The rationale for corticotropin-releasing hormone receptor (CRH-R) antagonists to treat depression and anxiety

Anxious-retarded depression: relation with plasma vasopressin and cortisol

Dysregulation of the hypothalamus-pituitary-adrenal (HPA) axis is related to melancholic or endogenous depression; however, the strength of this relationship depends on the definition of the specific depression subcategory. A two-dimensionally defined subcategory, anxious-retarded depression, is related to melancholic depression. Since arginine vasopressin (AVP) activates the HPA axis, and both major depression and the melancholic subcategory are associated with elevated plasma AVP levels, we investigated whether the plasma AVP level is also elevated in anxious-retarded depression, melancholic depression and anxious-retarded melancholic depression, and whether plasma AVP and cortisol levels are correlated in these subcategories. A total of 66 patients with major depression not using oral contraception were investigated. Patients with anxious-retarded depression had a highly significant AVP-cortisol correlation, while no such correlation was found in patients with nonanxious-retarded depression. Log-transformed mean plasma AVP values were higher in patients with anxious-retarded depression than in patients with nonanxious-retarded depression. Patients with anxious-retarded melancholic depression also had a significantly elevated level of plasma AVP and a highly significant correlation between plasma AVP and cortisol levels. The correlation was low in patients with melancholic depression. Anxious-retarded depression may be a useful refinement of the melancholic subcategory with regard to dysregulation of the HPA axis and plasma AVP release.

Nonpeptide vasopressin receptor antagonists: development of selective and orally active V1a, V2 and V1b receptor ligands

The involvement of vasopressin (AVP) in several pathological states has been reported recently and the selective blockade of the different AVP receptors could offer new clinical perspectives. During the past few years, various selective, orally active AVP V1a (OPC-21268, SR49059 (Relcovaptan)), V2 (OPC-31260, OPC-41061 (Tolvaptan), VPA-985 (Lixivaptan), SR121463, VP-343, FR-161282) and mixed V1a/V2 (YM-087 (Conivaptan), JTV-605, CL-385004) receptor antagonists have been intensively studied in various animal models and have reached, Phase IIb clinical trials for some of them. For many years now, our laboratory has focused on the identification of nonpeptide vasopressin antagonists with suitable oral bioavailability. Using random screening on small molecule libraries, followed by rational SAR and modelization, we identified a chemical series of 1-phenylsulfonylindolines which first yielded SR49059, a V1a receptor antagonist prototype. This compound displayed high affinity for animal and human V1a receptors and antagonized various V1a AVP-induced effects in vitro and in vivo (intracellular [Ca2+] increase, platelet aggregation, vascular smooth muscle cell proliferation, hypertension and coronary vasospasm). We and others have used this compound to study the role of AVP in various animal models. Recent findings from clinical trials show a potential interest for SR49059 in the treatment of dysmenorrhea and in Raynaud's disease. Structural modifications and simplifications performed in the SR49059 chemical series yielded highly specific V2 receptor antagonists (N-arylsulfonyl-oxindoles), amongst them SR121463 which possesses powerful oral aquaretic properties in various animal species and in man. SR121463 is well-tolerated and dose-dependently increases urine output and decreases urine osmolality. It induces free water-excretion without affecting electrolyte balance in contrast to classical diuretics (e.g. furosemide and hydrochlorothiazide). Notably, in cirrhotic rats with ascites and impaired renal function, a 10-day oral treatment with SR121463 (0.5 mg/kg) totally corrected hyponatremia and restored normal urine excretion. This compound also displayed interesting new properties in a rabbit model of ocular hypertension, decreasing intraocular pressure after single or repeated instillation. Thus, V2 receptor blockade could be of interest in several water-retaining diseases such as the syndrome of inappropriate antidiuretic hormone secretion (SIADH), liver cirrhosis and congestive heart failure and deserves to be widely explored. Finally, further chemical developments in the oxindole family have led to the first specific and orally active V1b receptor antagonists (with SSR149415 as a representative), an awaited class of drugs with expected therapeutic interest mainly in ACTH-secreting tumors and various emotional diseases such as stress-related disorders, anxiety and depression. However, from the recently described tissue localization for this receptor, we could also speculate on other unexpected uses. In conclusion, the development of AVP receptor antagonists is a field of intensive pharmacological and clinical investigation. Selective and orally active compounds are now available to give new insight into the pathophysiological role of AVP and to provide promising drugs.

Antagonistas do hormônio liberador da corticotrofina: atualização e perspectivas

Modelos genéticos e estudos epidemiológicos têm contribuído para a compreensão da fisiopatologia das doenças relacionadas ao estresse. O hormônio liberador da corticotrofina (CRH) pertence à família dos chamados peptídeos relacionados ao CRH, junto com a urocortina, urocortina II (ou peptídeo relacionado à estressecopina) e urocortina III (ou estressecopina). O CRH é o maior estimulador da secreção hipofisária de ACTH em humanos, e tem um papel importante na resposta fisiológica ao estresse. O CRH e seus receptores (tipos 1 e 2) estão difusamente distribuídos em todo o sistema nervoso central (SNC) e, em menor proporção, em tecidos periféricos. A distribuição dos receptores no SNC mostra ampla variabilidade entre as espécies. Os neurônios do CRH modulam a função autonômica e do sistema límbico. O CRH tem importantes efeitos, também, nos sistemas cardiovascular, metabólico e comportamental. As ações regionais deste peptídeo no SNC e na periferia são vários e apenas parcialmente conhecidos. Ações aberrantes do CRH estão implicadas em algumas condições psiquiátricas, incluindo depressão e ansiedade. Esta teoria tem sido corroborada por dados em ratos transgênicos que não expressam CRH e estudos pré-clínicos envolvendo a administração de antagonistas do CRH em macacos Rhesus. Embora ainda não disponível para uso clínico de rotina, dados preliminares de estudos conceituais envolvendo a administração oral de antagonistas do CRH em humanos são encorajadores. Entretanto, ainda permanece um desafio o desenvolvimento de antagonistas não peptídicos seletivos do receptor de CRH. Além disso, são extremamente necessários testes com estudos clínicos randomizados, que deverão trazer novas luzes sobre esta área.

Forced swim stress activates rat hippocampal serotonergic neurotransmission involving a corticotropin-releasing hormone receptor-dependent mechanism

Serotonin is important for adequate coping with stress. Aberrant serotonin function is implicated in the aetiology of major depression and anxiety disorders. Dysregulation of the hypothalamic-pituitary-adrenocortical axis, involving elevated corticotropin-releasing hormone (CRH) activity, also plays a role in these stress-related illnesses. Here we studied the effects of stress on hippocampal serotonin and the role of the CRH system using in vivo microdialysis. First, rats were subjected to a forced swim stress, resulting in a dramatic increase in hippocampal serotonin (1500% of baseline), which was associated with the occurrence of diving behaviour. The diving-associated increase in serotonin depended on activation of CRH receptors, as it was antagonized by intracerebroventricular pretreatment with D-Phe-CRH12-41. Secondly, the effects of intracerebroventricular administration of CRH and urocortin (0.03-1.0 microg) were studied. Both CRH and urocortin caused a dose-dependent rise in hippocampal serotonin (maximally 350% of baseline) and 5-hydroxyindoleacetic acid levels, suggesting the involvement of CRH receptor type 1. Because the effects of urocortin were prolonged, CRH receptor type 2 could play a role in a later phase of the neurotransmitter response. Experiments using adrenalectomized rats showed that CRH-induced serotonin changes were adrenally independent. These data suggest that the raphe-hippocampal serotonin system is able to mount, CRH receptor-dependent, responses to specific stressful situations that surpass the usually observed maximal increases of about 300% of baseline during stress and enhanced vigilance.

Magnesium and affective disorders

There are several findings on the action of magnesium ions supporting their possible therapeutic potential in affective disorders. Examinations of the sleep-electroencephalogram (EEG) and of endocrine systems point to the involvement of the limbic-hypothalamus-pituitary-adrenocortical axis as magnesium affects all elements of this system. Magnesium has the property to suppress hippocampal kindling, to reduce the release of adrenocorticotrophic hormone (ACTH) and to affect adrenocortical sensitivity to ACTH. The role of magnesium in the central nervous system could be mediated via the N-methyl-D-aspartate-antagonistic, gamma-aminobutyric acidA-agonistic or a angiotensin II-antagonistic property of this ion. A direct impact of magnesium on the function of the transport protein p-glycoprotein at the level of the blood-brain barrier has also been demonstrated, possibly influencing the access of corticosteroids to the brain. Furthermore, magnesium dampens the calciumion-proteinkinase C related neurotransmission and stimulates the Na-K-ATPase. All these systems have been reported to be involved in the pathophysiology of depression. Despite the antagonism of lithium to magnesium in some cell-based experimental systems, similarities exist on the functional level, i.e. with respect to kindling, sleep-EEG and endocrine effects. Controlled clinical trials examining the effect of Mg in affective disorder are warranted.

