CRF Administration Research Articles

Long‐term Somatic Hypoalgesia as a Marker of Pathological Conditions in Gastrointestinal Tract

Pain is traditionally considered as an evolutionarily developed defensive response to noxious stimulus. Short‐term pain suppression in response to stressful factors (stress‐induced analgesia) is an important adaptive reaction that is required for survival if further injury or death were threatened. In contrast, long‐term pain suppression may be considered as a sign of pain abnormality induced by disturbance of endogenous pain mechanisms under circumstances of pathology. Indomethacin (IM) is commonly used in clinic; however, it has a side ulcerogenic effect on the gastrointestinal tract. Previously we have shown that the formation IM‐induced injury in gastrointestinal tract is accompanied by a decrease in somatic pain sensitivity lasting, a least, for 72 h after IM injection (long‐term somatic hypoalgesia). Here we tested hypothesis that suppression of pathological process in gastrointestinal tract may prevent somatic hypoalgesia and normalize pain regulation in conscious rats. For this we studied effects of “stress preconditioning” on the gastrointestinal tract and somatic pain sensitivity under circumstances of ulcerogenic action of IM (35 mg/kg, sc). Preliminary (24 h) fasted rats were subjected one of four exposures (“stress preconditioning”) before IM administration: a) cold restraint (30 min, t=10 degree C, 1 h before IM); b) CRF (1.25 mkg/kg, ip, 30 min before IM) administration; c) capsaicin (0.5/kg, sc, 1 h before IM) administration, d) forced treadmill running (30 min, 1 h before IM). Pain sensitivity was assessed by tail flick latencies (tail flick test) or number of pain responses induced by acetic acid (“writhing test”). IM administration caused the formation of gastric erosion (2–4 h after injection) and small intestine injury (24, 48, 72 h after injection) that was accompanied by an increase in tail flick latencies (long‐term somatic hypoalgesia). Somatic hypoalgesia 48 h after IM injection was also supported by a decrease in number of pain responses induced by acetic acid. IM‐induced pathological process in the gastrointestinal tract was followed by changes in plasma corticosterone levels, cardiovascular (heart rate, blood pressure) and somatic (weights of thymus and adrenals, body weight) parameters. Each preconditioning exposure attenuated IM‐induced gastric mucosa injury and prevented somatic hypoalgesia. The results obtained suggest that long‐term somatic hypoalgesia may be one of characteristics of pathological process in the gastrointestinal tract induced by ulcerogenic action of IM.Support or Funding InformationThe study was supported by grant of Russian Science Foundation (RSF) №14‐15‐00790.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Discovery of 1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazoles as novel class of corticotropin releasing factor 1 receptor antagonists

A new class of corticotropin releasing factor 1 (CRF1) receptor antagonists characterized by a tricyclic core ring was designed and synthesized. Novel tricyclic derivatives 2a–e were designed as CRF1 receptor antagonists based on conformation analysis of our original 2-anilinobenzimidazole CRF1 receptor antagonist. The synthesized tricyclic derivatives 2a–e showed CRF1 receptor binding activity with IC50 values of less than 400 nM, and the 1,2,3,4-tetrahydropyrimido-[1,2-a]benzimidazole derivative 2e was selected as a lead compound with potent in vitro CRF1 receptor binding activity (IC50 = 7.1 nM). To optimize the pharmacokinetic profiles of lead compound 2e, we explored suitable substituents on the 1-position and 6-position, leading to the identification of compound 42c-R, which exhibited potent CRF1 receptor binding activity (IC50 = 58 nM) with good oral bioavailability (F = 68% in rats). Compound 42c-R exhibited dose-dependent inhibition of [125I]-CRF binding in the frontal cortex (5 and 10 mg/kg, p.o.) as well as suppression of locomotor activation induced by intracerebroventricular administration of CRF in rats (10 mg/kg, p.o.). These results suggest that compound 42c-R successfully binds CRF1 receptors in the brain and exhibits the potential to be further examined for clinical studies.

