An integrative approach method reveals the presence of a previously unreported species of Imparfinis Eigenmann and Norris 1900 (Siluriformes: Heptapteridae) in Argentina

Specimens of Imparfinis were recently collected in north-western Argentina from the Bermejo River basin (Salta and Jujuy Provinces), del Valle River (Salta Province) and Horcones River (Santiago del Estero Province). An integrative approach to taxonomy, combining a detailed morphological study and molecular phylogenetic analyses, was applied to determine the species identity of these specimens. A principal components analysis of morphological data clustered the specimens from north-western Argentina and from the Amazon basin, indicating a close morphological resemblance. Also, a molecular phylogenetic analysis showed populations of I. guttatus from Argentina and Peru forming a clade. According to the conducted haplotype network analysis these populations are distinct in two mutations. Thus, in the absence of morphological or molecular data indicating the contrary, the combined method supports the identity of the specimens from the tributaries of the Paraguay River in Argentina as I. guttatus, whose type locality is in the upper Beni River basin in Bolivia. This contribution is also the first record for this species from Argentina. The disjunct distribution of I. guttatus provides new evidence reinforcing the hypothesis for the origin of the Paraguayan ichthyofauna. We also provide an approach to the phylogenetic relationships of Imparfinis in Heptapteridae.

Redefinition of Heptapterus (Heptapteridae) and description of Heptapterus carmelitanorum, a new species from the upper Paraná River basin in Brazil

A new diagnosis and a new classification of Heptapterus are provided and a new species, H. carmelitanorum, is described. Heptapterus is diagnosed by the following character combination: adipose fin confluent with the caudal fin; non-bifurcate caudal fin; anal-fin insertion posterior to vertical through adipose-fin insertion; 10–23 anal-fin rays; anal fin not confluent with caudal fin; and extremely elongate body, with a head length of 16.1–24.9%SL. Species included in Heptapterus are H. borodini, H. carmelitanorum, H. carnatus, H. exilis, H. hollandi, H. mandimbusu, H. mbya, H. mustelinus, H. ornaticeps, and H. qenqo. Some of the character states diagnosing H. carmelitanorum among its congeners are the anal-fin insertion less than one eye diameter posterior to a vertical through the adipose-fin insertion (vs. more than one eye diameter in all congeners); the isognathous mouth (vs. slightly to moderately retrognathous, except H. borodini); and the keel formed by ventral procurrent caudal-fin rays shallow, far from reaching anal-fin base (vs. keel formed by ventral procurrent caudal-fin rays deep, continuing almost to the anal-fin base, except in H. borodini and H. hollandi).

Genetic assimilation and the evolution of direction of genital asymmetry in anablepid fishes

Phylogenetic comparative studies suggest that the direction of deviation from bilateral symmetry (sidedness) might evolve through genetic assimilation; however, the changes in sidedness inheritance remain largely unknown. We investigated the evolution of genital asymmetry in fish of the family Anablepidae, in which males' intromittent organ (the gonopodium, a modified anal fin) bends asymmetrically to the left or the right. In most species, males show a 1 : 1 ratio of left-to-right-sided gonopodia. However, we found that in three species left-sided males are significantly more abundant than right-sided ones. We mapped sidedness onto a new molecular phylogeny, finding that this left-sided bias likely evolved independently three times. Our breeding experiment in a species with an excess of left-sided males showed that sires produced more left-sided offspring independently of their own sidedness. We propose that sidedness might be inherited as a threshold trait, with different thresholds across species. This resolves the apparent paradox that, while there is evidence for the evolution of sidedness, commonly there is a lack of support for its heritability and no response to artificial selection. Focusing on the heritability of the left : right ratio of offspring, rather than on individual sidedness, is key for understanding how the direction of asymmetry becomes genetically assimilated.

The direction of genital asymmetry is expressed stochastically in internally fertilizing anablepid fishes

Animal genitalia vary considerably across taxa, with divergence in many morphological traits, including striking departures from symmetry. Different mechanisms have been proposed to explain this diversity, mostly assuming that at least some of the phenotypic variation is heritable. However, heritability of the direction of genital asymmetry has been rarely determined. Anablepidae are internally fertilizing fish where the anal fin of males has been modified into an intromittent organ that transfers sperm into the gonopore of females. Males of anablepid fishes exhibit asymmetric genitalia, and both left- and right-sided individuals are commonly found at similar proportions within populations (i.e. antisymmetry). Although this polymorphism was described over a century ago, there have been no attempts to determine if genital asymmetry has a genetic basis and whether the different morphs are accumulating genetic differences, as might be expected since in some species females have also asymmetric gonopores and thereby can only be fertilized by compatible asymmetric males. We address this issue by combining breeding experiments with genome-wide data (ddRAD markers) in representative species of the two anablepid genera with asymmetric genitalia: Anableps and Jenynsia. Breeding experiments showed that all offspring were asymmetric, but their morphotype (i.e. right- or left-sided) was independent of parental morphotype, implying that the direction of asymmetry does not have a strong genetic component. Consistent with this conclusion, association analyses based on approximately 25 000 SNPs did not identify markers significantly associated with the direction of genital asymmetry and there was no evidence of population structure between left- and right-sided individuals. These results suggest that the direction of genital asymmetry in anablepid fishes might be stochastic, a commonly observed pattern in species with antisymmetry in morphological traits.

Molecular and morphological convergence to sulfide-tolerant fishes in a new species of Jenynsia (Cyprinodontiformes: Anablepidae), the first extremophile member of the family

Freshwater sulfide springs have extreme environmental conditions that only few vertebrate species can tolerate. These species often develop a series of morphological and molecular adaptations to cope with the challenges of life under the toxic and hypoxic conditions of sulfide springs. In this paper, we described a new fish species of the genus Jenynsia, Anablepidae, from a sulfide spring in Northwestern Argentina, the first in the family known from such extreme environment. Jenynsia sulfurica n. sp. is diagnosable by the lack of scales on the pre-pelvic area or the presence of a single row of scales, continuous or not, from the isthmus to the bases of the pelvic fins. Additionally, it presents a series of morphological and molecular characteristics that appear convergent with those seen in other fish species (e.g., Poeciliids) inhabiting sulfide springs. Most notably, J. sulfurica has an enlarged head and postorbital area compared to other fish of the genus and a prognathous lower jaw with a hypertrophied lip, thought to facilitate respiration at the air-water interface. Analyses of cox1 sequence showed that J. sulfurica has two unique mutations resulting in amino acid substitutions convergent to those seen in Poeciliids from sulfide springs and known to provide a physiological mechanism related to living in sulfide environments. A phylogenetic analysis, including molecular and morphological characters, placed J. sulfurica as sister taxa to J. alternimaculata, a species found in nearby, non-sulfide habitats directly connected to the sulfide springs. Thus, it can be inferred that the selection imposed by the presence of H2S has resulted in the divergence between these two species and has potentially served as a barrier to gene flow.

Asymmetry in genitalia is in sync with lateralized mating behavior but not with the lateralization of other behaviors

Asymmetries in bilateral organisms attract a lot of curiosity given that they are conspicuous departures from the norm. They allow the investigation of the integration at different levels of biological organization. Here we study whether and how behavioral and asymmetrical anatomical traits co-evolved and work together. We ask if asymmetry is determined locally for each trait or at a whole individual level in a species bearing conspicuous asymmetrical genitalia. Asymmetric genitalia evolved in many species; however, in most cases the direction of asymmetry is fixed. Therefore, it has been rarely determined if there is an association between the direction of asymmetry in genitalia and other traits. In onesided livebearer fish of the genus Jenynsia (Cyprinodontiformes, Anablepidae), the anal fin of males is modified into a gonopodium, an intromittent organ that serves to inseminate females. The gonopodium shows a conspicuous asymmetry, with its tip bending either to the left or the right. By surveying 13 natural populations of Jenynsia lineata, we found that both genital morphs are equally common in wild populations. In a series of experiments in a laboratory population, we discovered asymmetry and lateralization for multiple other traits; yet, the degree of integration varied highly among them. Lateralization in exploratory behavior in response to different stimuli was not associated with genital morphology. Interestingly, the direction of genital asymmetry was positively correlated with sidedness of mating preference and the number of neuromasts in the lateral line. This suggests integration of functionally linked asymmetric traits; however, there is no evidence that asymmetry is determined at the whole individual level in our study species.