Vasopressin as a target for antidepressant development: an assessment of the available evidence

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is one of the key biological abnormalities described in major depressive disorder, occurring in 30-50% of depressed subjects. Corticotropin-releasing hormone (CRH) and vasopressin (AVP) are the main regulators of this stress system, with the two neuropeptides acting synergistically in bringing about adrenocorticotropin (ACTH) release from the anterior pituitary and cortisol from the adrenal gland. Based on the demonstration of elevated cerebrospinal fluid levels of CRH in depressives, and other evidence, it has been postulated that excess CRH and the resultant increased HPA forward drive form the basis of neuroendocrine dysregulation in depression. However, there is an accumulating body of evidence to support a significant role for AVP in the regulation of pituitary-adrenal activity in health and also in depressive disorder. This review, based on a Medline search from 1980 to 2001, focuses on the functional neuroanatomy, receptor pharmacology, VP synergism with CRH, and the data from clinical and pre-clinical studies that support an important role for AVP in the pathophysiology of major depression. We suggest that future antidepressants may target the vasopressinergic system.

GRK3 regulation during CRF- and urocortin-induced CRF1 receptor desensitization

The EC(50) values for concentration-dependent stimulation of cAMP accumulation by CRF (1.3nM) and urocortin (1.0nM) were equivalent in human retinoblastoma Y79 cells. The time course and magnitude of CRF- and urocortin-induced CRF(1) receptor desensitization were similar. A significant 3-fold increase in GRK3, but not GRK2, mRNA levels accompanied the emergence of CRF(1) receptor desensitization in Y79 cells exposed to CRF. In preliminary experiments, retinoblastoma GRK3 protein expression became upregulated during a 48-h CRF exposure. Neither GRK3 nor GRK2 expression increased in Y79 cells exposed to urocortin for 10 min to 48 h. We hypothesize that GRK3 upregulation may be a cellular negative feedback process directed at maximizing CRF(1) receptor desensitization by heightening GRK3 phosphorylating capacity during prolonged exposure to high CRF. Regulation of GRK expression associated with urocortin- and CRF-induced CRF(1) receptor desensitization appears to differ, despite a similar level of signaling via the cAMP-protein kinase A pathway.

Overexpression of corticotropin-releasing hormone in transgenic mice and chronic stress-like autonomic and physiological alterations

To gain a greater insight into the relationship between hyperactivity of the corticotropin-releasing hormone (CRH) system and autonomic and physiological changes associated with chronic stress, we developed a transgenic mouse model of central CRH overproduction. The extent of central and peripheral CRH overexpression, and the amount of bioactive CRH in the hypothalamus were determined in two lines of CRH-overexpressing (CRH-OE) mice. Furthermore, 24 h patterns of body temperature, heart rate, and activity were assessed using radiotelemetry, as well as cumulative water and food consumption and body weight gain over a 7-day period. CRH-OE mice showed increased amounts of CRH peptide and mRNA only in the central nervous system. Despite the presence of the same CRH transgene in their genome, only in one of the two established lines of CRH-OE mice (line 2122, but not 2123) was overexpression of CRH associated with increased levels of bioactive CRH in the hypothalamus, increased body temperature and heart rate (predominantly during the light (inactive) phase of the diurnal cycle), decreased heart rate variability during the dark (active) phase, and increased food and water consumption, when compared with littermate wildtype mice. Because line 2122 of the CRH transgenic mice showed chronic stress-like neuroendocrine and autonomic changes, these mice appear to represent a valid animal model for chronic stress and might be valuable in the research on the consequences of CRH excess in situations of chronic stress.

Further immunohistochemical evidence for impaired NO signaling in the hypothalamus of depressed patients

The cellular expression of nitric oxide synthase (NOS) was studied in neurons of the Nuc. suprachiasmaticus (SCN) of depressed patients and matched controls. The number of NOS-immunoreactive SCN neurons was significantly reduced in depression. We conclude that affective disorders are accompanied by impaired hypothalamic NO signaling.

Effects of antalarmin, a CRF type 1 receptor antagonist, on anxiety-like behavior and motor activation in the rat

Molecular studies point to a role for the type 1 corticotropin-releasing factor receptor (CRF(1)) in anxiogenic-like and activating effects of CRF and stress. However, CP-154,526, a selective CRF(1) antagonist, has yielded mixed results in such tests. Few studies have examined the behavioral effects of other CRF(1) antagonists. Therefore, we examined the effects of antalarmin, a structurally related analog of CP-154,526, on anxiety-like behavior and motor activation. Antalarmin blocked the anxiogenic-like effect of CRF in the elevated plus maze, without affecting anxiety-like behavior in vehicle-treated animals. Antalarmin decreased spontaneous defensive withdrawal behavior in a novel, brightly illuminated open field. Finally, antalarmin blocked the activating effects of CRF, but not D-amphetamine, without producing motor sedation. These findings indicate that the CRF(1) receptor mediates anxiogenic-like effects of novelty stress and the anxiogenic-like and activating effects of CRF and support the hypothesis that CRF(1) antagonists may be useful for the pharmacotherapy of pathological anxiety.

Preclinical models: status of basic research in depression

Approximately one half-century ago several classes of medications, discovered by serendipity, were introduced for the treatment of depression and bipolar disorder. These highly effective medications revolutionized our approach to mood disorders and helped launch the modern era of psychiatry. Yet our progress since those serendipitous discoveries has been disappointing. We still do not understand with certainty how those medications produce their desired clinical effects. We have not introduced newer medications with fundamentally different mechanisms of action than the older agents. We have not identified the genetic and neurobiological mechanisms underlying depression and mania, nor do we understand the mechanisms by which nongenetic factors influence these disorders. We have only a rudimentary understanding of the circuits in the brain responsible for the normal regulation of mood and affect, and of those circuits that function abnormally in mood disorders. In approaching these gaps in our knowledge, this workgroup highlighted four major areas for future investment. These include developing better animal models of mood disorders; identifying genetic determinants of normal and abnormal mood in humans and animals; discovering novel targets and biomarkers of mood disorders and treatments; and increasing the recruitment of investigators from diverse backgrounds to mood disorders research.

The combined DEX-CRH test in treatment course and long-term outcome of major depression

Neuroendocrine studies strongly suggest that the hypothalamic-pituitary-adrenocortical (HPA) system plays a crucial role in the development and course of depression. The interaction between the disease process and HPA system function in long-term course, however, is unclear. Since improvement of HPA system deterioration has been demonstrated to be associated with treatment response, the question has arisen whether the course of therapy response as reflected by, for example, early improvement or response (after 1 or 2 weeks of therapy) is also based on HPA system dysfunction and whether the course of HPA regulation during treatment is only a state marker or has additional predictive implications for long-term outcome. In order to elucidate these questions a long-term study was carried out to investigate whether HPA system disturbance is associated (1) with the course of treatment response, predominantly early treatment response, during acute depression and (2) with the long-term course of depression, i.e. number of episodes. Twenty patients with affective disorders who participated in earlier controlled antidepressant treatment studies over 6 weeks were enrolled in an exploratory follow-up study. Using the combined DEX/CRH test it was demonstrated that (1) early improvement, early treatment response and beneficial treatment outcome after 6 weeks were associated with a lower HPA system activity and that (2) in long-term course of depression the HPA system deterioration increases in parallel with the number of previous episodes. These findings suggest that HPA system alterations are closely related to treatment response and long-term outcome of depression.

Penetration of endogenous steroid hormones corticosterone, cortisol, aldosterone and progesterone into the brain is enhanced in mice deficient for both mdr1a and mdr1b P-glycoproteins

Numerous investigations have confirmed an important role for multidrug-resistance gene 1-type P-glycoproteins (MDR1-type P-gps) in the blood-brain barrier, protecting the brain against the accumulation of a wide range of toxic xenobiotics and drugs. Several studies have provided evidence in vitro that certain steroid hormones are transported by MDR1-type P-gps; however, the question of whether this might also apply to the situation in vivo still remained to be determined. We used mice deficient for both murine mdr1a and mdr1b P-gps [mdr1a/1b(-/-)] to determine the uptake of [3H]-cortisol, [3H]-corticosterone, [3H]-aldosterone and [3H]-progesterone into the plasma, brain, testes, liver, spleen, pituitary and adrenal glands. We provide evidence that the access of the endogenous steroid hormones corticosterone, cortisol and aldosterone is regulated by MDR1-type P-gps in vivo. As peripherally administered steroid hormones accumulate in the brain of mice deficient for MDR1-type P-gps, mdr1a/1b proteins are likely to transport these hormones out of the brain, providing a kinetic barrier to their entry. Intracerebral progesterone concentrations are influenced by MDR1-type P-gp function as well; however, the effects are only small. In addition, all four endogenous glucocorticoid hormones accumulated in the testes of mdr1a/1b(-/-) mice. Our findings underline the importance of MDR1-type P-gps as an endogenous barrier system controlling the access of endogenous steroid hormones at the blood-brain barrier to maintain homeostatic control and to protect central nervous system neurones.

