Brain corticotropin-releasing hormone receptors on neurons and astrocytes.

Corticotropin-releasing hormone (CRH) exerts many potent effects within brain and is considered an important brain neuroregulator. CRH acts via receptors that are widely distributed throughout brain which exhibits highest CRH receptor concentrations in extrahypothalamic regions. We have previously characterized CRH receptors in heterogeneous extrahypothalamic forebrain cell cultures consisting of neurons and glia, and have shown them to exhibit similar kinetic and pharmacological characteristics as CRH receptors in pituitary and in situ brain. However, it is not known whether CRH receptors are present on neurons, glia or both. We tested the hypothesis that CRH receptors are present on neurons in extrahypothalamic forebrain cell cultures derived from day 17-18 fetal rats by characterizing receptors in predominantly neuronal (N), glial/astrocytic (G) cultures and mixed (M) cultures. Mean CRH receptor concentrations (fmol/mg protein) in N (10.4), G (9.4), and M (9.8) cultures were similar. Following Scatchard analyses derived from competition curves, all cell populations exhibited similar mean high-affinity/low-capacity (Kd = 1.0-1.9 nM; Bmax = 183-388 fmol/mg protein) and low-affinity/high-capacity (Kd = 92-104 nM; Bmax = 2034-5008 fmol/mg protein) classes of binding sites. In conclusion: (1) Neurons and astrocytes in fetal extrahypothalamic brain cell cultures contain CRH receptors which exhibit similar concentrations and similar kinetic characteristics. (2) These observations suggest that biological effects of CRH in brain could be mediated via actions on neurons and/or glial astrocytes.     

Distribution of corticotropin-releasing hormone immunoreactivity in golden hamster brain.

The distribution of corticotropin-releasing hormone-immunoreactive (CRH-IR) neurons and fibers was observed in golden hamsters. CRH-IR neurons and fibers were observed within the hypothalamus, thalamus, amygdala, cortex, midbrain, and hindbrain. The largest numbers of CRH-IR neurons were seen within the magno- and parvocellular divisions of the paraventricular nucleus of the hypothalamus and within the septum, bed nucleus of the stria terminalis, preoptic area continuum. The highest density of immunoreactive fibers was observed in the external zone of the median eminence. In addition, many immunoreactive fibers were observed within the bed nucleus of the stria terminalis and the preoptic area. The distribution obtained in hamsters was compared with previously reported distributions from rats, and both were generally similar.     

Central corticotropin-releasing factor suppresses natural killer cytotoxicity

Corticotropin-releasing factor (CRF) administered as a single dose intraventricularly produces a dose-dependent suppression of rat splenic natural killer (NK) cell activity. Neither systemic CRF nor CRF in vitro significantly altered NK activity. The immunosuppressive effect of central CRF was antagonized by central, but not by systemic, preadministration of the CRF antagonist, alpha-helical oCRF residues 9-41. These data suggest that CRF released in the brain may have a role in the central modulation of natural killer cytotoxicity.     

Stress hormone responses to corticotropin-releasing hormone in substance abusers without severe comorbid psychiatric disease.

BACKGROUND: Preclinical data indicate a crucial role of stress in the acute effects of drugs of abuse, maintenance of self-administration, and susceptibility to relapse. Stress system activation may serve as a marker for a neurochemical dysfunction with prognostic significance in patients with addiction. METHODS: We tested pituitary adrenocorticotrophin (ACTH) and adrenal cortisol response to ovine corticotropin-releasing hormone (oCRH) to assess the reactivity of the hypothalamic-pituitary-adrenal (HPA) axis in seven nonsubstance-abusing subjects, 31 polysubstance-abusing subjects without depressive symptoms, and seven subjects with substance abuse and depressive symptoms. No subject met diagnostic criteria for depression or other severe psychiatric disease. RESULTS: Compared with normal control subjects, substance abusers showed significantly lower ACTH and cortisol responses over the course of oCRH stimulation (p <.0001). Substance abusers with depressive symptoms showed similarly blunted responses. CONCLUSIONS: Polysubstance abusers with no past or current diagnosis of other Axis I disorders show blunted ACTH and cortisol responses to oCRH administration. The finding of an activated HPA axis in this population suggests an overlapping role of central CRH and HPA axis activation in affective disorders and substance abuse, which is likely to constitute an endocrine milieu necessary for the maintenance of addictive behavior. These data support the role of future therapeutic trials with nonpeptide CRH receptor 1 antagonists in these patients.     

