Immunological detection of pro-corticotropin releasing factor (CRF) in rat hypothalamus and pancreatic extracts. Evidence for in vitro conversion into CRF

Extracts of both rat hypothalamus and pancreas were analyzed for their corticotropin releasing factor (CRF)-like immunoreactivity by radioimmunoassay (RIA). In the case of the hypothalamus, besides the rat CRF, further identified by high-pressure liquid chromatography (HPLC), two peptide components, a 20-kDa and a 10-kDa species were detected. The 20-kDa component was stable under acidic pH conditions and was further purified by reverse-phase HPLC. When exposed to proteolytic activities coeluting with 'high-molecular-mass CRF' at pH 6, processing was observed and the CRF generated was identified both by RIA, molecular sieve filtration and HPLC under different experimental conditions. It is concluded that this 20-kDa CRF may represent the CRF precursor and that hypothalamic extracts may contain processing enzymes involved in its selective post-translational cleavage. In the pancreatic extract two immunoreactive forms of CRF were detected, the smaller coeluting with the rat CRF and the other corresponding to the intermediate 10-kDa component detected in the hypothalamus. Pancreatic rat CRF, analyzed using RIA both by molecular sieve filtration and HPLC, was indistinguishable from the hypothalamic rat CRF.     

Brain‐derived neurotrophic factor,corticotropin‐releasing factor,and hypothalamic neuronal histamine interact to regulate feeding behavior

Brain‐derived neurotrophic factor (BDNF), corticotropin‐releasing factor (CRF), and hypothalamic neuronal histamine are anorexigenic substances within the hypothalamus. This study examined the interactions among BDNF, CRF, and histamine during the regulation of feeding behavior in rodents. Food intake was measured after treatment with BDNF, α‐fluoromethyl histidine (FMH; a specific suicide inhibitor of histidine decarboxylase that depletes hypothalamic neuronal histamine), or CRF antagonist. We measured food intake in wild‐type mice and mice with targeted disruption of the histamine H1 receptor (H1KO mice) after central BDNF infusion. Furthermore, we investigated CRF content and histamine turnover in the hypothalamus after BDNF treatment, and conversely, BDNF content in the hypothalamus after histamine treatment. We used immunohistochemical staining for histamine H1 receptors (H1‐R) in BDNF neurons. BDNF‐induced feeding suppression was partially attenuated in rats pre‐treated with FMH or a CRF antagonist, and in H1KO mice. BDNF treatment increased CRF content and histamine turnover in the hypothalamus. Histamine increased BDNF content in the hypothalamus. Immunohistochemical analysis revealed that H1‐Rs were expressed on BDNF neurons in the ventromedial nucleus of the hypothalamus. These results indicate that CRF and hypothalamic neuronal histamine mediate the suppressive effects of BDNF on feeding behavior and body weight.     

Brain corticotropin-releasing factor (CRF) and catecholamine responses in acutely stressed rats

Ether-laparotomy stress produced a rapid increase in rat hypothalamic CRF concentration, followed by a rapid reduction and subsequent increase. Cold-restraint stress significantly reduced hypothalamic CRF concentration at 15 min after stress onset. Serum ACTH and corticosterone levels were significantly elevated at 15 min after the onset of both stresses. The CRF responses in the medulla oblongata were not similar to the hypothalamic CRF responses. Norepinephrine concentration in the hypothalamus was reduced, whereas dopamine concentration in the hypothalamus and medulla oblongata was significantly increased. Epinephrine concentrations in these tissues did not show any significant change throughout the stress period. The observations lead to the following conclusions: hypothalamic CRF plays a major role in stimulating ACTH secretion under acute stress; the reduction in hypothalamic CRF is due to an excess release in the early phase of acute stress; hypothalamic CRF and medulla oblongata CRF are controlled by different mechanisms; norepinephrine in the hypothalamus may not be involved in stimulating hypothalamic CRF secretion in the early phase of acute stress; and catecholamines are regulated differently in the hypothalamus and medulla oblongata.     