Mice overexpressing CRH show reduced responsiveness in plasma corticosterone after a5-HT1A receptor challenge

Corticotropin-releasing hormone (CRH) overproduction and serotonergic dysfunction have both been implicated in a range of psychiatric disorders, such as anxiety and depression, and several studies have shown interactions between these two neurotransmitter systems. In this study, we investigated the effects of CRH challenge on hypothalamo-pituitary-adrenal (HPA) axis activity in female transgenic mice overproducing CRH. Furthermore, the effects of mild stress on HPA axis activity and body temperature were investigated in these mice. Pre- and post-synaptic 5-HT1A receptor function were studied by monitoring body temperature and plasma corticosterone levels after challenge with the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propyl-amino)-tetralin (8-OH-DPAT). Hypothermia in response to 8-OH-DPAT treatment did not differ between transgenic and wild type mice, indicating unaltered somatodendritic 5-HT1A autoreceptor function in mice overproducing CRH. In wild type mice 8-OH-DPAT increased plasma corticosterone levels, but not in transgenic animals. CRH injection, however, increased corticosterone levels in both groups. These data suggest desensitization of post-synaptic, but not pre-synaptic, 5-HT1A receptors in mice overproducing CRH. These findings resemble those seen in depressed patients following 5-HT1A challenge, which is in accord with the hypothesized role of CRH in the pathogenesis of depression.

The highly selective CRF(2) receptor antagonist K41498 binds to presynaptic CRF(2) receptors in rat brain

1. Novel analogues of antisauvagine-30 (aSvg-30), a selective antagonist for CRF(2) receptors, have been synthesized and characterized in vitro and in vivo. 2. The analogues were tested for their ability to compete for [(125)I-Tyr(0)]Svg binding and to inhibit Svg-stimulated adenylate cyclase activity in human embryonic kidney (HEK) 293 cells, permanently transfected with cDNA coding for the human CRF(1) (hCRF(1)), hCRF(2alpha) and hCRF(2beta) receptor. One analogue [D-Phe(11), His(12), Nle(17)]Svg(11-40), named K41498, showed high affinity binding to hCRF(2alpha) (K(i)=0.66+/-0.03 nM) and hCRF(2beta) (K(i)=0.62+/-0.01 nM) but not the hCRF(1) receptor (k(i)=425+50 nM) and decreased Svg-stimulated cAMP accumulation in hCRF(2) expressing cells. In conscious Wistar-Kyoto rats, K41498 (1.84 microg, i.v.) antagonized the hypotensive response to systemic urocortin (1.4 microg, i.v.), but did not block the pressor response to centrally administered urocortin (2.35 microg, i.c.v.). 3. K41498 was subsequently radio-iodinated, and in autoradiographic studies, specific (sensitive to rat urocortin, astressin and aSvg30, but insensitive to antalarmin) binding of (125)I-K41498 (100 pM) was detected in the heart and in selected brain regions including the nucleus tractus solitarius (NTS), spinal trigeminal nucleus, lateral septum and around the anterior and middle cerebral arteries. 4. Following unilateral nodose ganglionectomy, binding of (125)I-K41498 was reduced by 65% in the ipsilateral NTS, indicative of presynaptic CRF(2) receptors on vagal afferent terminals. 5. These data demonstrate that K41498 is a useful tool to study native CRF(2) receptors in the brain and periphery.

Effects of corticotropin-releasing hormone on distress vocalizations and locomotion in maternally separated mouse pups

The behavioral effects of corticotropin-releasing hormone (CRH) appear to depend on the baseline state of arousal of the animal. In this study, this hypothesis was tested using a 4-min maternal separation procedure in 7-day-old male and female mouse pups (outbred CFW strain). Two intensities of stress were used to assess the effects of intracerebroventricularly administered r/hCRH: a mild stress condition where the ambient temperature was close to nest temperature (30 degrees C) and rates of maternal separation-induced ultrasonic vocalizations (USVs) were relatively low (ca. 25/4 min), and a more stressful condition where the temperature was 19 degrees C and the rates of USVs were high (ca. 250/4 min). Differential effects of CRH on vocalization rate and locomotor behavior were observed to be dependent on the level of stress. In the more stressful 19 degrees C condition, r/hCRH dose-dependently reduced the number of USVs without affecting motor behavior, as indexed by grid crossings. In contrast, in the 30 degrees C condition, only the highest dose of r/hCRH reduced calling while r/hCRH activated motor behavior over a wider range of doses. These effects were independent of hypothalamus-pituitary-adrenal (HPA) axis activity, as measured by plasma corticosterone levels. The present study indicates that in mouse pups, the effects of CRH administration depend on baseline levels of arousal and that the behavioral effects of CRH administration can be dissociated under mild and more stressful conditions.

The CRH1 receptor antagonist R121919 attenuates stress-elicited sleep disturbances in rats, particularly in those with high innate anxiety

Excessive corticotropin-releasing hormone (CRH) secretion in limbic and prefrontal brain areas has been postulated to underly stress-related clinical conditions. Studies in mice with deleted or pharmacologically compromised CRH type 1 receptors (CRH-R1) point to a key role of the CRH/CRH-R1 signaling cascade as a potential drug target. Therefore, we compared the effect of a selective high affinity CRH-R1 antagonist (R121919) on sleep-wake behavior in two rat lines selectively bred for either high or low innate anxiety. We found that the subcutaneous injection of the solvent of R121919, a citrate buffer solution, transiently increased circulating levels of the stress hormones ACTH and corticosterone and reduced sleep, especially in high-anxiety animals. When R121919 was added to the solvent, hormone levels and sleep patterns returned to baseline and were indistinguishable between the rat lines. This finding is in accord with previous observations from a clinical trial in depressed patients and studies in rats with high innate anxiety that suggested major effects of CRH-R1 antagonism in the presence of a pathological (i.e. CRH hypersecretion) condition only.

Effects of transgenic overproduction of CRH on anxiety-like behaviour

Central administration of corticotropin-releasing hormone increases anxiety-like behaviour and arousal in rodents, and increased anxiety-like behaviour has been shown in mice overproducing corticotropin-releasing hormone on an elevated plus maze and in a dark-light emergence task. However, evidence is accumulating that measures obtained from different anxiety tasks may reflect different aspects of anxiety-like behaviour in animals. We therefore tested mice overproducing corticotropin-releasing hormone in a battery of paradigms, studying spontaneous behaviour after a mild stressor, tasks of innate anxiety-like behaviour (light-dark box), lick suppression (Vogel conflict), conditioned fear, and forced swimming. Exploratory behaviour was studied in a 16-hole board task. Furthermore, pain threshold, water intake, locomotor activity and sensorimotor learning/co-ordination were tested to control for confounding factors. In line with previous findings, increased anxiety-like behaviour of transgenic mice was observed in the light-dark box paradigm. However, no differences were seen in the conflict paradigm. Conditioned fear was decreased 1 h but not 24 h after conditioning in transgenic mice, and immobility was decreased [corrected] in forced swimming in corticotropin-releasing hormone overexpressors. Locomotor activity in a novel open field and on the hole board was reduced in transgenics. Exploratory behaviour (hole pokes) was reduced during initial exploration of an unfamiliar hole board. Moreover, sensorimotor performance on a rotorod was impaired, and water intake was reduced in corticotropin-releasing hormone overproducing mice, while no changes were seen in nociception. No differences in locomotor activity were seen in a second group of mice, tested in a familiar open field. When these animals were challenged with diazepam, transgenic mice were less susceptible to the sedative effects of the drug on locomotor activity. These data suggest that corticotropin-releasing hormone overproduction leads to specific effects in a subset of anxiety paradigms, and that these transgenic mice suffer from a motor deficit in addition to altered anxiety-like behaviour/arousal.

