Effects of corticotropin-releasing factor on neuronal activity in the serotonergic dorsal raphe nucleus

Urocortin 2 increases c-Fos expression in serotonergic neurons projecting to the ventricular/periventricular system

Serotonin plays an important role in the regulation of anxiety states and physiological responses to aversive stimuli. Intracerebroventricular (i.c.v.) injection of the stress- and anxiety-related neuropeptide urocortin 2 (Ucn 2) increases c-Fos expression in serotonergic neurons in the dorsal (DRD) and caudal (DRC) parts of the dorsal raphe nucleus. These regions contain a subset of serotonergic neurons that projects via the dorsal raphe periventricular tract to periventricular structures, including the subfornical organ and ependymal layer, and to the ventricular system. To determine if Ucn 2 activates ventricle/periventricular-projecting serotonergic neurons in the midbrain raphe complex, we made i.c.v. injections of the retrograde tracer Fluoro-Gold into the lateral ventricle, followed 7 days later by i.c.v. injection of Ucn 2. The DRD at -8.18 mm and the DRC at -8.54 mm and -9.16 mm bregma were analyzed using a combined bright field and immunofluorescence technique. Approximately 40% of the ventricle/periventricular-projecting neurons in the subdivisions sampled were serotonergic. Urocortin 2 increased c-Fos expression in ventricle/periventricular-projecting serotonergic neurons in the DRC and in non-ventricle/periventricular-projecting serotonergic neurons in the DRD and DRC. Of the total population of ventricle/periventricular-projecting serotonergic neurons in the DRC at -8.54 and -9.16 mm bregma, 35% expressed c-Fos following Ucn 2 injections. These data are consistent with previous studies showing that i.c.v. injection of Ucn 2 activates subpopulations of serotonergic neurons restricted to the mid-rostrocaudal DRD and DRC and further demonstrate that these include both subsets of serotonergic neurons that do and do not project to the ventricle/periventricular system.

Polymorphisms in CRHR1 and the serotonin transporter loci: gene x gene x environment interactions on depressive symptoms

Gene x environment (G x E) interactions mediating depressive symptoms have been separately identified in the stress-sensitive serotonergic (5-HTTLPR) and corticotropin-releasing hormone (CRHR1) systems. Our objective was to examine whether the effects of child abuse are moderated by gene x gene (G x G) interactions between CRHR1 and 5-HTTLPR polymorphisms. We used an association study examining G x G x E interactions of CRHR1 and 5-HTTLPR polymorphisms and measures of child abuse on adult depressive symptomatology. The participant population (N = 1,392) was African-American, of low socioeconomic status (60% with <$1,000/month family income), and with high rates of childhood and lifetime trauma. Depressive symptoms were measured with Beck Depression Inventory (BDI) and history of Major Depression by Structure Clinical Interview based on DSM-IV (SCID). We first replicated an interaction of child abuse and 5-HTTLPR on lifetime SCID diagnosis of major depression in a subsample (N = 236) of the study population-the largest African-American 5-HTTLPR cohort reported to date. We then extended our previously reported interaction with both a CRHR1 SNP (rs110402) and TCA haplotype interacting with child abuse to predict current symptoms (N = 1,059; P = 0.0089). We found that the 5-HTTLPR S allele interacted with CRHR1 haplotypes and child abuse to predict current depressive symptoms (N = 856, P = 0.016). These data suggest that G x E interactions predictive of depressive symptoms may be differentially sensitive to levels of childhood trauma, and the effects of child abuse are moderated by genetic variation at both the CRHR1 and 5-HTTLPR loci and by their G x G interaction.

Increased intrinsic excitability of lateral wing serotonin neurons of the dorsal raphe: a mechanism for selective activation in stress circuits

The primary center of serotonin (5-HT) projections to the forebrain is the dorsal raphe nucleus (DR), a region known for its role in the limbic stress response. The ventromedial subregion of the DR (vmDR) has the highest density of 5-HT neurons and is the major target in experiments that involve the DR. However, studies have demonstrated that a variety of stressors induce activation of neurons that is highest in the lateral wing subregion (lwDR) and includes activation of lwDR 5-HT neurons. Despite the functional role that the lwDR is known to play in stress circuits, little is known about lwDR 5-HT neuron physiology. Whole cell patch clamp electrophysiology in mice revealed that lwDR 5-HT cells have active and passive intrinsic membrane properties that make them more excitable than vmDR 5-HT neurons. In addition, lwDR 5-HT neurons demonstrated faster in vitro firing rates. Finally, within the vmDR there was a positive correlation between rostral position and increased excitability, among several other membrane parameters. These results are consistent with stressor induced patterns of activation of 5-HT neurons that includes, in addition to lwDR neurons, a small subset of rostral vmDR neurons. Thus increased intrinsic excitability likely forms a major part of the mechanism underlying the propensity to be activated by a stressor. The membrane properties identified in lwDR recordings may thereby contribute to a unique role of lwDR 5-HT neurons in adaptive responses to stress and in the pathobiology of stress-related mood disorders.

5-hydroxytryptamine 2C receptors in the basolateral amygdala are involved in the expression of anxiety after uncontrollable traumatic stress

BACKGROUND

Exposure to uncontrollable stressors often increases anxiety-like behavior in both humans and rodents. In rat, this effect depends on stress-induced activity within the dorsal raphe nucleus (DRN). However, the role of serotonin in DRN projection regions is largely unknown. The goals of this study were to 1) assess the effect of uncontrollable stress on extracellular serotonin in the basolateral amygdala during the anxiety test, 2) determine whether DRN activity during a poststress anxiety test is involved in anxiety-like behavior, and 3) determine the role of the serotonin 2C receptor (5-HT(2C)) in uncontrollable stress-induced anxiety.

METHOD

Rats were exposed to tail shocks that were either controllable or uncontrollable. On the following day, anxiety-like behavior was assessed in a Juvenile Social Exploration (JSE) test. Basolateral amygdala (BLA) extracellular serotonin concentrations were assessed during JSE by in vivo microdialysis 24 hours after uncontrollable stress, controllable stress, or no stress. In separate experiments, drugs were administered before the JSE test to inhibit the DRN or to block 5-HT(2C) receptors.

RESULTS

Exposure to uncontrollable shock reduced later social exploration. Prior uncontrollable stress potentiated serotonin efflux in the BLA during social exploration, but controllable stress did not. Intra-DRN 8-OH-DPAT and systemic and intra-BLA 5-HT(2C) receptor antagonist SB 242,084 prevented the expression of potentiated anxiety in uncontrollably stressed rats. Intra-BLA injection of the 5-HT(2C) agonist CP 809,101 mimicked the effect of stress.

CONCLUSIONS

These results suggest that the anxiety-like behavior observed after uncontrollable stress is mediated by exaggerated 5-HT acting at BLA 5-HT(2C) receptors.

The structure of the dorsal raphe nucleus and its relevance to the regulation of sleep and wakefulness

Serotonergic (5-HT) cells in the rat dorsal raphe nucleus (DRN) appear in topographically organized groups. Based on cellular morphology, expression of other neurotransmitters, afferent and efferent connections and functional properties, 5-HT neurons of the DRN have been grouped into six cell clusters. The subdivisions comprise the rostral, ventral, dorsal, lateral, caudal and interfascicular parts of the DRN. In addition to 5-HT cells, neurons containing γ-aminobutyric acid (GABA), glutamate, dopamine, nitric oxide and the neuropeptides corticotropin-releasing factor, substance P, galanin, cholecystokinin, neurotensin, somatostatin, vasoactive intestinal peptide, neuropeptide Y, thyrotropin-releasing hormone, growth hormone, leu-enkephalin, met-enkephalin and gastrin have been characterized in the DRN. Moreover, numerous brain areas have neurons that project to the DRN and express monoamines (norepinephrine, histamine), amino acids (GABA, glutamate), acetylcholine or neuropeptides (orexin, melanin-concentrating hormone, corticotropin-releasing factor and substance P) that directly or indirectly, through local circuits, regulate the activity of 5-HT cells. The 5-HT cells predominate along the midline of the rostral, dorsal and ventral subdivisions of the DRN and outnumber the non-5-HT cells occurring in the raphe nucleus. The GABAergic and glutamatergic neurons are clustered mainly in the lateral and dorsal subdivisions of the DRN, respectively. The 5-HT(1A) receptor is located on the soma and the dendrites of 5-HT neurons and at postsynaptic sites (outside the DRN). It is expressed, in addition, by non-5-HT cells of the DRN. The 5-HT(1B) receptor is located at presynaptic and postsynaptic sites (outside the boundaries of the DRN). It has been described also in the ventromedial DRN where it is expressed by non-5-HT cells. The 5-HT(2A) and 5-HT(2C) receptors are located within postsynaptic structures. At the level of the DRN the 5-HT(2A) and 5-HT(2C) receptor-containing cells are predominantly GABAergic interneurons and projection neurons. Within the boundaries of the DRN the 5-HT(3) receptor is expressed by, among others, glutamatergic interneurons. 5-HT(7) receptors in the DRN are not localized to serotonergic neurons but, at least in part, to GABAergic cells and terminals. The complex structure of the DRN may have important implications for neural mechanisms underlying 5-HT modulation of wakefulness and REM sleep.

