Characterization of the effects of corticotropin-releasing factor on prepulse inhibition of the acoustic startle response in Brown Norway and Wistar-Kyoto rats

Repeated norepinephrine receptor stimulation in the BNST induces sensorimotor gating deficits via corticotropin releasing factor

Intense stress precipitates symptoms in disorders such as post-traumatic stress (PTSD) and schizophrenia. Patients with these disorders have dysfunctional sensorimotor gating as indexed by disrupted prepulse inhibition of the startle response (PPI), which refers to decreased startle response when a weak pre-stimulus precedes a startling stimulus. Stress promotes release of norepinephrine (NE) and corticotrophin releasing factor (CRF) within the brain, neurotransmitters that also modulate PPI. We have shown that repeated stress causes sensitization of NE receptors within the basolateral amygdala (BLA) via CRF receptors and promotes long-lasting PPI disruptions and startle abnormalities. The bed nucleus of the stria terminalis (BNST) is another crucial brain region that could be involved in stress-induced alterations in NE and CRF functions to promote PPI changes as this anatomical structure is enriched in CRF and NE receptors that have been shown to regulate each other. We hypothesized that repeated infusions of NE into the BNST would cross-sensitize CRF receptors or vice versa to alter PPI. Separate groups of male Sprague Dawley rats received, CRF (200ng/0.5 μl), NE (20μg/0.5 μl), or vehicle into the BNST, once/day for 3 days and PPI was tested after each infusion. Repeated CRF-or vehicle-treated rats were then challenged with a subthreshold dose of NE (0.3μg/0.5 μl) while repeated NE-treated rats were challenged with CRF (200ng/0.5 μl), and PPI was measured. Surprisingly, initial/repeated CRF or vehicle in the BNST had no effects on PPI. In contrast, initial and repeated NE disrupted PPI. Sub-threshold NE challenge in rats that previously received repeated CRF had no effect on PPI. Interestingly though, intra-BNST challenge dose of CRF significantly disrupted PPI in rats that previously had received repeated NE infusions. Taken together, these results indicate that repeated stress-induced NE release could alter the activity of CRF receptors in the BNST to modulate sensorimotor gating as measured through PPI.

Importance of CRF receptor-mediated mechanisms of the bed nucleus of the stria terminalis in the processing of anxiety and pain

Corticotropin-releasing factor (CRF)-mediated mechanisms in the bed nucleus of the stria terminalis (BNST) have a pivotal role in stress-induced anxiety and hyperalgesia. Although CRF is known to activate two receptor subtypes, CRF1 and CRF2, attempts to delineate the specific role of each subtype in modulating anxiety and nociception have been inconsistent. Here we test the hypothesis that CRF1 and CRF2 receptor activation in the anteriolateral BNST (BNSTAL) facilitates divergent mechanisms modulating comorbid anxiety and hyperalgesia. Microinfusions of the specific antagonists CP376395 and Astressin2B into the BNSTAL were used to investigate CRF1 and CRF2 receptor functions, respectively. We found that CRF1 and CRF2 receptors in the BNSTAL had opposing effects on exploratory behavior in the elevated plus-maze, somatic mechanical threshold, and the autonomic and endocrine response to stress. However, CRF1 or CRF2 receptor antagonism in the BNSTAL revealed complementary roles in facilitating the acoustic startle and visceromotor reflexes. Our results suggest that the net effect of CRF1 and CRF2 receptor activation in the BNSTAL is pathway-dependent and provides important insight into the CRF receptor-associated circuitry that likely underpins stress-induced pathologies.

CRF1 receptor antagonists do not reverse pharmacological disruption of prepulse inhibition in rodents

RATIONALE

As enhanced corticotropin-releasing factor (CRF) transmission is associated with induction of sensorimotor gating deficits, CRF₁ receptor antagonists may reverse disrupted prepulse inhibition (PPI), an operational measure of sensorimotor gating.

OBJECTIVES

To determine the effects of CRF₁ receptor antagonists in pharmacological models of disrupted PPI and to determine if long-term elevated central CRF levels alter sensitivity towards PPI disrupting drugs.

METHODS

CP154,526 (10-40 mg/kg), SSR125543 (3-30 mg/kg) and DMP695 (40 mg/kg) were tested on PPI disruption provoked by D-amphetamine (2.5, 3 mg/kg), ketamine (5, 30 mg/kg) and MK801 (0.2, 0.5 mg/kg) in Wistar rats, C57Bl/6J and CD1 mice, and on spontaneously low PPI in Iffa Credo rats and DBA/2J mice. PPI-disrupting effects of D-amphetamine (2.5-5 mg/kg) and MK801 (0.3-1 mg/kg) were examined in CRF-overexpressing (CRFtg) mice, which display PPI deficits. Finally, we determined the influence of CP154,526 on D-amphetamine-induced dopamine outflow in nucleus accumbens and prefrontal cortex of CRFtg mice using in vivo microdialysis.

