Distribution and genesis of the RFRP-producing neurons in the rat brain: comparison with melanin-concentrating hormone- and hypocretin-containing neurons.

Prepro-RFRP-containing neurons have recently been described in the mammalian brain. These neurons are only found in the tuberal hypothalamus. In this work, we have provided a detailed analysis of the distribution of cells expressing the RFRP mRNA, and found them in seven anatomical structures of the tuberal hypothalamus. No co-expression with melanin-concentrating hormone (MCH) or hypocretin (Hcrt), that are also described in neurons of the tuberal hypothalamus, was observed. Using the BrdU method, we found that all RFRP cell bodies are generated between E13 and E14. Thus, RFRP neurons form a specific cell population with a complex distribution pattern in the tuberal hypothalamus. However, they are generated in one peak. These observations are discussed with data concerning the distribution and genesis of the MCH and Hcrt cell populations that are also distributed in the tuberal hypothalamus.

Visual representation of food in the brain : effects of repeated exposure and gut hormone secretion

The thesis at hand is concerned with the spatio-temporal brain mechanisms of visual food perception as investigated by electrical neuroimaging. Due to the increasing prevalence of obesity and its associated challenges for public health care, there is a need to better understand behavioral and brain processes underlying food perception and food-based decision-making. The first study (Study A) of this thesis was concerned with the role of repeated exposure to visual food cues. In our everyday lives we constantly and repeatedly encounter food and these exposures influence our food choices and preferences. In Study A, we therefore applied electrical neuroimaging analyses of visual evoked potentials to investigate the spatio-temporal brain dynamics linked to the repeated viewing of high- and low-energy food cues (published manuscript: "The role of energetic value in dynamic brain response adaptation during repeated food image viewing" (Lietti et al., 2012)). In this study, we found that repetitions differentially affect behavioral and brain mechanisms when high-energy, as opposed to low-energy foods and non-food control objects, were viewed. The representation of high-energy food remained invariant between initial and repeated exposures indicating that the sight of high-energy dense food induces less behavioral and neural adaptation than the sight of low-energy food and non-food control objects. We discuss this finding in the context of the higher salience (due to greater motivation and higher reward or hedonic valuation) of energy- dense food that likely generates a more mnemonically stable representation. In turn, this more invariant representation of energy-dense food is supposed to (partially) explain why these foods are over-consumed despite of detrimental health consequences. In Study Β we investigated food responsiveness in patients who had undergone Roux-en-Y gastric bypass surgery to overcome excessive obesity. This type of gastric bypass surgery is not only known to alter food appreciation, but also the secretion patterns of adipokines and gut peptides. Study Β aimed at a comprehensive and interdisciplinary investigation of differences along the gut-brain axis in bypass-operated patients as opposed to weight-matched non-operated controls. On the one hand, the spatio-temporal brain dynamics to the visual perception of high- vs. low-energy foods under differing states of motivation towards food intake (i.e. pre- and post-prandial) were assessed and compared between groups. On the other hand, peripheral gut hormone measures were taken in pre- and post-prandial nutrition state and compared between groups. In order to evaluate alterations in the responsiveness along the gut-brain-axis related to gastric bypass surgery, correlations between both measures were compared between both participant groups. The results revealed that Roux-en- Y gastric bypass surgery alters the spatio-temporal brain dynamics to the perception of high- and low-energy food cues, as well as the responsiveness along the gut-brain-axis. The potential role of these response alterations is discussed in relation to previously observed changes in physiological factors and food intake behavior post-Roux-en-Y gastric bypass surgery. By doing so, we highlight potential behavioral, neural and endocrine (i.e. gut hormone) targets for the future development of intervention strategies for deviant eating behavior and obesity. Together, the studies showed that the visual representation of foods in the brain is plastic and that modulations in neural activity are already noted at early stages of visual processing. Different factors of influence such as a repeated exposure, Roux-en-Y gastric bypass surgery, motivation (nutrition state), as well as the energy density of the visually perceived food were identified. En raison de la prévalence croissante de l'obésité et du défi que cela représente en matière de santé publique, une meilleure compréhension des processus comportementaux et cérébraux liés à la nourriture sont nécessaires. En particulier, cette thèse se concentre sur l'investigation des mécanismes cérébraux spatio-temporels liés à la perception visuelle de la nourriture. Nous sommes quotidiennement et répétitivement exposés à des images de nourriture. Ces expositions répétées influencent nos choix, ainsi que nos préférences