Brainstem reticulospinal neurons are targets for corticotropin-releasing factor-Induced locomotion in roughskin newts

Stress-induced release or central administration of corticotropin-releasing factor (CRF) enhances locomotion in a wide range of vertebrates, including the roughskin newt, Taricha granulosa. Although CRF's stimulatory actions on locomotor behavior are well established, the target neurons through which CRF exerts this effect remain unknown. To identify these target neurons, we utilized a fluorescent conjugate of CRF (CRF-TAMRA 1) to track this peptide's internalization into reticulospinal and other neurons in the medullary reticular formation (MRF), a region critically involved in regulating locomotion. Epifluorescent and confocal microscopy revealed that CRF-TAMRA 1 was internalized by diverse MRF neurons, including reticulospinal neurons retrogradely labeled with Cascade Blue dextran. In addition, we immunohistochemically identified a distinct subset of serotonin-containing neurons, located throughout the medullary raphé, that also internalized the fluorescent CRF-TAMRA 1 conjugate. Chronic single-unit recordings obtained from microwire electrodes in behaving newts revealed that intracerebroventricular (icv) administration of CRF-TAMRA 1 increased medullary neuronal firing and that appearance of this firing was associated with, and strongly predictive of, episodes of CRF-induced locomotion. Furthermore, icv administered CRF-TAMRA 1 produced behavioral and neurophysiological effects identical to equimolar doses of unlabeled CRF. Collectively, these findings provide the first evidence that CRF directly targets reticulospinal and serotonergic neurons in the MRF and indicate that CRF may enhance locomotion via direct effects on the hindbrain, including the reticulospinal system.

Swim stress enhances nociceptin/orphanin FQ-induced inhibition of rat dorsal raphe nucleus activity in vivo and in vitro: role of corticotropin releasing factor

The effects of nociceptin/orphanin FQ on putative serotonin (5HT) neurons of the dorsal raphe nucleus (DRN), known to modulate the behavioral responses to stress, were investigated in vivo and in vitro. In DRN slices from unstressed rats, nociceptin/orphanin FQ concentration-dependently inhibited the firing rate of putative 5HT neurons (EC(50) = 21.6 +/- 1.21 nM) and the selective NOP receptor antagonist UFP-101 shifted the concentration-response curve to the right (estimated pA(2) 6.86). Nociceptin/orphanin FQ potency was enhanced in slices prepared from rats previously subjected to a 15 min swim stress (EC(50) = 1.98 +/- 0.11 nM). Swim stress did not change the number or affinity of NOP receptors in DRN. Stress-elicited potentiation involved corticotropin-releasing factor (CRF)(1) receptors, GABA signaling and protein synthesis, being attenuated by pre-treatment with antalarmin (20 mg/kg, i.p.), diazepam (2.4 mg/kg, i.p.) and cycloheximide (2.5 mg/kg, i.p.), respectively. In anesthetized unstressed rats, locally applied nociceptin/orphanin FQ (0.03 and 0.1 ng/30 nl) inhibited the firing rate of DRN neurons (to 80 +/- 7 and 54 +/- 10% of baseline, respectively). Nociceptin/orphanin FQ inhibition was potentiated both 24 h after swim stress and 1 h after CRF (30 ng/30 nl intra-DRN). Stress-induced potentiation was prevented by the selective CRF(1) receptor antagonist, NBI 30755 (20 mg/kg, i.p.). In contrast, the inhibitory response of DRN neurons to the 5HT(1A) agonist, 8OH-DPAT (1 microg/1 microl, intra-DRN) was not potentiated by swim stress, ruling out a non-specific enhanced permeability of GIRK channel. Together, these findings suggest that CRF and the nociceptin/orphanin FQ/NOP system interact in the DRN during stress to control 5HT transmission; this may play a role in stress-related neuropsychopathologies.

Stress sensitive female macaques have decreased fifth Ewing variant (Fev) and serotonin-related gene expression that is not reversed by citalopram

Female cynomolgus monkeys exhibit different degrees of reproductive dysfunction with moderate metabolic and psychosocial stress. When stressed with a paradigm of relocation and diet for 60 days or two menstrual cycles, highly stress resilient monkeys (HSR) continued to ovulate during the stress cycles whereas stress sensitive monkeys (SS) did not. After cessation of stress, monkeys characterized as HSR or SS were administered placebo (PL) or S-citalopram (CIT) for 15 weeks at doses that normalized ovarian steroid secretion in the SS animals and that maintained blood CIT levels in a therapeutic range. After euthanasia, the brain was perfused with 4% paraformaldehyde. The pontine midbrain was blocked and sectioned at 25 microm. The expression of four genes pivotal to serotonin neural function was assessed in the four groups of monkeys (n=4/group). Fev (fifth Ewing variant) ETS transcription factor, tryptophan hydroxylase 2 (TPH2), the serotonin reuptake transporter (SERT), and the 5HT1A autoreceptor were determined at 7-8 levels of the dorsal raphe nucleus with in situ hybridization (ISH) using radiolabeled- and digoxygenin-incorporated riboprobes. Positive pixel area and cell number were measured with Slidebook 4.2 in the digoxigenin assay for Fev. Optical density (OD) and positive pixel area were measured with NIH Image software in the radiolabeled assays for TPH2, SERT and 5HT1A. All data were analyzed with two-way ANOVA. SS monkeys had significantly fewer Fev-positive cells and lower Fev-positive pixel area in the dorsal raphe than HSR monkeys. SS monkeys also had significantly lower levels of TPH2, SERT and 5HT1A mRNAs in the dorsal raphe nucleus than HSR monkeys. However, CIT did not alter the expression of either Fev, TPH2, SERT or 5HT1A mRNAs. These data suggest that SS monkeys have fewer serotonin (5-HT) neurons than HSR monkeys, and that they have deficient Fev expression, which in turn, leads to deficient TPH2, SERT and 5HT1A expression. In addition, the therapeutic effect of CIT is probably achieved through mechanisms other than alteration of 5-HT-related gene expression.

Comorbidity of insomnia and depression

During the last decade, several studies have shown that insomnia, rather than a symptom of depression, could be a medical condition on its own, showing high comorbidity with depression. Epidemiological research indicates that insomnia could lead to depression and/or that common causalities underlie the two disorders. Neurobiological and sleep EEG studies suggest that a heightened level of arousal may play a common role in both conditions and that signs of REM sleep disinhibition may appear in individuals prone to depression. The effects of antidepressant drugs on non-REM and REM sleep are discussed in relation to their use in insomnia comorbid with depression. Empirical treatment approaches are behavioral management of sleep combined with prescription of a sedative antidepressant alone, co-prescription of two antidepressants, or of an antidepressant with a hypnotic drug.

The response of neurons in the bed nucleus of the stria terminalis to serotonin: implications for anxiety

Substantial evidence has suggested that the activity of the bed nucleus of the stria terminalis (BNST) mediates many forms of anxiety-like behavior in human and non-human animals. These data have led many investigators to suggest that abnormal processing within this nucleus may underlie anxiety disorders in humans, and effective anxiety treatments may restore normal BNST functioning. Currently some of the most effective treatments for anxiety disorders are drugs that modulate serotonin (5-HT) systems, and several decades of research have suggested that the activation of 5-HT can modulate anxiety-like behavior. Despite these facts, relatively few studies have examined how activity within the BNST is modulated by 5-HT. Here we review our own investigations using in vitro whole-cell patch-clamp electrophysiological methods on brain sections containing the BNST to determine the response of BNST neurons to exogenous 5-HT application. Our data suggest that the response of BNST neurons to 5-HT is complex, displaying both inhibitory and excitatory components, which are mediated by 5-HT(1A), 5-HT(2A), 5-HT(2C) and 5-HT(7) receptors. Moreover, we have shown that the selective activation of the inhibitory response to 5-HT reduces anxiety-like behavior, and we describe data suggesting that the activation of the excitatory response to 5-HT may be anxiogenic. We propose that in the normal state, the function of 5-HT is to dampen activity within the BNST (and consequent anxiety-like behavior) during exposure to threatening stimuli; however, we suggest that changes in the balance of the function of BNST 5-HT receptor subtypes could alter the response of BNST neurons to favor excitation and produce a pathological state of increased anxiety.

