The corticotropin-releasing factor receptor-1 pathway mediates the negative affective states of opiate withdrawal

CRF2 receptor-deficiency eliminates opiate withdrawal distress without impairing stress coping

The opiate withdrawal syndrome is a severe stressor that powerfully triggers addictive drug intake. However, no treatment yet exists that effectively relieves opiate withdrawal distress and spares stress-coping abilities. The corticotropin-releasing factor (CRF) system mediates the stress response, but its role in opiate withdrawal distress and bodily strategies aimed to cope with is unknown. CRF-like signaling is transmitted by two receptor pathways, termed CRF(1) and CRF(2). Here, we report that CRF(2) receptor-deficient (CRF(2)(-/-)) mice lack the dysphoria-like and the anhedonia-like states of opiate withdrawal. Moreover, in CRF(2)(-/-) mice opiate withdrawal does not increase the activity of brain dynorphin, CRF and periaqueductal gray circuitry, which are major substrates of opiate withdrawal distress. Nevertheless, CRF(2) receptor-deficiency does not impair brain, neuroendocrine and autonomic stress-coping responses to opiate withdrawal. The present findings point to the CRF(2) receptor pathway as a unique target to relieve opiate withdrawal distress without impairing stress-coping abilities.

Role of corticotropin-releasing factor (CRF) receptor-1 on the catecholaminergic response to morphine withdrawal in the nucleus accumbens (NAc)

Stress induces the release of the peptide corticotropin-releasing factor (CRF) into the ventral tegmental area (VTA), and also increases dopamine (DA) levels in brain regions receiving dense VTA input. Since the role of stress in drug addiction is well established, the present study examined the possible involvement of CRF1 receptor in the interaction between morphine withdrawal and catecholaminergic pathways in the reward system. The effects of naloxone-precipitated morphine withdrawal on signs of withdrawal, hypothalamo-pituitary-adrenocortical (HPA) axis activity, dopamine (DA) and noradrenaline (NA) turnover in the nucleus accumbens (NAc) and activation of VTA dopaminergic neurons, were investigated in rats pretreated with vehicle or CP-154,526 (selective CRF1R antagonist). CP-154,526 attenuated the increases in body weight loss and suppressed some of withdrawal signs. Pretreatment with CRF1 receptor antagonist resulted in no significant modification of the increased NA turnover at NAc or plasma corticosterone levels that were seen during morphine withdrawal. However, blockade of CRF1 receptor significantly reduced morphine withdrawal-induced increases in plasma adrenocorticotropin (ACTH) levels, DA turnover and TH phosphorylation at Ser40 in the NAc. In addition, CP-154,526 reduced the number of TH containing neurons expressing c-Fos in the VTA after naloxone-precipitated morphine withdrawal. Altogether, these results support the idea that VTA dopaminergic neurons are activated in response to naloxone-precipitated morphine withdrawal and suggest that CRF1 receptors are involved in the activation of dopaminergic pathways which project to NAc.

The effect of intermittent alcohol vapor or pulsatile heroin on somatic and negative affective indices during spontaneous withdrawal in Wistar rats

RATIONALE

Once dependent on alcohol or opioids, negative affect may accompany withdrawal. Dependent individuals are hypothesized to "self-medicate" in order to cope with withdrawal, which promotes escalated alcohol and drug use.

OBJECTIVES

The current study aimed to develop a reliable animal model to assess symptoms that occur during spontaneous alcohol and opioid withdrawal.

METHODS

Dependence was induced using intermittent alcohol exposure or pulsatile heroin delivery and assessed for the presence of withdrawal symptoms during acute withdrawal by measuring somatic signs, behavior in the forced swim test (FST), and air-puff-induced 22-kHz ultrasonic vocalizations (USVs). Additional animals subjected to 8 weeks of alcohol vapor exposure were evaluated for altered somatic signs, operant alcohol self-administration, and 22-kHz USV production, as well as performance in the elevated plus maze (EPM).

RESULTS

During spontaneous withdrawal from pulsatile heroin or intermittent alcohol vapor, animals displayed increased somatic withdrawal signs, FST immobility, and 22-kHz USV production but did not show any behavioral change in the EPM unless the duration of alcohol exposure was extended to 4 weeks. Following 8 weeks of alcohol vapor exposure, animals displayed somatic withdrawal signs, escalated alcohol self-administration, and increased 22-kHz USVs.

CONCLUSIONS

These paradigms provide consistent methods to evaluate the behavioral ramifications, and neurobiological substrates, of alcohol and opioid dependence during spontaneous withdrawal. As immobility in the FST and percent open-arm time in the EPM were dissociable, with 22-kHz USVs paralleling immobility in the FST, assessment of air-puff-induced 22-kHz USVs could provide an ethologically valid alternative to the FST.

Increased motivation to eat in opiate-withdrawn mice

RATIONALE

In drug-dependent individuals, the primary excessive motivation is for drugs. Studies also indicate altered interest for "natural" rewarding activities associated with motivational disorders that may be relevant to drug dependence. However, to date, the impact of drug dependence and withdrawal upon motivation for "natural" rewards remains unclear.

METHODS AND OBJECTIVES

In the present study, we use a food-driven operant behavior paradigm to assess the impact of opiate intake and withdrawal upon the motivational properties of highly palatable food (HPF) in mice.

RESULTS

Our findings indicate that early (8-h) opiate withdrawal does not affect either the motivational or the discriminative properties of HPF intake. However, starting 32 h after the last morphine injection, opiate withdrawal increases operant behavior aimed at obtaining HPF. The increased HPF-driven behavior lasts at least 12 days following opiate withdrawal, indicating long-lasting effects upon motivation. Using a paradigm of reward contingency reversal, we also address the impact of opiate withdrawal upon cognitive functions. Our results indicate that opiate withdrawal does not affect the ability to learn a new operant rule to obtain HPF. Indeed, opiate withdrawal ameliorates the acquisition of the new HPF-driven operant task, most probably due to the persistent and long-lasting increased motivation. Finally, analysis of ambulatory activity and body weight (BW) changes reveal that motivational and cognitive effects are totally independent of caloric and/or motor effects of opiate dosing and withdrawal.

CONCLUSIONS

These results clearly demonstrate that excessive opiate intake and withdrawal produces dramatic and long-lasting motivational disorders relevant to drug dependence.