ВЛИЯНИЕ БЛОКАДЫ ГАМКА-РЕЦЕПТОРОВ НА ИЗМЕНЕНИЯ ОРИЕНТИРОВОЧНО-ИССЛЕДОВАТЕЛЬСКОЙ АКТИВНОСТИ И ТРЕВОЖНОСТИ, ВЫЗВАННЫХ КОРТИКОЛИБЕРИНОМ

The effect of the GABAA-receptor blockade with picrotoxin on the change in anxiety level under stress conditions induced by CRF was studied. In the T-maze test from the population of Wistar rats were selected animals with an active strategy of adaptive behavior, which in the elevated plus maze were divided into three groups: low anxiety (LA), high anxiety (HA) and mean anxiety (MA). Picrotoxin and CRF were injected intracerebroventricularly (ICV). The LA rats reacted to ICV administration of CRF with a decrease in the exploration activity, while the activity of the HA rats after the CRF injection was increased. The GABAA-receptor blockade with picrotoxin increased the exploration activity in HA and LA of rats, while simultaneously reducing the level of anxiety. After injection of CRF against of picrotoxin administration, the HA and LA rats demonstrated the decrease of exploration activity, and the level of anxiety increased only in LA rats. In animals from the MA group, the change in the behavioral response was observed only after the CRF and picrotoxin administration: the level of anxiety decreased, and the exploration activity increased. It is concluded that the vector of anxiety changes caused by CRF against the decrease in the activity of the stress-limiting GABA-ergic system depends on the initial psycho-emotional status of the animal.

Overexpression of corticotropin releasing factor in the central nucleus of the amygdala advances puberty and disrupts reproductive cycles in female rats.

Prolonged exposure to environmental stress activates the hypothalamic-pituitary-adrenal (HPA) axis and generally disrupts the hypothalamic-pituitary-gonadal axis. Because CRF expression in the central nucleus of the amygdala (CeA) is a key modulator in adaptation to chronic stress, and central administration of CRF inhibits the hypothalamic GnRH pulse generator, we tested the hypothesis that overexpression of CRF in the CeA of female rats alters anxiety behavior, dysregulates the HPA axis response to stress, changes pubertal timing, and disrupts reproduction. We used a lentiviral vector to increase CRF expression site specifically in the CeA of preweaning (postnatal day 12) female rats. Overexpression of CRF in the CeA increased anxiety-like behavior in peripubertal rats shown by a reduction in time spent in the open arms of the elevated plus maze and a decrease in social interaction. Paradoxically, puberty onset was advanced but followed by irregular estrous cyclicity and an absence of spontaneous preovulatory LH surges associated with proestrous vaginal cytology in rats overexpressing CRF. Despite the absence of change in basal corticosterone secretion or induced by stress (lipopolysaccharide or restraint), overexpression of CRF in the CeA significantly decreased lipopolysaccharide, but not restraint, stress-induced suppression of pulsatile LH secretion in postpubertal ovariectomized rats, indicating a differential stress responsivity of the GnRH pulse generator to immunological stress and a potential adaptation of the HPA axis to chronic activation of amygdaloid CRF. These data suggest that the expression profile of this key limbic brain CRF system might contribute to the complex neural mechanisms underlying the increasing incidence of early onset of puberty on the one hand and infertility on the other attributed to chronic stress in modern human society.