Corticotropin-releasing factor in the dorsal raphe nucleus: Linking stress coping and addiction

Addiction and stress are linked at multiple levels. Drug abuse is often initiated as a maladaptive mechanism for coping with stress. It is maintained in part by negative reinforcement to prevent the aversive consequences of stress associated with abstinence. Finally, stress is a major factor leading to relapse in subjects in which drug seeking behavior has extinguished. These associations imply overlapping or converging neural circuits and substrates that underlie the processes of addiction and the expression of the stress response. Here we discuss the major brain serotonin (5-HT) system, the dorsal raphe nucleus (DRN)-5-HT system as a point of convergence that links these processes and how the stress-related neuropeptide, corticotropin-releasing factor (CRF) directs this by a bimodal regulation of DRN neuronal activity. The review begins by describing a structural basis for CRF regulation of the DRN-5-HT system. This is followed by a review of the effects of CRF and stress on DRN function based on electrophysiological and microdialysis studies. The concept that multiple CRF receptor subtypes in the DRN facilitate distinct coping behaviors is reviewed with recent evidence for a unique cellular mechanism by which stress history can determine the type of coping behavior. Finally, work on CRF regulation of the DRN-5-HT system is integrated with literature on the role of 5-HT-dopamine interactions in addiction.

Consequences of post-weaning social isolation on anxiety behavior and related neural circuits in rodents

Exposure to adverse experiences in early-life is implicated in the later vulnerability to development of psychiatric disorders, including anxiety and affective disorders in humans. Adverse early-life experiences likely impart their long-term consequences on mental health by disrupting the normal development of neural systems involved in stress responses, emotional behavior and emotional states. Neural systems utilizing the neurotransmitters serotonin, dopamine and the neuropeptide corticotropin-releasing factor (CRF) are implicated in mediating emotive behaviors, and dysfunction of these neurochemical systems is associated with mood/anxiety disorders. These neural systems continue maturing until early or mid-adolescence in humans, thus alterations to their development are likely to contribute to the long-term consequences of adverse early-life experiences. A large body of literature suggests that post-weaning isolation rearing of rodents models the behavioral consequences of adverse early-life experiences in humans. Overall, the majority findings suggest that post-weaning social isolation that encompasses pre-adolescence produces long-lasting alterations to anxiety behavior, while measures of monoaminergic activity in various limbic regions during social isolation suggest alterations to dopamine and serotonin systems. The goal of this review is to evaluate and integrate findings from post-weaning social isolation studies specifically related to altered fear and anxiety behaviors and associated changes in neuroendocrine function and the activity of monoaminergic systems.

Influence of sex and corticotropin-releasing factor pathways as determinants in serotonin sensitivity

Stress sensitivity and sex are predictive factors in affective disorder susceptibility. Serotonin (5-HT) pathway recruitment by corticotropin-releasing factor (CRF) during stress is necessary in adaptive coping behaviors, but sex differences in such responses have not been investigated. Using selective 5-HT reuptake inhibitor (SSRI) administration to acutely elevate 5-HT in a genetic model of stress sensitivity, we examined behavioral and physiological responses in male and female stress-sensitive CRF receptor-2-deficient (R2KO) mice. Chronic SSRI treatment was used to confirm outcomes were specific to acute 5-HT elevation and not antidepressant efficacy. We hypothesized that R2KO mice would show a greater sensitivity to acute changes in 5-HT and that, because females typically are more stress sensitive, R2KO females would be the most responsive. Our results supported this hypothesis because females of both genotypes and R2KO males showed a greater sensitivity to an acute 10 mg/kg dose of citalopram in a tail suspension test, displaying decreased immobile time and increased latency to immobility. Furthermore, acute citalopram promoted significant anxiogenic-like effects that were specific to R2KO females in the elevated plus maze and light-dark box tests. Chronic citalopram did not produce these behavioral changes, supporting specificity to acute 5-HT modulation. Mechanistically, females had decreased hippocampal 5-HT transporter (SERT) levels, whereas R2KO mice showed reduced SERT in the prefrontal cortex, supporting a possible intersection of sex and genotype where R2KO females would have the lowest SERT to be blocked by the SSRI. This sensitivity to 5-HT-mediated anxiety in females may underlie a heightened vulnerability to stress-related affective disorders.

Stress-induced redistribution of corticotropin-releasing factor receptor subtypes in the dorsal raphe nucleus

BACKGROUND

The stress-related neuropeptide corticotropin-releasing factor (CRF) is involved in determining behavioral strategies for responding to stressors, in part through its regulation of the dorsal raphe (DR)-serotonin (5-HT) system. CRF(1) and CRF(2) receptor subtypes have opposing effects on this system that are associated with active versus passive coping strategies, respectively.

METHODS

Immunoelectron microscopy and in vivo single-unit recordings were used to assess CRF receptor distribution and neuronal responses, respectively, in the DR of stressed and unstressed rats.

RESULTS

Here we show that in unstressed rats CRF(1) and CRF(2) are differentially distributed within DR cells, with CRF(1) being prominent on the plasma membrane and CRF(2) being cytoplasmic. Stress experience reverses this distribution, such that CRF(2) is recruited to the plasma membrane and CRF(1) tends to internalize. As a consequence of this stress-induced cellular redistribution of CRF receptors, neuronal responses to CRF change from inhibition to a CRF(2)-mediated excitation.

CONCLUSIONS

Given evidence that CRF(1) and CRF(2) activation are associated with distinct behavioral responses to stress, the stress-triggered reversal in receptor localization provides a cellular mechanism for switching behavioral strategies for coping with stressors.

Fluoxetine potentiates the effects of corticotropin-releasing factor on locomotor activity and serotonergic systems in the roughskin newt, Taricha granulosa

The anxiety- and stress-related neuropeptide corticotropin-releasing factor (CRF) elicits behavioral changes in vertebrates including increases in behavioral arousal and locomotor activity. Intracerebroventricular injections of CRF in an amphibian, the roughskin newt (Taricha granulosa), induces rapid increases in locomotor activity in both intact and hypophysectomized animals. We hypothesized that this CRF-induced increase in locomotor activity involves a central effect of CRF on serotonergic neurons, based on known stimulatory actions of serotonin (5-hydroxytryptamine, 5-HT) on spinal motor neurons and the central pattern generator for locomotor activity in vertebrates. In Experiment 1, we found that neither intracerebroventricular injections of low doses of CRF (25 ng) nor the selective serotonin reuptake inhibitor fluoxetine (10, 100 ng), by themselves, altered locomotor activity. In contrast, newts treated concurrently with CRF and fluoxetine responded with marked increases in locomotor activity. In Experiment 2, we found that increases in locomotor activity following co-administration of CRF (25 ng) and fluoxetine (100 ng) were associated with decreased 5-HT concentrations in a number of forebrain structures involved in regulation of emotional behavior and emotional states, including the ventral striatum, amygdala pars lateralis, and dorsal hypothalamus, measured 37 min after treatment. These results are consistent with the hypothesis that CRF stimulates locomotor activity through activation of serotonergic systems.

Inhibition of serotonin outflow by nociceptin/orphaninFQ in dorsal raphe nucleus slices from normal and stressed rats: Role of corticotropin releasing factor

In the dorsal raphe nucleus (DRN) many inputs converge and interact to modulate serotonergic neuronal activity and the behavioral responses to stress. The effects exerted by two stress-related neuropeptides, corticotropin releasing factor (CRF) and nociceptin/orphaninFQ (N/OFQ), on the outflow of [(3)H]5- hydroxytryptamine were investigated in superfused rat dorsal raphe nucleus slices. Electrical stimulation (100 mA, 1 ms for 2 min) evoked a frequency-dependent peak of [(3)H]5- hydroxytryptamine outflow, which was sodium and calcium-dependent. Corticotropin releasing factor (1-100 nM), concentration-dependently inhibited the stimulation (3 Hz)-evoked [(3)H]5-hydroxytryptamine outflow; the inhibition by 30 nM corticotropin releasing factor (to 68 +/- 5.7%) was prevented both by the non selective CRF receptor antagonist alpha-helicalCRF(9-41) (alpha-HEL) (300 nM) and by the CRF(1) receptor antagonist antalarmin (ANT) (100 nM). The CRF(2) agonist urocortin II (10 nM) did not modify [(3)H]5- hydroxytryptamine outflow, ruling out the involvement of CRF(2) receptors. Bicuculline (BIC), a GABAA antagonist (10 microM), prevented the inhibitory effect of corticotropin releasing factor (30 nM), supporting the hypothesis that the inhibition was mediated by increased gamma-aminobutyric acid (GABA) release. Nociceptin/ orphaninFQ (1 nM-1 microM) exerted an antalarmin- and bicuculline-insensitive inhibition on [(3)H]5- hydroxytryptamine outflow, with the maximum at 100 nM (to 63+/- 4.2%), antagonized by the NOP receptor antagonist UFP-101 (1 microM). Dorsal raphe nucleus slices prepared from rats exposed to 15 min of forced swim stress displayed a reduced [(3)H]5-hydroxytryptamine outflow, in part reversed by antalarmin and further inhibited by nociceptin/orphaninFQ. These findings indicate that (i) both corticotropin releasing factor and nociceptin/orphaninFQ exert an inhibitory control on dorsal raphe nucleus serotonergic neurons; (ii) the inhibition by corticotropin releasing factor involves gamma-aminobutyric acid neurons; (iii) nociceptin/ orphaninFQ inhibits dorsal raphe nucleus serotonin system in a corticotropin releasing factor- and gamma-aminobutyric acid-independent manner; (iv) nociceptin/orphaninFQ modulation is still operant in slices prepared from stressed rats. The nociceptin/orphaninFQ-NOP receptor system could represent a new target for drugs effective in stress-related disorders.