The corticotropin releasing factor system in the kidney: perspectives for novel therapeutic intervention in nephrology

The adaptation to endogenous and exogenous stress stimuli is crucial for survival but also for the onset of various diseases in humans. Corticotropin releasing factor (CRF) system is the major regulator of stress response and homeostasis. The members of this family of peptides extend their actions also outside CNS to the periphery where they may affect various body systems independently, acting via vagal and/or autocrine/paracrine pathways. In search for peripheral targets, kidney has rarely been studied separately, regarding expression and action of CRF and CRF-related peptides. We reviewed the existing literature concerning expression and action of the CRF system in normal and pathological renal tissue and explored possible clinical implications in nephrology. CRF system components are expressed in the kidney of experimental animals and in humans. The intrarenal distribution is reported to be equally extensive, suggesting a physiological or pathophysiological role in renal function and in the occurrence of renal disease. Urocortins have given multiple interesting observations in experimental models of renal disease and clinical studies, showing robust effects in renal regulation mechanisms. We summarize the relevant data and put them in context, proposing applications with clinical significance in the field of hypertension, diabetic nephropathy, chronic kidney disease, cardiorenal syndrome, and peritoneal dialysis.

Restricted role of CRF1 receptor for the activity of brainstem catecholaminergic neurons in the negative state of morphine withdrawal

RATIONALE

Evidence suggests that corticotropin-releasing factor (CRF) system is an important mediator in the negative symptoms of opioid withdrawal.

OBJECTIVES

We used genetically engineered mice lacking functional CRF receptor-1 (CRF1R) levels to study the role for CRF/CRF1R pathways in the negative affective states of opioid withdrawal.

METHODS

Wild-type and CRF1R(-/-) offspring of CRF1R(+/-) breeders were identified by PCR analysis of tail DNA and were rendered dependent on morphine via intraperitoneal injection of increasing doses of morphine (10-60 mg/kg). Negative state associated with opioid withdrawal was examined by using conditioned place aversion (CPA), TH expression and TH phosphorylation were measured in different brain regions involved in addictive behaviours using immunohistochemistry.

RESULTS

The weight loss in morphine withdrawn CRF1R(-/-) animals was significantly (p < 0.05) lower versus wild-type. The aversion for environmental cues paired with opioid withdrawal was lower (p < 0.001) in the CRF1R-deficient versus wild-type. Using dual immunolabeling for c-Fos, data show that naloxone-induced withdrawal increases the number of TH positive neurons phosphorylated at Ser40 or Ser31 that coexpress c-Fos in the nucleus of tractus solitarius (NTS)-A2 from wild-type and CRF(-/-) deficient mice. By contrast, the number of phospho-Ser40 or phospho-Ser31 positive neurons expressing c-Fos was lower in the ventrolateral medulla (VLM)-A1 in CRF(-/-)-deficient mice.

CONCLUSION

Our study demonstrates an increased activity of brainstem catecholaminergic neurons after CPA induced by morphine withdrawal suggesting that CRF1R is implicated in the activation of A1 neurons and provides evidence that this receptor is involved in the body weight loss and in the negative aversive effects of morphine withdrawal.

Mitragynine attenuates withdrawal syndrome in morphine-withdrawn zebrafish

A major obstacle in treating drug addiction is the severity of opiate withdrawal syndrome, which can lead to unwanted relapse. Mitragynine is the major alkaloid compound found in leaves of Mitragyna speciosa, a plant widely used by opiate addicts to mitigate the harshness of drug withdrawal. A series of experiments was conducted to investigate the effect of mitragynine on anxiety behavior, cortisol level and expression of stress pathway related genes in zebrafish undergoing morphine withdrawal phase. Adult zebrafish were subjected to two weeks chronic morphine exposure at 1.5 mg/L, followed by withdrawal for 24 hours prior to tests. Using the novel tank diving tests, we first showed that morphine-withdrawn zebrafish display anxiety-related swimming behaviors such as decreased exploratory behavior and increased erratic movement. Morphine withdrawal also elevated whole-body cortisol levels, which confirms the phenotypic stress-like behaviors. Exposing morphine-withdrawn fish to mitragynine however attenuates majority of the stress-related swimming behaviors and concomitantly lower whole-body cortisol level. Using real-time PCR gene expression analysis, we also showed that mitragynine reduces the mRNA expression of corticotropin releasing factor receptors and prodynorphin in zebrafish brain during morphine withdrawal phase, revealing for the first time a possible link between mitragynine's ability to attenuate anxiety during opiate withdrawal with the stress-related corticotropin pathway.

CRF₂ mediates the increased noradrenergic activity in the hypothalamic paraventricular nucleus and the negative state of morphine withdrawal in rats

BACKGROUND AND PURPOSE

Recent evidence suggests that corticotropin-releasing factor (CRF) receptor signalling is involved in modulating the negative symptoms of opiate withdrawal. In this study, a series of experiments were performed to further characterize the role of CRF-type 2 receptor (CRF₂) signalling in opiate withdrawal-induced physical signs of dependence, hypothalamus-pituitary-adrenal (HPA) axis activation, enhanced noradrenaline (NA) turnover in the hypothalamic paraventricular nucleus (PVN) and tyrosine hydroxylase (TH) phosphorylation (activation), as well as CRF₂ expression in the nucleus of the solitary tract-A₂ noradrenergic cell group (NTS-A₂).

EXPERIMENTAL APPROACH

The contribution of CRF₂ signalling in opiate withdrawal was assessed by i.c.v. infusion of the selective CRF₂ antagonist, antisauvagine-30 (AS-30). Rats were implanted with two morphine (or placebo) pellets. Six days later, rats were pretreated with AS-30 or saline 10 min before naloxone and the physical signs of abstinence, the HPA axis activity, NA turnover, TH activation and CRF₂ expression were measured using immunoblotting, RIA, HPLC and immunohistochemistry.

KEY RESULTS

Rats pretreated with AS-30 showed decreased levels of somatic signs of naloxone-induced opiate withdrawal, but the corticosterone response was not modified. AS-30 attenuated the increased production of the NA metabolite, 3-methoxy-4-hydroxyphenylglycol, as well as the enhanced NA turnover observed in morphine-withdrawn rats. Finally, AS-30 antagonized the TH phosphorylation at Serine40 induced by morphine withdrawal.

CONCLUSIONS AND IMPLICATIONS

These results suggest that physical signs of opiate withdrawal, TH activation and stimulation of noradrenergic pathways innervating the PVN are modulated by CRF₂ signalling. Furthermore, they indicate a marginal role for the HPA axis in CRF₂-mediation of opiate withdrawal.