Paradoxical response to the sedative effects of diazepam and alcohol in C57BL/6J mice lacking the neuropeptide S receptor

The neuropeptide S (NPS) system is characterized by a unique pharmacology because it has anxiolytic-like effects and promotes arousal and wakefulness. To shed light on this peptidergic system, we tested the sedative effect of the central depressants diazepam and ethanol on the loss of righting reflex in mice lacking the neuropeptide S receptor (NPSR), NPSR(−/−). Furthermore, we tested the effect of the intracerebroventricular (ICV) administration of NPS on the sedative effect of diazepam and ethanol in NPSR(−/−) and their wild type counterpart NPSR(+/+). Finally, we evaluated the effect of the pro-arousal neuropeptides CRF and Hcrt-1/Ox-A in NPSR-deficient mice. Contrary to our expectations, the results showed that the NPSR(−/−) were less sensitive to the hypnotic effects of both diazepam and ethanol compared with their wild type littermates. ICV NPS was able to attenuate the sedative effect of both alcohol and diazepam in wild type mice, but not in the NPSR(−/−) line. The administration of CRF and Hcrt-1/Ox-A, two classic pro-arousal peptides, elicited the same effects in both NPSR(−/−) and wild type mice, ruling out the possibility that adaptive mechanisms occurring at the level of these two systems could have occurred during NPSR(−/−) development to compensate for the lack of NPSR receptors. Our findings demonstrated that the deletion of NPSR leads to minor changes in the arousal behavior of mice. Moreover, we demonstrated that the deletion of NPSR did not lead to compensatory changes in the vigilance-promoting effects of the CRF and Hcrt-1/Ox-A systems.

An intrinsic CRF signaling system within the optic tectum

Previous work indicates that CRF administration inhibits visually guided feeding in amphibians. We used the African clawed frog Xenopus laevis to examine the hypothesis that CRF acts as a neurotransmitter in the optic tectum, the major brain area integrating the visual and premotor pathways regulating visually guided feeding in anurans. Reverse transcriptase PCR revealed that cells in the optic tectum express mRNA for CRF and the CRF R1 receptor but not the CRF R2 receptor. Radioligand binding studies indicated that specific binding of [125I]-Tyr-oCRF to tectal cell membranes can be displaced by the CRF R1 antagonists antalarmin or NBI-27914. CRF increased the expression of mRNA encoding regulator of G-protein signaling 2 (rgs2) in tectal explants and this effect was blocked by antalarmin. CRF had no effect on basal glutamate or gamma-aminobutyric acid (GABA) secretion but inhibited secretion of norepinephrine from tectal explants, an effect that completely blocked by antalarmin. Using a homologous radioimmunoassay we determined that CRF release from tectal explants in vitro was potassium- and calcium-dependent. Basal and depolarization-induced CRF secretion was greater from optic tectum than hypothalamus/thalamus, telencephalon, or brainstem. We concluded that the optic tectum possesses a CRF signaling system that may be involved in modulating communication between sensory and motor pathways involved in food intake.

Non-pain-related CRF1 activation in the amygdala facilitates synaptic transmission and pain responses.

BackgroundCorticotropin-releasing factor (CRF) plays an important role in affective states and disorders. CRF is not only a “stress hormone” but also a neuromodulator outside the hypothalamic-pituitary-adrenocortical (HPA) axis. The amygdala, a brain center for emotions, is a major site of extrahypothalamic expression of CRF and its G-protein-coupled receptors. Our previous studies showed that endogenous activation of CRF1 receptors in an arthritis pain model contributes to amygdala hyperactivity and pain-related behaviors. Here we examined the synaptic and behavioral effects of CRF in the amygdala of normal animals in the absence of tissue injury or disease.ResultsWhole-cell patch-clamp recordings of neurons in the latero-capsular division of the central nucleus of the amygdala (CeLC) in brain slices from normal rats showed that CRF (0.1-10 nM) increased excitatory postsynaptic currents (EPSCs) at the “nociceptive” parabrachio-amygdaloid (PB-CeLC) synapse and also increased neuronal output. Synaptic facilitation involved a postsynaptic action and was blocked by an antagonist for CRF1 (NBI27914, 1 μM) but not CRF2 (astressin-2B, 1 μM) and by an inhibitor of PKA (KT5720, 1 μM) but not PKC (GF109203X, 1 μM). CRF increased a latent NMDA receptor-mediated EPSC, and this effect also required CRF1 and PKA but not CRF2 and PKC. Stereotaxic administration of CRF (10 μM, concentration in microdialysis probe) into the CeLC by microdialysis in awake rats increased audible and ultrasonic vocalizations and decreased hindlimb withdrawal thresholds. Behavioral effects of CRF were blocked by a NBI27914 (100 μM) and KT5720 (100 μM) but not GF109203x (100 μM). CRF effects persisted when HPA axis function was suppressed by pretreatment with dexamethasone (50 μg/kg, subcutaneously).ConclusionsNon-pain-related activation of CRF1 receptors in the amygdala can trigger pain-responses in normal animals through a mechanism that involves PKA-dependent synaptic facilitation in CeLC neurons independent of HPA axis function. The results suggest that conditions of increased amygdala CRF levels can contribute to pain in the absence of tissue pathology or disease state.