Corticolimbic transcriptome changes are state-dependent and region-specific in a rodent model of depression and of antidepressant reversal

Gene microarrays may enable the elucidation of neurobiological changes underlying the pathophysiology and treatment of major depression. However, previous studies of antidepressant treatments were performed in healthy normal rather than 'depressed' animals. Since antidepressants are devoid of mood-changing effects in normal individuals, the clinically relevant rodent transcriptional changes could remain undetected. We investigated antidepressant-related transcriptome changes in a corticolimbic network of mood regulation in the context of the unpredictable chronic mild stress (UCMS), a naturalistic model of depression based on socio-environmental stressors. Mice subjected to a 7-week UCMS displayed a progressive coat state deterioration, reduced weight gain, and increased agonistic and emotion-related behaviors. Chronic administration of an effective (fluoxetine) or putative antidepressant (corticotropin-releasing factor-1 (CRF1) antagonist, SSR125543) reversed all physical and behavioral effects. Changes in gene expression differed among cingulate cortex (CC), amygdala (AMY) and dentate gyrus (DG) and were extensively reversed by both drugs in CC and AMY, and to a lesser extent in DG. Fluoxetine and SSR125543 also induced additional and very similar molecular profiles in UCMS-treated mice, but the effects of the same drug differed considerably between control and UCMS states. These studies established on a large-scale that the molecular impacts of antidepressants are region-specific and state-dependent, revealed common transcriptional changes downstream from different antidepressant treatments and supported CRF1 targeting as an effective therapeutic strategy. Correlations between UCMS, drug treatments, and gene expression suggest distinct AMY neuronal and oligodendrocyte molecular phenotypes as candidate systems for mood regulation and therapeutic interventions.

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.

Aggressive encounters alter the activation of serotonergic neurons and the expression of 5-HT1A mRNA in the hamster dorsal raphe nucleus

Serotonergic (5-HT) neurons in the dorsal raphe nucleus (DRN) have been implicated in stress-induced changes in behavior. Previous research indicates that stressful stimuli activate 5-HT neurons in select subregions of the DRN. Uncontrollable stress is thought to sensitize 5-HT neurons in the DRN and allow for an exaggerated 5-HT response to future stimuli. In the current study, we tested the hypothesis that following aggressive encounters, losing male Syrian hamsters would exhibit increased c-Fos immunoreactivity in 5-HT DRN neurons compared to winners or controls. In addition, we tested the hypothesis that losers would have decreased 5-HT1A mRNA levels in the DRN compared to winners or controls. We found that a single 15-min aggressive encounter increased c-Fos expression in 5-HT and non-5-HT neurons in losers compared to winners and controls. The increased c-Fos expression in losers was restricted to ventral regions of the rostral DRN. We also found that four 5-min aggressive encounters reduced total 5-HT1A mRNA levels in the DRN in losers compared to winners and controls, and that differences in mRNA levels were not restricted to specific DRN subregions. These results suggest that social defeat activates neurons in select subregions of the DRN and reduces message for DRN 5-HT1A autoreceptors. Our results support the hypothesis that social stress can activate 5-HT neurons in the DRN, reduce 5-HT1A autoreceptor-mediated inhibition, and lead to hyperactivity of 5-HT neurons.

Decline in serotonergic firing activity and desensitization of 5-HT1A autoreceptors after chronic unpredictable stress

Chronic stressful life events are risk factors for contracting depression, the pathophysiology of which is strongly associated with impairments in serotonergic (5-HT) neurotransmission. Indeed, in rodents, exposure to chronic unpredictable stress (CUS) produces depressive-like behaviours such as behavioural despair and anhedonia. To date, there have not been many studies that especially explore in vivo changes in 5-HT neurotransmission associated with CUS in the rat. Therefore, using in vivo electrophysiology, we evaluated whether CUS that induces anhedonia-like behaviours concurrently impairs midbrain raphe 5-HT neuronal activity. Unlike unstressed and acutely stressed rats, CUS produced progressive reductions in sucrose intake and preference (anhedonia-like). These were associated with a decrease in the spontaneous firing activity (35.4%) as well as in the number of spontaneously active 5-HT neurons, and a desensitization of somatodendritic 5-HT1A autoreceptors in the dorsal raphe. These results suggest that CUS dramatically decreases 5-HT neural activity and 5-HT1A autoreceptor sensitivity, and may represent endophenotypic features of depressive-like states.

Differential sensitivity of the perioculomotor urocortin-containing neurons to ethanol, psychostimulants and stress in mice and rats

The perioculomotor urocortin-containing population of neurons (pIIIu: otherwise known as the non-preganglionic Edinger-Westphal nucleus) is sensitive to alcohol and is involved in the regulation of alcohol intake. A recent study indicated that this brain region is also sensitive to psychostimulants. Since pIIIu has been shown to respond to stress, we investigated how psychostimulant-induced pIIIu activation compares to stress- and ethanol-induced activation, and whether it is independent from a generalized stress response. Several experiments were performed to test how the pIIIu responds to psychostimulants by quantifying the number of Fos immunoreactive nuclei after acute i.p. injections of saline, 10-30 mg/kg cocaine, 5 mg/kg methamphetamine, 5 mg/kg amphetamine, 2.5 g/kg ethanol, 2 h of restraint stress, 10 min of swim stress, or six applications of mild foot shock in male C57BL/6 J mice. We also compared Fos immunoreactivity in pIIIu after acute (20 mg/kg cocaine) and repeated cocaine exposure (7 days of 20 mg/kg cocaine) injections in male C57BL/6 J mice in order to investigate the potential habituation of this response. Finally, we quantified the number of Fos immunoreactive nuclei in pIIIu after administration of saline, 2.5 g/kg ethanol, 20 mg/kg cocaine, or 2 h of restraint stress in male Sprague-Dawley rats. We found that exposure to psychostimulants and ethanol induced significantly higher Fos levels in pIIIu compared to stress in mice. Furthermore, repeated cocaine injections did not decrease Fos immunoreactivity as would be expected if this response were due to stress. In rats, exposure to ethanol, psychostimulant and restraint stress all induced pIIIu Fos immunoreactivity compared to saline-injected controls. In both mice and rats, ethanol- and cocaine-induced Fos immunoreactivity occurred exclusively in urocortin 1-positive, but not in tyrosine hydroxylase-positive, cells. These results provide evidence that the pIIIu Fos-response to psychostimulants is independent of a generalized stress in mice, but not rats. They additionally show that the pIIIu response to stress differs significantly between species.

Serotonergic systems, anxiety, and affective disorder: focus on the dorsomedial part of the dorsal raphe nucleus

Depressed suicide patients have elevated expression of neuronal tryptophan hydroxylase 2 (TPH2) mRNA and protein in midbrain serotonergic neurons, as well as increases in brain serotonin turnover. The mechanisms underlying these changes are uncertain, but increased TPH2 expression and serotonin turnover could result from genetic influences, adverse early life experiences, or acute stressful life events, all of which can alter serotonergic neurotransmission and have been implicated in determining vulnerability to major depression. Emerging evidence suggests that there are several different stress-related subsets of serotonergic neurons, each with a unique role in the integrated stress response. Here we review our current understanding of how genetic and environmental factors may influence TPH2 mRNA expression and serotonergic neurotransmission, focusing in particular on the dorsomedial part of the dorsal raphe nucleus. This subdivision of the dorsal raphe nucleus is selectively innervated by key forebrain structures implicated in regulation of anxiety states, it gives rise to projections to a distributed neural system mediating anxiety states, and serotonergic neurons within this subdivision are selectively activated by a number of stress- and anxiety-related stimuli. A better understanding of the anatomical and functional properties of specific stress- or anxiety-related serotonergic systems should aid our understanding of the neural mechanisms underlying the etiology of anxiety and affective disorders.