Mouse models of genetic effects on cognition: relevance to schizophrenia

Cognitive dysfunction is a core feature of schizophrenia. Growing evidence indicates that a wide variety of genetic mutations and polymorphisms impact cognition and may thus be implicated in various aspects of this mental disorder. Despite differences between human and rodent brain structure and function, genetic mouse models have contributed critical information about brain mechanisms involved in cognitive processes. Here, we summarize discoveries of genetic modifications in mice that impact cognition. Based on functional hypotheses, gene modifications within five model systems are described: 1) dopamine (D1, D2, D3, D4, D5, DAT, COMT, MAO); 2) glutamate (GluR-A, NR1, NR2A, NR2B, GRM2, GRM3, GLAST); 3) GABA (α(5), γ(2), α(4), δGABA(A), GABA(B(1)), GAT1); 4) acetylcholine (nAChRβ2, α7, CHRM1); and 5) calcium (CaMKII-α, neurogranin, CaMKKβ, CaMKIV). We also consider other risk-associated genes for schizophrenia such as dysbindin (DTNBP1), neuregulin (NRG1), disrupted-in-schizophrenia1 (DISC1), reelin and proline dehydrogenase (PRODH). Because of the presumed importance of environmental factors, we further consider genetic modifications within the stress-sensitive systems of corticotropin-releasing factor (CRF), brain-derived neurotrophic factor (BDNF) and the endocannabinoid systems. We highlight the missing information and limitations of cognitive assays in genetically modified mice models relevant to schizophrenia pathology.

Role of corticotropin-releasing factor in drug addiction: potential for pharmacological intervention

Drug dependence is a chronically relapsing disorder that places an enormous strain on healthcare systems. For treatments to have long-term clinical value, they must address the causes of relapse. Corticotropin-releasing factor (CRF), a neuropeptide central to the stress response, may be one key to solving the relapse cycle. CRF is hypothesized to mediate the elevated anxiety and negative emotional states experienced during the development of dependence. This review summarizes existing data on changes in the CRF system produced by drugs of abuse and the function of CRF receptors in regulating behavioural responses to drugs of abuse, with an emphasis on drug dependence. Drug-induced changes in neuronal excitability throughout the limbic system, as well as the reversal of these neuroadaptations by CRF receptor antagonists, are also addressed. CRF receptor antagonists, by reducing the motivational effects of drug withdrawal and protracted abstinence, are proposed to be novel therapeutic targets for drug abuse and addiction.

Enhanced dendritic availability of μ-opioid receptors in inhibitory neurons of the extended amygdala in mice deficient in the corticotropin-releasing factor-1 receptor

Activation of the corticotropin-releasing factor-1 (CRF-1) receptor in the anterolateral BNST (BSTal), a key subdivision of the extended amygdala, elicits opiate-seeking behavior exacerbated by stress. However, it is unknown whether the presence of CRF-1 affects expression of the μ-opioid receptor (μ-OR) in the many GABAergic BSTal neurons implicated in the stress response. We hypothesized that deletion of the CRF-1 receptor gene would alter the density and/or subcellular distribution of μ-ORs in GABAergic neurons of the BSTal. We used electron microscopy to quantitatively examine μ-OR immunogold and γ-aminobutyric acid (GABA) immunoperoxidase labeling in the BSTal of CRFr-1 knockout (KO) compared to wild-type (WT) mice. To assess regional specificity, we examined μ-OR distribution in dorsal striatum. The μ-ORs in each region were predominantly localized in dendrites, many of which were GABA-immunoreactive. Significantly, more cytoplasmic μ-OR gold particles per dendritic area were observed selectively in GABA-containing dendrites of the BSTal, but not of the dorsal striatum, in KO compared to WT mice. In both regions, however, significantly fewer GABA-immunoreactive axon terminals were present in KO compared to WT mice. Our results suggest that the absence of CRF-1 results in enhanced expression and/or dendritic trafficking of μ-ORs in inhibitory BSTal neurons. They also suggest that the expression of CRF-1 is a critical determinant of the availability of GABA in functionally diverse brain regions. These findings underscore the complex interplay between CRF, opioid, and GABA systems in limbic and striatal regions and have implications for the role of CRF-1 in influencing the pharmacological effects of opiates active at μ-ORs.

Type 7 Adenylyl Cyclase is Involved in the Ethanol and CRF Sensitivity of GABAergic Synapses in Mouse Central Amygdala

The GABAergic system in the central amygdala (CeA) plays a major role in ethanol dependence and in the anxiogenic response to ethanol withdrawal. Previously, we found that both ethanol and corticotropin releasing factor (CRF) increase GABAergic transmission in mouse and rat CeA neurons, in part by enhancing the release of GABA via activation of presynaptic CRF1 receptors. CRF1 receptors are coupled to the enzyme adenylyl cyclase (AC), which produces the second messenger cyclic AMP. There are nine isoforms of AC, but we recently found that CRF1 receptors in the pituitary were coupled to the Type 7 AC (AC7). Therefore, using an in vitro electrophysiological approach in brain slices, here we have investigated a possible role of the AC7 signaling pathway in ethanol and CRF effects on CeA GABAergic synapses of genetically modified mice with diminished brain Adcy7 activity (HET) compared to their littermate male wild-type (WT) mice. We found no significant differences in basal membrane properties, mean baseline amplitude of evoked GABA(A) receptor-mediated inhibitory postsynaptic potentials (IPSPs), or paired-pulse facilitation (PPF) of GABA(A)-IPSPs between HET and WT mice. In CeA neurons of WT mice, ethanol superfusion significantly augmented (by 39%) GABAA-IPSPs and decreased PPF (by 25%), suggesting increased presynaptic GABA release. However, these effects were absent in HET mice. CRF superfusion also significantly augmented IPSPs (by 38%) and decreased PPF (by 23%) in WT CeA neurons, and still elicited a significant but smaller (by 13%) increase of IPSP amplitude, but no effect on PPF, in HET mice. These electrophysiological data suggest that AC7 plays an important role in ethanol and CRF modulation of presynaptic GABA release in CeA and thus may underlie ethanol-related behaviors such as anxiety and dependence.