Corticotropin-releasing hormone-synthesizing neurons of the human hypothalamus receive neuropeptide Y-immunoreactive innervation from neurons residing primarily outside the infundibular nucleus

Immunohistochemical single- and double-labeling studies were performed on the hypothalami of postmortem human brains to elucidate the distribution of corticotropin-releasing hormone (CRH)-immunoreactive (IR) neuronal elements and their interaction with the neuropeptide Y (NPY)-ergic neuronal system. The great majority of CRH-IR perikarya were found in the paraventricular nucleus (PVN), whereas a considerable number of CRH-IR neurons were also observed in the periventricular and infundibular nuclei. The dorsomedial nucleus and the perifornical region contained only scattered CRH-IR neurons. Dense CRH-IR fiber networks were found throughout the hypothalamus. However, the medial preoptic, the dorsolateral part of the supraoptic, the suprachiasmatic, the ventromedial, and the different mammillary nuclei showed a relative paucity of fibers. The terminal fields of NPY-IR axons overlapped the distribution of CRH-IR neurons in the hypothalamus. NPY-IR axon varicosities were juxtaposed to both dendrites and perikarya of the majority of CRH-IR neurons residing in the paraventricular, periventricular, and infundibular nuclei. These neurons were frequently contacted by multiple NPY axons that either formed baskets around their perikarya or completely ensheathed the emanating CRH dendrites. Because NPY and agouti-related protein (AGRP) are co-contained in neurons of the human infundibular nucleus, we used AGRP as a marker of NPY fibers originating exclusively from the infundibular nucleus. Only a small proportion of CRH neurons in the PVN was contacted by AGRP-IR axon varicosities, suggesting that NPY-IR innervation of CRH neurons in the PVN derive mainly from regions outside the infundibular nucleus. The present morphological findings support the view that NPY regulates the CRH system of the human hypothalamus and therefore at least some of the effects of NPY on metabolic, autonomic, and endocrine functions may be mediated through CRH.

Corticotropin-releasing hormone receptor type 1-deficiency enhances hippocampal serotonergic neurotransmission: an in vivo microdialysis study in mutant mice

Corticotropin-releasing hormone plays an important role in the coordination of various responses to stress. Previous research has implicated both corticotropin-releasing hormone and the serotonergic system as causative factors in the development and course of stress-related psychiatric disorders such as major depression. To delineate the role of the corticotropin-releasing hormone receptor type 1 (CRH-R1) in the interactions between corticotropin-releasing hormone and serotonergic neurotransmission, in vivo microdialysis was performed in CRH-R1-deficient mice under basal (home cage) and stress (forced swimming) conditions. Hippocampal dialysates were used to measure extracellular levels of serotonin and its metabolite 5-hydroxyindoleacetic acid, and free corticosterone levels to monitor the status of the hypothalamic-pituitary-adrenocortical axis. Moreover, behavioural activity was assessed by visual observation and a scoring paradigm. Both wild-type and heterozygous mutant mice showed a clear diurnal rhythm in free corticosterone. Free corticosterone concentrations were, however, lower in heterozygous mutant mice than in wild-type animals and undetectable in homozygous CRH-R1-deficient mice. Homozygous CRH-R1-deficient mice showed enhanced hippocampal levels of 5-hydroxyindoleacetic acid but not of serotonin during the light and the dark phase of the diurnal cycle, which may point to an enhanced synthesis of serotonin in the raphe-hippocampal system. Moreover, the mutation resulted in higher behavioural activity in the home cage during the light but not during the dark period. Forced swimming caused a rise in hippocampal serotonin followed by a further increase after the end of the stress paradigm in all genotypes. Homozygous and heterozygous mutant mice showed, however, a significantly amplified serotonin response to the forced swimming as compared to wild-type control animals. We conclude that CRH-R1-deficiency results in reduced hypothalamic-pituitary-adrenocortical axis activity, in enhanced synthesis of serotonin during basal conditions, and in an augmented response in extracellular levels of serotonin to stress. These data provide further evidence for the intricate relationship between corticotropin-releasing hormone and serotonin and the important role of the CRH-R1 herein.

Neurobiology of relapse to alcohol in rats

Relapse to alcohol use after prolonged withdrawal periods is the major problem in the treatment of alcohol dependence in humans. However, until recently, relatively few preclinical studies concentrated on the elucidation of the neurochemical events underlying relapse to alcohol. In this article we will review recent data from studies in which alcohol-deprivation and reinstatement models were used to determine the mechanisms underlying relapse to alcohol in rats. In the alcohol-deprivation model, the intake of alcohol is determined after prolonged periods of forced abstinence in drug-experienced rats. In the reinstatement model, the ability of acute non-contingent exposure to drug or non-drug stimuli to reinstate drug seeking is determined following training for drug self-administration and subsequent extinction of the drug-reinforced behavior. We will review studies, which used these preclinical models, on the effect of specific pharmacological agents on relapse to alcohol seeking induced by re-exposure to alcohol and to alcohol-associated cues and by exposure to stress. Subsequently, we will describe potential neuronal circuits that may underlie relapse to alcohol. Finally, future directions and clinical implications of the study of relapse to alcohol in laboratory animals will be discussed briefly.

Sleep and the hypothalamo-pituitary-adrenocortical system

The intention of this review is to summarize the current knowledge on the bidirectional interaction between sleep EEG and the secretion of corticotropin (ACTH) and cortisol. The administration of various hypothalamic-pituitary- adrenocortical (HPA) hormones and their antagonists exerts specific sleep-EEG changes in several species including humans. It is well documented that corticotropin releasing hormone (CRH) impairs sleep and enhances vigilance. In addition, it may promote REM sleep. Changes in the growth hormone-releasing hormone (GHRH):CRH ratio in favour of CRH appear to contribute to shallow sleep, elevated cortisol levels and blunted GH in depression and ageing. On the other hand, in women GHRH appears to exert CRH-like effects on sleep. Acute cortisol administration increases slow-wave sleep (SWS) and GH, probably due to feedback inhibition of CRH, and inhibits REM sleep. With the mixed glucocorticoid and progesterone receptor antagonist mifepriston sleep is disrupted. Subchronic administration of the glucocorticoid agonist methylprednisolone desinhibited REM sleep. A synergism of elevated CRH and cortisol activity may contribute to REM disinhibition during depression. Also ACTH and vasopressin modulate sleep specifically but their physiological role remains unclear. For example acute icv vasopressin enhances wakefulness in rats, whereas its long-term administration increases SWS in the elderly. In various studies the interaction of sleep EEG and HPA hormones has been investigated at the baseline, after manipulation of sleep-wake behaviour and after environmental changes. Most studies agree that the circadian pattern of cortisol is relatively independent from sleep and environmental influences. Some data suggest a major effect of light on cortisol secretion. Sleeping is widely associated with blunting and awakenings are linked with increases of HPA hormones.

4-(2-Chloro-4-methoxy-5-methylphenyl)-N-[(1S)-2-cyclopropyl-1-(3-fluoro-4-methylphenyl)ethyl]5-methyl-N-(2-propynyl)-1, 3-thiazol-2-amine hydrochloride (SSR125543A), a potent and selective corticotrophin-releasing factor(1) receptor antagonist. II. Characterization in rodent models of stress-related disorders

The present study investigated the effects of the novel corticotrophin-releasing factor (CRF)(1) receptor antagonist 4-(2-chloro-4-methoxy-5-methylphenyl)-N-[(1S)-2-cyclopropyl-1-(3-fluoro-4-methylphenyl)ethyl]5-methyl-N-(2-propynyl)-1,3-thiazol-2-amine hydrochloride (SSR125543A) in a variety of rodent models of anxiety, including conflict procedures (punished drinking and four-plate), exploration models (elevated plus-maze and light/dark), a fear/anxiety defense test battery, and several procedures based on stress-induced changes in physiological (isolation-induced hyperthermia and tail pinch-induced cortical norepinephrine release) or behavioral (social defeat-induced anxiety, maternal separation-induced vocalization) parameters. Moreover, the effects of SSR125543A were investigated in acute (forced swimming) and chronic (chronic mild stress; CMS) models of depression. SSR125543A and the CRF(1) receptor antagonist antalarmin displayed limited efficacy in exploration-based anxiety models. In contrast, both compounds produced clear-cut anxiolytic-like activity in models involving inescapable stress, including the conflict procedures, the social defeat-induced anxiety paradigm and the defense test battery (3-30 mg/kg i.p. or p.o.). These effects paralleled those of the anxiolytic diazepam. In addition, SSR125543A and antalarmin antagonized stress-induced hyperthermia, distress vocalization, and cortical norepinephrine release. In the forced swimming test, 30 mg/kg p.o. SSR125543A and 3 to 30 mg/kg p.o. antalarmin produced clear antidepressant-like effects. These latter results were strengthened by the findings from the CMS, which showed that repeated administration of 10 mg/kg i.p. SSR125543A for 30 days improved the degradation of the physical state, the reduction of body weight gain, and anxiety produced by stress. Together, these data indicate that SSR125543A shows good activity in acute and chronic tests of unavoidable stress exposure, suggesting that it may have a potential in the treatment of depression and some forms of anxiety disorders.

