing factor (CRF) and vasopressin from parvicellular neurons into the portal circulation, and seconds later, the secretion of pituitary adrenocorticotropin (ACTH), leading to secretion of glucocorticoids by the adrenal gland. Corticotropin-releasing factor coordinates the endocrine, autonomic, behavioral and immune responses to stress and also acts as a neurotransmitter or neuromodulator in the amygdala, dorsal raphe nucleus, hippocampus and locus coeruleus, to integrate brain multi-system responses to stress. This review discussed the role of classical mediators of the stress response, such as corticotropin-releasing factor, vasopressin, serotonin (5-hydroxytryptamine or 5-HT) and catecholamines. Also discussed are the roles of other neuropeptides/neuromodulators involved in the stress response that have previously received little attention, such as substance P, vasoactive intestinal polypeptide, neuropeptide Y and cholecystokinin. Anxiolytic drugs of the benzodiazepine class and other drugs that affect catecholamine, GABA(A), histamine and serotonin receptors have been used to attenuate the neuroendocrine response to stressors. The neuroendocrine information for these drugs is still incomplete; however, they are a new class of potential antidepressant and anxiolytic drugs that offer new therapeutic approaches to treating anxiety disorders. The studies described in this review suggest that multiple brain mechanisms are responsible for the regulation of each hormone and that not all hormones are regulated by the same neural circuits. In particular, the renin-angiotensin system seems to be regulated by different brain mechanisms than the hypothalamic-pituitary-adrenal system. This could be an important survival mechanism to ensure that dysfunction of one neurotransmitter system will not endanger the appropriate secretion of hormones during exposure to adverse conditions. The measurement of several hormones to examine the mechanisms underlying the stress response and the effects of drugs and lesions on these responses can provide insight into the nature and location of brain circuits and neurotransmitter receptors involved in anxiety and stress.

Antagonistas do hormônio liberador da corticotrofina: atualização e perspectivas

Modelos genéticos e estudos epidemiológicos têm contribuído para a compreensão da fisiopatologia das doenças relacionadas ao estresse. O hormônio liberador da corticotrofina (CRH) pertence à família dos chamados peptídeos relacionados ao CRH, junto com a urocortina, urocortina II (ou peptídeo relacionado à estressecopina) e urocortina III (ou estressecopina). O CRH é o maior estimulador da secreção hipofisária de ACTH em humanos, e tem um papel importante na resposta fisiológica ao estresse. O CRH e seus receptores (tipos 1 e 2) estão difusamente distribuídos em todo o sistema nervoso central (SNC) e, em menor proporção, em tecidos periféricos. A distribuição dos receptores no SNC mostra ampla variabilidade entre as espécies. Os neurônios do CRH modulam a função autonômica e do sistema límbico. O CRH tem importantes efeitos, também, nos sistemas cardiovascular, metabólico e comportamental. As ações regionais deste peptídeo no SNC e na periferia são vários e apenas parcialmente conhecidos. Ações aberrantes do CRH estão implicadas em algumas condições psiquiátricas, incluindo depressão e ansiedade. Esta teoria tem sido corroborada por dados em ratos transgênicos que não expressam CRH e estudos pré-clínicos envolvendo a administração de antagonistas do CRH em macacos Rhesus. Embora ainda não disponível para uso clínico de rotina, dados preliminares de estudos conceituais envolvendo a administração oral de antagonistas do CRH em humanos são encorajadores. Entretanto, ainda permanece um desafio o desenvolvimento de antagonistas não peptídicos seletivos do receptor de CRH. Além disso, são extremamente necessários testes com estudos clínicos randomizados, que deverão trazer novas luzes sobre esta área.