Induction of FosB/DeltaFosB in the brain stress system-related structures during morphine dependence and withdrawal

The transcription factor DeltaFosB is induced in the nucleus accumbens (NAc) by drugs of abuse. This study was designed to evaluate the possible modifications in FosB/DeltaFosB expression in both hypothalamic and extrahypothalamic brain stress system during morphine dependence and withdrawal. Rats were made dependent on morphine and, on day 8, were injected with saline or naloxone. Using immunohistochemistry and western blot, the expression of FosB/DeltaFosB, tyrosine hydroxylase (TH), corticotropin-releasing factor (CRF) and pro-dynorphin (DYN) was measured in different nuclei from the brain stress system in morphine-dependent rats and after morphine withdrawal. Additionally, we studied the expression of FosB/DeltaFosB in CRF-, TH- and DYN-positive neurons. FosB/DeltaFosB was induced after chronic morphine administration in the parvocellular part of the hypothalamic paraventricular nucleus (PVN), NAc-shell, bed nucleus of the stria terminalis, central amygdala and A(2) noradrenergic part of the nucleus tractus solitarius (NTS-A(2)). Morphine dependence and withdrawal evoked an increase in FosB/DeltaFosB-TH and FosB/DeltaFosB-CRF double labelling in NTS-A(2) and PVN, respectively, besides an increase in TH levels in NTS-A(2) and CRF expression in PVN. These data indicate that neuroadaptation to addictive substances, observed as accumulation of FosB/DeltaFosB, is not limited to the reward circuits but may also manifest in other brain regions, such as the brain stress system, which have been proposed to be directly related to addiction.

Progress in corticotropin-releasing factor-1 antagonist development

Corticotropin releasing factor (CRF) receptor antagonists have been sought since the stress-secreted peptide was isolated in 1981. Although evidence is mixed concerning the efficacy of CRF(1) antagonists as antidepressants, CRF(1) antagonists might be novel pharmacotherapies for anxiety and addiction. Progress in understanding the two-domain model of ligand-receptor interactions for CRF family receptors might yield chemically novel CRF(1) receptor antagonists, including peptide CRF(1) antagonists, antagonists with signal transduction selectivity and nonpeptide CRF(1) antagonists that act via the extracellular (rather than transmembrane) domains. Novel ligands that conform to the prevalent pharmacophore and exhibit drug-like pharmacokinetic properties have been identified. The therapeutic utility of CRF(1) antagonists should soon be clearer: several small molecules are currently in Phase II/III clinical trials for depression, anxiety and irritable bowel syndrome.

Effects of corticotropin-releasing factor receptor-1 antagonists on the brain stress system responses to morphine withdrawal

The role of stress in drug addiction is well established. The negative affective states of withdrawal most probably involve recruitment of brain stress neurocircuitry [e.g., induction of hypothalamo-pituitary-adrenocortical (HPA) axis, noradrenergic activity, and corticotropin-releasing factor (CRF) activity]. The present study investigated t$he role of CRF receptor-1 subtype (CRF1R) on the response of brain stress system to morphine withdrawal. The effects of naloxone-precipitated morphine withdrawal on noradrenaline (NA) turnover in the paraventricular nucleus (PVN), HPA axis activity, signs of withdrawal, and c-Fos expression were measured in rats pretreated with vehicle, CP-154526 [N-butyl-N-ethyl-2,5-dimethyl-7-(2,4,6-trimethylphenyl)pyrrolo[3,2-e]pyrimidin-4-amine], or antalarmin (selective CRF1R antagonists). Tyrosine hydroxylase-positive neurons expressing CRF1R were seen at the level of the nucleus tractus solitarius-A(2) cell group in both control and morphine-withdrawn rats. CP-154526 and antalarmin attenuated the increases in body weight loss and irritability that were seen during naloxone-induced morphine withdrawal. Pretreatment with CRF1R antagonists resulted in no significant modification of the increased NA turnover at PVN, plasma corticosterone levels, or c-Fos expression that was seen during naloxone-induced morphine withdrawal. However, blockade of CRF1R significantly reduced morphine withdrawal-induced increases in plasma adrenocorticotropin levels. These results suggest that the CRF1R subtype may be involved in the behavioral and somatic signs and in adrenocorticotropin release (partially) during morphine withdrawal. However, CRF1R activation may not contribute to the functional interaction between NA and CRF systems in mediating morphine withdrawal-activation of brain stress neurocircuitry.

The role of CRF and CRF-related peptides in the dark side of addiction

Drug addiction is a chronically relapsing disorder characterized by a compulsion to seek and take drugs, the development of dependence, and the manifestation of a negative emotional state when the drug is removed. Activation of brain stress systems is hypothesized to be a key element of the negative emotional state produced by dependence that drives drug-seeking through negative reinforcement mechanisms, defined as the "dark side" of addiction. The focus of the present review is on the role of corticotropin-releasing factor (CRF) and CRF-related peptides in the dark side of addiction. CRF is a key mediator of the hormonal, autonomic, and behavior responses to stressors. Emphasis is placed on the role of CRF in extrahypothalamic systems in the extended amygdala, including the central nucleus of the amygdala, bed nucleus of the stria terminalis, and a transition area in the shell of the nucleus accumbens, in the dark side of addiction. The urocortin/CRF(2) systems have been less explored, but results suggest their role in the neuroadaptation associated with chronic drug use, sometimes in opposition to the effects produced by the CRF(1) receptor. Compelling evidence argues that the CRF stress system, including its activation of the hypothalamic-pituitary-adrenal axis, plays a key role in engaging the transition to dependence and maintaining dependence once it is initiated. Understanding the role of the CRF systems in addiction not only provides insight into the neurobiology of the dark side of addiction, but also provides novel targets for identifying vulnerability to addiction and the treatment of addiction.

Neurobiological mechanisms of addiction: focus on corticotropin-releasing factor

Drug addiction is a chronically relapsing disorder that is characterized by a compulsion to take drugs and loss of control in limiting intake. Medications that are on the market for the treatment of drug addiction target either the direct reinforcing effects of abuse (eg, naltrexone) or the consequent protracted abstinence syndrome (eg, acamprosate). Both conceptual and neurobiological advances in research have suggested that brain stress systems contribute to the withdrawal/negative affect and preoccupation/anticipation stages of the addiction cycle that promote the compulsivity of drug-taking in addiction. Validated animal models of the stress component of addiction and improved understanding of the neurocircuitry and neuropharmacological mechanisms involved in perturbations of this component suggest that corticotropin-releasing factor systems are a viable target for the development of future medications for drug addiction.