Description of a new species of the Neotropical cichlid genus Gymnogeophagus Miranda Ribeiro, 1918 (Teleostei: Cichliformes) from the Middle Paraná basin, Misiones, Argentina

Gymnogeophagus jaryi, new species, is described from Southern tributaries of the Middle Paraná basin in Misiones. It can be distinguished from all other members of the genus, except from G. australis and G. caaguazuensis, by the presence of a hyaline to grey anterior portion of the dorsal fin. Gymnogeophagus jaryi differs from G. caaguazuensis by a longer caudal peduncle, caudal fin not lyrate, central portion of scales on dorsal portion of trunk light iridescent blue and by white spots in soft portion of dorsal fin in adult males, and from G. australis by the light iridescent blue coloration of central portion of scales on the dorsal portion of trunk and tail, and by the lack of scales on the soft portion of the dorsal fin. Additionally, it can be diagnosed by the following unique combination of characters: 10-11 dorsal-fin branched rays, 27-30 E1 scales, absence of lips thickening, and, in males, by the possession of a hump in adults, caudal fin not lyrate, presence of large white spots forming transversal stripes distally and in anterior area of the dorsal fin's soft portion, central area of scales on the dorsal portion of the trunk light iridescent blue, lack of scales on the base of the dorsal fin's soft portion, absence of a conspicuous and oblique dark band from the eye to the anterior border of the head, anterior portion of dorsal fin hyaline to grey, scales of the midlateral spot each bearing a semicircular light blue blotch, head hump starting at the horizontal through the eyes, concave anterior profile in lateral view, base of unpaired fins yellow, and whitish hyaline spots on caudal fin. The new species, based on mtDNA phylogeny, is the sister species of G. caaguazuensis from the Paraguay basin and is closely related to G. australis.

A new species of Farlowella (Siluriformes: Loricariidae) from the upper Bermejo River, La Plata River basin, northwestern Argentina

ABSTRACT A new species of Farlowella is described from the Bermejo River basin, in Salta and Jujuy provinces, northwestern Argentina. The new species belongs to the Farlowella nattereri species group. The new species is diagnosed by the following combination of characters: marbled rostrum, five rows of lateral plates series, relatively short snout (snout-mouth length less than 50.0% of head length), complete half-moon shaped spot on caudal fin, and short predorsal distance (37.8-41.8% of standard length).

First record of Steindachnerina insculpta (Fernández-Yépez, 1948) (Characiformes, Curimatidae) in Argentina

Recent expeditions to northwestern Argentina revealed the presence of an unknown species of Curimatidae for the Bermejo river basin. The morphometric and meristic analyses of these specimens allow us to identify them as Steindachnerina insculpta (Fernández-Yépez, 1948), which is here reported for the first time in Argentina

Living in the waterfalls: A new species of Trichomycterus (Siluriformes: Trichomycteridae) from Tabay stream, Misiones, Argentina

A new species assigned to the genus Trichomycterus from the area of the waterfalls of Tabay stream, Paraná River basin, Misiones, Argentina, is described. Trichomycterus ytororo sp. nov. is distinguished from all other species in the genus by the presence of 31–35 dorsal procurrent caudal-fin rays and the combination of some external characters such as: coloration, number of pectoral–fin rays and pores of the laterosensory canals. The new taxon belongs to a presumably monophyletic group of species composed of T. crassicaudatus, T. igobi, and T. stawiarski based on the presence of 24 or more thickly ossified and rigid procurrent caudal-fin rays with a slender distal tip extending along the tips of at least ten neural spines.

Range extension of Hypostomus cochliodon Kner, 1854 (Siluriformes: Loricariidae) in Bermejo River, Salta, Argentina

Hypostomus cochliodon Kner, 1854 had been recorded from Paraguay and Paraná rivers in Argentina. We recorded for the first time specimens of H. cochliodon to the Bermejo River basin. It is also the first record of this species to Salta province, Argentina.

¿Qué factores determinan la distribución altitudinal de los peces de ríos tropicales andinos?

Altitudinal gradients represent an appropriate system to assess whether there is a relationship between richness patterns, environmental variables, and the ecological processes that determine the species type and number inhabiting a given area. In mountain streams freshwater fishes, the most prevalent relationship is a monotonic decrease in species richness with elevation. The objective of this study was to evaluate four hypotheses that can explain the negative relationship between local fish species richness and altitude, 1) the hypothesis of decreasing energy availability, 2) the hypothesis of increasing climate severity, 3) the hypothesis of habitat diversity, and 4) the hypothesis of isolation by physical severity of the environment. Fish and macro-invertebrates were collected following standard methods from 83 sites (between 200-4 000 meters) of two river basins in the Bolivian Amazon. The first hypothesis was tested by analyzing relationships between the density of macro-invertebrates, the richness of invertivorous fish species and altitude; while the second and third hypotheses were assessed by a multiple regression analysis (GLM) between fish species richness and several local and regional factors. Besides, assemblage dissimilarity between sites along the altitudinal gradient was analyzed using βsim and βness indices. Fish richness decreases linearly with increasing altitude. The density of macro-invertebrates tends to increase at higher altitudes, contrary to invertivorous fish species richness, suggesting that energy availability is not a limiting factor for fish species colonization. The GLM explained 86 % of the variation in fish species richness, with a significant contribution of water temperature, maximum slope in the river mainstem, and stream width. There is a higher species turnover (βsim) between sites at low elevation. Inversely, βness shows higher values in the upper parts, corresponding to change in assemblages mainly due to species loss. Taken together, these results suggest that climatic and physical severities create strong barriers to colonization, further explaining the decrease in fish richness along the altitudinal gradient.

First record of the banjo catfish Bunocephalus doriae Boulenger 1902 (Siluriformes: Aspredinidae) in the Bermejo River basin, Salta, Argentina

Intense sampling in the upper Bermejo River basin revealed the presence of specimens of the aspredinid genus Bunocephalus. After detailed morphological and morphometric analyses specimens were identified as Bunocephalus doriae. This is the first record of any member of the Aspredinidae in the upper Bermejo River basin.

[[Which factors determine the altitudinal distribution of tropical Andean riverine fishes]?]

Altitudinal gradients represent an appropriate system to assess whether there is a relationship between richness patterns, environmental variables, and the ecological processes that determine the species type and number inhabiting a given area. In mountain streams freshwater fishes, the most prevalent relationship is a monotonic decrease in species richness with elevation. The objective of this study was to evaluate four hypotheses that can explain the negative relationship between local fish species richness and altitude, 1) the hypothesis of decreasing energy availability, 2) the hypothesis of increasing climate severity, 3) the hypothesis of habitat diversity, and 4) the hypothesis of isolation by physical severity of the environment. Fish and macro-invertebrates were collected following standard methods from 83 sites (between 200-4 000 meters) of two river basins in the Bolivian Amazon. The first hypothesis was tested by analyzing relationships between the density of macro-invertebrates, the richness of invertivorous fish species and altitude; while the second and third hypotheses were assessed by a multiple regression analysis (GLM) between fish species richness and several local and regional factors. Besides, assemblage dissimilarity between sites along the altitudinal gradient was analyzed using βsim and βness indices. Fish richness decreases linearly with increasing altitude. The density of macro-invertebrates tends to increase at higher altitudes, contrary to invertivorous fish species richness, suggesting that energy availability is not a limiting factor for fish species colonization. The GLM explained 86 % of the variation in fish species richness, with a significant contribution of water temperature, maximum slope in the river mainstem, and stream width. There is a higher species turnover (βsim) between sites at low elevation. Inversely, βness shows higher values in the upper parts, corresponding to change in assemblages mainly due to species loss. Taken together, these results suggest that climatic and physical severities create strong barriers to colonization, further explaining the decrease in fish richness along the altitudinal gradient.