Reduced attention in mice overproducing corticotropin-releasing hormone

Data from several studies suggest that unrestrained secretion of corticotropin-releasing hormone in the CNS produces several signs and symptoms of depression. Recent evidence indicates that blockade of the CRH receptor 1 reduced depression scores in depressed patients. One of the symptoms that occur is depression is impairment in attentional processes. Whether these impairments are due to alterations in the CRH system are so far unknown. In order to investigate whether overproduction of CRH alters attentional process, transgenic mice overproducing CRH were tested on an operant five choice serial reaction time task, a task which taxes sustained and divided attention. Mutants showed impaired autoshaping. During initial discrimination learning, transgenics performed below wildtype level, but with extended training with long stimulus durations, transgenic animals reached similar accuracy levels as wildtype mice. When animals were tested at shortest stimulus duration (0.5s), a mild but significant impairment in accurate responding emerged in transgenics. This was accompanied by longer correct response latencies, while incorrect latencies did not differ between groups, suggesting attentional impairment in CRH transgenics. Because these animals have been reported to also show increased anxiety-related behaviour, animals were treated with the anxiolytic benzodiazepine diazepam. Diazepam failed to affect accuracy, but transgenic mice showed a stronger behavioural disinhibition. This suggests that the attentional impairment seen in CRH overexpressors is independent of alterations in anxiety-like behaviour. These findings may have implications for understanding the pathophysiology of psychiatric disorders such as depression, where it has been suggested that an overactivity of the CRH system accounts for a variety of symptoms, including hyper-arousal and attentional impairment.     

Brain corticotropin-releasing hormone increases arousal in stress

The effect of restraint stress on pentobarbital-induced sleeping time was examined in rats. Restraint for 60 and 75 min significantly shortened pentobarbital-induced sleeping time. The shortening of sleeping time by restraint was completely reversed by intracerebroventricular (i.c.v.) administration of alpha-helical CRH(9-41), a corticotropin-releasing hormone (CRH) receptor antagonist. In conjunction with our previous finding that i.c.v. administration of CRH shortens pentobarbital-induced sleeping time, the results suggest that restraint stress increases arousal through brain CRH.     

Human corticotropin-releasing hormone in depression--correlation with thyrotropin secretion following thyrotropin-releasing hormone

Twenty-two subjects (11 patients with major endogenous depression and 11 controls) received an intravenous test dose of 100 micrograms human corticotropin-releasing hormone (h-CRH). Corticotropin (ACTH), but not cortisol, responses were blunted in depressives. Basal cortisol secretion was higher in depressives than in controls and was negatively correlated to the corticotropin response following h-CRH. This finding indicates the integrity of the glucocorticoid-dependent negative feedback regulation in depression and supports the view that hypercortisolism in depression is primarily due to a suprapituitary disturbance. Comparison of ACTH responses after h-CRH with thyrotropin (TSH) output following thyrotropin-releasing hormone (TRH) revealed a positive correlation (r = 0.65, p less than 0.001). The concordance between ACTH and TSH responses after specific challenges suggests that regulation of both systems is at least in part under a common control.     

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.     