Demonstration of decreased activity of dorsal raphe nucleus neurons in depressed suicidal patients by the AgNOR staining method

BACKGROUND

Suicide and depression are closely related yet distinct phenomena. In both these phenomena, research has focused on central serotonergic system disturbances. The dorsal raphe nucleus (DRN) is the main source of serotonergic innervation of limbic structures crucial for the regulation of emotionally influenced behaviour.

METHODS

The study was carried out on paraffin-embedded brains from 23 depressed patients (12 suicides and 11 non-suicides) and 26 matched controls without mental disorders. The karyometric parameters of DRN neurons were evaluated by the AgNOR silver staining method.

RESULTS

The significant effect of suicide on the nuclear area was found in the cumulative analysis of all DRN subnuclei (ANOVA, P=0.032). A decreased mean value of this parameter was observed in the suicides group versus controls (t-test, P=0.032). This effect was especially pronounced in the violent suicide victims (t-test, P=0.001), who also demonstrated a decreased AgNOR area versus controls (t-test, P=0.007). No significant effect of depression or polarity on AgNOR parameters was found.

LIMITATIONS

A major limitation of this study is relatively small case number. A further limitation is given by the lack of data on drug exposure across the whole life span.

CONCLUSION

Our findings suggest that hypoactivity of DRN neurons is a distinct phenomenon in depression, specific only for suicidal subgroup of depressed patients.

Corticotropin-releasing factor increases GABA synaptic activity and induces inward current in 5-hydroxytryptamine dorsal raphe neurons

Stress-related psychiatric disorders such as anxiety and depression involve dysfunction of the serotonin [5-hydroxytryptamine (5-HT)] system. Previous studies have found that the stress neurohormone corticotropin-releasing factor (CRF) inhibits 5-HT neurons in the dorsal raphe nucleus (DRN) in vivo. The goals of the present study were to characterize the CRF receptor subtypes (CRF-R1 and -R2) and cellular mechanisms underlying CRF-5-HT interactions. Visualized whole-cell patch-clamp recording techniques in brain slices were used to measure spontaneous or evoked GABA synaptic activity in DRN neurons of rats and CRF effects on these measures. CRF-R1 and -R2-selective agonists were bath applied alone or in combination with receptor-selective antagonists. CRF increased presynaptic GABA release selectively onto 5-HT neurons, an effect mediated by the CRF-R1 receptor. CRF increased postsynaptic GABA receptor sensitivity selectively in 5-HT neurons, an effect to which both receptor subtypes contributed. CRF also had direct effects on DRN neurons, eliciting an inward current in 5-HT neurons mediated by the CRF-R2 receptor and in non-5-HT neurons mediated by the CRF-R1 receptor. These results indicate that CRF has direct membrane effects on 5-HT DRN neurons as well as indirect effects on GABAergic synaptic transmission that are mediated by distinct receptor subtypes. The inhibition of 5-HT DRN neurons by CRF in vivo may therefore be primarily an indirect effect via stimulation of inhibitory GABA synaptic transmission. These results regarding the cellular mechanisms underlying the complex interaction between CRF, 5-HT, and GABA systems could contribute to the development of novel treatments for stress-related psychiatric disorders.

Estrogen decreases 5-HT1B autoreceptor mRNA in selective subregion of rat dorsal raphe nucleus: inverse association between gene expression and anxiety behavior in the open field

We have recently shown that estrogen decreases anxiety and increases expression of tryptophan hydroxylase-2 (TPH2), the rate-limiting enzyme for 5-HT synthesis. However, the effects of estrogen on 5-HT release and reuptake may also affect the overall availability of 5-HT in the forebrain. Estrogen has been previously shown to have no effect on the inhibitory 5-HT 1A autoreceptor (5-HT(1A)) in the rat dorsal raphe nuclei (DRN); however the regulation of the inhibitory 5-HT 1B autoreceptor (5-HT(1B)) in the midbrain raphe by estrogen has not yet been investigated. Therefore, we examined the effects of estrogen on 5-HT(1B) mRNA in the rat DRN, focusing on specific subregions, and whether 5-HT(1B) mRNA levels correlated with TPH2 mRNA levels and with anxiety-like behavior. Ovariectomized rats were treated for 2 weeks with estrogen or placebo, exposed to the open field test, and 5-HT(1A) and 5-HT(1B) mRNA was quantified by in situ hybridization histochemistry. Estrogen had no effect on 5HT(1A) mRNA in any of the DRN subregions examined, confirming a previous report. In contrast, estrogen selectively decreased 5-HT(1B) mRNA in the mid-ventromedial subregion of the DRN, where 5-HT(1B) mRNA was associated with higher anxiety-like behavior and inversely correlated with TPH2 mRNA levels. These results suggest that estrogen may reduce 5-HT(1B) autoreceptor and increase TPH2 synthesis in a coordinated fashion, thereby increasing the capacity for 5-HT synthesis and release in distinct forebrain regions that modulate specific components of anxiety behavior.

Early life social isolation alters corticotropin-releasing factor responses in adult rats

Stress induced by early life social isolation leads to long-lasting alterations in stress responses and serotonergic activity. Corticotropin-releasing factor (CRF) is a neurotransmitter that mediates stress responses and alters serotonergic activity. We tested the hypothesis that the stress of early life isolation enhances responses to CRF in adulthood by determining the effect of CRF infusions into the dorsal raphe nucleus (dRN) on 5-HT release in the nucleus accumbens (NAc) of adult rats using in vivo microdialysis. Juvenile male rats were either isolated or housed in groups of three for a 3-week period beginning on postnatal day 21 after which, all rats were group-reared for an additional 2 weeks. Following the isolation/re-socialization procedure, infusion of 100 ng CRF into the dRN decreased 5-HT release in the NAc of group-reared rats. This treatment did not significantly affect 5-HT release in the NAc of isolation-reared animals. In contrast, infusion of 500 ng CRF into the dRN transiently increased 5-HT release in the NAc of both group-reared and isolated animals with isolated animals showing a more prolonged serotonergic response. Western blot and immunofluorescent staining for CRF receptors in the dRN showed that CRF(2) receptor levels were increased in the dRN of isolation-reared animals when compared with group-reared rats. Taken together, the results suggest that isolation during the early part of development causes alterations in both CRF receptor levels and CRF-mediated serotonergic activity. These effects may underlie the increased sensitivity to stress observed in isolates.

Failure to mount adaptive responses to stress results in dysregulation and cell death in the midbrain raphe

Stress is a common trigger in affective disorder onset, yet the mechanism and predisposing factors of vulnerability remain unknown. Effective disease prevention requires a critical balance of responses within the serotonergic raphe nucleus, including a coordination of corticotropin-releasing factor (CRF) actions at both of its receptors, CRF receptor-1 and CRF receptor-2. Mice deficient in CRF receptor-2 (R2KO) were used as a model of maladaptive stress responsivity to examine the physiological and molecular markers of stress dysregulation within the raphe in the absence of this receptor. After chronic stress, R2KO mice failed to display the robust stress-mediated adaptations characteristic of control mice, including elevations in tryptophan hydroxylase-2 and CRF receptor-1 expression and concordant increases in behavioral arousal. As a further indication of failed homeostatic mechanisms, R2KO mice displayed indices of cell death in the raphe after stress exposure, with elevations in proapoptotic factors but a failure to mount adaptive increases in antiapoptotic factors found in control mice. In vitro electrophysiological characterization of the specific influence of CRF on the raphe revealed both basal differences and a failure to respond to CRF administration in R2KO mice. These results support a requirement for homeostatic maintenance in response to stress in the raphe, where dysregulation may be a critical predictor of affective disorder onset.

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.

Antagonism of corticotrophin-releasing factor receptors in the fourth ventricle modifies responses to mild but not restraint stress

Repeated restraint stress (RRS; 3 h of restraint on 3 consecutive days) in rodents produces temporary hypophagia, but a long-term downregulation of body weight. The mild stress (MS) of an intraperitoneal injection of saline and housing in a novel room for 2 h also inhibits food intake and weight gain, but the effects are smaller than for RRS. Previous exposure to RRS exaggerates hypophagia, glucocorticoid release, and anxiety-type behavior caused by MS. Here we tested the involvement of brain stem corticotrophin-releasing factor receptors (CRFR) in mediating energetic and glucocorticoid responses to RRS or MS and in promoting stress hyperresponsiveness in RRS rats. Administration of 1.3 nmol alphahCRF(9-41), a nonspecific CRFR antagonist, exaggerated hypophagia and weight loss in both RRS and MS rats, whereas 0.26 nmol had no effect in RRS or MS rats. In contrast, 2 nmol of the nonspecific antagonist astressin had no effect on weight loss or hypersensitivity to subsequent MS in RRS rats, but blocked weight loss and inhibition of food intake caused by MS alone. MS rats infused with 3 nmol antisauvagine-30, a CRFR2 antagonist, did not lose weight in the 48 h after MS, but 0.3 nmol did not prevent weight loss in MS rats. These data suggest that inhibition of food intake and weight loss induced by RRS or by MS involve different pathways, with hindbrain CRFR mediating the effect of MS on body weight and food intake. Hindbrain CRFR do not appear to influence stress-induced corticosterone release in RRS rats.