Genetic modification of corticosteroid receptor signalling: novel insights into pathophysiology and treatment strategies of human affective disorders

Every disturbance of the body, either real or imagined, evokes a stress response. Essential to this stress response is the activation of the hypothalamic-pituitary-adrenocortical (HPA) system, finally resulting in the release of glucocorticoid hormones from the adrenal cortex. Glucocorticoid hormones, in turn, feed back to this system by central activation of two types of corticosteroid receptors: the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR) which markedly differ in their neuroanatomical distribution and ligand affinity. Whereas a brief period of controllable stress, experienced with general arousal and excitement, can be a challenge and might thus be beneficial, chronically elevated levels of circulating corticosteroids are believed to enhance vulnerability to a variety of diseases, including affective disorders. Corticosteroids are known to influence emotions and cognitive processes, such as learning and memory. In addition, corticosteroids play extremely important roles in modulating fear and anxiety-related behaviour. The mechanisms by which corticosteroids exert their effects on behaviour are often indirect, by modulating particular sets of neurons or neurotransmitter systems. In addition, the timing of corticosteroid increase (before, during or after exposure to a stressor) determines whether and how behaviour is affected. The cumulative evidence makes a strong case implicating corticosteroid receptor dysfunction in the pathogenesis of affective disorders. Although definitive controlled trials remain to be conducted, there is evidence indicating that cortisol-lowering or corticosteroid receptor antagonist treatments may be of clinical benefit in selected individuals with major depression. A more detailed knowledge of the GR signalling pathways therefore opens up the possibility to specifically target GR function. In recent years, refined molecular technologies and the generation of genetically engineered mice (e.g. "conventional" and "conditional" knock-outs) have allowed to specifically target individual genes involved in corticosteroid receptor signalling and stress hormone regulation. Given the fundamental role of corticosteroid receptors in hippocampal integrity and mental performance during aging and psychiatric disorders, the identification and detailed characterization of these molecular pathways will ultimately lead to the development of novel neuropharmacological intervention strategies.

Reduced startle reactivity and plasticity in transgenic mice overexpressing corticotropin-releasing hormone

BACKGROUND

Corticotropin-releasing hormone (CRH) hyperactivity in transgenic mice overexpressing CRH in the brain (CRH-OE(2122)) appears to be associated with chronic stress-like alterations, including increased CRH content in the hypothalamus, changes in hypothalamus-pituitary-adrenal axis regulation, and increased heart rate and body temperature. In the present study, we investigated if sensory information processing of startling auditory stimuli was affected in CRH-OE(2122) mice.

METHODS

CRH-OE(2122) mice (on C57BL/6J background) were subjected to a number of procedures probing sensory information processing mechanisms, including the acoustic startle response, habituation, and prepulse inhibition of startle.

RESULTS

CRH-OE(2122) mice displayed reduced acoustic startle reactivity and increased motor activity during startle testing compared to wild-type mice. Furthermore, transgenic mice did not show habituation of the startle response after repeated exposure to the auditory stimulus, or habituation across procedures. CRH-OE(2122) mice exhibited robust impairments of prepulse inhibition in two different paradigms.

CONCLUSIONS

The results in CRH-OE(2122) mice indicate that chronic CRH hyperactivity is associated with reductions in startle reactivity, habituation, and prepulse inhibition. The latter two abnormalities are also observed in schizophrenia patients. We conclude that chronic CRH excess may reduce behavioral reactivity to environmental stimuli and impair information processing mechanisms.

Multiple sites of control of type-1 corticotropin releasing hormone receptor levels in the pituitary

Hypothalamic corticotropin releasing hormone (CRH) stimulates pituitary ACTH secretion through interaction with type 1 CRH receptors (CRH-R1), the number of which varies during alterations of the hypothalamic-pituitary-adrenal (HPA) axis. CRH-R1 are essential for ACTH responses to stress but CRH receptor content in the pituitary does not correlate with corticotroph responsiveness. This indicates that a small number of receptors is sufficient for full ACTH responses probably through post-receptor interaction with vasopressin (VP) signaling. CRH binding and hybridization studies in adrenalectomized, glucocorticoid-treated or stressed rats revealed divergent levels of CRH receptors and CRH-R1 mRNA in the pituitary, with binding reductions but normal or elevated CRH-R1 mRNA levels during alterations of the HPA axis. Western blot analysis of CRH-R1 protein in pituitary membranes from adrenalectomized rats show unchanged CRH-R1 mRNA levels, but reduced CRH binding associated with significant increases in CRH-R1 protein, suggesting that the decrease in binding is due to homologous desensitization and not to reduced receptor synthesis. In contrast, decreased CRH binding following glucocorticoid administration is associated with reduction in CRH-R1 protein suggesting inhibition of CRH-R1 mRNA translation. Regulation of CRH-R1 translation may involve binding of cytosolic proteins, and a minicistron in the 5'UTR of the CRH-R1 mRNA. Post-transcriptional regulatory mechanisms allowing rapid changes in CRH receptor activity are important for adaptation of corticotroph responsiveness to continuous change in physiological demand.

4-(2-Chloro-4-methoxy-5-methylphenyl)-N-[(1S)-2-cyclopropyl-1-(3-fluoro-4-methylphenyl)ethyl]5-methyl-N-(2-propynyl)-1,3-thiazol-2-amine hydrochloride (SSR125543A): a potent and selective corticotrophin-releasing factor(1) receptor antagonist. I. Biochemical and pharmacological characterization

4-(2-Chloro-4-methoxy-5-methylphenyl)-N-[(1S)-2-cyclopropyl-1- (3-fluoro-4-methylphenyl)ethyl]5-methyl-N-(2-propynyl)-1,3-thiazol-2-amine hydrochloride (SSR125543A), a new 2-aminothiazole derivative, shows nanomolar affinity for human cloned or native corticotrophin-releasing factor (CRF)(1) receptors (pK(i) values of 8.73 and 9.08, respectively), and a 1000-fold selectivity for CRF(1) versus CRF(2 alpha) receptor and CRF binding protein. SSR125543A antagonizes CRF-induced stimulation of cAMP synthesis in human retinoblastoma Y 79 cells (IC(50) = 3.0 +/- 0.4 nM) and adrenocorticotropin hormone (ACTH) secretion in mouse pituitary tumor AtT-20 cells. SSR125543A is devoid of agonist activity in these models. Its brain penetration was demonstrated in rats by using an ex vivo [(125)I-Tyr(0)] ovine CRF binding assay. SSR125543A displaced radioligand binding to the CRF(1) receptor in the brain with an ID(50) of 6.5 mg/kg p.o. (duration of action >24 h). SSR125543A also inhibited the increase in plasma ACTH levels elicited in rats by i.v. CRF (4 microg/kg) injection (ID(50) = 1, 5, or 5 mg/kg i.v., i.p., and p.o., respectively); this effect lasted for more than 6 h when the drug was given orally at a dose of 30 mg/kg. SSR125543A (10 mg/kg p.o.) reduced by 73% the increase in plasma ACTH levels elicited by a 15-min restraint stress in rats. Moreover, SSR125543A (20 mg/kg i.p.) also antagonized the increase of hippocampal acetylcholine release induced by i.c.v. injection of 1 microg of CRF in rats. Finally, SSR125543A reduced forepaw treading induced by i.c.v. injection of 1 microg of CRF in gerbils (ID(50) = approximately 10 mg/kg p.o.). Altogether, these data indicate that SSR125543A is a potent, selective, and orally active CRF(1) receptor antagonist.

Gene-based SNP genetic association study of the corticotropin-releasing hormone receptor-2 (CRHR2) in major depression

An increasing amount of data suggests that affective disorders are related to dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, the stress-response system. Corticotropin-releasing hormone receptor-2 (CRHR2)-deficient mice display a stress-sensitive and anxiety-like phenotype suggesting that the CRHR2 is a plausible functional candidate gene influencing the reactivity of the HPA axis and therefore the liability to develop affective disorders. In this study, a gene-based single nucleotide polymorphism (SNP) map of the corticotropin-releasing hormone receptor 2 (CRHR2) was constructed containing one synonymous cSNP in exon 10, two intronic SNPs, and two SNPs in the 5' upstream regulatory region. No significant difference in allele or genotype frequency was found for four out of the five SNPs between Belgian unipolar (UP) patients and age-, gender-, and ethnicity-matched controls. The cSNP did show allelic and genotypic association with borderline significance (P=0.04). However, a replication study of this cSNP in a bipolar sample of Belgian origin and a Swedish UP sample did not show significant differences in allele and genotype frequencies.