Overexpression of corticotropin-releasing hormone in transgenic mice and chronic stress-like autonomic and physiological alterations

To gain a greater insight into the relationship between hyperactivity of the corticotropin-releasing hormone (CRH) system and autonomic and physiological changes associated with chronic stress, we developed a transgenic mouse model of central CRH overproduction. The extent of central and peripheral CRH overexpression, and the amount of bioactive CRH in the hypothalamus were determined in two lines of CRH-overexpressing (CRH-OE) mice. Furthermore, 24 h patterns of body temperature, heart rate, and activity were assessed using radiotelemetry, as well as cumulative water and food consumption and body weight gain over a 7-day period. CRH-OE mice showed increased amounts of CRH peptide and mRNA only in the central nervous system. Despite the presence of the same CRH transgene in their genome, only in one of the two established lines of CRH-OE mice (line 2122, but not 2123) was overexpression of CRH associated with increased levels of bioactive CRH in the hypothalamus, increased body temperature and heart rate (predominantly during the light (inactive) phase of the diurnal cycle), decreased heart rate variability during the dark (active) phase, and increased food and water consumption, when compared with littermate wildtype mice. Because line 2122 of the CRH transgenic mice showed chronic stress-like neuroendocrine and autonomic changes, these mice appear to represent a valid animal model for chronic stress and might be valuable in the research on the consequences of CRH excess in situations of chronic stress.

Hormones as indicators of stress

Animal welfare is of increasing importance and absence of chronic stress is one of its prerequisites. During stress, various endocrine responses are involved to improve the fitness of the individual. The front-line hormones to overcome stressful situations are the glucocorticoids and catecholamines. These hormones are determined as a parameter of adrenal activity and thus of disturbance. The concentration of glucocorticoids (or their metabolites) can be measured in various body fluids or excreta. Above all, fecal samples offer the advantage that they can be easily collected and this procedure is feedback free. Recently, enzyme immunoassays (EIA) have been developed and successfully tested, to enable the measurement of groups of cortisol metabolites in animal feces. The determination of these metabolites in fecal samples is a practical method to monitor glucocorticoid production.

Neuroendocrinology of stress

Stimuli that are interpreted by the brain as extreme or threatening, regardless of their modality, elicit an immediate stereotypic response characterized by enhanced cognition, affective immobility, vigilance, autonomic arousal and a global catabolic state. The brain's ability to mobilize this so-called stress response is paralleled by activation of corticotropin-releasing hormone (CRH) in several nuclei, including the hypothalamus, amygdala and locus ceruleus, and stimulation of the locus ceruleus norepinephrine (LC/NE) system in the brain stem. These systems perpetuate one another, interact with several other transmitter systems in the brain and directly activate the hypothalamic-pituitary-adrenal (HPA) axis and the three components of the autonomic nervous system, namely the sympatho-adrenal, the cranio-sacral parasympathetic and the enteric nervous systems. The widespread body system responses to stress are discussed, and the implications of aberrant stress system activity on physical and mental health are outlined. Moreover, the promise of nonpeptide CRH type-1 receptor antagonists to directly target the stress system in the brain is highlighted.

Psychological stress increases hippocampal mineralocorticoid receptor levels: involvement of corticotropin-releasing hormone

We investigated whether acute stressors regulate functional properties of the hippocampal mineralocorticoid receptor (MR), which acts inhibitory on hypothalamic-pituitary-adrenocortical activity. Exposure of rats to forced swimming or novelty evoked a significant rise in density of MR immunoreactivity in all hippocampal subfields after 24 hr, whereas exposure to a cold environment was ineffective. Time course analysis revealed that the effect of forced swimming on MR peaked at 24 hr and returned to control levels between 24 and 48 hr. In pyramidal neurons of CA2 and CA3, marked rises were already observed after 8 hr. Radioligand binding assays showed that corticotropin-releasing hormone (CRH) injected intracerebroventricularly into adrenalectomized rats also produced a rise in hippocampal MR levels; an effect for which the presence of corticosterone, but not dexamethasone, at the time of injection was a prerequisite. Moreover, pretreatment with the CRH receptor antagonist (d-Phe(12),Nle(21,38),alpha-Me-Leu(37))-CRH(12-41) blocked the effect of forced swimming on hippocampal MR levels. To investigate whether the rise in MR levels had any functional consequences for HPA regulation, 24 hr after forced swimming, a challenge test with the MR antagonist RU 28318 was conducted. The forced swimming exposed rats showed an enhanced MR-mediated inhibition of HPA activity. This study identifies CRH as an important regulator of MR, a pathway with marked consequence for HPA axis regulation. We conclude that the interaction between CRH and MR presents a novel mechanism involved in the adaptation of the brain to psychologically stressful events.