Enduring sensorimotor gating abnormalities following predator exposure or corticotropin-releasing factor in rats: A model for PTSD-like information-processing deficits?

A deficit in prepulse inhibition (PPI) can be one of the clinically observed features of post-traumatic stress disorder (PTSD) that is seen long after the acute traumatic episode has terminated. Thus, reduced PPI may represent an enduring psychophysiological marker of this illness in some patients. PPI is an operational measure of sensorimotor gating and refers to the phenomenon in which a weak stimulus presented immediately before an intense startling stimulus inhibits the magnitude of the subsequent startle response. The effects of stress on PPI have been relatively understudied, and in particular, there is very little information on PPI effects of ethologically relevant psychological stressors. We aimed to develop a paradigm for evaluating stress-induced sensorimotor gating abnormalities by comparing the effects of a purely psychological stressor (predator exposure) to those of a nociceptive physical stressor (footshock) on PPI and baseline startle responses in rats over an extended period of time following stressor presentation. Male Sprague–Dawley rats were exposed (within a protective cage) to ferrets for 5 min or left in their homecage and then tested for PPI immediately, 24 h, 48 h, and 9 days after the exposure. The effects of footshock were evaluated in a separate set of rats. The effects seen with stressor presentation were compared to those elicited by corticotropin-releasing factor (CRF; 0.5 and 3 μg/6 μl, intracerebroventricularly). Finally, the effects of these stressors and CRF administration on plasma corticosterone were measured. PPI was disrupted 24 h after ferret exposure; in contrast, footshock failed to affect PPI at any time. CRF mimicked the predator stress profile, with the lowdose producing a PPI deficit 24 h after infusion. Interestingly, the high dose also produced a PPI deficit 24 h after infusion, but with this dose, the PPI deficit was evident even 9d later. Plasma corticosterone levels were elevated acutely (before PPI deficits emerged) by both stressors and CRF, but returned to normal control levels 24 h later, when PPI deficits were present. Thus, predator exposure produces a delayed disruption of PPI, and stimulation of CRF receptors recapitulates these effects. Contemporaneous HPA axis activation is neither necessary nor sufficient for these PPI deficits. These results indicate that predator exposure, perhaps acting through CRF, may model the delayed-onset and persistent sensorimotor gating abnormalities that have been observed clinically in PTSD, and that further studies using this model may shed insight on the mechanisms of information-processing deficits in this disorder. This article is part of a Special Issue entitled ‘Post-Traumatic Stress Disorder’.