Characterization of (2S,4R)-1-[5-chloro-1-[(2,4-dimethoxyphenyl)sulfonyl]-3-(2-methoxy-phenyl)-2-oxo-2,3-dihydro-1H-indol-3-yl]-4-hydroxy-N,N-dimethyl-2-pyrrolidine carboxamide (SSR149415), a selective and orally active vasopressin V1b receptor antagonist

(2S,4R)-1-[5-Chloro-1-[(2,4-dimethoxyphenyl)sulfonyl]-3-(2-methoxy-phenyl)-2-oxo-2,3-dihydro-1H-indol-3-yl]-4-hydroxy-N,N-dimethyl-2-pyrrolidine carboxamide (SSR149415), the first selective, nonpeptide vasopressin V1b receptor antagonist yet described, has been characterized in vitro and in vivo. SSR149415 showed competitive nanomolar affinity for animal and human V1b receptors and exhibited much lower affinity for rat and human V1a, V2, and oxytocin receptors. Moreover, this compound did not interact with a large number of other receptors, enzymes, or ion channels. In vitro, SSR149415 behaved as a full antagonist and potently inhibited arginine vasopressin (AVP)-induced Ca2+ increase in Chinese hamster ovary cells expressing rat or human V1b receptors. The in vivo activity of SSR149415 has been studied in several models of elevated corticotropin secretion in conscious rats. SSR149415 inhibited exogenous AVP-induced increase in plasma corticotropin, from 3 mg/kg i.p. and 10 mg/kg p.o. upwards. Similarly, this compound antagonized AVP-potentiated corticotropin release provoked by exogenous corticoliberin at 3 mg/kg p.o. The effect lasted for more than 4 h at 10 mg/kg p.o. showing a long-lasting oral effect. SSR149415 (10 mg/kg p.o.) also blocked corticotropin secretion induced by endogenous AVP increase subsequent to body water loss. Moreover, 10 mg/kg i.p SSR149415 inhibited plasma corticotropin elevation after restraint-stress in rats by 50%. In the four-plate test, a mouse model of anxiety, SSR149415 (3 mg/kg p.o. upwards) displayed anxiolytic-like activity after acute and 7-day repeated administrations. Thus, SSR149415 is a potent, selective, and orally active V1b receptor antagonist. It represents a unique tool for exploring the functional role of V1b receptors and deserves to be clinically investigated in the field of stress and anxiety.

Genetically engineered mice for studies of stress-related clinical conditions

Genetically engineered mice with a specific deletion of targeted genes provide a novel and useful tool to study the endogenous mechanisms underlying aberrant behaviour. In this review we take the stress hormone (hypothalamic-pituitary-adrenocortical) system as an example to demonstrate how refined molecular technologies have allowed to target individual genes involved in stress hormone regulation. We describe different gene targeting methods: the generation of "conventional" knock-out mice enables us to delete a gene of interest in every cell of the body. Equally important for the studies of gene function in the mouse is the use of tissue-specific regulatory systems that allow gene inactivation to be restricted to specific tissues and, in some cases, to specific time points during development, such as the "conditional" knock-out, or the application of antisense techniques. Importantly, deletion of individual genes is not providing animal models for certain psychiatric disorders as these are caused by a manifold of minor changes in a series of so-called susceptibility genes. However, these gene targeting methods have become valuable tools to dissect the functions of individual components of complex biological systems in behavioural neuroscience: genetically engineered animals help to unravel the complex interactions and correlations between individual genes, hormonal regulation and behaviour, the most complex form of biological organization.

Design, synthesis and pharmacological characterization of new highly selective CRF(2) antagonists: development of 123I-K31440 as a potential SPECT ligand

Novel analogs of antisauvagine-30 (aSvg-30), a specific antagonist for corticotropin-releasing factor (CRF) receptor, type 2 (CRF(2)), have been synthesized and characterized in vitro and in vivo. The N-terminal amino acid D-phenylalanine in aSvg-30 was replaced by a D-tyrosine residue for specific radioactive labeling with 123I. Additionally, Met(17) of aSvg-30 was substituted by norleucine and the N-terminus of the peptide was acetylated to increase in vivo metabolic stability. The aSvg-30 analogs were tested for their ability to displace [125I-Tyr(0)]Svg in binding experiments and to inhibit Svg-stimulated adenylate cyclase activity in human embryonic kidney (HEK) 293 cells, permanently transfected with cDNA coding for the human CRF(1) (hCRF(1)), hCRF(2alpha) and hCRF(2beta) receptor. Ac-[D-Tyr(11), His(12), Nle(17)Svg(11-40), named K31440, showed high specific binding to hCRF(2alpha) (K(i) = 1.48 +/- 0.34 nM) and hCRF(2beta) (K(i) = 2.05 +/- 0.61 nM) but not the hCRF(1) receptor (K(i) = 288 +/- 13 nM) and decreased Svg-stimulated cAMP activity in hCRF(2)-expressing cells in a similar fashion as aSvg-30. In biodistribution studies specific uptake of 123I-K31440 was detected after 1 h in small intestine of BALB/c nude mice. These data demonstrate that 123I-K31440 may serve as a useful tool to detect native CRF(2) receptors and elucidate their role in gastrointestinal disorders and diseases such as irritable bowel syndrome or cancer.

The CRF peptide family and their receptors: yet more partners discovered

Abnormal signaling at corticotropin-releasing factor CRF1 and CRF2 receptors might contribute to the pathophysiology of stress-related disorders such as anxiety, depression and eating disorders, in addition to cardiac and inflammatory disorders. Recently, molecular characterization of CRF1 and CRF2 receptors and the cloning of novel ligands--urocortin, stresscopin-related peptide/urocortin II, and stresscopin/urocortin III--have revealed a far-reaching physiological importance for the family of CRF peptides. Although the physiological roles of the CRF2 receptor remain to be defined, the preclinical and clinical development of specific small-molecule antagonists of the CRF1 receptor opens new avenues for the treatment of psychiatric and neurological disorders.

Genetic basis of anxiety-like behaviour: a critical review

The way genetic and/or environmental factors influence psychiatric disorders is an enduring question in the field of human psychiatric diseases. Anxiety-related disorders provide a relevant example of how such an interaction is involved in the aetiology of a psychiatric disease. In this paper we review the literature on that subject, reporting data derived from human and rodent studies. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of anxiety, including inbred mice, selected lines, multiple marker strains, or knockout mice and review data reporting environmental components influencing anxiety-related behaviours. We conclude that anxiety is a complex behaviour, underlined not only by genetic or environmental factors but also by multiple interactions between these two factors.

Intravenous C-type natriuretic peptide augments behavioral and endocrine effects of cholecystokinin tetrapeptide in healthy men

Given the anxiogenic effects of the type-B natriuretic peptide receptor agonist C-type natriuretic peptide (CNP) in rodents, we investigated the influence of CNP pretreatment upon the behavioral and endocrine action of the panicogen cholecystokinin tetrapeptide (CCK-4) in healthy men. In a randomized double-blind balanced design, 20 male volunteers were given an intravenous infusion of 300 microg of CNP vs. placebo followed by 25 microg of CCK-4. The behavior was assessed using panic, anxiety, and dissociation questionaires before the infusion and after the CCK-4 stimulus. Furthermore, the stress-sensitive hormones adrenocorticotropic hormone (ACTH), cortisol, and prolactin were measured. CNP pretreatment enhanced the anxiogenic and prodissociative effects of CCK-4 and significantly augmented the ACTH surge after CCK-4. However, no effect of CNP was seen upon panic symptoms. Our preliminary data support a role of type-B natriuretic peptide receptors in anxiety modulation in normal man.

CRHR1 Receptor binding and lipophilicity of pyrrolopyrimidines, potential nonpeptide corticotropin-releasing hormone type 1 receptor antagonists

A series of compounds related to N-butyl-N-ethyl[2,5,6-trimethyl-7-(2,4,6-trimethylphenyl)pyrrolo[2,3-d]pyrimidin-4-yl]amine (1, antalarmin) have been prepared and evaluated for their CRHR1 binding affinity as the initial step in the development of selective high affinity hydrophilic nonpeptide corticotropin-releasing hormone type 1 receptor (CRHR1) antagonists. Calculated log P (Clog P) values were used to evaluate the rank order of hydrophilicity for these analogues. Introducing oxygenated functionalities (delta-hydroxy or bis-beta-ethereal) into 1 gave more hydrophilic compounds, which had good affinity for the receptor. Introducing an amino group or shortening the alkyl side chain was detrimental to CRHR1 affinity. The alcohol 4-[ethyl[2,5,6-trimethyl-7-(2,4,6-trimethylphenyl)pyrrolo[2,3-d]pyrimidin-4-yl]amino]butan-1-ol (3), bearing a terminal hydroxyl group on an N-alkyl side-chain, showed the highest CRHR1 binding affinity among these compounds (K(i)=0.68 nM), and is one of the highest affinity CRHR1 ligands known. Compounds 3-5, and 8, which are likely to be less lipophilic than 1, have high CRHR1 affinity and may be valuable probes to further study the CRH system.