Noninvasive monitoring of adrenocortical activity in roe deer (Capreolus capreolus) by measurement of fecal cortisol metabolites

A method for measuring glucocorticoids noninvasively in feces of roe deer was established and validated. The enzyme immunoassay (EIA) measures 11,17-dioxoandrostanes (11,17-DOA), a group of cortisol metabolites. Such measurement avoids blood sampling and reflects a dampened pattern of diurnal glucocorticoid secretion, providing an integrated measure of adrenocortical activity. After high-performance liquid chromatography, the presence of at least three different immunoreactive 11,17-DOA in the feces of roe deer was demonstrated. The physiological relevance of these fecal cortisol metabolites to adrenocortical activity was evaluated with an adrenocorticotropic hormone challenge test: cortisol metabolite concentrations exceeded pretreatment levels (31-78 ng/g) up to 13-fold (183-944 ng/g) within 8-23 h. Starting from basal levels between 13 and 71 ng/g, a suppression of adrenocortical activity after dexamethasone administration, indicated by metabolite levels close to the detection limit, was obtained 36-81 h after treatment, whereas unmetabolized dexamethasone was detectable in feces 12 h after its injection. Fecal glucocorticoid metabolite assessment via EIA is therefore of use in the monitoring of adrenocortical activity in roe deer. In a second experiment, capture, veterinary treatment, and transportation of animals were used as experimental stresses. This resulted in a 7.5-fold increase of fecal metabolites (1200 +/- 880 ng/g, mean +/- SD) compared to baseline concentrations. The administration of a long-acting tranquilizer (LAT), designed to minimize the physiological stress response, 2 days prior to a similar stress event led to a reduced stress response, resulting in only a 4-fold increase of fecal metabolites (650 +/- 280 ng/g; mean +/- SD). Therefore, LATs should be further investigated for their effectiveness in reducing stress responses in zoo and wild animals, e.g., when translocations are necessary.

Glucocorticoid and mineralocorticoid receptors are involved in the facilitation of anxiety-like response induced by restraint

In previous studies, we have shown that male Wistar rats exposed to a single inescapable stressor session (15 min restraint) exhibited 24 h later an anxiogenic-like behavior in the elevated plus-maze (EPM), which was reversed by inhibition of corticosterone (CS) synthesis with metyrapone (75 mg/kg i.p.) 3 h before stress. Since CS binds to two central corticosteroid receptors, the mineralocorticoid (MR) and the glucocorticoid (GR) receptors, involvement of MR and GR in the modulation of anxiogenic responses was assessed in the EPM. Administration of the GR agonist dexamethasone (Dex, 1.25 microg/kg s.c.) to metyrapone-pretreated rats 1 h before restraint restored the anxiogenic-like response induced by the stressor. Removal of the adrenals also inhibited the anxiogenic-like effect, which was restored by either Dex (1.25 microg/kg s.c.), the MR agonist deoxycorticosterone (0.8 mg/kg s.c.) or CS, the common endogenous agonist of MR and GR (5 mg/kg s.c.) administered 1 h before stress. Intracerebroventricular infusion to intact animals 15 min before restraint of either a selective GR antagonist (A-GR, RU 38486, 100 ng/2 microl), a selective MR antagonist (A-MR, RU 28318, 100 ng/2 microl) or a combination of A-GR and A-MR (100 ng of each one/2 microl), abolished the stress-induced anxiogenic-like effect. The present findings indicate that both MR and GR are involved in the long-term CS modulation of the anxiety response induced by restraint. Both receptors mediate CS effects in an independent manner.