First record of Pimelodella mucosa Eigenmann & Ward, 1907 (Siluriformes: Heptapteridae) in Formosa, Argentina and comments on the geographical distribution of P. howesi Fowler, 1940

The examination of the specimens re­cord­ed as Pimelodella howesi in Argentina reveals a misidentification that allow us to confirm the presence of Pimelodella mucosa for first time in the country.

Jenynsia luxata, a new species from Northwestern Argentina, with additional observations of J. maculataRegan and phylogeny of the genus (Cyprinodontiformes: Anablepidae)

Jenynsia luxata, a new species from northwestern Argentina, is described. This species is diagnosable from all other Jenynsia by the medial processes of left and right pelvic bones relatively reduced and separated from each other. The new species resembles J. multidentata, but it is further distinguished from this species by the absence of a swelling between the urogenital opening and the anterior base of the anal fin in females and details of coloration. Phylogenetic analyses, both under implied and equal weighting, recover the subgenera Plesiojenynsia and Jenynsia as monophyletic units. New information on previously missing characters of Jenynsia maculata is added. These data and phylogenetic characters coded for the new species herein described contribute to a better resolution of the phylogenetic relationships within the subgenus Jenynsia, which is herein supported by additional synapomorphies relative to previous phylogenies.

Temporal effect of adrenocorticotrophic hormone on adrenal glucocorticoid steroidogenesis: involvement of the transducer of regulated cyclic AMP-response element-binding protein activity

The availability of active steroidogenic acute regulatory protein (StAR) and side-chain cleavage cytochrome P450 (P450scc) are rate-limiting steps for steroidogenesis. Transcription of StAR and P450scc genes depends on cyclic AMP-response element-binding protein (CREB) phosphorylation and CREB co-activator, transducer of regulated CREB activity (TORC), which is regulated by salt-inducible kinase 1 (SIK1). In the present study, we investigated the relationship between TORC activation and adrenocorticotrophic hormone (ACTH)-induced steroidogenesis in vivo, by examining the time-course of the effect of ACTH injection (4 ng, i.v.) on the transcriptional activity of StAR and P450scc genes and the nuclear accumulation of transducer of regulated CREB activity 2 (TORC2) in rat adrenal cortex. ACTH produced rapid and transient increases in plasma corticosterone, with maximal responses between 5 and 15 min, and a decrease to almost basal values at 30 min. StAR and P450scc hnRNA levels increased 15 min following ACTH and decreased toward basal values at 30 min. Concomitant with an increase in nuclear phospho-CREB, ACTH injection induced nuclear accumulation of TORC2, with maximal levels at 5 min and a return to basal values by 30 min. The decline of nuclear TORC2 was paralleled by increases in SIK1 hnRNA and mRNA 15 and 30 min after injection, respectively. The early rises in plasma corticosterone preceding StAR and P450scc gene transcription suggest that post-transcriptional and post-translational changes in StAR protein mediate the early steroidogenic responses. Furthermore, the direct temporal relationship between nuclear accumulation of TORC2 and the increase in transcription of steroidogenic proteins, implicates TORC2 in the physiological regulation of steroidogenesis in the adrenal cortex. The delayed induction of SIK1 suggests a role for SIK1 in the declining phase of steroidogenesis.

A new species of Heptapterus Bleeker 1858 (Siluriformes, Heptapteridae) from the Río Salí basin, north-western Argentina

A revision of fish specimens previously identified as Heptapterus mustelinus from the endorheic Río Salí Basin, Tucumán, Argentina, reveals that they present several morphological differences from that species. This paper describes Heptapterus qenqo sp. nov. from the Río Salí Basin. The new species is diagnosed by a combination of the following characters: presence of small serrae on the anterior proximal margin of the first pectoral-fin ray; anal-fin rays iv-v, 11-13 (15-17 total anal-fin rays); adipose-fin base 40·9-47·4% standard length; small eyes (7·4-14·2% head length); adipose-fin confluent to caudal fin and maxillary barbel not reaching pectoral-fin base in adults, and reaching or scarcely surpassing the first pectoral-fin ray in small juveniles.

Vasopressin protects hippocampal neurones in culture against nutrient deprivation or glutamate-induced apoptosis

Vasopressin (VP) secreted within the brain modulates neuronal function by acting as a neurotransmitter. Recent studies show that VP prevents serum deprivation-induced apoptosis in the neuronal cell line, H32. To determine whether VP is anti-apoptotic in hippocampal neurones, primary cultures of these neurones were used to examine the effect of VP on neuronal culture supplement (B27) deprivation-, or glutamate-induced apoptosis, and the signalling pathways mediating the effects. Removal of B27 supplement from the culture medium for 24 h or the addition of glutamate (3-10μm) decreased neuronal viability (P<0.05) and increased Tdt-mediated dUTP nick-end labelling (TUNEL) staining and caspase-3 activity (P<0.05), which is consistent with apoptotic cell death. VP (10 nm) reduced B27 deprivation- or glutamate-induced cell death (P<0.05). These anti-apoptotic effects of VP were completely blocked by a V1 but not a V2 receptor antagonist, indicating that they are mediated via V1 VP receptors. The anti-apoptotic effect of VP in neurones involves activation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and inositol trisphosphate/protein kinase B (Akt) signalling pathways. This was shown by the transient increases in phospho-ERK and phospho-Akt after incubation with VP revealed by western blot analyses, and the ability of specific inhibitors to reduce the inhibitory effect of VP on caspase-3 activity and TUNEL staining by 70% and 35%, respectively (P<0.05). These studies demonstrate that VP has anti-apoptotic actions in hippocampal neurones, an effect that is mediated by the MAPK/ERK and phosphatidylinositol-3 kinase/Akt signalling pathways. The ability of VP to reduce nutrient deprivation or glutamate overstimulation-induced neuronal death suggests that VP acts as a neuroprotective agent within the brain.

House-level risk factors for triatomine infestation in Colombia

BACKGROUND

Chagas disease, transmitted domestically by triatomine bugs, is the most important vector-borne disease in Latin America. The association between triatomine infestation and housing characteristics was investigated based on a standardized survey in 41 971 houses in 15 Departments in Colombia.

METHODS

Multivariate logistic regression was used to test for associations of two highly correlated infestation measures of infestation (householders reporting having seen triatomines inside the house, and sending triatomines to the survey team), with 15 household-level risk factors. Risks were measured relative to a reference category of houses with up to three inhabitants, area up to 50 m(2), unplastered adobe walls, thatch roof and no outbuildings or domestic animals.