Reduction in brain immunoreactive corticotropin-releasing factor (CRF) in spontaneously hypertensive rats

The brain CRF concentration of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) was examined by rat CRF radioimmunoassay. Anti-CRF serum was developed by immunizing rabbits with synthetic rat CRF. Synthetic rat CRF was also used as tracer and standard. The displacement of 125I-rat CRF by serially diluted extracts of male Wistar rats hypothalamus, thalamus, midbrain, pons, medulla oblongata, cerebral cortex, cerebellum and neurointermediate lobe was parallel to the displacement of synthetic rat CRF. In both WKY and SHR the highest levels of CRF immunoreactivity were shown by the hypothalamus and neuro-intermediate lobe, and considerable CRF immunoreactivity was also detected in other brain regions. The CRF immunoreactivity in the hypothalamus, neurointermediate lobe, midbrain, medulla oblongata and cerebral cortex was significantly reduced in SHR and it may suggest that CRF abnormality may be implicated in the reported abnormalities in the pituitary-adrenal axis, autonomic response and behavior of SHR.     

Corticotropin-Releasing Factor Stimulates Catecholamine Release in Hypothalamus and Prefrontal Cortex in Freely Moving Rats as Assessed by Microdialysis

Abstract: In vivo microdialysis was used to measure changes in extracellular concentrations of catecholamines and indoleamines in freely moving rats in response to administration of corticotropin-releasing factor (CRF). Dialysis probes were placed stereotaxically in either the medial hypothalamus or the medial prefrontal cortex. We used a repeated-measures design in which each rat received artificial CSF or one dose of CRF 3–4 h apart, and each subject was retested with the same treatments in the reverse order 5–7 days later. With the dialysis probe in the hypothalamus, intracerebroventricular administration of CRF (17 or 330 pmol) dose-dependently increased dialysate concentrations of norepinephrine (NE), dopamine (DA), and all their measurable catabolites except normetanephrine. The effects on NE were substantially greater than those on DA. Dialysate concentrations of serotonin could not be measured reliably, but those of its catabolite, 5-hydroxyindoleacetic acid, were also elevated. Concentrations of NE and DA were elevated within the first one or two (20 min) collection periods, with a peak response at ∼ 1–2 h. Dialysate concentrations of catecholamines and metabolites normally returned to baseline within 3 h. Similar data were obtained with dialysis probes in the medial prefrontal cortex after intracerebroventricular administration of 17 or 167 pmol of CRF, except that the increases in DA exceeded those of NE in this region. Intraperitoneal administration of CRF (1 nmol) similarly elevated dialysate concentrations of NE, DA, 5-hydroxyindoleacetic acid, and all catecholamine catabolites except normetanephrine in both medial hypothalamus and medial prefrontal cortex. These results support earlier neurochemical data suggesting that CRF administered both centrally and peripherally stimulates the release of both DA and NE in the brain.     

Effect of morphine on hypothalamic corticotropin-releasing factor (CRF) and pituitary-adrenocortical activity

The effects of intraperitoneal and intra-third ventricular administration of morphine on the hypothalamic corticotropin-releasing factor (CRF) and the pituitary-adrenocortical activity were examined in unanesthetized, freely moving rats. Hypothalamic CRF was measured by rat CRF radioimmunoassay. Intraperitoneal or intra-third ventricular administration of morphine increased blood concentrations of ACTH and corticosterone while intraperitoneal administration tended to increase CRF concentration in the whole hypothalamus including the median eminence and intra-third ventricular administration increased CRF concentration in the hypothalamus excluding the median eminence. However, morphine seemed to inhibit the increase in CRF concentration in the hypothalamus induced by the ether-laparotomy stress. The main site of morphine action on the hypothalamo-pituitary-adrenocortical system seemed to be in the hypothalamic area.     

Hypothalamic and pituitary effects of prostaglandins on ACTH secretion

Various prostaglandins (PGs) were tested for their effects on ACTH secretion upon injection into the anterior pituitary, basomedial hypothalamus, basolateral hypothalamus, or a tail vein in anesthetized female rats. In some experiments, the PGs were injected in combination with a CRF preparation. The greatest effect seen was the stimulation of ACTH (and presumably CRF) secretion exerted at the basomedial hypothalamus. At the anterior pituitary, the PGs alone were without effect, but they did decrease the magnitude of the response to subsequent CRF.     

Immunohistochemical study on the development of CRF-containing neurons in the hypothalamus of the rat

Summary Appearance of immunoreactive corticotropin-releasing factor (CRF)-containing neurons was studied in developing hypothalamus of the rat by use of antisera against rat- and ovine CRF. These neurons were first recognized in the lateral and paraventricular nuclei on days 15.5 and 16.5 of gestation, respectively, when antiserum against rat CRF was employed. Antiserum against ovine CRF revealed the cells two days later exclusively in the latter nucleus. In both nuclei, the neurons increased in number with development. The neurons in the paraventricular nucleus appeared to project their immunoreactive processes to the median eminence via the periventricular and lateral pathways. In the median eminence, the immunoreaction with antiserum to rat CRF was first recognized in its anterior portion in the form of dots on day 16.5 of gestation but as beaded fibers in the external layer on day 17.5; these structures increased in amount with development in rostro-caudal direction. Although antiserum to ovine CRF was less potent in immunostainability than antiserum to rat CRF, it also revealed the beaded fibers in the median eminence on day 17.5 of gestation. Since evidence is available that the paraventricular nucleus is involved in corticotropin release, it is concluded that, in rats, the hypothalamic regulatory mechanism controlling the release of corticotropin initially appears on days 16.5–17.5 of gestation.     