Reversal by quercetin of corticotrophin releasing factor induced anxiety- and depression-like effect in mice

Quercetin is a bioflavonoid reported to produce variety of behavioral effects like anxiolytic, antidepressant, etc. Recent gathering evidences indicated that quercetin attenuates stress-induced behavioral and biochemical effects. It also decreases CRF expression in the brain. As CRF is commonly implicated in the high-anxiety and depression, we hypothesized that quercetin may involve CRF in its anxiolytic- and antidepressant-like effects. To support such possibility, we investigated the influence of quercetin on CRF or CRF antagonist (antalarmin) induced changes in social interaction time in social interaction test, and immobility time in forced swim test. Results indicated that quercetin (20–40 mg/kg, p.o.) or antalarmin (2–4 µg/mouse, i.c.v.) dose dependently increased social interaction time and decreased immobility time indicating anxiolytic- and antidepressant-like effect. These effects were comparable with the traditional anxiolytic (diazepam, 1-2 mg/kg, i.p.) and antidepressant (fluoxetine, 10–20 mg/kg, i.p.) agents. Administration of CRF (0.1 and 0.3 nmol/mouse, i.c.v.) produced just opposite effects to that of quercetin on these parameters. Further, it was seen that pretreatment with quercetin (20 or 40 mg/kg, p.o.) dose dependently antagonized the effects of CRF (0.1 or 0.3 nmol/mouse, i.c.v.) in social interaction and forced swim test. The sub-effective dose of antalarmin (1 µg/mouse) when administered along with the sub-effective dose of quercetin (10 mg/kg) produced significant anxiolytic-and antidepressant-like effect. These observations suggest reciprocating role of quercetin on the CRF-induced anxiogenic and depressant-like effects.

Participation of corticotropin-releasing factor type 2 receptors in the acute, chronic and withdrawal actions of nicotine associated with feeding behavior in rats

We investigated the role of corticotropin-releasing factor type 2 (CRF 2) receptors in acute, chronic and withdrawal effects of nicotine on feeding behavior in rats. Nicotine was injected intraperitoneally, whereas CRF, CRF 2 receptors agonist urocortin-1 or selective antagonist astressin2-B were administered directly into the hypothalamic paraventricular nucleus (PVN). In acute studies, nicotine, CRF or urocortin-1 produced dose dependent anorexia at 2 and 4 h post-injection time-points, however, astressin2-B did not alter the food intake. Prior treatment of CRF or urocortin-1 potentiated the anorectic effect of nicotine, while astressin2-B showed opposite response. Chronic administration of nicotine produced tolerance to anorexia and caused persistent weight loss. However, concomitant treatment with CRF or urocortin-1 resulted in early tolerance to nicotine-induced anorexia. In the same set of animals, while CRF pre-treatment potentiated the weight reducing effect of nicotine, urocortin-1 failed to do so. Although abrupt termination of chronic nicotine treatment caused hyperphagia and weight gain, administration of CRF or urocortin-1 prevented these effects. These results suggest that CRF 2 receptors, within the framework of PVN, may contribute to the acute, chronic and withdrawal responses of nicotine on feeding and body weight.

Studies on hypothalamo-pituitary corticoliberin system. IV. Quantitative changes in ACTH-immunoreactive anterior pituitary cells evoked by long-term intraventricular CRF administration and adrenalectomy.

The aim of the study was to investigate, by coupled immunocytochemical and stereologic methods, the effects of long-term intraventricular administration of ovine CRF (oCRF) on ACTH-immunoreactive cells of the rat anterior pituitary and to compare this effect with that of adrenalectomy. CRF-treated rats received 100 ng of oCRF daily for 8 days while control rats were administered with bovine serum albumin (BSA). After BSA administration number of ACTH-immunoreactive cells/mm2 was greater than in intact rats and CRF lowered their number, however, they were still more numerous than in intact rats. Neither average area nor average volume of studied cells were changed in control and CRF-treated animals if compared with intact ones. The total number of ACTH-immunoreactive cells was higher in the glands of BSA and CRF-treated rats than in intact animals. On the other hand, 60 h after bilateral adrenalectomy a marked increase in both, average area and average volume of ACTH-immunoreactive cells was found. The different response of rat corticotropes to intraventricular CRF administration and adrenalectomy may depend on the presence of operating negative corticosterone feedback in animals with adrenal glands intact. Moreover, the present study revealed the lack of correlation between the average area and average volume of ACTH-immunoreactive cells and the weight of the adrenal gland.