RESULTS

The probability of seeing triatomines was highest for households with over seven inhabitants (OR = 1.24, 95% CI 1.11-1.39), overhead storage space (OR = 1.16, 95% CI 1.03-1.32), grain shed (OR = 1.25, 95% CI 1.02-1.52), cats (OR = 1.27, 95% CI 1.14-1.42) and pigs (OR = 1.16, 95% CI 1.03-1.30). Lowest risks were in houses with wooden walls (OR = 0.46, 95% CI 0.34-0.61), fully plastered walls (OR = 0.78, 95% CI 0.68-0.88), roofs made of tiles (OR = 0.51, 95% CI 0.33-0.78) and flagstone floors (OR = 0.57, 95% CI 0.42-0.76). Results for householders returning triatomines support this set of risk factors, but with wider confidence intervals.

CONCLUSIONS

Surveillance of a few easily assessed household characteristics provides an accurate, rapid assessment of house-level variation in risk. Measured effect sizes for specific structural characteristics could be used to maximize the cost-effectiveness of programmes to reduce vector infestation and interrupt Chagas disease transmission by improving house quality.

Inhibition of vasopressin V1b receptor translation by upstream open reading frames in the 5'-untranslated region

The 5'-UTR of the vasopressin V1b receptor (V1bR) mRNA contains small open reading frames (ORF) located upstream (u) of the main ORF encoding the V1bR. The ability of the three proximal uORFs to be translated into peptides and their influence on V1bR translation was examined using fusion constructs of uORFs and V5 epitope, or ATG/ATA uORF mutations in the V1bR cDNA. In vitro translation and western blot analysis after transfection of uORF1-V5 or uORF2-V5 into cells revealed that uORF1 can be translated. As predicted by computer analysis, in vitro translation using a rabbit reticulocyte/canine microsome system, immunohistochemistry and western blot in membranes of transfected cells with uORF1-V5 revealed translocation of the uORF1 peptide into membrane fractions. In vitro translation of V1bR cDNA with mutations of the two uORFs proximal to the initiating methionine, uORFs 1 and 2 (Mut 1-2), or uORF2 (Mut 2) showed significantly increased translation of a 46 kDa band corresponding to the V1bR, compared with wild-type (WT) V1bR, an effect that was attenuated by cotranslation of uORF1-V5. Consistently, VP-induced inositol phosphate formation was higher in Chinese hamster ovay cells transfected with Mut 1-2 than with WT V1bR. Immunohistochemical and western blot analysis, using an antibody against uORF1, revealed peptide immunoreactivity in rat pituitary but not in liver. Pituitary uORF immunoreactivity increased following glucocorticoid administration. The present study shows that uORFs in the 5'-UTR of the V1bR mRNA inhibit V1bR translation, and suggests that translation of a 38-amino acid membrane peptide encoded by uORF1 exerts tonic inhibition of V1bR translation.

Interaction between oestrogen and oxytocin on hypothalamic-pituitary-adrenal axis activity

In addition to its role in reproduction, oxytocin has central actions modulating behavioural and hypothalamic-pituitary-adrenal (HPA) axis responses during late pregnancy and lactation. The hypothesis that ovarian hormones modulate the effects of oxytocin on HPA axis activity was studied in 7-day ovariectomised rats receiving oestradiol with or without progesterone replacement and intracerebroventricular (i.c.v) minipump infusion of oxytocin (100 ng/h). In an initial experiment, i.c.v. oxytocin had no effect on basal or restraint-stimulated plasma adrenocorticotrophic hormone (ACTH) and corticosterone concentrations or hypothalamic corticotrophin-releasing factor (CRF) mRNA expression with low oestradiol replacement alone but it had a stimulatory effect in the presence of low oestradiol and progesterone. To investigate further whether oestradiol modulates central actions of oxytocin, rats received low dioestrous (low), pro-oestrous (medium) or pregnancy (high) oestradiol replacement levels, yielding plasma concentrations of < 5, 17.3 +/- 4.5 and 258 +/- 32 pg/ml, respectively, with or without i.c.v. oxytocin. Oestradiol caused dose-dependent increases in basal plasma ACTH and corticosterone concentrations but decreased the ACTH response to restraint stress. In parallel to the changes in basal plasma ACTH, high oestrogen increased basal CRF hnRNA, CRF mRNA in the paraventricular nucleus and pro-opiomelanocortin (POMC) mRNA in the pituitary gland, while decreasing restraint stress-stimulated levels. Intracerebroventricular administration of oxytocin reduced basal and stress-stimulated plasma ACTH, hypothalamic CRF hnRNA (30 min), CRF mRNA and pituitary POMC mRNA (4 h) levels parallel to the increases induced by elevating plasma oestradiol. The present study demonstrates the converse effects of oestradiol on basal and restraint stress-stimulated basal HPA axis activity, and that the ability of central oxytocin to inhibit HPA axis activity depends on the levels of circulating oestradiol.

Inhibition of corticotrophin-releasing hormone transcription by inducible cAMP-early repressor in the hypothalamic cell line, 4B

We have shown recently that the rapid decline in corticotrophin-releasing hormone (CRH) transcription following activation by stress is associated with induction and binding to the CRH promoter of the repressor isoforms of cAMP responsive element modulator (CREM), inducible cAMP early repressor (ICER). The ability of ICER to inhibit CRH transcription was examined in the hypothalamic cell line, 4B, which expresses CRH. Co-transfection of the inhibitory isoforms of CREM, ICER I and II and CREMbeta, and CRH promoter-luciferase constructs in 4B cells blunted basal and forskolin-stimulated CRH promoter activity, an effect which was abolished by mutation of the CRE of the CRH promoter. Western blot analyses and electromobility gel-shift and super-shift showed increases in endogenous ICER after 3 h of incubation with forskolin. Consistent with an inhibitory effect of CREM on CRH transcription, chromatin immunoprecipitation assays in cells transfected with ICER I revealed recruitment of CREM by the CRH promoter in conjunction with decreases in Pol II association. The study shows that generation of ICER following prolonged stimulation with forskolin, or transfection of an ICER expression vector in hypothalamic cell lines expressing CRH, is associated with CREM binding to the CRH promoter and transcriptional repression. The data support the hypothesis that induction of repressor isoforms of CREM is part of an intracellular feedback mechanism contributing to the termination of CRH transcription during stimulation.

Regulation of pituitary corticotropin releasing factor type-1 receptor mRNA binding proteins by modulation of the hypothalamic-pituitary-adrenal axis

Long-term adrenalectomy (ADX) is associated with marked down-regulation of pituitary corticotropin releasing factor type-1 receptors (CRF-R1) but normal CRF-R1 mRNA levels, suggesting that regulation of receptor levels occurs at post-transcriptional sites. We have reported that adrenal cytosolic proteins, which bind to cis elements in the 5' leader sequence (5'LS) of the rat angiotensin II type 1a receptor (AT(1a)R) mRNA, participate in the regulation of AT(1a)R density by inhibiting AT(1a)R mRNA translation. In this study, we examined anterior pituitary cytosolic proteins that form RNA protein complexes (RPC) with the 5'LS of the CRF-R1 and the AT(1a)R. Competition studies and ultraviolet-crosslinking analysis suggest that formation of CRF-R1 and AT(1a)R 5'LS RPC require at least some proteins that are common to both receptor mRNAs. Pituitaries isolated from male Sprague-Dawley rats six days after ADX showed significant (P < 0.05) increases of 2.9-fold in CRF-R1 5'LS RNA binding protein (BP) activity compared to pituitaries from sham-operated rats; this effect of ADX was prevented by glucocorticoid replacement. By contrast, no differences in the number of pituitary AT(1a)R binding sites or pituitary AT(1a)R 5'LS BP activity were observed between sham and ADX rats, indicating that the effect of ADX on RPC formation was specific for CRF-R1 mRNA. Addition of pituitary cytosolic extracts inhibited in vitro translation of CRF-R1 mRNA by 79% under conditions that had no significant effects on the translation of a control mRNA. The data suggest that CRF-R1 translation is regulated by modulation of the HPA axis through pituitary cytosolic proteins binding to the CRF-R1 5'LS.