RESULTS

No CRF₁-antagonists improved PPI deficits in any test. CRFtg mice showed blunted PPI disruption in response to MK801, but not D-amphetamine. Further, D-amphetamine-induced dopamine release was less pronounced in CRFtg versus wild-type mice, a response normalized by pretreatment with CP154,526.

CONCLUSION

The inability of CRF₁ receptor antagonists to block pharmacological disruption of sensorimotor gating suggests that the involvement of CRF₁ receptors in the modulation of dopaminergic and glutamatergic neurotransmission relevant for sensory gating is limited. Furthermore, the alterations observed in CRFtg mice support the notion that long-term elevated central CRF levels induce changes in these neurotransmitter systems.

Interactions between corticotropin-releasing factor and the serotonin 1A receptor system on acoustic startle amplitude and prepulse inhibition of the startle response in two rat strains

Both the neuropeptide, corticotropin-releasing factor (CRF) and the serotonin 1A (5-HT(1A)) receptor systems have been implicated in anxiety disorders and there is evidence that the two systems interact with each other to affect behavior. Both systems have individually been shown to affect prepulse inhibition (PPI) of the acoustic startle response. PPI is a form of sensorimotor gating that is reduced in patients with anxiety disorders including post-traumatic stress and panic disorder. Here, we examined whether the two systems interact or counteract each other to affect acoustic startle amplitude, PPI and habituation of the startle response. In experiment 1, Brown Norway (BN) and Wistar-Kyoto (WKY) rats were administered ether an intraperitoneal (IP) injection of saline or the 5-HT(1A) receptor agonist, 8-OH-DPAT 10 min prior to receiving an intracerebroventricular (ICV) infusion of either saline or CRF (0.3 μg). In a second experiment, rats were administered either an IP injection of saline or the 5-HT(1A) receptor antagonist, WAY 100,635 10 min prior to receiving an ICV infusion of saline or CRF. Thirty min after the ICV infusion, the startle response and PPI were assessed. As we have previously shown, the dose of CRF used in these experiments reduced PPI in BN rats and had no effect on PPI in WKY rats. Administration of 8-OH-DPAT alone had no effect on PPI in either rat strain when the data from the two strains were examined separately. Administration of 8-OH-DPAT added to the effect of CRF in BN rats, and the combination of 8-OH-DPAT and CRF significantly reduced PPI in WKY rats. CRF alone had no effect on baseline startle amplitude in either rat strain, but CRF enhanced the 8-OH-DPAT-induced increase in startle in both strains. Administration of WAY 100,635 did not affect the CRF-induced change in PPI and there were no interactions between CRF and WAY 100,635 on baseline startle. The results suggest that activation of the 5-HT(1A) receptor can potentiate the effect of CRF on endophenotypes of anxiety disorders in animal models. This article is part of a Special Issue entitled 'Anxiety and Depression'.

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'.

Restraint stress-induced reduction in prepulse inhibition in Brown Norway rats: role of the CRF2 receptor

Stress plays a role in many psychiatric disorders that are characterized by deficits in prepulse inhibition (PPI), a form of sensorimotor gating. Corticotropin-releasing factor (CRF) is one of the most important neurotransmitters involved in behavioral components of the stress response. Central infusion of CRF reduces PPI in both rats and mice. In mice, it has been shown that CRF(1) receptor activation mediates the effect of exogenous CRF on PPI. However, the roles of the two CRF receptors in a stress-induced reduction in PPI are not known. We sought to determine whether CRF(1) and/or CRF(2) receptor blockade attenuates a stress-induced reduction of PPI in rats. In separate experiments, we assessed PPI in Brown Norway rats after exposure to 5 days of 2-h restraint, and after pretreatment with the CRF(1) receptor antagonist, CP-154,526 (20.0 mg/kg), or the CRF(2) receptor antagonist, antisauvagine-30 (10.0 μg). Repeated, but not acute, restraint decreased PPI and attenuated the increase in PPI caused by repeated PPI testing. Blockade of the CRF(1) receptor did not attenuate the effect of repeated restraint on PPI or grooming behavior. While CRF(2) receptor blockade did attenuate the effect of repeated restraint on PPI, repeated ICV infusion of the selective CRF(2) receptor agonist urocortin III, did not affect PPI. These findings demonstrate the effect of stress on sensorimotor gating and suggest that the CRF(2) receptor mediates this effect in rats.