Urocortin, corticotropin releasing factor-2 receptors and energy balance

Although there is considerable information regarding the role of brain CRF in energy balance, relatively little is known about the role of urocortin (UCN), which is an equally potent anorexic agent. Therefore, the effects of intracerebroventricular (icv) administration of UCN (0.01-1 nmol/day) on food intake and body weight were assessed over a period of 13 days and compared with data from CRF-infused counterparts. Although both peptides dose dependently reduced food intake and weight gain, the effects of CRF were much greater in magnitude than those of UCN, particularly on body weight. Pair-feeding studies suggested that, while the effects of CRF on body weight could not be completely explained by appetite suppression, the effects of UCN appeared to be due to its initial impact on food intake. CRF increased brown adipose fat pad and adrenal weights, whereas it reduced thymus and spleen weights. CRF also increased serum corticosterone, triglyceride, FFA, and cholesterol levels, whereas it reduced glucose. UCN did not produce any consistent changes in any of these indices of sympathetic nervous system activation. Concurrent administration of the CRF(2)-selective antagonist, antisauvagine-30 (ASV-30) (30 nmol/day) completely reversed or attenuated the effects of UCN and CRF (1 nmol/day) on food intake and body weight. ASV-30 did not significantly attenuate any of the above CRF-induced changes in tissue weights or serum chemistry. These data suggest that the central CRF(2) receptor may primarily mediate the anorexic, but not the metabolic effects of CRF.

Corticosteroids in relation to fear, anxiety and psychopathology

Corticosteroids play extremely important roles in fear and anxiety. The mechanisms by which corticosteroids exert their effects on behavior are often indirect, because, although corticosteroids do not regulate behavior, they induce chemical changes in particular sets of neurons making certain behavioral outcomes more likely in certain contexts as a result of the strengthening or weakening of particular neural pathways. The timing of corticosteroid increase (before, during or after exposure to a stressor) determines whether and how behavior is affected. The present review shows that different aspects of fear and anxiety are affected differentially by the occupation of the mineralocorticoid receptor (MR) or glucocorticoid receptor (GR) at different phases of the stress response. Corticosteroids, at low circulating levels, exert a permissive action via brain MRs on the mediation of acute freezing behavior and acute fear-related plus-maze behavior. Corticosteroids, at high circulating levels, enhance acquisition, conditioning and consolidation of an inescapable stressful experience via GR-mechanisms. Brain GR-occupation also promotes processes underlying fear potentiation. Fear potentiation can be seen as an adjustment in anticipation of changing demands. However, such feed-forward regulation may be particularly vulnerable to dysfunction. MR and/or GR mechanisms are involved in fear extinction. Brain MRs may be involved in the extinction of passive avoidance, and GRs may be involved in mediating the extinction of active avoidance. In the developing brain, corticosteroids play a facilitatory role in the ontogeny of freezing behavior, probably via GRs in the dorsal hippocampus, and their influence on the development of the septo-hippocampal cholinergic system. Corticosteroids can exert maladaptive rather than adaptive effects when their actions via MRs and GRs are chronically unbalanced due to chronic stress. Both mental health of humans and animal welfare is likely to be seriously threatened after psychosocial stress, prolonged stress, prenatal stress or postnatal stress, especially when maternal care or social support is absent, because these can chronically dysregulate the central MR/GR balance. In such circumstances the normally adaptive corticosteroid responses can become maladaptive.

Role of corticotropin-releasing factor, vasopressin and the autonomic nervous system in learning and memory

Learning and memory are essential requirements for every living organism in order to cope with environmental demands, which enables it to adapt to changes in the conditions of life. Research on the effects of hormones on memory has focused on hormones such as adrenocorticotropic hormone (ACTH), glucocorticoids, vasopressin, oxytocin, epinephrine, corticotropin-releasing factor (CRF) that are released into the blood and brain following arousing or stressful experiences. Most of the information have been derived from studies on conditioned behavior, in particular, avoidance behavior in rats. In these tasks, an aversive situation was used as a stimulus for learning. Aversive stimuli are associated with the release of stress hormones and neuropeptides. Many factors play a role in different aspects of learning and memory processes. Neuropeptides not only affect attention, motivation, concentration and arousal or vigilance, but also anxiety and fear. In this way, they participate in learning and memory processes. Furthermore, neuropeptides such as CRF and vasopressin modulate the release of stress hormones such as epinephrine. In turn, systemic catecholamines enhance memory consolidation. CRF and vasopressin are colocalized in neurons from the nucleus paraventricularis, which project to nuclei in the brainstem involved in autonomic regulation. The objective of this paper is to discuss the role of CRF, vasopressin, and the autonomic nervous system (ANS) in learning and memory processes. Both CRF and vasopressin have effects in the same direction on behavior, learning and memory processes and stress responses (release of catecholamines and ACTH). These neuropeptides may act synergistically or in a concerted action aimed to learn to adapt to environmental demands.