In vitro regulation of corticotropin-releasing hormone

Studies involving regulation of corticotropin-releasing hormone (CRH) in vitro have been used to validate findings obtained in vivo and more importantly have been used as model systems to better understand signalling mechanisms responsible for the expression of the CRH gene and peptide. Many in vitro studies examining CRH have utilized hypothalamic tissue while a few have focused on the amygdala. Clonal cell lines have also been utilized as models of central nervous system CRH neurons. Stimuli that have been implicated in regulating hypothalamic CRH regulation in vitro include protein kinase A (PKA) and protein kinase C (PKC) activators, glucocorticoids, biogenic amines, cytokines and the gaseous neurotransmitters. Amygdalar CRH levels in vitro are affected by some of the same stimuli that regulate hypothalamic CRH; however there is evidence supporting differential regulation of CRH in these two brain regions by some of the same stimuli. Only a few studies in aggregate have investigated signal transduction mechanisms and these studies have focused on PKA- and glucocorticoid-mediated changes in CRH expression. Thus, much more investigative work in better understanding CRH regulation in vitro is needed.

Single administration of interleukin-1 increased corticotropin releasing hormone and corticotropin releasing hormone-receptor mRNA in the hypothalamic paraventricular nucleus which paralleled long-lasting (weeks) sensitization to emotional stressors

Single exposure to the proinflammatory cytokine interleukin-1 induces sensitization of the adrenocorticotropin hormone and corticosterone responses to stressors weeks later (hypothalamus-pituitary-adrenal sensitization). Hypothalamus-pituitary-adrenal responses are controlled by corticotropin-releasing hormone and arginine-vasopressin secreted from parvocellular corticotropin-releasing hormone neurons of the hypothalamic paraventricular nucleus and may involve autoexcitatory feedback mechanisms. Therefore, we studied the temporal relationship between resting levels of corticotropin-releasing hormone, corticotropin-releasing hormone-R1 and arginine-vasopressin receptor (V1a, V1b) mRNAs in the paraventricular nucleus and the development of hypothalamus-pituitary-adrenal sensitization to an emotional stressor (novelty). The adrenocorticotropin hormone precursor molecule proopiomelanocortin hnRNA in the pituitary gland served as an index for acute activation. Single administration of interleukin-1 induced sensitization of the hypothalamus-pituitary-adrenal to novelty from 3 to 22 days later, but not after 42 days. Single administration of interleukin-1 induced biphasic increases in corticotropin-releasing hormone and corticotropin-releasing hormone-R1 mRNAs in the paraventricular nucleus: an early peak within 24 h, followed by a delayed (>7 days) increase that peaked after 22 days. Hypothalamic V1a and V1b mRNA levels were unaffected. In contrast, in the pituitary gland, there was an early decrease in corticotropin-releasing hormone-R1 mRNA (from 10.5 to 3 h after interleukin-1) and V1b receptor mRNA (3 to 6 h), which returned to control levels from 24 h onwards. Thus, interleukin-1-induced long-lasting hypothalamus-pituitary-adrenal sensitizations associated with prolonged activation of corticotropin-releasing hormone and corticotropin-releasing hormone-R1 mRNA expression in the paraventricular nucleus, but not with changes in the expression of proopiomelanocortin hnRNA or V1b receptor or corticotropin-releasing hormone R1 mRNAs in the pituitary gland. We propose that transient exposure to immune events can induce long-lasting hypothalamus-pituitary-adrenal sensitization, which at least in part involves long-term hypothalamic adaptations that enhance central corticotropin-releasing hormone signaling.

Corticotropin-releasing hormone (CRH) expression and protein kinase A mediated CRH receptor signalling in an immortalized hypothalamic cell line

Corticotropin-releasing hormone (CRH) is a 41 amino acid neuropeptide which plays an important role in the stress response in the hypothalamus. We describe the development of an immortalized hypothalamic cell line which expresses CRH. We hypothesized that this cell line would possess the relevant characteristics of parvocellular CRH-expressing neurones such as glucocorticoid receptor (GR) expression and vasopressin (VP) coexpression. For production of hypothalamic cells, embryonic day 19 rat pup hypothalami were dissected and dissociated into tissue culture dishes. They were immortalized by retrovirus-mediated transfer of the SV40 large T antigen gene at 3 days of culture and then screened for expression of CRH following dilution cloning. One cell line was chosen (IVB) which exhibited CRH-like immunoreactivity (CRH-LI) and expressed CRH, VP and CRH1 receptor RNA via the reverse transcriptase-polymerase chain reaction. In addition, the cell line expressed the neuronal marker, microtubule-associated protein-2. We verified that the CRH-LI from IVB cell lysates coeluted with CRH standard via reversed-phase high-performance liquid chromatography (HPLC). Furthermore, oxidation of the lysate converted its HPLC profile to that identical with oxidized CRH standard. In addition, IVB cells exhibited high affinity binding to CRH. Incubation of IVB cells with CRH lead to increases in cAMP levels and protein kinase A activity in a concentration-dependent manner. Incubation of IVB cells with CRH also resulted in increases in phospho-cyclic-AMP response element binding protein (CREB) immunostaining as detected by immunocytochemical analysis. Finally, CRH treatment of IVB cell lines has been linked to CREB-mediated gene expression as determined via the PathDetect CREB trans-reporting system. The characteristics of IVB cells, such as CRH and VP coexpression, GR expression and a biologically active CRH-R1-mediated signalling pathway, suggest that this neuronal cell line may serve as model of parvocellular CRH neurones.

Transcriptional and post-transcriptional mechanisms regulating the rat pituitary vasopressin V1b receptor gene

The number of V1b vasopressin receptors (V1bR) in the anterior pituitary plays an important role during adaptation of the hypothalamic-pituitary-adrenal axis to stress in rats. Regulation of V1bR expression involves transcriptional and translational mechanisms. One of the elements mediating transcriptional activation of the rat V1bR gene is a long stretch of GAGA repeats (GAGA box) in the promoter located near the transcription start point capable of binding a protein complex of 127 kDa present in pituitary nuclear extracts. There is a lack of correlation between changes in V1bR mRNA and the number of VP binding sites, suggesting that V1bR expression depends on the efficiency of V1b R mRNA translation into protein. Two mechanisms by which the 5' untranslated region (5'-UTR) of the rat V1bR mRNA can mediate either inhibition or activation of V1bR mRNA translation have been identified. First, upstream open reading frames (ORF) present in the 5'-UTR repress translation of the major ORF encoding the V1b receptor, and secondly, an internal ribosome entry site (IRES) activates V1bR translation. Stimulation of IRES activity through protein kinase C-mediated pathways results in V1bR mRNA translation increasing V1bR protein levels. The existence of multiple loci of regulation for the V1bR at transcriptional and translational levels provides a mechanism to facilitate plasticity of regulation of the number of pituitary vasopressin receptors according to physiological demand.