Swim stress excitation of nucleus incertus and rapid induction of relaxin-3 expression via CRF 1 activation

Relaxin-3 (RLX3), a newly identified member of the relaxin peptide family, is distinguished by its enriched expression in GABA projection neurons of the pontine nucleus incertus (NI), which are postulated to participate in forebrain neural circuits involved in behavioural activation and stress responses. In this regard, corticotrophin-releasing factor-1 receptor (CRF 1) is abundantly expressed by NI neurons; central CRF administration activates c- fos expression in NI; and various stressors have been reported to increase NI neuron activity. In studies to determine whether a specific neurogenic stressor would activate RLX3 expression, we assessed the effect of a repeated forced swim (RFS) on levels of RLX3 mRNA and heteronuclear (hn) RNA in rat NI by in situ hybridization histochemistry of exon- and intron-directed oligonucleotide probes, respectively. Exposure of rats to an RFS (10 min at 23 °C, 24 h apart), markedly increased RLX3 mRNA levels in NI at 30–60 min after the second swim, before a gradual return to basal levels over 2–4 h, while RLX3 hnRNA levels were significantly up-regulated at 60–120 min post-RFS, following a transient decrease at 30 min. Systemic treatment of rats with a CRF 1 antagonist, antalarmin (20 mg/kg, i.p.) 30 min prior to the second swim, blunted the stress-induced effects on RLX3 transcripts. Relative levels of RLX3-immunostaining in NI neurons appeared elevated at 3 h post-swim, but not at earlier time points (30–60 min). These results suggest that acute stress-induced CRF secretion can rapidly alter RLX3 gene transcription by activation of CRF 1 present on NI neurons. More generally, these studies support a role for RLX3 neural networks in the normal neural and physiological response to neurogenic stressors in the rat.

The effect of CRF and α-helical CRF (9–41) on rat fear responses and amino acids release in the central nucleus of the amygdala

The effects of intracerebroventricular injections of CRF and a non-selective CRF receptor antagonist, α-helical CRF (9–41), on the release of glutamate, aspartate, and GABA in the central nucleus of the amygdala (CeA), were examined in the course of testing rat anxiety-like behaviour in the conditioned fear test (a freezing response), using the microdialysis technique. It was found that CRF (1 μg/rat), given to animals exposed to the stress of novelty only, insignificantly increased the glutamate concentration in the CeA, up to 200% of the control level. In the fear-conditioned animals, the influence of CRF on the local concentration of aspartate, glutamate, and Glu/GABA ratio was much more pronounced (up to a 400% increase above the baseline level of aspartate concentration), preceded an increased expression of anxiety-like responses, and appeared as early as 15 min after the drug administration. The intracerebroventricular administration of α-helical CRF (9–41) (10 μg/rat) significantly decreased the rat freezing responses and increased the local concentration of GABA during the first 30 min of observation. In sum, these are new findings, which show an important role of CRF in the CeA in the regulation of fear-controlled amino acids release and suggest an involvement of amino acids in the central nucleus of the amygdala in the effects of this neurohormone on the expression of conditioned fear.

Regulatory changes of food intake upon CRF administration

Regulatory changes of food intake upon CRF administration

Thermoregulatory effects of central CRF administration

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The influence of CRF and α-helical CRF (9-41) on rat fear responses, c-Fos and CRF expression, and concentration of amino acids in brain structures

