Icv Corticotropin-releasing Factor Research Articles

Prior stress and vasopressin promote corticotropin-releasing factor inhibition of serotonin release in the central nucleus of the amygdala.

Corticotropin-releasing factor (CRF) is essential for coordinating endocrine and neural responses to stress, frequently facilitated by vasopressin (AVP). Previous work has linked CRF hypersecretion, binding site changes, and dysfunctional serotonergic transmission with anxiety and affective disorders, including clinical depression. Crucially, CRF can alter serotonergic activity. In the dorsal raphé nucleus and serotonin (5-HT) terminal regions, CRF effects can be stimulatory or inhibitory, depending on the dose, site, and receptor type activated. Prior stress alters CRF neurotransmission and CRF-mediated behaviors. Lateral, medial, and ventral subdivisions of the central nucleus of the amygdala (CeA) produce CRF and coordinate stress responsiveness. The purpose of these experiments was to determine the effect of intracerebroventricular (icv) administration of CRF and AVP on extracellular 5-HT as an index of 5-HT release in the CeA, using in vivo microdialysis in freely moving rats and high performance liquid chromatography (HPLC) analysis. We also examined the effect of prior stress (1 h restraint, 24 h prior) on CRF- and AVP-mediated release of 5-HT within the CeA. Our results show that icv CRF infusion in unstressed animals had no effect on 5-HT release in the CeA. Conversely, in rats with prior stress, CRF caused a profound dose-dependent decrease in 5-HT release within the CeA. This effect was long-lasting (240 min) and was mimicked by CRF plus AVP infusion without stress. Thus, prior stress and AVP functionally alter CRF-mediated neurotransmission and sensitize CRF-induced inhibition of 5-HT release, suggesting that this is a potential mechanism underlying stress-induced affective reactivity in humans.

Effects of Acute and Chronic Stressors and CRF in Rat and Mouse Tests for Depression

Depressive illness is frequently associated with life stress. Corticotropin-releasing factor (CRF) is believed to be a key brain mediator of behaviors associated with stress, and abnormalities in the function of CRF have been associated with depression. Therefore, we have studied the effects of acute and chronic footshock and restraint in tests used in rodents to assess depression-like activity and antidepressant effects: the forced swim test in rats and mice, and the tail suspension test in mice. We also tested the effect of intracerebroventricular (icv) CRF administration. The results were complex. In the forced swim test in rats, acute footshock and restraint reduced floating, whereas chronic footshock increased floating as did icv CRF. However, chronic restraint induced opposite effects, decreasing floating in the forced swim test. The results from mice were significantly different. In the forced swim test, acute footshock and restraint decreased floating, while chronic footshock increased floating, and chronic restraint decreased floating as it did in rats. However, icv CRF decreased floating. The results from the tail-suspension test paralleled those from the forced swim test except that chronic footshock tended to decrease the time spent immobile. Thus in rats, the behavioral effects of the chronic footshock in the forced swim test could be explained by a desensitization of the CRF systems, either decreased activation of CRF, or desensitization of its receptors. However, such an effect cannot explain the responses to restraint, nor the behavioral effects of chronic footshock and restraint in mice.

Corticotropin releasing factor influences aggression and monoamines: Modulation of attacks and retreats

Salmonids establish social hierarchies as a result of aggressive social interactions. The establishment of dominant or subordinate status is strongly linked to neuroendocrine responses mediated through the stress axis. In this study, we tested the effects of introcerebroventricular (icv) corticotropin releasing factor (CRF) on the behavioral outcome, plasma cortisol and monoamine function in trout subjected to a socially aggressive encounter. Rainbow trout were treated with an icv injection of artificial cerebrospinal fluid (aCSF), 500 or 2000 ng ovine CRF, or not injected. Fish were allowed to interact with a similarly sized conspecific for 15 min. Following the behavioral interaction, plasma cortisol and central monoamine concentrations were analyzed. Trout treated with CRF were victorious in approximately 66% of the aggressive encounters against aCSF-treated opponents. Trout injected with CRF exhibited a reduction in the total number of attacks and decreased latency to attack. When trout were divided into winners and losers, only victorious CRF-treated fish exhibited a reduced latency to attack and fewer retreats. Social stress increased cortisol levels in both winners and losers of aggressive interaction. This effect was enhanced with the additional stress incurred from icv injection of aCSF. However, icv CRF in addition to social stress decreased plasma cortisol in both winners and losers. While aggression stimulated significant changes in serotonergic and dopaminergic activity, the magnitude and direction were dependent on limbic brain region, CRF dose, and outcome of social aggression. With broad effects on aggressive behavior, anxiety, stress responsiveness, and central monoaminergic activity, CRF plays an important role in modulating the behavioral components of social interaction.