CRF1-R activation of the dynorphin/kappa opioid system in the mouse basolateral amygdala mediates anxiety-like behavior

Stress is a complex human experience and having both rewarding and aversive motivational properties. The adverse effects of stress are well documented, yet many of underlying mechanisms remain unclear and controversial. Here we report that the anxiogenic properties of stress are encoded by the endogenous opioid peptide dynorphin acting in the basolateral amygdala. Using pharmacological and genetic approaches, we found that the anxiogenic-like effects of Corticotropin Releasing Factor (CRF) were triggered by CRF₁-R activation of the dynorphin/kappa opioid receptor (KOR) system. Central CRF administration significantly reduced the percent open-arm time in the elevated plus maze (EPM). The reduction in open-arm time was blocked by pretreatment with the KOR antagonist norbinaltorphimine (norBNI), and was not evident in mice lacking the endogenous KOR ligand dynorphin. The CRF₁-R agonist stressin 1 also significantly reduced open-arm time in the EPM, and this decrease was blocked by norBNI. In contrast, the selective CRF₂-R agonist urocortin III did not affect open arm time, and mice lacking CRF₂-R still showed an increase in anxiety-like behavior in response to CRF injection. However, CRF₂-R knockout animals did not develop CRF conditioned place aversion, suggesting that CRF₁-R activation may mediate anxiety and CRF₂-R may encode aversion. Using a phosphoselective antibody (KORp) to identify sites of dynorphin action, we found that CRF increased KORp-immunoreactivity in the basolateral amygdala (BLA) of wildtype, but not in mice pretreated with the selective CRF₁-R antagonist, antalarmin. Consistent with the concept that acute stress or CRF injection-induced anxiety was mediated by dynorphin release in the BLA, local injection of norBNI blocked the stress or CRF-induced increase in anxiety-like behavior; whereas norBNI injection in a nearby thalamic nucleus did not. The intersection of stress-induced CRF and the dynorphin/KOR system in the BLA was surprising, and these results suggest that CRF and dynorphin/KOR systems may coordinate stress-induced anxiety behaviors and aversive behaviors via different mechanisms.

The dynorphin/kappa opioid system as a modulator of stress-induced and pro-addictive behaviors

Stress is a complex experience that carries both aversive and motivating properties. Chronic stress causes an increase in the risk of depression, is well known to increase relapse of drug seeking behavior, and can adversely impact health. Several brain systems have been demonstrated to be critical in mediating the negative affect associated with stress, and recent evidence directly links the actions of the endogenous opioid neuropeptide dynorphin in modulating mood and increasing the rewarding effects of abused drugs. These results suggest that activation of the dynorphin/kappa opioid receptor (KOR) system is likely to play a major role in the pro-addictive effects of stress. This review explores the relationship between dynorphin and corticotropin-releasing factor (CRF) in the induction of dysphoria, the potentiation of drug seeking, and stress-induced reinstatement. We also provide an overview of the signal transduction events responsible for CRF and dynorphin/KOR-dependent behaviors. Understanding the recent work linking activation of CRF and dynorphin/KOR systems and their specific roles in brain stress systems and behavioral models of addiction provides novel insight to neuropeptide systems that regulate affective state.

Elevated glucocorticoid levels are responsible for induction of tyrosine hydroxylase mRNA expression, phosphorylation, and enzyme activity in the nucleus of the solitary tract during morphine withdrawal

Chronic opiate exposure induces neurochemical adaptations in the noradrenergic system. Enhanced responsiveness of the hypothalamo-pituitary-adrenal axis after morphine withdrawal has been associated with hyperactivity of ascending noradrenergic input from the nucleus of the solitary tract (NTS-A(2)) cell group to the hypothalamic paraventricular nucleus (PVN). This study addressed the role of morphine withdrawal-induced corticosterone (CORT) release in regulation of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine biosynthesis in adrenalectomized (ADX) rats supplemented with low CORT pellet (ADX plus CORT). Present results show that in sham-ADX rats, noradrenergic neurons in the NTS-A(2) became activated during morphine withdrawal, as indicated by increased TH mRNA expression. However, this induction of TH expression is not detected in ADX plus CORT rats that are unable to mount CORT secretory response to morphine withdrawal. Total TH protein levels were elevated in the NTS-A(2) from sham-operated rats during morphine dependence and withdrawal, whereas we did not find any alteration in ADX plus CORT animals. Furthermore, high levels of TH phosphorylated (activated) at Ser31 (but not at Ser40) were found in the A(2) area from sham-morphine withdrawn rats. Consistent with these effects, we observed an increase in the enzyme activity of TH in the PVN. However, induction of morphine withdrawal to ADX plus CORT animals did not alter the phosphorylation (activation) of TH in NTS-A(2) and decreased TH activity in the PVN. These results suggest the existence of a positive reverberating circle in which elevated glucocorticoids during morphine abstinence play a permissive role in morphine withdrawal-induced activation of noradrenergic pathway innervating the PVN.

Subcellular plasticity of the corticotropin-releasing factor receptor in dendrites of the mouse bed nucleus of the stria terminalis following chronic opiate exposure

Chronic opiate administration alters the expression levels of the stress-responsive peptide, corticotropin-releasing factor (CRF), in the bed nucleus of the stria terminalis (BNST). This brain region contains CRF receptors that drive drug-seeking behavior exacerbated by stress. We used electron microscopy to quantitatively compare immunolabeling of the corticotropin-releasing factor receptor (CRFr) and CRF in the anterolateral bed nucleus of the stria terminalis (BSTal) of mice injected with saline or morphine in escalating doses for 14 days. We also compared the results with those in non-injected control mice. The tissue was processed for CRFr immunogold and CRF immunoperoxidase labeling. The non-injected controls had a significantly lower plasmalemmal density of CRFr immunogold particles in dendrites compared with mice receiving saline, but not those receiving morphine, injections. Compared with saline, however, mice receiving chronic morphine showed a significantly lower plasmalemmal, and greater cytoplasmic, density of CRFr immunogold in dendrites. Within the cytoplasmic compartment of somata and dendrites of the BSTal, the proportion of CRFr gold particles associated with mitochondria was three times as great in mice receiving morphine compared with saline. This subcellular distribution is consistent with morphine,- and CRFr-associated modulation of intracellular calcium release or oxidative stress. The between-group changes occurred without effect on the total number of dendritic CRFr immunogold particles, suggesting that chronic morphine enhances internalization or decreases delivery of the CRFr to the plasma membrane, a trafficking effect that is also affected by the stress of daily injections. In contrast, saline and morphine treatment groups showed no significant differences in the total number of CRF-immunoreactive axon terminals, or the frequency with which these terminals contacted CRFr-containing dendrites. This suggests that morphine does not influence axonal availability of CRF in the BSTal. The results have important implications for drug-associated adaptations in brain stress systems that may contribute to the motivation to continue drug use during dependence.