Acute effects of acephate and methamidophos and interleukin-1 on corticotropin-releasing factor (CRF) synthesis in and release from the hypothalamus in vitro

Acute effects of Ace, Meth and IL-1 on AChE activity, ACh and CRF mRNA levels in, and CRF-release from the hypothalamus were studied in vitro. The hypothalamus samples were dissected from the rat brain and were incubated in vitro with IL-1, Ace or Meth in the presence or absence of Dex, Atrop, PTL, PROP and GABA. Ace and Meth, but not IL-1, inhibited AChE activity, while all three compounds; (1) increased ACh and CRF mRNA levels in and CRF release from; (2) activated the CRE promoter region of CRF-gene in: and (3) increased cFos binding to the AP-1 region of the CRF-gene in the hypothalamus. Dex suppressed the effects of IL-1, possibly by inducing the nGRE regulatory sites of the CRF-gene. Dex, however, did not modulate the effects of Ace and Meth on the hypothalamus, which may be attributed to the failure of Dex to modulate the CRF-gene's nGRE regulatory sites. Atrop caused 80-90% inhibition of the effects of IL-1, but caused only 50-65% inhibition of the effects of Ace or Meth on CRF mRNA levels in and CRF release from the hypothalamus. PTL did not affect, while PROP slightly attenuated the effects of IL-1 and the insecticides on the hypothalamus. GABA attenuated the effects of the insecticides but not the effects of IL-1 on the hypothalamus. This suggests that the IL-1-induced augmentation of CRF synthesis in and release from the hypothalamus is mediated through a cholinergic pathway, while the insecticide-induced augmentation of CRF synthesis in and release from the hypothalamus is mediated through the cholinergic and GABAergic pathways. The insecticides, but not IL-1, disrupt feedback regulation of CRF synthesis in and release from the hypothalamus.     

Hypothalamic and pituitary effects of prostaglandins on ACTH secretion.

Various prostaglandins (PGs) were tested for their effects on ACTH secretion upon injection into the anterior pituitary, basomedial hypothalamus, basolateral hypothalamus, or a tail vein in anesthetized female rats. In some experiments, the PGs were injected in combination with a CRF preparation. The greatest effect seen was the stimulation of ACTH (and presumably CRF) secretion exerted at the basomedial hypothalamus. At the anterior pituitary, the PGs alone were without effect, but they did decrease the magnitude of the response to subsequent CRF.     

The Carboxyl-Terminus of Human Immunodeficiency Virus Type 2 Circulating Recombinant form 01_AB Capsid Protein Affects Sensitivity to Human TRIM5α

Human immunodeficiency virus (HIV) type 2 shows limited geographical distribution compared with HIV type 1. Although 8 genetic groups of HIV type 2 (HIV-2) have been described, recombinant viruses between these groups are rarely observed. Recently, three HIV-2 patients in Japan were described with rapidly progressive, acquired immunodeficiency. These patients were infected with an A/B inter-group recombinant designated CRF01_AB. Here, we characterize the capsid protein (CA) encoded by the viruses from these patients. HIV-2 CRF01_AB CA showed unique amino acid sequence almost equally distinct from group A and group B viruses. Notably, HIV-2 CRF01_AB CA showed potent resistance to human TRIM5α. In addition to the previously identified amino acid position 119 in the N-terminal domain of CA, we found that HIV-2 CRF01_AB-specific amino acid substitutions in the C-terminal domain also were necessary for resistance to human TRIM5α. These results indicate that retroviruses can evade TRIM5α by substitution at residues within the C-terminal domain of CA.     