Stressor- and corticotropin releasing factor-induced reinstatement and active stress-related behavioral responses are augmented following long-access cocaine self-administration by rats.

Stressful events during periods of drug abstinence likely contribute to relapse in cocaine-dependent individuals. Excessive cocaine use may increase susceptibility to stressor-induced relapse through alterations in brain corticotropin-releasing factor (CRF) responsiveness. This study examined stressor- and CRF-induced cocaine seeking and other stress-related behaviors in rats with different histories of cocaine self-administration (SA). Rats self-administered cocaine under short-access (ShA; 2 h daily) or long-access (LgA; 6 h daily) conditions for 14 days or were provided access to saline and were tested for reinstatement by a stressor (electric footshock), cocaine or an icv injection of CRF and for behavioral responsiveness on the elevated plus maze, in a novel environment and in the light-dark box after a 14- to 17-day extinction/withdrawal period. LgA rats showed escalating patterns of cocaine SA and were more susceptible to reinstatement by cocaine, EFS, or icv CRF than ShA rats. Overall, cocaine SA increased activity in the center field of a novel environment, on the open arms of the elevated plus maze, and in the light compartment of a light-dark box. In most cases, the effects of cocaine SA were dependent on the pattern/amount of cocaine intake with statistically significant differences from saline self-administering controls only observed in LgA rats. When examined after several weeks of extinction/withdrawal, cocaine SA promotes a more active pattern of behavior during times of stress that is associated with a heightened susceptibility to stressor-induced cocaine-seeking behavior and may be the consequence of augmented CRF regulation of addiction-related neurocircuitry.

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.

Central endothelin ETBreceptors mediate IL-1-dependent fever induced by preformed pyrogenic factor and corticotropin-releasing factor in the rat

Blockade of central endothelin ET(B) receptors inhibits fever induced by LPS in conscious rats. The contribution of ET(B) receptor-mediated mechanisms to fever triggered by intracerebroventricular IL-6, PGE2, PGF(2alpha), corticotropin-releasing factor (CRF), and preformed pyrogenic factor derived from LPS-stimulated macrophages (PFPF) was examined. The influence of natural IL-1 receptor antagonist or soluble TNF receptor I on endothelin (ET)-1-induced fever was also assessed. The selective ET(B) receptor antagonist BQ-788 (3 pmol icv) abolished fever induced by intracerebroventricular ET-1 (1 pmol) or PFPF (200 ng) and reduced that caused by ICV CRF (1 nmol) but not by IL-6 (14.6 pmol), PGE2 (1.4 nmol), or PGF(2alpha) (2 nmol). CRF-induced fever was also attenuated by bosentan (dual ET(A)/ET(B) receptor antagonist; 10 mg/kg iv) but unaffected by BQ-123 (selective ET(A) receptor antagonist; 3 pmol icv). alpha-Helical CRF(9-41) (dual CRF1/CRF2 receptor antagonist; 6.5 nmol icv) attenuated fever induced by CRF but not by ET-1. Human IL-1 receptor antagonist (9.1 pmol) markedly reduced fever to IL-1beta (180 fmol) or ET-1 and attenuated that caused by PFPF or CRF. Murine soluble TNF receptor I (23.8 pmol) reduced fever to TNF-alpha (14.7 pmol) but not to ET-1. The results of the present study suggest that PFPF and CRF recruit the brain ET system to cause ET(B) receptor-mediated IL-1-dependent fever.

Importance of the paraventricular nucleus of the hypothalamus as a component of a neural pathway between the brain and the testes that modulates testosterone secretion independently of the pituitary.