In the present study we have examined the influence of intracerebroventricullary administered CRF, and a non-selective CRF receptor antagonist, α-helical CRF (9–41), on rat conditioned fear response, serum corticosterone, c-Fos and CRF expression, and concentration of amino acids ( in vitro), in several brain structures. Pretreatment of rats with CRF in a dose of 1μg/rat, enhanced rat-freezing response, and further increased conditioned fear-elevated concentration of serum corticosterone. Moreover, exogenous CRF increased aversive context-induced expression of c-Fos in the parvocellular neurons of the paraventricular hypothalamic nucleus (pPVN), CA1 area of the hippocampus, and M1 area of the frontal cortex. A different pattern of behavioral and biochemical changes was present after pre-test administration of α-helical CRF (9–41) (10μg/rat): a decrease in rat fear response and serum corticosterone concentration; an attenuation of fear-induced c-Fos expression in the dentate gyrus, CA1, Cg1, Cg2, and M1 areas of the frontal cortex; a complete reversal of the rise in the number of CRF immunoreactive complexes in the M2 cortical area, induced by conditioned fear. Moreover, α-helical CRF (9–41) increased the concentration of GABA in the amygdala of fear-conditioned rats. Altogether, the present data confirm and extend previous data on the integrative role of CRF in the central, anxiety-related, behavioral and biochemical processes. The obtained results underline also the role of frontal cortex and amygdala in mediating the effects of CRF on the conditioned fear response.

Étifoxine : pharmacologie comportementale

Etifoxine, a benzodiazepine anxiolytic, exerts an autonomic regulatory activity. Two clinical studies have shown that etifoxine is effective in the treatment of adjustment disorder with anxiety. In view of the diversity of disorders associated with anxiety, with or without various autonomic manifestations, we were interested in the behavioural effects of etifoxine in animal models, particularly when animals exposed to stressful stimuli exhibit exaggerated autonomic signs other than those of cardiovascular origin. The effects of etifoxine were first evaluated in a stress-induced hyperthermia model in the rat. Manipulation of this animal causes an elevation of rectal temperature corresponding to a state of anticipatory anxiety. Again in the rat, etifoxine was evaluated in a conditioned fear test during which a more stressful stimulus constituted by the presentation of unavoidable, unpleasant electric shocks was applied. Behavioural blockade or freezing in response to this stress and the amplitude of colonic motor activity quantified by recording myoelectrical activity were measured. Subsequently, given the importance of the role played by corticoliberin or CRF, a hypothalamic neurohormone and/or neurotransmitter, in the co-ordination and mediation of autonomic responses to stress, we used a mouse model in which intracerebral administration of CRF mimics a major stress state, evidenced by a reduction in gastric emptying of a solid meal. The effects of etifoxine were evaluated in this model. A benzodiazepine (bromazepam or diazepam) was chosen as a positive control in each experiment. The elevation of rectal temperature following manipulation is significantly reduced in the presence of etifoxine (50 mg/kg). Likewise, etifoxine significantly and dose-dependently (12.5-50 mg/kg) reduces the duration of behavioural blockade or freezing following the application of unavoidable electric shocks. At the same time, the same stimulus causes an increase in the number of myoelectrical signals in the colon, which are significantly reduced by etifoxine. In the mouse, centrally administered CRF (0.35 μg/animal) reduces gastric emptying of a solid meal. This effect of CRF is dose-dependently antagonised by etifoxine. This series of results shows that etifoxine reduces the amplitude of autonomic manifestations in response to a stressful stimulus of variable intensity, such as hyperthermia, increased colonic motor activity or reduced gastric emptying. The anxiolytic properties of etifoxine are therefore exerted on both the behavioural and the autonomic aspects. These results provide a basis for evaluating this drug in anxious patients in whom autonomic nervous system manifestations constitute pathological symptoms.