Lipopolysaccharide endotoxin potentiates the effect of osmotic stimulation on vasopressin synthesis and secretion in the rat hypothalamus

Vasopressin secreted by magnocellular neurones of the hypothalamic supraoptic and paraventricular nuclei is essential for water balance. In this study, we examined magnocellular neurone responses to osmotic stimulation in vehicle-injected controls or rats receiving an intraperitoneal (i.p.) injection of 250 microg/100 g of lipopolysaccharide (LPS), 3 h or 6 h earlier. LPS injection had no effect on plasma vasopressin concentrations in control rats but it caused marked and transient potentiation of the responses to a single i.p. injection of hypertonic saline (five- and two-fold, 3 and 6 h after LPS, respectively). The enhancement of plasma vasopressin responses was independent of plasma sodium concentrations or changes in blood pressure. Basal vasopressin mRNA expression in the paraventricular and supraoptic nuclei decreased slightly 6 h after LPS injection, without changes in vasopressin transcription as indicated by vasopressin heteronuclear (hn) RNA levels. Parvocellular neurones showed expected increases in vasopressin hnRNA expression following LPS injection and a further increase after i.p. hypertonic saline injection (due to the painful component). In contrast to magnocellular vasopressin mRNA expression, the effects of LPS and hypertonic saline injections in parvocellular neurones were additive and not synergistic. Light microscopic immunohistochemical examination revealed an increase in size of vasopressin but not oxytocin axonal terminals in the neural lobe 3 h after LPS injection. Osmotic stimulation caused marked depletion of vasopressin immunoreactivity in axonal terminals of the neural lobe in both control and LPS-pretreated rats. The changes in vasopressin axon terminals were accompanied by induction of interleukin (IL)-1 beta and IL-6 in the posterior pituitary. The data show that endotoxemia causes morphological and functional alterations of the hypothalamic neurohypophyseal system, resulting in facilitation rather than inhibition of vasopressin synthesis, and secretion in response to osmotic stimulation.

A novel approach using transcomplementing adenoviral vectors for gene therapy of adrenocortical cancer

Current therapies for adrenocortical carcinomas do not improve the life expectancy of patients. In this study, we tested whether a gene-transfer therapy based upon a suicide gene/prodrug system would be effective in an animal model of the disease. We employed E4- and E1A/B-depleted, herpes simplex virus-thymidine kinase-expressing adenoviral mutants that transcomplement each other within tumor cells, hereby improving transgene delivery and efficacy by viral replication in situ. Transcomplementation of vectors increased the fraction of transduced of tumor cells. This increase was accompanied by greater tumor volume reduction compared to non-transcomplementing approaches. Survival time improved with non-replicating vectors plus GCV compared to controls. However, transcomplementation/replication of vectors led to a further significant increment in anti-tumor activity and survival time (p < 0.02). In treated animals, we observed a high number of apoptotic nuclei both adjacent to and distant from injection sites and sites of viral oncolysis. Ultrastructural analyses exhibited nuclear inclusion bodies characteristic of virus production in situ, and provided further evidence that this therapy induced apoptotic cell death within tumor cells. We conclude that the efficacy of suicide gene therapy is significantly amplified by viral replication and, in combination with GCV, significantly reduces tumor burden and increases survival time.

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.

Phlebotomine sandflies and leishmaniasis risks in Colombian coffee plantations under two systems of cultivation

The phlebotomine sandfly fauna of traditional (shaded) and intensified (unshaded) coffee plantations in Colombia was sampled by a variety of methods and the species composition and density under the two systems compared. Twenty species of Lutzomyia sandflies (Diptera: Psychodidae: Phlebotominae) were collected, of which eight were found only in the 'Coffee Axis' ('Eje Cafetero') of the departments of Caldas, Risaralda and Quindio, six were exclusive to the department of Norte de Santander and six occurred in both regions. Four species were collected only in traditional plantations and two exclusively in intensified ones. At least 13 species occurred in both plantation types. Fifteen species are opportunistic man-biters and eight are suspected vectors of leishmaniasis caused by Le. braziliensis, Le. panamensis or Le. mexicana. Seven species were collected inside houses and may be involved in intradomiciliary transmission of Leishmania. The dominant species in Norte de Santander was Lu. spinicrassa, which made up 93.8% of all the sandflies collected in this department. This species was absent from the Eje Cafetero and a number of others among the 15 recorded there might be responsible for Leishmania transmission in this region, including Lu. trapidoi, Lu. yuilli, Lu. gomezi, L. hartmanni and Lu. ovallesi. Sandfly population densities were significantly higher in traditional plantations than in intensified ones. Residents of traditional plantations were able to describe sandflies in significantly more detail than those of intensified plantations, based on seven basic characteristics related to the appearance and biting behaviour of the insects.

Direct stimulation of arginine vasopressin gene transcription by cAMP in parvocellular neurons of the paraventricular nucleus in organotypic cultures

The regulation of arginine vasopressin (AVP) gene transcription in the paraventricular nucleus (PVN) was studied in rat hypothalamic organotypic cultures using intronic in situ hybridization. While AVP heteronuclear (hn) RNA was not detected in the PVN under basal conditions, a marked induction of AVP hnRNA was observed after 2 and 3 h incubation of slices with forskolin. In contrast to the stimulatory effects of forskolin, phorbol 12-myristate 13-acetate (PMA) was completely ineffective in inducing AVP hnRNA in the PVN at any time examined (1-3 h). Forskolin-induced AVP hnRNA expression was unaffected by blockage of neurotransmission by the sodium channel inhibitor, tetrodotoxin, indicating that forskolin acts directly on AVP cells in the PVN. Dual staining in situ hybridization of forskolin-stimulated hypothalamic sections using both radio labeled AVP hnRNA and digoxigenin-labeled CRH mRNA probes revealed colocalization of both transcripts, indicating AVP hnRNA is expressed in the parvocellular neurons. The data demonstrate that cAMP directly activates AVP gene transcription in parvocellular neurons of the PVN.

Hypothalamic pituitary adrenal axis and hypothalamic-neurohypophyseal responsiveness in water-deprived rats

The differential effects of osmotic stimulation on magnocellular and parvocellular hypothalamic neurons were studied by analysis of corticotropin-releasing hormone (CRH) and vasopressin (VP) expression in controls and 48-h water-deprived rats subjected to either restraint for 1 h or a single lipopolysaccharide injection (250 microg/100 g). Water deprivation reduced basal CRH mRNA levels but the increments following 4 h of restraint or 6 h lipopolysaccharide (LPS) injection were similar to those in controls. In contrast, water deprivation had no effect on basal VP heteronuclear RNA (hnRNA) and mRNA levels in parvocellular neurons, but responses to restraint or LPS injection were reduced. VP expression in magnocellular paraventricular and supraoptic nuclei, and plasma sodium and vasopressin were higher in water-deprived rats, changes which were unaffected by restraint. LPS injection reduced VP mRNA but not hnRNA levels in magnocellular neurons and increased plasma vasopressin levels only in water-deprived rats independently of changes in plasma sodium. This was accompanied by an increase in vasopressin mRNA content in the posterior pituitary. The data show that the blunted ACTH responses to acute stress during chronic osmotic stimulation are correlated with the inability of parvocellular neurons to increase VP rather than CRH expression. In addition, LPS-induced endotoxemia causes disturbances of the magnocellular vasopressinergic system with an unexpected potentiation of osmotic simulated VP secretion. The lack of increase in VP transcription after LPS and changes in VP mRNA distribution suggest that endotoxemia affect the secretory process at the levels of the neurohypophyseal axon terminal.

Regulation of corticotropin-releasing hormone (CRH) transcription and CRH mRNA stability by glucocorticoids

1. The increases in corticotropin-releasing hormone (CRH) mRNA following long-term adrenalectomy are associated with low levels of CRH gene transcription, suggesting that glucocorticoids regulate CRH mRNA at the posttranscriptional level. In this study we determined the time course of transcriptional activation after early adrenalectomy by intronic in situ hybridization, and evaluated the effects of glucocorticoids on CRH mRNA stability. 2. Plasma corticosterone was undetectable 3 h after adrenalectomy, but CRH hnRNA increased only by 12 h, and remained elevated for the next 72 h. CRH mRNA increased 18 h after adrenalectomy and reached a plateau lasting from 2 to 6 days, despite very low CRH hnRNA levels. 3. Assessment of CRH mRNA stability, by incubation of slide-mounted hypothalamic sections in an intracellular-like medium at 37 degrees C, prior to measuring CRH mRNA levels by in situ hybridization, revealed a half-life (t1/2) of 11.5 min in sham-operated rats, and a slower decrease adrenalectomized rats (t1/2--26.3 min). Corticosterone administration for 3 days markedly decreased CRH mRNA t1/2 in both sham-operated and adrenalectomized rats (6.5 and 5.0 min, respectively). 4. The data show that adrenalectomy causes transient increases in CRH mRNA transcription, followed by decreases in the rate of CRH mRNA degradation. This suggests that glucocorticoids regulate CRH mRNA at two sites, by inhibiting transcription and by decreasing mRNA stability.