The potential role of a corticotropin-releasing factor receptor-1 antagonist in psychiatric disorders

The hypothalamic-pituitary-adrenal axis is a key mediator of the stress response in humans. The corticotropin-releasing factor (CRF) type 1 receptor (CRFR-1) in the pituitary gland is a gatekeeper for that response, and the CRFR-1 receptor is also present in many other mood- and cognition-related neural structures. Behaviorally, a number of relationships between stress and psychiatric disorders can be observed: chronic or repeated stress is associated with onset of depression; stressors can cause a recovering alcoholic to relapse; overactive stress responses mark many anxiety disorders; and insomnia can arise from an overactive stress response. Thus, a CRFR-1 antagonist could be useful for treating or preventing the consequences of CRF-mediated stress in depression, anxiety, insomnia, and substance abuse.

Moderate perinatal arsenic exposure alters neuroendocrine markers associated with depression and increases depressive-like behaviors in adult mouse offspring

Arsenic is one of the most common heavy metal contaminants found in the environment, particularly in water. We examined the impact of perinatal exposure to relatively low levels of arsenic (50 parts per billion, ppb) on neuroendocrine markers associated with depression and depressive-like behaviors in affected adult C57BL/6J mouse offspring. Whereas most biomedical research on arsenic has focused on its carcinogenic potential, a few studies suggest that arsenic can adversely affect brain development and neural function. Compared to controls, offspring exposed to 50 parts per billion arsenic during the perinatal period had significantly elevated serum corticosterone levels, reduced whole hippocampal CRFR 1 protein level and elevated dorsal hippocampal serotonin 5HT 1A receptor binding and receptor-effector coupling. 5HT 1A receptor binding and receptor-effector coupling were not different in the ventral hippocampal formation, entorhinal or parietal cortices, or inferior colliculus. Perinatal arsenic exposure also significantly increased learned helplessness and measures of immobility in a forced swim task. Taken together, these results suggest that perinatal arsenic exposure may disrupt the regulatory interactions between the hypothalamic-pituitary-adrenal axis and the serotonergic system in the dorsal hippocampal formation in a manner that predisposes affected offspring to depressive-like behavior. These results are the first to demonstrate that relatively low levels of arsenic exposure during development can have long-lasting adverse effects on behavior and neurobiological markers associated with these behavioral changes.

The role of prior stressor controllability and the dorsal raphé nucleus in sucrose preference and social exploration

Research investigating how control over stressors affects behavior often utilizes freezing and shuttle escape learning as the behavioral endpoints. These endpoints have been argued to reflect anxious or depressed states, but these descriptions are problematic. The present study sought to determine the impact of stressor controllability and the dorsal raphé nucleus (DRN) on sucrose preference and juvenile social exploration, putative measures of anhedonia and anxiety that are commonly used in studies of stress per se. In Experiment 1 rats were exposed to escapable stress (ES) or yoked-inescapable stress (IS) tailshocks. In Experiment 2 ES or IS was given 7 days before all rats received IS. In Experiment 3 the DRN was inactivated during IS by microinjection of 8-OH-DPAT. Sucrose preference and social exploration were tested for several days after stress. A fourth experiment confirmed that juvenile social exploration is sensitive to traditional beta-carboline and benzodiazepine manipulations. Both ES and IS reduced sucrose preference, but only IS reduced social exploration. Prior treatment with ES prevented the effect of IS on social exploration but did not prevent the effect of IS on sucrose preference and inactivation of the DRN prevented the effect of IS on social exploration but did not change sucrose preference. The present results indicate that social exploration but not sucrose preference is sensitive to prior stressor controllability, and that DRN activation mediates the effect of IS on social exploration. We argue that DRN-5-HT activation mediates a state of generalized anxiety produced by uncontrollable stress and that juvenile social exploration is a useful behavioral endpoint in stressor controllability studies.

Activation of raphe efferents to the medial prefrontal cortex by corticotropin-releasing factor: correlation with anxiety-like behavior

BACKGROUND

Parallel lines of research suggest that dysfunction affecting both corticotropin-releasing factor (CRF) and serotonin (5-HT) systems is involved in the pathophysiology of psychiatric illnesses such as anxiety and depression. The effect of CRF on behavior and on the accompanying change in activity of 5-HT neurons in the dorsal and median raphe nuclei (DR and MR) that project to the ventral medial prefrontal cortex (mPFC), a brain area implicated in mood and anxiety disorders, was studied.

METHODS

Male Sprague-Dawley rats with intra-mPFC deposits of fluorescent microspheres received injections of CRF (1 microg, intracerebroventricular [i.c.v.]) and were tested for CRF-enhanced startle, a behavioral assay believed to reflect stress- or anxiety-like states. C-Fos immunohistochemistry was used to measure CRF-induced activity in retrogradely labeled neurons in the DR and MR and correlate this level of activity with the level of CRF-enhanced startle.

RESULTS

The CRF-enhanced startle was accompanied by an increased c-Fos expression in retrogradely labeled cells in the raphe. In the DR and MR, there was a clear topography of activation, with a higher-percent activation in retrogradely labeled neurons in caudal sections. In the caudal DR, this effect was positively correlated with the level of CRF-enhanced startle. Co-expression of retrogradely labeled cells with tryptophan hydroxylase showed that the majority (> 90%) of raphe efferents to the mPFC were from serotonergic neurons.

CONCLUSIONS

These data indicate that CRF activates a subpopulation of cortical-projecting 5-HT raphe neurons and suggest that increased 5-HT release in the mPFC might be an important component driving some types of anxiety-like behaviors.

Distribution and regional stressor-induced regulation of corticotrophin-releasing factor binding protein in rainbow trout (Oncorhynchus mykiss)

The corticotrophin-releasing factor (CRF) system plays a key role in the co-ordination of the physiological response to stress in vertebrates. Although the binding protein (BP) for CRF-related peptides, CRF-BP, is an important player in the many functions of the CRF system, the distribution of CRF-BP and the impact of stressors on its expression in fish are poorly understood. In the present study, we describe the distribution of CRF-BP in the brain and peripheral tissues of rainbow trout (Oncorhynchus mykiss) using a combination of real-time reverse transcriptase-polymerase chain reaction, in situ hybridisation and immunohistochemistry. Our results indicate a widespread and highly localised distribution of CRF-BP in the central nervous system, but do not support a significant peripheral production of the protein. Major expression sites in the brain include the area ventralis telencephali, nucleus preopticus, anterior and lateral tuberal nuclei, and the posterior region of the pituitary pars distalis. We further characterise changes in CRF-BP gene expression in three discrete brain regions after exposure to 8 h and 24 h of social stress or hypoxia. The plasma cortisol concentration in subordinate fish was much higher than in dominant fish and controls, and was indicative of a relatively severe stressor. By contrast, the increase in plasma cortisol concentration in fish exposed to hypoxia was characteristic of the response to a mild stressor. Changes in CRF-BP gene expression were only observed after 24 h of either stressor, and were region-specific. CRF-BP mRNA in the telencephalon increased in both subordinate fish and fish exposed to hypoxia, but CRF-BP in the preoptic area only increased after 24 h of hypoxia exposure. In the hypothalamus, CRF-BP mRNA levels decreased in dominant fish relative to controls after 24 h. Taken together, our results support a diverse role for CRF-BP in the central actions of the fish CRF system, but a negligible role in the peripheral functions of circulating CRF-related peptides. Furthermore, the differential changes in forebrain CRF-BP mRNA appear to occur independently of the hypothalamic-pituitary-inter-renal axis.

The dexamethasone/corticotropin-releasing factor test in men with major depression: role of childhood trauma

BACKGROUND

The dexamethasone/corticotropin-releasing factor (CRF) test is considered to be the most sensitive measure of hypothalamic-pituitary-adrenal (HPA) axis hyperactivity and has been demonstrated to be altered in patients with major depression (MDD). Although childhood trauma is a demonstrated risk factor for MDD and patients with a history of childhood abuse and MDD demonstrate HPA axis hyperactivity, the dexamethasone/CRF test remains unstudied in this population. We determined the impact of childhood trauma on dexamethasone/CRF test results in patients with MDD.