We previously reported that in adult male rats, the intracerebroventricular (icv) injection of corticotropin-releasing factor (CRF) or the beta-adrenergic agonist isoproterenol (ISO) significantly inhibited the ability of human chorionic gonadotropin (hCG) to stimulate testosterone (T) secretion. The finding that this phenomenon also took place when LH release had been blocked with an LHRH antagonist suggested that icv CRF and ISO did not alter Leydig cell function by influencing the activity of pituitary gonadotrophs. We therefore proposed the existence of a neural pathway connecting the brain to the testes, whose activation by icv CRF or ISO interfered with T secretion. Based on the intratesticular injection of the transganglionic tracer pseudorabies virus, we recently identified the paraventricular nucleus (PVN) of the hypothalamus as a component of this neural link. The aim of the present work was to investigate the functional role of this brain area in mediating the ability of CRF and ISO to inhibit the ability of hCG to stimulate T secretion. We first demonstrated that local microinfusion of CRF or ISO directly into the PVN mimicked the effect of their icv injection, suggesting that the PVN does indeed represent a site of action of ISO and CRF in altering Leydig cell responsiveness to gonadotropin. In contrast, neither CRF nor ISO microinfusion into the central amygdala or the frontal cortex influenced hCG-stimulated T secretion. To further investigate the role of the PVN in ISO- and CRF-induced blunting of hCG stimulation of T, we determined the effect of icv CRF or ISO on testicular activity of rats with electrolytic lesions of the PVN. These lesions, which did not in themselves influence Leydig cell responsiveness to hCG, blocked the effect of both icv ISO and CRF on hCG-induced T release. Collectively, these results support the hypothesis that CRF- and ISO-induced activation of cells in the area of the PVN decreases the ability of gonadotropin to release T and suggests that this nucleus represents an important site of the proposed neural connection between the brain and the testes.

C-Fos expression as a molecular marker in corticotropin-releasing factor-induced seizures.

Expression of Fos-like protein has been shown to increase after seizures in several types of experimentally induced epilepsies. The intracerebroventricular (icv) injection of murine corticotropin-releasing factor (CRF) in rats (10 micrograms), shows an electroencephalographic (EEG) spiking activity restricted to the amygdaloid-hippocampal area. This EEG seizure pattern represents a unique model of localized epileptic activity induced by a neuropeptide. C-fos expression after icv CRF has been considered a useful tool in mapping areas involved in stress and in seizure activity. Our results show that 1 microgram and 10 micrograms CRF are able to induce c-fos activation in several brain areas. Moreover, the present study not only details c-fos expression increase in brain areas directly involved in spiking activation, such as the amygdaloid-hippocampal region, but also maps the possible contribution of other regions to seizure manifestations.

Behavioral, neurochemical, and immunological responses to CRF administration. Is CRF a mediator of stress?

The effect of subacute intracerebroventricular (icv 0.1, 0.5, and 1.0 microgram) administration of corticotropin-releasing factor (CRF) for 5 days on behavior, neurotransmitter concentrations, and immune functions was studied in rats. The results showed that CRF administration produced a dose-dependent increase in locomotor activity in the "open field" test compared with controls; rearing scores were also significantly increased. In the elevated plus maze apparatus, rats given 1.0 microgram CRF spent considerably less time on the open arms when compared with controls. Following 0.5 and 1.0 microgram of CRF infusion, the concentrations of noradrenaline (NA), dopamine (DA) and 5-hydroxy indole acetic acid (5-HIAA) were significantly increased in the hypothalamus. There was no significant change in the concentrations of neurotransmitters in the other brain regions. CRF administration also produced a dose-dependent increase in the levels of corticosterone in the serum. The immunological results clearly showed that subacute icv CRF administration caused a reduction of lymphocyte proliferation, a decrease in the percentage of lymphocytes, and an increase in neutrophil percentage in the differential white blood cell (WBC) count, a decrease in neutrophil phagocytosis, and elevated leucocyte adhesiveness/aggregation (LAA) compared with control animals. These results suggest that icv subacute administration of CRF has anxiogenic effects, increases biogenic amine concentrations in the hypothalamus, and changes in some aspects of immune functions that may reflect the stress-inducing properties of the peptide. These effects are time and dose dependent.

Effect of corticotropin-releasing factor antagonist on behavioral and neuroendocrine responses during exposure to defensive burying paradigm in rats

Defensive burying behavior is a coping strategy in rodents in response to an aversive stimulus where fear will facilitate burying and treatment with anxiolytics will result in less burying. To test the hypothesis that endogenous corticotropin-releasing factor (CRF) is involved in the defensive burying response, the effects of an ICV CRF antagonist were tested on defensive burying behaviors as well as the plasma adrenocorticotropic hormone (ACTH) and plasma corticosterone response. Rats were allowed to self-administer one mild electric shock (1.0 mA) through a probe mounted on the wall of the home cage by briefly touching it. Following this shock, control rats typically display burying behavior, as defined as moving the bedding material toward and/or over the shock probe. A CRF antagonist, α-hel CRF 9–41, was administered ICV (1, 5, and 25 μg) 1 min after they received the shock. The 5 μg dose of the CRF antagonist significantly attenuated the time spent in defensive burying compared to vehicle-treated controls. The 5 and 25 μg doses of α-hel CRF 9–41 increased the latency to display defensive burying. However, the enhanced release of plasma ACTH and plasma corticosterone concentrations in the stressed animals was not significantly modified over the 15-min period by either of the three doses of CRF antagonist. The results suggest that endogenous CRF is involved in the expression of defensive burying behavior and that the brain CRF receptors modulating the behavioral response may be different from the CRF receptors modulating the hormonal response of defensive burying.