Effect of repeated lipopolysaccharide administration on tissue cytokine expression and hypothalamic-pituitary-adrenal axis activity in rats

The effects of chronic immune challenge on cytokine expression and hypothalamic-pituitary-adrenal axis (HPA) axis responses to stress were studied in Wistar rats after administration of increasing doses of lipopolysaccharide (LPS). Repeated LPS (R-LPS) decreased body weight and increased adrenal weight and pituitary pro-opiomelanocortin mRNA levels. LPS injection increased plasma adrenocorticotropic hormone (ACTH) and corticosterone but the effect was attenuated in R-LPS. Plasma corticosterone but not ACTH responses to restraint were also reduced in R-LPS. Basal and restraint-stimulated corticotropin releasing hormone (CRH) mRNA levels were lower in R-LPS, but responses to a new LPS injection were similar to controls. In contrast, type 1 CRH receptor (CRH-R1) mRNA responses to both LPS and restraint were blunted in R-LPS. Vasopressin mRNA levels in parvocellular neurones were higher in R-LPS, and increased further after restraint but not after a new LPS injection. Glucocorticoid receptor (GR) levels in the paraventricular nucleus (PVN) increased after a single LPS or R-LPS (24 h after the last injection) but declined after a new injection in R-LPS. Interleukin (IL)-1beta and IL-6 mRNAs increased in the pituitary, spleen and circumventricular organs after single or R-LPS, suggesting that cytokines may contribute to the activation of the HPA axis though pathways from the circumventricular organs as well as paracrine effects in the pituitary. The data show that (i) adaptation of the HPA axis during repeated LPS injection involves increases in vasopressin : CRH expression ratios in parvocellular neurones; (ii) that hypothalamic CRH and vasopressin responses to acute stimulation are independent of CRH-R1 expression in the PVN; and (iii) there is a dissociation between pituitary and adrenal responses to acute stress suggesting a decrease of adrenal sensitivity to ACTH.

Hypothalamic and amygdaloid corticotropin-releasing hormone (CRH) and CRH receptor-1 mRNA expression in the stress-hyporesponsive late pregnant and early lactating rat

This study investigated the expression of corticotropin releasing hormone (CRH) and its receptor CRHR-1, and arginine vasopressin (AVP) mRNAs during the stress hyporesponsive periods of late pregnancy and lactation (day-3) and in virgin stress-responsive females. In situ hybridization histochemistry showed that basal CRH mRNA in the paraventricular nucleus (PVN) decreased in pregnant and increased in lactating rats (compared with virgin controls), whereas it increased after restraint stress only in virgin rats. Basal PVN CRHR-1 mRNA increased markedly in all groups but reached lower levels in pregnant rats. Basal AVP mRNA in the parvocellular PVN was higher in lactating rats, and in contrast to CRH mRNA, it increased after stress in all groups. In medial preoptic area (MPOA) CRH mRNA levels were higher in lactating females compared with virgin and pregnant rats, and unexpectedly they decreased markedly after stress only in virgin rats. CRH mRNA levels in the central and medial nuclei of the amygdala were higher in lactating rats than in virgin or pregnant ones, and stress had no effect in either group. These data suggest that these stress hyporesponsive periods: (1) do not depend on basal CRH mRNA expression in the PVN; (2) appear to have intact stress-activated afferent pathways to the PVN, as shown by preservation of CRHR-1 and AVP responses to stress, but the information may be differently processed; (3) are associated with an alteration in a CRH mediated pathway from the MPOA.

Regulation of pituitary corticotropin releasing hormone receptors

Corticotropin releasing hormone (CRH) stimulates pituitary ACTH secretion through type-1 CRH (CRH1) receptors. Stimulation of the hypothalamic pituitary adrenal (HPA) axis as well as increased corticotroph responsiveness during stress and adrenalectomy are associated with marked pituitary CRH binding downregulation. The presence of CRH1 receptors in the pituitary are essential to maintain ACTH secretion. Downregulation of CRH binding is associated with normal or elevated levels of CRH1 receptor mRNA and this may contribute to the maintainence of permissive levels of CRH1 receptors in the pituitary. Injection of either CRH or glucocorticoids in rats in vivo induces CRH binding and CRH1 receptor mRNA downregulation, whereas their simultaneous administration causes only transient CRH1 receptor mRNA loss. Vasopressin increases CRH1 receptor mRNA levels. This suggest that interactions between CRH, vasopressin and glucocorticoids accounts for CRH1 receptor mRNA upregulation during stress. The lack of correlation between CRH binding and CRH1 receptor mRNA indicates that the major sites for pituitary CRH1 receptor regulation are at the post-transcriptional level.

Inhibition of corticotropin releasing hormone type-1 receptor translation by an upstream AUG triplet in the 5' untranslated region

The influence of an upstream open reading frame (ORF) in the 5'-untranslated region (UTR) of the mRNA on corticotropin-releasing hormone receptor type 1 (CRHR1) translation was studied in constructs containing the 5'-UTR of CRHR1, with or without an ATG-to-ATA mutation in the upstream ORF, and the main ORF of luciferase or CRHR1. Upstream mutation in luciferase constructs increased luciferase activity when transfected into COS-7 or AtT20 cells compared with the native 5'-UTR. Transfection of CRHR1 constructs containing the upstream mutation into AtT20 or LVIP2.0zc reporter cells, resulted in higher (125)I-Tyr-oCRH binding and corticotropin-releasing hormone-stimulated cAMP production, without changes in CRHR1 mRNA levels (measured by RNase protection assay). In vitro translation of luciferase or CRHR constructs with or without mutation of the upstream ATG, and Western blot analysis with anti-luciferase and anti-CRHR1 antibodies confirmed that mutation of the upstream ATG increases translation of the main ORF. The mechanism by which the upstream ORF inhibits translation may involve translation of the upstream peptide, because in vitro translation, or transfection into LVIP2.0zc cells of a fusion construct of the upstream ORF and green fluorescent protein (GFP) yielded a band consistent with the molecular size of GFP protein. The study shows that the upstream AUG in 5'-UTR of CRHR1 mRNA inhibits receptor expression by inhibiting mRNA translation and suggests the short open reading frame in the 5'-UTR plays a role in regulating translation of the CRH receptor.

Vasopressinergic regulation of the hypothalamic-pituitary-adrenal axis: implications for stress adaptation

In addition to its role on water conservation, vasopressin (VP) regulates pituitary ACTH secretion by potentiating the stimulatory effects of corticotropin releasing hormone (CRH). The pituitary actions of VP are mediated by plasma membrane receptors of the V1b subtype, coupled to calcium-phospholipid signaling systems. VP is critical for adaptation of the hypothalamic-pituitary-adrenal (HPA) axis to stress as indicated by preferential expression of VP over CRH in parvocellular neurons of the hypothalamic paraventricular nucleus, and the upregulation of pituitary VP receptors during stress paradigms associated with corticotroph hyperresponsiveness. V1b receptor mRNA levels and coupling of the receptor to phospolipase C are stimulated by glucocorticoids, effects which may contribute to the refractoriness of VP-stimulated ACTH secretion to glucocorticoid feedback. The data suggest that vasopressinergic regulation of the HPA axis is critical for sustaining corticotroph responsiveness in the presence of high circulating glucocorticoid levels during chronic stress.