Diazepam-binding inhibitor and corticotropin-releasing hormone in cerebrospinal fluid

Diazepam-binding inhibitor (DBI) is a neuromodulatory peptide for gamma-aminobutyric acid (GABA) neurotransmission. Cerebrospinal fluid (CSF) levels of DBI have been found to be elevated in depression. CSF levels of the peptide corticotropin-releasing hormone (CRH) have also been found to be elevated in depression. Therefore, we examined for a relationship between DBI and CRH in human CSF. We found significant positive correlations between CSF levels of DBI and CRH in depressed patients, pathological gamblers, and normal controls. These data, along with the elevated CSF levels of DBI in depression, suggest the possibility that DBI may have a role in coordinating responses to stress in humans in addition to its possible role in the pathophysiology of depression.     

Endocrine responses to growth hormone-releasing hormone, thyrotropin-releasing hormone and corticotropin-releasing hormone in depression

To explore and to compare hypothalamic-pituitary-somatotropic (HPS), hypothalamic-pituitary-thyroid (HPT) and hypothalamic-pituitary-adrenocortical (HPA) axis function in depression, 30 subjects (15 patients with a major depressive episode and individually matched controls) received 50 micrograms growth hormone-releasing hormone-44 amide at 9:00, 200 micrograms thyrotropin-releasing hormone (TRH) at 9:00 and 100 micrograms human corticotropin-releasing hormone (CRH) at 18:00 on consecutive days as an i.v. bolus dose. Compared with controls, depressed patients showed blunted growth hormone (GH) responses to GHRH, decreased TRH-induced thyrotropin (TSH) release and reduced corticotropin (ACTH) but normal cortisol secretion following CRH. ACTH secretion following CRH and TRH-induced TSH release were positively correlated across depressed patients and controls but no significant correlations between GH responses to GHRH and TRH-induced TSH release or ACTH and cortisol secretion following CRH administration were demonstrated. Our findings suggest that altered HPT and HPA axis function associated with depression are triggered by factors that are at least partly different from those that cause HPS system dysfunction. We conclude that the pathophysiological process resulting in aberrant neuroendocrine secretory dynamics associated with depression may primarily occur at a suprapituitary site, and that HPS, HPT and HPA axis dysfunction may be precipitated by complex central and peripheral regulatory mechanisms involving largely independent factors.     

Social stress, dominance and blood cellular immunity.

The impact of chronic social coexistence on distribution and function of blood immune cells was examined in Long Evans rats. At the beginning of a 7 day period of chronic coexistence (confrontation), a wall was removed between two neighboring cages each consisting of a male-female pair. Winner and loser males were classified based on differences in their defensive behavior. On day 2 and 7 of confrontation, losers showed reductions in numbers of blood CD4 and CD8 T cells as well as profound suppression of in vitro NK activity and lymphocyte (LYM) proliferation. Numbers of granulocytes (GRAs) were more than doubled. Winner males showed similar immunological alterations only on day 2 of confrontation. On day 7 most changes were reversed. The persistent changes in loser males may reflect a less favorable state for effective immune response.     

Assessment of cellular and humoral immunity of myasthenics.

A close association of autoimmune diseases or autoimmune phenomena in myasthenia gravis is well known. A comprehensive immunological study of 22 patients with myasthenia gravis showed that changes in the immune system mainly involve the thymus-derived lymphocytes (T cells). Anti-thymus antibody was present in 90% of the patients, and it paralleled the frequency of thymic abnormality in myasthenia gravis. It is postulated that in myasthenia gravis the altered T cell functions caused by anti-thymus antibody result in the formation of an array of autoantibodies including the factor which blocks the neuromuscular transmission.     

The corticotropin-releasing hormone stimulation test in chronic schizophrenia

During a drug-free period a group of schizophrenic subjects (N = 9) showed normal mean basal plasma ACTH and cortisol levels in association with normal plasma ACTH and cortisol responses to an infusion of corticotropin-releasing hormone (CRH). Administration of fluphenazine had no effect on basal ACTH and cortisol levels or their responses to CRH (N = 8). These data differ from those previously reported in depressed patients, who showed elevated basal cortisol values in association with a blunted ACTH response to CRH, and add to a growing body of literature which suggests that hypothalamic-pituitary-adrenal regulation is less disturbed in schizophrenia than in depression.     