The effect of restraint stress on prepulse inhibition and on corticotropin-releasing factor (CRF) and CRF receptor gene expression in Wistar-Kyoto and Brown Norway rats

Stress plays a role in many psychiatric disorders that are characterized by deficits in prepulse inhibition (PPI), a form of sensorimotor gating. Corticotropin-releasing factor (CRF) is one of the most important neurotransmitters involved in behavioral components of the stress response, and central infusion of CRF decreases PPI in rodents. We recently demonstrated that restraint stress decreases PPI and attenuates the increase in PPI caused by repeated testing. To broaden our investigation into how restraint affects PPI, we subjected Wistar-Kyoto (WKY) and Brown Norway (BN) rats to 10 consecutive days of 2-hour restraint, or to brief handling, prior to assessing PPI. We next examined the effects of 1 or 10days of 2-hour restraint on plasma corticosterone levels in order to determine whether the endocrine response to stress parallels the behavioral effect of stress. Finally, we examined the effects of 1 or 10days of 2-hour restraint on CRF and CRF receptor gene expression in the amygdala, hippocampus, frontal cortex, and hypothalamus in order to determine whether a temporal pattern of gene expression parallels the change in the behavioral response to stress. The major findings of the present study are that 1) restraint stress attenuates the increase in PPI caused by repeated testing in both WKY and BN rats, and BN rats are more sensitive to the effects of restraint on PPI than WKY rats, 2) restraint-induced increases in corticosterone levels mirror the effect of restraint on PPI in WKY rats but not in BN rats, 3) laterality effects on gene expression were observed for the amygdala, whereby restraint increases CRF gene expression in the left, but not right, amygdala, and 4) some restraint-induced changes in CRF and CRF receptor gene expression precede changes in PPI while other changes coincide with altered PPI in a rat strain- and brain region-dependent manner.

Interaction between the effects of corticotropin-releasing factor and prepulse parameters on prepulse inhibition in two inbred rat strains and the F1 generation of a cross between them

Levels of prepulse inhibition (PPI) depend on the interval between the startling and prepulse stimuli. Brown Norway rats show less PPI of the acoustic startle response than Wistar-Kyoto (WKY) rats when the interval between the prepulse and startling stimulus is 100 ms. Central administration of corticotropin-releasing factor (CRF) decreases PPI at this inter-stimulus interval. Here, the effect of CRF on PPI over a range of inter-stimulus intervals was examined in WKY and BN rats, and in the F1 generation of a cross between them. Rats received an intracerebroventricular infusion of either saline or CRF 30 min prior to testing PPI. Test trials included startle stimulus alone trials, and trials on which a prepulse stimulus of either 6, 12, or 15 dB above background preceded the startling stimulus by either 20, 75, 100, 500 or 2000 ms. CRF decreased PPI in WKY rats at all inter-stimulus intervals and all prepulse intensities, while the effect of CRF on PPI in BN rats only occurred at intermediate intervals. BN and WKY rats showed different levels of PPI only at the intermediate intervals. Baseline PPI in the F1 rats resembled the WKY phenotype. The CRF-induced change in PPI in the F1 generation has some qualities of the effects in each of the progenitor strains. These results suggest that both the effect of rats strain and of CRF on PPI depend on the inter-stimulus interval, and that there is an interaction between prepulse stimulus intensity and the inter-stimulus interval.

CRF1 not glucocorticoid receptors mediate prepulse inhibition deficits in mice overexpressing CRF

BACKGROUND

Both corticotropin-releasing factor (CRF) and glucocorticoid receptors (GR) are implicated in the psychotic symptoms of psychiatric disorders. Correspondingly, it is of interest to determine their respective involvement in the sensorimotor gating deficits displayed by transgenic mice overexpressing CRF. These mice reveal lifelong elevations of CRF and corticosterone levels.

METHODS

Effects of the GR antagonists ORG34517 (5-45 mg/kg by mouth [PO]) and mifepristone (5-45 mg/kg PO) and the CRF(1) receptor antagonists CP154,526 (20-80 mg/kg intraperitoneally [IP]) and DMP695 (2.5-40.0 mg/kg IP) on prepulse inhibition (PPI) of the acoustic startle response were studied in mice overexpressing CRF and in their wild-type littermates. In addition, PPI was measured in both genotypes 2 weeks after adrenalectomy with or without exogenous corticosterone administration via subcutaneous pellet implant (20 mg corticosterone).