Corticotropin-releasing factor activates the noradrenergic neuron system in the rat brain

The effect of corticotropin-releasing factor (CRF) on central noradrenaline (NA) metabolism was examined by measuring levels of the major metabolite of NA, 3-methoxy-4-hydroxy-phenylethyleneglycol sulfate (MHPG-SO 4) in several rat brain regions. Various doses of CRF ranging from 0.5 – 10 μg injected ICV significantly increased MHPG-SO 4 levels in several brain regions including the hypothalamus, amygdala, midbrain, locus coeruleus (LC) region, and pons + medulla oblongata excluding the LC region. Plasma corticosterone levels were also significantly increased after ICV CRF administration up to 0.5 μg. The present results that CRF not only elevates plasma corticosterone levels but also increases NA metabolism in many brain regions suggest its neurotransmitter and/or neuromodulator role exerting the excitatory action on central NA neurons.

Lesions of the central nucleus of the amygdala, but not the paraventricular nucleus of the hypothalamus, block the excitatory effects of corticotropin-releasing factor on the acoustic startle reflex

Intracerebroventricular (icv) infusion of corticotropin-releasing factor (CRF) was previously found to produce a long-lasting, dose-dependent (0.1-1.0 microgram) increase in the amplitude of the acoustic startle reflex. The present study sought to determine where in the CNS CRF acts to increase startle. Intracisternal infusion of CRF (0.1-1.0 microgram) increased startle with a time course and magnitude similar to that produced by icv CRF, unlike intrathecal infusion, which produced a small, more rapid enhancement of startle. While lesions of the paraventricular nucleus of the hypothalamus had no effect on icv CRF-enhanced startle, bilateral lesions of the central nucleus of the amygdala significantly attenuated the excitatory effect of icv CRF but had no effect on intrathecal CRF-enhanced startle. Even though lesions of the amygdala blocked icv CRF-enhanced startle, local infusion of CRF into the amygdala did not significantly elevate startle. The present data indicate that the amygdala is part of the neural circuitry required for icv CRF to elevate startle, but does not appear to be the primary receptor area where CRF acts. The involvement of the amygdala in icv CRF-enhanced startle is consistent with the hypothesis that both the amygdala and CRF are critically involved in fear and stress.

Role of brain kallikrein-kinin system in regulation of adrenocorticotropin release.

We evaluated whether the brain kallikrein-kinin system plays a role in the regulation of adrenocorticotropin (ACTH) release in rats. Intracerebroventricular (icv) injection of bradykinin (0.24 nmol) increased plasma immunoreactive ACTH (irACTH) levels (from 93 +/- 4 to 200 +/- 12 pg/ml, P less than 0.01). This effect was prevented by icv kinin antagonist at 15.4 nmol/h (from 98 +/- 5 to 108 +/- 6 pg/ml; not significant). The antagonist did not alter the increase in plasma irACTH levels induced by icv corticotropin-releasing factor (CRF), arginine vasopressin, or prostaglandin E2. Melittin (7 nmol/h icv) increased plasma irACTH from 95 +/- 4 to 268 +/- 7 pg/ml (P less than 0.01). This effect was prevented by icv kinin antagonist (15.4 nmol/h), kallikrein antibodies (13 pmol/h), or indomethacin (0.28 mmol/h). ACTH response to melittin was not altered by antagonists of CRF or vasopressin. Intra-arterial injection of insulin (0.3 IU/kg body wt) reduced plasma glucose levels to a similar extent in rats given icv kinin antagonist or vehicle; the ACTH response to insulin-induced hypoglycemia was slightly less in rats given kinin antagonist than in those given vehicle (55 +/- 5 vs. 86 +/- 4 pg/ml, P less than 0.05). The brain kallikrein-kinin system may play a role in the regulation of ACTH secretion in stimulated conditions.