alimentaires. La première étude (Study A) de cette thèse investigue donc l'impact de ces exposition répétée à des stimuli visuels de nourriture. En particulier, nous avons comparé la dynamique spatio-temporelle de l'activité cérébrale induite par une exposition répétée à des images de nourriture de haute densité et de basse densité énergétique. (Manuscrit publié: "The role of energetic value in dynamic brain response adaptation during repeated food image viewing" (Lietti et al., 2012)). Dans cette étude, nous avons pu constater qu'une exposition répétée à des images représentant de la nourriture de haute densité énergétique, par opposition à de la nourriture de basse densité énergétique, affecte les mécanismes comportementaux et cérébraux de manière différente. En particulier, la représentation neurale des images de nourriture de haute densité énergétique est similaire lors de l'exposition initiale que lors de l'exposition répétée. Ceci indique que la perception d'images de nourriture de haute densité énergétique induit des adaptations comportementales et neurales de moindre ampleur par rapport à la perception d'images de nourriture de basse densité énergétique ou à la perception d'une « catégorie contrôle » d'objets qui ne sont pas de la nourriture. Notre discussion est orientée sur les notions prépondérantes de récompense et de motivation qui sont associées à la nourriture de haute densité énergétique. Nous suggérons que la nourriture de haute densité énergétique génère une représentation mémorielle plus stable et que ce mécanisme pourrait (partiellement) être sous-jacent au fait que la nourriture de haute densité énergétique soit préférentiellement consommée. Dans la deuxième étude (Study Β) menée au cours de cette thèse, nous nous sommes intéressés aux mécanismes de perception de la nourriture chez des patients ayant subi un bypass gastrique Roux- en-Y, afin de réussir à perdre du poids et améliorer leur santé. Ce type de chirurgie est connu pour altérer la perception de la nourriture et le comportement alimentaire, mais également la sécrétion d'adipokines et de peptides gastriques. Dans une approche interdisciplinaire et globale, cette deuxième étude investigue donc les différences entre les patients opérés et des individus « contrôles » de poids similaire au niveau des interactions entre leur activité cérébrale et les mesures de leurs hormones gastriques. D'un côté, nous avons investigué la dynamique spatio-temporelle cérébrale de la perception visuelle de nourriture de haute et de basse densité énergétique dans deux états physiologiques différent (pre- et post-prandial). Et de l'autre, nous avons également investigué les mesures physiologiques des hormones gastriques. Ensuite, afin d'évaluer les altérations liées à l'intervention chirurgicale au niveau des interactions entre la réponse cérébrale et la sécrétion d'hormone, des corrélations entre ces deux mesures ont été comparées entre les deux groupes. Les résultats révèlent que l'intervention chirurgicale du bypass gastrique Roux-en-Y altère la dynamique spatio-temporelle de la perception visuelle de la nourriture de haute et de basse densité énergétique, ainsi que les interactions entre cette dernière et les mesures périphériques des hormones gastriques. Nous discutons le rôle potentiel de ces altérations en relation avec les modulations des facteurs physiologiques et les changements du comportement alimentaire préalablement déjà démontrés. De cette manière, nous identifions des cibles potentielles pour le développement de stratégies d'intervention future, au niveau comportemental, cérébral et endocrinien (hormones gastriques) en ce qui concerne les déviances du comportement alimentaire, dont l'obésité. Nos deux études réunies démontrent que la représentation visuelle de la nourriture dans le cerveau est plastique et que des modulations de l'activité neurale apparaissent déjà à un stade très précoce des mécanismes de perception visuelle. Différents facteurs d'influence comme une exposition repetee, le bypass gastrique Roux-en-Y, la motivation (état nutritionnel), ainsi que la densité énergétique de la nourriture qui est perçue ont pu être identifiés.

Gonadotropin-releasing hormone secretion from hypothalamic neurons: stimulation by insulin and potentiation by leptin.

Insulin and leptin are peripheral metabolic factors signaling the body needs in energy to the central nervous system. Because energy homeostasis and reproductive function are closely related phenomena, we investigated the respective roles played by insulin and leptin in the hypothalamic control of GnRH secretion. We observed that increasing circulating insulin levels, by performing hyperinsulinemic clamp studies in male mice, was associated with a significant rise in LH secretion. This effect of insulin is likely mediated at the hypothalamic level, because it was also found to stimulate the secretion and the expression of GnRH by hypothalamic neurons in culture. Leptin was found to potentiate the effect of insulin on GnRH secretion in vitro but was devoid of any effect on its own. These data represent the first evidence of direct insulin sensing by hypothalamic neurons involved in activating the neuroendocrine gonadotrope axis. They also demonstrate that these neurons can integrate different hormonal signals to modulate net hypothalamic GnRH output. We propose that such integration is an essential mechanism for the adaptation of reproductive function to changes in the metabolic status of an individual.