Corticotropin-releasing factor-1 receptor antagonists decrease heroin self-administration in long- but not short-access rats

Dysregulation of the stress-related corticotropin-releasing factor (CRF) system has been implicated in the development of drug dependence. The present study examined the effects of administering CRF type 1 (CRF(1)) receptor antagonists on heroin self-administration in animals allowed short (1 hour) or long (8-12 hours) access to intravenous heroin self-administration sessions. The nonpeptide CRF(1) antagonists MJL-1-109-2 (1 hour versus 8 hours access) or R121919 (1 hour versus 12 hours access) were systemically injected in both short- and long-access rats. MJL-1-109-2 (10 mg/kg) and R121919 (10 and 20 mg/kg) reduced heroin self-administration in long-access animals without altering heroin intake in short-access animals. Both MJL-1-109-2 and R121919 decreased first-hour intravenous heroin self-administration selectively in long-access rats, with R121919 decreasing cumulative heroin intake across the 12-hour session. The results demonstrate that blockade of the CRF-CRF(1) receptor system attenuates the increased heroin intake of rats with extended access to the drug.

Electron microscopic localization of corticotropin-releasing factor (CRF) and CRF receptor in rat and mouse central nucleus of the amygdala

Corticotrophin-releasing factor (CRF) is expressed in the central nucleus of the amygdala (CeA), where the CRF receptor (CRFr) plays an important role in anxiety- and stress-related behaviors. To determine the subcellular sites of CRFr activation in this region, we examined the electron microscopic immunolabeling of antisera recognizing CRF or CRFr. The ultrastructural analysis was principally conducted in the lateral subdivision of the rat CeA, with comparisons being made in mice so as to optimally utilize mutant mice in control experiments. The CRFr labeling was seen in many small dendrites and dendritic spines as well as in a few somata, large dendrites, axons, and axon terminals or more rarely in glial processes. Approximately 35% of the CRFr-labeled dendrites contained CRF immunoreactivity, which was distributed diffusely throughout the cytoplasm, or specifically affiliated with either endomembranes or large dense-core vesicles. The CRF-immunoreactive vesicles also were present in somata and axon terminals with or without CRFr labeling. The CRF immunoreactivity was usually absent from both terminals and dendrites joined by asymmetric, excitatory-type synapses, where a postsynaptic location of the CRFr was commonly observed. Numerous terminals containing both CRF and CRFr were seen, however, within the neuropil and sometimes apposing the excitatory synapses. These results provide ultrastructural evidence for a primary involvement of CRF receptors in modulation of the postsynaptic excitability of CeA neurons, an effect that may be limited by the availability of CRF. The findings have important implications for understanding CRF mediation of rapid responses to stress.

Mu-opioid and corticotropin-releasing-factor receptors show largely postsynaptic co-expression, and separate presynaptic distributions, in the mouse central amygdala and bed nucleus of the stria terminalis

The anxiolytic effects of opiates active at the mu-opioid receptor (mu-OR) may be ascribed, in part, to suppression of neurons that are responsive to the stress-associated peptide, corticotropin releasing factor (CRF), in the central amygdala (CeA) and bed nucleus of the stria terminalis (BNST). The corticotropin releasing factor receptor (CRFr) and mu-OR are expressed in both the CeA and BNST, but their subcellular relationship to each other is not known in either region. To address this question, we used dual electron microscopic immunolabeling of mu-OR and CRFr in the mouse lateral CeA and anterolateral BNST. Immunolabeling for each receptor was detected in the same as well as in separate somatic, dendritic and axonal profiles of neurons in each region. CRFr had a plasmalemmal or cytoplasmic distribution in many dendrites, including those co-expressing mu-OR. The co-expression of CRFr and mu-OR also was seen near excitatory-type synapses on dendritic spines. In both the CeA and BNST, over 50% of the CRFr-labeled dendritic profiles (dendrites and spines) contained immunoreactivity for the mu-OR. However, less than 25% of the dendritic profiles containing the mu-OR were labeled for CRFr in either region, suggesting that opiate activation of the mu-OR affects many neurons in addition to those responsive to CRF. The dendritic profiles containing CRFr and/or mu-OR received asymmetric, excitatory-type synapses from unlabeled or CRFr-labeled axon terminals. In contrast, the mu-OR was identified in terminals forming symmetric, inhibitory-type synapses. Thus, in both the CeA and BNST, mu-OR and CRFr have strategic locations for mediation of CRF and opioid effects on the postsynaptic excitability of single neurons, and on the respective presynaptic release of excitatory and inhibitory neurotransmitters. The commonalities in the synaptic location of both receptors in the CeA and BNST suggest that this is a fundamental cellular association of relevance to both drug addiction and stress-induced disorders.

Disruption of the CRF(2) receptor pathway decreases the somatic expression of opiate withdrawal

Escape from the extremely aversive opiate withdrawal symptoms powerfully motivates compulsive drug-seeking and drug-taking behaviors. The corticotropin-releasing factor (CRF) system is hypothesized to mediate the motivational properties of drug dependence. CRF signaling is transmitted by two receptor pathways, termed CRF(1) and CRF(2). To investigate the role for the CRF(2) receptor pathway in somatic opiate withdrawal, in the present study we used genetically engineered mice deficient in the CRF(2) receptor (CRF(2)-/-). We employed a novel, clinically relevant mouse model of 'spontaneous' opiate withdrawal as well as a classical opioid receptor antagonist (naloxone)-precipitated opiate withdrawal paradigm. To induce opiate dependence, mice were treated with intermittent escalating morphine doses (20-100 mg/kg, i.p.). We found that 8-128 h after the last opiate injection, CRF(2)-/- mice showed decreased levels of major somatic signs of spontaneous opiate withdrawal, such as paw tremor and wet dog shake, as compared to wild-type mice. Similarly, challenge with naloxone 2 h after the last morphine injection induced lower levels of paw tremor and wet dog shake in CRF(2)-/- mice as compared to wild-type mice. Despite the differences in somatic signs, wild-type and CRF(2)-/- mice displayed similar plasma corticosterone responses to opiate dosing and withdrawal, indicating a marginal role for the hypothalamus-pituitary-adrenal axis in the CRF(2) receptor mediation of opiate withdrawal. Our results unravel a novel role for the CRF(2) receptor pathway in opiate withdrawal. The CRF(2) receptor pathway might be a critical target of therapies aimed at alleviating opiate withdrawal symptoms and reducing relapse to drug intake.