Endogenous opioids: role in prostaglandin-dependent and -independent fever

This study evaluated the participation of mu-opioid-receptor activation in body temperature (T(b)) during normal and febrile conditions (including activation of heat conservation mechanisms) and in different pathways of LPS-induced fever. The intracerebroventricular treatment of male Wistar rats with the selective opioid mu-receptor-antagonist cyclic d-Phe-Cys-Try-d-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP; 0.1-1.0 microg) reduced fever induced by LPS (5.0 microg/kg) but did not change T(b) at ambient temperatures of either 20 degrees C or 28 degrees C. The subcutaneous, intracerebroventricular, and intrahypothalamic injection of morphine (1.0-10.0 mg/kg, 3.0-30.0 microg, and 1-100 ng, respectively) produced a dose-dependent increase in T(b). Intracerebroventricular morphine also produced a peripheral vasoconstriction. Both effects were abolished by CTAP. CTAP (1.0 microg icv) reduced the fever induced by intracerebroventricular administration of TNF-alpha (250 ng), IL-6 (300 ng), CRF (2.5 microg), endothelin-1 (1.0 pmol), and macrophage inflammatory protein (500 pg) and the first phase of the fever induced by PGF(2alpha) (500.0 ng) but not the fever induced by IL-1beta (3.12 ng) or PGE(2) (125.0 ng) or the second phase of the fever induced by PGF(2alpha). Morphine-induced fever was not modified by the cyclooxygenase (COX) inhibitor indomethacin (2.0 mg/kg). In addition, morphine injection did not induce the expression of COX-2 in the hypothalamus, and CTAP did not modify PGE(2) levels in cerebrospinal fluid or COX-2 expression in the hypothalamus after LPS injection. In conclusion, our results suggest that LPS and endogenous pyrogens (except IL-1beta and prostaglandins) recruit the opioid system to cause a mu-receptor-mediated fever.

The role of the hormones of the hypothalamo-hypophyseal-adrenocortical system in the analgesic effect of corticotropin-releasing hormone

Experiments on anesthetized male rats were performed to study the role of the hormones of the hypothalamo-hypophyseal-adrenocortical system (HHACS) in analgesia induced by central or systemic administration of corticoliberin-releasing hormone (CRF). Studies of the contribution of HHACS hormones were performed by blocking HHACS function by administration of hydrocortisone at a pharmacological dose one week before experiments started. Blockade of HHACS function, resulting in the inability of the system to increase hormone levels, resulted in a decrease in the analgesic effect resulting from systemic administration of CRF and completely abolished the analgesic effect after central administration of CRF. These data lead to the conclusion that there are two components involved in increasing the pain sensitivity threshold in response to administration of CRF: 1) a component dependent on HHACS hormones in central and systemic administration of CRF; 2) a component independent of HHACS hormones on systemic administration of CRF.

The Hypothalamic-Pituitary-Adrenal Axis: What can it Tell us About Stressors?

The hypothalamic-pituitary-adrenal (HPA) axis is an extremely sensitive physiological system whose activation, with the consequent release of ACTH and glucocorticoids, is triggered by a wide range of psychological experiences and physiological perturbations (stressors). The HPA axis is also activated by a high number of pharmacological agents that markedly differ in structure and function, although the precise mechanisms remain in most cases unknown. Activation of the HPA axis is the consequence of the convergence of stimulatory inputs from different brain regions into the paraventricular nucleus of the hypothalamus (PVN), where the most important ACTH secretagogues (corticotrophin releasing factor, CRF, and arginin-vasopressin, AVP) are formed. Plasma levels of ACTH and corticosterone (the latter under more restricted conditions), are considered as good markers of stress for three main reasons: (a) their plasma levels are proportional to the intensity of emotional and systemic stressors, (b) daily repeated exposure to a stressor usually resulted in reduced ACTH response to the same stressor, that is termed adaptation or habituation; and (c) chronic exposure to stressful situations results in tonic changes in the HPA axis that can be used as indices of the accumulative impact of these situations. These changes can be evaluated under resting conditions (i.e. adrenal weight, CRF and AVP gene expression in the PVN) or after some challenges (administration of CRF, ACTH or dexamethasone) that are classical endocrinological tests. There is also evidence that the activation of the HPA axis may also reflect subtle changes in the characteristics of the stressful situations (unpredictability, lack of control, omission of expected rewards, presence of conspecifics), although this is a topic that requires further studies.