Neurally active stress peptide inhibits territorial defense in wild birds

It is unclear whether the behavioral effects of peptides in laboratory studies always reflect natural conditions. Here we test whether we can detect measurable behavioral changes after rapidly injecting peptides into the brains of wild birds. We used a modified stereotaxic-like technique to inject corticotrophin-releasing factor (CRF) and arginine vasotocin (AVT, the nonmammalian form of arginine vasopressin), two hormones important in the stress response, into the brains of wild, freely behaving, male white-crowned sparrows (Zonotrichia leucophrys). We then monitored subsequent territorial behavior to determine whether CRF or AVT altered this behavior. Surprisingly, the potent stressors of capture and surgery did not eliminate territorial behavior, with many birds resuming territorial defense within 60-90 min after surgery. Centrally acting CRF, however, significantly reduced territorial defense whereas centrally acting AVT had no effect. These results indicate that the behavioral affects of peptides can be studied under natural conditions.

Differential effects of CRH infusion into the central nucleus of the amygdala in the Roman high-avoidance and low-avoidance rats

Roman-high (RHA/Verh) and low (RLA/Verh) avoidance rats are selected and bred for rapid learning versus non-acquisition of two-way, active avoidance behavior in a shuttle box. RHA/Verh rats generally show a more active coping style than do their RLA/Verh counterparts when exposed to various environmental challenges. The central nucleus of the amygdala (CeA) is known to be involved in the regulation of autonomic, neuroendocrine and behavioural responses to stress and stress-free conditions, and it is considered in relation to coping strategies. Corticotropin-releasing hormone (CRH) seems to be a key factor in the control of the CeA output. Neuroanatomical studies have revealed that the majority of CRH fibers from the CeA have direct connections with autonomic regulatory nuclei in the brainstem, e.g. lateral parabrachial nucleus (lPB), ventrolateral periaquaductal gray (vlPAG). The modulating effects of CRH (30 ng) on CeA activity were studied by infusion of CRH into the CeA in freely moving male RHA/Verh and RLA/Verh rats under stress-free conditions. Heart-rate and behavioural activities were repeatedly measured before, during and after local administration of CRH or vehicle, after which early gene product FOS immunocytochemistry and CRH-mRNA in situ hybridisation were carried out in selected brain areas. CRH infusion into the CeA caused a long lasting increase in heart-rate and behavioural activation in the RHA/Verh rats, leaving the RLA/Verh rats unaffected. As a result of CRH infusion, the number of FOS positive cells in the CeA and lPB of RLA/Verh rats was increased whereas an opposite response was found in the RHA/Verh rats. However, CRH into the CeA of the Roman rat lines induced no pronounced effects on FOS staining in the vlPAG and CRH mRNA levels in the CeA. These results indicate that the CRH system of the CeA, connected with the output brainstem areas, is differentially involved in cardiovascular and behavioural responses.

Inhibition of stress-induced neuroendocrine and behavioral responses in the rat by prepro-thyrotropin-releasing hormone 178-199

A corticotropin release-inhibiting factor (CRIF) in brain has been postulated for several decades, based on increased plasma levels of ACTH and corticosterone after hypothalamic-pituitary disconnection. Recent in vitro studies indicate that prepro-TRH178-199 may function as an endogenous CRIF, prompting us to examine stress-related neuroendocrine and behavioral responses after in vivo administration to the adult male rat. Animals that were administered prepro-TRH178-199 intravenously 5 min before restraint stress exhibited a significant attenuation of stress-induced elevations of ACTH, corticosterone, and prolactin, as compared with controls infused with vehicle, whereas thyroid-stimulating hormone (TSH) secretion was not changed. In behavioral studies of stress responsiveness, either the vehicle or prepro-TRH178-199 was administered intracerebroventricularly (ICV) 5 min before testing. In the open field, prepro-TRH178-199 significantly increased grooming, locomotor activity, rearing, and sniffing behaviors. In the light/dark box, it significantly increased the time animals spent in the light compartment and increased the number of crossings between the light/dark compartments. In the plus maze, the peptide significantly increased the amount of time animals spent in the open arms. The same dose of peptide, administered ICV, had no effect on peripheral hormone release in response to restraint stress. Overall, these results support a role for prepro-TRH178-199 in the inhibition of the neuroendocrine responses to stress at the level of the pituitary and indicate that it has central modulatory influences over stress-related behaviors.