The mycobacterial cord factor adjuvant analogue trehalose-6,6'-dibehenate (TDB) activates the Nlrp3 inflammasome.

The success of a vaccine consists in the induction of an innate immune response and subsequent activation of the adaptive immune system. Because antigens are usually not immunogenic, the addition of adjuvants that activate innate immunity is required. The mycobacterial cord factor trehalose-6,6'-dimycolate (TDM) and its synthetic adjuvant analogue trehalose-6,6'-dibehenate (TDB) rely on the C-type lectin Mincle and the signaling molecules Syk and Card9 to trigger innate immunity. In this study, we show that stimulation of bone marrow-derived dendritic cells (BMDCs) with TDB induces Nlrp3 inflammasome-dependent IL-1β secretion. While Card9 is required for NF-κB activation by TDB, it is dispensable for TDB-induced activation of the Nlrp3 inflammasome. Additionally, efflux of intracellular potassium, lysosomal rupture, and oxygen radical (ROS) production are crucial for caspase-1 processing and IL-1β secretion by TDB. In an in vivo inflammation model, we demonstrate that the recruitment of neutrophils by TDB is significantly reduced in the Nlrp3-deficient mice compared to the wild-type mice, while the production of chemokines in vitro is not influenced by the absence of Nlrp3. These results identify the Nlrp3 inflammasome as an essential mediator for the induction of an innate immune response triggered by TDB.

Differential distribution of thyroid hormone receptor isoform in rat dorsal root ganglia and sciatic nerve in vivo and in vitro.

Using autoradiographic techniques carried out under precise conditions we previously demonstrated that both sensory neurons and peripheral glial cells in dorsal root ganglia (DRG) or sciatic nerve, possess specific [125I]-labeled T3 binding sites. Thyroid hormone receptors (TR) include several isoforms (TR alpha(1), TR alpha(2), TR beta(1), TR beta(2...)) The present study demonstrates that while sensory neurons and peripheral glial cells both possess functional TR, they express a differential expression of TR isoforms. Using a panel of antisera to specific for the TR alpha-common (alpha(1) and alpha(2)), TR alpha-1 or TR beta-1 isoforms, we detected TRs isoform localization at the cellular level during DRG and sciatic nerve development and regeneration. Immunohistochemical analysis revealed that during embryonic life, sensory neurons express TR alpha-common and TR beta-1 rather than TR alpha-1. The number of TR alpha-common and TR beta-1 positive neurons as well as the intensity of labeling increased during the first two postnatal weeks and remained more or less stable in adult life. TR alpha-1 immunoreactivity, which was undetectable in embryonic sensory neurons, became discreetly visible in neurons after birth. In developing DRG and sciatic nerves, Schwann cells exhibited TR alpha-common and TR alpha-1 rather than TR beta-1 immunolabeling. The appearance of TR alpha-common and alpha-1 isoform immunoreactivity in the sciatic nerve was restricted to a short period ranging from E17 up to two postnatal weeks. By comparing TR alpha-common and TR alpha-1 immunostaining we can deduce that Schwann cells primarily express TR alpha-1. Afterwards, in adult rat sciatic nerve TR alpha isoforms was no more detected. However transection of sciatic nerve caused a reexpression of TR alpha isoforms in degenerating nerve. The prevalence of TR alpha in Schwann cells in vivo was correlated with in vitro results. The differential expression of TR alpha and beta by sensory neurons and Schwann cells indicates that the feedback regulation of circulating thyroid hormone could occur by binding to either the alpha or beta TR isoforms. Moreover, the presence of multiple receptor isoforms in developing sensory neurons suggests that thyroid hormone uses multiple signaling pathways to regulate DRG and sciatic nerve development.

Mechanisms of the pressor response to intravenous thyrotropin-releasing hormone in the rat.