Role of alpha-1-adrenergic receptors in the regulation of corticotropin-releasing hormone mRNA in the paraventricular nucleus of the hypothalamus during stress

1. The role of alpha1-adrenergic receptors on CRH mRNA levels in the PVN was studied in control and stressed rats receiving i.c.v. injections of the alpha1-adrenergic agonist, methoxamine, or the alpha1- antagonist, prazosin. 2. Plasma ACTH increased significantly 60 min and 4 hr after a single injection of methoxamine (100 microg, i.c.v.). No desensitization of this response was observed after repeated injections every 6 hr for 24 hr. Concomitantly, POMC mRNA in the anterior pituitary increased by 25% at 4 hr after a single injection and by 96% after repeated injections. 3. CRH mRNA levels in the PVN increased by 131% after repeated injections for 24 hr, but were unchanged 4 hr after a single injection. Central alpha-adrenergic blockade with prazosin did not prevent the increases in CRH mRNA following 4 hr of acute stress, but significantly reduced the increases observed 24 hr after an i.c.v. injection of 75 microg of colchicine or after repeated i.p. hypertonic saline injections every 8 hr. 4. These studies demonstrate that while alpha1-adrenergic receptors contribute to longterm increases of CRH mRNA levels in the PVN during prolonged stress, other factors are likely to be involved in the stimulation of CRH mRNA following acute stimulation.

Vasopressin and oxytocin neurones of hypothalamic supraoptic and paraventricular nuclei co-express mRNA for Type-1 and Type-2 corticotropin-releasing hormone receptors

The presence of corticotropin-releasing hormone (CRH) receptors type-1 (CRHR-1) and type-2 (CRHR-2alpha) in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei, and the effects of i.c.v. injection of CRH and urocortin on arginine vasopressin (AVP) and oxytocin release, have suggested that CRH ligands have a role in osmoregulation. In this study, double labelling in situ hybridization using 35S-labelled CRHR-1 or CRHR-2alpha and digoxigenin-labelled AVP, oxytocin or CRH riboprobes was employed to examine the localization of CRHR-1 or CRHR-2alpha mRNA in the SON and PVN of control and osmotically stimulated rats. Rats received an i.p. hypertonic saline (1.5 M) injection or isotonic saline injection (controls), or 2% NaCl intake (salt loading) or tap water (controls) for 12 days. While CRHR-1 mRNA was undetectable in the SON and PVN in control rats, its expression was increased markedly at 4 h after i.p. hypertonic saline injection or after 12 days salt loading. Of the cells labelled with digoxigenin-AVP, 53% in the SON and 90% in the PVN coexpressed CRHR-1 mRNA after i.p. hypertonic saline injection. In oxytocinergic neurones, 73% in the SON and 91% in the PVN showed CRHR-1 autoradiographic grains higher than background levels after i.p. hypertonic saline injection. In addition, i.p. hypertonic saline induced CRHR-1 mRNA expression in digoxigenin-CRH stained cells in the parvocellular PVN. CRHR-2alpha transcripts were present in both the SON and PVN under basal conditions, and salt loading, but not acute i.p. hypertonic saline injection, further stimulated this expression. Double labelling in situ hybridization showed colocalization of CRHR-2alpha mRNA with AVP and oxytocin mRNA in the SON. These studies support a role for CRH and urocortin regulating the hypothalamo-neurohypophyseal system, and suggest a direct action of the peptides in the magnocellular neurones.

Isolation and characterization of the promoter region of the rat vasopressin V1b receptor gene

Regulation of pituitary vasopressin V1b receptors plays a critical role in regulating pituitary adrenocorticotropic hormone (ACTH) secretion during adaptation to stress. The objective of this study was to isolate the promoter regulatory region of the V1b receptor gene to better understand the molecular mechanisms involved in V1b receptor regulation. Screening of a rat genomic library using probes directed to the coding region and to the 5'UTR of the rat V1b receptor resulted in the isolation of several clones containing the 5'upstream regions of the V1b receptor cDNA. Sequencing of an 11.2 Kb fragment revealed 8.2 Kb upsteam of the reported cDNA sequence, which contains a putative promoter regulatory region. The 3' end of the clone contained 1472 base pairs corresponding to the recognized cDNA sequence, followed by 1506 bp of unknown sequence located at the end of the sixth transmembrane domain, probably corresponding to an intron, characteristic of these family of receptors. An additional 161 bp intron was found in the 5'UTR, similar to that described in the rat oxytocin receptor gene. 5'RACE and RNase protection analysis mapped two major putative transcription start points at -830 and -861 bp from the starting methionine. Analysis of the putative promoter region showed no indication of a proximal TATA box, but the presence of a CACA box, a GAGA box, several AP-1 and AP-2 sites and a cluster of Sp1 sites upstream of the AP-2 sites. A luciferase construct containing a 2.1-kb of putative promoter, and part of the 5'UTR including the first intron, showed promoter activity when transfected into COS-7, CHO and PC12 cell lines but not in AtT-20 cells. A similar construct without the intron and distal 5'UTR sequence has no promoter activity in the same cell lines. In summary, the V1b receptor gene contains at least 3 exons and 2 introns. The 5'flanking sequence contains several potential sites for transcriptional regulation, and induced luciferace activity only in constructs containing intron 1, suggesting that the latter is important for receptor gene activation. The data provide bases for future analysis of the regulatory elements controlling V1b receptor transcription.

Regulation of vasopressin V1b receptors in the anterior pituitary gland of the rat

Vasopressin secreted by parvocellular neurones of the hypothalamic paraventricular nucleus modulates pituitary adrenocorticotrophic hormone (ACTH) secretion by acting upon vasopressin V1b type receptors in the pituitary corticotroph coupled to phospholipase C. Regulation of V1b receptors contributes to the adaptation of the hypothalamic-pituitary-adrenal (HPA) axis to stress, as evidenced by the correlation between vasopressin receptor number and pituitary ACTH responsiveness. V1b receptor upregulation during chronic stress is associated with elevated circulating glucocorticoids and vasopressin expression in parvocellular neurones, suggesting that these factors control V1b receptor expression. Removal of circulating glucocorticoids by adrenalectomy causes sustained vasopressin receptor downregulation, but reduces V1b receptor mRNA only transiently. The latter effect is not mediated by increased corticotrophin-releasing hormone (CRH) and vasopressin release, since it is not prevented by lesions of the hypothalamic paraventricular nucleus. Adrenalectomy causes sustained V1b receptor loss in Brattleboro rats, which lack hypothalamic vasopressin, suggesting that vasopressin mediates V1b receptor mRNA recovery. Exogenous glucocorticoid administration downregulates pituitary vasopressin binding but increases V1b receptor mRNA and facilitates coupling of the receptor to phospholipase C, effects which may contribute to the refractoriness of vasopressin actions to glucocorticoid feedback. The lack of parallelism between changes in pituitary vasopressin binding and V1b receptor mRNA levels during manipulation of the HPA axis indicates that V1b receptor content depends on post-transcriptional mechanisms rather than steady-state V1b receptor mRNA levels. These studies suggest that interaction between glucocorticoids and vasopressin plays an important role in regulating V1b receptor mRNA expression during alterations of the HPA axis. In addition, the recent characterization of a major part of the V1b receptor gene provides a basis for studying the molecular mechanisms regulating the V1b receptor.