Corticosteroid receptor antagonists: a current perspective

This review aims to highlight a selection of antagonists for the mineralocorticoid and glucocorticoid receptors. Concepts of these receptor systems are described, as is the mechanism of action of these steroids in the brain and periphery. Examples of commonly available and newly synthesized antimineralocorticoids and antiglucocorticoids are given, together with their pharmacological profiles and, when appropriate, clinical and therapeutic applications.

Comparison of hCRF and oCRF effects on cardiovascular responses after central, peripheral, and in vitro application

Three assays have been used to show that the neuropeptides human corticotropin-releasing factor (hCRF) and the ovine analogue oCRF produced substantial dose-dependent cardiovascular responses. The assays included intracerebroventricular (ICV) and intravenous (IV) administration in conscious rats, and also in vitro experiments with resistance arteries. Central administration of the peptides (0.1-10 micrograms, ICV) caused an increase in blood pressure and heart rate, whereas peripheral administration (0.75-750 micrograms/kg, IV) produced a decrease in blood pressure and tachycardia. Isometric ring preparations of mesenteric resistance arteries (diameter 200 microns) relaxed in response to both peptides (1-100 nM). In all cases, the effects were more pronounced for hCRF compared to compared to oCRF. Furthermore, all effects were inhibited by the CRF analogue alpha-helical CRF(9-41), the effect of the analogue being most potent against oCRF. The results of all three assays indicate that the difference in structure between hCRF and oCRF produces differences in biological activity.

Behavioural activation produced by CRH but not alpha-helical CRH (CRH-receptor antagonist) when microinfused into the central nucleus of the amygdala under stress-free conditions

The central nucleus of the amygdala (CeA) is known to be involved in the regulation of autonomic, neuroendocrine, and behavioural responses in stress situations. The CeA contains large numbers of corticotropin-releasing hormone (CRH)-containing cell bodies and terminals. In the present study we examined (by continuous behaviour observations) the effects of a high dose of CRH (150 ng) and two doses of the CRH-receptor antagonist (alpha-hCRH: 1.0 and 0.1 micrograms) after microinfusion into the CeA in freely moving male Wistar rats under stress-free conditions. In comparison with control, alpha-hCRH infusion did not cause any behavioural activation. In contrast CRH-infusion revealed a long-lasting increase in grooming and exploration with a concomitant decrease in behaviours specified as resting. These results indicate that the CRH system in the CeA does not seem to be activated in stress-free conditions, but its activation is of importance for active behavioural responses.

Anxiolytic-like effects of selective mineralocorticoid and glucocorticoid antagonists on fear-enhanced behavior in the elevated plus-maze

The effects of intracerebroventricular (ICV) administration of the mineralocorticoid receptor (MR) antagonist, RU28318, and the glucocorticoid receptor (GR) antagonist, RU38486, were studied on behavior of rats exposed to a compartment previously associated with a stressor, and placed subsequently in an elevated plus-maze test. Fear-motivated immobility behavior was attenuated by the MR antagonist in a dose of 50 or 100 ng ICV, whereas the GR antagonist alone or simultaneous administration of both antagonists had no significant effect. In the elevated plus-maze, immediately after the exposure to the conditioned stressor, both the GR antagonist (50 ng) and MR antagonist (50 ng) increased the percentage of time the rats spent on open arms, and increased the amount of entries into these open arms. These data are interpretated in terms of the involvement of the GR and MR in fear and anxiety.