Stress-related impairments in cellular immunity

The percentages of total T-lymphocytes (OKT-3+), helper T-cells (OKT-4+), and suppressor T-cells (OKT-8+) were significantly lower in blood samples obtained from 40 medical students during examinations, compared to baseline values obtained 6 weeks earlier. In addition, the response of T-lymphocytes to stimulation by phytohemagglutinin and concanavilin A was also significantly lower during examinations, compared to baseline. Self-report data documented significantly greater distress associated with examinations. The data have implications for immunosuppressive disorders and stress-related illnesses.     

Psychotropic effects of corticotropin-releasing hormone stimulation in depressive patients

Synthetic human corticotropin-releasing hormone (hCRH) was administered as an intravenous bolus (100 micrograms) to 13 patients suffering from endogenous depression and to 12 healthy volunteers. Compared with controls, depressed patients showed a significant amelioration of mood and well-being 2 h after hCRH administration in the rating scales applied ('Befindlichkeits-Skala', 'Eigenschaftsw?rterliste', 'Kurzskala Stimmung-Aktivierung', Self-Rating Depression Scale, Hamilton Rating Scale for Depression). Based on our preliminary data, a psychotropic effect and at least a mediating function of hCRH regarding pathophysiology and etiopathogenesis of endogenous depressions must be assumed.     

Cocaine stimulates rat hypothalamic corticotropin-releasing hormone secretion in vitro

Acute or chronic cocaine administration exerts multiple behavioral and physiologic effects including stimulation of the hypothalamic-pituitary-adrenal (HPA) axis. Pharmacologically, cocaine shares major properties with at least 2 classes of pharmaceuticals. It is a local anesthetic and also a potent psychomotor stimulant. The psychomotor stimulant properties of cocaine are thought to be related to its ability to modify the metabolism and the activity of many neurotransmitter systems, such as acetylcholine (ACh), serotonin (5-HT), norepinephrine (NE), and dopamine (DA). We and others have shown that all these neurotransmitters are potent stimulants of hypothalamic corticotropin-releasing hormone (CRH) secretion. The present study was undertaken to examine whether cocaine stimulates hypothalamic CRH secretion and whether or not such an effect is mediated by any of the above neurotransmitters. To accomplish this task, we employed a rat hypothalamic organ culture system, in which CRH secretion form single explanted hypothalami was evaluated by specific radioimmunoassay (iCRH). Cocaine stimulated iCRH secretion in a dose-dependent fashion with peak of activity at 10(-8) M. Isolated or simultaneous pharmacologic blockade of cholinergic (atropine plus hexamethonium), serotonergic (ritanserin), alpha-adrenergic (phentolamine) and/or dopaminergic (compound SCH 23390) receptor subtypes failed to inhibit cocaine-induced iCRH secretion. On the other hand, cocaine-induced iCRH secretion was inhibited by GABA, a potent inhibitor of CRH secretion, dexamethasone, verapamil, a calcium channel blocker, tetrodotoxin, a sodium channel blocker, and carbamazepine, an antiepileptic and antidepressive agent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serotonergic stimulation of corticotropin-releasing hormone and pro-opiomelanocortin gene expression