METHODS

Forty-nine healthy men, ages 18-60 years, without mania or psychosis, active substance abuse, or eating disorder and medication-free were recruited into four study groups, including: 1) normal subjects with no childhood abuse history or psychiatric disorder (n = 14); 2) men with childhood abuse histories without current MDD (n = 14); 3) men with childhood abuse histories with current MDD (n = 15); and 4) men with current MDD and no childhood abuse history (n = 6). Plasma adrenocorticotropin (ACTH) and cortisol concentrations were measured in response to dexamethasone/CRF administration.

RESULTS

Men with childhood trauma histories exhibited increases in ACTH and cortisol responses to dexamethasone/CRF compared with non-abused men. In particular, abused men with current MDD showed increased responsiveness compared with control subjects and depressed men without childhood abuse experience. Increased response was associated with the severity, duration, and earlier onset of the abuse. The effects were not explained by concurrent posttraumatic stress disorder.

CONCLUSIONS

Childhood trauma increases HPA axis activity as measured with the dexamethasone/CRF test in adult men with MDD, potentially reflecting environmental risk for developing depression.

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.

Antidepressant-like effects of psoralidin isolated from the seeds of Psoralea Corylifolia in the forced swimming test in mice

The antidepressant-like effects of psoralidin isolated from the seeds of Psoralea corylifolia were investigated in the forced swimming test (FST) in ICR strain of male mice. Psoralidin significantly decreased immobility time and increased swimming behavior without altering climbing behavior in the mouse FST after oral administration for 1 h or 3 consecutive days. Psoralidin did not affect locomotor activity in the open-field test. After a 3-day treatment, psoralidin significantly increased 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels in various brain regions, as well as, changed dopamine (DA) levels in striatum in mice exposed to FST. Psoralidin also ameliorated the elevations in serum corticotropin-releasing factor (CRF), adrenal corticotropin-releasing hormone (ACTH) and corticosterone concentrations induced by swimming stress in mice. These results suggested that psoralidin possessed potent antidepressant-like properties that were mediated via the monoamine neurotransmitter and the hypothalamic-pituitary-adrenal (HPA) axis systems.

The central corticotropin releasing factor system during development and adulthood

Corticotropin releasing factor (CRH) has been shown to contribute critically to molecular and neuroendocrine responses to stress during both adulthood and development. This peptide and its receptors are expressed in the hypothalamus, as well as in limbic brain areas including amygdala and hippocampus. This is consistent with roles for CRH in mediating the influence of stress on emotional behavior and cognitive function. The expression of CRH and of its receptors in hypothalamus, amygdala and hippocampus is age-dependent, and is modulated by stress throughout life (including the first postnatal weeks). Uniquely during development, the cardinal influence of maternal care on the central stress response governs the levels of central CRH expression, and may alter the 'set-point' of CRH-gene sensitivity to stress in a lasting manner.

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 1 and 2 receptors in the dorsal raphé differentially affect serotonin release in the nucleus accumbens

Corticotropin-releasing factor (CRF) is a neurohormone that mediates stress, anxiety, and affects serotonergic activity. Studies have shown that CRF has dose-dependent opposing effects on serotonergic activity. This effect has been hypothesized to be differentially mediated by CRF(1) and CRF(2) receptors in the dorsal raphé nucleus. We directly tested this hypothesis by using in vivo microdialysis to determine the effects of CRF and CRF receptor antagonists in the dorsal raphé nucleus on serotonin (5-HT) release in the nucleus accumbens, a brain region implicated in the neuropathology of stress-related psychiatric disorders. Male urethane-anesthetized rats were implanted with a microdialysis probe into the nucleus accumbens, and CRF (0, 100 or 500 ng) was infused into the dorsal raphé. Infusion of CRF into the dorsal raphé nucleus had dose-dependent opposite effects, with 100 ng of CRF significantly decreasing 5-HT levels in the nucleus accumbens and 500 ng CRF significantly increasing accumbal 5-HT levels. In subsequent experiments, the raphé was pre-treated with the CRF(1) receptor antagonist antalarmin (0.25 microg) or the CRF(2) receptor antagonist antisauvagine-30 (ASV-30; 2 microg) prior to CRF infusion. Antagonism of CRF(1) receptors in the dorsal raphé nucleus abolished the decrease in accumbal 5-HT levels elicited by 100 ng CRF, and CRF(2) receptor antagonism in the raphé blocked the increase in accumbal 5-HT levels elicited by 500 ng CRF. These results suggest that the opposing effects of dorsal raphé CRF on 5-HT release in the nucleus accumbens are dependent on differential activation of CRF(1) and CRF(2) receptors in the dorsal raphé nucleus.

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 the serotoninergic system in the sodium appetite control

The present article reviews the role of the serotoninergic system in the regulation of the sodium appetite. Data from the peripheral and icv administration of serotoninergic (5-HTergic) agents showed the participation of 5-HT2/3 receptors in the modulation of sodium appetite. These observations were extended with the studies carried out after brain serotonin depletion, lesions of DRN and during blockade of 5-HT2A/2C receptors in lateral parabrachial nucleus (LPBN). Brain serotonin depletion and lesions of DRN increased the sodium appetite response, in basal conditions, after sodium depletion and hypovolemia or after beta-adrenergic stimulation as well. These observations raised the hypothesis that the suppression of ascending pathways from the DRN, possibly, 5-HTergic fibers, modifies the angiotensinergic or sodium sensing mechanisms of the subfornical organ involved in the control of the sodium appetite. 5-HTergic blockade in LPBN induced to similar results, particularly those regarded to the natriorexigenic response evoked by volume depletion or increase of the hypertonic saline ingestion induced by brain angiotensinergic stimulation. In conclusion, many evidences lead to acceptation of an integrated participation resulting of an interaction, between DRN and LPBN, for the sodium appetite control.

Corticotropin-releasing factor receptors in the dorsal raphe nucleus modulate social behavior in Syrian hamsters

RATIONALE

In Syrian hamsters (Mesocricetus auratus), social defeat produces a prolonged change in subsequent agonistic behavior termed conditioned defeat. This stress-induced change in behavior is marked by increased submissive and defensive behavior toward a novel, nonaggressive opponent and a complete loss of normal territorial aggression. Corticotropin-releasing factor (CRF) has been shown to affect serotonergic neurons in the dorsal raphe nucleus (DRN) and to modulate learned helplessness via a CRF type-2 receptor (CRF-R2) mechanism.

OBJECTIVES

In this study, we tested the hypothesis that a nonselective CRF receptor antagonist (experiment 1: 250 or 500 ng D: -Phe CRF in 200 nl saline), or a selective CRF-R2 antagonist (experiment 2: 500 ng anti-Svg-30 in 200 nl saline), injected into the DRN would reduce the acquisition of conditioned defeat in male hamsters. We also tested similar hypotheses for the expression of conditioned defeat (experiments 3 and 4).

RESULTS

Infusion of D: -Phe CRF into the DRN significantly reduced both the acquisition and expression of conditioned defeat compared to vehicle controls, whereas infusion of anti-Svg-30 into the DRN reduced expression but not acquisition. In particular, CRF antagonism in the DRN decreased fleeing from novel opponents but did not reinstate normal territorial aggression after social defeat.

CONCLUSIONS

Our results suggest that the increased flight associated with conditioned defeat is modulated by CRF-R2 activation within the DRN. Overall, social defeat is an ethologically relevant stressor that appears to activate at least some of the same neural substrates that have been implicated in the control of learned helplessness.

Corticotropin-releasing factor receptor 1-deficient mice show decreased anxiety and colonic sensitivity

Corticotropin releasing factor (CRF) is an important mediator in the stress response. Previous studies in rodent models demonstrated that stress-induced colonic hypersensitivity was inhibited by CRF1 receptor antagonism. As CRF(1)R-deficient mice have (+/+), CRF(1)R (+/-) and CRF(1)R (-/-) mice colonic sensitivity was assessed via a visceromotor behavioural response (VMR) induced by colorectal distension (CRD, 0-60 mmHg). In the CRF(1)R (+/+) mice there was a pressure-dependent increase in the VMR to CRD that was moderately attenuated in the CRF1R (+/-) mice. However in the CRF(1)R (-/-) mice a VMR to CRD was only observed at the highest distension pressure (60 mmHg). A CRF(1)R antagonist, NBI 30775 (30 mg kg(-1) i.p.) significantly decreased the VMR to CRD in CRF(1)R +/+ mice. An identical inhibitory effect of NBI 30775 was observed in 43% of the CRF(1)R +/- mice. This study provides pharmacological and genetic evidence for the importance of CRF(1)R in colonic sensitivity and suggests a link between stress and visceral perception.