Depression as a spreading adjustment disorder of monoaminergic neurons: a case for primary implication of the locus coeruleus

A model for the pathophysiology of depression is discussed in the context of other existing theories. The classic monoamine theory of depression suggests that a deficit in monoamine neurotransmitters in the synaptic cleft is the primary cause of depression. More recent elaborations of the classic theory also implicitly include this postulate, other theories of depression frequently prefer to depart from the monoamine-based model altogether. We suggest that the primary defect emerges in the regulation of firing rates in brainstem monoaminergic neurons, which brings about a decrease in the tonic release of neurotransmitters in their projection areas, an increase in postsynaptic sensitivity, and concomitantly, exaggerated responses to acute increases in the presynaptic firing rate and transmitter release. It is proposed that the initial defect involves, in particular, the noradrenergic innervation from the locus coeruleus (LC). Dysregulation of the LC projection activities may lead in turn to dysregulation of serotonergic and dopaminergic neurotransmission. Failure of the LC function could explain the basic impairments in the processing of novel information, intensive processing of irrational beliefs, and anxiety. Concomitant impairments in the serotonergic neurotransmission may contribute to the mood changes and reduction in the mesotelencephalic dopaminergic activity to loss of motivation, and anhedonia. Dysregulation of CRF and other neuropeptides such as neuropeptide Y, galanin and substance P may reinforce the LC dysfunction and thus further weaken the adaptivity to stressful stimuli.

Chronic pain, chronic stress and depression: coincidence or consequence?

Chronic pain and depressive illness are debilitating disease states that are variably resistant to currently available therapeutic agents. Animal models of chronic pain are associated with activation of the hypothalamo-pituitary-adrenal (HPA) axis, upon which chronic pain acts as an inescapable stressor. Inescapable stress is also associated with 'depressive-like' symptoms in experimental animals. Based on reports of the comorbidity between chronic pain and depressive illness in human patients, it is possible that these disease states are linked, via chronic stress-induced HPA dysfunction. Here, we discuss the possible involvement of the HPA axis in the aetiology of both chronic pain and clinical depression, and suggest a strategy for the development of novel pharmacotherapies.

Novel treatments for anxiety and depression: hurdles in bringing them to the market

Anxiety and depressive disorders are the most common psychiatric conditions. The medical need for newer, better-tolerated and more efficacious treatments remains high. However, drug development is time-consuming and has a high rate of failed or inconclusive trials. Improvements in study design, investigator training and early proof-of-concept studies are being discussed as means to decrease failure rates and the duration of development. So far, no uniformly applicable 'magic formulas' for success have been discovered. The most promising approach to overcome these hurdles appears to be a sound study design carried out by experienced professionals in the clinic and in industry.

Neither major depression nor glucocorticoid treatment affects the cellular integrity of the human hippocampus

In major depression, decreased hippocampal volume has been attributed to hypercortisolemia, a frequent sign of the disorder, because in animals an excess of corticosteroids has led to dendritic atrophy, astrogliosis and loss of neurons in this brain region. The present study is the first to investigate the structural integrity of the human hippocampus in major depression and following glucocorticoid treatment. Post-mortem hippocampal tissue from 15 patients who had had major depression or bipolar affective disorder, 10 patients who had been treated with glucocorticoids and 16 controls was assessed using haematoxylin-eosin, Nissl and Bodian staining. The patterns of reactive astrogliosis (glial fibrillary acidic protein, GFAP), synaptic density (synaptophysin), synaptic reorganization (growth-associated protein B-50) and early signs of Alzheimer's disease (Alz-50) were examined immunocytochemically. Multivariate analysis, with the patients' age, tissue fixation time and postmortem delay as covariates, was performed. There was no evidence of neuronal cell loss or other major morphological alterations in any of the groups, nor was there a significant change in the distribution pattern of synaptophysin or Alz-50. Changes in B-50 and GFAP staining were observed in the steroid-treated and depressed patients in areas CA1 and CA2 only. The human hippocampus in major depression and after glucocorticoid treatment does not reveal any major morphological changes or signs of neuronal cell death, but does show subtle alterations in B-50 and GFAP expression in selected parts of the pyramidal cell layer.

The molecular neurobiology of stress--evidence from genetic and epigenetic models

Knowledge of the genetic and molecular events underlying the neuroendocrine and behavioural sequelae of the response to stress has advanced rapidly over recent years. The response of an individual to a stressful experience is a polygenic trait, but also involves non-genetic sources of variance. Using a combination of top-down (quantitative trait locus [QTL] and microarray analysis) and bottom-up (gene targeting, transgenesis, antisense technology and random mutagenesis) strategies, we are beginning to dissect the molecular players in the mediation of the stress response. Given the wealth of the data obtained from mouse mutants, this review will primarily focus on the contributions made by transgenesis and knockout studies, but the relative contribution of QTL studies and microarray studies will also be briefly addressed. From these studies it is evident that several neuroendocrine and behavioural alterations induced by stress can be modelled in mouse mutants with alterations in hypothalamic-pituitary-adrenal axis activity or other, extrahypothalamic, neurotransmitter systems known to be involved in the stress response. The relative contribution of these models to understanding the stress response and their limitations will be discussed.

Antidepressant drug discovery in the postgenomic era

The progress made in genome research raises the question whether the new knowledge bases that have emerged may also lead to better antidepressants. The past has seen many remarkable improvements over traditional drugs, but not a real breakthrough. More recently hypothesis-driven research in depression has focussed upon stress-hormone regulation as a possible target, but validation of new drugs is not yet in sight. In parallel, we see an upsurge of systematic unbiased research in a biotechnology-driven drug discovery effort. This research can only lead to results if clinical research adapts to these new demands by phenotyping depressed patients not only according to psychopathological characteristics but also by utilising functional (e.g. neuroendocrine, neuropsychological, neurophysiological, neuroimaging and clinical drug response) data that are to be correlated with data from genotyping. To achieve the goal of genotype/phenotype-based differential therapy, large-scale efforts with regards to both patient samples and genotyping capacities are needed. In the long term, increasingly detailed patient information, if translated into specific pharmacological treatments, will lead to customized drugs and thus to a partial fragmentation of the antidepressant market. Concurrently, the improved genotyping/phenotyping efforts will also lead to more widely applicable drugs that promise to avoid side effects and refractoriness and also to hasten the time to onset of action. Once these goals are achieved notorious undertreatment of depression may come to an end.

Alterations in core body temperature, locomotor activity, and corticosterone following acute and repeated social defeat of male NMRI mice

Repeated social defeat of male NMRI mice, coupled with the stress of continuously living opposite a dominant animal, induces a citalopram-reversible increase in anxiety. The experiments reported in the present paper were performed in an attempt to further validate this paradigm by studying the effects of acute and repeated social defeat on corticosterone and the circadian rhythms of core body temperature and locomotor activity, measured by telemetry. Acute social defeat induced a large (controls: 37.14+/-0.29 degrees C; subordinates: 39.79+/-0.33 degrees C) increase in core body temperature and corticosterone (controls: 30.14+/-2.70 ng/ml; subordinates: 89.62+/-9.25 ng/ml). Repeated social defeat (24 defeats) induced a chronic elevation in core body temperature across 24-h (controls: 36.62+/-0.04 degrees C; subordinates: 37.11+/-0.16 degrees C) in subordinate animals and a very large increase in corticosterone (controls: 28.60+/-1.27 ng/ml; subordinates: 441.52+/-8.86 ng/ml). These results illustrate that the chronic social defeat procedure described in this paper induces a state of chronic stress in the subordinate animals. Further studies are warranted to ascertain if the chronic hyperthermia and increases in corticosterone observed in the subordinate animals could be attenuated by chronic antidepressant treatment, thus further extending the predictive validity of this model.