Effects of 5-HT-1A receptor agonists on CRF-induced behavior

Buspirone (2.0 or 4.0 mg/kg) and 8-hydroxy-2-(di-N-propylamino)-tetralin (8-OH-DPAT) (0.25 or 0.5 mg/kg) were used to examine the effects of serotonin 1A receptor agonists on the behavioral response of rats to centrally administered corticotropin-releasing factor (CRF). Behavioral observations were done with animals in their home cages. Parameters measured included locomotor activity, grooming and food consumption. CRF alone increased locomotor activity. 8-OH-DPAT also increased locomotion in both saline control and CRF-treated rats. Buspirone had no effect on basal locomotion or on CRF-induced hyperactivity. Both buspirone and 8-OH-DPAT antagonized CRF-induced grooming. Food consumption by fasted rats was suppressed by ICV CRF. 8-OH-DPAT suppressed eating by both ICV CRF and ICV saline-treated animals, while buspirone was without effect. These results demonstrate differences between the two putative 5-HT-1A agonists in their effects on CRF-induced behaviour but also demonstrate that both suppress CRF-induced grooming.

Acute and chronic effects of the atypical antidepressant, mianserin on brain noradrenergic neurons

Corticotropin-releasing factor (CRF), which may serve as a neurotransmitter in the noradrenergic nucleus, locus coeruleus (LC), has been postulated to be hypersecreted in depression. The present study was designed to test the hypothesis that antidepressants interfere with CRF putative neurotransmission in the LC. The acute and chronic effects of the atypical antidepressant mianserin on LC spontaneous discharge, LC sensory-evoked discharge, LC activation by a stressor which requires endogenous CRF, and LC activation by ICV CRF were characterized in halothane-anesthetized rats. Acute IV administration of mianserin (0.0001-1.0 mg/kg) increased LC spontaneous discharge and decreased LC discharge evoked by repeated sciatic nerve stimulation in a dose-dependent manner. Additionally, mianserin (0.1 mg/kg) inhibited LC activation by hemodynamic stress (IV infusion of nitroprusside) and by ICV administration of CRF (3.0 micrograms). In rats chronically administered mianserin LC spontaneous and sensory-evoked discharge rates, and LC activation by CRF were similar to those of untreated rats or rats chronically administered saline. Moreover, acute IV administration of mianserin (0.1 mg/kg) to rats chronically treated with mianserin was less effective in altering LC spontaneous and sensory-evoked discharge. In contrast, LC activation by hemodynamic stress was still greatly attenuated in rats chronically administered mianserin. This is similar to the previously reported effect produced by chronic administration of the antidepressant, desmethylimipramine. The present results demonstrate that acute administration of low doses of mianserin attenuates LC activation by a variety of stimuli and suggest that tolerance develops with chronic administration to some of the effects of mianserin on LC discharge characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticotropin-releasing factor elicits naloxone sensitive stress-like alterations in exploratory behavior in mice

A multicompartment chamber was used to study the investigatory behavior of mice in a novel environment. Restraint stress, subcutaneous morphine (1.75 mg/kg), and ICV corticotropin-releasing factor (CRF; 75 ng) each produced a decreased mean time per contact with novel stimuli. The effect of all three treatments was antagonized by a dose of naloxone that by itself had no significant behavioral effects (0.7–0.75 mg/kg). Naloxone alone at a higher dose (1.25 mg/kg), increased the mean time per contact with the stimuli. These results confirm previous reports of the effects of opiates and stress on this behavior in rats. The similarity of the effects of CRF and stress on the behavioral response to this chamber supports the possibility that CRF may act in the central nervous system to mediate certain behavioral responses in stress.

441 SIMULATION OF THE “ADRENAL EXHAUSTION” PHENOMENON BY icv CRF

Intracerebroventricular (icv) bolus injection of cortico-tropin releasing factor (CRF) induces hypermetabolism, catecholamine surge and excess adrenocortical hormone secretion. Chronic icv CRF infusion in rats induces this stress-like picture for 2-3 days. However, corticosterone (B) excretion falls below that of sham rats by day 5. This dampened response to sustained CRF resembles the “adrenal exhaustion” phenomenon described in severe trauma and led to the present study: Jugular catheters were placed prior to icv cannulation and chronic delivery of CRF 20 ug/d or of saline. Hypersecretion of B on day 2 (0.7 ±0.15 ug/d) in CRF rats was suppressed on day 5 (0.3 ±.05, n=8, p<0.01). A 10 ug iv CRF bolus on day 5 caused exaggerated ACTH coupled with elevated plasma B:These results suggest: a suppressed adrenal function induced by chronic icv CRF similar to that after severe trauma and 2) a hypothalamic abnormality rather than primary pituitary or adrenal failure.