Neurobiological substrates for the dark side of compulsivity in addiction

Drug addiction can be defined by a compulsion to seek and take drug, loss of control in limiting intake, and the emergence of a negative emotional state when access to the drug is prevented. Drug addiction impacts multiple motivational mechanisms and can be conceptualized as a disorder that progresses from impulsivity (positive reinforcement) to compulsivity (negative reinforcement). The construct of negative reinforcement is defined as drug taking that alleviates a negative emotional state. The negative emotional state that drives such negative reinforcement is hypothesized to derive from dysregulation of key neurochemical elements involved in reward and stress within the basal forebrain structures involving the ventral striatum and extended amygdala. Specific neurochemical elements in these structures include not only decreases in reward neurotransmission, such as decreases in dopamine and opioid peptide function in the ventral striatum, but also recruitment of brain stress systems, such as corticotropin-releasing factor (CRF), in the extended amygdala. Acute withdrawal from all major drugs of abuse produces increases in reward thresholds, increases in anxiety-like responses, and increases in extracellular levels of CRF in the central nucleus of the amygdala. CRF receptor antagonists also block excessive drug intake produced by dependence. A brain stress response system is hypothesized to be activated by acute excessive drug intake, to be sensitized during repeated withdrawal, to persist into protracted abstinence, and to contribute to the compulsivity of addiction. Other components of brain stress systems in the extended amygdala that interact with CRF and may contribute to the negative motivational state of withdrawal include norepinephrine, dynorphin, and neuropeptide Y. The combination of loss of reward function and recruitment of brain stress systems provides a powerful neurochemical basis for a negative emotional state that is responsible for the negative reinforcement driving, at least in part, the compulsivity of addiction.

A role for brain stress systems in addiction

Drug addiction is a chronically relapsing disorder characterized by compulsion to seek and take drugs and has been linked to dysregulation of brain regions that mediate reward and stress. Activation of brain stress systems is hypothesized to be key to the negative emotional state produced by dependence that drives drug seeking through negative reinforcement mechanisms. This review explores the role of brain stress systems (corticotropin-releasing factor, norepinephrine, orexin [hypocretin], vasopressin, dynorphin) and brain antistress systems (neuropeptide Y, nociceptin [orphanin FQ]) in drug dependence, with emphasis on the neuropharmacological function of extrahypothalamic systems in the extended amygdala. The brain stress and antistress systems may play a key role in the transition to and maintenance of drug dependence once initiated. Understanding the role of brain stress and antistress systems in addiction provides novel targets for treatment and prevention of addiction and insights into the organization and function of basic brain emotional circuitry.

The dysphoric component of stress is encoded by activation of the dynorphin kappa-opioid system

Stress is a complex human experience having both positive and negative motivational properties. When chronic and uncontrollable, the adverse effects of stress on human health are considerable and yet poorly understood. Here, we report that the dysphoric properties of chronic stress are encoded by the endogenous opioid peptide dynorphin acting on specific stress-related neuronal circuits. Using different forms of stress presumed to evoke dysphoria in mice, we found that repeated forced swim and inescapable footshock both produced aversive behaviors that were blocked by a kappa-opioid receptor (KOR) antagonist and absent in mice lacking dynorphin. Injection of corticotropin-releasing factor (CRF) or urocortin III, key mediators of the stress response, produced place aversion that was also blocked by dynorphin gene deletion or KOR antagonism. CRF-induced place aversion was blocked by the CRF2 receptor antagonist antisauvigine-30, but not by the CRF1 receptor antagonist antalarmin. In contrast, place aversion induced by the KOR agonist U50,488 was not blocked by antisauvigine-30. These results suggest that the aversive effects of stress were mediated by CRF2 receptor stimulation of dynorphin release and subsequent KOR activation. Using a phospho-selective antibody directed against the activated KOR to image sites of dynorphin action in the brain, we found that stress and CRF each caused dynorphin-dependent KOR activation in the basolateral amygdala, nucleus accumbens, dorsal raphe, and hippocampus. The convergence of stress-induced aversive inputs on the dynorphin system was unexpected, implicates dynorphin as a key mediator of dysphoria, and emphasizes kappa-receptor antagonists as promising therapeutics.

MPZP: a novel small molecule corticotropin-releasing factor type 1 receptor (CRF1) antagonist

The extrahypothalamic stress peptide corticotropin-releasing factor (CRF) system is an important regulator of behavioral responses to stress. Dysregulation of CRF and the CRF type 1 receptor (CRF(1)) system is hypothesized to underlie many stress-related disorders. Modulation of the CRF(1) system by non-peptide antagonists currently is being explored as a therapeutic approach for anxiety disorders and alcohol dependence. Here, we describe a new, less hydrophilic (cLogP approximately 2.95), small molecule, non-peptide CRF(1) antagonist with high affinity (K(i)=4.9 nM) and specificity for CRF(1) receptors: N,N-bis(2-methoxyethyl)-3-(4-methoxy-2-methylphenyl)-2,5-dimethyl-pyrazolo[1,5-a] pyrimidin-7-amine (MPZP). The compound was systemically administered to adult male rats in two behavioral models dependent on the CRF(1) system: defensive burying (0, 5, 20 mg/kg, n=6-11 for each dose) and alcohol dependence (0, 5, 10, 20 mg/kg, n=8 for each self-administration group). Acute administration of MPZP reduced burying behavior in the defensive burying model of active anxiety-like behavior. MPZP also attenuated withdrawal-induced excessive drinking in the self-administration model of alcohol dependence without affecting nondependent alcohol drinking or water consumption. The present findings support the proposed significance of the CRF(1) system in anxiety and alcohol dependence and introduce a promising new compound for further development in the treatment of alcohol dependence and stress-related disorders.