1. The purpose of this study was to examine the contribution of the sympatho-adrenomedullary system to the blood pressure response to an intravenous bolus of thyrotropin-releasing hormone (TRH) in conscious medullectomized and sham-operated rats. 2. The peak pressor effect of 0.5 mg TRH was significantly increased in rats having no adrenal medulla (+24.2 +/- 1.6 mmHg, mean +/- s.e.m., P < 0.01) as compared to sham-operated animals (+12.2 +/- 3.0 mmHg). 3. Blockade of alpha-adrenergic receptors with phentolamine abolished the pressor effect of TRH in control rats (+2.1 +/- 1.9 mmHg) but did not attenuate the blood pressure response of medullectomized rats (+21.5 +/- 4.7 mmHg). In contrast, beta-blockade with propranolol blunted the blood pressure responsiveness of rats subjected to adrenal medullectomy (+12.4 +/- 2.6 mmHg) but did not modify the effect of TRH in sham-operated controls (+10.9 +/- 2.9 mmHg). 4. The direct in vitro effect of TRH on isolated mesenteric rat arteries was also evaluated. TRH did not induce contractions of isolated arteries. 5. These results suggest that in rats with intact adrenals, the pressor effect of intravenous TRH is mediated primarily by a stimulation of alpha-adrenergic receptors. Adrenal medullectomy appears to enhance the blood pressure response to intravenous TRH. Activation of cardiac beta-adrenoceptors seems to contribute to the blood pressure increasing effect of intravenous TRH in medullectomized animals.

Mechanical properties of rat cardiac skinned fibers are altered by chronic growth hormone hypersecretion.

Chronic growth hormone (GH) hypersecretion in rats leads to increased isometric force without affecting the unloaded shortening velocity of isolated cardiac papillary muscles, despite a marked isomyosin shift toward V3. To determine if alterations occurred at the level of the contractile proteins in rats bearing a GH-secreting tumor (GH rats), we examined the mechanical properties of skinned fibers to eliminate the early steps of the excitation-contraction coupling mechanism. We found that maximal active tension and stiffness at saturating calcium concentrations (pCa 4.5) were markedly higher in GH rats than in control rats (tension, 52.9 +/- 5.2 versus 38.1 +/- 4.6 mN.mm-2, p < 0.05; stiffness, 1,105 +/- 120 versus 685 +/- 88 mN.mm-2.microns-1, p < 0.01), whereas values at low calcium concentrations (pCa 9) were unchanged. In addition, the calcium sensitivity of the contractile proteins was slightly but significantly higher in GH rats than in control rats (delta pCa 0.04, p < 0.001). The crossbridge cycling rate, reflected by the response to quick length changes, was lower in GH rats than in control rats (62.0 +/- 2.6 versus 77.4 +/- 6.6 sec-1, p < 0.05), in good agreement with a decrease in the proportion of alpha-myosin heavy chains in the corresponding papillary muscles (45.5 +/- 2.0% versus 94.6 +/- 2.4%, p < 0.001). The changes in myosin heavy chain protein phenotype were paralleled by similar changes of the corresponding mRNAs, indicating that the latter occurred mainly at a pretranslational level. These results demonstrate that during chronic GH hypersecretion in rats, alterations at the myofibrillar level contribute to the increase in myocardial contractility observed in intact muscle.

A growth hormone-releasing peptide that binds scavenger receptor CD36 and ghrelin receptor up-regulates sterol transporters and cholesterol efflux in macrophages through a peroxisome proliferator-activated receptor gamma-dependent pathway.

Macrophages play a central role in the pathogenesis of atherosclerosis by accumulating cholesterol through increased uptake of oxidized low-density lipoproteins by scavenger receptor CD36, leading to foam cell formation. Here we demonstrate the ability of hexarelin, a GH-releasing peptide, to enhance the expression of ATP-binding cassette A1 and G1 transporters and cholesterol efflux in macrophages. These effects were associated with a transcriptional activation of nuclear receptor peroxisome proliferator-activated receptor (PPAR)gamma in response to binding of hexarelin to CD36 and GH secretagogue-receptor 1a, the receptor for ghrelin. The hormone binding domain was not required to mediate PPARgamma activation by hexarelin, and phosphorylation of PPARgamma was increased in THP-1 macrophages treated with hexarelin, suggesting that the response to hexarelin may involve PPARgamma activation function-1 activity. However, the activation of PPARgamma by hexarelin did not lead to an increase in CD36 expression, as opposed to liver X receptor (LXR)alpha, suggesting a differential regulation of PPARgamma-targeted genes in response to hexarelin. Chromatin immunoprecipitation assays showed that, in contrast to a PPARgamma agonist, the occupancy of the CD36 promoter by PPARgamma was not increased in THP-1 macrophages treated with hexarelin, whereas the LXRalpha promoter was strongly occupied by PPARgamma in the same conditions. Treatment of apolipoprotein E-null mice maintained on a lipid-rich diet with hexarelin resulted in a significant reduction in atherosclerotic lesions, concomitant with an enhanced expression of PPARgamma and LXRalpha target genes in peritoneal macrophages. The response was strongly impaired in PPARgamma(+/-) macrophages, indicating that PPARgamma was required to mediate the effect of hexarelin. These findings provide a novel mechanism by which the beneficial regulation of PPARgamma and cholesterol metabolism in macrophages could be regulated by CD36 and ghrelin receptor downstream effects.