Detection of corticotropin-releasing hormone receptor 1 immunoreactivity in cholinergic, dopaminergic and noradrenergic neurons of the murine basal forebrain and brainstem nuclei--potential implication for arousal and attention

Corticotropin-releasing hormone (CRH) interacts with noradrenergic, dopaminergic and cholinergic systems of the brain, and these interactions are thought to be of relevance for the stress response, anxiety-related behavior, and cognitive function. CRH mediates its central effects through two high-affinity membrane receptors, CRH receptor subtypes 1 and 2. It is however unclear at present whether cholinergic or catecholaminergic cells express these receptors themselves or whether the effects of CRH are indirectly mediated through interaction with other neurotransmitter systems. Therefore, this study investigated whether choline acetyltransferase immunoreactive neurons of the murine basal forebrain and brainstem nuclei, and tyrosine hydroxylase immunoreactive neurons located within the locus coeruleus, ventral tegmental area and substantia nigra co-express CRH receptor 1, employing a double-immunocytochemical procedure. Using an antibody against the C-terminus of the CRH type 1 receptor (CRH-R1), CRH-R1-like immunoreactivity was found in all cholinergic basal forebrain nuclei except the nucleus basalis magnocellularis. In particular, the diagonal band of Broca (vertical and horizontal limbs) showed a high degree of co-localization of CRH-R1 immunoreactivity and choline acetyltransferase immunoreactivity (both limbs >90%). A less intense immunoreactivity but still high rate of co-localization was detected in the cholinergic neurons of the medial septum (80%), while lowest co-localization was observed in choline acetyltransferase immunoreactive neurons of the substantia innominata (58%). An intermediate degree of co-localization (75%) was seen in the brainstem pedunculopontine tegmental nucleus, while the other major brainstem cholinergic nucleus, the laterodorsal tegmental nucleus, showed an even higher degree of choline acetyltransferase immunoreactivity-positive cells also immunoreactive for CRH-R1 (92%). All catecholaminergic structures studied displayed a pattern of CRH-R1 immunoreactivity strongly overlapping the pattern of tyrosine hydroxylase immunoreactivity. The intensity of the CRH-R1 signal was relatively low within the ventral tegmental area and the substantia nigra pars compacta, while the CRH-R1 signal was very intense and detected in almost all of the neurons of the locus coeruleus. These results clearly demonstrate that the cholinergic and catecholaminergic systems provide direct anatomical substrates for CRH action through the CRH-R1. These findings are of particular relevance for understanding the action of recently developed CRH-R1 antagonistic drugs which may offer a new therapeutic approach to treat stress-related disorders such as anxiety and depression and their concomitant alterations in arousal and cognitive functions.

Comorbidity of mood and anxiety disorders

This article reviews data on the prevalence of panic, social phobia, generalized anxiety, and posttraumatic stress disorder, and research documenting the comorbidity of these disorders with major depression (MDD). These anxiety disorders are frequently comorbid with MDD, and 50-60% of individuals with MDD report a lifetime history of one or more of these anxiety disorders. The anxiety disorders are also highly correlated with one another, and approximately one-quarter to one-half of individuals with each of the anxiety disorders report a lifetime history of an alcohol or substance use disorder. Anxiety disorders rarely exist in isolation, with several studies reporting that over 90% of individuals with anxiety disorders have a lifetime history of other psychiatric problems. Implications for research are discussed, including the potential benefit of using combined categorical and dimensional rating scale approaches in future genetic, biochemical, neuroimaging, and treatment studies. The clinical implications of the findings are also discussed, and the results of recent clinical trials summarized. Available data suggests selective serotonin reuptake inhibitors are the first-line pharmacological treatment for these disorders, and that newer serotonin and norepinephrine reuptake inhibitors show significant promise, especially for comorbid cases. Comorbidity among depression and anxiety disorders is associated with greater symptom severity, and a considerably higher incidence of suicidality. Increased public awareness about these disorders and the availability of effective treatments is sorely needed.

Mice with targeted mutations of glucocorticoid and mineralocorticoid receptors: models for depression and anxiety?

Impaired corticosteroid receptor signaling is a key mechanism in the pathogenesis of stress-related psychiatric disorders such as depression and anxiety. Since in vivo expression and functional studies of corticosteroid receptors are not feasible in the human central nervous system, such analyses have to be done in animal models. Transgenic mice with mutations of corticosteroid receptors are promising tools, which allow us to investigate the role of these proteins in the pathogenesis of symptoms characteristic for depression and anxiety. This review summarizes the neuroendocrinological and behavioral findings that have been obtained in six different mouse strains with specific mutations that influence the expression or the function of the glucocorticoid or the mineralocorticoid receptor (MR). The analyses of these mice helped to define molecular concepts of how corticosteroid receptors regulate the activity of the hypothalamic-pituitary-adrenal (HPA) system. Furthermore, some of these mutant mice exhibited characteristic alterations in behavioral tests for anxiety and despair. However, so far, none of the mouse strains described here can be viewed as an animal model of a specific psychiatric disease defined by common diagnostic criteria. Using high throughput technologies for the identification of genes regulated by glucocorticoid receptor (GR) and MR in brain areas responsible for specific symptoms of stress-related disorders will yield potential new drug targets for the treatment of depression and anxiety.

Stressor specificity of central neuroendocrine responses: implications for stress-related disorders

Despite the fact that many research articles have been written about stress and stress-related diseases, no scientifically accepted definition of stress exists. Selye introduced and popularized stress as a medical and scientific idea. He did not deny the existence of stressor-specific response patterns; however, he emphasized that such responses did not constitute stress, only the shared nonspecific component. In this review we focus mainly on the similarities and differences between the neuroendocrine responses (especially the sympathoadrenal and the sympathoneuronal systems and the hypothalamo-pituitary-adrenocortical axis) among various stressors and a strategy for testing Selye's doctrine of nonspecificity. In our experiments, we used five different stressors: immobilization, hemorrhage, cold exposure, pain, or hypoglycemia. With the exception of immobilization stress, these stressors also differed in their intensities. Our results showed marked heterogeneity of neuroendocrine responses to various stressors and that each stressor has a neurochemical "signature." By examining changes of Fos immunoreactivity in various brain regions upon exposure to different stressors, we also attempted to map central stressor-specific neuroendocrine pathways. We believe the existence of stressor-specific pathways and circuits is a clear step forward in the study of the pathogenesis of stress-related disorders and their proper treatment. Finally, we define stress as a state of threatened homeostasis (physical or perceived treat to homeostasis). During stress, an adaptive compensatory specific response of the organism is activated to sustain homeostasis. The adaptive response reflects the activation of specific central circuits and is genetically and constitutionally programmed and constantly modulated by environmental factors.

Psychological stress increases hippocampal mineralocorticoid receptor levels: involvement of corticotropin-releasing hormone

We investigated whether acute stressors regulate functional properties of the hippocampal mineralocorticoid receptor (MR), which acts inhibitory on hypothalamic-pituitary-adrenocortical activity. Exposure of rats to forced swimming or novelty evoked a significant rise in density of MR immunoreactivity in all hippocampal subfields after 24 hr, whereas exposure to a cold environment was ineffective. Time course analysis revealed that the effect of forced swimming on MR peaked at 24 hr and returned to control levels between 24 and 48 hr. In pyramidal neurons of CA2 and CA3, marked rises were already observed after 8 hr. Radioligand binding assays showed that corticotropin-releasing hormone (CRH) injected intracerebroventricularly into adrenalectomized rats also produced a rise in hippocampal MR levels; an effect for which the presence of corticosterone, but not dexamethasone, at the time of injection was a prerequisite. Moreover, pretreatment with the CRH receptor antagonist (d-Phe(12),Nle(21,38),alpha-Me-Leu(37))-CRH(12-41) blocked the effect of forced swimming on hippocampal MR levels. To investigate whether the rise in MR levels had any functional consequences for HPA regulation, 24 hr after forced swimming, a challenge test with the MR antagonist RU 28318 was conducted. The forced swimming exposed rats showed an enhanced MR-mediated inhibition of HPA activity. This study identifies CRH as an important regulator of MR, a pathway with marked consequence for HPA axis regulation. We conclude that the interaction between CRH and MR presents a novel mechanism involved in the adaptation of the brain to psychologically stressful events.

Interaction between the cholinergic system and CRH in the modulation of spatial discrimination learning in mice

Both cholinergic and CRH systems have been linked to cognitive processes such as learning and memory, and neuroanatomical as well as neurochemical evidence suggests important interactions between these two systems. Moreover, recent reports of pro-mnestic effects of CRH open the possibility that CRH could have beneficial effects in animals with cholinergic dysfunction. In a first experiment, spatial discrimination of C57BL/6 mice treated with various doses of scopolamine (0.5--2.0 mg/kg IP) was tested in a two-choice water maze task. Scopolamine, but not methylscopolamine, impaired accuracy and decreased responsivity. In contrast, similar doses of the nicotinic antagonist mecamylamine had no effect on choice accuracy but altered responsivity, as indicated by increased errors of omission and a reduction in swim speed during early experimental stages. ICV CRH (0.5--1.0 microg) also failed to significantly affect accuracy, but a strong tendency was observed to impair percentage correct responses. Measures of responsivity, such as errors of omission, choice latency and distance traveled, and of thigmotaxis were not significantly affected by CRH. However, initial swim speed was reduced by the peptide. Combined treatment with scopolamine (0.5 mg/kg IP) and CRH (0.5 microg ICV) had only mild, and primarily independent, effects, but overall suggested that concomitant blockade of muscarinic receptors and activation of the CRH system would rather act synergistically to disrupt spatial discrimination learning. Synergistic effects were also observed when animals receiving a combination of mecamylamine (2.0 mg/kg IP) and CRH (0.5 microg ICV) were tested, both in terms of responsivity and thigmotaxis, and there was limited evidence that part of these effects were potentiating. Thus, the cholinergic and CRH systems interact in the modulation of learning, but CRH, contrary to prediction, worsens the impairment caused by cholinergic blockade.