The changes in AgNOR parameters of dorsal raphe nucleus neurons are related to suicide

Depression has been established as the main cause of suicide and the research has concentrated on disturbed central serotonergic system in both disorders. The dorsal raphe nucleus (DRN) of brain stem is the main source of serotonergic innervation of limbic structures fundamental in the regulation of emotionally influenced behavior. The study was carried out on paraffin-embedded brains from 10 depressive patients, among them 5 suicides and 5 non-suicides and 13 matched mentally healthy controls. The karyometric parameters of DRN neurons were evaluated by AgNOR (Argyrophilic Nucleolar Organizer) silver staining method. The significant effect of suicide on nuclear area and AgNOR-ratio found in the cumulative analysis of all DRN subnuclei could be relevant for forensic diagnostic. The results suggest DRN neurons hypoactivity specific for suicide. Whether observed phenomenon is a "common trait" existing also in other diagnostic groups of mental disorders remains an open question.

Co-localization of corticotropin-releasing factor and vesicular glutamate transporters within axon terminals of the rat dorsal raphe nucleus

Electrophysiological, microdialysis and behavioral studies support a modulatory role for corticotropin-releasing factor (CRF) in regulating the dorsal raphe nucleus (DRN)-serotonin (5-HT) system. CRF and 5-HT are implicated in the pathophysiology of depression, thus neuroanatomical substrates of CRF-DRN-5-HT interactions are of interest. Identification of co-transmitters within DRN CRF axon terminals is important for elucidating the complex effects underlying CRF afferent regulation of DRN neurons. This study investigated whether CRF-labeled axon terminals within the DRN contain immunoreactivity for vesicular glutamate transporters (isoforms vGlut1 and vGlut2) indicative of the excitatory neurotransmitter glutamate. Dual immunohistochemistry for CRF and either vGlut1 or vGlut2 was conducted within the same tissue section and immunofluorescence results indicated patterns of immunoreactivity consistent with previous reports. Abundant vGlut1- and vGlut2-immunoreactivity was found in puncta exhibiting a largely uniform distribution, whereas CRF-immunoreactivity was localized to topographically distributed varicose processes within the DRN. Profiles containing both CRF- and either vGlut1- or vGlut2-immunoreactivity were apparent in the DRN. Electron microscopy confirmed that immunoreactivity for CRF and vGlut1 was localized primarily to separate axon terminals in the DRN, with a subset co-localizing CRF and vGlut1. Examination of CRF and vGlut2 immunoreactivities in the DRN indicated that CRF and vGlut2 were found within the same axon terminal more frequently than CRF and vGlut1. Overall, these anatomical findings suggest that CRF may function, in part, with the excitatory neurotransmitter glutamate in the modulation of neuronal activity in the DRN.

Chronic low dose ovine corticotropin releasing factor or urocortin II into the rostral dorsal raphe alters exploratory behavior and serotonergic gene expression in specific subregions of the dorsal raphe

Corticotropin releasing factor (CRF) family peptides play key roles in integrating neural responses to stress. Both major CRF receptors have been pharmacologically identified in the dorsal raphe nucleus (DRN), a stress sensitive and internally heterogeneous nucleus supplying many forebrain regions with serotonergic input. Despite the involvement of chronic stress and serotonergic dysfunction in human mood and anxiety disorders, little is known about the effects of chronic CRF receptor activation on the DRN. We infused ovine CRF (1 ng/h), urocortin II (UCNII, 1 ng/h), or vehicle alone into rat DRN over 6 days. During infusion, animals were allowed to freely explore an open field for 15 min on each of 2 days, with the addition of a novel object on the second day. Following behavioral testing, 5-HT1A, 5-HT1B, 5-HT transporter (SERT), and tryptophan hydroxylase-2 (Tph2) expression was examined through the DRN by in situ hybridization. Ovine CRF infusion resulted in significantly decreased novel object touches, climbs, as well as increased latency to first novel object contact. UCNII had a similar but less dramatic effect, decreasing only climbing behavior. Both ovine CRF and UCNII blunted the decrease in corner time expected on re-exposure to the open field. Both peptides also produced regionally specific changes in gene expression: 5-HT1A expression was increased 30% in the mid-rostral ventromedial DRN, while SERT was decreased by 30% in the mid-caudal shell dorsomedial DRN. There also appeared to be a shift in the relative level of Tph2 expression between the ventromedial and core dorsomedial DRN at the mid-rostral level. Changes in 5-HT1A, SERT, and relative Tph2 mRNA abundance were correlated with novel object exploration. These findings suggest chronic intra-DRN administration of CRF agonists decreases exploratory behavior, while producing subregionally limited changes in serotonergic gene expression. These studies may be relevant to mechanisms underlying behavioral changes after chronic stress.

Physiology, pharmacology, and therapeutic relevance of urocortins in mammals: ancient CRF paralogs

Urocortins, three paralogs of the stress-related peptide corticotropin-releasing factor (CRF) found in bony fish, amphibians, birds, and mammals, have unique phylogenies, pharmacologies, and tissue distributions. As a result and despite a structural family resemblance, the natural functions of urocortins and CRF in mammalian homeostatic responses differ substantially. Endogenous urocortins are neither simply counterpoints nor mimics of endogenous CRF action. In their own right, urocortins may be clinically relevant molecules in the pathogenesis or management of many conditions, including congestive heart failure, hypertension, gastrointestinal and inflammatory disorders (irritable bowel syndrome, active gastritis, gastroparesis, and rheumatoid arthritis), atopic/allergic disorders (dermatitis, urticaria, and asthma), pregnancy and parturition (preeclampsia, spontaneous abortion, onset, and maintenance of effective labor), major depression and obesity. Safety trials for intravenous urocortin treatment have already begun for the treatment of congestive heart failure. Further understanding the unique functions of urocortin 1, urocortin 2, and urocortin 3 action may uncover other therapeutic opportunities.

Differential effects of CRF1 and CRF2 receptor antagonists on pain-related sensitization of neurons in the central nucleus of the amygdala

As a hormone in the hypothalamic-pituitary-adrenocortical (HPA) axis corticotropin-releasing factor (CRF) mediates stress responses. CRF can also act as a neuromodulator of synaptic transmission outside the HPA axis. A major site of extrahypothalamic expression of CRF and its G-protein-coupled receptors is the amygdala, a key player in affect-related disorders such as anxiety. The laterocapsular division of the central nucleus of the amygdala (CeLC) is important for the modulation of pain affect. This study determined the effects of CRF1 and CRF2 receptor antagonists in CeLC neurons in an arthritis pain model. Extracellular single-unit recordings were made from CeLC neurons in anesthetized adult rats. All neurons responded more strongly to noxious than to innocuous mechanical stimulation (compression) of peripheral tissues, including the knee. Evoked responses and background activity were measured before and during the development of a kaolin/carrageenan-induced knee joint arthritis. Drugs were administered into the CeLC by microdialysis before and/or after arthritis induction. All CeLC neurons showed increased responses to mechanical stimuli ("sensitization") 5-6 h postinduction of arthritis. A selective CRF1 receptor antagonist (NBI27914; 1-100 microM, concentration in microdialysis probe; 15 min) inhibited evoked responses and background activity in arthritis (n = 9) but had no effect under normal conditions before arthritis (n = 9). In contrast, a selective CRF2 receptor antagonist (Astressin-2B; 1-100 microM, 15 min) had no effect in arthritis (n = 7) but increased the neurons' responses under normal conditions (n = 8). These data suggest that CRF1 receptors in the amygdala contribute to pain-related sensitization, whereas the normally inhibitory function of CRF2 receptors is lost in the arthritis pain model.

Role of dopamine D1 and D2 receptors in CRF-induced disruption of sensorimotor gating

Corticotropin-releasing factor (CRF), a neuropeptide released during stress, has been reported to modulate startle behavior, including reducing the threshold for acoustic startle responding and reducing prepulse inhibition (PPI). The central mechanisms mediating CRF system regulation of startle and PPI are still unclear. Some antipsychotic drugs attenuate CRF-induced deficits in PPI in rats and mice. Here we tested the hypothesis that indirect activation of DA(1)-receptors (D(1)) and DA(2)-receptors (D(2)) contributes to the effects of CRF on PPI. We compared the effect of central administration of h/r-CRF (0.2-0.6 nmol) on PPI in mice with either a D(1) or D(2) receptor null mutation (knockout, KO) or in mice pretreated with D(1) or D(2) receptor antagonists SCH23390 (1 mg/kg) or haloperidol (1 mg/kg). D(1) and D(2) KO mice exhibited no significant differences in their sensitivity to CRF-induced disruptions of PPI. Similarly, neither SCH23390 nor haloperidol pretreatment altered the CRF-induced disruption in PPI, although both increased PPI at baseline. CRF-induced increases in startle also remained unchanged by any of the DA receptor manipulations. These results indicate that neither D(1)- nor D(2)-receptor activation is necessary for CRF to exert its effects on acoustic startle and PPI in mice.