Cooperative binding of estrogen receptor to imperfect estrogen-responsive DNA elements correlates with their synergistic hormone-dependent enhancer activity.

The Xenopus vitellogenin (vit) gene B1 estrogen-inducible enhancer is formed by two closely adjacent 13 bp imperfect palindromic estrogen-responsive elements (EREs), i.e. ERE-2 and ERE-1, having one and two base substitutions respectively, when compared to the perfect palindromic consensus ERE (GGTCANNNTGACC). Gene transfer experiments indicate that these degenerated elements, on their own, have a low or no regulatory capacity at all, but in vivo act together synergistically to confer high receptor- and hormone-dependent transcription activation to the heterologous HSV thymidine kinase promoter. Thus, the DNA region upstream of the vitB1 gene comprising these two imperfect EREs separated by 7 bp, was called the vitB1 estrogen-responsive unit (vitB1 ERU). Using in vitro protein-DNA interaction techniques, we demonstrate that estrogen receptor dimers bind cooperatively to the imperfect EREs of the vitB1 ERU. Binding of a first receptor dimer to the more conserved ERE-2 increases approximately 4- to 8-fold the binding affinity of the receptor to the adjacent less conserved ERE-1. Thus, we suggest that the observed synergistic estrogen-dependent transcription activation conferred by the pair of hormone-responsive DNA elements of the vit B1 ERU is the result of cooperative binding of two estrogen receptor dimers to these two adjacent imperfect EREs.

3-M syndrome associated with growth hormone deficiency: 18 year follow-up of a patient.

3-M syndrome is a rare autosomal recessive disorder that causes short stature, unusual facial features and skeletal abnormalities. Mutations in the CUL7, OBSL1 and CCDC8 genes could be responsible for 3-M syndrome.Here we describe the growth and evolution of dismorphic features of an Italian boy with 3-M syndrome and growth hormone deficiency (GHD) from birth until adulthood. He was born full term with a very low birth weight (2400 g=-3.36 standard deviation score, SDS) and length (40.0 cm =-6.53 SDS). At birth he presented with a broad, fleshy nose with anteverted nostrils, thick and patulous lips, a square chin, curvilinear shaped eyebrows without synophrys, short thorax and long slender bones. Then, during childhood tall vertebral bodies, hip dislocation, transverse chest groove, winged scapulae and hyperextensible joints became more evident and the diagnosis of 3-M syndrome was made; this was also confirmed by the finding of a homozygous deletion in exon 18 of the CUL7 gene, which has not been previously described.The patient also exhibited severe GHD (GH <5 ng/ml) and from the age of 18 months was treated with rhGH. Notwithstanding the early start of therapy and good compliance, his growth rate was always very low, except for the first two years of treatment and he achieved a final height of 132 cm (-6.42 SDS).

Thyroid hormone enhances transected axonal regeneration and muscle reinnervation following rat sciatic nerve injury.

Improvement of nerve regeneration and functional recovery following nerve injury is a challenging problem in clinical research. We have already shown that following rat sciatic nerve transection, the local administration of triiodothyronine (T3) significantly increased the number and the myelination of regenerated axons. Functional recovery is a sum of the number of regenerated axons and reinnervation of denervated peripheral targets. In the present study, we investigated whether the increased number of regenerated axons by T3-treatment is linked to improved reinnervation of hind limb muscles. After transection of rat sciatic nerves, silicone or biodegradable nerve guides were implanted and filled with either T3 or phosphate buffer solution (PBS). Neuromuscular junctions (NMJs) were analyzed on gastrocnemius and plantar muscle sections stained with rhodamine alpha-bungarotoxin and neurofilament antibody. Four weeks after surgery, most end-plates (EPs) of operated limbs were still denervated and no effect of T3 on muscle reinnervation was detected at this stage of nerve repair. In contrast, after 14 weeks of nerve regeneration, T3 clearly enhanced the reinnervation of gastrocnemius and plantar EPs, demonstrated by significantly higher recovery of size and shape complexity of reinnervated EPs and also by increased acetylcholine receptor (AChRs) density on post synaptic membranes compared to PBS-treated EPs. The stimulating effect of T3 on EP reinnervation is confirmed by a higher index of compound muscle action potentials recorded in gastrocnemius muscles. In conclusion, our results provide for the first time strong evidence that T3 enhances the restoration of NMJ structure and improves synaptic transmission.