The corticotropin releasing factor (CRF) neurosecretory system in intact, adrenalectomized, and adrenalectomized-dexamethasone treated rats. An immunocytochemical analysis

In general, antisera generated against ovine CFR do not reveal immunopositive neuronal perikarya in the rat. If animals are adrenalectomized significant amounts of immunoreactive CFR are present in the hypothalamus. By using this model, we have visualized the CFR system of the rat. Intact, intact pretreated with dexamethasone, adrenalectomized, and adrenalectomized pretreated with dexamethasone animals were used in the present study. In adrenalectomized and adrenalectomized plus dexamethasone treated animals the CFR-immunopositive neurons were observed in the parvocellular portion of the paraventricular nucleus. Distinct pathways of CRF fibers could be seen emerging from this hypothalamic nucleus. The greatest number of these fibers exited the PVN laterally and crossed either superior to or beneath the fibers of the fornix. The fibers then turned ventrally and cascaded to form a bundle of fibers above the superio-lateral margin of the optic chiasm. They turned caudally and followed the optic tract. As these fibers reached the level of the anterior median eminence, they turned medially to run along the inferior margin of the hypothalamus and enter the median eminence. A few fibers emerged from the PVN along the periventricular margin of the third ventricle, traveled caudally in the periventricular nucleus and entered the median eminence. Adrenalectomized and adrenalectomized-dexamethasone treated rats had very dense accumulations of immunoreactive CRF in the median eminence when compared with controls. Immunoreactive neurons and fibers were also observed in the central nucleus of the amygdala in the adrenalectomized and adrenalectomized-dexamethasone treated animals.     

A specific radioimmunoassay for Cortricotropin Releasing Factor (CRF) using synthetic ovine CRF

This newly developed specific radioimmunoassay for corticotropin releasing factor (CRF) had a sensitivity range of 25 pg/tube to 4 ng/tube. Intra and interassay coefficient of variation were 4.6% and 9.8%, respectively. Rat median eminence extracts showed a parallel dose response curve with synthetic ovine CRF and a significant cross reaction was not evident with other tested neuropeptides. The highest mean levels of CRF were found in the median eminence (6.61 ng/mg protein). Considerable amounts of CRF were found in the arcuate nucleus, paraventricular nucleus, dorsomedial nucleus, suprachiasmatic nucleus and ventromedial nucleus. The immunoreactive CRF of the rat medial basal hypothalamus coeluted with bioassayable CRF and with iodinated CRF on Sephadex G-75 chromatography. The results indicate that rat hypothalamus contains a CRF similar to ovine CRF.     

Differential profile of CRF receptor distribution in the rat stomach and duodenum assessed by newly developed CRF receptor antibodies

Peripheral corticotropin-releasing factor (CRF) receptor ligands inhibit gastric acid secretion and emptying while stimulating gastric mucosal blood flow in rats. Endogenous CRF ligands are expressed in the upper gastrointestinal (GI) tissues pointing to local expression of CRF receptors. We mapped the distribution of CRF receptor type 1 (CRF1) and 2 (CRF2) in the rat upper GI. Polyclonal antisera directed against the C-terminus of the CRF receptor protein were generated in rabbits and characterized by western blotting and immunofluorescence using CRF1- and CRF2-transfected cell lines and in primary cultured neurons from rat brain cortex. A selective anti-CRF1 antiserum (4467a-CRF1) was identified and used in parallel with another antiserum recognizing both CRF1 and CRF2 (4392a-CRF1&2) to immunostain gastric tissue sections. Antiserum 4467a-CRF1 demonstrated specific immunostaining in a narrow zone in the upper oxyntic gland within the stomach corpus. Conversely, 4392a-CRF1&2 labeled cells throughout the oxyntic gland and submucosal blood vessels. Pre-absorption with the specific antigen peptide blocked immunostaining in all experiments. Doublestaining showed co-localization of 4392a-CRF1&2 but not 4467a-CRF1 immunoreactivity with H/K-ATPase and somatostatin immunostaining in parietal and endocrine cells of the oxyntic gland. No specific staining was observed in the antrum with either antisera, whereas only antiserum 4392a-CRF1&2 showed modest immunoreactivity in the duodenal mucosa. Finally, co-localization of CRF2 and urocortin immunoreactivity was found in the gastric glands. These results indicate that both CRF receptor subtypes are expressed in the rat upper GI tissues with a distinct pattern and regional differences suggesting differential function.     