Hedonic Homeostatic Dysregulation as a Driver of Drug-Seeking Behavior

Drug addiction can be defined by a compulsion to seek and take drug and loss of control in limiting intake, and the excessive drug taking derives from multiple motivational mechanisms. One such mechanism is the emergence of a negative emotional state when access to the drug is prevented, reflecting hedonic homeostatic dysregulation. Excessive drug taking then results in part via the construct of negative reinforcement. The negative emotional state that drives such negative reinforcement is hypothesized to derive from dysregulation of key neurochemical elements involved in reward and stress within basal forebrain structures, including the ventral striatum and extended amygdala. Specific neurochemical elements in these structures include not only decreases in reward neurotransmission, such as decreases in dopamine and opioid peptide function in the ventral striatum, but also recruitment of brain stress systems, such as corticotropin-releasing factor (CRF), in the extended amygdala. Chronic exposure or extended access to self-administration of all major drugs of abuse produces during abstinence increases in reward thresholds, increases in aversive anxiety-like responses, increases in extracellular levels of CRF in the central nucleus of the amygdala, and increases in drug self-administration. CRF receptor antagonists block excessive drug intake produced by dependence. A combination of decreased reward system function and increased brain stress response system function is hypothesized to be responsible for hedonic homeostatic dysregulation that drives drug seeking behavior in dependence. Such hedonic dysregulation is hypothesized to extend into protracted abstinence to provide a residual negative emotional state that enhances the salience of cues eliciting drug seeking and relapse.

Stress-induced p38 mitogen-activated protein kinase activation mediates kappa-opioid-dependent dysphoria

The molecular mechanisms mediating stress-induced dysphoria in humans and conditioned place aversion in rodents are unknown. Here, we show that repeated swim stress caused activation of both kappa-opioid receptor (KOR) and p38 mitogen-activated protein kinase (MAPK) coexpressed in GABAergic neurons in the nucleus accumbens, cortex, and hippocampus. Sites of activation were visualized using phosphoselective antibodies against activated kappa receptors (KOR-P) and against phospho-p38 MAPK. Surprisingly, the increase in P-p38-IR caused by swim-stress exposure was completely KOR dependent; P-p38-IR did not increase in KOR(-/-) knock-out mice subjected to the same swim-paradigm or in wild-type mice pretreated with the KOR antagonist norbinaltorphimine. To understand the relationship between p38 activation and the behavioral effects after KOR activation, we administered the p38 inhibitor SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfonylphenyl)-5-(4-pyridyl)-1H-imidazole (i.c.v.)] and found that it selectively blocked the conditioned place aversion caused by the kappa agonist trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-benzeneacetamide (U50488) and the KOR-dependent swim stress-induced immobility while not affecting kappa-opioid analgesia or nonselectively affecting associative learning. We found that the mechanism linking KOR and p38 activation in vivo was consistent with our previous in vitro data suggesting that beta-arrestin recruitment is required; mice lacking G-protein-coupled receptor kinase 3 also failed to increase p-p38-IR after KOR activation in vivo, failed to show swim stress-induced immobility, or develop conditioned place aversion to U50488. Our results indicate that activation of p38 MAPK signaling by the endogenous dynorphin-kappa-opioid system likely constitutes a key component of the molecular mechanisms mediating the aversive properties of stress.

CRF-CRF1 system activation mediates withdrawal-induced increases in nicotine self-administration in nicotine-dependent rats

Nicotine, the main psychoactive ingredient of tobacco, induces negative emotional symptoms during abstinence that contribute to a profound craving for nicotine. However, the neurobiological mechanisms underlying how nicotine produces dependence remains poorly understood. We demonstrate one mechanism for both the anxiety-like symptoms of withdrawal and excessive nicotine intake observed after abstinence, through recruitment of the extrahypothalamic stress peptide corticotropin-releasing factor (CRF) system and activation of CRF(1) receptors. Overactivation of the CRF-CRF(1) system may contribute to nicotine dependence and may represent a prominent target for investigating the vulnerability to tobacco addiction.

The CRF1 receptor antagonist, R121919, attenuates the severity of precipitated morphine withdrawal

Corticotropin-releasing factor (CRF) regulates the hypothalamic-pituitary-adrenal axis, coordinates the mammalian stress response, and acting primarily via the CRF(1) receptor, has been strongly implicated in the pathophysiology of depression and anxiety. Furthermore, the behavioral and autonomic activation that occurs following withdrawal in drug dependent animals resembles the mammalian stress response. Concordant with this view is evidence of enhanced CRF transcription, release and activity following withdrawal from several drugs of abuse. Conversely, CRF receptor antagonists have been demonstrated to reduce the severity of many drug withdrawal symptoms, implicating a specific role for activation of CRF neurons in mediating the anxiogenic and stress-like reactions observed during withdrawal. To extend these findings, we investigated whether pretreatment with a selective CRF(1) receptor antagonist, R121919, is capable of similarly decreasing the autonomic, behavioral and neuroendocrine activation observed following precipitation of morphine withdrawal in dependent rats. The results indicate that pretreatment with R121919 attenuates the global severity of the precipitated morphine withdrawal syndrome as measured by the Gellert-Holtzman scale. In addition, rats pretreated with R121919 prior to precipitation of morphine withdrawal demonstrated decreased hypothalamic-pituitary-adrenal axis activation, as measured by plasma ACTH concentrations, and decreased early expression of the CRF gene in the paraventricular nucleus of the hypothalamus, as measured by CRF heteronuclear RNA. These findings suggest that activation of CRF neuronal systems via the CRF(1) receptor may be one element of the neurobiological mechanisms activated during drug withdrawal and that CRF(1) receptor antagonists may have a potential therapeutic role in the treatment of human drug withdrawal syndromes.

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.

Disruption of the CRF/CRF1 Receptor Stress System Exacerbates the Somatic Signs of Opiate Withdrawal

Escape from the extremely stressful opiate withdrawal syndrome may motivate opiate seeking and taking. The corticotropin-releasing factor receptor-1 (CRF1) pathway mediates behavioral and endocrine responses to stress. Here, we report that genetic inactivation (CRF1-/-) as well as pharmacological antagonism of the CRF/CRF1 receptor pathway increased and prolonged the somatic expression of opiate withdrawal. Opiate-withdrawn CRF1-/- mice also showed aberrant CRF and dynorphin expression in the paraventricular nucleus of the hypothalamus (PVN) and the striatum, indicating profound impairments in stress-responsive brain circuitry. Intake of nonstressful amounts of corticosterone effectively reduced the exaggerated somatic reactions of CRF1-/- mice to opiate withdrawal. Exogenous corticosterone also restored "wild-type-like" patterns of CRF and dynorphin gene expression in the PVN and the striatum of opiate-withdrawn CRF1-/- mice, respectively. The present findings unravel a key role for the hypothalamus-pituitary-adrenal (HPA) system and brain extra-hypothalamic CRF/CRF1 receptor circuitry in somatic, molecular, and endocrine alterations induced by opiate withdrawal.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).