Detection of human growth hormone doping in urine: out of competition tests are necessary.

The misuse of human growth hormone (hGH) in sport is deemed to be unethical and dangerous because of various adverse effects. Thus, it has been added to the International Olympic Committee list of banned substances. Until now, the very low concentration of hGH in the urine made its measurement difficult using classical methodology. Indeed, for routine diagnosis, only plasma measurements were available. However, unlike blood samples, urine is generally provided in abundant quantities and is, at present, the only body fluid allowed to be analysed in sport doping controls. A recently developed enzyme-linked immunosorbent assay (Norditest) makes it now possible, without any extraction, to measure urinary hGH (u-hGH) in a dynamic range of 2-50 ng hGH/l. In our protocol, untreated and treated non-athlete volunteers were followed. Some of them received therapeutical doses of recombinant hGH (Norditropin) for one week either intramuscularly (three increasing doses) or subcutaneously (12 i.u. every day). The u-hGH excretion after treatment showed dramatic increases of 50-100 times the basal values and returned to almost the mean normal level after 24 h. u-hGH was also measured in samples provided by the anti-doping controls at major and minor competitions. Depending on the type of efforts made during the competition, the hGH concentration in urine was dramatically increased. Insulin-like growth factor binding proteins and beta 2-microglobulins in urine and/or in blood could be necessary for the correct investigation of any hGH doping test procedure.

A large study of androgen receptor germline variants and their relation to sex hormone levels and prostate cancer risk. Results from the National Cancer Institute Breast and Prostate Cancer Cohort Consortium

Background: Androgens are key regulators of prostate gland maintenance and prostate cancer growth, and androgen deprivation therapy has been the mainstay of treatment for advanced prostate cancer for many years. A long-standing hypothesis has been that inherited variation in the androgen receptor (AR) gene plays a role in prostate cancer initiation. However, studies to date have been inconclusive and often suffered from small sample sizes. Objective and Methods: We investigated the association of AR sequence variants with circulating sex hormone levels and prostate cancer risk in 6058 prostate cancer cases and 6725 controls of Caucasian origin within the Breast and Prostate Cancer Cohort Consortium. We genotyped a highly polymorphic CAG microsatellite in exon 1 and six haplotype tagging single nucleotide polymorphisms and tested each genetic variant for association with prostate cancer risk and with sex steroid levels. Results: We observed no association between AR genetic variants and prostate cancer risk. However, there was a strong association between longer CAG repeats and higher levels of testosterone (P = 4.73 × 10−5) and estradiol (P = 0.0002), although the amount of variance explained was small (0.4 and 0.7%, respectively). Conclusions: This study is the largest to date investigating AR sequence variants, sex steroid levels, and prostate cancer risk. Although we observed no association between AR sequence variants and prostate cancer risk, our results support earlier findings of a relation between the number of CAG repeats and circulating levels of testosterone and estradiol.

Absonifibula estuarina sp. n. (Monogenea: Diclidophoridae) parasite of juvenile Cynoscion guatucupa (Osteichthyes) from southwestern Atlantic Ocean

Absonifibula estuarina sp. n. (Diclidophoridae, Absonifibulinae), is described from the gills of juvenile striped weakfish, Cynoscion guatucupa (Cuvier), from the southwestern Atlantic, Argentinean coast. This marine fish migrates to estuarine areas to spawn where exclusively juveniles are found parasitized; adult fish in marine water were never found to be parasitized by this monogenean. A. estuarina sp. n. is characterized mainly by the pedunculate clamps dissimilar in size, the shape of anterior jaw with sclerite 'a' attached to a sub-trapezoidal lamellate extension and fused to sclerites 'c' and 'd'. It differs from Absonifibula bychowskyi Lawler & Overstreet, 1976, the only known species of the genus, in the shape and arrangement of the genital corona, which is armed with six similar hooks disposed in circle and the sub-trapezoidal shape of lamellate extension ('b'). The restriction to juvenile sciaenids is a shared feature among the Absonifibulinae indicating an estuary-dependent life cycle.