Possible role of CRF peptides in burn-induced hypermetabolism

Hypermetabolism and anorexia are significant problems associated with major burn trauma. Recent studies have shown that hypothalamic corticotropin releasing factor (CRF) elevates metabolic rate, while neuropeptide Y (NPY) reduces it. CRF also elicits anorexia, while NPY stimulates feeding. We hypothesized that elevation of CRF and decrease of NPY may be mediators of these negative effects of burn trauma. Therefore, we assessed concentrations of CRF and NPY in hypothalamus of burned rats one, three, and twenty-one days after a 30% body surface area, full-thickness, open flame burn. In addition we determined whether a biochemical lesion of CRF receptors using 3rd ventricle injections of a saporin-CRF conjugated peptide would decrease resting energy expenditure (REE). We found a three-day period of anorexia, with REE significantly increasing three days after the burn trauma. Concentrations of NPY were increased in the PVN-containing dorsomedial region of the hypothalamus 1 and 3 days after burn trauma, but were increased further in the day 1 pair-fed rats suggesting this change was a consequence of the anorexia. Levels of CRF were decreased in the ventromedial region of the hypothalamus in day 1 and day 3 burned and PF rats. Treatment with the saporin-CRF conjugate normalized REE and reduced CRF receptor-2 density in the hypothalamus of burned rats, and blocked CRF-induced hypermetabolism in sham-burned rats. Although these results suggest a role of CRF receptors in mediating burn-induced hypermetabolism, CRF itself may not be the principle ligand, as suggested by the significant elevation of hypothalamic urocortin 15 days after burn injury.     

Effects of chlordiazepoxide on footshock- and corticotropin-releasing factor-induced increases in cortical and hypothalamic norepinephrine secretion in rats

Noradrenergic and corticotropin-releasing factor (CRF) neuronal systems within the brain have been implicated in stress and anxiety. Synaptic release of cerebral norepinephrine (NE) is increased during stress, and following intracerebral CRF administration. Benzodiazepines are commonly used anxiolytic drugs but information on their effects on the stress- and CRF-related release of NE is limited. We have used in vivo microdialysis to test the effects of the benzodiazepine, chlordiazepoxide (CDP) on the noradrenergic responses to footshock and intracerebroventricular CRF in the medial hypothalamus and the medial prefrontal cortex (PFM) of freely moving rats. Footshock (60 x 0.1-0.2 mA shocks in 20 min) significantly increased microdialysate concentrations of NE in the first sample collected after initiating the footshock. In the hypothalamus, microdialysate NE was augmented 64% above baseline. A second footshock session (100 min after the first footshock) increased microdialysate NE to 313% of the baseline. Thus the noradrenergic responses to footshock were enhanced by preceding footshocks. CRF (100 ng) administered into the locus coeruleus (LC) almost tripled microdialysate concentrations of NE in the PFM. CDP (5mg/kg, i.p.) had no statistically significant effects on the basal dialysate concentrations of NE, but it significantly attenuated both footshock- and CRF-induced increases in dialysate NE. CDP may exert a direct inhibitory effect on the noradrenergic neurons, alter the input to LC noradrenergic neurons, or alter the ability of CRF to activate the LC noradrenergic system.     

Corticotropin-releasing factor release from in vitro superfused and incubated rat hypothalamus. Effect of potassium, norepinephrine, and dopamine

We have compared the release of CRF induced by potassium depolarization, noradrenaline or dopamine as monitored either during superfusion of mediobasal hypothalamus or during incubation of whole hypothalamus. The superfusion device was improved in order to prevent gas leakage and to keep constant pO2 and pCO2 in the superfusion chamber. Basal CRF secretion as well as KCl- and norepinephrine-induced CRF release were comparable in superfusion and incubation experiments. Pharmacological investigations suggest that the stimulatory effect of norepinephrine on CRF release is mediated mainly through alpha 1 and alpha 2 adrenergic receptors, and partially through beta receptors.     

Ontogenetic development of corticotropin-releasing factor (CRF)-containing neural elements in the brain of the chicken during incubation and after hatching

Summary In chicken embryos of different ages and in young chickens after hatching, neural elements reacting with antibodies generated against synthetic ovine corticotropin-releasing factor (CRF) were studied by means of the peroxidase-anti-peroxidase (PAP) technique at the lightmicroscopic level. CRF-immunoreactivity was first observed in perikarya located in the periventricular part of the hypothalamus on the 14th day of the incubation period. CRF-containing neural elements were detected on the same day of incubation in the external zone of the median eminence, but not in all investigated animals. In extrahypothalamic sites, immunoreactive perikarya were demonstrable in the central gray of the mesencephalon on the 15th day of incubation. Furthermore, immunoreactive cells appeared in other brain regions such as nucleus accumbens and dorsomedial nucleus of the thalamus after hatching. The present observations provide information regarding the functional development of the hypothalamo-hypophyseal-adrenal axis in the chick embryo.