The neurotransmitter serotonin (5-HT) stimulates adrenocorticotropic hormone (ACTH) secretion from the anterior pituitary gland via activation of central 5-HT1 and 5-HT2 receptors. The effect of 5-HT is predominantly indirect and may be mediated via release of hypothalamic corticotropin-releasing hormone (CRH). We therefore investigated the possible involvement of CRH in the serotonergic stimulation of ACTH secretion in male rats. Increased neuronal 5-HT content induced by systemic administration of the precursor 5-hydroxytryptophan (5-HTP) in combination with the 5-HT reuptake inhibitor fluoxetine raised CRH mRNA expression in the paraventricular nucleus (PVN) by 64%, increased pro-opiomelanocortin (POMC) mRNA in the anterior pituitary lobe by 17% and stimulated ACTH secretion five-fold. Central administration of 5-HT agonists specific to 5-HT1A, 5-HT1B, 5-HT2A or 5-HT2C receptors increased CRH mRNA in the PVN by 15-50%, POMC mRNA in the anterior pituitary by 15-27% and ACTH secretion three- to five-fold, whereas a specific 5-HT3 agonist had no effect. Systemic administration of a specific anti-CRH antiserum inhibited the ACTH response to 5-HTP and fluoxetine and prevented the 5-HTP and fluoxetine-induced POMC mRNA response in the anterior pituitary lobe. Central or systemic infusion of 5-HT increased ACTH secretion seven- and eight-fold, respectively. Systemic pretreatment with the anti-CRH antiserum reduced the ACTH responses to 5-HT by 80% and 64%, respectively. It is concluded that 5-HT via activation of 5-HT1A, 5-HT2A, 5-HT2C and possibly also 5-HT1B receptors increases the synthesis of CRH in the PVN and POMC in the anterior pituitary lobe, which results in increased ACTH secretion. Furthermore, the results indicate that CRH is an important mediator of the ACTH response to 5-HT.     

Distribution of corticotropin-releasing hormone in the developing zebrafish brain

Corticotropin-releasing hormone (CRH) plays a central role in the physiological regulation of the hypothalamus-pituitary-adrenal/interrenal axis mediating endocrine, behavioral, autonomic, and immune responses to stress. Despite the wealth of knowledge about the physiological roles of CRH, the genetic mechanisms by which CRH neurons arise during development are poorly understood. As a first step toward analyzing the molecular and genetic pathways involved in CRH lineage specification, we describe the developmental distribution of CRH neurons in the embryonic zebrafish, a model organism for functional genomics and developmental biology. We searched available zebrafish expressed sequence tag (EST) databases for CRH-like sequences and identified one EST that contained the complete zebrafish CRH open reading frame (ORF). The CRH precursor sequence contained a signal peptide, the CRH peptide, and a cryptic peptide with a conserved sequence motif. RT-PCR analysis showed crh expression in a wide range of adult tissues as well as during embryonic and larval stages. By whole-mount in situ hybridization histochemistry, discrete crh-expressing cell clusters were found in different parts of the embryonic zebrafish brain, including telencephalon, preoptic region, hypothalamus, posterior tuberculum, thalamus, epiphysis, midbrain tegmentum, and rostral hindbrain and in the neural retina. The localization of crh mRNA within the preoptic region is consistent with the central role of CRH in the teleost stress response through activation of the hypothalamic-pituitary-interrenal axis. The widespread distribution of CRH-synthesizing cells outside the preoptic region suggests additional functions of CRH in the embryonic zebrafish brain.     

Association of a genetic marker at the corticotropin-releasing hormone locus with behavioral inhibition.

BACKGROUND: Behavioral inhibition to the unfamiliar (BI), a heritable temperamental profile involving an avoidant response to novel situations, may be an intermediate phenotype in the development of anxiety disorders. Corticotropin-releasing hormone (CRH) is a key mediator of the stress response through its effects on the hypothalamic-pituitary-adrenal axis and limbic brain systems. Transgenic mice overexpressing CRH exhibit BI-like behaviors, implicating this gene in the development of the phenotype. METHODS: We genotyped a marker tightly linked to the CRH locus in 85 families of children who underwent laboratory-based behavioral assessments of BI and performed family-based association analyses. RESULTS: We observed an association between an allele of the CRH-linked locus and BI (p =.015). Among offspring of parents with panic disorder, this association was particularly marked (p =.0009). We further demonstrate linkage disequilibrium between this marker and single nucleotide polymorphisms encompassing the CRH gene. CONCLUSIONS: These results are consistent with the possibility that variants in the CRH gene are associated with anxiety proneness.