RESULTS

ORG34517 and mifepristone did not influence perturbation of PPI in mice overexpressing CRF; reducing corticosterone levels by adrenalectomy likewise did not improve PPI. Further, elevation in corticosterone levels by pellet implantation did not disrupt PPI in wild-type mice. Conversely, both CRF(1) receptor antagonists, CP154,526 (40-80 mg/kg IP) and DMP695 (40 mg/kg IP), significantly restored PPI in CRF-overexpressing mice.

CONCLUSIONS

Sustained overactivation of CRF(1) receptors rather than excessive GR receptor stimulation underlies impaired sensorimotor gating in CRF-overexpressing mice. CRF(1) receptors thus may play a role in the expression of psychotic features in stress-related psychiatric disorders.

The effect of corticotropin-releasing factor on prepulse inhibition is independent of serotonin in Brown Norway and Wistar-Kyoto rats

Prepulse inhibition (PPI), a form of sensorimotor gating, is reduced in a number of psychiatric disorders. Two experiments were conducted to determine whether corticotropin-releasing factor (CRF), which decreases PPI, does so via effects on serotonin (5-HT). Wistar-Kyoto (WKY) and Brown Norway (BN) rats were used in both experiments in order to examine whether strain-dependent differences would be apparent in response to manipulations of the CRF and 5-HT systems. In the first experiment, WKY and BN rats received a subcutaneous injection of the 5-HT(2A/C) receptor antagonist, ketanserin (2.0 mg/kg). Ten minutes later, rats received an intracerebroventricular (ICV) infusion of either 6.0 microl saline or CRF (0.3 microg or 3.0 microg). CRF decreased PPI despite blockade of 5-HT(2A/C) receptors with ketanserin. In the second experiment, WKY and BN rats received an intraperitoneal injection of the 5-HT synthesis inhibitor, p-chlorophenylalanine (PCPA, 150 mg/kg), 48 and 24 h prior to testing. On testing day, rats received an ICV infusion of either 6.0 microl saline or CRF (0.3 microg or 3.0 microg). CRF decreased PPI despite 5-HT depletion. These findings suggest that CRF does not decrease PPI via effects on 5-HT, since neither blockade of 5-HT(2A/C) receptors nor 5-HT depletion attenuated this decrease.

Corticotropin-releasing factor (CRF) in stress and disease: a review of literature and treatment perspectives with special emphasis on psychiatric disorders

The CRF family of neuropeptides and receptors is involved in a variety of stress responses, in the regulation of appetite, metabolic and inflammatory processes as well as intestinal movements. From a primarily psychiatric perspective, the present paper reviews the literature on its anatomy, physiology and its involvement in psychiatric, neurological and inflammatory diseases. Finally, recent developments in the pharmacological aspects of CRF in these diseases are reviewed.

Role of corticotropin releasing factor in anxiety disorders: a translational research perspective

Anxiety disorders are a group of mental disorders that include generalized anxiety disorder (GAD), panic disorder, phobic disorders (e.g., specific phobias, agoraphobia, social phobia) and posttraumatic stress disorder (PTSD). Anxiety disorders are among the most common of all mental disorders and, when coupled with an awareness of the disability and reduced quality of life they convey, they must be recognized as a serious public health problem. Over 20 years of preclinical studies point to a role for the CRF system in anxiety and stress responses. Clinical studies have supported a model of CRF dysfunction in depression and more recently a potential contribution to specific anxiety disorders (i.e., panic disorder and PTSD). Much work remains in both the clinical and preclinical fields to inform models of CRF function and its contribution to anxiety. First, we will review the current findings of CRF and HPA axis abnormalities in anxiety disorders. Second, we will discuss startle reflex measures as a tool for translational research to determine the role of the CRF system in development and maintenance of clinical anxiety.

Effects of a Typical and an Atypical Antipsychotic on the Disruption of Prepulse Inhibition Caused by Corticotropin-Releasing Factor and by Rat Strain

Male Wistar-Kyoto (WKY) and Brown Norway (BN) rats (11-12 weeks, n = 184) received an injection of saline, haloperidol, or clozapine, followed by an intracerebroventricular infusion of saline or corticotropin-releasing factor (CRF). Rats were tested for prepulse inhibition (PPI) of the acoustic startle response. BN rats showed less PPI than WKY rats, and neither antipsychotic alone enhanced PPI. In WKY rats, both haloperidol and clozapine attenuated the CRF-induced decrease in PPI. In CRF-treated BN rats, clozapine-enhanced PPI. A clozapine-induced decrease in startle amplitude was seen in CRF-treated BN rats but not in CRF-treated WKY rats. Although the disruption of PPI caused by exogenous CRF administration can be reversed by acute antipsychotic treatment, baseline PPI is not altered.